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Electronics => Metrology => Topic started by: quarks on January 12, 2013, 04:42:41 pm

Title: Ultra Precision Reference LTZ1000
Post by: quarks on January 12, 2013, 04:42:41 pm
While waiting for the ESI gear I ordered for my resistance measuring stuff, I started to look for the best possible voltage reference.
I already have a few good DC Sources (Valhalla 2701C, Burster 6406, Knick SJ300 and a few Geller SVRs), but I do not have a "real" Voltage Reference Standard (like Fluke 732B or a Datron or any similar) to compare them to.

Besides "Josephson-Voltage-Standard" the next best still seems to be LTZ1000 and this is the reference I would like to give a try.

I read a lot of datasheets, Application Notes, Nuts&Volts posts, Bop Pease stuff, Joe Gellers info's (incl. his Patent), discussions in different blogs and many more sources.

Here are a few links I found good and worth reading (and translating):

http://www.linear.com/product/LTZ1000 (http://www.linear.com/product/LTZ1000)
http://www.maxmcarter.com/vref/ (http://www.maxmcarter.com/vref/)
http://www.febo.com/pipermail/time-nuts/2008-November/034723.html (http://www.febo.com/pipermail/time-nuts/2008-November/034723.html)
http://www.hellocq.net/forum/read.php?tid=139719 (http://www.hellocq.net/forum/read.php?tid=139719)
http://www.amobbs.com/thread-3593996-1-1.html (http://www.amobbs.com/thread-3593996-1-1.html)
http://www.eefocus.com/lymexbg2vo/blog/09-12/181353_9b971.html (http://www.eefocus.com/lymexbg2vo/blog/09-12/181353_9b971.html)

The last one shows a lot of boards, so I think of trying to get one or more, if that is possible.

Now I would be interested if anyone here in the forum has already done a LTZ1000 DIY project and is willing to share the outcome?
Or maybe one of you know where to get a well designed board or plans to do one and can offer to buy it?

thx
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: EEVblog on January 13, 2013, 07:29:22 am
The LTZ1000 is the 7V reference used in industry standard HP3458A 8.5 digit multimeter.
Part number 03458-66509
No oven, it just sits inside the meter case on it's own board with it's circuitry.
If it's good enough for the worlds best reference multimeter used in practically every cal lab, then it's good enough for any DIY project!

Dave.
Title: Re: Ultra Precision Reference LTZ1000
Post by: (In)Sanity on January 13, 2013, 08:01:34 am
The LTZ1000 is the 7V reference used in industry standard HP3458A 8.5 digit multimeter.
Part number 03458-66509
No oven, it just sits inside the meter case on it's own board with it's circuitry.
If it's good enough for the worlds best reference multimeter used in practically every cal lab, then it's good enough for any DIY project!

Dave.

This is a very interesting piece of information.  I had no idea the LTZ1000 reference was used in the 3458A.   I have a very nice condition 3457A which I believe uses the LM399 as a reference.   I have to wonder if their is any advantage to upgrading the 3457A to use an LTZ1000 or is it's 6 1/2 (7 1/2) digit resolution would see no real advantage?  It would of course need to be re-calibrated which I'm due for anyway.  I'm always looking to improve something just for the sake of doing so.   

On another note an interesting video might be one on temperature coefficients and techniques used to stabilize and/or compensate for temperature drift.   

Jeff
Title: Re: Ultra Precision Reference LTZ1000
Post by: PA4TIM on January 13, 2013, 08:15:04 am
Dave, it depends on how you look at it, like the LM399 the LTZ1000 has a heater resistor so it is inside his own little oven.

A member of the voltnuts list has just modded his solartron 7081 and replaced the zeners with a LTZ1000 board. He also did measurements on noise and stability. He is really good on this stuff. 

Voltnuts is a "sister" of timenuts. Several members made LTZ1000 references. Jim Williams has an appnote about a sub-ppm standard and he used a LTZ1000 too. I made his design but then using a LM399 because I have no source for a LTZ1000.

I have a Fluke 332, a guildline 4 Standardcell cabinet ( will all calibration reports since production) and several other Fluke, Philips and homebuild calibrators/references. (a gift from a company that closed down theirs calibration lab) Besides that ESI resistors, two Flukes and a ESI KV devider, standard capacitors and inductors ect. And the famous, still made GR-1620 capacitance bridge that was first used by the GenRad lab self, then when it closed moved together with a staff member to a national brittisch Cal-lab and later sold to a dutch call lab and finaly ended in my lab.

Network analyses, capacitors anf voltnutting is my thing. Nice to meet an other voltnut. Blackdog, here on the forum also has a lot of knowledge about voltreferences. If i remember well also with the LTZ1000 but i think we will see him here. LTZ1000 works like a magnet too voltnuts .

I'm very interested to see your design and the result. I read the hardest part is something with setting the heater current. But some say that is not, others say it is. As far as I found out it only was a problem on some old 3458 reference boards

The things that make it hard are the parts around it. My 10V LM399 bases reference is now powered on 24/7 for months. I monitored it for months and it becomes more stable every month but still it varies 2-4 ppm and that is a reaction on temperature and humidity. So one of my next projects Will be an oven for the reference and a relative humidity and temp meter that will serve to give me those values and work as a controller for the oven. ( as soon as i find out if it is nessaserry and possible to keep humidity in the oven constant) for temp I will use one of Williams early designs when he was stil working for MIT.
Title: Re: Ultra Precision Reference LTZ1000
Post by: (In)Sanity on January 13, 2013, 08:23:46 am
The things that make it hard are the parts around it. My 10V LM399 bases reference is now powered on 24/7 for months. I monitored it for months and it becomes more stable every month but still it varies 2-4 ppm and that is a reaction on temperature and humidity. So one of my next projects Will be an oven for the reference and a relative humidity and temp meter that will serve to give me those values and work as a controller for the oven. ( as soon as i find out if it is nessaserry and possible to keep humidity in the oven constant) for temp I will use one of Williams early designs when he was stil working for MIT.

So does this mean that my 1993 3457A should be far more stable then a fresh off the shelf LM399,  or do they degrade over time?   I fear becoming a volt nut,  I already fuss about stuff being out of tolerance by 10 uV,  let alone a fraction of that. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: PA4TIM on January 13, 2013, 09:16:02 am
40 dollar is rather cheap, i would not trust that. They also have grades. I bought 1027 from Farnell, they only had C grade, then I asked a sample from LT, the sended me one, B grade. Allready a few ppm better but they have A grade too. But no clue how to get one if you are not named Agilent or so.

Every reference needs to be "burned" in a good brand meter uses burned in references, it takes about 1000 hours. The yearly calibration will show you the behaviour. Then there will be a moment the changes between calibration become very small and you can extend the time between them. So for hobby use a nice aged calibrated meter with call history is most times good for many years of fun without the need for calibration. A friend bought a 3457, had it calibrated ( in the states that is very affortable, here is is allmost the pricec of a new meter) and it was still spot on. My Prema came with a cal report ( just cal, no adjustments made) . All measurement were spot on. 10V was 10.000,000V so i know it is allready stable and little chance in changing much in time. My new Keitley 2000 now changed around 10 uV in two years. But most of that happend the first months.
Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on January 13, 2013, 09:29:11 am
Look for used ones, and buy a dozen or so. Then you can sort them into 3 groups: dead, working but drift, and good.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 13, 2013, 10:06:06 am
The LTZ1000 is the 7V reference used in industry standard HP3458A 8.5 digit multimeter.
Part number 03458-66509

Hi Dave,
thanks for your reply. I knew that and I can add that Fluke also had a special version of it, called HP 3458A/HFL, where I believe they only changed one resistor on the LTZ1000 board to lower the heater temp but resulted in even better specs than the original HP meter.

About the part number, do you know or think that it is possible to order this as a spare part when you do not have the 3458 DMM?

thx
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 13, 2013, 10:37:32 am
Dave, it depends on how you look at it, like the LM399 the LTZ1000 has a heater resistor so it is inside his own little oven.

A member of the voltnuts list has just modded his solartron 7081 and replaced the zeners with a LTZ1000 board. He also did measurements on noise and stability. He is really good on this stuff. 

Voltnuts is a "sister" of timenuts. Several members made LTZ1000 references. Jim Williams has an appnote about a sub-ppm standard and he used a LTZ1000 too. I made his design but then using a LM399 because I have no source for a LTZ1000.

I have a Fluke 332, a guildline 4 Standardcell cabinet ( will all calibration reports since production) and several other Fluke, Philips and homebuild calibrators/references. (a gift from a company that closed down theirs calibration lab) Besides that ESI resistors, two Flukes and a ESI KV devider, standard capacitors and inductors ect. And the famous, still made GR-1620 capacitance bridge that was first used by the GenRad lab self, then when it closed moved together with a staff member to a national brittisch Cal-lab and later sold to a dutch call lab and finaly ended in my lab.

Network analyses, capacitors anf voltnutting is my thing. Nice to meet an other voltnut. Blackdog, here on the forum also has a lot of knowledge about voltreferences. If i remember well also with the LTZ1000 but i think we will see him here. LTZ1000 works like a magnet too voltnuts .

I'm very interested to see your design and the result. I read the hardest part is something with setting the heater current. But some say that is not, others say it is. As far as I found out it only was a problem on some old 3458 reference boards

The things that make it hard are the parts around it. My 10V LM399 bases reference is now powered on 24/7 for months. I monitored it for months and it becomes more stable every month but still it varies 2-4 ppm and that is a reaction on temperature and humidity. So one of my next projects Will be an oven for the reference and a relative humidity and temp meter that will serve to give me those values and work as a controller for the oven. ( as soon as i find out if it is nessaserry and possible to keep humidity in the oven constant) for temp I will use one of Williams early designs when he was stil working for MIT.

Do you remember the name of the voltsnuts guy or can give a hint how to identify him? I also read there from people planing transplating LTZ1000 into Valhalla, so that could be the next interesting project.

About the Jim Williams article, was it AN86 or the designfeature at edn you mean?  I think I have read most (if not all) of the relevant info's. It is so much theory that I feel I now have go practical to learn and understand it better.   

About your gear, you are a lucky man and now I can proof to my wife that I am not the craziest nerd on the planet  :-+ That helps a lot to get even more goodies.

thx
quarks

Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 13, 2013, 10:48:11 am
$40 a pop hmmm...
http://www.ebay.com.my/itm/IC-LINEAR-TO-99-LTZ1000ACH-/250886390149?pt=LH_DefaultDomain_0&hash=item3a69fe8185 (http://www.ebay.com.my/itm/IC-LINEAR-TO-99-LTZ1000ACH-/250886390149?pt=LH_DefaultDomain_0&hash=item3a69fe8185)

thx for the link. Have you tried this source? My feeling is unless one can confirm it is no fake I tend to stay away.

The min. order of 250$ and the price of 54.50$ (QTY 1-99) at Linear Technology is ok. But before that, I try to find a local (German/Europe) source to avoid shipping + tax + custom (which will easily double the sellers price). If anyone knows where to order, please share.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 13, 2013, 10:51:35 am
Look for used ones, and buy a dozen or so. Then you can sort them into 3 groups: dead, working but drift, and good.

do you know of a trustworthy source to buy from?

thx
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: muvideo on January 13, 2013, 01:40:22 pm
A member of the voltnuts list has just modded his solartron 7081 and replaced the zeners with a LTZ1000 board. He also did measurements on noise and stability. He is really good on this stuff. 

Do you remember the name of the voltsnuts guy or can give a hint how to identify him? I also read there from people planing transplating LTZ1000 into Valhalla, so that could be the next interesting project.

I think Fred is referring to Mickle T., see:
http://www.febo.com/pipermail/volt-nuts/2013-January/002322.html (http://www.febo.com/pipermail/volt-nuts/2013-January/002322.html)
He posted also other articles before,
for Mickle the 7081 is a buggy imperfect machine,
so he decided to make it better  :o
Hats off to him!

For the little I undertand, the reference itself
is only a part of the things needed to have e
stable voltage reference, that is an assembly
that has to be characterized as a whole.
Just see all the crazyness that goes to the
selection of the right resistors,
Fred can give many info about these things.

My Prema came with a cal report ( just cal, no adjustments made) . All measurement were spot on. 10V was 10.000,000V so i know it is allready stable and little chance in changing much in time.

I'm so curious about these meters, what model
do you have? Do you have some docs like spec
sheer and or manuals? How does it perform?
If you can post some pics ( a teardown maybe?)
I think it will be the first I've seen on the net.

Thank you
Fabio.
Title: Re: Ultra Precision Reference LTZ1000
Post by: jnd on January 13, 2013, 01:51:24 pm
40 dollar is rather cheap, i would not trust that. They also have grades. I bought 1027 from Farnell, they only had C grade, then I asked a sample from LT, the sended me one, B grade. Allready a few ppm better but they have A grade too. But no clue how to get one if you are not named Agilent or so.

Every reference needs to be "burned" in a good brand meter uses burned in references, it takes about 1000 hours. The yearly calibration will show you the behaviour. Then there will be a moment the changes between calibration become very small and you can extend the time between them. So for hobby use a nice aged calibrated meter with call history is most times good for many years of fun without the need for calibration. A friend bought a 3457, had it calibrated ( in the states that is very affortable, here is is allmost the pricec of a new meter) and it was still spot on. My Prema came with a cal report ( just cal, no adjustments made) . All measurement were spot on. 10V was 10.000,000V so i know it is allready stable and little chance in changing much in time. My new Keitley 2000 now changed around 10 uV in two years. But most of that happend the first months.
I wouldn't say $40 is cheap enough to be not trustworthy, it's comparable to new prices from Linear and Chinese always get them for better price. I just checked Taobao and there are lot of them for around $20.

Right now there are 4 sellers of LTZ1000 on eBay. Two of them, Polida and yankee_electronic claim new and use the same generic pic from web. Polida is just bulk part seller, I've seen few comments that people got fake parts but can't say for sure, I'd say both of them are questionable as they don't even have the real photo. Other two, hifi-szjxic and bbshonic, sell used and they claim 100% tested. bbshonic even "Gurantee exchange if it is fault" and have some history of selling them. However I didn't find any feedback for any of those sales.

For myself I'd rather buy used and burned in, working parts since I don't have any instrument which could be used to track any changes in the reference. I guess someone will have to try and report back what they got, so who's first? >:D

For the board, I haven't seen any for sale, only the ridiculously priced meter boards like Dave showed. Ideally I want some kit or finished board like what's been on the Chinese forums because getting all the precision parts around is single quantities must be PITA. So if anyone wants to make small run, I'm interested for one or two.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 13, 2013, 02:41:17 pm
I think Fred is referring to Mickle T., see:
http://www.febo.com/pipermail/volt-nuts/2013-January/002322.html (http://www.febo.com/pipermail/volt-nuts/2013-January/002322.html)
He posted also other articles before,
for Mickle the 7081 is a buggy imperfect machine,
so he decided to make it better  :o
Hats off to him!
thx for the link.

About Prema, it is a German company located in Mainz (nearby where I live) but unfortunately no longer produce any DMMs.

I don't know the model you are talking about, but here are some hopefully interesting (but German) links:
http://www.amplifier.cd/Test_Equipment/other/Prema-DMM.html (http://www.amplifier.cd/Test_Equipment/other/Prema-DMM.html)
http://www.amplifier.cd/Test_Equipment/other/Prema-5000.html (http://www.amplifier.cd/Test_Equipment/other/Prema-5000.html)
http://www.amplifier.cd/Test_Equipment/other/Prema-5017.html (http://www.amplifier.cd/Test_Equipment/other/Prema-5017.html)
http://ohh.de/homepage.htm (http://ohh.de/homepage.htm)
http://ohh.de/5017.htm (http://ohh.de/5017.htm)
http://ohh.de/6048.htm (http://ohh.de/6048.htm)
http://ohh.de/8017.htm (http://ohh.de/8017.htm)

I just checked my archive I only have found Prema 5000, 5017 and 6040 documents (all in German).
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 13, 2013, 03:04:18 pm
For myself I'd rather buy used and burned in, working parts since I don't have any instrument which could be used to track any changes in the reference. I guess someone will have to try and report back what they got, so who's first? >:D

For the board, I haven't seen any for sale, only the ridiculously priced meter boards like Dave showed. Ideally I want some kit or finished board like what's been on the Chinese forums because getting all the precision parts around is single quantities must be PITA. So if anyone wants to make small run, I'm interested for one or two.

I still hope someone here in the forum has already gone through this and is willing to share. For myself I would buy all the needed components (also more than I need for myself, to later on share) but I will probably not even try to do my own board, because my last layout is maybe from 30 years ago and was not as professional as I want this one to be.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TorqueRanger on January 13, 2013, 03:19:33 pm
For myself I'd rather buy used and burned in, working parts since I don't have any instrument which could be used to track any changes in the reference. I guess someone will have to try and report back what they got, so who's first? >:D

For the board, I haven't seen any for sale, only the ridiculously priced meter boards like Dave showed. Ideally I want some kit or finished board like what's been on the Chinese forums because getting all the precision parts around is single quantities must be PITA. So if anyone wants to make small run, I'm interested for one or two.

I still hope someone here in the forum has already gone through this and is willing to share. For myself I would buy all the needed components (also more than I need for myself, to later on share) but I will probably not even try to do my own board, because my last layout is maybe from 30 years ago and was not as professional as I want this one to be.

Do me a favor and just google LTZ1000 and look at all the pics...
Title: Re: Ultra Precision Reference LTZ1000
Post by: alm on January 13, 2013, 03:25:45 pm
This is a very interesting piece of information.  I had no idea the LTZ1000 reference was used in the 3458A.   I have a very nice condition 3457A which I believe uses the LM399 as a reference.   I have to wonder if their is any advantage to upgrading the 3457A to use an LTZ1000 or is it's 6 1/2 (7 1/2) digit resolution would see no real advantage?  It would of course need to be re-calibrated which I'm due for anyway.  I'm always looking to improve something just for the sake of doing so.   
The LTZ1000 is also used in various voltage references like the Fluke 732B and some Datron references. Note that HP ran the LTZ1000 at a very high temperature in the HP 3458A, which made the drift much higher than in voltage reference applications. Much lower drift could be achieved by lowering this temperature. Downside is smaller operating temperature range.

The accuracy of a a DMM is not just determined by the internal reference. It also depends on other factors like ADC linearity and the input resistor network drift. Note that the HP 3456a has better 90 day and 1y accuracy specs than the HP 3457a, even though they share the same selected LMx99 reference.

So does this mean that my 1993 3457A should be far more stable then a fresh off the shelf LM399,  or do they degrade over time?   I fear becoming a volt nut,  I already fuss about stuff being out of tolerance by 10 uV,  let alone a fraction of that. 
As some people already mentioned, the majority of the drift is in the first year or so. The reference should be much more stable than when it was produced. Note that HP would also have done a far amount of burn in and selection.

For the board, I haven't seen any for sale, only the ridiculously priced meter boards like Dave showed. Ideally I want some kit or finished board like what's been on the Chinese forums because getting all the precision parts around is single quantities must be PITA. So if anyone wants to make small run, I'm interested for one or two.
Someone used to be selling 3458a reference boards for around the $100 mark, probably from some surplus source. Haven't seen these for a while, though. PCB design (eg. guarding) is going to be critical, leakage currents can easily induce errors at the single ppm level that these circuits are operating.
Title: Re: Ultra Precision Reference LTZ1000
Post by: muvideo on January 13, 2013, 04:11:16 pm
About Prema, it is a German company located in Mainz (nearby where I live) but unfortunately no longer produce any DMMs.

I don't know the model you are talking about, but here are some hopefully interesting (but German) links:
http://www.amplifier.cd/Test_Equipment/other/Prema-DMM.html (http://www.amplifier.cd/Test_Equipment/other/Prema-DMM.html)
http://www.amplifier.cd/Test_Equipment/other/Prema-5000.html (http://www.amplifier.cd/Test_Equipment/other/Prema-5000.html)
http://www.amplifier.cd/Test_Equipment/other/Prema-5017.html (http://www.amplifier.cd/Test_Equipment/other/Prema-5017.html)
http://ohh.de/homepage.htm (http://ohh.de/homepage.htm)
http://ohh.de/5017.htm (http://ohh.de/5017.htm)
http://ohh.de/6048.htm (http://ohh.de/6048.htm)
http://ohh.de/8017.htm (http://ohh.de/8017.htm)

I just checked my archive I only have found Prema 5000, 5017 and 6040 documents (all in German).

Thank you for the links, I dont read German, but the web pages
can be translated by online translator, I previously have stumbled
in amplifier.cd  page about prema multimeters, but I forgot about that.
I found also PA4TIM's excellent page about his meter:
http://www.pa4tim.nl/?p=3624 (http://www.pa4tim.nl/?p=3624)

Fabio.
Title: Re: Ultra Precision Reference LTZ1000
Post by: saturation on January 13, 2013, 04:16:40 pm
There's a lot of discussion about the LTZ1000 in the archives.  One summarized some the work of this Chinese group, making, analyzing and dissecting the LTZ in an attempt to create a low cost improved reference, here one photo of an ambitious multiboard reference with an LTZ each.  The Chinese site also analyzed the 3458a reference board.

(http://[url=http://www.hellocq.net/forum/attachment/vbb/5/9/4/4/209071.attach?0]http://www.hellocq.net/forum/attachment/vbb/5/9/4/4/209071.attach?0[/url])

It spans 2006-2010, and the thread is 50+ pages.  Lots of photos and data sheets.

http://www.hellocq.net/forum/read.php?tid=139719&page=6 (http://www.hellocq.net/forum/read.php?tid=139719&page=6)
Title: Re: Ultra Precision Reference LTZ1000
Post by: PA4TIM on January 13, 2013, 04:57:40 pm
http://www.pa4tim.nl/?p=3624. (http://www.pa4tim.nl/?p=3624.) Prema 5017 7.5 digit benchmeter. Very solid build. The meter does not switch of totally uing the front powerbutton, the reference stays powered.
Teardowns not on this kind a stuff, only if i have to open it because of repairs. I do not like more dirt and dust inside just for pictures ;-)

I see the link to the modified 7081 allready is given by fellow Voltnut Fabio.

I have a Solartron 7061. I made some modifications too. I have not replaced the reference diode, if I remember well Fabio has done some experimenting in biasing it for better tempco. I just did a check up according the manual. And then I mounted a heatsinks on the outside with a fan on it. I made a temperature controller to drive the fan. The sensor is mounted inside de meter and the fan spins slow around 18 degrees roomtemp, speeding up if roomtemperature changes. It keeps the inside of the meter ( at the measure point) at 39 degrees.

The biggest problem with voltnutting is environment. My lab changes temp from about 17 to 33 degrees over a year and relative humidity from 20 to 40 %
If you want to keep everything tracking you need climate control. But that is not easy and i think costs a lot. Those of you in a all year long hot country probably have airco so maybe it then is possible.

I did not know the appnote number from the Williams reference , it is in my book Analog circuit design part 1, but i looked it up for you, according the book It should be number 86 a standards lab grade 20 bit DAC with 0.1 ppm/C drift. Look at the picture of the setup, a bunch of 3458, two KV dividers and his reference, that is a very expensive table.

My LM399 is made this way. I also used two KV's and the bufferamp. But I made a 10 turn potentiometer on the front that gives me about 800 uV. This for easy adjusting abd keep my KVs free for use with the 332. ( one for deviding, the second for checking)  This pot is the weakest part. The tempco is probably horrible. And mist of the drigpft at this time probably comes from this. If i am going to make the oven for it, the portentiometer will be changed.  I will make is so that 10 turns give me about  100 uV in that case tempco will not do much because one full turn (1K) will give 10 uV so if the tempco is 1000 ppm the resistance of the 10K pot will change 10 Ohm in total. So maybe this gives a 0.1uV fault / degree ( if i do the math correct, i have dyscalculus and no calculator at hand right now)
On the other hand if I  ditch the pot I maybe do not need the oven. Resistors I use are 0.05 to 0.01 % from dead a Fluke 8500 benchmeter.  There is guarding, i avoided mechanical stress ( the lm399 anf LTC1052 are mounted on sockets but without the ( leaking and dielectric) plastic. So no thermal stress to the components. After this everything is cleaned with ipa.
Only problem i have to solve is EMC ( if i power down everything except the prema or solartron and the LM or 332 or whatever and use a KV i get a nice linear behavour. So 1uV is 1uV on the meter and 10V is 10V. But if I leave the lights on ( halogene on a rail) everything goed wrong. There is about 150 uV deviation over 10V  in that case. And the strange thing the readings go down. It dies not matter if I use the 332, LM or whatever. The meter straight on the 332 and using its own divider gives no problem so it must be the cables from source to KV and from KV to meter ( but shielded, twisted, coaxial, triax ect all give the same problem.

Welcom to the darkside of voltnutting ;-)

Title: Re: Ultra Precision Reference LTZ1000
Post by: (In)Sanity on January 13, 2013, 05:17:03 pm
Thanks Alm for the replies.

This is a game I would love to get in to.   I thought about just getting a high grade LM399,  aging it for a long time and taking a measurement with my 3457A.   The idea being that the vref alone without any other components in play should in theory drift less then the combined circuit in my 3457.  I then of course run in to the issue of which one really drifted or did both,  etc.   It seams like you need 3 or 4 references to really figure out what's going on.  Also as I mentioned before a video on how all of this works and techniques to help compensate for it might be interesting.   Items like adding semiconductors in the right place to compensate for the drift of the resistors..etc.  I have a home brew power supply right now that's fairly stable,  it's only stable because the cheap op-amp just so happens to drift in the opposite direction as the cheap resistors,  etc.   I guess you could also say I just got lucky. 

So is a low grade LTZ1000 better then a high grade LM399 ?   

Jeff
Title: Re: Ultra Precision Reference LTZ1000
Post by: muvideo on January 13, 2013, 05:43:05 pm
I see the link to the modified 7081 allready is given by fellow Voltnut Fabio.

I have a Solartron 7061. I made some modifications too. I have not replaced the reference diode, if I remember well Fabio has done some experimenting in biasing it for better tempco. I just did a check up according the manual. And then I

Thank you for the onorific title, but I'm only a VoltNut
follower :) and unfortunately nothing to say about the
7061 stability, my lab is worse than yours and I'd like to
have at least another meter with similar or better specs
before trying anything on reference.

The biggest problem with voltnutting is environment. My lab changes temp from about 17 to 33 degrees over a year and relative humidity from 20 to 40 %
If you want to keep everything tracking you need climate control. But that is not easy and i think costs a lot. Those of you in a all year long hot country probably have airco so maybe it then is possible.

I throw in another element :)
I still dont have experience in building precision references,
it's a time (and money) consuming task, but one can learn
a lot. My question is if it's reasonable to build a temperature
and humidity controlled enclosure for the reference.
Once chosen the right components, and defined the layout
(quite a result, not easy ), the next thing to do should be
the charachterization, i.e. log the aging behaviour over time.
AFAIK the worse offenders remaining that screw up the
stability are temperature and humidity. Build an ovenized
enclosure can be done (and it's been done). I have never
seen a humidity controlled enclosure yet, but I've seen
around some solid state dehumidifiers, nothing cheap
unfortunately (google SPE dehumidifer).
Maybe that can compensate for poor lab enviroments :)

Fabio.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 13, 2013, 05:45:26 pm
There's a lot of discussion about the LTZ1000 in the archives.  One summarized some the work of this Chinese group, making, analyzing and dissecting the LTZ in an attempt to create a low cost improved reference, here one photo of an ambitious multiboard reference with an LTZ each.  The Chinese site also analyzed the 3458a reference board.

(http://[url=http://www.hellocq.net/forum/attachment/vbb/5/9/4/4/209071.attach?0]http://www.hellocq.net/forum/attachment/vbb/5/9/4/4/209071.attach?0[/url])

It spans 2006-2010, and the thread is 50+ pages.  Lots of photos and data sheets.

http://www.hellocq.net/forum/read.php?tid=139719&page=6 (http://www.hellocq.net/forum/read.php?tid=139719&page=6)

thx saturation,
your picture is missing but think I know which one you mean.
I have read all of this quite a while ago and I think you where the one who posted the link back then.
Title: Re: Ultra Precision Reference LTZ1000
Post by: (In)Sanity on January 13, 2013, 05:50:55 pm
Stupid question perhaps,   but is it possible to run one of these references inside of a vacuum to perhaps eliminate humidity from the picture?   Again it might be a stupid question.

Jeff
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 13, 2013, 05:54:32 pm
http://www.pa4tim.nl/?p=3624. (http://www.pa4tim.nl/?p=3624.) Prema 5017 7.5 digit benchmeter. Very solid build. The meter does not switch of totally uing the front powerbutton, the reference stays powered.

your website is just great I have walked through it several times already and always find new and interesting details.
Also the translation on the site works quite good for me.

Thx a lot

edit: I just saw this http://www.pa4tim.nl/?p=2733 (http://www.pa4tim.nl/?p=2733) so you are my man.
In another post I asked for infos/help https://www.eevblog.com/forum/reviews/esi-resitance-standard-sr1010-and-standard-resistor-sr104/msg171260/#msg171260 (https://www.eevblog.com/forum/reviews/esi-resitance-standard-sr1010-and-standard-resistor-sr104/msg171260/#msg171260) but unfortunately had no reply. And now I see you have the same Set ESI SR1010 (also the same values 10 Ohm to 100k).
Title: Re: Ultra Precision Reference LTZ1000
Post by: UPI on January 13, 2013, 05:59:24 pm
Reminds me of this relatively quick/inexpensive idea:

http://www.romanblack.com/xoven.htm (http://www.romanblack.com/xoven.htm)
Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on January 13, 2013, 06:03:57 pm
Not a vacuum, but in a sealed enclosure with a large sachet of silica gel inside to adsorb water. Heat it up in an oven to dry it out well and then place in the dry enclosure hot and then seal it up while it is still hot. Then it will make a very low humidity interior. you will need to have IP68 rated connectors in the box, and preferably a smaller inner box to hold the reference in an insulated place. You can have heaters in the outer box to keep it at a stable temperature, and this will keep the inner stable. All you need on the outer is to keep it to within 2C, as the inner insulation will attenuate the variances. I have seen this ( without the dessicant) in an appnote to get a inner box to be temperature stable to within millidegrees.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chrome on January 13, 2013, 06:08:32 pm
Can anyone tell my why 6.95V?

It seems like such an arbitrary value.

I'm sort of assuming it's inherit with the design maybe?
Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on January 13, 2013, 06:11:58 pm
Reminds me of this relatively quick/inexpensive idea:

http://www.romanblack.com/xoven.htm (http://www.romanblack.com/xoven.htm)

I did that years ago, and they work well.

6.95V as it is a stable point where the voltage is not quite avalance breakdown and not quite zener action. Lower and higher voltages have drift with temperature, this is a sweet spot in the characteristic. Often you get a 6V2 zener diode internally in series with a silicon diode to make a 6V8 unit, as this is also very stable as the tempco's of the zener and the diode are nearly the same but of opposite direction so they cancel out nearly totally.
Title: Re: Ultra Precision Reference LTZ1000
Post by: (In)Sanity on January 13, 2013, 06:20:15 pm
Thanks for the replies about the vacuum,  Potting I assume would be subject to moisture absorption and too slow to respond to temperature changes or corrections ?  So if it got cold for example it would take far to long to stabilize and perhaps have too much hysteresis?

Also which would be better for a 10.0000 volt reference,   a 6.95 and an op-amp or two 6.95's and a voltage divider ?   Which would be more stable ?

I'm full of questions at the moment.

Thanks,

Jeff
Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on January 13, 2013, 06:34:37 pm
Potting would also stress the references. the biggesst issue is the resistors you use, not the opamp. You can get an opamp that is chopper stabilised, which removes it's own drift, but the resistor drift determines the stability. Better to use a single reference and multiply it up to 10V, one less source of error.
Title: Re: Ultra Precision Reference LTZ1000
Post by: (In)Sanity on January 13, 2013, 06:53:08 pm
Potting would also stress the references. the biggesst issue is the resistors you use, not the opamp. You can get an opamp that is chopper stabilised, which removes it's own drift, but the resistor drift determines the stability. Better to use a single reference and multiply it up to 10V, one less source of error.

Thanks Sean,   that's what I was wondering.   I was looking to see which would be the lesser of the two evils.  To build one of these references correctly appears to be a very expensive endeavor with $90 references, $28 resistors and an equally expensive trim pot which should be avoided if possible,  ohh and let's not forget the chopper amp.   I may still pick up an LM399 just for experimentation sake and not breaking the bank.  I'm fortunate that I have a full finished basement and the temperature down here stays pretty constant relative to the rest of the house. So my 3457A also stays pretty stable.  I'm pretty good with long term projects,  so this could be fun.

Jeff
Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on January 13, 2013, 07:04:24 pm
Often the resistors are selected to be close, then a variable is used to get the final adjustment and is replaced by a fixed value. Leads to using Vishay foil on glass resistors in series and with final trim being by soldering a few low TC metal film resistors and then cutting resistor leads to trim up to the right value.
Title: Re: Ultra Precision Reference LTZ1000
Post by: PA4TIM on January 13, 2013, 07:11:14 pm
http://www.pa4tim.nl/?p=2531 (http://www.pa4tim.nl/?p=2531) my LM399 ( the last one at the bottom, all my reference projecs are on this page)

Quarks: i have the ESIs but I did no stability tests with them. If i use them to calibrate I measure all off thecterminals and then take the avarage. Then measure all in serie and that must be the same value as the 12 separate. I have the bar that sets them parallel and I'm told this is enhances the precision by averaging out the differences.

Mine all measure very constant. No significant differences between terminals of one unit.
Problem of monitoring drift, tempco ect ( Vrefs, resistors, capacitors ect) is you never know what is drifting, the DUT or the instrument or both  :)

Is it because australia is very far away or is it just me. This forum is very slow, it takes ages for pages to open, before I can type comments and many notifications never seem to arrive. ( do I made wrong settings 's ? )
It would be great is i could set notifications on permanent z
Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on January 13, 2013, 07:15:14 pm
Server is in the USA. They must be awake and watching movies............
Title: Re: Ultra Precision Reference LTZ1000
Post by: (In)Sanity on January 13, 2013, 07:55:27 pm
Server is in the USA. They must be awake and watching movies............

Haaa,  the only movies I watch are electronics related for the most part.  Sadly I can't stream anything in HD anymore,  even though I have a 20 Meg connection.  Everything is going to crap lately..but that's another topic.

Thanks for the information about not using a trim pot.  I kind of knew that in the back of my head,  but somehow was in denial about it actually being done that way.   I wonder if anyone has made any good references by balancing out the positive and negative temperature coefficients of the devices in the circuit?   I know most DMM's and such have a thermistor or ten to obtain somewhat of this behavior.  I guess it would be no better then just using an oven no matter which way you rolled it.   Perhaps a combination of the methods.   I'm such a newb at temperature stability issues.   

Also can't everything be corrected in software :)

Jeff
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 13, 2013, 08:14:50 pm
http://www.pa4tim.nl/?p=2531 (http://www.pa4tim.nl/?p=2531) my LM399 ( the last one at the bottom, all my reference projecs are on this page)

Quarks: i have the ESIs but I did no stability tests with them. If i use them to calibrate I measure all off thecterminals and then take the avarage. Then measure all in serie and that must be the same value as the 12 separate. I have the bar that sets them parallel and I'm told this is enhances the precision by averaging out the differences.

Mine all measure very constant. No significant differences between terminals of one unit.
Problem of monitoring drift, tempco ect ( Vrefs, resistors, capacitors ect) is you never know what is drifting, the DUT or the instrument or both  :)
Thx again,
I do also have  the optional parallel, serial-parallel compensation networks and the shorting bars and have measured allmost all possible  combinations.
What I am still interested in, is how resistance transfer works. If you could share some knowledge that would be great. But this is OT here  and I can, if there is any interest, update the other post with more details.
Tomorrow I will also pick up some more related ESI gear from custom.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Conrad Hoffman on January 15, 2013, 06:02:34 pm
FWIW, my Analogic 8200 6 1/2 digit voltage/current reference uses the LM399 and it's remarkably good. If you can find the circuit on-line, it uses analog switches to change the output from a master divider chain and is definitely worth studying.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 15, 2013, 06:31:41 pm
Hello Conrad,
analog switching sounds interesting and with LM199/299/399 I remember a Bop Pease article where he used multiple of them together. I will definitely try to have a look at it.

A first quick search for a Analogic 8200 schematic unfortunately showed no result for manual and service manual.
But the search lead to
https://www.eevblog.com/forum/projects/kelvin-varley-divider-(and-precision-voltage-source)/msg71081/?PHPSESSID=c8a26b98cc233fa3e62a0ec3c9f47bb1#msg71081 (https://www.eevblog.com/forum/projects/kelvin-varley-divider-(and-precision-voltage-source)/msg71081/?PHPSESSID=c8a26b98cc233fa3e62a0ec3c9f47bb1#msg71081)
so I tried also Data Precision also with no luck. Do you maybe have a link or can post a photo/scan?

thx
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: muvideo on January 15, 2013, 06:46:38 pm
quarks:
http://www.ko4bb.com/Manuals/09%29_Misc_Test_Equipment/DataPrecision_8200_6.5_Digit_Calibrator_Service_Manual.pdf (http://www.ko4bb.com/Manuals/09%29_Misc_Test_Equipment/DataPrecision_8200_6.5_Digit_Calibrator_Service_Manual.pdf)

I'm reading it now, it's a wonderful manual, almost an application note :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on January 15, 2013, 06:46:48 pm
I believe this (http://www.google.com/url?sa=t&rct=j&q=&esrc=s&frm=1&source=web&cd=1&cad=rja&ved=0CDYQFjAA&url=http%3A%2F%2Fwww.ko4bb.com%2FManuals%2F09)_Misc_Test_Equipment%2FDataPrecision_8200_6.5_Digit_Calibrator_Service_Manual.pdf&ei=XaP1ULKJEbK00AG7n4GoBQ&usg=AFQjCNHrdJ-98Kdm5OYIdMycj7Wo1IVtJg&sig2=dZ2zElyh6XqcawXVnk1lnQ) is it

Edit: Sorry muvideo I was too slow
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 15, 2013, 06:58:05 pm
great, thx a lot
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 17, 2013, 01:40:36 pm
in the Wavetek 1271 I just saw, they use a LM399 and a LTZ1000 Board
Title: Re: Ultra Precision Reference LTZ1000
Post by: free_electron on January 17, 2013, 03:11:39 pm
I believe bob pease had a circuit using a few lm399s to make a nanovolt reference.
Title: Re: Ultra Precision Reference LTZ1000
Post by: PA4TIM on January 17, 2013, 05:01:32 pm
The Czar of bandgap references himself, that must be a decent design.
Do you know where it was publiced ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: muvideo on January 17, 2013, 05:35:05 pm
I remember only one of his "What’s All This ___ Stuff, Anyhow?" series,
this one: http://electronicdesign.com/archive/what-s-all-long-term-stability-stuff-anyhow (http://electronicdesign.com/archive/what-s-all-long-term-stability-stuff-anyhow)
But I'd like to know if there is some more in-depth article...

Fabio.
Title: Re: Ultra Precision Reference LTZ1000
Post by: free_electron on January 17, 2013, 06:34:08 pm
i think it's in one of his Bob Pease Show video's... hang on ...

Precision Current Source (https://www.youtube.com/watch?v=2N6cjGS7lUE#)

or it may be in his book analog troubleshooting. he uses like 10 of em ...
Title: Re: Ultra Precision Reference LTZ1000
Post by: jnd on January 18, 2013, 12:16:41 am
i think it's in one of his Bob Pease Show video's... hang on ...

Precision Current Source (https://www.youtube.com/watch?v=2N6cjGS7lUE#)

or it may be in his book analog troubleshooting. he uses like 10 of em ...
I saw this one just week or two ago, there is one LM399. BTW TI's channel on Youtube have them reuploaded in better quality (I tried to search there for "anyhow") which is interesting. The new version is here, it's still pretty relevant to the precision talk here: Whats All This Current Source Stuff, Anyhow? (https://www.youtube.com/watch?v=Sv21wD3FRmY#)
Title: Re: Ultra Precision Reference LTZ1000
Post by: nukie on January 18, 2013, 01:57:02 am
These are 3 of my LTZ1000 references and geller svr 5V. Along with two Motorola SZA263 used in the Fluke 8840a and Fluke 731B voltage standard and Fluke 732A reference standard. Still waiting for free time to attack those SZA263 with solder iron. Please note, without high precision supporting passive components these parts are as good as nothing.

(http://img232.imageshack.us/img232/9430/77451258.jpg)
(http://img36.imageshack.us/img36/8523/83517661.jpg)

You can read more about it here
http://home.51.com/jj3055/diary/item/10053954.html (http://home.51.com/jj3055/diary/item/10053954.html)

Schematics here
http://bbs.38hot.net/read-htm-tid-36472.html (http://bbs.38hot.net/read-htm-tid-36472.html)

And finally here how to convert 7V to 10V
http://www.crystalradio.cn/thread-229749-1-1.html (http://www.crystalradio.cn/thread-229749-1-1.html)
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 18, 2013, 08:19:42 am
@ Mechatrommer, thx for your reply. I know it will be hard to get all the ideal parts but I at least want to try and find out.

@ nukie, that looks very promising. What you already have is exactly what I thinking to do. thx a lot for sharing.
I will read through your links and come back to you.
Title: Re: Ultra Precision Reference LTZ1000
Post by: PA4TIM on January 18, 2013, 08:59:53 am
Hmm, i think I am not good enough in Chinese (or Japanese ?)  to read the links from nukie.
Title: Re: Ultra Precision Reference LTZ1000
Post by: nukie on January 18, 2013, 09:35:57 am
Use Google Chrome there's auto translate. I can't read Chinese but the schematics and diagrams teaches a lot.


Title: Re: Ultra Precision Reference LTZ1000
Post by: muvideo on January 18, 2013, 09:50:57 am
nukie, the LTZ1000 is pretty costly, probably it
would be fun and cheaper form me to experiment
with cheaper references like the lm399, that will
also set a starting point to make comparisons.

What do you think about the SZA263?
How do they compare with LM399? I've seen them (the 263)
used in old fluke standards, and meters, there are
the schematics online, but it seems that
the 399 is simpler to use, am I correct?
Is there any cheap source for SZA263 references,
other than dismantling old fluke meters?

Thanks,
Fabio.
Title: Re: Ultra Precision Reference LTZ1000
Post by: nukie on January 18, 2013, 10:16:48 am
Most sza263 you can find today are mostly reclaimed from recycling Flukes. You can contact Fluke to see if they stock any surplus, they do it for military program maybe?

As for LM399 vs 263, I would settle for the LM399, its widely used and lots of example around. I bought 2 more than 15 months ago and has been burning in since, performance seems to be pretty stable after 4000hours. I am planning a 5x LM399 in parallel when I have more time.

The LTZ1000 I have are also from used equipment. They are sourced directly from a electronics recycling market in China. There are people who are willing to go out and source for the right equipment that carries the specific component.   The components are removed carefully and resold. They are not expensive. Same case with the foil resistors.

There are fake LTZ1000 floating around even the Chinese locals have encounter them. There are also companies that repackage these chips with new gold leads and new case, I suspect that's what you get from EBay.

Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on January 18, 2013, 10:52:35 am
Use Google Chrome there's auto translate. I can't read Chinese but the schematics and diagrams teaches a lot.

I read all through it. That's is really helpfull. Could you or anybody else download the schematics and can share it? Have you bought the boards and/or can you share where to get them?
Title: Re: Ultra Precision Reference LTZ1000
Post by: muvideo on January 18, 2013, 04:36:41 pm
The LTZ1000 I have are also from used equipment. They are sourced directly from a electronics recycling market in China. There are people who are willing to go out and source for the right equipment that carries the specific component.   The components are removed carefully and resold. They are not expensive. Same case with the foil resistors.

There are fake LTZ1000 floating around even the Chinese locals have encounter them. There are also companies that repackage these chips with new gold leads and new case, I suspect that's what you get from EBay.

This is interesting, can you share more details, also in PM if you want.
I'd like to know where to ask for these parts (LTZ1000 and metal foil resistors)
and the order of magnitude for the price I could expect for these parts.
Talking about ebay, what you say is that used parts are more trustable
than new ones?

Thanks,
Fabio.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Christe4nM on January 19, 2013, 11:21:24 am
You can read more about it here
http://home.51.com/jj3055/diary/item/10053954.html (http://home.51.com/jj3055/diary/item/10053954.html)

Schematics here
http://bbs.38hot.net/read-htm-tid-36472.html (http://bbs.38hot.net/read-htm-tid-36472.html)

And finally here how to convert 7V to 10V
http://www.crystalradio.cn/thread-229749-1-1.html (http://www.crystalradio.cn/thread-229749-1-1.html)

Looking at the pcb I can't stop wondering why these slots are milled. The voltage isn't that high that you need the extra creepage distance, and right now it seems to me it's only weakening the pcb's structural integrity. Worst case it introduces unknown offsets as the pcb will bend a bit either when moved, or with temperature changes. Am I overlooking something here?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rerouter on January 19, 2013, 12:54:01 pm
i would imagine to maintain the accuracy required the leakage currents (even if absolutely tiny) have to be mitigated somehow, and the slot probably is one of the easier ways to accomplish it,
Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on January 19, 2013, 01:10:14 pm
More there for thermal isolation, as the references are all enclosed in an insulating cover and this removes the path for heat leakage out. The thin connecting traces also reduce heat transfer down them.
Title: Re: Ultra Precision Reference LTZ1000
Post by: PA4TIM on January 19, 2013, 01:19:33 pm
Slots in pcbs are for limiting mechanical stress. A pcb is screwed in a cabinet so there is mechnical stress, due to movement, gravity, thermal stress ect. That is why the often make a sort of U slot around a reference.  ( i ould not see it sharp on the pictures so maybe you alk about other slots, because i work mobile)
There is app note about references, can not remember of it was about the LM399 of from LT. They lso describe the best locations on the pcb in relation to stress and return current paths.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Christe4nM on January 19, 2013, 01:37:54 pm
I indeed talked about the L-shaped slots around the LTZ1000. Thanks for your reply's.

As far as appnotes go I found at least these ones:
Linear AN42 Voltage Reference Circuit Collection (http://cds.linear.com/docs/Application%20Note/an42.pdf)
Intersil AN177 Voltage Reference Application and Design Note (http://www.intersil.com/content/dam/Intersil/documents/an17/an177.pdf)

Yet it seems they are not the one you (PA4TIM) mentioned. Might this be the one?
Linear AN82 Understanding and Applying Voltage References (http://cds.linear.com/docs/Application%20Note/an82f.pdf)

@everyone: the literature references mentioned at the last page of application notes are a great way to delve deeper into any subject.
Title: Re: Ultra Precision Reference LTZ1000
Post by: PA4TIM on January 19, 2013, 01:45:46 pm
Yes AN82 is the one that talks about the slots
Title: Re: Ultra Precision Reference LTZ1000
Post by: muvideo on January 19, 2013, 01:53:40 pm
Also here linear talks about mechanical stress problems pag 19-20:
http://cds.linear.com/docs/Datasheet/1460fc.pdf (http://cds.linear.com/docs/Datasheet/1460fc.pdf)

I learned about the strain problems watching pics of internals
of the datron meters, there is an example on these
pics (excellent ones) from tekfan, 4th pic, there are the
two matched zeners:
https://www.eevblog.com/forum/reviews/what-do-you-want-to-see/msg41015/#msg41015 (https://www.eevblog.com/forum/reviews/what-do-you-want-to-see/msg41015/#msg41015)

Fabio.
Title: Re: Ultra Precision Reference LTZ1000
Post by: keen101 on February 07, 2013, 11:15:49 am
Quote
For the board, I haven't seen any for sale, only the ridiculously priced meter boards like Dave showed. Ideally I want some kit or finished board like what's been on the Chinese forums because getting all the precision parts around is single quantities must be PITA. So if anyone wants to make small run, I'm interested for one or two.

I'm helping my dad produce a few replacement boards for the HP 03458-66509 boards. He is working on his prototypes now. I don't know much about it, but he went to a lot of trouble ordering a bunch of precision resistors and stuff. He is now working on getting the ltz1000 chips from linear. He worked for HP/Agilent for 45 years and he calibrated instruments like the HP 3458A. He is recently retired. He is thinking of sell these for cheaper than what the official HP boards would cost. I am helping him make the boards and he is doing the complicated stuff. These boards should be pin compatible. Is there any interest in them here?

(http://i1010.photobucket.com/albums/af224/keen101/electronics/DSCF1508_zpse7e72cf5.jpg)

(http://i1010.photobucket.com/albums/af224/keen101/electronics/DSCF1510_zpsae43bba7.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: saturation on February 07, 2013, 01:10:41 pm
Just thoughts: a worthwhile project, but a very limited market.  Owners of working 3458a are not likely to pop in a new board  for fear or having to re-calibrate it, which is not cheap.  Owners of ones requiring service and thus are likely to experiment with new boards are much fewer, reason being if you own this DMM chances are you have it in working order and calibrated, and if you are storing it for the day you'll repair it, meaning you also don't need it right now, its worth $3000+ not working, so its an easy sell on eBay.

You'd have to prove that your aftermarket voltage reference boards are >= the factory boards in terms of accuracy and at least equal in quality.  Until that is known, I'm not sure an owner will risk having their units drift out of spec due to unforseen issues with the boards stability, since just checking the unit via a cal lab is $500-600, and the gold calibration runs past $1300.




Quote
For the board, I haven't seen any for sale, only the ridiculously priced meter boards like Dave showed. Ideally I want some kit or finished board like what's been on the Chinese forums because getting all the precision parts around is single quantities must be PITA. So if anyone wants to make small run, I'm interested for one or two.

I'm helping my dad produce a few replacement boards for the HP 03458-66509 boards. He is working on his prototypes now. I don't know much about it, but he went to a lot of trouble ordering a bunch of precision resistors and stuff. He is now working on getting the ltz1000 chips from linear. He worked for HP/Agilent for 45 years and he calibrated instruments like the HP 3458A. He is recently retired. He is thinking of sell these for cheaper than what the official HP boards would cost. I am helping him make the boards and he is doing the complicated stuff. These boards should be pin compatible. Is there any interest in them here?

(http://i1010.photobucket.com/albums/af224/keen101/electronics/DSCF1508_zpse7e72cf5.jpg)

(http://i1010.photobucket.com/albums/af224/keen101/electronics/DSCF1510_zpsae43bba7.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: krivx on February 07, 2013, 04:27:09 pm
You'd have to prove that your aftermarket voltage reference boards are >= the factory boards in terms of accuracy and at least equal in quality.  Until that is known, I'm not sure an owner will risk having their units drift out of spec due to unforseen issues with the boards stability, since just checking the unit via a cal lab is $500-600, and the gold calibration runs past $1300.

Wow, is it really that expensive? I had no idea. I assume this is because of the high requirements on the calibrator/source equipment? How does this compare to having, say, a 3.5 or 4.5 digit meter calibrated?
Title: Re: Ultra Precision Reference LTZ1000
Post by: ve7xen on February 07, 2013, 04:33:44 pm
Just thoughts: a worthwhile project, but a very limited market.  Owners of working 3458a are not likely to pop in a new board  for fear or having to re-calibrate it, which is not cheap.  Owners of ones requiring service and thus are likely to experiment with new boards are much fewer, reason being if you own this DMM chances are you have it in working order and calibrated, and if you are storing it for the day you'll repair it, meaning you also don't need it right now, its worth $3000+ not working, so its an easy sell on eBay.
I think the idea is more for volt-nut types to build a decent house standard, not people trying to repair 3458's. Depends on cost, but if he can get it significantly cheaper than what the HP boards go for on the used market I expect he'll sell some. Not a large market, but large enough to make it worthwhile I think.
Title: Re: Ultra Precision Reference LTZ1000
Post by: saturation on February 08, 2013, 11:31:03 am
The 3458a is very popular metrology grade top of the line DMM; I wouldn't be surprised if nearly all metrology labs use one in lieu of its competitors, making it a defacto standard top line DMM.

Its thus, a bit more difficult to test the extremes of its range.  As a ball park, calibrating a 5.5 digit DMM is $100-200  in the US, and $200-300 for 6.5 digits, Agilent prices.  A reason for the range is that fully automated DMMs like say the 1272a are just plug-and-play calibration, while older DMM may need more labor.

The $500 calibration is a typical one but for its best specifications, the $1500 cal comes only from Agilent, AFIAK.  Even at $500 most folks will send it to Agilent to insure its done properly.

https://service.tm.agilent.com/infoline/Product-Service.aspx?pn=3458A&countryid=114

https://service.tm.agilent.com/infoline/product-service-query.aspx


You can type your Agilent device above and the website will quote you a charge, it varies by country.

The cost is proportionate to the labor, and at the lowest cost its basically mostly the cost of the calibrator and or references, buying and maintaining it.

You'd have to prove that your aftermarket voltage reference boards are >= the factory boards in terms of accuracy and at least equal in quality.  Until that is known, I'm not sure an owner will risk having their units drift out of spec due to unforseen issues with the boards stability, since just checking the unit via a cal lab is $500-600, and the gold calibration runs past $1300.

Wow, is it really that expensive? I had no idea. I assume this is because of the high requirements on the calibrator/source equipment? How does this compare to having, say, a 3.5 or 4.5 digit meter calibrated?
Title: Re: Ultra Precision Reference LTZ1000
Post by: keen101 on February 09, 2013, 09:28:57 pm
I think the idea is more for volt-nut types to build a decent house standard, not people trying to repair 3458's. Depends on cost, but if he can get it significantly cheaper than what the HP boards go for on the used market I expect he'll sell some. Not a large market, but large enough to make it worthwhile I think.

Okay i was just curious. I thought maybe something like this project might work for some of you, but like i said before i don't know much about it.

http://www.maxmcarter.com/vref/ (http://www.maxmcarter.com/vref/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: alm on February 09, 2013, 09:59:12 pm
This is exactly the volt-nuts kind of application that ve7xen was referring to. A good implementation of the LTZ1000 is non-trivial and requires several fairly exotic components. For the right price, I think you will get some buyers on this forum. No idea how many. I would certainly consider it.

I think the street price for a used 3458A reference was under $100 last time I saw one for sale on eBay. One advantage that the real Agilent units would have is that the LTZ1000 would be selected and burned in. I seem to recall a fair amount of variation in noise of the LTZ1000. This assumes that the references for sale on eBay were not factory rejects.

If he has access to a calibrated 3458A or similar DMM, than he might be able to offer calibration, as a high-end equivalent to the Geller Labs / Voltage Standard products. The reference would need to be burned in for bests results, which is likely to expensive/complex to make it worthwhile.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on February 12, 2013, 06:48:11 pm
Use Google Chrome there's auto translate. I can't read Chinese but the schematics and diagrams teaches a lot.

I read all through it. That's is really helpfull. Could you or anybody else download the schematics and can share it? Have you bought the boards and/or can you share where to get them?

So far nukie has not responded. Does anyone else know, where to get the boards nukie uses and can share the schematic?
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on February 12, 2013, 06:50:37 pm
I'm helping my dad produce a few replacement boards for the HP 03458-66509 boards. He is working on his prototypes now. I don't know much about it, but he went to a lot of trouble ordering a bunch of precision resistors and stuff. He is now working on getting the ltz1000 chips from linear. He worked for HP/Agilent for 45 years and he calibrated instruments like the HP 3458A. He is recently retired. He is thinking of sell these for cheaper than what the official HP boards would cost. I am helping him make the boards and he is doing the complicated stuff. These boards should be pin compatible. Is there any interest in them here?

that looks good. Do you and your Dad want to offer/sell these boards?
Title: Re: Ultra Precision Reference LTZ1000
Post by: keen101 on February 12, 2013, 11:19:23 pm
that looks good. Do you and your Dad want to offer/sell these boards?

He said he will probably try listing them on ebay soon. Maybe by next week, but i'm not sure. I honestly don't know if anyone will want to buy them, but we will see.

(http://i1010.photobucket.com/albums/af224/keen101/ltz1000_clone1_zps8a206777.jpg)

(http://i1010.photobucket.com/albums/af224/keen101/ltz1000_clone2_zps6454debe.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: JBeale on February 16, 2013, 12:59:50 am
I might be interested in a LTZ1000 reference board, but my interest level would depend on the price :-)   I am just starting to test a batch of LM399 references and finding that each one is quite individual as far as microvolts of noise/drift in any given frequency range. I care most about frequencies of 1 Hz and lower, so maybe better to call it "drift".

"...now working on getting the ltz1000 chips from linear."   From this link http://www.linear.com/purchase/LTZ1000 (http://www.linear.com/purchase/LTZ1000) and then
http://shopping.netsuite.com/s.nl?ext=F&c=402442&sc=2&category=&search=LTZ1000 (http://shopping.netsuite.com/s.nl?ext=F&c=402442&sc=2&category=&search=LTZ1000)
it looks like "Linear Direct" currently has 14 of the LTZ1000ACH#PBF parts in stock, but none of the other types.  But they also note "a minimum buy may apply".
Then again, they also said that on the order form about the LM399's I got, but then shipped me the six parts I requested anyway.
Title: Re: Ultra Precision Reference LTZ1000
Post by: amspire on February 16, 2013, 06:10:17 am
The device I use as my reference is a Thaler VR305A hybrid IC. 5V 0.01% initial accuracy. 0.6 pmm/C without an oven or on-chip heater. If you want to put them in an oven, it includes a diode junction for as a temp sensor. That means they are better then total 0.001% stability as the temperatures varies from 17 degC to 33 degC and no warm up time - good enough for me.  The LTZ1000 can obviously get an order of magnitude better temperature stability with its built in heater but you do have to give it over 5 minutes to stabilize after turn on.

The Thaler references use a buried zener based reference,  and I think resistors and thermistors on the ceramic substrate are then laser trimmed to zero the temp coefficient.

Long term stability is worse then the LTZ1000 - 6ppm in 1000 hours. Does it stabilize after 1000 hours? It seems to, but I don't know. I don't have any figures in how they actually perform long term after they have burnt in. There is much less in a  LTZ1000, so I guess there are much fewer components that can drift.

The problem with the Thaler references is they used to be very affordable - I think I got 5 for about $20 each from Thaler over 10 years ago.

Thaler were bought by Cirrus Logic (Apex Microtechnology) and since then, every time I look, the price has gone higher. A couple of years ago, they were $70 and Digikey have them currently for $93. Apex Microtechnology website does seem to offer samples. http://www.apexanalog.com/products/voltage-sine-wave-references/ (http://www.apexanalog.com/products/voltage-sine-wave-references/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: JBeale on February 16, 2013, 04:20:33 pm
I made a table of the specs on all the precision references I found referenced on the "volt-nuts" list. I lost interest in the VRE305 after I saw the price on DigiKey. It is by far the most expensive one on the list; twice as expensive as a LTZ1000 from Linear Tech (although to be fair, the LTZ1k needs several other expensive parts in the standard circuit).  Both the Apex product page and the data sheet actually call the VRE305 a "low-cost" part, which is actually true by reference to some of their other parts... Digikey lists the VRE102CA at $262.   I would be impressed if they were willing to sample any of these gold-plated parts to a hobbyist.
Title: Re: Ultra Precision Reference LTZ1000
Post by: amspire on February 16, 2013, 04:38:14 pm
I made a table of the specs on all the precision references I found referenced on the "volt-nuts" list. I lost interest in the VRE305 after I saw the price on DigiKey. It is by far the most expensive one on the list; twice as expensive as a LTZ1000 from Linear Tech (although to be fair, the LTZ1k needs several other expensive parts in the standard circuit).  Both the Apex product page and the data sheet actually call the VRE305 a "low-cost" part, which is actually true by reference to some of their other parts... Digikey lists the VRE102CA at $262.   I would be impressed if they were willing to sample any of these gold-plated parts to a hobbyist.
The datasheet Apex used is the Thaler datasheet with the name Thaler replaced. Nothing else was ever changed except for a fivefold increase in price. No new devices have been designed. Sad really.
Title: Re: Ultra Precision Reference LTZ1000
Post by: fmaimon on February 16, 2013, 04:39:36 pm
There is someone on ebay selling VRE305KS for less than $30 but there is no picture of the device. I've sent him a message asking for a photo of the IC.
Title: Re: Ultra Precision Reference LTZ1000
Post by: amspire on February 16, 2013, 11:10:56 pm
There is someone on ebay selling VRE305KS for less than $30 but there is no picture of the device. I've sent him a message asking for a photo of the IC.
If it is the ebay sale for US$22, it looks a good deal. They are the devices that can go down to -40C. Mine are only rated down to 0C.

The IC's are surface mount versions of the DIP8 package, like mine. Here is a photo, if it helps:

(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=39567)

Also I just found there very  cute 8mm x 8mm peltier devices for $4 inc postage that can shift up to 1/3W of heat. I thought they could be good for making a small temp controlled "oven" for voltage references, crystals, etc. It means an operating temp of something like 30 degC can be chosen, rather then having to pick something well above normal ambient, like 50 degC. The total heat you have to dissipate from the peltier is about 1.2W so that can be a small heatsink, or directly to a metal box. I have ordered a few to play with.

(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=39569)
http://www.ebay.com.au/itm/TES100701-DC-0-8V-0-33W-Peltier-Cooler-Thermoelectric-Cooler-Cooling-8-x-8-mm-/110900388714? (http://www.ebay.com.au/itm/TES100701-DC-0-8V-0-33W-Peltier-Cooler-Thermoelectric-Cooler-Cooling-8-x-8-mm-/110900388714?)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 17, 2013, 12:02:39 pm
LM399H and LM399AH can be bought at www.electronic-search.de (http://www.electronic-search.de) in germany. I did that a few months ago and made a small board with this milled slots to keep away mechanical stress and minimize thermal drop between the pins resulting in thermo voltages. Keep in mind that LM399 is available from LT and National Semiconductor, both with some small difference in spec. You could also ask them for the LTZ1000.

I'm sensitized with references at ebay. I bought a few MAX6350MJA (Buried Zener in a CERDIP package) from ebay and hoped that they were also used and recycled, because MAXIM don't stock them anymore. CERDIP because of the humidity influence to references plastic package is sensitive to.
The brand printing was the first indication, didn't look like MAXIMs original logo. The package marking on the bottom showed some code Linear Technology uses for their products (N12345) instead of a 7 digit letter combination plus a 4 digit date code, what is common. And also measurements showed that there is nothing but a bandgap reference inside, presumably a Ref02 or similar.
MAXIM now knows about that asian seller.

BTW: If some of you have a few (used) MAX6350MJA in private stock and want to sell them send me a message.
Title: Re: Ultra Precision Reference LTZ1000
Post by: amspire on February 17, 2013, 01:42:07 pm
branadic,

Have you looked at the Thaler/Cirrus/Apex VRE305KS that was mentioned above?

http://www.ebay.com/itm/Low-Cost-Precision-Reference-IC-VRE305-VRE305KS-NEW-/221065482973 (http://www.ebay.com/itm/Low-Cost-Precision-Reference-IC-VRE305-VRE305KS-NEW-/221065482973)

SOP-8 Ceramic package and almost compatible with the Maxim device. Most specs as good or better then the Maxim chip. Major difference is that the VRE305KS has a seperate GND and Reference GND, so that the reference output is not affected by the IC supply current. Other differences are that the VRE305 required 13.5V minimum compared to Maxim's 8V and consumes slightly more current, but has better long term stability figures. The VRE also has a temp sensor junction in case you want to use it in an oven.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alm on February 17, 2013, 02:00:35 pm
Any idea how it compares to the much cheaper LM399 in real world figures? The spec for long term stability of the LM399 is much worse (20 ppm / 1k hrs typ), but we know from the many devices designed around it (including the far majority of the 6.5 digit DMMs) that it can perform much better. Is the same true for the VRE305? I guess it should be better since it runs at a much lower temperature, everything else being equal. But of course everything else is not equal.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 17, 2013, 02:52:30 pm
branadic,

Have you looked at the Thaler/Cirrus/Apex VRE305KS that was mentioned above?


Yes, I once did, but I only payed 5.80€ for an new LM399H, you can guess what I prefered to buy.

"...Fairic is a Hong Kong based company with China offices in different provinces..."

ebay + China + Precision Voltage References --> all my alarm bells are ringing. Thanks for the link, but I would never again move any finger to click on the "buy it now" button. The last seller also had nearly 100% positive feedback. I'm not sure if the guys who bought the MAX6350MJA too where able to measure their devices? They should have noticed that the device behaves contrary the datasheet.

This is a typical example of such a fake:
http://www.ebay.com/itm/Maxim-MAX297-MAX293MJA-MAX294MJA-MAX297MJA-8-Cerdip-IC-/260653697527?pt=LH_DefaultDomain_0&hash=item3cb02bc9f7 (http://www.ebay.com/itm/Maxim-MAX297-MAX293MJA-MAX294MJA-MAX297MJA-8-Cerdip-IC-/260653697527?pt=LH_DefaultDomain_0&hash=item3cb02bc9f7)
Notice the brand, this is how the MAX6350MJA fake was looking like.
Title: Re: Ultra Precision Reference LTZ1000
Post by: fmaimon on February 19, 2013, 01:11:59 pm
The guy sent me this photo. It has some strange things.
So, what do you think?
Title: Re: Ultra Precision Reference LTZ1000
Post by: amspire on February 19, 2013, 02:45:28 pm
The ThC logo is the older logo of Thaler Corp, and my Thaler datasheet is Rev D 2001. I have posted it below.

The USA marking and omitting the "S" off the end is in line with the way Thaler do it. I thought I had purchased mine in the early 2000s, but it looks like I got it in 2007, so I have a late model with the newer TC logo.

The case style is unusual, so there may not be any other reference ICs in an identical case. Mine has no visible ceramic cement between the upper and lower half of the case, but that many be a refinement after 6 years. The metal contact construction in this 2001 IC are slightly different to my 2007 IC.

Why has he got a photo of a more accurate "A" model when he is offering a "K" model? I do not know the answer to that question, except for the fact that to quote the part as a VRE305KS, he is not reading it off a chip - that may be the code of a tube, box, bag, or somewhere else. The IC will have the part number VRE305K.

Given the market price, it is possible that someone has got a REF02A chip (or similar) and put it in the SOP-8 ceramic package to make a fake. It would work in the same circuit, except the initial accuracy would be over 10 times worse, and the long term drift over 20 times worse. In the photo, the IC is sitting on a PCB, and may be soldered onto the PCB. It is odd.

I did an image search on Google, and no match for that photo was found, so the seller may have actually taken the photo.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 23, 2013, 10:47:32 am

He said he will probably try listing them on ebay soon. Maybe by next week, but i'm not sure. I honestly don't know if anyone will want to buy them, but we will see.

(http://i1010.photobucket.com/albums/af224/keen101/ltz1000_clone1_zps8a206777.jpg)

(http://i1010.photobucket.com/albums/af224/keen101/ltz1000_clone2_zps6454debe.jpg)

Any news about that? Couldn't find the offer yet, but was interested in the price too. Have them seen a burn-in test or are they just new and directly soldered to the board?
Strange, can't find any "LTZ1000" with it as keyword on e**y, only by searching for "HP 3458" and similar I get a few hits. What's going on there?

I made a table of the specs on all the precision references I found referenced on the "volt-nuts" list.

You'd like to share your table with us?
Title: Re: Ultra Precision Reference LTZ1000 (table of Vref data)
Post by: JBeale on February 27, 2013, 07:31:59 am
I don't know if I can attach the spreadsheet here...  when I print a PDF it does not look good (long rows are split across too many pages). Anyway you can find my list of voltage reference specs here:  http://www.bealecorner.com/pcb/vr1/Vref-table-Feb2013.xls (http://www.bealecorner.com/pcb/vr1/Vref-table-Feb2013.xls)

I did this just for my own purposes, it may not be accurate, and is surely not complete. But if you do see any mistakes, let me know.
Title: Re: Ultra Precision Reference LTZ1000 (table of Vref data)
Post by: EEVblog on February 27, 2013, 07:43:43 am
I don't know if I can attach the spreadsheet here...  when I print a PDF it does not look good (long rows are split across too many pages). Anyway you can find my list of voltage reference specs here:  http://www.bealecorner.com/pcb/vr1/Vref-table-Feb2013.xls (http://www.bealecorner.com/pcb/vr1/Vref-table-Feb2013.xls)

I did this just for my own purposes, it may not be accurate, and is surely not complete. But if you do see any mistakes, let me know.

Reposted as a handy PDF.
Nice work.

Dave.
Title: Re: Ultra Precision Reference LTZ1000
Post by: JBeale on February 27, 2013, 07:50:27 am
By the way, I just got two of the LTZ1000ACH (direct from Linear Tech- the ebay versions did not look promising) and am trying one out using the simplified +Vref schematic that uses a single LT1006 opamp, and does not use the heater. 

Both this and the more complex heater-stabilized "7V Positive Reference Circuit" schematic on p.6 of the LTZ datasheet use a 1N4148 diode from the opamp output to the Vref out (LTZ pin 3, zener cathode).  Can anyone explain what that diode is for? This is a single-supply opamp circuit so there is no chance of the output going negative. Is it some protection for the opamp in case of a badly-behaved external load, or something about power-up or power-off behavior?

I have tried this circuit with the diode and without, and as far as I can tell, the only effect of the diode is to require the opamp supply voltage to be 0.7 V higher than it would otherwise need to be to prevent a dropout (unloaded Vsupply threshold of 9.1 V instead of 8.4 V , in the case of a LT1013 and my particular LTZ1000A which provides a Vout of 7.2406 V, with the temperature compensating R1 at 25 ohms and Iz = 4.27 mA).

EDIT: I suppose the circuit is (meta-)stable with both inputs and the output sitting at 0.000 V, so there might be a startup problem. If so, does that diode alone actually fix it?  There is a version with an additional 10k pullup on the output (Figure 65 on p.15 of AN42, http://cds.linear.com/docs/en/application-note/an42.pdf (http://cds.linear.com/docs/en/application-note/an42.pdf) ) suggesting that is the issue.

EDIT2: Thanks alm for pointing to the answer; I should have seen those threads before.
Title: Re: Ultra Precision Reference LTZ1000 (table of Vref data)
Post by: BravoV on February 27, 2013, 08:08:01 am
JBeale, thanks for the spreadsheet, really handy.  :-+

Btw, Intersil also carries quite some number of Vref ICs as well.

Just read the link in your sheet -> http://www.febo.com/pipermail/volt-nuts/2010-September/000447.html (http://www.febo.com/pipermail/volt-nuts/2010-September/000447.html) , quite interesting result about MAX6350.

Quote pics :

(http://phk.freebsd.dk/misc/20100911_max6350_2.png)

(http://phk.freebsd.dk/misc/20100911_max6350_1.png)
Title: Re: Ultra Precision Reference LTZ1000
Post by: alm on February 27, 2013, 07:12:14 pm
Both this and the more complex heater-stabilized "7V Positive Reference Circuit" schematic on p.6 of the LTZ datasheet use a 1N4148 diode from the opamp output to the Vref out (LTZ pin 3, zener cathode).  Can anyone explain what that diode is for?

As you already guessed, it is for startup. See this thread on EEVblog (https://www.eevblog.com/forum/projects/does-anyone-know-what-this-diode-is-for/) and this thread on volt-nuts (http://www.febo.com/pipermail/volt-nuts/2012-November/002200.html) for more information.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 27, 2013, 10:50:16 pm
Andreas Jahn determined in his measurements, that references in plastic packages are very sensitive to humidity compared to their brothers in ceramic package. This sensitivity results in additional drift next to tempco. This is also a reason why I was searching for the MAX6350MJA, it's the CERDIP version.
It seems, that I now found a trustable source for that part, but it's even more expensive (16,10€) compared to the LM399AH (9,95€).
The LTC6655 is now available in a ceramic smt package (LS8) with excellent specs, but up to now only available as a 2.5V reference. This could be a worthy alternative to the good old stuff, awaiting the 5V version. And as by a wonder it is again some Linear part.
Title: Re: Ultra Precision Reference LTZ1000
Post by: JBeale on March 13, 2013, 05:10:39 am
Quote
The LT1021-7 also comes to mind-- with fewer internal resistors, this part will show exceptionally low long-term drift.  Again, you can find the hermetic part from various vendors, and you would be wise to ovenize it (along with any circuitry you might add to gain it up to 10V).

Interesting you should mention the LT1021-7. I have three of those (plastic DIP) that I've been running for several weeks. I am seeing several ppm of short-term drift (10-100 sec) but just a few inches away, a pair of MAX6350 parts (also plastic DIP) is stable to less than 1 ppm over the same time period.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 13, 2013, 09:53:06 pm
Quote
As far as long term drift goes, probably the Burr-Brown REF102 (now the TI REF102) is the best available voltage reference that is not ovenized

Well, we need to have a look on the new Linear Technology LS8 packaged voltage references, such as the mentioned LT1236-LS8 or LTC6655-LS8.
It's interesting that manufactors seem to have "unlearned" what was already done in the LTZ1000. I wonder if there will be a heated, 5V output buried zener in LS8 package or similar in near future, supplied with moderate voltages around 5V, a (still) typical value in todays analog circuits.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BravoV on March 14, 2013, 02:05:03 am
At Intersil's voltage reference they're using the term so called "floating gate" technology, is this the same as buried zener ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: amspire on March 14, 2013, 02:32:22 am
At Intersil's voltage reference they're using the term so called "floating gate" technology, is this the same as buried zener ?
No - very different. The floating gate depends on a stored charge as the voltage reference - a bit like a eprom memory cell.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BravoV on March 14, 2013, 02:56:40 am
At Intersil's voltage reference they're using the term so called "floating gate" technology, is this the same as buried zener ?
No - very different. The floating gate depends on a stored charge as the voltage reference - a bit like a eprom memory cell.
Ah thanks, no wonder they're worrying that the trapped charge will somehow "leaked" caused by xray like their appnote -> X-Ray Effects on Intersil FGA References (http://www.intersil.com/data/an/an1533.pdf)

Curious if there are any advantages of this floating gate over other old & proven technology like buried zener ? Cheap to produce maybe ?  :-//

PS : I've been "imagining" to use this xray effect to deliberately fine tune the trapped voltage to get high absolute accuracy, and once finished, sealed it in thick lead box.  ;D
Title: Re: Ultra Precision Reference LTZ1000
Post by: amspire on March 14, 2013, 11:06:55 pm
I have never seen anyone use a floating gate reference in lab gear. I have never used one myself either so I have no experience, but I prefer standards somehow constructed as hardware - like a buried zener - rather then something that sounds as vulnerable as a stored charge that can be affected by radiation and probably by heat as well.

I wonder how much the reference changed when if goes though soldering?

Buried zener references have a good record of maintaining accuracy after 20 years or more. Wouldn't have a clue about the floating gate reference performance over 20 years.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Jay_Diddy_B on March 15, 2013, 12:07:24 am
Hi,
The X-ray doses mention in the Intersil document are pretty low. They are using a machine capable of 10uA to 1000uA

A medical X-ray machine, used in hospitals are typically 30, 50 or 80kW. The 300kW machines can typically do 500mA at 60kV. The 80kW machines can do 1000mA at 80kV.

This is a thousand times higher than the dose mentioned in the Intersil document.

I think the concern here is that if you X-ray the board after soldering, for example to examine BGA soldering, then the reference will drift.

I would also be concerned about X-ray inspection during shipment.

The floating gate is essentially a charged capacitor. I just don't like the idea of assuming the capacitor won't discharge over time.

Jay_Diddy_B

Title: Re: Ultra Precision Reference LTZ1000
Post by: BravoV on March 15, 2013, 02:02:12 am
I just don't like the idea of assuming the capacitor won't discharge over time.
I believe that the 1st thing that pop out at everybody's mind is the word "leak" when seeing the word "trapped" charge.  ;D
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on March 17, 2013, 12:32:09 am
In a don't think, just act manner, I cobbled together something with a chinese ebay LTZ1000A.
Other ingredients are spare PCB space from another project, General resistance econistors, LT1013,Cu-Te lab sockets from Multicontact and a pair of homemade Cu-Te cabling.
The worst  thing about it is the layout which was thrown together without any patience. Star ground right in front of the LTZ, and a king-sized "GUARD" polygon.
I have only a HP3456A, workplace has only a bunch of 34401A multimeters, so there is still a long way to go for telling if it is doing well. During the next weeks I will have a meeting with a local volt-nut who has a bunch of LTZ and more knowledge. If number  one is doing well, I still have 2 or 3 more boards so I could set up a horde of references or give them away for others.

My idea is to use the HP3456A in DC:DC Ratio mode, using the LTZ as one of the DCs to have a low-drift DMM. EZGPIB (or processing cough cough) could turn the RATIO reading into a maybe not overaccurate but hopefully low-drift voltage reading.


Attached is some show-off:
Title: Re: Ultra Precision Reference LTZ1000
Post by: saturation on March 17, 2013, 12:04:31 pm
All you need from a reference is stability over time and high precision, once you know how much it drifts and resolve down to 1uV with the 3456a, 'accuracy' is just offsetting with a trimmmer the reference output or just applying an algebraic correction to obtain the accurate value.  So, now its a waiting game. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 17, 2013, 01:46:40 pm
I allready found your post on volt-nuts archive yesterday. As far as I understood you are using a LT1013 for A1/A2 (7V Reference Includes A1 Heater Control Amplifier, A2 Zener Current Regulator
and LTZ1000A Zener. AN-86 p.46) and a further LT1013 as output buffer?
Refering to your high resolution but low quality picture (wouldn't it be better to downscale the picture, ~1.6MB of such bad quality doesn't make sense) I found a CERDIP packaged chip in the lower left corner (doesn't look like a LT product)  and a plastic packaged LT part (LT1013?) in the lower right/middle. Both are directly soldered to the pcb. I would have used a precision DIP socket instead.

The next steps are clear, a complete burn-in, also thermal cycling and monitoring the ouput as already mentioned by Andreas Jahn.

Are you sure the LTZ1000A is a genuine Linear Technology product and not a plagiarism? Is it a new one or already been used and desoldered from a pcb? I feel sick to buy such products from chinese sellers, you never know what's inside the package.

BTW: As far as I recognized you are from germany?  So you could get the LT1013ACJ8 from a german distributor:

http://www.electronic-search.de/cgi-bin/electronic.pl?t=temsearch&f= (http://www.electronic-search.de/cgi-bin/electronic.pl?t=temsearch&f=)*BEZEICHNUNG1&start=1&dif=100&c=LT1013ACJ8&submit=Suchen

After all my experience with plastic packaged chips and humidity in conjunction with CDCs for capacitive sensors and after all I have read about humidity concerning voltage references I'm extremly sensitized to that theme and would prefer a CERDIP packaged instead of a plastic type in such a high precision arrangement.
I didn't get why all the metal can packages and most of the CERDIP are obsolete today without giving any hermetically sealed alternative to them. Did we lose the requirements or is it that they are just through-hole parts? So lets hope that manufactors find back to ceramic based hermetically sealed packages, that can be made as smd part too.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on March 17, 2013, 09:08:42 pm
@saturation: I even thought  about replacing the LM399-family reference in the HP with this first but canceled that idea. Keeping it external has some advantages. I need to check drift - a german volt-nut lets me compare mine to his LTZ bunch, that will help, and maybe I somehow get a good voltage reading from a cal lab on a napkin or such. DC:DC ratio, GPIB readout and some calculations are the most convenient way to measure referenced to the LTZ.

@branadic: Sorry, I right now replaced the unneccesary big image with a much smaller one. Yes the LTZ is from china, came to me presoldered and is the single ebay part, Resistors are from Rhopoint, Sockets Multicontact, other parts from Farnell including the LT1013s who shouldnt sell foo. The buffer opamp was a second thought, I first was considering leaving it off and use the mounting holes for a output filter but decided that i drop it in finally.

I am not that afraid of plagiarism, as it performs better than its heated REF102 predecessor and as i try to not be a real volt-nut, i will be satisfied easily. What gives me trust is that the voltage readout changed at most 40 µV according to my meter from the first power-up after soldering thru flux removal with LR, a run in the dishwasher and a 3-hour 60°C (not 80, sorry) cycle in the thermal chamber, all over the course of the days since march 2, with the DMM in a living room instead of a tempered cal lab.

Further thermal cycling will follow.

Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on March 27, 2013, 03:04:42 pm
because I was very buisy lately, I just saw I missed quite a few posts.

But here is my short update:
I still have no board yet, but have most of the main parts (directly from LT) and orderd some sets of Vishay Z-Foil Resistors.
I decided to go for VHP101 and Z201 to be able to compare, if the much higher price of VHP is worth it.
Because the Vishay leadtime is quite long, I hope I will find a board meanwhile.

bye
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on March 27, 2013, 05:36:50 pm
Short update: I got sick so not a lot of work done, but I found a suitable power supply for the reference which has a linear regulator and is marked as a medical grade TYPE CF supply.

Tomorrow I will buy a outer case and hopefully mount everything next week.

 

Title: Re: Ultra Precision Reference LTZ1000
Post by: free_electron on April 07, 2013, 11:50:45 pm
Allright you voltnuts... i got a piece of real hardcore volt p.rn for you... a teardown of a real standard.... keep your eyes peeled... massaging the pictures right now...
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on April 20, 2013, 03:35:16 pm
Further progress with my reference: Its no longer hidden in a cardboard box and now its really transportable and self-contained due to a power supply fixed to it.

The power supply is a medical TYPE CF grade device (the secondary will only push very low currents in the direction of PE), and the tinned sheet metal case is placed inside a bigger plastic case.
Also, the always necessary required red power LED is added.
 
The additional yellow 4mm socket is a connection to the "guard", consisting of the metal case and a copper pour on the PCB.

What is missing is labeling...



Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 04, 2013, 02:19:26 pm
While still waiting for the Vishay Z-Foil resistors, I decided to try (with Diptrace) to make my own board.
Here are the first things I consider what the final board should have:

- dual layer, material FR4 with 18 or 35µm copper, Gold plated 
- choice to place different sized components (https://www.eevblog.com/forum/diptrace/make-your-own-components-with-multiple-pads/ (https://www.eevblog.com/forum/diptrace/make-your-own-components-with-multiple-pads/))
- stress relief cutouts around LTZ1000 (https://www.eevblog.com/forum/diptrace/stress-relief-cutouts-on-pcb/ (https://www.eevblog.com/forum/diptrace/stress-relief-cutouts-on-pcb/))
- Output probably 7.2V plus 10.00000V (and maybe 1.018V)
- thermal isolation housing for LTZ1000
- low thermal output connectors
- guard copper pour on both layers
- star ground
- switchable external PSU to battery/accu powered

Are these valid thoughts so far or are there better suggestions?
What else could be a good idea to consider?
Any hints and suggestions are welcome.

Thanks
Quarks

edit: changed a few things in the schematic (incl. error correction)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Hypernova on May 06, 2013, 01:20:26 am
I have been studying this problem for a very lonnnnnng time...

And that folks, is why Volt-Nuts have "nuts" to their name... In comparison the most accurate references I got are three MAX63xx (one of each voltage) references I got from digikey.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BravoV on May 06, 2013, 01:24:11 am
DiligentMinds, thanks for great post !  :-+

I have been studying this problem for a very lonnnnnng time...

Damn, I'm curious on how long is that ?  ???
Title: Re: Ultra Precision Reference LTZ1000
Post by: chickenHeadKnob on May 06, 2013, 06:45:53 am

I have been working in electronics (professionally) since 1975.  I have been working on this problem for about 3 years now.  I finally decided to go with the 18-bit DAC for trim (as opposed to the PWM method that Datron used in their 4910 voltage standard, which later became the Wavetek (and then Fluke) 7000 series voltage standard.  The 18-bit DAC [0.25 LSB INL] will easily provide for +/-1.3mV of trim, at about 10nV per count.

And yes-- I am a "Volt-Nut" (I own a Fluke 732B), "Resistance-Nut" (I own an ESI SR104 resistor), and a "Time-Nut" (I have a GPS disciplined 10Mhz OCXO and network time standard)-- (well, really, I guess I'm really a "Precision-Nut"... Then...).  Very few people (other than Cal-Labs) actually *need* this kind of precision-- but there are those of us that strive for the ultimate in precision because it's fun, (and because we can)-- it is also an area of electronics that requires great skill and "finesse" to squeeze out that last bit of accuracy...  OR-- maybe we are just sick...


I completely understand the psychological draw of precision nuttery, it activates the same part of the brain as mind teasers, crossword puzzles ect. with the added attraction that you are dealing intimately with the real physical world and not merely some mental construct . I am too pragmatic to spend my time solving crossword puzzles but after looking a bit through the volt-nut mailing list I became consumed with thinking about  high precision analog to digital conversion. Looking back maybe my posts indicated some derision, but really I am making fun of my own captivation.
Title: Re: Ultra Precision Reference LTZ1000
Post by: amspire on May 06, 2013, 06:57:02 am
I have been working in electronics (professionally) since 1975.  I have been working on this problem for about 3 years now.  I finally decided to go with the 18-bit DAC for trim (as opposed to the PWM method that Datron used in their 4910 voltage standard, which later became the Wavetek (and then Fluke) 7000 series voltage standard.  The 18-bit DAC [0.25 LSB INL] will easily provide for +/-1.3mV of trim, at about 10nV per count.
I would imagine that to the Datron/Wavetech/Fluke designers, the PWM solution is very much superior to the DAC solution as the errors and drift for the PWM are fully calculable. The errors for the DAC are not - you have to trust the specs of the DAC manufacturer and that is something metrology people hate to do. It is possible to get much better stability then an 18 bit dac with PWM but as always, when you get to that precision, it doesn't take much to destroy a few ppm accuracy.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 06, 2013, 10:19:57 am
Hello DiligentMinds.com,
wow that is a lot of very good and interesting Information. Thank you very much, for sharing your knowledge. That gives me indeed some new ideas.

...consider using an LT1051 instead of the LT1013 ... you could use a quad chopper (LT1053A)
I will check the LTC1051 and LTC1053

The two 70K resistors should be ultra-high quality metal-film type-- accuracy is not that important (they could be 0.1%), but they should have as low a temperature coefficient of resistance [TCR] that you can find-- probably 5ppm.

The 120-ohm, 12K/1K-divider, and 10V-output-divider resistors all need to be a metal-foil resistors from Vishay Precision Group-- their newest "Z1-foil" resistors are the best, and will have the best long-term stability.  These will be about $10 each, if purchased from an authorized distributor.  If you can afford it, the hermetically sealed type will have even better long term stability-- and will reduce variability due to humidity and barometric pressure changes.
I tried to find the best possible resistors and ordered Vishay Z-Foil (the hermetically sealed VHP101 and the lower cost Z201). They have very long lead time (probably 5 more weeks for me to wait). I wonder where your 10$ price point comes from, because I paid up to more than 50$ for one, so please let me know. 
The "LTZ1000(A)" does *NOT* need to be "stress relieved". 
That is good news, because I still have no idea how to do that with diptrace (but I am still interested to know if/how it is doable)

although it should be covered with something (both top and bottom), because any air flow (as in convection currents) will cause tremendous low-frequency noise (due to the thermal EMF's between the Kovar package leads and the copper PC board).  You can use anything for the cover-- you're just trying to stop air-flow-- not make an insulated box.
I have only thought of a top cover so far, but now will think about how to do a bottom one too
Your schematic doesn't appear to have any way to adjust the 10V output.  If I were doing this, I would make the 10V-divider a 3-resistor type (with 3 resistors in series).  The bottom resistor would always be 5K (for 5V) and the next two would total up to 5K, but their values would be governed by the actual voltage of the 7V reference output (after 300-hour burn-in).  When you order metal-foil resistors, you can specify the exact value you need, and they will supply you with that value (at the tolerance that you pay for).  The 10V-divider resistor tolerances should be (at least) 0.01%.  The reason for the 3-resistor divider, is that now you have a 5V node that can be used to adjust the 10V output.  At this 5V node, you would tie 1M-ohms to 5M-ohms of resistance (depending on the sensitivity you need) made up of one or more 5ppm metal-film resistors.  The other end of this large resistor would be tied to either a potentiometer (the Vishay Precision Group 1285G series) or (even better) an unbuffered 16-bit or 18-bit DAC (TI DAC8871 or Analog Devices AD5781).  You would tie the Vref-H directly to 10V-out at the banana jack, and Vref-L directly to ground at the banana jack-- do not use buffers (as their ap-notes say to do) on either the reference inputs or on the output voltage.  Without the buffers, the INL spec will suffer some, but the repeatability and time+temperature drift of the output will be ~0.05ppm.
About the trimming of the 10V, I have considered some options, but not decided yet which to choose. That is why the schematic still shows the AN86 suggestion with fixed Vishay VHD200 ratio set. But I have not orderd this and will probably go for either:

- similar to your suggestion with a precision trimming circuit as you decribed (also already ordered together with the other parts the Z-Foil Trimmers 1260 and 1285)

- with KVD as shown in AN86 (see att.), for this I could use my Fluke 720A and/or my ESI Dekapot
   In the drawing are X= solder copper juctions, how should/can this be done? Just leave a gaps and bridge it with solder or with a via and fill it with solder?

Your DAC suggestion is probably to complicated for me.
And I do not know yet if I even maybe leave it as simple as possible and just go for a chopper buffered nominal 7.2 Volt Output and do anything else externally (if I ever want/need it).

Another thing you could do is place a (fc=100mHz) low pass active filter between the reference output and the 10V amplifier-- something using a very low-noise amp (like the LT1112), and a DC-agnostic topology for the filter (like here):

http://www.millertechinc.com/pdf_files/MTI%20TN094%20Zero%20DC%20Offset%20LPF%20and%20the%20D%20Element.htm (http://www.millertechinc.com/pdf_files/MTI%20TN094%20Zero%20DC%20Offset%20LPF%20and%20the%20D%20Element.htm)

Another thing you might consider (especially if you are using an LT1053 quad chopper), is to use 2 of the chopper amps to "discipline" a low-noise amplifier (like the LT1097 for example)-- this will lower the DC error and 1/f noise of the LT1097, while at the same time, you will enjoy the low voltage noise.
I will check that
And finally, if you can afford it, I would do 2 additional things-- first, think about putting the whole circuit in an oven.  In this case, you would use the lower-cost LTZ1000 (not the 'A' version), and control the outer oven's heater with the LTZ1000's temperature sensing transistor.  In this configuration, the LTZ's internal heater is not used.  Set the oven temperature to keep the LTZ die at ~45-deg-C, for a reasonable compromise between a good environmental temperature range, and low long-term drift-- (higher temperatures cause more drift over time).  The other thing I would do (if you are really serious) is go with the hermetic resistors (as I mentioned above) and also use a hermetic packaged LT1053.  (The other amps and the buffer don't matter-- their drift is controlled by the LT1053, and the LT1112's drift will not affect the DC value of the reference if you use the DC-agnostic filter I showed you in the link).

If you can only afford one hermetic resistor, let it be the 120-ohm Zener current control resistor (or whatever value you use for this)-- as this resistor is the most critical in the circuit.  The other resistors (the temperature control divider and the 10V divider) will tend to drift together, and we are only interested in their ratio (mostly if you discount the error caused by the output trim circuit if the 10V divider drifts).

If you do all of the above, you would probably get around 0.75ppm (7.5uV) of drift per year, which is *VERY* good.  But if you REALLY want to get crazy, forget about the hermetic resistors and LT1053 (just use the epoxy versions) and place the whole circuit on top of a double-stack Peltier device-- all inside of a hermetic package (yes, they make them that big).  Inside of the hermetic package, you would insulate the circuit with silicone foam rubber (which can handle the high heat used to solder the cover on).  The hermetic package would then be fastened to a heat sink that would be fan-cooled.  So now, instead of controlling the LTZ's die temperature to 45-deg-C, you are controlling it to 10-deg-C (or even lower if you filled the package with nitrogen or argon before sealing).  Doing this would get the long-term drift down to less than 0.25ppm (2.5uV) per year-- which is phenomenal, and would far exceed anything currently available at any price (except for a Josephson Junction Array).

How do I know all of this?   I have been studying this problem for a very lonnnnnng time...

I have already bought several LTZ1000ACH, LT1013ACN8 and Z-Foil resistors (and have some Burster) to make two or maybe 4 boards.
The hermetic packaged LTC1051/LTC1053 I have not seen/found yet. Do you know where to get it?

About your really get crazy suggestion, I would like to talk about that in more Detail. 

Thanks again for your great post.

bye
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 06, 2013, 10:39:25 am
...yes-- I am a "Volt-Nut" (I own a Fluke 732B), "Resistance-Nut" (I own an ESI SR104 resistor), and a "Time-Nut" (I have a GPS disciplined 10Mhz OCXO and network time standard)-- (well, really, I guess I'm really a "Precision-Nut"... Then...). 
You are indeed a "Precision-Nut" and I probably have the same "sickness".
I already have build up my own/private small "Cal-Lab" also with ESI SR104 and other goodies. Unfortunately I do not have a Fluke 732B (or equiv.) thats why I hope to be able to make a very good LTZ1000 reference.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 06, 2013, 01:24:58 pm
Only LTC1051 was produced in hermetical sealed package:

LTC1051MJ8
LTC1051CJ8
LTC1051AMJ8
LTC1051ACJ8
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on May 06, 2013, 04:50:23 pm
The building phase of my LTZ1000A reference is over, besides a yet undecided buffer opamp removal which will happen after the next measurement for longterm behaviour after 1 or 3 months. Or not.

It was measured against a HP3458A for 31.75 h statistics: standard deviation 0,09 ppm, measured values spanning a range of 0,55 ppm. 24 h statistics: standard deviation 0,06 ppm, spanning 0,47 ppm.
(Measured in 5s intervals.)

Sure good enough for me. Thermal/Stress relief drills close to the LTZ1000A, stress relief milling for the connectors,
quarks knows the board.

BR

Hendrik
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 06, 2013, 06:29:32 pm
...What you are building here, is something close to (or possibly even better than) the Fluke 732B.

Close to a 732B, that would be a great result for my project.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 06, 2013, 06:33:23 pm
quarks knows the board.
yes thanks to Hendrik, I already have two of his boards for experimenting purposes
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on May 06, 2013, 06:59:49 pm
@quarks: And I think I am going to visit you when you have finished :)

I am very happy about the outcome of my reference. Way better than its ovenized REF102-based predecessor.

I am currently preparing a webpage about this device with basically the things I already told you and have shown here, where I will put the future measurements too. Just because there seems to be interest.

Having 2 useless HP boatanchors sitting here (HP6632B which spikes to full voltage and shuts output off see other thread here and a HP3455 that has trouble starting up and which 100V range reading of a 10V value is about 0.4% higher than in 10V range, possibly some switching FET died.) there are other things to do. But the LTZ Reference & Dekavider will certainly help with validating the 3455A repair, but still wish me luck and patience :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rufus on May 06, 2013, 07:19:56 pm
The "X"'s in the ap-note you attached are exactly what you said.  Just create a 2-lead symbol in your schematic editor and a footprint in your PC design package that it just 2 pads very close together-- these are shorted together with solder.  The reason this is done in this circuit is to balance the thermal EMF's of the various connections made with dissimilar metals.

So how is that supposed to work? If you have essentially identical copper->solder and solder->copper junctions in series how is that supposed to generate any emf unless there is a thermal gradient across the blob of solder?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 06, 2013, 07:44:27 pm
Quote
The Z-foil resistors you bought are quite good-- the newer Z1-foil resistors only have a slight improvement over them (mostly in load-life).  Since you will be operating the resistors at very low power levels (in relation to their ratings), there should not be much long term drift anyway.  Make sure you bake them in an oven at 125-deg-C (~257-deg-F) for 1000 hours before you install them-- this will help "season" them, so the initial drift will be very low.

You can also pre-age the resistors by power cycle the resistors near the specified maximum rating with an ac voltage, 1.5h power cycle, half an hour cooling and again...
Something similar is also described in Vishay's app notes.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 06, 2013, 08:03:32 pm
Quote
Yes-- if you have no thermal gradients, you will have no thermal EMF's.  Unfortunately, you can try to get rid of the gradients, but it is impossible to do so completely-- thus the need for other solutions.  I think I mentioned on an earlier post, that using epoxy-glass printed circuit material for this kind of precision circuitry is just *asking* for trouble.  This board material (like most epoxy materials) soaks up the water from the air, and then swells-- creating higher leakage and mechanical stress on the components.  With this kind of circuitry, it is wise to use a higher grade material-- like Rogers "RT/Duroid 6035HTC"-- they won an award for developing this material-- it is made of a mixture of powdered alumina and PTFE (Teflon)-- and so you get excellent electrical properties, with very low thermal impedance and gradients, which is exactly what is needed in this application.

What about using LTCC as substrate? In this range of precision this can't be that expensive and you could spend the second layer for an temperature control circuit such as this:

http://www.kuhne-electronic.de/en/products/crystal-heater/qh-40-a.html (http://www.kuhne-electronic.de/en/products/crystal-heater/qh-40-a.html)

a single sided design.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rufus on May 06, 2013, 08:22:34 pm
Wall of text omitted

So basically you can't say how it is supposed to work.
Title: Re: Ultra Precision Reference LTZ1000
Post by: c4757p on May 06, 2013, 10:20:41 pm
He's quoting your entire, long previous comment and leaving out the text so as not to fill the reader's screen.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chickenHeadKnob on May 07, 2013, 12:00:12 am
@diligentMinds:

I am still digesting the references you have given, thank-you. One question to clarify: you state that epoxy packaged parts are still useable if the entire unit is in a hermetic (ovenised) package, does that also apply to FR4 ?  For the hobbyist, not having to chase down exotic circuit board material and rare parts would be a great benefit. I am pretty sure I can construct an aluminum can with teflon gaskets and purge/fill with dry nitrogen at a lesser cost.

Edit: sorry I see you already answered this, use the best stuff you can get. I need to do some experiments in a chamber just to confirm to myself how good or bad FR4 is.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chickenHeadKnob on May 07, 2013, 08:45:59 am


Unless you use a package that has true hermetic sealing (borosilicate glass and Kovar steel, with the cover silver-soldered on), I'm not certain that you would be able to keep the humidity out.  Water vapor has a strange way of finding a path through most materials-- including most epoxies and most silicone compounds.  Like this (for example):

http://www.sinclairmfg.com/catalog/hybrid.html (http://www.sinclairmfg.com/catalog/hybrid.html)

The problem with the Kovar/Pyrex hermetic packages is that the Kovar leads make *great* thermocouples when in contact with copper-- this is *not* what we want-- (is there another way that is effective)?

I'll be the first to admit that I am *not* a mechanical engineer-- Is there someone on this forum that can speak to this?  How do we make a high-performance hermetic package using materials a hobbyist can obtain?  We want something that will stop water vapor from entering the package, and (secondarily) we want to mitigate the effects of barometric pressure changes.  (The temperature we will control actively).

I am way behind and trying to play catch-up hockey here, so my ideas are likely something you have already thought of and discarded. As I only possess a simple mind my solutions tend to the brutally  simple. Some ideas I have been toying with tonight:

with all of the above I am also considering an oil bath (degassed,dewatered mineral or silicone) with pressurized nitrogen headspace, connections to outside through nitrogen so that you wouldn't have leaking oil.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Hypernova on May 07, 2013, 12:32:55 pm
Regarding the issue of board thermal conductivity, how about metal core PCBs? Just wondering out loud.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 08, 2013, 07:27:18 pm
Quote
I'll be the first to admit that I am *not* a mechanical engineer-- Is there someone on this forum that can speak to this?  How do we make a high-performance hermetic package using materials a hobbyist can obtain?  We want something that will stop water vapor from entering the package, and (secondarily) we want to mitigate the effects of barometric pressure changes.  (The temperature we will control actively).

Well, there are a few possible ways. You could use second-hand double oven oxco's in the bay and reuse the package, buy hermetic packages from companies like Schott:

http://www.schott.com/epackaging/german/overview/products/gtms/index.html (http://www.schott.com/epackaging/german/overview/products/gtms/index.html)

or construct your own hermetic package using rf-metal cases, copper or brass sheet metal and feedthrough capacitors for the electrical contacts from inside to outside.
Avoid sealing materials such as silicon, this is not hermetic at all, no epoxy glue nor plastic. To reach hermetical sealing prefer soldering, welding and ceramic or glas as they are diffusion resistant, exactly what you want. I again would also recommend to use LTCC, the substrate you will find if you open for example an oscillator. This could be cheaper compared to your mentioned Rogers 6035HTC.
Dry the package and fill it with nitrogen before closing it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: muvideo on May 08, 2013, 08:12:55 pm
Quote
I'll be the first to admit that I am *not* a mechanical engineer-- Is there someone on this forum that can speak to this?  How do we make a high-performance hermetic package using materials a hobbyist can obtain?  We want something that will stop water vapor from entering the package, and (secondarily) we want to mitigate the effects of barometric pressure changes.  (The temperature we will control actively).

Well, there are a few possible ways. You could use second-hand double oven oxco's in the bay and reuse the package, buy hermetic packages from companies like Schott:

http://www.schott.com/epackaging/german/overview/products/gtms/index.html (http://www.schott.com/epackaging/german/overview/products/gtms/index.html)

or construct your own hermetic package using rf-metal cases, copper or brass sheet metal and feedthrough capacitors for the electrical contacts from inside to outside.
Avoid sealing materials such as silicon, this is not hermetic at all, no epoxy glue nor plastic. To reach hermetical sealing prefer soldering, welding and ceramic or glas as they are diffusion resistant, exactly what you want. I again would also recommand to use LTCC, the substrate you will find if you open for example an oscillator. This could be cheaper compared to your mentioned Rogers 6035HTC.
Dry the package and fill it with nitrogen before closing it.

Another option, for prototypes at least, is copper clad pcb board used as enclosure,
35um copper should be enough as moisture barrier.

As for sealing materials,  it's true that most polymers are unable to stop water.
Silicone is uneffective as barrier, it let pass water and also higher molecular weight
vapours,  we learnt the hard way, I had some headaches with white leds blackening,
and then understood that silicone dome is essentially transparent to most vapours.

The only exception I know is parylene, AFAIK it's used as conformal coating, and
is deposited using chemical vapour deposition, not easy to deal with.

I'm still wondering if there is any cheap way of pumping out the water, to keep the
umidity constant.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 09, 2013, 03:45:17 pm
I have worked on the schematic a little more (if I go for a experimenting board, where I can change between different OP amps and Output options), but do not yet know if I will go that way.
I have implemented the X=solder-copper-junctions and jumpers to be able to either connect to Zener + Sense directly or after the chopper amp buffer or if I want to, to connect the KVDs (like in AN86 Figure C7).
I also think about guard rings (as descr. in att.) but do not yet know how to exactly do it with DipTrance. 

For the best possible results I will probably make a design without any jumpers/sockets. But I first want to find out what is the best possible solution.

Comments and/or more hints or are welcome
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on May 09, 2013, 04:32:13 pm
I consider a big guard polygon sufficient, there is not a big need to count picoamps here and use guard rings which are seemingly a problem in DT. Compared to real picoampere applications where a leaked electron is gone when it is gone, the ZENER+ supply will provide the next one. I wouldnt put too much sub units (amplifiers) on the reference board; maybe you want the amplifiers behind a KVD, maybe not, and good housing is easier with a smaller PCB.

You can easily use an external buffer/amplifier circuit and measure the voltage difference from the well-known input coming from the LTZ to your output if it is external, an internal buffer hides the reference from you if you dont go for a test point. (My possible-problem, my buffer brings up a unknown value of 35-40 µV offset but hopefully stable.



Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 10, 2013, 09:20:04 am
The most sensitive point on this circuit is the base connection to the temperature sensor transistor on pin-6 of the LTZ1000.  You could create a guard-ring (which is just like all other traces in your PC design package) that surrounds all of the connections to this node (on all layers of the PC board).  The guard would be connected to the collector of that same transistor (pin-8 of the LTZ1000).  The rest of the circuitry will work just fine without any guarding. 

Very good, I will try the guard ring around pin-6.
What do you think about the guard copper pour on both layers connected to the case? Will this help if it is also inside the ring?

If you use higher quality PC material (the material I already suggested in a previous post, or the ceramic material already mentioned by others), then this guard ring could be left out-- *however* do *NOT* use water-soluble flux for soldering-- this leaves a residue behind that is very difficult to remove-- and it is conductive enough to cause problems with sensitive circuits such as these.

Does anyone know a PCB maker (pref. in Europe) offering PCBs with this material?
What is the best way and stuff to clean the board? I have tried several (IPA, Aceton, pure bio Ethanol), but I am not yet happy, if I look at it under my microscope after cleaning. Even "my special mix" for camera cleaning looks not quite perfect.

...LT1881, it seems that this part doesn't have sufficient common-mode [Vcm] down to ground on the Inputs...bias the LTZ1000 *must* work down to 0V on the inputs.

thanks I missed that (LT1881 is now off the list, already changed it in the schematic)

The LT1051A has excellent specs for this purpose-- and you can probably find original units in the ceramic package...
I'm guessing Minco-Tech will charge you ~$10-$20 for each one in small quantities.  ...
...I would use an LT1051A, because it has the best long-term (time) drift and temperature drift of all of the possibilities...
If your not going for the highest accuracy possible, then, what's the point?

That is the plan and I will try to do the best I can achieve (within my limits).
I will now first order the easy to get LTC1051CN8 package, so I can at least have a first look at it and compare to the LT1013 I already have.

Thanks again for sharing your knowledge
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on May 10, 2013, 09:56:19 am
Hi Quarks,

The guard ring: should be on both sides of the PCB, and be the first thing the guarded node sees, so no cooper pour inside the guardring. Dont just guard pin 6, but the whole node. I suppose you will not be able to discern if you lose anything when you don't guard but as it is free...

Advanced PCB substrate: Leiton HF provides rogers RF materials, will not be cheap. You might want to get a brick of teflon and press cooper nails in it and build your circuit from nail to nail.

For cleaning:  Run the populated board through the dishwasher gets rid of a lot. Or try to get your hands on dichlormethan (toxic!). I have Tetrahydrofuran as a plastics solvent at work, so not so healthy, if you want to give it a try and report back, i could bring you a sample.

You might want to do a hermetic housing for the reference circuit, suggestions:

Use the same tuner-style sheet metal boxes from otto schubert that I used. If you solder them all around you should have your hermetic seal and the sheet metal will spread heat if you use a double oven - cooler method.
To connect the power supply and extract the stable voltage and test points, use thru-hole capacitors - otto schubert or oppermann have them. Ceramics should block water better than silicone and plastics.

You could heat it up gently for a while - below 70°C for a extended period of time, and when sealing use cold air which contains low humidity and silicagel  to keep water vapour content out of the sealed box.

Include a heating resistor and a NTC inside the box, too, in case you want to double ovenize it one day or at least want to know the inside temperature.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 10, 2013, 11:08:40 am
Hello Hendrik,

yes I alredy planned to have the guard ring around all involved connected parts (similar i.e. see att. Datron/Wavetek board). That makes a ring around a "quite large" space. That is why I wonder, if I also should have the copper pour inside connected. 

If I can find a manufacturer with Rogers or similar material, I will hopefully not be shocked by the price. I already invested so much time and money, therefore it will probably not stop me to go for it. But we will see. 

About your dishwasher tip, I would not do that. I do not even like to use my ultrasonic cleaner, because I do not want the whole assembly ducked in the fluid.
About Tetrahydrofuran cleaner, that sounds like asking for cancer and I will stay away from it.

So far I have pre choosen ROSE housing like
http://www.reichelt.de/Rose-Aluform-Gehaeuse/ROSE-04-08-12-08/3/index.html?;ACTION=3;LA=5;ARTICLE=102470;GROUPID=5200;artnr=ROSE+04.08+12+08 (http://www.reichelt.de/Rose-Aluform-Gehaeuse/ROSE-04-08-12-08/3/index.html?;ACTION=3;LA=5;ARTICLE=102470;GROUPID=5200;artnr=ROSE+04.08+12+08)
It is not exactly hermetic housing but at least IP66 sealed.
But I also would like to see your solution, when we meet.

Temp meassurement inside the box is an option I have already thought of, but not yet implemented.

bye
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 11, 2013, 12:37:02 am
Quote
So far I have pre choosen ROSE housing like
http://www.reichelt.de/Rose-Aluform-Gehaeuse/ROSE-04-08-12-08/3/index.html?;ACTION=3;LA=5;ARTICLE=102470;GROUPID=5200;artnr=ROSE+04.08+12+08 (http://www.reichelt.de/Rose-Aluform-Gehaeuse/ROSE-04-08-12-08/3/index.html?;ACTION=3;LA=5;ARTICLE=102470;GROUPID=5200;artnr=ROSE+04.08+12+08)
It is not exactly hermetic housing but at least IP66 sealed.
But I also would like to see your solution, when we meet.

Dear countyman, you better use TEKO 371 / 372 / 373 / 374 / 392 / 393 / 394 / 1680 / 16120 or 16160 instead of your IP66 case.

I clean my pcbs with IPA in a bag in a heated ultrasonic cleaner, that works fine for me.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 12, 2013, 01:06:27 pm
Dear countyman, you better use TEKO 371 / 372 / 373 / 374 / 392 / 393 / 394 / 1680 / 16120 or 16160 instead of your IP66 case.

I clean my pcbs with IPA in a bag in a heated ultrasonic cleaner, that works fine for me.

Hello branadic,

thank you for your reply.
The TEKO could be good for inner shielding. But they only seem to be max. 28mm high (that is not enough, when I want to use my Burster resistors). For the outer box I want a decent + sealed one and the ROSE is so far overall the best I could find.

About your cleaning method, please confirm if I got it right.
You put the fully assembled board in a bag and then fill this bag with IPA and then put it in the heated ultrasonic cleaner.
What is your tip/method after that with the cleaned but "wet" assembled board?

bye
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on May 12, 2013, 01:39:21 pm
Please excuse my butting in.  IMO Ultrasonic cleaning only dislodges the dirt and gets in suspension/disolved in the cleaning solution. You must thouroughly rinse after the ultrasonic with virgin solvent that is at the purity level you are after. And that rinse should be a spray rinse not a dip rinse.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BravoV on May 12, 2013, 01:44:26 pm
And that rinse should be a spray rinse not a dip rinse.

Cause the dissolved contaminant even dilluted, will form an even "coating" throughout the object ? |O
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 12, 2013, 01:57:36 pm
There are bigger rf cases available, not at Reichelt but from several other providers:

http://www.ukw-berichte.de/ukw-docs/bau-lit/gehause.html (http://www.ukw-berichte.de/ukw-docs/bau-lit/gehause.html)
http://www.pollin.de/shop/dt/NjI5OTM1OTk-/Bauelemente_Bauteile/Gehaeuse/Gehaeuse_5.html (http://www.pollin.de/shop/dt/NjI5OTM1OTk-/Bauelemente_Bauteile/Gehaeuse/Gehaeuse_5.html)

You got me right, that is exactly the way I clean my circuits. The ultrasonic cleaner is filled with DI-water, sure. Avoid using acetone as not all parts and packages can withstand it. There are a few sorts of plastic that will get etched. I'm not sure how your Burster resistors will behave.
After cleaning I dry the board with compressed air, but you can also put it in an oven for a while.

I don't know a manufactor for LTCC or the mentioned Rogers 6035HTC in germany, but maybe the use of RO4003C is an alternative choice? There is a german guy who manufactures them for a fair budget www.pcb-devboards.de (http://www.pcb-devboards.de) also in 1.6mm. I expect this material has lower moisture absorption compared to FR4 and the Tg is much better Tg>280°C DSC (IPC-TM-650 2.4.24).
Even if it is said to be not nessecary I would nevertheless provide the slots in the substrate. Do what ever you can to get minimal stress to the leads. You will find statements that quote that this package is not sensitive to stress, but I wouldn't count on that if you want the last ppm.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 12, 2013, 03:46:57 pm
There are bigger rf cases available...

You got me right, that is exactly the way I clean my circuits...
After cleaning I dry the board with compressed air, but you can also put it in an oven for a while.

I don't know a manufactor for LTCC or the mentioned Rogers 6035HTC in germany, but maybe the use of RO4003C is an alternative choice? There is a german guy who manufactures them for a fair budget www.pcb-devboards.de (http://www.pcb-devboards.de) also in 1.6mm. I expect this material has lower moisture absorption compared to FR4 and the Tg is much better Tg>280°C DSC (IPC-TM-650 2.4.24).
Even if it is said to be not nessecary I would nevertheless provide the slots in the substrate. Do what ever you can to get minimal stress to the leads. You will find statements that quote that this package is not sensitive to stress, but I wouldn't count on that if you want the last ppm.
Thanks again.

the inner shielding would be nice to have, but if it not fits in size, I will have to change my board size, outer housing connector positions and so on. Therefore I think I will start with the ROSE and get a Teko 392 which seems to just fit inside. 

good, I got the cleaning part right. For a naked board this sounds good to me. But when I order my boards, I will hopefully get a perfectly clean surface. And for my soldered fully populated one, I still feel uncomfortable.

I will contact your suggested manufacturer. I also found a note, that my local PCB maker can offer a so called "Teflon" Type board (he descr. it Keramik-Polymer for HF and names Rogers, Taconic). I will try to find out details about it next week.
If I can, I will still try to get Rogers RT/Duroid 6035HTC and also ask for your suggestion RO4003C.

About the slots in the board, I still do not know, how to do it in Diptrace (other than just drill holes around the LTZ like Hendrik did, but still interested to find out). If it is easy doable and does not make problems with the rest of the layout I am considering it.

bye
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 12, 2013, 04:15:50 pm
Quote
And for my soldered fully populated one, I still feel uncomfortabe.

You can do the cleaning procedure twice, but up to know I had absolute no problems. As said I heat the ultrasonic bath too.

Quote
About the slots in the board, I still do not know, how to do it in Diptrace

Just draw the slots in the dimension layer and make them as suggested by the pcb manufactor (normally >2mm for the milling tool), that's it.

(https://www.eevblog.com/forum/index.php?action=dlattach;topic=15982.0;attach=44722;image)

https://www.eevblog.com/forum/projects/lm399-based-10-v-reference/msg219527/#msg219527 (https://www.eevblog.com/forum/projects/lm399-based-10-v-reference/msg219527/#msg219527)

But why not use an "off the shelf" program such as Eagle Light or KiCad?
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 12, 2013, 06:31:44 pm
You can do the cleaning procedure twice, but up to know I had absolute no problems. As said I heat the ultrasonic bath too.

with a "cheaper" design I would just give it a try, but here :-//


Just draw the slots in the dimension layer and make them as suggested by the pcb manufactor (normally >2mm for the milling tool), that's it.

(https://www.eevblog.com/forum/index.php?action=dlattach;topic=15982.0;attach=44722;image)

https://www.eevblog.com/forum/projects/lm399-based-10-v-reference/msg219527/#msg219527 (https://www.eevblog.com/forum/projects/lm399-based-10-v-reference/msg219527/#msg219527)
in principal I know what to do, but in Diptrace I just have not yet found out how to really do it.

Have you build the linked board? That really looks great  :-+!!!
What have you used to make it?
How did you make the thermal isolation block, is it Teflon or plastic?

But why not use an "off the shelf" program such as Eagle Light or KiCad?
I have used Eagle many years ago and now tried Diptrace, which I already like better.
KiCad I have not yet tried. Have you compared these programms?

bye
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 12, 2013, 07:12:36 pm
Yes I have build the linked board twice, one for a friend and one for me. It was also cleaned in IPA with ultrasonic. ;)
After first measurements I replaced the LT1001 by the CERDIP version, had the luck to find two of them in the bay.

I made a >300h thermal burn-in at 120° without power supply, it was then running a few weeks. I then assembled a heater on top of the resistors cause I only used 5ppm 0805 SMD resistors and it is now running a few weeks in the lab at 21.4°C and RH=32% with heated resistors. The reference is stable at 10.00179V-10.00180V there, measured with a 34401A the whole time. Still have no own >6.5 digit meter yet.

The board is normal black FR4, manufactured at pcb-devboards. The layout was inspired by the different pictures of boards with the LM399 in web.
The thermal isolation is made off PA6/6, two caps screwed together and filled with non-conductive foam, the slots are still free inside. It is just to keep airflow away. It's not that I have a use for this board as the voltage is also not common these days, but it was nice to see what can be reached with small amount of invest.

I've tried KiCad but decided to use Eagle Light as we have the "professional" version at work, so I can easy transfer bigger and multilayer designs at work and finish the layout there.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on May 12, 2013, 07:23:05 pm
@Quarks: There is a PCB distribution house right in your town, chances are good that you can ask them for Diptrace hints.
I can tell for sure as my wife was working there, spending a lot of time explaining customers (like me) how to do stuff with EAGLE, as that was the CAD system she was responsible for :-DD



Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 12, 2013, 07:40:08 pm
Quote
I can tell for sure as my wife was working there, spending a lot of time explaining customers (like me) how to do stuff with EAGLE, as that was the CAD system she was responsible for

There is no need to discuss about the quality of Eagle, it's far away from professional even in the "professional" version, the libs are mostly buggy and wrong in layout, but if you have updated most of the libs it is as easy to use as MS Paint :)
I have made a lot of boards with Eagle up to now, from rf to high resolution pcb based sensors, high precision or simple analog stuff, test equimpent like my DC-500MHz FET probe etc. It is up to the user to be able to calculate impedance matching and things like that, but it's not always a disadvantage to be able to do that. It's good to have the basic layout skills. ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 13, 2013, 09:36:13 am
@Quarks: There is a PCB distribution house right in your town, chances are good that you can ask them for Diptrace hints.

I already contacted them. They unfortunately do not seem to know Diptrace at all.

edit: with the kind help of fmaimon here is the solution http://www.diptrace.com/forum/viewtopic.php?f=4&t=8964 (http://www.diptrace.com/forum/viewtopic.php?f=4&t=8964)
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on May 15, 2013, 01:07:07 pm
Lets not start a hate-war-religion-thread about layout packages :-DD

Does any of you gentlemen seeing the need for burn-ins and big magic slots and guardrings and vhp202 resistors have a method to show or measure the improvements of those thingies against a easy "cheap-ass"approach as mine? How much better do you want to be ?

Title: Re: Ultra Precision Reference LTZ1000
Post by: saturation on May 16, 2013, 11:10:41 am
I wouldn't be surprised if your 732B actually is far less than 2ppm/year as its a much aged reference.  The real trick is measuring that because at least either the reference or your DMM will need calibration against a known standard in the calibration cycle to check the rate of drift of both.  From the factory the 732B is 0.8ppm in 3 months.  The real hard part in making a metrology setup is tracking the data over time to insure the stability is true.


It's not totally "easy" to make a voltage transfer standard that holds 2ppm per year-- but is can be done by the average engineer using average (and well known) approaches to the problem.  But-- (short of going out and buying a million-dollar Josephson Junction Array)-- to get below 2ppm per year takes a lot of study, hard work, patience, and help from your friends.

I already own a Fluke 732B, which (according to it's published specifications) will hold 2ppm (or less) per year.  So, I want something better.  I want *less* than 1ppm per year, and my goal is (somehow) to achieve 0.1ppm/year-- a lofty, but worthwhile goal (for me at least).  For most people, the Fluke 732B is "Good Enough"-- but not for me.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on May 16, 2013, 04:59:29 pm
The principle of calibration (how does a reference or DMM agree with a better one?) and the quest to distribute the SI representation is clear to me.

My cheapo-no-magic reference aka "Vbs" ( Volt babysitter) was compared to a volt-nuts 4 other references (including a LTZ in a 3458 which was used for the 24h, 31h, 1 Week and noise experiments) that haven't been calibrated relative to a cal-lab for a while but their behaviour is closely compared to each other regularly. (If one of them wants to go for a ride voltagically speaking, you wouldn't realise if it is alone, but it will visibly differ from its siblings!)

My Vbs  behaves closely like that cluster, how it differs in the long term I will see, got it back yesterdays from the first experiments. Now the Vbs is on its own for say one or three months...

What I meant with my last question is that it is increasingly getting harder to tell who is the reason for a deviation, the noise and drift of the Vbs is no longer easy to discern from that of the 3458A.

Also, in October iirc I will get a 34401A at work back from the Böblingen Cal lab of Agilent. This has not the greatest long-term-stability, but immediately after arriving it will be reasonable close to what they measured against their traceable references. Knowing the instruments error as noted by the lab, taking some readings from the babysitter volt abusing the 34401As gratuitous extra digits coming out of GPIB will give a cloud of datapoints for you know what... the VAgilent vs. Vbs and later Vbs against Vvolt-nut and also Vbs vs VQuarks .  :blah:

But I have to tell, the main reason for the LTZ reference is the predecessor, a REF102-based 10V, did not comply with my minimum requirement: Measure it at work, stuff it in the backpack, take it home and back to work the next day, measure again, delta only at the last digit. This one does so, after travelling much more. Now I can trust it for testing the DMM at home.

Greetings,
Hendrik
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 19, 2013, 05:36:15 pm
...any capacitor in the signal path should be high quality metal-film, or NP0 [aka: C0G]...

So far I have planned to use WIMA MKS for all caps. But also I will try to get NPO caps. Is there a recommended brand/type to go for? 
Title: Re: Ultra Precision Reference LTZ1000
Post by: saturation on May 20, 2013, 07:57:19 pm
Several years ago I explored doing a more robust reference but found the old Krohn Hite portable calibrators, like the MV106, incidentally also purchased by Dave about the same time.

Its rated for ~ 2ppm/yr, through a range of operating temps.  Since it was made over 30+ years ago, the references are well aged, and the unit robustly made.  But kept at room temperature over just short a year now, the accuracy is far better, <<= 1ppm.  You can find these on eBay for under $100, with some watchful waiting, or choose variations of that voltage references made by KH from that era; they have a similar look but differ in their dial-a-volt capacities.

(http://www.emeco-sa.com/img/productos/instrumentacion/patrones_laboratorio/krohn-hite_mv106.jpg)

Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on May 22, 2013, 04:07:30 am
@Dilligentminds.com

Looks like a reference diode Kindergarten to me :) Nice to see such a project coming up even if it differs from the topic LTZ1000A...

Does it differ from the 4400, and if, by how much ?

In my opinion its too many resistors for trimming, especially the trimpot. If it is not something special to cancel out individual drifts and tolerances, I would go for one single hi-spec feedback resistor at the op and the resistor to gound would be a slightly-too-low hi-spec value in series with a few lower-specced low-resistance types calculated for slightly too much resistance of the series circuit, and short each of the low-value resistors on the PCB.  This way I can use a knife to "activate" the additional low-resistors one by one - and solder bridge if i activated one too much. 

@Whoever is making a own circuit:
Learn from my fail (no test point for unbuffered voltage) and make a test point for the raw voltage before the amplifier !
This way you can either measure dc:dc ratio or simply the ~2.8V difference (with LTZ, ~3.1V here)  between your trusted Vref and what the amplifier does.

I will either accept what my buffer does to my reference or do a opampekcomy (decide later after watching longer-term drift), may set up a external chopper amp circuit which will be used with a existing KVD to make other voltages.

Still, I am confident that nailing together the AN86 circuit with standard means without black magic (teflon or Al2O3 board, stress relief slots, ultralow temperature, super secret thermal cycling and aging, VishayPG VHx Resistors) is sufficiently close to optimum that you you have a hard time to prove the difference to references made with black magic by usual means like 8.5 digit multimeters. 

Title: Re: Ultra Precision Reference LTZ1000
Post by: grenert on May 23, 2013, 01:29:54 pm
taking some readings from the babysitter volt abusing the 34401As gratuitous extra digits coming out of GPIB
Sorry for the off-topic (but in the spirit of volt-nuttery in this thread):
Does the 34401A put out more than 6.5 digits via GPIB?  I know the 3457A can do this, but had not heard the 34401A does the same.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 24, 2013, 04:34:33 pm
taking some readings from the babysitter volt abusing the 34401As gratuitous extra digits coming out of GPIB
Sorry for the off-topic (but in the spirit of volt-nuttery in this thread):
Does the 34401A put out more than 6.5 digits via GPIB?  I know the 3457A can do this, but had not heard the 34401A does the same.

Hello,

yes, definitely, 7 1/2 digits over the bus in each mode, if I remember right..
If you use the internal statistics, additional digits are also available.
I did not check recently, how stable the additional digit is, but have in mind that it's quite useful (for the LTZ1000 and on 4WOhm measurements), at least when additional averaging is applied.

Update: Just've checked by programming:
The GPIB output format is: x.xxxxxxx0E+yy, i.e. 8 digits, the ninth is zero.
The 7th digit is relatively stable.
It's better to average on 8 digits than on 6,5, because the average converges quicker.

The Min/Max function already delivers stable 7,5 digits for the average also, which I have used for measuring with higher resolution without GPIB.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: alm on May 24, 2013, 04:40:18 pm
You can get the extra resolution from averaging anyhow, so if it's down in the noise, you might as well average the 6.5 digit value.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alm on May 24, 2013, 06:21:13 pm
I believe the recent(ish) Keithley 200x meters give more digits over GPIB. No idea how significant they are.
Title: Re: Ultra Precision Reference LTZ1000
Post by: cyr on May 24, 2013, 10:39:35 pm
The 2015 does, not sure what the actual quantization steps are but seems like an extra digit or so of usable resolution. The 2001 on the other hand gives the exact same value as the display, at least by default.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 27, 2013, 07:40:20 am
Hello together,

On ordinary Zeners (1N829A) there exists a "zero tempco current" where the tempco is nearly 0 ppm/K.

On 2 samples of LTZ1000A with the standard 120 Ohms resistor, which gives around 4 mA zener current, I have measured a tempco of the zener element of around 50 ppm/K. So to come to the 0.05 ppm/K the heater stability has to be better than 1/1000 K.

Has anyone tried to find out the optimum current/resistor value for the zener of the LTZ1000(A) where the tempco gets zero?
That what I tried is to change the 70K Resistors. Lowering them to 50K will increase the tempco of the reference slightly.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rufus on May 27, 2013, 08:32:04 pm
On ordinary Zeners (1N829A) there exists a "zero tempco current" where the tempco is nearly 0 ppm/K.

It isn't an ordinary zener it is a zener + forward biased diode combination and the temperature coefficient of the diode forward voltage depends on the diode current. As far as I know zener avalanche breakdown voltage temperature coefficient isn't dependant on avalanche current.

The LTZ1000A nominally 7.2v 'zener' is the combination of the zener and transistor Q1 Vbe so is is the same and you can control Q1 emitter current by changing the collector resistor. If dropping from 70k to 50k made it worse I assume you were going the wrong way.

The LTZ1000 datasheet shows a circuit to trim the temperature coefficient when you don't bother to use the heater, you would think the same approach could also improve the temperature coefficient when you do.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 27, 2013, 09:31:24 pm
Quote
I would also encourage you to use (2) LTC2057 op-amps to control your LTZ1000(A)-- these op-amps have almost zero drift over time, and they have much lower wide-band and DC-10Hz noise than the LT1013 used in the original applications note. 
Thats good news for me the LTC2057 is noted on my wish-list. Up to now there are only samples available in LTC web shop. But I think they will be soon available on DigiKey too.

Quote
I strongly suspect that the ~7V buried Zener in the LT1034 is the exact same one that is used in the LTZ1000(A),
I cannot believe this: If I compare the "voltage change over current" diagrams of LTZ1000 and LT1034 at 1.25 mA the change of LT1034 is much larger (100mV) against the LTZ1000 (20mV). The LT1034 is developped as "micropower reference".

Quote
The LTZ1000 datasheet shows a circuit to trim the temperature coefficient when you don't bother to use the heater, you would think the same approach could also improve the temperature coefficient when you do.

Hello Rufus,

my intention is to use the sweet spot by changing the 120 Ohms resistor to either enhance the stability or be able to use cheaper resistors for the temperature setpoint. I know the cirquit from the datasheet which makes only sense if you need a low noise source. The additional resistor adds its own tempco to the cirquit and increases the output voltage by up to 1V.

So is there anyone who tried changing the 120 Ohms resistor and checked tempco before and after?
Or does anyone shurely know the maximum current limit for the LTZ zener without degradation?

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rufus on May 27, 2013, 11:07:00 pm
my intention is to use the sweet spot by changing the 120 Ohms resistor to either enhance the stability or be able to use cheaper resistors for the temperature setpoint. I know the cirquit from the datasheet which makes only sense if you need a low noise source. The additional resistor adds its own tempco to the cirquit and increases the output voltage by up to 1V.

In typical LTZ1000 circuits the zener current is very dependant on temperature (about -16uA/C) combined with the slope resistance of 20 to 60 ohms that gives a relatively huge -ve zener voltage temp co of around -640uv/C at 40 ohms. Yet that temp co + the avalanche temp co + Q1 Vbe temp co add up to almost nothing. That has to be by design. Who knows, they might even laser trim some deliberately added slope resistance to make them sum to nothing with 100uA Q1 emitter current.

So yes it seems adjusting the 120R will adjust the effect of the slope resistance temp co. Adjusting some added slope resistance (like the 200 ohm variable resistor in the datasheet circuit) will also adjust the slope resistance temp co. Adjusting Q1 collector resistor will adjust the Q1 Vbe temp co.

It is strange that the datasheet adjustment circuit seems to indicate you can null the overall temp co just by adding slope resistance without other component changes.

Which is best to adjust I don't know. I would imagine shipped parts are close to their sweet spot with 120R and 70k resistors, by design and/or trimming.

Won't there already be some 'voltnut' talk about stuff like this? I'm just looking at the circuit and making it up.

 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rufus on May 28, 2013, 02:14:01 am
Snip another wall of text with lots of knowledge and not enough understanding.

We are not trying to adjust an LTZ1000 Zener current to find a 'sweet spot' because there isn't one. Show me a reference that indicates zener avalanche voltage temperature coefficient depends on avalanche current.

We are trying to cancel the temperature coefficient of the zener avalanche voltage with the temperature coefficient of the Q1 transistor Vbe. Q1 Vbe temperature coefficient will drop by about 200uV/C per decade increase of collector current so changing the collector resistance is a valid way to adjust the temperature coefficient matching.

Additionally the recommended circuit configuration of the LTZ1000 gives the zener diode current the same temperature coefficient as the Q1 Vbe. That current temperature coefficient produces a zener voltage temperature coefficient proportional to the zener slope resistance / the 120R. Using the mid range datasheet slope resistance of 40 ohms means the effect of the Q1 Vbe temperature coefficient is multiplied by 1.3.

So yes you can change the balance of temperature coefficients by adjusting the 120R with the likely undesirable side effect of changing the zener current. You can also change the zener slope resistance in one direction by adding some resistance on top of the zener. As I said I would not be surprised if they add and laser trim some resistance on top of the zener to get the temperature coefficient match in the first place (has anyone cut the lid off one to look?).

Lol at sitting for hours with an LTZ1000 in an oven with Q1 collector base shorted to determine a perfect operating point which the circuit doesn't actually use. What winds me up is you are supposed to be the volt nut and I am just an electronics/software engineer who has never even seen an LTZ1000.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rufus on May 28, 2013, 09:17:01 am
Well, we will just have to disagree.  You keep talking about "avalanche mode" and I am talking about the transition point between "tunneling mode" and "avalanche mode";

I keep talking about avalanche mode because the zener in the LTZ1000 is required to operate with a +ve temperature coefficient of around 2.3mV/C which means the zener is predominantly if not completely in avalanche mode. The transition point (if it has one) is irrelevant it doesn't operate anywhere near the transition point.

We are trying to cancel the temperature coefficient of the zener avalanche voltage with the temperature coefficient of the Q1 transistor Vbe. Q1 Vbe temperature coefficient will drop by about 200uV/C per decade increase of collector current so changing the collector resistance is a valid way to adjust the temperature coefficient matching.

Good luck with that.  It didn't work in my simulations, nor did it work on the bench with any of the LTZ1000 circuits I tried.  But, maybe I did it all wrong-- why don't you show me the Right Way?

Andeas stated a couple of posts ago that changing the 70k to 50k did change the temperature coefficient of the reference slightly. Vbe temperature coefficient is proportional to log of collector current so I am not surprised a 30% change in current only made a slight difference. You might also consider this from the Fluke 732B manual
Quote
Biasing the Refamp for Low Temperature Coefficient 4-8.
As mentioned earlier, the Reference Amplifier contains an NPN transistor and a zener diode in series. The TC (Temperature Coefficient) of the Reference Amplifier is the sum of the TC of the zener voltage and the transistor base-emitter voltage. The zener voltage TC is negative and the transistor TC is positive with a value dependent on its collector current. Each Reference Amplifier is pretested to determine the collector current at which the two TCs cancel out yielding an overall Reference Amplifier TC very close to zero. To generate this same collector current in the standard, a voltage of 2.976V is generated across thin film resistor Z1-R3 on the Reference Hybrid (HR1). This resistor is pretrimmed with a laser to the value that results in the correct collector current.

So yes you can change the balance of temperature coefficients by adjusting the 120R with the likely undesirable side effect of changing the zener current. You can also change the zener slope resistance in one direction by adding some resistance on top of the zener.

Well, as I said, good luck with your experiment.

What experiment? The LTZ1000 datasheet already shows resistance added on top of the zener as a method of adjusting overall temperature coefficient. What do you think the intentionally introduced -ve temperature coefficient of zener current is going to do with the zener slope and any added resistance?

Thanks for the link to the LTZ1000 die photos. I don't see any trimming so I guess they just rely excellent temperature control which probably indicates there is scope for improved temperature coefficient nulling.

Therein lies the difference between you and I-- I have been working in electronics for over 30+ years, and have built my fair share of electronics projects.  And yes-- I have built many voltage references using almost all of the available components.  I have built dozens of circuits based on the LTZ1000, many of them with novel improvements which I cannot go into here due to patent issues.

If you have built so many LTZ1000 based references especially with novel improvements you ought but apparently don't know how they work.
Title: Re: Ultra Precision Reference LTZ1000
Post by: nukie on May 28, 2013, 11:25:34 am
I love how our friends in China are pushing the development of precision DIY references. Having easy access to affordable used/recycled precision parts sure helps alot. Unfortunately, it seems that used LTZ1000 is getting rare lately which drives up the prices. This is v3.0 of the LTZ1000 reference board I got(v2.0) from jj3055, use lots of high precision resistors. v3.0 improvement is low noise suitable for 10V buffer but it is not tested for long term stability. V2.0 is the 'community' standard.

http://item.taobao.com/item.htm?spm=0.0.0.0.jPEYqD&id=22720224575 (http://item.taobao.com/item.htm?spm=0.0.0.0.jPEYqD&id=22720224575)

More expensive version sports the AE metai foil oil filled resistors.

http://item.taobao.com/item.htm?spm=0.0.0.0.jPEYqD&id=17294769547 (http://item.taobao.com/item.htm?spm=0.0.0.0.jPEYqD&id=17294769547)

(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=49067;image)
Title: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 28, 2013, 09:10:13 pm
Dear fellow-nuts & EEVbloggers,

I’ve followed this thread here and in other forums around the LTZ1000 with great interest, especially the discussion about gimmicks (*), additional to the original simple design from the datasheet.

But on the implementation of those gimmicks I am desperately missing well-founded engineering & metrology practices, as:

1) A qualitative explanation, what their purpose is / how they work / root cause of additional instabilities (theoretical model)
2) A quantitative analysis, how much they  mitigate possible instabilities (error analysis calculus)
3) Practical stability measurements on realized LTZ1000 references, especially on the effects of additional gimmicks
4) An estimation, if the additional gimmicks noteworthy improve the LTZ1000s basic circuitry stability (e.g. 1ppm/yr., 0,2ppm/K), or if they contribute in the range of a few tenths ppm only, which would make them useless or exaggerated.

Instead, most designs only copy those gimmicks found in references of Datron, Fluke or HP, obviously without understanding, and forgetting the most obvious aspects.

I have to admit, that me too, have only copied the basic circuitry from the LT datasheet, but the few features I have considered or added, have been analyzed deeply in terms of 1) – 4).
Also, before I started, I had a design goal concerning the stability of my box, which was met.

I also have designed additional circuitry to set up a complete reference system, i.e. to calibrate the complete DCV range on a calibrator like the Fluke 332B, or a HP34401A, from one LTZ source.

I would like to present my design and my findings in the following days, also presenting some ideas, what perhaps is much more important than all those gimmicks (i.e. low hanging fruits)

Anyhow, I’m still interested in a profound discussion of those gimmicks, and would implement them in a future redesign, but only after given explanations 1) – 4).
 
Btw: The Chinese colleagues are doing a great job of showing the interior of the Holy Grails, and also in setting up LTZ boards in numbers, but sorry to emphasize that, I did not yet find any new/improved designs, or explanations there, either. (Hope I haven't overlooked that)

Anyhow, I would greatly appreciate, if some of them also would join the discussion here, or on Volt-Nuts.

And of course, I would also like to personally meet and exchange with Metrology-Nuts here in Germany.. 'babysitter' I already have met  :-+

Frank

(*) slots in the PCB, guarding rings, usage of “A” version, excess temperatures. metal foil resistors, zero offset OpAmps, ovenizing the complete LTZ circuitry, Burn-In on assembled PCB, cleaning in US bath, TempCo trimming .....
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 28, 2013, 09:24:42 pm
Which is best to adjust I don't know. I would imagine shipped parts are close to their sweet spot with 120R and 70k resistors, by design and/or trimming.

Won't there already be some 'voltnut' talk about stuff like this? I'm just looking at the circuit and making it up.
Definitely no trimming as you can see on the chip photo. Btw. the transistors Q1 and Q2 are built each out of 4 single transistors in a staggered configuration around the zener. This will shurely help to average out any temperature gradients on the chip.
On voltnut we talked about the additional 200 ohms resistor which is definitely no option for me. The TC of this resistor goes with a 1:7 ratio directly to the output voltage. The other resistors have a much lower influence on the output voltage.

Quote from: DiligentMinds.com
I have built dozens of circuits based on the LTZ1000, many of them with novel improvements which I cannot go into here due to patent issues.
Can you give us the affected patend numbers?

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 28, 2013, 09:41:29 pm
Instead, most designs only copy those gimmicks found in references of Datron, Fluke or HP, obviously without understanding, and forgetting the most obvious aspects.

Hello Frank,

one often overlooked gimmic from the datron schematic is the 100nF capacitor from the base of the temperature sensing transistor to the emitter. Especially if there is any connection outside the shielded box (power supply) this capacitor will help to stabilize the output voltage. Otherwise any mains disturbance has a direct influence on the temperature setpoint of the reference and the output voltage will drift.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 28, 2013, 09:55:32 pm
That's great, Andreas!

my references suffer from short termed disturbances, as such, obviously. (but that does not affect the more important long term stability)

The temperature control knot, i.e. the base of Q2 obviously is very sensitive to external influences, so far I've explored the circuitry by myself.

The box is currently undergoing a refurbishment, so I will add that.

Thanks.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on May 28, 2013, 10:13:06 pm
This very interesting tread contains a lot of hot air  :-DD but not very many builds (except from the ready built unit shown above).

The tread imo also contains quite heated arguments  :box: arising from different views on what really constitutes necessary elements in actually building a working reference. Some of the things mentioned in this tread are: Enclosure, PCB, Thermal Gradients  and EMF.

It amazes me however that some posters use all this energy on discussing the merits or lack of such for details of building without first checking datasheets (& more) from manufacturer(s). {I might be wrong, but I cannot find any references to the text below}.

Here is a "copy and paste" from  http://cds.linear.com/docs/en/datasheet/1000afd.pdf (http://cds.linear.com/docs/en/datasheet/1000afd.pdf)  :
(Please forgive me the lack of decent formatting - blame "Control-C"   :palm: ).

---

LTZ1000/LTZ1000A
4
1000afd
a
pplica
T
ions
i
n
F
or
M
a
T
ion
LT Z
1000 and
LT Z
1000A are capable of providing ultimate
voltage
reference
performance. Temperature
drifts
of
better
than
0.03
ppm/°C and long-term stability on the order of
1?V per month can be achieved. Noise of about
0.15
ppm
can also be obtained. This performance is at the expense
of circuit complexity, since external influences can easily
cause output voltage shifts of more than 1ppm.
Thermocouple effects are one of the worst problems and
can give apparent drifts of many ppm/°C as well as cause
low frequency noise. The kovar input leads of the TO-5
package form thermocouples when connected to copper
PC boards. These thermocouples generate outputs of
35?V/°C. It is mandatory to keep the zener and transistor
leads at the same temperature, otherwise
1
ppm to
5
ppm
shifts in the output voltage can easily be expected from
these thermocouples.
Air currents blowing across the leads can also cause small
temperature variations, especially since the package is
heated. This will look like
1
ppm to
5
ppm of low frequency
noise occurring over a several minute period. For best
results, the device should be located in an enclosed area
and well shielded from air currents.
Certainly, any temperature gradient externally
generated
,
say
from a power supply, should not appear across the
critical circuitry. The leads to the transistor and zener
should be connected to equal size PC traces to equalize
the heat loss and maintain them at similar temperatures.
The bottom portion of the PC board should be shielded
against air currents as well.
Resistors, as well as having resistance temperature coef-
ficients, can generate thermocouple effects. Some types of
resistors can generate hundreds of microvolts of thermo-
couple voltage. These thermocouple effects in the resistor
can also interfere with the output voltage. Wire wound
resistors usually have the lowest thermocouple voltage,
while tin oxide type resistors have very high thermocouple
voltage. Film resistors, especially Vishay precision film
resistors, can have low thermocouple voltage.
Ordinary breadboarding techniques are not good enough
to give stable output voltage with the
LT Z
1000 family
devices. For breadboarding, it is suggested that a small
printed circuit board be made up using the reference, the
amplifier and wire wound resistors. Care must be taken to
ensure that heater current does not flow through the same
ground lead as the negative side of the reference
(
emitter
of Q1). Current changes in the heater could add to, or
subtract
from, the reference voltage causing errors with
temperature. Single point grounding using low resistance
wiring is suggested.

---
Title: Re: Ultra Precision Reference LTZ1000
Post by: nukie on May 28, 2013, 10:33:04 pm
Hello Frank,
The Chinese community has more shared data and discussion on long term stability. Actually, it's a little hard to find schematics and implementation. You need to dig harder in the Chinese forums to find what you find missing.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on May 28, 2013, 10:46:54 pm

The temperature control knot, i.e. the base of Q2 obviously is very sensitive to external influences, so far I've explored the circuitry by myself.


Copied from the datasheet (link in earlier post):


It is mandatory to keep the zener and transistor leads at the same temperature, otherwise 1 ppm to 5 ppm shifts in the output voltage can easily be expected from these thermocouples.

The leads to the transistor and zener should be connected to equal size PC traces to equalize the heat loss and maintain them at similar temperatures.

..
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 29, 2013, 07:00:21 am

The temperature control knot, i.e. the base of Q2 obviously is very sensitive to external influences, so far I've explored the circuitry by myself.


Copied from the datasheet (link in earlier post):


It is mandatory to keep the zener and transistor leads at the same temperature, otherwise 1 ppm to 5 ppm shifts in the output voltage can easily be expected from these thermocouples.

The leads to the transistor and zener should be connected to equal size PC traces to equalize the heat loss and maintain them at similar temperatures.

..

No, I meant electrical / electromagnetic disturbances, those thermoelectrical aspects I have considered in the design and the enclosure sufficiently, I think.

If you simply measure the U(BE) of Q2 with a high impedance DMM, the stabilization circuitry will be easily disturbed and the regulation runs wild.
Accordingly, this is an entry point for EMC disturbancies, explaining perhaps my observed instabilities.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 29, 2013, 07:41:33 am
This very interesting tread contains a lot of hot air 

Where is your design?
Can you show us a photo? + Schematics?
Mine is shown on the profile picture.

(http://IMG_4671.JPG)

Instead of copying the whole text. A link to the datasheet would be sufficient.
The most important sentence is missing in your "citate"

Quote from: LTZ1000 datasheet
"The LTZ1000 and LTZ1000A references can provide superior
performance to older devices such as the LM199,
provided that the user implements the heater control and
properly manages the thermal layout."

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 29, 2013, 08:17:32 am
That's great, Andreas!

my references suffer from short termed disturbances, as such, obviously. (but that does not affect the more important long term stability)

The temperature control knot, i.e. the base of Q2 obviously is very sensitive to external influences, so far I've explored the circuitry by myself.

The box is currently undergoing a refurbishment, so I will add that.

Thanks.

Frank

Hello Frank,

i have looked up my measurements to this theme:

Without the 100nF I had following measurements on the heater output voltage (Setpoint  is 50 degrees for LTZ1000A):
5,4 V DC  + 6 mVpp with sporadic peaks of up to -40mVpp.

with 100nF at both bases of Q1 + Q2 transistors:
5,47V DC + 3mVpp with sporadic peaks of up to +/-5mVpp (10mVpp maximum).

further capacitors  C13,C14,C15 (10nF,100nF,100nF) around the heater OP-amp.
(Schematics is on Volt-Nuts).
5,49V DC + 0.5mVpp and no sporadic spikes.

My opinion: due to the large tempco of the zener section you should pay attention to the noise on the heater section too.

Theory: 40mV equals around 5.3uW heater power (300 Ohms) which will give 2.1 mK (400K/W) temperature fluctuation and 0.1ppm (50ppm/degree) output voltage variation.

With best regards

Andreas

edit:
damned: of course the heater power calculation is wrong: since the -40 mV are a offset to the 5.4V (minus 1 diode drop of 0.7V) we have to calculate the difference of 4.7V and 4.66V for the heater power which is effectiveliy 1248 uW. Or 0.5 degrees or 25ppm variation. (ok the thermal mass of the die will avoid large jumps).
Title: #1 - Setup - LTZ1000 Reference System
Post by: Dr. Frank on May 30, 2013, 06:30:43 pm
The goal of the design of the reference system was to calibrate a HP34401A on all DCV ranges, and a Fluke 332B, including its linearity to 1ppm of decks A, B; the uncertainty originating from one LTZ1000 reference only .

Here's the setup, as intended, for the case that the 34401A is the DUT.

The 332B simply serves as a high stability volt source (uncalibrated).

Its output of roughly 100V were first divided precisely (<0.5ppm) by 10.000  by a Hammond type divider (analogue to Fluke 752A).
The divided 10V were compared to the LTZ1000 box, which delivers different reference voltages, i.e.
7.1479788V for Ref_1, 7.1762318V for Ref_2, directly from both of the LTZ1000, 7.000000V divided very stable from one of the LTZs.

All three voltages can be very precisely (< 0.2ppm) amplified by 10/7, for the purpose to have usable calibration voltages for the instruments, in this case to 10.00000V.
(The 10,251760V and 10,211398V would also be accepted by the 34401A, and would have lower uncertainty).
 
The 1µV sensitive DVM compares the 10V reference to the divided one from the 332B, so that latter output is tuned to exactly  100.00000V.

Those 100.00000 V are fed into the HP34401A, for calibration.

All Cardinal Points: 1kV, 100V, +/-10V, 1V, and 100mV can be obtained precisely by different set ups of the 10:1 / 100:1 divider together with the LTZ box.


Later on, a HP3458A and a Fluke 5442A were available, so the stability and uncertainty could be checked.

The additional requirement then was, that the LTZ1000 references should be more long term stable than the 3458A. (1ppm/yr. vs. 8ppm/yr)

The 100:1 divider has a lower uncertainty on measuring 1000V (1ppm) than the 3458A (12ppm), because latter one has no compensation for the heat effect of its internal HV divider.

- to be continued -

Frank
Title: Re: #1 - Setup - LTZ1000 Reference System
Post by: Andreas on May 31, 2013, 09:58:30 am

Here's the setup, as intended, for the case that the 34401A is the DUT.

The divided 10V were compared to the LTZ1000 box, which delivers different reference voltages, i.e.
7.1479788V for Ref_1, 7.1762318V for Ref_2, directly from both of the LTZ1000, 7.000000V divided very stable from one of the LTZs.


Hello Frank,

nice gear.
I hope you will describe further how you get (with which parts) the precise division ratios.
By the way: do you know the (traceble) uncertainity of your references against PTB standards?

Another gadet that is missing in the datasheet cirquit of LTZ1000 is the bandwith limitation of the current source amplifier like C2 + R12 in the jj3055 cirquit ver3.gif in the posting above. Without this R/C-Combination the reference voltage output will be unstable with capacitive loads above around 1nF. (The current source will have heavy oscillations).

Also a output buffer is missing. Although introducing additional errors, the advantage is that with a short cirquit to ground at the output the setpoint voltage of the heater is not affected. The heater will go to the maximum possible temperature on a short introducing hysteresis or even ageing effects to the chip.

With best regards

Andreas



Title: #2 - Requirements - LTZ1000 Reference System
Post by: Dr. Frank on May 31, 2013, 10:50:51 pm
I'd like to ask for some patience..  |O practical stuff will be delivered definitely.

But first, here’s the summary of the requirements of the reference system, already with some instructional comments.

1) The Reference System should be capable of calibrating a HP34401A on each DCV range, over years. The HP34401As 24h specification is 15ppm for 10V, 20ppm on 1000V, 30ppm on 100mV.

For Good Metrological Practice, an uncertainty of <2ppm is required for each range of the Reference System.

That means, if the uncertainty (relative to SI) of the LTZ1000 output is known (i.e. calibrated once), all transfers to the different ranges must be done below that limit.
Also, all drift parameters should contribute in total below that limit.

2) The stability over time of a single LTZ1000 reference should reach realistically <= 1ppm/year:
LT specifies for the naked chip typ. 2µV/sqrt(khr.) @65°C, that’s 0.8ppm/yr.

This stability requirement (aging or deterioration) is most important, as it is not reversible, and cannot be mitigated or hardly be compensated (at most by elaborate trend analysis), like other instabilities.

3) The stability over temperature of the LTZ circuitry should reach realistically < 0.2ppm/K.

This instability is reversible, by returning to the nominal temperature, and can be cancelled statistically or even mitigated.
For that purpose, the reference system has to be operated in a stabilized / controlled environment. Temperature changes must stay within a few 1/10°C during 10 min, or over the measuring period (hours), and for long term stability measurements, the room temperature must be reproducible to e.g. +/- 2°C.

Otherwise, drift measurements on sub-ppm level are not possible.

Btw.: All other sources of similar instabilities, e.g. thermo electrical/mechanical force induced, humidity/leakage current, pressure, gravity, and so on, have to be analysed in value, relative to the ageing drift, i.e. if it's worthwhile to cancel them.
Like the temperature coefficient, those drift sources lead to spurious / reversible modulations of the reference output "only".   

4) Simply for convenience, the raw 7,2V output of the LTZ1000 has to be attenuated and trimmed precisely to a plain value of 7,00000V.
This secondary output should be very stable over time and temperature.
This transfer might be done by a 34401A with 2ppm uncertainty (linearity error), or with a 720A (<0.2ppm), or a 3458A (<0.05ppm). 

5) All reference outputs shall be amplified and buffered with low impedance by an exact factor of 10/7 to around 10V, so that the 34401A will accept this for calibration.
This amplification factor may be auto-calibrated at any required time with an uncertainty of < 0.2ppm, so that the stability / uncertainty of the LTZ1000 is maintained in the 10V output.

6) A decade divider with precise 10% steps, 0.1ppm nonlinearity, should provide a means for calibrating the linearity error of a Fluke 332B to 1ppm.

7) The experimental verification of the stability of the LTZ reference and the complete system is required, due to Good Metrological Practice.
A theoretical model about the instabilities is not sufficient on its own.

Therefore, a measurement system is required which is capable to perform sub-ppm comparisons, of the DUT against a more stable standard, or against a group of equivalent stable references.

8.) A Reference Divider should provide precise ratios of 10:1 and 100:1 with uncertainties of < 0.2ppm and < 0.5ppm of output, latter one for a burden of 1kV also (like a Fluke 752A)

- To be continued –  :=\

Frank
Title: #3 - Interior & Schematics - LTZ1000 Reference System
Post by: Dr. Frank on June 01, 2013, 03:25:40 pm
It’s teardown time; we’re on EEVBlog, aren't we?

First picture shows the double LTZ reference board.

It was intended as a Prototype design, to first check its characteristics, and some additional features.
It worked so well, that I left it in this state.

The PCB is single sided, and the LTZ1000 sits on the solder side (pic. 2).
That makes the thermal shielding of all solder junctions and the isolation of the LTZ much easier.
(Remember: Other ref. PCBs contain solder junctions on both sides and they are well exposed to air flow, especially in the 3458A, also in the Datron units)

The solder side is thoroughly cleaned with a strong solvent / PCB cleaner, and afterwards sealed with highly isolating plastic spray.
This method does not harm the other components.

The complete PCB is tightly assembled (with screws) on a polystyrene box, with additional small cavities for the LTZs, and the volume is filled with an additional foam cushion (pic. 3).
This easily fulfills the requirement that no air flow will affect the solder junctions, and also that the LTZ and its junctions are all on the same temperature, heated by its own power dissipation.

I have chosen an LTZ1000 (no A version!), so I could select 45°C as stabilization temperature for lowest drift.
That implies R1 = 1k, R2 = 12k. The rest of the LTZ circuitry is copied from the LT datasheet.
The LTZ1000A, as in ‘babysitters’ design, would require 10°C higher temperature, therefore 12.5k, and therefore 2 times higher drift rate, theoretically.

I have chosen wire wound resistors, because the necessary values were available instantaneously from stock, were reasonably cheap, and have low enough T.C. and specified long term stability of 25ppm/yr, no load. No load usually means, up to 10mW. Even the 120 Ohm resistor has 2.5mW only.

The OP07 simply were in my inventory, there’s no further idea behind using single opamps.

In the current budget schematic, (pic. 4) you see, that there are about 5mA flowing out of the negative side of the LTZ. That would have led to level shift on the negative line, especially as I connected both LTZs to one common GND.
So I added another OP07 to sink the negative current, that’s some sort of current cancellation, which is incomplete (and to be improved), but also used in the Fluke references (732B, 5720A).

That required a negative supply, so I have split the 15V to +12V/-3V, visible on the 2nd PCB.
The LTZ circuitry is effectively running on 12V only.   

The direct LTZ1000 output is divided by a resistive divider trim able precisely to 7,0000V.
This divider is set up by ordinary wire wound resistors also, i.e. T.C. ~ 3ppm/K, drift < 20ppm/yr., but the output is much more stable, i.e. 30 times more stable than those numbers.
That’s a metrological trick, I think, based on the fact, that at a division factor close to 1.0, all drifts will be suppressed strongly. The error calculus will be presented later.

Both LTZ1000 and one 7,000V outputs are fed directly to front jacks – gold plated Cu plugs.

The cables are Teflon isolated, to avoid leakage.

The precision switches allow choosing any of those 3 voltages, for amplification by a ChopAmp 7652 exactly by a factor of 10/7.

This is accomplished by 11 Vishay metal foil Z201 resistors, 49k99, which can be equally trimmed to 50k000 by a Wheatstone bridge, and from the front panel in Cal Mode.
The divider chain can be identified in pic. 1, on the right side, all those green components.
The linearity of this divider is 0.1ppm. This is acting like the first decade of a 720A Kelvin Varley divider. See 5th picture.

Therefore, the theoretical error of this 10/7 ratio transfer is 0.14ppm, which does not spoil the uncertainty/stability of the LTZ1000.

This is the 2nd metrological trick, as all other references (732A/B, 7001, etc) suffer on stability because of their fixed resistive amplification.

This divider delivers decade steps from 1 to 10, with an uncertainty of 0.1ppm of input , i.e. +/- 1µV on each output tap. (See 720A datasheet).
Therefore, 1V output is uncertain to 1ppm.

1V and buffered 10V are directly fed to output jacks, also all voltage steps can be selected by a 2nd switch.

Last, the calibrated 11 step divider can be used isolated for precision ratio measurements.

- To be continued -

Frank
Title: Re: #3 - Interior & Schematics - LTZ1000 Reference System
Post by: fmaimon on June 01, 2013, 05:53:25 pm
In the current budget schematic, (pic. 4) you see, that there are about 5mA flowing out of the negative side of the LTZ. That would have led to level shift on the negative line, especially as I connected both LTZs to one common GND.
So I added another OP07 to sink the negative current, that’s some sort of current cancellation, which is incomplete (and to be improved), but also used in the Fluke references (732B, 5720A).

That required a negative supply, so I have split the 15V to +12V/-3V, visible on the 2nd PCB.
The LTZ circuitry is effectively running on 12V only.   

Can you explain this part of the circuit? From the schematic, I see that you are forcing the bottom of the 120 resistor to 0V, using the opamp, but isn't this same current still going to ground through the opamp?

Maybe I'm missing the point on what's ground in your circuit The ground symbol (upside down triangle) is the negative of your power supply (-3V of the split supply)?

And what is that diode marked with an * doing?

Quote from: Dr. Frank
The direct LTZ1000 output is divided by a resistive divider trim able precisely to 7,0000V.
This divider is set up by ordinary wire wound resistors also, i.e. T.C. ~ 3ppm/K, drift < 20ppm/yr., but the output is much more stable, i.e. 30 times more stable than those numbers.
That’s a metrological trick, I think, based on the fact, that at a division factor close to 1.0, all drifts will be suppressed strongly. The error calculus will be presented later.

I'm looking foward to see this error calculus.


Quote from: Dr. Frank
The precision switches allow choosing any of those 3 voltages, for amplification by a ChopAmp 7652 exactly by a factor of 10/7.

This is accomplished by 11 Vishay metal foil Z201 resistors, 49k99, which can be equally trimmed to 50k000 by a Wheatstone bridge, and from the front panel in Cal Mode.

How do you select the cal mode  50K resistors? How close does they have to be to each other and how (why?) do you need the balance trimpot? As I see it, as long as all resistors (R1..R10) are trimmed to be the same is enough.

Felipe

Title: Re: #3 - Interior & Schematics - LTZ1000 Reference System
Post by: Dr. Frank on June 01, 2013, 10:42:23 pm

Can you explain this part of the circuit? From the schematic, I see that you are forcing the bottom of the 120 resistor to 0V, using the opamp, but isn't this same current still going to ground through the opamp?

Maybe I'm missing the point on what's ground in your circuit The ground symbol (upside down triangle) is the negative of your power supply (-3V of the split supply)?

And what is that diode marked with an * doing?

I'm looking foward to see this error calculus.

How do you select the cal mode  50K resistors? How close does they have to be to each other and how (why?) do you need the balance trimpot? As I see it, as long as all resistors (R1..R10) are trimmed to be the same is enough.

Felipe

Hi Felipe,

yep, the designators are not consistent, sorry for that.

I have +12V / GND / -3V; the triangle is -3V.

GND is the negative reference potential for each LTZ circuit.

My problem was, that I had to connect GND from the 1st and the 2nd LTZ circuit at the negative output jack, to have the opportunity to amplify each by the Chopper.

So, the negative sink currents of ~5mA for each ref. would have flown over those cables, which would have caused a (constant) voltage drop of several ppm, between the LTZ and the negative jack. So I reduced these currents and also the voltage drop by sinking them directly over the additional opamps, and only 300µA will flow to the negative jack.

Still, its not perfect.

Normally, you would sink the  currents directly at the LTZ negative output to the power supply, and would sense the negative potential with a separate tap, currentless.

Even then, you can only connect those negative sense lines without problems, if each LTZ circuit would have its own floating supply.

It was a first attempt, and I would redesign that , deleting the additional opamp, or would add several more precise current cancellation circuits, see 732B manual, or 5720A schematics.


The additional diode prevents reversing the voltage over UBE of Q1, by the additional OpAmp, which would otherwise cause the BE diode to go into Zener mode, which would destroy the chip.


The Wheatstone bridge is nothing special. It's simply a copy of the 720A bridge circuit, in its manual you may find a perhaps better description of the calibration  process.
In brief: The 50k resistors in the right leg are 0.1% wire wound, and both are trimmed by additional fixed resistors to nearly equal values (not drawn in the schematic).
The trim pot between them is the fine balance for exact match of upper and lower 50k.

The complete bridge has to be balanced to zero in each position, i.e. also if the positions of the 50k resistors in the right leg are reversed.
For that, you have to trim both pots, the trim of the DUT , and also the balance pot.
 
Only then, the resistor under test (R1..R10) exactly matches the reference resistor R11.
With 20V bridge excitation, and 0.5µV zero indication, the match is to 0.1ppm

Frank
Title: Re: #3 - Interior & Schematics - LTZ1000 Reference System
Post by: Andreas on June 15, 2013, 02:32:36 pm

The OP07 simply were in my inventory, there’s no further idea behind using single opamps.

Frank

Hello Frank,

When comparing the datasheets of OP07 and LT1013 from the LTZ1000 datasheet the main difference is the large signal amplification.
LT1013 has a order of magnitude more amplification than the OP07.
Especially for the current regulating loop a high amplification will reduce the steady state current error.
I dont know how large the remaining error is. But since the open loop amplification is temperature dependant I would prefer using a OP with high open loop amplification like LT1013, OP177 or something else.

By the way. At the moment I am comparing noise levels of different ADCs against the datasheet value of the HP3458A.
If I understood it right the HP3458A has 10e-8 rms noise with a integration time of 2 seconds (100 NPLC).
So this would be +/-0.3uVpp or 0.6uVpp in the 10V range. Can you confirm this value? What is your experience from practical measurements?

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on June 16, 2013, 08:48:21 am
Since about 2008, Fluke changed the design of the reference board in the 8508A DMM. In early versions were installed an LT1413A and LTZ1000. Now it is AD823A, LT1150 and LTZ1000A.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on June 16, 2013, 09:20:19 am
Dang Fluke, we all did everything wrong by selecting unsuitable chips... :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 16, 2013, 02:26:58 pm
Since about 2008, Fluke changed the design of the reference board in the 8508A DMM. In early versions were installed an LT1413A and LTZ1000. Now it is AD823A, LT1150 and LTZ1000A.

Do you have a cirquit diagram or at least a hint where the Chips are used? (heater section, current regulator, output buffer?)

I am guessing that the LTC1150 will be used as current regulator for the zener since he has a very high open loop amplification and very low offset longterm drift. The AD823 will be probably used as current buffer since the LTC1150 cannot deliver the 5mA which are needed.

Nice picture: Is the board under the isolation slotted or without slots?

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on June 16, 2013, 03:56:43 pm
I don't have any information about the new Fluke reference. All pictures taken from Web.

Title: Re: 3458A noise
Post by: Dr. Frank on June 16, 2013, 07:32:20 pm

Hello Frank,

Especially for the current regulating loop a high amplification will reduce the steady state current error.
I dont know how large the remaining error is. But since the open loop amplification is temperature dependant I would prefer using a OP with high open loop amplification like LT1013, OP177 or something else.

By the way. At the moment I am comparing noise levels of different ADCs against the datasheet value of the HP3458A.
If I understood it right the HP3458A has 10e-8 rms noise with a integration time of 2 seconds (100 NPLC).
So this would be +/-0.3uVpp or 0.6uVpp in the 10V range. Can you confirm this value? What is your experience from practical measurements?

With best regards

Andreas

Andreas,

I had to take a time-out, but now, several chapters will follow..

Concerning the noise of the 3458A, compared to different stable DC sources, here's a measurement, up to 1s (NPLC50).
You can see, that those sources come near the theoretical limit of the 3458A, but factor 2 higher.
I simply have calculated the statistics of a set of measurements and identified the variance as RMS noise. Perhaps it's Vpp instead, so a factor of 1/ 2.8 would be possible.

Perhaps a measurement on a stable battery would give better results.. I'll see later today, the box is running currently.


As the temperature stabilization of the LTZ is very sensitive, a high open loop gain may lead to instabilities. I'll see, just ordered 5 EA of LTZ1000, LTC1013 and LTC1052 from LT..

Frank

PS: On the 10V range, I've just measured one Weston cell, and the LTZ refs, NPLC 100, 25 samples each:
 
Mean= 1,0186060V, sigma= 195nV (output is drifting)
Mean=7,1479820V, sigma=146nV
Mean=7,1762512V, sigma=120nV

Therefore, I would judge, that NPLC100 really gives +/-1 digit stability on 8 1/2 length.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on June 16, 2013, 08:14:51 pm
HP 3458A 10 V noise (taken from volt-nuts thread on the bbs.38hot.net)
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on June 17, 2013, 09:09:14 am
Do I spot a certain LTZ1000A trace in Dr. Franks diagram?  ;)

My reference circuit will be shipped to another volt-nut this week (off-band for this forum) for further comparison. Also I will start building a LM399AH-based reference at work, or to be exact, prepare a design to be made by our trainee, will be used for performance tests of our 34401A at work (we have a scheme of buying fresh calibrated 34401A in place of a calibration sometimes and do a in-house comparison as performance/fitness check for the older ones, and some smaller fitness tests inbetween)

BR

Hendrik
Title: #4 – Reference Stability – model, calculation & component selection
Post by: Dr. Frank on June 17, 2013, 12:17:01 pm
The stability of the output voltage over time and temperature is determined mainly by the LTZ1000 chip, and the 5 resistors, R1-R5 (see datasheet).

Let’s first consider ageing (stability over time).

For the LTZ1000 chip and all of the resistor technologies there exists an exponential law over temperature, (Arrhenius), saying that ageing rate doubles every 10°C.

Such dependencies from operating temperature are often encountered in deterioration of material, e.g. the decay of LED luminosity and the life time of light bulbs, which is always driven by the operating temperature. The underlying process is the increase of defects in the crystalline structures, or the acceleration of diffusion processes. Therefore, reducing the operating temperature will reduce the ageing rates.

LT claims typical ageing of 2µV/sqrt(t/1000h) @ 65°C, that gives 0.8ppm/yr.
By lowering the temperature to 45°C, typical values of 0.2ppm/yr. may be achieved.
Therefore, the LTZ1000 version has to be used, with R4=12k, R4=1k. The reference then can be operated at an ambient temperature up to 35°C only.

Spreadbury (1) and also Pickering (2) have confirmed this experimentally for the LTZ1000 reference chip. The typical drift rates really apply in most cases. Intermittent operation of the LTZ1000 also will reduce its annual drift.
In the HP3458A the potential ultra-stability of the LTZ1000A is spoiled, by running it at 95°C, which leads to an 8 times higher ageing rate (continuous operation).

The 5 resistors also have to be operated on lowest possible temperature. This is fulfilled by Tamb. < 35°C and limitation of the self heating effect: Pmax. < 10mW. For those conditions, a Shelf Life ageing parameter is specified for precision resistors. In the LTZ1000 circuitry, R4=12k, 4mW, and R1 = 120, 2.5mW fulfill this requirement.

Additionally, there exists an influence from oxygen (and other reactive gases) and humidity on the crystalline structures, causing a sort of corrosion on resistors. Molded components, and to a lower degree conformally coated components suffer from that. Therefore all high quality / precision resistors as Thin Film, Wire Wound and Metal Foil types have similar specified ageing rates of 20...35 ppm/yr., (typical or maximum).

The LTZ1000 chip is hermetically sealed; therefore oxygen and humidity have no influence.

The resistors influence the reference voltage by changing the temperature set point (R4, R5), or by changing the current through the zener (R1).
The instabilities of R1, R4 and R5 are attenuated by a factor of 100; R2 and R3 by 300 and 500, respectively (see datasheet).
If all five resistors have the same instability values (over time or temperature), the total impact will be 0.035 times their instability.
Resistor ageing of 20ppm/yr. will add 0.7ppm/yr maximum.

Only the hermetically sealed, oil filled types (e.g. VHP202Z) give a big advantage. Their rate is typically 2ppm/6yrs., and therefore will add about 0.02ppm/yr only.
In picture 1 you’ll find long-term stability monitoring of 3 EA of my 5 VHP202Z. After 2 years, they really remain within < 0.5ppm of their initial value, so that is obviously no fake advertisement.
(Remark: The measurement stability was improved also during that time.)
 

Second, the temperature coefficient can be calculated in the same manner.

As the LTZ1000 chip is heated and thermally isolated, there is no further mechanism that would directly change its output voltage by change of ambient temperature.

The resistors will contribute with 0.035 times their own T.C.

Thin film resistors of 10ppm/k would give 0.35ppm/k, wire wound and metal foil have 2..5ppm/K max. T.C., which will yield 0.07... 0.18 ppm/K.

The metal foil resistors have no appreciable advantage over the wire wound types. Even the hermetical sealed VHP202Z, advertised as 2nd level standard and with typical T.C. of < 0.05 ppm/k will not give better results, because this extraordinary low value will not be achieved in reality. Also, the parabolic shape of the T.C. does not exist.

Picture 2 shows a high precision T.C. measurements on one of my 5 VHP202Z.
I measured values of 0.3, 0.6, 0.7, 0.8 and 1ppm/K, which is below the max. value of 2ppm/K, but far beyond the advertised typical 0.05ppm/K.

Therefore, an improvement can be made only by measuring the individual T.C. and selecting the ones with the lowest value. If R4 and R5 are matched concerning their individual T.C.s, this would improve the overall T.C. the most.

Conclusion: Using the LTZ1000, temperature set at 45°C, and using wire wound or metal foil resistors yield around 1ppm/yr. ageing. Using hermetically sealed, oil filled resistors may improve ageing to around 0.3ppm/yr.
Both resistor technologies yield a T.C. of < 0.2ppm/K.

Rem.: Sample variation of the LTZ1000 and other effects will lead to lesser stability figures.

(1) “ The Ultra Zener ... is it a portable replacement for the Weston cell?”,
P J Spreadbury, Meas. Sci. Technol. 1 (1990)
(2) “Setting new standards for DC Voltage Maintenance Systems. A Solid State DC Reference System”, John R Pickering, Metron Designs and Paul Roberts, Wavetek
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on June 17, 2013, 03:37:22 pm
Here is a short update, I received some more parts of my Vishay order, but still wait for the VHP101T. This feels like waiting forever.

Unfortunately (or better luckily) I am also quite busy right now, because I upgraded my lab with some gear that is planned to replace some/most of my actual calibration gear.   

@Mickle T., can you share where you found the Fluke 8508A details?
@Dr.Frank, are you planning to make a new PCB for your new ordered parts?

BTW Very interesting to see what is going on meanwhile.

@Dave + all interested, what do you think of the idea to try to design/make/build a kind of "EEVblog 10V Master Reference" based on LTZ1000 for this community?

bye
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on June 17, 2013, 03:59:03 pm
@Mickle T., can you share where you found the Fluke 8508A details?

Thread about the voltage references: http://bbs.38hot.net/forum.php?mod=viewthread&tid=969&extra=page%3D1&page=12 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=969&extra=page%3D1&page=12)
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on June 17, 2013, 06:05:12 pm
Hello Mickle T.,

thanks a lot. I had a look also at some other topics there and found a lot of infos from you. I am really impressed, great work!!!.

Bye
quarks 
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on June 17, 2013, 07:20:24 pm
Quote
@Dave + all interested, what do you think of the idea to try to design/make/build a kind of "EEVblog 10V Master Reference" based on LTZ1000 for this community?

Still I believe 10V are very uncommon today, just usable to check your DVM/DMM in one range but nothing more as most circuits require a reference voltage of 5V or less.
Sure, it's all about stability, but wouldn't it be worth having a LTZ1000 based voltage source with all common voltages of todays need? On the other hand, wouldn't it be worth to have a decade voltage output to verify all voltage ranges on your DVM/DMM instead of only the 10V range? Mh...

BTW: I wonder if there is knowledge in here about that rejustor stuff by Microbridge? Some american guys in here taken their sample offer to verify the improved stability of standard references? How could the LTZ1000 be improved by such a value und tc settable resistor?
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on June 17, 2013, 07:38:37 pm
Hi branadic,

Ich habe mir die rejustors mal im Zusammenhang mit Sensoren für den Aufbau von pga angesehen, ich denke trotz einstellbaren tc sind die letzten ppm Einstellung schwer. Und dass Prog-gerät plus Software eine über 1k Euro Sache.
Title: Re: 3458A noise
Post by: Andreas on June 17, 2013, 07:47:49 pm

As the temperature stabilization of the LTZ is very sensitive, a high open loop gain may lead to instabilities. I'll see, just ordered 5 EA of LTZ1000, LTC1013 and LTC1052 from LT..

Hello Frank,

The instabilities can be handled by frequency compensation without spoiling behaviour at DC.
Why not the brand new LTC2057? I fear that the LTC1052 cannot deliver enough current if the short cirquit current is around 5mA. The LTC2057 is now available at DigiKey.

With best regards
 
Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on June 17, 2013, 07:50:24 pm
Thanks babysitter for that info. One grand for only the programming device plus software is inacceptable to give it a try and to come a cropper in worst case.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Christe4nM on June 17, 2013, 08:18:43 pm
BTW: I wonder if there is knowledge in here about that rejustor stuff by Microbridge? Some american guys in here taken their sample offer to verify the improved stability of standard references? How could the LTZ1000 be improved by such a value und tc settable resistor?
This is the basically the same question I asked in the Keithley 2015 teardown topic (https://www.eevblog.com/forum/reviews/keithley-2015-teardown/msg246725/#msg246725) and was contemplating to ask here as well. Can anyone elaborate on this?

@babysitter, my German isn't that good that I can understand your post completely, but from what I understand you used those Rejustors and you found that even with "adjustable TC" it's hard to get the last ppm's down?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 17, 2013, 09:25:15 pm
Can anyone elaborate on this?

@babysitter, my German isn't that good that I can understand your post completely, but from what I understand you used those Rejustors and you found that even with "adjustable TC" it's hard to get the last ppm's down?

The key spec of precision is "long term stability".
On resistors we expect values below 25ppm/kHr or even less.

Mhm... What do you expect from a device which has a long term stability of 0.5%??? 50000ppm???
And when the adjustment range is +/-100 ppm I would not expect that you can get better than around 1/10th of it as stability. So in precision cirquits It might be useful at maximum to adjust the last 0.001% of trimming.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 17, 2013, 10:14:56 pm

Still I believe 10V are very uncommon today, just usable to check your DVM/DMM in one range but nothing more as most circuits require a reference voltage of 5V or less.
Sure, it's all about stability, but wouldn't it be worth having a LTZ1000 based voltage source with all common voltages of todays need? On the other hand, wouldn't it be worth to have a decade voltage output to verify all voltage ranges on your DVM/DMM instead of only the 10V range? Mh...

BTW: I wonder if there is knowledge in here about that rejustor stuff by Microbridge? Some american guys in here taken their sample offer to verify the improved stability of standard references? How could the LTZ1000 be improved by such a value und tc settable resistor?

You're right.. for a complete calibration, you have to transfer the basic voltage reference (e.g. 10.000V) to the desired range voltages, i.e. 1kV, 100V, 10V, 1V, 100mV.

So you need a very precise and linear divider, like the 720A and the 752A, or the HP3458A.
They will aos deliver "uncommon" reference volatges as 5.0000V...
And you need a very stable voltage source, which can be compared against your basic reference by means of the dividers.

That's all.  >:D

Frank
Title: Re: #4 – Reference Stability – model, calculation & component selection
Post by: Andreas on June 17, 2013, 10:16:31 pm

 Therefore all high quality / precision resistors as Thin Film, Wire Wound and Metal Foil types have similar specified ageing rates of 20...35 ppm/yr., (typical or maximum).


That is valid for the first year with decreasing ageing rates in the following years.
And ageing can be further stabilized by some burn in. I am currently ageing my Z201 resistors with around 100mW (1/3rd the precision rating) intermittend 1,5 hours on 0,5 hours off at room temperature to stabilize the resistors.

With best regards

Andreas
Title: Re: #4 – Reference Stability – model, calculation & component selection
Post by: Dr. Frank on June 18, 2013, 07:37:08 am


That is valid for the first year with decreasing ageing rates in the following years.
And ageing can be further stabilized by some burn in. I am currently ageing my Z201 resistors with around 100mW (1/3rd the precision rating) intermittend 1,5 hours on 0,5 hours off at room temperature to stabilize the resistors.

With best regards

Andreas

Hello Andreas,

I do not recommend a burn-In on Z201 resistors, neither does Vishay!

If you have the molded types, ageing is mainly determined by the oxygen and humidity reactions on the resistor active area. That you cannot influence by elevated temperatures.

If you have the hermetically sealed type, you will create a big ageing rate, as specified by Vishay by the parameter: "Load Life stability", that's about 50ppm @ full load, 20ppm @ 100mW (Z203).
If you simply leave those components as they are, drift is 2ppm/6yr only!

Compare those parameters: A burn-in makes no sense, obviously, if you use them in shelf life mode afterwards, i.e. with very low power dissipation.


Additionally, there's another serious problem on metal foil resistors:
They show a very pronounced hysteresis effect, if they are exposed asymmetrically to high temperatures and brought back to room temperature only.

I have not yet discussed 'conditioning of the LTZ ref. circuit'  (~ chapter 6),  but the other two VHP202Z resistors were re-measured by Vishay, @ 125°C and came back with a +5ppm shift. One of them creeped back to its initial value, but that took over one year. The other resistor did not creep back by itself, instead  I made a temperature cycling on it, analogous to degaussing, and was able to "reset" the hysteresis to < 0.2ppm of the initial value.


Burn-In normally is used for early failure detection (accelerated life test) on "ordinary" parts and assemblies, but I think, burn-in on  high precision devices is not always the right way.
That's also true for the LTZ1000, as I will demonstrate later.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on June 18, 2013, 01:44:14 pm
Still I believe 10V are very uncommon today, just usable to check your DVM/DMM in one range but nothing more as most circuits require a reference voltage of 5V or less.
Sure, it's all about stability, but wouldn't it be worth having a LTZ1000 based voltage source with all common voltages of todays need? On the other hand, wouldn't it be worth to have a decade voltage output to verify all voltage ranges on your DVM/DMM instead of only the 10V range? Mh...

With high precision gear (6.5 to 8.5 Digit DMM and Calibrators and especially traceable NIST/PTB calibration) all DC measurements are accuracy wise directly related to a 10V Standard Reference. Also with all gear using artefact calibration it is a must have. So at least for me it is the most common/important DC value to have/know.

All other DC values are delivered through a calibrator or as described by Dr.Frank with KVD/Reference Devider/Ratio/transfer measurement.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on June 18, 2013, 08:31:35 pm
Wow, a whole bunch of german guys in here :)

Quote
With high precision gear (6.5 to 8.5 Digit DMM and Calibrators and especially traceable NIST/PTB calibration) all DC measurements are accuracy wise directly related to a 10V Standard Reference. Also with all gear using artefact calibration it is a must have. So at least for me it is the most common/important DC value to have/know.

All other DC values are delivered through a calibrator or as described by Dr.Frank with KVD/Reference Devider/Ratio/transfer measurement.

This is like stating "We've done it always this way". As you know the Josehpson standard is everything but 10V, the value is reached by connecting serveral Josephson contacts in series. The definition of a 10V standard therefore is confusing itself. So the question might be is 10V still up to date?
Nothing we can really answer as there are enough people out there in the wrong positions stating the same as you do (We've done it always this way.), but please allow for this question.

BTW: SI unit uses 1 volt per definition, not 10V ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 18, 2013, 09:39:02 pm
Wow, a whole bunch of german guys in here :)



This is like stating "We've done it always this way". As you know the Josehpson standard is everything but 10V, the value is reached by paralleling serveral Josephson contacts. The definition of a 10V standard therefore is confusing itself. So the question might be is 10V still up to date?
Nothing we can really answer as there are enough people out there in the wrong positions stating the same as you do (We've done it always this way.), but please allow for this question.

BTW: SI unit uses 1 volt per definition, not 10V ;)

Well, Germans (e.g. Wernher-von-Braun) have put the first man on the moon, or not?  ;)

The SI definition currently is indirect, i.e. the VOLT is not one of the basic units.
The SI Volt uncertainty currently is not better than 2e-7 (e.g. volt balance), i.e. an HP3458A and a well designed LTZ 1000 reference are totally sufficient.

I'm waiting desperately for the redefinition of the kg, by a Si sphere, and/or the Watt balance.. then, the Josephson Volt and the von-Klitzing-Ohm will define those units directly and in accordance with SI with much smaller uncertainty.. up to  1e-16, or so.
Then it'll be the time to scrap the analogue DMMs..especially the 3458A.  :palm:

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on June 18, 2013, 09:47:21 pm
Quote
So, to answer your question, "10V" is the more modern cardinal point for this purpose.

Sorry, but this answer doesn't make me happy at all. A 10V based definition of a SI unit that is made by series connection of smaller value voltages can't be accepted by any physicist. It's the same stupid thing as nV/sqrt(Hz), this also makes physically no sense. It would be worth talking in a more physical language, not matematical.
The primary kilogram is what it is 1kg, not 10kg made by 33 parts à 303g. Got me?
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on June 19, 2013, 04:46:46 am
Thank you Dr. Frank for some real live experience and interesting explanations.

Whatever the output voltage is used for, in my eyes this thread is for discussion about care & feeding of LTZs, and together with some reading of the volt-nuts archives and discussion with Dr. Frank gave me an idea how to care and feed mine. Intentionally not going to the end in some directions, like selecting-from-batches the resistors and the LTZ itself due to self-inflicted money limits :) I didn't even try the high-end resistors but settled in the sub-10-eur-each league.

My reference was made for travelling (its predecessor wasn't stable when doing a round-trip from work, where the calibrated instruments are, and home.) And it successfully made it to Frank who inspected it further and has shown a quite good behaviour. For long-term experience it is just too young, but will go back to Frank for that. Also it will go to some other (hello quarks, your time will come soon! Lets have a Cali-barbeque with this weather when I bring the LTZ! :-+)  people just to collect experience and comparisons, and help giving a idea about the SI volt from some of them who are PTB-traceable to others who aren't (yet?). At home it will take some beating, being a transfer standard and part of a calibrator but also supplying sensors and some fooling around with oscillators and how they perform with a good voltage source, but also spending time off-line. So far I am happy with the results.

But sometimes I see men riding on black horses burning down metrology labs when I look at this thread and it goes into a certain direction...  :box: even metrologists know the art of multiplication and statistics, so why not 10V out of 30K Josephson elements? They even are happy with cesium clocks that probe more than a single but a bunch of cesium ions. And they swallow it that this bunch of atoms isn't even standing still but wobbling around in space and temperature range, giving some nasty effects.

I intend to send my reference to somebody off-forum today, then again to Frank and from there it will go to quarks.
Gotta go, our trainee will etch and populate his second PC today, and test... a LM399 Source as described a few posts above ! :)

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on June 19, 2013, 08:46:19 am
Quote
Anyway, it doesn't matter why 10V is the "de facto" standard cardinal calibration point, it just is, and we will all have to live with it.

Please allow for other opinions instead of yours. If you can accept this concept, fine.

Quote
Oh-- and I still don't see what this has to do with the original subject of this thread.

In this case I quote you: "... it just is, and we will all have to live with it..."

Quote
I intend to send my reference to somebody off-forum today, then again to Frank and from there it will go to quarks.

Can offer you to visit Stuttgart, several calibrated test gear is available Keithley 2002, Prema 5017, 34401A and my private Prema 5000.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on June 19, 2013, 09:08:47 am
Quote
So, to answer your question, "10V" is the more modern cardinal point for this purpose.

Sorry, but this answer doesn't make me happy at all. A 10V based definition of a SI unit that is made by series connection of smaller value voltages can't be accepted by any physicist. It's the same stupid thing as nV/sqrt(Hz), this also makes physically no sense. It would be worth talking in a more physical language, not matematical.
The primary kilogram is what it is 1kg, not 10kg made by 33 parts à 303g. Got me?

I don't accept the kilogram because "kilo" is Greek for 1000 and  don't :wtf: ing want one thousand small  :rant: grams. Give me ONE gram  :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: Jay_Diddy_B on June 19, 2013, 11:43:03 am
Hi,
I believe that 10V was chosen as the standard for voltage calibration to minimize the contribution made by thermal emfs.

This is quite different than the SI unit system where the unit of measurement is the volt.

In 1990 the volt was redefined, using Josephson junctions. Prior to this there was about 1.2 ppm difference between the North American Volt and the European Volt.

I have some old HP3455 meters with a green sticker with 1990 inside a diamond. This means the meter was calibrated with the 'new' volt.


Jay_Diddy_B
Title: Re: Ultra Precision Reference LTZ1000
Post by: nukie on June 19, 2013, 01:00:12 pm
10V is easy to calculate on the resistor divider such as the Fluke 720A
Title: Re: SI system, Volt definition & mise en pratique
Post by: Dr. Frank on June 19, 2013, 01:54:00 pm
Dear fellow-nuts,

please don't struggle about the absolute value of volt standards:

there's always an abstract definition of direct and derived SI units, and in most cases a totally different way to practically realize the unit. (called 'mise en pratique')

For the volt, the official SI-definition from 1948 is:

"The (SI) volt is the potential difference between two points on a conductor which carries a constant current of 1 Ampère, if the dissipated power between those two points equals 1 Watt"

You see, that this academical definition really is  "1 Volt" (based on kg, m,s).

(The kilo-gram is the only SI unit which is based on 1000 units of a gram, for practical reasons of its realization also, i.e. the kilogram artifact in Sèvres, France)
 
The realization of the SI Volt is done either by an Hg electrometer, by Clothier at al (1989) basically a balance, measuring the electrical force, uncertainty 0.27ppm, or a design by Funck et. al. (1991), measuring the force on a capacitor plate (0.31ppm uncertainty).
Both experiments are very complicated and clumsy, and might have been performed only once.

The output voltages of those primary standards (SI) can be different from 1V, given by the practical setup.


Then, there is a different representation of the Volt, that is a more easy-to-manage-way to deliver the volt.
Currently this is the Josephson Volt, a few mV in 1972 were amplified by a cryogenic divider to ~ 1V, 1V in 1985 by a Josephson Junction array, and 10V in 1987 by a longer array. (based instead on 2e/h)

Remark: The definition of the Representation of the Volt has been redefined in 1990, but not the definition of the Volt in the SI. The definition from 1948 is still valid!

The uncertainty between two different Josephson experiments can be as low as dV/V = 3e-19 for single JJs and  1.2e-17 for 0.6V arrays if you compare directly on the cryogenic (i.e. quantum) level.

Remember: The uncertainty between the Josephson Volt and the SI is still 0.4ppm!

10V for secondary reference standards has been chosen only for practical reasons in the analogous world (in contrast to the cryogenic world),  reasons are: the typical offset  of several µV, the limitation to measure volt differences to a few nV only, and because the typical cardinal points 1kV, 100V, 1V and 100mV are symmetrically situated around 10V, so that a 100:1 and a 10:1 divider is sufficient to transfer 10V to all of them.

Anyhow, if one selects a different standard value, e.g. 5V or 7,147V, it's also ok, as there  will be always the necessity to make a transfer to other needed calibration points (by KV divider, or by 3458A).

Therefore, the foregoing  discussion, which calibration point is the 'correct' value is simply a lack of knowledge of the concept of SI - 'Definition', - ' Realization' and - 'Representation'.

I recommend the lectures 'école de physique, Les Houches, “Quantum Metrology and Fundamental Constants” ', Blaise Jeanneret, "Volt metrology: The Josephson effect and SIS junction arrays":

http://www.metas.ch/LesHouches/downloads/talks/15_Jeanneret.pdf (http://www.metas.ch/LesHouches/downloads/talks/15_Jeanneret.pdf).

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 19, 2013, 06:25:31 pm
And finally ....

10V is the voltage which can be handled by +/-15V supplied OP-Amps without input voltage dividers.
Thus giving a nearly infinite input impedance instead of the 10 Meg in the other ranges.
10V is the normalization voltage of analog calculators.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on June 19, 2013, 07:01:35 pm
I don't accept the kilogram because "kilo" is Greek for 1000 and  don't :wtf: ing want one thousand small  :rant: grams. Give me ONE gram  :-DD

I do have a calibrated masspiece traceable to a national standard ( it is only 2 levels away from the standard SA kilogram, which is replica 56 of the International standard kilogram. It is 1.000g, with an error of 0.2 mg on that mass. Has held that over a few calibration cycles, as it is rarely used, only being used on a strain wire massmeter that has a resolution down to 0.1mg. It also has a 24 hour warm up time to be stable to that though, and you need to close the doors and not breathe, as it can detect that, and looking in through the doors will show up from the IR radiation you emit. I use it to check linearity across the measuring range, along with the 20,10 and 50g masspieces in the set. I actually had them all calibrated, even the 0.5mg masspieces.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 19, 2013, 07:18:14 pm
Hello,

just to bring up some discussion points to the original theme, I want to say some words to my design.
(see attached cirquit diagram below).

The main idea was to have a portable "transfer standard" which can be shipped hot.
To avoid mains disturbances it is also battery powered during operation.
So main concern is minimum current consumption.

This leads to a design with a LTZ1000A with around 50 degrees temperature setpoint.
Thus setpoint divider has 12.5K to 1K.

As resistors I choosed precision wirewound of type UPW50. Unfortunately the 12.5K and 70K values
where not available and had to be replaced by 10K+2K+0.5K and 50K+20k.

Further restriction: the whole cirquit should fit into a Euro-Card aluminium case.
For the first step it should be a unbuffered 7V output reference.

Cirquit description:

Power supply consists of 12 AA NiMh-cells.
The raw voltage of 17.5V (battery full) downto around 14V (empty) is stabilized with a low drop (0.17V), low noise (20uV), low power consumption (1mA) voltage regulator LT1763 down to 14.0V.

The reference section has some modifications to the datasheet.
R13 enables startup even with negative offset of the LT1013.
T2 removes the reference current from LT1013 lowering the self-heating of the LT1013.
Second effect: more headroom for the current regulation with low battery voltages.
R18 limits inrush current through the zener to about 14mA max during switch on.
R17 enhances stability of the current regulation loop since the load is now missing.

C11 + C12 are adapted from Datron cirquit. The effect is having lower noise on heater +
reference current regulation.
To further calm down heater current noise C13, C14 are added. C14 keeps RF noise away from the
negative input of the heater OP preventing the RF from being demodulated by the input diodes
which would give an offset. But this capacitor leads to loop instabilities which are compensated
by C13.
Similar C15 keeps RF away from current regulator OP. C8 together with the additional resistor

R19 compensate for loop stability.
C9 keeps RF from the output connector away from the reference.
C9 can only be added with R19+C8. The original cirquit from datasheet is not stable with
capacitive loads.

R16 is a NTC near the LTZ. So the temperature within the cirquit can be measured from outside.
The auxiliary connector J6 can be used for several things.
- changing the temperature setpoint (Pickering patent)
- heater monitoring (environment too hot/cold) or influencing
- buffered output (or voltage divider cirquit as calibrator)

J1 is a D-Sub connector which I use as main output. The advantage is that neighboured pins are nearly on the same temperature giving low thermoelectric voltages. The metal shield of the connector further equalizes the temperature of the pins.

J4 + J5 are auxiliary outputs.

Mechanical description will follow...

With best regards

Andreas
Title: #5 –Amplification to 10V
Post by: Dr. Frank on June 19, 2013, 09:28:12 pm
If the LTZ1000 and the other buried zener references SZA263 and LT-FLU potentially are stable to 0.2ppm/yr @ 45°C, including 0.02ppm/yr. by usage of hermetically sealed resistors as in the Datron 4910, why are they all specified no better than 1.5ppm/yr? (See picture 1.)

The main reason is, that 10.000V are generally used as a reference, not the raw 6.6 …7.2V of the reference amplifiers, and that those 10.000V have to be generated by resistive amplification.

The error calculus of such a resistive divider is given in picture 2

=> Output Stability (10.000V) = 0.52 *[(TC(R1)-TC(R2)dt +2*|AC(R)|dT]

A T.C. matching of R1 and R2 is required, so that the T.C. effect is nearly cancelled.

The ageing rate of both resistors cannot be matched, so their individual ageing rates add up instead.

Therefore ultra time stable (statistical resistor network in the 7001) or pre-aged resistors (wire wound, sealed types in 732B) must be used.
They still will contribute several tenths, or up to 1 ppm/yr.
Two hermetically sealed VHP202Z would contribute ~ 0.7ppm/yr.

Therefore it’s clear, that the 10.000V reference output is much less stable than the reference amplifiers itself.

The adjustable decade divider in my design will contribute 0.14ppm uncertainty only, and can be recalibrated at any time; therefore the basic stability of the LTZ circuitry is maintained in the 10.xxx V output.

To get plain 7.000V (and 10.000V) from e.g. 7.176V, an additional attenuation of 0.975 is required (see schematic of my design).

Therefore R2= 52k, R1=1k31=>

Output Stability (7.000V) = 0.0245 *[(TC(R1)-TC(R2)dt +(|AC(R1)| + |AC(R2|)dT]

All instabilities of this divider are attenuated by a factor of 40, i.e. T.C. < 0.05ppm/K without matching and A.C. < 0.02ppm/yr with VHP202Z are possible.


If the ultra linear HP3458A would be used to adjust the 7.147 => 10.000V transfer by a  non-inverting amplifier, an uncertainty of < 0.05ppm of the 10.000V output may be achieved.

(to be continued)
Title: Re: #5 –Amplification to 10V
Post by: Dr. Frank on June 19, 2013, 10:49:36 pm


I *think* the drift specs are *very* conservative figures for the first year-- all of the references listed "calm down" after a year (or a few years), and their real drift rate is far less-- and yes, I agree with you, most of this is due to the surrounding circuitry (especially the resistors) that control and/or condition the Zener device.

There was an interesting article on the Vishay Precision Group website about resistors in a hermetic network-- the gist of it was that the resistors in this case, (if they came from the same production lot, and were trimmed by the same person using the same equipment) will have a tendency to drift together over a long period of time-- for a divider (which we are mainly concerned with the ratio, and not the absolute value), then the long term drift can be quite small-- or at least that's what the article *says*-- you have to consider the source-- they are trying to sell resistors, so of course they will not show any data that make their resistors look bad-- all you see is the good outcomes.  You can find the PDF here:

http://vishaypg.com/doc?63512 (http://vishaypg.com/doc?63512)

I do like the architecture of your design-- I have stolen some of the concepts for my own use-- I hope you don't mind...

Well, thank you for the compliment.

I intended to share for copying - so I don't mind at all ..

But I also wanted to initiate some further reviews about the other "gimmicks", I have summarized in my first post.. for reuse in my own redesign..
(Several LTZ1000 directly from LT arrived just by today.)

The documents of Vishay have to be read very carefully, the "typical" parameters are sometimes very optimistic, but they always hold the maximum boundaries, which are mostly impressing, anyhow.
After all, if you dig in the last few tenths of ppm of your design, uncertainty by design or by specification is rarely possible, instead you always have to monitor your finished reference and select the most stable one as your "golden device".
That's what Fluke et al are doing also.

There was a classical document (1) by Fluke, where they monitored many different 732B over years.. and there was no sign of decrease of the ageing rates. The specifications are also quite realistic..
No, in contrary, for the 7001, even a linear drift prediction was specified, which might improve the uncertainty of this reference.

Only heavily drifting references like the one in the HP3458A may calm down, but only because they are operating far away from an equilibrium state.

Frank

(1) "Predictability of Solid State Zener References", David Deaver, Fluke Corp.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on June 20, 2013, 08:31:47 pm
A important point with those stable references is the enclosure. As shown, mine is sitting inside a tinned steel case (solderable) which is housed in a bigger ABS box. The power supply is simply fed thru a hole in the metal box, the output jacks are going thru their own hole each.

This was my simple, cheap and lazy approach but I know that with a few euros and workshop minutes more might have been possible ;D

If I really want to do it better next time (*) I would think about the following:
Discuss those things with me! I am bored if you dont :)

Use the same kind of solderable tinned sheet metal box again
Buy a batch of feed-thru capacitors
use only the feedthrus and hermetically solder the case
I would try to solder it in a nitrogen or co2 atmosphere, so the oxygen and humidity dont eat our resistors!

to get really esoteric, one could solder in two thin cooper tubes and use them to fill it with silicon oil (available as gear oil for RC cars), remove the air and have a good thermal conductor inside. pinch and solder the tubes to seal.

Also, did anybody consider sodium silicate as a coating to prevent moisture and oxygen reaching the resistors ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 20, 2013, 09:58:30 pm

Buy a batch of feed-thru capacitors
use only the feedthrus and hermetically solder the case

Also, did anybody consider sodium silicate as a coating to prevent moisture and oxygen reaching the resistors ?

Hello babysitter,

if the feed thru C's are really hermetically tight (sealed with glass) the pins probably will be COVAR pins (the only material with the same expansion coefficient as glass) having around 39uV/K against copper.

So you will need at least additional thermal shielding for the feed thru C's.

For me another question is more important.
What is better: having long legs on the LTZ1000 or keep them as short as possible together with a slotted board.
The pins are also of covar (because of the hermetically tight case).
So we are having 2 large thermoelectric junctions on each pin.
One between the bonding wire and covar pin, the other on the pcb between covar and copper.
The junction from the bonding wire to the aluminium mask are also a junction.

And unfortunately the bonding wires are not equally distributed (see chip photo)
http://www.amobbs.com/thread-3593996-1-1.html (http://www.amobbs.com/thread-3593996-1-1.html)
picture ourdev_464495.JPG

The heater pin (Pin 1) has 3 bonding wires (cooling the chip down at this edge) and the next 3 pins 8+7+6 of the temperature sensing transistor are also on the same side of the chip at the next edge.

The idea would be to find a geometry where all thermoelectric junctions (or at least those two of the Zener output) have the same temperature.

My idea would be the legs as short as possible and a slotted board having low thermal mass at the solder junctions. But since I have no thermal camera I cannot prove it.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on June 21, 2013, 03:19:36 am
It seems like the participants here may have some applied knowledge of thermal EMF generation.

Below is my current understanding as a starting point for a discussion on something that I have been curious about. I am not assuming what I state here is correct.

The thermal EMF generated in a conductor is caused by a thermal diferential/gradient from on end to the other. the gradient does not need to be uniform.

Two parallel identical conductors joined at one end with a thermal gradient have thermal EMFs but they are equal and cancel.

By joining two condutors at one end that have different Seebeck coeficients you will get the differential of the two different Thermal emfs generated by the temperature gradient, a thermocouple.

If you drop the thermocouple junction 200mm deep into a heated nonconductive liquid bath there will be negligible thermal gradient in the junction or the leads that are in the bath and all the gradient will occur in the conductors from the bath surface back to the cold junction. The actual junction itself is not generating the emf

The thermocouple law of intermediate metals states a third metal can be introduced in the juction between the two main leads of a thermocouple and as long as all three materials at the junction are the same temperature the thermocouple will give the same ouput.

This implies to me that no thermal emf is generated just by the contact of two dissimilar metals. The Thermal emfs occur only in the thermal gradients of the two materials. The contact is only an electrical connection.

Even though the mathematics is over my head currently on the inter relationships of the Thomson, Seebeck and Peltier effects. It seems that the Peltier effect is not purely a junction effect but has gradient aspects like the Seebeck effect and joule heating also.

I bring all this up because I think the frequently shown Thermal emf charts for paired metal combinations are extremely misleading They imply that the mere contact point of two particular metals will generate a certain µV/deg. As an example copper vs lead tin solder is listed at 5µV/degC.  So if I take a 2" long piece of copper wire and solder it to a 2" long piece of lead tin solder and maintain a 1 degC temperature difference between the end of the copper wire and the end of the solder and magicaly measure the temperature across that without introducing additional thermal emf  junctions I would read 5µV.

But if I make a Thermocouple out of two identical copper wires and use lead tin solder to make the junction according to thermocouple law of intermediate metals the solder will have no effect on the thermocouple output and since the two leads of the thermocouple are identical materials the output will be zero, no thermal emfs generated.

Should we discuss this here or should I cut and paste this a new thread?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rufus on June 21, 2013, 04:55:22 am
So if I take a 2" long piece of copper wire and solder it to a 2" long piece of lead tin solder and maintain a 1 degC temperature difference between the end of the copper wire and the end of the solder and magicaly measure the temperature across that without introducing additional thermal emf  junctions I would read 5µV.

But if I make a Thermocouple out of two identical copper wires and use lead tin solder to make the junction according to thermocouple law of intermediate metals the solder will have no effect on the thermocouple output and since the two leads of the thermocouple are identical materials the output will be zero, no thermal emfs generated.

If there is no thermal gradient across the solder bit of the connection. 

How about you take a loop of copper and put a blob of solder on one side? I reckon that will make a thermocouple as long as the solder blob experiences some of the temperature gradient and you could argue there isn't any junction.

The solder effectively changes the seebeck coefficient of that part of the circuit to something between copper and solder. Probably in proportion to the relative cross sectional area and electrical resistance.

So easy to test I just spent 5 minutes trying it. Attached is photo of 2 22 swg tinned copper loops one with some 60/40 solder blobbed on one side. Playing a flame on the end of the loop produced more than 20uV at the other end of the one with the solder and less that 1uV (possibly nothing) with the other.
Title: Re: Ultra Precision Reference LTZ1000
Post by: eevblogfan on June 21, 2013, 09:12:11 am
hey


Flame ?  isn't that <700C ? 

at <700C that's rughly 29nV !

witch is 0.0029ppm/C  at 10V

and 0.029ppm/C at 1V

is that so bad ?

oh and another question : does High silver load of soldier helps ?

if so . can you check that somehow ?

PS , 20uV is too low to be sure you measured 100% of that affect , can you investigate further more and confirm us that it was 20uV ?  ( I know that even 5% if accuracy is enough for that test bt I am wondering if those 20uV are fully result of that thermo couple junction )

Thank you
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on June 21, 2013, 09:30:29 am
just to bring up some discussion points to the original theme, I want to say some words to my design.
(see attached cirquit diagram below).
...
Mechanical description will follow...

Hello Andreas,

thanks a lot.
That is exactly the kind of info/input I hoped to see, when I opened this post. 
I hope this will lead to a well thought through optimized design.
 
bye
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on June 21, 2013, 09:33:28 am
It seems like the participants here may have some applied knowledge of thermal EMF generation.
...
Should we discuss this here or should I cut and paste this a new thread?

I think this discussion fits very well to the subject.
But please feel free to open a new thread.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on June 21, 2013, 11:54:56 am
"The voltage is not generated at the junction of the two metals of the thermocouple but rather along that portion of the length of the two dissimilar metals that is subjected to a temperature gradient. Because both lengths of dissimilar metals experience the same temperature gradient, the end result is a measurement of the difference in temperature between the thermocouple junction and the reference junction."

The "characteristic voltage difference (is) independent of many details (the conductors' size, length do not matter)".

http://en.wikipedia.org/wiki/Thermocouple (http://en.wikipedia.org/wiki/Thermocouple)


You can also choose whatever practically implemented "couple" coupling joint you want as long as it is made of one and the same material and its endpoints are at the same temperature (which means no net temperature gradient).

So 1 inch of thin copper wire soldered to 1 foot of thin iron wire as in the symbol < with temperature t1 to the right (both endpoints at one and the same temperature t1) and temperature t2 at the soldered junction to the left will give the same voltage as 1 yard of copper bar and 1 inch of iron bar interconnected with 2 feet of lead tube provided that the two junctions now created at the left side both are at temperature t2. This holds only in equilibrium, i.e. all connecting points and endpoints have settled.

This is imo implications from the link. Please check for yourself. A search 'thermocouple theory" gives several sources stating similar propositions.
Title: Re: #5 –Amplification to 10V
Post by: Andreas on June 21, 2013, 07:21:58 pm

There was a classical document (1) by Fluke, where they monitored many different 732B over years.. and there was no sign of decrease of the ageing rates. The specifications are also quite realistic..
No, in contrary, for the 7001, even a linear drift prediction was specified, which might improve the uncertainty of this reference.

Only heavily drifting references like the one in the HP3458A may calm down, but only because they are operating far away from an equilibrium state.

Frank

(1) "Predictability of Solid State Zener References", David Deaver, Fluke Corp.

Hello Frank,

perhaps I have overlooked something. But I cannot find any statement for a linear drift in the document (1).

As far as I understand they are simply comparing all references which where calibrated at Fluke during a certain time against the predicted drift. And not monitoring several specific devices over time.
The only monitoring for drift over time is made for 1 single device where the drift is interpolated linear and nonlinear with the result that for the nonlinear drift model the limits are halved against the linear model for this particular reference.

http://www.vishaypg.com/doc?63003 (http://www.vishaypg.com/doc?63003)

Quote from: Dr. Frank
I do not recommend a burn-In on Z201 resistors, neither does Vishay!

I will do it anyway just to be shure having done all what I could do.
Vishay offers PMO services to stabilize "foil resistors"

http://www.vishaypg.com/doc?49789 (http://www.vishaypg.com/doc?49789)

The only recommendation that I see is that PMO cannot be used for wire wound, and film resistors.
Of course it is mentioned especially on the hermetically VHP resistors.

And yes, you are right. The soldering shock after the pre-ageing will shift further the molded resistors with some hysteresis.
But since I am doing at least 1-2 gentle thermal cyclings (15-40 degrees centigrade environment) for measuring the tempco of the whole reference the introduced hysteresis should be mostly removed.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on June 22, 2013, 03:26:14 am
@ Rufus
That is an interesting take on the situation that I had not considered. It makes sense that that solder blob has effectively changed the "alloy" therfore the Seebeck coeficient of the wire with the blob is different now.  You have inspired me to do some experiments myself.

@ quantumvolt
So we are both picking the same internet info to believe about thermocouple theory.

@ All interested
I welcome your comments on my current opinions: That a plating on a connector can have no appreciable affect on a connection because it is too thin and intimately connected to the connector base metal to have any significant thermal gradient that would produce a thermal emf.   Likewise that the mere fact of soldering a good mechanicaly coupled copper to copper joint with lead tin solder is not going to create a thermocouple with the charts 5µv/degC thermal emf.  So here are some tests that hopefuly illustrate my point.

Twisted tinned copper wire soldered with thermocouple next to it.
(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=52424;image)

Loop of copper wire only and then the twisted wire that was soldered. In both cases the heat was on the junction/bend only to heat the junction to as uniform a temp as possible
(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=52426;image)

Heat on one leg only of the twisted soldered copper to get a thermal gradient across the juntion.  Full scale is 1.78µV delta V for the 85degC rise was 1.424µV = 17nV/degC.  The up down ramp effect of the heated section is from moving closer to and further away from the junction itself on the one leg.
(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=52428;image)

Then I made this very small area soldered junction from swaged tined copper wire to have minimal solder volume.
(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=52430;image)

I strapped my thermocouple to my heat gun for a fixed position and set the temp to be stable at 115C. Then I tried the three positions heat on each side of the juntion then centered on the junction itself. 
(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=52432;image)

Straight line section is ambient temperature then one side of junction heated then the other side of juntion heated then natural cooling to the center then repeat both sides of junction and then heat the juntion itself.  The heated juntion is basicaly zero output. The minor undulations are minor variatons in centering the heat on the junction. Full scale is 3.543µV and the delta V for 115degC rise was 1.5945µV = 14nV/degC.
(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=52434;image)

Here is one leg of tinned copper sodered to one leg of flux core solder as a thermocouple. The delta for a 55degC rise is 294.8µV which equals 5.36µV/degC.  That is very close to the published 5µV/degC for copper vs lead tin solder.
(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=52436;image)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rufus on June 22, 2013, 04:23:13 am
@ Rufus
That is an interesting take on the situation that I had not considered. It makes sense that that solder blob has effectively changed the "alloy" therfore the Seebeck coeficient of the wire with the blob is different now.  You have inspired me to do some experiments myself.

Good work. I don't find any of your results surprising but nice to see them all the same.

On changing 'alloy' I think it more like two conductors shorted together along their length. The emf you get must depend on the output impedance of the seebeck effect. I don't have a clue what that output impedance is, but, I guess it has to be inversely proportional to the conductor cross sectional area. Then the resistance of the conductors doing the shorting might be significant or perhaps not.

If you twisted equal gauge solder and copper together to make one side of a thermocouple do you think you would get about half the 'notional' solder/copper junction emf?
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on June 22, 2013, 08:16:05 am
Here is an easy-to-understand scholarly article that might describe the 'blob'-thing. http://www.msm.cam.ac.uk/utc/thermocouple/pages/Drift.html (http://www.msm.cam.ac.uk/utc/thermocouple/pages/Drift.html)

"Drift (permanent change) occurs because of metallurgical changes of the thermoelements ...."

"... a change in Seebeck coefficient is a necessary condition to have drift, but it is not a sufficient condition for it: the change in Seebeck coefficient needs to occur in a region of temperature gradient ..."

"... changes at the junction of the thermocouple usually does not play any role in drift, as it can be assumed that the junction is at constant temperature ..."

I suggest you take a nice clean piece of wire and shape it as a U (no sharp bends). Heat it locally at the bottom of the U. Versions (apply a thin layer of solder on):

1. Half of the curved part of the U. Thermocouple effect.

2. The bottom part of the U (the entire curved part of the wire).  No thermocouple effect.

3. A small blob at the far end of one of the legs of the U. If the blob is not heated too much, little or no thermocouple effect.


BTW The statement "... a change in Seebeck coefficient is a necessary condition to have drift, but it is not a sufficient condition for it: the change in Seebeck coefficient needs to occur in a region of temperature gradient ..." explains why there not neccesarily is a  thermocouple effect on every contact point of different materials - the connection is at thermal equilibrium (and having no or small current) ...
Title: Re: #5 –Amplification to 10V
Post by: Dr. Frank on June 22, 2013, 01:25:25 pm


Hello Frank,

perhaps I have overlooked something. But I cannot find any statement for a linear drift in the document (1).

As far as I understand they are simply comparing all references which where calibrated at Fluke during a certain time against the predicted drift. And not monitoring several specific devices over time.
The only monitoring for drift over time is made for 1 single device where the drift is interpolated linear and nonlinear with the result that for the nonlinear drift model the limits are halved against the linear model for this particular reference.



I will do it anyway just to be shure having done all what I could do.
Vishay offers PMO services to stabilize "foil resistors"

http://www.vishaypg.com/doc?49789 (http://www.vishaypg.com/doc?49789)

The only recommendation that I see is that PMO cannot be used for wire wound, and film resistors.
Of course it is mentioned especially on the hermetically VHP resistors.

And yes, you are right. The soldering shock after the pre-ageing will shift further the molded resistors with some hysteresis.
But since I am doing at least 1-2 gentle thermal cyclings (15-40 degrees centigrade environment) for measuring the tempco of the whole reference the introduced hysteresis should be mostly removed.

With best regards

Andreas

Hello Andreas,

I have never spoken about linear drift concerning the Fluke study of the 732A/B!

In this document, they analyse the drift prediction of up to 7 measurements on the same device.
The real behavior (either linear or other function over time) is not described in detail, that's right.

But one can see, that the specification of say 3ppm/yr. for the 732B, is not very conservative, as many devices (with SZA263) are on the edge of this spec, and will also not improve noteworthy after some years.

It's only a myth, that such devices get very stable, if one waits long enough.
That might happen on a few devices, but on many others, the ageing rate might increase again.

The study shows that, indirectly, because the drift prediction is quite uncertain.

For the 7000 reference only, Fluke specifies a typical drift rate of -0.7ppm/yr, and also an ucertainty of the prediction.
This parameter is specified as being linear, isn't it?


Vishay offers an PMO for the VHP101, and the details disclose, that this PMO is definitely no Burn-In!

Burn-In means: Storage for an extended period of time at constant high temperature.

PMO includes temperature cycling, in form of temperature shocks.

All metal foil resistors show hysteresis, therefore for real precision applications, a careful "degaussing-like" cycling is necessary.


I have shown my own T.C. measurements over a range of 10...35°C, and there you can hardly see any hysteretic effects.. that's only for greater temperature ranges.. >30°C in one direction, and therefore, 'gentle' cycling won't bring them back to zero.
You'll need trips to -23°C, up to +60°..80°C, whatever you have available in your home..

Anyhow, soldering ultra stable VHP resistors is always done with a heat transfer pincer, so that there is no heating of the resistive element.

Frank



Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on June 22, 2013, 08:17:37 pm
to protect Parts from the thermal solder shock, i use hemostat clamps (the latching clamps for blood vessels) on the wires quite often to dissipate heat away fm the Part.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 22, 2013, 09:15:35 pm
Part 2 LTZ1000A of Andreas

Mechanical

All is placed in a aluminium Euro-Card case EG2 of ProMa with dimension 168*103*56 mm.
http://www.reichelt.de/Proma-Gehaeuse/GEH-EG-2/3//index.html?ACTION=3&GROUPID=5199&ARTICLE=50424&SHOW=1&START=0&OFFSET=16& (http://www.reichelt.de/Proma-Gehaeuse/GEH-EG-2/3//index.html?ACTION=3&GROUPID=5199&ARTICLE=50424&SHOW=1&START=0&OFFSET=16&)

[attach=1]

Top side from left to right:

D-Sub connector for the main output with neighboured pins for the Zener output.
Next to the D-Sub is the auxiliary connector for a daughter board


Below the D-Sub you can see one of the auxliary 4 mm banana plug connectors (Hirschmann).
Both connectors are placed intentionally on the same height of the reference.
I cannot understand why on most instruments the positive (red) plug is always higher
(and hotter) than the negative (black) plug which is then cooler. Especially when having
a device with a power consumption that makes it necessary to use a fan.

In the middle the reference section with the parts around LTZ1000A. They are all placed into a TEKO 3710 metal shield with top cover.
http://www.reichelt.de/Teko-Stahlblech-Gehaeuse/TEKO-3710/3//index.html?ACTION=3&GROUPID=5202&ARTICLE=34042&SHOW=1&START=0&OFFSET=16& (http://www.reichelt.de/Teko-Stahlblech-Gehaeuse/TEKO-3710/3//index.html?ACTION=3&GROUPID=5202&ARTICLE=34042&SHOW=1&START=0&OFFSET=16&)

The teko shield has the intention to equalize thermal gradients from outside to the reference section.
And calm down air currents.

All resistors (pre-aged before use) are in the upper half of the shield.
The LTZ1000 is thermally shielded with some foam.
Since the PCB is not plated through I could not settle the LTZ1000A directly on the PCB.
So the legs of the LTZ are surrounded by additional foam to keep air currents away.
This can be better seen on the closeup (IMG_4671.JPG) which I posted May 29, 2013 (page 12) in this thread.
The BF245C FET for the current source is above the LT1013.
The NTC for temperature sensing of the board temperature is near the LTZ
(between the FET and the LTZ).

[attach=3]

The air gap between the top plate of the TEKO and the rest of the cirquit
is filled with additional polystyrene foam material (plate with 10mm thickness).

The right half of the aluminium case is filled with 12 AA cells in 2 battery holders
which are fed by a simple constant current charger during charging.

Between the TEKO inner shield and the battery holder some parts of the voltage regulator can be seen.

[attach=2]

Bottom side:

On the bottom side you can see that the zener voltage is Kelvin sensed at the LTZ1000A
and going directly to the neighboured pins of the D-Sub connector only being connected
to the output filter capacitor.

There are many additional capacitors and some cirquit modifications which where not planned
from the beginning but which are already included in the cirquit diagram.
The base emitter capacitors at the LTZ are connected as close as possible to the LTZ1000 pins.

On the right side lower the low noise 14V power supply around the LT1763 is built.

Unfortunately the Aluminium case has not much place on the side below the pcb.
So there can be no metal plate for the LTZ-Section on the lower side.
There is only room for a 4 mm polystyrene foam sheet for thermal isolation.

By the way: for first firing of the cirquit I did not use the LTZ1000A but replaced the
zener section with a self built "refamp" consisting of a ordinary zener and a transistor.
Just to look whether the current regulation will do it's job properly, especially
when powering up/down.


Shielding and guarding:

ince I use a battery powered design where all components are within the aluminium case,
and no mains line can introduce any common mode noise to the cirquit,
the topic of shielding and guarding can be much simplified:

I have only a guard and dont need a outer shield (connected to eart ground)
All parts are "inguard".
A 2mm banana plug connected directly to the EG2 aluminium case can be used to connect
to the guard pin (or if not available to the negative pin) of the multimeter or calibrator.

Of course I have a large metal plate connected to earth ground on my desk which I use as outer shield
during my measurements. The guard of the LTZ is isolated against shield by some bumpers.

problems observed with the cirquit:

A short ciruit to the (unbuffered) output will set the heater setpoint to a large value.
This shifts the output voltage of the LTZ1000A. (Hysteresis probably due to the die attach).
Fortunately I could remove the hysteresis by simply power cycling the reference for several times.

When measuring immediately after charging Im observing some shift to the output voltage.
Probably this is due to thermal gradients going across the PCB due to the "hot" AA-cells.

todo list will follow ...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 22, 2013, 09:25:24 pm
Part 2 LTZ1000A of Andreas

...

Nice, compact design, Andreas.. like it.

I will later show some LTZ1000 hysteresis measurements, I have encountered similar trips to extreme temperatures and hysteresis on one of my references also, but was able to reset it.

See Pickering patent.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on June 22, 2013, 09:37:55 pm
For a future design, there are feed through capacitors available by the ham guys, that are affordable:

http://server3.gs-shop.de/200/cgi-bin/shop.dll?AnbieterID=9187&Seite=frameset.htm&PKEY=9D07 (http://server3.gs-shop.de/200/cgi-bin/shop.dll?AnbieterID=9187&Seite=frameset.htm&PKEY=9D07)

They are made of a zylindrical ceramic with inner and outer metallization. In the inner on a wire is soldered, the outer side can be directly soldered into a hole of your galvanically tinned metal case.

So you are able to fully encapsulate your bord with your reference, the buffer circuit and the current regulator. You are then also able to fill the case with what ever you want (hydrogene, nitrogene etc.) and hermetically seal it by soldering the lid to the rest of the case.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on June 22, 2013, 09:51:30 pm
Exactly what i talked about. You can solder in tubes for filling and sealing in advance. The feedthru caps are fine. I need to come out as being a ham :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on June 23, 2013, 06:26:16 pm
What about long-term stability of multiple paralleled references? Does it to average decrease? All I could read about is improved noise, sure by sqrt(N), but nothing more. Any experience about that?

We all know that it needs at least three references to find which one drifts in which direction and by what value, so wouldn't it be worth building a 3ref-ADC-DAC system regulating the voltage output after initial calibration?
Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on June 23, 2013, 06:29:26 pm
5 devices would be better for long term drift, as you can use it to check which ones have the most variation from the average.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on June 23, 2013, 06:33:23 pm
With heated refs having a bunch might help spreading the thermal aging. Also, averaging groups was described by pease, using 4x4 lm399.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on June 23, 2013, 06:38:42 pm
Inspired by the Datron/Wavetek 4910, I thought 4 would be perfect, that is why I ordered 4 LTZ1000A.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 23, 2013, 09:21:12 pm
Inspired by the Datron/Wavetek 4910, I thought 4 would be perfect, that is why I ordered 4 LTZ1000A.

Yes 4 is the minimum for maintaining the "volt". At least 3 are on your site and you can find out a defective one.
The fourth you can send for calibration and import the calibrated volt to the group.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on June 23, 2013, 09:35:21 pm
Quote
Inspired by the Datron/Wavetek 4910, I thought 4 would be perfect, that is why I ordered 4 LTZ1000A.

Are they paralleled or compared against each other?
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on June 24, 2013, 06:34:23 am
Yes 4 is the minimum for maintaining the "volt". At least 3 are on your site and you can find out a defective one.
The fourth you can send for calibration and import the calibrated volt to the group.
@Andreas, for this the 4910 would not be the right choice (but Fluke 732 and 7000 would be see picture)

Are they paralleled or compared against each other?
@branadic, see 4910 Front Panel with 4 individual cells (10V each) plus average (see schematic)
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on June 24, 2013, 09:15:12 am
Sorry I was a bit handy-capped by using only my mobilephone which has no english dictionary, so entering those twitterlike short posts was hard work :)
My bit of thermal management was

* a "starlike" layout at the LTZ footprint, same-thickness, same-length traces on both sides of the PCB, if they are needed or not. Kept the "equalisation" star part free of other traces.

* cooper pour used as GUARD, will help spread out heat to reduce gradients.

* small bottle cap over the LTZ keeping regional airflow off

* Tinned metal sheet (heat-spreading) inside ABS outer enclosure (insulating).

Regarding DIY hermetically housing (close soldered box, feedthru capacitors):

Putting the feedthrus in close proximity will give only small temperature gradient. Symmetrical construction will help cancel out thermal EMFs. Putting all feedthrus on one side would allow using a socket or PCB.

BR
Hendrik

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 24, 2013, 10:17:37 pm

* a "starlike" layout at the LTZ footprint, same-thickness, same-length traces on both sides of the PCB, if they are needed or not. Kept the "equalisation" star part free of other traces.

Regarding DIY hermetically housing (close soldered box, feedthru capacitors):

Putting the feedthrus in close proximity will give only small temperature gradient. Symmetrical construction will help cancel out thermal EMFs. Putting all feedthrus on one side would allow using a socket or PCB.


So if I understand it right: up to now you have no slots or cutouts within the PCB.

The feedthrus from "Geist" have copper leads as inner lead according to data sheet.
So on one side you will have lesser problems with thermoelectric effects. On the other side
I fear that the hermetical tightness is only a question of time.
How do you plan manage the barometric / temperature pressure relief with your close soldered box?

Has anyone a Idea how we can test the quality of a thermal design.
What is better: having long or short legs. Slotted or non slotted PCB.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on June 25, 2013, 06:38:29 am
Quote
Has anyone a Idea how we can test the quality of a thermal design.
What is better: having long or short legs. Slotted or non slotted PCB.

I think that is something you can only answer by measuring the heat spread with a thermal cam at an exemplar and as you expect I have access to one. Maybe one of those questions we can answer at one weekend?

BTW: Does anyone have the "ultimate" LM399 circuit that is worth building? Have build the "10V Buffered Reference" circuit with LT1001ACJ8 shown in the datasheet, but there are a few LM399 left, waiting for something useful.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 25, 2013, 09:38:59 pm
I think that is something you can only answer by measuring the heat spread with a thermal cam at an exemplar and as you expect I have access to one. Maybe one of those questions we can answer at one weekend?

BTW: Does anyone have the "ultimate" LM399 circuit that is worth building? Have build the "10V Buffered Reference" circuit with LT1001ACJ8 shown in the datasheet, but there are a few LM399 left, waiting for something useful.

Sounds good. This would be a good possibility to verify the design.

Mhm, why not use some LM399 to verify the thermal design. Principally they have a similar layout. But are much cheaper. And possibly the higher chip temperature gives an advantage in seeing temperature differences.

My ultimate idea (not already a complete design) would be building some kind of "calibrator" from 0-10V with a LM399 as basis. Either with a PWM divider (EPN cirquit idea) (cheap but noisy) or 2 interleaved 16 Bit DACs giving about 28 Bits resulting (more expensive but less noise) resolution. When having 2 independent calibrators of this sort and a 24 bit low noise ADC with some relays or MUX switches you could build a "self calibrating" system which calibrates out the non-linearities below around 1ppm. Similar to Franks 10V/1V divider but with a binary adjusting scheme.

For e.g. Set the first output to 10V the second to 5V compare the output voltages as 0V + 5V and 10V - 5V and re-adjust the 5V output to get the exact PWM/DAC values for half of the range. Store the values and determine + store the ADC INL error for half of the range. Then measure the difference of both outputs and adjust the first output to exact the 5V value of the 2nd output. Repeat the same for 5V and 2.5V and the 7.5V points. And so on.... until the linearity error of the DAC + ADC (e.g. 4-8 ppm) are well below 1ppm. I guess that about 32 - 256 measurement points should be sufficient as a basis.

By the way Frank: How often is it necessary to re-calibrate the 10V/1V divider to maintain the 0.1ppm divider accuracy. Which drift over time did you observe after calibration?

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: tinhead on June 25, 2013, 09:53:21 pm
BTW: Does anyone have the "ultimate" LM399 circuit that is worth building?

no, but i'm thinking about REF102CP with the QH40A crystal heater attached to it.

At 40° there is almost no drift at all, see attached picture (QH40A temp drift is between two blue lines)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 25, 2013, 09:57:12 pm



By the way Frank: How often is it necessary to re-calibrate the 10V/1V divider to maintain the 0.1ppm divider accuracy. Which drift over time did you observe after calibration?

With best regards

Andreas


Andreas,

this kind of divider (720A, K.V.) is 0.1ppm of input, i.e. 1ppm of output @ 1V!

This is stable for 3 months or more, I guess.
I did not calibrate it more often.

I monitored the 10/7 output only, and that was accurate to ~ < 0.5ppm for 1 year, or so.

If you need more precise 10:1 division, have a look on the Hammon type divider, it's also much easier to switch and to calibrate!

Also have a look on the Fluke 5440A self calibration scheme, it has a nice 0.1ppm linear DAC ( 2x 1bit) and automatic  range calibration, uncertain to < 0.5ppm, or better.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 25, 2013, 10:00:17 pm
At 40° there is almost no drift at all, see attached picture (QH40A temp drift is between two blue lines)

I have measured the tempco of many references. But no one of them had ever seen the "idealized" curve out of the data sheet. In reality you will have to select many references to find one which has a maximum or minimum in the range of 40 degrees. Further the maximum/minimum will probably be shifted by hysteresis effects.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on June 26, 2013, 08:41:43 am
I have not yet calculated the forces due to pressure on the DIY hermetic can, as I dont have decided for a size and know very little about the pressure behaviour of the gas yet. But my boss as a physicist will :) Nitrogen could be a good match as a filling gas, as most of air is it. Pressure exchange without mixing of internal gas and ambient air could be done with a flexible membrane, say, a hole in the close-soldered can, with a brass ring soldered in the inside and a piece of copper foil soldered on the ring. The cooper foil might be shaped to improve movement, cold-forming concentric rings like done with pressure sensor membranes comes to mind.

Man, I didn't want to go for gimmicks... :)

Lets see if our trainee is free for building the LM399 voltage source today...

EDIT: Have a look at those: http://www.servometer.com/products/metal-bellows/standard-bellows/ (http://www.servometer.com/products/metal-bellows/standard-bellows/)
These might be a off-the-shelf practical membrane for pressure relief. Just solder it to the case with one end and solder it close on the other end.



Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on June 26, 2013, 06:37:46 pm
If you want a pressure equaliser bellows cheap go get an old mechanical fridge thermostat, there is a nice phosphor bronze capsule inside with a capillary tube attached. Vent the gas and solder the cap tube to the finished case and it will flex to accommodate the expansion of the fill gas or oil.

If I was building one I would fill it with an inert refrigerant gas like R134A,  all the housing has to do is be capable of being pumped down to a vacuum for a short time then filed and sealed with a standard method, either a schraeder valve or a soldered pinch tube.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on June 26, 2013, 06:51:42 pm
Quote
My ultimate idea (not already a complete design) would be building some kind of "calibrator" from 0-10V with a LM399 as basis. Either with a PWM divider (EPN cirquit idea) (cheap but noisy) or 2 interleaved 16 Bit DACs giving about 28 Bits resulting (more expensive but less noise) resolution. When having 2 independent calibrators of this sort and a 24 bit low noise ADC with some relays or MUX switches you could build a "self calibrating" system which calibrates out the non-linearities below around 1ppm. Similar to Franks 10V/1V divider but with a binary adjusting scheme.

I was more thinking of using three references, several switches, an adc and "a dac."

1. Initial calibration for one of the three references. Therefor Ref1 is connected to the dac and output voltage of a specific digital word is measured, you just need to know its initial output voltage.
2. Ref1 is divided and act as the adc ref, Ref2 and Ref3 are divided to be within the range of the adc and are measured.
3. Ref2is divided and act as the adc ref, Ref1 and Ref3 are divided to be within the range of the adc and are measured.
4. Ref3 is divided and act as the adc ref, Ref1 and Ref2 are divided to be within the range of the adc and are measured.
5. Now the drift and the new digital word for Ref1 connected to the dac is calculated as well.
6. Start again at point 2.

After inital calibration the system needs to stay powered up.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 28, 2013, 04:28:59 am

Also have a look on the Fluke 5440A self calibration scheme, it has a nice 0.1ppm linear DAC ( 2x 1bit) and automatic  range calibration, uncertain to < 0.5ppm, or better.

Frank

Hello Frank,

I had a look on the documentation (hope I picked the right one)
http://assets.fluke.com/manuals/5440B_AFsmeng0000.pdf (http://assets.fluke.com/manuals/5440B_AFsmeng0000.pdf)

But with my experiences from a PWM-divider (see EDN cirquit)
http://www.edn.com/design/other/4326640/DC-accurate-32-bit-DAC-achieves-32-bit-resolution (http://www.edn.com/design/other/4326640/DC-accurate-32-bit-DAC-achieves-32-bit-resolution)
I expect that besides the selection of the FETs (1 Ohm) in the 5440 unit a part of the linearity is hidden within the calibration constants.

Otherwise you have too much problems with "voltage dependancy of the switch (High/low)", "charge injection from PWM to output", "different rise times high/low" which makes it hard to get around below 2 ppm linearity even with tweaking all resistors.
See attached pictures. Linearity deviation is in mV referenced to 5000 mV of the reference. So 0.005 mV would correspond to 1 ppm linearity deviation.

There are different switches (CD4053, 74HCT4053 and MAX4053 without and with tweaking of the surrounding resistors) with different results ranging from about 100ppm to 4 ppm maximum deviation.

With best regards

Andreas

Edit: of course the genious trick of the 5440 with cutting out the non-linear range near zero (and full scale) by a offset would help at least for the tweaked cirquit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 21, 2013, 07:25:55 pm
Part 3 LTZ1000A of Andreas (Todo list):

For the next 2 devices I plan the following.

- Using pre-aged Z201 resistors (100mW power cycling).
  the main intention is to have more room within the shielded area for additional improvement measures
  like cut outs on the PCB against the wirewound types.

- perhaps I can find also another suitable case with more room
  I would also like to have larger battery capacity.
  The 12 AA cells are only good for around 36-48 hours with heater on.
  I have already found the "Fischer TUG V 17" aluminium case which would be ideal in 160-220 mm length.
  But unfortunately its so new that there are no dealers who sell them in small quantities.
  The other solution would be the "ProMa EKG 3" aluminium case but the mounting possibilities
  for PCBs are very limited.
  Anyone better ideas for similar cases?

- use the additional room within the shield for some slots around the LTZ to keep thermal gradients
  away from the legs. The base emitter capacitors will remain as 0402/0603 capacitors directly at the LTZ.
  The LTZ will be mounted directly to the PcB (platet through PCB is necessary).
  My prefered solution up to now is using short legs and a slotted board.
  In this case I believe that the critical thermal junctions between PCB
  and LTZ have the lowest temperature differences.
  But if branadic gets other results with his thermal camera I will use the optimum solution.

- perhaps (depending on space used) additional isolation (slots) to the FET and the heater transistor.

- replacing the Hirschmann banana plug connectors with POMONA low emf connectors (equal height for both pins)

- buffered output with 10V probably with a LTC2057 low noise low drift amplifier (recently arrived from DigiKey)
  The resistors for the divider could be the trimmed version of the VSMP series which is offered by DigiKey.
  The fine trimming could be done by a DAC. And all on on a PCB cutout which can be thermally regulated.
  Of cause I will check the crystal oven heater which was recommended by branadic (good idea) as an option.

- I bought some LT1013A-devices in hermetically tight case (CERDIP) some time ago.
  One for the price of a half LTZ1000A. I wanted to use them to see if
  I could get more stability over time against the standard plastic case.
  And all pictures of references that I could see with an LT1013 had usually a TO-99 metal case
  which is now unobtanium.

  But now I have the LT2057 which is more stable over time and temperature,
  has more open loop amplification lesser problems with thermal emf and less noise than LT1013A.
  So at least I will give the LT2057 a try with the option to use the LT1013A as backup.

- The 14V voltage regulator and the battery pack should get at least a slot in the PCB for thermal isolation
  eventually further measures like additional (styrofoam-)wall between power supply and LTZ section.
  With a larger case I will put the batteries above the whole cirquit with a thermal isolation between
  the battery compartment and the rest of the cirquit. So the idea with the slot will only be for the
  local voltage regulator.

- Doing further thermal cycling (-18 degree celsius) after soldering (thanks Frank for the idea).
 
  With a AD586LQ-device I have made the experience that a gentle cyclical stress has a positive effect on
  the ageing rate. Of course every stress will give a new starting point
  (usually with a higher momentary ageing rate) for the device.
  But if you have luck the ageing will stabilize as can be seen on the graph.
  At the moment I repeat the same for a LT1236AILS8-5 device which has a too high ageing rate for my purposes.

  To the picture:
  Day 200 is start of the measurements with ADC13 and AD586LQ reference
  measuring a LTZ1000A by a capacitive LTC1043 2:1 divider (giving around 3600mV).
  The first firing of the reference is day 0.
  Initial ageing rate around 3.4ppm/sqrt(kHr) referenced to day 0.
  Around day 415: begin of cyclical stress during night with 15mA
  load at the output of the reference.
  Ageing slope increases new ageing rate around 2.4ppm/sqrt(kHr) referenced to day 415.
  Around day 460: Ageing stabilises to around 1-2 ppm/year cyclical stress continued.
  Around day 540: Finishing cyclical stress.

Any further Ideas for the LTZ?
How is the pre-ageing for the LTZ1000 done at the manufacturers of metrology equipment?

With best regards

Andreas




Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on July 24, 2013, 07:47:15 pm
Quote
But if branadic gets other results with his thermal camera I will use the optimum solution.

It will take some time, but I'm working on that.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on July 25, 2013, 06:53:54 am
Part 3 LTZ1000A of Andreas (Todo list):

For the next 2 devices I plan the following.

- Using pre-aged Z201 resistors (100mW power cycling).
  the main intention is to have more room within the shielded area for additional improvement measures
  like cut outs on the PCB against the wirewound types.


Once again, I cannot recommend that at all.
This is necessary only for stabilization of the load life stability of the resistors, which is not the case for LTZ references (P< 10mW)
Also, you will get hysteretic resistance value shifts of several ppms, which you might want to remove by thermal cycling (similar to demagnetization)
If you use heremetically sealed VHP202Z, the drift is so low from the fab, that a "stabilization" as you want to do, causes more harm (i.e. several ppm of non reversible value shift) to the resistor than the ultra low natural drift (2ppm/6yrs.).


..
  The LTZ will be mounted directly to the PcB (platet through PCB is necessary).
  My prefered solution up to now is using short legs and a slotted board.
  In this case I believe that the critical thermal junctions between PCB
  and LTZ have the lowest temperature differences.
  But if branadic gets other results with his thermal camera I will use the optimum solution.


Try to use a single sided PCB, so all thermal junctions are on that side and can easily be shieleded thermally by a single layer of foam.
Again, the effects of slots in the board have not yet been explained, neithertheir physical mechanism, nor the quantity.

In contrast, a noisy power supply, or bad shielding cause shifts of up to several ppm, obviously by rectifaction of those AC disturbance signals on the temperature measuring Q1, therebyd shifting the temperature. To mitigate this effect, is much more important.
(I use an external PSU, so the transformer and its magnetic field is outside the case)

- The 14V voltage regulator and the battery pack should get at least a slot in the PCB for thermal isolation
  eventually further measures like additional (styrofoam-)wall between power supply and LTZ section.
  With a larger case I will put the batteries above the whole cirquit with a thermal isolation between
  the battery compartment and the rest of the cirquit. So the idea with the slot will only be for the
  local voltage regulator.


A magnetic shielding and multiple filtering of AC disturbance signals are much more important.


- Doing further thermal cycling (-18 degree celsius) after soldering (thanks Frank for the idea).

You have misunderstood me.
Thermal cycling means, that you apply temperature differences from the stabilization point (e.g. +50°C) cyclicly, with decreasing amplitude.
E.g. you have to apply -18°C (delta T ~ -68K), +100°C  (+50K), -10°C, +80°C, 0°C, +70°C, ... and so forth, until you are below ~ +/- 20K, where all hysteresis is gone. See also the patent of Pickering, realized in the Fluke 7001 reference (but which does not work properly in the 7001, I assume)

  To the picture:
  Day 200 is start of the measurements with ADC13 and AD586LQ reference
  measuring a LTZ1000A by a capacitive LTC1043 2:1 divider (giving around 3600mV).
  The first firing of the reference is day 0.
  Initial ageing rate around 3.4ppm/sqrt(kHr) referenced to day 0.
  Around day 415: begin of cyclical stress during night with 15mA
  load at the output of the reference.
  Ageing slope increases new ageing rate around 2.4ppm/sqrt(kHr) referenced to day 415.
  Around day 460: Ageing stabilises to around 1-2 ppm/year cyclical stress continued.
  Around day 540: Finishing cyclical stress.



I do not understand your diagram correctly, I fear, please help me:.

The drift shown comes from the AD586 only, the difference of both LTZ outputs is constant to ~ 1ppm in 1 year or so, therefore the drift rates of 3.4ppm/sqrt(khr) you have additionally drawn apply to the AD 586, but not to the LTZs.
Those are rock stable and need no further improvement. (I have measured similar behaviour over 4 years)



Any further Ideas for the LTZ?
How is the pre-ageing for the LTZ1000 done at the manufacturers of metrology equipment?


I doubt they make real pre-aging.
The LTZs and the peripheral components are so stable that the total drift mainly depends on the different LTZ samples, i.e. on fabrication variation.
The first might drift 1ppm/yr. (@60°C), the next 0.7ppm/yr. only, and so forth.
So they do a monitoring over 3-6 months only, and select the most stable references.

To my understanding of the physics, at such low drift levels, a pre-aging makes no sense, but causes more harm (higher drifts, hysteresis...) than it would really stabilize the reference even more.

I will publish my own results (measurements) soon, as an indicator for that thesis.

regards Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on July 25, 2013, 08:07:15 pm
Travelling Reference Info: My LTZ1000A cam back a few days ago, will visit Dr. Frank soon and after that it could travel south, to Quarks and Branadic !

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 25, 2013, 09:41:34 pm
It will take some time, but I'm working on that.
Fine we are all curious on the results.

Once again, I cannot recommend that at all.

Try to use a single sided PCB, so all thermal junctions are on that side and can easily be shieleded thermally by a single layer of foam.
Again, the effects of slots in the board have not yet been explained, neithertheir physical mechanism, nor the quantity.

Sorry but my ageing experiment is already running some 1000 hours. So I should have known it last year in February. On the other side: when looking at the derating diagram the 100mW will heat about 17 degrees.
Thats nearly the temperature change between winter and summer of my "lab".  I will see the result in the run-in phase of the LTZ.

If using a single sided board I cannot use slots. So this will be only a option if the slots worse the temperature distribution between the pins. I have now a board without slots so I will most probably try one with slots the next time.

In contrast, a noisy power supply, or bad shielding cause shifts of up to several ppm, obviously by rectifaction of those AC disturbance signals on the temperature measuring Q1, therebyd shifting the temperature. To mitigate this effect, is much more important.
(I use an external PSU, so the transformer and its magnetic field is outside the case)

A magnetic shielding and multiple filtering of AC disturbance signals are much more important.

I will use a AC wall plug adapter only during charging. In operating mode I will use battery power.
The best shielding at line frequency is keeping far away from transformers.

You have misunderstood me.
Thermal cycling means, that you apply temperature differences from the stabilization point (e.g. +50°C) cyclicly, with decreasing amplitude.
E.g. you have to apply -18°C (delta T ~ -68K), +100°C  (+50K), -10°C, +80°C, 0°C, +70°C, ... and so forth, until you are below ~ +/- 20K, where all hysteresis is gone. See also the patent of Pickering, realized in the Fluke 7001 reference (but which does not work properly in the 7001, I assume)
Ok now I got it. But the first point at my side is the 270 degrees soldering temperature when using short legs.


I do not understand your diagram correctly, I fear, please help me:.

The drift shown comes from the AD586 only, the difference of both LTZ outputs is constant to ~ 1ppm in 1 year or so, therefore the drift rates of 3.4ppm/sqrt(khr) you have additionally drawn apply to the AD 586, but not to the LTZs.
Those are rock stable and need no further improvement. (I have measured similar behaviour over 4 years)
Yes you are right.
My test setup are the 3 references, fed trough a multiplexer, then divided by a capacitive 2:1 divider (LTC1043) and then measured by a 24 Bit ADC with a temperature compensated reference AD586LQ.
So if you assume the LTZ1000A as being constant you see the inverse ageing of the AD586. If the reference voltage of AD586 goes down you see the measurement going up in the diagram.
Unfortunately I do not have the absolute ageing rate of my LTZ1000 references up to now.

To my understanding of the physics, at such low drift levels, a pre-aging makes no sense, but causes more harm (higher drifts, hysteresis...) than it would really stabilize the reference even more.

I interpret the diagram above as follows: Every stress on the device will start a new ageing cycle with usual higher ageing rate as before.
It may be accidently in the test above or perhaps can be repeated: (I will know this in a few 1000 hours with a LT1236AILS8). After the stress (training) the reference is falling to its "sweet spot" remaining stable.

My theory:
I blame the hysteresis effects of hermetically tight packages on the "die attach" of the chip.
On AD586 change notes you can see that it is usually a silver filled epoxy compound.
I do not know how they dose the glue on the Kovar plate/lead frame of the housing but probably this
process is the one with the most errors in fabrication. And every manufacturer has its own mixture.
With temperature cycling the erratic connections of the die attach at the edges of the chip might be egalized somewhat giving better results.
The interesting thing with a LT1236AILS is that the hysteresis of the chip seems to have a time constant/delay of about 50 minutes (measured on one device). So the hysteresis curve on this device is drastically changed between a temperature slope of 0.1K/minute against 0.3K/minute. So also this effect could be some creeping effect of the die attach.

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on July 26, 2013, 07:38:57 am

Sorry but my ageing experiment is already running some 1000 hours. So I should have known it last year in February. On the other side: when looking at the derating diagram the 100mW will heat about 17 degrees.
Thats nearly the temperature change between winter and summer of my "lab".  I will see the result in the run-in phase of the LTZ.

I think, that effect is so small (e.g. attenuation 1:100), that you won't be able to identify it, or distinguish it from other effects.



I will use a AC wall plug adapter only during charging. In operating mode I will use battery power.
The best shielding at line frequency is keeping far away from transformers.
The battery mode is the best you can do.
Although I use an improved DC - out wall plug adapter also, my LTZ refs still struggle from other AC irraditions.
There is even a small effect from the GPIB cable, if the measurement is running.
Therefore the next LTZ design will include multiple shielding and a double filtered DC supply.
 
Ok now I got it. But the first point at my side is the 270 degrees soldering temperature when using short legs.

I used heat removal pliers, and left the legs long.
If in doubt, whether the LTZ has "seen" this heating, you should do this thermal cycling afterwards.

For the first of my two references I was able to prove, that it did NOT see any hysteresis effect from soldering and only small other heating effects, because after a thermal cycling, its output value went back to exactly the initial value.
That means, that this LTZ reference  drifted less than 0.5ppm in about 3-4 years!!

So if you assume the LTZ1000A as being constant you see the inverse ageing of the AD586. If the reference voltage of AD586 goes down you see the measurement going up in the diagram.
Unfortunately I do not have the absolute ageing rate of my LTZ1000 references up to now.

Simply trust on the datasheet-stability of the LTZs..the AD586 drifts, but not the LTZs..

Well  8), you indeed HAVE absolute ageing rates of your LTZs already!!
Simply create a diagram where you draw the change of the difference in output voltage over time, i.e. LTZ_1 minus LTZ_2 and LTZ_1 minus LM_2 (what's that kind of ref? not the LM1236 ?).
Those two graphs will show, that these 3 refs drift apart not more than 1-2ppm/2years!!

The individual drifts will not be more than those determined values, theoretically half of that for each one.
So, you already own two/three ultra-stable references, based on a design with "simple" wire wound resistors, like "babysitter" and me...

I interpret the diagram above as follows: Every stress on the device will start a new ageing cycle with usual higher ageing rate as before.

That's another argument for NOT doing a pre-ageing stress on the LTZs, as they might behave the same, but on a much smaller scale.


regards Frank

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 26, 2013, 06:30:37 pm
Therefore the next LTZ design will include multiple shielding and a double filtered DC supply.

I have already tried to filter out the interference of a (switchmode) power supply X+Y capacitors + chokes. But with very little effect.
I guess one will have to use a transformer with a shield like on most metrology gear between primary + secondary side to get effective filtering.
So let me know if you have a solution.

Simply create a diagram where you draw the change of the difference in output voltage over time, i.e. LTZ_1 minus LTZ_2 and LTZ_1 minus LM_2 (what's that kind of ref? not the LM1236 ?).

LM #2 is one of my LM399 references now running 24/7 since 2008.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 27, 2013, 04:57:47 am
Hello Ken,

thanks for sharing. This will be another point on my todo list: At least providing the space for ferrite beads on PCB at critical points.

Do you have any practical experiences with these parts mentioned in LT AN101?

When having a closer look to AN101 I see that J.W. has not used a real switching supply but has generated the waveforms by a "artificial circuit".
The main difference is that he supplies the spikes in differential mode to the input of the analog regulator (a LT1763 which I also use). The noise from a real switch mode supply usually clocks in as common mode so the noise will be equally on the +supply and the GND pin. At least this is true for a wall wart with 1.5 m cord length on the 24V side.
So instinctively I would use 2 ferrite beads on the input. Preventing that the input capacitor of the analog regulator will feed the noise on the GND line to the input of the regulator after the bead on the +supply again.
But why is he using especially this ferrite bead having only around 50 Ohms at 100 MHz. I would go for a higher Impedance e.g. 300-1000 Ohms at the critical frequency of 100 MHz if the DC voltage drop due to the DC resistance would permit this.
Further I would never use only a electrolytic capacitor alone on input and output of voltage regulator like it is shown in AN101. I always use additional 100nF ceramics to short the RF spikes to the GND pin of the regulator.

With best regards

Andreas
 
Title: #6 Measurement Results: Monitoring, Conditioning & hysteresis effects
Post by: Dr. Frank on July 27, 2013, 02:17:07 pm
Monitoring Setup

If you want to find out how well your LTZ reference performs, you have to compare it to either one much more stable standard, or to several equally good ones.

This much better standard would be a JJ primary standard only.

Equally good ones would be supervised Zener standard banks as Fluke 734B, 7010 or Datron 4901, or an ensemble of at least 3 DYI LTZ1000 references, or similar.

Also, a precise transfer standard is needed, to be able to compare the raw 7.xxx volt precisely against the 10V references.

I use 2 different kind of references, the first one is the internal LTZ1000A of a 3458A, running on 65°C (instead of 95°C), and a Fluke 5442A which is based on the SZA263.

The HP3458A also serves as a very precise transfer standard, due to its linearity.

Both devices are well aged, 13 years for the HP3458A, 23 years for the Fluke 5442A, and both are running intermittently only. During power down times, their drift should be close to zero. Their combined drift over 3 ½ years is obviously 1ppm maximum, see figure 1.

Both of the DIY LTZ1000 references, including the 7,147V => 7,0000V => 10,0000V transfer derived from Ref_2, have been running continuously for 3 ½ years, and were compared also against the HP3458A. Therefore, my reference ensemble consists of 4 equivalent sources.

Long Term stability measurements

During the first 2 years, I have checked only, that all references were stable to within 1ppm of their initial values. Therefore, intermediate data points were missing.

In June 2011, I have moved my complete analogue equipment to the basement, where a stable room temperature of 20.0 … 22.5 °C is available during all seasons.
The room temperature may be constant to +/- 0.2K during several hours and to +/- 1.0K during successive measurement days. 
This measure improved the short term stability of all measurements significantly.
In other words, without a stable environment, sub-ppm stability measurements are not possible at all.

Ref_2 and its 10V output drifted about 1ppm in 3 ½ years. (See figure 2)
The 7,000V output has been calibrated initially only, but the 10/7 transfer was calibrated several times, about 2 times a year.

On Ref_1 I performed some experiments, so it was “mistreated” several times, i.e. the temperature control got out of regulation. Thereby it encountered several temperature trips to 100°C (estimated).
Afterwards, its output voltage then restarted at a lower value, and drifted much more than Ref_2, (see figure 3). As the output voltage of the LTZ1000 is lower at 100°C, the reference @ 45°C obviously memorized its short trip to 100°C, and drifted towards that direction.

Conditioning

The last such accident happened in June 2013, which left a hefty additional shift of -3ppm.

I remembered the patent of Pickering, to remove temperature induced hysteresis effects in the LTZ1000.

So I temperature-cycled the complete box to remove the hysteresis (see figure 4).

To do that cycling right, it is important to have big enough, but decreasing temperature differences, related to the stabilization temperature, in this case compared to +45°C.
This means, +100°C gives +55K, storage at -23°C gives a dT of -68K, +80°C equals dT = +35K and so forth.

I found out (see fig. 4 also), that below a difference of about +/- 20K, there is no big hysteresis effect.
So I really doubt, that the Fluke 7001 really did operate efficiently in removing hysteresis, because at a stabilization temperature of +45°C, the lowest available negative temperature difference at around 22°C room temperature (i.e. -23K) is too small to deliver a sufficient 'reset' effect. (The 7001 has been terminated by Fluke in the meantime.)

During that procedure, Ref_2 also showed a hysteresis effect, but in the end returned to its initial value of 3½ years before. This indicates that the cycling really removed the hysteresis in both references.

Ref_1 ended at about +1ppm, and its future drift behavior will show, if it’s now more stable. If it resides at about +1ppm, possibly the LTZ1000 had been heated too much during soldering, although I used a thermal transfer pincer and soldered very quickly.

Further effects

It is important to have a proper shielding (e.g. case connected to ground) and a quiet power supply.

An external wall plug power supply was used, to avoid magnetic disturbance from the transformer. In first instance, its output  of 18V AC induced disturbances on the LTZ temperature regulation.
The case had to be connected to ground of the LTZ output, and that induced a shift of 0.5ppm of each output. Exactly this same effect could also be demonstrated on another LTZ based reference, designed by 'babysitter'.
When I redesigned the wall plug in for an output of 25V DC, the LTZ references became more short term stable, and the 0.5ppm shift vanished.


Short Term stability measurements

Figures 5 and 6 show short term stabilities of Ref_1 versus HP3458A during 10 minutes and 35h, using an aperture time of 2 seconds, i.e. NPLC100.

The internal temperature of the HP3458A increased continuously from 33.7 to 34.8°C during those 35h. ACAL was performed only once, before the start of the measurement.
 
The 10min measurement shows  fluctuations of +/- 0.05pm, which is very well consistent with the transfer specification of the HP3458A,  +/-  0.1ppm, and especially with the noise specification of the LTZ1000, i.e. 2µVpp (equivalent to +/- 0.15ppm).

The average 35h drift of ca. 0.3ppm is well below the HP3458A 24h specification, i.e. +/- 0.55ppm, or its T.C. of 0.5ppm/K without ACAL.



Conclusion:

The basic LTZ1000 circuitry, output of around 7,2V, running on 45°C and built with wire wound resistors is capable of drifts well below 1ppm/year. Noise and short term stability are below +/- 0.1ppm.

Sophisticated shielding and a low noise DC PSU are very important for obtaining that degree of stability.

The influence of additional ‘gimmicks’ as summarized in part #1, have not been demonstrated yet, but they have to compete in value with the effects demonstrated here.

<end>
Title: Re: #6 Measurement Results: Monitoring, Conditioning & hysteresis effects
Post by: Andreas on July 27, 2013, 03:54:32 pm
To do that cycling right, it is important to have big enough, but decreasing temperature differences, related to the stabilization temperature, in this case compared to +45°C.
This means, +100°C gives +55K, storage at -23°C gives a dT of -68K, +80°C equals dT = +35K and so forth.

After such a "mistreatment" with a output voltage shift (shorting the 7V output by a unpowered ADC) I simply switched off the power of my LTZ#1 for some minutes to cool down and switched on again. The deviation was much smaller so I repeated power cycling on the LTZ until the deviation was small.

With best regards

Andreas
Title: Re: #6 Measurement Results: Monitoring, Conditioning & hysteresis effects
Post by: Dr. Frank on July 27, 2013, 04:09:38 pm

After such a "mistreatment" with a output voltage shift (shorting the 7V output by a unpowered ADC) I simply switched off the power of my LTZ#1 for some minutes to cool down and switched on again. The deviation was much smaller so I repeated power cycling on the LTZ until the deviation was small.

With best regards

Andreas

I did not mention that: Although I unplugged the box for several days after such an event, the Ref_2 output recovered a little bit, but afterwards quickly drifted towards negative values.
Therefore, "resetting" at 21°C did not really help.

Another indicator: Under normal conditions, the outputs recover stably to their initial values, i.e. to within a few tenths of a ppm, if the box is switched off for a longer period of time and then switched on again..

My wife tested that for me when she saw the illumination of  the multiple socket outlet, and switched it off to 'save energy'   :scared: (the box consumes around 2,5W).
3 weeks later, I was very relieved to determine, that absolutely no drift occurred afterwards.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 27, 2013, 04:18:49 pm
Hello Frank,

Would be interesting if the LTZ1000A are easier to get to the initial condition than the LTZ1000 or if my accident was simply not so hard as yours.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on July 27, 2013, 04:23:41 pm
Hello Frank,

Would be interesting if the LTZ1000A are easier to get to the initial condition than the LTZ1000 or if my accident was simply not so hard as yours.

With best regards

Andreas

Hello Andreas,

currently I don't want to test that again. No experiments on the revised box any more..
Perhaps I could do that when I assemble those five new LTZ1000..

I assume that the hysteresis depends on sample variations.
And the LTZ1000A should heat up to a higher temperature than the LTZ1000, due to its higher thermal isolation.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 27, 2013, 04:43:30 pm
currently I don't want to test that again. No experiments on the revised box any more..
Perhaps I could do that when I assemble those five new LTZ1000..
I can understand this ;-) And I do not know if I wanted to repeat the experiment with only having 7 devices.
Except when having one candidate with a very large drift over time.

I assume that the hysteresis depends on sample variations.
And the LTZ1000A should heat up to a higher temperature than the LTZ1000, due to its higher thermal isolation.
Of course so we would have to test many samples to get a statistical prove.
And dont forget: I have only a voltage regulator in SO-8 which will go easier to current limiting than other voltage regulators.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on July 28, 2013, 09:28:55 am
Quote
So let me know if you have a solution.

http://www.haufe-uebertrager.de/ (http://www.haufe-uebertrager.de/)

delivers shielded (toroidal core) transformers. If the transformer is not shielded it should be shielded within your case. An important point is the way you arrange the transformer compared to the pcbs. Place it so that coupling by its field into your pcbs is as small as possible. You don't need to use expensive mu metall but galvanically tinned metal sheet / rf sheet metal is a perfect choice.
I would avoid using switching supplies in such an application at all and use linear components instead. But if not avoidable my tip is: There is a good book by Würth Elektronik you might want to have a look to, you will find all the info about ferrite beads and filter strategies using them.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 28, 2013, 03:57:59 pm
At 100Mhz, a few pF looks like a low impedance.  This is not an easy problem to fix, and there is no guaranteed "recipe" that will always work in any situation-- theory is not very helpful here-- only experience.

Good Luck!

-Ken

True words.
I worked on EMC optimized PCB layouts for some years. The 3rd truth is that you have to fight against every mil line length producing high impedances for filter capacitors shifting the maximum usable frequencies towards dramatic lower values.

Quote
So let me know if you have a solution.

http://www.haufe-uebertrager.de/ (http://www.haufe-uebertrager.de/)

delivers shielded (toroidal core) transformers. If the transformer is not shielded it should be shielded within your case. An important point is the way you arrange the transformer compared to the pcbs. Place it so that coupling by its field into your pcbs is as small as possible. You don't need to use expensive mu metall but galvanically tinned metal sheet / rf sheet metal is a perfect choice.
I would avoid using switching supplies in such an application at all and use linear components instead. But if not avoidable my tip is: There is a good book by Würth Elektronik you might want to have a look to, you will find all the info about ferrite beads and filter strategies using them.

Hello branadic,

perhaps I have not explained it correctly: I do not want to use a transformer within my device. I am looking for a solution of keeping external mains disturbances like the "green" switchmode supplies away from my cirquit so that I could (optional) charge while measuring. My shielding and guarding concept does not allow a transformer within the device.
For this I would need a outer shield connected to earth ground additional to my existing housing which is a floating guard.

And there is a difference between the magnetic shield (a outer ferromagnetic housing around the transformer) which they offer as option for standard parts and a electrostatic shield (a single ended isolated metal foil connected to earth ground) reducing the coupling capacity between primary and secondary side of the transformer.

So I will most probably try to get some enhancement by some ferrites.
Which of the books did you mean on the Würth homepage?
The "Trilogy of Magnetics" or one of the other books?

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on July 28, 2013, 04:09:23 pm
Quote
Which of the books did you mean on the Würth homepage?
The "Trilogy of Magnetics" or one of the other books?


Yes, this is the title I think to remember to. I have bought this book for work and think it's pretty helpful.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 05, 2013, 05:06:21 am
Of course... Pk4ts. There is the Same Part in normal thermal emf available for comparisons, too.

Sent from my mobile
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 05, 2013, 05:34:31 am
IT is in their t&m catalog! I dont know a Distributor, price around 12 Euro each. Minimum Order around 60 euro. Br Babysitter
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on August 05, 2013, 07:50:05 am
so far I have not found a source for the SLS410-TS and the SL425-A/TS, if you find them please share
(what I do not like is, both have solder connection only)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 05, 2013, 08:12:13 am
so far I have not found a source for the SLS410-TS and the SL425-A/TS if you find them please share
(what I do not like is, both have solder connection only)


I've ordered the PK-4TS directly @ MC Germany, therefore I assume that you may also get the other parts there.
Perhaps you ask them first, also for pricing.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 05, 2013, 08:55:21 am
Price was about 7-8 eur for the plugs iirc.
Minimum order of ~60 euro in germany !

Greetings from the Babysitter
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 05, 2013, 08:09:15 pm
http://www.edn.com/design/other/4326640/DC-accurate-32-bit-DAC-achieves-32-bit-resolution (http://www.edn.com/design/other/4326640/DC-accurate-32-bit-DAC-achieves-32-bit-resolution)

Interesting about that is, that on volt-nuts the mistakes in the articel were never really identified and that W Stephen Woodward, Chapel Hill, NC; Edited by Martin Rowe and Fran Granville never showed a picture of the circuit (pcb-layout or photo of the pcb) or sold ready to use pcbs. Does anybody have the full text article?

@ DiligentMinds.com

You might want to draw your idea into a real world circuit?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 06, 2013, 06:15:10 am
Hello together,

there are other articles from Woodward who explain the circuit more in detail:
http://www.edn.com/design/analog/4323340/Fast-settling-synchronous-PWM-DAC-filter-has-almost-no-ripple (http://www.edn.com/design/analog/4323340/Fast-settling-synchronous-PWM-DAC-filter-has-almost-no-ripple)
http://www.edn.com/design/analog/4329365/Combine-two-8-bit-outputs-to-make-one-16-bit-DAC (http://www.edn.com/design/analog/4329365/Combine-two-8-bit-outputs-to-make-one-16-bit-DAC)

formerly it was possible to download the whole article as pdf and not only the schematics.

I have built the 32 Bit DAC cirquit mentioned above with slight variations. And could by far not reach the the values mentioned in the article.

That what I got is around 4 ppm INL (ok maybe only 3 ppm since my ADC is only linearized to around 1 ppm).
But when thinking twice: Woodward does not mention the switching times in his accuracy formulas neither he mentiones how he gets to the 23 bits as the effect of charge injection of the switches.

R7 has to be carefully adjusted to reach the 4 ppm INL. And naturally should be tracked with the chip temperature of the MAX4053 chip. With a simple 5.1 Ohms Resistor INL was around 13 ppm (65uV change) as can be seen on the diagrams of June 28th in this thread.

Also noise with 2uVpp only seems to consider the OP-Noise of the chopper. And not the additional effects of the switches and the error of the integrator producing some kind of "staircase noise" with much larger amplitude (around 15uVpp measured with a 4th order 10 Hz low pass filter) in my case.

So all in all the circuit idea is not bad. The settling time is excellent. But there is much room for enhancements.

So I for my part will rely on a 2 DAC solution with a precision ADC in loopback as in AN86.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on August 06, 2013, 07:37:36 am
Quote
http://www.edn.com/design/other/4326640/DC-accurate-32-bit-DAC-achieves-32-bit-resolution
This article is like a joke. Even ancient (30-years old) Datron 4000 calibrators have a two PWM DACs and provide 0.03 ppm of internal resolution with 0.1 ppm INL. But schematics is far more complicated, "The devil is in the details."
http://www.ko4bb.com/Manuals/09)_Misc_Test_Equipment/Datron/Datron_D4000A/Datron%204000A%20Ref%20Div%20Text.pdf (http://www.ko4bb.com/Manuals/09)_Misc_Test_Equipment/Datron/Datron_D4000A/Datron%204000A%20Ref%20Div%20Text.pdf)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 06, 2013, 10:03:56 am
Well, I think, that the steering and auto-calibration software for that dual-DAC concept is substantial to get low INL figures.

A very good description is contained in the service manual of the Fluke 5440/5442, which use also this same approach.
These instruments (like its successor, the actual 5720A) have an internal resolution of 27 bit (0.005 ppm), 0.1ppm front panel resolution, and 0.5 (0.3) ppm +/- 1.5µV output linearity.

The trick is, not to use very low PWM rates (<10 units) on the upper DAC, this nonlinear region is covered by the lower DAC.
All offset and gain errors /drifts are measured and compensated first, and then only those ultra linear specifications are possible, but realistically not much below those given linearity figures.

Therefore, claiming 32bit resolution for a DAC sounds great, but is totally nonsense for physical reasons.
To be checked is the characteristics of the much more simply built DYI divider, i.e. if it's possible to to achieve < 1ppm INL or output uncertainty by appropriate steering of both DACs.


I have measured the linearity of my 5442A by means of the 3458A, and present them here in two versions:

The first version is the linearity referred to the input (13V = 2 x SZA263), that should be the same as the INL, and is well below 0.05 ppm.

The second calculation is related to the output, and tells you, what uncertainty of output you really get.
(That's the specified linearity parameter of 0.5ppm + 1.5µV for the 5440A.)
It's clear, that this parameter diverges towards zero output (covered in the spec by '+/- 1.5µV'), but between 1V and 11V, the deviation is less than about 0.3ppm (w/o offset).

This level of uncertainty is really necessary for usage as a precision divider in a LTZ1000 based reference, otherwise a resistive divider would be more precise.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: bingo600 on August 06, 2013, 01:47:38 pm
Hello together,

there are other articles from Woodward who explain the circuit more in detail:
http://www.edn.com/design/analog/4323340/Fast-settling-synchronous-PWM-DAC-filter-has-almost-no-ripple (http://www.edn.com/design/analog/4323340/Fast-settling-synchronous-PWM-DAC-filter-has-almost-no-ripple)
http://www.edn.com/design/analog/4329365/Combine-two-8-bit-outputs-to-make-one-16-bit-DAC (http://www.edn.com/design/analog/4329365/Combine-two-8-bit-outputs-to-make-one-16-bit-DAC)

formerly it was possible to download the whole article as pdf and not only the schematics.


Could be those attached ?

/Bingo
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 06, 2013, 08:40:01 pm

This design can be further improved by having more PWM circuits that divide the ~7.2V to control the oven temperature of the LTZ1000(A), and the temperature of the multi-stage Peltier refrigerator that houses the entire circuit.  If the refrigerator is set at 0-deg-C, then we can run the LTZ1000(A) at 10-deg-C, and (hopefully) it will show very little drift in comparison to current state-of-the-art voltage references.  WIth the microcontroller in control of the LTZ oven and the refrigerator temperatures, the temperature cycling (ala the Pickering patent) can be used to condition the entire circuit if there is ever an extended power failure.

This is about as far as I have come with this design.  I am doing some experiments with an LTZ-based reference to see if I can coax the device to operate in a mode where "very good" temperature compensation is achieved at the chosen die temperature-- (which is not easy, as the data sheet is devoid of much needed information).

A Peltier element, great idea, at least this should make the Pickering patent work, finally..
Have you mentioned those bugs in his patent, i.e. that asymmetrical temperature interval, which will not work theoretically for 'degaussing'? Neither in practise, in the 7001, as 45°C is far too near room temperature.

I still think, the 7001 box was not successful, as the hysteresis effect is so low for a power down situation, or buried under other effects, that this technique does not give real advantages.
Below 20..30K temperature intervals, the hysteresis is very small.

How do you plan to realize the duty cycle programming?
Any calibration features?

Btw: The famous Datron 4910 reference, doesn't this device contain PWMs for the 7.2V => 10.0000V transfer also, instead of a resistive divider?
How's this realized?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 06, 2013, 09:27:13 pm
The 500KHz is used on the final output to provide a gain of 2. 

Really 500 kHz? = 2000ns.
how much will the break/before make time > 15 ns and the difference between rise and fall time (30-40 ns) affect the 2:1 ratio?

One other question: Why do the calibrators use 125 Hz as PWM. It's neither a multiple of 50 nor 60 Hz line frequency and might give a beat frequency with both NPLC integration times.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on August 07, 2013, 10:26:50 am
Quote
Btw: The famous Datron 4910 reference, doesn't this device contain PWMs for the 7.2V => 10.0000V transfer also, instead of a resistive divider?
How's this realized?
No problem. 4910 schematic is well-known.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 07, 2013, 11:17:39 am
No problem. 4910 schematic is well-known.

Mickle,

thank you very much!!
Partly I've seen the schematics, as I remember now..

The content of the Vishay resistor array still is not known yet?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on August 07, 2013, 11:26:11 am
PIN
1-2:48.7795K  1-3:48.6536K  1-4:48.6543  1-5:47.9947K  1-6:38.9950K  1-7:38.9952K  1-8:39.0165K
2-3:127.422ohm  2-4:127.326ohm  2-5:786.248ohm  2-6:9.78619K  2-7:9.78629K  2-8:9.80740K
3-4:0.3380ohm  3-5:659.267ohm  3-6:9.65917K  3-7:9.65927K  3-8:9.68048K
4-5:659.163ohm  4-6:9.65910K  4-7:9.65920K  4-8:9.68033K
5-6:9.00017K  5-7:9.00028K  5-8:9.02140K 
6-7:0.3355ohm  6-8:21.5500ohm
7-8:21.4520ohm
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on August 07, 2013, 11:28:01 am
The content of the Vishay resistor array still is not known yet?
which one do you mean (part# 315532)?
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on August 07, 2013, 12:02:44 pm
PIN
1-2:48.7795K  1-3:48.6536K  1-4:48.6543  1-5:47.9947K  1-6:38.9950K  1-7:38.9952K  1-8:39.0165K
2-3:127.422ohm  2-4:127.326ohm  2-5:786.248ohm  2-6:9.78619K  2-7:9.78629K  2-8:9.80740K
3-4:0.3380ohm  3-5:659.267ohm  3-6:9.65917K  3-7:9.65927K  3-8:9.68048K
4-5:659.163ohm  4-6:9.65910K  4-7:9.65920K  4-8:9.68033K
5-6:9.00017K  5-7:9.00028K  5-8:9.02140K 
6-7:0.3355ohm  6-8:21.5500ohm
7-8:21.4520ohm

I guess that answers my question.
Your meassurement looks close to what it really is (an array of 8 resistors some in series and some parallel).

If there is interest I can probably deliever all details you like to know, because I have the original datasheet somewhere.
I also was in contact with VPG and they offered me to make my own personal part number, if I want this obsolete part. 
But I stopped there, because I do think this is not as good as you can do today.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 07, 2013, 01:05:56 pm
I guess that answers my question.
Your meassurement looks close to what it really is (an array of 8 resistors some in series and some parallel).

If there is interest I can probably deliever all details you like to know, because I have the original datasheet somewhere.
I also was in contact with VPG and they offered me to make my own personal part number, if I want this obsolete part. 
But I stopped there, because I do think this is not as good as you can do today.

Hi,

you have the original datasheet of that Datron specific part.
Well, should be 5 different resistors only, i.e.
21.2, 127, 39k for the reference, 21.2 for improvement of T.C., 127 for the 4mA Zener current, 39k as collector resistor.

Then, 9k over 659, as divider for the heater control, but regulated additionally from outside the module.

So, the complete schematic may be sketched in a nicer way.
Also, the points which have that guard ring, might be drawn in a schematic... I still would like to understand, what Datron has done there, and which influence this might have.

I agree, todays components have improved a lot, especially the oil filled resistors are superior, and allow a more stable design also without the elaborate heater control in the 4910.
Anyhow, the schematic is interesting, for improving the sensitivity of the regulation part. Datron has included some caps there..

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on August 07, 2013, 01:54:52 pm
you have the original datasheet of that Datron specific part.
Well, should be 5 different resistors only, i.e.
21.2, 127, 39k for the reference, 21.2 for improvement of T.C., 127 for the 4mA Zener current, 39k as collector resistor.

Then, 9k over 659, as divider for the heater control, but which regulated additionally from outside.

So, the complete schematic may be sketched in a nicer way.
Also, the points which have that guard ring, might be drawn in a schematic... I still would like to understand, what Datron has done there, and which influence this might have.

I agree, todays components have improved a lot, especially the oil filled resistors are superior, and allow a more stable design also without the elaborate heater control in the 4910.
Anyhow, the schematic is interesting, for improving the sensitivity of the regulation part. Datron has included some caps there..

Frank

there are 8 resistors in 4 diff. values (5x 64R, 659R, 9k and 39k)
Tolerance of the individual resistors is only 1% and abs. TCR is 3ppm/K.
Tracking is mentioned to be 0.5ppm/K for all 64R and for the others only 4ppm/K
my copy (Rev E from 11/92) is not very good but see the schematic
there is nothing about the guard
Besides the surprise that it is not as percise as I guessed, I did not really understand why it is as it is.
Maybe you or Mickle or anyone else can explain what could be the idea behind it.

bye
quarks

edit: I just saw, I am probably missing pages, because I only have page 1/4+2/4
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 07, 2013, 07:24:14 pm
Wouldn't it be enough to use two 16bit pwm, one for pre-dividing and the second for boosting it to 10V?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 08, 2013, 05:04:09 am

The analog switch I am looking at is the Analog Devices ADG1419-- which has 2.1-ohm switches, and will transition in about 200nS.


Did you already do some linearity checks with the ADG1419 for your 2 first stages?
How does it compare against the results (13 ppm INL un-tweaked and 3-4 ppm INL tweaked circuit ) that I got with the MAX4053A? see Diagrams (x-axis digital code y-axis error voltage in mV against 5000 mV full scale) of  June 28th in this thread?

With best regards

Andreas

 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 10, 2013, 02:06:45 pm

I have only done simulations at this point,


Hello,

which simulation program do you use?
and from where do you get the models of the ADG1419?

I am not the simulation expert. And doing simulations mostly with LTSPICE.
My experience with simulations is that the models are only simplified.
Simulation of deviations below the 100 ppm level seem for me to be
very hard to simulate with a spice based simulator.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 10, 2013, 03:54:20 pm
Looks like he used LTSpice. My guess is, that he used a simple Voltage Controlled Switch model behind the ADG1419 since there is no spice model available from Analog Devices.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on August 12, 2013, 10:08:25 am
because of new interesting discussions here, I kind of paused my DIY LTZ1000 project, to wait and see what I can possibly adopt.

But yesterday I saw something totally unplanned but interesting hapen.
It is topic related, because the used gear (a calibrator and two DMMs) has internal LTZ1000 references.

Here is what I did/observed:

- all three units were started at the same time (no warm up time at all)
- all were connected together and setup to measure 10VDC with 6 digit resolution (for fast reading)
- no adjustments (like Zero or offset corrections) were made

Result was stable 10.000 00 V reading from a few minutes after start until around 2 h when I stopped

This morning I repeated it but with 8 digit resolution and this time with Peak to Peak (PKPK average stat) monitoring running.
Start value was almost spot on 10.000 000 0V
difference between the two DMMs readings was most of the time <1µV (=0,1ppm of 10V)
Overall PKPK was around +10µV  (=1ppm of 10V) running >2h
Final value after >2h was around 10.000 010 0V
Ambient 24,3°C to 24,9°C at 57% rel. humidity during measurement

That altogether is an agreement of within 1ppm of all three units from switching on to >2h.
BTW the gear is of different age and origin and the DMMs are not tweaked/adjusted/calibrated to show this behavior.

Besides I am very pleased with that result, I really wonder how this can statistically be.

Is this possibly only by accident/random, although I alredy repeated it?

Or is it really possible that the warmup drift of all three units almost match identical?
If that could be the case, in future I could save a lot of time, because so far (for serious measurement) I always waited the recommended at least 4h to warm up the gear, before I started to measure anything. But with that finding, I would only have to make sure to start at the same time and could expect to be within 1ppm.

bye
quarks
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on August 12, 2013, 05:14:39 pm
Can you tell us what equipment you have?

In the test I used Wavetek 4808, 1271 and Fluke 8508A
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 12, 2013, 05:58:18 pm
Can someone please link to the "Pickering Patent", would be great if all mentioned patents would be linked so it's easier to follow.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 12, 2013, 08:48:46 pm
Hello DiligentMind, nice thoughts!


Just turning off the 3458A, and waiting 1 day, then turning it back on (and waiting 4 hours), then doing an auto-cal, I noticed that the reading at 10V can be different by as much as +/-0.2ppm.
I see the same fluctuations of 0.2ppm in the monthly  measurements of 3458A vs, 5442A, as I also switch them off. (Energy is very expensive here in Germany).
That's perhaps not a pure hysteresis effect, as the difference drifts forth and back.
Pure hysteresis would add up or stick to fixed output values, as both oven see two different temperatures only, i.e. RT and 65°C only.

It is much more difficult to get the last 2 digits to behave well, but the next to the last digit can be made to be very stable (long term and through power cycles) if the room temperature is kept at 23C +/-0.5C, and there is at least a 4-hour warm-up period before I auto-cal.  So, with care, 7.5 stable digits are possible-- the last digit is always bobbling around-- and I have an idea that it is DC-10Hz noise from the 732B (combined with the DC-10Hz noise of the DMM).

My measurements (10min stability) of the 5442A and of the DYI LTZ1000 also show jitter on the last digit only, i.e. on the order of 0.01ppm, @NPLC100, const. temp.
I also relate that to the Zener noise only, after I improved the circuitry by better PSU and shielding. The 3458A itself should be more stable / less noisy than that.

That in itself makes me confident that if the DMM manufacturers put a carefully designed LTZ1000A based reference in their 6.5 digit DMM's, then they could be made stable to 1ppm per year (ie., the last digit would change no more than +/-1 per year) on their best DC accuracy figures.  I would pay a lot of extra money (up to $500 extra) to have that in a 6.5 digit DMM.

Well, I prefer the LTZ1000 @ 45°C, and this reference can be built much better than HP by yourself for about 100$.

Indeed, using highly selected components together with the special hand tuned wire-wound resistors in the boost circuit of the 732B are key to the unit's stability.  I'm not certain that these techniques could be applied by the home experimenter-- you need a vast inventory just for the selection process, and this can become very expensive very quickly.  ...

To my opinion and experience, instead of hand made / selected wire wound resistors, those hermetical oil filled VHP201Z will do the same job, perhaps even more stable.


Note that resistors will have double the drift rate for each 10C rise in temperature-- so keeping them cool (but at a constant temperature) is best.  How cool?  I don't know-- but I imagine that there is a point of diminishing returns-- so there is probably an optimum temperature to keep all of the circuitry at. 

Room temperature is sufficient for 2ppm/6yrs for the VHP201Z resistors.
And that level of stability is over sufficient for the LTZ1000 circuitry.
Any heating or cooling will lead to more problems.

Another problem is temperature hysteresis-- and this occurs in the LTZ1000, as well as any op-amps that you are using-- and as Dr. Frank has proven-- in foil resistors too.  (I'm not certain what hysteresis effects there are in wire-wound resistors, but I am willing to bet a premium beer that they at least have some hysteresis effects).

The hysteresis effect of the metal foil resistors is relatively low (5ppm after 125°C), and due to the 100:1 attenuation effect, does not play a big role.
On +/- 15K, there is no appreciable hysteresis, so if you take care, there's no problem at all.
Afaik, the wire wound types have neglect-able hysteresis effect, only the tightness of the winding has to be relaxed first.
Some time, we all should meet for a beer, anyhow.

 
The only way I can see around this is to run the LTZ1000 at cryogenic temperatures-- like in liquid nitrogen (LN2).


Will cause problems due to the thermal shock, and will stress the tightness of the package.
Also, as the internal gas will dilute and create a vaccum, the package might implode, or will get a leak and suck LN2 inside. 


 This would result in an absolutely stable temperature, because the LN2 always boils at a specific temperature--

No, that's not really the case. (I worked with cryogenic liquids for years, and was also responsible for air and nitrogen liquefaction in our institute for some time).

LN2 will quickly soak oxygen from the surrounding air, so the boiling point will rise from 77.2K (or so) to above 80K within a few hours, depending on the amount of liquid you use.

I used LN2 as a reference bath for a low temp thermo couple, and it was important to always use 'fresh' LN2 from the Philips liquefier. 

1 l of LN2 used to cost around 50 Cents, or so, LHe4 was 10-20 times more expensive.
A usual 50l cryostate (Dewar) will cost 500-1k $/€ only,  but a complete JJ  is how much? 100k, I think.
A lot of first class calibrations can be paid from that.  8)

I think, the stability of the LTZ1000 circuitry at RT is fully sufficient, and putting it completely in an oven or a crogenic bath will only cause problems and complications
Chose those ultrastable external components instead. Compared to that LN2 steadily boiling off, it is a one time investment only.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 12, 2013, 09:24:31 pm
Can someone please link to the "Pickering Patent", would be great if all mentioned patents would be linked so it's easier to follow.

http://www.google.de/patents/US5369245 (http://www.google.de/patents/US5369245)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 13, 2013, 07:08:55 am
Quote
http://www.google.de/patents/US5369245

Thanks in advance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 13, 2013, 01:20:17 pm
I propose a volt-nuts beer meeting at the Weinheimer UKW-Tagung ham festival (September 13th-15th). I will be there, Quarks is living less than 20 km from there, affordable trip for branadic and Dr. Frank too... bargain hunting on the flea market is possible, at the camping site a few km away we could sit down for some $BEVERAGE.

Greetings

Hendrik


Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 13, 2013, 05:04:48 pm
Quote
I propose a volt-nuts beer meeting at the Weinheimer UKW-Tagung ham festival (September 13th-15th).

Beer sounds good, but I'm outta town this time.

Quote
I will be there, Quarks is living less than 20 km from there, affordable trip for branadic and Dr. Frank too...

I'm sure for Andreas too.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 13, 2013, 07:58:32 pm

I'm sure for Andreas too.

The saturday after flea market in the morning sounds good to me.
But I would prefer some coffee.

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 13, 2013, 11:07:25 pm
Sorry, I hope to travel to Guadalajara exactly at that time.

Another date, and I will fetch my equipment for that meeting.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 14, 2013, 04:13:13 am
That is quite some response!  :-+

I suggest a meeting at 10:30 in/at/near the "coffee tent" on the meadow in the center of the open-air part.
PM me for my phone number if you think you need a support hotline.
This should give everyone the possibility to hunt for nice stuff on the flea market early and also add just little delay for those who have to leave early.

Myself will stay a little longer, lingering on the camping site from saturday to sunday too. This will improve my Weinheim look & smell :-DD

Greetings

Hendrik
Title: Slot or Not
Post by: branadic on August 17, 2013, 06:29:50 pm
As announced by Andreas we wanted to find out what is best: "Using a solid pcb or spend some slots around the heat controlled voltage reference?" and furthermore: "Keep the leads as long or as short as possible?".
Therefore Andreas provided two LM399H (National Semiconductor) and me the pcb. The layout, similar to the one you can find in the world wide web for the LTZ1000, contains two equal trace arrangements but one of them has milled slots.
The test starts pretty simple, the two LM399 are soldered into the board keeping the leads as long as possible and with nearly equal lenght for both references. A 7k5 resistor for each reference as given in the datasheet and supplied with 15V from a bench PSU.
The pcb is arranged on a styrofoam with a window inside so that the IR cam can record the bottom of the pcb. To keep other IR sources away that can produce reflection on the tinned copper traces some foam was put around the references and another styrofoam box was put on top. At some places a black tape was necessary, to avoid reflection.
In the following pictures the references were running 30min minimum. To verify the results I always made a picture of the pcbs top side.

I used same temperature scale for all pictures, but as I have the raw data here I can change that if necessary.

So what can we see? With long leads and slots (left side) the temperature of the pcb seems to be higher compared to the version without slots (right side). However, in both versions all 4 pins seem to have the same temperature, no thermal gradient visible.
As expected the pcb gets more hot with short leads...

So let's start the discussion :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 17, 2013, 06:53:20 pm
A very good experiment, good to see the IC itself spreads the heat evenly around itself. Thanks to HSG too? 8)

Glass as main ingredient of PCB material is a known bad conductor for heat, the second ingredient epoxy resin is also not that good, and cooper a good known conductor (Yes, there is a rule that eletrical conductivity is often similar to heat conductivity..) , knowledge of those properties allows for some thermal designing. The cooper pour on my PCB was intended to spread the heat evenly.

What we not see, however, are the air currents I am afraid of, slots on the PCB allow them to circulate and I suppose they will be very erratic and turbulent in such an environment. Possibly I will study some liquid-to-liquid-turbulences at some time during the next few months, maybe I can put such a circuit in my test jig then ?

BTW, the Volt-Nut Meetup at Weinheim gains some traction !

Greetings
Hendrik
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 17, 2013, 07:34:05 pm
Thanks and yes, it's great having access to such equipment at weekend, one of the advantages working there. But I'm sure the cam is happy to have a sense and I also hope that you guys are happy that you can profit by this too. ;)

About the turbulences I wouldn't care if the critical parts are put into foam, this can avoid air flow, see picture attached.
Title: Re: Slot or Not
Post by: Andreas on August 17, 2013, 09:30:56 pm

So what can we see? With long leads and slots (left side) the temperature of the pcb seems to be higher compared to the version without slots (right side). However, in both versions all 4 pins seem to have the same temperature, no thermal gradient visible.
As expected the pcb gets more hot with short leads...

So let's start the discussion :)

Ok.

Mhm.

The pictures are really surprising me.

This will change my picture of the thermal world.

My favourite up to now was the short leads with the slotted pcb.
I would have expected all pins and the pcb around the pins at the same temperature.
And the large temperature gradient on the lines till the outer rings.
(Why should Datron have made them if they would not be necessary).
The thermal gradients are much more locally around the reference than I expected.

In my opinion we do not only have to regard wether all pins are equally but also the heat distribution within the solder junction.
The lead of the reference (in the middle of the solder junction) is made of Kovar which has around 40 uV/K against copper (at the edge of the solder junction).
Solder itself has around 3uV/K against copper. So lets assume that Kovar against solder has around 37uV/K.

So from middle to edge of the solder junction it seems for me to be much more critical for the slotted board with short legs than the not slotted board with long legs.

So long legs and large thermal mass (perhaps the PCB material which diligent minds recommends) seem to be the best.
Of course you have to take more care keeping air currents away from long legs.

Other opinions?

@ branadic: with the raw data it should be more easy to evaluate the gradient within the pads than for me having difficulties with the colour gradients of the picture.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 18, 2013, 07:33:28 am
Branadic,

those are great measurements!

2 simple conclusions:

- short leads will increase the temperature of the PCB, long leads will give more thermal isolation between component and PCB => long leads preferred
- slots in the PCB give higher thermal isolation between solder joint area and outer PCB area, thereby reducing cooling of the solder joints through the PCB, and in turn increasing the local heating of the solder joints. Higher solder joint temperatures might cause temperature differences more easily and  will increase thermo voltages.

So I still do not understand the purpose of those slots, especially in the Datron PCB, where the LTZ1000 at a temperature of ~60°C is used.

I'm now very confident that 45°C and a PCB without slots is the most stable solution.

Thanks for sharing.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Jay_Diddy_B on August 18, 2013, 08:55:35 am
Hi,
Just a little observation for you.

I noticed that your thermal camera is pointing at tinned traces on the PCB. These have a very low emissivity compared to the Fibreglass (FR4).

I suggest that you could try painting the traces with liquid paper, type correcting fluid, or give the board a quick spray with black paint (flat or matte).

Jay_Diddy_B
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on August 18, 2013, 09:00:03 am
Very interesting, so long legs and no slots look thermally good.

But what about mechanical stress relief, what I though is the main reason for the slots?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 18, 2013, 09:21:44 am
Very interesting, so long legs and no slots look thermally good.

But what about mechanical stress relief, what I though is the main reason for the slots?

Yeah, what about??

Does "mechanical stress" cause any deviations in output voltage or decrease stability?
How does "mechanical stress" affect those electrical characteristics?
How is "mechanical stress" defined in this situation?

I still cannot see any mechanism, how that buzzword "mechanical stress" would have influence on the electrical output.

Especially, as all of the relevant components are leaded parts, not SMD parts, where you really would have mechanical forces on the solder joints, due to differences in thermal expansion between component and PCB.

Cold versus hot areas on the PCB may lead to bending / distortion of the PCB, but what would be the electrical effect of that, once again, when using leaded components?

Such mechanical effects would be relevant for oven temperatures of 90°C.. down to 60°C perhaps, but at 45°C, that's completely irrelevant.

Does anybody have any other ideas?

Sorry, but I am still searching for solid real physical effects and their explanations.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on August 18, 2013, 10:25:08 am
Hi nV freaks,

I'm passionate too with this subject and follow this daily but I'm happy with 6 1/2 digits.

There is "the multimeter" you need on eBay with a failure but I suppose it should not be to bad to fix it.

http://www.benl.ebay.be/itm/261263662099?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649 (http://www.benl.ebay.be/itm/261263662099?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649)

eurofox
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 18, 2013, 11:57:54 am
Hi,

as said the emission coefficient of metal is really worse, it's rather an infrared mirror reflecting all infrared sources from the surrounding.
The resolution of the cam is about 0,3K so with the sum of both you can't see a thermal gradient along the leads or the temperature of the solder junctions (they're also reflecting) directly. What you can do is cover the surface with a coating as pointed out by Jay, but I found that this wasn't necessary here.
The FR4 material in this case radiates enough to make things visible although glas is an infrared isolator (you can hide behind a glas but not behind a silicon wafer).
We can assume that the solder junctions are of the same temperature like the pcb material, so one can calculate the temperature gradient along the leads.
The heat conductance of the pcb material is worse but better compared to glas only. Because of the smaller thermal mass with slots the temperature is a bit higher, but not critical. The heated reference over-radiates the pcb temperature at bottom view, so the top view is more significant in this case.

About the stress with or without slots the only answer can give a measurement and the board exists so let's do some measurement and find out, shall we?
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on August 18, 2013, 12:15:35 pm
Yeah, what about??

Does "mechanical stress" cause any deviations in output voltage or decrease stability?
How does "mechanical stress" affect those electrical characteristics?
How is "mechanical stress" defined in this situation?

I still cannot see any mechanism, how that buzzword "mechanical stress" would have influence on the electrical output.

Especially, as all of the relevant components are leaded parts, not SMD parts, where you really would have mechanical forces on the solder joints, due to differences in thermal expansion between component and PCB.

Cold versus hot areas on the PCB may lead to bending / distortion of the PCB, but what would be the electrical effect of that, once again, when using leaded components?

Such mechanical effects would be relevant for oven temperatures of 90°C.. down to 60°C perhaps, but at 45°C, that's completely irrelevant.

Does anybody have any other ideas?

Sorry, but I am still searching for solid real physical effects and their explanations.

Frank

I do not know the answers, but my thoughts (until now) are influenced by the fact that the Datron/Wavetek design is with the slots.
Also the gear that uses this design (like 4808, 4910 and 1281 to name a few) is representing and rated top notch.
So my guess is, there probably is a good reason for slots.

In the LT Application Note AN82
http://cds.linear.com/docs/en/application-note/an82f.pdf (http://cds.linear.com/docs/en/application-note/an82f.pdf)
there is a statement (page 6) that Metal Packages are largely immune to board stress
(DiligendMinds also stated this before, especially for the LTZ1000ACH),
but negative effects are described/shown there (see att.).

Also on http://www.amplifier.cd/Technische_Berichte/Spannungsreferenzen/Spannungsreferenz.html (http://www.amplifier.cd/Technische_Berichte/Spannungsreferenzen/Spannungsreferenz.html)
(sorry forgot the translation to english)
http://translate.google.de/translate?sl=de&tl=en&js=n&prev=_t&hl=de&ie=UTF-8&u=http%3A%2F%2Fwww.amplifier.cd%2FTechnische_Berichte%2FSpannungsreferenzen%2FSpannungsreferenz.html&act=url (http://translate.google.de/translate?sl=de&tl=en&js=n&prev=_t&hl=de&ie=UTF-8&u=http%3A%2F%2Fwww.amplifier.cd%2FTechnische_Berichte%2FSpannungsreferenzen%2FSpannungsreferenz.html&act=url)
there are some findings about mechanical stress.

At least for me that is good evidence to think there probably must be something behind it.
But if it is not worth the effort to implement it, than of course that is good news, because things get a lot easier.

bye
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 18, 2013, 12:24:13 pm
I will have AT our zwick AT work for pushing and pulling on pcbs. sent from mobile.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 18, 2013, 12:41:36 pm
But what about mechanical stress relief, what I though is the main reason for the slots?

Ok that would be another thing of consideration.

I still cannot see any mechanism, how that buzzword "mechanical stress" would have influence on the electrical output.

As is stated in many datasheets of precision voltage references mechanical stress applied to the PCB shifts output voltage.
And you can simply measure it.
Usually I do this with any of my "ADCs" and try to keep the influence to below 5uV drift due to mechanical bending of the PCB. With every 5V reference that I tried up to now I got many 100uV shift when all pins where soldered to the PCB. So up to now this ended always in this way that only the GND-Pin is soldered to the PCB and the other PINS are wired with a thin VERO wire. This is a bit tricky for SMD devices but it works.

I was very surprised when testing the VRE3050AS reference which is in a hermetically sealed package with gull wing leads. In this case I thought that the influence of the PCB to the chip would be negligible. But this was not the case. I measured values from -16 to +186 uV against untwisted PCB.
Other references have other values depending on construction and individual make.
A LT1236ACS8 gave around 400uV between minimum and maximum value.

Unfortunately I did not do a test with my LTZ1000 boards. And now I don´t know if I shall risk a new ageing cycle.

On the other side a LTZ1000A should have a better behaviour than a LTZ1000 because of the different die attach.

A similar test like the LTZ1000 could be done with the LM399-Board of branadic.

About the stress with or without slots the only answer can give a measurement and the board exists so let's do some measurement and find out, should we?

Yes of course.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 18, 2013, 12:42:10 pm
We have a "Zwick" too and also a second push/pull machine with temperatur control, but I guess this is breaking a butterfly on a wheel. A simple alternating force an top of the voltage reference is more than enough.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 18, 2013, 12:55:44 pm
We have a "Zwick" too and also a second push/pull machine with temperatur control, but I guess this is breaking a butterfly on a wheel. A simple alternating force an top of the voltage reference is more than enough.

I do not put force on the top of my references (because this would also change temperature)
I simply bend the board by applying forces to the edges of the board.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 18, 2013, 01:32:47 pm

I do not know the answers, but my thoughts (until now) are influenced by the fact that the Datron/Wavetek design is with the slots.
Also the gear that uses this design (like 4808, 4910 and 1281 to name a few) is representing and rated top notch.
So my guess is, there probably is a good reason for slots.


Yep, and that's exactly, what's always done during Copy-And-Paste designs ... i.e. copying possible errors or nonsense also.

Many people in this or in the Asian community simply copy the LTZ1000 'A' version, available from China, because it's sitting in the venerable 3458A, including the 95°C operating temperature, without thinking.

Perhaps, Datron did not calculate anything also, and simply introduced those slots by similar hand waving arguments also.
All those instruments you mention, base on the same reference module (afaik), so that's no argument, either.

And there exist also several successful  designs without any slots, I think in the 732B, the ceramic substrate doesn't have those, either.

If there's a physical effect, it should be obvious, or should be measurable in an appropriate experiment.


The cited AN or the experiment in the CD forum deal with a different effect, than directly on the PCB, I think!

It's well known, that molded IC are sensitive to bending, due to their internal construction.
The mold compound might imply pressure on the chip directly, and the base lead frame, where the chip is epoxied onto, is flexible, because it's a thin sheet of copper only.

So, if you bend or distort the legs of such molded IC, you will easily bend the chip itself.

But that is perhaps not the case for the hermetical TO case. There's no mold compound, it has long legs, and the chip carrier is more solid.
And I do not see an advantage of those slots, if you want to avoid flexing of the PCB.
In contrary, slots might intensify bending forces on the legs, because slots can move, but a solid PCB area can not by that amount.
 
Sorry, no, I still can not identify any causality in there.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 18, 2013, 02:01:53 pm
As is stated in many datasheets of precision voltage references mechanical stress applied to the PCB shifts output voltage.
And you can simply measure it.
...
I was very surprised when testing the VRE3050AS reference which is in a hermetically sealed package with gull wing leads.


Andreas, I have read that also, but always in conjunction with molded components only.
And that mechanism I can understand, due to the mechanical construction.

Unfortunately I did not do a test with my LTZ1000 boards.

Well, that would have been very interesting, as the TO case is a totally different mechanical construction.

On the other side a LTZ1000A should have a better behaviour than a LTZ1000 because of the different die attach.


Why? In the LT datasheet, the different die attach is reasoned only for better thermal insulation, not for better mechanical stability.
The only effect is that the required heater power is decreased a lot. (What other mechanical effect should exist there comparing the different die attaches??)
And that is important (only) if you run the LTZ1000 on higher temperatures (95°C), as in the HP3458A, or in the Keithley DMM.

Other instruments at lower temperature (Datron 49xx, Fluke 7001) simply use the LTZ1000 version.

 
A similar test like the LTZ1000 could be done with the LM399-Board of branadic.



With best regards

Andreas


Yes, that's right.
But I could imagine, that there's an effect in the solder joint only, i.e. that thermal voltages are depending on mechanical forces also. (But I could not name or cite anything around such an effect.)

Regards Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 18, 2013, 03:02:30 pm

On the other side a LTZ1000A should have a better behaviour than a LTZ1000 because of the different die attach.


Why? In the LT datasheet, the different die attach is reasoned only for better thermal insulation, not for better mechanical stability.
The only effect is that the required heater power is decreased a lot. (What other mechanical effect should exist there comparing the different die attaches??)


The reason is simple:
AFAIK normally the die is directly attached (by some silver filled epoxy resin) to the Kovar bottom plate of the TO-99 package.
(http://cache.ourdev.cn/bbs_upload782111/files_17/ourdev_464495.JPG)

If you do some thermal isolation it is very likely that it will be something that is not so stiff (ideally some kind of foam or maybe low density glass filled epoxy)  than the bottom plate. Thus introducing less forces to the chip.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 18, 2013, 03:38:07 pm
Okay, okay... we have the Kovar package with gold finish but what are the bond wires made of? Obviously the chip metallization is not gold, so I expect this is not an aluminium bond wire?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 18, 2013, 03:50:35 pm
Andreas, Quarks,

sorry that's all not convincing.

The speculation about the consistency of the isolation material does not bring any new information.
Additionally, I don't see at all, how bending forces on the PCB could propagate into the chip. Definitely not over the bond wires  :--, and hardly via the very stiff chip carrier.
 
In the AN 82 from LT, the robustness of the TO package against mechanical stress, compared to molded components  is pointed out definitely.

The diagram from AN 82, of a slotted vs. a stiff PCB, is made on a molded component (LT1460)  in SO8 package, definitely!
To use this as an indicator, that there possibly might be some appreciable effect on the LTZ1000 also, is more than far-fetched.

Sorry again, up to now, there is no document or experiment yet, supporting this mechanical stress theory on the LTZ1000 package.

The contrary is the case, to my impression.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 18, 2013, 03:59:57 pm
Okay, okay... we have the Kovar package with gold finish but what are the bond wires made of? Obviously the chip metallization is not gold, so I expect this is not an aluminium bond wire?

bond wires used to be pure gold, but now were changed in the whole electronics industry to pure copper.

aluminium is always used for the top chip metallization, and the bond landing pattern .

On that photograph, obviously LT uses aluminium bond wires also.

Afaik, this material is used in power semiconductors, and for low bond temperatures, therefore low resistance may have been the argument here.
http://heraeus-contactmaterials.com/en/products/aldr/productpage_smt_adhesives_3.aspx (http://heraeus-contactmaterials.com/en/products/aldr/productpage_smt_adhesives_3.aspx)

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 18, 2013, 04:11:49 pm
Quote
bond wires used to be pure gold, but now were changed in the whole electronics industry to pure copper.
aluminium is always used for the top chip metallization, and the bond landing pattern .
On that photograph, obviously LT uses aluminium bond wires.
Afaik, this material is used in power semiconductors also, therefore low resistance may have been the argument here.
.

I doubt they used aluminium bond wires unless the chip metallization is known and this is not gold (see the picture), what you would need for an aluminium bond wire.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 18, 2013, 04:18:12 pm

I doubt they used aluminium bond wires unless the chip metallization is known and this is not gold (see the picture), what you would need for an aluminium bond wire.

Excuse me, branadic.. I receive PCNs (Product Change Notification) every day, from all relevant semiconductor suppliers worldwide.

So I can tell for sure, that for the chip metallization, usually and definitely aluminium IS used!

Follow the Heraeus link, available bond wires are made of Au, Cu or Al, and can well be distinguished by their color.
And the most probable material in the LTZ1000 cut-off is aluminium bond wires.

The bonding process  is some sort of creating an alloy; Au alloys very nicely with aluminium.
In short, equal metals are not required for bonding, but aluminium/aluminium bonding is of course possible, why not?

This avoids diffusion problems. 

Anyhow, does that play a role in this actual discussion?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 18, 2013, 04:28:39 pm
Quote
Excuse me, branadic.. I receive PCNs (Product Change Notification) every day, from all relevant semiconductors suppliers worldwide.

So I can tell for sure, that for the chip metallization, usually and definitely aluminium IS used!

This is only true if the bond wire is gold. You can't bond an aluminium wire to an aluminium surface, sorry but I studied microsystem technology and still work in a field where bonding is one way to connect bare dies to a pcb or mid ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 18, 2013, 04:37:52 pm


This is only true if the bond wire is gold. You can't bond an aluminium wire to an aluminium surface, sorry but I studied microsystem technology and still work in a field where bonding is one way to connect bare dies to a pcb or mid ;)

Ok, that I didn't know.. learnt something.

Do you also know the reason for that behavior, it's not obvious for me?

I also read those magazines about power electronics, with many macro photographs of bare die technology, there's often aluminium used for the bond wires, but the metallization also have a silver color.

Do you know anything about that?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 18, 2013, 06:02:39 pm
Quote
I was very surprised when testing the VRE3050AS reference which is in a hermetically sealed package with gull wing leads. In this case I thought that the influence of the PCB to the chip would be negligible. But this was not the case. I measured values from -16 to +186 uV against untwisted PCB.
Other references have other values depending on construction and individual make.
A LT1236ACS8 gave around 400uV between minimum and maximum value.

If this is true you should have no change using the LS8 package right?

Concerning the die attach, using glue with silver particles could be a hint that the backside of the die is connected to ground/case and not for thermal purpose only. The thickness of the glue in any case should be as low as possible. The transparent brown mass on the picture is so called underfill. This is used because the filled conducting glue has low adhesion and with underfill mechanical stability is increased.
I agree that hermetical packages have improved mechanical stability but they are not stress immune. Stress to the pcb and so to the package (a leg of the package will transfer the force over the bond wire to the chip, even if this is orderes of magnitude lower compared to molded chip packages) will have an influence in any case, the question is "Is it big enough that you can measure it?" I don't now because you can't seperate all the effects from another. Bending the pcb will also change the temperature relations inside the chip package and whatever.

The references are running and I will observe if I can see an influence or difference if bending the board.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 18, 2013, 07:09:25 pm
... The TO-style metal cans are 100% immune to mechanical board stress.  More than likely, the slots in the PC board were to reduce heat-loss, and (in turn) reduce power consumption when running on battery for the 4910 reference.  I am guessing that the engineer at Datron that designed this left the company, and then following engineers simply copied the design without understanding why.  The "A" version of the LTZ1000 did not show up for a while-- so Datron only had the LTZ1000 to work with-- and it is going to use more power for the heater than the "A" version-- thus the need to not only reduce heat loss through the PC material, but also to insulate the LTZ1000 with foam.

You can use slots on your LTZ1000(A) design if you want-- this will reduce heater power a very small amount (and even smaller on the "A" version).  If you intend for your reference to run on battery power for extended periods of time, this may be important to you.  If your reference is line-powered only, then I just don't see any benefit to the slots.

...

Your explanations are really striking!

Me also, would also accept different expertise about those darn slots, if a measurement can demonstrate to have effects above 0.1ppm over whatever kind of parameter.

Up to now, the best naked LTZ1000 stability which can be achieved on an ordinary concept (evaluated by test, model and calculation) is around 0.3ppm/yr and below 0.05ppm/K.

If the influence would be below those ppm-numbers, it would be fully useless to spend any effort in this feature.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 18, 2013, 07:34:08 pm
Okay, I made the test. Setup: Philips PM 2534 and Prema 5000 measuring the voltage difference between the references. Both meters are in 6.5 digit mode. One reference side is fixed in a bench vise the other reference side is bend. The leads of the voltage references are as short as possible from the last thermal test. So if there were stress at the leads the references would get it with the maximum amount.
I can't see any change if the board is bend and I can't see a difference between both layouts. So whatever the slots are good for can only be due to thermal purpose. The result is hard to show, but I hope you trust my statement.
What is true for the LM399 is sure true for the LTZ1000.

So my conclusion is, it's worth making the leads of the reference as short as possible to keep the temperature gradient along the legs small and the solder joints at nearly the same temperature as the reference. This is what Keithley does in its 2002 device with the LTZ1000 and sure in other gear too. Against air flow they provide this little black cap what certainly improves temperature stability.
The slots are neither good nor bad. You have to decide individual on your design, because the reference is followed by an amp. If you pass on slots you can put your amp as close as possible to the reference. This can be helpful or causes trouble.

However, sad that such an investigation was never performed or published before. But with the pictures shown everybody can get an idea of what's best. No space for manipulation or speculation ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 18, 2013, 08:11:02 pm
Quote
And there you have it...  'nuff said...

To quote my boss: "An experiment does not forget any question."

But I agree, art work is pretty cool and it would be worth people would spend some more time in designing their pcbs. Everybody could profit by rf design (pcb based filters etc.). At the end of the day electronics can raise a claim to look art like and stimulate the eye.
I call myself esthete.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 18, 2013, 08:27:59 pm
If you are assured by your approach go for it and let uns know your results :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 18, 2013, 08:41:49 pm
I just return from the basement, where I also tested mechanical stress on the PCB, where an LTZ1000 is sitting beneath.
See my first tear down photo on p. 13 (reply #180).

I simply pressed hard with a screw driver near the LTZ, to bend the PCB locally.
The bending effect from local heating  caused by the reference itself will for sure be much, much smaller.

The output of 7,147 975 5 V did not change under this disturbance, only the normal fluctuations on the last digit could be observed.

This quick and dirty test is no proof, I have to admit.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: alm on August 18, 2013, 09:06:08 pm
This is kind of interesting.  The 0.05ppm/C figure comes from the original Ap-Note.  So, the temperature sensing transistor will have about -2mV/C response.  Using the original circuit in the Ap-Note, many experimenters have found that the ouptut voltage of the LTZ1000(A) will have ~50ppm/C drift with the oven not used.  This means that to achieve the 0.05ppm/C performance we have to maintain the die temperature +/-0.001C.
You can't assume the tempco to be stable over temperature unless you tested it. Tempco will often vary as a function of temperature, current and other parameters. See the Solartron calibration of the 7081 zener current for example. Or the temperature setting on an OCXO.

The 0.3ppm/year stability figure is for the original circuit-- perhaps running the die at 45C.  If you drastically lower the die temperature (to say, 0-deg-C), then you might expect long-term drift to be far less than that-- perhaps as low as 0.1ppm/year (on selected devices of course-- the "average" device will be slightly higher).  This can be done using a multi-stage Peltier device to chill the case of the LTZ1000(A) to -10C, then run the on-chip oven (which has superior temperature control over the Peltier device controller) at 0C.  The results should be quite striking-- almost "spooky" JJA-like stability...
Maybe, but does anyone have data to support this? You can't make solid predictions based on extrapolation. The stability may very well plateau below a certain temperature. It may also be that the high tempco (see above) at 0°C will mess up this idea. Or moisture (condensation).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 18, 2013, 09:47:13 pm
If this is true you should have no change using the LS8 package right?

The LS8-package (LT1236AILS8-5) I did not test with all pins soldered to the PCB. Because I knew that this would have a significant influence.
In a earlier publication (New Product Catalog August 2012) LT published a humidity coefficient for "Humidity (25% RH Change) < 10ppm" for the LT1236 with the LS8 package. I asked them if this was due to the PCB expansion and if I could reduce the rH dependency by some kind of dead bug mounting. The answer was "yes". And with the next version of the data sheet the rH parameter was removed and replaced by "However, PC Board material may absorb moisture and apply mechanical stress to the LT1236LS8. Proper board materials and layout are essential."

And although only having soldered one of the pins to a wire connected directly to the board I have measured
-2 .. +5uV giving a span of 7uV for the LS8-device on my ADC17.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 18, 2013, 10:12:42 pm
Quote
Most PC board materials exhibit piezoelectric (and/or triboelectric) effects with mechanical stress

Do you have a publication to that statement?
Title: Re: Ultra Precision Reference LTZ1000
Post by: alm on August 18, 2013, 10:14:20 pm
No-- I have seen no study with a statistically large enough population that would indicate to any level of certainty that my assertions are correct.  However the Spreadbury study did produce some interesting results [see figure 4 in the attached file], and if you can believe the theory that the drift of the LTZ1000 chip will be reduced by 1/2 with each 10C lowering of die temperature, then it is worth an experiment.
I agree, fig. 4 looks promising. Still, no way to know without testing. I certainly wouldn't assume better stability than 25°C without evidence.

It is possible that this theory is wrong, or that there are other limiting factors that would prevent such low levels of annual drift-- only experimentation with hundreds of units over several different wafer lots would prove this-- and this would take a great deal of money and a great deal of time-- perhaps at least 3 years--
I'm not convinced that you need hundreds. If the drift of individual samples is close enough and the temperature produces a major improvement, then say 5 at 0°C and 5 at some higher temperature may already be enough to show an improvement. You would need to measure over fairly long time periods because of the small magnitude of the drift, and quantifying long term drift may indeed prove interesting.

The only thing we can do as hobbyists, is build a few of these, and see how they drift against each other-- not as good as having a JJA, but it would tell us something at least.
What if at 55°C the references all have a drift of between -2 and -3 ppm/y, but at 0°C the drift would be between +1 ppm/y and -1 ppm/y. Without an independent observer, the latter wouldn't be any better (similar spread). The Spreadbury paper unfortunately doesn't provide enough data to tell if the spread in drift also decreases with temperature.
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on August 18, 2013, 10:32:26 pm
You need to be more Diligent :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 19, 2013, 10:34:40 am
Quote
No I do not-- I was reading about it on the Internet a few weeks ago, and silly me, I did not bookmark the page-- and I am too lazy to try to search for it-- but, if *you* find it, post a link and then we can all enjoy it-- (and I will read it again-- my memory is not as good as it used to be when I was younger).

I can't find any hint to such a problem in the web for FR4 substrate. And I don't see any physical background that the glas epoxy mixture can produce piezoelectric voltages. I can only imagine that LTCC have possibly such effects but I don't know for sure.

Maybe you mixed it up with the problem of piezoelectric effect of smd ceramic capacitors on pcb?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 19, 2013, 11:12:09 am
This quick and dirty test is no proof, I have to admit.
Hello,

But together with the test of branadic this convinces me that at least the LM399 and the LTZ1000 are insensitive to mechanical stress.

Are you certain that it was package stress causing the shift in output voltage?
 I could believe this with an epoxy package, but not the LS8 (ceramic LLC)-- can you make a movie of this and put it on YouTube so we can all enjoy it?

Yes it is repeatable. And  the LT1236AILS8-5 references have a push pull output with a very low impedance. So the impedance of the meter does not play a role when regarding static electricity.
And no. I will not do Daves (video-) job just to repeat a measurement where I have already the data that I need.
Usually I am doing the mechanical stress test only once at the begin of the life of my ADCs.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on August 19, 2013, 01:56:14 pm
Our laboratory researches wasn't confirmed the insensitivity of the LTZ1000 to mechanical (thermo-mechanical) stress. Output voltage drift is small, but measurable even in 7.5 digits mode and well explained via strain compatibility conditions of LTZ1000 and PCB's.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on August 19, 2013, 02:18:17 pm
Hello Mickle,

Thanks for your information. As I know, you have done a lot of very impressive projects and research around them. I would like to know what you learned and what you would sugest to implement, if you would build your next LTZ1000 board.

Bye
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 19, 2013, 04:31:54 pm
Interesting results, but is it really due to stress or is the reason to be searched in the change of thermal distribution?

(http://cache.ourdev.cn/bbs_upload782111/files_18/ourdev_483176.jpg)

This picture in mind I can imagine a donat like heat distribution. If you now bend or tild the board the distributions emphasis will change.
On the other hand the deformation in your simulation is quite big, compared to the board size, isn't it?
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on August 19, 2013, 04:39:29 pm
FEA simulations usually exaggerate displayed deformations so it can be visualized.

What about the strain gage effects (resistance change) of the conductors as being the primary cause? Either circuit board traces, chip leads, or chip die level.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 19, 2013, 04:55:31 pm
Quote
FEA simulations usually exaggerate displayed deformations so it can be visualized.

Sure, but ±0,5mm is at least 1mm deformation!
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on August 19, 2013, 04:59:25 pm
I see what you mean, that is much more deflection than what would occur naturally even with poor handling.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 19, 2013, 05:06:26 pm
Our laboratory researches wasn't confirmed the insensitivity of the LTZ1000 to mechanical (thermo-mechanical) stress. Output voltage drift is small, but measurable even in 7.5 digits mode and well explained via strain compatibility conditions of LTZ1000 and PCB's.

Hello Mickle,
those are interesting findings!

But I do not understand them yet, sorry, it's always me.

What in fact is your explanation of the offset, what you call strain compatibility LTZ/PCB?
I still do not see, which physical effect causes this shift of voltage, and where this effect is located: in the solder junction, in the package, on the chip?

It's clear, high temperatures on a PCB cause strain between rigid bodys of different thermal expansion coefficient , e.g. SMD ceramic components (R, C) versus the PCB itself.
But that's not valid for leaded components, as the leads will simply follow the PCBs expansion.
Only if you have a torsion of the PCB, I could imagine, that the different leads of the TO8 package see different forces in different directions, as you obviously want to demonstrate by your measurement (what was your measurement setup?) and your finite elements simulation.

I see no reason why the PCB should perform such a torsion , if the PCB simply is heated in the middle of the LTZ.

Then, it's not clear to me, why the PCB should heat up to 65°C, if the reference is at this stabilization temperature, or at much lower values (e.g. if run on 45°C), as there is a thermal gradient between the TO 8 package and the PCB.

So, is the observed/measured shift just an exaggeration of this (still not named) effect?

For me, it would be very interesting, how you construct LTZ references today, i.e. which resistor types from Vishay, LTZ A type or not, which temp?
Well I could first investigate on your 7081 modification, but it would be nice, if you would answer specifically to the open questions here.


Thank you very much!

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 19, 2013, 05:08:36 pm
FEA simulations usually exaggerate displayed deformations so it can be visualized.

What about the strain gauge effects (resistance change) of the conductors as being the primary cause? Either circuit board traces, chip leads, or chip die level.

Which resistors do you mean?

I thought of such an effect in first instance also, but there is no such resistor element, perhaps SMD, as all precision resistors are leaded parts also.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 19, 2013, 05:13:12 pm
Quote
FEA simulations usually exaggerate displayed deformations so it can be visualized.

Sure, but ±0,5mm is at least 1mm deformation!

The graphic exaggeration is not what bothers me..
Such strain by temperature always creates very small dislocations (µm) on the PCB, but the forces this generates on the components may be extremely high nevertheless, but only on rigid bodies, i.e. SMD parts only.


Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on August 19, 2013, 05:17:48 pm
FEA simulations usually exaggerate displayed deformations so it can be visualized.

What about the strain gauge effects (resistance change) of the conductors as being the primary cause? Either circuit board traces, chip leads, or chip die level.

Which resistors do you mean?

I thought of such an effect in first instance also, but there is no such resistor element, perhaps SMD, as all precision resistors are leaded parts also.

Frank

What about the circuit board traces that are connecting the precision resistors to other elements of the circuit. Those traces are part of the circuit resistance and will change resistance with strain. The cross sectional area of a typical trace will be much greater than a strain gage but the effect will still be there. It might not be large enough to have any appreciable influence. I am just thinking out loud.  You guys are way past my knowledge on this but I find it interesting anyhow.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 19, 2013, 05:31:35 pm


What about the circuit board traces that are connecting the precision resistors to other elements of the circuit. Those traces are part of the circuit resistance and will change resistance with strain. The cross sectional area of a typical trace will be much greater than a strain gage but the effect will still be there. It might not be large enough to have any appreciable influence. I am just thinking out loud.  You guys are way past my knowledge on this but I find it interesting anyhow.

Hey, that's perfectly okay!

Brainstorming is always a good thing, especially, when nobody else has an idea..

The trace resistance should not make a problem for the output, as the voltage is measured by a high impedance instrument.

The Zener feeding current might be affected, but this has to be calculated. (I feel, that this effect would be too small, but guess what?)

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 19, 2013, 06:10:34 pm
Hi there,

there is a lot going on today!

Even as I don't expect a big piezoelectric - even less a triboelectric - effect on FR4 PCBs, I can offer some little experiment:

At work I have little PCBs with a "interdigital" or entwined finger-like electrodes on a single side. I can connect each electrode to a 34401A and give them a really harsh bend or hit, either in the direction of the fingers or perpendicular to it.

Ceramics might be something different, it just has this "smell of piezo". Also, Bob Pease wrote somewhere that he found isolated wires to have a piezoelectric effect, but only certain type of isolating material (piezo-material PVDF, Polyvinylidene fluoride, comes to mind immediately, have to look up the source.) A reason to keep the wires outside the test gear fixed during measurement ?

BR Hendrik
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on August 19, 2013, 06:17:00 pm
The trace resistance should not make a problem for the output, as the voltage is measured by a high impedance instrument.
.....
The Zener feeding current might be affected, but this has to be calculated. (I feel, that this effect would be too small, but guess what?)

Frank

I know right now the thread is focused on the affects of the reference only, but what about the trace resistance variation from strain on the pcb traces connecting the precision resistors when looking at the entire circuit?
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on August 21, 2013, 12:48:32 am
I just happen to have a excellent micro ohm meter that is offset compensated and gives very stable single digit micro ohm readings. It will be easy for me to measure if there is an appreciable resistance change of a trace. Even if it is significant, wouldn't it be a simple matter to increase trace widths or copper thickness to reduce it to insignificant levels?  When I get a chance I will post some values on the delta R for various trace widths, lengths, and deflections.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Robert763 on August 21, 2013, 07:52:33 am
Hi,
This is my first post here. I suggest you research strain gauges. This is a known science (and art). Vishay are a big player in the market. I understand, but have no reference, that the Vishay foil resistors were a side benefit of their research into low TC strain gauge materials. This is another area where "RF like" PCB layout can help. If you have opposite arms of a bridge or divider as identical  tracks opposite each other on two sides of a PCB (like a stripline) the PCB bending induced stress changes cancel out.

Robert.
Semi volt nut, DMM's to 7.5 digits, couple of LTZ1000 references, LM399's, Diff. Voltmeters, JRL VDR-107 KVD.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 24, 2013, 01:27:19 pm
I have also IR-videos from the heat-up phase with long and short leads, but no webspace to put them on. On the other hand I don't won't to register at youtube. Someone out there with some webspace for the videos?
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 24, 2013, 03:11:34 pm
To prevent messing up this server, I suggest my Youtube-Account and some of my Webspace to embed it at.
What camera did you use ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 24, 2013, 03:45:26 pm
Quote
What camera did you use ?

It's a VarioCam hr:

http://www.infratec.de/de/thermografie/waermebildkameras/variocamr-hr-head-600-serie.html (http://www.infratec.de/de/thermografie/waermebildkameras/variocamr-hr-head-600-serie.html)
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 28, 2013, 06:54:20 am
Just throwing Ideas at you right as you requested, not really thought thru ;)

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 28, 2013, 07:06:51 am
But, what if I'm wrong?  Would it be possible to use the regular LTZ1000 (not the 'A' version), and just use the on-chip temperature sensing transistor to control the Peltier device and still maintain +/-0.001K die temperature, or would the control function be too unruly?  Before i run out and spend a small fortune experimenting on this, does anyone have thoughts on this?

Hello,

for the first: I´d never try to cool down something because I fear that the condensing humidity would change my output values. But perhaps you have the perfect rooms with humidity control.

Of course the thermal regulation will have to be much slower with a large thermal mass than only with the chip alone.
Otherwise the controller will oscillate.
For my thermal chamber I use a 2 stage concept to speed up the heat up times:
One sensor is mounted to the middle of the PCB with the references. (this would be the LTZ1000 sensor).
The other sensor is mounted directly to the aluminium heat spreader plate where the heater foil is mounted.

Since there is some self heating of the references the PCB is usually 4 degrees celsius warmer than the heater setpoint.
For a temperature of 50 degrees on the PCB the heater has to be kept around 46 degrees in steady state.

So I have 2 control loops.
A fast P (+D part for heat up) control loop for the heat spreader with a setpoint around 46 degrees
and a slow I part for the PCB with a setpoint of 50 degrees.

The I part is managed by correcting the setpoint (46 degrees) of the outer control loop.
For this the temperature on the pcb is measured. If the pcb temperature is only changing slowly (steady state) then the difference between actual temperature (e.g. 50.3 degrees) and setpoint (50 degrees) is subtracted (with a time constant factor e.g. 0.33/minute) from the setpoint. In this case in the first minute the setpoint is corrected to 49.9 degrees. (0.3 degrees times 0.33/minute).

I don´t know if its possible to reach 0.001 degrees stability with this method. A good thermal management (keeping air currents away from the chip, and stable environment temperature) will be necessary to get a stable regulation loop.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 28, 2013, 07:17:13 am
(Advertising for sheet metal boxes and feedthrough capacitors again to realize small spaces with pretty good temp and humidity control, and also excellent for electromagnetic compatibility resons :))
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 28, 2013, 08:37:49 am
OK, I'm looking for some additional ideas on my Peltier-cooling idea.  I originally was thinking that there is no way that the Peltier device could maintain the die temperature of the LTZ1000 at +/-0.001-deg-K (in the same way that the on-chip heater can with proper external circuitry).  So, I thought that I would have to use an LTZ1000A, then chill that down to (say) 10 or 15 degrees-C lower than the chosen die temperature, then use the on-chip heater to heat the die back up to where you want it.  This is going to use a lot more power though-- more power to chill it down further (and to fight the on-chip heater), then add even more power for the on-chip heater.  This is not good for battery operation.

But, what if I'm wrong?  Would it be possible to use the regular LTZ1000 (not the 'A' versio n), and just use the on-chip temperature sensing transistor to control the Peltier device and still maintain +/-0.001K die temperature, or would the control function be too unruly?  Before i run out and spend a small fortune experimenting on this, does anyone have thoughts on this?

Forget all about that:
In an oven assembly, you always need high thermal gain, especially when you strive for 1mK stability.
That's always coupled with a small-as-possible thermal resistance  between heater/cooler and the sensor.

The thermal resistance of the LTZ1000 is about 80K/W, the A version even worse for that purpose, 400K/W, and both much too high to make a stable, well regulated oven.

If you simply use another sensor, outside the LTZ1000 case, then the case itself may be temperature regulated, but not the reference amplifier, again due to the high thermal resistance. The self heating will always create a temperature difference, and te temperature of the reference amplifier will be free to fluctuate strongly.

Only if the reference amplifier is also thermally coupled tightly to the sensor and heater, this might work.

Frank

PS: Best read are the articles of Richard Karlquist, one of the most experienced designers of the HP OCXO oven technology.
eg.: www.karlquist.com/oven.pdf (http://www.karlquist.com/oven.pdf)
Title: Re: Ultra Precision Reference LTZ1000
Post by: cosmos on August 29, 2013, 05:19:23 pm
Just a thought..
Dealing with fast external variations one might have a look at what some heatpumps for houses do (those are the ones I know).
They look at the house as balanced energy system, where the goal is to generate exactly the correct amount of energy on the inside to balance the energy leaking out.
This assumes the heat leakage out of the house is constant (should be true for a oven too).
Tuning it is a matter of selecting a gain variable matching the heat leakage and multiplying that with the temp difference inside to out to get a target energy level.
The leakage trough the walls change near instantly with temperature changes.
Stored energy inside a house creates a delay that messes with the regulation when it is only based on inside temperature.

If the mass inside the oven has limited ability to store heat I guess the above has little effect and that measuring temperature directly is the simplest way.
Using the temp difference to control the gain of the regulation loop might still improve the precision?
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 29, 2013, 08:28:14 pm
Well, there are uncounable ways of optimizing, but you get into the "crazy" area quickly:

[li}Several shells of thermal mass for equalisation and thermal insulation, [/li]
[li]Spread Temp Sensors everywhere, log, look for patterns, use programmable heater control to play compensation games like "start decreasing inner temp when you realize the outer ambient is heating up even before the decrease appears outside[/li]
[/list]

Most thoughts in this field are immediately related to your mechanical construction.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 29, 2013, 09:47:59 pm

I wonder if there's a hybrid approach-- something with the main temperature sensor close to the temperature driver (heater or chiller)-- and this would control the temperature, but then we mix-in the [conditioned] signal from the LTZ1000's on-chip temperature sensor, in order to steer the final die temperature closer to the ideal.  To me, this seems at least possible, because the internal burden heat from the Zener current of the LTZ1000 would be constant.  Just thinking out loud here...

Have a look on the tear downs of the 732B.. a hybrid is used with the heater and all the aligned circuitry on the ceramic PCB. 
I do not remember, if the LTFLU is used as a bare die, or housed... Bare die would be bad, because it would be prone to humidty/oxygen.

But this design comes near to what you propose..

The Fluke 5720 calibrator also has got a hybrid with two stacked LTFLU.

Anyhow, to my opinion, the stability can be improved, w/o such big effort.

Simply select the most stable external components( e.g. VHP202Z) and chose 45°C for the LTZ1000, and that's it.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on August 29, 2013, 09:57:20 pm

I wonder if there's a hybrid approach-- something with the main temperature sensor close to the temperature driver (heater or chiller)-- and this would control the temperature, but then we mix-in the [conditioned] signal from the LTZ1000's on-chip temperature sensor, in order to steer the final die temperature closer to the ideal.  To me, this seems at least possible, because the internal burden heat from the Zener current of the LTZ1000 would be constant.  Just thinking out loud here...

Have a look on the tear downs of the 732B.. a hybrid is used with the heater and all the aligned circuitry on the ceramic PCB. 
I do not remember, if the LTFLU is used as a bare die, or housed... Bare die would be bad, because it would be prone to humidty/oxygen.

But this design comes near to what you propose..

The Fluke 5720 calibrator also has got a hybrid with two stacked LTFLU.

Anyhow, to my opinion, the stability can be improved, w/o such big effort.

Simply select the most stable external components( e.g. VHP202Z) and chose 45°C for the LTZ1000, and that's it.

Frank

If you use 5 LTZ1000 with all perfect conditions specified in the different posts and make the average it will be even better  :-DD

eurofox
Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on August 29, 2013, 10:49:15 pm

I wonder if there's a hybrid approach-- something with the main temperature sensor close to the temperature driver (heater or chiller)-- and this would control the temperature, but then we mix-in the [conditioned] signal from the LTZ1000's on-chip temperature sensor, in order to steer the final die temperature closer to the ideal.  To me, this seems at least possible, because the internal burden heat from the Zener current of the LTZ1000 would be constant.  Just thinking out loud here...

Have a look on the tear downs of the 732B.. a hybrid is used with the heater and all the aligned circuitry on the ceramic PCB. 
I do not remember, if the LTFLU is used as a bare die, or housed... Bare die would be bad, because it would be prone to humidty/oxygen.

But this design comes near to what you propose..

The Fluke 5720 calibrator also has got a hybrid with two stacked LTFLU.

Anyhow, to my opinion, the stability can be improved, w/o such big effort.

Simply select the most stable external components( e.g. VHP202Z) and chose 45°C for the LTZ1000, and that's it.

Frank

If you use 5 LTZ1000 with all perfect conditions specified in the different posts and make the average it will be even better  :-DD

eurofox

I didn't mean a "hybrid integrated circuit"-- I meant a hybrid system approach to temperature control (as opposed to an oven inside of a refrigerator).

As far as averaging multiple LTZ1000's-- yes, this will reduce noise by the square-root of the number of references you average (and more than 4 would be cost prohibitive).  The problem with long term drift is that the LTZ1000's all seem to drift in one direction (IIRC, in the "down" direction)-- it's just that some drift more than others.  A better idea would be to select the best references that drift the least, and throw the rest away (or sell them on eBay or something).

What I want to do is get better long term stability than the standard circuit can provide.  Let's say the best you can get with the standard LTZ1000 circuit is 0.3ppm/year-- well I want better than that.  0.1ppm/year would even be better-- and I want to be able to recreate this multiple times without having to make 1000's of references, and throw away all but the few that meet my spec.  That's why I'm looking into cooling the reference as opposed to heating it (to maintain a stable die temperature).

Cooling should be easy with a peltier element and add some control with PID to keep the temperature accurate to 0,1 °C
I suppose aging of the LTZ1000 is worst with high temperature, so by keeping it "cold" it should drift less.
Why not averaging LTZ1000 with another one from another supplier with similar tolerance.

Just another idea but I have no experience in this field just to input maybe new ideas, use precision frequency to voltage controller, based on a rubidium standard you can have an extreme stable frequency, of course your converter will drift as well with aging and temperature.

eurofox
Title: Re: Slot or Not
Post by: Andreas on September 08, 2013, 03:43:56 pm
As announced by Andreas we wanted to find out what is best: "Using a solid pcb or spend some slots around the heat controlled voltage reference?" and furthermore: "Keep the leads as long or as short as possible?".

So let's start the discussion :)

Ok, I have finally evaluated the measurements = .csv tables of Branadic from the LM399 thermograpic measurement.

Long leads without slot:   around 5 degres stray within pad  + 1,7 degrees from pad to pad
Long leads with slots:      around 5-6 degres stray within pad + 2,3 degrees from pad to pad
Short leads without slot: around 9-11 degres stray within pad + 3,1 degrees from pad to pad
short leads with slots:     around 12-15 degres stray within pad + 6,6 degrees from pad to pad

So from the measurement the conclusion is that with long leads the stray (=thermoelectric voltage) within pad is lower than with short legs. And the thermoelectric voltage between different pads is lower without slot.
If there should be mechanical issues the slots should be at least around 15 mm from the reference to give the pads the possibility to equalize the temperature.

2 simple conclusions:

- short leads will increase the temperature of the PCB, long leads will give more thermal isolation between component and PCB => long leads preferred
- slots in the PCB give higher thermal isolation between solder joint area and outer PCB area, thereby reducing cooling of the solder joints through the PCB, and in turn increasing the local heating of the solder joints. Higher solder joint temperatures might cause temperature differences more easily and  will increase thermo voltages.

I'm now very confident that 45°C and a PCB without slots is the most stable solution.

So the conclusions of Frank are now quantified.

Before the measurements I planned to make slots near the reference and short leads. Now I will go for long leads and at least keeping the slots far away from the reference. (e.g. at the edges of my inner metal shield).

@branadic
When regarding the videos (the flimmering of the heat) I had the idea that the result should be also be visible by noise measurements. So its a pity that we did not measure the noise voltages of the references in parallel to the thermographic measurements.

With best regards

Andreas

============================== evaluation in detail ==============================

Long leads without slot
=======================

pin upper left:

min   27,64
max   32,81
avg   29,59356083
stddev   1,144305683
max-min   5,17

pin upper right:

min   28,02
max   33,15
avg   30,25453333
stddev   1,000260225
max-min   5,13

pin lower left:

min   27,8
max   33,18
avg   29,33930796
stddev   1,031510593
max-min   5,38

pin lower right:

min   28,87
max   33,48
avg   31,08652597
stddev   0,855853162
max-min   4,61


all in all: around 5 degres stray within pad
1,7 degrees from pad to pad


Long leads with slots
=====================

pin upper left:

min   30,1
max   35,46
avg   32,78116883
stddev   1,173468631
max-min   5,36

pin upper right:

min   28,44
max   33,54
avg   30,48031128
stddev   1,148254067
max-min   5,1


pin lower left:

min   29,24
max   34,46
avg   31,80304
stddev   1,342351664
max-min   5,22

pin lower right:

min   29,3
max   35,7
avg   31,30611111
stddev   1,183186142
max-min   6,4

all in all: around 5-6 degres stray within pad
2,3 degrees from pad to pad


short leads without slot
========================

pin upper left:

min   36,649
max   47,527
avg   42,58773745
stddev   3,146954606
max-min   10,878

pin upper right:

min   38,599
max   49,453
avg   43,66859498
stddev   2,401555908
max-min   10,854

pin lower left:

min   37,141
max   45,726
avg   41,45009881
stddev   2,115676062
max-min   8,585

pin lower right:

min   38,552
max   48,064
avg   44,64691221
stddev   2,080904881
max-min   9,512

all in all: around 9-11 degres stray within pad
3.1 degrees from pad to pad

short leads with slots
======================

pin upper left:

min   41,186
max   55,277
avg   46,75962041
stddev   3,418151728
max-min   14,091

pin upper right:

min   39,226
max   50,78
avg   44,88190295
stddev   3,051374117
max-min   11,554


pin lower left:

min   42,81
max   58,327
avg   50,25318644
stddev   3,742872955
max-min   15,517


pin lower right:

min   40,915
max   56,608
avg   48,35819758
stddev   4,061728375
max-min   15,693

all in all: around 12-15 degres stray within pad
6,6 degrees from pad to pad



Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on September 10, 2013, 05:57:43 am
I think it will be less stable.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on September 10, 2013, 06:10:21 am
The problem with long term drift is that the LTZ1000's all seem to drift in one direction (IIRC, in the "down" direction)-- it's just that some drift more than others.
Looks like the LM399 drifts upwards. If the two references were summed with the LTZ1000 given a 4:1 weight, perhaps the net stability would be better than the LTZ1000 by itself?  And it would be cheaper than a second LTZ1000, even with some good resistors at the summing point ;D
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on September 13, 2013, 08:40:13 am
Off to Weinheim. See some of you tomorrow !
Title: Re: Ultra Precision Reference LTZ1000
Post by: BiOzZ on September 13, 2013, 08:42:37 am
i have used these before but i had to buy 20 of them from digikey and that was a real bitch to write off but i can see they have been all but one used up!
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on November 10, 2013, 08:56:59 am

I wonder if there's a hybrid approach-- something with the main temperature sensor close to the temperature driver (heater or chiller)-- and this would control the temperature, but then we mix-in the [conditioned] signal from the LTZ1000's on-chip temperature sensor, in order to steer the final die temperature closer to the ideal.  To me, this seems at least possible, because the internal burden heat from the Zener current of the LTZ1000 would be constant.  Just thinking out loud here...

Have a look on the tear downs of the 732B.. a hybrid is used with the heater and all the aligned circuitry on the ceramic PCB. 
I do not remember, if the LTFLU is used as a bare die, or housed... Bare die would be bad, because it would be prone to humidty/oxygen.

But this design comes near to what you propose..

The Fluke 5720 calibrator also has got a hybrid with two stacked LTFLU.

Anyhow, to my opinion, the stability can be improved, w/o such big effort.

Simply select the most stable external components( e.g. VHP202Z) and chose 45°C for the LTZ1000, and that's it.

Frank

Do you have have schematic for the stacked LTFLUs. I looked in http://assets.fluke.com/manuals/5720a___smeng0200.pdf (http://assets.fluke.com/manuals/5720a___smeng0200.pdf) (576 pages!), but the ref board on p. 522 seems not to have a schematic.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 10, 2013, 05:45:27 pm
I have saved a copy before Fluke removed the schematics. June 1996, 39MB.
It's on the site of a voltnuts member Didier Juges, ko4bb... Or so, i just do not have access to the link right now.
There you have to work yourself through the drawings carefully.
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on November 10, 2013, 05:49:32 pm
Thanks. I will look for it at the kobb-site.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on November 10, 2013, 05:53:08 pm
http://www.ko4bb.com/Manuals/Fluke/Fluke_5700A_5720A_Multi-Function_Calibrator_Service_Manual.June_1996.pdf (http://www.ko4bb.com/Manuals/Fluke/Fluke_5700A_5720A_Multi-Function_Calibrator_Service_Manual.June_1996.pdf)
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on November 10, 2013, 07:16:46 pm
The 5720 is just to be replaced by the brand new 5730.
https://www.eevblog.com/forum/testgear/new-fluke-5730a-calibrator/msg296208/#msg296208 (https://www.eevblog.com/forum/testgear/new-fluke-5730a-calibrator/msg296208/#msg296208)
Both are much too expensive if you do not earn money with them.
Therefore my favorite is the unfortunately discontinued Wavetek 4808, which playes in the same league.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on November 10, 2013, 07:42:54 pm
To come back to the OT. I would like to modify a HP3458A reference board to HFL spec (if possible).

Does anyone have details about the Fluke HFL mod?

So far I found at febo/voltnuts that all the boards are suppose to be the same and only aged and selected. I also know from Dr. Frank about his mod and will do the same as a first step.

Because the HFL has not only better DCV but also better resistor accuracy, there must be more changes than only the lower heater temp.

Any hints are welcome.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on November 11, 2013, 07:14:24 am
Thanks Diligentminds,
that is a good confirmation and summary of all things I already knew and have discussed with Dr. Frank.
But I still wonder, if it is really not more to it, why HP/Agilent never offered or does not sell it anymore. Also they never have reached the resistance specs of the Fluke HFL. Besides the document you attached (which I already had), do you know of anything more documented? The only I know of is the att. selection guide.

About calibration, I have actually bought a 3458 mainly because of the artefact calibration, which I already have done and I like it very much. With my lab gear, also I still do not have a real 10V Reference like 732B (or similar 7000/4910), I can repeat the cal any time I like. So far my experiment LTZ1000 board still is the one from Babysitter (7.xxx Volt Output). 

Bye
quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: captbilly on November 26, 2013, 08:03:38 am
You can read more about it here
http://home.51.com/jj3055/diary/item/10053954.html (http://home.51.com/jj3055/diary/item/10053954.html)

I am fairly sure the slots are there to keep the pcb from transferring mechanical stress to the LTZ1000.  Linear Technology discusses this problem in an app note, but essentially the issue is that movements of the pcb (from temperature, humidity, or even from the user applying force on the board) transfer stress to the reference IC package, as well as the die itself.  The stress effects the output voltage and, according to Linear Technology, is part of the reason that references drift over time (the stresses tend to slowly decrease over time as the board and package slightly flow).  Linear Technology recommend slotting around the reference so that movements on the rest of the board do not transfer to the reference itself.

Leakage currents could be a problem if there are high impedance paths in the circuit, but that is uncommon in voltage reference circuits.

Schematics here
http://bbs.38hot.net/read-htm-tid-36472.html (http://bbs.38hot.net/read-htm-tid-36472.html)

And finally here how to convert 7V to 10V
http://www.crystalradio.cn/thread-229749-1-1.html (http://www.crystalradio.cn/thread-229749-1-1.html)

Looking at the pcb I can't stop wondering why these slots are milled. The voltage isn't that high that you need the extra creepage distance, and right now it seems to me it's only weakening the pcb's structural integrity. Worst case it introduces unknown offsets as the pcb will bend a bit either when moved, or with temperature changes. Am I overlooking something here?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on November 26, 2013, 06:27:36 pm
Quote
Board stress has no effect on IC dies packaged in hermetic TO packages-- it only applies to devices in plastic packages, and surface mount packages are more sensitive to this effect than through-hole [plastic DIP] packages are.

Quote
AFAIK, the slotted PC board design for the LTZ1000 came from the original Datron 4910 voltage reference design, and because that unit could run off of batteries, in order to reduce the battery energy depletion rate they needed to minimize heat-loss from the LTZ1000-- the slots in the PC board (as well as added insulation) help with this.  The slots are there for NO OTHER REASON.  The voltage reference design on the Chinese "volt-nut" BBS simply copies this technique without knowing why it was done in the Datron design.  If you're not going to run your device on batteries, then you don't need slots or insulation.

You guys know about the investigation that was done on the LM399 with the question what influence these slots have?

http://dg3hda.primeintrag.org/doku.php?id=lm399_thermographie (http://dg3hda.primeintrag.org/doku.php?id=lm399_thermographie)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 26, 2013, 07:08:59 pm

AFAIK, the slotted PC board design for the LTZ1000 came from the original Datron 4910 voltage reference design, and because that unit could run off of batteries, in order to reduce the battery energy depletion rate they needed to minimize heat-loss from the LTZ1000-- the slots in the PC board (as well as added insulation) help with this.  The slots are there for NO OTHER REASON.  The voltage reference design on the Chinese "volt-nut" BBS simply copies this technique without knowing why it was done in the Datron design.  If you're not going to run your device on batteries, then you don't need slots or insulation.

Note that the LTZ1000 (and ideally the support circuitry too) does need some kind of cover to prevent air currents from causing thermal EMF's generated by thermocouples created by the Kovar-leads of the TO package to the copper PC board traces.

Hi,

that's the first reasonable explanation I've read (thermal insulation for saving of battery energy).
If the LTZ1000 would run on 45°C, the circuitry would not need so much energy as in the Datron 4910, running on 60°C.

 I totally agree, that the Asians simply have copied, copied, copied and copied those stupid slots, without thinking, why they are there..
And everybody else copied from the Asians.. the slots and the "A" Version, which is copied from the 3458A and which makes sense on that 95°C temperature. (Violating the LTZ1000 as being an LM399)

Although the temperature distribution on the PCB is influenced, observable only at high stabilization temperatures as with the LM399, up to now I don't see any influence on the stability of the reference circuitry, and that'much moremost important, so those slots can be omitted easily.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 26, 2013, 07:11:38 pm
You guys know about the investigation that was done on the LM399 with the question what influence these slots have?

Know that, sure.
But it has not been demonstrated any influence on the stability of ref amps, especially not on the LT1000 @ 45°C.

No influence from mechanical deformations on the Output voltage, as you yourself have found out.

So, really nice IR Pictures and experiments, proving that there is no practical use for the slots.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: codeboy2k on November 26, 2013, 10:14:42 pm
So, really nice IR Pictures and experiments, proving that there is no practical use for the slots.

I read the linked article with the IR pictures , and I thought the conclusion was that the slots actually help to maintain the heat at the junction of the can's leads with the copper foil, thus minimizing any delta K and thus minimizing the thermal junctions formed there (copper/kovar)

This is, in fact, still consistent with why it was done in the Datron 4910 battery based design -- to minimize heat loss giving longer battery life.

However, in non-battery applications there might be some useful reason still. 

I'm not a voltnut, and thus not an advocate for slots or no slots, just commenting on the blog I read with the IR photos.


Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on November 29, 2013, 05:21:54 pm
What do you guys think about my cheap connection ?

Its simple single core cooper wire that I gave a 1-minute dip in gold electrolyte...

Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on November 29, 2013, 08:54:49 pm
Single core copper is the best possible for low EMF connection and with direct gold plating the oxidation problem should also be fixed.

Can you share how you have done the plating?
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on November 30, 2013, 08:31:41 am

I got a 3 ml bottle gold electrolyte but it has been sitting for 10+ years, and was completely dry.
Demineralized water and a night on the heater revived it obviously.

The process is easy - a victim electrode and the wire-to-be-plated in a little container with the liquid, applying about 2V (no I didnt start a high precision meter for this...  :-DD) and 1-2 minutes later - golden goodness ! Obvious process improvements: Get fresh electrolyte, use a gold victim electrode (goldfingers of old PC cards, maybe?)

Now I will carry it in my pocket a few days to see if it degrades, I suppose cooper would turn black when exposed to warm sweat like this.
Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on November 30, 2013, 09:05:43 am
If the coating is not thick enough, and if you did not put a nickel plate over the copper to provide a backing then yes it will corrode under the gold layer.  To gold plate first you need a chemically clean oil free surface, then etch it with PCB etchant for a second or two ( chemical etch to roughen surface), rinse well then plate with nickel to give an even matt finish. then rinse again twice in pure water then apply the gold plate. When it is bright then rinse and dry.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on November 30, 2013, 09:32:53 am
The etching of the copper is to remove the copper oxid, the nickel is a diffusion barrier layer and adhesion promoter for the final gold finish.

What do you want to do with such a soft gold surface? Solder? If you want to use it for probing you better have a hard gold surface.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on November 30, 2013, 07:41:52 pm
My wife was for a while working at a PCB shop, I am well aware of the Ni/Au standard process but am I allowed to play by law! ;) This is cheap and easy enough to prepare the wires right before the experiments and dispose them as soon as they start to degrade. I am already mistreating them and I will figure out how bad they behave compared to Multi-Contact CuTe components living in happy dry storage.

@branadic: Says a guy who I suppose applies gold to plastics when I am thinking about your employer >:D

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on December 01, 2013, 12:31:48 pm
Quote
@branadic: Says a guy who I suppose applies gold to plastics when I am thinking about your employer >:D

Sure, but the golden surface of the MIDs is only for assembling technologies (soldering, glueing, bonding, FlipChip) not for mechanical use.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on December 01, 2013, 01:06:18 pm
I want to use it between those screw terminals which are made of 4mm jacks like Multicontact PK4TS i used on my reference. Ghetto connection O0
Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on January 06, 2014, 01:26:47 pm
"The voltage is not generated at the junction of the two metals of the thermocouple but rather along that portion of the length of the two dissimilar metals that is subjected to a temperature gradient. Because both lengths of dissimilar metals experience the same temperature gradient, the end result is a measurement of the difference in temperature between the thermocouple junction and the reference junction."

The "characteristic voltage difference (is) independent of many details (the conductors' size, length do not matter)".

http://en.wikipedia.org/wiki/Thermocouple (http://en.wikipedia.org/wiki/Thermocouple)


You can also choose whatever practically implemented "couple" coupling joint you want as long as it is made of one and the same material and its endpoints are at the same temperature (which means no net temperature gradient).

So 1 inch of thin copper wire soldered to 1 foot of thin iron wire as in the symbol < with temperature t1 to the right (both endpoints at one and the same temperature t1) and temperature t2 at the soldered junction to the left will give the same voltage as 1 yard of copper bar and 1 inch of iron bar interconnected with 2 feet of lead tube provided that the two junctions now created at the left side both are at temperature t2. This holds only in equilibrium, i.e. all connecting points and endpoints have settled.

This is imo implications from the link. Please check for yourself. A search 'thermocouple theory" gives several sources stating similar propositions.

Right  :-+ :-+

When I have to make a quick thermocouple I just twist the 2 wires without welding and work like a charm.

eurofox
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kjelt on January 06, 2014, 01:33:03 pm
When I have to make a quick thermocouple I just twist the 2 wires without welding and work like a charm.
Yeah for awhile. Welding it is not so difficult, use a big low voltage high amp transformer and just short the wires or use a big elco that can deliver 50 Amps for a short while. Transformer works perfect.
Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on January 06, 2014, 01:51:30 pm
When I have to make a quick thermocouple I just twist the 2 wires without welding and work like a charm.
Yeah for awhile. Welding it is not so difficult, use a big low voltage high amp transformer and just short the wires or use a big elco that can deliver 50 Amps for a short while. Transformer works perfect.

When I say "quick" is just for some temperature testing, is used +/-1 hour and removed after the test, I did it many times to test temperature of glass in thin film solar cells production because of <> of temperature on the surface.

eurofox
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 16, 2014, 06:58:55 am
Mind if I join this club?  :o

(https://www.eevblog.com/forum/testgear/restoration-glory-of-keithley-2001-dmm/?action=dlattach;attach=76909;image)

Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on January 16, 2014, 09:47:46 am
Hello Volt Nuts,

I got my version on the LTZ1000A working on slotted PCB with thermal isolation.
I already put it in a box with a power supply, 24V AC outside the box.
I added a switch on the front panel to be able to select output voltage from the LTZ1000A and output of and AD706 with 2 precision resistors (0,1% 15 PPM), a trimmer to set exact 10 V output.

I still have to work on fine tuning of the trimmer part, still to sensitive to set the 10 VDC with the 10nV exactly.



eurofox
Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on January 16, 2014, 03:10:03 pm
Some pictures

Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on January 16, 2014, 03:26:03 pm
Hello Volt Nuts,

I would like the add that I did some test with this unit and the Geller Lab that is mounted in the same box with the same power supply.

I use Pomona special cables (Shielded and I think they are twisted as well).

No influence of change on the latest digit (10nV) by touching the cable or moving the reference box, it is immune to noise from outside (of course in the area of my lab but there is a RF phone and a computer near with no influence)

This mean that if you have some instable measurement you have to look to your cabling, grounding, connector but basically it is not that critical.

eurofox
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on January 16, 2014, 04:41:31 pm
Hello Volt Nuts,

..
No influence of change on the latest digit (10nV) by touching the cable or moving the reference box, it is immune to noise from outside (of course in the area of my lab but there is a RF phone and a computer near with no influence)

..
eurofox

Hey, eurofox.

Your LTZ circuit is really extremely insensitive, extremely accurately trimmed (10^-9), and your measurement is extremely high resolution.

Could you please tell me the model and manufacturer of your 9 1/2 digits DMM?  :-//

And at which NPLC setting the DMM measures stable on the last digit?
Thanks!

And the slotted PCB is from China?
At which temperature did you set the LTZ?
(Or which resistor over the 1k did you use?)

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on January 16, 2014, 05:17:42 pm
Hello Volt Nuts,

..
No influence of change on the latest digit (10nV) by touching the cable or moving the reference box, it is immune to noise from outside (of course in the area of my lab but there is a RF phone and a computer near with no influence)

..
eurofox



Hey, eurofox.

Your LTZ circuit is really extremely insensitive, extremely accurately trimmed (10^-9), and your measurement is extremely high resolution.

Could you please tell me the model and manufacturer of your 9 1/2 digits DMM?  :-//

And at which NPLC setting the DMM measures stable on the last digit?
Thanks!

And the slotted PCB is from China?
At which temperature did you set the LTZ?
(Or which resistor over the 1k did you use?)

Frank

Hello Frank,

Maybe I did not express myself corectly, I mean that moving the reference box (box with inside the power supply closed), touching the cables, there is no influence on the reading with my LTZ1000A or the Geller lab, and yes of course after stabilisation periode and call of the HP3458A the last digit (10nV) change value but stay in the range of the last digit (usually less than 5 with NPLC 100).

I will post the schematic after cleaning up, it is basically the application note wiith a few changes.

The PCB is comming from Germany (at least I bought it there).

eurofox
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on January 16, 2014, 05:31:23 pm
HP3458A the last digit is much more than 10 nV  :D
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on January 16, 2014, 05:36:06 pm

Hello Frank,

Maybe I did not express myself corectly, I mean that moving the reference box (box with inside the power supply closed), touching the cables, there is no influence on the reading with my LTZ1000A or the Geller lab, and yes of course after stabilisation periode and call of the HP3458A the last digit (10nV) change value but stay in the range of the last digit (usually less than 5 with NPLC 100).

I will post the schematic after cleaning up, it is basically the application note wiith a few changes.

The PCB is comming from Germany (at least I bought it there).

eurofox

Hello eurofox

(the heck, what's your real 1st name?)

Sorry, I just wanted to tease you a little bit.... >:D

The 3458A in the 10V range resolves 8 digits only, that's 100nV, not 10nV!

Well, 5 digits of fluctuation (500nV) fits to what I have measured @ 100 NPLC on LTZ references from babysitter and my two ones.

See 10min stability diagram here: https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/270/ (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/270/)

Who designed the PCB? And what temperature did you chose?

Well,

each of those LTZ references is very susceptible to external AC sources.
So I banned a nice new LED lamp from my analogue lab, because its switch mode PSU disturbed the reference up to 1 ppm, inside its shielded box.
So I think, your even less shielded case will show even worse behavior, if treated with the "right" HF noise source .
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on January 16, 2014, 05:50:53 pm
Hello Frank,

Yes you are right on the 10V it is 100nV, I'm confused because when use my Time Electronics calibrator I really go to the 10nV in the 10mV range of the calibrator.
I'm quite new with this instrument and start now to be familliar with it.

eurofox
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on January 27, 2014, 05:54:17 pm
Hello Everyone!

I've taken the last month (or there about) to read though this thread, the posted pdf's, associated forums on the LTZ (volt-nuts, etc), and several scientific papers (IEEE, Metrologia) on modern voltage transfer standards.

Let me just say... Wow!

I'm overwhelmed by the shear amount of high quality "amateur" knowledge that is available on this subject. Thank you all for your contributions!


After reading all this information, I've had a few ideas, but I wanted to check with the experts here before I let my mind go too far...

There seems to be a body of information on the environmental conditions that effect the LTZ's long term stability -- atmospheric pressure, humidity, mechanical stress*, etc etc.

There have been a few suggestions in this forum on how to 'seal' a LTZ and its associated hardware away from most ambient conditions (O2, H2O), but has anyone seen a design that has placed the reference board in a vacuum? If so, can you post a link?

Secondly, has anyone seen a study on the effects of ionizing radiation on the LTZ (or semiconductor references in general)? If so, a link would be helpful.


* metal packaging with long leads aside (Dr. Frank, et al)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 27, 2014, 09:54:59 pm
There have been a few suggestions in this forum on how to 'seal' a LTZ and its associated hardware away from most ambient conditions (O2, H2O), but has anyone seen a design that has placed the reference board in a vacuum? If so, can you post a link?

Secondly, has anyone seen a study on the effects of ionizing radiation on the LTZ (or semiconductor references in general)? If so, a link would be helpful.

Hello,

I think placing a reference board in vacuum is usually beyond the capabilities of a amateur.
And further it does not solve all problems since you would have to use kovar leads to get through the glas sealing.

I would never place a metrology grade reference into ionizing radiation.

I can remember that there is a application note from Intersil on the ISL21009 on the output voltage shift of their FGA references. But since the voltage is stored into a EEPROM-like cell the shift is more likely than on other references.

And there are some annotations on the Linear Technology LT1021 in the /883 version.
http://cds.linear.com/docs/en/datasheet/RH10215fe.pdf (http://cds.linear.com/docs/en/datasheet/RH10215fe.pdf)

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 27, 2014, 10:30:03 pm
And not to forget to mention the problem of gas emission of the pcb itself. I would prefer a solder process of the case under shielding gas conditions with feedthrough capacitor for electrical connections trough the case. IMO the most promissing approach for homebrew application.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on January 27, 2014, 11:04:38 pm
I think placing a reference board in vacuum is usually beyond the capabilities of a amateur.
And further it does not solve all problems since you would have to use kovar leads to get through the glas sealing.

I would never place a metrology grade reference into ionizing radiation.

I can remember that there is a application note from Intersil on the ISL21009 on the output voltage shift of their FGA references. But since the voltage is stored into a EEPROM-like cell the shift is more likely than on other references.


I've read that note from Intersil. As I remember the gist there is they have a MOS-capacitor that stores a reference charge level. That charge level is set before it leaves the factory -- relying on the near-zero leakage rate of the capacitor to store the same charge level for 10+ years. The worry is that an ionizing particle will whiz though the capacitor, altering the charge level.

The effect that I am thinking of in the case of a zener reference is a bit different (changes to the semiconductor structure).  However, I have to admit its simply that -- my imagination. So I was wondering if anyone had seen an expert talking on that subject.

While I don't know much about the subject, but common sense would tell me not to (intentionally) expose a reference to high energy...  anything. But we're awash in radiation day-to-day.  A cosmic ray probably interacts with the zener cross section at some rate of 1's of strikes per day. Of course, you can't really shield against cosmic rays, but other lower energy (terrestrial) sources can be shielded or avoided -- concrete, ceramics, etc etc.

As far as the vacuum idea is concerned, it really depends on the level of vacuum. Ultra high vacuum? Yeah, forget it you might as well build yourself a JJ array. A vacuum on the order of 1's or 10's of Pascals.... definitely achievable.  Sustainable in the long term? Maybe.  It'd have the advantages of isolating the reference from atmospheric conditions and removing convection as a heat transfer mode. But as you've pointed out, it would add construction and design difficulty. I am considering building one, but before I sit down to design it, I wanted to ask for some feedback from the group here.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on January 27, 2014, 11:12:18 pm
And not to forget to mention the problem of gas emission of the pcb itself. I would prefer a solder process of the case under shielding gas conditions with feedthrough capacitor for electrical connections trough the case. IMO the most promissing approach for homebrew application.

I have a few of these feed-though "gizmos" ( http://www.omega.com/pptst/MFT.html (http://www.omega.com/pptst/MFT.html) ) laying around from another project. Three to be exact.

I considered the de-gassing problem and I have to admit, I have no experience with that. Slow degassing could be handled by several pump-down sessions. But I would be worried about placing a large stress on the components during the (relatively) quick pump-down. Has anyone ever seen an LTZ explode? Sounds fun, but I can think of better ways to spend my money.

I considered back-filling with argon. Which would take care of the oxygen, water vapor, and (most) pressure changes, but it would.... I forget a lot of my heat transfer... increase convection(?).







Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 28, 2014, 05:49:27 pm
Almost ready for thermal sim :)

Board - FR4 4-layer 40x80mm

+15VDC input
LTZ1000A schematics from datasheet
LT1112A Opamp
PZT3904 NPN in SOT223
Three MAX6610 temperature sensors.
LT1761ES5 5V LDO for temp sensors
Planed resistors: Vishay Z202

Inner layers right now pretty much solid power ground (opamp GND and heater- GND).

Temperature sensor locations:

Sensor 1: Near Opamp with copper plane under it.
Sensor 2: On wires, glued to top of LTZ1000A in dead-bug position.
Sensor 3: On bottom near LTZ1000A

Will run temperature simulation to try get approximate temperature gradients, and tune accordingly before gerber out.

Any ideas?  :-//
Title: Re: Ultra Precision Reference LTZ1000
Post by: sync on January 28, 2014, 06:09:46 pm
A general question about the LTZ1000 circuits from the data sheet. The output is directly connected to the LTZ1000 (ZENER SENSE). Can it used for a reference with external output (long leads, current injection from the DMM, ...) or is a buffer needed?
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on January 28, 2014, 06:35:12 pm
Almost ready for thermal sim :)

What program do you use for the thermal simulation?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 28, 2014, 07:21:46 pm
A general question about the LTZ1000 circuits from the data sheet. The output is directly connected to the LTZ1000 (ZENER SENSE). Can it used for a reference with external output (long leads, current injection from the DMM, ...) or is a buffer needed?

If you short the output (a uncharged capacitor is sufficient) then the temperature setpoint will rise to infinity. -> The heater goes to 100% -> The chip will get a (more or less permantent) voltage shift on the output.
So I do not recommend to use a unbuffered LTZ1000 (like mine) as working standard.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: iTist on January 28, 2014, 08:38:43 pm

Secondly, has anyone seen a study on the effects of ionizing radiation on the LTZ (or semiconductor references in general)? If so, a link would be helpful.
* metal packaging with long leads aside (Dr. Frank, et al)

Hi,

here is some information from the  JPL (jet Propulsion Lab)
http://nepp.nasa.gov/docuploads/6A935FBA-65D1-42CE-827076A3DE0C7384/PrecRef-97.pdf (http://nepp.nasa.gov/docuploads/6A935FBA-65D1-42CE-827076A3DE0C7384/PrecRef-97.pdf)


Greetz

Oliver

Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on January 28, 2014, 10:15:08 pm

Hi,

here is some information from the  JPL (jet Propulsion Lab)
http://nepp.nasa.gov/docuploads/6A935FBA-65D1-42CE-827076A3DE0C7384/PrecRef-97.pdf (http://nepp.nasa.gov/docuploads/6A935FBA-65D1-42CE-827076A3DE0C7384/PrecRef-97.pdf)


Greetz

Oliver

I didn't even think of space electronics. Good find!

It would seem the crux of article would suggest its probably not an issue for anything that's kept on the Earth's surface. If I'm doing my maths right, an equivalent exposure for an Earth-based LTZ1000 would occur over the period of 10,000's of years (for natural radiation ~2000 strikes/m^2/s @ 1GeV). And since the LTZ in the article only shifted by 10's of ppm for that level exposure....

It makes me a little sad to think my DNA is drifting more than the LTZ is.


Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on January 29, 2014, 12:19:07 am
If you short the output (a uncharged capacitor is sufficient) then the temperature setpoint will rise to infinity. -> The heater goes to 100% -> The chip will get a (more or less permantent) voltage shift on the output.

The datasheet mentions multiple times about using PWM to drive the heater, and you're implying that's bad?  I've been wondering about that myself... PWM would seem to have a lot of undesirable effects on the rest of the circuit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 29, 2014, 04:45:12 am
Almost ready for thermal sim :)

What program do you use for the thermal simulation?

I'll try to use Solidworks Flow Simulation, using still air box primitive. Problem is to transfer traces from PCB CAD to Solidworks.
Plan to use LTZ1000 datasheet temperature data to reach as a target first, so will have that as a reference for simulation jig
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on January 31, 2014, 05:16:44 pm
And not to forget to mention the problem of gas emission of the pcb itself. I would prefer a solder process of the case under shielding gas conditions with feedthrough capacitor for electrical connections trough the case. IMO the most promissing approach for homebrew application.

I've been considering both the vacuum and inert gas ideas in the past few days. However I'm stuck on one problem -- trimming the circuit.

My common sense tells me that if there's any merit to either idea, one would want to place the entire circuit (op amps, current source, resistors, divider, etc) in the shielded environment. But if everything is nicely setup inside of a sealed container, how does one access the circuit to adjust it for the first time?

One method might be just to build it, insert it into the sealed container, start it up, and accept whatever value it starts with (7.xxxxxx V) as being the reference point -- valuing the (potential) higher stability above having a nice round number (7.000000 V).

But if there was a way to adjust a resistor (or a set of dip switches, etc?) from outside the container, I'd sure like to use that method.

Any ideas?
Title: Re: Ultra Precision Reference LTZ1000
Post by: iTist on January 31, 2014, 06:10:20 pm
Hi,

you can use a DAC for controlling the see:
Maybe at the FLUKE website or her:

http://www.elcal.ch/files/11749-eng-01-a.pdf (http://www.elcal.ch/files/11749-eng-01-a.pdf)

Page3 Figure 5


Greetz

Oliver
Title: Re: Ultra Precision Reference LTZ1000
Post by: SimonSatCom on February 02, 2014, 01:51:43 pm
This is how far I am with my LTZ1000A project. It is not an easy project...but I have learned a lot in here. :)

http://www.simonthenerd.com/LTZ1000A.htm (http://www.simonthenerd.com/LTZ1000A.htm)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 02, 2014, 03:37:42 pm
Hello,

Nice project, from where do you get the housings for your references?

The temperature setpoint of your LTZ is rather low for a LTZ1000A.
In my lab (up to 32 degrees) I would not go below 12K5 for the temperature setpoint resistor.

Do you have a temperature stabilized lab?

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 03, 2014, 10:10:12 am
This is how far I am with my LTZ1000A project. It is not an easy project...but I have learned a lot in here. :)

http://www.simonthenerd.com/LTZ1000A.htm (http://www.simonthenerd.com/LTZ1000A.htm)

...but you also made the mistake to buy the A version and 2nd to set it to a too low stabilization temperature.
A temperature difference of 15-20°C above maximum room temperature is necessary for proper operation.

The LTZ1000A is intended for battery operation and for elevated temperatures.
It is badly abused @ 95°C in the HP3458A and in the Keithley 2002, with mediocre 8 ..10ppm/yr.

Burn-in (storage at high temperatures) is also a fault, due to the pronounced hysteresis, which will in turn create a longterm creeping drift, which would not be present by avoiding any elevated temperatures.

The LTZ1000 (non A) can be set to 45°C with <1ppm/yr, which is easily achievable.

Fluke 7000 and Datron 4910 are the most stable references (<1ppm/yr.) and are based on the LTZ1000 (non-A) with 45/55°C!
 
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 03, 2014, 10:24:21 am
But what would be the best operation point for LTZ1000A then?
Asking in practical reason, as have A-based reference in design as well.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 03, 2014, 10:53:38 am
But what would be the best operation point for LTZ1000A then?
Asking in practical reason, as have A-based reference in design as well.

Well, 15-20°C above max. ambient temperature, therefore 50-60°C stabilization temperature (12k5 - 13k over 1k).
If you can guarantee metrology grade environmental conditions, i.e. 18-28°C max. all the time,  45°C,  equivalent to 12k over 1k, is tightly sufficcient. But pay attention to sample variation of the LTZ, as +/-5°C can happen easily.

For my references (non A version), running on a nominal  45°C +/-5°C, at 23°C max. RT, the regulation headroom is >20°C, which is safe under all conditions.


Perhaps it is necessary to ship the reference for comparison at a fellow volt-nut, then the expected temperature there has to be taken into account.

Btw.: I cannot understand why people still buy the A-version, even directly from LT.
It is much more expensive (12$) and less suited for high stability.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 03, 2014, 12:11:41 pm
Ok, thanks.
I plan to have 40°C as max ambient, so this gives 55°C as reference temperature.

I bought A, because of experience lack, and A-version opamps from LT usually better specs (per datasheets), so thought same regarding zener, lol.
It's still first zener I got, so $12 not a big deal for knowledge.

And actually i still did not decided if I'll have it running battery-backed either. Need check proper battery size/weight to keep reference hot during shipping (I'd take 2 weeks for it, as average).
Title: Re: Ultra Precision Reference LTZ1000
Post by: iTist on February 03, 2014, 12:32:19 pm
Hi,

has someone experience with the technique described in this Patent:

http://www.google.de/patents/US5369245 (http://www.google.de/patents/US5369245)

Greetz

Oliver
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 03, 2014, 01:30:46 pm
Ok, thanks.
I plan to have 40°C as max ambient, so this gives 55°C as reference temperature.

....

And actually i still did not decided if I'll have it running battery-backed either. Need check proper battery size/weight to keep reference hot during shipping (I'd take 2 weeks for it, as average).

For 40°C ambient, better use 13k/1k, i.e. 65°C.
I pimped my HP3458As reference to that value, because a dirty fan filter will rise the interior from 34°C to 40°C, max. (at 23°C rooom temperature.
This still would give 1ppm/yr. as default.

...

Batteries will give less output noise / disturbance compared to AC mains supply.
The LTZ itself does not need permanent operation; stability is <1ppm with intermittent operation.

Possibly, resistance based dividers/amplifiers (to 10.0000V) may need constant powering for achieving <  1ppm stability.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 03, 2014, 01:54:04 pm
Hi,

has someone experience with the technique described in this Patent:

http://www.google.de/patents/US5369245 (http://www.google.de/patents/US5369245)

Greetz

Oliver

That's the well known Pickering patent used in the Wavetronik/Fluke 7000 reference, for conditioning the LTZ1000 after power down.

I have collected some experience: I did several tests concerning temperature cycling (refrigerators / heater), but not using that schematic.

This patent at first indicates, that temperature excursions of the LTZ induce hysteresis, and if this hysteresis is not removed, by symmetric cycling, it will  in turn induce creeping drift.

From that it directly follows, that any "burn-In" process is bad for the LTZs stability!

I have seen hysteresis of several ppm on both of my LTZ references, but only if the temperature deviation from the nominal value is > +/-25°C. (I accidentially heated one of the LTZs to >90°C.)

If the temp. excursion is less, there is no noteworthy hysteresis, perhaps a few tenths of ppm only.

That means, at 45°C stabilization temperature, as in the Fluke 7000, the conditioning does not improve uncertainty that much.. The reference at this temperature is already very stable without further measures, also in intermittent operation.

I measure that on the HP3458A, each time I power it on again, and two times already in the last 4 years, when I removed my constantly powered LTZ references from the mains for several weeks. Each of those 3 LTZs return to their default value to < 1ppm deviation, every time. Exactly the same goes for the Fluke 5442A calibrator, which uses 2 SZA263.

Only if very high (>70°C) or very low (<15°C) ambient temperature excursions  are encountered, this feature might theoretically have some effect...

But then, as the lower conditioning temperature is limited to room temperature, i.e. 20°C, the complete or symmetric conditioning circle, as described, can not be passed through. 0°C would be necessary, to reset a trip to 90°C, as shown in the  patent in fig. 2.

Therefore, this patent is nice for theory, but did obviously NOT work in the Fluke 7000.
Perhaps this was one of several reasons, why Fluke terminated that product.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: SimonSatCom on February 03, 2014, 02:46:52 pm
Hi all

It is a nice little project but it has not been easy. Information about both the LTZ1000 and the LTZ1000A is pretty
hard to come by. I do think that Linear Tech could do better on they datasheet. :)

First about the temperature set point. Again...I have not been able to find any formula so that I could calculate the
exact set point. A collegue of mine figured out that my setpoint is about 46.5C. I did not have a 13k000 precision
resistor...but I did have a 12k100 resistor. In the article "The Ultra-Zener...is it a portable replacement for the
Weston cell?" I was able to see what happened if the value of R4 is changed. I understand now that this is the LTZ1000
(not the A-version) but since no information was available I decided to try it out. In the document it is claimed that
the aging (ppm/year) will be lower with a lower temperature setting (which makes sense). This leads me to the next
question about the temperature in my lab.

My lab is located in the basement of my building. The temperature in the basement varies from 15C to 20C and the plan
with this reference project is to ovenized it the entire thing. The idea is to set the temperature to 35C since I can
not see the temperature rise to more then that (its always cold in Denmark). In the LTZ1000 and LTZ1000A datasheet I
did not find that much help only that the A-version is set 10C higher then the "not A-version".

And Dr. Frank thinks that I made a mistake by using the A-version...could you specify why that is? I got the A-version
as a sample from Linear Tech and thought the A-version was an improvement over the LTZ1000. But you don't seem to
think so...why is that?! :)

Do any of you have the formulas used to calculate your LTZ1000 projects? It seems there is a lot of discussions about
the correct settings for all the precision values. How did you (Dr. Frank) reach the value for your project? :) And do
you have a lot of experience with the LTZ1000?

Best regards

Simon
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 03, 2014, 04:30:04 pm
Do any of you have the formulas used to calculate your LTZ1000 projects?

From page 5 of the datasheet:
"With the values given in the applications, temperature is normally 60°C. This provides 15°C of margin above a maximum ambient of 45°C, for example. Production variations in emitter-base voltage will typically cause about ±10°C variation. Since
the emitter-base voltage changes about 2mV/°C and is very predictable, other temperatures are easily set."


The values given in the datasheet for R4:R5 are 13k:1k across the ~7 output of the reference.  You then have to know that Vbe has a negative temperature coefficient.  From that, I determine that T = 310 - 7*500*R5/(R4+R5)

Quote
And Dr. Frank thinks that I made a mistake by using the A-version...could you specify why that is? I got the A-version
as a sample from Linear Tech and thought the A-version was an improvement over the LTZ1000. But you don't seem to
think so...why is that?!

From the electrical characteristics section of the datasheet, we see the only difference between the two is the thermal resistance.  80C/W for the LTZ1000 and 400C/W for the LTZ1000A. And on page 5,
"Because higher temperatures accelerate aging and decrease long-term stability, the lowest temperature consistent with the operating environment should be used. The LTZ1000A should be set about 10°C higher than the LTZ1000. This is because normal operating power dissipation in the LTZ1000A causes a temperature rise of about 10°C."

So the LTZ1000A runs hotter in most applications making it less stable.  So why have the LTZ1000A at all? The datasheet says "To simplify thermal insulation".  In other words, so you don't have to put it in a temperature controlled box, and it will stay warm with very little power.  If you put a LTZ1000 in an oven which is 10C above ambient, then it will run at the same temperature as an LTZ1000A sitting outside the oven, with potentially similar performance.  If you're going to go through the trouble of ovenizing, then the non-A is preferable.
Title: Re: Ultra Precision Reference LTZ1000
Post by: SimonSatCom on February 03, 2014, 05:05:18 pm
Ahh...okay...now I get it. So I should consider getting the non-A version.

The choice of 12k100 works fine at the moment...but would it make sense to increase it to 14k000 (which I have in the resistor box)...?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 03, 2014, 06:12:05 pm
Ahh...okay...now I get it. So I should consider getting the non-A version.

The choice of 12k100 works fine at the moment...but would it make sense to increase it to 14k000 (which I have in the resistor box)...?

Definitely not 14k! That would give 75-80°C, and higher annual drift
12,1k is ok, depending on your envirnonmental condition. Simply calculate.
Perhaps you got another 400Ohm resistor to add for 50°C.
Afaik, you got low TC resistors, wirewound, n'est pas?
And perhaps, you might heat the whole basement to 20-21°C during winter (as I do),

As you have received the LTZ1000A for free, it's definitely no fault, but you have to live with it.

It gives a fine reference also, totally sufficient for ones needs.

Frank

PS: I think I have some experience, as I published the theoretical background and made solid measurements on nearly all of them.
Title: Re: Ultra Precision Reference LTZ1000
Post by: SimonSatCom on February 03, 2014, 07:06:12 pm
Hi

Okay, I will see what I can do. But I think that I will try to get the LTZ1000 version instead of the A-version. I will of course stay away from the 14k000. One of the reasons for ovenizing the whole circuit is because the precision resistors I use are "only" 2ppm resistors. So I figured that keeping the entire circuit (LTZ reference and 7V-to-10V amplifier circuit) at a constant temperature would be a good idea.

If I switch to the non-A-version I guess it would not be a problem with the 12k100 when the complete circuit would be inside a 35C environment. Or what do you think?

Thanks for clearing things up. I had a hard time finding the information I really needed.

Btw...do you have a homepage with more LTZ info? :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 03, 2014, 07:51:05 pm
Hi

.. One of the reasons for ovenizing the whole circuit is because the precision resistors I use are "only" 2ppm resistors. So I figured that keeping the entire circuit (LTZ reference and 7V-to-10V amplifier circuit) at a constant temperature would be a good idea.

If I switch to the non-A-version I guess it would not be a problem with the 12k100 when the complete circuit would be inside a 35C environment. Or what do you think?

Thanks for clearing things up. I had a hard time finding the information I really needed.

Btw...do you have a homepage with more LTZ info? :)

Well, you just should start READING (RTFM).

It's all inside the datasheet, or within in this blog. No, I don't have a personal HP.

12k or 12k1 would be perfect for an LTZ1000.

If you avoid that external oven @35°C, and keep the reference below 30°C, 12k1 is also fine for the LTZ1000A.

What the heck do you mean with resistors, 2ppm???

2ppm of tolerance or 2ppm/yr. or - if assume right - you mean 2ppm/K wirewound resistors?

That is just perfect! That's top notch, not beaten even by those miraculous Vishay metal foil resistors.
I use 3ppm/K econistors, and the circuit is rock stable.

Why?

Once again, please simply read that f****d specification of LT!!!

All instabilities or variations are attenuated by a factor of 100 at least!!

A 2ppm/K drift on any resistor will translate into 0.02ppm/K drift of the reference, only.
A 20ppm/year (which is typical for such wirewounds) will translate into 0.2ppm/year for the reference.

Both are phantastic values!!

Therefore, an additional oven is not necessary, if you feel ok with that level of stability.


But somehow, I just feel if I repeat what I already have stated earlier in this thread...

Please, begin to READ this thread thoroughly.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 03, 2014, 08:32:14 pm
For my references (non A version), running on a nominal  45°C +/-5°C, at 23°C max. RT, the regulation headroom is >20°C, which is safe under all conditions.

While we're on the subject, how'd you get the +/-10°C mentioned in the datasheet down to +/-5°C?  I still haven't decided how I'm ultimately going to thermally stabilize the reference, but most of my ideas involved measuring Vbe in situ and computing a resistance from that rather than choosing a resistance to target a temperature.  That +/-10°C was just too big a spread.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on February 03, 2014, 08:39:12 pm
Maybe we should split this thread into a section with fairy dust and one without :)

best regards,
the double babysitter
(cured from ltz-esotherics)  :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 03, 2014, 08:50:56 pm

the double babysitter


[off topic]
congratulations! and my best wishes for your growing family.
[/off topic]

best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on February 03, 2014, 08:51:39 pm
Thank you Andreas !  :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 04, 2014, 06:32:47 am


While we're on the subject, how'd you get the +/-10°C mentioned in the datasheet down to +/-5°C?  I still haven't decided how I'm ultimately going to thermally stabilize the reference, but most of my ideas involved measuring Vbe in situ and computing a resistance from that rather than choosing a resistance to target a temperature.  That +/-10°C was just too big a spread.

Well yes, I didn't remember the max. variation in the datasheet correctly..

I also measured the VBE at room temperature carefully, i.e. with small current and without heating, and then estimated the stabilization temperature. It was very close to those 45°C with 12k/1k.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on February 04, 2014, 06:05:34 pm
Dr. Frank: Could you detect the AfE tower demolition in the output of your LTZ?   :-BROKE
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on February 06, 2014, 10:41:07 am
@Dilligent Minds: The fluffy alternative to foaming enclosures!  O0 but I would never be scared to start fires with such filling - I wouldnt even expect melting temperatures for polyolefines in such low power circuits, without Tantal Capacitors there is just a low risk of flames forming and (ceramics, ok, different story) and in a sleeping bag filling I would expect some flame retardants.

Also, I am the "tuner tin can guy", dont forget !  ^-^ this will contain the fire if it breaks out I guess, without having analyzed the risks yet.

Hollow fiber insulation doesn't belong to the fairy dust class, as it is effective: On the northern hemisphere you can try this with a corresponding sleeping bag.

At work I just got a sample of a Lackwerke Peters Polyurethane potting material which is quite nice to work with. Good if you are confident that you never need to repair the embedded circuit, but I like the thermal mass and thermal conduction properties. No chance for even forced airflows below unpleasant levels :phew:
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rerouter on February 06, 2014, 10:41:42 am
you could always do a low voltage spot weld to the copper if you wanted to get fancy (where you have the weld tips in contact before applying current from a super-cap or single turn output transformer) that reduces it to what ever fun the copper and the lead material cook up,

it just comes down to if this is a better or worse thermocouple
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rerouter on February 06, 2014, 11:18:55 am
I would think as you want minimal heat loss from the reference and power planes anywhere near it would soak up way too much, where by tiny little copper traces on essentially an insulator are almost invisible to the heat-source (now mounting that thing in a shielded box might be an option if you where that concerned with noise coupling, but you would still risk it coming in on your leads,

equally star grounding and ground planes can be very bad, it really comes down to what your doing, the best way to lay out references like this is to treat every trace with resistance and every connection as a thermocouple, and pick where you connect your traces wisely, for instance the 2 input pins of your chopper amp, if there is a small temperature gradient across the board from the references heat source then you could have a few nV-uV more generated in the input pins solder joint closest to the reference and offset your reading,
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 06, 2014, 01:27:17 pm
Hello folks,
                 attached the top and bottomview of the voltage reference circuit of the ultimate HP/Agilent 3458A - 8 1/2 digit DMM. What struck me observing the approach of the PCBs is the lackof a solid ground plane, short - wide power rails, wide power tracks, star grounding - any thoughts about improving the overall quality of these PCBs - would a ML-4 or ML-6 layer approach contribute to this ?

Thanks !

This reference is one of the weak components of the 3458A.

HP ignored several design rules to make it more stable.
One of those rules (see LT datasheet for the LTZ1000), is the thermal shielding of all solder junctions, another one - having supreme negative impact - is keeping the stabilization temperature at  65°C or lower.

Some simple improvments on this reference, for metrological use:

- Reduce Tstab. from 95°C to < 65°C. Simply replace the 15k metal foil by 13k (or parallel it with 100k)
- Replace LTZ1000A by LTZ1000 and set Tstab to 45-50°C (12k-12.5k)
- Replace both 70k resistors by metal foil or wirewound types.
- Use instrument at Tamb < 30°C, i.e. at 23°C +/- 5°C only and keep fan always clean => max. internal temperature of < 38°C

=> will give <= 1ppm/yr. DCV stability.

- Put complete reference PCB into a closed box to avoid any air draught from the rear fan.

=> willl reduce medium term random noise

Any further measures are not necessary!
The original LT circuitry, as it is also realized on this PCB, is stable enough to achieve an ultra stable reference.

The reference is prone to external AC noise, which might also cause random unstabilities.
But obviously this is no problem inside the HP3458A, as the PSU and shielding measures around the DC conditioning PCB is extremely good. Therefore, any additional layers or star points, or whatsoever is also not necessary.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on February 06, 2014, 05:58:45 pm
Two of the high-end digital multimeters - Prema 6047 and 6048 was designed in the 1988. Both was build on the Prema's ASIC ADC chip (but not a well-known PRI5610). Model 6047 have a LM399 voltage reference, 6048 - LTZ1000, but in DIP8! Is it possible?  8)
Title: Re: Ultra Precision Reference LTZ1000
Post by: JBeale on February 06, 2014, 07:54:49 pm
Well, it is possible to bend the 8 leads of a TO-5 or TO-99 can to fit into the through-hole locations of a DIP-8 footprint...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 06, 2014, 07:59:36 pm

Any further measures are not necessary!


Is there no calibration after changes necessary?
My LTZ1000A have around 50ppm/K drift when changing the temperature setpoint.

- LTZ1000, but in DIP8! Is it possible?

I do not know any datasheet which shows a DIP8 package.
At that time many manufacturers used plastic spacers which spreaded the TO-99 pins into a DIP8-pattern on the PCB side.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 06, 2014, 09:32:12 pm
Last year, Linear Tech introduced the LTC2057(HV), which is a zero-drift op-amp that also has very low noise-- even lower than the LT1013.  There is simply no excuse anyone can make for using anything other than two LTC2057's in this circuit if it were redesigned today.
It's nigh impossible to find new parts in hermetic packages any more.  I can find some CERDIP 1013s on ebay, though.  Are these opamps humidity sensitive at all?  "For humid environments, surface coating may be necessary to provide a moisture barrier." is the only datasheet reference I can find to it (in the 2057 datasheet.)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 06, 2014, 10:49:03 pm
It's nigh impossible to find new parts in hermetic packages any more.  I can find some CERDIP 1013s on ebay, though.  Are these opamps humidity sensitive at all?  "For humid environments, surface coating may be necessary to provide a moisture barrier." is the only datasheet reference I can find to it (in the 2057 datasheet.)

You can also find CERDIP LT1013A on RS-Components. (from TI)
If the chip is sensitive to forces any humidity will change the characteristics. Either the PDIP package swelling or from PCB changes which are creating forces to the chip through the PINs of the package.

Even a hermetically packaged voltage reference like VRE3050A or AD586LQ or LT1236AILS8-5 is sensitive to forces through the PCB (like humidity changes) if not carefully decoupled from the board.

A chopper like the LTC2057 does not need to be in a hermetically package. Due to the self adjustment the effects of humidity will be canceled out by the chopper.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: mrflibble on February 06, 2014, 10:58:52 pm
It's nigh impossible to find new parts in hermetic packages any more.
I came across these recently:
http://www.digikey.com/product-highlights/en/ls8-reference-family/51750 (http://www.digikey.com/product-highlights/en/ls8-reference-family/51750)
Title: Re: Ultra Precision Reference LTZ1000
Post by: dannyf on February 07, 2014, 01:21:49 am
Quote
if I were designing a replacement board for the 3458A,

Wouldn't that depend on why you are redesigning the board?

Many times, we don't design for the highest performing products.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 07, 2014, 05:30:28 am
You can also find CERDIP LT1013A on RS-Components. (from TI)
Obsolete packaging according to the datasheet.  rs-components in the US, aka alliedelec, does not have it.  I went to the german site, and there indeed was the AMJ... but boy do you pay a lot for the M version! 

Quote
If the chip is sensitive to forces any humidity will change the characteristics.
...
A chopper like the LTC2057 does not need to be in a hermetically package. Due to the self adjustment the effects of humidity will be canceled out by the chopper.
I contacted Linear Tech, and asked about this.  The answer is that the LTC2057 will self-compensate for any temperature and/or humidity caused drift-- this is caused by the die being "stressed" when the epoxy package changes dimensions, and since it is "inside the zero-drift control loop", it is compensated for.
Makes sense, and confirmed by Linear, even!  Thank you both :)  The 2057HV is surprisingly affordable, too.

Quote
(such as ... Peltier coolers, etc.).
This is what I've been playing with, and part of why I'm very concerned about humidity.  So far, I can get my, uh, "oven" to Ambient-10C with 1W and Ambient-18C with 4W; still a lot of things for me to learn and play with.  Temperature controlled boxes have been fascinating so far.  I'm aiming to eventually implement your suggestion from much earlier in this thread.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 07, 2014, 07:03:21 am
Obsolete packaging according to the datasheet.  rs-components in the US, aka alliedelec, does not have it.  I went to the german site, and there indeed was the AMJ... but boy do you pay a lot for the M version! 


Hello,

you looked at the wrong datasheet from LT. On Texas Instruments the package is still active.
The chip is identical to the LT chip according to a interview of a LT representative in a paper.

And yes: precision is not cheap if not using low noise choppers.

With best regards

Andreas
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Blackart on February 07, 2014, 07:21:21 am
Gentlemen first post here.

I recently acquired a Datron 4700 and I plan to "have a go at calibrating it" so I need a 10V ref. I would then use the 4700 etc to keep my 34401A and bank of old 3400A/B/400E/F/Gs etc in line. I have been eavesdropping here and on volt-nuts for a week or so trying to get the threads/approaches clear in my mind.

I think Ive decided to go down the LTZ1000 path with ;
approx 45C ref temp
vishay S102 resistors plus a couple of others I have in stock ( better if the $ are kind when I ask texasinst for a quote )
LTC2057 opamp
unbuffered ref out
10V buffered ref out
self design PCB
powered by a double regulated low noise supply Ive already done.
lots of thermal & magnetic/RF shielding

If your listening, I was wondering if a couple of you could clear up a couple if things I can't work out from my couple of readings of the blog.

Dr Frank
You made a ref with 2 off LTZs, it look like one has the ref and heater supplies buffered by a transistor and the other is driven as per the LT data sheet. Why ? was this to compare the performance of the two approaches ? If so what was the outcome ?
OR
Was the above idea dropped and you were you seeking to combine the references as per the LT data sheet to improve stability and noise etc if so how did this work out ?

Andreas
You also added the ( FET in this case ) buffer i.e. a BF245. How do you think this performed ? as I thought that any self heating in the driver opamp would be nulled out in the FB in steady state. Or is the ref noise/drift such that the opamp has to work hard to maintain a constant current ?

regards Lucas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 07, 2014, 09:24:20 am
Dr Frank
You made a ref with 2 off LTZs, it look like one has the ref and heater supplies buffered by a transistor and the other is driven as per the LT data sheet. Why ? was this to compare the performance of the two approaches ? If so what was the outcome ?
OR
Was the above idea dropped and you were you seeking to combine the references as per the LT data sheet to improve stability and noise etc if so how did this work out ?

regards Lucas

Well, I really tried both designs.
The transistor gives more current capability at the output jack, as the OP07 is limited to a few mA only.
On the other hand, it gives more gain, so that at last, I skipped it again, because I feared instability of the circuit due to oscillation.

The whole circuit is quite sensitive to external AC noise, which may lead to disturbance and even unlatching of the temperature regulation.

The transistor is really not needed at that point, and the additional resistor from V+ to the reference high side unloads the Op07 also.

My advise: keep the circuit as simple as possible.

I would also not use a chopper OpAmp, as they create more noise than regular ones.

The LT1013 do not influence the stability so much, so they are fully sufficient.
ank
Title: Re: Ultra Precision Reference LTZ1000
Post by: jd on February 07, 2014, 06:08:35 pm
I would also not use a chopper OpAmp, as they create more noise than regular ones.

With the exception of the LTC2057(HV).  This part exceeds the LT1013 in almost every spec, including noise [and it is better in *all* of the important specs for this circuit].  Note that the LTC2057 is a completely new architecture than most chopper amps [and Linear Tech is not revealing *exactly* how they did it].  For other chopper amps, I would agree with Dr. Frank.

MAX44246 looks quite useful for DC precision. It looks like it might be lower noise than even LTC2057. Also, is chopper amplifier noise not of a different character, being free of 1/f behaviour? So longer integration times continue to reduce fluctuations. Perhaps for use with a null detector/comparison circuit or 7.2:10V booster.

(But I think Franks point was that in the actual LTZ1000 reference circuit the LT1013 opamp errors are not significant in any case).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 07, 2014, 08:06:10 pm

Andreas
You also added the ( FET in this case ) buffer i.e. a BF245. How do you think this performed ? as I thought that any self heating in the driver opamp would be nulled out in the FB in steady state. Or is the ref noise/drift such that the opamp has to work hard to maintain a constant current ?


Hello,

there were 2 reasons for the FET:

1. to keep away heating from the OP-Amp.
    5mA * 7V = 35mW @ 130K/W gives around 5K self heating.
    Offset drift is up to 2.5uV/K = 12.5uV
    that sounds not much but:
    12.5uV/2mV/K Heater setpoint = 6mK Temperature setpoint drift.
    together with the 50ppm/K drift of the zener there is up to 0.3ppm drift of the LTZ.

2. Battery powered design with only 14V regulated voltage.
    I simply feared that with 1V less voltage against the 15V datasheet design
    there would be not enough headroom to fully stabilize the zener current loop.
    The negative pinch off voltage of the FET compensates for the lower power supply voltage.

Other effects are that with lower load current and with lower excitation of the output the open loop gain (= current regulation precision) increases.

So in a design with LTC2057 only the second point would still have some meaning.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 07, 2014, 08:32:21 pm

(But I think Franks point was that in the actual LTZ1000 reference circuit the LT1013 opamp errors are not significant in any case).

Note: In the more serious (long term stable) desings (AN86 + Datron reference board) they used a LT1013 in the now obsolete hermetically TO-99 case.
Ok this would also be a possible enhancement for the HP-reference board.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 08, 2014, 05:23:26 am

As far as the LT1013 is concerned, the note on page 5 of the data sheet for the LTZ1000 says:
"BOTH A1 AND A2 CONTRIBUTE LESS THAN 2uV OF OUTPUT DRIFT OVER A 50°C RANGE"

Hello,

With my calculation above this is only possible with the "typical" drift spec of a LT1013AC = 0.3uV/K.
With the maximum spec of a non "A" device of 2.5uV/K the 2uV drift is already eaten up by the self heating of 5K.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on February 08, 2014, 01:21:21 pm
Hello Dr. Frank, Andreas, all VoltNuts,
                                                      Would it be possible to send me your most stable implementation containing all modifications (minor - major) as schematic for review - so that we can reach common sensus - I am willing to put effort in it - in order to create a nice schematic in Altium out of it and upload schematics as (*.schdoc ) and as(*.PDF) on EEVBLOG so that people on the forum have a reference and do not get lost in the big forest ... - as a next step we can make up a list of best engineering practices to implement the LTZ1000(A) as it should be done with and without extra temperature controlled mini-oven ...
I do not really need a nice CAD drawing, something hand-written (scanned) to start with is fine, as long as the paper contains all major & minor details ... it is OK for me.

Thank You !
ps.: You can mail it to forum or send me a PM.
                                     

Good idea because now information is scattered.

I already have a word file with a lot of information that I collected and I have myself a LTZ1000 with a slotted PCB and isolation.
I use the extra 70k resistor to lower the working temperature of the LTZ1000.


eurofox
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 08, 2014, 01:34:36 pm

Good idea because now information is scattered.


I think all information is within this thread.

And: there is no single truth. Every cirquit built here has its special targets.
It makes a difference if you want to have a "primary standard" a "working standard" or a "transfer standard".

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 08, 2014, 02:24:09 pm
And collecting related data will be thru personal preference prism, some might think about items which are not important to others, and vise versa.
But in case such work to be done - do it public, so others can benefit.

I don't have any experience yet, and collecting ideas and data, so following this thread as well. Just calibrated my EDC MV106 according to my calibrated 2001, which is only 4 days after cal in Tektronix/Keithley lab.
My first reference will be LTZ1000A, with direct output. MV106 was around 120ppm off (http://dev.xdevs.com/issues/955). I have it constant powered on, so just another reference for future tests.

Also curious, why nobody tried implementing reference with resistor networks? Datron, Fluke in their 8508A (http://dev.xdevs.com/projects/rnd/repository/entry/Fluke/8508A/3_15_3e391ce1b9395fb%20(1).jpg) are using networks, which can be explained by matched tempco. After all, on output it's important
to keep constant resistor divider ratios, not actual resistance values of individual resistors. And networks fit this job best, as their elements are fitted on same substrate, and drift same or very close,
reducing mismatch significantly.
Am I missing something?

Maybe better option would be order needed network from VPG? I'm thinking of doing so, but again, i have zero hours of practice with LTZ, only diode resting in a bag waiting for PCB.

P.S. Fluke 8508A used AD823A and LTC1150 in their reference + custom R network.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 08, 2014, 02:43:53 pm

Am I missing something?


Hello,

for first: usually you will have to order large quantities of those "specialized" networks. (so no hobbyist will afford it).
second: the tempco will only cancel out if the resistors are of similar kind. (resistor film/foil thickness).

If you pair a large (70K) + a small (120R) on the same network. The network will either use a very large area (costs) or the tempco will not cancel out.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 08, 2014, 07:56:19 pm

Also curious, why nobody tried implementing reference with resistor networks? Datron, Fluke in their 8508A (http://dev.xdevs.com/projects/rnd/repository/entry/Fluke/8508A/3_15_3e391ce1b9395fb%20(1).jpg) are using networks, which can be explained by matched tempco. After all, on output it's important
to keep constant resistor divider ratios, not actual resistance values of individual resistors. And networks fit this job best, as their elements are fitted on same substrate, and drift same or very close,
reducing mismatch significantly.
Am I missing something?

Maybe better option would be order needed network from VPG? I'm thinking of doing so, but again, i have zero hours of practice with LTZ, only diode resting in a bag waiting for PCB.

P.S. Fluke 8508A used AD823A and LTC1150 in their reference + custom R network.

The answer is obvious:
- very high cost for low volume production
- useful for the temperature regulator only, i.e. the 12k over 1k divider

If you study the calculations in the datasheet, or what I have calculated in this thread, you would recognize, that especially this divider ratio of 1:13 should be very stable, by matching the T.C. of both resistors.
Vishay offers such matched dividers with 0.2ppm/K, and these should also be oil filled for stability of ~4ppm/6yrs.  Resulting impact on the LTZ circuit would be 0.002ppm/K and 0.007ppm/yr.

The 70k resistors don't need to be that stable, as all their drifts are attenuated by a factor of 500.

The 120 Ohm resistor should have low drift values, i.e. low T.C. and low long term drift, i.e an oil filled VHP202Z should be used. The 100:1 attenuation of its drifts would give an impact of 0.01ppm/K and 0.004ppm/yr. Useless to match with the others; and also there is no matching counterpart left.

If an amplifier to 10V is added, this should also be based on a divider in one case. But this would of course add 100 times higher instabilities to the 10V output compared to the naked 7.2 V output of the LTZ1000.
 
So you easily see, that the array of the Datron designs is not necessary, and used perhaps only for convenience of the PCB design.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Blackart on February 09, 2014, 04:44:05 am
Thanks for the responses.

I was worried about the chopper noise and since Ive never used a chopper amps, I have no real experience on the actual spectral makeup ( if any ) of the left over chopper noise. Also I looked at the Maxim MAX44246 data and compared it to the LTC. My worry is that the maxim device doesn't seem to like driving capacitive loads, unless buffered by a resistor c100Ohm. Which just adds more tempo issues to deal with. Since Dr Frank raised concerns about the ref circuit susceptibility to RF instabilities I think the LTC might be the one to try.

Given that others on the forum have successfully tried the LTC1013 I think Ill try the LTC2057 If only to add some more experience the thread.

I was wondering about the 400k tempo resistor required for the LTC1000A implementation. I have not found much discussion on the threads about it apart from it being miss applied in a couple of instances. Since the data sheet notes it is for "TC compensation" - OF WHAT ? the opamps or the LTC1000 ref. i.e. should it be located anyware special i.e. near the REF can or near the opamps.. any thoughts ?

regards Lucas

Oh and with reference to Gazelles question and I agree with the others; both forums ( inc VOLT-NUTS ) are worth the read. Not only for the REF discussions but the insights into the quest.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 09, 2014, 08:45:57 am

I was wondering about the 400k tempo resistor required for the LTC1000A implementation.


Hello,

According to the data sheet the 400k resistor is only necessary for the LTZ1000 and not for the LTZ1000A.
The feed back is with heater power (i.e. the LTZ serves as temperature sensor).

On my LTZ1000A I have tested the TC without the resistor.
over a 10-42 °C range there where around 1.7ppm shift (including noise and hysteresis) which corresponds well with the 0.05 ppm/K from the data sheet.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 09, 2014, 10:14:34 am
Quote
If you can live with 30K instead of 70K for the two collector resistors, you can get 5 resistors in a 16-pin ceramic LCC.  60K resistors are twice as wide, so you would have to move up to a 24-pin ceramic LCC or a 14-pin side-brazed ceramic DIP.

Have you ever tried this possibility of individual VSM85, 86, 87, 88, 89 network from Vishay? Can you tell something about the prices for a single piece? I'm looking for 5x 5kohms or 5k/20k (20k made of 4x 5k internally) network, for a gain setting application.

Edit: No need to be a network, can be an array too.
Title: Re: Ultra Precision Reference LTZ1000
Post by: jd on February 09, 2014, 12:30:27 pm

I was wondering about the 400k tempo resistor required for the LTC1000A implementation.


Hello,

According to the data sheet the 400k resistor is only necessary for the LTZ1000 and not for the LTZ1000A.
The feed back is with heater power (i.e. the LTZ serves as temperature sensor).

On my LTZ1000A I have tested the TC without the resistor.
over a 10-42 °C range there where around 1.7ppm shift (including noise and hysteresis) which corresponds well with the 0.05 ppm/K from the data sheet.

With best regards

Andreas

Hi Andreas,

I found that you can use the resistor to fine-tune the temperature coefficient in the LTZ1000 circuit, so start with 400 K and put the circuit in a temperature controlled environment (I used a beer fridge that could heat/cool  :)) Then you might change it to e.g. 470k to reduce the TC below even 0.05ppm/K.

This will also take care of any concerns about opamp TC.

The resistor itself does not have to be ultra-stable as far as I can see.



Title: Re: Ultra Precision Reference LTZ1000
Post by: jd on February 09, 2014, 02:30:58 pm
The answer is obvious:
- very high cost for low volume production
- useful for the temperature regulator only, i.e. the 12k over 1k divider

Hi Frank,

Have you looked at LT5400? http://www.linear.com/product/LT5400 (http://www.linear.com/product/LT5400) Networks of 4 resistors,  2ppm / 2k hours long term ratio stability. And not that expensive really.

A unique part as far as I have seen. On paper they look very interesting for making ratios, provided you can get lucky with the values available. But look, you can make the temperature controller divider using R4=(10+1) in series and R5=(10+1) in parallel. = 11k and 0.9090909k, equivalent to 12.1k + 1k. Perfect!

John
Title: Re: Ultra Precision Reference LTZ1000
Post by: jd on February 09, 2014, 03:37:04 pm
Hello John - the two 70k resistors can be build with LT5400-2 in parallel and LT5400-1 in series, in theory at least but need to be tested in the field. [100k||100k]+[10k+10k] but their 8ppm/K is NOK.
Hello gazelle,

No no no, I was thinking for ratio use only! :) As you mention the absolute TC is mediocre and the absolute value long term stability is completely unknown (I asked them). But for ratio use it ought to be very good.

Quote
The R4:R5 ratio is little bit more tricky - you want to have a matched tracking ratio, all resistors need to be part of same device to maintain matched tracking ratio - meaning to take LT5400-1 and LT5400-4 to build your 12.1:1 ratio - that would offer 0.2ppm/K matched tracking.

Yes sorry, from memory I thought there was a single device with 2x10k and 2x1k but it is 2x100k+2x10k, absolute values too high I think.

I don't think your two-device solution gives matched tracking unfortunately.

In fact I have been working with the -6 which has 2x5k and 2x1k. This gives a ratio of 11k:1k which still works but you have to reduce the 70k collector resistor to 10k say. However my results are not so great, I got about 3ppm drift in the first 6 months or so. But there could be other causes which I am still looking into...

One possibility is the absolute values change too much, since the divider is loaded slightly by the base current this would shift the operating point. Or it could be some other blunder.

Quote

So for the four resistors R2 ... R5 in LTZ1000 ref. design can be replaced with LT5400-x network, and R1=120 ohm should remain a high quality type Vishay PG preferable with Kelvin Varley connections.

:-)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 09, 2014, 05:42:35 pm
The answer is obvious:
- very high cost for low volume production
- useful for the temperature regulator only, i.e. the 12k over 1k divider

Hi Frank,

Have you looked at LT5400? http://www.linear.com/product/LT5400 (http://www.linear.com/product/LT5400) Networks of 4 resistors,  2ppm / 2k hours long term ratio stability. And not that expensive really.

A unique part as far as I have seen. On paper they look very interesting for making ratios, provided you can get lucky with the values available. But look, you can make the temperature controller divider using R4=(10+1) in series and R5=(10+1) in parallel. = 11k and 0.9090909k, equivalent to 12.1k + 1k. Perfect!

John

What for?
My design goal was < 1ppm/yr., and I achieved that without any schmuck devices or exotic PCB slots.
Use ordinary precision wirewound resistors and solid thermal management. That's it.

Stability is now < 1ppm / 4yrs.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 09, 2014, 06:10:21 pm
Quote
My design goal was < 1ppm/yr., and I achieved that without any schmuck devices or exotic PCB slots.
Use ordinary precision wirewound resistors and solid thermal management. That's it.

Maybe you have one of those tiny little beasts that tend to have less drift compared to the average? You can't say for sure that it is just the way your circuit is build up, because you can't make a statistical announcement to that, right? So maybe you had also a portion of luck with your reference?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 09, 2014, 06:50:45 pm
Quote
My design goal was < 1ppm/yr., and I achieved that without any schmuck devices or exotic PCB slots.
Use ordinary precision wirewound resistors and solid thermal management. That's it.

Maybe you have one of those tiny little beasts that tend to have less drift compared to the average? You can't say for sure that it is just the way your circuit is build up, because you can't make a statistical announcement to that, right? So maybe you had also a portion of luck with your reference?

Maybe no scientifically correct statistics.... but I have 2 working references, really existing, and very stable, at least.
The third one is the modified reference in my 3458A, which also is very stable, without any Schickimicky gadgets...
And the fourth one is at "babysitter", a 1: copy of this design, which shows drift < 0.3ppm after 1/2 year.
All those really existing devices all fit within the theoretical calculations and estimations, i have done.

Everything else, I see here on the net, is theoretical stuff only, most of it even without any solid background. Only nice gadgets, without any hint or even proof, that those are useful.

Up to now, I haven't seen any real stability measurements from somebody else.. again.. I have to stress..only speculations all around.

So, you better show something practical,i.e. real circuits with real improvements over my stuff, instead of bringing up such weak arguments.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: jd on February 09, 2014, 07:38:31 pm
Hi Frank,

Have you looked at LT5400? http://www.linear.com/product/LT5400 (http://www.linear.com/product/LT5400) Networks of 4 resistors,  2ppm / 2k hours long term ratio stability. And not that expensive really.

A unique part as far as I have seen. On paper they look very interesting for making ratios, provided you can get lucky with the values available. But look, you can make the temperature controller divider using R4=(10+1) in series and R5=(10+1) in parallel. = 11k and 0.9090909k, equivalent to 12.1k + 1k. Perfect!

John
What for?
My design goal was < 1ppm/yr., and I achieved that without any schmuck devices or exotic PCB slots.

Use ordinary precision wirewound resistors and solid thermal management. That's it.
I had assumed that the slots are for thermal management. They should prevent any external thermal gradient from appearing across the zener terminals. On the Datron reference they also have wide copper tracks around the periphery of the square, which would tend to "short out" any thermal gradient. (Provide a "thermally grounded enclosure") Also the long thin PCB segments will tend to further isolate the LTZ1000 thermally, i.e. the temperature of the zener lead junctions will be nearly that of the LTZ1000 rather than the rest of the board.

Quote
Stability is now < 1ppm / 4yrs.
Frank
My original interest was for use in the 7.2:10V step up, but I think a PWM approach will be better for that. But in fact it ought to be a good solution for the temperature controller divider too, cheaper than two wirewounds, and much more compact of course. But in fact for my next reference I am using wirewounds for the precision resistors (as you suggest). And no slots either :)

John
Title: Re: Ultra Precision Reference LTZ1000
Post by: jd on February 09, 2014, 07:58:02 pm
Hello all volt nuts - has anyone already experience using the LT5400-6 and LT5400-7 as matching resistor network [0.2ppm/K matching temperature drift] ... - one can easily fabric the 12.5k:1k0 and 12k0:1k0 ratios 12k5 = 5k0 + 5k0 + 1k25 + 1k25  or 12k = 5k0 + 5k0 + 1k0 + 1k0. The LT5400-x networks are low cost.

I don't think either of those get you the ratio, you need to do both parts of the divider in a single device as far as I can see. I.e. the 1k resistor has to be part of the same device as the 12.5k or 12k. The best I could find is (5+5+1)k : 1k, or 11:1, which only works if you use a much smaller R3 ~10k.

Quote
Another idea I got in mind - has anyone already considered to replace the Op Amp controlling the heater element with a low power (galvanic isolated) microcontroller that is executing a PID algorithm ? How close could we get in delta mK - would a sensor based on a thermo-couplebe accurate enough ?

Well I have considered it. There is some kind of LTZ heater PWM going on in the Datron reference circuit, but I have not figured it out exactly yet; not sure if it is only used for transportation mode for example.

I don't think a thermocouple would be accurate, you are probably not going to improve on the on-die sensor. If using an external sensor a thermistor is best for non-extreme temperature measurement.

Really, the more I study the canonical datasheet circuit, the more perfect it looks already.

Title: Re: Ultra Precision Reference LTZ1000
Post by: EEVblog on February 09, 2014, 10:48:52 pm
NOTE: Several silly argument posts removed.
Come on guys, talk about voltage references instead...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Blackart on February 11, 2014, 02:42:13 am
Thanks for you responses re the 400k Ill play with this in the prototype unit. Ive order all the bits for my ref and now have to wait for them. Then the fun begins.

As for checking the drift I don't have the luxury of a 3458A/1082 8 digit meter. But I do have a datron 4700. I was thinking I could weakly calibrate this to one of the one of the LTZ1000 REFs and then null the others of against it. At least the intrinsic drift go the 4700 is pretty low to start with.

Does any body have a better idea ? Oh Ive bought 5 off LTZ1000 to play with.

Lucas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 12, 2014, 05:48:08 am

I found that you can use the resistor to fine-tune the temperature coefficient in the LTZ1000 circuit, so start with 400 K and put the circuit in a temperature controlled environment (I used a beer fridge that could heat/cool  :)) Then you might change it to e.g. 470k to reduce the TC below even 0.05ppm/K.

This will also take care of any concerns about opamp TC.

Hello,

when looking up to my TC-measurements (LTZ1000A) that I did, I cannot see how the TC could be bettered by such a measure. (especially above 20 °C environment temperature).
Most of the TC above 20 degrees is related to some kind of hysteresis. There is no linear relation to the environment temperature which could be compensated in my case. The hysteresis might come either from the temperature gradient, from PCB, the LT1013 in plastic case or some effect on the LTZ1000A.

The best measure would be to heat the whole reference to a constant temperature in my case. But with battery operated device this will not be possible.

The diagrams show output voltage (divided by 2) over ambient temperature of the reference and over the internal temperature sensor near the LTZ1000A on the PCB.
Temperature gradient is 0.1K / minute.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 12, 2014, 07:37:01 am
Hello,

when looking up to my TC-measurements (LTZ1000A) that I did, I cannot see how the TC could be bettered by such a measure. (especially above 20 °C environment temperature).
Most of the TC above 20 degrees is related to some kind of hysteresis. There is no linear relation to the environment temperature which could be compensated in my case. The hysteresis might come either from the temperature gradient, from PCB, the LT1013 in plastic case or some effect on the LTZ1000A.

The best measure would be to heat the whole reference to a constant temperature in my case. But with battery operated device this will not be possible.

The diagrams show output voltage (divided by 2) over ambient temperature of the reference and over the internal temperature sensor near the LTZ1000A on the PCB.
Temperature gradient is 0.1K / minute.

With best regards

Andreas

Hello Andreas,

best candidate for this kind of hysteresis is the LTZ itself.

This has already been pointed out by Pickering, but without any hint of the magnitude order of this effect.

I also have seen hysteresis, but to a much higher degree, as I changed the LTZ temperature from -18  to +80°C, i.e. -18° for the whole circuit, +80°C for the LTZ alone. That rules out hysteresis effects from the other components.

Effects from the PCB and the LT1013 case also have not yet been demonstrated yet.

You also use wirewound resistors, normally they do not show hysteresis at all, in constrast to metal foil types.


What I do not understand: The absolute change in Uref is - 0.08ppm/K only, although it should be -50ppm/K.

Have you really compensated the T.C.?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: jd on February 12, 2014, 10:27:41 am

Hello,

when looking up to my TC-measurements (LTZ1000A) that I did, I cannot see how the TC could be bettered by such a measure. (especially above 20 °C environment temperature).
Most of the TC above 20 degrees is related to some kind of hysteresis. There is no linear relation to the environment temperature which could be compensated in my case. The hysteresis might come either from the temperature gradient, from PCB, the LT1013 in plastic case or some effect on the LTZ1000A.

The best measure would be to heat the whole reference to a constant temperature in my case. But with battery operated device this will not be possible.

The diagrams show output voltage (divided by 2) over ambient temperature of the reference and over the internal temperature sensor near the LTZ1000A on the PCB.
Temperature gradient is 0.1K / minute.

With best regards

Andreas

Hi Andreas,

I have not looked properly at hysteresis so I may have missed it. I did not notice any but it could be there, I will check more next time.

Here are some plots I made with two different TC resistors, the datasheet 400k and 330k. With my particular layout there was a clear TC with 400k which could be made to vanish with 330k.

The red line shows the temperature of the LTZ "module"; it is self-regulating to an extent so the excursion is a lot less than the module "ambient" (fridge) temperature it is in. The black line is the 3458a internal temperature which tracks that of the room.



Title: Re: Ultra Precision Reference LTZ1000
Post by: jd on February 12, 2014, 04:48:08 pm


JD, are you using the LTZ1000 or the LTZ1000A?

Hi,

I am using LTZ1000.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 12, 2014, 08:38:02 pm

What I do not understand: The absolute change in Uref is - 0.08ppm/K only, although it should be -50ppm/K.

Have you really compensated the T.C.?


Hello Frank,

perhaps I did not explain it clearly enough:

The tempco of the LTZ1000(A) without heating (or by changeing the temperature setpoint) is around +50ppm/K.
In the measurement above the internal heater of the LTZ1000A was active. So the datasheet value of 0.05ppm/K is the target.
So the TC is not compensated but the chip temperature is held more or less constant.

TC compensation is done only on my ADCs (LTC2400) which I use for measuring the LTZ output values.

I plan on using a 16-bit PWM instead of a divider resistor for the temperature control set-point--   

If the Zener is making about 7.2V, then a 16-bit PWM should give me about a 0.05-deg-C step for each count-- thus allowing very fine grained control.

This 0.05 K step will produce about 2.5ppm/step (50ppm/K) output voltage change.
The interesting question here is how the remaining ripple of the PWM after filtering is minimized.
In order not to increase the noise of the LTZ (1.2uVpp) the remaining ripple should be well below 0.003K (or 7uVpp).


I have not looked properly at hysteresis so I may have missed it.

The red line shows the temperature of the LTZ "module"; it is self-regulating to an extent so the excursion is a lot less than the module "ambient" (fridge) temperature it is in. The black line is the 3458a internal temperature which tracks that of the room.


In your case the temperature change near the LTZ is only around 8 degrees against 25 degrees of my PCB temperature change. Since the hysteresis squares (approximately) with the excursion of the temperature it should be negligible in your case.
Btw. what is the exact type of beer cooler that you are using?
I use a standard thermoelectric cooler (car box).
But I have to use additional ice packs in styrofoam + some fan controller to reach the +10 degree Celsius.


What I am wondering, is which device has less thermal hysteresis-- the LTZ1000, or the LTZ1000A?  Does anyone have data on this?

Interesting question.

According to my measurements on several AD586LQ references the hysteresis shows large differences between individual devices.

Further I have the suspect that the hysteresis is larger on newer devices. And AD: has changed the type of die attach for the hermetically devices according to a change note on their web side. (probably due to ROHS?)

So you would have to test several LTZ1000 + LTZ1000A from around the same date code to answer the question.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 14, 2014, 06:04:25 pm
Of course there are the other bits that need to be addressed as well-- I want my 10V reference to have battery backup for an extended period of time (for shipping the device "hot" to/from a cal-lab that has a JJA)....  I am leaning towards the CALB 40Ah if I finally decide to go with the Peltier-cooler method...
In my experimenting with Peltier cooling so far, cooling performance of the hot side is very important for performance of the cold side.  This would seem to further complicate mailing it "hot", where the reference will be inside a bunch of packing material.  Did you have a plan for mailing a peltier-cooled reference or is not mailing it a reason you don't care the CALB isn't flight qualified?
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on February 15, 2014, 12:06:10 am

Yes-- the Peltier system will need to breath outside air in order to function correctly.  My plan is to build a special carrier with inlet/outlet vents for airflow from the fan that cools the hot-side of the Peltier device.  The carrier will act as the "shipping container".


You could pipe the heat to phase-change sink of some sort. Dry ice (maybe too cold)? Regular ice? One of those semi-solid freezing gel packs? etc
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on February 15, 2014, 03:46:41 am
Hmmmm... That's a good thought-- but are those things allowed on cargo planes-- (I know that some of those you mentioned are not allowed in the cabin of a passenger airliner)?

Air flow might be questionable:
(http://p3.img.cctvpic.com/program/bizasia/20111213/images/1323758629567_1323758629567_r.jpg)

But I'm sure you can find something that'd be allowed. Kerosene?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 15, 2014, 08:14:37 am

Maybe the easiest thing to do is restrict the time of year to ship the reference off for calibration to the more temperate seasons-- (avoiding winter and summer-- perhaps in the fall when it is dryer)...  This would only happen once a year anyway...

I do not know how the humidity behaves in your region.
Here in my region the smallest change in humidity is in spring after winter.
So this is the best time to calibrate all your gear if you want to import the "volt" into your lab with the smallest changes during transport.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on February 15, 2014, 09:56:11 am
What is the ideal value/range regarding humidity in your opinion?

My very best gear uses LTZ1000 and I now have a Fluke 732A. So far I have not seen an effect with changes from 45% up to 55% on this gear.

Right now I have around 45% and made very interesting meassurements with my TEK 4050. As I already posted several times, the Fluke 8846A / TEK DMM 4050 are great meters. In my opinion the very best you can buy. I only wonder how it is possible with "only" a LM399 reference inside, because  my 4050 even challenges my gear with LTZ1000 reference.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 15, 2014, 11:23:10 am
Hello,

There is no best value. In best case it is constant.
Most instrument datssheets specify < 80% rH non condensing.
The effect is 0.5 ppm/%rH with buried zener voltage references in plastic case. (LT1027CN)
Something similar has been shown in early datasheets from LT1236AILS8 in hermetic case mounted on pcb material.
In this case the changes of the pcb create forces on the chip.

With references (LM399) that have good decoupling from pcb the effect is lesser.
I see around 1-2 ppm over 1 year (cycle) when comparing a well decoupled (from pcb) AD586LQ against a LTZ1000A.
So with a 6.5 digit multimeter you might probably have difficulties to see it.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 15, 2014, 09:45:22 pm
I don't know how radical I need to get in cooling the LTZ1000--- maybe just running it at 25C die temperature (+/- 0.001C) will be sufficient, and further chilling might be wasted because of no further decrease in drift rate.  All of that remains to be determined after construction and testing.  My plan is for a die temperature of 0C, but that may be "overkill", and if 25C *is* sufficient, then the Peltier device will have much less work to do, and the power needs from the battery will be more reasonable.
I'm thinking of trying a three layer approach, where the die temperature and the support circuitry are both held at 10C.  I'm not sure if I'd ever know I succeeded in reducing thermal gradients on the leads, but it seemed like a neat idea.  I'm also guessing 10C should be better for the stability of all the precision parts, so long as they're hermetically sealed.  My lab tends to be 15-20C, 25-65% humidity; so 10C is above the highest dew point and relatively low power to maintain, simplifying the build.  Still many Saturdays and parts orders to go before I know if it's within my abilities to realize this 3-layer design, hehe.

It will take some things out of their tempco sweet spot, but hopefully the temperature regulation will be tight enough to compensate. I will need some good power filtering, too, since having an inner peltier cooler means bringing that bucked voltage into the shielding box. Thanks for posting your PWM filter :)

As this is going to be the most stable thing I have by several orders of magnitude, I may never know if I chose well.  If I ever go for calibration against a primary standard, my "plan" is to have a road trip ;) 
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on February 16, 2014, 12:34:12 am

 I am going to contact them to see if they would give us "Volt-Nuts" a break on calibrations-- (no certificate of compliance, just a "before" and "after" if an adjustment is involved). 

You had better put your game-face on. Calibrations at NIST start around $10k. And all they do is hook your machine up, hit the go button, and tell you how far you are off. Forget having time to tweak it.

I'm reminded of the book "Foundations of Mechanical Accuracy" in which the story of replicating the meter standard in the 1970's was told. The Moore Tool Co would send a rep to France with a briefcase that contained what they though was some fraction of a meter. The guy hops on a transatlantic flight, sets up the standard next to the one in Sèvres, waits how ever many hours/days you need to make sure everything's at the right temperature, and finally shines a laser at the ends of each to figure out how much they are off. The guy gets the report, flies back home, sets up the standard in a room inside a room in the sub-basement of the Moore Tool Co. and they take like a month to file off their best guess at another nanometer. All this just to fly back to France and try again and again until they've gotten "close enough" or they've gone too far.


Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 16, 2014, 01:36:35 am

.. Well, after 2 weeks of this torture, the readings in the 3458A suddenly dropped 0.25ppm (when it had been solid, with no discernible drift, for the first part of the year). ...

 and the 3458A dropped another 0.25ppm!  [The 3458A has never recovered-- even though the humidity has been around 8% for months now, it is still low by 0.5ppm-- so I think it was permanently affected].  ...

 My Fluke 732B did not suffer at all through this (as far as I can tell-- I don't yet own a JJA)-- the important resistors in the 732B are all hermetically sealed.



Hi,

If you don't have an JJ, how did you distinguish, or decide, that the 3458A was drifting absolutely and not your 732B?

I assume you noticed the drift by comparing the 3458A against the 732B?

You know, what I mean, the "man with the 1 clock, 2 clocks, or 3 clocks" problem.

Anyhow, if it was really the 3458A, there are 2 possibilities of a permanent shift.

First, the sudden high humidity caused a sudden shift , i.e. an irreversible ageing, of one or two of the bulk metal foil resistors, about 25ppm in total.

Second, the humidity caused the temperature stabilization to fail, heating the LTZ even more than 95°C, where it is supposed to be normally.
Maybe you did not log that event.

This might have caused a reversible but permanent  hysteresis, resulting in a smaller reference value, so the 3458A reading should go up afterwards.

Would be interesting what  you have observed, and how you argue about the 3458A/732B comparison.

And I am interested, how you basically monitor the 3458As stability , against that single 732B only?
Do you leave the 3458A always on?
What if you switch it off, does it return to its former value?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 16, 2014, 01:44:53 am

I don't know where in the country you are, but Sandia Labs has a Cal-Lab that is humidity controlled (one of the few in the USA), and their uncertainty for Zener reference calibrations is 0.017ppm !!! 

No big deal, if they own a JJA and a decent nV voltmeter. Comparisons to the level of <= 0.001 ppm should be possible.

But which Zener based references have that level of stability?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on February 16, 2014, 02:43:39 am
I'm reminded of the book "Foundations of Mechanical Accuracy"

One of the most treasured books in my library. It inspired me to buy (3) 18" square surface plates and take them to 15µinch flatness using the 3 plate method back when I was about 22. I studied that book like the bible and the skills I learned from it served me well thru my mechanical career. I ended up buying a Moore #3 measuring machine where I worked and many trips to the Moore special tool co.
Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on February 16, 2014, 06:48:36 am
If you are going to have very precise references you will note the accuracy and cal specs require them to be in a temperature and humidity stable location at all times, just for the ageing. Every cal lab will have all of the precision equipment in a room with a hermetic seal on all the doors and no windows aside from a small one in the door, with airconditioning just for the room and a heat exchanger on the room ventilation. This will be to keep the standards at constant temperature and humidity. The standards lab near me has the mass standards in glass cases with felt linings, all in a room with thick brick walls inside the middle of the building. There is a balance in there as well to check the transfer standards against them. Those then go into the room next door where they can bring the equipment in that they are calibrating.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on February 16, 2014, 07:40:35 pm

I did not think about the hysteresis problem-- is there any way of determining if that is the cause, and if so, is there a way to fix it (put the reference board in the freezer or something)?


I just had an image of a kegerator-style DMM flash into my mind.  Mmmm... 8 1/2 digits of frothy precision.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on February 17, 2014, 12:56:18 am
I have an idea to fix this calibration cost problem for us "Volt-Nuts".  If it turns out to be feasible, I will announce the solution here and on the "Volt-Nuts" list.

I've been thinking that rather than calling and asking nicely, we (the collective group here) should publish a paper on our experiences. If we could get it into Metrologia, I'm sure Sandia (or whomever) would be much more receptive to returning your calls.
Title: Re: Ultra Precision Reference LTZ1000
Post by: hgg on February 17, 2014, 02:48:41 pm

Do you know what is the initial %accuracy of the LTZ1000?
I cannot find any info in the data sheet.  Only its stability of 0.05ppm/C is emphasized. 

I've bought a MAX6325 1ppm/C 2.5V reference with a 0.02% initial accuracy.
How does it compare with the LTZ1000 in terms of initial accuracy?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 17, 2014, 05:09:27 pm
It's first item in electrical characteristics on page 3. Anything from 7.0 to 7.5V with Iz 5mA, or from 6.9 to 7.45 with Iz = 1mA.
Title: Re: Ultra Precision Reference LTZ1000
Post by: hgg on February 17, 2014, 05:21:27 pm
Excuse my ignorance, but is the LTZ1000 a reference that you have to calibrate in the beginning,
but after that it will keep its calibration for a long time?

In the datasheet of the MAX6325, it lists the output voltage to be between 2.499 & 2.501
Title: Re: Ultra Precision Reference LTZ1000
Post by: hgg on February 17, 2014, 06:39:44 pm
Hello Ken,

Very detailed explanation.   Thank you!

Title: Re: Ultra Precision Reference LTZ1000
Post by: casinada on February 17, 2014, 06:40:50 pm
Doug @ http://www.voltagestandard.com/ (http://www.voltagestandard.com/) still sell some nice products. with 2 year free calibration
Title: Re: Ultra Precision Reference LTZ1000
Post by: hgg on February 17, 2014, 06:47:57 pm
Geller Voltage Reference : better than +/- .0005% absolute (+/- 5 ppm)    Wow, that's accurate!
Pitty he stopped producing them.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on February 18, 2014, 01:32:26 am

Do you know what is the initial %accuracy of the LTZ1000?
I cannot find any info in the data sheet.  Only its stability of 0.05ppm/C is emphasized. 

I've bought a MAX6325 1ppm/C 2.5V reference with a 0.02% initial accuracy.
How does it compare with the LTZ1000 in terms of initial accuracy?

Table 6.7 in "The Art of Electronics" lists the LTZ1000's accuracy at 4%.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on February 18, 2014, 07:37:13 pm
Just to expose what got me started on this subject: A REF194AG transportable standard.
Unfortunately, it was not sucessful to export the Volt from my workplace DMM to my home DMM.

With the LTZ it is...



Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on February 18, 2014, 08:21:04 pm
All three are available - this is the one I lend to people with low-digit meters saying it is ok for 4.500 V +/- 5 mV,
the LTZ is doing very very well and circulates between me and frank,
otherwise it is really used, often with a kvd to null out voltages or generate low voltages and stuff, i almost think it is the only one used for stuff here. :)

A battery powered LM399 reference was born a few weeks ago. Not really figured out how well i did it yet, but also ok for backpack transfer.

Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on February 18, 2014, 10:33:20 pm
I found out the reason that most <= 6.5 digit DMM manufacturers still use the LM399 (as opposed to the provably more stable LTZ1000) is that the LM399 exhibits remarkably low hysteresis between power cycles-- and the LTZ1000 may actually have more (without some kind of [proprietary] "pre-conditioning" process).  So, for a bench meter that gets used day-to-day (and sometimes in "non-laboratory" environments), the LM399 is a better choice.

The LM399 is absolutely fabulous for short-term work, but as you probably already know, it takes over 10 years of operation to reach ~1ppm/year stability-- so for very long-term stability, the LTZ1000 is the preferred device.  From what I understand, the DMM manufacturers have racks full of LM399's that they "burn in" for a very long time before they are used in a final assembly.  Some manufacturers (like Fluke) burn them in much longer than others (Rigol, Keithley-- with Agilent/Keysight somewhere in the middle).  That's also why very old DMM's (like the HP3457A) can be scary-stable-- their reference (and the cheap metal film resistors they used in the design) have had decades to become very stable.

The LM399 might also be used because of a pricing decision, not only on the part itself but by the required support circuitry and mechanics (dont forget the mold for a injection molded cap which is already shipped with and mounted at the 399 but strongly sugessted for serious LTZ application), while matching to what you usually want from a 6.5 digit device. I am quite happy with my HP3456A at home and the 34401As at work.

What I dislike about the LM399 it is the FLUKEing very hot temperature setpoint - of course required to use it all over the world even in crammed racks without aircon, but here in mild climate of germany I wouldnt mind if it is anything above 40°C. the fridge with ice packs is close, for those rare very hot days.

The REF194AG reference was made because parts laying around, easily good enough for 3 digit meters but frustrating for transfer from work to home - the backpack trip of 20 minutes has thrown it off for more than 1 mV in any direction. But it is very small and handy as you see.

The LTZ1000A was selected because part available on ebay and known to be a instant near-perfect device without any hassle. I tried to keep out most voodo which doesn't appear inside the datasheet but at the omniscient landfill aka the internet. It works well, it travelled from home to work to hobby room and back, to Dr. Frank and another guy. My cheap and lazy open source design is good enough as shown by Frank that it attracted other people already; selling leftover PCBs helped mitigate the part costs a bit :) And in the short time since its birth, it did very well.

The LTZ reference even gets some non-meter-and-references-comparing exercise, e.g. I do internal calibration of some 34401A and (painful) 34405A at work; when one of the main meters come back from calibration, I use those fresh ones to check some lower-class meters which we need only in certain ranges; which I can do with a Dekavider. Also, during testing sensor front-ends i like to use the LTZ and the dekavider. Either to inject a voltage via a buffer, or null out some voltages.

The LM399 was more or less an afterthought as I felt that I skipped an important step. This is now a battery-powered reference; only the standard application again, a battery undervoltage monitor and again cheap and lazy.

When the babies allow it, I will compare the buried zener devices against each other sometimes, and against the workplace DMMs, and Dr. Frank had my LTZ two times for now. All my refs are allowed to travel :)


Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on February 19, 2014, 05:59:24 am
Check out TiN's awesome teardown of a Keithley 2002 complete with several choice pictures of the LTZ.

https://www.eevblog.com/forum/testgear/keithley-2002-8-5-digit-dmm-review-and-teardown/ (https://www.eevblog.com/forum/testgear/keithley-2002-8-5-digit-dmm-review-and-teardown/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 19, 2014, 09:03:57 pm
Hello Ken,

why do you use the LTC1144 instead of a LTC1043 for voltage division?

Ok it is faster in settling time due to the higher frequency.

But since it is designed for power supply applications the charge transfer of the switches is not specified.
On the other side I can remember that a standard charge pump has only about 10ppm stability against 1ppm of the LTC1043.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 19, 2014, 10:34:59 pm
Quote
Check out TiN's awesome teardown of a Keithley 2002 complete with several choice pictures of the LTZ.

https://www.eevblog.com/forum/testgear/keithley-2002-8-5-digit-dmm-review-and-teardown/ (https://www.eevblog.com/forum/testgear/keithley-2002-8-5-digit-dmm-review-and-teardown/)

Interesting pictures, especially the LTC1043 section. They used 680nF Mylar caps by Cornell Dubilier with 5mm grid.
Also interesting is the way the did the shielding. On the lower LTC1043 you can see a guard trace around pin5 and pin18 that is running all the way to the noninverting input of LTC1050. On the upper LTC1034 there is no such a guard trace on any pin.
The bottom view of the pcb shows another interesting point. They surrounded the cap with the signal of pin3 around pin2 on both LTC1043 with the traces coated, but upper and lower layout are different in that particular case.
Would be interesting to know in what configuration they use the switched capacitor building blocks.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 20, 2014, 05:34:33 am
Honestly, I don't know which is better in this application-- the LTC1043 or the LTC1144. 

When looking at the datasheet: the LTC1144 operates only at voltages > 4V in this application.
I.e. if it is sufficient for you that the output voltage range is limited to 4..10V you can use the LTC1144 too.
The LTC1043 has a seperate power supply pin and is not restricted with input voltage.
But when you want to use full accuracy of the LTC1043 you will have to increase the integrator time constant. (R1/C4).
According to my tests you should not deviate from the around 450 Hz switching frequency which are set by the 10nF capacitor on the LTC1043.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 25, 2014, 05:22:27 am
Certainly a nice reduction in the number of primo resistors! You're really close to the output current limit of the 2057, aren't you? Were you able to divine the heater's temp co from the datasheet, or did you experiment?

I presume you're going with the LTZ1000A so that its temperature changes less as the room temperature changes?  Any idea how much it will vary with 1C room temp change? 

My amateur attempts at a stable TCE have only yielded 0.1C regulation thus far (with ambient changing by 4C), so perhaps I'll be able to learn more on that from this thread, too :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on February 25, 2014, 05:23:39 am
This might seem counter-productive to have a heater inside of a refrigerator, but it is the best way to give the LTZ1000A the best chance at long-term stability.  The only way I can see around this is to run the LTZ1000 at cryogenic temperatures-- like in liquid nitrogen (LN2).  This would result in an absolutely stable temperature, because the LN2 always boils at a specific temperature-- and so the LTZ1000 would be kept at this temperature.  You are not going to get much colder than LN2 (well, unless you can afford liquid helium, and if you can afford that-- then you can afford a JJA), and so I would expect the drift rate of the LTZ1000 to be at it's minimum under these conditions.  But-- who can afford LN2 to "play" with?

It's six months past said, but here it is: my first experiment with LN2...

https://www.eevblog.com/forum/projects/the-cryogenic-p-n-junction/ (https://www.eevblog.com/forum/projects/the-cryogenic-p-n-junction/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 25, 2014, 08:27:08 am
No, the LTC2057 will output quite a bit of current-- see the data-sheet.

I'm seeing 19mA min, 30mA typ for short circuit current with a 30V supply...  Oh, derp: I misread your schematic.  Sorry.

Quote
Note what I said in the message-- this is intended for a TCE.
Since the TCE is going to be stabilizing the temperature of some thermocouple or something, and not the temperature of the LTZ1000, then the die temperature of the LTZ1000 will vary as the TCE varies the Q it's moving.  The change in temperature of the LTZ1000 will be less than the change in room temperature; how much less depends on more factors than I know, so I was asking about it ;)  You're clearly allowing for it to vary some, or you wouldn't bother with the temperature feedback in the zener current.

It's a neat idea using the heater as a temperature sensor instead of a heater.
Title: Re: Ultra Precision Reference LTZ1000
Post by: fmaimon on February 25, 2014, 09:54:06 pm
Can't you use Jim Williams circuit from Linear AN45 page 7 to find out the Vbe x temperature relationship? Won't be as accurate as your method but will get you in the right ballpark.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 26, 2014, 09:08:08 pm
Hello Ken,

wow, your cirquit proposal is far away from being usual.
I am very eager to hear from measurement results when you have built your samples.

Just to look if I have understood it right.
The pull up R2 + the heater resistor are in parallel and give around 100 Ohms. They are in series with the 7.2V zener so this will give around 0.5V more output voltage than the usual 7.2V (i.e. a total of around 7.7V).

R2 + heater are now directly adding to the output voltage with a rejection of around 15:1 against the >100:1 relation of the datasheet circuit for the resistors. So any drift of the both resistors will add significantly to the output stability. The temperature drift will be compensated. (as per design). So the ageing drift and the hysteresis of the 2 resistors has to be tracked carefully. A typical "shelf life" drift of a Z201 resistor of 25ppm/year would shift the output voltage by 1.67 ppm/year. So this resistor has shurely to be significantly better.
What kind of resistor did you plan for R2?

Further some questions arise:
- Do you have any ageing data for the silicon resistor of the heater?
  As heater it is negligible since it is part of a regulation loop in the datasheet circuit.
  As compensation resistor any change will affect output voltage by around 1:50 of the heater resistor drift.

- Is there any known hysteresis for the silicon resistor?
  Since it spans the largest area on the chip without any compensation patterns a hysteresis might be likely.
  (Just in case your battery power gets lost during transport).

- how is the output impedance affected by the series resistor?
  the dynamic impedance of the datasheet cirquit is "specced" with around 5 Ohms for the refamp cirquit.
  If the impedance is higher leakage currents of the buffer amplifiers + pcb material have to be observed.

- How will the diode connected transistors perform?
  In the datasheet the only specification is for a collector current of around 100uA. Nothing is given for 5mA.
  Will the long term stability still be the same for a 50 fold current?

I have still not understood the current stabilisation. (There is no direct measurement of the zener current.) Only that the relation R2+R3 has to do something with it. I hope that there will be no thermal run away. And also hope that there is no current overshoot when switching on/off of the reference.

What function has the cirquit R1+R4+D1? Is it only to ensure start up of the circuit?

So I think you are right: there is much to learn + explore if leaving the usual path.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: fmaimon on February 26, 2014, 11:39:03 pm
In AN45-p7, JW is using the delta-current method, which is great if you want to use any random NPN transistor as a sensor, and you only need +/-1C accuracy.  The problem is that *IF* you are going to use the JW LTZ circuit "as is", then you need to know what voltage to set the divider to, so that you can get the die temperature you want-- and this requires knowing the slope and offset of the Q2 temp-sensor transistor inside the LTZ.  My method will yield (typically) 0.25C accuracy (because the transistor response is not exactly linear).  Knowing the absolute value for Q2 Vbe at the die temperature you want, plus the actual Zener output voltage (after TempCo compensation) is the only way I know of accurately selecting the divider values.  As I wrote before, if you don't want to do all of this precision work for *each* LTZ you are going to use-- then just set the divider to 13K:1K, which will set the LTZ die temperature to 10C higher than it needs to be-- but will guarantee that the heater control circuit has enough "headroom" for proper control [up to 35C ambient] just in case the particular LTZ you are using is 10C lower than the average one.  If you do this, you will have to accept [for the average LTZ] about *double* the long-term drift rate than you otherwise would if you want to do the actual work.

You can still use JW circuit. Read the temperature and vbe with the heater turned off. Turn on the heater slightly, wait for the temperature to stabilize and read another data point. Now you have you two points to calibrate your slope.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Blackart on March 01, 2014, 12:10:44 am
Thanks DilligentMinds

The LTC2997 is interesting , sounds like a ideal way of conditioning the LTC1000s they are around $5 at farewell/element etc. The data sheet says the accuracy is based on the "Ideality Factor" of the junction being tested. They are designed for a generic 3904 NPN but sound like they would only be a few degrees C off, if the factor for the specific device is NOT known ( good enough for a burn in bench I would think ). I found a link here to measuring it http://www.bentongue.com/xtalset/16MeaDio/16MeaDio.html. (http://www.bentongue.com/xtalset/16MeaDio/16MeaDio.html.) Im not sure Ill go that far for burning in, but this would be better than my previous idea of just strapping a temp sensor to the LTC100 case. I might get a few while I await my refs to arrive.

Has anyone out there measured the "Ideality Factor" of the junctions in the LTC1000s already ?

Lucas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 01, 2014, 08:23:55 am
Hello Ken,

yes I have some questions.

The LT1013 has up to 2mV influence over a 50 degree temperature span on the output voltage of the LTZ1000.
Additional the LT1013 is no longer available in a hermetically case (at least from LT).
It would be interesting if Bob agrees that replacing the LT1013 by the LTC2057 (lower offset drift, lower ageing, higher gain) will improve performance of the cirquit.

Is there any "zero TC current" on the LTZ1000 as it can be observed with 1N829A Zeners?

The best chip of LT after the LM399 is the LT1027. When will it be sold in a hermetically package again? (or will I still have to use the AD586 chips?)

With best regards

Andreas




Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 01, 2014, 08:38:35 am
Hello Ken,

my questions to LT:

- do they think, that their TO package is hermetically tight, regarding oxygen and humidity, and did they fill it with an inert gas?
- What was the purpose of the A version: lower heating loss for application at higher temperatures (> 60°C) only?
- What do they know / have measured concerning drifts to possible thermally induced stress as torsion of the package, and possible strain effects on the solder junctions or the internal junctions. Is there any advantage of the A version over the non A version in this regard?
- Have they made some stability tests (over time) at lower temperatures, i.e between  40 an 60°C, as implied by Spreadbury and Pickering?
- Are the LTZ1000 and the LTFLU similar chips concerning Si-structure of the buried zener and transistor, so that they both have similar stability figures? (I know that's an indiscrete question)
- Is the LTFLU available from LT on demand?

THX Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 02, 2014, 07:01:20 pm

- do they think, that their TO package is hermetically tight, regarding oxygen and humidity, and did they fill it with an inert gas?



+1
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on March 02, 2014, 11:46:41 pm
Proposed question to Bob Dobkin:

LTC has hundreds of demo boards  http://www.linear.com/demo (http://www.linear.com/demo). Many of them use LT1236 and LTC6655.

I suggest a dedicated LTZ1000 10/5/2.5/1.0 V Voltage Reference Board. LTC has the chip and op amps as well as the LTC1043 and the LT5400. With a few components sourced elsewhere, ageing and calibration - this board will eliminate the need of finding very expensive boards from HP3458A.

Combined with an educational user manual / litterature reference / application note in the spirit of the late Jim Williams, this board will imo add great independent value to the metrology hobbyist / volt-nut community.

(Edit: LT1043 to LTC1043)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 03, 2014, 04:33:45 am
Such board would be still few hundreds USD, as usually expensive part is aging and calibration, as it requires huge time investments.
And most of volt-nuts built their own boards for specific needs anyway.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BravoV on March 03, 2014, 04:43:40 am
Ken, please try to invite Bob to join this forum, and show him this particular thread (> 600 posts now  :o), hopefully he will do that once he noticed the huge discussion only for this special chip alone.

Its worth a shot, imo.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chickenHeadKnob on March 08, 2014, 10:20:30 pm

  Ken, thank you for doing this. I don't think I can add to  the list of questions generated by you and Dr. Frank, save for one area. What does LT recommend with respect to circuit board mounting methods and device characterization before and after. What I am getting at is that both LT and subsequent "major customers" are testing and aging devices in sockets (presumably) and then usually solder mounting with the exception of the recent Agilent 34461-lm399. What do they know that they are not telling us? Agilent might want to keep trade secrets but LT should be able to share their statistical knowledge. If a device receives a thermal shock from soldering what does it do to the long-term aging?

  I am contemplating using gas tight gold-plated sockets of my own design instead of solder simply because I don't know  what the resultant effects of  shock/reset will be, and I don't have the resources to buy large sample lots and perform  the necessary tests.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 09, 2014, 12:22:52 am

Most of the manufacturers that are using the LTZ1000A are building it onto a module, and then "burning-in" the whole module-- not just the LTZ. 

Do you know if the modules are powered during this burn-in time?
Title: Re: Ultra Precision Reference LTZ1000
Post by: fmaimon on March 09, 2014, 01:17:04 am
According to the "rumors"-- yes.  And their outputs are monitored as well.  The module for the 3458A has a cheap resistor on it that doesn't appear to be used for anything [R419, 2K67]-- not even on the main board that you plug the reference board into.  The resistor is connected from -15V to ground-- and nothing on the board uses -15V.  It's my theory that they are "watching" the drift of this cheap resistor [in the "burn-in" fixture] to know how far they have come in the burn-in process.  I could be wrong, but it's the only thing that makes sense.

Maybe this resistor is "nulling" the gnd pin current from the main board to the module. 15V @ 2K67 is about 5.6 mA, about the right value considering 5 mA for the  zener curent, considering that the heater goes to another power pin...
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 09, 2014, 09:49:14 am
Have you ever seen a board with solder stop mask that was driven to  temperatures up to 125°C or even 150°C over and over again for hours, weeks or months? Its color changes, the color of the solder joints, the board itself and several parts on the board too.
I've done a high temperature storage at 120°C on my LM399 reference board for more than 300h and the color has changed clearly. I  can't see such an evidence on the pictures of the reference boards or even the pcb material on the 3458A reference boards.
Whatever burn-in means for several manufactors, power the circuit up or power the circuit up driving a temperatur profil, most things discussed help keeping a myth alive.
I appreciate an offical publication that do away with all that fairy tales.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 09, 2014, 11:06:04 am

I've done a high temperature storage at 120°C on my LM399 reference board for more than 300h and the color has changed clearly. I  can't see such an evidence on the pictures of the reference boards or even the pcb material on the 3458A reference boards.
Whatever burn-in means for several manufactors, power the circuit up or power the circuit up driving a temperatur profil, most things discussed help keeping a myth alive.
I appreciate an offical publication that do away with all that fairy tales.

leaded solder gets soft from 105°C onwards, leadfree a little bit higher.
That softening (euthetic phase) will harm the solder junction.

Therefore, any storage or cycling of soldered PCBs above 110°C will definitely destroy the solder junctions, or at least deteriorate the reliability greatly.
It's possible only to make such  high temperature storage of non assembled components. Here, the max. die temperature of about 150°C is a limit.
Getting close to that temperature will also harm the silicon structure already, due to Arrhenius law.

Burn-In usually is done on components, which have a big drift rate intrinsically, and the purpose of the burn-in is to accelerate those drifts to a state, which otherwise would be reached only years later.

Another technique is to burn-in a completely assembled  PCB (at 90°C max.) to detect early failures and so to get more reliable PCBs, especially under rough conditions as spacecraft, military and automotive applications.
But latter goal is not ultimately required for volt references.
 
So I stick to my opinion, that a real burn-in on ultra precision components, i.e. on components which have low drift rates by design already, will do more harm than really improve the stability further.
 Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 09, 2014, 11:13:47 am

The highest performance DMM's on the market today are the HP/Agilent/Keysight 3458A and the Fluke 8508A.  They both use the LTZ1000A, and they use "reference modules" that are burned-in separately from the rest of the instrument.  They are *not* doing this "because it seemed to be the right idea"-- they are doing it because they have spent a ton of money and manpower on this problem, and they both reached the same conclusion.



Hi Ken,

what do you know about the interior of the Fluke 8508A?

I also assumed, this instrument is very similar to the Datron 1281 (very similar manual), an dwould have the same LTZ1000 reference module(s) as in the Datron 4910, but quarks has sent me a photo indicating, that the 8508A is very differently built.
The reference has a resistor ceramic hybrid on it, which resembles more the Fluke 732B assembly inside the oven part.

I'm still collecting all reference types (LTZ/A, SZA, LTFLU) of the instruments, and their different stabilization temperatures.

Fluke 8508A and the Keithley 2002 are still lacking.

PS: The engineers who designed the 3458A reference board have ignored many rules for getting a stable reference, as too high stabilization temperature, using the A version, and exposing the solder junctions to airflow. That's the only reason, why they are always struggling with the stability, and why they have to make such a big effort in selecting the references for 8 / 4 / 2 ppm/yr.

Thanks Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 09, 2014, 01:01:41 pm
Quote
I'm still collecting all reference types (LTZ/A, SZA, LTFLU) of the instruments, and their different stabilization temperatures.

By the way, LTFLU is currently available on ebay eBay auction: #111063925120.

Quote
Fluke 8508A and the Keithley 2002 are still lacking.

The pictures by TiN didn't help?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 09, 2014, 01:17:55 pm
Quote
I'm still collecting all reference types (LTZ/A, SZA, LTFLU) of the instruments, and their different stabilization temperatures.

The pictures by TiN didn't help?

Nope. Also not the BOM of the circuitry, which I've found on the Keithley site..
I've expected precision divider resistors in the range between 1k:12k and 1k:15k, but there are no resistor relations like this, neither multiple of those.

So I assume, Keithley uses a different scheme to set the temperature. perhaps some PWM or DAC, or so.
It would be useful, if somebody would determine the temperature by measuring the UBE voltage directly.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 09, 2014, 02:58:30 pm
I'll do all that later, when recovering schematics.
I just don't want to disassemble meter every time, for this or that, it's still likely in cal.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 09, 2014, 08:48:03 pm
Somewhat off topic but since the LTZ needs precision resistors too:

perhaps this fits to Franks results for the TC of the resistors.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: casinada on March 10, 2014, 04:37:52 pm
Is anybody familiar with this unit?
VALHALLA 2720GS
http://www.adret-electronique.fr/valhalla_2720/adret_valhalla_2720.html (http://www.adret-electronique.fr/valhalla_2720/adret_valhalla_2720.html)

It has 0.01 ppm and suppose to be able to calibrate 8 1/2 digit DMMs :)
10.0000000V :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on March 10, 2014, 04:56:11 pm
I am a big fan of Valhalla gear and saw this unit before.
But so far I have never seen a real one and only have seen very litte details. 
see att. Prices and HSR specs
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 10, 2014, 04:58:30 pm
"2 Year Spare Parts" ?

Does it require regular oil changes?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on March 10, 2014, 05:05:28 pm
Valhalla 2720GS = Solartron 7081 (PWM ADC) + Datron 4000A (8x 1N829 zeners and PWM DAC)  ;D

2720GS has a very old and noisy PWM type ADC for a such measurements. 0.01 ppm resolution is absolutely useless.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 11, 2014, 12:34:21 pm
There is dead one on ebay for sale for a while for 1K.

Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on March 11, 2014, 07:44:15 pm
Freshly calibrated 34401A@work arrived from cal today, will measure my LTZ source soon :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 12, 2014, 05:41:58 am
Freshly calibrated 34401A@work arrived from cal today, will measure my LTZ source soon :)

Too late: you are already outside the 24hrs calibration window.
For the 90 days tolerances the accuracy is +/- 190uV for a 7V source.

And did you measure the 34401a before shipping?
Or how can you tell that the device did not drift during transport back from calibration?

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on March 12, 2014, 08:26:23 am
Hi Andreas,

its too late to use the 24h-window, yes.
But its not too late to do exactly what I am able to do, although it will be one more day I am afraid.

I have a second 34401A sitting here which was compared to the cal'd one right before shipping, should be able to give a hint from it how the difference between departure and (late) arrival is.

However, Agilent screwed up a bit this time, the meter was out for about one month, they requested more and more order confirmations totalling at 3 (upfront at InfoLine, on paper with signature in the box and after their 3rd request as email again), cal was on 6th and arrived here on 11th.

It only gives a bigger window of where the actual voltage might be. But I dont expect the LTZ to have wandered too far.

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 12, 2014, 09:41:00 pm
Thanks for sharing all this information.

Quote
7) Note that for LM399-based designs, the slots in the PC board [plus a lot of insulation top and bottom] make sense-- Bob said that the less power the heater requires, then the more stable the output voltage will be.  So, in this case, the slots [plus insulation] are helping with this.  Oh-- and he also said that the LM399 should be run at about 1mA of Zener current for best stability.  The more stable you can make the Zener current, the more stable will be the output voltage.  He said that there is about 1uV of voltage change for 1uA of current change.

9) For the LM399 and both of the LTZ parts, he said a good burn-in routine would be to operate them at 125C [in an oven] for 2 weeks.  After that, you can cycle the power on and off 10 to 15 times at normal operating temperature, and this will get them to settle down.  This process should remove most of the initial drift that these devices exhibit.  [So, my initial guess for a burn-in cycle was pretty good-- there is nothing wrong with a burn-in 10 times longer than this.]


That confirms the way I realized my first LM399 reference, a slotted pcb design with a thermal encapsulation on both sides and a thermal burn-in of the board for more than 300h, but sure without powering the circuit, as I had no adequate cables at hand. The reference seems to be very stable and that makes me believe that the humidity depended drift I can observe is the drift of the 34401As reference itself, because all the mentioned actions are not realized in this DMM.

Once again, thanks for sharing.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on March 12, 2014, 10:51:39 pm
Thnks for sharing Dilligentminds
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on March 12, 2014, 11:34:34 pm
Thank you very much to Bob Dobkin and to you DiligentMinds.com.

I have been working a lot with the SZA263-type AmpRef/RefAmp circuit, and have found that HP used the circuit/component already in 1963, while Fluke seems to use it first time around 1971. The circuits are so similar that it is imo unreasonable to argue for any originality in the Fluke 731A.

So may be it could be an idea for US based volt-nuts to contact Fluke and ask them to "free" the LTFLU-1.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 13, 2014, 12:02:36 am
Did you happen to get an address that we could send a thank you card to?
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on March 13, 2014, 12:54:25 am
 :-+ great information
Thanks a lot for sharing
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on March 13, 2014, 01:41:22 am
Thanks for the great information :-+

That gives me confidence to continue my practice of only turning on my 8846A when using it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on March 13, 2014, 02:24:49 am
Thank you very much to Bob Dobkin and to you DiligentMinds.com.

I have been working a lot with the SZA263-type AmpRef/RefAmp circuit, and have found that HP used the circuit/component already in 1963, while Fluke seems to use it first time around 1971. The circuits are so similar that it is imo unreasonable to argue for any originality in the Fluke 731A.

So may be it could be an idea for US based volt-nuts to contact Fluke and ask them to "free" the LTFLU-1.

Good luck with that!  Fluke was purchased by the evil Danaher corporation (along with Keithley and Tektronix)-- they pretty much fire everyone over the age of 30 [thus losing the people that actually know *why* things were done in the past], then they cancel anything that isn't making huge profits, and then milk their "captive customers" for everything that they are worth.  I seriously doubt if they are going to budge even one inch in giving us access to *anything*.  But you can *try*... Let us know how that goes!

I sure will  >:D  Nothing to lose...

I do however not expect much. After seeing the 6-in-1 launch timer/clock running negative overtime far to long after count-down, I sent an email to Tek's Quality Dept. The timer was taken away a few hours later. But they didn't thank me - they are now repeatedly filling my email inbox with US located seats for some post-launch sessions.

But I have seen a video on YT with Fluke's Chief Corporate Metrologist Mr. Jeff C. Gust. If it is not all circus for the masses, I suppose he will at least answer my mail.

I'll be back in due time  :-BROKE
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 13, 2014, 02:45:38 am
Did you happen to get an address that we could send a thank you card to?

No, I did not, but you can probably send it to the main office in Milpitas, CA and it will get to him.

I'm going to send him a thank you card from the [Volt-Nuts].

I think it'd be nice if he could see the international cross section of people that have benefited from his advice. PM me if you want your name or handle in the signed-by section. Include what you want to be called and a city and country if you don't mind.

I'll post a picture of the card before I send it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 13, 2014, 04:59:16 am
Great, thanks!

Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 13, 2014, 05:39:19 am

No need for the private message-- you could find out who I am anyway just from the domain name registration for DiligentMinds.com ...


The judge said I have to stop cyber-stalking people ... its part of my parole.  ;)

Your name will be the first on the list.
Title: Re: Ultra Precision Reference LTZ1000
Post by: macfly on March 13, 2014, 11:27:15 am
@ DiligentMinds.com

Thanks a lot for sharing your informations  :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 13, 2014, 08:09:51 pm
Quote
19) The Zener in the LTFLU-1 is the exact same one as is in the LTZ1000.

Really? So what is different to LMx99?
I expected the LTFLU is completely similar to the LMx99, a 4 pin TO package with heater and zener diode.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on March 13, 2014, 09:36:45 pm
Quote
19) The Zener in the LTFLU-1 is the exact same one as is in the LTZ1000.

Really? So what is different to LMx99?
I expected the LTFLU is completely similar to the LMx99, a 4 pin TO package with heater and zener diode.

The LTFLU-1 and the earlier SZA263 have no heater. They are zener (avalanche) diodes nominally 6.2 V accompanied with a transistor for temperature compensation and reference voltage amplification.

The pins are Collector, Base, Emitter and Anode (Kathode is common with Emitter).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 13, 2014, 10:05:53 pm
Hello Ken,

thanks for sharing the information.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 13, 2014, 10:19:44 pm
Really? So what is different to LMx99?
I expected the LTFLU is completely similar to the LMx99, a 4 pin TO package with heater and zener diode.

Hello branadic,

a refamp comes usually as refamp-set with (perfectly) adjusted resistors.
See e.g. fluke 8840A handbook.
So a LTFLU without the adjusted resistor set will be only half of the truth.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 13, 2014, 10:40:35 pm
Quote
The LTFLU-1 and the earlier SZA263 have no heater. They are zener (avalanche) diodes nominally 6.2 V accompanied with a transistor for temperature compensation and reference voltage amplification.

The pins are Collector, Base, Emitter and Anode (Kathode is common with Emitter).

Thanks for that, couldn't find such info yet and there is nothing mentioned about LTFLU in the "Current  Sources & Voltage References" by Linden T. Harrison.

Quote
Hello branadic,

a refamp comes usually as refamp-set with (perfectly) adjusted resistors.
See e.g. fluke 8840A handbook.
So a LTFLU without the adjusted resistor set will be only half of the truth.

Thanks, so it's no good idea to go for LTFLU unless you want to spend much time and money for the perfect resistors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on March 13, 2014, 10:52:37 pm
Really? So what is different to LMx99?
I expected the LTFLU is completely similar to the LMx99, a 4 pin TO package with heater and zener diode.

Hello branadic,

a refamp comes usually as refamp-set with (perfectly) adjusted resistors.
See e.g. fluke 8840A handbook.
So a LTFLU without the adjusted resistor set will be only half of the truth.

With best regards

Andreas

I doubt that one single 'refamp'-type IC has been sold from any chip maker with any resistors. It is the instrument makers that sell matched sets in order to keep their boxes within tempo spec after repair. This is nothing special for the refamp. Even the EDC/Krohn Hite volt boxes (there is an EEVBlog video showing the reference) with a simple 10 USD 1N829A requires a very precise current setting.

There is no magic here. Anyone with good enough instruments to detect changes in net tempco for small changes in current can select resistor(s).

This technology is old and only based on the appr. +- 2 mV tempco of the avalanche diode and the PN-junction respectively. It was used by Hewlett Packard with the Motorola part SZA263 long before Fluke or Linear Technology came into the picture.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 14, 2014, 05:38:12 am

There is no magic here. Anyone with good enough instruments to detect changes in net tempco for small changes in current can select resistor(s).


According to 8840A handbook there are 3 resistors in the ref amp set.
It seems that 2 resistors adjust the output voltage.
So the other resistor seems to adjust the "Zero TC" current.
Further there are the magical -50mV in the circuit diagram.

Since I cannot imagine that all the resistors do not influence each other:
Does anybody know a "adjustment specification" for the resistors with minimal effort for trimming?

With best regards

Andreas
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 14, 2014, 07:10:06 am
Hello fellow forum users,

I just finished with a telephone conversation with Bob Dobkin, and he was short on time, so I was not able to get all of the answers to every question I [and we] had, but here are the ones I was able to get:


3) The LTZ1000A has a different die attach than the LTZ1000, but they are both isolated quite a bit from external lead stress.  Both of them will respond a small amount to lead stress, but the 'A' version if far less susceptible to this.  Bob said that this can show up as a drift in output voltage with changes in barometric pressure.

8: All voltage references *do* age faster at higher temperatures.  So, since the LTZ1000 can be run about 10-deg-C lower than the 'A' version, it will have lower [about 1/2] long-term drift than the LTZ1000A under otherwise identical conditions.  [But, the 'A' version has *other* differences that are positive-- my words.  There are other sources of drift that the 'A' version is less susceptible to-- barometric pressure changes is one of them].

9) For the LM399 and both of the LTZ parts, he said a good burn-in routine would be to operate them at 125C [in an oven] for 2 weeks.  After that, you can cycle the power on and off 10 to 15 times at normal operating temperature, and this will get them to settle down.  This process should remove most of the initial drift that these devices exhibit.  [So, my initial guess for a burn-in cycle was pretty good-- there is nothing wrong with a burn-in 10 times longer than this.]

15) The TO packages are filled with *DRY AIR*-- not even nitrogen-only [so you would expect some degradation from this-- my words]-- but, Bob says that they don't have any parts that are degraded by this.

16) The LTZ1000 will use a lot more power than the LTZ1000A, so for battery operated circuits, it's best to go with the LTZ1000A, and insulate it to save power.

17) There is probably not a scenario where you can get zero-TC out of the LTZ-- he said you probably would have to operate Q1 at around 1uA, and that is not practical.

18) He said that it is not necessary to use the LTC2057, as the drift and noise of the Zener contribute far more than the LT1013.  Bob said that you could use almost any precision op-amp, and the drift would not be affected by much even by the less precise amps.  [I'm still going to use the LTC2057 anyway-- they are as cheap as popcorn, and have very little noise.  Since I *do* need a zero-drift amp in the follow-on boost circuitry, and it's more economical to keep the number of unique parts on the BOM as low as possible.]

19) The Zener in the LTFLU-1 is the exact same one as is in the LTZ1000.  He said that even though the exclusivity portion of the contract with Fluke is no longer in effect, they are not going sell these to the public because they don't want to anger a customer that buys millions of dollars in other parts from them.  Even if they did want to sell it to others, it has not been characterized and there is no data sheet-- so there would be a lot of work just to build that.  It's just not going to happen...

Regards,
Ken

Hello Ken,

thanks that you made the interview, sharing with us.

Actually, there were several myths being busted around the LTZ1000.

Concerning "Burn-In", he missed the point of strong hysteresis after a 125°C trip, which will definitely NOT be removed by simply switching off 10-15 times.

I feel confirmed, to keep the LTZ1000 PCB as simple as possible, at 45°C, with good thermal management/insulation.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 14, 2014, 07:45:41 am
I hope that this is not too far off-topic, but [I *think*] Hewlett-Packard make a model 735A "Transfer Standard"; and the Fluke 731B looks an awful lot like it.  What happened there-- did HP sell it's 735A technology to Fluke, or did Fluke make a "copycat" version of it?  Anybody know?

Sorry, but the HP735As schematic  does not ressemble the Fluke 731A at all. At least in the manuals, which are hosted on agilent site.

In the 735A, an ovenized, simple zener diode is used, no sign of a RefAmp device.

Anybody (Quantumvolt??) who can refer correctly to a HP device with a RefAmp, from the 60ties?

Did not find that, not in the 745A, and not in the 740A. All were based on a simple zener diode.


I've read ("Hewlett Packard, the early years") that  Packard and Fluke were close friends. They worked for GE and later both  joined Navy .

Later they made an arrangement to not interfere on certain businesses, so that Fluke made all those analog standards, but kept out of building DMMs and counters, I think. 

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on March 14, 2014, 09:21:34 am
I have also read stories about the persons behind HP & Fluke, but I do not know enough to comment on that.


The HP735A contains an ovenized 1N829A. Very high tech for 1966. And documentation in a class of its own:

http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1966-03.pdf (http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1966-03.pdf)
 
http://www.hpmemory.org/an/pdf/an_70.pdf (http://www.hpmemory.org/an/pdf/an_70.pdf)


The HP3440A is described in 1963:

http://www.hpmemory.org/timeline/dave_cochran/hpj_nov63.htm (http://www.hpmemory.org/timeline/dave_cochran/hpj_nov63.htm).

The manual I have found on the web contains the "refamp" - which as HP part was called "Amp., Ref.". This edition contains pages that are revised in May 1970:

http://www.pa.msu.edu/~edmunds/DVM_HP_3440a/hp_3440a_dvm_manual.pdf (http://www.pa.msu.edu/~edmunds/DVM_HP_3440a/hp_3440a_dvm_manual.pdf)


The HP3050A has a reference supply that is very similar to Fluke 731A, except that it uses a 'discrete' op amp. This manual also contains pages that are revised in May 1970. If I am not wrong, the Fluke 731A is from 1971.

http://cp.literature.agilent.com/litweb/pdf/03450-90007.pdf (http://cp.literature.agilent.com/litweb/pdf/03450-90007.pdf)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 14, 2014, 10:38:11 am
Thanks for the hints!

The HP3420A (1971) also uses a RefAmp. Origin not determinable.

The HP3440A uses a 4JX19A519 from G.E.


Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on March 14, 2014, 11:36:22 am

There is no magic here. Anyone with good enough instruments to detect changes in net tempco for small changes in current can select resistor(s).


According to 8840A handbook there are 3 resistors in the ref amp set.
It seems that 2 resistors adjust the output voltage.
So the other resistor seems to adjust the "Zero TC" current.
Further there are the magical -50mV in the circuit diagram.

Since I cannot imagine that all the resistors do not influence each other:
Does anybody know a "adjustment specification" for the resistors with minimal effort for trimming?

With best regards

Andreas

I am referring to http://assets.fluke.com/manuals/8840A___imeng0300.pdf (http://assets.fluke.com/manuals/8840A___imeng0300.pdf) Figure 5-6 p. 5.8.

Assume U702A is ideal. Then both inputs are at 0 volt. Hence the collector of U701 is at 0 volt. To avoid possible reverse bias C-B the base of U702 is biased at -0.05 volt (which gives 6.95 volt headroom for the REFAMP zener appr. 6.5 volt + Vbe appr. 0.45 volt).

Assuming first that the bias current of U702 U701 can be ignored, the bias divider Z701 is fixed in resistor ratio. Choose resistors that give a reasonable current (a few hundred uA or 1 mA or ? - it doesn't matter at the first try) and give appr. the wanted -0.05 V and -7 V.

Now adjust R701 (it will imo only affect bias for U702A) for minimum tempco in the -7 volt.

If TP701 has changed away from -7 volt, adjust U701 base voltage by changing the Z701 ratio marginally, and repeat. If necessary, choose a different Z701 current and start over.

---

I might be totally wrong  :-\. But I could always ask on the forum for resistor values from a real box and start from there ...
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 14, 2014, 04:50:03 pm
It would have been helpful to ask Bob what is his opinion... does really make sense to preselect references before solder and age them? Would have been interesting if he could have shared any experience to that.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 16, 2014, 06:53:24 am
Quote
For the LM399, I'm guessing the soldering process doesn't hurt it as much as other references, because Fluke has the most stable 6.5-digit DMM, and they solder the LM399 *after* burn-in...

Thanks Ken for your response, but I doubt that the soldering process is without influence. At least one pin of the TO package is directly connected with the case and will heat up the die attach while soldering.
Title: Re: Ultra Precision Reference LTZ1000
Post by: macfly on March 16, 2014, 09:57:57 am
[Clever!]

Yes, it is!!

Many manufacturers offer a "super grade" version of their voltage references with guaranted initial tolerance and temperature drift. They are measured on 100% of chips. But how?

There's sometimes an advised "TEMP" output on voltage references (With a kind of linear dependance with temperature). This internal circuit is used to test chips after packaging (Internal die temperature is monitored through "TEMP" pin, and the chip is heated i.e. by injecting current through an ESD protection diode. An external control system can provide precise temperature regulation).

In this paper, such a system is diverted from its initial use to provide nearly 0ppm/K temperature drift, with a common plastic-case voltage reference chip :

http://electronicdesign.com/analog/internal-oven-provides-voltage-reference-less-1-ppmdegc-drift (http://electronicdesign.com/analog/internal-oven-provides-voltage-reference-less-1-ppmdegc-drift)

How does this circuit work  :-// ? IMO is could NOT!

1. There is only a positive supply voltage, so the output voltage of the opamp's can only be positive.
2. IC2B is connected as inverting amplifier. It gets a positive voltage from pin 1 of the reference, buffered by IC2A.
3. This should result in a negative output voltage of IC2B, but it could not, due to the lack of negative supply voltage.

Or I am a completely wrong ?

Regards

macfly



Title: Re: Ultra Precision Reference LTZ1000
Post by: fmaimon on March 16, 2014, 11:04:06 am
How does this circuit work  :-// ? IMO is could NOT!

1. There is only a positive supply voltage, so the output voltage of the opamp's can only be positive.
2. IC2B is connected as inverting amplifier. It gets a positive voltage from pin 1 of the reference, buffered by IC2A.
3. This should result in a negative output voltage of IC2B, but it could not, due to the lack of negative supply voltage.

Or I am a completely wrong ?

Although it only have one supply, the voltage reference IC is being fed by a 5V zener, so the applied 12V, through the 10 ohm resistor is always going to foward bias the internal esd diodes.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on March 16, 2014, 12:09:15 pm
The comparator is referenced to VREF = 2.5 V. Nothing goes negative relative to the potential at the GND level.

The sensor voltage at pin 1 falls as the chip cools. When it is 0.53 volt LOWER than VREF (which means the chip has cooled below 75 degrees), the buffer/inverter will have converted the marginal fall to a rise on the noninverting comparator input which then goes positive relative to VREF, and a new heating impulse is initiated.

Since VREF is the only voltage stable enough to use for comparison - the main task for this circuit is to convert the passing of the sensor pin below VREF-0.53 volt to a trig signal for the VREF-referenced comparator. In effect it is an AC-signal at a few hundred hertz.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 16, 2014, 12:27:15 pm
Quote
For the LM399, I'm guessing the soldering process doesn't hurt it as much as other references, because Fluke has the most stable 6.5-digit DMM, and they solder the LM399 *after* burn-in...

Thanks Ken for your response, but I doubt that the soldering process is without influence. At least one pin of the TO package is directly connected with the case and will heat up the die attach while soldering.

The pictures of HP34401A reference that I find in web show a LM399 within a socket (horror).   :o |O
I do not know if this is a unmodified unit but with my bad experiences of socket related voltage shifts I would not do that.

(http://www.mikrocontroller.net/attachment/91696/20101105205754.jpg)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: rf-design on March 16, 2014, 04:10:30 pm
4) It's been 20 years, so he didn't know the exact numbers, but Q1 is only rated to a few hundred micro-amps of collector current.  [This means my single-resistor idea will *not* work! -- back to the original circuit from the ap-note!]  Q2 will have a max rating of around 1mA, and the Zener can take quite a bit more.

5) They *could* make a model for LTspice, but the temperature effects are very difficult to simulate, and the market need is not large enough to support the development effort [my words].  He said the best way is to build the circuit and test it out in real life.

17) There is probably not a scenario where you can get zero-TC out of the LTZ-- he said you probably would have to operate Q1 at around 1uA, and that is not practical.

Refering to the chip photo posted early in this thread I could see 6 heater ring resistors, 4 equal sized diffusion isolated npns, 2 equal sized diffusion resistors and 2 possible lateral pnps or diodes. All in a very old single metal bipolar process. Is this one still in production? Or was it all time before shutting down the process?

Did anyone check the corrospondence between the schematic in the appnote and the circuit seen in the photo?

Based on the layout dimensions operating current ratios of mA to uA for optimum temperature stabilisation seams unlikely. The main target for the circuit operation would be the die temperature. For better understanding it would be very helpful to have a full schematic for modelling purposes which must include thermal coupling of the devices. Did anyone tried such a model?

One aspect of the thermal regulator is that if the interlayer between the die bottom and package is not even the thermal surface plot would get a gradient which is not foreseen in the bipolar layout placement and configuration. To be immune it should circular interdigitized which is not. Further the 4 bipolars are not crosscoupled. So a thermal conductivity gradient in the axis connecting the two electrical groups would give also a gradient between the bipolars vbe. So I see this as a design flaw. But back to the model that could be integrated in thermal coupling resistors as a mounting imperfection.

If the temperature cycle amplitude is less than 20K the hysteris will be closed. So there is no aging but another unidentified process. Is there any idea?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 17, 2014, 07:05:22 am
4 equal sized diffusion isolated npns, 2 equal sized diffusion resistors and 2 possible lateral pnps or diodes.

If the temperature cycle amplitude is less than 20K the hysteris will be closed. So there is no aging but another unidentified process. Is there any idea?

Hello,

https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg279145/#msg279145 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg279145/#msg279145)

Sorry I see 4 large transistors (horizontal and vertical) connected all to each other building Q1.
And 4 smaller transistors (45 degrees interleaved) building Q2.
The emitters on the outside of the transistors are all connected together.

Hysteresis is usually related to the package of the device.
I.e. the die attach consisting usually of silver filled epoxy resin.
(and perhaps hollow glass filled (low density) resin for the A-device)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: macfly on March 17, 2014, 11:30:09 am
The comparator is referenced to VREF = 2.5 V. Nothing goes negative relative to the potential at the GND level.

No!
I refer to figure 1 of the article.
The complete OP amp's supply are referenced to ground. The supply of the reference also.
The voltage on R1C can only be positive above ground. But a positive voltage feed
into RN2A (buffered by IC2A) would  (with a negative supply voltage for the OP) result in a negative output voltage of IC2B.
But without negative supply, the output voltage will always stay near zero volts or an erroneous phase-reversal occurs.
Title: Re: Ultra Precision Reference LTZ1000
Post by: muvideo on March 17, 2014, 12:42:56 pm
The comparator is referenced to VREF = 2.5 V. Nothing goes negative relative to the potential at the GND level.

No!
I refer to figure 1 of the article.
The complete OP amp's supply are referenced to ground. The supply of the reference also.
The voltage on R1C can only be positive above ground. But a positive voltage feed
into RN2A (buffered by IC2A) would  (with a negative supply voltage for the OP) result in a negative output voltage of IC2B.
But without negative supply, the output voltage will always stay near zero volts or an erroneous phase-reversal occurs.

From a rapid eye to the circuit, I'm with you on this.
If I understand correctly when the die cools down the
voltage at IC1 pin 1 goes up, in order to begin a new
heating cycle IC2C pin 10 must go above pin 9.
So IC2A/B must buffer and amplify the signal in
non-inverting configuration, so I dont understand IC2A/B
in this circuit. Also IC2D could not work as intended if
opamps input offset voltage is on the "wrong" side  :-//
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on March 17, 2014, 01:45:40 pm
Well ... I guess the schematic needs some adjustments.

The last line in the article reads: "Ensure that the ?5-V supply is on whenever the 12-V supply is on. With the ?5-V supply off and the 12-V supply on, the controller loop applies the heat current continuously."

I am sure the circuit (which is nothing but a meta-thermostat) will work after debugging...
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 18, 2014, 01:09:46 am

I just finished with a telephone conversation with Bob Dobkin, and he was short on time, so I was not able to get all of the answers to every question I [and we] had, but here are the ones I was able to get:


Did Bob give you any indication as to the spread of drifts of the LTZ (or 399) after burn-in? Or the percentage that are rejected even before they are sold to someone like HP?

 
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 18, 2014, 04:27:22 pm
No one wanted their name on the thank you card so I just ended up writing a simple note on some plain 'Thank You' stationary:



Dear Bob,

Thank you for taking time out of your schedule to answer our questions on the LTZ1000. That level of support from you and Linear means a lot to us!

Sincerely,
The [Volt-Nuts]


Went out in today's mail.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 18, 2014, 10:49:53 pm
Did Bob give you any indication as to the spread of drifts of the LTZ (or 399) after burn-in? Or the percentage that are rejected even before they are sold to someone like HP?

The more interesting thing would be how the criteria for selections are.
For a instrument with 35ppm/year the drift of the reference should be below 18ppm (the other ppm for resistor + tempco).
To guarantee (3 sigma) that the measured drift of the reference alone should be even below 6 ppm/year or 2ppm/kHr (assuming sqrt (9khrs) = a factor of 3 difference between 1kHr and 1year).

From my measurements about 50% of LM399 are below 1-2ppm/kHr after 2000 hours ageing under power (15 hrs on/7 hrs off per day) without previous burn in.
Now after 4000 hrs further devices seem to stabilize below this limit.

But probably you will have further tests (0.1Hz - 10Hz) noise or even lower frequency noise to filter out the bad references.

I do not know if it is a really good idea to do a burn in at 125 degrees C. Since the heater is off above 90 degrees the aging mechanism will probably change. And changes to the heater will create relative large changes to the output voltage. E.g. changing the heater voltage supply will create several ppm/V output change especially around low (10V) heater voltage.
Although the temperature and so the heater power are regulated on chip.
Of cause it could be that all aging is mainly not related to the chip itself but related to the die attach (epoxy) between chip and package. In this case a burn in at higher temperatures would  make sense.

Good aged LM399 based instruments have about 1-2 ppm drift per year.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: rf-design on March 19, 2014, 10:48:21 am
Did Bob give you any indication as to the spread of drifts of the LTZ (or 399) after burn-in? Or the percentage that are rejected even before they are sold to someone like HP?

The more interesting thing would be how the criteria for selections are.
For a instrument with 35ppm/year the drift of the reference should be below 18ppm (the other ppm for resistor + tempco).
To guarantee (3 sigma) that the measured drift of the reference alone should be even below 6 ppm/year or 2ppm/kHr (assuming sqrt (9khrs) = a factor of 3 difference between 1kHr and 1year).

From my measurements about 50% of LM399 are below 1-2ppm/kHr after 2000 hours ageing under power (15 hrs on/7 hrs off per day) without previous burn in.
Now after 4000 hrs further devices seem to stabilize below this limit.

But probably you will have further tests (0.1Hz - 10Hz) noise or even lower frequency noise to filter out the bad references.

I do not know if it is a really good idea to do a burn in at 125 degrees C. Since the heater is off above 90 degrees the aging mechanism will probably change. And changes to the heater will create relative large changes to the output voltage. E.g. changing the heater voltage supply will create several ppm/V output change especially around low (10V) heater voltage.
Although the temperature and so the heater power are regulated on chip.
Of cause it could be that all aging is mainly not related to the chip itself but related to the die attach (epoxy) between chip and package. In this case a burn in at higher temperatures would  make sense.

Good aged LM399 based instruments have about 1-2 ppm drift per year.

with best regards

Andreas

(http://www.rf-design.de/project/usref/lm399_schematic.jpg)

The LM399 shows two possible entrys for a temperature change related mechanical stress effect. The first and most reasonable is that the regulation temperature change with mechanical stress. The second would be that the buried zener voltage change because of the stress. The second argument is not reported up to now but for the first argument there is much material.

(http://www.rf-design.de/project/usref/mechanical_stress_vbe_shift.jpg)

from:

Package Shift in Plastic-
Packaged Bandgap References
Vishal Gupta
Prof. Gabriel A. Rincón-Mora

So the hysteresis effect is reported by LT as be a square law dependence on the temperature amplitude.

(http://www.rf-design.de/project/usref/ltc6655_note9.jpg)

To my understanding the aging as well as the temperature hysteresis depend on the mechanical stress change of the die attach epoxy over temperature and time. If the temperature change for instance at warmup or at the start of the burn in mechanical stress will built up but will realease after some time to lower level. This effect will repeat but with memory from previous cycles.

(http://www.rf-design.de/project/usref/zymet_zero_stress.jpg)

Zymet Zero-Stress Adhesive

There are alternates for bonding. Interesting is the reduced stress at higher temperatures for silver-filled expoxy. But the zero-stress point is above 150°C.

So the best burn in will be at target operation. A burn in at higher temperature will possible leave a greater stress at lower operating temperature. The effect will either change the regulation temperature or direct the bandgap voltage. So it will impact the obsolete LTZ1000 and LM399 buried zener as well as newer bandgap based designs.

Does anyone know about a IC level temperature regulated bandgap?

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 19, 2014, 09:47:44 pm
Does anyone know about a IC level temperature regulated bandgap?

The LT1019 has a 400 ohms heater on board. (Pin7 to GND).
The info is deleted from newer data sheets. But the heater is still there. (see AN42 p 15 figure 66)
The disadvantage is that the heater current has no separate GND return path, so it affects the output voltage.

And unfortunately the metal can case is obsolete.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: rf-design on March 20, 2014, 01:46:36 am
Does anyone know about a IC level temperature regulated bandgap?

The LT1019 has a 400 ohms heater on board. (Pin7 to GND).
The info is deleted from newer data sheets. But the heater is still there. (see AN42 p 15 figure 66)
The disadvantage is that the heater current has no separate GND return path, so it affects the output voltage.

And unfortunately the metal can case is obsolete.

With best regards

Andreas

I guess that the heater is for curvature trimming on wafer w/o complete wafer chuck heating. It is possible be faster or simpler. I think it is not for normal operation because otherwise there should be some temperature control. There are 3 DNC pins which are missing in the schematic. Do you know if the third DNC is connected somewhere?

BR

Reiner

"The LT®1019 is a third generation bandgap voltage reference
utilizing thin film technology and a greatly improved
curvature correction technique. Wafer level trimming of
both reference and output voltage combines to produce
very low TC and tight initial output voltage tolerance."
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 22, 2014, 08:54:08 am
Somewhat off topic, but does anyone know what kind of oil is used in Vishay resistors VHP100, VHP101, VHP102 & VHP103 series (Ultra High Precision Hermetically Sealed Resistor with Almost Zero TCR) or similar products with hermetical sealing?

I know that in some pressure sensor application silicone oil is filled in, but silicone is unwelcome.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 22, 2014, 11:18:33 am
The discussion on Volt-Nuts speaks of "white mineral oil" (purified oil) similar to "baby oil" (without flavor)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 22, 2014, 01:49:52 pm
Quote
The discussion on Volt-Nuts speaks of "white mineral oil" (purified oil) similar to "baby oil" (without flavor)

Thanks, I found that pure mineral oil is available in drugstores, I will give that a try.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 22, 2014, 04:18:56 pm
Since we've been talking about burn-in methods, I thought some of you might enjoy this paper I'm reading now:

http://link.springer.com/article/10.1007%2FBF02504039 (http://link.springer.com/article/10.1007%2FBF02504039)

It talks about Datron's burn-in method for its 4000 calibrator and a proposed 'accelerated' method to get the job done more quickly using "soft thermal shocks".


edit: I'm realizing now that many of you might not have access. PM me if you want the paper.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 22, 2014, 04:54:09 pm
Does anyone have experience with this kind of 'oil': http://en.wikipedia.org/wiki/Krytox (http://en.wikipedia.org/wiki/Krytox)

In some of my reading I've come across the use of this stuff in precision references as a thermal transfer fluid. Its Fluorocarbon nature made me wonder if it was oxygen or water vapor resistant?
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on March 22, 2014, 07:31:21 pm
As I had trouble with the spoiling of plant oil and mineral oil (you smell it..) i went at work to a silicon oil sold in small quantities as modelcar differential oil. It is in a makeshift thermal bath (not cal lab grade). Have a good feeling about that stuff. Vacuum and heat extraction sounds resonable.

Title: Re: Ultra Precision Reference LTZ1000
Post by: SArepairman on March 22, 2014, 08:05:51 pm
Somewhat off topic, but does anyone know what kind of oil is used in Vishay resistors VHP100, VHP101, VHP102 & VHP103 series (Ultra High Precision Hermetically Sealed Resistor with Almost Zero TCR) or similar products with hermetical sealing?

I know that in some pressure sensor application silicone oil is filled in, but silicone is unwelcome.

Vishay Precision Group uses silicone oil when filling their hermetic packages with oil.  How do I know?  I asked them.

Mineral oil breaks down over time and becomes acidic.  I would not use mineral oil for a permanently sealed package.  OTHO-- silicone oil will dissolve silicone rubber compounds, so it may not be compatible, and you may be forced to use mineral oil-- just make sure you leave a way to exchange it.

All of these oils absorb both water and gases.  If you don't want these in the oil, you have to extract them first.  Silicone oil absorbs less than mineral oil, but this may still need addressing, depending on your application.

Vishay Precision Group uses a proprietary method of extracting water and gases from the silicone oil before sealing it in a hermetic package.  [Probably a combination of heat and vacuum].

they may also have more elaborate gimics for gas separation, I imagine that making it "rain" oil in a vacuum environment would help degassing, essentially you want to increase the surface area of what you are degassing. Or maybe just a flat dish..
Title: Re: Ultra Precision Reference LTZ1000
Post by: Blackart on March 24, 2014, 01:06:44 am
Hi Guys Ive been away for a while, just caught up with the thread.

Thanks Dillegent minds for organising the chat with Bob Dobkin... great stuff, to hear from a legend in the field. I contacted Bob Pease a few years ago as he mentioned he still used HP 3400As for noise measurement. I was having trouble with mine as the chopper neons were almost dead. He replied immediately and said he'd discuss it with Jim Williams. A few weeks later I got several hand written notes from Jim ( on graph paper ) outlining mods etc to the 3400A. Its terrific that even blokes at there level can take the time to disseminate their knowledge down the chain to us.

I was interested in the thermal fluid discussion as my refs have arrived ( pron pics attached ) so Im onto the design of the burn in rig. I got some nude vishay foils which I thought I might glue to each other for thermal tracking so maybe a oil bath would also improve matters. I downloaded the MSDS for the Krytox and was a little concerned about the "flu like symptoms" which result from burning it - What happens if the ref developed a shorts etc and fills the room with some horrible toxic smoke film etc. Other alternatives Silicone and white mineral oil seem much better in this respect with Silicon having a hight flash point than the mineral oil. I found the MDDS for the mineral oil on the Vishay site incidentally labelled MM ( the ones that make strain gauges etc ). So I might play with some designs using the oils.

Interesting to hear Bobs idea on the LM399s as I got 10 of them and was planning something like the Pease app note. It will be interesting to compare with the LTZ1000 design. Im way behind a lot of you blokes but plan to get the refs all burning soon. So I can get on with the design of the final units.

Lucas

attachments : Pics of Refs as packed from Linear tech - good and easy to deal with, took about 4 weeks to arrive in Oz.
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on March 24, 2014, 01:37:50 am
... I contacted Bob Pease a few years ago as he mentioned he still used HP 3400As for noise measurement. I was having trouble with mine as the chopper neons were almost dead. He replied immediately and said he'd discuss it with Jim Williams. A few weeks later I got several hand written notes from Jim ( on graph paper ) outlining mods etc to the 3400A. Its terrific that even blokes at there level can take the time to disseminate their knowledge down the chain to us.

Hello blackart, any chance of sharing that information with the forum?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Blackart on March 24, 2014, 08:09:01 am
Robrenz

Sure, I was originally planning on putting it all on a webpage anyway along with other 3400A stuff I've learnt while keeping mine going. However, I had to move house and the mentioned letters from Jim and Bob are still safely stored for upload. Unfortunately both of them died before I could ask them re permission but I would assume its ok now. Ill post to the eevblog forums under another more suitable thread. ( but it may take a while ). PM me if you want my recollections of them sooner. ( I've got 9 out of which 3 are in spec, the rest we sacrificed for the 3 )

Lucas
Title: Re: Ultra Precision Reference LTZ1000
Post by: robrenz on March 24, 2014, 11:29:24 am
Thanks Blackart,  I am in no hurry I don't even have a 3400 yet. I do have a 3410 that I am going to restore.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 24, 2014, 03:18:07 pm

Unfortunately both of them died before I could ask them re permission but I would assume its ok now.


I think you'd be doing the world a service by posting it.

Which reminds me... does anyone know if they donated their "professional papers" to a library or other organization? (e.g. http://spec.lib.vt.edu/scitech/ (http://spec.lib.vt.edu/scitech/) )
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on March 25, 2014, 10:43:42 am
As I said I would do in an earlier post, I contacted Fluke with a letter to Mr. Jeff Gust, Chief Corporate Metrologist, Fluke Calibration.

I got a very kind and helpful answer, and it seems that the Fluke management probably is not willing to actively do anything to facilitate the LTFLU-1 being a product for unrestricted sale. I am not willing to reproduce the email here due to privacy reasons. If anyone wants to read the full email, I will have to seek permission first. But the general information given below is really all there is to know.

Mr. Gust gave the advice to work with LTZ1000 and to pick up used LTFLU-1 devices. He wrote "... there is very little difference between the LTZ1000 and the LTFLU-1.", which is more or less the same as Mr. Dobkin from LT said. Furthermore - and this is all he said:"What makes the LTFLU-1 special is what we do to the product after we purchase it from LT."

Everyone's guess ... I guess. Whatever it is ... - a big "Thank You" to Mr. Gust for a swift and kind answer.
Title: Re: Ultra Precision Reference LTZ1000
Post by: bdivi on March 26, 2014, 11:27:13 am
... there is very little difference between the LTZ1000 and the LTFLU-1.

I cannot understand how LTFLU-1 is similar to LTZ1000.

LTFLU-1 is a 4 legged design which is thought to be a remake of SZA263 from the 70s. These are often specified as Reference Amplifiers and are not ovenized - just a zenner and compensation emitter junction.

Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on March 26, 2014, 11:56:36 am
I do not want to bother Mr. Gust anymore. He was just about to leave for a trip abroad.

I just sent an email to the "Contact us" address on Fluke's website marked "Attention Mr. Jeff Gust, Chief Corporate Metrologist". Anyone can send their questions this way. But as everyone knows - Fluke is not LT ...

To the post over there is nothing to say but: The LTZ1000 is just a RefAmp (even though the configuration of the 6.2 V diode and the tempcompensating transistor is turned "upside down"). But instead of putting the RefAmp in an oven with a thermistor, LT put a tempsensor transistor and a heater element in the same can as the RefAmp.

If the LTZ1000 was in any way far superior - no Fluke box would ever be used to check/calibrate any HP3458A ...

Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 26, 2014, 01:32:04 pm
If the LTZ1000 was in any way far superior - no Fluke box would ever be used to check/calibrate any HP3458A ...

All beers are superior to Bud Lite. But still people drink it. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rigby on March 26, 2014, 01:57:21 pm
All beers are superior to Bud Lite. But still people drink it.

I've seen people get their asses whipped and hospitalized because they WEREN'T drinking Bud Light.  The very one-sided fight was preceded immediately by "Check out that fag and his fag beer!"

Bud Light people could fall off the Earth and I think the world would be at least twice as awesome as it is now.

edit: speeling
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 26, 2014, 02:01:26 pm
Oh-- and he also said that the LM399 should be run at about 1mA of Zener current for best stability.  The more stable you can make the Zener current, the more stable will be the output voltage.  He said that there is about 1uV of voltage change for 1uA of current change.


This is something that's been on my mind since you had your conversation with Bob. We talk a lot on this forum about the zener side of the circuit, but I haven't read a great deal about the current sources for these devices.

I picked up a copy of "Current Sources and Voltage References" (a pdf of which can be found though an easy google search). I'm only half way though it now, but its clear the authors want the reader to understand that (from a circuit design stand point) voltage and current standards are really two sides of the same coin -- its a coupled problem. In fact it might even be proper to say that a Fluke 732 is more a thermodynamic standard than an electrical standard (as the circuit in its totality is comparing concentrations, diffusions, drifts, etc).

I bring the topic up because I am planing a long term drift experiment where a number of zeners (40'ish) are going to be energized for several months -- their voltages being compared every few hours.  And the current source in my design is still an unsolved problem.

Does anyone have any thoughts on this? Do any of the LTZ1000 based references stand out in terms of their current sources?

Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 26, 2014, 02:25:19 pm
Oh-- and he also said that the LM399 should be run at about 1mA of Zener current for best stability.  The more stable you can make the Zener current, the more stable will be the output voltage.  He said that there is about 1uV of voltage change for 1uA of current change.


This is something that's been on my mind since you had your conversation with Bob. We talk a lot on this forum about the zener side of the circuit, but I haven't read a great deal about the current sources for these devices.

I picked up a copy of "Current Sources and Voltage References" (a pdf of which can be found though an easy google search). I'm only half way though it now, but its clear the authors want the reader to understand that (from a circuit design stand point) voltage and current standards are really two sides of the same coin -- its a coupled problem. In fact it might even be proper to say that a Fluke 732 is more a thermodynamic standard than an electrical standard (as the circuit in its totality is comparing concentrations, diffusions, drifts, etc).

I bring the topic up because I am planing a long term drift experiment where a number of zeners (40'ish) are going to be energized for several months -- their voltages being compared every few hours.  And the current source in my design is still an unsolved problem.

Does anyone have any thoughts on this? Do any of the LTZ1000 based references stand out in terms of their current sources?

If you supply the zéner current for the LM399 from its own amplified output (e.g. 10V), by a stable resistor (i.e. 3k, ww., <5ppm/K), this already is a stable current source.

The LTZ1000 circuitry also contains two such intrinsic current sources, one for the zener diode, set up by the stable UBE voltage and the 120 Ohm resistor, and the other one for the collector current, built by the zener voltage and the 70k resistor.
The stability of those sources is already included in the stability calculation in the datasheet, stating 1/100 .. 1/500 of influence from the stability of the resistors.
Similar calculation can easily be done for the above described current source for the LM399H.

So everything is fine, it is not required to use external current sources.

Simply build your circuit that way, there are other, more prominent drift mechanisms than those currents.

If you try to monitor your references, question arises, against which other superior or equally stable source you want to measure?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 26, 2014, 02:37:24 pm


Simply build your circuit that way, there are other, more prominent drift mechanisms than those currents.

If you try to monitor your references, questions comes up, against which other superior or equally stable source you want to measure?



In my case I'm using the LM329 which is just a buried zener. Effects of temperature is what I'm after (77K, 200k, 273k, and 333k). So I'm going to compare them to themselves -- relative drift wrt temp.

My initial plan was to wire them in series using a single current source (~1mA). But that's a fairly non-standard source (280V @ 1mA).
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 27, 2014, 10:21:54 am
Time to join club, first LTZ online.

More details and bunch of photos in my thread. (https://www.eevblog.com/forum/projects/project-kx-diy-calibrator-reference-sourcemeter/msg414092/#msg414092)

Title: Re: Ultra Precision Reference LTZ1000
Post by: bingo600 on March 27, 2014, 07:04:59 pm
I'd like to join the LTZ club , but would need some finished PCB's (2..3)
Does any posters have some surplus boards ie. Branadic or ... ?

TIA
Bingo
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on March 27, 2014, 07:55:10 pm
I might have a leftover possibly, if I didnt give everything to Quarks (It was stuffing a half-used pcb panel and had some overproduction)

EDIT: No, sorry, no leftovers.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 27, 2014, 08:56:02 pm
I'm not in the LTZ but in the LMx99 club, that's fine for me up to know.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 27, 2014, 10:57:25 pm
I want to see the LTZ design that uses hot glue, bailing wire, and tar paper. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: bingo600 on March 28, 2014, 06:26:21 am
I might have a leftover possibly, if I didnt give everything to Quarks (It was stuffing a half-used pcb panel and had some overproduction)

EDIT: No, sorry, no leftovers.

@babysitter
Damm  :'(

Any other ?

/Bingo
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 28, 2014, 07:41:46 pm
Anyone see anything fishy here:

http://r.ebay.com/FY1E33 (http://r.ebay.com/FY1E33)

http://r.ebay.com/mZh1JL (http://r.ebay.com/mZh1JL)


I feel bad for the guy that bought the second unit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: codeboy2k on March 28, 2014, 08:34:32 pm
Anyone see anything fishy here:

http://r.ebay.com/FY1E33 (http://r.ebay.com/FY1E33)

http://r.ebay.com/mZh1JL (http://r.ebay.com/mZh1JL)


I feel bad for the guy that bought the second unit.

Batteries dead.  No In-Cal light ...
an expensive recalibration in the future :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 28, 2014, 09:19:40 pm
Anyone see anything fishy here:

http://r.ebay.com/FY1E33 (http://r.ebay.com/FY1E33)

http://r.ebay.com/mZh1JL (http://r.ebay.com/mZh1JL)


I feel bad for the guy that bought the second unit.

Batteries dead.  No In-Cal light ...
an expensive recalibration in the future :)


I'm talking about the fact its the exact same auction: copy and pasted. One seller is a surpluser, the other is a brand new ebay member with zero feedback. 

Note to self: make thousands running fake ebay sales of precision references.
Title: Re: Ultra Precision Reference LTZ1000
Post by: codeboy2k on March 28, 2014, 09:35:41 pm

I'm talking about the fact its the exact same auction: copy and pasted. One seller is a surpluser, the other is a brand new ebay member with zero feedback. 

Note to self: make thousands running fake ebay sales of precision references.

yes, that does seem rather fishy..  Although I didn't notice it at first as you did.

I think those final prices are a little high for an out of cal unit, though. More like I want to pay just $300. :)



Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 29, 2014, 02:02:44 am
  The calibrations of this thing are very overpriced by Fluke-- so much so that I can't afford it, and am looking for a hobbyist friendly way to get it done.


Besides Fluke uses the "Canadian Volt"... which I think is 2/3rds English and 1/3rd French?
Title: Re: Ultra Precision Reference LTZ1000
Post by: ManateeMafia on March 29, 2014, 06:31:50 pm
Anyone see anything fishy here:

http://r.ebay.com/FY1E33 (http://r.ebay.com/FY1E33)

http://r.ebay.com/mZh1JL (http://r.ebay.com/mZh1JL)



I feel bad for the guy that bought the second unit.

Batteries dead.  No In-Cal light ...
an expensive recalibration in the future :)


I'm talking about the fact its the exact same auction: copy and pasted. One seller is a surpluser, the other is a brand new ebay member with zero feedback. 

Note to self: make thousands running fake ebay sales of precision references.

It's possible that eBay [or PayPal] security will stop this transaction before any money changes hands-- since they are liable to restore the buyer's losses [well, most of them anyway].

If something seems too good to be true, it probably is.  I bought my 732B from a dealer.  The calibrations of this thing are very overpriced by Fluke-- so much so that I can't afford it, and am looking for a hobbyist friendly way to get it done.

Good luck to the buyer. I noticed it the day it showed up and reported it to eBay as a potential fraud.
eBay does not care and they will not allow you to state why it is a potential fraud. The fact they do not reply and ask for further information proves they only care about making their quick buck.

Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on March 29, 2014, 06:40:29 pm

Good luck to the buyer. I noticed it the day it showed up and reported it to eBay as a potential fraud.
eBay does not care and they will not allow you to state why it is a potential fraud. The fact they do not reply and ask for further information proves they only care about making their quick buck.

I did the same thing. As you point out... a lot of good it did us.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Rigby on March 29, 2014, 08:59:40 pm
Caveat emptor.

Also if you're paying with PayPal you have some protection there, if you're quick enough.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 02, 2014, 03:07:56 pm
http://www.sciencedirect.com/science/article/pii/S0026271401002517 (http://www.sciencedirect.com/science/article/pii/S0026271401002517)

Quote
In this paper, an accelerated life test and noise measurements during the test for subsurface Zener diodes are carried out. The correlation between the reference voltage degradation and the 1/f noise in the devices is analyzed on the test data, and the physical mechanism leading to the correlation is discussed. In addition, a reliability screening approach using 1/f noise measurement is proposed.

PM if you're interested.
Title: Re: Ultra Precision Reference LTZ1000
Post by: JBeale on April 02, 2014, 04:14:38 pm
Right now there are 4 sellers of LTZ1000 on eBay. Two of them, Polida and yankee_electronic claim new and use the same generic pic from web. Polida is just bulk part seller, I've seen few comments that people got fake parts but can't say for sure, I'd say both of them are questionable as they don't even have the real photo. Other two, hifi-szjxic and bbshonic, sell used and they claim 100% tested. bbshonic even "Gurantee exchange if it is fault" and have some history of selling them.
FWIW, I purchased four used 0.01% 10k resistors from hifi-szjxic in 2012 and as far as I can tell, they are as claimed. The values are consistent but I don't have an absolute reference standard to compare with. I assembled the four into a full bridge and with 10 V excitation, measured an imbalance of 0.1 mV so the ratios of those two pairs are mismatched by 0.001% or 10 ppm.

(edit: oops- confused about the date; didn't realize that post was more than a year old)
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 02, 2014, 04:26:07 pm
Right now there are 4 sellers of LTZ1000 on eBay. Two of them, Polida and yankee_electronic claim new and use the same generic pic from web. Polida is just bulk part seller, I've seen few comments that people got fake parts but can't say for sure, I'd say both of them are questionable as they don't even have the real photo. Other two, hifi-szjxic and bbshonic, sell used and they claim 100% tested. bbshonic even "Gurantee exchange if it is fault" and have some history of selling them.
FWIW, I purchased four used 0.01% 10k resistors from hifi-szjxic in 2012 and as far as I can tell, they are as claimed. The values are consistent but I don't have an absolute reference standard to compare with.

(edit: oops- confused about the date; didn't realize that post was more than a year old)

Got a link?
Title: Re: Ultra Precision Reference LTZ1000
Post by: cyr on April 02, 2014, 04:40:13 pm
http://stores.ebay.com/HIFI-AUDIO-IC (http://stores.ebay.com/HIFI-AUDIO-IC)

I bought some used 0.01% vishay resistors from the same seller a year or so ago as an experiment. I mounted them om dual banana plugs and measured them on the 8508A at work:

1k - 1.000101k
10k - 9.99986k
100k - 100.0074k

Title: Re: Ultra Precision Reference LTZ1000
Post by: Blackart on April 04, 2014, 04:37:35 am
Thermocouple accuracy
After reading that Datron ageing paper ( thanks CaptYellowShirt ) Ive embarked on a oven to thermally work my refs & resistors for use ( and final ref boards ). To that end I've decided to build a automatic oven to do the c110 C ageing. The first step was to get some reliable temperature readings. I had 5 off new type K thermocouple made with "nude" i.e. welded and unprotected ends. Then hooked them up to a HP 34970A mix data acquisition unit. Then mounted the thermocouples in contact with a large block of copper. The first surprise was just how temperature sensitive they were even walking around workshop would show up as temperature disturbances. So I wrapped up all the sensors in a sealed plastic bag and further insulated them. The result is a on the graphs below called RAW data. Yo can see 100 readings at 30s intervals. Note almost 0.3C variance of the thermocouple all off the same real of with made in the same batch. I then applied calibration factors and re ran the test. As you can see in the next graph they are all pretty much in aggreance. I might further tweak TC#5 down abit. NB I have not calibrated these absolutely just to each other. I wanted to be sure they all drift at a similar rate.

Note the rise at 550s is me closing the workshop door by about 200mm ! Allowing the room to heat a bit.

I think I/we can be fairly confident that the thermocouples are good enough to use in the oven and for further a characterising of the Refs after I build them. I what to have consistency in the equipment through this process.

Lucas
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 04, 2014, 09:40:11 pm
Does anyone have experience with this kind of 'oil': http://en.wikipedia.org/wiki/Krytox (http://en.wikipedia.org/wiki/Krytox)

In some of my reading I've come across the use of this stuff in precision references as a thermal transfer fluid. Its Fluorocarbon nature made me wonder if it was oxygen or water vapor resistant?

Hey, good find!  If I had to hazard a guess, I would have to say that it is at least water-vapor resistant.  The fluorocarbon family of compounds is the only thing I have found that is 100% water-vapor proof, but I don't know if that extends to Krytox.  It's always best to go right to the source-- ask your Dupont FAE directly, [and post the answer here please!]

They didn't have data on water vapor, but they did have it for O2 and N2 solubility at 20degC....

O2: 218 ppm
N2: 123 ppm

The rep said hydrocarbon oils are typically in the range of 1000-2000ppm for O2.

No permittivity data was available.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on April 05, 2014, 02:21:31 pm
Thermocouple accuracy
After reading that Datron ageing paper ( thanks CaptYellowShirt ) Ive embarked on a oven to thermally work my refs & resistors for use ( and final ref boards ).

...

Lucas

Thanks to Brandon, I also read this interesting paper.

Anyhow, I still disagree to try to pre-age the LTZ1000, or hermetically sealed, oil filled metal foil resistors, if you use them for the reference.

The paper describes the fast ageing of 1N829 zener diodes, which are used in the Datron 4000, but definitely NOT the LTZ1000, which sits in the Datron 4910!

The big difference is, that the LTZ1000 already has such a small typical drift (1ppm/yr.) from the beginning, that further ageing makes no sense.

The 1N829 have typically 20 ppm/yr, and may be stabilized by that method to  a drift level where the LTZ begins.

The LTZ on the other hand shows strong hysteresis of several ppm, if its chip is heated to high temperatures as 110°C, which may lead to a strong creeping drift behaviour in the following years.

Therefore, a heat shock leads to a less stable reference.

Same goes for metal foil resistors, the oil filled types have such low annual drifts, (and also hysteresis) that any heating will have negative influence on stability.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on April 05, 2014, 03:23:32 pm
Excuse me for being not a expert isn't comparing those physically quite different devices a bit unfair, subsurface Zener Diode in the LTZ vs. 1N829 which I consider a stacked-cylinder-Design with surface effects ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 05, 2014, 04:04:08 pm
Hm, I have a questions to ones who have LTZ's running.
Any one used "bad" resistors with tempco 25-50ppm/C ?

Since I'm still waiting on proper resistors, I built one LTZ ref to try, and seeing
big voltage/temperature drifts over time.

Like in attached log.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on April 05, 2014, 04:22:01 pm
All of my old LTZ references were based on the "bad" wirewound MRH resistors with 15 ppm/C tempco (max) and metal-film S2-29V with up to 50-100 ppm/C (max). All have a typical datasheets specs without any problem.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 05, 2014, 04:22:55 pm
What are the two temperature columns?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 05, 2014, 04:32:44 pm
There was Honeywell Pt1000 RTD HEL-705 and MAX6610 in deadbug position superglued to top of LTZ can.
So 111 is RTD temp and 902 is calculated MAX6610 temp (T = Vout - 0.75V / 10mV).
Whole board was put into small cardboard package box and wrapped with 2 layers of packaging bubble-wrap.

(http://xdevs.com/kb/kx/vref_a01/small/hel_zener.jpg)

Also what is current consumption of your references?

Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 05, 2014, 05:16:31 pm
Ah I see now. Thanks.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 05, 2014, 06:22:15 pm
Since I'm still waiting on proper resistors, I built one LTZ ref to try, and seeing
big voltage/temperature drifts over time.

Since the resistor tempco is divided down by a factor of around 100 to the 7V output it is evident that you should have at maximum around  some 10uV change.
Do you use a switchmode power supply?
Try to use batteries.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 05, 2014, 08:53:13 pm
I used KI 2400, which is kinda switchmode.
Need to find battery which can hold 50mA 15V for quite a time first...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 05, 2014, 10:07:38 pm
I used KI 2400, which is kinda switchmode.

Does the output voltage change when you put your hand over/on the reference or
the power supply or the DMM?

Perhaps 2*100nF capacitors between base + emitter (short!) of the LTZ-Transistors will give a little improvement.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 05, 2014, 11:47:14 pm


6) After telling him that I wanted a voltage transfer device, he said a better way might be to use [at least 6] LM399's in parallel [like the Bob Pease idea].  He said that the burn-in procedure would be to operate these in an oven set to 125C for 2 weeks, which would be equivalent to 1000's of hours of normal operation.  Any LM399's that are drifting too much after that can be replaced [i.e., you burn-in more than you need, and select the best units for the array].  The LM399 is much more sensitive to board stress than the LTZ [because the LTZ has a special mechanical arrangement in the die mount]-- so the LM399 should be mounted off of the PCB a little bit to allow for this.  The long term stability of the array of LM399's will be directly related to the power required to run the heater-- and this can be minimized with insulation-- the more the better!  The LM399's do not age when they are turned off, and have almost no hysteresis-- so keeping the reference *off* until a few hours before you need to use it [and/or calibrate it] is the best way to keep the long-term drift minimized.

7) Note that for LM399-based designs, the slots in the PC board [plus a lot of insulation top and bottom] make sense-- Bob said that the less power the heater requires, then the more stable the output voltage will be.  So, in this case, the slots [plus insulation] are helping with this.  Oh-- and he also said that the LM399 should be run at about 1mA of Zener current for best stability.  The more stable you can make the Zener current, the more stable will be the output voltage.  He said that there is about 1uV of voltage change for 1uA of current change.


I'm running a small experiment to test these two ideas in another thread. I'd love to get some peer review on my thoughts (especially the math section).

https://www.eevblog.com/forum/projects/long-term-lm399-stability/msg419452 (https://www.eevblog.com/forum/projects/long-term-lm399-stability/msg419452)
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 13, 2014, 07:32:26 pm
A few weeks ago there was a discussion on this thread about the effects of humidity on the Fluke 732a/b.

I'm reading a paper (http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=377817 (http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=377817)) that discusses these humidity effects on a set of 732a's. The paper claims that humidity effects the 1.018 v output -- around  - 1uV /  + 10% change in relative humidity and time constant in the 20-30 day range.

However, the paper claims there is no detectable change on the 10 v output.

The authors seem to imply that the change could be a product of the 1.018 v voltage divider or internal leakage paths.

For those of you with a 732 (or similar), what can you say about this? Seems weird to me that one would change and the other wouldnt?
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 13, 2014, 07:52:46 pm
The cited paper on the physics of moisture effects is here:


"Moisture solubility and diffusion in epoxy and epoxy-glass composites"
http://domino.research.ibm.com/tchjr/journalindex.nsf/0b9bc46ed06cbac1852565e6006fe1a0/0521bda5a94455f085256bfa0067f5f7 (http://domino.research.ibm.com/tchjr/journalindex.nsf/0b9bc46ed06cbac1852565e6006fe1a0/0521bda5a94455f085256bfa0067f5f7)!OpenDocument

 
Anybody here work for IBM?
Title: Re: Ultra Precision Reference LTZ1000
Post by: acbern on April 13, 2014, 07:59:47 pm
the problem is that although I have a 732a and a 4910, I cannot really tell which one is drifting when, unless i would correlate to an external standard. too expensive.
the only other way to test would really be humidity cycling, one against teh other. have no chamber either.

however, I have done some general tests on precision resistors (z-foil, highest grade, not hermetic) agains an hermetic one (said to drift by less than 0.5ppm/a by vishay). within a year, a 1k drifted by 10ppm, a 100k drifted by 3.4ppm (assuming a stable 10k hermetic). both reduced their resistance values. that also is in line what vishay states and mostly related to humidity influence, hence the hermetic versions. oxigen seems oi be of minor importance. vishay also states the effect is reversible.
not having disassembled my 732a, maybe the anser is to check the different resistors used. now probably they are not vishay, but may be a first indication.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ManateeMafia on April 13, 2014, 09:58:02 pm
I have a couple of pics of the reference board inside one of my newer rev 732A. I replaced the 10V pot and thought I should take some pics. These were taken a year ago.

I apologize for keeping these to myself for so long.

These were taken as a visual aid for reassembly of the oven and to note some of the design details not shown in the schematics.

The second picture shows the four resistors used in the 1V and 1.018V dividers. I believe these were a rev to the original design and I don't know what prompted the change.
Perhaps the sensitivity to humidity may have been a factor?

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 14, 2014, 09:25:20 pm
I want to refresh the discussion about the substrate. I already mentioned that LTCC could be interesting, but is that really the case? I reviewed a few datasheets. As always, units seem to be a real problem for some guys :)

Isola IS410
Thermal Conductivity: 0.5 W/mK
Coefficient of Thermal Expansion X, Y: 13 ppm/°C (Post-TG)
Coefficient of Thermal Expansion Z: 250 ppm/°C

RO4003C
Thermal Conductivity: 0.71 W/m/°K @ 80°C
Coefficient of Thermal Expansion X: 11 ppm/°C (-55 to 288°C)
Coefficient of Thermal Expansion Y: 14 ppm/°C
Coefficient of Thermal Expansion Z: 46 ppm/°C

9K7 GreenTape
Thermal Conductivity: 4.6 W/m-K
TCE, (23° - 300°C): 4.4

951 GreenTape
Thermal Conductivity: 3.3 W/mK
TCE, (25° - 300°C), ppm/°C: 5.8

A6M
Thermal Conductivity: 2 W/mK
Thermal Coefficient of Expansion: 7 ppm/°C

L8
Thermal Conductivity: >3 W/mK
Thermal Coefficient of Expansion (25-300°C): 6ppm/°C

So for what I see, the use of more available RO4003C instead of expensive LTCC could be worth a try. It has better thermal conductivity (good for all pins on same temperature) and smaller TCE. LTCC would be quite better, but on what price?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 15, 2014, 05:10:47 am
Hello branadic,

kovar has a TCE of around 5.9 if I found it right.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 15, 2014, 07:11:08 am
 I've been following along here on the LTZ1000 reference discussion for a few months - this is a really great forum and the best discussion I've seen on LTZ1000a!

I've built several hundred of these over the years for specialize production test equipment on laser diode/detector fab lines - and so far we've never had an issue with using just wirewound resistors (3ppm units typical, some have 1~2ppm parts for the 120 ohm resistor), no slots or gimmicks, lots of copper on a small board and put the ref board in a can, and use a linear pre-regulator.  I promise you that the units in the field for 20 yrs have gotten very, very stable, and drift rates of less than 1ppm / yr are really pretty typical. LTZ1000a devices, and we did some LM199 / 399 also (those are very good also) .  No voodoo. 12.5k over 1k WW for heater circuit, and everything basically as in app notes.   The only boards we had trouble with were when we bought the expensive hermetic magical Vishay resistors - Dr Franks discussion on the hysterisis effect has been our experience also, if the temp gets too warm especially - they will take quite a while to recover.    The Vishay's worked OK but were never worth the extra expense (at least for us). The regular wirewounds - and heck the 5/ 10 /20 ppm surface mounts work fine also if you have reasonable temperature control.  Unless you're running the ref outside, you should have good results with even moderately good resistors.  We've tested the expensive resistor-parts units, and after a 5 & 10 & 15 year tests we're reminded how optimistic Vishay's datasheets are.  LT1013 for the op-amp, we've never had trouble with - plastic package or metal TO in the early days. Humidity has never been an issue for us since our boards are running in a humidity-controlled environment anyway in the clean rooms.  We've never really had any of these refs fail outright, and the older they get the better they are, and its really amazing how well they hold up over time.  Kind of like me (I wish)  :-DD

And then tonight I stumbled across this -   We've been doing it  all wrong all these years...

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=261407717248 (http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=261407717248)

What could go wrong?  I asked the seller what the drift rate per year is, and he says you don't need to keep it on - its always good and it never ages... But you don't want to keep it on a lot...  He says he had an Electrical Engineer with 40 yrs experience look at it and was astounded at the results!  I see he's sold 4, as of tonight. 

Thanks again Dave & Co. for the great forum and discussion!


Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 15, 2014, 03:35:12 pm
He says he had an Electrical Engineer with 40 yrs experience look at it and was astounded at the results!


Hmm... only 40 years of experience? For my money, his imaginary friend would need at least 41 years.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 15, 2014, 05:24:07 pm
I would be astounded too, if it works.  I was almost going to buy one for fun, then I realized I had better use for the time & money.  I also asked what the load regulation was, and no answer from seller yet.

I think I'll stick to stuff I know works, and works well for a long, long time.  Like Buried Zener refs.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 15, 2014, 10:24:08 pm
This might not exactly belong in this thread with LTZ1000a's (except to do a direct comparison about vrefs for general knowledge), but this is the seller's response when I asked about drift rates on his  ebay device.  I'm not even sure I can understand it.  It might be a pot attached to an LM317 for all I know. I think he's convinced himself its better than a 732a:

Quote
We do a burn-in to minimize drift. These units do not need to be run continuously like a Fluke 732A/B. So, the drift over time is not coherent. These units have a specified drift per first 1,000 hours of use (~10ppm, and much less for the second and subsequent 1,000 hours). They require roughly five minutes to settle to maximum accuracy. As long as the unit is not powered on for extremely long periods (250 hours or more), it should hold the standard indefinitely.

The stability is greater than the maximum error of the 732A. In the null setup photo, the unit drifted from +3uV to -4uV. -4uV was the maximum error in relation to the 732A. The 732A has a maximum error of 0.6ppm, which @ 10VDC is 6uV. So, the maximum error of the unit using the 732A as a reference is 10uV. We spec the unit @ +-75uV, because reference standards require integrity and reliability. We may change that spec when we have more experience with the units.

We have an electrical engineer with forty years experience, conducting R&D on special mock-ups of this device, and the results have been astounding. But for now I'm sticking with the original spec of +-75uV. But the temperature at calibration is marked on the each unit. If this temperature is observed, the accuracy is in excess of 10x the official spec. Our testing has shown that the units are unaffected by repeated power ups. The drift is in relation to cumulative hours of power-up
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 15, 2014, 10:28:31 pm
There's nothing to understand. Its just double speak and audiophoolery.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 15, 2014, 11:26:21 pm
Maybe we should offer an independent test? Intercompare it with our standards?
Title: Re: Ultra Precision Reference LTZ1000
Post by: jd on April 16, 2014, 12:11:00 pm

3) What is the voltage reference inside the box?  Is he not saying because it would be embarrassing?  Is it a voltage reference with a non-hermetic package?  What is the temperature coefficient [TempCo]?  Is the TempCo compensated?  What is the hysteresis of the part if it experiences radical temperature excursions during shipping?

Hi,
The listing "item specifics" says that it is a LT1021-10. So one of those in a little plastic box I guess.

JD
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 17, 2014, 02:04:19 pm
...or keep the plastic Vref package at constant temp, and give it a jacket of Tfe coating, then its impervious to the local weather.  That helps for just about any Vref.  Most of the stuff on eBay just isn't built that carefully.

The plastic package absolute Vref can sometimes be used for precision work to -some- degree -  IF its really the same die inside (as metal version), and you have good thermal management & humidity control- which normally we do anyway.  We do that on all Vrefs to give them the best chance, and when we build a box with multiples for averaging calibrators - say 35 vrefs in one temperature-controlled box - each Vref circuit or Vref group is replaceable as its own module.  You can spot the drifters that way.  But you have to keep an eye on them - if you have a wonky drifter in the group that's not playing well with the other Vrefs to contribute to a low-noise average, he has to go.

The reason we have to use plastic package Vrefs sometimes is the availability on the Metal cans means kind of a long wait for production, and sometimes we can't do that.   Sometimes a customer can't wait, and we're forced to use plastic - and take all the precautions.

Regardless of plastic or metal package, the big trouble with any absolute ref on a die is they tend to drift -much- more over time than a well-built, stable LTZ1000a / LM399.  The LTC6655 does pretty well (for an absolute ref) , although we don't have any to test for 10yr drift - yet.

Sorry for the thread interruption - back to the good LTZ1000a's...




 
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 17, 2014, 02:14:30 pm
Dr. Frank has discussed the effects of heater set-point temperature on the LTZ1000's drift rate. A lower temperature results in a lower drift rate, however I am wondering about the long-term total drift between a 'hot' and 'cold' LTZ. Will they end up with the similar amounts of total drift over the course of many years -- temperature simply affecting the rate at which they asymptotically approach that point? Or will a higher temperature tend to diverge in total drift when compared to a lower temp reference?
Title: Re: Ultra Precision Reference LTZ1000
Post by: acbern on April 17, 2014, 02:40:26 pm
I was wondering the same, and have nowhere seen any comments/tests. In general, higher temp means faster aging, a simple law of physics (arrhenius law). aging means drift. that is in line with the temp setting observations of the 3458a ltz1000. of course, always, there are additional effects. the ltz, according to the data sheet, needs some time to settle and decrease in drift rate. and of course, there are more and less stable devices. it is beyond me why a 3458a opt. 2 may or may not be powered and still meet its accuracy while all precision references must be on. also, this is a little bit like saying if you have a precision test equipment, keeping it on is better. in my experience, the opposite is the case. of, course, not the exact same thing, and not as simple as that, but anyway.
it woud be worth while doing a test with a set of ltz1000, keeping them on initially until stabilized per data sheet, determining their drift rates, and then switching some off. i bet there is not much difference, maybe the ones in off-state are even more stable, given their initial drift is already over.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 17, 2014, 05:50:54 pm
Digilant makes some good points, but there other factors too.  The drift story actually begins much earlier in the manufacturing process.

One of the huge mechanisms affecting initial drift rates happens when the die is separated from the wafer - the more energy and stress that's put into dicing the wafer into individual chips - this can cause larger fluctuations in the inertial crystal lattice strain, especially near the chip edges.

Once the wafer is diced, each chip now has to distribute the newly created edge strain around each newly formed faces on four sides - and whether this happens from the wafer saw, diamond scribe or laser scribe process will affect the crystal lattice - and thus electron migration properties.  The crystal lattice can not be the same near an edge as it is in the main body of the die.  So just the fact that the chip is separated from the original wafer starts the stress drift process from the exact moment it is born.

If the die has rough, dusty edges that means it has a lot of stress raisers that will affect all electrical properties as it heats.  Some of this we can't control, and is just the physics of the substrate itself.  Some die will work better because they were handled better or the original substrate batch was easier purified.  At every step the variations are minimized, but in the end each substrate batch is slightly different, and therefore so is each die.  It is just the nature of the beast.

For instance:  You can measure a diffused resistor in a circuit while the die is in company of all its neighbors on a wafer, while its all one piece.  Now dice the wafer into chips by whatever process, and then temperature cycle to help re-distrubute stress.  Those resistors (especially on die that were originally near the wafer edges) will now have different properties - because the substrate they sit on has now been altered.  The die near the edges of the wafer will change differently than the die near the center, and so on.  Also, how these chips re-distribute the stress created by making lots of new faces is also time variant - so some die will relax faster than others.  Wherever there is a change of crystal lattice, you have strain - and strain is everything.  All properties of the lattice - both electrical and mechanical - are changing in areas where the substrate lattice is stressed.

On some substrate materials, like those used for laser diodes (say InPh. GaAS, etc), we can cleave the edge onto a near perfect lattice plane, and that in itself produces a crystal edge with fairly low stress and strain - and is fairly stable as it heats and goes through billions of high-range temperature cycles.  But these substrates do not lend themselves to making particularly good buried zeners.

Then there is the die attach and wire bonding process:  Each of these can put an additional strain on the substrate crystal lattice - some of which can be controlled, and some that can't. 

If you try to make an absolute reference and use a laser to trim resistors on a chip - you also just changed the lattice strain again from the laser heat.  And guess what:  Now the device will behave and drift just a bit differently than every other chip in the batch.  That's one of the reasons absolute refs drift much, much faster than buried zeners. 

Realize that when a wafer is separated and during the wire bonding process, there are regions of the substrate lattice that are liquified for a very brief  instant, and the freeze again into a crystal or can even change into an amorphic region in some cases.  This event can form a new crystal plane depending on the cooling rate; and if its not in perfect alignment with the main substrate, you have a new area of stress.  You can't get away from it.

All of the above effects can be measure acoustically and with Atomic Force microscopes.  You can measure the crystal planes and internal stress pretty accurately, but you can't really cure lattice plane troubles once its in the chip.  You have to minimize these effects during manufacture - and that's the hard part.

What you have to realize when you're building a good Voltage Reference:  You aren't building a voltage reference at all.  You want to build a very in-sensitive thermometer out of something that at atomic scales is really as unstable as "Jell-o" when you look at it close enough.  Getting a steady, non-drifting voltage out of the device is just a by-product of how much of a "bad thermometer" it is.  In other words - everything in the die is related to how electrons move through the lattice, which is all related to heat and stress.


 
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 17, 2014, 07:25:10 pm
... how these chips re-distribute the stress created by making lots of new faces is also time variant - so some die will relax faster than others.  Wherever there is a change of crystal lattice, you have strain - and strain is everything.  All properties of the lattice - both electrical and mechanical - are changing in areas where the substrate lattice is stressed.


This is the conclusion I'm starting to come to though my academic reading.

I'm surprised that there isn't more written on the topic. I have found tons of material on the reliability of semiconductor technology (including zeners) with respect to conditions that lead to complete failure. However,  I've found very little on the subject of drift. The literature shows me: 1) that it does happens, 2) when it happens, 3) how to predict it happening, and 4) how to correct for it. But I'd like to know more about the underlying causes of it.

I'm familiar with the relationship between band structure and strain. Are there any books or papers that deal with the 'art' of semiconductor production -- specifically dealing with stress, creep, and band structure interaction?
Title: Re: Ultra Precision Reference LTZ1000
Post by: rf-design on April 17, 2014, 07:48:26 pm
If all aging is because of stress change, either from die internal stress or from die external stress from the adhesive die attach what would be the impact on the final reference voltage?

To my knowledge the stress changes the bandgap voltage. That would impact the final temperature point because the regulator is based on Vbe. But up to now I do not know a direct effect of stress on the zener voltage.

Is there a significant effect on the buried zener?
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 17, 2014, 08:29:02 pm
Capn': At the company I work for we build some of the equipment used to dice wafers into individual chips, and especially laser diodes, and we solve problems like these for manufacturers.  What we tend to see are the guys on the production line that notice these drift effects on analog (and sometimes digital) circuits, but sometimes the design engineers laying out the circuit masks are half a world away and don't really get to see the hands-on interaction of what's -really- happening at chip level production.  And the Fab line won't talk to Engineering, &  vice versa. And the bean counters just want good sales, not necessarily good parts, so good engineering investigations (that take TIME) don't get rewarded very well. Not all the time but we see it a lot - just how big corporations tend to work.  Sometimes people want to just come to work, push some buttons, get paid, and go home. 

Granted, when you're working at the wafer / chip level you can't even see what you're working on without a microscope - but you -can- study these stress & drift effects.  Its like working with PCB's except much, much smaller.  With a wafer prober, an acoustic microscope (these generate say 1Mhz mechanical waves that we inject sideways into the wafer to watch for reflections - i.e. stress - in the whole wafer) and generally an Atomic Force microscope, where we scan the wafer surface and look for out-of-place crystal planes buried inside the wafer - again this translates to strain & stress in the crystal.  Almost always this will turn up later as a drifting analog circuit later on.

I been at a facility, training people on a new piece of equipment, and they will put on a wafer to dice up into chips - mind you nobody knows what it is, because Engineering didn't tell them.  But I can look at the chip and tell them "Uhh these resistors / transistors / diodes that are over here right on the edge of the die are probably going to be trouble. Just sayin'".... and sure enough in a few weeks after they get 98% rejection during test the production circuit mask gets changed.  That's happened more than once - but it shouldn't happen very often.

What's frightening is the new designers just starting out that lay out masks - and blindly trust what the CAD software produced.  You have to really look at the whole circuit / wafer / die as a whole system, then build some, then test & tweak - no CAD software is a substitute for hand's on experience.  Sorry, Mentor Graphics. 

And strangely enough, you can't Google the answer to some of these questions - you have to go in the lab and study, test, and re-design sometimes until it works.  And the bean-counters really, really hate that... <Laughing!>
Title: Re: Ultra Precision Reference LTZ1000
Post by: quantumvolt on April 17, 2014, 09:40:18 pm
@MisterDiodes

Allow me to say that I really like your posts. They have a certain flavour of theoretical knowledge mixed with hands on experience.

There is a picture of the internals of LTZ1000 in this thread (and on the web). Could you and/or others who feel competent, give us an introduction on how to 'read' it?
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 18, 2014, 12:35:49 am
My favorite sign on my office door - someone gave it to me and its floating around on the web - and I think this is a good description if the this whole thread - and in particular ultra precision voltage refs:

"Where Theory Ends and Reality Begins"

About looking at Die Photos - very,very short story - :
Usually the manufacturers get really upset if you publish a highly detailed images and description of their complete mask pattern - and Linear Technology, Intersil, Analog Devices, etc. are our friends, so its probably best to not go into high detail here. That is their IP.

For Fun: Generally when you're looking at an analog die in the microscope (much easier with your eyes, not a video or photo), anything gold or pink-ish or borwn-ish gold is a conductor.  It depends on what metal was deposited on the die for conductors, and there are myriad combinations.  Sometimes you see where conductors cross and you can make out the insulator (or resistor) between the conductors.  On RF devices it is not uncommon to see square coil structures or waveguides, and sometimes these will have a delicate Air Wire crossover - where you literally have conductor lift up and over another conductor like a freeway overpass - and there is nothing but air in between - a matter of a few microns or less sometimes.  At high frequencies that crossover is also acting as a capacitor or virtual inductor too.  Terminology varies by manufacturer.  But typically you won't see these on Vrefs.

Remember also - when you're looking at a die, you're only looking at the top layer.  If you're doing a real investigation, you can etch away the various deposition materials, and go down into the die layer by layer.  But you can usually get a general idea by looking at the top.

Resistors can be darker brown / black, or will appear yellow or dull grey (for deposited foil).   Its good to use vertical illumination on the microscope so you can really see the contrast (generally not a ring light here) and detail, and you want adjustable zoom.   Follow the path from the wire bond pad, have the schematic in hand and start tracing - and don't forget the substrate is part of the action also - or not.  Depending on how the device is made the substrate can be a 100% insulator, or if its been doped it can be a diode junction to ground, or what they generally call "backside metalization", which would be metal (usually sputtered aluminum / gold but can vary) on the bottom of the device.  Its easier to tell when you're looking through a microscope directly because you can change the light / focus and get an idea of what areas are taller / shorter.  You can usually see larger fets and BJ transistors - some can be pretty hard to see without going to high magnification.  Out at the very edge of the die you can see what's called the "Scribe Street" or "Wafer Channel" and this is usually where you can see the surface of the substrate itself, before it had the circuits masked on more near the middle of the die.

If you have a stereo scope with a Nomarski filter / illuminator system, you can see flat surfaces in sharp detail and high contrast - for instance if you're looking at the edge of the die, you can tell how it was diced apart from the main wafer.   Its in the Channel where the device was separated from its neighbors, and how rough or chipped out that side face is tells you how well the dicing process went that day (think like your looking at a bullet's rifling pattern or the edge of a sawn wooden board)) - and the Nomarski will really bring that detail out.  If we see chips that had a lot of trauma on the edges - something was either wrong or the channel had some sort of grey nitride passivation applied, which is a real challenge to separate - because its almost as hard as diamond.

The heater resistors will probably a pattern of a zig-zag repeating pattern back and forth, and judging by the simplified schematic on LTZ1000a's these are probably diffused into the substrate itself, without an insulating layer -  that's why there is a "diode" junction circuit between them and down into the substrate proper.  That is just an educated guess though.



Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 18, 2014, 01:41:16 am
For those of you who haven't seen the pictures...

We can thank our Russian and Chinese counterparts for posting them.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 18, 2014, 04:00:30 pm
The structure in the center is the Zener, where it should be, surrounded by the heaters.  Of even more interest to drift studies: In the larger monochrome photo you can see the die edges.  They are fairly rough, and characteristic of what happens when silicon is sawn.  This isn't too bad, but realize at each of the those chipped out places is a spot where the die will be -very- highly stressed during heating / cooling.  Normally this isn't a huge issue for most circuits, but when we're shooting for sub ppm..."everything" makes a difference.  Again, the crystal lattice can not be the same at the edges as it is on the interior of the device, so the more edges there are, the more stress in that region of an edge (this wafer has ~millions of small edges on each side face).

Short Story: If we were to measure that die acoustically, say transmitting at some Mhz from the left edge to the right edge (without any circuit placed yet) - we would see an echo ping that would measure say maybe 3/4's the way across the device.  The sound wave going left to right would reflect off the edge stress discontinuity region in the crystal lattice, not the actual right edge - and then travel back to the left edge - and by timing the arrival of the reflected pulse we can tell how much of the die is actually acting as single crystal.  The speed of sound through the material changes at a discontinuity of the stress region, and we can use that to determine how good the substrate is after its diced into a chip.  It works just like if you were measure a cable with a Time Domain Reflectometer, or shining a laser at a piece of glass - you get a reflection wherever the wave front changes speed.   Simply:  When you measure the die size acoustically, and the closer your acoustic measurement correlates to the actual die size, the better edges you have, because that means there are no big large discontinuities inside the crystal.

The above is a simplification, but you get the basic idea.  There are more details, but I'm kind of distilling it down to the bare basics.

On some materials, like GaAs or InP, there are vertical crystal planes normal to the top surface, so we can cleave a -perfect- mirror edge with a diamond scribe process.  Silicon substrates like these will have a crystal plane running 45° to the top surface (which means a cleaved crystal plane  would leave an angled edge), and so these devices shown in the photo are typically sawn or laser scribed.  These processes leave vertical edges, but rough - because the crystal has no natural plane in that direction.  If you look at the side face you will see small short faces following the crystal plane, never a smooth surface.  And therefore it is will have much higher strain levels near the edges.  If you had an amorphic material like glass, you could achieve a smooth face if you polished it out, but not really with a single crystal if the edge is not lined up to an atomic plane.

So maybe on the die you're looking at, the middle 50% area of the die is probably low-stress, and the internal strain increases as you get closer to the edges - with highest stresses typically in the corners.  That's one of the reasons we try to avoid the corners as much as possible for critical circuits, or use those for non-critical or digital I/O.  These designers did very well - the chip is large compared to the circuit, and the business end of the device is in the middle - where stress changes are smallest. 

Still: If you were to measure the Zener at a known current while these die were in a whole 4" wafer (or whatever size they make these on - 2" thru 6" diameter are common) - and then measure the exact same device after dicing, the device characteristics will be -slightly- different.  Yes, even though the chip-outs and edges are relatively far from the zener.  We're talking ppm here.

It is my theory that this - and other lattice stresses that are induced during manufacturing -  is what contributes to initial drift, and then as time moves on the drift is more dominated by basic electron migration across junctions.  Which is a slow process, but will still happen faster at higher temperatures.  Electrons at higher energy will statistically have a better chance at crossing a PN junction.  Heat the die hot enough and the junctions will become useless.

I think one of the main reasons these buried Zeners work better than anything else is that they are -not- laser trimmed.  Laser trimming gets a desired output voltage, but with damage to the underlying substrate - and that damaged lattice certainly contributes to long term drift.  If that effect can be minimized, the better the device will be.  The Intersil Vref uses a floating gate to acheive a ref voltage, but that has a whole other set of problems.

I think in the end, to be practical there is only so much that can be done with external devices to correct for drift with buried Zener references - that's why when we built these with Wirewound or expensive Vishays for load resistors, the results we had 10 years later the results are not that much different - the Wirewounds stood up even better over time, and are one tenth the cost.  You can control drift up to a point working "outside" the package, and some of the drift is built into the device itself.

So that's why we use other approaches to build a stable calibrator box:  Don't use just one Vref, build a box with 4 or 10 or 25 or 250 refs inside, and average the best performers.  At the very least you get a calibrator standard where you know the whole box is drifting slowly one direction <Grin!> and you still have to calibrate against other sources over time.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 18, 2014, 11:50:54 pm
So that's why we use other approaches to build a stable calibrator box:  Don't use just one Vref, build a box with 4 or 10 or 25 or 250 refs inside, and average the best performers.  At the very least you get a calibrator standard where you know the whole box is drifting slowly one direction <Grin!> and you still have to calibrate against other sources over time.

I love this idea of averaging an array of references. I've been thinking about it a bit on and off recently.

Personally, I see a set of zeners wired in series. If we assume that the fluctuations any one of them experiences w.r.t. time is uncorrelated then the errors add as the root of the square of the sums of their voltages (better than a simple linear sum). Here I'm talking about  error sources like crystal defects and the associated current constriction in the chip but not things like room temperature or atmospheric pressure. The downside here is if one of the zeners goes belly-up, you loose the entire set.

MisterDiodes: do you have any thoughts on these crystal defects? Its something I've only read about. What cause them? Processing speed? Bad design? Just random things noone can control?
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 19, 2014, 05:18:39 am
CapnYellow: Regarding averagers for Vrefs:
This is a good way to tell if you have a drift problem, and the commercial averager standards will typically have 4 or 5 Vrefs.  I say if you've spent all this time losing sleep thinking about one Vref, coming up with good thermal management, getting good wirewound resistors and parts, etc - why stop at building just one?  Anything worth doing is worth doing to excess!  The building part is the least time you've spent and the cheapest if your time is worth anything, so I suggest you make up a batch of 5 or 10 or 20 Vref boards or whatever.  Burn them in and pick the best performers.  Keep a few spares, & give away the rest of the batch to your buddies to check their DVM's.  That's what I do.  You will be very popular.  Or just keep the extras  burning in longer, like a year or two longer, and sometimes they become useable over time.

People have to get used to much longer time scales when working with good Vrefs - when I say "burn in" that means at least -several- weeks - but for a good Vref let it burn in until it stops drifting too much - say 6 weeks ~ 6 months or maybe a year.  So another reason you might as well make up a batch of these instead of just one.

Put the good ones in a box and average them out electrically or computationally - measure each Vref's circuit deviation from the average, and if one Vref is mis-behaving you will know right away.  The averaging can be done with a master output op-amp, or you can use a CPU or FPGA to do a computational average to set an output DAC or whatever is fun for you.  All of these have been done.  It works.  In the end the simpler methods really work the best, though.

The "perfect world" theory says you'll get a reduction of noise by the square root of N Vrefs - so using 4 Vrefs should get you a noise reduction of about 1/2.  Sorta.  In my experience, if you actually do this you'll find you need more like 5 Vrefs to get a solid, honest noise reduction of 50% from where you started out.  Use 17 or 18 Vrefs to reduce the noise by 4, etc.  This is one of those times where you have number theory meeting up with reality - and reality wins every time. 

If it were me, I like to put the Vrefs on their own module board so swap-outs are easy.  But that's me.

In terms of reliability - Like I said we really haven't had much in they way of failures because the circuit has such a low component count, and the currents are low in the Vref itself.

BUT when you work with chip-scale circuits, and do forensic analysis on failures - you will understand why you want to keep your important equipment powered on - in general.  On those die edges, wherever there is a small chunk missing along the edge (a chipout) - that is a potential stress raiser where a crack can form when the die is under maximum stress - and that's when it is heating or cooling at the maximum rate.  i.e. when you turn the power on or off.  If the built-up strain is great enough to start the crystal lattice bonds breaking, then there is enough energy to drive a crack straight across the die.  Sometimes you get lucky where a crack can start and then turn around and run back to the edge, and in this case all that happens if you have another piece of substrate dust floating around in the can.

The other failure mode is at the wire bond pads - They are pretty forgiving, but given enough thermal cycles these can be another weak link in the chain.

Of course there are myriad other things to go wrong - an ESD zap, power supply failure, etc.

The worst is when you zap a die with static that has enough energy to just START a crack in the substrate, but it doesn't drive it far enough in to affect the circuit "today", but it will fail in 20 minutes or 20 years.  That's what we call a "very expensive service call crack".

The rule of thumb for bathtub mortality rates on simple circuits:  If the device works for at least a few weeks/months of torture-test thermal cycling & burn-in, it'll probably be fine for the next 40 or 80 years.  The above failure modes are a very good reason to do a very thorough burn-in before you put your Voltage Ref averager system into dependable service:  You want to break it right away if possible - and get the whole system as stress-relieved as you can.






Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 19, 2014, 03:15:57 pm
Fascinating. Again, thanks for the great info.

If you flip back several pages ( https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg404500/#msg404500 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg404500/#msg404500) ) you'll see DiligentMind's conversation with LT and Bob Dobkin.

In this, he says the LTZ packages are back filled with dry air before they're sealed up.  What do you think about that in terms of stability? Is that a common practice?
Title: Re: Ultra Precision Reference LTZ1000
Post by: rf-design on April 20, 2014, 12:31:39 pm
I guess that the passivation is not up to the level of modern CMOS process which require inert gas filling. It is a tribut on having a monolithic buried zener with bipolar based temp control.

Some posts ago I had taken a look at the avaible foundry processes beween 0.5u BiCMOS and 0.13u SiGeBiCMOS and there is no deep n+ to deep p+ implant or buried layer diodes avaible which could make the buried zener. So it seems that this old 1-metal, diffused isolated bipolar process is the only way to go for buried zener with bipolar temp regulator.

Some foundries offering zener but I guess there are all extend to surface because they are lateral built. So they they suffering from less stability because of the surface trap effect.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on April 20, 2014, 03:07:25 pm
So it seems that this old 1-metal, diffused isolated bipolar process is the only way to go for buried zener with bipolar temp regulator.

Have you found any source for a simple buried zener -- no compensation circuity included on the IC?
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on May 02, 2014, 12:24:13 am
Lots of interesting reading in the LTZ1000 thread :-)

This is one of my first posts here.

Now a comment and question on the LTZ1000 circuit.

I made a breadboard with the same schematics as in the datasheet. The R2 and R3 values in the datasheet are given as 70K and R4/R5 as 13K/1K. I have made some measurements by making small changes (0.1%) up and down, to temperature setting nominal 1:13, while changing the value of R3 in steps from 40K (edit , extended from 60K) up to 130K. The result; lines straight as a ruler for the output voltage, with a constant 75uV per 0.1% change in R4/R5. This is about 1ppm/100ppm change of output, pretty close to what is specified in the datasheet.

The output also changes by a very constant 765uV per 3K change in the value of R3, over the whole tested R3 range 40K  to 130K, i.e. 0.185ppm change in output voltage per 100ppm change of resistor value at 70K, as given in the datasheet. This is slightly better than the 0.2ppm / 100ppm given in the datasheet.

The interesting part is that it seems one could use just about any value for R3, at least between 60K and 130K. A value like 100K would seem very practical. High values would be preferred as the sensitivity to resistance errors will be lower, but one may run into stability problems if the resistor value is too high / currents get to low. I used the 2N3904 for the NPN.

Any thoughts on this? Anyone made similar measurements?

I also made some measurements at 1:12 (1K:12K) for R4/R5 but the stability is not as good as for the higher temperature setting of 1:13. This is especially true for R3 values above 80K or so.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 02, 2014, 08:13:42 am

Any thoughts on this? Anyone made similar measurements?


Hello,

I have made tempco measurements over change of the 70K resistors.
In my design there are a 50K + a 20K in series.
So I wanted to save the 20K.

But with 50K instead of 70K the tempco of the reference slightly increases when I change the temperature setpoint from 50 to 60 degrees.

Btw.: 12K+1K for temperature setpoint is much too low for a LTZ1000A.
12.4-12.5K is the limit for the A-Device.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on May 02, 2014, 09:37:29 am
Turning the heater fully on-off, I got a tempco minimum (near zero) at 80K for R3 too. That matches what is indicated the datasheet and what is used for example in the 3458A DMM.

But making small temperature changes, I got the same tempco regardless of R3 value (range 40K to 130K).

So either

If my measurements are right then there is no minimum for the R3=>tempco, but still just below the 0.2ppmV/100ppmR in the datasheet. The good news would be that "any" resistor value could be used for R3 and most likely for R4 too.

That's why I ask if someone else made measurements with small temperature steps, not the on-off method, and what the result was?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 02, 2014, 10:54:11 am

Measuring the R3-to-tempco with the on-off method gives other results than the small temperature step method, i.e. the correlation is non-linear.


Hello,

I think we have to be more specific.
- Which device LTZ1000 / LTZ1000A ?
  My results are with 2 LTZ1000A references.
  With nominal setpoint 12K5 + 1K = 50.5 degrees C

- Kelvin sensing of the output voltage?
  my output voltage is directly

- Switchmode power supply?
  my setup is fully supplied from batteries all on a metal ground plane.
  switchmode noise gives a large influence on the temperature setpoint pin

On #1 I get 20.3mV output voltage change between heated / unheated. (22 to 50 degrees?)
With additional 22K resistor in parallel with the 1K (Setpoint = 61.25 degrees)
I get 3.7mV change or 48ppm/K

Changeing R2 from 70K -> 50K gives 4mV output voltage change for 50/61 deg C = 52 ppm/K.

On #2 I did only the test with 70K: with around 54ppm/K change on output voltage for a 10K step.

Since the tempco of the zener is around 50ppm/K I cannot imagine that you get a zero tempco with just changeing R3.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 02, 2014, 12:02:20 pm

Unfortunately the video is in French ... : 


Hello,

OMG:
that was the only protection that they could not copy the reference perfectly.
Now with the 2 hints they can.  :palm:

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 02, 2014, 02:00:36 pm
Buy from Linear and you will not have a problem :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on May 07, 2014, 05:25:37 am
I have been trying to characterize my ltz1000.  I've got Q2 set up similarly to how Q1 is in the datasheet so I can measure it's Vbe, Q1 Vbe, Vz, and I have ammeters on pin 3, pin 5, and pin 8.  All three currents have been trimmed to 100uA. After making a bunch of measurements, I started to move towards a heated configuration.  However, it seems like applying any voltage at all to pins 1&2 is affecting all my other measurements, even if pin 1&2 are at the same voltage.  (I either have the heater at 1-10V or I leave it floating.) My guess is that I'm looking at some leakage current through those "substrate devices, do not forward bias", but it's causing millivolts of difference!  Is something wrong with my test setup, or is there something that mitigates this effect in practice?

Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on May 07, 2014, 08:05:33 am
Some characterizing I have done on the LTZ1000AHC

- Two ICs, two different boards, nominally:
- R1: 120R
- R2 & R3 68K
- R4 / R5 12.5K and 1K

Measured ranges:
- R1 120R, varied by +1%
- R2 & R3: 40K to 130K in steps of 3K and steps of 9K
- R4/R5: 12, 12.5 and 13, varied by +1%

Results

From a couple of hours of measuring, in total about 300 different data points

Output change versus resistor change i.e. ppmVolt/ppmOhm


Some comments

- The sensitivity to R1 variation was surprisingly low, 92uV / 1R1, averaged over 25 step changes, all within 89-95uV / 1R1)

- Also the sensitivity to R3 was lower than indicated in the datasheet

- The R4/R5 sensitivity does not change at all with R3, but decreases slightly with increasing R2 (0.0125 to 0.0093 over R2 values from 40K to 130K)

- Output sensitivity versus R4/R5 ratio decreases, but marginally, over increased R4/R5 (0.0129 at 12.4, 0.0118 at 13.2)

- Stability for low R4/R5 at low values: stable at 12.4 at room temperature, not stable at 12.0, unless cooled to 18C. Stability increases with lower values of R2 and R3.

- Output versus load current: no measurable change (<1uV) to output with current sourced / drained between +5mA and -9mA. The output is very DC stable. (sensitivity to ripple voltage on the supply was not measured). When changing load, the voltage changed by up to 10uV at 0-5mA load

- Output change versus supply voltage: no measurable change to output (<1uV). This is as expected as the power supply is only to the opamps and the heater transistor. The circuit is very tolerant to input voltage level.

- Output change versus low supply voltage, near dropout: unmeasurable, <1uV, down to dropout at
7.5V supply. This is a characteristic of the opamp only.

- The LTZ1000A output voltage was measured directly on the IC pins
- The power came from a linear bench power supply and there was a AS2954 LDO regulator on the LTZ1000AHC board, set to 11V
- The measurements where made with a NI 4021, 7.5 digit DMM (LTZ1000-based)
- The LTZ1000AHC was tested on a PCB made specifically for testing, with breakout jumpers for all components
- The board was populated with thin film 25ppm resistors. The resistors that where varied, where wired from a separate breadboard, with 1% metal film 100ppm resistors.

If of interest I can post photos, data and diagrams...

PS: ignore the results in my previous posts, they where the result of regulation collapsing, using R4/R5 ratio of 12...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on May 07, 2014, 08:41:14 am
Measurement results from lymex/BG2VO:
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 07, 2014, 09:12:49 am
Quote
If of interest I can post photos, data and diagrams...

Please do :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on May 07, 2014, 11:04:10 am
As I got some requests, I will post more, but give me a couple of days.

Thanks for posting the Lymex data. If we multiply my data by 100, for 100ppm resistor changes we get:

-DatasheetLymexJanaf
R110.14-0.14
R20.30.4-0.4
R3 0.20.03-0.07
R4/R5 1.00.95+1.2

A couple of conclusions:
- It seems the R1 and R3 values are not as critical as given in the datasheet. Or both Lymex and I are wrong.
- Put your money on R4/R5 and R2 while R1 and R3 are less critical.

In the end, the errors of resistors are uncertain :-DD, it is not meaningful to dive too deep into the decimals.
EDIT: changed signs in the table.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on May 07, 2014, 11:17:40 am
Galaxyrise, could you have damaged your LTZ1000? I's rated 0.1V max forward bias on the heater pins relative to pin 4 which would usually be at around 0.5V, ie pin 2 and 3 must always be higher than 0.5V
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on May 07, 2014, 09:48:39 pm
Galaxyrise, could you have damaged your LTZ1000? I's rated 0.1V max forward bias on the heater pins relative to pin 4 which would usually be at around 0.5V, ie pin 2 and 3 must always be higher than 0.5V

It's certainly possible, which is part of why I'm asking here.  But my heater has only ever been floating, or at least at 1V.  Is floating bad?
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on May 08, 2014, 05:42:40 am
I do not think floating could do damage. What about at power on / off, with non-floating heater?
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on May 08, 2014, 05:55:36 am
A plot of Impedance of the LTZ1000 zener only, at room temperature, no temperature stuff. Possibly some self heating but the measurements where in mS long bursts only. The impedance was approximately (edit) 33 ohm (0.2V / 6mA) for two samples. Measured with a NI 4132 precision SMU.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 08, 2014, 06:13:21 am
A plot of Impedance of the LTZ1000 zener only, at room temperature, no temperature stuff. Possibly some self heating but the measurements where in mS long bursts only. The impedance was approximately 0.03 ohm (6mA / 0.2V) for two samples. Measured with a NI 4132 precision SMU.

Sorry, but differential resistance R = dU/dI, not the other way round.
Therefore R= 0.2/0.006 ~ 33 Ohm, which is in accordance with the datasheet (20..60 Ohm)

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on May 08, 2014, 06:14:37 am
 :palm: :palm: :palm: how embarrassing, but who cares about Ohms law anyway..... File updated.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 08, 2014, 06:12:06 pm
While updating the 8.5 Digit DMM thread, I had the idea to show a comparision of the LTZ1000 board designs used in these DMMs.
So here is first collection. If anyone has more/other/better pics please share.

(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=92893;image)
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on May 08, 2014, 08:27:12 pm
So, now I am curious... Why is there an LM199A [LM299A/LM399A] in the Datron/Wavetek 1271 [as well as an LTZ1000]?

1271 using LTZ1000 + LM399
1281 using 2x LTZ1000
That is the main design difference and the reason why the 1271 specs are not quite as good as the 1281.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on May 10, 2014, 05:20:48 am
I've been wondering about the 'under power' aspect of the burn-in process. Does it matter if the device is powered at all during this period? Annealing would seem to be dominated by temperature effects. And only if one gets into high current densities does electromigration take effect?
Title: Re: Ultra Precision Reference LTZ1000
Post by: ManateeMafia on May 20, 2014, 12:57:34 am
Ken,

Are you thinking of AN42? Page 4 shows 4ma for the LTZ1000.

I also came across this link http://indico.cern.ch/event/162546/contribution/3/material/slides/1.pdf (http://indico.cern.ch/event/162546/contribution/3/material/slides/1.pdf) while searching. The circuit is listed on page 25.
I have not seen it before and I was wondering if this was from another publication or from an actual design.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on May 20, 2014, 09:33:36 pm
How much do the econistors run?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 21, 2014, 04:48:39 pm
I today received this little board, okay it didn't receive I had to collect it from the toll. It was named to be a LTZ1000 reference. The curious fact is, that the IC that used to be the reference has absolut no marking on it, but the circuit indicates a LTZ like style schematic.
Does anybody know something about such a board? It seems to be part of some test gear, beside the Linear Technology label and the date code 10/84 there is a mirrored "Superman" icon on top of the pcb. On the backside is another date code 46-84 and an icon that seems to be a growing sun?

I guess the first thing to do is to reverse engineer the schematic before powering up the beast.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 21, 2014, 05:05:08 pm
So that was you who snatched it off my ebay bid list.
Great job  :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on May 21, 2014, 05:41:19 pm
Very interesting... maybe someone at Linear-Tech is taking stuff out of the garbage bin and selling it on fleaBay...

Bob Dobkin's retirement plan? :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 21, 2014, 05:48:36 pm
Quote
So that was you who snatched it off my ebay bid list.
Great job  :)

Me, what?  >:D

Quote
That appears to be a similar board to the one used in Linear-Tech ap-note #86.

You are damn right. Wow, I didn't expect that.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on May 21, 2014, 06:03:05 pm
Is it a LM7872? Is it a LM399? No it is a LTZ1000!

I prefer resistors to lay flat but besides that... beautiful !
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 21, 2014, 06:29:38 pm
Those prices really close to Z202's from VPG. And yes, I'm still waiting for my order.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on May 21, 2014, 06:47:07 pm
Those are pricey, i will need to see about precisionresistor.com as well.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 21, 2014, 09:29:41 pm
I today received this little board,

Who grabbed it from J.W. s desk at the museum?

I priced out a 10K resistor [standard 0.01%], and here are the prices I got:
10K, 0.01% p/n "8G16A10K"

You will only need the 0.1% types they should be available at around half the price.

RS-Components has some resistors out of the UPW50 + UPW25 series which are similar.
I have them in my design. see:

https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=49180;image (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=49180;image)

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: ManateeMafia on May 22, 2014, 03:33:39 am

Those are pricey, i will need to see about precisionresistor.com as well.

I'm *know* that "Econistors" have an excellent track record over many years of use in military, aerospace, and automotive circuitry.  The resistors from Precision Resistor *may* be just as good [or even better!], but I have no historical information about them, and so I am hesitant to use them...  If anyone has long experience successfully using their products, please post about your experiences here!


I have purchased three of their MC-7 kits, one standard and two with values of 2.5 and 5. They were extremely helpful and quoted me accurate lead times of 10 weeks for the two non-standard sets. I also had them make a 10M 2.5W resistor that rounded out my original MC-7 kit. The prices were not cheap, but the kits were made using 1W non-inductively wire wound parts. I used them since I frequently travel near their business.

If you price out similar resistors, you will find that the 1W 5ppm resistors can cost much more. I have not priced smaller wattage units, but you can expect a quick reply from them if you send them your specs. I would imagine that the pricing would be competitive to what you will find elsewhere.


I do not have the capability to accurately verify the tempco but they measure well within tolerance on my 3458A. The quality seems to be excellent but I do not have much historical information on their performance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 22, 2014, 06:33:04 am
Anyway, what I said earlier still stands-- I think one could build up an LTZ1000(A) based voltage reference using these resistors, and the circuit would be just as stable as one built with foil resistors...  Only one resistor needs to be "special order"-- the 12K5 for the LTZ1000A, [or 12K for the LTZ1000].

Regards,
Ken


As described here: https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/180/ (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/180/), we already DID it! (baysitter an me)

For the LTZ1000, the 5 needed ECONISTOR resistors of 120, 1k, 12k, 2x70k, all 0.1% are available from stock, between 6 and 10 € today, I would guess.

My two references are still stable / in accordance against HP3458A and Fluke 5442A to around 1ppm after > 5 years.

babysitters LTZ1000A reference did not move more than 0.2ppm after 1/2 year or so.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 22, 2014, 10:46:52 pm
I've analyzed the circuit board I got, there are a few little different values for the resistors used, here is what I found:

R1: 125R Vishay KS24248L4 0.1% (datasheet value 120R)
R2: 79k7 0.1% (datasheet value 70k)
R3: 79k7 0.1% (datasheet value 70k)
R4: 11k91 0.25% (datasheet value 13k)
R5: 970R 5ppm (datasheet value 1k)

I will post the complete schematic and circuit board if completed.
Title: Re: Ultra Precision Reference LTZ1000
Post by: max666 on May 23, 2014, 12:38:09 am
I've analyzed the circuit board I got, there are a few little different values for the resistors used, here is what I found:

R1: 125R Vishay KS24248L4 0.1% (datasheet value 120R)
R2: 79k7 0.1% (datasheet value 70k)
R3: 79k7 0.1% (datasheet value 70k)
R4: 11k91 0.25% (datasheet value 13k)
R5: 970R 5ppm (datasheet value 1k)

I will post the complete schematic and circuit board if completed.

Yikes!  Those resistors seem to have drifted a little!

I don't think branadic measured these values. I think he just read the labels on the resistors   ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: retrolefty on May 23, 2014, 12:48:08 am
I've analyzed the circuit board I got, there are a few little different values for the resistors used, here is what I found:

R1: 125R Vishay KS24248L4 0.1% (datasheet value 120R)
R2: 79k7 0.1% (datasheet value 70k)
R3: 79k7 0.1% (datasheet value 70k)
R4: 11k91 0.25% (datasheet value 13k)
R5: 970R 5ppm (datasheet value 1k)

I will post the complete schematic and circuit board if completed.

Yikes!  Those resistors seem to have drifted a little!

I don't think branadic measured these values. I think he just read the labels on the resistors   ;)

 In that case we can't blame drift.  ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 23, 2014, 07:22:37 am
Quote
I don't think branadic measured these values. I think he just read the labels on the resistors

Correct, this are just the printed values on the parts, I didn't measure them!
Title: Re: Ultra Precision Reference LTZ1000
Post by: max666 on May 23, 2014, 03:28:01 pm
In that case we can't blame drift.  ;)

We can blame the engineer drifting from the recommended datasheet values   ;D
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 23, 2014, 05:47:41 pm
Here is the reverse engineered schematic and board layout.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 23, 2014, 07:39:02 pm
Hello Branadic,

where is the 1 Meg resistor in series to C1 from the datasheet?

R1,R2,R3 are not critical in value. They need only stability.
The R4/R5 value is 12.2 so it would be ok for a LTZ1000 (but not for the A-type).
But I think the 12K resistor is no precision device in your case. (low TC).
The ratio is very critical.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 23, 2014, 07:52:00 pm
Andreas,

compared to the datasheet C1 is not 100nF, but some film cap instead (the upper right cap), with now unkown value.
Why? When the board received the solder junction were full with solder flux, so I had to clean it with IPA. The damn thing about that is, that this way I loosed the printing on the caps. WTF!
There is no 1meg resistor in series, as pictured in the datasheet. Also the diode CR2 between heater and ground was added later and not planed in the original board design.
The 12k (11k91 in my case) equals R5 in the photo and I guess it is some precision type too, even though I don't know the manufactor of the resistors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on May 24, 2014, 05:32:51 pm
  You can read about it here:

http://www.edn.com/design/analog/4427151/The-last-half-century--Wirewound-resistors-Part-one

http://www.edn.com/design/analog/4427940/The-last-half-century--Wirewound-resistors-Part-two


From Part Two:

"Film resistor users should note that most precision film resistor’s specifications calls for operation at a small fraction of their stated power capacity.  This is indicative of the film resistor’s inherent flaws; they cannot operate with any kind of power applied to them and maintain any semblance of stability.  Their TCR curves literally go out the window with power.  Our TCR’s are linear and flat over their operating range, no hyperbolic curves to correct for, no worries about what applying power to them will do; it has no effect upon them.  There are no applied voltage coefficients either and long term stability under power is better than film resistors sitting on a shelf."
Title: Re: Ultra Precision Reference LTZ1000
Post by: CaptnYellowShirt on June 06, 2014, 01:09:52 am
I have some ideas on the LTZ drift but it will cost $100k to test and I can't justify that.


Volt-Nuts bake sale?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 06, 2014, 05:43:17 am
No news at all..

That drift mainly in the negative direction of the LT references had been investigated by Fluke, comparing the 732B drifts of the Motorola against the LTFLU:
"predictability of solid state zener references", D. Deaver, Fluke, ca. 2001

An asymmetrical drift of (-0.8 +/- 0.7) ppm/yr. is already in the datasheet of the Pickering reference, the 7000 reference module, now terminated by Fluke.

I think, that is caused by the physics of the LTZ silicon, degenerative processes, and hardly to be mitigated by any odd "burn in " process. (still no description about that, from Bob Dopkins, I think?)

So the goal of building ultra references is to bring all external drifts (i.e. from the Rs) to near zero and then to compare, and select the reference with the smallest drift.

It will take 1 year of monitoring for 0.5ppm/yr, and 2years for 0.3ppm/yr predictability, typically.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on June 06, 2014, 06:52:19 am
If anyone is interested, here are some of the Fluke 7000 voltage reference pictures, posted by lymex on the 38hot.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on June 07, 2014, 03:38:14 am
Nice copper ring, though... soldermasked and not connected to anything... just some thermal mass?  LT1413 instead of LT1013, too, nice little bit of "modernization."
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on June 07, 2014, 05:32:50 am
LT1413 opamp for LTZ1000CH was introduced in the Fluke 8508A nearly at the same time (2002) as in the 7000 series. Somewhat later (~2008) Fluke 8508A received a new "modded" reference with LTZ1000A and AD823A/LTC1150 instead of LT1413.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on June 09, 2014, 11:33:53 am
Nice copper ring, though... soldermasked and not connected to anything... just some thermal mass?  LT1413 instead of LT1013, too, nice little bit of "modernization."

Maybe the same reason as the guard cooper pour on my board besides the electrical: helping the thermal coupling to reduce temperature difference between LTZ1000 pins as advised by the datasheet already on page 4:

Quote
It is mandatory to keep the zener and transistor leads at the same temperature, otherwise 1 ppm to 5 ppm shifts in the output voltage can easily be expected from these thermocouples.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on July 04, 2014, 11:29:30 am
I just got some ceramic hollow feedthrus for soldering.

Great to embed a voltage reference hermetically in my beloved tuner boxes and having one massive copper wire going uninterrupted from the inside to the outside.

i.d. 2.5 mm, length 12mm, thin part od 5mm, thick part od 7mm.

Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on July 04, 2014, 03:43:16 pm
No Part number, coming from a ham surplus dealer.
The manufacturer was Stettner, which has been first renamed to Stelco and is now
Sumida

http://www.sumida-components.com/en/welcome-to-sumida-components-gmbh/?no_cache=1 (http://www.sumida-components.com/en/welcome-to-sumida-components-gmbh/?no_cache=1)

They offer pinless feedthru capacitors, thats how you can see those.

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on July 04, 2014, 04:43:05 pm
Quote
No Part number, coming from a ham surplus dealer.

And can you tell us who is the ham surplus dealer? Up to now I only found those feedthrough caps in a leaded version. The one in your picture looks somewhat different.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on July 04, 2014, 05:56:15 pm
Oh, sorry, of course! Didn't want to hide my great personal source to sell 65 cent parts to you for 5 euro/each... only if you really want :)

http://www.oppermann-electronic.de/ (http://www.oppermann-electronic.de/)

Its in the ceramic section. Sorry, german page for the foreigners, but I have some spare parts :)

Title: Re: Ultra Precision Reference LTZ1000
Post by: ltz2000 on July 04, 2014, 08:08:35 pm
Great to embed a voltage reference hermetically in my beloved tuner boxes and having one massive copper wire going uninterrupted from the inside to the outside.

Certainly a major improvement, but don't expect to get hermetic seal comparable to glass-metal. Any pressure difference will slowly equalize.

It is possible to get extremely low leakage (similar to glass-metal) with metallized ceramic feedthrough by carefully selecting the ceramic material and metallization for that purpose. But the material it is attached to (the box, wire and solder) affects the most. Difference in thermal expansion coefficients will cause the plating to peel off when soldered and creates a microscopic route between the inside and the outside world.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on July 05, 2014, 10:33:07 am
@ltz2000

We discussed pressure relief before; see [url]https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg252548/#msg252548]https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg252548/#msg252548] [url]https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg252548/#msg252548 (http://[url=https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg252548/#msg252548)[/url] and SeanB's remark.

Thermal expansion is still there...
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on July 12, 2014, 11:46:49 pm
Well, I think I've waited long enough for someone else to say something about this.  The 70xx series was designed long after the Datron 1281 or the 4910.

!!! L@@K !!! NO SLOTS !!!!

I hope this ends [forever] the debate on slots vs. no-slots...

--Ken

(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=96661)

<Laughing>  We built some LTZ1000 vrefs almost 20 years with slots, and some in the same batch without.  Tried all sorts of voodoo - even oil-immersed resistors.  Absolutely No difference in the end.  I wish I had a time machine so that my 20-year later self could go back and tell me to quit wasting time and money.

What helped the most out of everything?  Let the Vrefs run about 10 ~15 years or more and quite worrying about yearly drift.  See if they do well over 3~6 months.  They just get better over time, at least any of the ones I've tracked.    Using -good- wirewound resistors worked just as well as any other expensive magical Voodoo resistor in the end.

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on July 13, 2014, 05:38:57 pm
Finally i got recovered schematics of KI2002's LTZ1000 VREF.

Enjoy (https://www.eevblog.com/forum/testgear/keithley-2002-8-5-digit-dmm-review-and-teardown/15/).

No voodoo magical resistors, just PTF56 68.1K, wirewound 120ohm and precision 2R network. No slots either, just a plastic cup on top and bottom. :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 13, 2014, 05:54:48 pm
Hello,
 
can you verify R268?
The value between Pin 1 + Pin 2 makes no sense. It should be more in the 1K - Range (perhaps 1.1K)

So the resistor divider seems to be the most "valuable" resistor pair of the whole cirquit.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on July 13, 2014, 06:12:28 pm
KI's repair manual (http://dev.xdevs.com/projects/kei2002/repository/entry/service_manual/2002_902_01B.pdf) (page 138) lists R268 as RES NET, 13.1K, 13.3K, 0.1%, 100MW, THINFILM.
You think it's a typo there? and it's 1.1K/13.3K ? :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on July 14, 2014, 04:21:52 am
Also the inclusion of R251 at 200k can be a problem.  That was included for LTZ1000, but for the A version it is not used.  Some people use it anyway, we found it caused more problems with the LTZ1000a over time.  Linear tells you right in the datasheet to not use it for '1000a.  They are correct in most applications.

Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on July 14, 2014, 05:41:04 pm
Just a note:  The 12k / 12.5k advice is good for applications where ambient temperature is low, but does not apply in every case.  The instrument makers go on the high side of the ratio, say 13k ~15K : 1k or more to raise the temp of the LTZ1000(a).  If the ratio is too low for a warmer ambient climate, then the LTZ1000 zener Vref becomes a thermometer and starts tracking ambient temp.  Its been my experience that if you know you'll be operating at below 85°F ambient, then the lower ratio is good. (Which is probably most of the time).  If you know your device will be above 90°F a lot of the time, then a higher ratio will give you better drift performance.  For instance, if we knew a a Vref would be used on a rack full of hot equipment (Ambient say 105°F to 115°) , the heater ratio would usually be set for 13k or even the standard 15k to 1k.  In other words you need to have the Vref Zener temp. higher than the changing ambient.  The more ambient is fluctuating, you will tend to want a higher ratio.

The other technique that works well is to just forget the on-chip temp transistor and just control the temperature of the space around the LTZ1000 directly with good thermal mass.  It isn't as fast for warm up time, but you'll get as good or better steady Vref performance.   You basically just make yourself an ovenized / potted Vref,  and that can cost a lot less for production than magical, expensive Whoop-Dee-Doo resistors.   Over a long time frame we found this technique is probably one of the better ways to make a solid Vref - IF you can stand a longer warm up, say an hour or two. 

Most of the time the stuff we make is never turned off, so warm-up time is usually not an issue.  That is good advice for any serious PPM-range Vref.

It just depends on application. 

 
Title: Re: Ultra Precision Reference LTZ1000
Post by: ltz2000 on July 17, 2014, 07:41:10 am
For the 3458A, it was also designed for use in up to 55C environments [don't ask me why-- I have no clue]

Business? The ratio of instruments sold must be something like metrology labs 1 - automated test systems 100.

Title: Re: Ultra Precision Reference LTZ1000
Post by: HighVoltage on July 19, 2014, 04:56:45 pm

I'm reminded of the book "Foundations of Mechanical Accuracy" in which the story of replicating the meter standard in the 1970's was told. The Moore Tool Co would send a rep to France with a briefcase that contained what they though was some fraction of a meter. The guy hops on a transatlantic flight, sets up the standard next to the one in Sèvres, waits how ever many hours/days you need to make sure everything's at the right temperature, and finally shines a laser at the ends of each to figure out how much they are off. The guy gets the report, flies back home, sets up the standard in a room inside a room in the sub-basement of the Moore Tool Co. and they take like a month to file off their best guess at another nanometer. All this just to fly back to France and try again and again until they've gotten "close enough" or they've gone too far.

Sounds like an interesting book, that I never heard of before.
 .... but it is $ 186 on Amazon

http://www.amazon.com/Foundations-mechanical-accuracy-Wayne-Moore/dp/B0006CAKT8/ref=sr_1_1?ie=UTF8&qid=1405788804&sr=8-1&keywords=Foundations+of+Mechanical+Accuracy (http://www.amazon.com/Foundations-mechanical-accuracy-Wayne-Moore/dp/B0006CAKT8/ref=sr_1_1?ie=UTF8&qid=1405788804&sr=8-1&keywords=Foundations+of+Mechanical+Accuracy)

May be I can find a PDF of it.

Title: Re: Ultra Precision Reference LTZ1000
Post by: jpb on July 19, 2014, 07:38:40 pm
Sounds like an interesting book, that I never heard of before.
 .... but it is $ 186 on Amazon

http://www.amazon.com/Foundations-mechanical-accuracy-Wayne-Moore/dp/B0006CAKT8/ref=sr_1_1?ie=UTF8&qid=1405788804&sr=8-1&keywords=Foundations+of+Mechanical+Accuracy (http://www.amazon.com/Foundations-mechanical-accuracy-Wayne-Moore/dp/B0006CAKT8/ref=sr_1_1?ie=UTF8&qid=1405788804&sr=8-1&keywords=Foundations+of+Mechanical+Accuracy)

Out of curiosity I had a check on Abe books and they are even more expensive....
http://www.abebooks.co.uk/servlet/SearchResults?an=Wayne+R+Moore&sts=t&tn=Foundations+of+mechanical+accuracy (http://www.abebooks.co.uk/servlet/SearchResults?an=Wayne+R+Moore&sts=t&tn=Foundations+of+mechanical+accuracy)

Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on July 20, 2014, 05:27:07 am
I would expect to see a voltage reference standard or 8 1/2 high end multimeter based on LTZ1000A installed in a climatized lab room between 20°C ... 24°C [68°...74.2°F] and not being stacked on a pile of hot T&M equipment - at least that is how I would do ...
The 12k5:1k00 is a compromise between max. expected temp. in lab room - minimizing long term stability - I my case I opt to minimize the long term drift.
It is hard for me to imagine what the lab room conditions are if you would recommend the use of a 15k0:1k00 ratio - at least on planet Earth.

That's a lot easier to imagine than you think, and this is what the Pickering paper failed to take into account:  On a production line situation, you can't always control the environment.  Its not really the top-end heat setting over ambient, its how much its changing throughout the course of a day, or how much wind is blowing by / or not blowing by.  For instance, the modules we make had to fit behind and under a stack of test equipment, and it was either hotter/ colder than we wanted in the cabinet, OR the best place in the clean room that was convenient for the rest of the workflow meant the cabinet had to be next to the air-lock door, with people coming and going countless times per day.  Every time that door opens there is extra breeze blowing across that part of the room that we have no control over, and the cabinet cooling system couldn't keep a perfectly stable interior temp with the automatic door nearby.  Even though the clean room temp is relatively constant (within a degree or two), the air flow over the control cabinet is not.

The other problem is if the equipment gets hotter or cooler depending on what type of product is running through the machine (the motorized motion slides are running longer or shorter distances), and about a zillion other "gotcha's" that pop up.

If you place an LTZ1000a in this location, you'll find that the system Vref becomes a tracking thermometer in a hurry if the die temp is too low.  We did indeed have to build several versions with a 15k/1k ratio in order to keep the die temp from responding to local rapidly changing local atmosphere conditions that we have no control over.  Generally we found that in real life, about 13k ~ 14k/1k gave the best performance, but we would go to 15k or higher as required.  And yes, the Vref is covered, but you'd be surprised how much the entire enclosure heats or cools - that's a lot of surface area, and airflow has a pretty large heat conduction effect on the enclosure as a whole system.

You actually have to do this in real life to see what I'm talking about - if you use a 12.5k/1k ratio, your Vref will be more wobbly than you want in a real world production situation.  Granted, if you're in a lab you can get away with the lower ratios, but sometimes you have to use these Vref's in non-lab conditions.

I can guarantee you - if you have a rack- stack of 3 or 5or 10 HP3458a' (which I have seen and not uncommon in a semicon QC area) they will NOT be even close to the same temp. inside, and if you run the 12.5k/1k ratio, your boxes will NOT have great stability, even over an hour.  Now if if its a solo 3458a by itself in a cal lab, then you will probably have it work pretty well at the lower ratios. But from experience, when you have 10 high-end DMM's in a cluster rack, you have to have the higher die temp on the Vref - otherwise you have a very large, expensive, sensitive  thermometer.

And then of course there was the situation where you get the system installed and running, and then the room gets re-arranged, and now the cabinet is acting much different than before; you have a new hot piece of equipment covering what you thought was an air vent, etc.  Sometimes, no matter how hard we try, the customer always finds a way to circumvent the resistor selection.  That's why we design these to run at a little higher die temp than book-theory dictates.

Also, a lot of times these are used where you really don't care what the drift is over the course of a year.  Sometimes you want good drift performance over 30 ~ 90 days, and what you're after is an extremely low noise Vref that you know is good over the next -several weeks-.   On a semicon production line that is doing critical testing with wafer probers, the Vrefs can be swapped out as often as needed and calibrated against the master transfer standards back in the cal room.  When you're in a main assembly room where say 10,000 parts are produced per hour, 24/7, and each device is worth $250 ~ $500, then nobody is going to chance that the Vref they are using hasn't been calibrated within the last month or so.  The devices are just too valuable - so the Vrefs tend to get swapped out fairly often - and you aren't really after 365-day drift stability numbers.  Its something good to shoot for, but not really always cost effective in all applications.

So, yes, sometimes you really have to go for the higher resistance ratios on the heater circuit, depending on the application.

Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on July 20, 2014, 10:38:45 am
If someone is interested on ebay France, the reference module for HP3458A

I'm not involve in it :)

http://www.benl.ebay.be/itm/161371505611?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649 (http://www.benl.ebay.be/itm/161371505611?ssPageName=STRK:MESINDXX:IT&_trksid=p3984.m1436.l2649)
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on July 20, 2014, 03:14:53 pm
Well, 15k/1k how 3458a's come supplied, last I checked.  Do they supply a different ratio on newest units?

"Modifying" the DMM  would be to drop the heater resistor ratio down to 12.5k/1k, and that works also, as long as the environment is compatible.  We've built Vrefs that way sometimes.  For a solo unit by itself in a temperature-controlled room , that can work.  When you run a cluster stack, or are running in a really fluctuating environment its been my long experience that you'll want the higher ratio.  For a large cluster of DMM's (don't care what brand) You will find that the boxes in the top / middle / bottom of the stack will have much different temps inside than what you thought.  In a clean room where floor real estate is at a premium, the DMM's had better run to spec when sitting in a tall stack.

Or in the case of what I design, the Vref sitting in machinery sharing space with a motion control system / processor board / probe board inside of a control cabinet.  You need to have the die temp -well above- whatever the crazy changes in ambient temp are happening around the Vref, even though it might be covered from direct airflow.  Especially the rate of change of temperature.  Calculating for a steady-state ambient temperature is one thing, but when you move the design into reality, then you'll see that sometimes you need a higher ratio for best overall performance - and that includes those Un-controllable environmental issues.   Also known as "Real World":  It'll get you every time <Grin!>   

Nobody on a production line that I know of will make any modification to their 8.5 digit DMM though.  They want them to run in spec as supplied from the manufacturer, and nobody I know if will be changing out heater resistors if its a company-owned DMM.  I have never seen that at least.

You just select the resistors for intended application, that's all.  This isn't a one-size-fits-all design.  You test it out and make adjustments as you go until you get the performance you need.  If the 12.5k/1k heater resistor combo works for your situation, then that is "perfect" for -your- application.  It is not perfect for -every- application though.  A for-profit business may not be at all interested in 365-day drift numbers, they just want their products shipped out and running, and they will calibrate their test systems as often as needed.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on July 20, 2014, 07:17:30 pm
Gaz,
Most of the high-end DMMs on the production line will be 3458's, as far as I can see.  Sometimes a Fluke or Kiethly, but usually its mostly 3458's at least in my circles.  In fact, in more than one plant they will have a guy that works for Agilent/Keysight with his own office down the hallway.  These DMM's are the units in battle zone.  Down in the cal room where its quiet, really temperature controlled and you don't have 200 people stomping by every hour, that's where the expensive Fluke calibrator / transfer standards / precision resistors / etc will be found.

Re: Dr. Frank's observations - I agree mostly with those:  Yes, if you were to ask me to build you an LTZ1000a circuit, you would get good wirewound resistors on a copper-filled board; if I didn't know where the unit was going I'd give you 13k/1k heater resistors to start out, and you would never see any sort of expensive Vishay magical foil (and even more magical datasheet) resistor anywhere on the board.  If you're paying more than $5 or $7 per resistor, you're doing something wrong - I least from what my experience tells me.  The Op-amp would be sealed, and you could run the thing under water if you wanted to. No slots, goofy copper layouts or other gimmicks.

The designs I use have lots of hours on them, they run a long, long time - over decades time spans.  The older they get the better they run.  I figure it takes at least 2 or 5 years for the crystal lattice strain to level out on the die, and then you should be getting much better drift numbers after 5 or 6 years.

If I knew you were going to baby it in a very climate-controlled room, I'd give you a 12.5k/1k heater resistor setup.  If it has to work in the real world the ratio would be more like 13.5~14k/1k and if it had to work really hard  for a living in any hard hot/cold situation it would be 14.5k~15k/1k heater resistors.

I would probably not take the time to swap out an LTZ1000a for an LTZ1000 because for me, there is not a lot of long-term benefit in that.  The LTZ1000a's were invented to be less sensitive to surrounding environment changes, and nobody I know in a profitable business worries about 3ppm per year drift vs. 1ppm year drift.   I'm not saying its a bad thing to do, I'm saying that 5, 10 or 20 years down the road - something I have experience with - the '1000a and '1000 will probably drifting at just about the same rate, all else being equal.  If you did do this swap, down the road you would have wasted a good LTZ1000a part, spent money on a LTZ1000 and used up 4 to 8 weeks burn in time.  I dunno.  Maybe if the Vref board you had had a falied LTZ1000a, maybe it would be worth it - but that might be rare.

Outside of the Volt-Nuts crowd - very nice people by the way - I don't know of a lot of people really -needing- a 1ppm /yr  drift circuit.  I know the hobbyists enjoy chasing after low drift numbers for fun and entertainment - and I get it.   If you're a cal lab or on a production line, you'll be doing calibrations MUCH more often than once a year, and you'll probably be using a Fluke calibrator anyway, not some hacked-up board with a Dixie cup on top. <I say that tongue in cheek because I have one of those on my desk now>. :-DD

Its all fun, I understand - and there is certainly more than one way to build the circuit.  Use what works best for you! 

Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on July 20, 2014, 08:29:59 pm
Dear Mister Diodes,

the discussion about the LTZ1000A circuitry began years ago, when the mediocre annual stability of the 3458A compared to other 8.5 (!!) DMMs, partly with the very same reference element, got obvious.

To remind you, besides some nice, harmless Volt-Nuts, the 3458A is also often used in metrology labs, and there, a 8ppm/a stability is really undesirable in many cases.
Yep, if this instrument features 8.5 digits AND 0.02ppm linearity (of input), then 8ppm/a really does not fit to this class of instruments.
No, 8ppm/a make 8.5 digits nearly worthless..


HP could have assembled equally an LM199 inside the 3458A, if they let the LTZ run on 90°C.

Maybe the discussion in this thread is quite academic, but for the design (from amateurs) of a separate LTZ1000 reference, the 3458A instrument and its reference implementation was very instructional. And that was the core of this thread, the idea to pimp the 3458A was more or less a by-product.

Also, the 1989 commercial flyer promoted the 3458A to be a metrological class instrument...
(reprint here: http://cp.literature.agilent.com/litweb/pdf/5965-4971E.pdf (http://cp.literature.agilent.com/litweb/pdf/5965-4971E.pdf))
It would have been easy at that time to achieve a lot more of (metrological) stability by some simple means.
Instead, HP offered specially selected 4ppm/a references for a fortune.


By the way, for none of these 8.5 digits instruments it is specified, that/if their annual stability applies on intermittent or non-intermittent operation.

For the 3458A it's quite clear, from Service Note 18A, that the 90°C reference may show strong hysteresis, if it's NOT operated continuously.
That may be up to 15ppm!

And HP once again did not specify clearly, if that has been a temporary problem of certain S/N, like the SN18A implies by its title description, or if ALL LTZ references suffer from that problem.

Latter one I assume to be the truth, and that additionally would be a reason to reduce the LTZ temperature.. as such strong hysteresis obviously is only present on big excursions over room temperature.
Otherwise, if a spare instrument in a fab site is retrieved from stock, that would cause a big problem... also the high energy prices here in Germany may foil continuous operation.


Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on July 20, 2014, 10:54:25 pm
DR Frank:

I agree with you more than you think, and if my previous message didn't covey that then I apologize.  Let me try again:

Your observations are correct, but I am talking about production line operation here, not hobby use - and a production line is always running 24/7, so that the power-up hysteresis effect is not as much as an issue.  Generally when a new DMM comes online, it will be running in warm-up mode for several hours - at least one shift - before it becomes operational.  Then it is running in parallel with another unit to double check that the go- no-go tests are working right, and then a few shifts later the oldest unit on the stack is powered down and sent to the cal room for testing.  Also what we're looking for at least some of the time is relative differences between two voltage measurements.  The absolute accuracy needs to be good, but relative measurements are more important sometimes.

I understand that in some countries, you can't afford the power cost (especially in a home lab), so of course you would be more aware of power-on hysteresis.  But even in Germany the production clean rooms are "on" 24/7, correct?  It is very expensive to power down a clean room / semicon production facility, so in most cases its better to leave the critical equipment on.  I know here in the States I don't know of any production facility that shuts down completely even for holidays. - the costs would be enormous to get everything turned on and warmed up again.

OF COURSE for a Volt-Nut hobbiest that making the resistor modifications would be great idea if you need those 8,5 digits, and your power cost is so high you can't afford to leave the critical equipment on all the time.  I agree!

How much does it cost to keep an '3458 powered up 24hrs per day where you are??  I know it really adds up over a year I think.

For my equipment, what we're after is more the low-noise and short-term stability characteristic (90 days) of the Vref, in which the LTZ1000(a) is better at than the 199/399. 

That being said, and LM199, or even 20~40 or so LM399's in parallel for lower noise makes a good Vref too, I will agree! 

At least here in the states, I've not seen a 3458 used in metcal lab as a master voltage - test reference for a long time; that job has gone to the Fluke calibrators anyway.  It might be used as a secondary test ref for sure.  But I know our local metcal just sold off its last 3458, I think they are just all 100% Fluke calibrators now.  But different labs have different setups I know.

But on the production lines, you see lots of 3458's more than any other 8.5 digit DMM running on the test probers.  At least with what I work with.  Almost all the probers I know of are designed to work with the 3458's as the DMM device, but you do see other vendors sometimes.  Not often but there are other DMM's at work.  Generally you will need several DMM's at a probing station if you want any throughput, and in general you want all the same model DMM at the prober.  Sometimes you don't need that though, it just depends on the product going through the prober.

HP ripping off people with the "better" Vref and charging people $$$$ for it: I 100% agree with you that's a dirty practice.

I'm still not clear on the Volt-Nuts crowd chasing after a 3ppm / yr drift with LTZ1000A vs maybe 1ppm/yr with LTZ1000, and why that is a net benefit, but I am all for people giving it a try if that's what they want.  Go for it!   I am looking at more the net benefit 10 or 20 years later, and from what I've seen - there just isn't a lot a difference between the two devices over long time spans.  If you have a different experience on devices running 20 years, then that's good to know.  I will stand by my advice: If you have a good, quiet stable LTZ1000a, and you've dialed the heater resistor down to 12.5k~13k over 1k, there may not be a huge benefit to swapping out the LTZ1000a with a LTZ1000.  You might be trading out a "good" LTZ1000a for a "bad" LTZ1000.

In any case years down the road they will be drifting at about the same rate, and I have seen that over and over again.  That's all.  If you see a good benefit over the first 4 or 5 years, then that's a good thing to know.

I keep telling my buddies that want to play with these Vrefs at home, and this will apply to 199/399/LTZ1000(a):  Get an older one that's been in use at least 4~5 years.  That will get you a head start on good stability.

I guess that's all part of the fun!
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on July 21, 2014, 04:51:11 am
Quote
Generally you will need several DMM's at a probing station if you want any throughput, and in general you want all the same model DMM at the prober.
That's why K2002 have so called 3458A-compatibility mode for GPIB interfacing, I guess.

I'm still not clear on the Volt-Nuts crowd chasing after a 3ppm / yr drift with LTZ1000A vs maybe 1ppm/yr with LTZ1000, and why that is a net benefit, but I am all for people giving it a try if that's what they want.

I'm asking that question myself every day :)
Probably real answer is that one have some extra cash to spend on toys for fun, same as buying 8.5d DMM for home lab, and leaving it off most of time.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ltz2000 on July 21, 2014, 08:37:50 am
It seems that this has become a "fight" between the metrologists and the industry guy MisterDiodes. I have no experience of his playground, the semiconductor industry, except once visited a factory and spotted a number of 3458As, but I think he has a good point.

I believe too that the 3458A was not designed for the metrology labs. Of course they market and sell it to every possible application they can, but the emphasis must have been where the money comes from. They could have easily made a sister version, but I guess the market was not big enough.

We think the the 3458A is an expensive high end meter used only for the most demanding applications. But for example in military and aviation $10k is nothing. Hourly service rate can be higher as well as the simplest spare part. The 3458A is specified because it is known to be good, it is used everywhere else, the GPIB commands can be copy-pasted and believe or not because it is a full rack width unit (no need to play with flimsy half rack adaptation kits). It was quite common to see a 3458A in a "wrong company" with a function generator and a programmable power supply measuring something as simple as the supply voltages and their ripple.

For the 3458A, it was also designed for use in up to 55C environments [don't ask me why-- I have no clue]

Business? The ratio of instruments sold must be something like metrology labs 1 - automated test systems 100.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 21, 2014, 07:15:31 pm
Hello Andreas - long time ago you posted in this thread this schematic and I have a few questions:
T2 is an n-ch JFET boost stage that also acts as a pull up to force the start up of U2A in positive direction, well I am wondering why:
- you have added an extra pull up R13 (47k) ?
- you have added a min. load resistor R17 (22k) but you have already other resistive loads available (R4/R5) ?
- If you add 10k series gate-resistor to T2 (to limit output current of U2A in boundary situations), you could remove (short ?) D2, as T2 fulfills same task - even better to replace T2 with a BSS159 (depl. MOSFET) - did you consider this (removing D2) ?
- Why is R9 present ? Even LTC confirms in its ref. design that it should not be used with LTZ1000A-version.
Thanks and have a nice day !
Best regards,
gazelle

Hello gazelle,

Ok R13 is not necessary if the FET is already populated.
But I also wanted to have a fallback solution in case the FET would not work.
So R13 is populated.

R4 / R5 are not visible to the OP-Amp. The FET (or the diode) act only in one direction
this will make oscillations of the LT1013 rather likely.

I adopted the cirquit from a LM399 (together with a BF245A/B).
There I had (small) oscillations without the pull down.

D2 was also intended as fallback solution to the original cirquit.
Then I decided to let it in to avoid gate currents through the FET diode.

I did not consider a depletion MOS-Fet. (The BF245C were already in my drawer).
Question: how do you plan to limit the inrush current on power on
with a low ohmic device like the BSS159?

By the way the BF245C is no longer produced in TO-92.
So you would have to use the SMD part (= BF545C).

With R9 you have found a weak point in documentation.
It is not populated with my LTZ1000A, but I did not mention this on the plan.
(The cirquit could also be used with LTZ1000 as fall back solution).

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 21, 2014, 09:17:46 pm

Isn't there a conductive path from output of U2A through D2 feeding R4 / R5 ?
I assume D2 is stuffed.

Hello,

D2 is populated.
D2 is normally not conducting since the gate of the FET is more negative than the source.
(and more negative than the zener voltage).

I have around 6V at the OP-Amp (U2 Pin 1) with 7.2V at the Zener.
So I gain about 2V of supply voltage headroom against a 1N4148 diode.

with best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on July 22, 2014, 05:00:37 pm
OK, I want to make one thing VERY Clear:  I -really- do appreciate all the work and generous sharing of information provided by DR Frank, Andreas, Digelent, and everyone else and this is a GREAT discussion, and a GREAT collection of very smart guys.  It is an honor to post some data once in a while.   My hats off to all of you because I know how much time and patience all of this takes.  Why do I tell you to wait a few years and re-test Vref when its settled down?  Because that's what we are dealing with here.   What I am trying to provide to the discussion is some feedback from the real world, and trust me - I understand the Volt-Nut vibe - its fun and addicting, for sure!  But I have to mix the desire for ulta-precision with pleasing customers (enough to pay their invoice) and to make a profit in a reasonable time frame: Truth be told, my main goal is to not get a phone call at 2am because some machine went down halfway around the world, so I have learned to really make the stuff last.  Other designers scoff because I tend to over-design, but then again most of the stuff we made in 1985 is still running - except for a brain-dead EPROM here and there.

I'm also old enough and lucky enough to have the stars align to have met the likes of Jim Williams and Bob Pease (working on other projects, not Vrefs) and they really were absolutely brilliant, and great to work with.

I didn't know I was in a "fight" with anyone, that is the very last thing I want to do -  I think what I failed to make clear is the difference between a carefully controlled lab at home or a very carefully temperature controlled metcal lab (I think this is Dr Franks expertise) vs. a production environment where you can't trust how abused these things will get, and how long does something last - and that is something I deal with on a daily basis.

As David Jones points out, if you are designing a Vref for a product, the "Ambient temperature" can be "a real trap for young players".  And what you will find missing on almost all high end DMM / Vref datatsheets is the RATE of CHANGE of ambient temperature that is allowed, and this will bite you in the butt every time when you deliver a product if you're not ready for it, and no SPICE simulator will handle this at all. This is one of the places where THEORY ends and REALITY begins.  For instance, the '3458 is rated for 55°C ambient, but you'll see in a moment why that is only part of the story.

Now:  Here are some real world numbers I jotted down from a facility I was at yesterday.  I tried to take pictures for you guys but it is not allowed.

The setup:
Test Prober station #6 has 4ea HP/Agilent 3458a's.  All are on 90-day recal schedule, and they are staggered so that there is only one new unit running at a time.  They range in age from 4yrs old to 14 yrs old.  None have had their Vref replaced or modified, but two of the older units have new VFD front panel displays replaced. There is one box with a pretty dim display that will need a repair soon, but as a computer-controlled DMM it is running fine.

 These are in a 19" rack, stacked near the middle.  Overhead are some test prober relay switcher boards and a couple blade PC's (one is running the prober & DMM's, the other one is dedicated to data logging and sending data to the inventory-control system, because at this station every working device is serial numbered and sorted into quality bin lots).  Under the DMM's are some power supplies, more relay boards and more power supplies.  Because the prober is known to create a small amount of dust, it is surrounded by a plexiglas glazing safety shield doors and the enclosure is under slight negative pressure to keep the dust inside. The doors are only opened up when a stack of wafers are installed or removed.   The whole thing is in a cabinet against a wall, on the other side of the wall is an air compressor and chiller and a bank of vacuum pumps.  There is also a high-pressure Osmosis - De-ionized water processing station. In other words the wall is fairly warm to touch.  To the right of the cabinet is another machine's motion control cabinet and power supply.  It is very warm also.

The room itself is running about 27~29°C on a very warm day outside.  You have to wear a Tyvek bunny suit, hood, mask, booties and gloves, and you wish they would have the temperature lower, but that's what we have on the menu today.

Inside the '3458a boxes, with the machine idle, bottom to top, the interior temps are 38, 41, 43 and 40°C.

Now here's the fun part:  When the prober starts, and then when the machine on the right starts, and then when you notice more vacuum pumps are online on the other side of the wall... The interior DMM temps are now reading 43, 46, 50 and 44°C when I check again, about 15 minutes after everything starts up.  Typically a 5 degree jump in about 15 minutes, or a rate of change of 20°C / hour.

NOW:  What makes this work in this situation is the data being collected is 6 or 7 digits, and the software compensation / ACAL routines running inside the '3458 are able to compensate well enough so that the testing operation is still working right.  AND the Vref Die temp is running at the higher temperature for stability during temp changes. The manager mentioned that they do get special support from Agilent in the form of customized firmware, and they do calibrations at more like 34 or 35°C.

So this is a different situation that you would encounter in a Volt-Nit or metrology lab situation.  BUT as a designer, I have to plan ahead for major abuse.

Bottom Line:

YES, for a cooler, temperature controlled lab, running the LTZ1000(a) at a lower temp makes perfect sense.  If your VRef is going into a very abusive environment where the temperature swings are sudden and relatively rapid - well then you really need to raise the Vref die temp to keep your Vref relatively stable, no matter what's going on around it.  That's one of the reasons '3458 have the die temp set as they are, and I've never really seen one that has "degraded performance" if the DMM has to work hard for a living, at least not over the 90-day calibration period (recommend by Agilent when these units are used like this - nobody ever expects these to run over a year without recal in this setup).  Even then you will need some compensation software to help smooth out the dips and glitches, and the '3458's do a pretty good job at that.

They have tried other DMM's on this rack, but the '3458's run the best while being abused.  At least in this setup.  I know there are other brands and I will not argue with you that they work well also in other situations.

Oh and by the way:  This is something else Vishay leaves off the data sheets of their very expensive magical resistors:  See how the tempco acts during high-rate-changes of temperature, and compare that to a wirewound - and then remind me why the Magical Vishays cost 10 times as much.  Lets just say I have never seen a 10 times performance increase, but that's just me.  I have never seen any sort of cost benefit ratio at all, at least for the stuff I design (like 20 / 24 bits DACs/ ADCS and high-precision current sources).  The main point I keep streesing:  After 10 or 20 years, these Vrefs tend to settle down and become very good performers even without any voodoo, magical datasheet gimmicks at all.

Your milage will vary, and to all Volt Nuts: I love reading about what you do and how you get there.   Honest!    The generous sharing of information here is fantastic!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on July 22, 2014, 05:41:50 pm
Mister Diodes,

me also, I do not see any "fight" here, but a objective - excited discussion.
And I really appreciate your very interesting descriptions from those rough industrial conditions.
By the way, the high MTBF of the 3458A is another argument for these applications, I think.

Anyhow, what we have found out here in this thread, is that it would have been quite easy and cheap for HP to offer a metrological option also, let's say OPT 03 with 1ppm/a  @ Ta < 35°C, as it was done by the FLUKE 3458A/HFL modification, with 3ppm/a DCV stability, a more stable reference resistor,  and specified Ohm Transfer stability.

Reading again the HP Journal 4/1989 about the LTZ reference, the HP engineers obviously did not think about that at that time, 8ppm/a was top notch for them.


I was one of the early users of this instrument, at university in 1990 or so.
The laboratory was not air conditioned (+10..+15°C), and the instrument was placed in a rack with other instruments (+10°C), so it had up to 50°C internally.

Therefore it was good, that the LTZ was running on high temperatures.

On the other hand, a better annual stability would have been better for the calibration of the current sources and the thermometers over the years.

But it was ok, 100ppm was required.

And the 100k/16Bit sampling capability @low SNR was the key feature of my experiments.

Well, that's yet another use case besides industrial applications.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: ltz2000 on July 23, 2014, 11:52:20 am
Andreas,

Slightly off topic, but could you (or other members) recommend an easy and economical way for recording humidity. You seem to have some sort of electronic sensor with voltage output (?) in your automated data collection system.

And totally off topic, what is the name and version of your schematic editor. The "style" looks very familiar but I can't remember the name of the software.

https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=102804;image (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=102804;image)
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on July 23, 2014, 02:31:37 pm
Andreas,

Slightly off topic, but could you (or other members) recommend an easy and economical way for recording humidity. You seem to have some sort of electronic sensor with voltage output (?) in your automated data collection system.

And totally off topic, what is the name and version of your schematic editor. The "style" looks very familiar but I can't remember the name of the software.

https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=102804;image (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=102804;image)

Just introducing a Lascar EL-USB-2 at work, right now it runs a competition against a more expensive logger. ~80 EUR and with free Software.
Very easy, less economical depending on where you are.
If you dont mind to read out data by yourself, a DHT-11 or SHT-11 might be an option, too.
Very economical, but you need some readout.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on July 23, 2014, 04:53:33 pm
Another intangible factor about what DMM is more popular (or not) on a real world situation is the customer service you get when you buy a product.

For instance, the particular facility I was at on Monday has an agreement with Agilent / Keysight that if they have trouble with a unit, it just "gets fixed".  There is a local tech less than an hour away they can call in anytime, and if a unit needs to go back to Colorado for repairs, there is a replacement unit online within an hour or two.  Anything shipped to / from Colorado travels via special courier van on an airbag mat in the vehicle; it doesn't travel by common freight carrier.  That way the chance of rough handling is minimized, and you know your instrument didn't sit broiling in the sun on some shipping dock somewhere.

I know other vendors offer these kinds of services, but in this case the production manager had a lot of praise for Agilent for keeping the products running.   They do have other DMM's, but in this case the other vendors aren't able to offer the same level of customer support at this location.

You have to pay for this and be a big customer, but it is an example of why a facility selects one instrument vendor over another, and this is a factor that doesn't show up on basic performance spec sheets.

My advice to anyone shipping a high-end product:  Keep your customers happy, no matter what.  In general they are happy to pay more for a product if that includes excellent customer service.  A lot of vendors have forgotten that good customer service is a major part of the sale.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on July 29, 2014, 07:02:47 pm
4) It's been 20 years, so he didn't know the exact numbers, but Q1 is only rated to a few hundred micro-amps of collector current.  [This means my single-resistor idea will *not* work! -- back to the original circuit from the ap-note!]  Q2 will have a max rating of around 1mA, and the Zener can take quite a bit more.
I dug out my LTZ1000 with the dodgy heater isolation to do some more experimenting with it over the weekend, and I can report that it still functions after a 5mA Q1 collector current for about an hour (till I remembered this post and cut power.)  It was being run with a TEC+heatsink+fan (cycling the TEC on and off), which may have helped it survive.  It should be noted that driving the transistor that hard made the TC of the reference about 2.5x worse. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on July 30, 2014, 03:23:01 am
In the various threads concerning the voltage divider required for the LTZ1000/A (actually two dividers would help....can anybody guess where the other divider goes?)

Are you referring to the technique (I first saw explained by Dr Frank  https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg240405/#msg240405 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg240405/#msg240405)) of using one divider to trim the zener output to exactly 7, then using 10 "identical" resistors to implement the gain divider to get to 10V?

You are in the right neighborhood, Dr. Frank's setup is quite interesting but a bit complex and all those Vishays are going to cost.  It does indeed involve the LTZ1000/A's zener diode and its TC... keep thinking you are close.  The 12.5K / 1K divider could also benefit as well.

Moving this conversation here since it's specific to the LTZ1000 circuit.  Has anyone else been noodling on this?  Now that I'm in the head space of the LTZ1000 circuit, I gave it another go using the hint provided. The zener has a positive TC, the two Vbe have a negative TC.  The "theory" is that the TC of Q1 and of the zener are matched such that Vbe going up (which increases Iz as well) compensates Vz dropping (and vice versa) so VRef doesn't change. But in practice, the result is usually a net TC of about +50ppm/C.

This means the temperature set point changes with reference temperature.  VbeQ1 could be used to counterweight the set point and remove that voltage shift.  Something like the attached image? 

Does this actually matter? There should still be a single temperature that the control loop targets even without this extra resistor. This has several side effects I an think of.  First and most obviously, this resulted in a final set point about 1mV lower if the other resistors aren't changed.  Second, I think this would effectively add to the proportional gain of the PI controller.  I don't know if that would be good or bad if using the datasheet provided gain values! I think 100ppm change of this added resistor would change the final output by like 0.002ppm, so that's not an issue.  Am I missing anything?  Are there going to be any noise issues with a largish resistor there?

So, on to the ~7->10 divider.  The same trick can be applied to the non-inverting input of the amplifier, though it drops the input voltage (and very slightly raises the zener current.)  Ah... this is why you were saying Dr Frank's approach is close: The divider he uses to bring the voltage from 7.x down to 7 would also serve to reduce the TC of the circuit if it was between VRef and VbeQ1 instead of VRef and ground!  With the values I'm simulating with, the voltage would have to be dropped all the way down to 6.22 to completely cancel the TC of the reference, and dividing it that low means that a 100pm shift in that divider contributes 13ppm error in the 10V output (instead of < 3ppm by trimming to 7.)
 Trimming to 7 appears to reduce the TC by about 10%, with very little other consequence.  Not bad!

Thanks for the puzzle!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on July 30, 2014, 06:05:40 am
The most thorough analysis of LTZ1000: http://bbs.38hot.net/forum.php?mod=viewthread&tid=88278 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=88278) (use google translate)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on July 30, 2014, 06:56:27 pm
Edwin was referring to an LTZ1000A circuit that I shared with him.  Placing 20R to 22R of resistance in series with the Zener [at the cathode] with the anode resistor at 100R, and the Q2 collector resistor at 34K lowers the +50ppm/K TempCo of the LTZ to less than 5ppm/K [and that is without the heater].
Putting a resistor at the zener cathode is the datasheet solution to reduce TC, so I wasn't really considering that as an answer.  I'm surprised only 5ppm/C can be achieved this way, but I haven't tried it yet myself.  I hadn't thought of that resistor as part of a divider, though, that's an interesting perspective.  I'd considered that since Iz goes up when VbeQ1 goes up, putting a resistor in series is a way of adding more contribution from VbeQ1 and thus increasing the contribution of its TC.

Why lower the collector resistor to 34k?  (Btw, the datasheet calls the temp sensing transistor Q2, but I think you're talking about the TC compensation transistor.)  This would seem to work against the goal of reducing TC because a higher collector current will reduce TC of the transistor and require a larger cathode resistor.  I would think that the collector resistor should be increased to compensate for the increase in reference voltage and try to keep collector current at 100uA.

Mickle T: Thanks for the link! Will have to digest that this weekend.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on August 09, 2014, 06:43:30 pm
I made up a model of the LTZ1000 complete circuit in LTspice guessing a 5087 for Q 1 and Q2, as they are small signal transistors, anyway it seemed to me to be on the verge of oscillation without some help to tame its frequency response, so I can understand Mickles comment about noise sensitivity.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on August 10, 2014, 04:25:59 pm
Hello MK,

I think that the 2N5087 probably has a little too much gain for the circuit, a minimum  hFE of 250 up to 800, I've found a lot of the 2N5087s tend to have gain around 500-600.  I would think a gain of roughly 100-200 would be closer to the mark.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on August 10, 2014, 06:54:57 pm
Perhaps he meant to say a 2N5088 instead, similar specs.  I missed the PNP, should be a NPN of course.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on August 11, 2014, 07:51:40 pm
Hi,

my mistake, it was the 5089 I used as a small signal transistor to model the npn's on the die, but as Edwin says the beta is probably too high for some aspects of modelling what is happening.

Does anyone have any other suggestions for a small die transistor to act as Q1 and Q2? but now that I know there is a huge size difference, is there an even smaller transistor available to use for Q2?

MK
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 19, 2014, 04:45:12 pm
Hey folks.
How much time does properly designed and constructed LTZ1000(A) ref takes to get stable output, counting from power on?

Also what is usual current consumption of reference, given that temp set to 12K/1K resistors and powered from +12 or +15VDC?
Is 10.5mA sounds corrent?

(http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/small/ltz1000_initial.jpg) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/ltz1000_initial.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on August 19, 2014, 05:13:59 pm
Hey folks.
How much time does properly designed and constructed LTZ1000(A) ref takes to get stable output, counting from power on?

Also what is usual current consumption of reference, given that temp set to 12K/1K resistors and powered from +12 or +15VDC?
Is 10.5mA sounds corrent?

(http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/small/ltz1000_initial.jpg) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/ltz1000_initial.jpg)

What a beautiful banana plugs in 2002 :-D It is some type of punk?
Title: Re: Ultra Precision Reference LTZ1000
Post by: SeanB on August 19, 2014, 06:26:45 pm
To ensure a very clean connection of course.......
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 19, 2014, 08:18:31 pm
Hey folks.
How much time does properly designed and constructed LTZ1000(A) ref takes to get stable output, counting from power on?

Also what is usual current consumption of reference, given that temp set to 12K/1K resistors and powered from +12 or +15VDC?
Is 10.5mA sounds corrent?

Hello,

I have around 20 mA / 21 mA @ 23 deg C environment with 14V and LTZ1000A and setpoint 12K5 / 1K with good thermal isolation.
so 10.5 mA is rather low.
You either have a perfect isolation of your LTZ or something went wrong.
The zener alone needs already 4-5mA the Op-Amp also 1mA and the Setpoint divider also 1mA. So there is almost no heater current.
I also think that 12V is too low (will need a long startup-time).
I have not measured the startup time (since my devices are on 24/7) but it should be around 15-30 minutes.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 19, 2014, 11:33:04 pm
I see, then I f'up somewhere again, as voltage still bounces around way more than few ppm.   :-BROKE
With +15V current is 12 mA, which is still seem too low.

As of connection, I just stuffed something proper size to keep copper UTP5 wire in banana connector fixed and not have big thermal mass :) Cleaning sticks are just perfect size for bananas  :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 20, 2014, 05:45:22 am
Hello,

I guess you have interchanged Collector and Emitter of your heater transistor.

how high is the heater voltage?
If I have calculated right you should have around 6V+0.7V (Diode) at Pin 1 of the LTZ1000.
Which would give around 20mA at 28 deg room temp / 40 deg setpoint for the heater (300 Ohms).
The Op-Amp output should be around 0.7V(+0.2V resistor) higher (at 7.6V)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 20, 2014, 06:46:16 am
No, that was fixed already. It was inverting input resistor connected incorrectly to VREF out, so heater was not heating :)
Now it's running. I'll do measurements when get home.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 20, 2014, 09:36:33 am
Thanks!

Initial data with working reference (http://dev.xdevs.com/attachments/1034/unit3_log.png). Spikes and sags are due to dirty lab environment with lots SMPS's turn on/off around :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 08, 2014, 03:43:15 pm
Had LTZ1000 + LTC2057 ref running over couple weeks, discovered wierd low-frequency oscillation on output.
I think it's heater circuitry control, as consumption current is following trend, going from ~28.5 to 30.5mA.
Probably temperature setpoint is too low, this ref using 12K + 1K resistors.

Will test other units with different opamps and LTZ1000A, too see if it happens there too.

REF was powered from Keithley 2400 SMU, +13.000VDC set.
Sampling speed is every 2000ms, settings are:

Code: [Select]
:SENSE:FUNC 'VOLT:DC';
:SENS:VOLT:DC:DIG 8.5;
:SENS:VOLT:DC:NPLC 10;
:SENS:VOLT:DC:RANG:UPP 20;
:SENS:VOLT:DC:AVER:COUN 10;
:SENS:VOLT:DC:AVER:STAT OFF;
:READ?

8.5digit, 10 NPLC, Autozero syncronous.

  :-/O

Reference was enclosed in foam box and taped around, which was put into small plastic cage.
Tried various ambient temperatures, +24c to +30C, was same result.

Started study on LabView to setup nice logging setup. I already got Keithley 2001-TCSCAN card for my 2002, which is 10-channel scan card.

Have idea to use Keithley 7001 as a box for multiple LTZ1000's references. It have nice shielded compartment, can have one scan/digital card to mux outputs/ratios.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 08, 2014, 06:22:57 pm
And you are shure that the 2002 is stable?
I also had around 2uV unstability on a K2002 with my references.

I would try the following:

- Measure the difference between 2 LTZ1000 (higher resolution)
- install a 10-100nF Cap between base + emitter of the temperature sensing transistor of the LTZ (Pin 6+7).
- how does the LTZ temperature (your sensor) behave during shifts?
- does the heater voltage change also?

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on September 08, 2014, 06:48:15 pm
Well,

12k/1k is perfectly fine and stable for 45°C on a LTZ1000, but environmental temperature is limited, and it's not suited for the A version (??).
(The photo is not sharp at all, but I think you have an ACH type here, and then, 45°C is too low.)

Your measurement seems to be 17 min time span, I guess, if your time scale is seconds.
Your output shows about 1µVpp (=0.15ppm) short term noise plus possible superimposed 3.5 µV (=0.5ppm) of longer termed oscillation, period of ca. 2.5 minutes.

I also use 12k over 1k , LTZ1000, LT standard circuitry, and get less than 0.15ppm = 1µVpp noise, see again a typical measurement on my LTZ1000, NPLC 100.
That is totally normal, covered in the datasheet.

If your superimposed oscillation of about 0.5ppm is real, something else is fishy, either in the Keithley instrument, or as the period seems to be about 2.5 minutes, some thermal issue like a regular air draught or so.. Maybe there's a fan going on and off..
Hope all of the solder junction are also thermally isolated.

Besides that, the amplitude of the basic noise of your circuitry is very acceptable.


Frank

PS: Added the 10min stability figure from a "quiet" time area, the noise is even less: +/- 0.05 ppm = 0.7 µVpp.
PPS: I use NPLC 100 , but 4 sec measurement time, with Auto Zero On which doubles the measurement time, and I take data as fast as possible.

Check whether your Keithley is set up properly, e.g. if it also does Auto Zero on each measurement (synchronous AZ doesn't tell me anything).

And your 2000ms measurement time does not fit to NPLC 10 (which is 166 or 200ms). Or do you average 10 samples for one data point?

PPPS: Be aware, that your self built reference is or might probably be more stable than your Keithley instrument!
At least, as you measure the "naked" output voltage, whereupon your instrument (and any other 8.5 digit instrument ) includes additional circuitry or measurement modes which in sum are less stable.

Therefore, distrust your Keithly more than your circuitry, in first instance..   

4PS: One last idea.. the other guys mull something about mains beat frequency and AC disturbance, .. naah wouldn't explain directly oscillation with 2.5minutes.. But on the other hand, if you operate that circuitry unshielded, it is extremely susceptible to AC noise signals... those spikes you see in your measurement, and in mine, are evidences for that.

I also observed longer termed changes (dips & more) due to AC noise pickup, especially when I turned on my LED light, which has an switching mode PSU..

Afterwards I have thrown out all switched modes PSUs of my analog lab, and I am using light bulbs again, which run on 50Hz, here.

Problem solved. Maybe you check shielding and turn off ALL switch mode PSUs in your lab..

Is your environmental temperature stable during measurement??

I can achieve a few tenths of °C over 35h..w/o air conditioning.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 08, 2014, 07:08:20 pm

If your superimposed oscillation is real, something else is fishy, either in the Keithley instrument, or as the period seems to be several minutes, some thermal issue as regular air draught or so..


Perhaps wrong mains frequency? or a beat frequency with mains?

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on September 08, 2014, 07:11:42 pm
perhaps your thermal set point circuit has an rf oscillation that is affecting the setpoint? or pehaps with a low demand temperarure you need to slow down the max rate of heat input so that the heatup and cooldown timeconstants are not too far apart, put a resistor in series with the heater for instance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 09, 2014, 03:57:58 pm
I have quite wonky setup right now to collect data by LabView, so time scales and sampling speed is longer than actual measurement.

I gathered data from unaged another LTZ1000A-based reference, but now added EDC MV106 output (measured by cal'd K2001)
and added current output data from K2400 (which is powering LTZ ref to +15.000VDC)

Here's overnight data with airconditioned room, where all gear reside, with temperature variance shown on graph.
LTZ1000A definately looks way more stable than non-heated zener-based MV106.

Autozero on both K2002 and K2001 set to syncronous, which means:

Quote from: manual
Synchronous (the default mode) is the most accurate,
but slowest mode. In this mode, each trigger causes
three A/D conversions: one for input signal, one for an
internal zero, and one for an internal gain. This mode
also yields a constant reading rate.

And all instruments powered from 60Hz 110VAC.
There are few other gear working around, so I cannot say it's pure clean environment.

I will try with capacitor between pin 6 and 7 later.

Next plan is to make an assembly board with 3 x references powered from Linear LT3081ER LDO and powered from separate linear power supply, or maybe even car two car batteries :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 09, 2014, 09:31:48 pm
Hello,

whats that:
the LTZ1000A (heater-) current increases when temperature is rising????
Are you shure that the op-amp pins are not interchanged?

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 10, 2014, 12:24:20 am
Sorry, i missed label :) Heater works correctly, current goes down with temperature raise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 10, 2014, 01:07:55 pm
More data, LTZ1000A raw output overnight.

Upper chart - EDC MV106 +7.13663 VDC output to Keithley 2001
Lower chart - KX LTZ1000A ref output to Keithley 2002

Both run NPLC 10, 8.5 digit mode.

Current "spikes" - I manually turned off +15V source, to "sync" graphs, as right now all data is collected by two separate labview modules,
will work later to use one labview app to get data from both SMU and multimeters.

Next step, run group test on all five LTZ references with Keithley 2002 + scan card as logger. Also will gather MAX6610's temperatures.
Title: Re: Ultra Precision Reference LTZ1000
Post by: JesT on November 05, 2014, 03:27:19 pm
This is my first post on this forum.

A while ago I stumbled over Dave Jones’ videos and that revived my longtime slumbering interest in electronics (actually, I started building stuff over 60 years ago, mostly audio and test instruments, including an oscilloscope).

I have always had an interest in accurate measurements but have never owned any really good instruments, simply because they were too expensive. I was therefore intrigued to see in DJ´s videos all the quality vintage stuff you can buy at reasonable prices (until DJ promotes them, that is!). I had no idea these treasures existed.

Later I dug into the eevblog forums - especially this LTZ1000 forum and other fora on voltage references, precision resistors, power supplies and DMMs.

I have learned a lot during the last 4-5 months and I´m so impressed by all the people in here - professionals and amateurs - who readily share their knowledge, academical as well as practical, make experiments and discuss possible solutions to problems, all in a very friendly tone. I have been through these 62 pages (including links) several times and learned something new each time.

I believe I´m now ready for action. My plan is to build 4 units with LTZ1000 and 4 units with LM399. I have got the components, the references are burning in and I´m going to make PCBs (Eagle is new to me, too, I´ve only made PCBs with photoresist over 40 years ago).

Why on earth am I doing this and what do I expect to get from it?

Well, I´m doing it mostly for the fun of it. I think the fun comes from the fact that it is really challenging to do these things well. If I didn´t know beforehand, I know it now, thanks to all the good people who contributed.

Hopefully, the result will be that I have some references that will give me confidence in my (presently 8 ) DMMs without the need to formally calibrate all the time.

Regards

JesT 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 05, 2014, 09:47:35 pm
Hello JesT,

welcome to the club.

4 references of each is a good number to start ageing comparisons.
I hope you will publish your design here.
And dont forget to use a good thermal isolation for the references.

Which resistors did you chose for the LTZ cirquit?

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: wiss on November 06, 2014, 10:28:27 pm
I am currently working on a design for a "poor man's thermal converter" that can be used to measure AC waveforms very accurately.

Please start a thread on this subject! :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: bingo600 on November 07, 2014, 09:28:56 pm
if you are like me you will be compelled to make or buy some ultra high precision and/or stable resistors.  It just gets more crazy after that...

Ohh yes to the CRAZY part

I started with a HP34401A , and a Geller SVR/SVR-T
Then i build a LM299 Ref (Branadic version) , and i now have all the parts for a LTZ1000 ref (PCB sponsored by quarks).
Note that the LM299 & LTZ1000 are the cheap parts ... The resistors (Outchh)

Then i got a new problem ... How to accurately measure a LTZ1000.

Solution (Big Outchh) ... But i got my dream meter


/Bingo

Ohh , on the picts i have't done the ACAL ALL yet (my first power on)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 07, 2014, 10:04:14 pm

The resistors (Outchh)

Then i got a new problem ... How to accurately measure a LTZ1000.

Solution (Big Outchh) ... But i got my dream meter


Hello Bingo,

Which resistors did you choose?

Your problem is still not solved: LTZ1000 accuracy is around 1-2 ppm/year.
HP3485A is specced with 8 ppm/year.

So you will at least need one (up to 4) Fluke 732B to calibrate the HP each time before you measure the LTZ.

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: bingo600 on November 07, 2014, 10:19:06 pm

The resistors (Outchh)

Then i got a new problem ... How to accurately measure a LTZ1000.

Solution (Big Outchh) ... But i got my dream meter


Hello Bingo,

Which resistors did you choose?

Your problem is still not solved: LTZ1000 accuracy is around 1-2 ppm/year.
HP3485A is specced with 8 ppm/year.

So you will at least need one (up to 4) Fluke 732B to calibrate the HP each time before you measure the LTZ.

With best regards

Andreas

Andeas i suppose you meant 3458A .... It's an OPT-002 (4 ppm/yr) from early 90's so well aged reference.

And i know ... Was thinking about a 732A , but have spend my "toy budget for a while".

If i get the 732A , the next i need a ESI SR104  ... It never stops.

I got econistors , but was thinking about getting a "set from edwin" , didn't you get some from him ?

Next project is to replace the 3458A calram , and prob. the storage rams also , and then while i have it open ...
Upgrade with OPT-001 (only 10$) in ram chips.

/Bingo
Title: Re: Ultra Precision Reference LTZ1000
Post by: HighVoltage on November 07, 2014, 10:28:06 pm
Solution (Big Outchh) ... But i got my dream meter
Congratulations on fulfilling your dream.
Your 3458A looks very clean, even inside the binding post copper area.
Now you need a Fluke 8508A for comparison
It seems like a never ending spiral for just one more digit of precision and accuracy.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 08, 2014, 02:01:15 pm

Andeas i suppose you meant 3458A .... It's an OPT-002 (4 ppm/yr) from early 90's so well aged reference.

And i know ... Was thinking about a 732A , but have spend my "toy budget for a while".

If i get the 732A , the next i need a ESI SR104  ... It never stops.

I got econistors , but was thinking about getting a "set from edwin" , didn't you get some from him ?

/Bingo

Hello,

yes of course the 3458A.

Caution the Fluke 732A  is specced with 6 ppm/year.
I meant the Fluke 732B which is specced with 2 ppm/year for the DMM.

For the resistors: I still have no price indication from Edwin for his resistors.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: JesT on November 09, 2014, 12:36:12 pm
Hello JesT,

welcome to the club.

4 references of each is a good number to start ageing comparisons.
I hope you will publish your design here.
And dont forget to use a good thermal isolation for the references.

Which resistors did you chose for the LTZ cirquit?

With best regards

Andreas

Hello Andreas,

Thank you for your welcome!

I chose 4 units from the following reasoning:
1 unit: You feel happy, but really, you know nothing
2 units: Maximum uncertainty, if different, which one is right?
3 units: Better, the two agreeing are (probably) right
4 units: Even better, three units agreeing can’t be wrong (or?)
You could go on forever...but you have to stop at some point.

I will in due time present my project in detail. For the time being i will just say that there will be 4 units with a buffer to unify to 7 V for each unit, a separate unit to boost the individual unit or the average to 10 V and 5 isolated external linear power supplies.

In my humble view the most critical parts are the PCB (avoiding EMFs from temperature imbalance) and the resistors in the boost unit. I see resistors for the LTZ1000 circuit itself as a lesser problem when it comes to their contribution to the total error budget.

For the LTZ1000 circuit I have bought 5 sets of used Vishay S102 0.01% resistors. They have pretty short leads so they will, no doubt, be influenced somewhat by soldering.

I will first make a prototype with one of the 5 sets in order to check the working points, stability (additional compensation?), temperatures and TC in the circuit with all four LTZ1000. This may lead to changes in the final version. The prototype will NOT be able to determine whether the resistors are good enough.

The booster will be a copy of dr. Franks (first post on page 13), only with 10K wirewound resistors instead of 50K (yes, 50K would have been better). I’ve bought 20 old new ones, unknown manufacturer, 0.01%, all of them still within 0.0035% with a TC of 3-5 ppm/?C by a rough test. I will match these resistors by value/temperature compensating each resistor until “perfect” tracking (0.2-0.4 ppm?). It can be repeated anytime in order to conserve accuracy, so ageing is out of the equation.

I have comtemplated using LTC1043 for dividing/transferring voltages up and down. On paper the specifications look very promising, but according to your own experiments it is not that easy. Anyway, I have bought some and will play with them - someday.

And, no, I won’t forget isolation! Who could after reading Bob Dobkins comments? (Thanks, DiligentMinds)

Best regards

JesT
Title: Re: Ultra Precision Reference LTZ1000
Post by: JesT on November 09, 2014, 03:17:38 pm
<snip>
Why on earth am I doing this and what do I expect to get from it?

Well, I´m doing it mostly for the fun of it. I think the fun comes from the fact that it is really challenging to do these things well. If I didn´t know beforehand, I know it now, thanks to all the good people who contributed.

Hopefully, the result will be that I have some references that will give me confidence in my (presently 8 ) DMMs without the need to formally calibrate all the time.

Regards

JesT

Well, it sounds like you have been bitten by the "precision bug".  Many of us here in this thread and many on the "Volt Nuts" and "Time Nuts" mailing list also have this affliction.  It can be a rewarding hobby, but at least for me has also been a very expensive one-- always striving for the best possible absolute accurracy.  In real life [as in engineering and technician work] this kind of precision is rarely [if ever] needed.  But that hasn't stopped me from buying a lot of ultra high precision gear.  {...sigh...}  It seems that there is no end in sight.  After building and calibrating [which is the hard part] some precision references, if you are like me you will be compelled to make or buy some ultra high precision and/or stable resistors.  It just gets more crazy after that...  I am currently working on a design for a "poor man's thermal converter" that can be used to measure AC waveforms very accurately.

Hello DiligentMinds,

Yes, I've been bitten. But, officially, I'm not a real "volt nut" - yet - as I do not have a 8 1/2 digit DVM. I have restricted myself to buying 6 1/2 and 7 1/2 meters because the improvement in drift from 6 or 7 digits to 8 digits comes with a very high price tag, both initially and later on (calibration). I really do not need absolute accuracy to perform my experiments with LTZ1000 references, the differences (or lack of such) they will show will be sufficient. Resolution and short term stability, on the other hand, are essential and here, I think, 7 1/2 digit is enough. Furthermore, in my environment, I'm afraid, a 8 1/2 digit meter will not fully come to its right.

BTW, my three HP 3456A (three different series, not the first one with a lot of problems), one of which has been calibrated in 2014, have shown remarkable stability. The two uncalibrated ones differ less than 20 ppm from the calibrated one - after more than 20 years since last calibration. And they have best TC of all my meters. Amazing.

So far I have been able to restrain myself, maybe because I have set up the rules of the game for myself (no 8 1/2 DVM, no high end calibrators, no SR104). Keep it at a reaonable level and get the most fun possible out of it. Only time can show whether "craziness" really catches up with me!

And, yes, so far it has been rather expensive, because I have also bought some other gear (vintage scopes, decade resistors, KV divider, precision voltage supplies and quite a lot of electronic components). I'm looking forward to bringing these beautiful instrument back to their former glory, as far as I can (I do not possess Robrenz' skills, helas!).

Best regards

JesT   
Title: Re: Ultra Precision Reference LTZ1000
Post by: Awesome14 on February 04, 2015, 09:26:37 pm
He says he had an Electrical Engineer with 40 yrs experience look at it and was astounded at the results!


Hmm... only 40 years of experience? For my money, his imaginary friend would need at least 41 years.

My engineer is 78 years old and he is still doing engineering. Presumption is the greatest form of arrogance!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Awesome14 on February 04, 2015, 09:46:13 pm
I would be astounded too, if it works.  I was almost going to buy one for fun, then I realized I had better use for the time & money.  I also asked what the load regulation was, and no answer from seller yet.

I think I'll stick to stuff I know works, and works well for a long, long time.  Like Buried Zener refs.

Let's have a look at someone who actually tried the device. eBay feddback: "Very Fast Shipping, 1hr warm-up on Agilent 34461A & D105 - 10.00000, Fantastic!"

That's not me saying it! It's someone I have no control over; someone I don't know. And the 732A IS within its calibration. I fear what I've done is to unintentionally trivialize the efforts  of others, by making a 2ppm standard that sells for 100.00. It's easier for some to maintain their faith in their own standards/references, by intentional and purposeful ignorance! The only means to find out the truth is to test the device. I have not had anyone tell me that the device is > 2ppm error, regardless of temperature.

I have the most data on this device, so I am qualified to speak. There is zero snake oil. I am an independent research scientist with 25 years experience. When university students my age were taking intro physics, I was enrolled in graduate-level physics classes. I don't design a product by trial and error, or by copying another product with minor changes. This is the holy grail! I must thank God for giving it to me, because I inspired the original aspects of the design. My scientific and mathematical background allowed me to understand the inspiration from a practical perspective.

Electricity doesn't lie! This is the dawn of a new era! But even if others might build the exact same device, it will not work like the ones we make. There is a counterintuitive secret that lurks within the device.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Awesome14 on February 04, 2015, 09:47:45 pm
I would be astounded too, if it works.  I was almost going to buy one for fun, then I realized I had better use for the time & money.  I also asked what the load regulation was, and no answer from seller yet.

I think I'll stick to stuff I know works, and works well for a long, long time.  Like Buried Zener refs.

The D-105 IS a buried-zener ref.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Awesome14 on February 04, 2015, 10:41:13 pm
I would be astounded too, if it works.  I was almost going to buy one for fun, then I realized I had better use for the time & money.  I also asked what the load regulation was, and no answer from seller yet.
The D-105 has a 17 ppm drop from 1mA to 10 mA load.

Quote
It's probably some cheap voltage reference chip in an epoxy package-- enough to not be fraudulent, but not sufficient for an ultra-precise reference.
Prejuduce! The device performs as stated: +- 2ppm from 16-26C. And it only gets better with age! If you want a 10VDC precision reference with an error < 2ppm, then you need the LTZ1000.

Quote
There is no mention of any calibration of the Fluke 732A the seller is using to set the references he sells.
We don't necessarily state what should be assumed of any legitimate source. The 732A is calibrated.

Quote
Unfortunately [and sadly], this is going to make everyone else selling a voltage standard look bad-- whether they are doing it right or not...
If our product makes the competition look bad, it isn't "our" fault. It's their fault for making an inferior product. Every criticism I've seem thus far is without merit, unsubstantiated and based purely on arrogant presumption!

Quote
To make a proper laboratory voltage reference you are going to have to use an LTZ1000(A), or a rather large statistical array of some other type of reference [with temperature compensation].
That's the way it used to be, before the D-105.

Quote
If it's just a "transfer standard",
just a transfer standard ... The Fluke 732B is a "transfer standard."
Quote
Since it is not explained what is in the box, I say: "Caveat Emptor" ["Buyer, beware!"]

If I was an amateur, I would explain what is in the box. I am an honest and honorable professional who is attempting to prove a point: calibration labs have long held electronic amateurs as  second-class customers, practically ignoring them, and doing nothing to accommodate issues specific and unique to amateurs. The D-105 is the device that can help set the amateurs free from commercial calibration labs; basically an "up yours" type of thing. At this stage of my life I am much more concerned with satisfaction than vastly increasing my wealth.

But if the price is too low for you, I'll jack it up a few hundred Dollars.

Given the amount of training and experience, coupled  to the years of work required to produce the D-105, it must be protected by trade-secret. Thus, we don't publish the design. I don't want professionals purchasing the product. That's why I sell it on eBay. I could get a much a higher price, but that's not why I embarked on this project. I evaluated whether or not technology and manufacturing had sufficiently advanced that the project was even possible.

I believed it was possible, and I was correct. Things change every day. Innovative thinking changes the world every day; some in  small ways, some in larger ways.  Protecting the value and usefullness of inferior or obsolete devices by denying the truth about new technology--in a baseless fashion--preserves ignorance. It isn't that much different from some--not all--Arabs who cling to ancient ways in the third millennium.

How would anyone know whether they like toilet paper until they've tried it. But to many in the middle east it's just diabolical western evil-on-a-roll, evil that can only spell the eventual downfall of the western world.

So, if anyone would "try" the D-105, I'm sure he would like it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Awesome14 on February 04, 2015, 10:58:17 pm
This might not exactly belong in this thread with LTZ1000a's (except to do a direct comparison about vrefs for general knowledge), but this is the seller's response when I asked about drift rates on his  ebay device.  I'm not even sure I can understand it.  It might be a pot attached to an LM317 for all I know. I think he's convinced himself its better than a 732a:

Quote
We do a burn-in to minimize drift. These units do not need to be run continuously like a Fluke 732A/B. So, the drift over time is not coherent. These units have a specified drift per first 1,000 hours of use (~10ppm, and much less for the second and subsequent 1,000 hours). They require roughly five minutes to settle to maximum accuracy. As long as the unit is not powered on for extremely long periods (250 hours or more), it should hold the standard indefinitely.

The stability is greater than the maximum error of the 732A. In the null setup photo, the unit drifted from +3uV to -4uV. -4uV was the maximum error in relation to the 732A. The 732A has a maximum error of 0.6ppm, which @ 10VDC is 6uV. So, the maximum error of the unit using the 732A as a reference is 10uV. We spec the unit @ +-75uV, because reference standards require integrity and reliability. We may change that spec when we have more experience with the units.

We have an electrical engineer with forty years experience, conducting R&D on special mock-ups of this device, and the results have been astounding. But for now I'm sticking with the original spec of +-75uV. But the temperature at calibration is marked on the each unit. If this temperature is observed, the accuracy is in excess of 10x the official spec. Our testing has shown that the units are unaffected by repeated power ups. The drift is in relation to cumulative hours of power-up

The D-105 is superior to the Fluke 732A in that the D-105 can be power cycled. Please keep in mind that the above prose are not a technical manual, but an email message; an email message that was edited for effect, and then taken out of the context of the thread it was a part of. it doesn't matter. Calibratory, LLC has succeeded where all others have failed! Say what you want, but electricity cannot lie.
Title: Re: Ultra Precision Reference LTZ1000
Post by: EEVblog on February 04, 2015, 11:23:05 pm
Electricity doesn't lie! This is the dawn of a new era! But even if others might build the exact same device, it will not work like the ones we make. There is a counterintuitive secret that lurks within the device.

Oh dear   :scared:
Title: Re: Ultra Precision Reference LTZ1000
Post by: Awesome14 on February 04, 2015, 11:36:12 pm
Quote
1) "The 732A has a maximum error of 0.6ppm": How does the seller know the 732A has an uncertainty of 0.6ppm?
The spec on the 732A is <= 0.6ppm/month.
Quote
Where is the link to the PDF of the 732A's calibration certificate?
Suspicion is the device of a guilty mind.
Quote
If he only has one 732A/B voltage standard, how does he know that the voltage standard is not drifting off into the weeds?
By statistical probability that all the lab instruments will probably not drift off into the weeds suchwise that the problem would not be detected.

Quote
2) "the unit drifted from +3uV to -4uV":  That is HORRIBLE!
You can't be serious! That's 0.7ppm.
Quote
This CANNOT be useful for any kind of transfer reference.  A good reference needs to be rock-solid with less than 0.2ppm of peak-to-peak noise [0.1Hz to 10Hz or "1/f" noise] in order for it to be useful to transfer the calibration to a more stable reference, and the lower the 1/f noise, the better.
0.7ppm is great for our price.

Quote
3) What is the voltage reference inside the box?  Is he not saying because it would be embarrassing?
Did you try asking? It is the best 10VDC IC reference available.
Quote
Is it a voltage reference with a non-hermetic package?  What is the temperature coefficient [TempCo]?  Is the TempCo compensated?  What is the hysteresis of the part if it experiences radical temperature excursions during shipping?
Our experience has been that the device withstands shipping and storage in harsh environments, and associated shock, very well!

Quote
As I said before, Buyer Beware!  Don't waste your money on this unless the seller discloses what is in the "magic box"...!!!  [Just knowing the reference part number is good enough-- you can find out everything else you need to know from that].

-Ken

If you want to know something, ask.
Title: Re: Ultra Precision Reference LTZ1000
Post by: richiem on February 05, 2015, 12:19:19 am
Call me silly, but I decided to see what this D-105 can do. When it comes, I'll give it a go and report back. I've had good ideas in the past; some worked, some didn't, some were crazy, and some were just plain based on ignorance. I'm giving Awesome14 the benefit of the doubt, since the D-105 is a price I can live with, good or bad. At Tektronix, Monsanto, and other companies, I watched NIH at work, and some really great ideas got cold-shouldered. Stay tuned.
Title: Re: Ultra Precision Reference LTZ1000
Post by: rx8pilot on February 05, 2015, 12:39:14 am
I have a few notes to share.

I don't know anything about Awesome14 and only know a little about the D-105 from what I have read and seen pictures of. I am in the market for a DC reference and looked at this before the conversation started. I am not specifically looking for the bargain basement unit, but rather something that I can trust. Since I would like to have a few references to cross check I was hoping to find units that are affordable. For $100, there is very little risk in trying.

While I have neither the skill or the equipment to confirm the specs, I would have to trust the unit works. Thankfully there is an active group of people that love to test specs and have the means and skills to do so. While I am NOT a scientist, I have worked with many of them. A key part of the scientific community is cross checking claims. Any good scientist should welcome others to cross check for anything out of place and confirm the results are repeatable. I hear a very defensive conversation here where the scrutiny should be welcomed. There is also a "magic" claim that will always have people running away. There are claims that this is the holy grail of voltage references that overcomes the challenges that have vexxed any and all engineers that have attempted to tackle this level of precision and stability.

Awesome14, surely you can expect this community of engineers to pick your claims to the edge of death. The images that were posted show a construction that most of us would have last seen in the 7th grade. I work with far less precision circuits that absolutely require a well considered PCB layout for them to function well and have any sort of consistency from unit to unit.

I do not doubt your sincerity, integrity, or intelligence. I hope that this unit is proven to be what you claim - if so I will buy 4 of them. Let those with the questions and the curiosity verify everything you say. When/if they do maybe you can add that to the eBay listing and raise the price. Independent verification is far more powerful than anything you could possibly type yourself anywhere on the internet.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 05, 2015, 12:40:59 am
Perhaps we can take this to https://www.eevblog.com/forum/testgear/calibratory-d-105-dc-precision-voltage-reference-standard/ (https://www.eevblog.com/forum/testgear/calibratory-d-105-dc-precision-voltage-reference-standard/)

I'm also making a home reference (or three), including with LTZ1000, and I'm quite happy something like the Geller references is available again.  I look forward to how it works for others, as I'm still quite a number of Saturday evenings away from having working, stable refs of my own.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on February 05, 2015, 06:50:05 am
While I think the D-105 discussion doesn't belong here - it has its own thread - I want to see way more cross-comparison between amateurs like us! The D-105 although with its ugly construction is reported to survive shipping stress, so might be a possible subject of such cross-comparisons. My own LTZ1000A standard will visit Dr Frank again in the coming days. It was off for most (all) of the time, just recently put up my PC on its own desk after moving so my electronics desk just got useable again. So this time we will see the "cold" effects. After that, I think it will get more runtime until next comparison at Franks...


Edit: Emphasis, colouring and text size added afterwards.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MrAl on February 05, 2015, 10:05:10 am
Hi,

Interesting thread.

It's not that difficult to build your own oven.  A small light bulb or even a power resistor for the heater, and an analog op amp based circuit similar to a soldering iron station control circuit.
The housing has to be well insulated, perhaps double insulated, with a thermally conducting shield between insulation layers.  Good for crystals or voltage refs.

i got one of the 399 type references for $1 on a store sale a long time ago, but i should have purchased more than one unit at the time.   I didnt realize they would go up in price so much back 20 years ago.

Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on February 05, 2015, 10:39:53 am
If there are any comments on D-105 DC, please post in the other thread!!!
https://www.eevblog.com/forum/testgear/calibratory-d-105-dc-precision-voltage-reference-standard/ (https://www.eevblog.com/forum/testgear/calibratory-d-105-dc-precision-voltage-reference-standard/)

Many thanks

quarks
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on February 05, 2015, 08:10:31 pm
For some reason, I have not been receiving notification of further comments on this thread (or any others) for several months, be that as it may, I have been busy and have not taken the time to check in here very often, partially due to manufacturing resistors and other duties.

In reply to Andreas' assertion (Nov. 8 &9 posts) that I have not provided any pricing.....I do not recall him asking for any pricing nor if I would provide samples to him.  Anyone on this forum who has taken the time to contact me and ask about pricing or any other information, I have replied to.  I have not seen any other manufacturer posting pricing here, however, if it will be of any help, here are some current examples of resistors being used in the LTZ1000A circuitry:

Resistors are Ultrohm style 805 (physically equivalent to Rho 8e16), ±0.1%, 0 ±3PPM/°C, -55°C - +125°C:

Value    1-9       11-24
120?   $6.85    $5.14
1K        $6.34    $4.76
10K      $7.28    $5.46
12.5K   $7.43    $5.57
70K      $8.25    $6.19

Regards,

Edwin
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 05, 2015, 09:03:55 pm

Value    1-9       11-24
120?   $6.85    $5.14
1K        $6.34    $4.76
10K      $7.28    $5.46
12.5K   $7.43    $5.57
70K      $8.25    $6.19

Regards,

Edwin

Hello Edwin,

pricing sounds reasonable to me.
I guess the 12K resistor (for the friends of LTZ1000)
would be in the same region as the 10 and 12.5K resistor.
What would be the shipping costs to germany?
E.g. for 5 sets with 120R, 1K, 12.5K, 70K + 70K

In my case I would prefer shipping by a mail order firm who
does all that customs handling (import tax 19%). (UPS? / DHL?)

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on February 05, 2015, 09:11:13 pm
Thread recovered ! :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on February 05, 2015, 11:42:36 pm
Hi Andreas,

Yes, that is 10-24 in quantity.  I have not shipped to the EU before, I understand there are a lot of nasty fees (tax in disguise) and tax (VAT), I can ship by USPS first class or priority international mail, Fedex or UPS, I've been told that there can be delays depending on which country it is going to.  I am flexible in the shipping arrangements as possible.

You are correct, there would be minor differences in the pricing for slightly different values, such as a 12K would be about $7.35.

I would suggest contacting me through the more private e-mail from the regular forum, that seems to work a bit faster, for more details.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on February 06, 2015, 06:01:17 am
Regarding shipping: On the EU side, you can expect the following tolls, taxes and fees:


Shipments from USA both at work and at home came via (by popularity)
zero trouble during shipping.

Sicne a few months, however, they look for a CE mark and product safety - close to impossible to import devices without CE mark, I can use the exemption for radio amateurs as you are certified to take care of the necessary actions in your own responsibility.

For electrical components there is a exemption and a position paper from ZVEI in germany that might help the local guys to understand that thery are exempted. Don't try to go the chinese way and declare that it is a gift or low value article for 5$.

For international shipments with a travelling transfer standard going a round trip there are ways to reclaim tax and fees on return - did something like that once with a germany-turkey-germany round trip.

Title: Re: Ultra Precision Reference LTZ1000
Post by: bingo600 on February 06, 2015, 12:35:25 pm
Regarding shipping: On the EU side, you can expect the following tolls, taxes and fees:

  • 0€ extra fees with a value below 22€,
  • 19% tax (EUSt) at a value between 22 and 120€ and
  • 19% EUSt tax plus toll plus customs fees above 120€ value. Value includes shipping cost plus object value. Got



That limit would be "below" 80DKK (~10€) for DK , and 25%VAT + a €20 VAT handling fee to DK-Mail if above the  limit :--

/Bingo
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 06, 2015, 01:20:15 pm
Regarding shipping: On the EU side, you can expect the following tolls, taxes and fees:

  • 0€ extra fees with a value below 22€,
  • 19% tax (EUSt) at a value between 22 and 120€ and
  • 19% EUSt tax plus toll plus customs fees above 120€ value. Value includes shipping cost plus object value. Got

Shipments from USA both at work and at home came via (by popularity)
  • FedEx,
  • UPS and
  • USPS ,
zero trouble during shipping.

Sicne a few months, however, they look for a CE mark and product safety - close to impossible to import devices without CE mark, I can use the exemption for radio amateurs as you are certified to take care of the necessary actions in your own responsibility.

For electrical components there is a exemption and a position paper from ZVEI in germany that might help the local guys to understand that thery are exempted. Don't try to go the chinese way and declare that it is a gift or low value article for 5$.

For international shipments with a travelling transfer standard going a round trip there are ways to reclaim tax and fees on return - did something like that once with a germany-turkey-germany round trip.

What I found about CE marking, all electronic parts are excluded (print that on each 0402 resistor..) and only "low voltage devices" running at >50V need this mark.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on February 06, 2015, 02:11:34 pm
It is off topic, but I can share some information about the CE Mark, because I tried to buy and failed to import some old reference gear
like a LOM-510A (from robrenz) or a ESI 242D (back in 2013, when I did my research on my resistance measurement thread
https://www.eevblog.com/forum/chat/help-wanted-low-and-high-ohm-measuremet/msg169139/#msg169139 (https://www.eevblog.com/forum/chat/help-wanted-low-and-high-ohm-measuremet/msg169139/#msg169139) )

I was informed by the German custom about the need to have a CE Mark if I want to import any gear that has as connector/cable to be connected to mains (in Germany 230VAC). They also adviced me to contact the regional council (Regierungspräsidium) if I have any questions.

I followed this advice before I bought the gear I wanted.

Here is what was replied to me (sorry if the translation is bad):

-----------------------------------------------------------------------------
Products that are provided as part of a business process on the market, displayed or used for the first time, subject to the Product Safety Act (ProdSG). (ProdSG, § 1, para. 1).
Also import for personal use will be considered as a business activity to provide products on the market.

Excluded from the Product Safety Act are products that
1) are antiques,
2.) prior to their use or repair Act must be reprocessed if the economic operator to those to whom they are issued, gives adequate notification. (ProdSG, § 1, Section 2, 1 to 2).
The economic operator would be in the specific case of the seller; the person to whom the products are made, the importer would be (you =).
In these cases, it is possible to prove that the products meet certain minimum requirements.

As far as the above derogation is not satisfied, must to ensure that the product meets the requirements for the placing on the market within the meaning of ProdSG, as in ProdSG called §3 and possibly §6.
Accordingly, subject to electrical appliances with power acc ProdSG, Section 3, Paragraph 1 of the "Regulation on the marketing of electrical equipment designed for use within certain voltage limits - (1 GPSGV)"... This requires that devices that fall under this Regulation shall be equipped with a CE mark (1 GPSGV, §3).
The requirements for the installation of a CE mark are set out in Directive 2006/95 / EC (Low Voltage Directive).
-----------------------------------------------------------------------------

I also called and tried to explain that I only want to buy 30+ years old gear for privat and educational purpose.
The short answer was "no way", so I gave up.

Title: Re: Ultra Precision Reference LTZ1000
Post by: acbern on February 06, 2015, 02:50:01 pm
I read this with great interest, as I am importing a lot of test gear from the US for my personal use, and never had an issue in the customs office, and so this sounded scary initially. So I looked up the ProdSG in German, and it seems to me it is sufficient to certify, it is for repair and/or refurbishment.

Excempt from CE marking is:
"gebrauchte Produkte, die vor ihrer Verwendung instand gesetzt oder wiederaufgearbeitet werden müssen, sofern der Wirtschaftsakteur denjenigen, an den sie abgegeben werden, darüber ausreichend unterrichtet"

As you have translated, but I just did not get it in the english wording. Sorry for the German, but I tinks those who are potentially affected understand it, so helps. It does not even require repair, "aufgearbeitet" (to refurbish) is a wide field, it may also mean calibrate and adjust or whatever. So I would not accept this abitray judgement of the local guy, bring this up to the local head of the department, this was not lawfull.
In German, sorry: es handelt sich um einen Zoll-Verwaltungsakt, gegen den man zumindest Einspruch einlegen kann. Ggf. auch klagen, (wenn man viel Zeit hat. Der Einspruch geht schneller, und den entscheiden meistens Leute die mehr Ahnung haben und dann sollte es das normalerweise gewesen sein).
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on February 06, 2015, 02:51:42 pm
Bureaucrats! So if you sent a piece of pre 'CE' test gear back to a foreign manufacturer for calibration it wouldn't be allowed back into the country?

What about equipment imported from another EU country? I don't believe there are many checks when driving across borders within the EU.

Is it just Germany taking this stance, over-zealously appyling EU CE regulations or can we expect this madness to spread across all EU states?

It's enough to make you despair; I'm currently reading a book 'In The Interests Of Safety: The Absurd Rules That Blight Our Lives' which includes the absurd example of the snaps having to be removed from all the Christmas crackers in a consignment being sent to troops in the Falkland Islands, because explosives are not permitted on Royal Air Force planes!  |O
Title: Re: Ultra Precision Reference LTZ1000
Post by: acbern on February 06, 2015, 03:05:12 pm
Still off topic (LTZ1000) here:
In principle it applies to all imports to the EU. And within the EU, you can freely ship it (unless it is a controlled item such as military electronics or so, we normally dont own these).
I would think that the specific case was an exception, I had to deal with many guys from customs over many years, at the local customs office and through freight companies like fedex, and I only buy used stuff, never been a problem.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on February 06, 2015, 03:22:05 pm
I read this with great interest, as I am importing a lot of test gear from the US for my personal use, and never had an issue in the customs office, and so this sounded scary initially. So I looked up the ProdSG in German, and it seems to me it is sufficient to certify, it is for repair and/or refurbishment.

Excempt from CE marking is:
"gebrauchte Produkte, die vor ihrer Verwendung instand gesetzt oder wiederaufgearbeitet werden müssen, sofern der Wirtschaftsakteur denjenigen, an den sie abgegeben werden, darüber ausreichend unterrichtet"

As you have translated, but I just did not get it in the english wording. Sorry for the German, but I tinks those who are potentially affected understand it, so helps. It does not even require repair, "aufgearbeitet" (to refurbish) is a wide field, it may also mean calibrate and adjust or whatever. So I would not accept this abitray judgement of the local guy, bring this up to the local head of the department, this was not lawfull.
In German, sorry: es handelt sich um einen Zoll-Verwaltungsakt, gegen den man zumindest Einspruch einlegen kann. Ggf. auch klagen, (wenn man viel Zeit hat. Der Einspruch geht schneller, und den entscheiden meistens Leute die mehr Ahnung haben und dann sollte es das normalerweise gewesen sein).

As stated, I even had a personal discussion about that with no luck and just gave up.

In your own case, if your custom official in charge does not look/care, then you are just lucky.
But if they care, they will/can send the gear in question to an official place to have it checked for CE conformity and you will have to pay for shipping and the test if you want to have the gear in your hands. If you do not agree, you can of course try to fight against this "Zoll-Verwaltungsakt" but that is not worth it (at least for me).
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on February 06, 2015, 03:29:41 pm
What about equipment imported from another EU country?

Very stupid but within the EU you can buy gear without CE Mark with no problems, probably because this is not handeled as an import. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on February 06, 2015, 05:32:17 pm
Coincidentally I asked for a quote for Edwin's resistors a few days ago and thought I would post the reply (with permission) as it does provide some more information and pricing which may be of interest to others here:


Hello Mr. xxxxx,

Thank you for your inquiry, your request is a bit complicated for a simple reply but I'll try to keep it to a short novel.  All of my resistors are rated to military temperature range so a lab environment would be quite soft and 0 ±3PPM/°C TCR is standard for nearly all of my resistors.  I presume you would prefer the resistor values called out by Linear Tech as these have proven to be the best values that work, only the heater value may need to be tweaked if the units are operated at elevated temperatures, the LTZ must always be above the maximum expected ambient temperature to maintain Vref.  I am currently manufacturing these sets for other customers with minor variations in heater resistor values.  ±0.1% tolerance is quite sufficient for those resistors.

Your home lab standards, 1 ohm, at the moment is a bit difficult as very low TCR alloy in larger diameters is a hit or miss even today, I just made some 10 ohm resistors for a customer with the 'best' low TCR wire I have at that big of a size, its TCR is slightly higher than I normally accept (by about 10%) but I can't always get the TCR I want.  Basically what this means is that the final TCR batch range may be shifted by 0.3PPM/°C, not much really.  While it is not impossible to make a 1 ohm resistor from this stock, it will be quite difficult as the length of wire will be quite short, 1.5" and at 0.010" diameter, not much to work with.  Unfortunately, trying to parallel multiple low ohm resistors and keep reasonably close tolerance and particularly low TCR is very tricky, a problem I was working on for the Bob Pease project that was mentioned in the forum threads.  I can try and make a 1 ohm resistor from this stock but I'm not real sure how it would turn out.  The 100 ohm is no problem nor the 10K, I have made working standards with 0 ±10PPM tolerance from 100 ohms up to 10M.  At low ohm values, lead resistance becomes very significant, small variations in the lead spacing will cause significant measurement errors.  As a point of interest, transfer standards (also known as working standards) have a TCR of 0 ±5PPM/C° at ?100?, higher than my resistors.

I haven't made any real low ohms in several years, I work mainly with the Evanohm alloys and they usually are not available (easily) in larger sizes and low TCRs unfortunately, I'm told it is a quirk of the alloy, the smaller the diameter, the lower the TCR possible, an inverse relationship.  Given the current circumstances, any resistance below about 10 ohms is considered on request, it is not so much that I don't know how to make them, it is a matter of getting the necessary materials.  At this time I generally decline making resistors below 1 ohm.

A dozen 1K resistors is easy, tolerance is no problem, quite easy, even ±0.005%.

Long term stability is specified at 0 ±5PPM/year, data indicates the actual 'drift' is < 2 PPM/year.  At rated power, rated temperature range, drift is 0 ±10PPM/year or less.

A website is under construction as are new data sheets.

Approximate pricing, standard TCR, 0 ±0.1%:

Value    1-9       11-24
1R        $8.10    $6.08
100R   $6.85    $5.14
120R   $6.85    $5.14
1K        $6.34    $4.76
10K      $7.28    $5.46
12.5K   $7.43    $5.57
70K      $8.25    $6.19

For 1K,     ±0.1%, <= 1PPM/°C, quantity of 12, each: $6.76
For 1R,     ±0.1%, <= 1PPM/°C, quantity of 1, each $10.10
For 100R, ±0.1%, <= 1PPM/°C, quantity of 1, each $8.85

Note, selection of TCR is labor and time intensive, it is likely that the batch will be close to your TCR limit anyway, unless you are sure you really need such selection, I would recommend accepting the straight production run.

My 242D resistance bridge at 1 ohm, has an accuracy of better than 5 PPM, an uncertainty of 0.5PPM.

Quote based on using my 805 style which is the same as the often noted 8e16 from Rhopoint, 0.250" D x 0.500" L, measurement spacing is standard 0.375" from resistor body (1.25" C-C).  There are no exact equivalent resistors to mine, only in general terms and physical dimensions, electrically no one else can claim the same specifications or performance.

If the envelope meets requirements, the International first class package service rate would be approximately $10, the International priority package rate would be approximately $25.  The paperwork requires an address and specific details to get a more exact rate.

Best regards,

Edwin G. Pettis

Pettis Engineering / Ultrohm Plus
125 Vista Grande Dr.
Grand Junction, CO  81507-1427
1-970-242-4929
pettiseng@q.com






Hi,

I'm interested in purchasing some of your precision resistors. I understand that firm pricing probably depends on the precise order so approximate pricing will be Ok. for now.

These would all be for lab use so TCs below 10C or over 35C may be greater.

I'd like between 1 and 4 sets of resistors for an LTZ1000 reference; standard 0 to +3ppm parts should be OK.

I am also interested in some resistors for use as home lab 'standards'. The number obviously depends on pricing but at least 1R, 100R and 10K would be required. Are you still able to supply selected, < 1ppm, parts? If 1R is not available in < 3ppm TC, could you quote for the minimum number of paralleled resistors that would achieve 1R, < 3ppm and < 1ppm? 1% tolerance would be acceptable but I would like to know the measured value. What would be the measurement uncertainty please?

Are you able to supply low value, < 10mohm 10W resistors? If so what would the be the price and specification?

Could you supply a set of 12, approximately 1k resistors matched to 1% or better with TCs matched to < 1ppm? What if they were matched to .1%?

How much would shipping to the UK cost for 20 resistors?

Do you have a web site?

Do you have any data available on long term, room temperature stability?

Thanks,
    xxxxxxx
Title: Re: Ultra Precision Reference LTZ1000
Post by: HighVoltage on February 06, 2015, 08:08:25 pm
What about equipment imported from another EU country?

Very stupid but within the EU you can buy gear without CE Mark with no problems, probably because this is not handeled as an import.

Correct, anything from an EU country is not handled by customs. Sometimes I have items shipped to a friend in the  Netherlands, where the customs is much more relaxed than in Germany. But I found a different way for gear without CE marking. If you have a customs import number in Germany (EORI) and you make a statement that this gear is for research and development (Forschung und Entwicklung) then the German customs will release it to you on your own risk and you have to sign a release form. But in any case it is a hassle.

Another great way to bypass German customs has worked a few times for me in the last few month. Just tell the seller to write on the custom forms: "Adult Plastic Toys" and suddenly it is delivered to your house without anyone from customs touching it.
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on February 06, 2015, 08:30:25 pm
High Voltage,

Adult plastic toys.....that is hilarious!  My resistors would fit into just the right size box for that trick!
Title: Re: Ultra Precision Reference LTZ1000
Post by: macfly on February 07, 2015, 09:32:26 am
Hi voltnuts,

problems with the customs at import to the EU ?

That's really unbelievable for me. During the past 14 years I bought nearly all my
test gear in the U.S. and never had any problem with CE marking.
My last buy was october last year.

Perhaps I am a lucky guy .... ::)

Regards,

macfly
Title: Re: Ultra Precision Reference LTZ1000
Post by: bingo600 on February 07, 2015, 02:12:24 pm
I haven't had any probs. with CE markings either here in DK.

Only customs , and i don't even think "Adult toys" would slip by , as DK-Mail can claim the 20€ in fee for every package that's above 10€.

I even had a package once bought for 12$ from an ebay seller , but DK-Mail (Customs) claimed i had to prove the value by sending them a print of the paypal transaction.

They really want the 20€ in fee.

/Bingo
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 08, 2015, 07:50:24 pm
The Edwin P resistors, I'm in for three sets if there is a group order.
3x120R
3x1K
3x12K5
6x70K
If it gets too complicated, I can order directly from him.

Jan
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 08, 2015, 10:23:43 pm
Hello Ken,

do you have a higher resolution photo of the chip?
From the first view it looks rather different from the LTZ chip.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on February 09, 2015, 06:09:19 am
<guessing>
By the looks of it I believe that it is a stacked, combined and averaged bunch of sources until its figured out better.
Even probing the single contributors and disconnecting the bad apples is possible IMHO, or the single cells might be prepared to have different tempcos and then select them so they cancel.
</guessing>
Or does somebody have a better interpretation of this l.q. photo?


Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 09, 2015, 07:09:49 am
<guessing>
By the looks of it I believe that it is a stacked, combined and averaged bunch of sources until its figured out better.
Even probing the single contributors and disconnecting the bad apples is possible IMHO, or the single cells might be prepared to have different tempcos and then select them so they cancel.
</guessing>
Or does somebody have a better interpretation of this l.q. photo?

For me it looks like having 16 references all in parallel on LTFLU.

Similar to the LTZ1000 where the transistors Q1 + Q2 are splitted
into 4 elements each staggered in 45 degree arangement.

The tempco on LTFLU will most probably be adjusted by adjustment of the zener current.
Usually these parts are sold as a complete RefAmp-Set (the reference + the proper adjusted resistors).

With best regards

Andreas
Title: Re: D-105 DCV standard test results
Post by: richiem on February 09, 2015, 07:36:26 am
For those interested who haven't visited the D-105 voltage standard thread, the one I ordered arrived, and I posted some brief results of testing there; look for my post near the bottom of page 15:

https://www.eevblog.com/forum/testgear/calibratory-d-105-dc-precision-voltage-reference-standard/210/ (https://www.eevblog.com/forum/testgear/calibratory-d-105-dc-precision-voltage-reference-standard/210/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 09, 2015, 11:12:27 am
In case anyone miss, I have two references (https://www.eevblog.com/forum/buysellwanted/) for sale.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 09, 2015, 11:41:43 am
Just in case anyone is interested, here is a photo of a Linear-Tech LTFLU-1ACH with the top of the can cut off:

(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=135113)


Hi Ken,

I've compared this chip with the known LTZ1000 chip..
This one, of the presumed LTFLU, looks very strange, and I especially could not find any resemblance to the LTZ1000 chip, although the buried zener should be identical, acc. to Bob Dobkin.

Therefore, are you sure, that this is not a photo of a fake chip?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on February 09, 2015, 04:10:00 pm
I am in the process of setting up a dedicated webspace used for voltage and resistance standards. I am not yet behind the idea stage, but maybe I am making progress with the community.

http://wildvolttaming.schaffenburg.de (http://wildvolttaming.schaffenburg.de) is the temporary location.

I think about using a Wiki-Style to have a "public device history file", with a unique ID assigned to every device.
The idea is to stick a QR code plaque to the Device so the hosts can see the history of their guest devices and add their own results to it.
The home labs can have a Wiki page there, too. Maybe later online comparison tools will be available.
This will support cross-comparison of hobbyists standards.

Does this idea get some love here?
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on February 09, 2015, 08:42:51 pm

I've heard stories [or fables] that *some* very old Fluke 732A's hold the volt to +/-0.1ppm per year.   I don't know if this is true, but if I owned one of those, you would have to use dynamite to get it out of my hands...

So, some projects that have been "stewing" in my lab are:
  • Poor-man's primary voltage transfer standard [based on LTZ1000(A)]
  • Poor-man's voltage transfer device
  • Poor-man's multi-junction thermal converter for AC/DC transfers
  • Poor-man's resistance standards [1R, 10R, 100R, 1K, 10K, 100K, 1M, 10M, 100M, 1G]
  • Poor-man's resistance synthesizer [that uses the above resistors to get any value]
  • Poor-man's direct current comparator bridge for low resistance measurement
  • Poor-man's electrometer for high resistance measurement
  • Poor-man's calibrator for DCV, ACV, DCI, ACI
  • Poor-man's automatic LCR bridge
  • (and a few others that are still in the idea stage)
There's enough there to keep me busy for a very lonnnnnnnng time...

Almost anything on your list is/was also on my list and probably on many others list too.
But I wonder what you mean by "Poor-man's ...".
Can you share what accuracy and stability you like to achive or find good enough for your listed projects?
If some is DIY, what are your candidates for the parts?

To make a start, for DIY resistance standard I started to select and test parts.
The top canditates (I already have) are from Isabellenhuette, Burster, VPG and Caddock. Because I can measure the values with quite good accuracy myself, I did not look for much better than 0.01% types.  I mainly care for low TCR and long time stability.

So far I have not really managed a good 1Ohm solution and nothing adequate for 100 M and 1 GOhm.

Maybe we should open a new thread for this.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 09, 2015, 10:44:28 pm
Here are some results from measurements I made on the heaters of two LTZ1000A
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on February 10, 2015, 04:34:26 am
Anyway, yes, I agree, these are probably better discussed in another thread.  I planned on launching some threads with the "[Metrology] " prefix, so that they would be easier to search for.

Very good, please do so
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 10, 2015, 11:09:28 am
Here is a diagram for setting the temperature of the LTZ1000A. The values are calculated from datasheet, not measured. I hope it's useful to someone.
Title: Re: Ultra Precision Reference LTZ1000
Post by: richiem on February 13, 2015, 06:57:59 am
I have an HP 3458A ref board, REV A 03458-66509. Can anyone confirm whether this board rev has an LTZ1000 or 1000A? The HP part number for the LTZ is 1826-1860 -- I have a good HP X-ref, but this part # isn't in it. I've put a 12.1K metal foil resistor in the place of the 15k Vishay for temp control. This value would be OK for the 1000, but possibly marginal for the 1000A. Solid info will be very welcome!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 13, 2015, 07:35:49 am
Hi Dick,
As far as commonly known, HP used the A version only, due to the nominal 95•C.
12.1k sets  the oven to about 45•C but the interior temp already will be 35.. 40•C at least, so the difference is much too small, as the A version requires 10•C overhead plus some additional regulation margin, at least.
The self heating of the 3458A adds  13•C to room temperature ,plus 5 •C more for a dirty filter, plus 10•C if placed in a rack.
Therefore, I always recommend to set the temp to 65•C , ie 13k, or 100k in parallel to the 15k, if the lab is not warmer than 30•C

The reference ages only, when it is powered.
Therefore, drifts < 1ppm/year can be expected on 65•C,  if the 3458A is not running continuosly.

If you use the ref board outside the 3458A, then 12.5k is the correct value, for about 55•C.
45•C is a little bit critical for the A version, otherwise you have to make sure, that the ambient temperature will not exceed 30•C. And there should be a thermal shielding around the TO 99, which should allow heat exchange, ie not too good an isolating material.





Frank


Title: Re: Ultra Precision Reference LTZ1000
Post by: ltz2000 on February 13, 2015, 10:32:25 am
I've heard stories [or fables] that *some* very old Fluke 732A's hold the volt to +/-0.1ppm per year. I don't know if this is true, but if I owned one of those, you would have to use dynamite to get it out of my hands...

True. Sometimes it happens that the drifts of the zener and the amplifier (resistors) are approximately the same magnitude but opposite direction resulting a very low net drift. However that is not "real" stability because the individual drifts can be and usually are still quite high. Would be risky to assume the net drift to stay constant forever because it is very sensitive to changes in individual drifts.
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on February 13, 2015, 03:11:31 pm
I have an HP 3458A ref board, REV A 03458-66509. Can anyone confirm whether this board rev has an LTZ1000 or 1000A? The HP part number for the LTZ is 1826-1860...

that is an interesting question. I have several boards with the same revision as yours and I read original LTZ1000ACH and also 1826-1860 on older ones (which is probably only printed on for HP). In the schematic (see att.) it says clearly LTZ1000 and there also is R417 200k which should be 400k, according to LT reference design. But even more interesting is, that it should not be populated when LTZ1000A is used, but the resistor is on all boards I have seen so far.

https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg440601/#msg440601 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg440601/#msg440601)

I wonder if there is a good explanation.  Would be great if anyone could share knowledge.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 15, 2015, 11:07:24 am
I found 0.3-0.8ppm/°C Precision zener-based references (http://caxapa.ru/thumbs/391414/voltagerefapps.pdf) today. Maybe of interest for someone?

Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on February 15, 2015, 11:44:14 am
I have a similar 10 V chip - APEX VRE310J. It is the worst reference I know >:( Low-frequency noise is ~60 uV p-p (0.01-10 Hz).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 15, 2015, 12:00:43 pm
Thanks Mickle,

the first who can confirm my results.


Although this is off topic in the LTZ1000 tread:

I thought I was the only one who got 2 mondays devices (VRE3050AS) from APEX.
They are noisy as hell too, have large temperature hysteresis, bad PSRR.
The only good thing is T.C. even when one device was maginal at 25 deg C.
For the price I can get easily a hand full of other good references and select out the best.

By the way Thaler was acuired from APEX so the company name has changed.
The components are still called VRExxxx (available at DigiKey).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: retrolefty on February 15, 2015, 12:22:30 pm
I found 0.3-0.8ppm/°C Precision zener-based references (http://caxapa.ru/thumbs/391414/voltagerefapps.pdf/) today. Maybe of interest for someone?

Hello Branadic - for some reason your link is broken ...

BR
gazelle

Just remove the trailing / on the URL
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 15, 2015, 12:58:54 pm
I found 0.3-0.8ppm/°C Precision zener-based references (http://caxapa.ru/thumbs/391414/voltagerefapps.pdf/) today. Maybe of interest for someone?

Hello Branadic - for some reason your link is broken ...

BR
gazelle

It should work now.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 20, 2015, 02:45:24 pm
Recently playing around with back to back low cost glass zeners observed virtually zero tc at certain current and wondered about fitness for precision voltage references. How they compare (noise, hysteresis, etc) with the "buried" type like found in LTZ1000. Discussing with a client who is a semi product engineer he stated the difference was minor compared to other issues but wasn't able to direct me to any documentation on comparisons. No luck with net search either.

This thread seems to have top experts in this area so I was wondering if anybody had experience with discrete glass zeners vs buried type or know of any links to comparisons.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 20, 2015, 04:29:21 pm
Thank you for that summary. I've read this thread twice and your post saved me from going through again. In addition to making those discussions clearer did bring up a couple points I don't recall mentioned. Greatly appreciated.

In my case, not owning real precision gear, a $50 dollar part like LTZ1000 not in consideration. Because  of a self imposed challenge even a $10 LM399 out ATM. Mostly this is for low cost DIY projects like the 5 digit $5 Ebay meter and some 24 bit ADC chips in my junk box which need a reference. Right now my best hope is bandgap or homegrown zener circuits and the best resolution possible. Long term stability is not really a big concern right now either so just trying to stay in the "pennies not dollars" range for parts. No plans to build 8 1/2 digit voltmeter but hopefully at least a couple orders of magnitude less.

Your description certainly gave more info/details and bigger picture than Wikipedia which was my best source so far. Thanks again.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on February 20, 2015, 06:17:16 pm
I would say that the most stable discrete zener reference I have heard of is Microsemi's USR series.
http://www.microsemi.com/document-portal/doc_view/10943-sa6-35-pdf (http://www.microsemi.com/document-portal/doc_view/10943-sa6-35-pdf)
top spec 934
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 20, 2015, 07:23:47 pm
I didn't know about the URS931! The 1N829 is also rated 5ppm/C, I have not seen any drift data. I think additionally compensated and presaged 1N829 where used in the Solartron 8.5digit DMMs.

URS931 are obsolete? while you can still buy 1N829.

http://www.microsemi.com/document-portal/doc_download/125462-lds-0220 (http://www.microsemi.com/document-portal/doc_download/125462-lds-0220)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on February 20, 2015, 07:51:02 pm
The 1n939 was used in the Solartron 7055
USR932 was used in the 7065, crudely ovened.
ovenized selected USR932 was used in the 7075.
All Solartron models btw.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 20, 2015, 09:06:21 pm
Mmmm... looks like I came to the right place for information on this.

0.0005%/C is way more than needed for my purpose and  temperature range -55deg to 100deg means the "S curve" is nowhere near as short as hinted earlier. At least in the ball park with initial tests (0.1mv) on some homegrown zener parts I've been tracking for last couple weeks.

Prices for USR, 1n829, and 1n939 are more than an LM399 so just as out of reach as the LTX1000 for my budget so it looks like the DIY parts at 2 cents each are for me. I hope performance of cheapies is close enough. The circuit looks a lot more manageable to compared to LTZ too which is another plus. Even simpler because I don't need negative ref. I got OP07s but maybe not even any op amp will be needed if ADC ref input impedance is high and I use software calibration constants.

Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on February 21, 2015, 03:49:48 pm
Recently playing around with back to back low cost glass zeners observed virtually zero tc at certain current and wondered about fitness for precision voltage references. How they compare (noise, hysteresis, etc) with the "buried" type like found in LTZ1000. Discussing with a client who is a semi product engineer he stated the difference was minor compared to other issues but wasn't able to direct me to any documentation on comparisons. No luck with net search either.

This thread seems to have top experts in this area so I was wondering if anybody had experience with discrete glass zeners vs buried type or know of any links to comparisons.


You'll find it hard to beat WarrenS's experience from his volt-nuts postings. See:

https://www.febo.com/pipermail/volt-nuts/2013-January/002362.html (https://www.febo.com/pipermail/volt-nuts/2013-January/002362.html)

https://www.febo.com/pipermail/volt-nuts/2013-January/002372.html (https://www.febo.com/pipermail/volt-nuts/2013-January/002372.html)

So it's quite straightforward to make a good reference so long as you're not in a hurry:

https://www.febo.com/pipermail/volt-nuts/2011-September/001046.html (https://www.febo.com/pipermail/volt-nuts/2011-September/001046.html)

Quote
Please note that not all 1N825, 6.2 volt reference diodes are created equal.
This one is cherry picked from my special supply of ones which I've:

1) Aged at 50 MA for a year,
2) Run in at 7.5 MA for another year,
3) Then No power Aged for another 5 years,
4) Tested for stable and repeatability for better than 1PPM,
5) Tested for low noise for better than 0.1PPM,
6) Has a room temperature 'Zero TC' under of 0.1PPM
7) and the Zero TC current is a under 5 ma.
 


You didn't need it before 2022 did you?  >:D

And if you wondered how he could afford to test such large batches of 1n829s which cost $10 or so apiece:


Quote
If you're interested, I'll send you the zener, because I got a lot of them
on EBay a long time ago when they where only 1 cent each.


Splin
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 21, 2015, 04:26:17 pm
Wow, just when I think I got all the leads I need Splin comes along with those volt-nuts links. I've not really checked out that site because not being a real volt-nut didn't think there was benefit and also I thought it was German only. How wrong I was.

So 1 cent to 10 dollars. Makes me wonder just what the real difference is between 1n829 and the ones that are still cheap. Maybe like Iphone it's just a matter of fashion. People talk, price skyrockets.

Quote
Yes the main difference is the zero TC current, with some parts there is no zero TC current.

Using my patented "hot finger" method :) I was able to check 200 pcs (thats right... whole $2 worth) in little over an hour but didn't find any that failed to zero. So looks like I'll have to do testing to see just how the S curve varies from one to the other. That will probably take more than an hour.

Besides trying to match the LTZ1000 7v I also tested many with much lower voltage. All the way down to 2v thinking it would be nice to get away with 5v only instead of needing 15v plus multiple regulators. They all had a 0 TC but the current was surprisingly high. Up to 10x more than the few milliamps mentioned previously. That needs looking into.



Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 21, 2015, 06:13:35 pm
YES! That is exactly the circuit I've been looking for. Except for the $20 op amp we do seem to be on the same poor man's wavelength now. OP07 will have to do instead of chopper. At 10 cents ea I did pick up a bunch of LT1034 but to be honest the penny zeners thrill me more so probably try it with those first.

I do have experience with TC ovens. See my "Worlds Smallest and Cheapest" below. I found bipolar gets ±2deg but FET like 2N7000 as you might make out in the closeup gets ±0.5deg. Super thin 40awg wire and the 1" foam block not only help with that but keeps power consumption down to about 4-5ma. That an order of magnitude better than equivalent commercial units. The 2 wire device is NTC thermistor for independent verification.

ps. I have even smaller using tiny (aka expensive) NTC with 2N7002 SOT-23 but no photos. I also have units big enough to keep a loaf of bread at "just the right temperature". Of course current consumption a lot more than few milliamps.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 21, 2015, 07:34:13 pm
The LTC2057 is around US$2.50 in small quantities

Strangely almost 10x that on Ebay:

http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=LTC2057&_sop=15 (http://www.ebay.com/sch/i.html?_from=R40&_sacat=0&_nkw=LTC2057&_sop=15)

I don't know where you are getting LT1034 at 10-cents, can you share where you bought those?  I can only find them at US$2.50

More accurately they were closer to 20 cents shipped (5/$2.99 30% sale) on Aliexpress. Inconvenient for me to dig up the order link from my current location and searching is always a tedious process there but here's a USA Ebay seller I paid 40 cents to get them quicker. Too bad because they ended up on a shelf. 4040a were cheaper and better for my application.

http://www.ebay.com/itm/381138383313?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT (http://www.ebay.com/itm/381138383313?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT)

At this time and probably never any intention to match LTZ performance but I would like to improve on the Ebay 5 digit meter hence current interest in better references. I will probably not be getting involved with DIY wirewound or $40 foil resistors either. However I do have rather large selection and quantities of 10ppm Vishay 0805 left over from a day job client. I have experimented with "adjusting" values using dremel disk and fine tune with nail file. The only issue seems to be sealing them for long term stabilty. It would be wonderful if they had Teflon paint or 2 part glue. For now I'm using epoxy and polyurethane hoping to resist oxygen and water.

ps. BTW I don't see any need in my applications for R3 at all. I need stable but not exact voltage as I plan to calibrate the meter in EEPROM.

Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 21, 2015, 08:24:28 pm
Always go with through-hole due to board stress [PC material TCE, and humidity] causes changes in surface mount resistors-- they act like strain gauges.

At 100x the cost it's unlikely though-hole are in the cards for me ATM. For now the Vishay 10ppm will have to do. Specially considering they cost me zilch. However IMO even new 25ppm SMD at ten cents or so are a good deal for those on a budget.

BTW note that in terms of mechanical stress SMD can become through-hole by tacking on a couple lengths of #30 ww wire. Using appropriate heat sinks of course. I did try it with a few of of the 10ppm 0805 then realized for my current project such extreme measures not required.

I think you're advice is sound though and really appreciate you taking time. Specially like the idea about double wall shrink. Already ordered couple meters.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 22, 2015, 01:32:07 am
With careful adjustment of R3, you can get the TempCo to be very close to zero,

DM, I wired up your circuit and it might be working but one thing bothers me. R3 seems to have no effect on TC. It appears to be voltage trim which I have no need for since my application requires stable but not exact voltage. Did you mean adjust R1 or R2 instead? Can you explain the circuit operation a little more?

(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=137902)
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 22, 2015, 03:16:32 am
I'm not in the shop right now but IIRC adjusting R3 varied output by somewhat less than a volt so that's what should be across R1. I'm using back to back 6v2 zeners for D1 and they are thermally attached to the PNP so I was hoping this would work. The only other thing different is OP07 instead of the 2057 which I also thought was ok. Resistors are 1% with high ppm/C. I wasn't sure if by critical you meant value or TC.

ps. I notice it's a one transistor circuit like LTZ1000 but with PNP instead of NPN so not sure if it's really similar. And D2 is for startup?

Can you describe a brief theory of operation?
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 22, 2015, 04:29:16 am
Maybe not hours but better part of one so far and I do like soldering.

OK, so apparently there is no attempt to adjust the zener itself for zero TC but just get close and compensate for the difference. When you said adjust R3 I thought only TC changes but didn't realize output does too so I'll take another look with that in mind. I'm not able to change the op amp but will try with a real 1034 when I get access early in the week. At this time I don't need a perfect  or long term reference so once I verify operation will continue to experiment with modifications.

ps. So basically this works by temperature COMPENSATION only like the D105 while the published LTZ circuit has the advantage of using HEATING and compensation. So things should get even better adding a temperature controlled oven to the mix. I think I'm getting the picture. Thanks for the jump start.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 22, 2015, 12:09:02 pm
So taking another look with your comments in mind I see the circuit is actually working with penny zeners and 2n3906. The changing output voltage was confusing and R3 is uncomfortably close to the end with my components so not perfect. Also it is considerably more difficult to adjust than the simple zeners with resistor I've been playing with. Hot finger method does not work but as you hinted holding the whole thing over a heater and then fanning the whole thing does.

R1 is *way* too large in that circuit

Yours does not have an anode resistor. What effect does that have?  Will adding one alllow me to re-center R3?

If you tweak the TC to near zero, then add an oven, it will be very stable.

How to adjust zener current? Your 110R?

Or is it not as simple as that and they interact in a more complicated way? So far haven't played with those because they are soldered in. I've still only been at this minutes not "hours". It would be interesting to see how this compares with basic zero TC zener with resistor and the bandgaps. I know there are noise and other issues but my goal is only to get 5-6 digit reference not 8 1/2 and I want the easiest lowest cost solution.

(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=40273;image)
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 22, 2015, 12:40:44 pm
I have been doing measurements on the LTZ1000ACH circuit to see how variations of the resistors changes the output voltage of the whole circuit. I have simply made small changes to the nominal resistor values and measured the change in output voltage.

It turns out that the output voltage changes are very predictable by size and sign.

This table summarizes the results and compare to those given in the datasheet.
ResistorDatasheetMeasurements
R11/100-1/770
R21/330-1/250
R31/500-1/1400
R4/R51/1001/100
The biggest difference is that the R1 and R3 values do not seem as sensitive as the datasheet tells, while R2 is slightly more sensitive. And that the values are negative, ie increasing resistance lowers output voltage. Except for R4/R5 where an increased ratio increases output voltage.

I have posted these results earlier but think they are worth repeating. I have also corrected the sign, some where wrong earlier.

Actually the summary is based on hundreds of measurements, the matrix is as follows

ResRangedr
R180R-1K1R2, 10R
R2&R347K-120K100R,1K
R4&R51:12-1:15500R

The results table is a summary only. The resuls are fairly constant over a wide range. No sweet spots.

For R1. Higher R1, i.e. lower zener current, lowers the sensitivity somewhat, (but at the price of higher noise). It can be noted that the zener current does not change the circuit total power as the sum of zener and heater is constant for a given temperature.

R2 tends to get better attenuated / less sensitive at higher values, it decreases by about 30% going from 47K to 120K.

The value of R3 does not change it's sensitivity / attenuation in the measured range.

For the most important value, R4/R5, a higher temperature i.e. higher R4/R5 ratio lowers the sensitivity of those resistors values somewhat, from 1/80 at 1:12, to 1:110 at 1:15 (but of course with the price of increased drift).

As a summary, The measured changes in sensitivity/attenuation are fairly marginal, not big enough to cause alarm, no sweet spots.

On the contrary, if the resistors are stable enough, without hesitation I'd use any of the values below, and expect at most, marginal changes in performance:

- R1: 80R to 150R
- R2 and R3: 50K to 100K
- R4: 10K to 30K with matching R5


Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 22, 2015, 01:28:15 pm
If of interest I can post photos, data and diagrams...

I have been browsing this thread from the start but only recently become interested in specific LTZ circuits. I've collected dozens of diagrams but sure which are current or relevant. Could you please re-post the schematic for your data?
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 22, 2015, 01:35:32 pm
Hi,

Plain vanilla circuit out of the datasheet except:

- I used two LT2057 opamps
- No diode out of the opamp that supplies the zener
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 22, 2015, 01:54:11 pm
A simple test anyone with a LTZ1000 circuit can do:

- Put a 10K resistor in parallel with the 120R. The resistance will then go down from 120 to 118R58, I.e. decrease by 1R42 which is 1.18%. The output voltage should then go UP by approximately 0.0118 * 1/770 * 7V = 0.108mV

If it does, it matches my measurements  ;D
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 22, 2015, 04:05:17 pm
I'm not sure if 6 digits over months but not years is considered "stellar". This is what I'm trying to figure out. I'm definitely not interested in 8 1/2 digits that are dead on 20 yrs after last cal.

As far as resistors there are 10ppm Vishay SMD here with some selection and ability to trim. That's what I have to work with for the moment. No wirewound or foil for me yet.

Would 5000ppm/year time drift be 'OK' with you?

LOL. Well no because early indications are that the simple zener/resistor and bandgaps are showing one or two orders of magnitude better than that. I've been tracking a dozen or so of these cheap references for nearly 4 weeks now and they do appear time stable enough for my purpose. Mostly I want to know if I can send a reference out to have it checked and see if it still measures similar on my equipment as it did before I sent it. So 6 digits useable over a month or two would be great for now. I wouldn't mind having to re-calibrate a meter against my AD584 reference couple times a year.

The other question is short term temperature stability and noise. I'm looking at 3 basic categories each with cost/performance tradeoffs:

1. Simple zener with resistor trimmed for zero TC.
2. Bandgap parts obviously more convenient with no trim but noise and maybe long term issues.
3. More complicated transistor/opamp circuits which are not as easy to adjust but have the edge in performance.

All of these would benefit from an oven but that is a separate project for after I get a handle on the references.

I'm looking for the lowest cost version of each and potential for use with 6 digit maybe stable for months but not years. There is indication the glass zeners are useable as indicated by reviews of Solartron DMMs. So right now I'm trying to correlate similarities/differences of the one transistor circuits and greatly appreciate your input so far helping me understand them. Thanks.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 22, 2015, 06:53:59 pm
How are you doing that?

Well I think by now you know I am not a metrology lab or anything close to a volt-nut. Penny-nut is more like it since cost it the top priority even if all else fails. This is direct opposite of everyone else in this thread and most on the site for that matter who behave like cost is no object. Or at least in their advice to others.

To answer your question my crude tests use the 5 digit Ebay meter ( https://www.eevblog.com/forum/projects/ (https://www.eevblog.com/forum/projects/)$5-voltmeter-with-5-digit-%280-1mv%29-resolution/ ). It is known to have reliable 0.1mv resolution and excellent accuracy from testing against 6 1/2 and 8 1/2  digit lab grade instruments. It uses a $2 Microchip ADC with built-in reference and little else. In my case I've attached a 16 channel 4051 based multiiplexer to read multiple channels and OP07 with gain of 10 and offset to boost effective resolution to 6 digits in the range of interest (2.5v).

From my first post here it was obvious you were very "diligent" and this definitely works in my favor. If I ignore 90% of your advice that I might consider overly cautious for my application that still puts me way ahead. Fortunately nearly everything you tell me rings true and I'm grateful for your help. Any differences we have are mostly due to disparate goals. You seek perfectionism and I'm after economy and minimalism.

But I do think your comments about 4 digit limit may be overly pessimistic since many existing devices, not just the $5 panel meter, but many expensive commercial instruments like Solartron, do not depend on LTZ1000 or LM399 or anything similar. So time will tell just how far off my pipe dreams are. For now probably better not to clutter up this thread because you have satisfied my needs for information ATM and I'm grateful. Thanks again.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 22, 2015, 07:59:38 pm
Paulie,

There is a seller on Ebay selling LM399 at $4.60. I bought handful and they where good. No expensive external components needed, just a good stable regulated voltage supply and some resistors. The LM399 do not suffer much hysteresis so you can shut it off when not in use.

If that's too much, i can send you a dozen LM329CZ to tinker with. Just PM. When done with those, you may want to go to the LTZ1000. Or not.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 22, 2015, 08:24:00 pm
Actually the cost of LM399 on Ebay has increased big time recently. Can't even even get one for 2x that now. I think the volt-nut craze caught on and there is a big rush for these parts.

When I first learned of LM399 and found the zener could be purchased separately I did a search but found they were even more expensive than the LM399 at that time. Cost of the LM329 has come down but if you can pop a couple in an envelop and send letter rate I might like to give one or two of those a try. Doubt it will be a "gateway drug" for LTZ100 but I'm very interested in how they really compare with the surface diodes. I'll have a chance to check out the 1034 too sometime next couple days which will be interesting.

DM, I'd have to agree on both counts. Today LTZ, being king of the references, probably would be most cost effective for a commercial 6 1/2 digit meter and definitely for 8 1/2. Even at thousands of dollars a unit those guy can't afford to fart around with selecting and fine tuning. I also know more than one person on this site has swapped out for an LTZ so right again.

In my "special" case not so anxious to pay 10x more for a reference than I did for the meter. I would like to see if I can match or beat the cost for a DIY version and if possible add another order of magnitude resolution.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on February 22, 2015, 09:08:43 pm
It was Mickle T. who transplanted the ltz1000 into the Solartron 7081.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 22, 2015, 09:34:29 pm
LM399: This is the seller that was selling them at $4.60 recently. Closed for holidays now. Try in a couple of days. http://www.ebay.com/usr/polida2008 (http://www.ebay.com/usr/polida2008)

Here you have two for $10: http://www.ebay.com/itm/2pcs-LM399H-Precision-Reference-LM399-/181669101870?pt=LH_DefaultDomain_0&hash=item2a4c52812e (http://www.ebay.com/itm/2pcs-LM399H-Precision-Reference-LM399-/181669101870?pt=LH_DefaultDomain_0&hash=item2a4c52812e)
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 22, 2015, 10:01:32 pm
why anyone would pay more than this from an unknown buyer on the 'bay' is beyond understanding...

Shipping and handling where Fleabay still comes out ahead. There is that "fake" factor but as mentioned before I consider largely urban myth. Very popular romantic notion but in most cases turns out unjustified.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 22, 2015, 11:03:12 pm
Here you have two for $10: http://www.ebay.com/itm/2pcs-LM399H-Precision-Reference-LM399-/181669101870?pt=LH_DefaultDomain_0&hash=item2a4c52812e (http://www.ebay.com/itm/2pcs-LM399H-Precision-Reference-LM399-/181669101870?pt=LH_DefaultDomain_0&hash=item2a4c52812e)

Actually $15 for two so like I said about twice what they used to go for. Polida has none now. I suspect surplus units getting rare as hens eggs.

FYI Polida is one of my favorite sellers. Very helpful and relatively honest. Over 1500 deals last couple years for work.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 23, 2015, 12:18:32 pm
BTW are you guys aware "buried zeners" in LM399 and LTZ1000 do not even vaguely resemble a zener diode? Actually somewhat complicated integrated circuits with literally dozens of additional components. In recent conversation with an FAE was told there are even more undocumented and parasitic devices not shown in the internal diagrams.

So virtually zero chance of emulating with discrete components. Why can't life be simple?


Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 23, 2015, 01:08:09 pm
Yes Polida still have them, just wait until vacations are over. I bought a dozen, all tested OK.

Last time I bought from LT it was US$ 45.98 shipping i.e. $65 for two LM399. Ebay: US$11 for two including shipping.

Dealbreaker if on a tight DIY budget. If you have a real budget and tight time-plan, of course go to a authorized distributor.


Linear Tech sells these direct:

LM399H#PBF :: (1-99): US$6.64 (100-999): US$5.47

LM399AH#PBF :: (1-99): US$9.37   (100-999): US$7.72

You can order by sending an email to orders@linear.com ....

So, why anyone would pay more than this from an unknown buyer on the 'bay' is beyond understanding...

The 'A' version is simply tested to better specs.  The non-'A' version does not have this extra testing [the DMM manufacturers like to do this themselves].
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 23, 2015, 03:50:22 pm
BTW are you guys aware "buried zeners" in LM399 and LTZ1000 do not even vaguely resemble a zener diode?
That's the LM399, and it's true pins 1 & 2 are not just a zener or even just a diode-compensated zener.  But D3 is still a "buried zener" diode.  And while that is called out in the datasheet, it is easy to miss, as evidenced by one of the discussions in the LM399 thread (https://www.eevblog.com/forum/projects/lm399-based-10-v-reference/). The extra circuitry has a nice description in this old TI app note (http://www.ti.com/lit/an/snoa589c/snoa589c.pdf).

The LTZ1000 is much simpler inside.  Check out the die picture which was posted earlier in this thread (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg279145/#msg279145).

Perhaps you should start your own thread for trying to squeeze out the best voltage reference for under a dollar? (or whatever price point it is that you've set yourself.)
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 23, 2015, 05:04:54 pm
I attached a picture of the setup I used to measure on the LTZ1000AHC.

The first version was a regular PCB with a couple of cheapo 1% resistor decades connected.

The second version is pictured.
The small value toggle switch meant that the main resistor value could be changed by approximately 1%. The accuracy of the delta R would be 1/100*1/200 = 50ppm. The voltage changes would be in the order of 100-1000 times larger, ie 5000-50000 ppm. The voltage was read with a 7.5 digit LTZ1000 based dmm. As the transfer functions are quite linear (or even constant), I consider these to be quite feasible values.

The objective was to see if there where any sweet spots for resistor values. I was assuming the datasheet variation of output voltage, based on resistor variation, where uncertainties for the output. It turned out they where NOT, but actually dependencies, i.e. very predictable errors.

I re-did the measured two preliminary boards, once with the later, better, setup. In all, I used three different LTZ1000ACH. The measurements all show very similar results.

Bottom line: The output voltage changes, caused by variation of each resistor, is very predictable within limits!

i.e by monitoring / measuring the drift of resistor values it should be possible to predict the output voltage drift caused by the resistors (but of course not by the drift of the zener itself).

I never intended to do absolute voltage measurements. It would be meaningless as the LTZ1000AHC is rated 5% anyway.

I also did not intend to produce results down to the ultimate decimals. In the end, the resistor specs are uncertainties, ie not very predictable, unless you somehow map them individually and match them or correct the output of the circuit.

Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on February 23, 2015, 08:56:41 pm
Hi Janaf,

just take an 1N829 run at approx 7.5 mA find the zero tempco current of your sample, age for a year or so and you will have about a 6.5 digit capable reference of your own, at room temps that is.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 23, 2015, 11:31:48 pm
That's the LM399, and it's true pins 1 & 2 are not just a zener or even just a diode-compensated zener.  But D3 is still a "buried zener" diode.

The LTZ1000 is much simpler inside.  Check out the die picture which was posted earlier in this thread (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg279145/#msg279145).

So we agree there is no actual zener available in either device. And thanks for the TI link which was best description of that diode circuit inside LM399/LM329 so far. I'm no semi engineer but it looks like many many junctions in the LTZ photo so it may be simpler but not by much. I would love to find out what is really inside that IC that's being called a zener.

Perhaps you should start your own thread for trying to squeeze out the best voltage reference for under a dollar? (or whatever price point it is that you've set yourself.)

Good idea. I've already gotten a couple offline inquiries so will almost certainly follow your advice. My original post here was specific to the LZT1000 and I suspect if that had been in another thread there would have been very few useful replies. This was the goto place for what I needed and I'm very happy Diligent and the others were on tap. Google sucks.

ps. In response to your comment about my price point, ATM it's around 9 cents for a complete reference module including things like tl431 or pair of zeners, noise filter, low TC resistor, and something to mount it all on.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 23, 2015, 11:53:44 pm
So we agree the is no actual zener available in either device.
No, both have a buried zener inside but other stuff too.
LM399 has more because it has the complete temperature compensation, heater and regulation in the chip.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 24, 2015, 12:07:04 am
We were basically referring to just the "zener" part and the conclusion was no actual diode available to the user. In both cases part of a more complicated circuit. I'm not sure if the heater "resistor" they refer to is actually a resistor or, like the zener, part of a collection of components too. I would love to see a diagram of the actual internal LTZ circuit and also a description similar to the one in the TI app note.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 24, 2015, 12:14:19 am
I posted a schematic of just the 399 "zener" couple pages back but it was at the end of the page so in case you missed it  here it is again:

(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=138236;image)

Not a diode, at least not available to the outside world.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 24, 2015, 09:01:05 am
I posted a schematic of just the 399 "zener" couple pages back but it was at the end of the page so in case you missed it  here it is again:

(https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=138236;image)

Not a diode, at least not available to the outside world.

Definitely.. the Buried Zener is D3, and together with Q13, they even form sort of a Reference Amplifier, like in the SZA263/LTFLU.
The rest of the circuitry consists of some cc sources and amplifiers, similar to the external circuits of the LTZ1000.

There's a detailed description in the original AN-161 from National Sem., which I'd like to upload also.

So, as National explicitly speaks of a buried zener, D3, I don't understand, why you negate that statement?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 24, 2015, 12:45:15 pm
I think this is obviously a language issue and no need for further discussion. I'm very pleased to have learned a bit about the LTZ/LM399 references that was not discussed previously in this thread and also zeners in general. So moo-chow-grassy-ass guys. And thanks too for the motivation for another Worlds Cheapest thread.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on February 24, 2015, 12:55:25 pm
The big LM399 thread: https://www.eevblog.com/forum/projects/lm399-based-10-v-reference/ (https://www.eevblog.com/forum/projects/lm399-based-10-v-reference/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on February 24, 2015, 01:05:22 pm
Yes, I've gone through this thread twice but 3 times for that one. Mainly because it's only 1/3 as long but also that part is cheaper. In both cases an enormous learning opportunity. Not just for the target devices but many (way) off topic discussions and science in general.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 08, 2015, 06:13:57 pm
I post this again to ask that someone repeats one of my tests on the LTZ1000 circuit.
It's simple, only requires a 10K 1% resistor and a 6.5 digit DMM or better.

I'd really appreciate if someone could do this! Please  :-DMM
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 08, 2015, 06:53:08 pm
Hello,

already did a similar measurement on my LTZ#2 by increasing setpoint +9.6 deg C with 24K7 resistors.
Result is a 3.73 mV change of output or around 50ppm/K.

With best regards

Andreas


23.12.2010 LTZ1047 #2
=================
Bestimmung Tempco
Setpoint 50.5  = 12K5 + 1K                = 533,3  mV
Setpoint 60.14 = 12K5 + (1K||(22K+2K7))   = 514,06 mV -> 19,27mV -> 9,64 Grad

Setpoint 50.5 (22:31-22:35)
ADC4 -> 3592.48702 = 7185.02534
ADC8 -> 3592.48546 = 7185.00504

22:35 22K gesteckt
Setpoint 60.14 (22:41-22:45)
ADC4 -> 3594.35358 = 7188.75846
ADC8 -> 3594.35320 = 7188.74052

ADC4: 3594.35358 - 3592.48702 = 2*1.86656 = 3.73312 mV / 9,64K = 387uV/K = 53.9 ppm/K
ADC8: 3594.35320 - 3592.48546 = 2*1.86774 = 3.73548 mV / 9,64K = 387uV/K = 53.9 ppm/K

22:55 22K gezogen

Edit: was LTZ#2 not LTZ#1

Data for LTZ#1 is similar with 22K

22.10.2010 LTZ1000A #1
==================
Bestimmung Tempco
Setpoint 50.5  = 12K5 + 1K
Setpoint 61.25 = 12K5 + (1K||22K)

Setpoint 50.5  -> 3571.8537
Setpoint 61.25 -> 3573.7066 -> 2*1.8529 mV = 3.7058mV/10.75K = 345uV/K = 48ppm/K


Title: Re: Ultra Precision Reference LTZ1000
Post by: JohnnyBerg on March 08, 2015, 07:01:40 pm
already did a similar measurement on my LTZ#1 by increasing setpoint +9.6 deg C with 24K7 resistors.
Result is a 3.73 mV change of output or around 50ppm/K.

Fascinating.
Stability from the LTZ1000 is the stability from the temperature control, would be my (maybe to simple) conclusion :P
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 08, 2015, 07:38:32 pm
Andreas: If I get you right:

You changed from 1:12.5 to 1:13 ratio for the heater, which gave 3.733mV output change?

That would be a 4% resistor change versus approximately 0.0519% voltage change, ie 0.0125 ppmU/ppmR.

(Or as given in the datasheet 1.29ppm change in voltage for 100ppm resistor ratio, while in the datasheet says 1.0ppm/100ppm) My measurements are close to yours, I got around 1.25ppmU/100ppmR

ie the V/R ratio you get matches well the datasheet and even better with my measurements! Nice to know!

Yet, for R1, 120R, my measured values are very different from whats given in the datasheet, therefore I'm still very interested in some "R1 results".

Jan
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 08, 2015, 07:59:37 pm
Hello Jan,

sorry I mixed up the 120R with the 1K resistor.
On the 120R resistor I have no possibility to measure without removing all thermal isolation.
(the temperature setpoint pin is accessible on a sub-board connector to have the possibility for "degaussing").
And the pin itself is also like the temperature setpoint very sensitive to RF injection.
So you have to solder with very short wires to the 120 R resistor.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 08, 2015, 08:07:55 pm
Thanks Andreas, I hope someone else can do it!
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on March 08, 2015, 08:32:17 pm
Hi,

I came across some liquid at work with interesting behaviour which might be of interest for those who want to keep moistore away from precious resistors:

Novec 7100 by 3M, which is a H-FKW. Nonconducting, not aggressive to most plastics, not corrosive to metals, due to quite big molecules it doesn't enter too much into most plastics at all. Aggressive to PTFE and other polymers that contain a amount of F. Water is almost insoluble in it. I am not testing its electric behaviour, but it has almost no surface tension, leaks out of about everything - I am used to keep syringes with water without a cap to store them for a while, H-FKW will leak.

Could be a (quite cheap) alternative to silicone and mineral oils for those who want to put their reference in hermetically sealed containers.

Other news: My LTZ1000A is seeing power supply again, and I found that one of my low thermal emf cable had a bad soldering point: variable between 200-600 miliohm by twisting the cable, after reflowing its back to 86 miliohm just like its same-length cousin.

The "cant look at my reference" period seems to be over, finally.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 08, 2015, 10:38:03 pm
?
Stability from the LTZ1000 is the stability from the temperature control, would be my (maybe to simple) conclusion :P
Stability to surrounding temperature is absolutely dependent on temperature control.

I have never seen any explanation on why the LTZ1000 has better aging characteristics than other buried zeners. Is it simply a characteristic of the devise or does the circuit somehow compensate for a "known" aging process? I've never seen any suggestion on this either, just wild speculation....
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 09, 2015, 04:37:30 am
janaf
I can do measurements for you as well, what is this intended for tho?

Also decided to make a calculator for LTZ, since there is LOADs of data already on web, but no place where everything valuable consolidated in one page.
Picking up bits here and there across all forums is kinda troublesome for voltnut beginners.
Here's what I got so far: http://xdevs.com/ltz1000/ (http://xdevs.com/ltz1000/)
If anyone have ideas - feel free to suggest.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on March 09, 2015, 07:25:46 am
My take on the calculator is that one does not need R2 and R3 to be equal, the transistors are slightly different sizes anyway, and for R3, lower gives less noise, so the temperature stability can be as good as possible, whilst for R2, the zener is noisy anyway, so you might as well run at a lower current there for a higher vbe tc, that will reduce the sensitivity of the zener transistor combination a little bit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 09, 2015, 09:25:58 am
I can do measurements for you as well, what is this intended for tho?
The intention is to see how sensitive the circuit is to resistor stability which simply tells where to put the money when selecting resistors. My measurements indicate that some of the data in the datasheet are not valid. As an extension, it may be possible to select resistors characteristics to compensate each other.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 09, 2015, 10:03:06 am
But how you can judge from different references we have, as well as measurement gear and resistor themselves?
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 09, 2015, 10:20:05 am
Long story, please see my previous posts. A summary of my measurements is:

So what I'm asking is if someone else can make the SIMPLE & FAST test I suggested, to verify (or reject) the results I got.
Title: Re: Ultra Precision Reference LTZ1000
Post by: max666 on March 09, 2015, 02:29:35 pm
But how you can judge from different references we have, as well as measurement gear and resistor themselves?
He has to compare his results to other references, that's an important point. If he finds a particular resistor isn't as critical as mentioned in the datasheet, but other members can't replicate the result on other references, then it's not a general result. It might just be a fluke with his reference.
Different measurement gear should not be that critical, because he's only asking how big the relative change is. Besides, all the voltnuts here probably first thing in the morning they switch on a 6 1/2 digit (at least) multimeter, before they even have coffee (http://i.imgur.com/k7sdcqu.gif)
And regarding different resistors, I think there isn't a model for the reference, if I'm not mistake. So having these measurements at different resistor values would be necessary for building a model.
I'm guessing this being the case, from reading along the thread. I'm not good enough to be able to call myself a voltnut yet  ^-^
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 09, 2015, 03:44:50 pm
Alright, you got it going. But to make it proper, it will take two days.
I had my 2002 with open hood last days, got it assembled back and took one of LTZ's to do janaf's measurement request.

KX module #3 (Red), +7.1367 VDC, LTC2057, VHP203: 70K, Z202's: 13K+1K tempset, 120R. Powered from +12V moto battery.
KI2002 input - LTZ output.
KI2001 = Battery voltage monitor.

Tonight it will capture data with 120R, tomorrow with 10K000 VHP202Z.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 09, 2015, 06:23:25 pm
Hi,

I wrote a summary of some of my measurements on R1 and made an effort to make it understandable, the why, how and results.

Attached.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 09, 2015, 06:25:37 pm
Alright, you got it going. But to make it proper, it will take two days.

Great!

I also just posted a summary page on some of the measurements I did on R1.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 10, 2015, 02:54:51 pm
UPDATED: With both data collected.

Initial reference data with 120R only:

(http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf_120R_s.png) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf_120R.png)

With 10K 0.01% VHP203Z in parallel.

(http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf_120R_P10K_s.png) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf_120R_P10K.png)

RAW datalog 120R: TXT file (http://dev.xdevs.com/projects/kx/repository/entry/datalog/vref_a01/janaf_120R.log), 1.5MB
RAW datalog 120R+10K : TXT file (http://dev.xdevs.com/projects/kx/repository/entry/datalog/vref_a01/janaf_120R_10K.log), 1.5MB
Format (columns left to right) is battery voltage (input for reference), LTZ1000A output, hour, minute, second, day, month.

Measurement setup:

(http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf/_BLI8087-1.jpg) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf/_BLI8087.jpg) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf/_BLI8088-2.jpg) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf/_BLI8088.jpg)

(http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf/_BLI8089-3.jpg) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf/_BLI8089.jpg) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf/_BLI8090-4.jpg) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf/_BLI8090.jpg)

After 10K added to 120R:

(http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf/_BLI8091-5.jpg) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf/_BLI8091.jpg)

Output voltage raise ~ +134.9 uV, or +18.90 ppm.
Measurement little bit crippled, as battery voltage not exactly same, but should not be big enough impact.

Thank you for PDF, I like your way of reporting things using fixed PDF, which easy to save/store for future use, rather than forum post :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 10, 2015, 04:33:14 pm
Thanks! Calculating exactly like for my values, I get a change of -0.00159 ppmV/ppmR, slightly higher than my value, -0.00128. Lymex posted a value of 0.0014 some time ago and so did I (-0.0014) from another series / another board and LTZ1000 but all four are quite similar and all are far away from the 0.01 in the datasheet!

Maybe the data-sheet data where taken on the LTZ1000 and different, not adjusted for the LTZ1000ACH??

Anyone has a plain LTZ1000 (non-ACH) to test?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 10, 2015, 04:39:59 pm
I have LTZ1000 version as well, with different setpoint tho (12K0 + 1K0).
Can repeat test on it as well. Also your PDF is somehow corrupted formatting-vise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 10, 2015, 04:41:06 pm
TiN,

you obviously get the same behaviour, i.e. an attenuation of the instability of R1 of about 630.

(dR/R = -11857ppm, dU/U = +18.7ppm)

To first order, R1 together with the transistor constitute a constant current source for the zener diode.

The change of R1 changes this zener current, and so you can calculate the zener diode differential resistance, in this case, that is 2.97 Ohm (*)

That explains the very small influence of R1.

The datasheet specifies a change of typical 80mV, maximum 240mV by changing the current from 1mA to 5mA.. From that very big change, one would calculate 20..60Ohm for the differential zener resistance.. maybe LT has taken this value for the stability calculation.

As the LT references seem to be manufactured very similar, I assume also, that this is a generally valid result.

And yes, please, repeat that measurement with LTZ1000, as I also have 5 EA waiting.

Frank

(*) 0.45V Ube assumed
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 10, 2015, 04:43:49 pm
Reply to this older post. This may make the R1 even less sensitive, can't quite wrap my brain around it. I think I'll do some measurements...
....Bob Dobkin's ap-note on page 6 of the data sheet shows a way to make the LTZ1000 more stable at room temperature-- but this same idea can be extended to a heated device.  The circuit shows a potentiometer-- and this is probably not a good idea-- this resistor will be smaller than the 120-ohm resistor [because you need less than one Vbe for proper compensation].  As a wild guess, it will be somewhere between 15-ohms and 25-ohms. ...
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 10, 2015, 04:52:48 pm
Somehow I managed to export the whole raw ugly data...  File updated now.

I have LTZ1000 version as well, with different setpoint tho (12K0 + 1K0).
Can repeat test on it as well. Also your PDF is somehow corrupted formatting-vise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 10, 2015, 05:07:05 pm
I got the question on the other resistors. In my measurements

- R2 is slightly more important than the datasheet indicates, -0.4ppmV/100ppR compared to 0.3ppmV/100ppR in the datasheet. Not a very significant difference (apart from the sign!)
- R3 was less sensitive. I got -0.07ppmV/100ppR compared to 0.2ppmV/100ppR. A quite significant difference but low values anyway.
- R4/R5 I got slightly higher value than the datasheet and same sign, positive. Not very significant difference.

- For R2 the sensitivity decreased a bit with increased resistor value (range 40K-100K), but not very significant
- For R4/R5 the sensitivity decreased a bit with higher ratio/higher temperature setting, but not very significant
- For R3, the sensitivity was unchanged over the range (40K-100K)
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 10, 2015, 05:22:15 pm
For a more complete model, one should do the full Jacobian matrix, i.e. vary each resistor versus all the other. That would take at least 15 measurement series, each with, for example, 10 data-points. Quite an effort.... I'm only trying to map which ones are significant and which are not.

On the whole, the result seems to be a confirmation that the R4/R5 divider are the most critical part without comparison, while R1 seems less important than R2. R3 is relatively unimportant, it seems no exotic hi-end $$$ resistor needed there.


While at it: if the R4/R5 are important, a divider to reach 10.00000V is much more difficult than R4/R5........
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 11, 2015, 08:00:54 am
Thanks, I should have read better.... I guess I should do some measurements on that....
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 11, 2015, 02:27:21 pm
Updated post with measurement 120R vs 120R+10K. Sorry for little drift in second case, as ambient temperature reduced from 21.5°C to 19.5°C, raining days here  :bullshit:
Time to test LTZ1000CH.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 11, 2015, 02:58:35 pm
Thanks,

If I take data from 20% to 40% of the 120+10K file, would that be approximately the same temperature as the second half of for the 120 only?

I'm not looking for ultimate accuracy as there may be individual differences anyway, I just want confirmation just if the attenuation is in the order of 1:100 or 1:700......

PS: This circuit is very immune to power supply voltage variations as it only powers the OP-amps and the heater transistor. I have verified this by measurements by varying the supply from 15V to 9V and it did not show any output change, down to the resolution of my 7.5 digit DMM. (It might depend a little a bit on what op-amp you use). But I would not worry about supply variations.

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 11, 2015, 05:02:51 pm
I do agree regarding input voltage immunity. I use LTC2057 on all except one references.
Reason why have battery power is to isolate reference from input AC power noise, as it's not on primary spot which had dedicated mains line during this test.

LTZ1000CH test:

Unit Rev B01 PCB, LTZ1000CH, LTC2057, 12K/1K heater , base 7.1304749 VDC @ +23.6°C ambient (power on from cold state).

(http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf/ltz_b01_s.jpg) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_a01/janaf/ltz_b01.jpg)

1. 120R

(http://dev.xdevs.com/projects/kx/repository/entry/img/vref_b00/ltz_b01_120R_s.png) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_b00/ltz_b01_120R.png)

2. 120R+10K

(http://dev.xdevs.com/projects/kx/repository/entry/img/vref_b00/ltz_b01_120R_10K_s.png) (http://dev.xdevs.com/projects/kx/repository/entry/img/vref_b00/ltz_b01_120R_10K.png)

About +134uV as well, so same with LTZ1000CH
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 11, 2015, 09:08:51 pm
Reply to this older post. This may make the R1 even less sensitive, can't quite wrap my brain around it. I think I'll do some measurements...
....Bob Dobkin's ap-note on page 6 of the data sheet shows a way to make the LTZ1000 more stable at room temperature-- but this same idea can be extended to a heated device.  The circuit shows a potentiometer-- and this is probably not a good idea-- this resistor will be smaller than the 120-ohm resistor [because you need less than one Vbe for proper compensation].  As a wild guess, it will be somewhere between 15-ohms and 25-ohms. ...

No, it won't make R1 less sensitive, but it will make the R4/R5 ratio less sensitive [about 1000:1 vs. 100:1].

But what does it "cost"?

Even if its only around 20 Ohms with 5 mA it will increase the output of the reference by 100mV.
These 100 mV have the full tempco of the 20 Ohms resistor.
So the 20 Ohms resistor contributes 1/70 to the 7V output voltage.
So now this gets the most sensitive resistor in the cirquit.
The datasheet value is 200 Ohms -> only 1/7 reduction on resistor drift.

According to the datasheet of a Z201 all resistors below 100 Ohms have a higher tempco spec than those above 100 Ohms.

Maybe I am wrong?

So Ken: what are your measurement results to this suggestion?

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 12, 2015, 10:04:11 am
So basically, we'd de-sensitise R4R5 but get a new pair R1-"R6" that is slightly more critical?
Title: Re: Ultra Precision Reference LTZ1000
Post by: max666 on March 12, 2015, 01:07:45 pm
If you have them wirewound by hand anyway, why not wind both resistors on the same bobbin?

(http://i.imgur.com/tCcjjrn.png)

Like example 2 or 4, but feed all 4 ends out separately.
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on March 12, 2015, 06:35:34 pm
If the 20ohm resistor "R6" according to Andreas has 1/70 sensitivity and 120ohm R1 according to Janaf, Lymex and TiN has about 1/700 sensitivity it seems strange that they should track?

If it was only the same 5mA current through the resistors R1 as "R6" it should be more like 6 times higher sensitivity on R1?

Has I missed something?

Also if Mr.Pettis can make matched wire pairs of 20 and 120ohms he might be able to do 1k and 12 or 12.5k instead of an extra precision resistor?

Lars Walenius
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on March 12, 2015, 06:51:22 pm
To MAX666,

Technically speaking, they are but are not wound by hand, the hand is only used in guiding the wire as it is wound onto the bobbin and yes, there is a technique to doing it correctly, otherwise the resistor may not turn out quite right.  In PWW resistors, all the details are important to the final outcome (as it should be in any precision resistor), very small variances can lead to significant effects on the final characteristics, for instance, it can change the TCR from being very low to being significantly higher, perhaps 3 to 5 times higher is quite possible, it has happened.

Theoretically, it certainly is possible to wind more than one individual resistor on a bobbin, however there are many constraints as to whether or not it can be practically accomplished, in most cases it turns out to be impractical.  For instance, two resistors on a single bobbin almost always requires four terminals, the smaller bobbins cannot accommodate two lead assemblies at each end, the bobbin is too small.  For the larger bobbins, they must be retooled to accept two lead assemblies per end, new collets must be purchased to accept the double leads (and they are quite expensive) and welding the wires to the terminals becomes a bit restricted by having two leads near each other.  Having multiple lead assemblies also complicates the calibration process as it is very difficult to rotate a resistor with four leads sticking out of it and keep a true four terminal, low resistance contacts.

In the case of the resistors being mentioned here, the 120R0 and 12K (for example), a larger bobbin must be used as each value (using the same wire size as proposed) basically fills a bobbin (8E16 size as an example, my 805), a possible candidate may be my 807 (8E24) but that still leaves the termination problem.  I have considered such bobbin modifications in the past and other ideas to produce a possible multi-resistor bobbin design, they do have some advantages but the major drawback is the cost of implementing them.  They must be designed in such as manner as to not compromise the precision characteristics of the resistors I currently make while giving some advantage to warrant the cost of it.  You are not the first one to ask about or propose such resistor designs, in the past, the easiest solution was to put the resistors into a close fitting container and fill it with good thermal conductive filler.  This did save on expensive tooling but was still more expensive than two (or more) individual resistors.  Another method which works better than you might think is to wrap copper adhesive tape around the resistors, while this does increase the thermal time constant a bit, it works quite well if the ambient temperature does not vary wildly quickly.  As is the usual suggestion when working with temperature sensitive circuitry, encase the whole works and eliminate drafts, that is very important.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 12, 2015, 06:54:03 pm
Welcome Lars!

A2 opamp keeps the voltage over R1 and Q1, the temp-compensation transistor (pin 4 & 5) equal at all times. That's what keeps the output voltage constant and variations in R1 are to a high degree compensated for. One of the very clever details in this circuit! Variations in "R6" would not be compensated for. I guess that's the difference. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: richiem on March 12, 2015, 07:24:51 pm
LTC2057 is not a $20 opamp -- I bought some for under $5 ea.... but they are SO8 pkg which is the smallest I can work with by hand. Having the chopper amp is essential for temp reasons unless you are going to ovenize the circuit, and the 2057 is the best chopper amp.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 12, 2015, 07:42:22 pm
Lars Walenius

Welcome Lars !

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on March 12, 2015, 08:08:56 pm
If the 20ohm resistor "R6" according to Andreas has 1/70 sensitivity and 120ohm R1 according to Janaf, Lymex and TiN has about 1/700 sensitivity it seems strange that they should track?
You're comparing the sensitivities from different circuits.  Changing R1 changes the zener current, which has a different result in the output voltage based on whether or not R6 is present.
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on March 12, 2015, 09:39:41 pm
If the 20ohm resistor "R6" according to Andreas has 1/70 sensitivity and 120ohm R1 according to Janaf, Lymex and TiN has about 1/700 sensitivity it seems strange that they should track?
You're comparing the sensitivities from different circuits.  Changing R1 changes the zener current, which has a different result in the output voltage based on whether or not R6 is present.
Ok.

Anyone with an idea how the output sensitivities for R1 and "R6" changes with "R6" inserted? As I understand they need to cancel each other if the "tracking pair" should work?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on March 12, 2015, 10:24:42 pm
Actually, the mandrel is that part of the bobbin on which the wire is wound, a collet is what holds the lead assembly of the bobbin and the collet is screwed into a shaft driven by the motor.  The diameter of the mandrel is what limits the possibility of putting two lead assemblies into each end of the bobbin, this is a physical limitation.

Evanohm is welded using a CD welder, that is the simple part of it, the rest of the detail is in the design of the resistor, lead assemblies and electrodes.  As I told DiligentMinds, it is not the type of welding that can easily be accomplished by a novice in order to achieve a quality weld.  If you are just interested in trying your hand at making a basic resistor with a fairly low TCR, then I suggest Alloy 294 (Constantan) which can be soldered too and has a moderate resistance.

DO NOT under any circumstances use acid flux on electronics, there are no exemptions to this rule unless you are a plumber working with copper pipes.  Zeranin-30 (a variant of Manganin) can be soldered to with regular solder but these alloys must be heat treated after 'winding' to remove stress and being mainly a copper alloy will remain sensitive to additional heat, soldering can and will cause a permanent change in the heated wire.  These alloys are of very low resistance so as a matter of practicality, you cannot wind high resistance values unless you have lots of space.  If you imagine that you might be able to make a high precision wire wound resistor with very low TCR on your own, I'm sorry, it isn't going to happen.  If that was the case, everyone would be making great PWW resistors and that is just not the case.  The same thing can be said for metal foil resistors, that isn't something you're going to do on a Saturday afternoon in the garage either. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 13, 2015, 12:35:16 pm
Seriously guys, despite the amount of effort people are putting into the voltage references, we are not on solid ground with the LTZ1000. See current discussion on resistor sensitivity analysis and dr Frank's projection of need for improvements in the coming years.

Frankly, the datasheet for the LTZ1000 is rudimentary only. We need a totally re-written revision up to today's standard, on par with LT's current datasheet. That would be an update in several orders of magnitude in information for users. We should also have a SPICE model for the LTZ1000 itself so one could simply evaluate things like. LT surely have tools and knowledge to make measurements an to convert measurements to model.

What are the odds of this happening? Is it likely? Is it simply a cost for them that they will not recover?

If it's not likely LT will do it, I think community should and I'm willing to do my share.

- Collect and organize data that is available. A wiki?
- Do "complete" static measurements on the LTZ1000 including temperature dependency
- Create a spice model
- Measure and model aging ...

Measuring the LTZ1000 should be doable. Two transistors and a zener which all can be measured independently or together.

Any takers? Thoughts? Realistic? Has any of this already been done? Am I out in deep waters? Stepping on toes?

Does someone have the right LT contacts to forward this message to?

Janaf
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 13, 2015, 03:53:20 pm
Another reason is likely that main customers for LTZ who buy it in thousands are likely already did many years of characterization and would not need model/update on datasheet anyway.

As of us, I do want to commit in own way to get details, by doing next:

* Build prototype boards to measure real data. Done, 5 boards built (3 x ACH, 2 x CH, LTC2057 on four of them, LT1097 on one).
* Burnin 1000 hours all boards. Done.
* Build preamp for noise measurement. In progress, schematics phase.
* Charaterize refs with temperature. Need define method. Have TEC and KI 2510, waiting CNC vendor to make enclosure metal box.
* Characterize voltage dependency. 24VDC to 8VDC power in 0.1V steps (KI 2400 SMU) - pending
* Build reference backplane with 10VDC, 2VDC and 20VDC output, both positive and negative. Idea stage
* Build 24bit DAC and 24bit ADC for datalog. In idea stage
* Capture realtime data and show online during 1 year period - testing frontend with javascript now

It should be both static data hosted on dedicated public site, where anyone can gather verified data and learn thru analysis, and where newcomers can get idea of whats current status of things, without reading 73 pages of forums. While as participants progress, we keep discussion using this forum as communication platfrom.

I get feeling that some of people would like to try LTZ for their fun, but after reading page or two here where talks about custom unobtanium resistors, they got carried away rather quickly.

P.s. as end result my vision is to have practical application how LTZ ref used to generate stable current like 10.00000mA standard or <1ppm DAC/ADC system. So I  going forward to use my site as hosting for all findings/data already. Its own server, so its have no space/toolkit limitations. Trying to get ahold some javascript and python to make webpage where I can display measurement data realtime from LabView. (i am hardware guy, not software wizard :((
Title: Re: Ultra Precision Reference LTZ1000
Post by: macfly on March 14, 2015, 04:41:45 pm
......
The 50ppm/K natural [unheated] TC of the LTZ is reduced to something less [maybe 2-5 ppm/K], and so when you turn on the heater circuit [which holds +/- 1.0mK], the TC drift is now a great deal less than 0.05ppm/K [or, if you want, the heater R4/R5 ratio no longer has to be so accurate to achieve 0.05ppm/K TC].

Hello,

I have made a Q&D test with one of my LTZ1000ACH's with external heating. At a chip temperature between 40 to 45 deg. Celsius the temperature coefficient drops vom 28ppm (without cathode resistor) to < 1ppm with a 20 Ohms S102K as cathode resistor. Anode resistor was a 120 Ohms S102K.

Regards,

macfly
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 16, 2015, 05:58:01 pm
That sounds little similar to CSNG ones I got before (2.5 ohm). Ended up with around $75 per each.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on March 16, 2015, 07:09:07 pm
......
The 50ppm/K natural [unheated] TC of the LTZ is reduced to something less [maybe 2-5 ppm/K], and so when you turn on the heater circuit [which holds +/- 1.0mK], the TC drift is now a great deal less than 0.05ppm/K [or, if you want, the heater R4/R5 ratio no longer has to be so accurate to achieve 0.05ppm/K TC].

Hello,

I have made a Q&D test with one of my LTZ1000ACH's with external heating. At a chip temperature between 40 to 45 deg. Celsius the temperature coefficient drops vom 28ppm (without cathode resistor) to < 1ppm with a 20 Ohms S102K as cathode resistor. Anode resistor was a 120 Ohms S102K.

Regards,

macfly

Looks like you got lucky getting the value close to right.  I guess we are calling this new resistor "R6", though I think that conflicts with other resistors in the original design.

This technique will be at it's best if R1 [the anode resistor] and "R6" [the cathode resistor] track well with temperature.  At a minimum, they should be placed close together on the PC board [flat side to flat side for the VPG foil resistors].

I asked VPG how much it would be for a VHP100 in values at below what the data sheet has as a lower limit [100 ohms], and they said that they could do it, but it would be 3-4 times the price of a similar 100-ohm resistor with the same specs.

So, I started looking at alternatives.  It turns out that VPG makes a resistor that is specifically designed for low-ohms values in the range we need, and that is the VPR221Z.  If you made an R1 and an "R6" with these, their heat-sink tabs [made of aluminum] could be glued together [using thermally conductive high-temperature adhesive] with the leads on opposite sides.  After a bake at 125C for 72 hours to drive off all moisture, they would then be sealed in dual-wall PTFE/FEP heat-shrink to make them "almost hermetic".  These are 4-wire units, but it doesn't stop you from using them as 2-wire resistors [just use the 2 leads on each side connected in parallel].  That will shift the TCR a bit, but that's OK in this application.  So now, we have a hermetically sealed [well, "almost hermetic"] resistor pair that is thermally coupled.  I don't know if it would do any good [or if you would just be wasting your money], but you can ask VPG to make these TCR track to +/- 0.1ppm/K for more money [and be sure to tell them that you will be using these as 2-wire resistors so they are trimmed correctly].  They may TCR-track naturally anyway, or maybe they could be selected as an alternative?

With "R6" in place, the heater circuit's divider now has relaxed specifications, and that opens up the possibility for a number of lower-cost divider techniques that were not previously available.

If you were to use a 4 lead resistor for R1 then you could use one of the leads for the ground side as the sense for the 10 volt low.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 17, 2015, 02:34:19 pm
Yesterday I received WW resistors from Pettis, in all took a couple of weeks including shipping to Europe.

Today, hermetics arrived from Vishay, earlier than expected, about 12 weeks in total. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 17, 2015, 08:22:30 pm
Sure, I can post data on these. I'm waiting for some components to build a mini-thermal chamber but depending on time, could do some quick-and-dirty test before the thermal thingie has been built.
Title: Re: Ultra Precision Reference LTZ1000
Post by: richiem on March 18, 2015, 03:57:43 am
I have gotten my spare HP 3458A reference board put into an aluminum case with power supply and buffer amp. Thought I'd share some initial data. The R411/R412 ratio is 12.5:1, and the buffer amp for the zener voltage output is an LTC2057 in unity gain. I'm using a metal foil 12.1k with a 402R metal film in series to get 12.5k -- I've ordered resistors from Edwin Pettis and will replace that combo with a 12.5k ww. The top of the LTZ and the bottom side of the board under it are sandwiched in open-cell foam for minimum air current disturbance yet with some heat exchange.

The main supply is from an LM317 at 17.3VDC (couldn't get to 18V with my little wall-wart transformer which puts out a *nominal* 17VAC -- I wanted this to run with mains voltage as low as 110) and, like Max Carter and HP, I put in a -15V supply from a 79L15 for the 2.67k R419 resistor to nowhere. I'm still not sure which LTZ1000 this is -- non-A or A; Dr. Frank thinks HP only used A versions.

I've been moving the box from 22°C to 24.5°C and back, monitoring temps with a calibrated thermistor, with several hours between moves. The output variation is 0.3ppm/°C as read by my HP 3458A running at a nearly constant internal temp of 36.4°C, (+/- 0.2°C). Hope this info is useful to those building an LTZ1000 based supply modeled on the Linear Tech-HP design.

It will be interesting to see what difference if any the ww 12.5k resistor makes. I put in a second LTC2057 to boost the 7.13453xV zener output to 10V. I used metal film resistors and cermet pots for feedback and cal, and unfortunately, but not unexpectedly, the 10V variation over temp is 25ppm/°C -- useless. Edwin's ww resistors and Vishay foil trimmers should help here.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 27, 2015, 08:51:49 am
I got the question on the other resistors. In my measurements

- R2 is slightly more important than the datasheet indicates, -0.4ppmV/100ppR compared to 0.3ppmV/100ppR in the datasheet. Not a very significant difference (apart from the sign!)
- R3 was less sensitive. I got -0.07ppmV/100ppR compared to 0.2ppmV/100ppR. A quite significant difference but low values anyway.
- R4/R5 I got slightly higher value than the datasheet and same sign, positive. Not very significant difference.

- For R2 the sensitivity decreased a bit with increased resistor value (range 40K-100K), but not very significant
- For R4/R5 the sensitivity decreased a bit with higher ratio/higher temperature setting, but not very significant
- For R3, the sensitivity was unchanged over the range (40K-100K)


Hi Jan,

your measurement results were somehow familiar to me, and now I know why..

The Chinese blog bbs38hot.net contains several similar threads about the LTZ reference, and in one the author bg2v0 also measured the influence of the different resistors.. exactly the same what you've found. See screenshot

https://translate.google.com/translate?sl=zh-CN&tl=en&js=y&prev=_t&hl=de&ie=UTF-8&u=bbs.38hot.net%2Fthread-46-1-1.html&edit-text=

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 27, 2015, 11:17:27 am
As I got some requests, I will post more, but give me a couple of days.

Thanks for posting the Lymex data. If we multiply my data by 100, for 100ppm resistor changes we get:

-DatasheetLymexJanaf
R110.14-0.14
R20.30.4-0.4
R3 0.20.03-0.07
R4/R5 1.00.95+1.2

A couple of conclusions:
- It seems the R1 and R3 values are not as critical as given in the datasheet. Or both Lymex and I are wrong.
- Put your money on R4/R5 and R2 while R1 and R3 are less critical.

In the end, the errors of resistors are uncertain :-DD, it is not meaningful to dive too deep into the decimals.
EDIT: changed signs in the table.

Frank,

Great!
It may be the same guy "Lymex" that I compared to before.

In any case, I'm pretty confident about the data now as at least two other people get very similar results to mine.
Edit: TiN being the third person...
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 27, 2015, 01:28:08 pm
I'm appending a file with diagrams for the measurements I have done of the LTZ1000ACH. So far. To be continued and cleaned up. Most of these measurements, I have not seen published elsewhere.

I estimate that what I publish now represents less than half of the measurements that I intend to do.

If someone from LT sees this, some samples of LTZ1000ACH would be appreciated as support for the work :)

(EDIT: changed attached file to pdf)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 27, 2015, 01:40:32 pm
My word does not show any data :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 27, 2015, 02:42:01 pm
Sorry, should have been the pdf. Uploaded now.

It's just the diagrams, no data.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 27, 2015, 03:00:41 pm
It's same family as Star Office but OpenOffice 4.1. Essentially MS Office equivalent, it has less detailed functionality than the full MS equivalent but works very well. And is free. I have it on my Samsung phone too. MS and OO should be able to exchange files but in in my experience it only works to 90% .

OO suffers from the usual word processor problem that "everything moves", i.e. not good at neatly aligned, repetitive, identical plots.
Title: Re: Ultra Precision Reference LTZ1000
Post by: richiem on March 28, 2015, 09:34:43 pm
Presumed reasons -- thermal and mechanical isolation.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on March 28, 2015, 10:20:47 pm
As previous poster, much less heat leak, and much smaller mechanical strain on the kovar leads, but at the expense of much increased fragility. Impressive though, but still not sure how much it gains one.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 28, 2015, 10:37:23 pm
As said, probably the ideas is to isolate thermally. Not convinced that it really helps. Japanese? Seen some similar designs on Chinese sites.

Looks cool anyway!
Title: Re: Ultra Precision Reference LTZ1000
Post by: chickenHeadKnob on March 29, 2015, 03:02:04 am
It's not for mechanical reasons since the LTZ1000/LM399 aren't sensitive to stresses on their leads (Cf. Datasheet). It makes sense for thermal reasons, but although eye catching, this design is far from optimal : The aim here is to make the temperature uniform among the leads. This should be done by a lot of copper near the solders, and as small spacing between traces as possible. The "flying" traces should be made as thin as possible to avoid thermal gradients due to another thermal source/leak on the PCB. The quite large traces unfortunately ruins the benefits of the slotted areas.

35µm copper is about 10 times more thermally conductive than its 1.6mm FR4 substrate.

In attached file : A draft of what I believe more optimal.

The width of the traces was the first thing to catch my eye, vis a vis the LTZ1000 board in the new 34470
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on March 29, 2015, 08:34:54 am
With a 7 volt source and the 70K resistor for R2, what is the room temperature superdiode that any of you get? i.e. gnd to pin 7, pins 4 and 5 connected to 70K and other end of 70 K connected to 7 or 10 volts? that way we can get the scaling of the transistor and get a better handle on the vbe vs temp. dont connect up the zener or heater for this and you can be certain it is at room temp.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 29, 2015, 10:48:33 am
With a 7 volt source and the 70K resistor for R2, what is the room temperature superdiode that any of you get? i.e. gnd to pin 7, pins 4 and 5 connected to 70K and other end of 70 K connected to 7 or 10 volts? that way we can get the scaling of the transistor and get a better handle on the vbe vs temp. dont connect up the zener or heater for this and you can be certain it is at room temp.
Please re-formulate a bit clearer. Do you mean the voltage over the diode at room temperature? It's current dependent. If you search my previous posts in this thread, you will find some plots. Anyway, i'ts around 6.6V for the zener only at typical 5mA.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on March 29, 2015, 03:23:16 pm
With a 7 volt source and the 70K resistor for R2, what is the room temperature superdiode that any of you get? i.e. gnd to pin 7, pins 4 and 5 connected to 70K and other end of 70 K connected to 7 or 10 volts? that way we can get the scaling of the transistor and get a better handle on the vbe vs temp. dont connect up the zener or heater for this and you can be certain it is at room temp.
Please re-formulate a bit clearer. Do you mean the voltage over the diode at room temperature? It's current dependent. If you search my previous posts in this thread, you will find some plots. Anyway, i'ts around 6.6V for the zener only at typical 5mA.

I mean, just the vbe of the pin4 pin5 pin7 transistor at about 10 uA and at room temperarure. Pin 4 and pin 5 connevcted together and dont connect up the zener or heater, I thought that was quite clear.

http://www.ti.com/ww/en/bobpease/assets/www-national-com_rap.pdf (http://www.ti.com/ww/en/bobpease/assets/www-national-com_rap.pdf)         
go to page 115 and you will then understand why I am asking this.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 29, 2015, 04:48:23 pm
OK, get it! And when Bob Pease is involved, it always get interesting!

I have just gone by the datasheet "very predictable 2mV/K" and experimentally in the full circuit; put a trimmer on the temperature adjustment divider, turn down until the output voltage gets unstable, then turn it up again by suitable margin.

The datasheet states that the CE voltage is uncertain to within 10C.
But I will surely do the measurement, maybe later tonight.

Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on March 29, 2015, 05:28:08 pm
with that single measurement and Bob Pease's graph you can predict the temperature to about +-1 degree at a current of your choice. That will also help you fine tune the current through the zener with any particular R1 value and allowing for the temperature rise that imposes on you.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 29, 2015, 06:11:55 pm
Measurements attached. Pick your current. Note the slight temperature drift.

(MOD updated attached file)

Jan




Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 29, 2015, 06:27:32 pm
Looking at the data, the difference between the two measurement sets is in the order of 0.01 volt which would be equivalent of 5C  ???

Can't explain that other than "something" was moving, maybe meter, actual devise temp (handled and moved it before measuring...). With the very low current (mod): and 1mS measurement time (/mod), it could hardly be self heating? I also waited something like half a minute between each data point.
 
I can leave it for a while to stabilize and try again...
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 29, 2015, 06:41:24 pm
Hello Jan,

I think that the x-axis in the diagram (current) is scaled by a factor 10 too low.

And a big  :-+ for doing all the measurements.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 29, 2015, 07:08:59 pm
Hi, Just realized. The scale is right, the measurements wrong. Should be in the order of 0.1mA, not 0.01mA. New results coming....
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on March 29, 2015, 07:49:05 pm
Hi, Just realized. The scale is right, the measurements wrong. Should be in the order of 0.1mA, not 0.01mA. New results coming....

I believe that 6.8 Volts and 70K is approx 10uA, and that Bob Deakin has recommended running those transistors at less than 50uA. They are not designed to cope with the full zener current ever.

Also for 10uA I would have thought you might want a longer measurement to allow it to settle. 50 micro watts is not going to warm the device, to any degree that you could measure.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 29, 2015, 07:59:23 pm
Fooled me too but ; 7V/70K = 1/10000A = 0.1mA = 100uA

I'll upload a new file now. The measurements are now very much more consistent. Just remember that the datasheet specs are "within 10C" for this.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 29, 2015, 08:16:09 pm
Fooled me too but ; 7V/70K = 1/10000A = 0.1mA = 100uA

I'll upload a new file now. The measurements are now very much more consistent. Just remember that the datasheet specs are "within 10C" for this.

Jan, that's great!

Would you mind uploading the original xls file, instead of that crappy pdf assembly?

THX

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 29, 2015, 08:47:58 pm
Sorry Frank.

I uploaded the correct PDF now, the messy one should never be there  |O
I'm keeping the spreadsheet for now, it's too messy.
 
Sometime I'll summarize it all in a neat format, graphs and data.

 
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on March 29, 2015, 09:30:49 pm
Fooled me too but ; 7V/70K = 1/10000A = 0.1mA = 100uA

I'll upload a new file now. The measurements are now very much more consistent. Just remember that the datasheet specs are "within 10C" for this.

Ooops, should have looked closely at my spreadsheet, I had an extra 0 for the resistance....
Also cannot see the pdf now?
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 30, 2015, 08:47:09 am
Hi,

The data is attached to this post: https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg640218/#msg640218 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg640218/#msg640218)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 30, 2015, 05:32:10 pm
Hi all.

Sorry to interrupt, but can anyone highlight usual tempco of LTZ reference? I am testing my K2001 and comparing LTZ direct ref to EDC MV106 DC box, and getting little misleading data (http://xdevs.com/datalog/), to which it seem that LTZ have ~1ppm/°C sensetivity, which is kinda high. I suspect it's more of a drift of 2001 itself, rather than reference, but
will have time only next week to check with thermostat box. Resistors are VPG foils, which specced below 2ppm/C.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 30, 2015, 06:55:54 pm
Hi all.

Sorry to interrupt, but can anyone highlight usual tempco of LTZ reference? I am testing my K2001 and comparing LTZ direct ref to EDC MV106 DC box, and getting little misleading data (http://xdevs.com/datalog/), to which it seem that LTZ have ~1ppm/°C sensetivity, which is kinda high. I suspect it's more of a drift of 2001 itself, rather than reference, but
will have time only next week to check with thermostat box. Resistors are VPG foils, which specced below 2ppm/C.

Hello,

thats what I have on my 2 references:
With respect to 25 deg change in PCB temperature (or 33 deg C environment).

LTZ1000A #1 around 4.5uV (* 2) = -9uV change / 7V = 1.3 ppm / 25K = -0.05 ppm/K
LTZ1000A #2 around 5uV (* 2) = 10 uV change / 7V = 1.4 ppm / 25K = 0.06 ppm/K

all with UPW50 resistors specced with 3 ppm/K (not tested)


Edit:
Y-Axis Output voltage in mV (after 2:1 precision divider LTC1043 based)
X-Axis temperature in deg C

red: ltz output voltage
pink: averaged value (noise reduced)
blue: temperature sensor on PCB near LTZ1000
green: (right Y-axis) temperature sensor outside the aluminium box (environment).

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 30, 2015, 09:59:29 pm
Nice!

So both boards increased output with temperature? Can't quite interpret the scales of the plot.

Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 30, 2015, 10:11:47 pm
Today's measurement: Temperature versus power (dissipation) in the LTZ1000ACH.


RESULT: Surprisingly linear, around 0.36C/mW (360C/W) and quite near the 400C/W stated in the datasheet.
Note that the zener itself dissipates about 6.5V*5mA = 33mW, which could cause a temperature rise to around 35C without any heater. In reality, the self-heating would be lower, when soldered to a PCB.

In the attached doc there is one plot for a narrow range around 30-40C and another over a wider range.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 31, 2015, 05:05:39 am
Nice!

So both boards increased output with temperature? Can't quite interpret the scales of the plot.

Sorry
as common with my measurements:
Y-Axis Output voltage in mV (after 2:1 precision divider LTC1043 based)
X-Axis temperature in deg C

red: ltz output voltage
pink: averaged value (noise reduced)
blue: temperature sensor on PCB near LTZ1000
green: (right Y-axis) temperature sensor outside the aluminium box (environment).

so LTZ #1 has a negative T.C.
and LTZ #2 has a positive T.C.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: macfly on March 31, 2015, 07:15:27 am
....
RESULT: Surprisingly linear, around 0.36C/mW (360C/W) and quite near the 400C/W stated in the datasheet.
Note that the zener itself dissipates about 6.5V*5mA = 33mW, which could cause a temperature rise to around 35C without any heater. In reality, the self-heating would be lower, when soldered to a PCB.
...

Hi janaf,

35 degree's ? I can't retrace this:

dT = Pv x Rth = 0.033W * 400K/W = 13.2 K


Regards,

macfly
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on March 31, 2015, 10:19:18 am
macfly: 22.7C surrounding temp plus dT 13.2K temperature rise = 35C (approx) Slightly less with my 360C/W

EDIT: This is an indication on why temperature setting below R4/R5 of 1:12 (nominally near 40C) gets difficult.

Title: Re: Ultra Precision Reference LTZ1000
Post by: macfly on March 31, 2015, 04:27:33 pm
macfly: 22.7C surrounding temp plus dT 13.2K temperature rise = 35C (approx) Slightly less with my 360C/W

EDIT: This is an indication on why temperature setting below R4/R5 of 1:12 (nominally near 40C) gets difficult.

Sorry, I overlooked the '... to around'  ::)

Regards,

macfly

Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 02, 2015, 07:52:09 am
Edit: (SOLVED)
Does someone have a spare LTZ1000CH ie the "non-A" version to sell me? It can be used, if there are no new ones around, as long as it's fully OK. I'd like to do some measurements on it. Just buying a single one from LT will cost me around $100 incl shipping, a bit steep....
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 04, 2015, 08:09:43 pm
Hi janaf,

I might order some stuff from LT next month (may), including few LTZs, i could add one more for you to save shipping cost for you, if you are not in rush.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 04, 2015, 09:49:31 pm
Thanks TiN but I solved it.

Also, Digikey have a small stock of LZT1000 now, also in single quantities. I haven't seen them on Digikey for years.
I order other parts from them quite frequently.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 05, 2015, 09:25:46 pm
Hello,

Todays measurement: addition of a resistor in series with the zener cathode. I have called it "R60" to avoid confusion with the R6 used in the LTZ1000 datasheet.

The measurements show, as discussed earlier, that adding a resistor to the zener cathode, decreases temperature sensitivity ie also the sensitivity of the R4/R5 ratio. At the optimal point, "R60", somewhere near 20R, the sensitivity to R4/R5 (temperature) seems totally eliminated.

The bad news is that the sensitivity of the R60 (and R60/R1) will be almost identical to what it was for the original R4/R5 ratio was. So in all, maybe nothing is gained. I can not say if one is better than the other.

Also note that if no other component values are changed, then the output voltage of the circuit increases with "R60". At it's optimal value, 20 ohm, the output voltage from the circuit is up by (EDIT: wrong: one volt, up from 7.1V to around 8.1V) 0.1V from 7.1 to 7.2V (/EDIT)

This also means that all voltages & currents of the circuit will change somewhat, for example the temperature set-point will decrease.

Food for thoughts....
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 05, 2015, 10:27:29 pm
At it's optimal value, 20 ohm, the output voltage from the circuit is up by one volt, up from 7.1V to around 8.1V.

Hello Jan,

Did you really measure a 1V increase?
On the first view I would expect only 20 Ohms * 5mA = 100mV increase of the voltage.
What happens there?
Is the cirquit oscillating by adding the resistor?
Is the temperature control loop out of regulation?

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on April 06, 2015, 06:46:00 am
Looking at the pdf, I see an increase of79,000 microvolts, or about 80mV increase in output level, so that is about right.
It does mean the temperature sensitivity is reduced, but the R60 and R1 need to track, but R1 is needed to be very stble anyway, that does add up to one less ultra stable resistor I think, as anything between 16 and 25 ohms means r4/r5 is more than 5 times less critical, and at 20 ohms shows about 50 times less critical.
I see that as a slight gain in the overall behaviour.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 06, 2015, 09:57:41 am
Yes, MK you are right, it's around 0.1V increase (0.079V). I got that an order of magnitude wrong in my head.
You are also right about that it reduces the number of sensitive resistors from five to four. It could also mean further simplifying, omitting R4/R5, an op-amp, diode, feedback etc. But without further testing, I'd keep them. Or ovenize the whole board. The 20R value might need some trimming....
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 06, 2015, 10:07:17 am
At it's optimal value, 20 ohm, the output voltage from the circuit is up by one volt, up from 7.1V to around 8.1V.
Did you really measure a 1V increase?
On the first view I would expect only 20 Ohms * 5mA = 100mV increase of the voltage.
My misstake. You can see the right values in column C of the PDF, in uV.

The measurements where very stable until "R60" was somewhere above 25 ohm, then output started drifting. I did not investigate why, but it happened repeatedly.

Regards
Title: Re: Ultra Precision Reference LTZ1000
Post by: macfly on April 06, 2015, 12:20:04 pm
....
 At it's optimal value, 20 ohm, the output voltage from the circuit is up by one volt, up from 7.1V to around 8.1V. This also means that all voltages & currents of the circuit will change significantly, for example the temperature set-point will decrease. ....

Hi Jan,

I think, there is something wrong. Are you sure about the value of the resistor ?
Perhaps you noticed it before: I have made the same measurement with a 20 Ohms resistor and
as expected, the voltage raised only ~ 100mV.

Regards,

macfly
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 06, 2015, 03:03:09 pm
Yes, you are right, as mentioned a couple of posts up, it's around 0.1V increase (0.079V). I got that an order of magnitude wrong in my head.

The actual values are in column C of the pdf file (add the nominal 7.1xxx, in blue for absolute values).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on April 06, 2015, 04:19:50 pm
The measurements where very stable until "R60" was somewhere above 25 ohm, then output started drifting. I did not investigate why, but it happened repeatedly.
As a guess, raising the output voltage without changing the R4:R5 ratio lowers the temperature setpoint; perhaps you lowered it beyond stable regulation.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 06, 2015, 04:28:26 pm
Galaxyrise, I don't think so, I was looking at the current to and it was still pretty warm, total current was above 30mA and is usually stable at least down to 25mA in this setup. But I may have overlooked something. In any case, there should be no reason to go above 25R for this resistor (with R1 = 120R)

Any questions, I'd be glad to help.

For measurements and calculation questions, I think it's easiest done column-wise as in the pdf, with the column headers, ie A,B,C.....
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 07, 2015, 09:34:43 am
Attached is an update for the latest pdf. 

I have added sensitivity of R1 over varying values of "R60". It turns out, as expected, that R1 and R60 cancel each others changes to output, should track each other for best performance.

It also shows that the sensitivity of R1 increases with R60, from the nominal -0.0016 (dV/dR) to around -0.01 at R60=20R, ie the same sensitivity as for R60, as expected.

Sometimes it's good to get confirmations on things that you think you know.

So, bottom line, adding an R60 of 20R, more or less eliminates temperature sensitivity of the circuit and thereby also the demands on R4/R5. But instead you get the R1/R60 pair with high demands on stability and tracking of resistance ratio.
One note is that R4/R5 have one common node, pad 6 of the LTZ1000, while R1/R60 connect to two different adjoining pads, 3 and 4.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 07, 2015, 08:18:55 pm
Teaser 1 for my next post.  8)

You may remember from an earlier post that for R2, over a range around the nominal 70K, that the output voltage sensitivity to R4/R5 decreased somewhat with increasing R2. At the same time the sensitivity of output to R2 itself remained constant. I measured this for R2 of 40K to 130K.

I attach that plot again.

Now suppose we increase R2 more, what happens?

Teaser 2: It gets interesting! :-DMM
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on April 07, 2015, 08:38:38 pm
I think the curve continues it existing tragectory, and that r4/r5 ratio becomes a little less important, look at the temp dependance of VBE in Bob Pease's "what's all this VBE stuff", it goes from 2mv to 2.3 mV sensitivity as Ic reduces, eventually the noise becomes significant.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 07, 2015, 08:47:01 pm
Yes, it does get interesting!

I kept increasing R2 further and further, and at values in the order of 5.6Mohm, yes, the sensitivity of output to R4/R5 (temperature), passes zero!

At the same time the sensitivity of output to R2 remains constantly near 0.004 (attenuation 1:250)

So by increasing R2 to about 5M6, temperature sensitivity is essentially gone! (like with R60=20R) while the relative sensity of R2 remains the same, no penalty as for R60.

I measured this on 4 different LTZ1000ACH and they all landed in the same region. The spread is such that even if the R2 value is not "spot on", the sensitivity of R4/R5 can be very low without trimming the R2 value. The 5M6 specs do not need to be very high in terms of accuracy, only in stability.

So essentially: Increase R2 to 5M6, the stability / TCR specs remain unchanged, while the two most sensitive resistors, R4/R5 can be replaced with cheapo equivalents.

Then, the bad news: a 5M6 resistor with high stability is hard to get, expensive, whatever. I asked Edwin and yes, he can make them, but they will be big and several times more expensive than the 70K equivalent. The Caddoc USF may be an alternative. Available at 5M. Foils? Don't know if they are made at that high resistances.

Attached; Page 1-2 measured data, page 3 overview wide range plot, page 4 plot near zero crossing for four different LTZ1000ACH

Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 07, 2015, 09:12:04 pm
A PS to the previous post: Just checked the sensitivity to R1 and with high R2, R1 actually gets slightly less sensitive, going from 1:700 at R2=70K, goes down to 1:900 for R1 with R2 at 5M6. Not much but at least the right way, no degrading....
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 07, 2015, 09:20:00 pm
I think the curve continues it existing tragectory, and that r4/r5 ratio becomes a little less important, look at the temp dependance of VBE in Bob Pease's "what's all this VBE stuff", it goes from 2mv to 2.3 mV sensitivity as Ic reduces, eventually the noise becomes significant.
Noise does not seem to go up visibly, but I was only measuring with the DMM at 1s aperture. Could it be that while the collector current will go towards zero the base current remains unchanged? Suppose the collector resistor goes to infinity, shut off, what happens to noise then?
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 08, 2015, 12:06:15 am
Thanks for the input on noise!
 
The current over the resistor is around 1uA (6V/6M). If the transistor optimistically has 1nV/sqrtHz at 1mA, it would have 33nV/sqrtHz at 1uA, or about 100nV to 10Hz. I think the zener (or circuit) has a 1.2uV noise 0.1-10Hz. So even with 6Mohm, and even if the 1nV/sqrtHz was over-optimistic, transistor noise would seem acceptable. But the the 6M resistor noise should also be around 1uV at room temp. 

I think I need to get the noise amp and batteries connected.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on April 08, 2015, 12:49:25 am
According to the datasheet the zener has 50nV root Hz at 1Hz, so a 5.6 M resistor for r2 would about double the noise.

I cant see that being viable, but it does show a larger value may be helpful
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 08, 2015, 06:39:52 am
Thanks for the input on noise!
 
The current over the resistor is around 1uA (6V/6M). If the transistor optimistically has 1nV/sqrtHz at 1mA, it would have 33nV/sqrtHz at 1uA, or about 100nV to 10Hz. I think the zener (or circuit) has a 1.2uV noise 0.1-10Hz. So even with 6Mohm, and even if the 1nV/sqrtHz was over-optimistic, transistor noise would seem acceptable. But the the 6M resistor noise should also be around 1uV at room temp. 

I think I need to get the noise amp and batteries connected.

You are comparing apples with pears.
nV/sqrtHz is rms voltage (effective AC voltage)
0.1-10Hz is peak to peak voltage
there is at least a factor 6-7 between both.

at low frequencies the (rms) noise voltage of semiconductors
has a 1/f behaviour so you have to carefully look at the measurement frequency.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on April 08, 2015, 07:40:47 am
When I played around with lowering the collector current, I remember the difference being pretty obvious on an oscilloscope.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 08, 2015, 07:40:57 am
You are right, the datasheet 1.2uV 0.1-10Hz is ptp.

The 1/sqrthz was a crude guestimate, to get a ballpark value of where it may end. Without good measurements or a good spice or other model, noise is out in the unknown...
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 08, 2015, 09:27:42 am
I did a quick noise measurement 1s aperture on the DMM for 150 seconds. Results; pretty much that I can not measure noise in this setup, mains power, no shielding.
 
I measure near 0.6 uVrms noise with both 68K and 5M6 for R2, while the DMM measures near 0.28uVrms.

The 1.2uVptp 0.1-10Hz should be around 0.0625uVrms (1.2/6/3.2) -1Hz. Right? ie an order of magnitude lower. Hard to measure noise at this level....

Time allowing, I'll add an AC-coupled 0.1Hz-10Hz signal amp, shielding and battery box.

Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 09, 2015, 02:15:28 pm
There is a possibility that a combination of an R60 of a smaller value and an R2 of a higher value will get you there without adding a lot of noise [the transistor noise is inversely proportional to the square root of the collector current, and at some point becomes significant over the Zener noise].
Good idea. Just tested it. Using half R60 on a linear scale (10R) and half R2 on a log scale (around 600K) we also get a zero for temperature sensitivity. We also get half the sensitivity of R20 (0.005 instead of 0.01) and unchanged for R2 at 0.004. Maybe a usable compromise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on April 10, 2015, 03:21:53 pm
That leaves the 7V->10V boost circuit, which is a different topic, and considerably more difficult to get right.  I'm still working on a PWM based circuit, but am trying to work through the variation of Tr, Tf, Tpd, Rsw,
I have a LTC1043 approach that works pretty well in simulation for 7.2V; I'll have to check if there's a good ratio for 7.15.  I've also been considering using more LTC1043s to do the temperature compensation (adding 1/6 of Vbe.)  Time will tell if I can make it work in practice :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 10, 2015, 06:24:28 pm
I have a LTC1043 approach that works pretty well in simulation for 7.2V; I'll have to check if there's a good ratio for 7.15.

The perfect ratio would be adding 7.15 * 2 / 5 to the already existing 7.15 V giving 10.01V

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 10, 2015, 07:49:25 pm
Hello,

just a quick and dirty simulation of the proposal:

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 11, 2015, 02:42:13 pm
I attach a plot of measured output noise levels for the whole circuit. The circuit is a plain vanilla datasheet schematic but uses LTC2057 opamps.

I have varied R1 from 80R to 1000R, equivalent to between 7.4 mA and 0.6mA

The values are normalized to R1=120R as my absolute noise levels are a bit different from the LT datasheet, of a few reasons. I will get back with more when I have looked into the absolute values.

The measurements where done with a noise amp based on a LTC2057 with a gain of 1000, 1:st order HP at 0.1Hz and LP at 10Hz, followed by a 4th order LP at 10Hz, gain 1. This was enough to mains power 50Hz noise well below DUT noise.

Sampling was done in 20s blocks, 1kHz with a 24-bit ADC, data was numerically bandpass filtered at 0.1Hz and 10Hz.

Result: Noise varies linearly in a log-log plot, see attached pdf for values.

I will get back with more about the absolute noise level and noise for high R2 values later.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 11, 2015, 04:46:20 pm

The measurements where done with a noise amp based on a LTC2057 with a gain of 1000, 1:st order HP at 0.1Hz and LP at 10Hz, followed by a 4th order LP at 10Hz, gain 1. This was enough to mains power 50Hz noise well below DUT noise.

Sampling was done in 20s blocks, 1kHz with a 24-bit ADC, data was numerically bandpass filtered at 0.1Hz and 10Hz.


Hello,

Which ADC are you using for this?
When having the numerical filtering at 0.1 + 10 Hz and the external band pass at 0.1 + 10 Hz then you will have -6db amplification at the corner frequencies instead of -3 db. Right?
(This will play no role in comparative measurements but possibly when trying to get absolute values).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on April 11, 2015, 06:12:10 pm
The perfect ratio would be adding 7.15 * 2 / 5 to the already existing 7.15 V giving 10.01V

For 7.2, I was able to get the perfect 1.388 ratio (25/18) using 3 ICs.  For my LM399 rig (7.06879V) I came up with 1.4166 (17/12).  The best I can do with just 2's and 3's for 7.15 is 1.40625 (13/32), which is not as good as your proposal. But I worry about splitting a single division stage across two LTC1043 modules as I think differences in when they switch will show up on the output as more noise.  I was already planning to drive them with an external clock, at least.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 11, 2015, 06:18:52 pm
I'm using a PXI-4461 module. It has an adjustable pre-amp, I'm using the +/-0.3V range. Don't know the actual ADC inside. I could also use the DMM, think I can reach > 20Hz at 6.5 digits which is enough after the noise signal has been amplified.

Filter; I have to look into both analog and digital filtering more. That's why I'm not prepared to give absolute levels.

For example, the PXI-4461 has a built in DC-blocking which has a cut-off in the order of 1Hz, so it gives too low readings, by about 25%. When I disabled it I had problems with the grounding, the signal was drifting, giving a too high reading. The software filter; will have to dig into that too. It's very steep, brick-wall type.

Making measurements down to 0.1Hz and preferably an order of magnitude below, is very time consuming. Measurements in at 100nVrms level is challenging. So each step needs careful double-checking. I want to set up one or several signal generator that I can verify somehow, and test different ways, also at uV signal levels and something like 0.01Hz to 100Hz.

In the end, the actual noise number that comes out will be much influenced by what filtering is used. Any standards?

In any case, I can post a dump of an averaged amplitude FFT tomorrow night. Gives you an idea of the total filtering.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 11, 2015, 07:27:17 pm
  I was already planning to drive them with an external clock, at least.

Yes you are right:
my proposal will only work with synchronous clocks for the 3 LTC1043.


Making measurements down to 0.1Hz and preferably an order of magnitude below, is very time consuming. Measurements in at 100nVrms level is challenging.

In the end, the actual noise number that comes out will be much influenced by what filtering is used. Any standards?


True words.
Its not a easy task to amplify the 0.1 Hz to 10 Hz noise to a level where you can measure it.
You have either low noise amplifiers with large offset requiring several stages with cascaded high passes (higher order).
Or you have low offset amplifiers with high noise.
So the LTC2057 is a good compromise.

There are many different approaches for measurement so no real standard.
Some ideas might be in AN83/AN124 of Linear Technology.

I do not think that it makes sense to measure below 0.1 Hz. (10 seconds minimum measurement time).
At 0.01 Hz you will need a minimum measurement duration of 100 seconds.
If you do not have very stable environment conditions you will see temperature drifts within noise measurement.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 12, 2015, 06:57:16 pm
I have looked through the whole signal path, sorted out details and re-done measurements.

Now the absolute reading I get for R1=120R is 0.213uVrms which by rule of thumb, multiplied by a factor 6 is the ptp value, in this case 1.28uVptp for the plain vanilla LTZ1000ACH circuit.

I also checked a few other current settings, R1 values, and the ratios in the diagram I posted the other day are repeatable. For example, with 249R for R1, I get 0.28uVrms noise. With the ratio from the other day, 1.33 for 249 ohm, times today's 0.213uVrms = 0.283uVrms.

The most important change from the other day was to get rid of the AC coupling for the ADC, replacing the cap with an external 50x larger value (2.2uF instead of the internal 0.047uF) which with an input impedance of 1Mohm gives a -3dB HP at 0.07Hz.

The second thing was that I changed the sample rate down to 32Hz. The instrument manual said the minimum is 1000Hz (set by a DDS) but when I query the instrument, it replies that the valid sample rate range is down to 32Hz. As it's a delta-sigma converter, now that I sample at 32Hz, the mains frequency is gone, no need for analogue LP filtering. I sill added 0.1-10Hz brick-wall filtering. Without it, the noise was about 25% higher, as expected.

Now to the strange and hopefully very positive part. Setting R2 to 5.6Mohm, did NOT increase the noise! As far as I can see.

I have checked everything I can. The instrument noise is more than 2 orders of magnitude lower than the measured value. The OP noise should be a factor 6 lower than the measured value (0.2uVptp 0.1-10Hz). The signal "looks" OK, no clipping or abnormal offset. The voltage from the circuit is the same as the other day, 6.999xxx V with the 5.6M setting, currents look OK etc.

Can someone confirm this experimentally? Is there a theoretical explanation? Could the noise cancel? Or did I simply make some lousy mistake?

The best would be if someone could confirm / reject this experimentally. IE: throw in a 5.6M resistor for R2 instead of the nominal 68K. And measure noise for both R2 values.

Of course, the problem of getting ultra stable resistors at 5+ meg remains.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 12, 2015, 07:56:10 pm
Its not a easy task to amplify the 0.1 Hz to 10 Hz noise to a level where you can measure it.
You have either low noise amplifiers with large offset requiring several stages with cascaded high passes (higher order).
Or you have low offset amplifiers with high noise.
So the LTC2057 is a good compromise.

That's an amazingly nice hammer, I don't think there is a better all around hammer in the world right now.

AFAICS a simple low noise JFET common source amplifier even without chopping will outperform it in this case though.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 12, 2015, 09:43:11 pm

The second thing was that I changed the sample rate down to 32Hz.
As it's a delta-sigma converter, now that I sample at 32Hz, the mains frequency is gone, no need for analogue LP filtering. I sill added 0.1-10Hz brick-wall filtering. Without it, the noise was about 25% higher, as expected.

I have checked everything I can. The instrument noise is more than 2 orders of magnitude lower than the measured value. The OP noise should be a factor 6 lower than the measured value (0.2uVptp 0.1-10Hz). The signal "looks" OK, no clipping or abnormal offset. The voltage from the circuit is the same as the other day, 6.999xxx V with the 5.6M setting, currents look OK etc.

Is there a theoretical explanation? Could the noise cancel? Or did I simply make some lousy mistake?


Hello Jan,

I am not really shure if I understand what you are really doing. (a schematics of the setup/(filter) amplifier would be nice).
The first what I would do is measuring noise floor of the amplifier (with a 7.2 NiMh battery pack of AA cells or similar instead of the reference).
The 0.2uVpp is only the voltage noise of the LTC2057. Depending on your input cirquit/impedance there will add some current noise.

No filtering: I think you will need at least a high pass at the input of the amplifier.
I do not see how 32 Hz sample rate cancels out line frequencies (50 Hz?).
The sample rate has to be usually a exact multiple of 20 ms for this. (Might also be more dependant on the order of sigma delta modulator).

I guess in the .pdf the 22nV rms should read as 220nV rms (2*10e-7)
Are the rms values measured as true rms signal or calculated as RMS?
Is the raw signal a peak to peak (DC) measurement?

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 12, 2015, 10:20:45 pm
Hi,

OK, I'll make a "complete" walkthrough of hardware and software tomorrow. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 13, 2015, 07:31:52 pm
First step. Her's the pre-amp schematics (attached).

From input to output:
- DC blocking / 1st order HP at 0.07Hz
- Input amp with gain 1000 and first order LP at 10Hz
- Two stages with each, unity gain, 2:nd order LP at 10Hz
- Output AC coupling, again 0.07Hz first order HP

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 13, 2015, 09:52:50 pm
Hello,

Is R9 including the input impedance of your measurement system?
Or is there another pull down (limiting the lower band width).

The upper -3dB bandwith is most probably more on the 4 Hz than the 10 Hz.

And with 1Meg input impedance the LTC2057 alone (without the resistor noise)
has a factor 15 more current noise than voltage noise (at least at 1 kHz).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 13, 2015, 10:07:17 pm
Yes, R9 is the input of the instrument.
And yes, I can see on the measurements that it starts dropping off at 3-4Hz.

As-is, it looks like noise is approximately 50nVrms, input referred. Will be back with more about the measurements.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 13, 2015, 10:38:37 pm
-3dB; dumb of me to just add the sections, all with the same -3dB. Have to change some component values....

Current noise; how did you calculate that? Remedy?

Too tired now. Searching for hours for something causing glitches now and then. It turned out to be a BNC connector...

Hello,

Is R9 including the input impedance of your measurement system?
Or is there another pull down (limiting the lower band width).

The upper -3dB bandwith is most probably more on the 4 Hz than the 10 Hz.

And with 1Meg input impedance the LTC2057 alone (without the resistor noise)
has a factor 15 more current noise than voltage noise (at least at 1 kHz).

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 14, 2015, 04:19:35 am
Current noise; how did you calculate that? Remedy?

Hello,

the datasheet parameter is 170 fA / sqrt(Hz)
* 1 Meg = 170 nV / sqrt(Hz) (neglecting the 72 Ohms at the negative input).
this compares to the voltage noise with 11 nV / sqrt(Hz)

See also figure G18 / G19 in datasheet.

So the LTC2057 is only useful for input impedances (sum of + and - input) below around 50kOhm.

Noise measurements around 1uVpp are not so easy to get reliable.
It needed me 5 tries and several months with some help until I had a working cirquit.

Battery supply for the amplifier and the DUT together with a cookie box also helps a lot.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 14, 2015, 08:41:50 am
The current noise develops a voltage across the input impedance in parallel with the source impedance, so input impedance should be irrelevant here ... only source impedance is relevant (with 72 Ohms on the other input it won't generate much voltage there).
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 14, 2015, 10:13:36 am
Thanks Marco, that was how I saw it too. The input impedance is not the source impedance...
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on April 14, 2015, 04:02:59 pm
Thanks Marco, that was how I saw it too. The input impedance is not the source impedance...

No, but the source impedance is still significant in this cct:

Z = sqrt((Vref output resistance)^2 + (1/2/pi()/f/2.2uF)^2)) // 1M

Ignoring the Vref o/p resistance which should be negligible in this context, I calculate Zsource to be approx 72k at 1Hz and 586kHz at .1Hz

The LTC2057 datasheet shows the input current noise spectrum is flat down to .1Hz at 150fA/sqrt(Hz) with Vcc of +/-15V. So noise due to input noise current will be approx 11nV at 1Hz rising to 88nV at .1 Hz

Looking at page 528 of my copy of the 3rd ed. of the Art of Electronics which just arrived, the AD8628 might be a better choice with voltage and current noise densities of approx 21nV and 50fA respectively at .1Hz (with no 1/f noise).

But this is all academic since the circuit is already built and its own noise is easy to measure by shorting the input - perhaps I have missed the results of this test?

Splin
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 14, 2015, 05:43:33 pm
Ehh, okay you're right ... but it drops off pretty fast. The AD8628 starts off with 500 nVpp 0.1 to 10. AFAICS you won't get close that with the LTC2057 even with the current noise.

You could also use a larger input cap on the LTC2057 with a smaller amplification, the RC time gets large, but without too much amplification it will be below clipping pretty fast and the subsequent high pass filter can get rid of the rest.

PS. if you want really low noise you'll need to go discrete of course.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 14, 2015, 07:55:04 pm
Thanks all for the feedback and the interest! Lots of things to reply to.

First, the noise amp was for measuring the noise from the LTZ1000 circuit, which is expected to be in the order of 200nVrms 0.1-10Hz. (ie not measuring another LTC2057  8) ) I choose that amp because of the very low, low frequency noise, in the order of 33nVrms 0.1-10Hz. Honestly, did not give the current noise much thought because the ltz1000 circuit has a low impedance output. There are other chopper amps with lower input bias current but then of course with higher input noise. I can surely try lower input impedance as I have some big fat foil caps on the shelf. Have a 70uF polyprop, big as my fist. It's not a permanent setup anyway, was for comparing different parameters in the LTZ1000 circuit.

Even if it would be interesting, no need to go to discrete JFET input stage. I'm de-touring from the LTZ1000 all the time anyway. But in longer term I'm interested in looking at discrete JFET input stage. 

The LP filter stuff; I stared with this before realizing that the ADC I'm using can sample at rates well below the mains frequency. I'ts a Delta-Sigma so brick-wall LP anti-aliasing filtering comes in the box, I don't need to add a steep analogue LP, can chuck that out. (according to all docs, the ADC supports sample rates down to 1kHz but actually samples at rated down to 32Hz. Tested, works, attenuates mains frequency by at least 100dB :) . Someone lese may elaborate on how & why DS-ADCs effectively block higher frequencies without aliasing problems... I made a small paper on results only. Attached. Comments welcome.

So right now it looks ike: Larger input cap, lower input impedance, get rid of the 2nd order LP, sample at low frequency, make sure the ADC brick-walls mains, do some additional band pass filtering in software....

Yes, the most sensitive measurements are done with battery power, in the Universal Shielding Device, aka cookie box.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on April 14, 2015, 09:02:26 pm
try this link for a low noise amp...
users.cosylab.com/~msekoranja/tmp/04447683.pdf

also, on page 5:
www.janascard.cz/PDF/Design%20of%20ultra%20low%20noise%20amplifiers.pdf (http://www.janascard.cz/PDF/Design%20of%20ultra%20low%20noise%20amplifiers.pdf)
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on April 14, 2015, 11:17:05 pm
Ehh, okay you're right ... but it drops off pretty fast. The AD8628 starts off with 500 nVpp 0.1 to 10. AFAICS you won't get close that with the LTC2057 even with the current noise.

You could also use a larger input cap on the LTC2057 with a smaller amplification, the RC time gets large, but without too much amplification it will be below clipping pretty fast and the subsequent high pass filter can get rid of the rest.

PS. if you want really low noise you'll need to go discrete of course.

It drops off with frequency but not fast enough - I calculated the .1 to 10Hz RMS input referred noise with Rin = (2.2uF//1Mohm) to be:

LTC2057 Vn: 30nV, In x Rin: 339nV, Total: 340nV rms.
AD8628   Vn: 76nV, In x Rin: 113nV, Total: 136nV

So nearly 3x less noise. Except it turns out that the AD8628 datasheet spec for the input noise density is actually 5fA/root(Hz) not the 50fA shown in the AoE*, giving:

AD8628  Vn: 75nV, In x Rin: 11nV, Total: 76nV

So much better than the LTC2057.  The LTZ1000 noise spec is 1.2uV p-p or 181nV rms, so even 76 nV isn't brilliant, but probably good enough for this purpose. The LTC2057's 340nV is way too high but increasing the input capacitor to 11uF (5 x  2.2uF) and reducing the 1M to 200k ohms should reduce the LTC2057 input noise to approx 74nV rms.

Have a 70uF polyprop, big as my fist.

70uF/31k should reduce the total input noise further to aprox 32nV.

Splin

* Inexcusable - they've had 26 years to get it right (Ok, the AD8628 hasn't been round that long)!  >:D
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 15, 2015, 02:49:42 am
LTC2057 Vn: 30nV, In x Rin: 339nV, Total: 340nV rms.

Could you show me the integral? I know I shouldn't trust Spice if I can't do the math, but it still puts a doubt in my head ... with a 100 sec simulation with 100u max integration step and noise intervals I get nowhere near that (needed to do a bit of experimentation to get the noise spectrum for the current source right'ish). That's with resistor noise and significant noise energy below 100 mHz.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 15, 2015, 08:52:26 am
I found a opamp noise calculator that I like, it makes it easier to understand the basics and tinker with values.
http://www.dicks-website.eu/noisecalculator/index.html (http://www.dicks-website.eu/noisecalculator/index.html)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 15, 2015, 09:10:46 am
Doesn't specifically have a calculator for this case, I have seen it said that for first order filters you should take noise bandwidth as 1.57 the -3 dB point (in which case the calculator gives me ~45 nV RMS) ... but not being able to do the math any more, I'm not sure if it's valid here :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 15, 2015, 09:25:38 am
The attached, from that site, is the same, apart from no DC blocking and filtering?
Doesn't specifically have a calculator for this case,
How do you get images inline in the posts here?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 15, 2015, 09:34:02 am
I used the first one though, can't even set bandwidth or specify a coupling capacitor in any of the others.
Title: Re: Ultra Precision Reference LTZ1000
Post by: rf-design on April 15, 2015, 10:03:46 am
The LTC2057 is kind of strange due to it's input arrangement.  Usually for a "normal" op-amp, you want to keep the input resistance the same on both inputs to minimize drift.  Well, with the LTC2057, most of the input leakage is due to the switching action of the chopper disciplined amp, and so [up to about 70C] is doesn't help to balance the input resistances.

Could you explain why an impedance balance on the input of a chopper amplifier does not help!

I thought that the chopper switch arrangement internal to the OP is symmetric. So the switch charges should be balanced up to the internal mismatch and the effect on the external network impedance is minimized if for instance the capacitance is equal.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 15, 2015, 10:52:38 am
The calculator the way I used it:

1) Specify source signal characteristics. I set it as expected from the LTZ1000 circuit; 0.2uVrms, to 10Hz, pessimistically 1 ohm (it's actually much less).
2) Hit the "Calculate Signal Source Properties"
3) Enter the op-amp data, I used 11nV/sqrtHz and 0.17pA/sqrtHz for both inputs
4) Enter resistor values.
5) Hit the "Calculate..." button.

Result attached. Shows all noise contributions on the output and, among a lot of things, a 15dB SNR. As expected. (1.2uV/0.2uV=15.6dB)
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 15, 2015, 01:52:19 pm
I did measurements now on a new board:

- 2.2uF in
- 1.3M input impedance
- Ri/Rf 1ohm/100K
- Output 2.2uF to 1M in instruments
No other components except decoupling caps.
- Sample rate 49Hz / 24.5Hz bandwidth
- It runs on 2x9V batteries, all in a metal can.

The OP is rated 11nV/sqrtHz
11*srt(24.5) = 54nVrms
The GBW of the amp is 1.5MHz so with gain 100000 it should start dropping off at 15Hz.

I'm measuring around 70nVrms 0.1-24.5Hz, i.e. a bit high as the overhead noise from resisotrs etc should be quite small. With the noise calculation being a bit fuzzy to me.

However, noise is still less than 1/4 of the LTZ1000 circuit noise.

It looks to me like there may be a low frequency problem, air convection? I put the amp in a sock :o , helped a bit, it was worse before.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 15, 2015, 02:32:35 pm
Have you sanity checked yet? (ie. use a signal generator with a 1 Mega Ohm/1 Ohm divider to test the transfer function.)
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 15, 2015, 03:43:35 pm
No sanity check :scared: with this one. I did it with the previous one with 1000:1 gain. But I really should do it with this one too.

What I just did though; shorted the input on the OP side of the input cap. The measurements I posted an hour ago, the input was shorted on the "outside" of the input cap. Then, the results where a bit high and very sensitive to movements in the room etc.

Now, it's solid as a small rock, the signal LOOKS like white noise, the FFT is flat, the noise is stably at 55nVrms.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 15, 2015, 03:55:44 pm
What I just did though; shorted the input on the OP side of the input cap.

That's not really fair though, it's not equivalent to having a low impedance source attached.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 15, 2015, 04:20:53 pm
"Fair", no it's the baseline, for the OP-amp and measurements.

Now I'm measuring with 40K input impedance, not shorted. Then measuring around 68nVrms.

Next: with 40K and 70uF cap shorted. Back in a few minutes.

 
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on April 15, 2015, 04:51:15 pm
Mea culpa - my calculations were wrong - despite checking it multiple times, I still managed to miss out a sqrt(f) term  |O

I used the (corrected) attached spreadsheet to numerically integrate the noise. Note that the LTC2057 noise current is specced at 150fA/sqrt(Hz) at 5V Vcc - the 170fA figure is for Vcc = 2.7V.

The noise due to the noise current now works out to be 32nV rms to give a total of 44nV so Marco was right. With a 70uF capacitor the current noise becomes negligible at 1nV to give a total of 30nV rms.

If you want the exact integral I reckon it is:

Vn^2 = In^2 x R^2 x Integral[sqrt(f)/(1 + (2 x pi() x R x C x f)^2) df] over the interval .1 to 10 Hz

So the integral is of the form   f^(.5)/(1 + af^2) df which is beyond my maths. However an excellent site for this problem is:

http://www.integral-calculator.com/ (http://www.integral-calculator.com/)

I've attached a picture of most of its output. (Note that I adjusted the constant a to scale the graph appropriately).

Splin
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 15, 2015, 06:53:36 pm
For good performance one should not use so much amplification for the single OP amp stage - this will give extra noise, as the input is not close to zero at the chopper frequency or even at 50 Hz / 60 Hz. Even an amplification of something like 100 times should be OK to bring the signal to a level that is easy to handle.
Title: Re: Ultra Precision Reference LTZ1000
Post by: rf-design on April 16, 2015, 08:58:18 am
The LTC2057 is kind of strange due to it's input arrangement.  Usually for a "normal" op-amp, you want to keep the input resistance the same on both inputs to minimize drift.  Well, with the LTC2057, most of the input leakage is due to the switching action of the chopper disciplined amp, and so [up to about 70C] is doesn't help to balance the input resistances.

Could you explain why an impedance balance on the input of a chopper amplifier does not help!

I thought that the chopper switch arrangement internal to the OP is symmetric. So the switch charges should be balanced up to the internal mismatch and the effect on the external network impedance is minimized if for instance the capacitance is equal.

It's all in the data-sheet for this part.  The "normal" behavior that you would expect [where it helps to have balanced resistance on the inputs] doesn't begin until about 70C.  Before that temperature, the total input leakage is dominated by chopper switch action and not op-amp input leakage, and so the direction of the leakage currents is wrong to get cancellation with a balanced input resistance.  The Good News is that up to about 70C, the input leakage current remains relatively flat.  So, the bottom line is for this part, don't worry about balanced input resistances.

Also of note on this part, the input current noise appears to be linked with power supply voltage [charge injection from the switches?].  There is no chart for it, so we don't know if it's linear; and it is only specified at certain fixed rail voltages, but not for a total Vs of 15V [or 12V], which is what most people will use with the LTZ1000(A).

Thank you for the information. I am surprised that the switching-charge based input bias current of the inputs is nearly opposite in polarity. I expect that a textbook chopper switch arrangement generate some common mode bias current which could be common-mode voltage dependend and also have bias current offset which of lower magnitude because of matching.
In this sense the LTC2057 could not optimize the bias current contribution to offset error and noise by matching the impedance. LT possible prefer a different switch arrangement for possible better offset voltage or drift.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 16, 2015, 09:36:26 am
Not sure I follow you. You mean the ripple at mains frequency and switching frequency would fold down into the low frequency? It does not seem to be the case as the GBW and gain limit the bandwidth to 15Hz.

But sure I can decrease the gain, but LTspice tells me that there is a gain range approaching instability without capacitance over Rfb. I was considering that as a sanity check; just decrease gain ratio by increasing the Rin to 10K. That would also be a sanity check for input noise as Rin would give significant noise contribution, a raise by sqrt (10.000) = to the contribution by Rin.

For good performance one should not use so much amplification for the single OP amp stage - this will give extra noise, as the input is not close to zero at the chopper frequency or even at 50 Hz / 60 Hz. Even an amplification of something like 100 times should be OK to bring the signal to a level that is easy to handle.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 16, 2015, 09:38:49 am
Moderator: Are we steering off-topic? Start a new thread on LF noise and move some posts there?
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 16, 2015, 10:28:14 am
I got a PM on other stuff and a comment about the 7-digit realm this stuff is in.

No pun at all to the poster but for noise, I'd be happy if I can establish it accurately with two digits, maybe even one digit accuracy.

It's not important to me to establish if the 0.1-10Hz noise is 49.8 or 49.7nVrms. It be excellent to know with some certainty if it's 49 or 50nVrms, two digits, probably quite enough for me if I know with some certainty if its 40 or 50 or 60nVrms, ie one digit.

With the right amplifier and an 8-bit ADC one could do these measurements with enough accuracy. Amp gain accuracy of 1% is enough. 
 
I looked at the LT1028 and it seems (datasheet and LTSpice) it's noise can actually be lower than the LTC2057, all the way down to 0.1Hz. I'll give it a try as I still have problems with the LTC2057 below 1Hz, when increasing input impedance and adding DC blocking. Makes no reals sense.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on April 16, 2015, 12:12:55 pm
How do you get images inline in the posts here?

If you mean expanded image mixed in with the text here's one way:

1. Click on the thumbnail to expand it then right click and select image info.
2. Cut and paste the highlighted part (or an image URL elsewhere) into your post.
3. Add  [ img] and [ /img] tags to the HTML.

There's probably an easier way like some other sites have but this only takes a few seconds with practice and works on virtually all forums.

ps. What I would like to know is what do those yellow squares mean in everybodies avatar? They seem to increase and decrease  randomly.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on April 16, 2015, 12:51:54 pm
With the right amplifier and an 8-bit ADC one could do these measurements with enough accuracy. Amp gain accuracy of 1% is enough. 

Funny you mention that. My own voltage reference logger uses one of the low res AVR analog inputs fed from the peak detector fed from the noise amp fed from the 10x reference amp:

(https://www.eevblog.com/forum/projects/low-cost-voltage-reference-experiment/?action=dlattach;attach=143884;image)

No point wasting one of the 6 digit meter channels on noise because high precision not required and noise only once every 65536 voltage samples. I scaled the total gain so that full scale about 4x my worst voltage reference noise (one of the penny zeners) hoping no future devices would be much more than that. Surprisingly noise from bandgaps did not seem to be a lot higher than the zeners including my LM399 as previously suggested. But the amp noise was about 1/10th that of quietest reference and everything fits quite nicely into an 8 bit byte.

See? Inline image EASY!
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 17, 2015, 10:04:53 am
I'm stuck. Defeated by low frequency noise. |O

DC coupling, no problem. Nice and stable, easy to measure, measurement match spice and datasheet. High gains, not a problem either, within the usual stability limits & cures. Fore example the LT1028 is stable with 10nF over the Rfb, it has a phase margin of 60 deg.

But with A/C coupling it all goes sour, i.e. follows the theory. My bad, I did not quite have a grip, still don't entirely have one.
 
The bottom line; with A/C coupling, the input impedance noise source is equivalent to the Rin noise. I think.

To get the kind of noise levels I need to compare to LTZ1000 with some SNR, Rin should preferably be no more than 100ohm-ish. Matching input impedance, we end up with a ginormously humongous input cap. A 10.000uF cap + 150ohm would give a 0.10Hz cutoff but I suspect that cap leakage current would have the offset going all over the place.... Verifying things take an awful time. Maybe 1000uF +150ohm and just measure from 1Hz...

Actually, with the LTC2057, the zero correcting did work decently even with the wrong input impedance. I guess nulling took care of some.... but the output signal was weird, probably due to the zeroing going on. In all, I could produce some useful results, even if the noise was higher than expected, SNR was fairly poor.

I'm depressed. I need a new approach.  :-//

One good approach to problems is to ignore them, estimate noise, move on with the LTZ1000 ;D

The reason for the noise side-track was the R2, increasing it to 5.xMeg nulled the temperature sensitivity and my crude noise measurements could not detect any noise increase which caused some discussions....
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 17, 2015, 11:42:49 am
Not sure, if I agree with your diagnosis ... but if you want you can DC couple it. Just throw a big capacitor in series with Rg, and add a switch from the input to the capacitor with some resistance to quickly charge it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 17, 2015, 12:06:13 pm
Not sure if I agree either :-)

Problem 1) With DC coupling, I can have a gain of 1 or a little more.
Problem 2) With AC coupling, I get the noise down to uV level because of current noise. With JFET, current noise s low enough but voltage noise and 1/f noise is prohibitive? Modern choppers seem to be best compromise so far.

It also made me remember this AN by Jim Williams on the subject, in this case measurig noise of the 6655 reference, which is almost as low as the LTZ1000....

Title: 775 Nanovolt Noise Measurement for A Low Noise Voltage Reference
Subtitle: Quantifying Silence

http://cds.linear.com/docs/en/application-note/an124f.pdf (http://cds.linear.com/docs/en/application-note/an124f.pdf)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 17, 2015, 12:16:28 pm
The LT1028 is good for very low impedance sources (e.g. 50 Ohms), but just the wrong chip after an AC coupling capacitor. There are several options for lower noise at higher Impedance so that the AC coupling capacitor stays reasonable. Still you have to take care of things like thermal EMF and turbulances: so cover it.

A more conventional option would be a classical low noise OP like a OP27 or LT1037 possibly also LT1013 or OP177 if smaller caps are used. The noise specifications are better than the LTZ1000. They need a resonable size AC coupling cap (e.g. a few hundred µC). Not all electrolytic types will work and they may need some time (e.g. 12 h) of settling before leakage currents (and thus noise) come down. A simple short as a ref. may not work because of missing polarization - one may have to uses something like a 3 or 9 V battery as a low noise Ref.

An auto zero Amp like the LT2057 should work too - still the coupling capacitor should not be to small, as there is some bias and current noise. It also needs some care not to get to high current during power up or when connecting to a source. The Auto zero Amp may also be more sensitive to EMI - so good shielding is needed. A very high amplification and thus a low BW may also cause trouble.

Another option may be using some batteries in series to bing down the voltage from the ref., than have a DC coupled amplification (e.g. 10 fold with an OP27) and have AC Coupling only after this.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 17, 2015, 12:51:26 pm
Problem 1) With DC coupling, I can have a gain of 1 or a little more.

As I said, you can just put a big cap in series with Rg (resistor from negative input to ground). If you make Rg 1 kOhm (just 13 nV RMS to 10 Hz) then for a 0.1 Hz "-3 dB" (it's not really a first order filter, but close enough) point you need 1.66 mF ... that's not really a problem, 8 220 uF lytics in parallel for instance. The only problem is that it will take a huge time to stabilize after turn on, so you need to speed that up a bit.

PS. hmmm, leakage might be a bit of an issue with electrolytics I guess.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 17, 2015, 03:59:07 pm
Marco, you mean A/C couple the inverting side to ground and DC-couple the non-inverting? Interesting!
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 17, 2015, 04:01:29 pm
Another option may be using some batteries in series to bing down the voltage from the ref., than have a DC coupled amplification (e.g. 10 fold with an OP27) and have AC Coupling only after this.

I like the battery idea :-) But wouldn't batteries generate noise, even if current is virtually zero?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on April 17, 2015, 05:51:49 pm
Yes batteries produce noise by the chemical reaction, while they can be 'cleaner' than some power supply sources, they are as often not.  They are very good for isolation of course if that is needed.

That tantalum capacitor that Jim used in his ap note is still available for a rather large amount, the last time I priced it it was around $1.100,00 and a special order.  I have found large polypropylene capacitors on ebay, a 1400uF once for a very reasonable price, leakage is probably as good or better than the tantalum but you are still looking at least 24 hours settling time for a measurement.

By the way, an oscilloscope is the only accurate method to measure P-P noise in real time, this is how Linear Tech and everybody else does it.  Using an ADC integrates the noise which produces an inaccurate result as the integral of gaussian noise is constantly changing and does not repeat itself.  The data sheets for these devices all use scopes for the measurements.  It is very easy to verify this, call your LT rep and ask, he'll (or she'll) be happy to tell you all about it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 17, 2015, 06:09:05 pm
You can buffer the reference with a separate opamp and switch the output into the capacitor with a small resistance ... once it's charged, flip the switch again.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on April 17, 2015, 07:14:22 pm
I have a two of noise measurement setups now. The first device have a cheap russian 800 uF 50V wet slug tantalum capacitors battery (10$), two PWW resistors and EM Nanovoltmeter. The second scheme is an adaptation of AN124. Both devices gives a similar results on the all of my voltage references, but #1 have a <10 minutes settling time and 20 nV p-p input short noise, #2 only 20-30 minutes and 160 nV respectively.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 17, 2015, 07:53:26 pm
Mickle T  :-+ :-+ :-+

The $1.100,00 cap, OK, I'm interested to map the noise but not THAT interested. But reading the app note makes me feel a bit better. It's not supposed to be simple to measure noise at this level.

Once beyond the initial amp stage, a gain of 10 or 100, the rest should be relatively simple. As I wrote before, a 8-bit ADC should really be enough. I've mostly been measuring rms, estimating peak to peak. To me the rms value is more relevant anyway. Eventually, I want to see what tinkering with various options (like the huge R2) will do to noise. But even with an analog or digital scope, once the signal is low-pass filtered to below 10Hz, the difference should IMO be academically small.

I was also thinking of another solution; set up a second LTZ1000, trim it to have output level the same (within millivolts) as the DUT and measure the direct difference. The difference signal can then be amplified a lot, like 60dB, without A/C coupling involved. But frankly it sucks to have to build two setups......

I have now got a 18.000uF 80V E-cap charged to 80V. The first minute, the leakage was 1.5mA. After half an hour down to 0.1mA. I'll leave it for a day or two and see. When lowering to 7V it may be usable :-)

A related side track. TI have a new 32-bit D/S ADC as preview since February: ADS1262 / ADS1263. But very little data is available so far. One nice feature is that the sample rate is specified from 2.5Hz up to 38kHz. The accuracy will of course not be anywhere near 32 bit but resolution / noise may be useful....
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 17, 2015, 07:58:06 pm
Another thing you might do is take a look at the HP/Agilent/Keysight 34420A's input low-noise amp.
Will definitely take a look. I think Keithley had a really low noise amp too.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 17, 2015, 08:18:39 pm
The *reason* that Jim used the low-noise dual-JFETs in his design is that it is near impossible to get both low-noise and high input impedance at the same time in a tiny op-amp die.  This is a matter of physics-- for a JFET, you need a large die area to get the noise down, and this is not going to happen in an op-amp IC.
I'm beginning to see that. As you say, you can get the low noise or the impedance but not both in an op-amp.
It seems you can get pretty far though, maybe "good enough" to measure the 200nVrms 0.1-10Hz but margins are very small. As mentioned before, I might also be happy measuring something like 1-10Hz, as long as the measurements are comparable & stable.

I downloaded the 34420A manual from Keysight but the scanned schematics where of practically unreadable quality. Any other source?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 17, 2015, 09:48:44 pm
For the problem of building an amplifier to measure LF noise of the ref. there is a solution in a German language forum:
http://www.mikrocontroller.net/topic/207061#2060389 (http://www.mikrocontroller.net/topic/207061#2060389)

The Input stage is just a LT1037 OP-Amp with a selected low leakage 3000 µF Elko. Not even a special tantalum type, but likely good AL types. selected for low leakage. The drawback is that it takes something like overnight (possibly a few day for the caps - so keep them charged all the time) settling.

Preparing and selecting a few caps may be worth a test - no special gear needed, just a battery (e.g. 9V), a meter with nA resolution and a few days of time. Something like 2200 µF 63 V cap's are not that expensive and still useful if they don't turn out to be good enough.

One conclusion was that the rather complicated circuit from AN124, combining an OP amp with JFETs was not such a good idea. So there is no need to think so complicated.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 17, 2015, 10:18:28 pm
Thanks, i have some few e-caps on full voltage now, I will put them on 7V (or 9V) later.
Title: Re: Ultra Precision Reference LTZ1000
Post by: fmaimon on April 17, 2015, 10:57:27 pm
Preparing and selecting a few caps may be worth a test - no special gear needed, just a battery (e.g. 9V), a meter with nA resolution and a few days of time. Something like 2200 µF 63 V cap's are not that expensive and still useful if they don't turn out to be good enough.

No need for meters with nA resolution. Just do as Jim Williams did and put a 1k resistor in series and read it's voltage.
Title: Re: Ultra Precision Reference LTZ1000
Post by: paulie on April 18, 2015, 12:12:50 am
Thanks, i have some few e-caps on full voltage now, I will put them on 7V (or 9V) later.

The two chinese 1000uf caps seen in my photo used for the filter required 2 days to form and then about an hour to stabilize each time after that. If they go a month unused then must start over. Of course as mentioned previously my requirements were an order of magnitude less stringent.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on April 18, 2015, 12:39:08 am
@Klienstein,

Oh really, you think you know more about the subject than Jim Williams, perhaps you should get in touch with Linear Tech and let them know there is a replacement available for Jim.  I do not intend any insult here but it is obvious that some here do not grasp the underlying design principals involved  in trying to measure very low noise levels accurately.....note that word - accurately, not in the ball park measurements.

Seriously, Jim did it that way because that was the correct way to do it at the time, moving on a few years, yes, you might be able to sub a few of the components, such as a polypropylene capacitor for that tantalum and maybe some other minor changes but the circuit as done cannot be significantly improved on nor can you duplicate it with cheaper, lower quality parts.  This is not the jelly bean project some seem to think it is.

Again, you cannot measure a Gaussian noise source with an integrating or sampling ADC (that includes DVMs), it is not accurate, it does not repeat, it does not measure peak-to-peak nor RMS but will give you a sort of kind of average variable of the noise.  Unless you are using a very long period of measurement, tens of seconds at least, the average of a DC-10Hz noise band will not be accurate in any way, shape or form and in the case of a voltage reference, you need to know the noise characteristics accurately and that includes peak to peak as well as RMS, average is of little use.  Noise is the limiting factor in a reference, not just drift.

Pardon me if I sound a bit terse.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 18, 2015, 05:17:59 am
The long settling time is not so the capacitor can charge up to voltage [although that's part of it], but rather so that the dielectric absorption [DA] can dwindle down to zero.  DA, even on a huge high-voltage capacitor will look like a large leakage current until the process is complete.

That doesn't really matter if it has no significant component above 0.1 Hz ... a subsequent high pass filter gets rid of it.

Same as with the leakage current (as long as the output doesn't hit the rails).

PS. simply putting a zener across Rf would be the easiest way to quickly charge it.

PPS. flicker noise is surprisingly high for metal film resistors, but at ~0V across it it's unlikely to be an issue here.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 18, 2015, 07:56:29 am
Hello,

rant: the tread is going more and more off topic.
The construction of a low noise amplifier would be worth a own thread.
(as can be seen on the length of the german thread).

Ontopic:
You never should draw a current more than about 1-2 mA from a unbuffered LTZ1000(A).
Otherwise the temperature setpoint will go to infinity introducing at least a hysteresis to the LTZ1000 output.
So your calibration will get lost and perhaps the LTZ is quickly aged.
Usually you can see the influence of such a "event" as drift up to a half year.
So charging a large capacitor from a unbuffered LTZ is a strong NO NO.

Even charging a 1uF capacitor from unbuffered LTZ will introduce a visible shift of the output voltage.
So I would not use a zener to clamp the 1k resistor further.
Instead I would introduce a further resistor during charging of the input capacitor to avoid the LTZ being toasted.
(And I do not complain about the additional time when measuring noise).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 18, 2015, 09:55:29 am
I said a zener across Rf , I was assuming the capacitor being in the feedback loop. When the capacitor isn't charged the opamp will go to the positive rail, with a (low leakage) zener diode across the feedback resistor it can charge the capacitor until it hits 7V.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on April 18, 2015, 11:04:39 am
rant: the tread is going more and more off topic.
Yes. New thread started: https://www.eevblog.com/forum/projects/low-frequency-very-low-level-dc-biased-noise-measurements/msg654777/#msg654777 (https://www.eevblog.com/forum/projects/low-frequency-very-low-level-dc-biased-noise-measurements/msg654777/#msg654777)

Mod /Dave: imo, move basically all posts in this thread from #1174 and forward.
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on April 20, 2015, 07:51:59 pm
For the first time I have built a reference with an LTZ1000. Got two unused LTZ1000ACH-PBF with date code 0733 from a friend. I followed the LT datasheet for the design except added a 22ohm cathode resistor ("R60) and R1 was 13kohm. I built the circuit on a prototype board (RE201EP from Reichelt). For R1-R4+R60 I had a parallell resistor with 100 times higher resistance that I could select with a jumper. For R60 I also could short the resistor. I even used a socket for the LTZ so I could switch between the two LTZ's. As I only have a 6-digit DMM (Keithley 2000) I got a resolution of about 1.5ppm. I was glad to see  that even if I switched jumpers, LTZ's or was blowing on the LTZ I could only see a shift of one digit (1.5ppm) going back to the same configuration.

I did the test with a switching lab supply (Korad KA3005D). As the circuit worked fine down to 9.2V I choose 12V. Current draw was about 20mA. From 10 to 15v I could see no change (less than 1.5ppm change).

This is my result of the sensitivity test (ppm voltage for 100ppm resistance change as in datasheet):

With R60 shorted (original circuit with R1=13k)
LTZ#1   
7.16822V
R1 -0.17ppm
R2 -0.42ppm
R3 -0.10ppm
R4  1.14ppm

LTZ#2
7.13327V
R1 -0.18ppm
R2 -0.42ppm
R3 -0.08ppm
R4  1.00ppm

With R60=22ohm
LTZ#1
7.24931V
R1 -1.08ppm
R2 -0.47ppm
R3 -0.01ppm
R4  0.00ppm
R60 1.12ppm

LTZ#2
7.21639V
R1 -1.15ppm
R2 -0.47ppm
R3 -0.00ppm
R4  -0.14ppm
R60 1.15

/Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 20, 2015, 08:19:13 pm
. As I only have a 6-digit DMM (Keithley 2000) I got a resolution of about 1.5ppm.

I did the test with a switching lab supply (Korad KA3005D).

Hello Lars,

Thanks for the results.

Have I understood it right: you are making a 1% resistor change
and calculate the result linearly down to 100ppm change?

If you had 2 sockets you could measure the difference of the 2 LTZs having a resolution of 0.015 ppm in the 200mV range.

Mhm: my Korad KA3005D has a linear transformer + power stage
(only a digital display and keys to set the voltage setpoint by a D/A converter).

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on April 20, 2015, 09:30:41 pm

Have I understood it right: you are making a 1% resistor change
and calculate the result linearly down to 100ppm change?



Yes, I have used Excel with the resistor values I have used and scaled it to 100ppm resistor change.

If you had 2 sockets you could measure the difference of the 2 LTZs having a resolution of 0.015 ppm in the 200mV range.


I will make another board later but want better resistors before I do that.

Mhm: my Korad KA3005D has a linear transformer + power stage
(only a digital display and keys to set the voltage setpoint by a D/A converter).


So I guess my also is linear (got it from Reichelt last week).

/Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 26, 2015, 03:40:15 pm
Question about all the talk about dual PWM DACs a few dozen pages back ... basically there is no known monotonic by design way to combine two PWMs for higher resolutions? (Datron/Fluke calibrators seem to rely on calibration to correct for gain/offset errors in the resistor combiners of the MSB/LSB PWMs.)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 26, 2015, 04:24:44 pm
Question about all the talk about dual PWM DACs a few dozen pages back ... basically there is no known monotonic by design way to combine two PWMs for higher resolutions? (Datron/Fluke calibrators seem to rely on calibration to correct for gain/offset errors in the resistor combiners of the MSB/LSB PWMs.)

Hello,

you will also have to calibrate out the INL of the MSB PWM (at least).

On PWM INL results from different resistances in HIGH/LOW state (temperature dependant).
Further you may have different (HIGH/LOW) switching times (also temperature dependant).
Further charge injection errors.

So the adding of the 2 resistors may be your least problem.

If you didn't already see this article, you can find some valuable informations in there :

http://www.edn.com/design/other/4326640/DC-accurate-32-bit-DAC-achieves-32-bit-resolution (http://www.edn.com/design/other/4326640/DC-accurate-32-bit-DAC-achieves-32-bit-resolution)

But be carefully: the values given are very optimistic.

And: the formula for adding the 2 PWMs to the output signal is simply wrong.
You will never get a output voltage larger than VREF * 65535/65536 by
combining 2 PWMs with a resistor divider instead of a summing amplifier.
So the half reference voltage will be reached at 0x80008000 instead of 0x80000000

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 26, 2015, 05:13:58 pm
you will also have to calibrate out the INL of the MSB PWM (at least).

You could low pass and buffer the MSB/LSB parts separately, then the switch resistance at least becomes irrelevant (offset voltage differences become relevant instead).

Any way, so no monotonic by design implementations? (ie. not like plain PWM, thermometer DACs and buffered Kelvin Varley with "small enough" offset voltage errors.)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on April 26, 2015, 05:18:52 pm
Regarding the 32-bit DAC story: http://www.edn.com/design/other/4326640/DC-accurate-32-bit-DAC-achieves-32-bit-resolution (http://www.edn.com/design/other/4326640/DC-accurate-32-bit-DAC-achieves-32-bit-resolution)

This was later discredited as not working and not providing anything better than the current 24-bit DACs on the market so don't waste your time with this, it does not work, not even theoretically.  The noise floor is much too high in the first place to get beyond maybe 24 bits at best just for resolution, forget accuracy, with good luck it might just do 1 PPM accuracy with a lot of tweaking.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 26, 2015, 05:23:08 pm
Combining 2 PWM Signals is difficult. With some modern µCs very high timing resolution (e.g less than ns) is possible, and thus very high resolution PWM, like 24 Bit. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 26, 2015, 06:52:55 pm
With some modern µCs very high timing resolution (e.g less than ns) is possible, and thus very high resolution PWM, like 24 Bit.

And how do you switch your precision analog voltage reference (e.g. 7V) with this PWM.
Usual analog switches have about 100 ns switching time and a part of this as break before make time.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on April 26, 2015, 07:47:02 pm
It would probably be better to have two SPST switches and do your own break before make timing.
Title: Re: Ultra Precision Reference LTZ1000
Post by: acbern on April 26, 2015, 10:21:53 pm
A PWM DAC (e.g. two stage), for use as a precision reference divider, working from 2 LZTs in series to be able to generate a voltage close to 10V without an amplifier (which you want to avoid) does not have to have good DNL/INL. All you need to be able is to set the voltage close enough to the 10V and keep that stable, i.e., the switching period... must be stable as well as the analog summing amp (it can be calculated that the summing amp drift is not the problem in a normal environment). The Datron 4910 solved this long ago, the schematics are available on the net. It is not a simple design though, and switching noise, filtering are just a few of the challanges.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on April 26, 2015, 10:27:23 pm
Hello Emmanuel,

While there are some 24-bit DACs on the market, most of them do not perform anywhere near 24-bits in reality, resolution is just that, nothing more, beyond 20-bits it is just noise.  The closest DAC I know that exceeded 20-bits was built by Jim Williams in Linear's AN86.  This accurately measured 1 PPM with linearity to 0.1PPM, while it is not overly complicated, it required more than just one chip but it worked quite well.    http://cds.linear.com/docs/en/application-note/an86f.pdf (http://cds.linear.com/docs/en/application-note/an86f.pdf)

I am not entirely familiar with the AD5491 but any ADC/DAC over 16-bits in real accuracy is no easy matter to make and at 20-bits, it really is pushing state of the art for accuracy.  Most anyone can achieve resolutions of high numbers, but resolution has very little to do with accuracy or repeatability and math cannot improve what is not accurate to begin with, as we say in computers - garbage in garbage out.

With my 242D resistance bridge, I can achieve up to 11 digits of resolution and to some extent I can repeat to 10 digits at least, however at best, in absolute accuracy I can 'only' achieve ~1PPM accuracy with an uncertainty of ~0.2PPM at best, therefore I usually will not give a calibration reading that exceeds the 7th decimal place at best because the rest of it is only resolution and it is known to not be accurate.  It is nearly impossible to match this accuracy with any other method of measurement, there are too many variables involved and uncertainties to even approach 1 PPM accuracy otherwise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on April 30, 2015, 08:17:03 pm
Hi Emmanuel,

The only 24-bit DACs I can find are all audio types, not really any good for DC, there are a few current units, the AD1852, CS4398 and PCM1789 to name a few of them.  I could not find an AD5491 but I did find a AD5791 which is a 20-bit accurate DAC from Analog Devices, kind of expensive as expected and is rated for DC operation.  Its specifications are very close to the multi-chip DAC that Jim Williams designed.

Getting back to the Vref subject, I found some rather interesting information from the NIST about the ohm, concerning the quantum ohm standard, it can only be read with an uncertainty of 0.2PPM at best, no matter what national lab in the world it is, all agree on this uncertainty.  Furthermore, this uncertainty is not included in calibration certificates as it is understood by all labs that it is there, all uncertainties provided on the certificate of calibration are in addition to this 0.2PPM.  The document is here: 

http://www.nist.gov/customcf/get_pdf.cfm?pub_id=31431 (http://www.nist.gov/customcf/get_pdf.cfm?pub_id=31431)

It also provides other information about the process of calibrating primary standards, uncertainties and the bridges/methods used.

Another interesting document is the calibration pricing sheet here:  http://www.nist.gov/calibrations/resistance.cfm (http://www.nist.gov/calibrations/resistance.cfm)

You can get your SR-104 certified to the best accuracy in the world for only $3.385,00 plus shipping.

Another very interesting tidbit of information from the NIST about solid-state Vrefs:  if it is an LTZ1000/A or LM399, the design should be using PWW resistors if you want the results to mean anything when you get the device back.  They will tell you that right up front and to get that Vref certified, $2206 covers a couple measurements per day over 12 to 15 days, then they send you the average result.  Cost to ship it back is $519 to you and they would prefer that the device is battery powered for a minimum of 30 days but they will provide up to 50 watts of mains power if it has to be plugged in.

The calibration pricing for Vrefs of various types can be found here:  http://www.nist.gov/calibrations/voltage.cfm (http://www.nist.gov/calibrations/voltage.cfm)

As usual there is more information on voltage standards and particularly the solid-state references.

And that gentlemen, is why I do not send my standards to the NIST, I use a primary certified lab who paid the big bucks up front to the NIST and can provide almost identical uncertainties in their readings at a much lower cost, not that it doesn't cost a lot, it just isn't in the thousands of dollars.

Note the comment on DVMs and other similar instruments on this page.

Regards,

Edwin
Title: Re: Ultra Precision Reference LTZ1000
Post by: acbern on May 02, 2015, 12:58:31 am
Re. linearity of PWM and other DACs, I think you are misising the point. 20 bit e.g., which is available, equates about 1ppm resolution. That is good enough to adjust a voltage reference (even with bad DNL/INL).
The real issue is, what is the stability over time. If it is good (Including all its resistor and  opamp drifts), then a 20bit DAC is a good solution.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ltz2000 on May 02, 2015, 09:17:53 am
You can get your SR-104 certified to the best accuracy in the world for only $3.385,00 plus shipping.


Calibration Uncertainties for Low-power DC Resistance Standards

Nominal   Uncertainty ( 95 % confidence level )

          NPL (UK)  NIST (USA)

100 uohm   2.5 ppm    4 ppm
1 mohm    0.85 ppm  1.2 ppm
10 mohm    0.8 ppm  0.8 ppm
100 mohm  0.18 ppm  0.5 ppm
1 ohm     0.06 ppm  0.3 ppm
10 ohm    0.05 ppm  0.3 ppm
100 ohm   0.05 ppm  0.2 ppm
1 kohm    0.05 ppm  0.2 ppm
10 kohm   0.06 ppm  0.2 ppm
100 kohm  0.08 ppm  0.8 ppm
1 Mohm    0.12 ppm  0.8 ppm   
10 Mohm    0.2 ppm  3 to 8 ppm
100 Mohm   0.4 ppm  5 to 12 ppm
1 Gohm     1.6 ppm  10 to 25 ppm


Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 02, 2015, 05:13:56 pm
Hi folks,

Sorry for double post, but since DAC topic was discussed in this derailed thread, I'd like to get some comments on AN86-based voltage generator I'm trying to make.
Thread with schematics for discussion (https://www.eevblog.com/forum/projects/project-kx-diy-calibrator-reference-sourcemeter/msg665044/#msg665044).

Thanks!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on May 02, 2015, 05:53:32 pm
@ Itz2000,

First, the documents linked to were dated 2003 and 2004, so they are a little out of date, should be newer documents on the NIST website.

Secondly, the uncertainties/accuracies quoted in the document ares what the regular, run of the mill calibrations are done to, it is not the actual capabilities of NIST.  By appointment only, NIST will certify a standard to a higher accuracy than the standard rates quoted in the document and that was noted in the documents.  I know for a fact that NIST can read the national 1 ohm standards to PPB, in fact they state that the average drift of their primary group of 1 ohm standards are drifting by .0046PPM/year compared to the international legal ohm standard (SI).  They use the same DCC bridge techniques as other national labs do, in short, the NIST absolute accuracy to the SI ohm is as precise as any other national laboratory, including the British, of which you so kindly listed their current uncertainties.  This said, the SI ohm standard is still no better than the 0.2PPM uncertainty to the quantum ohm which is known to all national labs and is the current legally defined absolute 'ohm' standard.

The secondary calibration labs, the ones who service most of industry, including my standards, all quote similar accuracies and uncertanties given in the NIST documents for regular level of certification, anything better than that is considered special as noted in the documents.  The British and likely all other national labs will have the same tier of certifications as NIST.  Calibration to these levels of accuracy and uncertainty is no trivial matter and a national lab will not do special certifications for just anybody.

So I still stand by my statement that the NIST is as good as it gets.

As far as I know, the absolute accuracy and uncertainty of resistance standards are of no consequence to anyone on this blog except possibly me since I must adhere to resistance certifications in order to build accurate resistors, I know precisely how accurate my SR-104 is and my 242D bridge.  The fact that someone may own an SR-104 does not mean they are also as accurate without the proper bridge equipment, DVMs are not standards.  Vishay must also adhere to the same requirements, except that they have a habit of buttering their specifications, which has nothing to do with their calibration lab.  I have not seen or read any comments directly from another resistor house here.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 02, 2015, 06:51:27 pm
Sorry folks, to interrupt:

you're wondering about the 0.2ppm SI / absolute / Klitzing Ohm...

It's quite easy, and still actual, as somebody else already mentioned:

Currently, the SI Ohm is uncertain to about 0.2ppm only!
Same goes for the SI Volt!

That's due to the current definitions (from 1990) and/or mise en pratique, derived from other SI base units, like the kg, frequency, length, and several "unprecise" constants of nature.
Best mise en pratique of the Ohm (in terms of SI units) is the Thompson-Lampard capacitor ( calculable capacitor).

The Ohm is NOT defined or derived from the Hall / von Klitzing standard; at the moment latter one is ONLY the best way to have a repeatable, site independent standard. 
The von Klitzing constant for the Hall effect resistance (combination of e and h) currently is an approximation only, also 0.2ppm uncertain relative to the SI.

Therefore,the absolute uncertainty as per today can not be any better than these 0.2ppm, nowhere!
Therefore, the NIST declaration is very reputable..

In 2018, probably a new SI will be adopted:

The kg will be defined by the silicon sphere and/or by the Watt balance.
Several constants of nature will be defined with zero uncertainty, especially h and e.

As a consequence, the Ohm and the Volt, defined AND mise en pratique by the Klitzing and the Josephson quantum effects/standards, will also have zero uncertainty!
That means, that both effects are already proven to be 1e-17.. 1e-19 stable or reproducible on cryogenic level. (That is: SQUIDs for null detection, superconductivity, no thermal voltages)
That will be as stable as the second / frequency quantum standards (Hg or Al optical clocks).

The problem to connect these cryogenic standards to the real world, will still be persistent.

The difference between both worlds are thermal voltages of the order of several nV, which limit the achievable real world uncertainty to about 1e-8.. 1e-9, but that will be 1 or 2 orders of magnitude better than before.

What's lacking also, are working / secondary standards for Ohm and Volt, being as stable as << 1e-7.

Therefore, even when the new SI 2018 will be gone into effect, there will be no big improvement in practice, as we will certainly still discuss the stability / T.C., etc. of PWW and BMF resistors...

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on May 21, 2015, 06:01:04 pm
Below is die picture of LTZ1000. I did noticed that 4 inner heating elements are not used and only the two outermost are used.
Do you have any idea why?
One bond wire ( pin 6) torn.
I will follow up with more voltage references die images ( on my desk are prepared VRE3050,VRE310, LT1027) but it will be more difficult digging than die of LTZ1000.
Teardown of LTFLU can be also interesting, but I did not find any cheap or not working on ebay yet ;-)

Thanks TiN for providing sample.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 21, 2015, 07:07:34 pm
Cool! Can you drop a high resolution version as well?

I think using further heater coils help with less gradient across active components. You dont want creating hotspot around zener parts.
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on May 21, 2015, 08:24:33 pm
I will try to make better image without charging artifacts later.
If you do not mind I can make cross section. It looks like that reference is OK except pin 6.
Here is limit for upload 1MB :-( Full image is about 1GB.
To reduce gradient there is symetric design, I was really surprised how symetric layout is.
Additioal heating elements can be also for higher temperature or who knows different elements are used on LTZ1000A vs LTZ1000.
Do you remeber if it was A version or non A?
Also I have no idea why pin 7 is connected above burried zener in centre...
Title: Re: Ultra Precision Reference LTZ1000
Post by: SArepairman on May 21, 2015, 08:35:17 pm
thermal dummies, you want heat to radiate out isotropically, are you sure all the heaters are not used, i.e. multiple layer connections  for whatever reason? also, thermal conductors/heatsinks to increase thermal capacitance at that area maybe, so heating is more stable (thermal filter).
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on May 21, 2015, 08:44:10 pm
thermal dummies, you want heat to radiate out isotropically, are you sure all the heaters are not used, i.e. multiple layer connections  for whatever reason? also, thermal conductors/heatsinks to increase thermal capacitance at that area maybe, so heating is more stable (thermal filter).

There is no via visible, two wires from pin 1 are connected to two from six outermost heating elements and third pin 1 bonding wire is connected to layer below two outermost elements.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on May 21, 2015, 10:43:06 pm
Notice that this die is a 1988 version, so it is one of the earlier dies and Linear may well have 'tweaked' it further since then.  The date is right next to pad 2 in the photo.  It is also not unusual for a die to have additional 'components' which are or are not used depending on the version being manufactured.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 22, 2015, 01:05:59 am
You can upload here any size you want (http://doc.xdevs.com/contact/) at my host. I will do size processing and rehost as bunch of smaller pics.

It was LTZ1000A from 2013, bought from LT direct shop. 

I posted photo of it in my KX thread before:
(http://fotkidepo.ru/photo/115530/9515ZdJQKBoMHD/964275w.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on May 22, 2015, 03:43:15 am
To Ken: Thanks for info! So I do not understand why there is visible probing on unused heater pins. It looks like thay are at least measuring them prior contacting the die in package.
To Edwin: Date on die is 1983, due to bad stitching setting it looks like 1988 :-) Sorry
To TiN: So it is prety recent unit. Do you remember whats went wrong with unit? Or it is only pin 6 issue?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 22, 2015, 04:41:40 am
I'm pretty sure wirebond 6 was damaged due mechanical when sawing a can.
Issue was that after some countless experimentation with resistor and opamps it refused to give correct output zener voltage, and provided almost 13V output, and
was taking must more current than normally should do (>50mA). I suspect it was due incorrect heater setpoint, which caused die to overheat way over 100°C.
This was very first LTZ I got, so it was a sacrifice for learning curve. 5 units after it still working like a charm :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on May 28, 2015, 02:11:38 pm
Mmmm... looks like I came to the right place for information on this.

0.0005%/C is way more than needed for my purpose and  temperature range -55deg to 100deg means the "S curve" is nowhere near as short as hinted earlier. At least in the ball park with initial tests (0.1mv) on some homegrown zener parts I've been tracking for last couple weeks.

Prices for USR, 1n829, and 1n939 are more than an LM399 so just as out of reach as the LTX1000 for my budget so it looks like the DIY parts at 2 cents each are for me. I hope performance of cheapies is close enough. The circuit looks a lot more manageable to compared to LTZ too which is another plus. Even simpler because I don't need negative ref. I got OP07s but maybe not even any op amp will be needed if ADC ref input impedance is high and I use software calibration constants.

If you *REALLY* want to go down this road, take a look at the LT1034:

http://www.linear.com/product/LT1034 (http://www.linear.com/product/LT1034)

Bit late to this party, but the LT1021-7 is cheaper and comes with a built in regulation circuit very similar to the unheated LTZ1000 reference design.

BTW, aren't most discrete zener diodes subsurface? The Motorola/OnSemi manual for discrete zener diodes mentions a "drive in cycle" which puts a passivation layer on top of the junction.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 28, 2015, 04:17:22 pm
Definitively no:

A glass passivation of a surface zener is not the same as a ion implant subsurface zener.

And also you cannot compare the (long term) stability of the LTZ1000 with that of a LT1021

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on May 28, 2015, 05:18:07 pm
A glass passivation of a surface zener is not the same as a ion implant subsurface zener.

I only asked if the zeners weren't all subsurface.

"The resultant junction profile is determined by the background
concentration of the starting substrate, the amount of dopant
placed at the surface, and amount of time and temperature
used during the dopant drive-in. This junction profile
determines the electrical characteristics of the device.
During the drive-in cycle, additional passivation oxide is
grown providing additional protection for the devices
.
After junction formation, the wafers are then processed
through what is called a getter process. The getter step
utilizes high temperature and slight stress provided by a
highly doped phosphosilicate glass layer introduced into the
backside of the wafers. This causes any contaminants in the
area of the junction to diffuse away from the region. This
serves to improve the reverse leakage characteristic and the
stability of the device. Following the getter process, a second
photo resist step opens the contact area in which the anode
metallization is deposited."

The glass passivation is a different step.

Quote
And also you cannot compare the (long term) stability of the LTZ1000 with that of a LT1021

No, but you can compare it to the LT1034 which was being suggested as a low cost source of a buried zener diode ... if you just want a cheap'ish buried zener reference without resistor divider the LT1021-7 provides that.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on May 31, 2015, 05:01:18 pm
Hi, Been away a few weeks. Got to make a living  :-//

Latest measurements: Temperautre sensing transistor of the LTZ1000.
- Had 0.1mA over them for about a minute ( ((7.1-0.6V)/70K) = 0.093mA ) base-colector to emitter
- Room temperature 24.3C
- Eight different ICs from the same batch

Result:
Average of the eight: 0.6027V  (ie very near 0.60V at 25C)
Max-to-min value of the eight, 6.2mV, equivalent to 3.1C

All for today...
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 31, 2015, 05:46:57 pm
Can you guys make a small how-to step by step to do your test? I can measure my 4 references. I can supply 100uA from 2400 SMU.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on May 31, 2015, 06:27:09 pm
Hi,

What you can do is simply apply 7.1V over a 70K or 68K collector(8) (Plus) to emitter(7) (minus), tying base(6) to collector (8). Nothing else connected. You can use standard 1% resistors. Sketch attached. 

Then measure voltage over collector-emitter. Measure room temperature. 

If you have had your fingers on the LTZ1000, let the temperature of the LTZ1000 stabilize for several minutes.

You can measure Q1 in the same way tying positive collector(5) and base (4) and measure to negative emitter (7) 

I have the privilege of having a source-meter, then it's simple....
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 31, 2015, 06:41:54 pm
I have both A and non-A units.
So if I use SMU then just supply 7.1V with 100uA compliance, no need for 70K resistor, correct?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 31, 2015, 07:51:47 pm
Hello,

I would not rely on a 100uA current from a SMU.
Usually leakage currents of power stages are in the 0.1-1mA range (per transistor).

So I would use 7.1V (perhaps limited to 1mA) + the 70K resistor.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on May 31, 2015, 08:19:40 pm
I have both A and non-A units.
So if I use SMU then just supply 7.1V with 100uA compliance, no need for 70K resistor, correct?
If you trust the SMU, go ahead, that's what they are for. Mine has read-back for current / voltage, separate of the set point. Never had issues with it. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on May 31, 2015, 10:09:09 pm
I measured 3x LTZ1000 ( non A) with SMU 2636B
#1 0,595641 V
#2 0,601472 V
#3 0,604123 V
@ 100uA/23.2°C.
Date Code 1443.
Pulse measurement will follow.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on June 01, 2015, 07:53:46 am
Thanks Plesa. I'll sum them all up as if / when more data arrives.

That's one serious SMU you have! Me envy  :-DMM
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on June 03, 2015, 07:08:24 pm
Measured Q2 Ube in 50uA->200uA range as Bob Dobkin proposed, pulse measurement (width 1ms with 100ms period).
This can be interesting for some VoltNuts http://etd.library.vanderbilt.edu/available/etd-08262013-170646/unrestricted/Atkinson_PhD.pdf (http://etd.library.vanderbilt.edu/available/etd-08262013-170646/unrestricted/Atkinson_PhD.pdf)
I'm thinking about to assemble the LTZ1000 ( non A) with R4/R5 12/1 divider and Q1/Q2 current set to minimal drift (75-50uA   - > R3,R2 100k-140k).
What do you think with this modification, did someone tried it already? Or rather stay with R3,R2 in 70k reqion?
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on June 05, 2015, 01:05:59 pm
Done it (edit post #1159 in this thread), if you go back a page or two in this thread. Actually did lots of measurements on lot's of things. If I may say so, many go far beyond what you find in the datasheet. Some day I'll collect and summarize them all. As you have first class equipment, I'd very much appreciate if you can repeat / expand some, especially those that differ from the LTZ1000 datasheet. I also did most of my measurements on the ACH.

R2:
If you increase R2, the temperature sensitivity of the LTZ1000 circuit goes down, and crosses zero(!) at R2 around 5M5. The sensitivity /demands on R2 itself remain unchanged. The bad news is that it's hard & expensive to get ultra-stable resistors at that Mega-ohm values. 

Edit: Changing R2 up to 150K hardly makes any difference at all as far as I can see. There is a trend but you need to go into the mega-ohms to have real benefits.

R3: I could not see any advantages or disadvantages or trends by changing R3 up/down at least between 40K and 150K
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on June 05, 2015, 02:39:55 pm
Done it (edit post #1159 in this thread), if you go back a page or two in this thread. Actually did lots of measurements on lot's of things. If I may say so, many go far beyond what you find in the datasheet. Some day I'll collect and summarize them all. As you have first class equipment, I'd very much appreciate if you can repeat / expand some, especially those that differ from the LTZ1000 datasheet. I also did most of my measurements on the ACH.

R2:
If you increase R2, the temperature sensitivity of the LTZ1000 circuit goes down, and crosses zero(!) at R2 around 5M5. The sensitivity /demands on R2 itself remain unchanged. The bad news is that it's hard & expensive to get ultra-stable resistors at that Mega-ohm values. 

Edit: Changing R2 up to 150K hardly makes any difference at all as far as I can see. There is a trend but you need to go into the mega-ohms to have real benefits.

R3: I could not see any advantages or disadvantages or trends by changing R3 up/down at least between 40K and 150K

Thanks! I needs to read whole thread once again. There are several candidates for new R2 from Caddock.
They have 2ppm/K USF240 series http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeUSF.pdf (http://www.caddock.com/Online_catalog/Mrktg_Lit/TypeUSF.pdf)
Or in the 5ppm/K region
TK634 http://www.caddock.com/Online_catalog/Mrktg_Lit/TK134.pdf (http://www.caddock.com/Online_catalog/Mrktg_Lit/TK134.pdf)
TK633 or TK639 http://www.caddock.com/Online_catalog/Mrktg_Lit/TK134.pdf (http://www.caddock.com/Online_catalog/Mrktg_Lit/TK134.pdf)

I'm going to repeat your measurement with 3x LTZ000, probably end of next week.
Title: Re: Ultra Precision Reference LTZ1000
Post by: janaf on June 05, 2015, 03:03:42 pm
I have looked at the USF240, they seem only available on special order. Digikey stock 5M USF340, got one. The temperature coeffs are enough but the long term drift, 20ppm/per year maybe, depends on your demands. Will check out the others.

I forget to say there may be a noise issue too. Someone theoretically minded may be able to tell if there is a noise penalty from these resistors if the noise cancels somehow. Else, I can soon measure...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Marco on June 05, 2015, 03:58:06 pm
If you increase R2, the temperature sensitivity of the LTZ1000 circuit goes down, and crosses zero(!) at R2 around 5M5. The sensitivity /demands on R2 itself remain unchanged. The bad news is that it's hard & expensive to get ultra-stable resistors at that Mega-ohm values.

What's wrong with the datasheet way of doing zero tempco? (ie. a resistor on top of the zener)
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on June 06, 2015, 07:40:46 am
I have looked at the USF240, they seem only available on special order. Digikey stock 5M USF340, got one. The temperature coeffs are enough but the long term drift, 20ppm/per year maybe, depends on your demands. Will check out the others.

I forget to say there may be a noise issue too. Someone theoretically minded may be able to tell if there is a noise penalty from these resistors if the noise cancels somehow. Else, I can soon measure...

The minimal order quantity for custom made USF240 like 5.6M is 250 pieces..
USF240-5.00M-0.1%-2ppm 32 USD. Few of them should be on stock and delivered withing week or two.
The long term drift is about 10 times higher than Z foil. Do we have another alternative?
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on July 21, 2015, 07:24:34 pm
Componets arrived. I hope that soon will be ready first prototype of LTZ1000.
Tube of  Bourns 3250 (50ppm/K) wirewound resistors recomended by Edwin for better long term stability, I was surprissed how big they are (see photo). Also some Vishay 1280G (15ppm/K). One box of each (all 100ppm/K) Copal CT20 trimer and Bourns 3299.
And buch of additional Vishay UXB resistors. For final circuit I would like to use PWW resistors. Only needs to define right values.
For burning process 4x LTZ1000 and also 16x LM399.
Title: Re: Ultra Precision Reference LTZ1000
Post by: macfly on July 23, 2015, 02:21:21 pm
Hi butterfly,

I think, you are right. The 'block diagram' in the datasheet on page 4 shows the parasitic diodes in parallel to the heater.  The pins 1 and 2 have to be interchanged in the schematic of the 'Negative Reference'.

Regards,

Macfly
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 23, 2015, 07:26:21 pm
I have only spotted this in the drawing of the negative voltage reference ... - am I overlooking something ?
I cannot understand that issue is still left in the datasheet - after 3 decades ...  ?
Any further ideas to improve this implementation of the negative version are welcome ?

Hello Butterfly,

obviously no one built ever the negative reference.
And finally you found the bug of the century.

If you look at AN42 of LT (figure 68) the pins 1 + 2 are exchanged against the datat sheet.
http://cds.linear.com/docs/en/application-note/an42.pdf (http://cds.linear.com/docs/en/application-note/an42.pdf)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on July 24, 2015, 05:43:46 pm
I tried to compare Bours 3250W 10k and Vishay 1280G and found that the wirewound 3250 pots has smaller hysteresis or deadband.
It is simple setup, does anybody have idea how to provide more empiric measurement with normal equipment?
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 28, 2015, 05:44:16 am
Side note which might be interesting for supporting parts like Opamps in epoxy case:
I recently started playing with oxygen sensors and I am measuring the time it takes for the oxygen sensor to respond to a step change of ambient air athmosphere to carbon dioxide and back, going thru different silicones as cover layers.
(These oxygen sensors are little pieces of foil with a dye, using the fluorescence quenching method. Basically oxygen reduces the fluorescence activity by physical means, no chemical exchange happens. The interrogator device stimulates with light modulated by a intensity sinewave and measures phase and amplitude of the light coming back. )

2mm of silicone allow quick gas exchange at the sensor with a delay in a 15-30 minute window.
My boss suggested polyvinyl alcohol as a barrier material to prevent gas exchange, and even a tiny little layer was working so well - stopping dead, no visible response after hours. I read up a bit on this stuff and found that it is also used as a humidity blocker in foods packaging. Its available cheap as a form releasing agent.

Maybe this stuff can be used to supress humidity exchange of epoxy cased parts.

Title: Re: Ultra Precision Reference LTZ1000
Post by: richiem on August 28, 2015, 05:58:54 am
Hi babysitter -- what's the life of PVA used this way -- will it last a long time?
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on August 28, 2015, 06:30:21 am
I just had the first experiences, on flexible substrates this form releasing agent dries but gets brittle when substrate gets moved, maybe a cover layer is required. I think about looking for known humidity sensitive parts (right in this thread?) , maybe I buy/borrow/beg/steal some and just paint them.

Also, my own experience is using it as a barrier against exchange of oxygen and co2.

(Maybe the first part i should paint is a humidity sensor?)

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on August 28, 2015, 12:32:05 pm
For the reference part, there is the option to use a closed metal casing with the few signals going in and out through ceramic feed through capacitors. Sometimes these caps are misused as a feed through to vacuum vessels - so they should be rather thight. Keeping HF signals out is not that bad either.  I would not worry so much about humidity at the OPs - the LF noise of the LTZ1000 is still way higher than typical drift / LF Noise of good OPs like the LT1013, LT1007, ... even in plastics case.  Its the whole circuit that would profit from stable humidity levels.

I would be sceptical that there is much way for improvements through this slight compensation of residual TK effects with this extra 5.6 M resistor. Feedback from the heater is at least sensitive to the termal enviroment. So having extera / other  thermal insulation would need a different resistor.

There might be a chance to tweek / improve temperature regulation a little:
With the resistor as heating element, the regulation loop is nonlinear (in this respect the LM399 is better designed). So tuning of the temperature regulator must be done for the worst case (highest gain), which would be very low temperatures. There are two ways to improve here: either linearize the heater through some extra nonlinear circuit  or avoid the very low temperatures by an extra layer of temperature control. This extra layer could be a moderate temperature, only aktive at low to normal enviromental temperature.

Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on September 07, 2015, 02:15:55 pm
Hi,

Wow - what a thread - 265 pages of dense pdf not to mention the linked docs. Took me a week of spare time reading and I feel I need to go back and read it all again to see if I missed anything :)
Very educational, and many thanks.

To add a bit more data and ask a couple of questions...

I just acquired 3 x 03458-66509 ref boards with the aim of building a sort of Fluke 7001 clone. Attached is a little basic measured data FWIW - no noise or stability #s yet. I see that the accepted wisdom is that HP set these to run at ~90C rather than a preferred ~60C.

I also see from the 3458a schematic (e.g. http://www.maxmcarter.com/vref/hp3458-1.gif (http://www.maxmcarter.com/vref/hp3458-1.gif) ) that the bases of the embedded temperature sensing transistor and the temperature control transistor are connected off the board as J400(1) and J401(1). I can't quite see from the CLIP where these go to and what they're used for. Anyone else figure this out yet?

Also I need to make some covers for the refs to keep out the drafts :) I can't see any detailed images of the HP design, so I've spun my own (also attached).

Any feedback? - I really don't know much about thermal. I've taken some inspiration from the L399 cover which has a double wall.

Regards, Alan
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on September 07, 2015, 05:11:10 pm
I hope that your boards were cheaper than 03458-66509  on ebay ( 99 USD). 
I suppose that new LTZ1000 and PWW resistors from Edwin Pettis can be cheaper alternative.
Of course with proper burn-in and with lower temperature setpoint than HP used.

But everything depends on your reference purpose ( consider using multiple LM399).
Title: Re: Ultra Precision Reference LTZ1000
Post by: richiem on September 07, 2015, 07:15:05 pm
@alanambrose -- just ignore those base connections that go off-board. I'm not sure where they go either, but I think they are used for temp monitoring in the 3458. For your purposes, they are unconnected.

I like your idea of having the three boards as a 7001/Datron 4910 type standard. I can fully recommend changing R411/15k to 13k using Ed Pettis' PWW resistors, having done this for my 3458 board-based standard.

I've used LTC2057s for buffer amps -- one unity gain to buffer the 3458 board's zener output. and one with gain to provide a 10V output. Were I to do what you are doing, I would buffer the three board individually, and have a fourth set of buffers that mix the outputs of the three boards to give an average of their individual outputs. Good luck to you on this.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on September 08, 2015, 04:56:44 pm
>>> just ignore those base connections that go off-board. I'm not sure where they go either, but I think they are used for temp monitoring in the 3458. For your purposes, they are unconnected.

Thanks, but the reason I asked was that I had a suspicion that we might learn something useful. If HP decided to route the connections off the board they must have had a reason. Could be something simple like identifying when the LTZ was up to temperature, but could be something smart. There's a sense in this thread (and others) that HP could have been a bit cleverer with their LTZ ref board - not making a lower temp / lower drift version for metrology labs etc. However, as this is still the go to 8.5 digit meter and it has been since the early 90's, I'm happy to give them the benefit of the doubt. Will take a closer look at the CLIP.

Alan
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on September 08, 2015, 05:15:09 pm
Hi, these additional connections are not used in the 3458A, as far documented in its CLIP.
There's only this connection to -18V over a resistor, which is intended as a current cancellation path for the zener and collector currents, and the OpAmp supply. So the GND supply towards this PCB is virtually current free.

But this PCB may also  work well as a reference w/o this feature.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 08, 2015, 10:01:26 pm
  The LTZ's 1/f noise is guaranteed to be <=2uVpp, but it is on a Poisson distribution, and about 90% of them will have exceptionally low 1/f noise.  This is not something that most hobbyists will even be able to see, nor should they worry about it.

Why not?
It is not too difficult to measure the noise.
Its simply a low noise amplifier + a oscilloscope.
And its the simplest way to find out wether a reference behaves "strange" or if it works most probably on spec.
Its one of the parameters that I want to know besides T.C. and long term drift.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: 6thimage on September 08, 2015, 10:36:46 pm
Was HP's initial decision of using a 90 deg C oven temperature over 60 deg C anything to do with ambient temperature? As if they used 60 deg C the multimeter wouldn't be able to be used (comfortably) in a 50 deg C environment (i.e. racks).

I know there is a lot of magic that goes into making a good ltz1000 circuit (and I'm not trying to fanboy HP-Agisight), but it seems strange that they would have gone with a 90 deg C circuit, without knowing it has worse stability than a 60 deg C. I would have thought that the engineers at HP would have been on first name terms with the right people at Linear and, if that was the case, would this choice be purely a trade off they needed to make rather than incompetence? But this does beg the question of why they never offered a high stability option with a large note of 'keep the unit's temperature below x'.

I'm not sure if anyone has asked this (or answered this) - I've tried to keep up with this thread, but there is just so much information.
Title: Re: Ultra Precision Reference LTZ1000
Post by: richiem on September 09, 2015, 01:54:15 am
Max spec'd operating temp for the 3458A is 55°C -- assuming an internal temp of 15°C above ambient, that means a temp at the LTZ of 70°C -- so running the LTZ at 90°C +/- 5 makes a lot of sense. I agree that HP should have made a metrology version (do we know they didn't?) with the ref running at lower temp, which is one (but only one of several) of the things that Fluke has done with their high accuracy version of the 3458.

I take Ken's observations seriously, and he and Frank are in agreement that the "current-cancelling" of -15V thru a 2.67K resistor to ground is most likely unneeded; nevertheless, I am using that on my little LTZ box.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on September 09, 2015, 11:15:54 am
Well my approach is to try and extract everything from the other designs even if the conclusion is that some things may not be optimal or that the designers might have had slightly different objectives from mine. I see that while the temp sensing transistor Vbe connection isn't used in the CLIP, the heater transistor connection apparently is. It runs through a DG211CJ analogue switch and then to HEATER/R123 (page 51 on the pdf I have). Curiously, this then plunges into the middle of the 'sentry DC input amplifier' - I can't quite see why ATM. Maybe the two connections might also have been used in test / burn-in? I did notice some production-style test points on the bottom of the board also.

Re LTH A version selection and temperature objectives - I think it's fairly well accepted that in that period HP was selling a vast quantity of equipment to the military, hence the spec. Some folks on volt-nuts think that we're unlikely to see those kind of volume sales to a price-intensive customer again soon - and therefore the likelihood of a vendor improving on the tech in the 3458a is low. I guess metrology sales were fairly low in comparison and anyway HP's partner, Fluke, was king of that game - so maybe HP marketing didn't want to go there. It would also have required HP marketing dept to understand both the ref temperature options along with the market opportunity (as apparently Fluke did) and like what they thought.

Re the thought that these boards might be dodgy - I'm guessing they're either test cast-offs that have been sitting around for 20 years somewhere, or that they're spares that have been sitting in some quartermaster's stores for the same period. (They have the HP logo on.) Guess I won't know until I measure the TC / drift / noise, but also I'm planning to spin my own boards at the right time. A couple of questions if I may:

+ how do you guys measure TC? Have you got test chambers?
+ was there a conclusion from the 'best' way to get from 7.x -> 10V discussions?

Alan
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 09, 2015, 04:51:09 pm
The switched capacitor divider is not effected as much by the speed of the transitions of the control signal. This is different from PWM. The tricky part here are parasitic capacitance from the caps and lines to ground and so on. So humidity may change this. The other problem is charge injection.

There is also the version to go from 7 V to a nominal 10.5 V via switched capacitor circuit, and than down to 10 V with the resistiv divider. Here only the 0.5 V difference is really effected by the drift of the resistors, so its less sensitive than the direct 7 V / 10 V step by about a factor of 5. It gets even better it you start at 6.8 V or so.
Title: Re: Ultra Precision Reference LTZ1000
Post by: HighVoltage on September 09, 2015, 05:08:29 pm
There never was any consensus on the best way to get 10V from the 7V[ish] reference output:
What a nice summary.
Thank you !
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 09, 2015, 07:59:03 pm
There never was any consensus on the best way to get 10V from the 7V[ish] reference output:
What a nice summary.
Thank you !

Thank you Ken.

So I have only to give some hints:

My "temperature chamber" is shown in the following thread:
https://www.eevblog.com/forum/projects/t-c-measurements-on-precision-resistors/msg462298/#msg462298 (https://www.eevblog.com/forum/projects/t-c-measurements-on-precision-resistors/msg462298/#msg462298)
A peltier car box with a added heater. (it is better to heat against the cooler than switching on/off the cooler).
A 30 deg C temperature range around room temperature is possible.

Up to now I have done no 7 to 10V transfer.
The latest idea for a fixed 10V reference is to use a cirquit similar to the Fluke 7000 system.
A (halfway) stable resistor divider (low noise) which gets a correction by a processor controlled DAC (12 Bit?).
I want to correct absolute voltage (drift) and the T.C. of the resistor divider with a resolution around 0.1ppm.
So the resistor divider has to be adjusted to the reference voltage within 100ppm.
I do not want to build an oven around the resistor divider since I want a battery supply.

For a variable output calibrator the idea is to use a 7V reference + LTC1043 capacitive divider * 3 / 4.
This gives around 5.2-5.4V Reference voltage for a correction loop ADC.
The main output is done by either 2 16 Bit DACs or a 24-30 Bit PWM DAC + a resistor divider for the 10V output.
The correction loop is responsible for T.C. correction and linearity.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on September 16, 2015, 12:43:02 pm
Pah, I wrote a longish post yesterday that has been lost in the ether...

Thanks Andreas for the pointer to the temp chamber thread.

This is where (~centre / right - marked as 'HEATER' on CLIP pdf page attached) the 3458a LTZ board heater connection interferes with the 3458a input amplifier. Anyone make sense of that?

Regards, Alan

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 16, 2015, 04:11:06 pm
The resolution of the PDF file  makes a little difficult to read all the values. The heat signal seems to have the option to be coupled back to amplifier in the higher amplification (likely 100 times) mode after quite some attenuation.
So this would add some offset and intentional drift (depending on heater signal) to the output. This is somewhat strange, as I can't see an adjustment to choose the optimal amout of correction and in addition the heater signal is not linear in temperature. So this will not compensate a linear TC, but a therm that approximately depends on the square root of 90 C - case temperature.
It also does not make sense to use this as a way to measure the heater current (e.g. during startup) for diagnostic purpose - there should be much better points to choose the input.

Llikely most of the time the relay will turn off this extra component anyway. To me this does not make much sense, as the relay is quite some efford and it will likely make temperature drift worse, not better. If I were to correct thermal dirf, I would add a simple sensor and do the corrections in the µC. The sensor for the case temperature is likely allready there.

So my best guess is this part will not be populated in many units. Possibly just a kind of joke to make the chineese think about magic. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: lukier on September 30, 2015, 04:22:04 pm
So, I *think* I found a link between the LT1088 and the LTZ1000 [probably the special die mount technique of the LTZ1000A, and the special die arrangement of a circular heater with a diode in the center].  Jim Williams may have left us a clue.  Look at the bottom of Ap-Note-22, and reference #3:  "Renez, Repus ..."

http://cds.linear.com/docs/en/application-note/an22.pdf (http://cds.linear.com/docs/en/application-note/an22.pdf)

"Renez Repus" is "Super Zener" spelled backwards!

Great find! One has to read Jim Williams very carefully :) My personal favorite are footnotes saying "See note above"  :D
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on September 30, 2015, 04:42:25 pm
wow, nice finding. It is a pitty that LT1088 is obsolete.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 30, 2015, 06:46:23 pm
So, I *think* I found a link between the LT1088 and the LTZ1000 [probably the special die mount technique of the LTZ1000A, and the special die arrangement of a circular heater with a diode in the center].  Jim Williams may have left us a clue.  Look at the bottom of Ap-Note-22, and reference #3:  "Renez, Repus ..."

http://cds.linear.com/docs/en/application-note/an22.pdf (http://cds.linear.com/docs/en/application-note/an22.pdf)

"Renez Repus" is "Super Zener" spelled backwards!

-Ken

If you google Renez Repus you find more about that:

http://analogfootsteps.blogspot.de/2014/03/pranking-prankster-jim-williams-and.html (http://analogfootsteps.blogspot.de/2014/03/pranking-prankster-jim-williams-and.html)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Bud on September 30, 2015, 06:58:42 pm
Look at the bottom of Ap-Note-22, and reference #3:  "Renez, Repus ..."

http://cds.linear.com/docs/en/application-note/an22.pdf (http://cds.linear.com/docs/en/application-note/an22.pdf)

"Renez Repus" is "Super Zener" spelled backwards!

And it was published in "Private communication, Linear Technology"
 :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: slashdev on October 01, 2015, 01:57:27 pm
Quote from: AN-22, page 4
The test structure in the die center is not used. it is designed to offset effects described by Counts Theorem (see References).

Quote from: References
5. Counts Theorem, propounded by L. W. Counts at the 1986 ISSCC, states that 9 != 10.

What a great Easter Egg!
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 01, 2015, 02:05:35 pm
There are few LT1088's on ebay for $40, in case someone feeling extreme... I skip for now, enough toys here.
Title: Re: Ultra Precision Reference LTZ1000
Post by: retrolefty on October 01, 2015, 05:16:31 pm
There are few LT1088's on ebay for $40, in case someone feeling extreme... I skip for now, enough toys here.

 I saw that when I checked, several sellers all around the same price. Do you think these are pulls or NOS?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 01, 2015, 05:19:40 pm
Seem to be NOS, pins not soldered and date code is 2001. But I think it's somewhat offtopic here.

To stay on topic, anyone have photos or know what is different on Fluke's 3458A/HFL ref compared to usual HPAK 3458A? I'm trying to make up my mind around various options of 3458A. Better resistors around LTZ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: HighVoltage on October 01, 2015, 07:37:37 pm
To stay on topic, anyone have photos or know what is different on Fluke's 3458A/HFL ref compared to usual HPAK 3458A? I'm trying to make up my mind around various options of 3458A. Better resistors around LTZ?
I have been reading about the 3458A only and I do not have one - may be in the future.
But What I have read is that the 3458A HFL has as the only difference, the lower reference temperature.
May be there is more.
Title: Re: Ultra Precision Reference LTZ1000
Post by: richiem on October 02, 2015, 03:06:25 am
I *think* the Fluke HFL 3458A version not only has a much tighter spec for the reference, but also has better/more robust/less thermally sensitive dividers for the 100V and 1kV ranges.
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on October 05, 2015, 07:10:28 am
Several months ago I make a research related to differences between 3458A, 3458A opt. 002 and 3458A HFL.
And 3458A HFL should have better 40k Ohm resistor for Ohm AutoCal. 3458 Opt002 is using LTZ1000A and not LTZ1000.
The rest seems to be identical, maybe selected from bigger batch.

I have question about burn in of LTZ1000. Are you burn-in reference with heater on or off? For me logic was that heater should be off, otherwise zener temperature will be out of operation range window ( 125°C + 50°C in my case for LTZ1000 and for LM399 125°C+90°C)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 05, 2015, 10:42:45 am
So far all 3458A references I saw online are using LTZ1000A, not the usual one.

Then temperature, LM399 regulation is internal, so if you run in +125 ambient, heater would be off anyway.

As of LTZ, you have both control using heater and ambient. Modules I had were left running +90c (heater setpoint only) for 2 month, then to normal temp. Last time I measured 4 of them they were within 5 ppm of last reading (likely closer, but I had used 2001 with bit higher ambient temp).
I'll have to do new testrun after rusty 3458A back in business (i hope :))
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 05, 2015, 07:01:36 pm
I have question about burn in of LTZ1000. Are you burn-in reference with heater on or off? For me logic was that heater should be off, otherwise zener temperature will be out of operation range window ( 125°C + 50°C in my case for LTZ1000 and for LM399 125°C+90°C)

Hello,

I do not burn in my LTZ1000A references up to now. (only a normal run in phase of 6-12 month before first calibration).
After a burn in it is very likely that you get a more or less large hysteresis.
(as I experienced by accidently shorting the output and setting the heater setpoint to infinity).

By thermal cycling you can partly remove this hysteresis.
But the last ppm will be stored for at least some months.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on October 05, 2015, 09:34:26 pm
Thanks both for input.
So I will keep my references in oven running at 125°C with heater on for next few weeks and we will see.
At the end I'm planning to make cyclyng according to Pickering patent or similar to cycling described in one document from CERN (they are burning LTZ by internal heater, I have also LM399 so it is not possible for me):
The burn-in procedure is the following:
- Put all the measurement probes on the testpoints corresponding to VB1
- Set the heater OFF by using the appropriate jumper switch
- Set the oven to 80ºC
- After the temperature of the oven is stabilised (some hours), measure and note
down VB1
- Set oven to 120ºC
- After the temperature of the oven is stabilised (some hours), measure and note
down VB1
- Set oven to 130ºC
- After the temperature of the oven is stabilised (some hours), measure and note
down VB1
- Put the heater ON and change the measurement probes to measure the value of the
current – I . This current is measured through a 10Ohm resistor.
- Set the oven to 80ºC and let the temperature of the oven stabilise (some hours).
- Adjust the current “I” through the use of the potentiometer box, to a value of
19mA.
- Change the measurement probes to measure the value of VB1, wait the necessary
time for the temperature to stabilise (if you were forced to open the oven door)
and then measure and note down VB1. This value should be within the interval
VB1@120ºC and VB1@130ºC
Adjust the heater current using the potentiometer box to have on VB1 the average
value between VB1@120ºC and VB1@130ºC.
- Measure the current on I testpoint and note it down. It should be close to 19mA
- Keep the setup at 80ºC during 3..4 weeks but pulsing the supply voltage to have
the heater + zener powered during 45minutes and unpowered during 15minutes
per hour. Each 2 days, adjust the current to the value corresponding to a VB1
which is the average value between VB1@120ºC and VB1@130ºC.
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on October 09, 2015, 05:51:56 pm
video related to LM399 and LTZ1000 references, it is quite long and in French:-(
https://jipihorn.wordpress.com/2015/07/15/reference-de-tension-utilime-ltz1000-comment-ca-marche/
Title: Re: Ultra Precision Reference LTZ1000
Post by: Gyro on October 20, 2015, 12:31:56 pm
Sorry if this has already covered, I've been following as many of the 90 pages as I could over the past months.

Has anyone had significant success with the "Adjusting Temperature Coefficient in Unstabilized Applications" typical application circuit on the LTZ1000 datasheet? The one where you cycle the heater on and off at one minute intervals while tweaking the bias current for minimum TC.

I was wondering how low a TC it is possible to achieve using this method. Given that the datasheet specifically states that drift increases with high temperature, then for an ultimate goal of minimum long term drift, I'm wondering if this first order temperature compensation, maybe coupled with a thermometer (standard cell style of working) and/or basic external oven is a viable option. Minimizing Kovar lead thermocouple issues too.

It looks from the "LTZ1000 - Heater resistance - Possible fakes" thread that HP are generally thought to have done the wrong thing in using the LTZ1000A variant at higher temperature rather than the non-A at lower.

As I say, sorry if this has already been covered.  :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 20, 2015, 01:10:17 pm
Has anyone had significant success with the "Adjusting Temperature Coefficient in Unstabilized Applications" typical application circuit on the LTZ1000 datasheet? The one where you cycle the heater on and off at one minute intervals while tweaking the bias current for minimum TC.

I was wondering how low a TC it is possible to achieve using this method. Given that the datasheet specifically states that drift increases with high temperature, then for an ultimate goal of minimum long term drift, I'm wondering if this first order temperature compensation, maybe coupled with a thermometer (standard cell style of working) and/or basic external oven is a viable option. Minimizing Kovar lead thermocouple issues too.

As I say, sorry if this has already been covered.  :)

Hello,

no problem, I think nobody ever has given a final conclusion about that feature.
And I think, I have read every entry here!

First of all, you are mixing T.C. and long term drift.
Both characteristics have nothing in common, and must be discussed separately.

Long term drift is determined by the oven temperature, the lower, the better.
45°C gives about -1ppm/year.
High quality external resistors (5 EA) add about +/- 0.3ppm/year or less, as their impact on all drifts is attenuated by factors of 1/100.. 1/1000.


The T.C. for a stabilized solution (using the internal oven) is determined only by the external resistors ( to first order), and therefore being < 0.1ppm/°C in most cases (using < 3ppm/°C resistors)

The reference element itself has a T.C. (un-stabilized, no oven) of about 50ppm/°C.
Only if you do NOT use the oven, a trimming of this characteristics is needed /makes sense.

In the stabilized case, the oven regulation is so good, that it reduces these 50ppm/°C to  unmeasurable values, i.e. being much lower than the impact of the external resistors.

This fact and the probable complication of the trimming resistor  might explain, why nobody has put much effort in this feature.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Alex Nikitin on October 20, 2015, 02:02:13 pm
The reference element itself has a T.C. (un-stabilized, no oven) of about 50ppm/°C.

50ppm/°C at room temperature or at elevated temperature?

Cheers

Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: Gyro on October 20, 2015, 02:40:41 pm
Thanks Frank,

Glad I haven't missed any too obvious discussions then.  :)

Yes, agreed, Drift and TC need to be considered separately but I don't think moving from active heating to passive TC compensation should adversely affect drift. With well aged external resistors and low overall power dissipation (eg, no op-amp and transistor drive for the heater) hopefully at room temperature drift would be very low indeed.

For the TC, I'm not sure if your 50ppm/°C includes the Vbe of the compensating transistor or not, I'm assuming that it does (I can't find a figure in the datasheet). That particular application circuit seems to be tweaking the zener current to optimise the tracking of the zener and compensation transistor TCs (hopefully by shunting a 200R long term stable resistor with a high value less critical shunt one). It's a question of how close that tracking / compensation can get over a limited (room) temperature range, which it sounds as if nobody's really looked into.

It also occurs to me that if the heater is not in active use then there is also the sense transistor available which could maybe be employed in a second order compensation circuit?

At least having the on-chip heater would make the thermal cycling nice and easy for trimming... and maybe for 'relaxing' any hysteresis too.

Of course I don't actually have an LTZ1000 but the possibility is making me edge towards about a Digikey order!

EDIT: Though I suppose if adverse effect on drift is already so low when heated, then there may not be too much milage in this approach. I just like the elegance of a room temperature solution that doesn't have as many issues with thermocouple effects with a heated package.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on October 20, 2015, 03:58:06 pm
The old good Datron reference board :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 20, 2015, 04:26:24 pm
Thanks Frank,

Glad I haven't missed any too obvious discussions then.  :)

Yes, agreed, Drift and TC need to be considered separately but I don't think moving from active heating to passive TC compensation should adversely affect drift. With well aged external resistors and low overall power dissipation (eg, no op-amp and transistor drive for the heater) hopefully at room temperature drift would be very low indeed.

For the TC, I'm not sure if your 50ppm/°C includes the Vbe of the compensating transistor or not, I'm assuming that it does (I can't find a figure in the datasheet). That particular application circuit seems to be tweaking the zener current to optimise the tracking of the zener and compensation transistor TCs (hopefully by shunting a 200R long term stable resistor with a high value less critical shunt one). It's a question of how close that tracking / compensation can get over a limited (room) temperature range, which it sounds as if nobody's really looked into.

It also occurs to me that if the heater is not in active use then there is also the sense transistor available which could maybe be employed in a second order compensation circuit?

At least having the on-chip heater would make the thermal cycling nice and easy for trimming... and maybe for 'relaxing' any hysteresis too.

Of course I don't actually have an LTZ1000 but the possibility is making me edge towards about a Digikey order!

EDIT: Though I suppose if adverse effect on drift is already so low when heated, then there may not be too much milage in this approach. I just like the elegance of a room temperature solution that doesn't have as many issues with thermocouple effects with a heated package.


Well, afair, it is nearly impossible for the LTZ reference, to trim its T.C. (unheated, of course superposition of zener and BE diode) to near zero.

Therefore, a room temperature solution w/o oven is absolutely wishful thinking.

The other Fluke topology, i.e. BE diode on top of the zener, that is SZA263 and LTFLU, they may be really trimmed to near zero T.C.

Fluke used that feature in the 731B, transfer standard, and in the 5200A, AC standard.

But these achieve 1 ppm/°C at best, and maybe the initial T.C. trimming may not last forever.

So you may try that, but such a solution has nothing to do with an Ultra Precision voltage standard, as we discussed here.
W/o an oven, you simply cannot achieve ultra high stability with Reference Amplifiers.

It is also worthless to make things complicated.

With the intended mechanism (oven), stable resistors, and a LTZ1000CH at 45°C, with the simplest circuit possible, you will definitely achieve  stabilities in time and temperature, which you will have big difficulties to verify with amateur based tools.

Thermo voltages are also not a problem at all with proper layout and thermo-mechanical setup.

The existence of all these ovenized references and standards are a simple proof for that!

The LTZ oven is not a good choice for temperature cycling, if you have a relatively low oven temperature.
This cycling, intended to remove hysteresis, only works correctly, if you have a symmetrical temperature swing below and above the stabilization temperature.

With 45°C, you may cycle between 25°C (r.t.) and 65°C. For these low temperatures, you might see no hysteresis at all, it's simply not working.

So you might select 65°C, to have a +/- 40°C swing, but this setting increases the timely drift, as a big disadvantage.

At 45°C, you may try to avoid any excess temperature of the LTZ, or do the temperature cycling of the whole assembly from 0°C to +90°C, in a climate chamber.


Frank

Title: Re: Ultra Precision Reference LTZ1000
Post by: Gyro on October 20, 2015, 06:12:20 pm
Well I've long been known for my wishful thinking (for want of a better term) :D

My interest really was piqued by the LT application circuit - they must (still) think it's possible for them to have kept the circuit in the current datasheet for what is, after all, a very high end device. There are lots of cheaper solutions for average TC performance (or better - My SVR-T is under 1ppm/C at room temperature for what WAS similar money to the bare chip, which thankfully all I need). Maybe it's an app circuit intended to be used in an external oven (part substitution?), after all, an on-chip oven is always going to be a 'poor mans' alternative to a full circuit oven. Who knows, curious thing to include without a relevant comment though.

I agree, there's no point in arguing against the more or less universal use of ovens for high precision references, still feels a bit more brute force than finesse though. I think everyone would like to get away from warm-up, operating current, Flukes with batteries and transport time issues given half a chance.

Thanks for the additional thoughts and comments.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 20, 2015, 06:30:04 pm
As little offtopic, reading this discussion reminds me myself a year ago when I started my reference design. I was thinking too about improving existing appnote design, but after experimentation on first prototype and eventually killing first LTZ chip, I roll back to proven circuit used by industry with just lower temppoint. We talking about 300$ BOM in parts just for one module (most of cost are VPG resistors), so it's rather limiting for testing many various options without proper multiK$ gear around... Sorry for interrupt :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Gyro on October 20, 2015, 06:48:54 pm
Glad it brings back some memories - blue sky thinking is great until reality drags you down to earth again  :) You'll always end up being dragged down the route trodden by those with a larger R&D budget than you do!

Sooner or later I'm going to run out of my little pile of  '70s wirewound resistors (as in my Hamon divider) and have to start buying instead like you and Dr Frank - that comes hard to an inveterate hoarder!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on October 20, 2015, 06:56:24 pm
After damaging the heater on my LTZ, I did play around with compensating it, and I could get its TC very close to zero.  I experimented with two different approaches, both of which were pretty successful.  I did the datasheet approach, and I also did one where I used an inverting opamp to amplify vbe. But getting it to near zero and keeping it there are very different levels of challenge.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Gyro on October 20, 2015, 07:13:18 pm
Thanks, interesting that the app circuit does 'sort of' work then. I wonder what drifted off over time then (don't worry, I don't expect anyone to answer that one!). I suppose it could be anything from die damage due to the heater accident to drift in the opamp or gain setting components, even Zener TC shifting that would normally be masked.
Title: Re: Ultra Precision Reference LTZ1000
Post by: bitslice on October 20, 2015, 07:25:21 pm
(Apparently) some pictures of LTZ1000.
Only posting because they look different to the ones posted earlier

(http://i1132.photobucket.com/albums/m562/bitslice/eevblog/ourdev_464495.jpg)

(http://i1132.photobucket.com/albums/m562/bitslice/eevblog/ourdev_483176.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on November 19, 2015, 07:55:25 pm
Assembled 4 boards with LTZ1000. For testing I used 25ppm resistors. but soon will be replaced by PWW.
LTZ1000 has been aged in oven for three weeks at 125°C. After PWW will be placed I will cycle it according to John Pickering.
All 4 units I would like to put into one box (similar to which use e.g wekomm use for their resistance standards).
I'm impressed how stable it is on table with 25ppm resistors, temperature of reference is 12k/1k so about 40-45°C.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 19, 2015, 11:11:04 pm
Cool. Perhaps you can make bunch of pics and post in my kx thread? That would revive it a bit.

Happy to see it in use.

I would suggest to put resistors parallel to PCB, horizontally. Having them standing like this can cause thermal gradient over resistor body (due different length of pins and thermal mass), producing higher thermal EMF.  ;) Just form leads in C-shape and solder horizontally.

Why all four in one box? Perhaps better keep them separate, so you can compare directly?
Title: Re: Ultra Precision Reference LTZ1000
Post by: ltz2000 on November 23, 2015, 09:22:04 pm
A (low resolution) photo from the US Air Force Primary Standards Lab. I was able to count 56 Fluke 732B Voltage standards...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 23, 2015, 09:34:45 pm
Nice visit,
Do you also have a high resolution photo?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on November 23, 2015, 09:35:53 pm
A (low resolution) photo from the US Air Force Primary Standards Lab. I was able to count 56 Fluke 732B Voltage standards...

Multiplied by quoted price (8k USD) it is fortune. I'm looking for some decent surplus ones.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ltz2000 on November 23, 2015, 09:43:49 pm
Nice visit, Do you also have a high resolution photo?

Unfortunately I wasn't there. Just an internet find that I had saved in the funny pictures folder. Well, probably absurd rather than funny...



Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 23, 2015, 09:45:28 pm
Assembled 4 boards with LTZ1000. For testing I used 25ppm resistors. but soon will be replaced by PWW.
LTZ1000 has been aged in oven for three weeks at 125°C. After PWW will be placed I will cycle it according to John Pickering.
All 4 units I would like to put into one box (similar to which use e.g wekomm use for their resistance standards).
I'm impressed how stable it is on table with 25ppm resistors, temperature of reference is 12k/1k so about 40-45°C.

I don't know, which oven temperature you'll use, maybe 45°C?
Then I wish you good luck for your try to remove the huge hysteresis, you've induced.
You were aware, that you have to apply symmetrical and very precise temperature changes around oven temperature, if Pickerings patent should work at all..
At 45°C oven temperature, vs. 125°C max., that would be -35°.. +125°C with decreasing amplitude. That needs a well controlled temperature chamber.

These parts are good for  drifts well below 1ppm/yr, if handled with care, and no excessive heating upfront.

Don't be disappointed, if you (very probably) encounter drifts of several ppm in the first years, until they finally / hopefully stabilize again.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on November 23, 2015, 09:51:38 pm
Assembled 4 boards with LTZ1000. For testing I used 25ppm resistors. but soon will be replaced by PWW.
LTZ1000 has been aged in oven for three weeks at 125°C. After PWW will be placed I will cycle it according to John Pickering.
All 4 units I would like to put into one box (similar to which use e.g wekomm use for their resistance standards).
I'm impressed how stable it is on table with 25ppm resistors, temperature of reference is 12k/1k so about 40-45°C.

I don't know, which oven temperature you'll use, maybe 45°C?
Then I wish you good luck for your try to remove the huge hysteresis, you've induced.

These parts are good for  drifts well below 1ppm/yr, if handled with care, and no excessive heating upfront.

Don't be disappointed, if you (very probably) encounter drifts of several ppm in the first years, until they finally / hopefully stabilize again.

Frank

I'm going to cycle them according to John Pickering. Or in case the drift will be huge I will buy new ones LTZ1000 references.
If Mr.3458A (TiN) will have more PCBs I can assemble another 4 pieces for direct comparison.
At least after that we can make the final conclusion what is better :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on November 23, 2015, 10:04:07 pm
You were aware, that you have to apply symmetrical and very precise temperature changes around oven temperature, if Pickerings patent should work at all..
At 45°C oven temperature, vs. 125°C max., that would be -35°.. +125°C with decreasing amplitude. That needs a well controlled temperature chamber.

I have controlled environment, so it is not big deal. Yes, I going to little bit further ( safety margin ) -40°C  .. 130°C. I only needs to set the time on each step. I suppose that 5°C step with 20 minutes stabilization will be enough. Maybe I should check the 7001 manual how long this whole procedure takes.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 24, 2015, 02:23:48 am
I have some boards. If you don't mind bodging older rev (red one, have power on zener opamp reversed and heater transistor incorrect collector-emitter) I can send you 10 of those :D

Quote
I was able to count 56 Fluke 732B Voltage standards...
Who cares 732B, if you have two JVS rigs :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: HighVoltage on November 24, 2015, 10:36:08 am
Nice visit,
Do you also have a high resolution photo?

Frank

I found a higher resolution picture and a pdf that explains a little about this military lab.
http://www.wpafb.af.mil/shared/media/document/AFD-150707-006.pdf (http://www.wpafb.af.mil/shared/media/document/AFD-150707-006.pdf)
Page 9 of the PDF
It seems like money is no limitation factor for this lab.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 24, 2015, 10:39:50 am
Well, they still use LHe cooled PJVS (~300k$), not standalone cryocooled version (~400K$), so money are a little factor  :box: >:D
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 24, 2015, 11:09:17 am
Well, they still use LHe cooled PJVS (~300k$), not standalone cryocooled version (~400K$), so money are a little factor  :box: >:D


In any case you'll need liquid He(4) @ 4.2K for these Josephson arrays.

In this picture, a commercial transportable dewar vessel (50 or 100l of liq. He4) is on display.
This lasts for a few weeks, until the He4 has evaporated.
Then you need to order a fresh vessel, and then transfer the PJVS over room temperature from the old vessel to the new one.

That's always a temperature shock, but modern array chips are assumed to be more ruggedized.

There also exist He4 circulation refrigerators, which only require an initial reservoir of liq-He4, and then may operate without further service.. that's probably what you meant.

You are not depending on the delivery of new vessels, and theoretically never have to remove the PJVS from the 4.2K environment.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 24, 2015, 11:14:02 am
No, i meant cryocoolers, some of which NIST used to go for 4K. JJA die does not generate lot of heat, so multistage cryopumps working on Stirling effect are suitable to do the job, I'd expect.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 24, 2015, 11:19:30 am
No, i meant cryocoolers, some of which NIST used to go for 4K. JJA die does not generate lot of heat, so multistage cryopumps working on Stirling effect are suitable to do the job, I'd expect.

Yeah, that's clear. But these cryo-coolers also operate with liquid He4, what else?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 24, 2015, 11:28:53 am
They don't need liquid He supply, only gas, which supplied by He compressor, forming closed loop.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on November 24, 2015, 01:56:15 pm
Such big labs usally have a supply of liquid He anyway - some even have there own recycling system. Still it is expensive to operate. Usually on can refill the cryostat with new Helium. So there is no need to warm up the setup so often. Transfering liquid He from one container to another is not simple, but it works with well insulated tubes. 

With liquid He one usually can get very stable temperature and no problem with a power outage.  The cryocooler also needs quite some electricity and maybe service every few years. The cooler may also produce extra noise.

An interesting question would be if one could get away with liquid nitrogen and high temperature superconductors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 24, 2015, 06:17:54 pm
Such big labs usally have a supply of liquid He anyway - some even have there own recycling system. Still it is expensive to operate. Usually on can refill the cryostat with new Helium. So there is no need to warm up the setup so often. Transfering liquid He from one container to another is not simple, but it works with well insulated tubes. 

With liquid He one usually can get very stable temperature and no problem with a power outage.  The cryocooler also needs quite some electricity and maybe service every few years. The cooler may also produce extra noise.

An interesting question would be if one could get away with liquid nitrogen and high temperature superconductors.

Well, on the picture from this AF lab, and also at the PTB, you'll see the standard transport He4 dewars, like from Air Liquide, Linde or in the past from Messer-Griessheim.
These have one standard flange for He4 transfer only, but this usually is used to stick the probe holder inside.

If they would use a stationary Dewar, like from Oxford-Instruments, these would have separate probe and He transfer flanges, and a refill would be  possible.

But it seems easier and cheaper to transfer the probe holder, instead.

At KfA Jülich they already demonstrated a Josephson standard with High Tc superconductors, an array with YBCO @ 77K, as far as I remember.
This was ok for about 1E-7.. 1E-8 uncertainty.
At these high temperatures, and with these amorphous superconductor structures, the Shapiro steps were sort of washed out, or the noise was too high, I don't remember that quite well.

So currently no option, also SQUIDs on HTcSC is still mediocre.

Frank

PS.: Here's the title of this paper:
"DC Voltage Calibrator Based on an Array of High-Temperature Superconductor Josephson Junctions
Alexander M. Klushin, Alexander V. Komkov, Valentina D. Gelikonova, Solomon I. Borovitskii, and M. Siegel"

Biggest problem with these materials still is, that monocrystalline films and structuring is not possible like Nb based SC.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ltz2000 on November 25, 2015, 05:54:31 pm
The immunity against small changes in power supply voltage of the LTZ1000 basic datasheet circuit is "good enough". But has anyone here actually tried / succeeded to measure the output [ppm] / input [V] relation?
Title: Re: Ultra Precision Reference LTZ1000
Post by: wiss on November 27, 2015, 02:09:41 pm
Such big labs usally have a supply of liquid He anyway - some even have there own recycling system. Still it is expensive to operate. Usually on can refill the cryostat with new Helium. So there is no need to warm up the setup so often. Transfering liquid He from one container to another is not simple, but it works with well insulated tubes. 

With liquid He one usually can get very stable temperature and no problem with a power outage.  The cryocooler also needs quite some electricity and maybe service every few years. The cooler may also produce extra noise.

An interesting question would be if one could get away with liquid nitrogen and high temperature superconductors.

I think these might be interesting.

A.M. Klushin, L.E. Amatuni, E. Sodtke, W. Prusseit, S.I. Borovitskii, V.D.
Gelikonova, and K.A. Ai. Development and investigation of shunted ybco
bicrystal josephson junction arrays for voltage standard. In Precision Electromagnetic
Measurements Digest, 1996 Conference on, pages SUPL13–SUPL14,
June 1996.

A.M. Klushin, M. He, and A.S. Katkov. Constant-voltage steps at 0.1 volt
from a series array of high-tc josephson junctions. In Precision Electromagnetic
Measurements Digest, 2008. CPEM 2008. Conference on, pages 104–105,
June 2008.

S.K. Khorshev, A.I. Pashkovskii, S.M. Goryunov, N.V. Rogozhkina, Yu.M.
Gryasnov, E.E. Pestov, and A.M. Klushin. Towards a voltage standard based
on an array of high-temperature josephson junctions. In Precision Electromagnetic
Measurements (CPEM 2014), 2014 Conference on, pages 126–127,
Aug 2014.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 27, 2015, 09:14:12 pm
The immunity against small changes in power supply voltage of the LTZ1000 basic datasheet circuit is "good enough". But has anyone here actually tried / succeeded to measure the output [ppm] / input [V] relation?

Hello,

I did a measurement when I built my LTZ1000.
But it is with a input voltage regulator of around 14V.
The power-supply was relative noisy. (Thyristor pre-regulated supply).
So it is not clear if the effects in drop out are due to EMI or heating effects.
I really should repeat the measurement with a better supply.

All in all I have 3uV after 2:1 divider or 6uV @ 7V change over the whole input voltage range of 12-18V

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on December 05, 2015, 12:14:11 pm
Assembled 4 boards with LTZ1000. For testing I used 25ppm resistors. but soon will be replaced by PWW.
LTZ1000 has been aged in oven for three weeks at 125°C. After PWW will be placed I will cycle it according to John Pickering.
All 4 units I would like to put into one box (similar to which use e.g wekomm use for their resistance standards).
I'm impressed how stable it is on table with 25ppm resistors, temperature of reference is 12k/1k so about 40-45°C.

Time to change Yageo metal film MF0 resistors [25ppm/K] used for basic testing with quality PWW from Edwin.
12k/1k for temperature settings (20°C above ambient temperature ~ 45°C) and 100k for Q1 and Q2 to minimize current for long term lowest drift.
According to initial measurement all resistor except one were far below 0,1% initial accuracy (average about 0.04%)
So I will make poor man tempco measurement (50°C and 10°C) prior assembling resistor to LTZ board.
1k/12k resistor will be close together on board coupled by copper tape to improve their temperature tracking.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 05, 2015, 12:48:33 pm
So I will make poor man tempco measurement (50°C and 10°C) prior assembling resistor to LTZ board.
1k/12k resistor will be close together on board coupled by copper tape to improve their temperature tracking.

Dont forget the room temperature. According to my measurements many of Edwins PWW resistors have a parabolic shape with flat T.C. near room temperature.
I guess that copper tape will not be necessary (at least if you have a metal housing for the whole cirquit). Most of the heat transfer is through the wires.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 16, 2015, 03:43:23 pm
I don't have VHD200, but I have pair of Z202 10Ks and VPG's custom hermetic (likely VHP101-based) 10Ks network (3-pins), which I can test, but it would take some time.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ltz2000 on December 16, 2015, 04:02:59 pm
PCB slots revisited (Keysight 34470A)

https://youtu.be/_QpApuKdcqQ

from 15:30
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on December 16, 2015, 05:37:02 pm
>>> Does anyone have a clue about the TCR

Edwin has mentioned the Vishay LT5400 networks a couple of times - 100 ppm (A grade) / 250 ppm (B grade) matching tolerance, 0.2ppm tracking TC. I'm planning to check these out in a  new design. Unfortunately, duh, I didn't notice (below) that they have a central pad, and I dual-foot-printed them with standard 1206 networks for testing purposes. That's not going to work unless I fiddle something in with some kapton tape, so I may be waiting for another spin from the pcb fairies...however they do sound promising. Clearly there's a question there about the impact of the reflow / soldering heat.

(http://anagram.net/nuts/Misc/Images/LT5400%20dual%20footprint.JPG)

Alan
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 16, 2015, 05:40:48 pm
I have few of those too. I can toss all into metal can and cycle all from 20? to 60? , measuring by scanner in 2002, if that is what you looking for.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on December 16, 2015, 05:45:12 pm
That would be pretty interesting if you have the time.

A.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 16, 2015, 05:55:52 pm
What is that, time?
Ok, will do on weekend then.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on December 16, 2015, 06:26:45 pm
To Butterfly,

Basically, the TCR / tracking TCR of a resistor is very stable over time and temperature, however external factors can and do influence the actual results.  In the case of tracking TCR, a major factor is how good the thermal coupling is between resistors, all else aside, the tracking TCR can be as low as under 0.2PPM/°C.  Differences in power loads will affect tracking as well, especially when attempting fractional PPM tracking, thermal coupling does help iron out the difference.  Linear Tech's LT5400 has very good tracking TCR but as the resistors are quite small, soldering temperatures are dangerous.  The 'A' grade which has the better specs may or may not cost more than equivalent PWW resistors and note that the resistors are all the same value on the chip, limiting your options for ratios.  Their absolute TCRs are not that good, only the ratio mode TCR are very low.

In many cases, the tracking TCR as specified is done under the most favorable conditions to achieve best performance specs, under real world conditions, that level of performance is not likely to be matched.  In critical performance, it it often a question of trial and error to find the best possible performance under the required conditions.  Depending on the application's actual parameters, a great set of resistor specifications on paper may not be possible.

Anytime performance is expected to be in the low PPM to sub-PPM area, you must expect that otherwise ignored conditions are going to jump up and bite you in the keester, every little thing you could get away with ignoring at higher PPM levels are now going to be demanding attention.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on December 16, 2015, 08:02:04 pm
Thanks for that Edwin - do you have any thoughts on how these should be soldered given they're smd parts?

TIA, Alan
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on December 16, 2015, 08:05:25 pm
Just the usual warnings, solder as quickly as possible, lowest possible wattage iron that gets the job done, ect.  Even a poor heatsink is better than nothing if possible.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on December 16, 2015, 11:26:25 pm
Well I was imagining a custom made heatsink but then I noticed this...

(http://anagram.net/nuts/misc/LT5400%20footprint.JPG)

... which kind of suggests reflow including the central pad? The central pad is apparently floating - so maybe it's there to reduce thermal variations over the die, rather than noise, and doesn't in fact need to be soldered down?

A.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on December 16, 2015, 11:44:38 pm
Unless there is an actual window with metal in it under the package, then no there is no soldering necessary, for that matter the pad may have little effect on heat sinking but it certainly won't hurt to have it there.  Note the exposed die pad option.....so I don't think there is any exposed pad on the MSOP package to solder to on the standard package.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on December 17, 2015, 12:58:20 am
After looking at the LT5400 data sheet, there is a bonding pad on the bottom of the package and this does need to be attached to a pad on the PCB for best thermal considerations.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on December 17, 2015, 07:32:21 am
Quote
After looking at the LT5400 data sheet, there is a bonding pad on the bottom of the package and this does need to be attached to a pad on the PCB for best thermal considerations.

Really? What kind of datasheet do you have? I can't see anything you mentioned in the datasheet.

However, it's all written within the datasheet:

Where to Connect the Exposed Pad

The exposed pad is not DC connected to any resistor terminal. Its main purpose is to reduce the internal temperature rise when the application calls for large amounts of dissipated power in the resistors. The exposed pad can be tied to any voltage (such as ground) as long as the absolute maximum ratings are observed.
There is capacitive coupling between the resistors and the exposed pad, as specified in the Electrical Characteristics table. To avoid interference, do not tie the exposed pad to noisy signals or noisy grounds.
Connecting the exposed pad to a quiet AC ground is recommended as it acts as an AC shield and reduces the amount of resistor-resistor capacitance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on December 17, 2015, 05:03:11 pm
I do not understand, the pad on the bottom of the LT5400 is a thermal heat sink to be attached to a pad on the PCB as it is said in the data sheet and in your own statement, where is the problem?

"Its main purpose is to reduce the internal temperature rise when the application calls for large amounts of dissipated power in the resistors."  Just as I said.

Regards.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on December 17, 2015, 07:47:57 pm
Sure, for thermal issues but it's not a bonding pad whatsoever ;) And the exposed pad does need to be attached in special cases, not for normal use.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on December 17, 2015, 07:59:29 pm
Technically, but for best thermal performance at any level, the pad should be attached to the pad on the PCB, it helps spread the heat around a bit better than without it, but no you don't have to bond it to the PCB in all cases, that was not what I was saying, in my opinion it is better to bond it for all cases for best performance, even mW differences can make a difference.  I do not see any controversy here, perhaps splitting hairs but that is all.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 20, 2015, 01:42:30 pm
Hello,

Santa left some goodies for christmas:

Guess it could be to place a LTZ1000/LTZ1000A on it.
Either with Z201 or PWW resistors.
Alternatively a LT1013A or two LTC2057

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 20, 2015, 01:50:42 pm
LTZ1047B? Huh :)
That's a most bizzare wierd layout I saw for LTZ circuit. No voodoo magic, virgin nude cutouts and shields? How come?
Looking forward for some tests  >:D
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 20, 2015, 01:58:19 pm
Hello,

sorry to dissapoint you:
there is some shield intended to place around the LTZ

http://www.reichelt.de/Teko-Steel-Plate-Enclosures/TEKO-3710/3/index.html?ACTION=3&GROUPID=5202&ARTICLE=34042&SEARCH=teko%203710&OFFSET=16&WKID=0& (http://www.reichelt.de/Teko-Steel-Plate-Enclosures/TEKO-3710/3/index.html?ACTION=3&GROUPID=5202&ARTICLE=34042&SEARCH=teko%203710&OFFSET=16&WKID=0&)

And LTZ1047B is only the working title for the layout.
(Revision B of a older version started in 2010 week 47)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 20, 2015, 02:01:25 pm
The two OPs at the standard LTZ1000 circuit are not that critical with respect to drift - the transistors allready add some gain.

The transitor for the voltage output might be prone to oscillation. I think the LT1013 is perfectly Ok here - it seems to be stable with the extra gain.  If looking for a different OP, I would consider one with external compensation or an added compensation in the circuit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 20, 2015, 02:12:45 pm
Hello,

the cirquit is very close to the one on page 15 of this thread:
so I have already external compensation.
And a additional FET for the current power stage to
reduce the necessary amplification of the current loop.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 21, 2015, 07:13:52 pm
Hello,

SMD parts are mounted on soldering side.
(example with LTC2057 as OP).

And some hours later low profile parts on component side.
(example with LT1013A except for output buffer)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 22, 2015, 10:36:51 pm
Hello,

carefully soldering the precision resistors.
(cooling by a "helping hand" with aligator clips during soldering).

First PCB done for the critical resistors.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on December 22, 2015, 11:14:37 pm
DB25?  :-//
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 23, 2015, 02:55:00 am
What will be going on with large empty area at side?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 23, 2015, 06:03:46 am
Hello,

DB25?

I like D-SUB connectors: they are cheap, have golden contact surface, and neighboured contact pins have low thermal differences (=EMF) (also because of the metal shell around the contact area).
So I have the unbuffered LTZ-voltage and the NTC outputs and the power supplies on the DB25 connector.
Perhaps I will have later a 7 to 10 volt translation cirquit attatched to this connector.
see also similar cirquit diagram:
https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg249123/#msg249123 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg249123/#msg249123)

What will be going on with large empty area at side?

The batteries (12 NIMH cells) see picture on page 17:
https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg250759/#msg250759 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg250759/#msg250759)

The whole is put into a compact aluminium case.

The design is not really different from the previous design. (only a revision).
The main difference is the buffered output on the 4 mm banana jacks,
and the possibility to use different precision resistor types + OP-Amps.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Alex Nikitin on December 23, 2015, 09:09:42 am
I am planning to build LTZ1000 reference on the AD5791 Evaluation board (http://www.analog.com/en/design-center/evaluation-hardware-and-software/evaluation-boards-kits/EVAL-AD5791.html#eb-overview).  I'll be using LTZ1000 plain, non-"A" version and somewhat changed resistors values (87K in place of 70K and 100 Ohm in place of 120 Ohm), plus I'll lower the IC temperature by changing the divider values in the regulator. Any comments on changing these resistors values or experience with that particular board layout?

Cheers

Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: acbern on December 23, 2015, 09:22:22 am
Hello,
I like D-SUB connectors: they are cheap, have golden contact surface, and neighboured contact pins have low thermal differences (=EMF) (also because of the metal shell around the contact area).

D-Subs are perfectly fine, they are closed (no air flow) and have a surrounding metal case ensuring low thermal differences. Datron also used it on its rear panel inputs on the 1281 DMM.
As a general remark, the EMF issue often seems to be overestimated here with lots of approaches fighting it (frankly, sometimes reminds me a little on certain high end audio type theological  discussions). I have actually not seen any considerable differences once equilibrium has been reached after connecting metals, at least not on the level we are talking here (say 0.1ppm/1uV, things change when we talk nanovolt).
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on December 23, 2015, 09:56:18 am
I am planning to build LTZ1000 reference on the AD5791 Evaluation board (http://www.analog.com/en/design-center/evaluation-hardware-and-software/evaluation-boards-kits/EVAL-AD5791.html#eb-overview).  I'll be using LTZ1000 plain, non-"A" version and somewhat changed resistors values (87K in place of 70K and 100 Ohm in place of 120 Ohm), plus I'll lower the IC temperature by changing the divider values in the regulator. Any comments on changing these resistors values or experience with that particular board layout?

Cheers

Alex

I have build my 4x LTZ1000 with focus on minimal long term drift. Based on recommendation from Bob Dobkin R2/R3 is 100k, die temperature to 45°C (12k/1k). For zener current change from 5mA to 7,2 mA I have no opinion. Like Ken mentioned LTFU is using higher zener current (20mA) and according to Bob LTZ1000 max zener current can be increased to 20mA.
But who know the long term and stability effects? Layout comparison between LTZ1000 and LTZFU can give us some hint, maybe.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 23, 2015, 10:46:23 am

I have build my 4x LTZ1000 with focus on minimal long term drift. Based on recommendation from Bob Dobkin R2/R3 is 100k, die temperature to 45°C (12k/1k). For zener current change from 5mA to 7,2 mA I have no opinion.

With 12K/1K + higher zener current the temperature controller will fall out of regulation at a lower temperature.
(this will limit environment temperature range further).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 23, 2015, 11:02:28 am
Also higher current does help for lower noise but for long-term stability it's opposite (similar to aging, faster happening with high current and/or temperature). So you may want actually lower current and lower temperature, to get better long-term perf. Also if hysteresis not a problem for you, it worth to think about keeping references OFF until you need them.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Alex Nikitin on December 23, 2015, 11:48:44 am

I have build my 4x LTZ1000 with focus on minimal long term drift. Based on recommendation from Bob Dobkin R2/R3 is 100k, die temperature to 45°C (12k/1k). For zener current change from 5mA to 7,2 mA I have no opinion.

With 12K/1K + higher zener current the temperature controller will fall out of regulation at a lower temperature.
(this will limit environment temperature range further).

With best regards

Andreas

Hi Andreas, reducing the zener current sensing resistor from 120 to 100 Ohm would increase the current from 5 to 6mA. It is just I have already some 100 ohm Bulk Foil resistors, that is all. Also I use "non-A" version so the additional 7.5mW dissipation should not be a problem. If required I'll just increase the temperature a bit. I may use a metal can LM35 to accurately measure the case temperature of the LTZ1000.

Cheers

Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 23, 2015, 12:28:59 pm
There is no real need to measure the case temperature of the LTZ1000. The important part is the inside temperature. To see if the thermostat is still in the active region, just look at the heater output - if this goes to zero, or very close regulation is lost. At the very low power end the regulation may not work so good and could need some help to compensate the square law for the power from a resistor.

If you want to measure temperature, the more imortant one in likely that of the resistors.

The change from 70 K to 87 K will also give a slightly lower temperature (e.g. 5 K). Otherwise this change should not be that important. Changing the resistor ratio (e.g. 12K/1 K ) to set the temperature will also change the TC a little bit - the transistors TC of U_BE is smaller (less negative) at a higher voltage used to set a lower temperature. So the overall TC will be slightly more positive. Depending on the unit this might be positive or not.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 23, 2015, 03:13:19 pm
Quote
There is no real need to measure the case temperature of the LTZ1000
+1, it's will not even indicate correct relative temperature. I tested before with 50C and 75C setpoints, difference on case was only ~11C (readout by Fluke Ti32 on black matte tape on top of LTZ can).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Alex Nikitin on December 23, 2015, 03:28:01 pm
Quote
There is no real need to measure the case temperature of the LTZ1000
+1, it's will not even indicate correct relative temperature. I tested before with 50C and 75C setpoints, difference on case was only ~11C (readout by Fluke Ti32 on black matte tape on top of LTZ can).

Was it on LTZ1000 or LTZ1000A?

Cheers

Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 23, 2015, 03:32:39 pm
ACH.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Alex Nikitin on December 23, 2015, 03:49:28 pm
ACH.

OK, thanks. That is hardly surprising as the thermal resistance on the "A" version is five times more and you have to run it hotter to get the temperature to stabilize. I am not sure that an internal heater is such a great idea. The only real advantages compared to an external "oven" approach are a quick start-up time and cost?

Cheers

Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 23, 2015, 04:10:46 pm
I am not sure that an internal heater is such a great idea.

Hello,

I am very shure that the LTZ _lives_ from the internal heater.
The zener cirquit has a raw TC of 50 ppm/K.
So the oven needs a stability of 0.001 K for the 0.05 ppm/K specced for the LTZ.
With a external oven you would need a much more stable zener with a "zero TC".

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 23, 2015, 04:10:54 pm
Internal heater allows way smaller power and better accuracy, as you need to keep only die temperature constant. OCXO is a good example of external heater design, at best, yet still bulky and power hungry beasts.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Alex Nikitin on December 23, 2015, 04:38:54 pm
I am not sure that an internal heater is such a great idea.

Hello,

I am very shure that the LTZ _lives_ from the internal heater.
The zener cirquit has a raw TC of 50 ppm/K.
So the oven needs a stability of 0.001 K for the 0.05 ppm/K specced for the LTZ.
With a external oven you would need a much more stable zener with a "zero TC".

With best regards

Andreas

Hmm, the Fluke 732B uses that approach, with a low tempco reference and an external oven, isn't it? I have achieved <1ppm/K tempco on my JVR with a metal can FET and wire-wound Ultrohm resistors and plan to use an external oven approach so I could test the long-term stability (so far it did drift less than 2ppm over 700 hours powered up and measured at the same temperature). I plan to run it against the LTZ1000 as my Fluke 731 has a noticeable (~1.5ppm/K) temperature drift (thought the long-term stability seems to be excellent).

Cheers

Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 23, 2015, 04:50:41 pm
An external heater usually requires more power and one might have difficulties to bring down temperature differences as well. The slower system also makes low drift analog control more difficult. On the up side the slower system smooths out fast variation - however the Zener referene has quite some 1/f noise anyway, so not a problem here. Also other parts like resistors could be kept at temperature to.

A large heat source in an instrument makes life hard for the rest of the circuit.

Even with an internal heater, there is still the option to add a second layer of temperature control, e.g. for the whole circuit. Though you would usually still keep the internal heat for the internal temperature. But there usually is no option for an internal heater if not allready there.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on December 23, 2015, 09:31:23 pm
Hi,

As a belt-and-braces kind of guy, I wonder whether all 3 together might work well.

I'm also wondering whether there might be a much more sophisticated approach to maintaining a constant thermal environment. I don't have all the pieces figured out in my head yet, but I'm thinking the level of sophistication of a good filter design (but in the thermal domain) where the 'input signal' is the lab temperature environment and the objective is v low pass filter giving near 'thermal DC'. As EE-types, we have a tendency to bodge a bit of arbitrary plastic / foam / copper foil around a voltage ref and call it a day. But I'm imagining a modelled thermal environment with 3D printed / CNCed / lasercut materials chosen with the right characteristics to maintain optimum minimal temperature variation with fairly low power. A basic start would be say picking a temperature for the outside of the ref (maybe halfway from the die temp to max ambient) and designing the right thermal environment with some sort of iso-thermal case surrounding the key electronics - and then that surrounded by the right insulation to get the appropriate thermal heat flow out together with a means of targeting the temperature of the iso-thermal case. Am I making any sense?

Alan
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 23, 2015, 11:15:26 pm
Hello,

next step:

All the high profile through hole parts.

1st PCB with LT1013A in CERDIP hermetically case.
2nd PCB populated with 2 choppers instead.
So only the LTZ1000A is missing.

Mmh, shall I populate it immediately?
Perhaps its better to check the new design with a "crash test dummy".
A 6V2 zener and a small signal transistor would give a
appropriate load to test at least the current regulator.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on December 24, 2015, 04:10:16 am
The power required to maintain the temperature equilibrium, i.e. just to compensate the leaks, is : P=S.Lambda.Delta_T, which is roughly (0.05*0.05)*6*0.04*(50-20) = 0.018W. It's not that bad :)

18mW isn't bad if you have 1m thick insulation but if it's only 1cm you're looking at 1.8W. Though you probably don't need 50mm height - 10mm should be enough. And improving the insulation using, for example 20mm thick aerogel (.014W/m/K), would reduce power requirements somewhat - 200mW may be achievable.

[Edit] corrected aerogel thermal conductivity from .14 to .014W/m/K
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 24, 2015, 10:47:49 am
A good thermal isolation is a two sided thing: The circuit inside will produce some heat, and this heat will give a minimum temperature rise above the enviroment. So the better the insulation, the higher will the minimum temperature be. The same happens to the LTZ1000: the A Version has higher internal thermal resistance and thus a high minimal set temperatur to work.

There is a minimal difference from enviroment to internal temperature with the LTZ1000 - so the outer box temperature temperature should be choosen just low enough for the inner heater to work. You don't want much extra power from the internal heater to heat up your outer oven. Also one should keep out all heat sources that don't have to be on the inside (e.g. the driving transistor for the heater, possible current buffering transitor for the output). Only than one can add isolation to the point to keep the power requirement low. Normally you have to consider something like 4 times the power of the internal circuit for the heater, so you have some room to go up and down in power.

One difficult with the outer temperature regulation might be that the time constant is rather long so the regulator needs to include long time constants ( > minutes) - this migh be difficult analog and require a digital (e.g. µC) control. Also to keep the innertemperature as low as possible one might consider a controlled fan if the ambinet temperature is rather high. It might be an interesting option but I think this is something for a different thread.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Alex Nikitin on December 25, 2015, 12:30:32 am
Christmas presents  ;) !

Cheers

Alex

(http://www.ant-audio.co.uk/Service/Ref/LTZ_01.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on December 25, 2015, 04:25:12 am

I have build my 4x LTZ1000 with focus on minimal long term drift. Based on recommendation from Bob Dobkin R2/R3 is 100k, die temperature to 45°C (12k/1k). For zener current change from 5mA to 7,2 mA I have no opinion.


Hi Andreas, reducing the zener current sensing resistor from 120 to 100 Ohm would increase the current from 5 to 6mA. It is just I have already some 100 ohm Bulk Foil resistors, that is all. Also I use "non-A" version so the additional 7.5mW dissipation should not be a problem. If required I'll just increase the temperature a bit. I may use a metal can LM35 to accurately measure the case temperature of the LTZ1000.

Curious where these current numbers are coming from. I thought the datasheet values result in ~4mA, not 5.  Even taking into account the Vbe rise from reduced temperature, I'd still think 100R is around 5ma.  (This is consistent with measurements I have made of my own LTZ1000, too.)

Remember that the datasheet lists +-10C temperature variation! So 12k:1k isn't reliably 45C (unless you've measured your own unit to be sure, of course.)

Measuring the temperature coefficients of mine is something I did this holiday, and I had a bit of trouble with it.  (I need a proper climate-controlled box...) I got -2.57mV/C for Q1, -2.1mV/C for Q2, 5.5C self heating (4mA zener current, non-A version, not quite in free air) and 55ppm/C for the reference voltage.  Is that consistent with other people's measurements? My gut is that I got the TC of Q1 off by about 10%.  I was using Pin4 as the die thermometer, so if the other numbers seem off by 10% it would be confirmation of my suspicion.
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on December 25, 2015, 09:35:16 am
Christmas presents  ;) !

Cheers

Alex

(http://www.ant-audio.co.uk/Service/Ref/LTZ_01.jpg)
Santa has pretty recent LTZ1000:) What resistor you are going to use?

Remember that the datasheet lists +-10C temperature variation! So 12k:1k isn't reliably 45C (unless you've measured your own unit to be sure, of course.)
I measured 4x LTZ1000 and difference between them was 2K, of course you needs to measure Vbe. All are in region 42-44°C with 12k/1k.

I did not measure self heating but I'm curious to measure it, maybe I will buy another LTZ1000 to measure self heating for 4mA to 16mA zener current.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Alex Nikitin on December 25, 2015, 10:59:08 am
Santa has pretty recent LTZ1000:) What resistor you are going to use?

 Digikey Santa was very quick, I've ordered the chip on 22nd and received it on 24th! I've found some 110 Ohm W/W Ultrohm, may use that, or 100 Ohm Bulk Foil.

Cheers

Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 25, 2015, 03:13:17 pm
I got -2.57mV/C for Q1, -2.1mV/C for Q2, 5.5C self heating
...
so if the other numbers seem off by 10% it would be confirmation of my suspicion.

Hello,

how did you measure that?
Any switchmode power supply involved.
Long measurement lines?

The both bases are very sensitive to noise from environment.
I recommend battery supply + to put a capacitor between base + emitter of the temperature sensing transistor.
(on the current loop there is already the 22nF).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on December 25, 2015, 04:02:32 pm
I really enjoy this discussion of the great LTZ1000 Zener. Now it's my turn to contribute a few items.
I had a damaged LTZ1000A from 1995 so I opened it up. I was a little careless with the grinder and damage a few bond wires. Then I took the chip to a friend with a $60,000 microscope. He could rotate things so we could get a relatively clear side view of the chip and it's attachment glue. The chip looks to be 15 mil thick (0.015 inches) and the glue is 5 mil. It's hard to measure the size of the insulating spheres in the glue but they look to be around 2.5-3 mil in diameter.

Thanks for all the great discussions!
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 25, 2015, 04:08:40 pm
Those are some great photos, thank you. Would be interesting to see similar ones for non-A in future as well.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dr.diesel on December 25, 2015, 04:53:53 pm
I really enjoy this discussion of the great LTZ1000 Zener. Now it's my turn to contribute a few items.

Thanks Chuck! 

Would love to see a LTFLU as well.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 25, 2015, 06:19:52 pm
Thanks for all the great discussions!

Hello Chuck,

beautiful pictures: thank you.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 25, 2015, 11:09:12 pm
Hello,

"first firing" of PCB #5 with LTC2057 and dummy zener. (connected with spring clips to the resistors).

Battery voltage:      UBat 16.98V
14V after LTC1763: U14  14.011V
current without dummy LTZ: 4.22mA
(expected value around 4.7mA for the 3 LTC2057 = 3*0.9mA + LTC1763 = 0.3mA + some resistors)

After connecting the LTZ simulator:
current with dummy LTZ: 10.96mA??? (expected around 8.9 mA)

Zener voltage    Uz: 6.9656 V
Buffered output UBuf: 6.9650 V
BF245C Gate:    UGate: 5.3052 V (from current regulator OP-Amp)
Voltage R1:        UR1:  0.5805V -> 4.84mA
Voltage R5:        UR5: 0.5464 * 13.5 = 7.38V???
Voltage R6:        UR6: 0.878V (should be the same as R5)
Voltage U2,Pin5:        1.6785V

Mhm: 2 fishy points:
 
1. voltage drop over R6.
This can be explained by a input protection cirquit of the LTC2057.
In datasheet there is a maximum differential input voltage specced from +/-6V
(clamp cirquit over the inputs).
So obviously the Setpoint divider (12K5/1K) gets some current from the 70K pull-up resistor
across the inputs of the LTC2057 because the temperature sensing transistor is missing.
-> this should be no issue when the temperature regulator is working.

2. where comes the excess current from:
Will have to oscilloscope the current regulator loop.

CHA (blue) ON-signal from function generator 2Hz 20% duty.
CHB (red)  current (as voltage over R1 = 120R)
CHC (green) 14V regulated voltage LTC1763

The current over R1 looks nearly perfect.
Relative low overshoot when switching on. (max 650mV = 5.4mA around 12%)
The LTC2057 regulates dammned fast to the final value.
I remember that this was much more with the LT1013 of my previous design.
Flat behaviour in "ON" state.
Only during drop-out near 8V supply when switching off/on some small oscillations.

Strange: from where does the excess current come from?

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on December 26, 2015, 12:06:55 am
V interesting pics of A version. Does anyone have any ideas what the unused bonding points are used for? Would it be possible to connect to them? Would this be interesting?

A.
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on December 26, 2015, 12:17:08 am
V interesting pics of A version. Does anyone have any ideas what the unused bonding points are used for? Would it be possible to connect to them? Would this be interesting?

A.

They are for two inner heater elements. It has been discussed here while ago when I posted  images from TiN damaged LTZ1000ACH.
https://doc.xdevs.com/doc/xDevs.com/KX/Die_LTZ1000_small.jpg (https://doc.xdevs.com/doc/xDevs.com/KX/Die_LTZ1000_small.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on December 26, 2015, 12:36:56 am
Thanks, I see here:

https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/1260/ (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/1260/)

Still curious whether something interesting could be got from those connections?
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on December 26, 2015, 07:07:43 am
Thanks, I see here:
https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/1260/ (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/1260/)
Still curious whether something interesting could be got from those connections?

The chip similarities between the LTZ1000 and the LT1088 have always interested me. Attached is a scan from page 4 of App Note 22 in the 1990 LTC Linear Applications Handbook (this is why I never throw any data books away). The online LTC App Note 22 does not have good resolution for the photos. Both chips have concentric heaters. The LT1088 has 50 ohm and 250 ohm heater rings. It also looks like there are two groups of 4 paralleled transistors in the middle along with a strange circular feature. Has anyone put a (now obsolete) LT1088 chip under a microscope? I will upload higher resolution files (12MB) of this page to TiN's ftp site.

If anyone wants to donate an LT1088 or a LTZ1000 non A chip for microscope analysis, I can see about getting some pictures taken. I just got 10 LTZ1000 chips from Digikey but I don't feel like destroying a working part.

 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 26, 2015, 01:35:34 pm
Hello,

got it:

OP-Amp output of Current regulator is oscillating.
But obviously this cannot be seen on the current shunt resistor (120 R).

CHA (blue) ON-signal from function generator 2Hz 20% duty.
CHB (red)  current (as voltage over R1 = 120R)
CHC (green) 14V regulated voltage LTC1763
CHD (yellow) gate of BF245C/PIN1 of U2

When zooming into the interesting part: 400mV amplitude and 460kHz.
-> the LTC2057 is really fast.

First try: remove the EMI capacitor C15 which I added for the LT1013
into the cirquit to enhance the behavior when a switchmode charger is connected.
-> it works
A manual try of different capacitors between 1 nF and 1uF shows that the cirquit
oscillates with all values. So the LTC2057 is not usable for this kind of EMC-hardening.
-> to avoid problems with the heater cirquit also C14 has to be removed.

After changes:
the cirquit works under all tested conditions.
Only small oscillations or overshoots when running out of or into drop out mode (around 8V supply).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on December 27, 2015, 02:53:48 pm
@EmmanuelFaure

Hi, sorry to be slow replying - xmas stuff plus I was reading the article and thinking your post over. Thanks for the calculations and the link.

>>> The power required to maintain the temperature equilibrium, i.e. just to compensate the leaks, is : P=S.Lambda.Delta_T, which is roughly (0.05*0.05)*6*0.04*(50-20) = 0.018W. It's not that bad :)

A single LTZ1000A board dissipates ~560mW (26mA heater + 5mA ref @ 18V) at ~22C ambient, so that suggests less insulation is needed. (The LTZ case is ~40C in this case with the die at ~90C).

The article is interesting - pity it doesn't have any pictures. One good thought is that the thermal control needs to be inside the thermally-controlled environment.

>>> With some clever design you can integrate the heating resistor + controller directly on the pcb, and you save a lot of assembly work & trouble.

Good point.

>>> Filtering daily temperature variations would be quite impractical because it would require an enormous mass/volume of thermal mass and insulation. The best way is the active/feedback control method.

Agreed, so the thermal capacity should filter out the ambient thermal noise and the active feedback the daily and annual slow variation.

>>> The key to successful thermal filtering is a good insulation AND a good thermal capacity.

So if some typical lab thermal noise was measured, that should let us calculate the required thermal capacity? This is similar-ish to a simple LP filter?

Is this the picture (below)?

I can't quite see the best way to get at the unknowns right now (target temperature for thermally controlled environment / heater power / etc). Is this a control theory problem or are there some rules-of-thumb?

Regards, Alan

(http://anagram.net/nuts/High%20Stability%20Voltage%20Ref/Images/Thermal-design-1.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on December 27, 2015, 06:11:53 pm
The power required to maintain the temperature equilibrium, i.e. just to compensate the leaks, is : P=S.Lambda.Delta_T, which is roughly (0.05*0.05)*6*0.04*(50-20) = 0.018W. It's not that bad :)
(Also @alanambrose)
That result looks fishy to me.  Dimensional analysis: m*m*(K*m*m/W)*K != W.  I think you mean to divide by 0.04: 11.25W. You can easily get better (and thicker!) insulation, like Foamular would be almost 20x better at its default 1" thickness so you're "only" looking at 700mW.

I am exploring an approach not unlike this, but I'm opting to cool the metal shell instead of heating it.  My goal is that the ref stays with +-10 of room temperature through the power cycle.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 27, 2015, 07:14:26 pm
The Power is caclulates as area * delta T * thermal conductivity / thickness of isulation. So with 20 degree temperature difference and 1 cm thickness, I get 1.2 W. That is not little, but also not that bad. Even 2 cm of isolation is not too much.

The power of the circuit inside should be kept small, as to keep the minimum temperature low or the maximum room temperature high. But even if the oven gets out of regulation at more than 30 C in the room this is still an improvent.

The critical part of the LTZ1000 circuit only needs about  6  mA at about 7.x volts plus the heater - this is 40-50 mW. In an controlled enviroment not much power for the heater is needed, maybe a similar amount at most - just to get some room for regulation.  Things like the OPs and especially the current driving transistor(s) should be better outside - also normal LTZ1000 circuits put the transistor that drives the heater and possible power resistors well away from the rest.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on December 27, 2015, 08:10:51 pm
The Power is caclulates as area * delta T * thermal conductivity / thickness of isulation. So with 20 degree temperature difference and 1 cm thickness, I get 1.2 W. That is not little, but also not that bad. Even 2 cm of isolation is not too much.
Ah, I'd guessed the 0.04 was an R-Value (so power=area*detlaT/R), but your correction makes more sense: 0.04 is awfully small for a 1cm polystyrene R-Value. I was certain something was up, though :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on December 27, 2015, 08:48:39 pm
OP-Amp output of Current regulator is oscillating.

First try: remove the EMI capacitor C15 which I added for the LT1013
-> to avoid problems with the heater cirquit also C14 has to be removed.

I also had trouble with oscillations using your circuit on voltnuts.  However, I opted to remove C12.  I didn't check for oscillation on the heater side, but I would think C13 would be better to remove than C14?  However, I'm using a LT1112 right now; I wanted to run without a chopper at first and then introduce the chopper to see how that affected output spectrum. 

(Just to make sure we're reference the same schematic: I have C11 from pin6 to pin7, C12 from pin4 to pin 7, C13 from OUT to IN- of the temp opamp, C14 from IN- to IN+ of the temp opamp, and C15 from IN- to IN+ of the current opamp)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 27, 2015, 09:15:45 pm
I also had trouble with oscillations using your circuit on voltnuts.  However, I opted to remove C12.  I didn't check for oscillation on the heater side, but I would think C13 would be better to remove than C14?  However, I'm using a LT1112 right now; I wanted to run without a chopper at first and then introduce the chopper to see how that affected output spectrum. 

(Just to make sure we're reference the same schematic: I have C11 from pin6 to pin7, C12 from pin4 to pin 7, C13 from OUT to IN- of the temp opamp, C14 from IN- to IN+ of the temp opamp, and C15 from IN- to IN+ of the current opamp)

Hello,

the current schematic is here:
https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=189655 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=189655)

unfortunately there is no preview of the PDF visible in my post of yesterday:
https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg829618/#msg829618 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/msg829618/#msg829618)
so the LTZ1047B.PDF is somewhat hidden.

C12 is uncritical for oscillations, as long as R19 (which is not in LT cirquit diagram) + C8 are populated.
C12 is at the most sensitive point of the cirquit so it supresses a lot of EMI effects.

The idea of C14, C15 is that a capacitor from OP-Amp GND-Pin to the negative input will always be critical for oscillations.
Between +/- pin normally the voltage is essential zero. So a capacitor is less critical for oscillations here.
(and with the capacitor from + pin to GND a series connection to GND is given against EMI.)
This works for the LT1013 in my cirquit. But it seems that faster OPs like the LTC2057 do not like this.

By the way: with a LT1112 you will need a negative supply rail for the OPs.
The common mode range is not sufficient for a single supply operation.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on December 27, 2015, 11:17:02 pm
C12 is uncritical for oscillations, as long as R19 (which is not in LT cirquit diagram) + C8 are populated.
C12 is at the most sensitive point of the cirquit so it supresses a lot of EMI effects.
Thanks for the pdf re-link, I had indeed missed it in the images. And I didn't have R19 + C8, so C12 was a problem.

Quote
As for C14,
The idea of C14, C15 is that a capacitor from OP-Amp GND-Pin to the negative input will always be critical for oscillations.
Between +/- pin normally the voltage is essential zero. So a capacitor is less critical for oscillations here.
(and with the capacitor from + pin to GND a series connection to GND is given against EMI.)
This works for the LT1013 in my cirquit. But it seems that faster OPs like the LTC2057 do not like this.
Hmm, my experience was that the temperature loop was the most sensitive to EMI, because it could reset the integrator and cause a temperature swing that took minutes to recover.  Something like C14 was how I addressed that issue.  I guess since you've put an integrator on the current loop as well, it could suffer from the same problem. I will have to play with this some more.

Quote
By the way: with a LT1112 you will need a negative supply rail for the OPs.
Yeah, I have pin7 raised by a diode drop relative to the LT1112 V-.  I wanted this anyway so I could buffer pin7.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 28, 2015, 06:01:53 am
Hmm, my experience was that the temperature loop was the most sensitive to EMI, because it could reset the integrator and cause a temperature swing that took minutes to recover.  Something like C14 was how I addressed that issue.  I guess since you've put an integrator on the current loop as well, it could suffer from the same problem. I will have to play with this some more.

Of course you are right. The base of the temperature sensing controller is even more sensitive.

But that was a thing that I fixed first, because I saw noise on  the heater voltage in the range of several mV without the capacitor on the Base pin of the temperature loop.
Actually the noise measured was around 6mV pp with sporadic dips of -40mV on a heater voltage of around 5.4V.
I could not imagine that this behaviour is good for a low noise reference.
So I adapted the capacitor from the datron reference cirquit.
With the capacitor the heater noise is reduced to around 0.6 mV pp. Without any dips.

On the current loop the integrator is needed for stability with capacitive loads like C9 (for EMI reason) of the (unbuffered) reference.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 28, 2015, 07:56:12 am
Hello,

first measurements on the 2nd sample LTZ#3 (with LT1013A instead of LTC2057)
with dummy zener. (no heater dummy cirquit).

Current without Zener 3.13 mA.        (around 3.6 mA expected)
Current with dummy zener 7.45 mA. (around 7.8 mA expected)

again the same channels.

CHA (blue) ON-signal from function generator 2Hz 20% duty.
CHB (red)  current (as voltage over R1 = 120R)
CHC (green) 14V regulated voltage LTC1763
CHD (yellow) gate of BF245C/PIN1 of U2

Even with C14+C15 mounted no oscillations on the gate of the FET.
But this time overshoot to around 800mV = 6.7 mA of zener current.
Also the zener voltage shows some overshoot  (CHC (green)  = zener voltage)
of around 240 mV up to 7.2V.
No oscillations on outputs (unbuffered + buffered zener) with decade
capacitors in the range of 1nF - 10uF as load.

Temperature setpoint voltage on R5 = 0.5158V * 13.5 = 6.9633V (the voltage of the dummy zener)
So with LT1013A there is no "cross current" from +/- inputs in case of open regulator loop.

So I will let the C14+C15 mounted for the LT1013A.

with best regards

Andreas




Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 29, 2015, 10:07:58 pm
Hello,

and now the money shot:
around $80 per square inch component cost within the "inner circle".

LTZ1000A is now on board.
So ready for further tests.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 30, 2015, 04:30:52 am
Let's see some ppm's.  ::)
Looking forward, making me desperate to find time to build few of my own...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 30, 2015, 06:20:49 am
Let's see some ppm's.  ::)
Looking forward, making me desperate to find time to build few of my own...

Keep calm,
before we can get into ppm´s I need to verify if all is running smooth.

LTZ1000A#5 (with all LTC2057)

First picture:
CHA (blue) 14V regulated voltage LTC1763
CHB (red)  current (as voltage over R1 = 120R)
CHC (green) voltage on base of heater transistor (J6 pin 12)
CHD (yellow) zener voltage (U1 pin 3)

Its amazing: only 200ms full heater current
Steady state reached after around 500 ms.

But whats that: the zener current (red) decreases with rising temperature.
(starting with 511mV down to 435mV).
Now its getting clear why HP uses a 111R resistor with the higher temperature setpoint.
Its just to compensate the reduced base emitter voltage at higher temperatures.

2nd picture
CHC (green) voltage on buffered output (J5 pin 1)
Obviously the chopper (LTC2057) has some startup delay.
I can live with that.

3rd picture
Start delay from "ON" signal
CHC (green) on signal (J5 pin 1)
around 17ms until the zener current rises.

4th picture like 1st with pwm signal on "On" signal

5th picture like 2nd with pwm signal on "on" signal
so sometimes the startup delay of the buffered output
adds some extra voltage on top.
Thats a bit annoying.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 30, 2015, 06:35:25 am
Hello,

and the same set of pictures for LTZ1000A#3
with LT1013A for the LTZ1000A and only the buffered output with LTC2057

1st + 2nd picture: obviously the heater makes a rest during startup when the zener current overshoots.
3rd picture: buffered output with startup delay of chopper.
4rth picture: around 16ms delay from on signal to zener current rising.
5th picture: heater reaction to pwm on on signal
6th picture: buffered output with pwm: in this case there is always annoying overshoot on the buffered output voltage.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on December 31, 2015, 03:57:31 pm
Attached are some measurement I gathered from a new LTZ1000 and an aged LTZ1000A. The chips were in an environmental chamber from -50 deg C to +150 deg. I have not seen the data altogether in one spot like this so I decided to post it. Testing details are in the last attachment.

The heater resistance and the Zener resistance both seem to have a 4000 ppm / deg temp co. So maybe the resistance is all from the aluminum traces on the die. The kelvin voltage sensing of the Zener voltage by the base of Q1 (at the center of the die) may remove the resistance of one of the Zener traces. The next step is to activate part of the chip to understand that.

With a passive chip the Zener voltage changes at high bias current because of chip heating. I will need to activate the heater to control chip temperature while checking voltage at higher currents (20ma).

Suggestions for other testing are welcome.

Title: Re: Ultra Precision Reference LTZ1000
Post by: ltz2000 on December 31, 2015, 05:02:15 pm
Attached are some measurement I gathered from a new LTZ1000 and an aged LTZ1000A.

Great contribution!

Suggestions for other testing are welcome.

Zener + Q1 from -50 to +150 and back. I know, not easy to do, requires a stable current source and another LTZ1000 to compare with...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 31, 2015, 07:49:04 pm
Hello chuckb,

thanks also from my side.
For me the zener voltage in a built up cirquit at around 50 deg C would be interesting.
And the Q1 base voltage with the standard cirquit. (120 Ohms / 70K)

I have just recorded some operation points on my 2 built up references.

What I am concerned about is that there is a large difference in Q1 base voltage
between your measured value at 100uA and my totally built up cirquit.

The Q2 base values at 50 deg C are about the same 530 vs 550 mV @ 100uA.
But the Q1 base values differ totally.
Around 440mV in the complete cirquit on my side. (resulting in 3.7mA zener current).
And around 580 mV on your measured value with base + collector shorted.
(but this should give around equal values).
So did you test the VBE voltage already in a complete cirquit?

To the measurements:
most of them are done with a 4.5 Digit multimeter which is around -0.13% off (shows too small numbers).
The values show that all regulation loops work as intended.
At a direct short cirquit at the buffered output the zener voltage changes by around -1mV. (ground line impedance).
Total current with short cirquit is 50 mA so short cirquit current at output is around 30mA (which corresponds to the typical LTC2057 datasheet value).

With best regards

Andreas




Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on December 31, 2015, 10:30:49 pm
Attached are some measurement I gathered from a new LTZ1000 and an aged LTZ1000A.
Thanks! nice to have someone else's (way better) data to compare against!  Since my previous post on measuring Q1 temp co, I tried again with a different approach and a lot more logging.  The number that fit my new data best was -2.22mV/C, but I know there's still error--I need a proper thermal chamber.  Your data, at 100uA from 25C to 0C gives -2.2mV/C; matches my new number very closely!
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on January 01, 2016, 04:44:46 am

What I am concerned about is that there is a large difference in Q1 base voltage
between your measured value at 100uA and my totally built up cirquit.

The Q2 base values at 50 deg C are about the same 530 vs 550 mV @ 100uA.
But the Q1 base values differ totally.
Around 440mV in the complete cirquit on my side. (resulting in 3.7mA zener current).
And around 580 mV on your measured value with base + collector shorted.
(but this should give around equal values).
So did you test the VBE voltage already in a complete cirquit?


When TiN check the LTZ1000 in his K2002 he had 60mv difference between the Vbe of the heater transistor and the current transistor.
https://www.eevblog.com/forum/testgear/keithley-2002-8-5-digit-dmm-review-and-teardown/msg482280/#msg482280 (https://www.eevblog.com/forum/testgear/keithley-2002-8-5-digit-dmm-review-and-teardown/msg482280/#msg482280)

I just checked 8 operational LTZ1000As running on a burn in pcb. The circuit is from the LTZ data sheet but the resistors are all cheap.
One had 30mV difference between the Vbe of the heater and the current control transistors. The current control voltage (Q1) is lower than the temperature sensor (Q2). This is just the opposite of what I measured in an environmental chamber when I just checked one component at a time. I will have to triple check my wiring and run it active.

Two LTZs on the burn in pcb had 60mV difference.
Three had 70 mV difference.
One had 100mV.
One had 110 mV.

So your difference of  90mV is in the middle of my distribution and similar to what Tin measured (60mV) on the K2002. 
Sorry my data caused you a concern but we will learn either I messed up or there is a very interesting thing going on inside the chip when it's active.
I'm leaving on a 10 day vacation in a few days so I may not get to much resolved in the next few weeks.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on January 01, 2016, 05:30:13 am
Well the setup wiring is ok so that leaves a strange operation of the chip.

The Vbe of Q1 is 20 mv greater than Q2 when they are all check by themselves. In a full, active circuit the Vbe of Q1 is 30-110mV below Q2. That's something to look into.

Have a great new year!

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 01, 2016, 06:48:25 am
Well the setup wiring is ok so that leaves a strange operation of the chip.

The Vbe of Q1 is 20 mv greater than Q2 when they are all check by themselves. In a full, active circuit the Vbe of Q1 is 30-110mV below Q2. That's something to look into.

Have a great new year!

Hello chuckb,

thanks for checking.
and also thanks for the link to TiNs measurement values.
He has also 440 mV on the current regulator inputs with slightly higher temperature setpoint.
Now I am confident that my cirquit is working as it should. (even with only 3.7 mA).

Together with the statement of Ken
it would explain that the Vbe on Q1 is higher than on Q2 with base + collector connected.


 The two transistors in the LTZ are *not* matched-- Q1's geometry is significantly smaller than Q2, and so much less current will be going through Q2 than the Zener when the operation point reaches equilibrium. 

So a possible explanation would be that the hfe of Q1 is significantly higher than that of Q2 for the active cirquit.
And the large stray of 50 mV from your samples in active cirquit could indicate that the hfe is very different between samples.

I think I should get a socket for LTZ1000A to check this. (too late for the current 2 references).

I wish you also a great new year!

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 01, 2016, 07:07:18 am
Happy volts everyone!
I'll be back home 3rd Jan, so I can do some more measurements, just let me know what exactly.

My plan is to build one module with socket and wirewound resistors to test my chips (three LTZ1000CHs from 1990 and one LTZ1000A from 3458A A9 board (with popcorn noise). I can also compare with my three older modules with VPG resistors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 01, 2016, 10:30:23 am
Hello,

the first ppm measurements. (TiN will have to wait until after his holydays)  >:D

The resistor sensitivity measurements are done by simply paralleling a 1% resistor to the existing 0.01% resistors to get at least around 10ppm Uz change.
The values are corresponding to the results of Lymex/Janaf with except of R3 which seems to have a larger stray and is somewhat higher in my case.
So I will have to keep a eye on this resistor.

As I got some requests, I will post more, but give me a couple of days.

Thanks for posting the Lymex data. If we multiply my data by 100, for 100ppm resistor changes we get:

-DatasheetLymexJanaf
R110.14-0.14
R20.30.4-0.4
R3 0.20.03-0.07
R4/R5 1.00.95+1.2

A couple of conclusions:
- It seems the R1 and R3 values are not as critical as given in the datasheet. Or both Lymex and I are wrong.
- Put your money on R4/R5 and R2 while R1 and R3 are less critical.

Thanks to Janaf I have selected the resistors in a manner that the more uncritical 70K resistors have the higher T.C.
And the R4/R5 resistors are paired with a maximum T.C. difference of 0.2ppm/K.

As a side effect I get the T.C. measurement of the unheated zener which is 53 or 56 ppm/K in my case.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 01, 2016, 11:06:28 am
The different size of the transistors does not mean a different amplification factor. It just means the smaller one needs less (emitter-) current to get the same U_BE voltage or at the (nearly) same current as in the normal circuit the smaller transistor has the higher U_BE.

The direction of change with the resitors changed should be the same in all cases.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 01, 2016, 02:30:45 pm
The different size of the transistors does not mean a different amplification factor. It just means the smaller one needs less (emitter-) current to get the same U_BE voltage
Hello,

That is exactly that what I wanted to say.
Smaller area gives larger Vbe voltage in the diode connected case.
(collector + base connected)

The different behaviour in the datasheet cirquit might be a matter of hfe.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 02, 2016, 07:00:47 am
Hello,

before mounting all the thermal isolation stuff and the inner shield I am doing preliminary 1/f noise tests.
I use a 4th order bandpass 0.1Hz-10Hz with 10000 fold amplification and a analog scope for this.

LTZ#3:
evaluation of 22 measurements 0.2uV/Div 1s/Div gives:

Average   1.097272727
Stddev     0.122146775
min           0.92
max           1.4  (outlier? all others below 1.26uVpp)

so this corresponds to the datasheet.
A typical sample with 1.08uVpp (img2244) attached.

LTZ#5

first also measured with 0.2uV/Div
but found that there is massive popcorn noise which exeeds the screen.

Average   1.325263158
Stddev     0.228297323
min          1
max         1.68  (= maximum screen heighth)

so did 2nd measurement with 0.5uV/Div

Average   1.206521739
Stddev     0.263052461
min          1
max         1.9

Pictures attached also (2268 + 2276 are with 0.2uV/Div / 2290 + 2295 with 0.5uV/Div)
one sample typical without popcorn noise the other with popcorn noise.

So now I have a problem:

Where does the popcorn noise come from.
Is it the LTZ
Or is it the LTC2057 perhaps together with the removed EMI capacitors?
This is the first LTZ1000 where I see this.
And it is the first time that I use no LT1013.

Any opinions or own measurement results for the LTZ?

With best regards

Andreas




Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 02, 2016, 07:09:59 am
What is your amplifier setup? I'd like to join for this too. Also even for preliminary test i'd recommend having everything in cookie metal can to avoid airflows. Those can also cause big jumps.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 02, 2016, 09:31:12 am
The modified circuit with all the extra caps is more sensitive to OP noise, at the higher frequencies. In principle this is good, as at higher frequencies the OPs noise should be lower that that of the reference itself.

However the low frequency part (e.g. < 10 Hz) is still controlled by the transistor from the LTZ1000, so even if the OP is producing such noise, the LTZ would suppress the noise quite a lot (up to about 200 fold) - this is also why the noise (and drift) of the OP is not critical in the original circuit.

My suggestion would be to try a slightly higher current (e.g. test with a resistor in parallel to the 120 Ohms) - the zener diode might work better at a different current.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on January 02, 2016, 09:47:42 am
@andreas, i have same "pop corn" problem before, and i didnt quite know the way to solve it.

i had so much of it when i did "wrong" stuff to my K2015. the 2 things in my case that gave the problem is SOT23 BJT, due to my poor soldering work (mechanical problem), the leads are stressed. if i tap on the SOT23 lightly with a insulator stick, it can trigger/reproduce the noise. the 2nd is temperature problem, when ever anything warm up over approx 41C, readings/log also show popping more often. it appears (or at least to me) when i tap around on parts i have soldered before, if it aid in the noise, it showed that i either did it wrong or the part is not good post soldering/warm-up, and that become my method of "checking". all the parts that show popping early or after warming, i threw away :( . maybe the problem in your case could be similar ? maybe some leads is accidently "supplied" some stress and need to resolder?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 02, 2016, 04:51:50 pm
Hello,

What is your amplifier setup? I'd like to join for this too. Also even for preliminary test i'd recommend having everything in cookie metal can to avoid airflows. Those can also cause big jumps.

Sorry, did not mention that. Have a look into my cookie box:
Without this you will have only 50Hz line frequency hum.
The noise amplifier in the background has its own aluminium case within the cookie box.
And also a thermal shielding of the pre-amplifier.
The LTZ carries its preliminary thermal shielding.
(also on the solder side of the PCB).
The setup actually shows heater noise voltage measurement.

Attached is the schematics of the filter amplifier.
The input electrolytics are selected for < 20uA nA leakage current.

Caution you cannot connect a unbuffered LTZ reference to the low impedant input,
which is necessary to get a low current noise of the input stage.
(this will degrade the LTZ/introduce a large hysteresis because the heater setpoint is set to infinite temperature).

So you have to remove the jumper when attaching the voltage reference.
After 1-2 minutes when the input capacitors are charged you have to install the jumper for the measurement.

You need a oscilloscope with 2mV/div (or at least 5mV/div) sensitivity with DC coupling if you want to measure a LTZ.
Otherwise you will need a further amplification stage.

My suggestion would be to try a slightly higher current (e.g. test with a resistor in parallel to the 120 Ohms) - the zener diode might work better at a different current.

I will try this (I have a UPF 1K resistor with 2 ppm/K)  but this would prove that the LTZ itself has a problem.
I fear that the popcorn noise is gone at the current working point and will re-appear at another. (eg over temperature).
So in this case I would opt to replace the LTZ.

it appears (or at least to me) when i tap around on parts i have soldered before, if it aid in the noise, it showed that i either did it wrong or the part is not good post soldering/warm-up, and that become my method of "checking". all the parts that show popping early or after warming, i threw away :( . maybe the problem in your case could be similar ?

Also a idea at least worth a try.
But it might be difficult to tap on parts in a cookie box.
I will look how I can manage that.

In the mean time I tried to measure the noise on the heater voltage (J6 pin 12 = base of heater transistor).
AC-coupling by a 10uF foil capacitor to the 1Meg input of the scope.
10 kHz bandwith limit on the oscilloscope.

LTZ3 has larger heater noise
than LTZ5 (the one with popcorn noise at the output).
But most of the noise is from the oscilloscope.

With best regards

Andreas

Edit: changed uA to nA

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 02, 2016, 05:22:38 pm
The base of the temperature controller is mainly reproducing the noise of the reference, there should be only minor traces coming from the temperature noise. The better place to look at temperature noise would be the output of the OP.

Just for noise testing even a more normal resistor would be OK to test a different current. Its allways the possiblity to have a certain current or temperature  the zener diode does not like. So it might be interesting to do a slow temperature ramp (e.g. 1 degree), while doing a longer noise measurement.

One could also do slight changes in current or temperature by changing R2 and R3 - these are the less critical ones. So this wold likely be the point where one could couple in the ramp. The collector of the current sensing transistor is changing at about 400 mV/K with an impedance of some 60-70 K. So something like a 1 M resistor to a 0-10 V ramp would result in a 1.6 K ramp.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on January 02, 2016, 11:48:04 pm
Andreas
I like your low noise amplifier design. Capacitive coupling of all the stages should make the overall design easier to operate.

Unstable capacitor leakage currents can look like popcorn noise in the Zener. In AN124 Jim Williams took special care with the coupling capacitor to reduce capacitor noise. "Selected commercial grade aluminum electrolytics can approach the required DC leakage although their aperiodic noise bursts (mechanism not understood; reader comments invited) are a concern." Page 7 of the app note, Note #1.

I have had better luck using 35V (or higher voltage) Aluminum electrolytics for the input coupling capacitors for a low noise 7-10V application. The leakage current really drops off when you have a larger margin between rated voltage and working voltage. About 5 years ago I checked several brands of 1000-2000 ufd 35V caps and there was one version of either Panasonic or Nichicon that had lower, more stable, leakage current than the rest. I am on vacation so it will be a bit before I can supply that partnumber.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 03, 2016, 06:11:24 am
@chuckb

according to branadic standard 85 degree types are better than low ESR 105 degree types.
I simply choosed among that what I had in drawer (25V types) after 2 days formation time with 10V.
The 2200uF is a ELNA and the 1000uF is a YAGEO. Among 10 capacitors you will usually find 2-3 which are usable.
The rest of the 1000uF capacitors you can use instead of the 470uF bypass capacitors.
So you are right: having a good voltage margin will be a advantage.

And there is a trick: If not used I put a 9V Block on the input of the amplifier to keep the capacitors charged.
Otherwise I would have to wait 2 days before each measurement until the leakage current
drops again below the 20nA limit. (and creates strange noise patterns).

Soldering heat is also a problem. It easily changes the leakage currents by magnitudes of order.
But the discussion of the 1/f amplifier would be worth a own thread.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 03, 2016, 10:36:43 am
I've measured a batch of several capacitors and found, that the 85°C types from Yageo deliver fair leackage currents <5nA after 24h forming in a combination of 2200µF/35V and 1000µF/25V that were finally used for the noise amplifier. 105°C types had decades worse leakage.
Wet tantal are hard to get and Sanyo Oscon deliver only small voltage ratings.
There was a document available, that delivers some explanation, but it's in german. (see attachement)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 03, 2016, 09:40:35 pm
The base of the temperature controller is mainly reproducing the noise of the reference, there should be only minor traces coming from the temperature noise. The better place to look at temperature noise would be the output of the OP.
Hello,

Do you really think that I am doing noise measurements at the base of the LTZ internal temperature sensing transistor?
I thought it is clear when I write J6 pin 12 as measurement point that it is the heater power transistor (BC639).
But obviously this is not the case.

@Branadic:
I do not think that OS-Con have low leakage current.
They are optimized for low ESR and high ripple current in low size.
I have some old stock 150uV/16V that I will charge over night.

With best regards

Andreas

Edit: measured values of leakage current as voltage drop over 100K resistor after 20 hours charging.
OSCON 150uF/16V (through hole, pink shrink tube, new old stock)
#1   1.6mV = 16nA
#2 11.7mV = 117nA
#3   0.7mV = 7nA

For 3200uF one would have to parallel 21 pcs of those to get the capacity.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on January 03, 2016, 09:49:55 pm
Well the setup wiring is ok so that leaves a strange operation of the chip.
I'm looking at a puzzling behavior that may be related.  Started a separate thread for it here (https://www.eevblog.com/forum/beginners/puzzling-ltz1000-circuit-behavior/) rather than lengthen this thread with back and forth over my circuit.  (but if it's interesting, I'll reproduce the conclusion here.)  Short version is that I'm seeing an effect on Pin4 from Pin6 even when I don't expect there to be one.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on January 05, 2016, 06:36:44 pm
A while ago I made myself a spice circuit of the LTZ1000 using some 2n5088/2n5089 parts for the small Q1 and Q2, just used a btz6.2 zener as the core zener just for modelling how it behaved, it seems prone to oscillation almost no matter what I did, could it all be oscillating quietly?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 07, 2016, 09:20:37 pm
Hello,

@andreas, i have same "pop corn" problem before, and i didnt quite know the way to solve it.

if i tap on the SOT23 lightly with a insulator stick, it can trigger/reproduce the noise.

Just for noise testing even a more normal resistor would be OK to test a different current. Its allways the possiblity to have a certain current or temperature  the zener diode does not like. So it might be interesting to do a slow temperature ramp (e.g. 1 degree), while doing a longer noise measurement.

I did several tests on LTZ#5:
Knocking on critical components -> no additional events.

Changed current through Zener: 1K resistor in parallel to R1=120 R -> no change in behaviour.
Additionally changed temperature setpoint: 22k resistor in parallel to R5 = 1K -> the first measurements showed no popcorn noise events. Then I did my "last noise measurement". Result: extreme number of popcorn noise within this measurement.
The following measurements showed again numerous popcorn noise events.
So the problem was not gone. (only a "statistical" improvement).

I decided to built the 2 further references immediately to check wether the chopper (LTC2057) is the guilty.
So the 2nd device with LTC2057 (LTZ#6) showed no popcorn noise.
Whereas on LTZ#4 (with LT1013A) showed 1 single (small 0.35uV event = within 3 sigma limits) during 15*100 sec measurement time.

I tried to differentiate between OP-Amp and zener by measuring noise at the OP-Amp Output (the gate of the BF245C FET).
The interesting result is that the noise at this point is a factor 2.9-7.6 higher than at the zener.
The average relative amplitude on LTZ#5 between noise is factor 2.9
The average relative amplitude of the popcorn noise jump heigth is factor 2.0
So the probability is higher that the Zener is the guilty.

But anyway: I think I will try exchanging the current regulator OP first. (since it is cheaper).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 07, 2016, 10:26:13 pm
The transconductance of the BF245 is rather low compared to the load impedance, which is only the zener and 120 Ohms. So the sourcefollower will have an AC  gain of only about 1/3 to 1/2. This is why noise is higher at the OPs output.

However this hardly can explain more than a factor of 3. There might be excessive LF noise from the FET: the transistor in the LTZ and the OP will compensate for that - thus the noise of the FET would appear at the gate, which is the OPs output. Still I don't think the noise of the FET will be a problem as it will hardly make it to the output.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on January 10, 2016, 10:26:49 pm
So a possible explanation would be that the hfe of Q1 is significantly higher than that of Q2 for the active cirquit.
How would one safely measure hfe of Q1 in a LTZ1000?  My attempt worked for my mock ltz but gave a garbage value for the real thing.  (I wonder if I've killed another one, now.)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on January 10, 2016, 11:24:52 pm
Why can't you just trust the data-sheet value of 200?  Anything you measure will be for your LTZ anyway-- and since there are always process variations, your value of hfe will not necessarily be the same as the typical data-sheet value, or as someone else's LTZ.
Gives me confidence that I understand what's going on and everything is as it should be.  Having gotten a garbage value demonstrates that at least one of those two is not correct.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on January 11, 2016, 04:57:19 pm
i have some OT Qn. did mickle T have a thread about how he modded his solartron with LTZ1k?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on January 11, 2016, 05:31:33 pm
i have some OT Qn. did mickle T have a thread about how he modded his solartron with LTZ1k?
I believe he modded his 7081. I have a document about it, look on here.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ManateeMafia on January 12, 2016, 02:48:49 am
Try here http://www.ko4bb.com/manuals/index.php (http://www.ko4bb.com/manuals/index.php)

Search for 7081. The file is ~100MB.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on January 12, 2016, 06:06:44 am
^^^That looks like it, a very large djvu file.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 12, 2016, 09:14:56 pm

So the probability is higher that the Zener is the guilty.

But anyway: I think I will try exchanging the current regulator OP first. (since it is cheaper).


Hello,

I did exchange the current regulator OP (LTC2057) and the FET (BF245C).
-> no change. Still having the popcorn noise.
So before I exchange now the LTZ I will try if the noise cures when doing a run-in phase
with a higher temperature setpoint for some weeks.

Has someone experiences in this direction?

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on January 12, 2016, 11:58:12 pm
Hello,

I did exchange the current regulator OP (LTC2057) and the FET (BF245C).
-> no change. Still having the popcorn noise.
So before I exchange now the LTZ I will try if the noise cures when doing a run-in phase
with a higher temperature setpoint for some weeks.

Has someone experiences in this direction?

With best regards

Andreas

Andreas, don't do it!  :palm: :palm: :palm:
Yep, I have some -bad- experience in treating these LTZs with higher temperatures..

You will definitely have hysteresis, and after removing hysteresis, you will have bigger drifts the next 1-2 years, compared to a LTZ w/o excessive temperature increase.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 13, 2016, 07:32:13 am
Hello,

@Frank: too late: I already put a 5K resistor between J6 Pin 10 + 11 to gently increase the setpoint.
I will not go above 15:1 (like HP) so dont worry.
It´s just trying to ride a dead horse. (I think I will have to exchange the LTZ anyway).

I have read somewhere that the ageing rate of zeners (probably 1N82x) is correlated to the noise.
I think that "popcorn noise" is meant. So this candidate will have anyway a higher ageing rate.
I will try to automate this: e.g. 10 sec high setpoint to 10 sec low setpoint.
I hope that if there is a fault in the die attach that then this may be cured by temperature cycling.

@3roomlab
No certainly not.
warm up time is around 500 ms to (near) steady state.
The popcorn noise events are 1 per minute in average.
(some minutes no event, other minutes up to 4 events).

After setting the setpoint 9 degrees higher there were no events for some minutes.

See also:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg837667/#msg837667 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg837667/#msg837667)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 13, 2016, 04:59:25 pm
If it is the noise from the zener diode, I think chances are better to try a even higher current than higher temperature. Even if chances are not that good a lower current might be worth a try too, as this is a low risk try. Just for noise tests the current setting resistor does not have to be high stabilitiy. Just in case the popcorn noise is comming from the transistor inside the LTZ1000, one might try using the transistor with a slightly higher collector voltage (e.g. add a resistor (100 K range) from the regulated 7 V to the inverting input of the OP).

It is rather unlikely that high temperature burn in will change much. Though chances are there if you go to a range where significant dift occurs. However this irreversible - so it's more like a last chance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 13, 2016, 08:39:43 pm
Thanks to our small volt nut meeting last saturday I'm now owner of one of Andreas LTZ1047B boards. So I started building up the circuit as far as I could.
Therefor I used our 3D printer to print a small spacer (material: thermoset) for the LTZ1000 (with 0.7mm holes) that keeps away airflow at the pins and increases the distance between pcb and reference to support long wires at the reference.

The Edwin G. Pettis LTZ resistor set is already placed and thermally coupled with some copper tape.

There are still some components missing, that I need to order as quick as possible to get the beast finished.  :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 14, 2016, 04:48:58 am
That Jamicon capacitor hurt's my precision eye  :P.
Nice job, I see you used jelly-bean 2057 too. Don't you love that little guy?
Fresh LTZ too.

What's your plan on usage for this module?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 14, 2016, 06:54:42 am
Hello,

That Jamicon capacitor hurt's my precision eye  :P.

never mind it´s only to calm down the on board (low drop) voltage regulator.
It will do it´s job.

@Branadic: nice stand off.
Do you have any data sheet about the thermoset material?

But I never expected that you would divide up the 400K resistor into 2 parts.
I would use this guy (which is within a 1% tolerance).
http://www.reichelt.de/1-4W-1-100-k-Ohm-976-k-Ohm/METALL-402K/3/index.html?ACTION=3&GROUPID=3080&ARTICLE=11793&SEARCH=402k&OFFSET=16&WKID=0& (http://www.reichelt.de/1-4W-1-100-k-Ohm-976-k-Ohm/METALL-402K/3/index.html?ACTION=3&GROUPID=3080&ARTICLE=11793&SEARCH=402k&OFFSET=16&WKID=0&)

But I personally think that the tolerance of this resistor is not critical.
(except when you adapt it especially on each individual LTZ).

With best regards

Andreas



Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 14, 2016, 05:45:33 pm
The suitable resistor for the "400 K" resistor will rather much depend on the LTZ1000 unit, possbly the OP used and also on the thermal design and likely the temperature setpoint (would expect higher resistors at lower temperature) used.  It is a try to compensate the residual temperature coefficient / imperfection of temperature control. So the right value can change a lot - should be more something in the 200 K - 5 M range depending on the individual unit and thermal setup. So I would not expect to need a tight tolerance and also no super low drift - especially with just the first guess of 400 K is used.

The more interesting question is to find a procedure to find (measure) the best value for a give setup - might need to measure temperature coefficient and optimize. So this step might need quite some time, especially without good procedures to follow.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 14, 2016, 10:17:17 pm
Quote
@Branadic: nice stand off.
Do you have any data sheet about the thermoset material?

But I never expected that you would divide up the 400K resistor into 2 parts.
I would use this guy (which is within a 1% tolerance).
http://www.reichelt.de/1-4W-1-100-k-Ohm-976-k-Ohm/METALL-402K/3/index.html?ACTION=3&GROUPID=3080&ARTICLE=11793&SEARCH=402k&OFFSET=16&WKID=0& (http://www.reichelt.de/1-4W-1-100-k-Ohm-976-k-Ohm/METALL-402K/3/index.html?ACTION=3&GROUPID=3080&ARTICLE=11793&SEARCH=402k&OFFSET=16&WKID=0&)

But I personally think that the tolerance of this resistor is not critical.
(except when you adapt it especially on each individual LTZ).

With best regards

Andreas

As I sad, I used what I had lying around, but as I have to order some parts the 400k made of two 200k resistors will be replaced by 402k. However, 400k in value is somewhat uncommon. I wonder why the used that special value instead of something available in the e series, if the it is not that important.  :-//
The datasheet for the material is confidential, but as said it's a thermoset.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 14, 2016, 11:00:40 pm
Hello,

again some measurements.
PSRR on LTZ#3. (With LT1013A)

For this I have supplied the LTZ at the output of the voltage regulator. (so without stabilisation).
Yes, the LT1763 is one of the few regulators which can be used this way without damage.

From 8.75V to 18.25V the change is around -13uV at ADC input (after 2:1 divider)
 so -26 uV or less than 4 ppm over a 9.5V input range.
Giving -0.4ppm/V for the LTZ cirquit.

below 8.3V the output voltage is in dropout.
Until 8.3V it is stable.
 (ok should have waited some more time to stabilize between switching on
and starting measurement from 9V downto 8.3V)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 16, 2016, 08:03:58 am
Hello,

next measurements: PSSR on LTZ#5
(with LTC2057 which has Rail to Rail output)

Same setup as on LTZ#3

From 8.5 to 18.5V the change is around -11uV  at ADC input
so 22uV or around 3 ppm over a 10V span.
Giving -0.28 ppm/V as regression curve.

Dropout starts (as expected due to Rail/Rail output)
at the lower value of around 7700mV
Until 7750mV the unbuffered output is stable.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: ltz2000 on January 16, 2016, 11:05:46 am
PSRR on LTZ#3. (With LT1013A)

Many thanks!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 16, 2016, 11:35:30 am
PSRR on LTZ#3. (With LT1013A)

Many thanks!

But be aware that I have a additional BF245C
against the original cirquit for the current regulator.
Without this the drop out voltage will be much higher.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 16, 2016, 10:48:16 pm
Hello,

added automated temerature setpoint increasment cirquit
on LTZ#5:
A timer (PIC) switches 2 4K7 resistors via small signal MOSFET
between J6 pin 10+11.
(which is in series to a 2K7 and all in parallel to the 1K setpoint resistor).
So every 10 minutes the setpoint is switched between 12.5 / 1 and 15 / 1.
(roughly 40 deg C temperature change each time).

So lets have a look if this has a influence on the annoying popcorn noise.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on January 17, 2016, 06:11:09 am
That is a pretty interesting idea.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 17, 2016, 01:35:00 pm
That is a pretty interesting idea.

Hello,

See Pickering patend.
But in my case I only increase the setpoint.

Some measurement values from the setpoint excitation on LTZ#5 with LTZ1000A:

first:
Current for the whole unit measured between battery and the voltage regulator.
After changeing setpoint it needs the full 10 minutes to finally stabilize for the current.
When setting the low setpoint it needs several seconds (around 10-15s) until the heater is switched on again.
(The rest of the cirquit consumes around 7mA).

The difference between high (around 90 deg C) and Low (around 50 deg C) temperature is around 8mA in current in steady state.
So having around 0.2 mA / deg C. (most probably not linear).

2nd:
Zener output voltage (unbuffered).
On heating the output voltage rises quickly (within 2 seconds until less than around 2ppm of final value).
On cooling down we have the 10-15 sec delay until the zener output is near stability.
Voltage rises from 7204 mV to 7220 mV (around 2220 ppm) or 54 ppm/deg C.

By the way: the "step" within the curves is due to the fact that the 2 resistors are switched on/off with around 4-5 sec delay one after the other.
The X-axis of the voltage measurements is number of measurements with 10 NPLC+offset compensation (0.4 sec/measurement).

3rd:
Setpoint voltage (measured over 1K Resistor).
Setpoint voltage behaves inversely with temperature.
At ~50 deg C we have 533.3 mV
At ~90 deg C we have 451.4 mV
Again the cooling phase needs longer whereas the heating phase goes "instantly".

With best regards

Andreas





Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 17, 2016, 08:53:44 pm
Looks like thermal regulation woks really well. The temperature of the chip itself seem to stabilize in just 1 second or so, even on the short step in between. Only the low temperature takes longer as the heater off state is reached with the rather large step down. There is a little bit of overshoot visible in the temperature (U_z and "Setpoint"), but not really much - so thats about how you want it when adjusting a regulator.

Its only the heating current that needs longer to reach a stable value - likely that is the time it takes for the case of the LTZ1000 to reach its equilibrium value.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 20, 2016, 10:15:35 pm
Hello,

in the meantime I did some measurements on LTZ1047B #3:

When comparing the unbuffered to the buffered output I recognized that the buffered
output had +24 uV more output than the unbuffered output.
-> much too much for the offset voltage of the LTC2057.

Putting 100nF across the buffered output made the both output voltages near equal.
-> obviously the output buffer picks up some noise from the wiring.

When soldering the 100nF across the buffered output I recognized on the unbuffered output that the
voltage drifted down by around -2 ppm (-14uV).
After soldering the voltage creeped slowly (around or less than 1uV/minute) upwards again.
Also a PSRR test with 14-18.5V instead of the battery showed around +0.5 .. 1 ppm drift.
Near the voltage regulator I measured a 2 deg C temperature increasement
The voltage regulator itself is stable at the output above 14.25 V input.
-> so most probably I have a thermal problem.

Is it the LT1013A with his hermetically housing (and KOVAR Pins)?
-> will have to do additionally tests.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 21, 2016, 04:49:47 pm
The OPs at the LTZ1000 are not that critical, when it comes to offset dirft or offsets from thermal EMF. So at least from the Offset it is not needed to use something like the LTC2057 here. The transistors in the LTZ1000 give a gain of about 100-200 - so something like a 100-200 µV offset from the OP would only result in 1 µV at the output or 1 µV at the sensing PN jinktion giving about 0.5 mK in temperature, which at 50 ppm/K would give someting like 0.2 µV at the output.

With AZ OPs, it might not be a good idea to use more than one in a circuit, as the AZ OPs cause some noise in the range of there chopping frequency and they are a little sensitive to noise in this range. So if usuing more than one AZ op - good filtering might be essential to isolate them. Also remember that HF interference (e.g cell phone, FM radio) might cause offsets. So to be really on the safe side, a closed case with proper HF isolation (ferrites+ (feedtrough)-caps would be the way to go.

The 22 Ohm at the output of the buffer for isolation is not that much - a higher value is likely a good idea. You don't want to drive much current from that OP anyway, as this would heat up the OP and can cause an extra Offset due to internal heating.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 21, 2016, 08:23:58 pm
Hello,

The OPs at the LTZ1000 are not that critical,

Good that you remind me.
between my old design LTZ#2 and LTZ#3 the only 2 differences are the
- LT1013 PDIP against CERDIP
- relative short legs against long legs of the LTZ1000A.
So either I have overlooked the sensitivity on #2 or the long legs are the reason.

With AZ OPs, it might not be a good idea to use more than one in a circuit, as the AZ OPs cause some noise in the range of there chopping frequency and they are a little sensitive to noise in this range. So if usuing more than one AZ op - good filtering might be essential to isolate them. Also remember that HF interference (e.g cell phone, FM radio) might cause offsets. So to be really on the safe side, a closed case with proper HF isolation (ferrites+ (feedtrough)-caps would be the way to go.

So its time that you do a tear down of your design here.
I am shure that we can learn a lot of it.

The 22 Ohm at the output of the buffer for isolation is not that much

Both outputs (buffered + unbuffered) are tested with capacitive loads from 1nF to 10uF.
Contrary to the datasheet design there are no oscillations.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 01, 2016, 08:01:38 pm
Hello,

did some noise measurement on LTZ#5 after 2 weeks of temperature setpoint cycling.

see also here as reference:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg833804/#msg833804 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg833804/#msg833804)

and here for he setup:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg844021/#msg844021 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg844021/#msg844021)

so it seems that the popcorn noise has changed to something like softer "noise bursts"
But if it really helps ironing out the noise down to the typical 1,2uVpp?
Lets give a further try.
Or will the popcorn noise return after a longer time at normal temperature?

one measurement with 200nV/div and two measurements with 500nV/div.
all in all I did 52 measurements with 10 seconds duration so every 170 seconds a event.

with best regards

Andreas

Edit:
drift on LTZ#5 during temperature setpoint treatment was -29uV
compared to -5uV on LTZ#3 without treatment. (only running 24/7).

Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 03, 2016, 05:20:50 pm
Hi,

Well some more LTZ drift and noise results to throw into the pot...

This is of a '94 vintage 3458A ref board (unmodified) as measured by two old 3458As. Internal temps, line frequency (as ppk from 50Hz), noise and voltage (as ppm of nominal 7.086V) were recorded at 2 NPLC. This test is still running but I will probably end it after 3 days. I deliberately introduced some ambient temperature variations to try and calculate the tempco. (Ambient was measured with a K2000 using a K thermocouple - this gives fairly nonsense readings because of the lack of a proper cold junction but it does show when the ambient temp changed). Both meters were autocaled at the start. The numbers in the panel in the middle btw are the regression coefficients.

The results so far seem to be:

(edit: updated at day 7)

+ one 3458A has a drift of 0.6 ppm per day, one is fairly flat and on spec at 0.1ppm per day.
+ the meters have opposite tempcos (#1074 is an 002 but they're both so old this shouldn't make a difference)
+ the relationship between internal temperature and ppm DCV seems to be immediate and fairly linear although opposite for each meter
+ there a positive relationship between DCV and line frequency

There are 3 moving pieces here of course including the ref board that is being measured, so it is possible that some other interpretation is possible. I'm particularly curious regarding the relationship with line frequency. Any thoughts?

Regards, Alan

(http://anagram.net/nuts/MeterDrift/Images/3458A%20ref%20drift%20and%20noise%20vs%202x3458A e.png)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on February 03, 2016, 06:51:40 pm
Line frequency is usually rather constant. So this should not be a real concern. It is well possible to have a correlation between line frequency and line voltage and than an influence of line voltage (e.g. through heat from regulators) - also a correlation with time of day is possible. There is also a small possibility that a change in the integration time, e.g. from rounding could also have a  minimal effect - but this should be small and could well be highly nonlinear up and down. With something like 0.2 ppm/Hz this is a rather small effect as the frequency is usually only changing by small fractions of a Hz.

Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 04, 2016, 04:54:00 pm
Hi,

Yeah, line frequency apparently varied from 49.857 to 50.189 (i.e. -0.3% to +0.4% from nominal) over the couple of days of that test. So if the co-efficient of frequency impact on DCV is O(10^-7), as it appears to be, then it wouldn't be critical. (*1) I have on my list to run the individual regressions to see where the R^2 is. I can't quite get my head around the interaction between line frequency, the internal crystal, the integrator, and the dual-slope algorithm. Probably greater minds than mine have a better picture :)

*1 - (edit) of course ~0.3 ppm per Hz x ~0.3 Hz freq change ~= 0.1 ppm - so it might have some minor effect

On another subject - Andreas are you now preferring the LT1013 or LTC2057?

Alan
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 04, 2016, 05:13:10 pm
I like Alan's posts, so colorful :)
My TEC in resistor temperature chamber died on me, so I have meter "free" and will run my LTZ module in attempt to compare.
I have to ask though, why 2 NPLC ? If I read scales correctly, your source tempco is around 1ppm/C, which is bad unless you are not measuring LTZ output?
I'd think NPLC 10 or 50 to be used for such a test, to rule out ADC.

Also with 0.9ppm/day (similar to 1ppm/day I had on second A3 PCBA here) I'd consider A3 PCBA "broken". You can check if it's A9 LTZ drift or ADC by running ACAL. If ACAL brings readings back to initial value, your LTZ is stable, and it's A3 PCBA problem.

SN18 also mentions that if unit even with 002 option remained cold for long time, reference change it's condition to "pre-aged" and need to be run burn-in for few weeks to get stability back.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 04, 2016, 07:21:03 pm

On another subject - Andreas are you now preferring the LT1013 or LTC2057?


Hello,

up to now no clear winner.
I will have to make more tests. (e.g. T.C. measurement)
 
The LTC2057 has advantages at very low power supply voltages (more headroom).
But I fear that it is more sensitive to EMI pulses (without the capacitors which I had to remove).
-> so another test to do.

but at the moment my largest problem are temperature gradients around the LTZ itself.
Depending on which side of the LTZ I apply my hot air gun the output voltage rises or falls.
So I will have to do better thermal isolation or at least a slot between the voltage regulator and the LTZ.
Perhaps also soldering the inner housing to the PCB to get better equalizing of the temperature.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 04, 2016, 07:43:04 pm
>>> I like Alan's posts, so colorful

Thank you TiN, my Excel skills? I'm sure they stem from a childhood preoccupation with crayons.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 05, 2016, 03:02:42 am
Had my LTZ hooked and running overnight, reading stays well <1ppm window, with ambient change from 22.1C to 21.3C. Live data here (https://xdevs.com/datalog_ltz1/).
Low noise ripple is ~4 uV, with pink noise jumps ~5uV sometimes. I'll heat up room when get back home tonight, to see the tempco in similar conditions to yours.
Meter sampling at 100 NPLC and AZ is on.

Hope this helps for your data analysis.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 05, 2016, 10:36:00 am
Hi TiN & Andreas,

>>> I have to ask though, why 2 NPLC ? If I read scales correctly, your source tempco is around 1ppm/C, which is bad unless you are not measuring LTZ output? I'd think NPLC 10 or 50 to be used for such a test, to rule out ADC.

I chose 2 NPLC to be able to measure ~DC-10Hz noise as well as drift. I agree with you that it picks up more meter noise that way - ~0.04 of RMS noise and ~0.15ppm of 'gain error' @ 7V reading if I read the specs correctly. I guess those will average out though and it is interesting for me to see when the noise spikes are - I have not located the source yet.

>>> Also with 0.9ppm/day (similar to 1ppm/day I had on second A3 PCBA here) I'd consider A3 PCBA "broken". You can check if it's A9 LTZ drift or ADC by running ACAL. If ACAL brings readings back to initial value, your LTZ is stable, and it's A3 PCBA problem.

Yes it looks suspect and I'm going to leave the test running for a while to see what happens to #1045. It's still got v1 of the slave processor firmware so that may have something to do with it. I have ordered the 8051 (which is where I think the slave firmware is) from Keysight but they are being a bit random - yesterday they sent me a box 50x30x20cm with one button in it < 1x1x1cm, ho ho ho.

Many thanks for running that similar test. I'm away for the weekend but will run the data through the same analysis for comparison when I get back. BTW my simple test setup below - no screening atm. The cover for the ref btw is 3d printed, double walled, and on the bottom of the board also.

Andreas re:

>>> The LTC2057 has advantages at very low power supply voltages (more headroom). But I fear that it is more sensitive to EMI pulses (without the capacitors which I had to remove).

Thanks for that feedback, I also found, on another board, that I had to remove decoupling from input and output to stop it acting up. In particular, a 100nF on the output resulted in a nice 250kHz oscillation. I'm trying to remember what I once thought I knew re xfer functions and stability :) I was thinking of trying the LT1013, which is why I asked.

>>> Depending on which side of the LTZ I apply my hot air gun the output voltage rises or falls.

Well that's a fairly severe test - that probably happens (I have not tried it) with say the HP layout?

Alan

(http://anagram.net/Nuts/MeterDrift/Images/IMG_2555.JPG)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 05, 2016, 12:33:30 pm
Ouch :) Have direct connection to A9 terminals, without those terminal blocks. They can cause big thermal EMFs.
I set it 2 NPLC, will leave overnight. So far from data log I'm seeing variance ~0.5ppm or so:

Code: [Select]
05/02/2016-20:23:23;[     829]: 7.136742640 , dev -0.5409 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.16 hPa
05/02/2016-20:23:23;[     830]: 7.136742906 , dev -0.5036 ppm, T:33.7 , EXT_T:21.43 , RH:74.32 , Press:1019.18 hPa
05/02/2016-20:23:23;[     831]: 7.136745218 , dev -0.1796 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.17 hPa
05/02/2016-20:23:24;[     832]: 7.136743529 , dev -0.4163 ppm, T:33.7 , EXT_T:21.42 , RH:74.31 , Press:1019.20 hPa
05/02/2016-20:23:24;[     833]: 7.136744685 , dev -0.2543 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.16 hPa
05/02/2016-20:23:24;[     834]: 7.136744062 , dev -0.3416 ppm, T:33.7 , EXT_T:21.43 , RH:74.32 , Press:1019.18 hPa
05/02/2016-20:23:24;[     835]: 7.136745041 , dev -0.2044 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.17 hPa
05/02/2016-20:23:25;[     836]: 7.136744240 , dev -0.3167 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.18 hPa
05/02/2016-20:23:25;[     837]: 7.136744774 , dev -0.2418 ppm, T:33.7 , EXT_T:21.43 , RH:74.32 , Press:1019.15 hPa
05/02/2016-20:23:25;[     838]: 7.136742284 , dev -0.5907 ppm, T:33.7 , EXT_T:21.43 , RH:74.32 , Press:1019.16 hPa
05/02/2016-20:23:25;[     839]: 7.136743618 , dev -0.4038 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.20 hPa
05/02/2016-20:23:25;[     840]: 7.136743796 , dev -0.3789 ppm, T:33.7 , EXT_T:21.42 , RH:74.31 , Press:1019.16 hPa
05/02/2016-20:23:26;[     841]: 7.136744685 , dev -0.2543 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.17 hPa
05/02/2016-20:23:26;[     842]: 7.136744151 , dev -0.3291 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.20 hPa
05/02/2016-20:23:26;[     843]: 7.136745041 , dev -0.2044 ppm, T:33.7 , EXT_T:21.42 , RH:74.31 , Press:1019.19 hPa
05/02/2016-20:23:26;[     844]: 7.136743084 , dev -0.4786 ppm, T:33.7 , EXT_T:21.42 , RH:74.31 , Press:1019.16 hPa
05/02/2016-20:23:27;[     845]: 7.136742906 , dev -0.5036 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.16 hPa
05/02/2016-20:23:27;[     846]: 7.136744596 , dev -0.2668 ppm, T:33.7 , EXT_T:21.42 , RH:74.31 , Press:1019.16 hPa
05/02/2016-20:23:27;[     847]: 7.136744418 , dev -0.2917 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.21 hPa
05/02/2016-20:23:27;[     848]: 7.136744329 , dev -0.3042 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.17 hPa
05/02/2016-20:23:27;[     849]: 7.136742995 , dev -0.4911 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.16 hPa
05/02/2016-20:23:28;[     850]: 7.136744062 , dev -0.3416 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.17 hPa
05/02/2016-20:23:28;[     851]: 7.136744062 , dev -0.3416 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.18 hPa
05/02/2016-20:23:28;[     852]: 7.136742817 , dev -0.5161 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.18 hPa
05/02/2016-20:23:28;[     853]: 7.136744329 , dev -0.3042 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.17 hPa
05/02/2016-20:23:29;[     854]: 7.136744062 , dev -0.3416 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.17 hPa
05/02/2016-20:23:29;[     855]: 7.136744151 , dev -0.3291 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.16 hPa
05/02/2016-20:23:29;[     856]: 7.136743973 , dev -0.3541 ppm, T:33.7 , EXT_T:21.43 , RH:74.31 , Press:1019.15 hPa

I need to change my 12V battery, so I could run ref with clean power to see if it can be better.

V1 firmware? What slave processor you talking about? MCU on ADC?
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 05, 2016, 02:56:55 pm
Yes, my thermal emfs are all over the place :), I've been researching low emf cables etc but no conclusion so far.

>>> V1 firmware? What slave processor you talking about? MCU on ADC?

To put it another way, the answer to REV? is 9,1 which I believe is the masked rom in the 8051 on A3, which is what I ordered a week or so ago. If Keysight are consistant with their shipping 'system' they'll probably deliver this huge part in its own container.

(http://anagram.net/nuts/misc/Images/container.jpg)

Interested in your results on clean power, I'm assuming for the moment that my big noise spikes are power-related.

A.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 05, 2016, 03:19:54 pm
So you ordered 8051 chip alone?
Mine REV? says 9,2. You got me thinking...

Meanwhile, 2 NPLC seem more noisy but span is very similar. No wild jumps as of now :)
Only if I moved cable, readings jump. Like now, just did it, deviation changed from ~0.6ppm to ~3.2ppm. So it's important to leave setup alone and have it located away from main working table which get vibrated/stressed often.

Use usual UTP ethernet cable with single strand wires, it's copper and very good for such connections. Clean copper wire fresh, without any oxidation, solder one end to A9 PCB test points. Crimp other end right to DMMs terminals. Keep them tight.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 05, 2016, 08:28:59 pm


>>> The LTC2057 has advantages at very low power supply voltages (more headroom). But I fear that it is more sensitive to EMI pulses (without the capacitors which I had to remove).

Thanks for that feedback, I also found, on another board, that I had to remove decoupling from input and output to stop it acting up. In particular, a 100nF on the output resulted in a nice 250kHz oscillation. I'm trying to remember what I once thought I knew re xfer functions and stability :) I was thinking of trying the LT1013, which is why I asked.

>>> Depending on which side of the LTZ I apply my hot air gun the output voltage rises or falls.

Well that's a fairly severe test - that probably happens (I have not tried it) with say the HP layout?


Hello,

most amplifiers will oscillate with 100nF (more than 100pF-1nF) directly at the output. (except some special OPs like AD826).
You will need a isolation cirquit with a 10-100 Ohms resistor and a feedback capacitor. (See my LTZ cirquit for the buffered output).

The heating test sounds more dramatic as it is.
The temperature that I use is 100 deg C and I do apply only for a few seconds over a larger area.
Unfortunately it is not good reproducable.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 05, 2016, 10:53:56 pm
My board is now assembled too. Need to check each solder joint tomorrow and clean the board before powering it up for the first time.  :popcorn:
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 06, 2016, 10:53:26 am
My board is now assembled too.

Photo?

From my heatgun experiment I have made a diagram for LTZ#5
The heatgun is a hot air heater from a SMD rework station set to 100 deg C (minimum temperature).

21:59 heating south (below Pin 8 ) of LTZ
22:08 heating east (right from Pin 2) of LTZ
22:14 heating north (above Pin 4) of LTZ
22:19 heating west (left from Pin 6) of LTZ

peak amplitude is around 50uV = 7 ppm output change per heating.
heating west gives a negative jump. (all others positive).

22:25 heating the Z201 resistors north of the LTZ.
(not shure if that jump is from the resistors or more likely from LTZ).

The NTC north east from LTZ shows temperatures from 26-32 deg C (averaged temperature over 1 minute)

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 07, 2016, 01:28:21 am
Well the setup wiring is ok so that leaves a strange operation of the chip.

The Vbe of Q1 is 20 mv greater than Q2 when they are all check by themselves. In a full, active circuit the Vbe of Q1 is 30-110mV below Q2. That's something to look into.

Together with the statement of Ken
it would explain that the Vbe on Q1 is higher than on Q2 with base + collector connected.


 The two transistors in the LTZ are *not* matched-- Q1's geometry is significantly smaller than Q2, and so much less current will be going through Q2 than the Zener when the operation point reaches equilibrium. 

So a possible explanation would be that the hfe of Q1 is significantly higher than that of Q2 for the active cirquit.
And the large stray of 50 mV from your samples in active cirquit could indicate that the hfe is very different between samples.

I attempted to replicate chuckb's results.  I used p-channel jfet+resistor current sources to drive Pin1, Pin5, and Pin8; and 2057s to drive Pin4 and Pin6.  I also provided for easy attachment of a resistor to each base via jumper, to act as the "regular circuit" for comparison.

I measured a hfe of about 200 for both transistors, consistent with the datasheet and an indication I haven't damaged the transistors (yet).  Pin4 was around 650mV and Pin6 was 623mV.  Then I tried adding a resistor from Pin6 to Pin7.  If this produced a change, I couldn't see it.  I removed that resistor and put in the resistor at Pin4.  Pin6 showed a slow drop from self heating, but Pin4 had 100mV immediate drop and the slow heating drop.  Removing that resistor had the opposite effect.  I tried roughly doubling the resistance, and the drop was now 50mV.

That seems to be consistent with Andreas running at 440mV heated+complete circuit vs chuckb's 580mV unheated + no zener current.

Could it be that die traces + bond wires add up to enough resistance to pin 4 to cause that shift?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 07, 2016, 08:05:20 am
Hello,

wow. you made a own PCB only to measure this. Impressive.
What FETs do you use. P-Channel are relatively rare.

Would be nice if you could provide a larger image of the cirquit diagram. The numbers are hard to read.

Could it be that die traces + bond wires add up to enough resistance to pin 4 to cause that shift?

Mhm. roughly 4 mA change give 90 mV voltage drop.
As resistance this would be 22 Ohms.
I am not a expert but 22 Ohms is a value which seems too high for me.

I know that if you activate the undocumented heater (400 Ohms) in
a LT1019 reference the ground level on the chip (measured as output voltage change)
 is shifted by around 1.25 mV (at 30 mA heater current).
This would give around 40 mOhms for the pin.

So for me there must be a different explanation for the 90 mV.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 07, 2016, 07:52:37 pm
Quote
Photo?

Sure, here we go...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 07, 2016, 08:29:02 pm
What FETs do you use. P-Channel are relatively rare.
MMBFJ177LT1G (https://www.digikey.com/product-detail/en/MMBFJ177LT1G/MMBFJ177LT1GOSCT-ND/1139803). I got 10, characterized them for 100uA, and choose the closest match for Q1 and Q2.

Quote
Would be nice if you could provide a larger image of the cirquit diagram. The numbers are hard to read.
Done.  I turned on part names, used a clearer font, and left if at the native resolution.  Updated the image in my earlier post (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg862127/#msg862127)  (the _Flip is because I swapped the positive and negative inputs on the schematic symbol.)

Quote
So for me there must be a different explanation for the 90 mV.
Using chuckb's images (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg829128/#msg829128) I computed about 42 "squares" along the trace to pin 4, which would be a resistivity around 0.5 ohm/sq to cause that shift.  That seemed high but not impossible, and it fit the nice linear relationship of the voltage shift to current.  Ah well :)

Thanks
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 08, 2016, 07:19:00 am
Sure, here we go...

 :-+

which would be a resistivity around 0.5 ohm/sq to cause that shift.  That seemed high but not impossible, and it fit the nice linear relationship of the voltage shift to current.

So if I understand you right you should be able to measure the 22 Ohms of pin 4  in series to the zener and also in series to the base/emitter of Q1.
The zener would be easy to measure. The datasheet states a typical zener voltage change of 80 mV for a 1 to 5mA difference. (so around 20 Ohms for both sides of zener + the zener itself).
But usually discrete zeners (directly contacted) in that voltage range have also dynamic resistances around 10 Ohms.

The base / emitter would be more difficult. In normal operating the base current should be around 1uA.
But I think that up to 50 or even 100uA you will be on the safe side.

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 08, 2016, 03:02:23 pm
Hi,

Interesting results when we were away for the weekend (the whole graph is updated in my previous message above):

+ the temperature was very stable
+ there were still a few noise excursions - I'm suspecting mains noise
+ there were a couple of interesting artifacts (below) - I'm suspecting mains voltage droop. Exactly how this gets into the reading I'm not sure - atm the ref heater is powered by a E3631A and the ref by an Advantest R6144. I'm not logging these right now.

Otherwise the coefficients were similar to before -

(http://anagram.net/Nuts/MeterDrift/Images/3458A ref drift 7 day coefficients.jpg)

- although you can see the time drift starting to mean revert be more square root like (rather than linear). I guess its possible to repeat this analysis this with a square root model for time drift. Interestingly whereas we're normally interested in high R squared, low R squared is what we're looking for here i.e. ideally the readings tend towards random processes with the coefficients all zero.

TiN - if you give me a link to your data I can do a preliminary analysis - you could copy the existing file without stopping the test. Were you impacted by the earthquakes?

p.s. >>> So you ordered 8051 chip alone? Mine REV? says 9,2. You got me thinking...

? :)

A.

(http://anagram.net/Nuts/MeterDrift/Images/3458A%20ref%20drift%20and%20noise%20vs%202x3458A%20weekend.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 08, 2016, 03:48:07 pm
Alan,

My data CSV is here (https://xdevs.com/datashort/kxr_3458_nplc200_tin_00000.csv). Graph here (https://xdevs.com/datalog_ltz1/) (takes long time to draw due to number of points, sorry).
There are many delays due to abnormal hangs of linux-gpib or my python capture app, so it's not that consistant :(.
-3ppm drop at start of NPLC2 data capture was due moved cable from reference to DMM.
It was just slight shake in Taipei, nothing like south part, so here everything is alright, except GPIB datalog stopped same moment 3:20am, perhaps cable got lose. :)

I'm trying now crude air thermal chamber test (https://xdevs.com/tmeas_prc_1meg/) with 55W TEC module and K2510, to get setup for temperature cycling of references and resistors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 08, 2016, 08:39:02 pm
The zener would be easy to measure. The datasheet states a typical zener voltage change of 80 mV for a 1 to 5mA difference. (so around 20 Ohms for both sides of zener + the zener itself).
But usually discrete zeners (directly contacted) in that voltage range have also dynamic resistances around 10 Ohms.
Heh, the datasheet actually calls out this behavior! If you look at the "Zener Voltage vs Current" chart, it shows the sum of zener + Q1 going up more slowly than just zener alone--Q1 must be going down as zener current increases.  That chart has a non-linear change for Q1 below 2mA, though; too bad the datasheet doesn't explain the mechanism ;).  A resistor there may suffice for a spice model.

I wonder if my LTZ is 80mv or is up towards the datasheet max of 240... perhaps I'll try to measure it some day. 


Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 08, 2016, 10:19:23 pm
OK a quick check. I've just taken the 1st day for the time being before the big 4ppm move. I'm getting -0.4ppm per day and -0.9ppm per K. For comparison MM's 3458A-8451 meter had +0.1ppm per day and -0.3ppm per K vs. a 732 (if I remember correctly) and my 3458A-1704 also 0.1ppm per day and +0.2ppm per K vs. an old A9 board. Your data is vs. one of your own ref boards? How aged is the LTZ on that one? Wow you guys in Taipai were lucky not to be near the centre.

(edit - actually looking at this graph more closely (see blue circle and black trend line) - the reading is moving before the internal temp of the meter suggesting that it's the ref that's shifting)

>>> I'm trying now crude air thermal chamber test

Yes thermal chamber is the way to go - I'm getting bored with my home lab being either freezing or stifling as I'm running these tests :) ... and you can't separate out the tempco of the meter from the tempco of the ref.

A.

(http://anagram.net/Nuts/MeterDrift/Images/TiN%20ref%20drift%201a.png)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 09, 2016, 01:25:57 am
There is another issue with thermal box, as seem that EMI from TEC cause readings to jump a bit (1Meg 4W OHMF), even with Guard terminal of DMM wired to metal box with resistor.
Now since I can get temperature stable to ~0.005°C, let's try same test with LTZ ref. Yes, it's one of my early reference modules. It's Rev A01 PCB, LTZ1000ACH, LTC2057, 13K/1K heater.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 09, 2016, 10:05:12 am
To determine tempco vs time drift and also calc RH and pressure coefficients, of course, we want variations in the 'independent variables'. So, some temperature jumps, ramps etc would be good - the kind of thing you might do if you were characterising a filter or other transfer function in the time domain. As an initial approximation, the tempco relationship seems pretty fast and somewhat linear, which is helpful for characterisation. I am also seeing a fall off in time drift with larger time scales which I'm putting down to 'square root' behaviour. (I will post some data presently - I need to write some more code.) With more data I should be able to fit these relationships fine. Actually, the 'better' the ref/meter / the more the variations are down to random fluctuations rather than easily observed xfer functions / the harder it will be to pull the relationships out of the noise. I don't think we're anywhere near that point yet though. I'm hoping to get a thermal chamber device set-up here also over the next couple of weeks.

A.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 10, 2016, 06:44:56 am
Seems like I have hard time measuring tempco of LTZ module.
At first glance everything was okay, but when I got temp 4K up, i had strange -0.5ppm dip. Then bumped temp another +7K, it was bit stabilized.
Drop to original +24C (-11K) output barely changed, if take just two nearest hours with 11K temperature delta - simple math gives 0.009ppm/K.
Temperature of 3458A was measured as +0.118ppm/K due to sun in the morning, warming up meter 3.4K. ACAL brought signal back 0.7ppm down.

Should I crank chamber temp to +50°C, so we can see something ?

Details about setup covered in this EEVBlog thread (https://www.eevblog.com/forum/projects/project-kx-diy-calibrator-reference-sourcemeter/msg864294/#msg864294).

(https://xdevs.com/doc/xDevs.com/KX/vref_tct_1.png) (https://xdevs.com/doc/xDevs.com/KX/vref_tct.png)

Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 10, 2016, 01:21:11 pm
OK will take a look at that data.

For amusement, here is the plot of regression coefficients vs elapsed time from the beginning of my drift experiment.

(see https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg858685/#msg858685 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg858685/#msg858685))

This suggests:

+ a simple linear model isn't bad (as these coefficients are fairly stable)
+ the time-drifty meter is stabilising a bit

I'm going to swap out the 8051 on that one and see if anything changes.

(http://anagram.net/nuts/MeterDrift/Images/A9%20ref%20drift%20vs%202x3458A%20regression%20coefficients.png)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 10, 2016, 01:33:21 pm
If I would be you, I'd perhaps created separate 3458A thread, and first thing would be to measure A9 output of drifty meter with stable one, to confirm it's not the ref (maybe it was done before?).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 10, 2016, 07:46:27 pm
Hello Tin,

Seems like I have hard time measuring tempco of LTZ module.

Should I crank chamber temp to +50°C, so we can see something ?


yes it is no easy task.
There are different influences on the LTZ.
First you have temperature gradients which also have a influence
(see my PSRR experiment and the heat gun experiment).
Further there is shurely some influence from mechanical stress of the PCB.
Which might also vary over time when the Epoxy "flows" or soaks some humidity.

And that is also the reason why I do a slow ramp (around 0.1 deg C / minute)
down to 10 deg C up to 40 deg C and back to room temperature.
The shift from gradients appears as hysteresis in that case and can be averaged out.
See attached pictures of my LTZ#1 versus ambient temperature and PCB sensor temperature (which are quite different).

50 deg C might be too much for your temperature setpoint.
If you fall out of regulation the tempco will increase to 50 ppm/K.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 11, 2016, 07:05:00 am
So your total test time is 5 hours?

What I see is that voltage output jumps caused by non-temperature related effects are far larger than change of temperature itself, to isolate tempco from other effects.
I'll test second module, and then will test both in same chamber. Perhaps differential measurement of two LTZs in chamber would be more useful, to avoid own DMM's effect impact results.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 11, 2016, 12:43:08 pm
Hey Andreas,

Very interesting results. If I understand correctly:

+ no hysteresis between ambient and the outside of the ref
+ some thermal hysteresis between the outside and inside of the ref measured with Vbe
+ apparently some unaccounted for hysteresis in the ref itself
+ some non-linear ref tempco but approx -0.03 ppm per K (assuming the meter is at a stable temp)

Is that right? 6K per hour is quite a rapid temp rise for a lab in practice of course. Does the hysteresis loop change much if you increase/decrease the ramp speed? Could the apparent hysteresis in the ref just be an artifact from time-based meter drift?

p.s. a left scale in ppm nominal ref voltage would be easier to read :)

Hi TiN,

>>> If I would be you, I'd perhaps created separate 3458A thread, and first thing would be to measure A9 output of drifty meter with stable one, to confirm it's not the ref (maybe it was done before?).

I don't think anything could top your repair thread :) mine would be dead boring in comparison. I only mention the drifty meter for amusement's sake btw - I'm focused more on LTZ drift measurement and characterisation. Hence all the dull stats. I have a 4xLTZ test coming up.

Alan
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 11, 2016, 12:47:24 pm
Let the clash of LTZs begin :)  Perhaps we can have some specific test list and conditions which all of us can try to run? Would be more interesting to compare more "apple-apple" scenario..
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 11, 2016, 01:19:42 pm
>>> Perhaps we can have some specific test list and conditions which all of us can try to run? Would be more interesting to compare more "apple-apple" scenario..

Good point. I'm planning on logging mean voltage and noise (say 2NPLC/azero on) from 4xLTZ1000A (as unmodified A9 boards) with LTC2057 followers supplied by lowish noise supplies using my 3D printed thermal covers / plus supply voltage and ambient temp / switched with a standard K2000 scan card / measured by a 3458A / logged on a PC with C#. No special EMF or thermal shielding / no special thermal EMF precautions / no temperature chamber / fairly stable home lab temperature environment with a few planned ambient temperature excursions / running for a week or so. The intention is to observe, compare and characterise the time drift / get an overall (meter plus ref) tempco. I'm expecting that regressions and some kind of n-cornered hat analysis (which I haven't figured out yet) will help.

A.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 11, 2016, 02:05:29 pm
Challenge accepted.  :bullshit: :box:
 I had similar idea, with exception of thermal box and using TCSCAN-2001 card in 2001. And using my own LTZ modules. I think I can get forth back from unsuccessful K2001 conversion.

Changed to second module, took a photo. Here's my module setup:

(https://xdevs.com/doc/xDevs.com/KX/kxtest_1.jpg) (https://xdevs.com/doc/xDevs.com/KX/kxtest.jpg)

This one is LTZ1000CH (2014 week 16), LTC2057 opamp, 12K/1K for low temperature setpoint.
Battery powers MAX6610 sensor, located on bottom side at center.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 11, 2016, 10:45:57 pm
So your total test time is 5 hours?

its more 12-15 hours.
ramping down and up and with 1 hour rest at minimum and maximum temperature + some overlapping because at the beginning the ramp speed starts at zero and behaves different when finally ramping down.

Hey Andreas,

Very interesting results. If I understand correctly:

+ no hysteresis between ambient and the outside of the ref
+ some thermal hysteresis between the outside and inside of the ref measured with Vbe
+ apparently some unaccounted for hysteresis in the ref itself
+ some non-linear ref tempco but approx -0.03 ppm per K (assuming the meter is at a stable temp)

Is that right? 6K per hour is quite a rapid temp rise for a lab in practice of course. Does the hysteresis loop change much if you increase/decrease the ramp speed? Could the apparent hysteresis in the ref just be an artifact from time-based meter drift?

p.s. a left scale in ppm nominal ref voltage would be easier to read :)


I think you are mis-interpreting the diagrams.
They are both the same except for the x-axis.
In one case (tPCB) the NTC near the LTZ on the PCB is on the x-axis.
Since I did not remove the Y-axis for this sensor he shows no hysteresis but the other sensor.

In the other case (tAMB) I have a second NTC outside of the aluminium case of my reference as x-axis.
So this sensor shows no hysteresis but the PCB-sensor lags against the ambient temperature.

Vbe is never measured in the diagrams (This would change the setpoint of the LTZ).
The hysteresis on the reference appears mainly because the temperature is neither the same of the one or other NTC.
The other part could be some effect due to temperature gradient.

I think you did not mention the 2:1 divider in the measurement (so you should not divide by 7200 mV but by 3572 mV
when calculating T.C. (around 0.06 ppm/K).

My "meter" is a LTC2400 based ADC with temperature compensation in this case.
It is rather noisy (the ADC itself + the around 0.1ppm quantisation noise of temperature compensation giving around 0.25ppm standard deviation) but has almost no drift over time.

Changeing the ramp speed has it´s limits.
Increasing is not possible for the whole temperature range (the peltier cooler is at its limit with 0.1 K/minute).
Slowing down would need running over night or splitting the measurement over several days.

With best regards

Andreas




Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 12, 2016, 06:05:04 am
Well, second module was no good:

(http://xdevs.com/doc/xDevs.com/KX/vref_tct2_1.png) (http://xdevs.com/doc/xDevs.com/KX/vref_tct2.png)

+0.67 ppm/K, from 10K change. Something definately not right on this one. I see no point of testing this one any more before issue is fixed.

Also I forgot that I had Rev.B module in 3245A, so I cannot test it directly.

-----------------------------

Changed to 3rd module (still Rev.A, 13K/1K setting, ACH-zener, different opamp this time, LT1097):

(http://xdevs.com/doc/xDevs.com/KX/ltz_mod3_1.jpg) (http://xdevs.com/doc/xDevs.com/KX/ltz_mod3.jpg)

Next tests will be more interested, with old LTZ chips and sockets, and also wirewound resistors instead of Vishay foils.  ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 12, 2016, 05:48:12 pm
Hello,

here some results from my tilting experiment.
The LTZ is oriented in all directions.
The output voltage is measured as voltage difference between
LTZ#3 and #5 in the 100mV range with 100NPLC. (averaged over 1 minute).
One reference in normal position and the other is changed in orientation.

0 = N = Normal (all pins down)
1 = 4 = Pin 4 pointing up
2 = O = up side down
3 = 8 = Pin 8 pointing up
4 = 6 = Pin 6 pointing up
5 = 2 = Pin 2 pointing up

LTZ#3 has around 0.6 ppm difference through the orientations.
LTZ#5 has around 0.15-0.2 ppm when calculating out the drift.

So the question is: is the larger difference of #3 due to the LT1013A or is it a feature of the LTZ itself.

For the drift probably the treatment with the setpoint change is a reason.
So I will repeat the measurement this weekend after 1 week with constant setpoint.

With best regards

Andreas




Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on February 12, 2016, 06:51:05 pm
Even though the change in voltage is only about 2 µV at the output from the normal position, the OPs should not show that much effect. To get 2 µV at the output, the offset at the OP must change by 400 µV or about 1 mV. The more likely source is the temperature abound the Pins of the LTZ1000. One could check this be repeating with a different cover.

The difference between the two modules might be due to the different position of the OPs as a heat source.

Another possible factor could be the earths magnetic field - though likely not a big factor. At least I have not seen data on this.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 13, 2016, 06:22:54 pm
My LTZ1000CH, based on the PCB from Andreas and resistors from Edwin Pettis, is alive. My meter shows 07.200V. Have to verify the exact value with different meters right know.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on February 13, 2016, 08:44:38 pm
My LTZ1000CH, based on the PCB from Andreas and resistors from Edwin Pettis, is alive. My meter shows 07.200V. Have to verify the exact value with different meters right know.
What kind of ballpark figure is a set of hand made resistors, like yours, from Edwin going to set me back? Or is it "if you have to ask, it's too expensive for you!"  :-DD

Any stock wirewounds that could be available?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 13, 2016, 09:56:36 pm
Quote
ou might want to obtain a small amount of "down" [or a synthetic version of it like the stuffing for sleeping bags], and put some inside the metal box.  Not a lot-- you are not trying to insulate, but to stop convection currents in the air surrounding the LTZ and other components.  I'm assuming that there is a metal lid for the metal box.

Sure, there is a lid for the metal box and yes, there will be some cotton batting put inside. My LTZ is already sitting on a small 3D printed plastic spacer, as can be seen here:

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg841924/#msg841924 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg841924/#msg841924)

Only a small part on this spacer at the solder junction is senitive for possible air flow problems.

Quote
What kind of ballpark figure is a set of hand made resistors, like yours, from Edwin going to set me back? Or is it "if you have to ask, it's too expensive for you!"  :-DD

Any stock wirewounds that could be available?

They were affordable and fast available, nothing fancy, but I could have used Econistor:

https://www.rhopointcomponents.com/components/resistors/precision-through-hole/wirewound-econistor-3ppmc-8e16-8g16-series.html (https://www.rhopointcomponents.com/components/resistors/precision-through-hole/wirewound-econistor-3ppmc-8e16-8g16-series.html)

or Miniohm instead too:

https://www.rhopointcomponents.com/components/resistors/precision-through-hole/wirewound-miniohm-3ppmc-5e10-5g10-series.html (https://www.rhopointcomponents.com/components/resistors/precision-through-hole/wirewound-miniohm-3ppmc-5e10-5g10-series.html)

Maybe they are any good for you too. Frank is pretty happy with his Econistors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 13, 2016, 11:35:46 pm
Maybe they are any good for you too. Frank is pretty happy with his Econistors.

How do you know that?

https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg624931/#msg624931 (https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg624931/#msg624931)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 14, 2016, 12:03:32 am
Quote
How do you know that?

That's what he always wrote when talking about building a LTZ circuit in this thread.
Title: Re: Ultra Precision Reference LTZ1000
Post by: deadlylover on February 14, 2016, 01:18:17 am
What kind of ballpark figure is a set of hand made resistors, like yours, from Edwin going to set me back? Or is it "if you have to ask, it's too expensive for you!"  :-DD

Here are the prices a year ago that DiligentMinds posted for us, I'd imagine they'd be roughly the same today, prices in USD;

Resistors are Ultrohm style 805 (physically equivalent to Rho 8e16), ±0.1%, 0 ±3PPM/°C, -55°C - +125°C:

Value    1-9       10-24
120?   $6.85    $5.14
1K        $6.34    $4.76
10K      $7.28    $5.46
12.5K   $7.43    $5.57
70K      $8.25    $6.19

I'll be ordering some soon and can post updated prices with a few different values. AUD is like monopoly money now though...  :'(
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 14, 2016, 09:29:48 am
Here is what was payed a year ago:

120R   6,85€
1K      6,34€
12K5   7,43€
70K      12,38€
12K0   7,35€

plus customs duty plus shipping.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 15, 2016, 11:07:22 am

What kind of ballpark figure is a set of hand made resistors, like yours, from Edwin going to set me back? Or is it "if you have to ask, it's too expensive for you!"  :-DD

Any stock wirewounds that could be available?

As you are located in UK, you might order most easily from Rhopoint Components.
They offer PWWs, called 'econistor' from Prime Technology / General Resistance.
I had some trouble with the 120 Ohm type, they had too high a T.C.
I received 5 new ones, directly from G.R, not stellar, but inside spec. limits.

All other values were also 'ok', especially the 12k/1k resistors, to realize an LTZ1000 - reference with a numerical T.C. of about 0.05ppm/K.

Rhopoint also offer BMF resistors from AE, 'FLCY', which are quite good.

Btw.: Did anybody calculate the influence of the 200k "T.C. compensation resistor" in the LT circuit?
I wonder, whether this can be chosen to trim to near zero T.C., with given overall T.C. of the five precision resistors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on February 15, 2016, 12:37:18 pm
Btw.: Did anybody calculate the influence of the 200k "T.C. compensation resistor" in the LT circuit?
I wonder, whether this can be chosen to trim to near zero T.C., with given overall T.C. of the five precision resistors.
I was hoping someone would bring this up.  In the LT datasheet, the positive reference circuit feeds the 400k compensation resistor with heater voltage plus the Vf of the 1N4148 which has a strong negative tempco.  But in the negative reference circuit, there is no diode Vf, but instead has the ~7.2V reference voltage in series with the heater voltage feeding the 400k.   Is there a way of analyzing the optimum value for the tempco compensation resistor or must this be empirically derived?   I suspect the latter...
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on February 16, 2016, 06:59:04 pm
What about humidity sensitivity for wire wound resistors like UPW50 and new Econistors? I haven´t tested UPW50 but many old 8E16. I have seen up to 2ppm/%RH on 8E16. That is 60ppm for a 30%RH variation, 100ppm for 50%RH and 160ppm for 80%RH. For me that is worse than temperature coefficients up to 5ppm/C that also is easier to compensate. On the 8E16 and also on metal foils like RN55 and BMF like S102 and VSMP it seems that higher values, like 10k and 100kohm, is worse with around 1ppm/%RH and 100 and 1kohm sometimes is close to zero sensitivity but variation might be large. As time constants is weeks or maybe months humidity sensitivity is difficult to test.

For the LTZ1000 this means that if you are unlucky you can have say 1ppm seasonal variations that is tricky to check. Seasonal variations may also make your drift assumptions to be completely wrong.

If you are lucky with your wire wounds the 1-12.5-70kohm humidity sensitivities to LTZ sensitivities cancel a little but you never know.

Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 16, 2016, 07:28:22 pm
Quote
I suspect that a larger than the theoretical 0.05ppm/K TempCo was discovered when the LTZ1000 was used, and the ~400K resistor was a "hack" to fix the symptoms instead of fixing the real problem.  Honestly, you should leave this 400K resistor out of your build, and use proper mechanical design that addresses the thermal issues instead of hacking on your circuit until it works

Well, interestingly you wont find this 400k resistor in the circuit diagram of the LTZ1000 (none A) in the paper "The Ultra-Zener ... is it a portable replacement for the Weston Cell?" (Reveived 15 December 1989).
Leads to ask at what time this resistor was put into the circuit diagram.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on February 16, 2016, 08:21:44 pm
Many analog circuits run at a temperature well above room temperature - could be intentional or just a nice side effect. This keeps down relative humidity - a 10 K temperature rise already reduces humidity to about half. So variations in humidity are not that large anymore (e.g. only half as well) - at least for instruments that run continuously.

The reduced humidity also helps to keep leakage currents down - surface leakage get worse at high humidity levels (e.g. above about 50% for glass).

With the 400 K resistor for temperature coefficient compensation, I am a little suspicious, as the the voltage at the heater varies with the square root of the heater power which is about linear in temperature. So the effect of the resistor would be larger at a low temperature set-point. Also the thermal design (e.g. long vs. short leads) would have an influence.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 17, 2016, 09:27:20 am
As a couple of data points re humidity - when I ran some regressions on MM's 3458a data a while back (I still need to do some more) I didn't get any obvious coefficients re pressure or humidity - drift was mostly a function of time and internal temperature. Another data point is the Fluke 732 analysis (I appreciate not an LTZ1000, but indicative of precision refs in general) - they hinted at some 'seasonal variations' (which I took to mean RH) with their fitting equation. Fluke didn't elaborate further. This all suggests to me a relatively minor role for humidity and pressure in built refs. Lars - btw how did you calculate your RH coefficients / do your RH experiment?

A.

p.s. I was hoping to get my drift experiment underway before I left for vacation. However, I discovered a lot of noise on my 'low noise' power supply :) It will have to wait until I'm back now.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 17, 2016, 07:48:44 pm
Hello,

What about humidity sensitivity for wire wound resistors like UPW50 and new Econistors?

BMF resistors in epoxy packages can vary as much as 25ppm from 0% to 100%, and they can do this in 30 minutes or less!  PWW resistors on epoxy bobbins will also be affected by humidity if there is inadequate spacing between the winding and the bobbin, and also if the welds to the resistance wire are not good [letting the wire move while the epoxy is flexing due to the humidity and/or temperature changes].

in my T.C. measurements I blame the "ageing drift" which I measure over 3 days (up to 5-6 ppm) to the fact that my peltier box traps some humidity over this time.
I have also put a dry-pack into the box and the drift changed direction after this.
In principle I have no significant difference between Z201 and PWW resistors. (both up to 6 ppm within 3 days depending on air humidity).
Both have a epoxy housing which swells with humidity (more or less depending on actual resin) and no one can tell me that this has no influence on the wire.
You simply cannot fully isolate the wire (= strain gauge) mechanically from the epoxy.

I think it has its reason why precision voltage dividers use mica cards for their wire wound resistors.

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 17, 2016, 07:51:40 pm
Well, interestingly you wont find this 400k resistor in the circuit diagram of the LTZ1000 (none A) in the paper "The Ultra-Zener ... is it a portable replacement for the Weston Cell?" (Reveived 15 December 1989).
Leads to ask at what time this resistor was put into the circuit diagram.

Hello,

interesting, they use a FET for the zener current like my cirquit.
But they have forgotten the pull down resistor at the gate of the FET.
Without this the LT1013 may get instable...

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 17, 2016, 11:22:44 pm
68k collector resistors, too; closer to 100uA than 70k.
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on February 18, 2016, 11:57:14 am
Lars - btw how did you calculate your RH coefficients / do your RH experiment?


About every second month I spend a couple of hours to measure a couple of hundred resistors (and many DIY 10V refs) against my HP3456A. I have done this for almost 20 years.

Lately I have also started to use ice-cream boxes and large bags of silica gel prepared for different humidity’s. Right now I have a VREF10 from Voltage standard under test.
See also https://www.eevblog.com/forum/metrology/calibratory-d-105-dc-precision-voltage-reference-standard/msg803701/#msg803701
 (https://www.eevblog.com/forum/metrology/calibratory-d-105-dc-precision-voltage-reference-standard/msg803701/#msg803701)for an example of my use of the box that revealed a 20ppm change due to humidity on the 2ppm specified D105 ref.

For the long-term tests with the HP3456 I use regression in Excel to get temperature, humidity and aging. I enclose a couple of screen shoots from Excel with temperature compensation but not aging and humidity.

The first chart is 100ohm, 1k, 10k and 100kohm wire wound 8E16. The 1Mohm is ordinary 1% metal films I happened to have 20 years ago, if I remember correct I selected four 220kohm + some smaller to get to 1Mohm with low tempco. (As a side note I have seen up to 1000ppm/year drift on some new 0.1% metal films from Reichelt).

From 1997-2001 the values are relative to the 3456 and a small extra humidity sensitivity about 0.1-0.2ppm/C can be seen due to the 3456. From 2001 I got a GR1440-10k that is the reference and the 100ohm, 1k, 100k and 1M is related though a home built resistance decade. I enclose a picture of one of many home-built decades I have including my parallel and series-parallel adapters.

I also enclose a chart showing 100ohm, 1k, 2 pcs 10k and 100kohm VHP resistors I have had six years. Remember that the 3456 has 1ppm resolution and to get from the 10k GR1440 to for example the 1kohm I have to measure the GR, the VHP and series-parallell 10x1k+ series 10x1k+one of the 1k. So the ripple is not so bad, sometimes it also can be seen that I have some wrong values. Nowadays I have an automated routine that takes 20 samples with 10PLC but disturbances can still occur. Earlier I averaged a few samples with 100PLC in my head.

The last chart is two each of 100ohm, 1k and 10k of VSMP 1206SMD soldered on two small FR4 board.

Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 18, 2016, 01:12:44 pm
This is what I call dedication. Appreciate efforts and sharing results.
Title: Re: Ultra Precision Reference LTZ1000
Post by: blackdog on February 18, 2016, 01:31:54 pm
Hi,


If you want to know how to measure realy low noise references, look @ this webpage:
http://www.edn-europe.com/en/measuring-2-nv/-8730-hz-noise-and-120-db-supply-rejection-in-linear-regulators-the-quest-for-quiet-part-2.html?cmp_id=7&news_id=10008095&vID=1328&page=0 (http://www.edn-europe.com/en/measuring-2-nv/-8730-hz-noise-and-120-db-supply-rejection-in-linear-regulators-the-quest-for-quiet-part-2.html?cmp_id=7&news_id=10008095&vID=1328&page=0)

Happy reading  ;)

Kind regarts,
Blackdog
Title: Re: Ultra Precision Reference LTZ1000
Post by: fmaimon on February 18, 2016, 10:57:41 pm
If you want to know how to measure realy low noise references, look @ this webpage:
http://www.edn-europe.com/en/measuring-2-nv/-8730-hz-noise-and-120-db-supply-rejection-in-linear-regulators-the-quest-for-quiet-part-2.html?cmp_id=7&news_id=10008095&vID=1328&page=0 (http://www.edn-europe.com/en/measuring-2-nv/-8730-hz-noise-and-120-db-supply-rejection-in-linear-regulators-the-quest-for-quiet-part-2.html?cmp_id=7&news_id=10008095&vID=1328&page=0)

Or, better yet, read from the pdf from Linear AN159 (http://cds.linear.com/docs/en/application-note/an159f.pdf).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 20, 2016, 10:10:41 am
Hello,

after 2 weeks without temperature cycling the popcorn noise on my LTZ#5 has restored.  :(

see reduced noise after temperature cycling
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg856965/#msg856965 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg856965/#msg856965)

and previous behaviour
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg833804/#msg833804 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg833804/#msg833804)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 20, 2016, 10:44:11 pm
Hello,

further results on
LTZ#4 (LT1013) and
LTZ#6 (LTC2057)

First the operating points compared to the LTZ#3 and LTZ#5 values

and then the PCB twisting test (to check the influence of mechanical stress to the PCB).
I am bending the PCB on different directions and record the zener voltage of the LTZ
as difference to another zener in 100 mV range of a meter.

Result is around 4 uV change (or 0.5ppm) when bending the PCB
with no significant difference dependant of operational amplifier.
-> a good value (I will not try to bend the PCB within metal housing).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 21, 2016, 09:22:07 pm
Hello,

today I improved thermal management:
a additional PCB slot between voltage regulator and the LTZ1000
zener to keep the waste heat (battery voltage dependant) somewhat away from the LTZ.

Battery voltage was sweeped between 14 and 18.5V (typical operating range around 14.5 to 17.4V)

Without slot on LTZ#3 the voltage output change was around 5uV / 4.5V (0.15ppm/V) as regression curve.
With slot the change is reduced to 2.9uV / 4.5V (0.09ppm/V).

On LTZ#5 I have 2.1uV/4.5V (0.06 ppm/V) with the slot.
Unfortunately I missed to measure the "before" data.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 22, 2016, 04:09:09 am
How about tempco of your design? Any plans on those tests?
I'm getting some interesting results during last 2 weeks on my three proto LTZ modules. Going to make summary analysis after all data aligned.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 22, 2016, 06:28:54 am
Hello Illya,

of course I have planned the T.C. measurements.
But those will be the last tests after all shieldings are finally installed.
on #5 this will take some time. Since I probably have to exchange the zener anyway (popcorn noise)
I want first do a test with short legs and the influence on tilting and local heating.

And with the results of local heating I suspect that the T.C. will appear different according to ramp speed.

Another question is if there is a dependency of T.C. of zener voltage like on LM399.

with best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on February 22, 2016, 04:27:29 pm
The correlation of TC and zener voltage will be likely similar to the LM399 or other similar refs. It's a more or less fixed feature of silicon zener diodes.

There is some popcorn noise, but not that much. The reference may still be useful. The popcorn noise also looks a little strange, showing a sharp jump and a slow relaxation after that in this case even sufficient filtering might be a sufficient countermeasure. This somewhat makes me think the noise could even originate from the temperature stabilization part (e.g. the sensing transistor). For classical popcorn noise I would more expect something like sharp steps up and down at more or less random times, thus essentially jumping between a high and low value.  This would a way nastier case.

It could also be a candidate to test higher currents for the zener diode and the transistors (70 K resistor). The two 70 K resistors in the originally circuit do not have to be the same - the same value is just convenient. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 22, 2016, 07:48:50 pm
The popcorn noise also looks a little strange, showing a sharp jump and a slow relaxation after that in this case even sufficient filtering might be a sufficient countermeasure.

Hello,

for me it does not look strange.
Do not forget that there is a high pass with a time constant of 3 sec within the amplifier.
The simulation shows the same behaviour for a 1 sec rectangular jump.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on February 22, 2016, 08:29:22 pm
The filter in the amplifier explains the shape. So nothing unusual there.

Still jumps of something like 1 µV or 1.5 µV are not that bad, that is within the noise specs of the LTZ1000. It may be that other people just can resolve these jumps and see it as 1/f noise. So ref. 5 might not be the best one, but still OK.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 25, 2016, 08:12:39 pm
I was running three of my prototype boards for some TCR measurements and testing few ideas how to improve it. I think few tricks could work for my boards.
Still one more thing to check, and then I'll try to post all data and my take on it.

Setup jig:

(http://doc.xdevs.com/doc/xDevs.com/KX/REFb/setup_m3_top_1.jpg) (http://doc.xdevs.com/doc/xDevs.com/KX/REFb/setup_m3_top.jpg) (http://doc.xdevs.com/doc/xDevs.com/KX/REFb/setup_m3_bot_1.jpg) (http://doc.xdevs.com/doc/xDevs.com/KX/REFb/setup_m3_bot.jpg)

Final reference will go into own box, such as this:

(http://doc.xdevs.com/doc/xDevs.com/KX/REFb/setup_box_1.jpg) (http://doc.xdevs.com/doc/xDevs.com/KX/REFb/setup_box.jpg)

(http://doc.xdevs.com/doc/xDevs.com/KX/REFb/setup_box_t_1.jpg) (http://doc.xdevs.com/doc/xDevs.com/KX/REFb/setup_box_t.jpg) (http://doc.xdevs.com/doc/xDevs.com/KX/REFb/setup_box_b_1.jpg) (http://doc.xdevs.com/doc/xDevs.com/KX/REFb/setup_box_b.jpg)


Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on February 25, 2016, 10:29:38 pm
>>> Still jumps of something like 1 µV or 1.5 µV are not that bad, that is within the noise specs of the LTZ1000. It may be that other people just can resolve these jumps and see it as 1/f noise.

Just reading my new (to me) copy of Henry Ott - he points out that the noise is gaussian (both johnson and 1/f) with unbounded tails, so (in principle at least) any jump is possible. Some kind of noise distribution would be a nice way to compare refs.

A.
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on February 26, 2016, 12:12:42 am
Here is my version :)
The red cup covering LTZ1000 is SP163 (http://www.tme.eu/gb/katalog/?art=SP163# (http://www.tme.eu/gb/katalog/?art=SP163#))
The board fits into Fischer TUF-series encolsure.
Photos below.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 26, 2016, 12:49:20 am


Here is my version :)
Photos below.

Beautiful board, welcome! Output is direct 7V or scaled, based on second LT1013 presence?

Looking forward for your tests ;).
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on February 28, 2016, 03:25:37 am
Thanks Guys!

@TiN: First LT1013 works in typical application scheme, the second LT1013 buffers direct LTZ1000 output and buffers a divider giving ca. 7V* similarly to DrFrank's project.

P.S.1 TiN, on xdevs.com there is a "LTZ1000 calculator". Is it finished and working?

P.S.2 Question to the people who did their boards/ experiments with LTZ1000: what is the output voltage  in Your case (R1=120R, typical LT app note) ?
*I'm considering using not 7,00000V but 7,10000V as divided output, because the TC of divider's resistors would have ca. 3x lower dependency on divided output voltage TC. The divided output would be then a good point for inter-comparisions of many boards using a null voltmeter (because my K2001 is not stable enough on the 20V range). Any Comments?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 28, 2016, 07:42:36 am
Let me fix calc tonight. I did not expect anyone notice it :) I don't think that it works currently.

Five modules I had built have around 7.15V (120R, 1K, 12 or 13K for low temp, 70K resistors).

Here is old log, taken by K2002 with scan card.

Logged data (http://dev.xdevs.com/attachments/download/1065/kxdata_1.xlsx).

(http://dev.xdevs.com/attachments/download/1064/kxdata_1.png)

I almost finished tempco testing for three modules, last one today.

I'll have one more built soon, with socket for LTZ. Will see how bad is the socket idea for such a design :).
Nullmeter tests will follow too, when my Fluke 845AB arrives.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 28, 2016, 04:02:35 pm
First T.C. measurement:

I decided to make a preliminary T.C. measurement on #5 (before shortening the legs to have "before" data).

I evaluated with 3 ADCs and 2 6,5 Digit Multimeters in 10 V range connected in parallel.
Room temperature changed about 3 deg C during measurement so the Multimeters (not shown in diagram) both drifted around 4.5 ppm.
The ADCs which are temperature compensated behaved much more stable. (below 1.2 ppm)

ADC16 shows best stability. Which is due additional temperature controller to 27 deg C environment.
The other 2 ADCs drifted around 4-5uV during measurement.

Picture over time:
the ADCs are additionally filtered with a 21 sample moving average filter additionally to the 1 minute integration time.
red ADC16 (around 2.5uV change)
pink ADC13 (5.4 uV change)
light blue ADC15 (4.2 uV change)


due to the large thermal mass I have difficulties to get the intended -0.1K/minute slope below 20 deg C.
And also minimum temperature reached was only 14 deg C instead of around 10 deg C.

there are 3 temperature sensors involved:
pink: heat spreader below the LTZ aluminium case (sensor of temperature controller).
green: NTC on top of the aluminium case of the LTZ#5
blue: NTC on PCB inside aluminium case (near zener) of LTZ#5

Picture ADC16 shows the noisy raw values together with the moving average filtered values
over LTZ#5 "environment" temperature (NTC on top of aluminium case).

The output voltage shows no dependancy from temperature.
The shift is more or less contributed by the ramp direction.
Negative temperature ramp gives a somewhat higher output voltage than
positive temperature ramp.

T.C. calculation is a bit useless in this case.
If I take the 2.5 uV filtered value as box T.C. together with the
14-37.8 deg C outside temperature. (23.8 K difference).
I get a "box TC" of 0.015 ppm/K.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 29, 2016, 08:53:37 pm
Hello,

now I wanted to know it if all LTZ are with "zero T.C."

so yesterday I measured LTZ#3 (with LT1013A in CERDIP8 package instead of LTC2057).

This time I used the 6.5 digit DMMs not as absolute voltage measurement but as difference voltage in 100mV range between the known good LTZ#5 and the DUT = LTZ#3.
The ADCs remained as absolute volt measurement after 2:1 capacitive divider.

The shocking results:
ADC16 shows 15.4 uV change with moving average filter over a 23.7 deg C environment temperature range
(measured on top of the aluminium case). So a 0.091 ppm/K "box T.C"
Or -87 ppb/K as regression curve.

The 6.5 digit multimeters show 14.5 / 14.6 uV change under same condition. (0.086 ppm/K "box T.C.")
The regression coefficient is -80 ppb/K.  (against 50 ppb/K in data sheet).

The PSRR (due to voltage regulator heating) was also worse on  LTZ#3 than on LTZ#5.
...  will have to do further testing on this.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 29, 2016, 10:10:15 pm
It could have been worse I thought yesterday.

and it came worse  :-//

Today I measured LTZ#4 (with LT1013A)

around 36 uV or 5 ppm over 22 deg C environment change.

Edit: exact evaluation

ADC16: 35.7 uV over 22.1 deg C measured on top of aluminium case
giving box T.C. of -0.224 ppm/K
regression curve also gives -0.224 ppm/K

Both 6.5 digit DMMs show 36.3 / 36.4 uV change in 100mV Range as difference between LTZ4-LTZ5 = 0.229 ppm/K box T.C.
regression curve gives  -0.228/-0.229 ppm/K

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 01, 2016, 10:15:31 pm
And now the last of my 4 new references:

LTZ#6 this time again with LTC2057 as OP-Amp.

ADC13 measured 6.5 uV shift absolute over 22.7 deg C change.
The 2 DMMs both measured 6.3 uV shift.
So a box T.C. of below 0.9 ppm/22.7 deg = 0.04 ppm/K.
So with the 2 LTC2057 based references I cannot complain.

Was the LT1013A with hermetically package and KOVAR leads the wrong decision?
But in Datron reference there is also a hermetically package (Metal case) for the LT1013.
And Datasheet of LTZ states a maximum error of 2 uV over 50 deg C for the LT1013.

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 06, 2016, 07:06:54 am
Hello,

measured LTZ#4 on some temperature points together with different values of R9 (the 400K resistor for LTZ1000)

Result is attached as diagram.
Without the resistor I have around -0.26 ppm/K
A 1 Meg resistor changes this to  around -0.22 ppm/K
The 402K resistor gives around  -0.18 ppm/K
A 100K resistor gives between +0 and +0.14 ppm/K depending on temperature range.
(so a large T.C. trimming gives a non-linear behaviour).

So the truth for LTZ#4 would lie somewhere in between 100K and 402K.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on March 06, 2016, 08:36:17 pm
Finished 2x KX boards with Edwin resistors. Setpoint is 45°C (12k/1k). Additional two boards waiting for resistors - few 100k ones were out (5ppm/K).
All 120R were about 2,5 ppm/K and the rest were <1ppm/K, which is quite good.
Both are now up and running connected to null meter to compare them directly.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 06, 2016, 10:05:03 pm
Hello Plesa,

 :-+

waiting for your measurement results (especially T.C. where I had only 50% luck).
Also waiting for T.C. results of TIN.

Today I removed the LT1013A from LTZ#4 and replaced it by 2*LTC2057. (also removed C14+C15).
First quick test indicates 22.5 uV change over 13.7 deg C temperature giving the already known -0.228 ppm/K
So the KOVAR leads of the hermetically LT1013A are definitively not the reason for the large T.C.
(should have known this as Kleinstein always explains that the critical amplification is already on the LTZ chip).

So it seems that not all LTZ1000A reach the typical 0.05ppm/K.

with best regards

Andreas

Edit: @Plesa: are the resistors the standard size 805?  (6.3 * 13 mm) For me they look somewhat smaller.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 12, 2016, 04:16:13 pm
Hello,

update: T.C. of LTZ#4 with R9 = 220K

The box output voltage variation is reduced from around 5 ppm to 1.8 ppm. (So still too high value).
So a negative T.C. of LTZ can be (more or less) cured by the appropriate value for R9.
I will have to check the influence on output noise when I have found the correct R9 value.
(the heater voltage drifts in the mV range).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 12, 2016, 07:40:48 pm
The TC of the final reference module has more factors than just the TC of the Chip itself:

The first part is the TC of the zener/transistor that might be at somewhere in the 50 ppm/K range.. Here the thermal regulation reduces the temperature change by a certain factor. How good the thermal regulation works depends mainly on the internal positions of the heater / sensor and sensitive part. Looking at the gain of the thermal loop, the OPs open loop gain should not jet be the limiting factor - a gain or more than about 1000 should be enough. So not much advantage of the LTC2057 here either.

Other factors are to a much smaller part the TC of the divider for the temperature setpoint. Attenuated by a factor of about 100 from the circuit this should not give a big deal. Still to get 0.05 ppm/K one needs a better than 5 ppm TC matching for these resistors.

Another factor is thermal EMF from the leads of the LTC1000 chip itself. Here a change in temperature causes a change in power to the internal heater and thus in the heat flow from the chips trough the covar leads. So a rather symmetric thermal setup is needed to prevent temperature differences between the pins. My rough estimate gives about 1/5 of the temperature difference to appear in the board. So to get the 0.05 ppm/K goal, the symmetry must be so good that the temperature rise of the pins is within about 2% - so a not so perfect thermal design can be an issue too. So in principle one might be able to tune the TC by adjusting the thermal cut-outs around the reference.
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on March 17, 2016, 10:32:03 pm
Can someone explain the first graph on page 3 of the data sheet, 'Zener voltage v current,' please? 'Zener voltage alone' is obvious enough but what exactly is being measured in the 'Zener with Kelvin sensed Q1' case and what is its significance? I'm sure it's obvious to most but I can't see it.

Is it the change in Vz + Vbe (Q1) versus Iz, as R1 is varied (in the usual cct)?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 17, 2016, 10:41:48 pm
Can someone explain the first graph on page 3 of the data sheet, 'Zener voltage v current,' please? 'Zener voltage alone' is obvious enough but what exactly is being measured in the 'Zener with Kelvin sensed Q1' case and what is its significance? I'm sure it's obvious to most but I can't see it.

Is it the change in Vz + Vbe (Q1) versus Iz, as R1 is varied (in the usual cct)?

The zener alone has around 20 Ohms dynamic resistance (20mV/mA)
Together with Q1 you are getting around 5 Ohms (5mV/mA).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 17, 2016, 10:51:11 pm
Hello,

today I shortened the legs of LTZ#4. (After removing R9 again).

So first results:
Current consumption increased by 12% (22.6 mA -> 25.2 mA) (more heater power necessary).
Zener output voltage decreased by around 130-140uV (around -20ppm)
Of course the heating up time increased also. (Termal mass of PCB).

Will check PSRR and tilting on week end.

With best regards

Andreas



Title: Re: Ultra Precision Reference LTZ1000
Post by: tszaboo on March 18, 2016, 02:07:40 pm
Someone remind me to post my experiences with the LTZ1000 in about 10 month. I had a design, few hundred of these were built into some equipments, and my NDA will be over by then.
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on March 21, 2016, 05:20:37 pm
Can someone explain the first graph on page 3 of the data sheet, 'Zener voltage v current,' please? 'Zener voltage alone' is obvious enough but what exactly is being measured in the 'Zener with Kelvin sensed Q1' case and what is its significance? I'm sure it's obvious to most but I can't see it.

Is it the change in Vz + Vbe (Q1) versus Iz, as R1 is varied (in the usual cct)?

The zener alone has around 20 Ohms dynamic resistance (20mV/mA)
Together with Q1 you are getting around 5 Ohms (5mV/mA).

With best regards

Andreas

Thanks Andreas, so you mean the load regulation which makes sense. That's not exactly obvious from the graph showing the change in zener voltage with zener current - in the kelvin sensed case they really mean the current in the *virtual zener* comprised of the zener, Q1 and the LT1013.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 24, 2016, 07:18:33 pm
Since I've got known measured LTZ ref in my lab, I'm running DCV/DCV Ratio measurements last days using 3458A.
Here's setup and ratio on first module.

(https://xdevs.com/doc/xDevs.com/KX/REFX/_LAB7170_1.jpg) (https://xdevs.com/doc/xDevs.com/KX/REFX/_LAB7170_1.jpg) (https://xdevs.com/doc/xDevs.com/KX/REFX/m1_ltz_1.png) (https://xdevs.com/vtx_ltz_t2/)

Reference unit (A9 PCB from HP3458A) is in DIY TEC thermostat, at +23.4°C +/-0.01°C.
Unit under test - my KX LTZ reference design is at ambient temp, battery powered.

Second module comparison (https://xdevs.com/vtx_ltz_t3/)

A9 Reference measurements (https://xdevs.com/vtx_ltz1_t1/), with various temperatures (constant +23.4, temp at which it was measured by calibrated last summer 3458A, ramp +23.4 to +46C in 0.1C/10 minute speed, constant +50C). Measured value is +7.184609VDC, so after a day of warmup calibrated my 3458A to CAL 7.184609VDC.

I could not figure out what is tempco of A9 Ref. It's stock module, no tweaks/mods. Originally I wanted to use K2002 in parallel to measure A9 ref value as well, but impedance of meter not high enough and cause ratio to change ~4ppm.

Title: Re: Ultra Precision Reference LTZ1000
Post by: TheAmmoniacal on March 24, 2016, 07:34:47 pm
Anyone got working LTZ1000 board PCBs to sell?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 24, 2016, 07:44:18 pm
Originally I wanted to use K2002 in parallel to measure A9 ref value as well, but impedance of meter not high enough and cause ratio to change ~4ppm.

Hello,

the K2002 has > 10 G input impedance in 20V range.
So even with worst case calculation of 5 Ohms for the zener you should get something in the ppb range and not PPM.

I think that one of your references picks up some RFI noise when connecting additionally antennas.
See the problem with my buffered output without 100nF capacitor where I have a "offset" of +3ppm without the capacitor.
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg846835/#msg846835 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg846835/#msg846835)

Unfortunately you have to be very carefully with capacitors on the output with the original datasheet cirquit.
(the current regulator may oscillate).

with best regards

Andreas

Edit: just measured the change between 10Meg and >10G on HP34401A (10V range LTZ#4) with the K2000 (100mV range) in differential mode (LTZ#4-LTZ#5).
it is around 0.3-0.4 uV for the 10 Meg input resistance.
A 1Meg Resistor across LTZ#4 gives 3.4uV change. (so less than 0.5ppm).
So we have less than 0.5 Ohms for the unbuffered zener voltage.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 25, 2016, 04:14:41 pm
Likely you are right, as I used not shielded twisted cable wire to connect. I'll have to redo it better next try, to be sure.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on March 26, 2016, 10:46:52 pm
Am I misunderstanding the schematic in https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg902577/#msg902577 (https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg902577/#msg902577) or did CERN go with proportional-only temperature control?  Any idea why? That would seem to me to add more temperature sensitivity.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 27, 2016, 07:46:00 am
Hello,

C80 gives some I-part to the controller.
But this is limited by the 330K resistor.

On the other side you have additional current amplification by the
power stage transistor T2 against the datasheet cirquit (A = 1).

Anyway: Without a capacitor from base to emitter of the sensing transistor Q2
the temperature controller is very noisy.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 27, 2016, 09:09:05 am
Not having a capacitor at the base of the sensing transistor should not be such a big problem with noise, at the low impedance there you can't effectively filter the LF noise from the zener reference anyway. Here the capacitor at the 7 V level might be more effective than at the sensing transistor. Still a capacitor there might be a good idea for EMI reasons.

The 330 K resistor in feedback makes this a proportional type controller - no more integral part left. The gain is rather high so it may not be a problem after all.  Still it is well possible that the quality if temperature control is simply limited on how well the heater and sensor are placed inside the LTZ1000. You can't do better than that.

Still I don't think this modified version of temperature control is an improvement, more like a poor example. For example short time fluctuations on the temperature of the driving transistor and the diode would require the controller to react - so this may be a reason why a real integral part is not helping with that type of output stage. Also the 2.2 K resistor from the divider to the OP will slightly shift the temperature setpoint and in this sense makes the whole circuit sensitive to the temperature of the diode and transistor. 

If I were to improve on the regulator part, I would try to compensate the square law of the heater, not to reduce regulator gain when the power goes down - this might give improvements at low heater power and should allow for twice the gain in the normal case, as there is no need for extra stability reserve at high power. With improved performance at low power one might consider a second level of regulation if really needed. With the often rather high temperature inside instruments this might be well something like a temperature controlled fan and suitable shielding against direct air flow of the sensitive parts.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 27, 2016, 12:47:28 pm
Not having a capacitor at the base of the sensing transistor should not be such a big problem with noise, at the low impedance there you can't effectively filter the LF noise from the zener reference anyway.

Hello,

my measurements tell something other for the LF noise.
I get a reduction from 6mVpp to 0.6mVpp with the capacitor.
And also the sporadic dips of -40mVp are gone on the heater voltage.

with best regards

Andreas



Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 27, 2016, 01:18:18 pm
Hello,

summary of my measurements with shortened legs on LTZ#4:

power supply current
edit: increased from 22.6mA  to 24.0 mA (+6%) for LT1013A
increased from 22.6mA  to 25.2 mA (+12%) when changeing from LT1013A to LTC2057

PSRR 14-18.5V battery voltage
no significant change: from 0.076 ppm/V to 0.084ppm/V

Tilting LTZ#4
no significant change: from 0.25-0.31ppm to 0.26-0.29 ppm

Noise LTZ#4 unbuffered output:
from 1.19 uVpp to 1.05 uVpp in average (15 measurements over 100 secs)

T.C. of reference (without R9).
decreased from -5.1 ppm over 22 deg C  (-0.23 ppm/K) to -2.1 ppm (-0.095 ppm/K)

so all in all:

higher power consumption, slightly lower noise (could be within statistics) and large reduced amount of T.C.
so I will try wether R9 = 402K will give near zero T.C.

attached the T.C. before shortening the legs and T.C. after shortening the legs.

Also attached the FFT of a noise measurement.
nothing unexpected here.
Above 10Hz the edge of the filter amplifier is seen. And of course some 50Hz mains hum.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 27, 2016, 04:46:48 pm
Is there an explanation for the change in voltage due to the shorter leads  (130 µV noted down below) ? 

I am surprised to see so much change, as normally the slight higher thermal current should not change much. There is thermal EMF at the leads, but this should compensate to a very good approximation. The design must be terribly off if differences as large as 3 K exist.

It might be interesting to compare to the change when changing the thermal shield - this can also have an influence on the heater power.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 27, 2016, 06:52:34 pm
Is there an explanation for the change in voltage due to the shorter leads  (130 µV noted down below) ? 

The design must be terribly off if differences as large as 3 K exist.

130uV are around 18 ppm so less than 0.4K for the zener  (50-55 ppm/K without thermal regulation).
So how do you calculate 3K difference?

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 27, 2016, 08:11:17 pm
The 3 K change would be from the about 40 µV/K thermal EMF. So this estimate only shows that this is not the source.

If you calculate back to the zener temperature, this would be 0.4 K - but this would be a huge change against a temperature regulator.  As the feedback loop itself has rather high gain and ideally (e.g perfect position of sensor/heater) should get the temperature stable to mK or better. So I really doubt the hole chip changes by 0.4 K - this would suggest a surprisingly poor thermal design. The more likely part would be having a change in the difference for the zener and compensating transistor. So more like a change in temperature difference by 0.06 K. Still this does not sound like a good thermal design for the non A LTZ1000.  In this case a different thermal isolation cap could also have quite some effect.

With so much sensitivity to the thermal design / heat flow one might really consider using a second layer of thermal stabilization.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on March 27, 2016, 08:16:40 pm
The 3 K change would be from the about 40 µV/K thermal EMF. So this estimate only shows that this is not the source.

If you calculate back to the zener temperature, this would be 0.4 K - but this would be a huge change against a temperature regulator.  As the feedback loop itself has rather high gain and ideally (e.g perfect position of sensor/heater) should get the temperature stable to mK or better. So I really doubt the hole chip changes by 0.4 K - this would suggest a surprisingly poor thermal design. The more likely part would be having a change in the difference for the zener and compensating transistor. So more like a change in temperature difference by 0.06 K. Still this does not sound like a good thermal design for the non A LTZ1000.  In this case a different thermal isolation cap could also have quite some effect.

With so much sensitivity to the thermal design / heat flow one might really consider using a second layer of thermal stabilization.

Or perhaps that the old (long-leg) design was a poor choice for the non-A LTZ1000.  The datasheet does explicitly call for short legs, after all.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 27, 2016, 08:40:00 pm
I see that the data for the short legs look better (lower TC) - but this still means the point with a higher heater power and thus more internal temperature gradients. 

This makes me think, if if might be even better not to use the internal heater, but only the internal sensor and an external heater instead. As the heat flow would be only due to the rather constant internal loss, there should be much better temperature stabilization. I know an external heater would need more power and is slower, but who cares in a 24/7 line powered application.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 27, 2016, 08:51:16 pm
Or perhaps that the old (long-leg) design was a poor choice for the non-A LTZ1000.  The datasheet does explicitly call for short legs, after all.

Hello,

where have you found this?
Up to now I have only found that "thermal layout"  is essential to get full performance.

And in my opinion you get lesser thermal EMFs (more equal temperatures on solder joints) when leaving the leads long.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 27, 2016, 08:55:55 pm
I see that the data for the short legs look better (lower TC)

This is only true for my sample LTZ#4.
On LTZ#5  I have "zero T.C." with long legs.
So I guess I would get a +0.15 ppm/K T.C. if I shorten the legs on LTZ#5.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on March 27, 2016, 09:25:06 pm
Or perhaps that the old (long-leg) design was a poor choice for the non-A LTZ1000.  The datasheet does explicitly call for short legs, after all.
where have you found this?

Whoops, I was looking at the wrong datasheet!  I didn't have enough of the filename showing, sorry.  :palm:
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 28, 2016, 05:24:08 am
Mhm,

would be anyway interesting which device calls for short legs.

By the way: I did some error in comparison of the power consumption.
The 25.2 mA are for LTC2057 instead of LT1013A.
After changeing back to LT1013A I have only 24.0 mA.
So only a increasement of 6%.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 28, 2016, 09:18:51 am
Quote
would be anyway interesting which device calls for short legs.

Well, LM199 calls for short legs, refering to AN-161 and similar thermal mass at each pin:

"...Thermocouple effects can also use errors. The kovar leads from the LM199 package from a thermocouple
with copper printed circuit board traces. Since the package of the 199 is heated, there is a heat flow along
the leads of the LM199 package. If the leads terminate into unequal sizes of copper on the p.c. board
greater heat will be absorbed by the larger copper trace and a temperature difference will develop. A
temperature difference of 1°C between the two leads of the reference will generate about 30 ?A.
Therefore, the copper traces to the zener should be equal in size. This will generally keep the errors due
to thermocouple effects under about 15 ?V.
The LM199 should be mounted flush on the p.c. board with a minimum of space between the thermal
shield and the boards. This minimizes air flow across the kovar leads on the board surface, which also
can cause thermocouple voltages. Air currents across the leads usually appear as ultra-low frequency
noise of about 10 ?V to 20 ?V amplitude..."
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 28, 2016, 10:17:13 am
There are several differences between long and short leads:

As advantage of short leads and thus not so good thermal insulation there is less temperature rise due to the internal power - so the set temperature might be chosen slightly lower (e.g. 2-5 K). Also thermal regulation might be slightly faster and thus could allow a faster regulation loop - but that is likely not an issue anyway. At least usual the thermal regulation is not build for ultimate speed.

Thermal fluctuations under the chip can also be avoided with a spacer or padding - so this is a rather weak argument for short leads.

With short leads one has a higher heat-flow through the leads and thus more sensitivity to unbalanced thermal layout. Also more power is needed to stabilize the temperature so chip internal temperature differences are also expected to be larger. This last point might be rather critical - at least for me it's the best explanation for the change in voltage just from changing the thermal setup. Often extra insulation is used to keep the thermal resistance high - so I see no good reason not to do that with leads too.

It might be interesting to check how much influence the thermal insulation has - it is well possible to have the TC separated into an effect of heat flow through the leads and heat flow through the cap part. I would also expect the TC is more an effect of the heat flows and less of the direct TC, as at least the sensor part of the chip should have a very stable temperature. With an effect due to heat flow it somewhat makes sense to have the 400 K compensation resistor from the heater voltage, though the heater power and thus the heater voltage squared should be more suitable.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 28, 2016, 10:53:20 am
I'm under impression that long leads cause large thermal gradient from zener to copper tracks on PCB, causing uneven EMF. No matter how balanced is layout, it would not be exactly perfect anyway. By having chip close to PCB (mostly it's bottom sitting right on PCB surface!) PCB get warmer and there is less temperature gradient.
Title: Re: Ultra Precision Reference LTZ1000
Post by: IanJ on March 28, 2016, 05:50:58 pm
Hi all,

Just a wee note on the LTC2057..............I tried it on my precision digital voltage source on the final output after the DAC a few months ago but found it had a rather annoying glitch that I couldn't get rid of. Don't remember the exact nature of the glitch apart from it was just a few tens of uV.
I did try a few (same batch) to no avail, but changing to a different device the problem went away immediately.

Ian.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on March 28, 2016, 06:41:09 pm
would be anyway interesting which device calls for short legs.
I remembered the one from the LM399, but looked at the LT1007 datasheet when I checked if the LTZ1000 had a similar entry.  But the LT1007 doesn't have much self-heating to worry about, and the LM399 doesn't usually have its leads under a wind screen.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 28, 2016, 07:33:48 pm
Hello Ian,

sorry but the info from your side is a bit vague for me.

How did you measure the tens of uV change? (Oscilloscope or multimeter)
Which bandwith/NPLC settings did you use?
Wiring capacitance of your setup? (long coax-line?)
What was the other part number with no issues? (bipolar or CMOS?)
Is your output stage a voltage follower or a inverting cirquit?

I also had some problems with some uV drift measured on DMM for the LTC2057 in voltage follower cirquit.
I blame it on the CMOS protection diodes at the negative input.
But as Ken already described this can be solved with a output filter capacitor and a capacitive isolation cirquit.
It is generally a good idea to have some kind of isolation cirquit on precision outputs.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: IanJ on March 28, 2016, 07:57:33 pm
Hello Ian,

sorry but the info from your side is a bit vague for me.

How did you measure the tens of uV change? (Oscilloscope or multimeter)
Which bandwith/NPLC settings did you use?
Wiring capacitance of your setup? (long coax-line?)
What was the other part number with no issues? (bipolar or CMOS?)
Is your output stage a voltage follower or a inverting cirquit?

I also had some problems with some uV drift measured on DMM for the LTC2057 in voltage follower cirquit.
I blame it on the CMOS protection diodes at the negative input.
But as Ken already described this can be solved with a output filter capacitor and a capacitive isolation cirquit.
It is generally a good idea to have some kind of isolation cirquit on precision outputs.

With best regards

Andreas

Hi,

Yes a bit vague because it was a few months ago and I don't remember much about the exact nature of the noise. I do remember though that it wasn't at the chopper switching freq, it was a lot less.....I think at the time I thought it was picking up noise from something else on the pcb (lcd, Atmel uC etc)......and that I was a bit surprised to see it given I had tested quite a few other chopper op-amps and none of the rest exhibited the same issue......at all!

To answer your questions:-
- Not drift, but glitching. I have never had a problem with drift using any of the choppers I tested.
- Oscilloscope (Rigol 2202) and using a ground clip on the standard Rigol scope lead.
- The 2202 is a 200MHz scope, I tried with the 20MHz limit in & out (as I usually do).
- Output not connected to any DMM or any other leads used when testing noise with the scope.
- Voltage follower x2 gain (5ppm/degC resistors)
- My circuit has a similar setup by way of series resistor to isolate, and a snubber etc.
- The feedback cap is not in my circuit as standard, but only because it made no difference. My circuit is quite noise free (well, as much as the noise floor of the Rigol will allow). I remember trying the feedback cap on the LTC2057 but it made no difference.

I have tried a couple of other precision choppers.

LTC2050 - Limited to 11.5vdc supply max, nice op-amp, but output relatively easily damaged. No current limit or short circuit protected.

LTC1250 - Advertised as a bridge amplifier, but works great in all respects. The best all round solution for me, albeit the most expensive op-amp. Robust output.

I tried a bunch of others.......don't have the part numbers to hand.

Hope that helps.

Ian.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 28, 2016, 08:43:56 pm
Chopper OPs can be a little more sensitive to EMI problems and poor decoupling. Also high impedance sources can be a problem and may require an extra capacitance to ground. The input bias current is different from other FET OPs: as charge injection current the Bias is about opposite sign for both inputs - so no compensation  trough equal source impedance. Also the temperature dependence is not as strong as with other FET OPs. So the 30 pA for the LTC2057 are also valid at 50°C not only at 20 C.

For the LTZ1000 Reference I see not real need for a chopper OP, as reference chip has gain inside. The buffer Chip right after the reference is way more critical.

For the thermal design, the thermal resistance of a board without strong thermal cutouts will be somewhat comparable to the thermal resistance of the chip and pins - so the temperature of the solder joints will not follow the chip temperature, but only about half the way - maybe a little more with cutouts and less with a solid board with much copper. What really helps is that only the difference between the solder joints is what counts, and the coupling between the joints is usually way better than to the outside. Making the board thermal resistance really large compared to the pins is not that easy - one would need rather thin copper lines (e.g. 0.1-0.2 mm over 50 mm length). So I would still see an slight advantage for the longer pins - though I don't think the thermal EMF is really a problem in both cases.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on March 29, 2016, 02:56:49 am
Another consideration of the opamp is the tempco of the bias current, better to be small, to allow the divider pair to have larger values other than 1k:13k, for instance 2k:26k, 3k:39k or any value that not too large and having the same ratio. This is very helpful when buying off-shell parts where the value selection is limited.

Looking at the datasheet of LT1013, the temco of the bias current is about 30pA(per deg C), less than 0.1ppm of the current of the divider pair(around 500uA). We all know that the divider pair has about 1:100 ratio on final voltage, so this 30pA variation will affect the final voltage by 0.001ppm(=0.1ppm/100).
Therefore, if you don't mind "increasing" the tempco by 0.001ppm/K, you can use an 2k:26k pair.

While the voltage noise of a LT1013 looks a bit high(a little below half of the typical LTZ1k), the current noise of the bias is small enough to be ignore safely.
Apart from choppers, there are other options to replace LT1013, such as OPA2188 and OP727.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 29, 2016, 11:17:35 am
Due to the internal amplification, the OP used directly at the LTZ1000 is not that critical. So the LT1013 is fine and
there is little reason to use an auto zero OP, as the low drift, low LF noise and high DC gain are not needed.
More important parameters are power consumption and stability in the loop with extra gain  - some AZ OPs could have a problem here and may need adaption of the circuit.

The higher frequency noise is usually set by the OP, due to the filter function of the circuit, so here the noise of the OP might be important.

There is one more effect of longer leads - the long leads could have a resistance up to the 0.1 Ohms range and this way have an significant influence at pin4 with the typical 120 Ohms resistor. As the resistance of kovar is not that stable with temperature it can also contribute to the TC.  However resistance of the wires also sets a limit on how good thermal isolation on the board can be made.
Title: Re: Ultra Precision Reference LTZ1000
Post by: xyrtek on March 29, 2016, 06:45:00 pm
Anyone got working LTZ1000 board PCBs to sell?

For anyone interested in the pcb design please check this.
https://xdevs.com/article/kx-ref/

My apologies for cluttering the thread.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 29, 2016, 08:13:58 pm

There is one more effect of longer leads - the long leads could have a resistance up to the 0.1 Ohms range and this way have an significant influence at pin4 with the typical 120 Ohms resistor. As the resistance of kovar is not that stable with temperature it can also contribute to the TC.  However resistance of the wires also sets a limit on how good thermal isolation on the board can be made.

When calculating with the data:
http://www.calfinewire.com/datasheets/100105-kovar.html (http://www.calfinewire.com/datasheets/100105-kovar.html)

I get about 3.1 Ohms/m for the 0.45 mm diameter of the wire.
with 12.7mm (shortable) wire length this gives about 39mOhms for Pin 1 where I have influence.
Over 20 degs temperature difference the 0.35%/K give a factor 1.07 or 2.7 mOhm difference.
so against the 120 ohms around 23 ppm resistor change.
With the factor 0.14/100ppm this gives a error 0.032 ppm over a 20 deg C range.
Or 0.002ppm/K.

I guess I cannot measure that.
So the thermal isolation has much more effect.

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 29, 2016, 08:37:46 pm
The wire resistance has an effect mainly with pins 3 and 4, as here the highest current flows.
With pin 3 and 4 mA zener current, a 2.7 mOhms change in resistance for a 20 K increase in temperature gives 10-12 µV of extra voltage. However the Kovar wire will also partially profit from temperature stabilization, so a smaller effect of maybe half the size is more realistic. So about an additional +0.04ppm/K for the TC with longer leads. That is quite a lot for chip that should reach 0.05 ppm/K.

The other effect would be from Pin 4 - from Andreas' calculation this effect is much smaller. So even with opposite direction it can not fully compensate.

So the length of the wires is not only important for the thermal part.

Besides the extra TC the lead resistance can also explain much of the change in absolute value.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 29, 2016, 09:30:10 pm
The wire resistance has an effect mainly with pins 3 and 4, as here the highest current flows.
With pin 3 and 4 mA zener current, a 2.7 mOhms change in resistance for a 20 K increase in temperature gives 10-12 µV of extra voltage. However the Kovar wire will

At least for pin 4 the behaviour is not linear.
A 100 ppm change on R1 gives 0.14 ppm change of the zener voltage.
So for Pin 4 its only 0.22 uV (and not 5-6) over 20 deg C.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 29, 2016, 09:38:15 pm
Hello,

Measurement on LTZ#4 with short leads. LT1013A again as OP-Amp.
And R9 = 402K to compensate the remaining -0.1ppm/K.

For R9 = 1 Meg I get a T.C. increasement of around +0.04ppm/K
100K give around +0.4ppm/K over 20 deg C.

While the K2000 had some warm-up delay for the first hour,
both the HP34401A in 100mV range against LTZ#5 and ADC16 (with 2:1 divider)
show a nearly zero T.C. (less than 2uV change) between 20 and 32 deg C environment temperature range.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 30, 2016, 06:05:50 pm
The extra resistance of the longer leads at pin 3 can explain rather well the drop in voltage from shortening the leads. However one would extect an more negative TC with the shorter leads, but the observed change is in the other direction  - so the change in TC must have another explanation. The wires at pin 4 should have even less influence, so they cant be the cause either.

The with the compensation with R9, the TC gets smaller, but the curve also get quite nonlinear. Here I don't think the effect is due to nonlinear influence at pin4, but due to the nonlinear relation ship with heater voltage. So the heater voltage might not be such a good choice for compensation. As the relationship heat voltage to power gets more linear at higher power / higher set temperature, the curvature could well be less critical at higher temperature setting.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 22, 2016, 09:17:42 pm
Hello,

I did some changes to LTZ#3 which had a too high amount of T.C. (-80ppb/K).

see also:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg881955/#msg881955 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg881955/#msg881955)

now it is nearly in final state:
- slot between regulator and LTZ
- TEKO shield soldered
- and: I tried to reduce the T.C. by "half shortening the legs"

from LTZ#4 I know that mounting the reference directly on the pcb makes a difference of around +0.1ppm/K against long legs.
So I did not want to "overcompensate" the T.C. and tried a shortening of around 5 mm on the legs.

The result:

The T.C. regression curve has changed from -80ppb/K to around -40ppb/K.
Which is now "within spec". (50ppm/K of datasheet)

Now the question is: shall I do further shortening the legs leaving a rest of 2 mm to obtain "zero T.C." or not?

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on April 23, 2016, 12:13:32 am
Now the question is: shall I do further shortening the legs leaving a rest of 2 mm to obtain "zero T.C." or not?
That's entirely up to to your requirement.
My suggestion is to leave it untouched, and compensate this little T.C. in later stages such as 7V to 10V step-up since there will be additional TC introduced which will void the zero T.C. you may have achieved.
Also, I don't recommend adding a critical component to solve a none critical problems since the stability is the number one priority than T.C. in most cases.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 23, 2016, 10:14:55 am
I forgot where I read it [maybe in the LTZ's datasheet?], but Linear-Tech recommends 1mm spacing between the bottom of the TO99 package and the PC board. 


Hello,

I could not find this in the LTZ datasheet.
Has anyone a hint where this info can be found?

But if I think about it then I did a error when shortening the pins of LTZ#4 to zero.
On the other side the T.C. on #4 was very widely off without this measure.

This cathode resistor should be very stable [Edwin's PWW with stabilization or VPG foil with PMO].

That is not my way of adjusting the T.C. You need a additional very stable component. (and my PCB layout is not prepared for this).
And finally the copper traces on the layout determine a large amount of the T.C. of that additional component.
In a small range I can adjust the T.C. by populating R9 (which is already in Layout). And here I can use a standard 1% metal film resistor.
For a working point of 50-55 deg C the compensation is around +0.04 ppm/K for each 1 Meg resistor.

That's entirely up to to your requirement.

I think it was more or less a rhetorical question. As a volt nut I have at least to try it.

The 10 V output is still far away.
I think I will have to use a DAC and a NTC to compensate for the temperature changes
in order not to worse the 0.05 ppm/K spec of the reference.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on April 23, 2016, 11:50:53 am
I forgot where I read it [maybe in the LTZ's datasheet?], but Linear-Tech recommends 1mm spacing between the bottom of the TO99 package and the PC board. 
I could not find this in the LTZ datasheet.
Has anyone a hint where this info can be found?

There is info about the lead diameter only, same nor similar to LM399.
LEAD DIAMETER IS UNCONTROLLED BETWEEN THE REFERENCE PLANE
AND THE SEATING PLANE (0.254mm – 1.143mm)

One of my LTZ was almost impossible to insert close than 1mm due to the leads angles.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 27, 2016, 09:26:50 pm
Hello,

further shortening of leads on LTZ#3
See also:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg924793/#msg924793 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg924793/#msg924793)

now measuring 7.5 mm from top LTZ to PCB.
(should have been 0.5-1.0 mm shorter but its difficult to keep exact height when the TEKO shield is already soldered).

Result: reduction from -42 ppb/K to -22 ppb/K for the regression curve.
Still not "zero T.C." but a value I can live with.

Further I changed LTZ#6 with R9 = 1M8.
Regression curve changed from -28ppb/K to -15ppb/K.

Had expected to be closer to Zero T.C. with the formula +40ppb/K for each 1 Meg resistor (or +22ppb/K for 1M8),
 but obviously this is not always exact.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 28, 2016, 03:49:18 pm
The compensation via R9 is nonlinear, as the heater voltage is nonlinear depending on the temperature, so the compensation might only work for a limited temperature range and is likely also influenced by the thermal setup (e.g. isolation cap, cutouts around the LTZ1000) and the length of the wires: Shorter wires need more heating and thus R9 has more effect.  With a relatively small value for R9 one might even have to make sure that R9 itself is stable enough.
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on May 03, 2016, 03:14:25 pm
Progress:
-inox front and rear panel done (photos). As You can see it is designed to be stand-alone voltage reference or to be an OEM module to be built into some instrument.

-top and bottom LTZ1000 covering cup made of SUNDPLAST SP163.

-4 units assembled. Banana terminals are Pomona low thermal EMF type.

-TC measured (I don't use 400k resistors for temperature compensation):
Unit#1 with Vishay Z201 resistors T.C.=+0,03ppm/C
Unit#2 with precision wirewound resistors T.C.=-0,14ppm/C
Unit#3 with precision wirewound resistors T.C.=-0,08ppm/C
Unit#4 with precision wirewound resistors T.C.=-0,11ppm/C

By the way, I've bought some G.R. 8G16D wirewound resistors and some of them have T.C. as high as 7...8ppm/C instead of declared max. +/-5ppm/C. Does anyone else notice similar problem ?


To do:
-laser engraving of text on front and rear panels

-making better temperature chamber with PID controller

-redesign PCB to allow testing of CERN or PREMA solution with a JFET. My goal is to develop an EVAL board that allows testing different configurations.

-perform LF noise testing

P.S. Is someone of colleagues interested in putting one of my units into T.C. testing?
I could borrow one to compare the results (please send a PM).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 03, 2016, 08:44:54 pm
Hello,

Frank had a issue with one value (120R) of the econistors:
https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg624931/#msg624931 (https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg624931/#msg624931)

For the T.C.: is it measured on the direct zener output or after some buffer/divider?
(I am still missing for your schematics).
Over which temperature range did you test. (ramp or fixed points with how long rest time at the temperature?)

I would try to compensate the T.C. by R9 = 400K on Unit#2+#4 and perhaps around 500-680K on unit #3.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on May 03, 2016, 10:56:53 pm
Hello Andreas,

Quote
Frank had a issue with one value (120R) of the econistors:
https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg624931/#msg624931 (https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg624931/#msg624931)
Thanks, I haven't seen that before. This agrees with my observations. I measured T.C. close to 8ppm/C for 120 ohm econistors.
So this explains exactly the meaning of this "eco" prefix. You get what You pay for. All in all they are good for the 70k collector resisitors :)

Quote
For the T.C.: is it measured on the direct zener output or after some buffer/divider?
I use typical  LT application LTZ1000ACH + LT1013 and additionally a follower made of OPA2277.
I'm measuring the voltage at the buffer's output.

Quote
(I am still missing for your schematics).
I will show them before the next iteration of PCBs.

Quote
Over which temperature range did you test. (ramp or fixed points with how long rest time at the temperature?)
I tested the reference in three points: 15'C ; 22'C ; 30'C because my setup allowed only that points. I gave 4 hours (before each measurement) to thermically stabilize. Now I'm working on better PID controlled chamber.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 04, 2016, 09:17:55 am

Quote
Frank had a issue with one value (120R) of the econistors:
https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg624931/#msg624931 (https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg624931/#msg624931)
Thanks, I haven't seen that before. This agrees with my observations. I measured T.C. close to 8ppm/C for 120 ohm econistors.
So this explains exactly the meaning of this "eco" prefix. You get what You pay for. All in all they are good for the 70k collector resisitors :)


I cannot confirm, that these econistors are really a bargain.

I confirm, that certain values have higher T.C.s than expected.
I got replacement for these 120 Ohm types, which were in spec, i.e. around +3..5ppm/K
Keep in mind, that the 120 Ohm is less critical, like both 70k resistors.

The 12k all were very good, around +1ppm/K or less.
1k were between +3..5ppm/K.

Therefore, these latter resistors numerically give around 0.04 ppm/K in the completed LTZ circuit. Shall I say 'only'?

I got the feeling, that the overall T.C. in the end simply has to be measured, and other T.C.  compensation been added (length of leads, 200k .. 1M of "T.C. compensation resistor, and so on).

I think, that it's not useful to strive for the best possible (towards zero T.C.) parts, as even the best selected resistors may give much higher T.C.s, than expected.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on May 05, 2016, 11:25:08 am
How about Datron LTZ1000 TC corrections? Datron 4000, 4700, 1271 e.t.c. have one.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 06, 2016, 09:52:00 pm
How about Datron LTZ1000 TC corrections? Datron 4000, 4700, 1271 e.t.c. have one.

Hello,

Could be a interesting method for compensation of the 7 -> 10V Divider.

Attached I have a overview of the 4 LTZ1000A references #3-#6 (7V) with all tweaking and measures done.

T.C. is trimmed from up to 230 ppb/K down below 25 ppb/K on all devices. Either per trimming lead length or by adjusting with suitable R9.

PSRR is reduced from up to 0.15ppm/V down to 0.05-0.06 ppm/V by slots between the voltage regulator and the LTZ.
The soldering of the teko inner housing has also contributed a part.

The slots and TEKO also help against voltage shifts by tilting the reference. (now less than 2uV or 0.15ppm).

R9 and shortening the legs have no visible impact on 1/f noise of the zener.
The popcorn noise on LTZ#5 is still there.
I decided not to exchange the zener by another LTZ1000A because the tempco of this device is near zero without shortening the legs / using R9.

Next steps:
- record ageing drift of the devices (against my pre-aged references #1 + #2 with around -1 and -2 ppm/year drift).
  here I hope to see wether the (popcorn-) noise has a correlation to ageing.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on May 07, 2016, 05:58:28 am
A classic Datron schematics in the small form-factor (another DMM modding).
TC 20-40 ppb/K without any adjustment or compensation (R9=0).
Title: Re: Ultra Precision Reference LTZ1000
Post by: acbern on May 07, 2016, 07:06:30 am
Looks very interesting! Can you elaborate a little bit about it (parts used, circuitry details..).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on May 07, 2016, 07:27:40 am
It's a simplificated Datron circuit without guarding and Vishay custom resistors network.
R2, R3 - hermetic foil type S5-61, R1 - hermetic foil type R2-67, R4-R5 - foil Alpha Electronics FLC.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on May 07, 2016, 09:43:13 am
A copper chamber with the all sides heating. Was taken from the metrological level standard cells group H488/1.
Title: Re: Ultra Precision Reference LTZ1000
Post by: acbern on May 07, 2016, 12:59:23 pm
It's a simplificated Datron circuit without guarding and Vishay custom resistors network.
R2, R3 - hermetic foil type S5-61, R1 - hermetic foil type R2-67, R4-R5 - foil Alpha Electronics FLC.

What values for R16 and R18 did you use? R9=0ohms, right. R7 and R15 are 160 ohms?
I would think one can also modify this to work on non-symmetric voltages (12V), with all signals referenced to 0V being AC-coupled.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on May 07, 2016, 01:10:02 pm
R16+R18 is needed for DMM mod only. The exact value (~3.4k) is individually adjusted for each ref module.
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on May 12, 2016, 01:01:12 pm
Hi, Mickle T.
What are the advantages of the temperature control section proposed by DATRON?
Is Linear approach somehow worse ?
What are Your observations ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on May 12, 2016, 04:19:54 pm
The Datron temperature regulation uses a more simple compensation (one less series resistor) and a different output stage. Both changes are rather independent.
The current controlling output stage does not look good to me, as it has less gain at low currents / power and thus makes the nonlinear heater curve even more nonlinear. So I don't see this as an advantage, but more a not so good decision.

The removed resistor in series to the feedback cap reduces the gain in an intermediate frequency range. It depends on the thermal properties on how important this is for regulation. AFAIK LT uses the same for both the LTZ1000 and LTZ1000a despite of different thermal characteristics. Also the heater curve is a square law, so loop gain is lower at high environmental temperature or lower set-point. So the circuit is not really tuned for a very fast response, which is not needed nor best for low noise. To really judge on the regulation one would need to measure the properties of the thermal system.

It depends on the environment if more gain is better or worse. If there is not much external variations (e.g. well shielded, not much  uncontrolled turbulence) the lower gain can be a small advantage. In a more turbulent environment higher gain would be better as in this case noise of the temperature sensor is lower than thermal variations.  Anyway the difference will be small as the thermal variations of the sensor itself should not contribute significant to reference noise in the relevant frequency range (e.g. 0.1 .. 10 Hz). So it may be just economics to use smaller caps, omit one resistor and save a few cents.
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on May 15, 2016, 02:37:25 pm
I'm placing final photos and the schematic diagram of my version.
The temperature controller is taken from the LT app note.
The Zener section combines Datron and LT schematics, so You can test both configurations.
Future revision C will have minor changes, but I'm satisfied with current revision B.
Using Z201 resistors in the temperature setpoint divider and Zener current sense + Econistors in the rest of the circuit I'm obtaining T.C. in +/-0,06...+/-0,03ppm/K range without additional compensation (initial tests). That's fine for me and shows that there are no big errors in the (thermal) layout.
Still waiting to finish better temperature chamber. Then I will publish my measurements.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 15, 2016, 04:33:41 pm
Very nice, one of best looking assembled LTZ units (if not the best) :) Looking forward for testing and performance results.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 15, 2016, 07:00:06 pm
I'm placing final photos and the schematic diagram of my version.

Still waiting to finish better temperature chamber.

Hello,

thanks for the schematics.
There are some ideas where I still have not thought of:
- guarding
- using ferrites

What do you plan for the temperature chamber?
I think you already know my low cost chamber from the T.C. measurements thread.
https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg462298/#msg462298 (https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg462298/#msg462298)

I simply use a peltier cooling box for cooling. (which is running continously for the cooling phase).
And 2 heater foils mounted on a aluminium sheet which is used as heat spreader.
Controlling is done by a FET power stage via RS232-signals (RTS/CTS) for the heater.
And by a SCR-Relays via RS232-signals for the 230V peltier cooling box.
The controller runs on PC. Simply switching on/off  the heater every second.
(with a small p-controller part generating some kind of PWM within 0.3 deg C of the setpoint).

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 17, 2016, 05:02:32 am
I'm parsing data and got retested HP 3458A's reference module (A9 PCBA) in thermal box.

(https://xdevs.com/doc/xDevs.com/xfer_volt/img/hp_ref_may2016_1.png) (https://xdevs.com/doc/xDevs.com/xfer_volt/img/hp_ref_may2016.png)

Having hard time to find out tempco of it, no visible change over 15°C delta.
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on May 25, 2016, 09:54:12 pm
Below  mesurements of first assembled unit.
I used Fluke 732A + Fluke 720A + Fluke 845AR. The test setup is quite good, but I think I'm observing also the tempco of my measuring setup (for example 720A KVD has max. +/-0.1ppm/K tempco according to the manual). Any ideas how to solve this ? Maybe comparing results at different room temperatures would be OK, but it would take very long time.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 26, 2016, 04:37:38 am
Have the reference with constant temperature and vary room temp with all gear, taking samples.
Best go both ramps, up and down in temperature. Then you can get linear TC of setup, and approximate result using it as multiplier to actual measurement.
If TC is linear, you can get pretty close.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on May 26, 2016, 05:12:49 am
Hello TiN,

nice article on xdevs.  :clap: :-+

https://xdevs.com/article/kx-ref/
Title: Re: Ultra Precision Reference LTZ1000
Post by: Alex Nikitin on May 26, 2016, 10:05:43 am
Hello TiN,

nice article on xdevs.  :clap: :-+

https://xdevs.com/article/kx-ref/

Nice article! Could somebody tell me what is the purpose of CR1 diode in the LTZ1000 circuit there (the one between the heater and ground)?

Cheers

Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on May 26, 2016, 10:20:21 am
Could somebody tell me what is the purpose of CR1 diode in the LTZ1000 circuit there (the one between the heater and ground)?
Read data sheet "Pin Functions" section and reference "Block Diagram".  CR1 diode prevents parasitic substrate diodes within LTZ1000 structure from becoming forward biased.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Alex Nikitin on May 26, 2016, 10:28:53 am
Could somebody tell me what is the purpose of CR1 diode in the LTZ1000 circuit there (the one between the heater and ground)?
Read data sheet "Pin Functions" section and reference "Block Diagram".  CR1 diode prevents parasitic substrate diodes within LTZ1000 structure from becoming forward biased.

1) No, it does not. It can not protect against a negative polarity voltage on the heater (pins 1 and 2) relative to pin 4. Only if that diode is in series with pin 1 than it would be useful.

2) In a circuit with a single supply as in this article, this protection is irrelevant in any case.

Cheers

Alex

Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on May 26, 2016, 07:38:35 pm
Could somebody tell me what is the purpose of CR1 diode in the LTZ1000 circuit there (the one between the heater and ground)?
Read data sheet "Pin Functions" section and reference "Block Diagram".  CR1 diode prevents parasitic substrate diodes within LTZ1000 structure from becoming forward biased.

1) No, it does not. It can not protect against a negative polarity voltage on the heater (pins 1 and 2) relative to pin 4. Only if that diode is in series with pin 1 than it would be useful.

2) In a circuit with a single supply as in this article, this protection is irrelevant in any case.

Cheers

Alex
I answered assuming the referenced circuit "Schematics 2: xDevs.com KX voltage reference (Rev.B00) reference" was operating in steady-state conditions.  Therefore, it is assumed heater current is flowing which will forward bias CR1 into conduction.  In doing so, pin 2 is now at roughly the same voltage as pin 4 (referenced to pin 7, ground).  In reality, it's slightly positive since the Vf of CR1 (at room temperature) is greater than the Vbe of Q1 (pin 4 to pin 7) which is heated above room temperature (owing to the roughly -2mV/C temperature coefficient of Vbe).  Thus, the substrate diode between pin 2 (cathode) and pin 4 (anode) is reverse biased.  This satisfies the requirement that the substrate diode(s) not be forward biased.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 29, 2016, 04:25:47 pm
Hello,

Shi(f)t happens ...

I accidently shorted the unbuffered output of my best aged LTZ (LTZ#1) which had a annual drift of about -1 ppm.
This resulted in a low setpoint voltage for the heater -> infinite temperature -> stress + hysteresis to the zener.
After curing a part of the hysteresis by power cycling several times
the remaining shift is about -1.9 ppm.   :-//   |O

By the way: I read in a german forum that precision OP-Amps are not always a perfect means to prevent shorting the output.
The reason is that most of the precision amplifiers have protection diodes between both inputs.
So if a unity gain follower without any series resistors is shorted to GND on the output, the positive input is clamped to 0.7 V.
see figure 3 of OP27 datasheet:
http://www.analog.com/media/en/technical-documentation/data-sheets/OP27.pdf (http://www.analog.com/media/en/technical-documentation/data-sheets/OP27.pdf)

On my new references I tested short cirquits on the buffered output having around 1 mV influence on the zener voltage.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on May 29, 2016, 04:46:57 pm
Ouch. How long was it shorted? I'm pretty sure that was how my first LTZ chip died, after short temp loop went out of bounds and shorted the zener.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 29, 2016, 05:34:45 pm
Hello,

Not really long.

It was a unpowered ADC (LTC2400 with LTC1043) connected to LTZ#1
I had a DMM as difference voltage to LTZ#2.
And I soon recognized during connection that the DMM had not a few mV as expected
but 7V as measurement value.

So perhaps 5 seconds short cirquit time.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on May 30, 2016, 12:38:43 am
Hello Andreas,

I cannot find the idea 'switched capacitor idea for the 7V->10V boost' of yours mentioned by DiligentMinds.com at the other thread, can you give me the reference?

I had this ideal as well by using a LTC1043 or ADG1236 to multiply 7V by 1.5 times to 10.5V, and use resistor networks to divided down to 10V, I wonder if they are similar. I bought some LTC1043 and ADG1236 long time ago but cannot find time for the implementation. I made some simulation and functionally it's working. I had two LTZ1000 with voltages slightly below 7V that particularly suitable for this kind of application. Also, there are some low voltage compensated zeners(namely 2DW232, 6.3V) which good for this as well.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 30, 2016, 04:57:54 am
Hello,

one suggestion is here (5.2V out of 7V by *3/4 transfer)

https://www.eevblog.com/forum/projects/building-a-7-decade-voltage-calibrator/msg304819/#msg304819 (https://www.eevblog.com/forum/projects/building-a-7-decade-voltage-calibrator/msg304819/#msg304819)

the other here (* 3/2 transfer to get 10 V out of 7V)

https://www.eevblog.com/forum/projects/building-a-7-decade-voltage-calibrator/msg298350/#msg298350 (https://www.eevblog.com/forum/projects/building-a-7-decade-voltage-calibrator/msg298350/#msg298350)

both cirquits only simulated by now (just had no time to build a complete calibrator).

Edit: and of course you will need a high impedant/low leakage buffer at the output.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on May 30, 2016, 06:50:24 am
Thanks Andreas, here is my simulation.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 30, 2016, 07:30:14 pm
Hello,

the cirquit looks good.
But in the diagram the voltage ripple is rather large. (and average voltage too low).
Is the measurement instrument simulated as a pull down resistor ? (which value ?)

So round about estimation is 200ms time constant (50mV ripple in 1 ms).
Which would give a 1 Meg resistor as load.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on May 31, 2016, 01:29:45 am
That's right, I suspect the simulation program(Multisim) is not very good, and it had difficulty running the simulation(errors, adjustment, roll-back).
There are many times that Multisim gives contradictory results. For instance, how can a Vpp be 221uV but Vrms is 21.1V?
There is no apparent source of leakage from the circuit, there must be some equivalent leakage resistors in the capacitor or in the switch.
Title: Re: Ultra Precision Reference LTZ1000
Post by: necessaryevil on June 02, 2016, 01:35:08 pm
Hmm... how about a Weston Cell from ebay instead of an LTZ1000? I know, a Josephson voltage standard would be more accurate, but  I don't think they fit on my bench nicely. Also, they are not available on ebay for a price which agrees with my budget.

Quote
. For instance, how can a Vpp be 221uV but Vrms is 21.1V?
DC offset?
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on June 02, 2016, 02:26:03 pm
Hmm... how about a Weston Cell from ebay instead of an LTZ1000? I know, a Josephson voltage standard would be more accurate, but  I don't think they fit on my bench nicely. Also, they are not available on ebay for a price which agrees with my budget.

Quote
. For instance, how can a Vpp be 221uV but Vrms is 21.1V?
DC offset?
Poor ones, not worth considering. Good ones, often suffered from transport effect.

There is no DC offset apart from 10V, which is much smaller than 21.1V. I do come across several instances where the output of an opamp gone up to 10kV :palm:
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on June 02, 2016, 03:05:55 pm
Sometimes simulations have trouble with convergence and start with crazy values like 10 kV at an OP.  This can also happen with LTspice, not a Multisim exclusive. The 21 V RMS at 220 µV_pp look faulty - but at least the is obvious.

The ripple could be real, because if internal effects in the CMOS switches. So switches have significant charge injection. Though I don't think the effect should be that large - could be a problem with the model. Another point could be not so perfect capacitors used in the simulation. As perfect parts sometimes cause trouble in simulations, the program might use more realistic models by default.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on June 02, 2016, 04:39:32 pm
Yes, large capacitor should be chosen to weaken the charge injection effect. They use 1uF most of the time in the datasheet examples. I use smaller values(and 100kHz frequency) in the simulation to speed up the process.
Title: Re: Ultra Precision Reference LTZ1000
Post by: necessaryevil on June 02, 2016, 05:02:21 pm
I'm sure circuit simulators are great tools, but they are no panacea. Creating a good simulation model is probably more difficult than breadbording (and perhaps than flying to the moon).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on July 20, 2016, 09:14:19 pm
The LT1677 is not such a good choice, the LT1013 is better in at least three parameters:
The current noise of the LT1677 is rather high (1.2 pA/Sqrt(Hz) at 10 Hz - compared to 0.07 pA/Sqrt(Hz) for the LT1013.
As the OPs sense the rather high output signals at the collectors (e.g. 70 K impedance), current noise in the pA range is more important than low voltage noise.  So the LT1677 is lower noise only with low source impedance (< about 30 K), but not with the typical LTZ1000 circuit.

At low input voltage, the bias current is huge (e.g. 400 nA) and thus a negative supply is needed. Otherwise the LT1677 would be worse than an LM358.

The other point is current consumption - the LT1677 take quite some extra power (e.g. 6 times more).

Bias current drift could also be worse with the LT1677, though the data-sheet does not specify it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 20, 2016, 09:21:27 pm
then the LT1677 is superior to the LT1013 in almost every important spec,

Hello Ken,

really?

I personally believe that for the current regulation loop the amplification should be as high as possible.

At 5 mA (roughly 2K-Ohms) load the LT1013 has a factor 10 higher amplification,
with a power consumption of 1/10 th of the LT1677.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on July 20, 2016, 10:52:10 pm
The dynamic impedance at the transistors collector is not given by voltage divided by current. The transistor is working essentially as a constant current source and thus has a very high output impedance. The typical data-sheets don't give it for such a small U_CE. A simple simulation for the 2N3904 in LTspice is about 500 K. So this node is really about 70 K impedance.

The noise of the LTC1677 (or that of most OPs) would be still swamped be the LTZ1000. But at more than about 30 K source impedance the noise of the LTC1677 is higher than that of the LT1013.

The current regulation loop has the additional gain of the transistor and it's working at an essentially fixed condition. So a limited gain by itself would not be a problem at all. Only when changing with time or temperature it might be a small problem. But with the additional factor of about 200-250 from the transistor, anything above 50.000 should be enough to cause an contribution of less than 1 µV to the output.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on July 21, 2016, 04:59:32 pm
The impedance at the transistors collector depends on wether you look at the closed loop case, or the open loop case. In close loop the point is rather low impedance (simulation shows something like 300 Ohms, using a 2N3904 model for the transistor). A signal due to added current appears nearly same size at the output. Voltage noise and drift an noise of the OP at low frequencies (e.g. less than about 1 KHz) are attenuated by a factor of about 200. So to compare current and voltage noise one has to reduce the voltage noise by this factor or multiply the current noise or impedance with it. So the effective impedance for the current noise is about 60 kOhms. Not by accident this is the same as the impedance of the node when looking at it in the open circuit noise. So for the choice of the OP one should consider an source impedance of about 60 K (slightly less than the 70 K resistor, due to the finite output admittance of the transistor).

For this high impedance the LT1013 and LTC2057 are good choices, but the LTC1677 or an similar LT1007 are not. So low and stable bias and low current noise are important.

Looking at the simulation of the current loop, there is a rather low phase margin in the 1-10 kHz range. This could become a problem with an AZ OP, as AZ OPs tend to have extra phase shifts in this frequency range. To be on the safe side one might want to modify the circuit to add extra phase margin if an AZ OP is used.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 07, 2016, 07:12:57 pm
I know some guys here going to hate me for this, but let's do some myth-busting. There are lot of talk about long/short legs, sockets and all that around LTZ-designs.
So here it comes. Built one more module with leftover parts.

(https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_ltz_1.jpg) (https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_ltz.jpg)

Design configuration:
* xDevs.com KX LTZ1000 PCB, Rev.B01 (https://xdevs.com/article/kx-ref/) board
* LTZ1000CH made in 1991, legs are NOT trimmed
* AUGAT gold-plated socket for LTZ
* Linear LTC2057 opamps for both drive and thermostat
* VPG VHP 1K000 0.2ppm/K + 10K+2K wirewound for temp setpoint
* Wirewound 120R. 10K is Z202 VPG
* Paralleled Fluke 3ppm/K 100K+250K resistors as 71.5K for bias
* Film capacitors for all signal path locations except 22nF (Which is C0G 1210)
* 392K for LTZ1000CH option installed

(https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_side_1.jpg) (https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_side.jpg)

Board is covered in box and shielded from airflow now.

Closeup on parts:

(https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_tcl_1.jpg) (https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_tcl.jpg)(https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_dr_1.jpg) (https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_dr.jpg)

Had to bodge some copper wiring to fit these giant resistors..

(https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_naked_1.jpg) (https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_naked.jpg)(https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_bot_1.jpg) (https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_bot.jpg)

Board is powered from K2400 at +15V and measured via 3458A@NPLC100. Also turned on pair of my previous LTZ modules, hooked to K2002's for comparison.

(https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_tst_1.jpg) (https://doc.xdevs.com/doc/xDevs.com/KX/VREF_WW/kx6_tst.jpg)

Live data:

(https://xdevs.com/doc/xDevs.com/KX/VREF_WW/refz3.png) (https://xdevs.com/dcv_kltz/)

I have 3 more LTZ1000CH from same batch, and dodgy (1ppm shot noise) desoldered LTZ1000ACH from ebay 3458A's PCBA. So I'll have each chip run for some time and then proceed with swapping. Then rotate in opposite direction, to see if any voltage shifts due to socket connections.

If have any ideas - feel free to ask.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 07, 2016, 09:24:19 pm
I know some guys here going to hate me for this, but let's do some myth-busting. There are lot of talk about long/short legs, sockets and all that around LTZ-designs.

Hello Illya,

we all can only learn from any experiment.
For me the procedure is clear (at least for the LTZ1000A with 12K5 setpoint resistor).

Step 1:
let the legs long and do not populate R9.
Measure T.C. of reference (with LTZ properly thermal shielded).

Step2:
Shorten legs if T.C. is < 0 T.C. will increase around +40ppb/K for half shortened and around +130ppb/K for full shortened legs.
I think its better to have at least 10 mils distance between PCB and the bottom of the LTZ to avoid stress to the chip.
Measure T.C. of reference again (with LTZ properly thermal shielded).

Step 3:
If T.C. is still <0 populate R9. 400K will compensate around 80 ppb/K. 2 Meg around 20ppb/K.
But this compensation is non-linear.
Measure T.C. of reference again (with LTZ properly thermal shielded) and eventually repeat Step 3.

For the layout:
keep all non constant heat sources away from the LTZ.
The heater transistor is not necessarily a problem if the supply voltage is constant.
But the voltage regulator from changeing battery voltage is critical. (here the slots will help).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 08, 2016, 04:29:09 am
But experiment results and execution often vary. Hence the discussion.

I still have difficulties measuring TC in sub-ppm zone. I had shown TC test with ramp +24C to +44C with stock HP 3458A A9 PCBA (https://xdevs.com/vtx_ltz1_t1/), which did not allow to calculate any TC. Perhaps method should be changed to test two different temperatures for very long time, instead of ramping temperature (speed was +1K each 2 hours) ?

There are no extra heat sources on LTZ module (except 5mA LED perhaps?). Also I did not see any measurable supply voltage dependency on output when tested before. Output was same either with 10V input or 16V. I usually use 15V or 12V from battery.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 08, 2016, 07:14:33 pm

I still have difficulties measuring TC in sub-ppm zone. I had shown TC test with ramp +24C to +44C with stock HP 3458A A9 PCBA (https://xdevs.com/vtx_ltz1_t1/), which did not allow to calculate any TC. Perhaps method should be changed to test two different temperatures for very long time, instead of ramping temperature (speed was +1K each 2 hours) ?


Hello Illya,

you will have to find out where your measurement problem is.
I have a typical repeatability/noise of around 1uV for a 7V reference.
So over 20 deg C you should be able to detect at least 0.05ppm/K.

I measure either with (good warmed up, my K2000 needs longer than the 34401A) 6.5 digit instruments in 100mV range
as difference measurement against my "best" 7V reference,
or with one of my 24Bit temperature compensated ADCs (if the room temperature gradient is not too high).
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg907048/#msg907048 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg907048/#msg907048)

I average all measurement values within 1 minute. (This is possible since I have checked for a gaussian distribution).
And for the ADC I sometimes have to build a sliding average over 20 minutes.
I use ramp speeds typical of 0.1 deg C / minute. (not below 0.05 deg C/minute and not above 0.3 deg C/minute).
I measure ramp up and ramp down to average out temperature measurement delays.
Without a closed loop I would not be able to detect drift/hysteresis of my measurement setup.
And without continous ramping I would not be able to detect non linear response of the LTZ.
(e.g. large drift when the temperature regulation loop is out of control).

So I think its not a good idea to do only two temperature points.
Of course a constant temperature might be the starting point to look how to improve the stability of the setup.

I use also battery supply for my references and for my ADCs to avoid ground loops and mains noise.
For critical measurements I try to use a grounded metal plate where I put all my devices and wiring on.
(Where is the side wall of my desktop?).

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 09, 2016, 04:37:19 am
Thank you for settings, that's helpful. I think part of problem that I was measuring direct reading, not the delta like you. Even though I use 3458, it's own TC much larger than source, and my environment is very far form desired +-0.1K and still air conditions... I'll have to build thermal chamber for 3458A to solve this...

Last night results with LTZ chip 8 (dark-blue) vs HP A9 PCBA (cyan, TEC cooled +23.40°C) and my old LTZ module (orange) : https://xdevs.com/dcv_kltz8/
That's with 1 minute average (10 samples). Raw samples are displayed by green dots.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 09, 2016, 02:26:33 pm
There is 3458, but following this idea Keithley 182 or Keithley 2002 + EM A10 preamp on 20uV range will work much better.
Currently I have least 2 pairs of LTZ modules which are within <10uV from each other. Thanks for idea, I'll try this.
I have suitable relays for this job.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 09, 2016, 02:51:23 pm
And many many boxes of thermal and air insulation around everything.
Ok, added one more item into lloooong ToDo list. I have few more urgent projects to finish next weeks, but after that I'll be fully equipped to start on this challenge.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 09, 2016, 03:28:11 pm
Ken and TiN,

sorry to disturb, but I think, nV- measurements are over-engineered, and not really solving the problem.

I agree, to measure the difference between an environmental- temperature - stabilized LTZ1000 and a environmental -temperature-changing DUT, if the 3458A itself cannot be used in a constant environment.

Anyhow, if you want to determine a 0.01ppm/K dependency, as worst case, that would be about 71.5nV/K  for a typical 7.15V output.
Measuring, let's say over a 10°C range, that would be about 715nV.
Both orders of magnitude can be well measured with a 3458A, and using statistics would give a reasonable T.C. = dU/dT calculation.

The problem at that point is of course the extreme sensitivity of such a measurement, which a nV meter would probably not improve in principle.

I mean, what do you really measure, the T.C. of the LTZ1000 circuitry, or any thermocouple (asymmetry) inside the measurement loop?

Even if you reverse the output of the LTZ1000, you will still have thermocouples left between the relays and the output directly at the LTZ1000 pins, which you cannot distinguish from the LTZ-circuitry -T.C.

Therefore, this LTZ-T.C. measurement, and all this trimming to lowest possible T.C.s (below 0.1ppm/K level) is mostly esoteric... or do I miss something ?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 09, 2016, 04:53:59 pm
Dr.Frank

For me it's not so much for nV-measurements themselves, but rather to change method of measuring TC to see if results correlate.
As with just direct measurement LTZ's output over environmentally unstable 3458A does not provide any clear result, leading to erroneous results or inability to see relation between LTZREF temperature shifts and output voltage variations. I don't feel comfortable just applying average(256) filter and analyzing likely meaningless data.

Here just today's example with raw data (https://xdevs.com/dcv_kltz9/).
* HP 3458A A9 PCBA in TEC-thermostat controlled at +23.4°C with +/-0.04°C, from 10pm to 11pm.
* Cyan line, moving average 10 samples at NPLC100
* Variation Vout = 1.4uV(pk-pk) which is double of your theoretical 715nV over 10K.

Or I interpret result incorrectly, and we dealing here with furry carpet stairs (https://e2e.ti.com/blogs_/b/precisionhub/archive/2013/09/03/trying-to-find-adc-non-linearity-look-under-the-carpet)?
Also old initial results on all three modules show much higher TC (0.5 to 1.5ppm/K) (https://xdevs.com/tmeas_kx_t2c/), not talking about <0.1ppm/K TC's.
So still need clear answer for myself if it was design problem in module/components or measurement error.

Alternative to that is building thermal chamber for DMM to stabilize its conditions, which technically is easier, but would occupy lot of space in the homelab.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 09, 2016, 07:10:10 pm

Therefore, this LTZ-T.C. measurement, and all this trimming to lowest possible T.C.s (below 0.1ppm/K level) is mostly esoteric... or do I miss something ?

Hello Frank,

Perhaps its not so essential if one has a temperature stable home lab in the basement.
But with my lab under the roof I have typical 6 deg C (24-30 deg C) variation over the day in summer.
Extreme values may be up to 10 deg C during one measurement.

So my references have to be a factor 10 better than someone elses with only 1 deg variation.

Besides that I had more problems with EMI-noise (from PC + USB-cables) than with thermocouple voltages.
If I can keep air drafts away from the setup by cloth and use thermally coupled connectors (D-SUB) the later should be avoided.
The EMI can be detected by putting the hand on/over the power supply batteries or the wiring.
I had up to 38uV output voltage difference (depending on sample) between unbuffered and buffered LTZ output before soldering the 100nF capacitor across the output.
(capacitive load isolation cirquit is necessary to avoid oscillation of the buffer).
After the change the difference between unbuffered and buffered output (LTC2057 offset) were near my noise limit (1-2uV).

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg846835/#msg846835 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg846835/#msg846835)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 09, 2016, 08:49:53 pm

That *is* why they all us "Volt Nuts", no?


What, ME telling?  O0 O0 O0

I really think, at this point, there is a natural, physical limit, where it's not useful anymore, trying to measure something, which is buried too deeply in other effects, like e.m.f.s, zener and circuit noise, etc. If you were able to have a "chopper" principle available, (like Lock-In), to cancel all e.m.f.s, and other drifts, then you would be done... but that's not the case here, as  these effects are inside the circuitry.

Also, a nV meter, i.e.  < 10nV noise, would dig into the 0.001ppm/K region, which makes absolutely no sense anymore.. simply look at this order of magnitude..

That has also nothing to do, that we as "amateurs" would be limited in means, compared to standards labs. I think that we are pretty close to them.
And they also are limited by the rules of physics. I really doubt, that they would give much better StD or T.C. figures for that circuitry.



I like to take the chance to present my latest measurements on a newly assembled LTZ1000 circuit, PCB and schematic by Andreas (many thanks again!!).
It's running on 45°C, the PWW resistors are selected, to give a theoretical T.C. of about +0.045ppm/K, 430k resistor for "T.C. compensation" assembled.
Measurement is done in constant environment, max. 0.8°C RT change, absolute voltage measured at NPLC 50 with the 3458A, which also was stable to 0.2 / 0.5°C, internally.

The first diagram shows the datasheet assembly, i.e. only these 3 cap's, and the LTZ in a socket. No electrical or thermal shielding, besides a styrofoam cup on top of the LTZ.
1h-noise is about 750nV, or about 0.1ppm. Not the best performer of my five new LTZs. 

(https://www.eevblog.com/forum/index.php?action=dlattach;topic=13392.0;attach=246706;image)

Second diagram shows the same LTZ, soldered fix into the PCB w/o cutting its legs. I avoided to heat the chip during soldering.
The circuit is equipped with all capacitors, as defined by Andreas, except C14, C15 (fear capacitors), and C13, which I think would spoil the ovens feedback constant of C1, R7. The metal shield is also in place, but no thermal enclosure on PCB bottom yet.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=246708;image)


1h noise has gone down to about 270nV, or 0.04ppm. These 0.5ppm dips, and glitches were gone, at least these are much, much smaller.
So, all these capacitors, which Andreas has introduced into his circuit really improve the performance.

What's left is a random medium term noise, or drift, of about 0.05 .. 0.1 ppm, see trend line (200 points average).
That may further be improved by completing the thermal shield, and putting the whole assembly into the aluminium box.

The 16h stability, that is the combination of the 3458A and the LTZ1000 circuit, is on the order of about +/- 0.1ppm.

First conclusion, this is a quite stable measurement, mainly due to stable temperature.. it really can be done that way..

Second conclusion, despite the stable output voltage, you still see a lot of medium term noise, or variation, on the order of several 100nV.
Maybe this is caused by thermal draught, but probably also by zener instability, i.e. random walk, popcorn noise, or whatever you would like to classify this.
And I really cannot imagine, how to  principally improve this, so to be able to extract changes on the order of 0.01ppm, caused by temperature variation.

Third conclusion, although there is RT change, and 3458A temperature variations, there is no correlation visible between T and U. In other measurements also, I never have seen a correlation.

Illya wonders, why he also does not see a correlation in his measurements.

Maybe, that's because there is no effect, or the effect is buried under other effects.

Well, of course, I will also try to measure the T.C., when my box will be finished.
But I will definitely stop at this 0.05 ppm/K (~100nV) perception frontier..


Andreas, I really think that 0.05ppm/K is realistic, and that all your LTZ circuits are already having that T.C. or better, by design. No need to worry further. 
At a 10°C change, that would be below a 1ppm output change, which would be extraordinarily fine.

I agree, that shielding and EMI is a superior problem over the T.C. .. I also see changes on the order of ppm, depending on the configuration of the shield (outer case to ground, or using the inner shield as a guard).

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 10, 2016, 04:17:29 am
Andreas,

Is the schematics posted on page 58 latest? I'd like to try few capacitors you used on my module to see how it affects results.
If you have updated one, please post in PDF format for reference. Thanks.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 10, 2016, 06:20:42 am
Hello Illya,

If you mean this one:
https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=189655 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=189655)

yes it is the latest schematic of my current PCB. Only the 100 nF capacitor at the output of the buffer is missing.
And I do not populate C16-C19. (no filtering against the inner shield).
Edit: C14,C15 cannot be populated together with fast OP-Amps like LTC2057. C13 is only necessary if C14 is populated (see Frank).

If you have the datasheet cirquit not all capacitors are possible without cirquit modification.
E.g. C9 will require R19 and C8 to prevent oscillation.
R21, R22 and C22 prevent the output buffer from oscillation with capacitive loads.

So from datasheet cirquit I would start with C11 and C12.
And if possible add C8,C9 and R19.
See also revision history.

With best regards

Andreas



Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 10, 2016, 11:13:22 pm
I've added C8,C9,C12 (film SMD caps) and R19 (10K Fluke wirewound). Had also to R13 (50K Fluke WW) or circuit would not start.
Output shifted +0.96ppm. Set to datalog, will see how it goes in some hours. Wiring/settings not changed.

(https://xdevs.com/doc/xDevs.com/KX/VREF_WW/mod_andreas_1.jpg) (https://xdevs.com/doc/xDevs.com/KX/VREF_WW/mod_andreas.jpg)

Live data (https://xdevs.com/dcv_kltz7trima/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 11, 2016, 04:45:09 am
Hello Illya,

I am missing C11.
For R19 and R13 simple SMD or metal film resistors are sufficient.
A PWW resistor for R19 might pick up more magnetic noise.

C11 and C12 are directly at the LTZ pins.
See also my very first PCB LTZ1000A where I added some components manually.
C11 + C12 at the LTZ circle.
R19 as metal film below the LTZ.

By the way.
I have difficulties to interpret your diagrams.
For me there is too much information on them.
I would prefer a diagram with not more than 3 lines on it.
(1 LTZ unfiltered+filtered + 1 temperature sensor).

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on August 11, 2016, 02:27:47 pm
In my opinion, the measurement of T.C. of a voltage reference should be done by comparison instead of direct measurement. This is mainly because the T.C. and hourly stability of an 8.5 digit meter is usually not as good as the reference to be measured. Some multimeters such as 3458A, they have very good noise and short term(<=10 min) specifications but not very good hourly or daily, the period often required when measure T.C. of voltage references.

The reference should be better(ideally much better) than the voltage to be compared, should be noiseless, good short-term stable and most of all low T.C. If the low T.C.  cannot be guaranteed, use constant temperature chamber, temperature lag, or temperature correction/compensation, or some/all.

By means of comparison, back-to-back(as mentioned above by DiligentMinds.com) is a very simple and effective. However, it only works for two references of equal nominal voltage, we cannot back-to-back an 7V with an 10V for instance. A switch(preferably an automatic one) can be used here together with a low-noise, high linearity meter such as 3458A to compare references of different voltages such as 7V and 10V. The switch can be made of an latching relay with 2-Z contacts(or even 1-Z). Automatic switches have the advantage of multi-readings and averaged later to give more confident result.

I don't think the thermal EMF matters very much, because the reference now days are very large in value(>=7V). Plus, constant thermal EMF has no effect on T.C. measurement result.

Below is a comparison measurement of mine(with my 4910-AV) for 16 voltage references for 30 hours, purple line is the ambient temperature in degree C.
(https://www.eevblog.com/forum/metrology/repair-datronwavetek-4910-voltage-standard/?action=dlattach;attach=205579;image)

All the curves are very thin indicating a low noise system.
Many curves are straight(not vary with temperature much) indicating low T.C.
Some curves show clear variation with temperature, and can be further processed to obtain the actual T.C.
The curve marked with grn4 is the worst, indicating there are problems with it( https://www.eevblog.com/forum/metrology/repair-datronwavetek-4910-voltage-standard/msg885426/#msg885426 (https://www.eevblog.com/forum/metrology/repair-datronwavetek-4910-voltage-standard/msg885426/#msg885426) ) 
Andreas probably excuse me for violating his saying of 'not more than 3 lines' because my lines are much more straight.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 11, 2016, 02:58:22 pm
In my opinion, the measurement of T.C. of a voltage reference should be done by comparison instead of direct measurement. This is mainly because the T.C. and hourly stability of an 8.5 digit meter is usually not as good as the reference to be measured. Some multimeters such as 3458A, they have very good noise and short term(<=10 min) specifications but not very good hourly or daily, the period often required when measure T.C. of voltage references.

The reference should be better(ideally much better) than the voltage to be compared, should be noiseless, good short-term stable and most of all low T.C. If the low T.C.  cannot be guaranteed, use constant temperature chamber, temperature lag, or temperature correction/compensation, or some/all.

By means of comparison, back-to-back(as mentioned above by DiligentMinds.com) is a very simple and effective. However, it only works for two references of equal nominal voltage, we cannot back-to-back an 7V with an 10V for instance. A switch(preferably an automatic one) can be used here together with a low-noise, high linearity meter such as 3458A to compare references of different voltages such as 7V and 10V. The switch can be made of an latching relay with 2-Z contacts(or even 1-Z). Automatic switches have the advantage of multi-readings and averaged later to give more confident result.

I don't think the thermal EMF matters very much, because the reference now days are very large in value(>=7V). Plus, constant thermal EMF has no effect on T.C. measurement result.


All the curves are very thin indicating a low noise system.
Many curves are straight(not vary with temperature much) indicating low T.C.
Some curves show clear variation with temperature, and can be further processed to obtain the actual T.C.
The curve marked with grn4 is the worst, indicating there are problems with it( https://www.eevblog.com/forum/metrology/repair-datronwavetek-4910-voltage-standard/msg885426/#msg885426 (https://www.eevblog.com/forum/metrology/repair-datronwavetek-4910-voltage-standard/msg885426/#msg885426) ) 
Andreas probably excuse me for violating his saying of 'not more than 3 lines' because my lines are much more straight.

Hello, Zlymex,

principally you are right about the 3458A stability, on the other side, its LTZ reference is as good as the external LTZs, we want to measure.

The back-to-back method is better only, if the backing reference is better or equally stable as the DUT, otherwise, the absolute method is fully equivalent, as far as the A/D and amplifier stage are stable, too..
This is the case also for the 3458A in the 10V range.


In the volt-nuts thread, somebody measured several solder junctions; all had about 3µV/K, which is 0.5ppm/K related to 7 V.
Therefore, this is relevant if you resolve fluctuations to 0.1ppm or smaller.


Your diagram is 15ppm wide, in contrast to mine, which in comparison is zoomed 15  times, ie. 1ppm wide, resolving 0.01ppm or better.
So yours only looks better at the moment..

Would you mind providing a similar resolution, so to better see, how stable these 732B references are, in comparison to LTZs, and in comparison between differential vs. absolute measurement?

Thank you

Frank

Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on August 11, 2016, 03:17:20 pm
......Would you mind providing a similar resolution, so to better see, how stable these 732B references are, in comparison to LTZs, and in comparison between differential vs.
Sure. But now it's getting very late here, I'll do it tomorrow.

..soldered junctions; all had about 3µV/K, .....
This per K is for temperature difference between two thermal junctions.
When we change the temperature of a voltage reference for 10 degree K(say) for testing T.C. we don't get 10 degree K difference for thermal EMF junctions. Usually very much less if properly handled.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 11, 2016, 03:24:53 pm
This per K is for temperature difference between two thermal junctions.
When we change the temperature of a voltage reference for 10 degree K(say) for testing T.C. we don't get 10 degree K difference for thermal EMF junctions. Usually very much less if properly handled.


.. provided if you balance all junctions in pairs.. if you have an unpaired junction, that might be different, isn't it?

But you're right, practically, such effects mostly cancel out.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 11, 2016, 05:19:21 pm
Andreas, Dr.Frank
Sorry, I just got used to overdo my logs with all data possible and often include multiple instruments logs, as I have only one GPIB dongle to run experiments.
I did excel graph with three datasets over same sample time.

This is RAW samples, no average at all. NPLC100, AZERO ON. Only math is in excel to remove offset, so graphs match same point.

(https://xdevs.com/doc/xDevs.com/KX/VREF_WW/graph_same_axis.png).

Based on this, I see no difference in result, and all three measurements resemble Dr.Frank's second graph closely, both in span <0.2ppm and spike behavior.

Baseline - is my original circuit with PWW's, which I shown on previous page with plenty photos. TEMP? was lower, room was airconed.
Trimmed - same stuff, but cut legs so LTZ chip sits within 1mm of socket. TEMP? around +44, no aircon
Andreas - same as trimmed, but with caps/resistors mod. TEMP? around same, no aircon

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on August 11, 2016, 06:06:22 pm
Solder junctions are only a problem if there are temperature differences inside the solder junction itself.  If you want to compensate, it is important to have the same thermal conditions on both junctions. If the thermal conditions can't be matched well it is likely better not to add an extra junction, but better make sure the temperature gradient at the junction is small. 

With the joints at the LTZ itself there is essentially no way to compensate. With the typical LTZ1000 circuit there are only the connectors, where you have extra connections. Here the junctions are usually balanced / symmetric anyway. But it is still important to keep temperature gradients small in these areas and get the gradient of the thermal chamber in the pure, preferably unbend wire.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 11, 2016, 08:25:34 pm
Andreas, Dr.Frank
Sorry, I just got used to overdo my logs with all data possible and often include multiple instruments logs, as I have only one GPIB dongle to run experiments.
I did excel graph with three datasets over same sample time.

This is RAW samples, no average at all. NPLC100, AZERO ON. Only math is in excel to remove offset, so graphs match same point.

(https://xdevs.com/doc/xDevs.com/KX/VREF_WW/graph_same_axis.png).

Based on this, I see no difference in result, and all three measurements resemble Dr.Frank's second graph closely, both in span <0.2ppm and spike behavior.

Baseline - is my original circuit with PWW's, which I shown on previous page with plenty photos. TEMP? was lower, room was airconed.
Trimmed - same stuff, but cut legs so LTZ chip sits within 1mm of socket. TEMP? around +44, no aircon
Andreas - same as trimmed, but with caps/resistors mod. TEMP? around same, no aircon

Yes, seems to be similar. In the end, they have to be..
Though, the indicators are incorrect, the lines are 0.1 ppm apart, so the vertical arrows are 0.2ppm and 2ppm.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on August 12, 2016, 01:18:41 pm
.......
Your diagram is 15ppm wide, in contrast to mine, which in comparison is zoomed 15  times, ie. 1ppm wide, resolving 0.01ppm or better.
So yours only looks better at the moment..

Would you mind providing a similar resolution, so to better see, how stable these 732B references are, in comparison to LTZs, and in comparison between differential vs. absolute measurement?

Thank you

Frank
Here is the same chart but 1ppm wide, 0.1ppm per line for voltage, for 18 hours. I measure these references by 3458A, NPLC=50, AZ=on like always.
The green line is raw 732B data except offset.
The orange line is 732B compared to 4910-AV, eliminated most of the influence from 3458A, but of course added influence from 4910AV.
The other two lines are channel 1&2 of 4910 compared to 4910-AV.
As can be seen from these 4 lines that comparison is better than measurement.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 13, 2016, 01:25:23 pm
Here is the same chart but 1ppm wide, 0.1ppm per line for voltage, for 18 hours. I measure these references by 3458A, NPLC=50, AZ=on like always.
...
As can be seen from these 4 lines that comparison is better than measurement.

Thank you very much, zlymex!

Your statement depends on, what you are after.

If you compare both methods concerning pure noise, see left frame, 4h - 6h, in your diagram, then I would guess, that both methods give equivalent results.
Would be nice, if you could do an StD analysis on this time frame for both methods, and I estimate both give about 100..200nVrms of noise.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=247622;image)

If you take the right frame, 10h - 12h, there is an additional thermal drift visible, caused by the T.C. of the 3458A, as its internal temperature rises proportionally to the RT.
This is the parameter w/o ACAL, i.e. <=0.5ppm/K, which compares to <=0.15ppm/K for backing of each of two references, as per their individual specifications.

From your measurement, I would estimate the 3458As T.C. as having about 0.2ppm/2K = 0.1ppm/K, and the backing method about 0.05ppm/2K = 0.025ppm/K.

Therefore, the references "beat" the 3458A in the category of their T.C.s only, but not necessarily concerning noise.

The absolute method may be a bit more noisy, due to the different noise figures (at NPLC100) of the 3458A, for the 10V ( => 100nVrms), and the 100mV (=> 20nVrms) range.  Your StD analysis may tell.

Here's again my latest measurement, absolute method, Andreas optimized circuit, 2.5x zoom, with stability noise figures for 1h. Let's see, how this compares to the 732B.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=247624;image)
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on August 13, 2016, 02:56:03 pm
Hi Dr. Frank.

The noise or drift is time frame dependent.
For normal low frequency noise, we are talking about 0.1Hz to 10Hz, the noise of 3458A in this time frame is superb.
By specification, 3458A will drift less than 0.1ppm in 10 minutes, which is still very good.
What about 24 hours? 0.5ppm, which is not very good, considering the drift of 732B is only 0.3ppm for 30 days.
(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=247633;image)
If we assume linear behavior in between, the two lines intersect at about 1800 second. In another word, 3458A performs worse than a 10V standard for hourly measurement or above. That is why I prefer comparison rather than direct reading for T.C. measurement of voltage reference which usually takes several hours.

It may argue that the actual or selected 3458A performs better than specified, the actual or selected voltage references may perform even better than specified.
The drift of 3458A is not only thermal, it consist of other factors that drift in longer period even if the temperature is stable, that can be seen from my previous chart.
(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=247635;image)

Although this 732B is not LTZ based, one channel of 4910 (LTZ based) performs very similar to 732B.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 13, 2016, 04:32:45 pm
Hi Dr. Frank.

The noise or drift is time frame dependent.
For normal low frequency noise, we are talking about 0.1Hz to 10Hz, the noise of 3458A in this time frame is superb.
By specification, 3458A will drift less than 0.1ppm in 10 minutes, which is still very good.
What about 24 hours? 0.5ppm, which is not very good, considering the drift of 732B is only 0.3ppm for 30 days.


If we assume linear behavior in between, the two lines intersect at about 1800 second. In another word, 3458A performs worse than a 10V standard for hourly measurement or above. That is why I prefer comparison rather than direct reading for T.C. measurement of voltage reference which usually takes several hours.

It may argue that the actual or selected 3458A performs better than specified, the actual or selected voltage references may perform even better than specified.
The drift of 3458A is not only thermal, it consist of other factors that drift in longer period even if the temperature is stable, that can be seen from my previous chart.

Although this 732B is not LTZ based, one channel of 4910 (LTZ based) performs very similar to 732B.

We both agree on that, as you are talking about the timely drift, over a 24h time frame.
Per specification, the 732B is 4 times more stable than the LTZ inside the 3458A.

That would be 0.1ppm/24h drift for the 732B, and 0.4ppm/24h drift for the 3458A.
Both values are worst case, and are valid for virgin references only.
This will go down for mature references, so probably it won't play a role here.
The drift we both see in our ~ 24h measurements, is caused mainly by temperature changes, not by timely drift.

Also, my 3458A is pimped to 65°C, so it will also have a drift of < 2ppm/year, if I would run it continuously.
In my case, I really compare the external reference on par with the 3458A, regarding this parameter.

The 732B will probably drift more, due to the resistors drift, which does not apply to the 3458A (due to ACAL).


The 3458A '10min Transfer Accuracy' is not identical with the timely drift, as this includes the linearity of 0.05ppm max.
The timely drift would be theoretically about 0.03ppm.


Anyhow, when discussing your measurements, I focused on the 1h or 2h 'pure' noise, where the timely drift has practically no effect under all circumstances... and where both of our 3458As are performing much better than these worst case parameters from the specification..

So, I'm still interested on your 1..2h Standard Deviation / Noise-RMS numbers of the 732B vs. 4901, to get an idea, how well Andreas modification performs.

Btw.: For 24h and longer, you may calculate the difference of both methods from the 3458A datasheet:

Absolute method:
10V range => 100nVrms noise, 5µV/K T.C.

Differential method:
100mV range => 20nVrms noise, 0.2µV/K T.C.

Therefore, concerning noise, the differential method is only about 5 times better, but will be superior, if the references are on the order of 100nVrms noise also.

Concerning T.C., the differential method is even 25 times better, therefore constant room temperature is mandatory for such absolute measurements.

Therefore, having no constant RT, requires the differential method.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on August 14, 2016, 01:20:37 am
Hi Dr. Frank.

It's true that there are some 732Bs with not very good stepping up resistors making them drift over time. But there are many good 732Bs that drift very little, being used as secondary standards in many labs through out the world. Plus, there are other references such as 4910 that employ PWM method in 7V to 10V step up which inherently don't sufer from resistor drift. I always use my 4910-AV as the reference, which not only with low noise, but drift very little over time(<0.2ppm per year by average).

On the other hand, there was a design/implementation flaw in 3458A by using that big customize chip which contains many paring resistor with very strict requirements that often fail to meet. Your 3458A is good today, my 3458A is good today, doesn't mean they will be good always, doesn't mean other 3458As are all good. My 3458A was bought 10 years ago 1st hand from an authorized Agilent dealer, but about two months after, I found out it was drifting all the time, they provided free repair of course - they replaced the big customize chip. I myself once try to fixed a drifting 3458A that ended up with suspecting that chip and can do nothing about. I Think TiN has the similar feeling about it.
Even with 'good' 3458As, they require frequent ACAL to cancel the drift of resistors within the big chip(better hourly), which is not possible for T.C. measurement that often automatic, continuous for several hours.

HP/Agilent knows the flaw and prepares many big chips for replacement(not publicly available I'm afraid).
(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=247742;image)

Attached also some bad big chips that one of my friends replaced when repairing 3458A.

To summarize, 3458A is a legend multimeter with unbeatable low noise and linearity for 10V range, but probably apply to short period only. In order to make the best use of it, I use frequent comparison(to a good reference, by a scanner/switch) rather than direct measurement.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 14, 2016, 06:41:04 am
They are soldered. I did not see behaviour change after one desolder-solder cycle , in terms of drift. Also I do not agree on uselessness of good ADC for long term tests. Its capable to stay <1ppm over week without ACAL.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on August 14, 2016, 01:49:04 pm
Hi Dr. Frank.
..
On the other hand, there was a design/implementation flaw in 3458A by using that big customize chip which contains many paring resistor with very strict requirements that often fail to meet.



Your 3458A is good today, my 3458A is good today, doesn't mean they will be good always, doesn't mean other 3458As are all good. My 3458A was bought 10 years ago 1st hand from an authorized Agilent dealer, but about two months after, I found out it was drifting all the time, they provided free repair of course - they replaced the big customize chip. I myself once try to fixed a drifting 3458A that ended up with suspecting that chip and can do nothing about. I Think TiN has the similar feeling about it.
Even with 'good' 3458As, they require frequent ACAL to cancel the drift of resistors within the big chip(better hourly), which is not possible for T.C. measurement that often automatic, continuous for several hours.

.

Hello zlymex,

I totally disagree, that this property is a design flaw., that's not correct, if you read about the design goals (see hpj 4-1989) of this instrument.
That is, that it should be a very fast A/D converter, also, or in first instance.

This demands, that the integrating resistors would have to be split in different weights (multiple of 2, in this case).

Correct, the disadvantage is, that now the stability depends on the ratio of these integrating resistors.

And I pray, that my, and also your ASIC will stay hermetically tight, so that there will be no degradation, like TiN encountered in several of his A3 PCBs.

Anyhow, my instrument, and also your instrument, are good enough to make stability measurements on the order of a few tenth ppm.


Still, it would be nice, if you would provide these statistical characterization of the 4910A and 732B, so that we volt-nuts in this thread have a baseline for our DIY references.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: acbern on August 14, 2016, 05:36:31 pm
@zlymex:
so it seems that these chips are available, if your friend replaced them. I always thought they are not.
can you shed some light on that please.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on August 14, 2016, 11:15:04 pm
@zlymex:  Are this chips soldered in, or are they in sockets?  If soldered in, how in the heck do you remove them?
I refer the gentleman to Dave's previous video on the subject (and subsequent videos where he begins to appreciate it!)

https://www.youtube.com/watch?v=Ft50m8UU5WQ&ab_channel=EEVblog (https://www.youtube.com/watch?v=Ft50m8UU5WQ&ab_channel=EEVblog)

Also known as the Duratool ZD-915, etc... I got mine for £30 from a fella down the road.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 15, 2016, 06:15:56 am

So, I'm still interested on your 1..2h Standard Deviation / Noise-RMS numbers of the 732B vs. 4901, to get an idea, how well Andreas modification performs.


Hello,

I think the best would be calculating the Allan deviation over a longer time period.
Then you can see clearly the 1 hour or short time stability at one glance.


Here one 8hr measurement (1 minute averages) for my newest ADC with LT1027DCLS8-5 and LTZ#4:

At the moment the T.C. is not calibrated so I have a drift with temperature.
This also can be seen on the Allan deviation diagram.
Best stability is around 0.25 uV after 2:1 voltage divider for up to 20 minutes measurement time.
After 20 minutes with the temperature drift creates standard deviations up to 1.5uV.
This corresponds to 0.5 uV and 3uV with respect to the undivided 7 or 10 V input voltage.

So I hope that with temperature compensation of the ADC I will have the 0.5uV over the whole 8hr range.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on August 15, 2016, 11:12:47 am
.....
I think the best would be calculating the Allan deviation over a longer time period.
Then you can see clearly the 1 hour or short time stability at one glance.
Agreed. However, there are two things that make the actual calculation difficult
- the temperature variation like you said will affect the result
- the result is the measurement instrument and the reference combined. In order to get the pure Allan deviation of the measurement instrument or the reference, you need to test three times in a triangle,  and make the calculation by solving equations.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on August 15, 2016, 11:22:50 am
@zlymex:
so it seems that these chips are available, if your friend replaced them. I always thought they are not.
can you shed some light on that please.
They were coming from a service center indirectly and unofficially several years ago. HP/Agilent posses those chips before, but it seems to me that their policy had changed to replacing the whole A3 board rather than replacing U180 chip alone later.
The photo shows how they replace the chip for my 3458A, leaving a lot of flux residue.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on August 15, 2016, 11:32:50 am
@zlymex:  Are this chips soldered in, or are they in sockets?  If soldered in, how in the heck do you remove them?
It soldered in. There are two ways they actually desolder the chip, one is use the desoldering gun like Macbeth said, the other way is to use a solder pot of the right size and fill solder to the brim and dip the pins in the pot.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on August 15, 2016, 12:20:46 pm
Hi Dr. Frank.

3458A was not flawless wasn't it? Having the same trouble for so many units. It just like someone designed a ladder/lift to the Moon but cannot find strong enough building materials to support it. The design of 3458A is ahead of time and cannot implement all the necessary resistor groups that satisfy the specification reliably.

That chart in my previous post was tested 5 years ago when my 3458A was still in excellent condition, but recently my 3458A at last suffered from drifting problems after all. Although I don't mind this because I always use comparison and the drift won't affect me at all. However, it is 2 out of 1 for my 3458A, that is 200% of chance. I don't think it's unluck for me, rather, it's kind of destined. There are a very large portion of 3458A that having drift problems. Many people who own 3458A just don't realize this because either they don't do tests or don't known how to test or don't have the condition to test.

Back from the beginning, the reason I suggest comparison rather than direct measurement are:
 - the drift of 3458A is worse than a voltage reference in the long run
 - the T.C.

The Vp-p for the comparison in the blue box is 0.168ppm, but for the measurement, it is 0.197ppm, 16.7% worse.
The Vp-p for the comparison in 16 hours is 0.243ppm, but for the measurement, it is 0.370ppm, 52% worse.
This shows that even for good 3458A, comparison is better than measurement. The longer the period, the better the comparison.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on September 03, 2016, 05:01:31 am
I picked up an LTZ1000 reference unit off of TaoBao, for about $100. There's a picture of the PCB and parts, which look like they might be pulls.

https://world.taobao.com/item/537238134609.htm?fromSite=main&spm=a1z3o.7695460.0.0.tQsd0b

Now, what you see in the picture is not what  you get. You get the blue tape wrapped square aluminum case.

Inside the case is an unbuffered LTZ1000 design, with the output coming out of two of the cover screw holes. Teflon coated wire.  On the end of the case is a PCB, which appears to be a heater controller. The unit has about 8 turns of heater wire under the blue tape, and warms the case to a comfortable temperature. The vendor uses Lymex' name (and yes, the initial board that you see does look like Lymex' work).


It is an interesting find. Anybody seen anything like this? Thoughts on the unbuffered output (other than, handle with great care)? It came with a little calibration note, out to 7 places. My ancient 5.5 Fluke reads it dead on, my 34401A is about 5 counts low, and flickers on the least significant digit - which I think might be noise, as the 34401A I have is usually stable on the last digit. Yes, I am a neophyte only able to work to a still-suspect 6.5 digit level.





Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 03, 2016, 09:59:10 am
The square PCB board was indeed my very first version but the major components and soldering were not mine.
The narrow PCB and all other work is certainly have nothing to do with me, guessing the seller just use my name.
Those oven-board-at-one-end thing was first used by one of my friend(thy888) in 2010.

I didn't like the idea of having an oven for LTZ1000 PCB at first, but now I accept it if the oven temperature is low(<33 degree C) and well regulated.
Back in 2008, I did sell some unbuffered board at very low price(about $25 each) among Chinese volnuts and bare PCB as well.
The unbuffered board(if same as the datasheet) has disadvantage that it cannot handle capacitive load which might be the source of the noise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on September 04, 2016, 06:44:06 am
More pictures.

You can see the thermocouple that senses the temperature: it runs down a channel of the case. The whole thing runs lukewarm to the touch. There must be about 6 turns of heater wire under the blue tape,

There's plenty of room inside the case for a buffer board.

The LTZ1000 looks kind of beat up. Maybe that's good. 

Lymex, thanks for clearing up the source. The seller links to long articles on the Chinese forums. Seems that there's quite the voltnut movement in China.

Title: Re: Ultra Precision Reference LTZ1000
Post by: klaus11 on September 04, 2016, 08:00:17 am
(https://gd3.alicdn.com/bao/uploaded/i3/TB1S9W1JVXXXXb0XpXXXXXXXXXX_!!2-item_pic.png_600x600.jpg)


https://world.taobao.com/item/522894165585.htm?spm=a312a.7700714.0.0.lqRGB8#detail (https://world.taobao.com/item/522894165585.htm?spm=a312a.7700714.0.0.lqRGB8#detail)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 04, 2016, 08:30:02 am
It is rather strange to see an thermocouple to sense the temperature, as this needs a second sensor at the outside and is not very precise. usually I would choose something like an PT100, NTC or a diode/transistor as a temperature sensor for the constant temperature part.

The position of the TC is also strange, it is rather close to the transistor that drives the LTZ heater, thus a relatively large heat source. With changing voltage the heat source could also change. At least the heater current should be relatively constant - so not that much change in the power of the transistor. Still it would be better to have the sensor more at a low power region, like in between the precision resistors.

An interesting point could be the heater current, to see how much work the LTZ1000 internal heater has to do.

There seems to be the 400 K resistor for TC compensation - I am not sure this is still the correct value and needed with this setup.

Anyway I would not change anything there, if you want to keep the "calibration" of the actual voltage.

I you want to add a buffer, one might consider having the 7 V to 10 V step (if needed) also inside the constant temperature box. The extra circuit should be reasonable low power, as extra power lowers the temperature up to which the unit can work.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on September 04, 2016, 08:10:53 pm
Seems to me that a thermocouple is hard work compared to the other options, although more precise. It is also about 1" down inside the screw channel in the extruded case, so the transistor should not matter too much. I wonder how they calibrate it - maybe they swap out resistors.

As a module, the case + oven is kind of clever. It is small, has room for two boards, and provides a shielded, thermally stable environment for the electronics. I've not found any other source for the heater board. Pricewise, it is pretty good - just about $100 for the full unit, which includes an LTZ1000 and the precision resistors.

A couple of questions.

1) Not sure there is any value in a PWM heater circuit, other than eliminating the power consumption of the series pass transistor. If I were thinking about doing a new oven board, I might switch to a microcontroller and see how tightly the temperature can be controlled.

2) A good 7 to 10V step up would be nice. With the right resistors, you can get close enough to use something like 5k / 11k and a 250 ohm pot. But you need about 1k of swag room to deal with the full voltage range of an LTZ1000, orgo with a much bigger pot.  If the pot is only 2% of the total resistance, its TCR is not so influential. Especially in an oven - although I prefer designs that have thermal drift minimized even without the oven.

3) Best would be digital 7V to 10V adjustment. Not sure what the best approach is there, Anybody got any good ideas? Preferably, tiny surface mount stuff with minimal need for precision parts.

Like I said, I am still at a suspect 6.5 digit level, so lots of things look good. More meters, more standards all start to point to better understanding of where my numbers sit.


Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 04, 2016, 09:05:30 pm
Using a thermocouple as a sensor in the oven makes no sense: the only advantages are small size an fast reaction - neither is needed here. The thermocouple way is not precise at all, as it depends on a second sensor that is not at constant temperature. Just a simple 1N4148 would have been way better: it's more precise, less drift and easier to deal with. Depending on the temperature set-point of the oven and the LTZ1000, the transistor can be quite a heater and thus a hot spot on the board. The power should be reasonably constant, but it is still about the worst place to put the sensor, as heat conduction could change by aging of the board material and maybe air pressure / orientation.

PWM for the heater saves some power, but there is also the alternative of using the transistor that controls the power also as a heater, like keeping the voltage about constant and chance the current. Also a controlled current through a string of diodes in series can be a heater that can be controlled with not that much waste heat. Both alternatives also give an about linear power control, which is good if analog regulation is used. If well shielded PWM might not be so bad, but avoidable. If the oven board is reasonably working, I see no big incentive to change it  - normally the LTZ1000 can well work without it. The oven is not only about the TC but it also calls for an always low humidity, so even an really poor oven can help.

For a precision voltage ration, I would avoid classical pots as much as possible. Even choosing 1% of the shelf resistors is better than essentially any pot you can buy. So at least the first part should be more like finding the right resistor(s) and only do the very last part (< 0.1 %)  with a pot - maybe even a digital pot. As a voltage divider digital pots are quite good and affordable. The down side is that they are usually just 7 or 8 bits.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Gyro on September 04, 2016, 09:32:05 pm
Are you sure that's a thermocouple? The junction looks so much bigger than the wires (which aren't colour coded). It looks like a tiny glass bead thermistor to me.
Title: Re: Ultra Precision Reference LTZ1000
Post by: guenthert on September 04, 2016, 09:39:25 pm
Having read Agilent's 'practical temperature measurements' [1], I got the sense that for precision temperature measurements you would want to use RTDs.  Thermocouples would be used where other sensors can't be used (as they are very robust).  For small temperature differences, the voltage differences of a thermocouple would be very small and difficult to measure precisely.  A TC would be a odd choice here, are you sure it is one?


[1] https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwjv0OOU1fbOAhUJwGMKHeESDW0QFghbMAM&url=http%3A%2F%2Fcp.literature.agilent.com%2Flitweb%2Fpdf%2F5965-7822E.pdf&usg=AFQjCNHl8Du_x4yxRMYG4VZLZ81Le-PzTg&sig2=POaea5cDk4eERIiD6k7gcA (https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=4&cad=rja&uact=8&ved=0ahUKEwjv0OOU1fbOAhUJwGMKHeESDW0QFghbMAM&url=http%3A%2F%2Fcp.literature.agilent.com%2Flitweb%2Fpdf%2F5965-7822E.pdf&usg=AFQjCNHl8Du_x4yxRMYG4VZLZ81Le-PzTg&sig2=POaea5cDk4eERIiD6k7gcA)
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on September 04, 2016, 11:02:46 pm
I think you guys are right - looking at my original photo, the sensor looks like a smooth bead of shiny material, not a thermocouple weld. That would be a much easier solution.

Maxim has a 10-bit digital pot with 5 ppm TC in ratiometric mode. With an op amp, it should be possible to create an offset voltage for the buffer amp that is down in the last three digits of the reference.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 05, 2016, 12:34:59 am
That friend of mine(thy888) who is very successful in making these small-case references that he sold many.
He uses NTC(bead type) as the sensor and uses both wire and a transistor as heaters.
He tried many circuits and components before, the latest is to use VHD200 as the step up of 7V to 10V.
However, the metal-case thing is just the core, a case with binding posts, power, batteries and thermal insulation are needed to complete as a reference.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on September 05, 2016, 12:45:47 am
The bashed up parts are a little worrying. On the one hand it would be great to get a well worn in LTZ1000 but on the other I've read of the people who recover these that they will snip off old legs and spot weld new ones using their cheap crap wire that becomes a load of hotspot thermal junctions and renders the LTZ unfit for purpose? 5.5 digits may be ok :palm:
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 05, 2016, 12:47:54 am
.......
3) Best would be digital 7V to 10V adjustment. Not sure what the best approach is there, Anybody got any good ideas? .......
He uses analog approach, and everything is hand adjusted with foil resistors, no pot is used.

Well, 7001(of Wavetek/Fluke) uses digital(DAC) for fine adjustment.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 05, 2016, 01:01:44 am
The bashed up parts are a little worrying. On the one hand it would be great to get a well worn in LTZ1000 but on the other I've read of the people who recover these that they will snip off old legs and spot weld new ones using their cheap crap wire that becomes a load of hotspot thermal junctions and renders the LTZ unfit for purpose? 5.5 digits may be ok :palm:
Those weld-legs parts were pretended to be new that my friends and I would never buy. We buy LTZ1000 either new or with original legs and original marking.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on September 05, 2016, 01:12:45 am
Where does THY888 sell his units? They look interesting.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dr.diesel on September 05, 2016, 01:20:08 am
Where does THY888 sell his units? They look interesting.

Ditto, my stack of various references isn't quite tall enough either.   :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 05, 2016, 01:56:18 am
Where does THY888 sell his units? They look interesting.
He sells most of his stuff at 38hot.net, such as http://bbs.38hot.net/forum.php?mod=viewthread&tid=98892 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=98892)
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 05, 2016, 02:57:59 am
(https://gd3.alicdn.com/bao/uploaded/i3/TB1S9W1JVXXXXb0XpXXXXXXXXXX_!!2-item_pic.png_600x600.jpg)


https://world.taobao.com/item/522894165585.htm?spm=a312a.7700714.0.0.lqRGB8#detail (https://world.taobao.com/item/522894165585.htm?spm=a312a.7700714.0.0.lqRGB8#detail)
"Out of stock" replied by the seller. Obviously a fishing bait.
Title: Re: Ultra Precision Reference LTZ1000
Post by: lowimpedance on September 05, 2016, 03:20:58 am
The bashed up parts are a little worrying. On the one hand it would be great to get a well worn in LTZ1000 but on the other I've read of the people who recover these that they will snip off old legs and spot weld new ones using their cheap crap wire that becomes a load of hotspot thermal junctions and renders the LTZ unfit for purpose? 5.5 digits may be ok :palm:
Those weld-legs parts were pretended to be new that my friends and I would never buy. We buy LTZ1000 either new or with original legs and original marking.
An interesting pile there !, what were they sniped from ?.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 05, 2016, 04:16:04 am
Those weld-legs parts were pretended to be new that my friends and I would never buy. We buy LTZ1000 either new or with original legs and original marking.
An interesting pile there !, what were they sniped from ?.
That is the question I've been asking. But all I got is something like these.
Title: Re: Ultra Precision Reference LTZ1000
Post by: lowimpedance on September 05, 2016, 04:38:22 am
Good collection of vishay resistors and other expensive parts on the PCB too !.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 05, 2016, 05:31:20 am
Good collection of vishay resistors and other expensive parts on the PCB too !.
Sorry I didn't make myself clear, I meant " all I got is something like these photos". I don't posses that board. Those photos were coming from a seller of used LTZ1000.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 05, 2016, 06:12:16 pm
As the LTZ1000 does not really need a controlled temperature, I don't think the extra oven needs to be that stable. If the conditions are not to bad, even a slow, e.g. simple proportional control might be good enough.
It might be interesting to have the option to set the temperatures to a few different values to check for the TC of the circuit inside and maybe get the right value for the 400 K resistor.

The soldering on the temperature control board does not look that good. But the circuit might be good enough. For stability the sensor should be in reasonable contact to the case - so take care when moving it.

Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on September 05, 2016, 11:44:24 pm
Heater voltage readings for the blue case LTZ1000 reference from TaoBao.

Screened cable connected to the heater electrodes, connected at the diode and the transistor emitter.
Allowed 30 - 60 minutes to stabilize.

Temperature is maybe 22 - 23 c. Can't find my Raytek.

Heater voltage at startup 8.4 volts. Holds there until ref hits temp, then drops quickly.

Test                                              LTZ1000 heater voltage
Hanging in free air, no case             7.78 - 7.80. Blow on it, 7.95. This is why people put foam on the part.
Case only, no case heater               7.353 - millivolt movement over minute or two.
Case with case heater active           5.863  - millivolt movement over a minute  or two

Case heater is about 1.4W (14V 0.1A)

Agree that the case heater doesn't have to be that precise. It is very helpful with all the other parts - there's no temp drift as long as the outside temp is less than the case setting. Plus, the EM shielding is good. Now, as I noted I am still at a suspect 6.5 digits. So this is still junior stuff.

When I pull the heater sense wire, i'll put some thermal goop back in. I'll have to trace the circuit out, see what it takes to calibrate the heater.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 07, 2016, 09:23:35 pm
Hello,

update from my measurements on LTZ#3-LTZ#6
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg935102/#msg935102 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg935102/#msg935102)

here the updated table with averaged drift from all measurements and the charts:

I recorded (weekly) readings to determine ageing drift against my ADCs and against LTZ#2 with two 6.5 digit DMMs in 100 mV range.
LTZ#5 was needed most of the time for measurement of the T.C. of the LT1027 references. So there are some gaps in the charts.

Evaluation is from day 128 (after all adjustments done) to day 238 so around 3 kHrs.
The readings indicate all below 2 uV / kHr or below 2 ppm/year compared to my measurement setup.

LTZ#2 drifts about -1.57ppm/year.
the ADCs drift also in the range of 1-2 ppm over one year with some seasonal changes.
All in all there is not much difference in LMS slope between the (absolute) ADC readings and the DMM differential reading.

Up to now LTZ#6 and LTZ#4 seem to be with the least ageing drift.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on September 07, 2016, 10:08:11 pm
Andreas,

Are these long term drift tests continuously powered or just powered up for each weekly measurement? Can you provide a link to your current test proceedure - you've done a lot of posts so not easy for me to find the relevant one!

Also could you post spreadsheet data so that we can create a graph for each ADC/DMM showing all four LTZs?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 09, 2016, 09:33:12 pm
Hello,

my battery powered references are all running 24/7
Also the battery powered ADCs.
The 6.5 digit DMMs are only running when being used (with >= 2 hrs warm up time).
All ADCs are connected in parallel to the DUT - Reference.
The DMMs are connected between DUT-Reference and LTZ#2 reference.
The HP is running with 100NPLC and the K2000 with 10 NPLC (=maximum) integration time.
The measurement values are averaged over 5 minutes measurement time to reduce noise.
Temperature varies from 20-32 deg C in my "lab" in summer.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 21, 2016, 04:09:07 am
One thing I notice during 4920M service (https://xdevs.com/fix/d4920m/) is rather thin PCB substrate for LTZ1000 module.

(https://xdevs.com/doc/Wavetek/4920M/img/ltz_side_1.jpg) (https://xdevs.com/doc/Wavetek/4920M/img/ltz_side.jpg) (https://xdevs.com/doc/Wavetek/4920M/img/lm399_side_1.jpg) (https://xdevs.com/doc/Wavetek/4920M/img/lm399_side.jpg)

Seems like it would help for better thermally decoupling of hot LTZ oven from rest of the circuit.
Also nice copper plane right under LTZ location on main A/D board. EMI shielding? :)

(https://xdevs.com/doc/Wavetek/4920M/img/ad_ref_bot_1.jpg) (https://xdevs.com/doc/Wavetek/4920M/img/ad_ref_bot.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 21, 2016, 05:20:51 am
Hello,

Interesting: the LM399 as auxiliary reference besides the LTZ1000 module.
Don´t they trust the LTZ alone?

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: lowimpedance on September 21, 2016, 05:31:03 am
The thin PCB has been used in other Datron equipment, as I found with the ref. module in a 4808. (thickness 0.6mm).
pics here;
https://www.eevblog.com/forum/testgear/datron-voltage-reference-pcb-module-pics/msg813331/#msg813331 (https://www.eevblog.com/forum/testgear/datron-voltage-reference-pcb-module-pics/msg813331/#msg813331)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Mickle T. on September 21, 2016, 12:26:16 pm
1271 uses the same thin PCB too.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 22, 2016, 09:26:14 pm
The LT6011 has slightly better specs than the LT1013, and is not that much more expensive.

Mhm:
you will need a negative power supply for the LT6011 (Common mode input range 1.5V above negative rail).
The output current may be marginal for the 5mA current source. (5mA only specified as short cirquit current with 1V overdrive).
Gain is only specified at around 2 mA (5kOhms load) and not at 5 mA (2K Ohms) needed for the current regulator.
I do not know if this is really a upgrade.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on September 23, 2016, 02:08:16 am
I will keep looking...
Did you already rule out the actual upgrade of the 1013, the 1413?
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 23, 2016, 04:08:00 pm
I will keep looking...
Did you already rule out the actual upgrade of the 1013, the 1413?

There is also the LT1213 as well a the LT1413.  I'm going for lower power if I can.  There are some promising parts from Linear Tech and also ADI.  I have not yet checked TI, because their website search tool does not work for me, and I'm trying to find a browser that will work with it.  Still looking...

What about OP727? It's better than LT1013 for many params such as Vos, Ib, Is, PSRR and LF noise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 24, 2016, 12:56:41 am
......  I'm still having trouble with the TI website (this has been going on for years now-- their website designers should be fired IMHO)...

I found out nothing at TI website if the auto-zero opams such as OPA2188 or OPA2180 are ruled out. The only one near LT1013 is TLE2022BC.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 24, 2016, 05:11:49 am
I think you have overlooked the Burr Brown "equivalent" of the LT1013:  OPA2234

But open loop gain is a factor 7-8 lower.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: EmmanuelFaure on September 24, 2016, 01:28:19 pm
In my opinion, the discussion about what op amp to choose spanning all over this topic look exactly like this :
https://en.wikipedia.org/wiki/Law_of_triviality
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 24, 2016, 02:21:57 pm
The LT1013, LT1413, OPA2234 and AD797 and likely some more are well good enough. So there is no real need to look for something better - the 4 types listed are very similar anyway.  From first sight I would expect that even an LM358 would not make a significant difference.

The real points that can matter are the thermal design, lead / wire resistance and the 400 K resistor (not the resistor type but value and position for compensation) for the non A version to compensate the TC. Power dissipation of the OPs is not that critical either: the Reference zener takes some 5 mA and the divider to set the temperature about 0.5 mA.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on September 24, 2016, 04:52:20 pm
Quote from: DiligentMinds.com
...
True-- we are saving only about 600uA in a circuit that uses about 40mA-45mA (including the heater circuit), ..

Which kind a version do you mean?
I use LTZ1000, with external thermal isolation, at 45°C, 12k/1k, LT1013, powered with 12Vdc, standard circuit, plus modifications by Andreas.

The circuit consumes around 50mA initially, but 22mA only when stabilized.
So to which solution relates your 45mA current consumption?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 24, 2016, 05:17:15 pm
Hello,

according to my measurements:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560)

I have 20-24 mA at room temperature. Even with 3*LTC2057 OpAmps which consume nearly 1 mA each.
So with 12*NiMH AA cells you will have easily 2-3 days of operation even if the cells are somewhat older.

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 24, 2016, 09:21:11 pm
Even in the compensated circuit, there is something like a 5 mA zener current that is needed to get the low noise. So even than it does not make a big difference if the OPs take 600 µA or 300 µA. One might get away with lower zener current it is only for the good long therm stability and not the LF noise.

If you really needs to go for low noise and low power, there would be the rather crazy way of using a battery (e.g. 7.2 V nominal) as an intermediate reference to provide low noise and use some kind of filtering / adjustment to get the long term stability of the LTZ1000 (that might than run at lower current). So the battery (with companion circuit) as kind of low pass filter in the mHz range.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 25, 2016, 05:18:36 am
Hello Ken,

do you have a S&H cirquit which generates no charge injection (noise) above that level?

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 25, 2016, 08:35:00 am
For just a reference charge injection is not that critical, as this will be largely a constant offset. So the critical part would be only the drift in charge injection. The H11F1 is also relatively slow (and speed may show drift) - this could add quite some dead time and thus require a low frequency.

Even with pulsing the zener, one would not get away with all the 1/f noise of the reference. It still is the same chip and thus long lived metastable states can still survive the pulsing, and new ones can get populated.  I am not even sure that this would give a real advantage in 1/f noise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 26, 2016, 03:22:02 am
......
AFAIK, the 1/f noise of a Zener operated in avalanche mode [like the LTZ1K is], will be inversely proportional to the square root of the Zener current.  So, going from 5mA to 20mA would (theoretically) reduce the 1/f noise by 1/2.  I got that from my ancient Motorola Zener Diode Handbook (https://www.amazon.com/ZENER-DIODE-HANDBOOK-Motorola/dp/B000KUHHF6).

That is true. However, there is one thing I don't understand, because I don't know the physics behind the zener LF noise.
I thought the LTZ1k is the best as far as the LF noise is concerned, specifying at 1.2uVpp typical at 5mA zener current.
But, there is this 2DW233(of a particular maker), showing much small LF noise than LTZ1k at 5mA, typically 0.4uVpp :scared:  This is equivalent to a LTZ1k operating at 45mA. Anyone can explain the possible reason?
( https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg938465/?topicseen#msg938465 (https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg938465/?topicseen#msg938465) )
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 26, 2016, 06:28:33 am
....... 
Is there any way to speak with a scientist or engineer at the factory where those Zeners were made to get some additional information on them?

I tried but no result. I cannot find anything of related publications neither. They didn't mention that 2DW233 in their website in particular(such as special process or ultra-low noise). Those low noise 2DW233 is selling at similar price(all very cheap) as other manufactures with severe noise. The low noise feature of this 2DW233 is only recognized by amateurs like me.
Title: Re: Ultra Precision Reference LTZ1000
Post by: JS on September 26, 2016, 02:49:26 pm
....... 
Is there any way to speak with a scientist or engineer at the factory where those Zeners were made to get some additional information on them?

I tried but no result. I cannot find anything of related publications neither. They didn't mention that 2DW233 in their website in particular(such as special process or ultra-low noise). Those low noise 2DW233 is selling at similar price(all very cheap) as other manufactures with severe noise. The low noise feature of this 2DW233 is only recognized by amateurs like me.

Maybe it's just a typo  :-\

JS
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 26, 2016, 03:12:14 pm
....... 
Is there any way to speak with a scientist or engineer at the factory where those Zeners were made to get some additional information on them?

I tried but no result. I cannot find anything of related publications neither. They didn't mention that 2DW233 in their website in particular(such as special process or ultra-low noise). Those low noise 2DW233 is selling at similar price(all very cheap) as other manufactures with severe noise. The low noise feature of this 2DW233 is only recognized by amateurs like me.

Maybe it's just a typo  :-\

JS
If you meant the noise, no.
There is no specification for the noise in the datasheet. The ultra-low noise feature of 2DW233 was found out by actual measurement of many people at different places and on different times.
Title: Re: Ultra Precision Reference LTZ1000
Post by: JS on September 26, 2016, 03:41:19 pm
....... 
Is there any way to speak with a scientist or engineer at the factory where those Zeners were made to get some additional information on them?

I tried but no result. I cannot find anything of related publications neither. They didn't mention that 2DW233 in their website in particular(such as special process or ultra-low noise). Those low noise 2DW233 is selling at similar price(all very cheap) as other manufactures with severe noise. The low noise feature of this 2DW233 is only recognized by amateurs like me.

Maybe it's just a typo  :-\

JS
If you meant the noise, no.
There is no specification for the noise in the datasheet. The ultra-low noise feature of 2DW233 was found out by actual measurement of many people at different places and on different times.

Oh, that's nice then, thanks for the info!

JS
Title: Re: Ultra Precision Reference LTZ1000
Post by: chickenHeadKnob on September 26, 2016, 04:39:05 pm

I tried but no result. I cannot find anything of related publications neither. They didn't mention that 2DW233 in their website in particular(such as special process or ultra-low noise). Those low noise 2DW233 is selling at similar price(all very cheap) as other manufactures with severe noise. The low noise feature of this 2DW233 is only recognized by amateurs like me.

I tried to buy these from the ali-express seller you mentioned but after 75 days and no shipment I canceled the payment. At least Aliexpress claims they refunded me - I haven't checked my credit card bill yet. It was the first time I tried aliexpress  so I don't know what the transaction failure rate is. It is apparently less reliable than ebay. I have never had any problems with chinese ebay sellers. Its all for the good though, I changed my mind on what approach to take and testing these would just be a waste of time now. There is some value in the pursuit references that are temp compensated, non-ovenized,  cheap  and maybe a little drifty  but ultra low noise. Say for longscale ADCs that can be disciplined once a day (or more often) to a stable master lab reference.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 27, 2016, 09:47:54 am

I tried to buy these from the ali-express seller you mentioned but after 75 days and no shipment I canceled the payment. .........

I'm sorry to hear that. I didn't know AliExpress before I came across some people at an electric unicycle forum who often buy electronic parts from AliExpress with free international shipping(which is slow). I buy most of my electronic parts at taobao.com that backstaged by the same Alibaba but has a dedicated on-line chat system allowing sellers and buyers to talk. One difference(of taobao and aliexpress with eBay) is that they don't charge/tax e-stores on per item base therefore the average unit price tends to be very low and the number of items in a e-store is huge so is the number of daily packages. These often result in poor management and poor service especially when they are short handed.

Any way, I've bought 500+ pieces of 2DW233 just in case they stop producing it using the same technique(and I may not find the ultra-low noise zener anywhere in the world in that case).
Title: Re: Ultra Precision Reference LTZ1000
Post by: chickenHeadKnob on September 27, 2016, 01:43:03 pm

I tried to buy these from the ali-express seller you mentioned but after 75 days and no shipment I canceled the payment. .........

I'm sorry to hear that. I didn't know AliExpress before I came across some people at an electric unicycle forum who often buy electronic parts from AliExpress with free international shipping(which is slow). I buy most of my electronic parts at taobao.com that backstaged by the same Alibaba but has a dedicated on-line chat system allowing sellers and buyers to talk. One difference(of taobao and aliexpress with eBay) is that they don't charge/tax e-stores on per item base therefore the average unit price tends to be very low and the number of items in a e-store is huge so is the number of daily packages. These often result in poor management and poor service especially when they are short handed.

Any way, I've bought 500+ pieces of 2DW233 just in case they stop producing it using the same technique(and I may not find the ultra-low noise zener anywhere in the world in that case).

No need to be sorry! If it wasn't for your interesting insight into the the Chinese semiconductor scene I wouldn't have known about these. My plan was to try with 80 parts, characterize them, and hope that was enough for a lifetime buy. Yes I realize it is too uncertain to source these parts for someone not in China, even the diamond brand factory may not exactly  know how to reproduce them from one batch to another. My plan now is to use LT1027 with a Walt Jung style noise reduction circuit.
best regards
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 28, 2016, 12:39:26 am
Using a copper block is a good idea. I've build a test circuit without one and the noise is not as low as expected.
2DW233 is a temperature compensated (two identical zeners back to back) on its own, and altering the applied current will find the zero-TC spot.
Title: Re: Ultra Precision Reference LTZ1000
Post by: acbern on September 28, 2016, 05:58:29 am
Does anybody have data re. the aging rate of the 2DW233? Is it comparable to the LTZ1000?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kjelt on September 28, 2016, 07:22:07 am
This is getting confusing, is it an idea to start a seperate topic on the 2DW233 ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on September 28, 2016, 11:45:11 am
Sure, discussion of 2DW233 is here https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/ (https://www.eevblog.com/forum/metrology/ultra-low-noise-reference-2dw232-2dw233-2dw23x/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on October 05, 2016, 06:56:01 pm
After difficulties with PWW resistors I finally finished all 4 LTZ1000 boards from TiN and started collecting data.
Almost all resistors are PWW made by Edwin except 4x 100k resistors which were out of tempco spec.
He has some manufacturing issues with potting.
Missing PWW were replaced by pre-selected Vishay UXB series resistors.
Initial measurement by 34411A/34410A is rock stable, so I used ratio measurement with 34401A and 34420A.
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on October 05, 2016, 09:24:54 pm
After difficulties with PWW resistors I finally finished all 4 LTZ1000 boards from TiN and started collecting data.
Almost all resistors are PWW made by Edwin except 4x 100k resistors which were out of tempco spec.
He has some manufacturing issues with potting.
Missing PWW were replaced by pre-selected Vishay UXB series resistors.
Initial measurement by 34411A/34410A is rock stable, so I used ratio measurement with 34401A and 34420A.

Very cool!  I'm looking forward to your measurement results!  Is that your temperature chamber on the right side of the photo?

-Ken

Only usable for measurement seems to be 34420A, 34401A in ratio mode is much more fluctuating (2 last digits) on same references. It is not temperature chamber, only the polystyrene box from pharmacy without any heater. But it seems to be good enough.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 06, 2016, 04:57:00 am
Neat setup. I see my earpick trick works for you too  :-DMM. Will you have datalogging running as well?
Would like to see reference board pics in your setup, once you done with measurements.

And what would be the ultimate plan of using these modules? Long-term testing or some practical application, if that's ok to ask?
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on October 07, 2016, 09:22:15 pm
Data sheet thermal resistance specification for the LTZ1000 (non-A version) doesn't seem right.  Looking at the "Die Temperature Rise vs Heater Power" graph in the data sheet, I see 85C rise with 0.5W of heater power which equates to 170 C/W or about twice the specified 80 C/W data sheet value.  The "A" version does looks about right: ~82C rise with 0.2W is close to the 400 C/W data sheet value.  Can anyone explain this discrepancy?   Am I supposed to add normal circuit configuration power dissipation of the transistors & zener to the heater power when doing this calculation?

I ask because I'm leaning towards a 4-layer board layout with considerable copper pours for the leads and inner layers to equalize lead temperature per data sheet recommendation.  I'm wondering what this will cost by way of heater power.  To answer this, I'm trying to determine how much heat escapes by way of the leads versus the case.  I thought comparing thermal resistances of the highly isolated "A" part versus non-A would yield insight.   Instead, I can't seem to make the numbers add up...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 07, 2016, 10:58:48 pm
Usually the thermal resistance for a TO99 is about 160 K/W. Also the similar size TO39 is in that range. So I guess the 80 K/W number is wrong, or in forced air or with rather short leads.

The thermal resistance of the wire can be estimated form the dimensions and the known material. My calculation give something like 900 K/W for the 8 full 15 mm leads, and about 300 W/K for 5 mm leads. So there is quite some power going through the leads, especially if short. With extra thermal insulation around the case the heat flow through the pins can be the major part.

Title: Re: Ultra Precision Reference LTZ1000
Post by: JS on October 08, 2016, 12:49:23 am
Data sheet thermal resistance specification for the LTZ1000 (non-A version) doesn't seem right.  Looking at the "Die Temperature Rise vs Heater Power" graph in the data sheet, I see 85C rise with 0.5W of heater power which equates to 170 C/W or about twice the specified 80 C/W data sheet value.  The "A" version does looks about right: ~82C rise with 0.2W is close to the 400 C/W data sheet value.  Can anyone explain this discrepancy?   Am I supposed to add normal circuit configuration power dissipation of the transistors & zener to the heater power when doing this calculation?

I ask because I'm leaning towards a 4-layer board layout with considerable copper pours for the leads and inner layers to equalize lead temperature per data sheet recommendation.  I'm wondering what this will cost by way of heater power.  To answer this, I'm trying to determine how much heat escapes by way of the leads versus the case.  I thought comparing thermal resistances of the highly isolated "A" part versus non-A would yield insight.   Instead, I can't seem to make the numbers add up...

  Wouldn't that add to the mechanical stress on the board? As some are using thinner PCBs and/or cut outs to allow for less mechanical stress, I guess adding 2 extra layers would be against that effort. Some soft thermal potting or pad may help equalize the lead temperature without adding mechanical stress.

JS
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on October 10, 2016, 09:29:31 am
Neat setup. I see my earpick trick works for you too  :-DMM. Will you have datalogging running as well?
Would like to see reference board pics in your setup, once you done with measurements.

And what would be the ultimate plan of using these modules? Long-term testing or some practical application, if that's ok to ask?

Yep, they are amazing.Earpick is in lab easy available :)
Data logging is in progress. I upgraded RPi to latest Raspbian Jessie kernel and it stopped working.
I would like to use them for 10V reference including 10k reference in better case.
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on October 10, 2016, 01:29:15 pm
Usually the thermal resistance for a TO99 is about 160 K/W. Also the similar size TO39 is in that range. So I guess the 80 K/W number is wrong, or in forced air or with rather short leads.

The thermal resistance of the wire can be estimated form the dimensions and the known material. My calculation give something like 900 K/W for the 8 full 15 mm leads, and about 300 W/K for 5 mm leads. So there is quite some power going through the leads, especially if short. With extra thermal insulation around the case the heat flow through the pins can be the major part.
Thanks for the confirmation data sheet figure of 80 K/W is wrong.  I just looked at LT1012 data sheet where TO-5 has Rth-JA = 150 K/W and Rth-JC = 45 K/W which further attests to the error.

Once a plastic cap is placed over the part and insulation placed about leads to kill air currents, it looks like overall thermal resistance will be just as high as the "A" part and the majority of heat flow will be through the leads.   It makes sense now why the data sheet recommends equal size PC traces to equalize heat loss and maintain them at similar temperatures.

@JS  The wire leads will offer plenty of mechanical compliance in the x-y axis.  If z-axis (direction of leads) mechanical compliance is necessary, I could add a "S" bend to each lead before soldering into board.   But I doubt mechanical stress is even an issue for a TO-5 part.  I realize someone flexed their reference board and saw several uV of change, but it wasn't clear how much of that came from stress on resistors and op-amps versus the LTZ1000.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 10, 2016, 06:45:29 pm
Due to the extra about 300 K/W extra internal thermal resistance the A version can operate with a lower heating power if the temperature is choose for the same maximum ambient 
temperature. However the difference is not that big - comparing long an short leads can be a similar difference.
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on October 10, 2016, 11:22:49 pm
Due to the extra about 300 K/W extra internal thermal resistance the A version can operate with a lower heating power if the temperature is choose for the same maximum ambient 
temperature. However the difference is not that big - comparing long an short leads can be a similar difference.
I totally agree.   But now that we know it's 150 K/W (instead of 80) for non-A and 400 K/W for A part, the difference is smaller.  Couple that with everyone putting insulation around the parts, and long leads (best for equal lead temperature at the board per this thread) and now majority of heat flow is out the leads to the PCB.  So, not much difference between A and non-A parts.  Makes me wonder if non-A designs run short of thermal margin of heater setting...

I forgot to mention, I looked at the "Die Temperature Rise vs Heater Power" graph from the data sheet again, and it does extrapolate to zero temperature rise at zero heater power.  So the rest of the die elements are assumed de-energized for this graph.  But I agree with what DiligentMinds is saying- when doing design, die (zener et.el.) dissipation will subtract from heater power necessary to reach target temperature.  If that quantity goes zero/negative, you've lost thermal regulation and your reference turns to crap.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 12, 2016, 04:16:56 pm
Well, hope nobody mind if I jump in with few practical items into this nice talk.
I was talking to one of volt-nuts (not known member here), and we decided to build and test another KX LTZ-reference (https://xdevs.com/article/kx-ref/) for him.
Complete assembly will be tested for tempco and aged for 168 hours and later shipped cold to the final destination via regular mail.

To keep things bit more exiting for me, I decided to try few new things this time.

A. Use VPG VHD200 divider, 1K/13K hermetic oil-filled resistor. My previous LTZ references were using separate resistors.
In theory this should provide better thermal stability, as temperature setpoint divider is now tightly coupled thermally in same oil-filled package.

Rest of resistors are custom 2 x VPG 75K 1%, VPG 120R 0.01%. These have custom PO VFR part-numbers, but I'd expect they are VHP101-based.
Whole lot was bought for 190$USD from eBay, including unrelated resistors on photo.

Chip will be LTZ1000ACH.

(https://xdevs.com/doc/xDevs.com/KX_STR/vhp_top_1.jpg)

B. I want to try ADA4522-1ARZ opamp instead of my usual LTC2057's to see if any difference would be visible on output noise/short-term stability (I expect none, but who knows).

(https://xdevs.com/doc/xDevs.com/KX_STR/vhp_bot_1.jpg)

And initial check, using 3458A.

(https://xdevs.com/doc/xDevs.com/KX_STR/vhp120_1.jpg)

Usual datalog:

(https://xDevs.com/doc/xDevs.com/KX_STR/vhp120r.png)

Not a bad start, eh? -1ppm from 120 &Omega;. :)
Ignore first hour when ACAL was ran. 8:15 to 10:30 is measurement with DELAY 5 on 100ohm range. Few samples were overflow, as 3458A's max overrange is just 120 ohms, so data from 11:15 is with 1K&Omega; range and DELAY 1. All samples NPLC100, AZER ON, with resistor right at therminals as on photo.

P.S. Bonus quiz, what are rest resistors are for?  ;D
Title: Re: Ultra Precision Reference LTZ1000
Post by: Nuno_pt on October 12, 2016, 05:54:50 pm
Well, looks like I've to start gathering some parts, to build one too.

 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 12, 2016, 06:02:39 pm
The extra resistors looks like current shunts, maybe for the SMU project.

There is rather little sense in using an ADA4522 for the reference circuit. It could even cause trouble from RF interference and maybe phase shift in the 10 Hz range. Also the noise of the reference is way higher than that amplifier or the LT1013. So the LT1013 is perfectly fine for the LTZ1000 circuit. The critical part of the amplification is done by the transistor inside the LTZ1000. So at the output one sees the noise of the reference zener (which is by far the main component) plus the noise of the transistor (rather low, better than most OPs) and only about 1/200 of the noise (and drift) of the OP used. It is only at higher frequencies (e.g > 100 Hz) where the noise of the OP gets visible to 100% and here the AD4522 is not that exceptionally good. Also current noise of the ADA4522 is a little on the high side, as it sees an about 50-70K source.

The point's where one might want an improvement over the DS circuit is more like RF immunity, tolerance to capacitive loading and may be additional temperature monitoring.

The ADA4522 is a good companion for the shunts.
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on October 12, 2016, 07:03:52 pm
The 3458A's TC spec is 4ppm on the 120ohm range so between 8:15 and 10:30 you have a resistor with -4ppm and a 3458A with a +4ppm TC plus 1.6ppm pk-pk noise. Or vice versa. Or any combination inbetween including both being 0ppm.

The resistance was on average unchanged between 8:15 and 10:27 when the temperature dropped from 26.2 to 24.1C, but then shifted by approx .8ppm when the temperature returned to 26.2. So is that hysterisis in the resistor, the 3458A or both? It seems like quite a lot frohm a temperature change of only 2.1C.

[EDIT] Ignore the above - I was misreading your graphs. I do find them hard to work out what's what though. Any chance of annotating one of your charts sometime to show exactly which lines relate to which scales? E.G. what are the orange dotted and blue dashed lines?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 12, 2016, 07:47:17 pm

P.S. Bonus quiz, what are rest resistors are for?  ;D


The 634 Ohm, 9 Ohm and 0.1 Ohm are intended for your 3458A, current shunts, R209, R211, R213.

I think, we both already discussed to improve their T.C.


Frank

Btw.: Where did you get this 0.1Ohm in small quantities? Directly from Vishay?
Ah, really everything from ebay?!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on October 13, 2016, 12:07:30 am
Either ebay, or Taobao. I'm starting to like the latter.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 13, 2016, 12:17:21 am
Dr.Frank is sharp as always. Yes, everything from eBay this time. 1 ohm I already have VPG VPR5 4wire as well.

I'll redo a graph for better clarity and legend, sorry.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Nuno_pt on October 14, 2016, 09:44:43 am
Hi guys,
Does any of you guys have some boards for the LTZ, and are willing to let maybe 1 or 2 of them go, I'm looking for maybe 2 boards to start building my first LTZ.

Thanks.
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on October 18, 2016, 10:51:33 pm
After difficulties with PWW resistors I finally finished all 4 LTZ1000 boards from TiN and started collecting data.
Almost all resistors are PWW made by Edwin except 4x 100k resistors which were out of tempco spec.
He has some manufacturing issues with potting.
Missing PWW were replaced by pre-selected Vishay UXB series resistors.
Initial measurement by 34411A/34410A is rock stable, so I used ratio measurement with 34401A and 34420A.

Very cool!  I'm looking forward to your measurement results!  Is that your temperature chamber on the right side of the photo?

-Ken

Measurement with freshly calibrated 3458A started, first reference made by Edwin PWW is within day within +/- 1ppm - cold start.
Each reference will be measured one week minimum to give me some level of confidence in short term stability.
Any tips for low EMF relay for scanner?
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on October 19, 2016, 12:35:08 am
Measurement with freshly calibrated 3458A started, first reference made by Edwin PWW is within day within +/- 1ppm - cold start.
Each reference will be measured one week minimum to give me some level of confidence in short term stability.
Any tips for low EMF relay for scanner?
Looks quite normal, except some spikes at the beginning. What is the NPLC used? Is AZ on?
As for the low EMF relay for scanner, try latching relay, such as those used by Fluke 5720A, DS2E-ML2-DC5V. I use similar relays in my DIY scanner: https://www.eevblog.com/forum/projects/diy-low-thermal-emf-switchscanner-for-comparisons-of-voltage-and-resistor-stand/msg610755/#msg610755 (https://www.eevblog.com/forum/projects/diy-low-thermal-emf-switchscanner-for-comparisons-of-voltage-and-resistor-stand/msg610755/#msg610755)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 19, 2016, 06:20:34 am

Measurement with freshly calibrated 3458A started, first reference made by Edwin PWW is within day within +/- 1ppm - cold start.
Each reference will be measured one week minimum to give me some level of confidence in short term stability.
Any tips for low EMF relay for scanner?

As a 10 channel scanner, you may get the old HP3488A plus 44470A, which are quite cheap.

These spikes indicate that your setup may be disturbed by RF noise, bad grounding, and lacks all the blocking caps, like in Andreas design.

Short term stability, like noise and fluctuations may be determined within one hour already, i.e. 10 min and 1h stability. That should be <= 0.2ppm
Up to 24h will give mostly the temperature dependency of your LTZ1000 references, plus the 3458A w/o ACAL (especially U180 test).
Constant RT, dT <= 0.2°C should also give dU <= 0.2ppm.
One week will already show the initial burn-in drift of the LTZ1000, if applicable, and depending of your oven temperature.

Depending on the history of your LTZ1000 (e.g. solder heating, preliminary heating / cycling), the initial burn-in drift may take months or years.

Frank


Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on October 19, 2016, 04:03:00 pm
Measurement with freshly calibrated 3458A started, first reference made by Edwin PWW is within day within +/- 1ppm - cold start.
Each reference will be measured one week minimum to give me some level of confidence in short term stability.
Any tips for low EMF relay for scanner?
Looks quite normal, except some spikes at the beginning. What is the NPLC used? Is AZ on?
As for the low EMF relay for scanner, try latching relay, such as those used by Fluke 5720A, DS2E-ML2-DC5V. I use similar relays in my DIY scanner: https://www.eevblog.com/forum/projects/diy-low-thermal-emf-switchscanner-for-comparisons-of-voltage-and-resistor-stand/msg610755/#msg610755 (https://www.eevblog.com/forum/projects/diy-low-thermal-emf-switchscanner-for-comparisons-of-voltage-and-resistor-stand/msg610755/#msg610755)

Hi zlymex,

NPLC is 200 with synchronous autozero. The spikes are still there, I suspect the switching furnace in basement behind wall.
Thanks for relay type, I will order them. Scanner I'm going to use 34970A, it a pity that it does not have low emf connection.


Measurement with freshly calibrated 3458A started, first reference made by Edwin PWW is within day within +/- 1ppm - cold start.
Each reference will be measured one week minimum to give me some level of confidence in short term stability.
Any tips for low EMF relay for scanner?

As a 10 channel scanner, you may get the old HP3488A plus 44470A, which are quite cheap.

These spikes indicate that your setup may be disturbed by RF noise, bad grounding, and lacks all the blocking caps, like in Andreas design.

Short term stability, like noise and fluctuations may be determined within one hour already, i.e. 10 min and 1h stability. That should be <= 0.2ppm
Up to 24h will give mostly the temperature dependency of your LTZ1000 references, plus the 3458A w/o ACAL (especially U180 test).
Constant RT, dT <= 0.2°C should also give dU <= 0.2ppm.
One week will already show the initial burn-in drift of the LTZ1000, if applicable, and depending of your oven temperature.

Depending on the history of your LTZ1000 (e.g. solder heating, preliminary heating / cycling), the initial burn-in drift may take months or years.

Frank


Thanks Frank,

Scanner is 34970A I only needs to use proper low EMF relays. All cards for 34970A which I have do not have low EMF connection/relays (~3uV), but maybe with Panasonic ones it will be the same. Needs to check.
The grounding and RF noise is not ideal, It is placed in polystyrene container without metal shield.
The LTZ1000 has been burned for few weeks @125°C followed by temperature cycling. If the CERN recommendation works the drift should be minimal now.
Remaining LTZ1000 boards I will measure only few days, but two do not have full set of Edwin PWW resistors (tempco outliers) and for R2/R3 resistor were used Vishay UXB.
I used R4 12k (40-45°C) and 100k R2/R3 resistors for minimal drift.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on October 19, 2016, 05:56:32 pm

Depending on the history of your LTZ1000 (e.g. solder heating, preliminary heating / cycling), the initial burn-in drift may take months or years.

Frank

Thank You Dr. Frank!!

I'll jump in here with some suggestions & thoughts after a few decades of building these for industrial use.  Again:  I build custom LTZ circuits for my customers that need to be used - not for PPM-chasing  entertainment purposes. 

These are just some observations picked up from decades of making various custom test systems:

1.  When we assemble an LTZ circuit, we power it up (and add power cycles at least a few times per day) and let it run a couple years.  That die inside is going to take a while for the crystal lattice to stress-relieve itself, and there's no way of knowing where your die came from out of the initial wafer.  Every die singulated out of the wafer will have a different strain pattern once it becomes a single die, and every LTZ1000x is going to behave differently.  It also depends on if the die was diamond-scribed or cut with a wafer saw, lasered, etc.  Manufacturing processes change slightly over time, even though the basic  die layout hasn't changed in decades.  The random crystal edge damage seen along every die will have an effect on final performance, good and bad.

Usually one of these things will happen:

A) The LTZ circuit will be initially jumpy, but after a few year's operation it will settle down and become quite stable.  Sometimes these 'grow up' to be the best stable references you've ever seen.

B) The LTZ will be initially fairly stable, but stability doesn't improve as much over time.

C) The LTZ will just stay wobbly and jumpy.  If they are still doing this after 2 or 3 years, they probably aren't going to improve.

D) You might find a Golden LTZ now and then.  These are born pretty stable form Day One, and then just get better.  These are not common, and these are the jewels that would get picked for a Super 3458a (002 option) along with other hand-selected components.

E) There is always the LTZ that starts out rock solid, then as it settles in you see more drift.  These aren't common either.

The point is:  You have to be patient, and plan on a long time scale before you start taking any serious measures of your circuit.

What we do is assemble the LTZ circuits, just do an initial check to see if they are running, then burn them in for a few years.  We use a 'hotter" heater resistor combo with extra 1k's in series with the final top resistor (like 15k~16K over 1k) and then maybe jumper out a 1k or two to get to final heater resistor ratio - and then let that settle in for another 6 months to a year.  The final heater resistor value will depend on it's final running application, but minimum is 13k over 1k, and that is only for coolest environments.  You might be able to get away with less, depending on application.  We have plenty of LTZ circuits running in the field with 14k ~ 15k/1k ratio running 24/7 for decades, and they don't drift maybe 1 or 2ppm per year and get more stable - so I definitely do not agree with Pickering's suggestions about lower heater resistor ratios in every case.  Just speaking from experience here after looking at a lot of LTZ's.  SOME LTZ's might benefit from a lower heater ratio, but it really depends on where you'll be running these in their work place - and each LTZ is different.

For instance right now in 2016 we're processing LTZ circuits that will be delivered in 2019 to a wafer fab production line test system.  This is how HP / Agilent / Keysight Vref boards are done also.  It's not like they are soldered together and delivered the next day.

2.  Stick to the LT datasheet circuit especially if this is your first time building an LTZ circuit. Suggest that you DO NOT use any other op-amp besides LT1013 - that amp is tailor made for LTZ circuit, and will get you best noise performance overall.  The small Vos of the LT1013 isn't really going to have much impact since it's used as a current driver.  If you try another auto-zero amps ('2057 et. al.) you have to give serious consideration to noise generated especially in the rest of you circuit - let alone the current noise on the inputs.  I have never seen any other amp work as good at LT1013 in the long haul.

If you call LT applications engineering, they will tell you exactly the same thing, and they've seen a lot fo LTZ circuits also.  This is good advise.

KEEP ALL SURFACE MOUNT ceramic caps AWAY from any LTZ circuit.  They are microphonic and pick up all sorts of mechanical noise.  Use high quality poly film caps or better, and Thru Hole works better over long term, especially if your PCB is going into an un-stable temperature area.

3.  Adding slots to your PCB may hurt you - I've made boards with and without 'thermal' slots, and never noticed any huge difference either way.  We had one design with slots that all it did was pick up vibration from a vacuum pump running about 20 feet away on the production line - and it showed up on the Vref output as noise.  Make the board compact and thermally uniform.  Keep drafts away, and don't run a serious LTZ out in the open.   Pay attention to about every Linear Tech and HP Schematic that shows star grounding techniques.

4.  If your ambient temperature is stable, then something like cheaper PTF56, 5ppm TC  resistors work just as well in the end for your LTZ as $80+ Vishay Magical Voodoo resistors.  Spending a lot of money on the Vishay Magicals will generally reduce back pain since your wallet is a lot lighter, but that's about it.  You will not get 40 X more performance out of an LTZ made with expensive resistors, guaranteed -  I've never seen that happen, not even close, and I've compared several different assembly methods and parts BOM's over time.

5. PWW 3ppm resistors work fine especially if your ambient temperature is changeable.  I have never seen a Vishay Magical Voodoo work any better in an LTZ circuit than PWW.  Remember, the whole point of LTZ is that the resistor Drift RVal is attenuated by over 100 to 1 - and this is conservative.  You won't see much difference in the Vref if it was made with 1ppm or 3ppm resistors if your ambient temp is changing even several degrees.  The heater resistor ratio is most important to keep an eye on to make sure stays stable AS A RATIO.  The other resistor values are not too critical as long as they are stable...so don't waste money on tight tolerance resistors if you don't need them.

6. Don't be afraid of good quality PWW trimmer pots to make adjustments in a VBoost circuit.  In fact we've got several 3456a that go in for calibration, and they are still in cal after decades with the pots never been touched since the 80's.  You can do the same with LTZ boost circuits IF your final circuit is thermally uniform and doesn't see a lot of vibration.

7. I would NOT recommend ever changing out the heater resistor in a perfectly running 3458a.  I have seen people do that, and all that happens is now they have a driftier 3458a, because the problem wasn't in the heater resistor.  Know what you're modifying!  The ambient temp inside a 3458a is not your lab temperature, and these instruments are designed to run on racks alongside other warm equipment!  I wouldn't try putting a 12.5k heater resistor into a 3458a unless you had a very well ventilated area.

8.  STAY AWAY FROM eBAY LTZ's.  That's only going to end in tears.  If you take a used LTZ from an unknown source - and who knows how it's been mis-treated while it was demounted - and you solder it in to a new circuit:  Your still looking at a multi-year burn-in cycle to see how it's really going to perform over time.  Every time you get a soldering iron anywhere close to an LTZ chip - expect to see at least a year or two to return to stability.  Yes, it really takes that long - You can try other thermal cycle techniques to convince yourself you can speed up the process - and then you realize it took 18 to 24 months before you see real stability again.

With that type of time commitment involved, I suggest that it's never worth your time to save a few bucks on unknown, used garbage from eBay.  It will never save you a dime.

We have always purchased direct from LT, and I can't think of a single time over hundreds of circuits that we've gotten a bad, out of spec LTZ.  Maybe once, but that was an obvious dead transistor we saw right on power up - but LT happily replaced it.

Some LTZ's will be better performers of course - but generally we've never been steered wrong buying direct from the source.  Seen enough problems from eBay garbage to last a lifetime, so we will never purchase there.

Final Suggestion:  If you are running profitable business and need a good, solid, low drift 10V Voltage Reference, stay with a Fluke 731 / 732 series and keep it cal'd.  You won't be able to roll your own and save any money if your time is worth anything.

Don't get me wrong - Of course playing and chasing PPM for entertainment purposes is always fun too!  I've just been around this long enough that chasing the final PPM or two drift is basically the point of vanishing returns.  In terms of profit margin - that last few PPM is not going to ever pay back except in the most critical applications.



 




Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on October 19, 2016, 06:30:40 pm
Thank you for that informative post! Your post and the infos from Mr. Pettis encourage me to build one or two LTZ-references for myself, since i now see that i dont need to spend that much money on vishay-resistors.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 19, 2016, 07:11:06 pm
Hello,

thanks from my side too for the comprehensive summary.

to point 2.
what about using LTC2057 for long term stability?
The hermetically LT1013A are very expensive compared to plastic LTC2057.
And in my cirquit every input of the OP-Amp carries a filter capacitor anyway to reduce EMI.

to point 5.

As a volt-nut you may want to have the tolerance of the temperature setting resistors less or equal to 0.1% especially if using a lower temperature setpoint. ( e.g. 1K/12K resistor).
Of course you can use 1% resistors if using a higher temperature setpoint.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on October 19, 2016, 10:03:51 pm
As noted, the LT1013 is intended as the best match for the LTZ, its drift is inconsequential as it is operated as a current device, it is very stable long term.  I do not think that a hermetic LT1013 is important, the circuits referred to are not hermetic in practice and the LTZ apps and notes do not specify a hermetic.

For external inference (EMI) is it better to use a shield (if necessary) for the enclosure rather than bypassing inputs all over the place, a shield made out of copper PCB built around the LTZ module and grounded can be much more effective, ceramics can also be sensitive to some RF signals and couple them into the circuit themselves.  Bypass the power supply input at the LTZ module, possibly using an RCL filter if needed.  LT specifically rules out using ceramic caps, no exceptions, I've talked to them too.

The exact ratio of the temperature setting resistors is not so important as reasonably close tracking of the two resistors, ±0.1% tolerance is quite acceptable as long as the two resistors have very similar TCRs.  The exact temperature is not important as long as the resistors are reasonably long term stable, we're not talking PPM in this case.  15K:1K is about right for just about all circumstances, it won't hurt the chip in the least.

Another advantage of the copper PCB shield is that you can completely shield against external air drafts, the PCB doesn't pass outside air temperature changes very well, helping to keep the internal temperature stable.

Linear Tech has a vast amount of long term data on their LTZ chips, HP (Keysight) also keeps such data and shares with LT, the LT engineers know more about how these LTZ chips work and perform than anybody else, they know what works for breaking in these references and will tell anyone who asks, it isn't a secret (well, maybe Keysight might not tell all).
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on October 19, 2016, 11:25:10 pm
Hello,

thanks from my side too for the comprehensive summary.

to point 2.
what about using LTC2057 for long term stability?
The hermetically LT1013A are very expensive compared to plastic LTC2057.
And in my cirquit every input of the OP-Amp carries a filter capacitor anyway to reduce EMI.

to point 5.

As a volt-nut you may want to have the tolerance of the temperature setting resistors less or equal to 0.1% especially if using a lower temperature setpoint. ( e.g. 1K/12K resistor).
Of course you can use 1% resistors if using a higher temperature setpoint.

With best regards

Andreas

#2. What long term stability issue?  The LT1013 has a slight Vos drift which doesn't matter a lot as a in an LTZ current driver circuit. The Zener + Transistor base stability in the LTZ will overwhelm that.

Hermetically sealed?  If humidity is a concern use PTFE or parylene coating, both of which make the circuit immune to humidity effects.  And then seal it again in a good EMI enclosure  Just because you get a plastic IC package doesn't mean you don't seal the system yourself.   If you're building a robust circuit for industry or military, modules will almost always be sealed anyway.  These guys don't want a bare circuit board - you supply them a sealed box...power in >>> stable voltage out.  Bulletproof and reliable. 

Look at the huge current noise on '2057 inputs, and limited bandwidth - both are also concerns if you're driving a fast SAR ADC VRef input.  A different story though.

LT recommends the LT1013 only, and that's what we use, and we seal up the circuit also.  They do NOT want a '2057 in there creating current noise issues.

Never been a problem with LT1013 and I have circuits running in Finland, Georgia, USA and very humid Thailand.  That means we go from about 5% humidity to about 100% -  They are doing fine and stable over long time periods.  Other amps have been a problem either with noise on the output or having to be very careful with supply bypassing, and messing up a circuit someplace else.  Those chopper switches inside any A-Z amp don't come cheap when you're keeping the analog system as quiet as possible, and watch out if you're using them as a buffer.  Those op-amp response poles will come around and bite you. <Grin>

It's not that the AZ amps don't have their place - but you have to consider the high current input noise carefully.

#5.  I suppose.  But I've never found a location for a properly sealed, robust circuit container that would be running that cool in our application on a test rig.  A 1% matched resistor pair - as long as they have a stable ratio and good TC in ratio mode - are usually fine.  You just need a resistor ratio that is rock solid - absolute value is not as critical unless ( as you correctly point out) - you get down closer to 12k over 1k.  Now you have to watch out if you're that close to the edge   That's kind of pushing the envelope on the cool side, but if your environment tolerates it...

Listen, I just got a 4yr old Keysight 3458a back from Cal lab, with Z-540 data - and this has the standard 15k/1k heater pair, LT1013 plastic - and it hasn't moved 2ppm over the year, and it doesn't even have option -02.  Running 24/7 in a warm cabinet.  You set the heater resistor ratio for the environment it's running in, and you want it warm enough to regulate the thermal changes of the surrounding area.  So just because it's 15k over 1k doesn't mean it'll drift more.  Reducing the heater temp will save a little power (good for battery power), but from what I've seen - it doesn't have a HUGE effect on EVERY LTZ drift rate... that's all I'm saying.  The drift rate of an LTZ is what it's going to be..
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on October 19, 2016, 11:50:53 pm
Thank you for that informative post! Your post and the infos from Mr. Pettis encourage me to build one or two LTZ-references for myself, since i now see that i dont need to spend that much money on vishay-resistors.

You'll be fine.  Now the only other thing to consider before you build an LTZ1000/ LTZ1000a circuit is monitoring.  You see lots of people here presenting data from a 3458a - which is sort of OK "if that's all you have" (not joking - a 3458a by itself is not necessarily good enough) - but you have to remember that in the case of an LTZ circuit:  You are building basically the same reference circuit that the 3458a is using - and so in a sense what the measurement data shows is the drift rate of the 3458a compared to the circuit under test - IF you're just looking at absolute voltage value on the DMM.  Which doesn't tell you much about how your circuit is drifting or not.

Ideally if you have access to a 732b (which is about the only source stable and quiet enough) and a 7-decade voltage divider, you can use the 3458a, 3456a or other capable NULL meter to watch your Vref noise & drift voltage.  You really want to do this occasionally during your Vref burn in period or else you'll never know when you've achieved real stability on your new circuit.  Plan on it taking a while.

If you're making an LTZ circuit with a 10V boost circuit added, you can use a null meter comparison directly at 10V, and watch for drift from there.

The concept here is that you don't use the reference in the 3458a to measure the absolute value of your newly built reference - because you really want to measure it against a better reference if possible.

In the case of the LTZ1000x, that gets very hard to do unless you have a JJ-array laying around - because LTZ's are about as good as it gets!

In fact my lab 3458a jsut came back from Cal lab - and the Fluke calibrators aren't accurate enough to do the complete cal routine on the 3458a.  You need also a 732b (or averaged 734b preferred, which is basically four 732's in a frame) and /or a "golden" 3458a which is freshly cal'd with -02 option.  Those get categorically more expensive.

Good Luck!



Title: Re: Ultra Precision Reference LTZ1000
Post by: ManateeMafia on October 19, 2016, 11:56:14 pm
@MisterDiodes

What percentage of LTZ's make the final cut in your projects? In other words, if someone wanted to build a LTZ based reference, how many would you recommend starting with for the 2-3 year process?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 20, 2016, 04:07:36 am
No less than 5, I'd expect. You can't really tell if measurement equipment acting up with less than 3 references anyway.  :-DMM

Btw, I'll just leave a link (https://www.eevblog.com/forum/metrology/(ft)-ltz1000a-fairy-tale-or-the-story-of-little-jumper/msg1052290/#msg1052290) here for LTZ module study I've done last week, in case thread get forgotten.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on October 20, 2016, 12:45:49 pm
@MisterDiodes

What percentage of LTZ's make the final cut in your projects? In other words, if someone wanted to build a LTZ based reference, how many would you recommend starting with for the 2-3 year process?

I would start with at least a minimum of 4~5 units.  All of them will probably work fine in-spec, but if you want to be able to compare, pick and choose the best performers for an extra-critical application - build yourself a few extra to sort thru.  The more the merrier.

For instance if we do a production order for 20 units, we'll start processing say 25~26 units, and do a sort after 18 ~24 months or so depending on application.  Some of them will get in their comfortable place sooner than their siblings.  Even the leftovers will still be running better than most any reference and can be used for other less-critical backups - or save them on the shelf for the next order or in case the customer physically damages a unit, warranty replacement etc.  Stuff happens.

As with any production situation, on occasion a unit won't pass muster for some reason - and that's why you really want to have some other better reference to null-check check against - like a 732, or similar (like a parallel group of known working refs, more 3458a's, etc.).  If you JUST have one 3458a - again no joke here - all you can check is the drift rate of your new circuit vs. drift rate of 3458a, which will tend to be on same sort of scale.  So you won't learn everything - the new reference you're measuring is PROBABLY fine if it looks good on one 3458a, but no real way to tell what the true absolute drift rate is of either the reference OR 3458a - all you know is how they are drifting relative to each other over time.

You can gain more confidence if your circuit is measured against a better reference (732 is at least somewhat better), or perhaps cross-check across multiple 3458a, etc.  At most cal labs the goal is to try to measure against a standard that is 10 times more accurate than the unit under test - but that is harder to do with an LTZ circuit, because that IS about as good as it gets. 

So now you have a good excuse to get more 3458a's or some 732b / 734 - or wherever your PPM adventure takes you!  :-DD

If you get in touch with your Volt-Nut side, just remember: If it's something worth doing, it's worth doing to excess!!

Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on October 31, 2016, 04:01:05 pm
How important are guard rings around the collectors (pins 5 & 8 ) of the LTZ and why are they used in many LTZ layouts?  If for control of leakage currents, what about the 10's of nA bias current of the LT1013?  If to reduce capacitive coupling, what about 4-layer designs where you already have appreciable capacitance to ground?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 31, 2016, 05:03:00 pm
The guard traces are not that important, but the effort may be rather low to have them. The typical current through the transistors is 100 µA, and for every 100 ppm change in current there will be about a 1 ppm change in reference voltage. The input bias of the LT1013 is relatively stable - it is only the change in current (e.g. due to temperature or aging) that really matters. Leakage currents are prone to be changing but hardly reach the nA range unless in a dirty humid environment.

Capacitive coupling is not a problem - this might give slight changes at high frequencies like above 10 kHz, nothing one cares about in an DC reference. The circuit should be tolerant to parasitic capacitance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zlymex on November 01, 2016, 04:02:51 am
Measurement with freshly calibrated 3458A started, first reference made by Edwin PWW is within day within +/- 1ppm - cold start.
Each reference will be measured one week minimum to give me some level of confidence in short term stability.
Any tips for low EMF relay for scanner?
Looks quite normal, except some spikes at the beginning. What is the NPLC used? Is AZ on?
As for the low EMF relay for scanner, try latching relay, such as those used by Fluke 5720A, DS2E-ML2-DC5V. I use similar relays in my DIY scanner: https://www.eevblog.com/forum/projects/diy-low-thermal-emf-switchscanner-for-comparisons-of-voltage-and-resistor-stand/msg610755/#msg610755 (https://www.eevblog.com/forum/projects/diy-low-thermal-emf-switchscanner-for-comparisons-of-voltage-and-resistor-stand/msg610755/#msg610755)

Hi zlymex,

NPLC is 200 with synchronous autozero. The spikes are still there, I suspect the switching furnace in basement behind wall.
......
I always use NPLC=50, as I see not much difference compare with NPLC=100 or more, and save a lot of time for each measurement.
Setting NPLC=200 is like put 4 eggs in a basket while I only put one. In the case of a spike, I just throw one away instead of 4 and keep the other 3. Short integration time also help to identify smaller spikes.

Why I'm not using even smaller NPLC values such as 20 or 25? Because my scanner works better on NPLC=50, and I can monitor the digits on the display of 3458A more clearly. Plus, the sampling time for NPLC=50 is the unit of time(1 second).
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on November 18, 2016, 11:47:39 pm
Little update about my version of the LTZ1000 reference (RFS121B).
I mounted 4 units.
It seems that this version is quite insensitive to RFI from ringing mobile phone 10cm from the supply input and output terminals and shorting of the 7.0V buffered output.

Some data : short circuit current : 35mA.
Recovery time after short (to 0,1ppm level): 2 minutes.
Change of the voltage during simple RFI test: less than 0,1ppm.

P.S. more pictures below.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 19, 2016, 11:26:53 am
Hello,

my circuits are more sensitive to switch mode power supply ripple or USB-cables from my ADC-devices than from mobile phones.
Usually the sensitivity to RF is relative small band so a narrow band test with a mobile phone might not detect the sensitive frequencies.

But of course the ferrites that you have in your cirquit are a good measure against frequencies above 100 MHz.
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=225190 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=225190)

So I think its a good idea for my C-Sample design.
And also the trimmable 7V output is a good idea (and a basis for a 10V output with a LT5400 with the idea from Lars).

By the way: what cables / lugs did you use as wiring for your measurement setup.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on November 19, 2016, 05:58:59 pm
For voltage measurement i use Klotz MY206 shielded  cable + 'Laboratory plug ø 4 mm CAT I, LS 4, Multi-Contact' from elfa distrelec.
For resistance I use PTFE insulated 4 wires in shield + LS 4 plugs (unfortunately there is no marking on the cable).

For the RFI testing I used 30cm copper (unshielded) twisted pair.
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on November 19, 2016, 07:43:57 pm
For voltage measurement i use Klotz MY206 shielded  cable + 'Laboratory plug ø 4 mm CAT I, LS 4, Multi-Contact' from elfa distrelec.
For resistance I use PTFE insulated 4 wires in shield + LS 4 plugs (unfortunately there is no marking on the cable).

For the RFI testing I used 30cm copper (unshielded) twisted pair.

The shielded cable on picture looks like Belden RG142 ( double shielded, silver plated), similar cable is also made by Habia.
Thanks for tip for Klotz cable, it can be good for its flexibility. Do you know its insulation resistance?
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on November 19, 2016, 08:45:00 pm
What You see on the picture is 3mm 75ohm coax with inner and outer teflon insulation and it is silver plated copper. I have about 50m of that from some surplus auction and sometimes I use it. It is used as 1 wire (shield and wire shorted).

Let me use my good old HP4329A :)
Real measurements of insulation resistance of Klotz MY206 cable (test voltage: 100V, measured resistance is between shield and both inner conductors shorted, length: 1.5m, Temp=25.6'C ) R=1.5E+14 ohm. (that's nice result)
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on November 19, 2016, 09:49:49 pm
Let me use my good old HP4329A :)
Real measurements of insulation resistance of Klotz MY206 cable (test voltage: 100V, measured resistance is between shield and both inner conductors shorted, length: 1.5m, Temp=25.6'C ) R=1.5E+14 ohm. (that's nice result)

Thanks, that numbers forced me to look where I can buy it :) How satisfied you are with 4329A meter, can we expect teardown? :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on November 19, 2016, 10:34:24 pm
User pa4tim did teardown on his website: http://www.pa4tim.nl/?p=2269 (http://www.pa4tim.nl/?p=2269)
Very interesting description is in the HP Journal 1971 , Volume , Issue March-1971.
Title: Re: Ultra Precision Reference LTZ1000
Post by: VintageNut on November 20, 2016, 05:41:36 am
Hello Plesa

You can take this measurement with a KE2450. You have to use the rear triax cables. The current measure is the HI cable. There is an adapter with a part number 7078-TRX-BNC. This adapter connects the triax GUARD to BNC shield.

To take the measurement, you have to create an open circuit and press the REL. This measures the current offset and makes that current value a new zero.

After the REL, you force voltage and measure current.  For the above example of 1.5 x 10^14 ohms at 100V, the current is 0.6667 pA. That is well within the capabilities of the 2450 1nA range with 6 1/2 digits.

Be aware that the technique of making BNC shield at GUARD potential creates a shock hazard if you use high voltage to test insulation. For this reason I choose between 1v and 10V for the test voltage. The 2450 has no problem measuring 0.67pA at 1V or 6.7 pA at 10V.

I have performed this measurement for an ordinary solid core hookup wire and and the resistance is on the order of 10^13. I use an enclosure and make this enclosure at GUARD potential. This mitigates any current flowing from HI to LO in the air inside the enclosure.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 2N3055 on November 20, 2016, 10:44:35 am
Keithley as app note Number 3262 about that...
Title: Re: Ultra Precision Reference LTZ1000
Post by: VintageNut on November 20, 2016, 02:53:47 pm
Keithley as app note Number 3262 about that...

Unfortunately, that app note is missing the vital step to characterize and remove the current source offset and the current measure offset.

for the 10nA range, the 2450 has a source uncertainty of 100pA and a measure uncertainty of 50 pA. If you are measuring 0.67pA and there is a significant offset, the measurement is invalid.

To make an accurate measurement of this type, it is necessary to follow the steps of the app note for an open circuit condition and allow the measurement to stabilize. Note the current for later subtraction during the actual measurement or use the REL function.

Then perform the measurement as described in the app note with the added step of removing the offset that was previously measured.

I have successfully used a 2450 for this measurement an it is vital to remove the offset. The good news is that the offset is stable enough to be removed. The uncertainty of the measurement is much much lower than the worst case datasheet numbers.

Title: Re: Ultra Precision Reference LTZ1000
Post by: 2N3055 on November 20, 2016, 03:05:24 pm
Keithley as app note Number 3262 about that...

Unfortunately, that app note is missing the vital step to characterize and remove the current source offset and the current measure offset.

for the 10nA range, the 2450 has a source uncertainty of 100pA and a measure uncertainty of 50 pA. If you are measuring 0.67pA and there is a significant offset, the measurement is invalid.

To make an accurate measurement of this type, it is necessary to follow the steps of the app note for an open circuit condition and allow the measurement to stabilize. Note the current for later subtraction during the actual measurement or use the REL function.

Then perform the measurement as described in the app note with the added step of removing the offset that was previously measured.

I have successfully used a 2450 for this measurement an it is vital to remove the offset. The good news is that the offset is stable enough to be removed. The uncertainty of the measurement is much much lower than the worst case datasheet numbers.

Sorry for not being clear... Your steps are absolutely gold.... I merely pointed out that even Keithley is marketing SMU for this kind of usage.. And as with any  manufacturers app note it's a starting point... they tend to be a bit optimistic...  At this level of measurements, measuring practice and discipline is all... Currents are miniscule, errors creep in...
And we are lucky that people like you are willing to share this kind of "ninja" knowledge with us...
Thanks!!

Take care!!
Title: Re: Ultra Precision Reference LTZ1000
Post by: VintageNut on November 20, 2016, 03:42:43 pm
Keithley as app note Number 3262 about that...

Unfortunately, that app note is missing the vital step to characterize and remove the current source offset and the current measure offset.

for the 10nA range, the 2450 has a source uncertainty of 100pA and a measure uncertainty of 50 pA. If you are measuring 0.67pA and there is a significant offset, the measurement is invalid.

To make an accurate measurement of this type, it is necessary to follow the steps of the app note for an open circuit condition and allow the measurement to stabilize. Note the current for later subtraction during the actual measurement or use the REL function.

Then perform the measurement as described in the app note with the added step of removing the offset that was previously measured.

I have successfully used a 2450 for this measurement an it is vital to remove the offset. The good news is that the offset is stable enough to be removed. The uncertainty of the measurement is much much lower than the worst case datasheet numbers.

Sorry for not being clear... Your steps are absolutely gold.... I merely pointed out that even Keithley is marketing SMU for this kind of usage.. And as with any  manufacturers app note it's a starting point... they tend to be a bit optimistic...  At this level of measurements, measuring practice and discipline is all... Currents are miniscule, errors creep in...
And we are lucky that people like you are willing to share this kind of "ninja" knowledge with us...
Thanks!!

Take care!!

You are welcome. I am happy to share what I know. On balance, I am learning more here than I contribute.

The now obsolete Keithley 23X sourcemeters are quite capable of taking this measurement and cost much less on eBay than a 2450. I have performed this measurement with my KE236. The offset was very nearly zero for my KE236 on the 1nA range. The last digit represents 10fA.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 20, 2016, 04:44:52 pm
Time to start thread "Measuring nanoamps like a ninja"! Jokes aside,  Perhaps worth to try K2400 (1uA min range) and 3458 too? 2400 can drive guard too, but no triax.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 20, 2016, 04:45:44 pm
What You see on the picture is 3mm 75ohm coax with inner and outer teflon insulation and it is silver plated copper.

Hello,

Thanks, that´s what I wanted to know: the transparent interesting looking cables.
And the spade lugs.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 20, 2016, 04:52:55 pm
Hello Andreas - can you send a pointer to the post from Lars you are referring to below ?

And also the trimmable 7V output is a good idea (and a basis for a 10V output with a LT5400 with the idea from Lars).
Andreas

Thanks
Flinstone

Hello,

I don´t know where I have seen the circuit from Lars.
It was a LT5400 with 2*100K in parallel and 2*10K in series.
So actually a 7:5 divider.

This together with a TL431 based heater could give a good basis for a 7->10V transfer.
See bottom of page:
http://www.techlib.com/electronics/ovenckts.htm (http://www.techlib.com/electronics/ovenckts.htm)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: VintageNut on November 20, 2016, 04:54:55 pm
Time to start thread "Measuring nanoamps like a ninja"! Jokes aside,  Perhaps worth to try K2400 (1uA min range) and 3458 too? 2400 can drive guard too, but no triax.

I will start that thread to stop pollution of this thread.

Your question about 2400 and 3458A is a good question. My opinion is that if the instrument is using banana jacks on the front/rear connections(s) you will never achieve the good results possible with the instruments that have triax jacks.

I used a 2410 recently to try to force 1nA and measure leakage of a device. The results were very slooooooowwww. At 10 nA the results were much better.

A KE237 taking the same leakage measurement at 1nA was much faster than the 2410 and better results. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 20, 2016, 04:59:22 pm
I also has Agi 4142B with 41421B SMU, which begs to be used. It's lowest range is 1nA with triax and remote sense all the way with 20fA resolution ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on November 20, 2016, 09:33:57 pm
Hello Andreas - can you send a pointer to the post from Lars you are referring to below ?

And also the trimmable 7V output is a good idea (and a basis for a 10V output with a LT5400 with the idea from Lars).
Andreas

Thanks
Flinstone

Hello,

I don´t know where I have seen the circuit from Lars.
It was a LT5400 with 2*100K in parallel and 2*10K in series.
So actually a 7:5 divider.

This together with a TL431 based heater could give a good basis for a 7->10V transfer.
See bottom of page:
http://www.techlib.com/electronics/ovenckts.htm (http://www.techlib.com/electronics/ovenckts.htm)

with best regards

Andreas

Thanks, that's a pretty good hint. I guess you will have this solution populated on your next pcb revision?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 20, 2016, 10:01:04 pm
Thanks, that's a pretty good hint. I guess you will have this solution populated on your next pcb revision?
Hello,

I am not certain: from the thermal design (isolation),
it might be better to have either a sub-board or a external cirquit
(at the expansion D-Sub).

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on November 29, 2016, 10:14:41 pm
About my LT5400 based amplifier that Andreas mentioned:
Well I have probably described it somewhere but don´t remember when.

My LTZ1000A based board is just a simple prototype board with the usual LTZ design from the data sheet using 13k:1k, 120 and 70k. To make it even worse I use  a socket for the LTZ, the resistors are metal film from Farnell and the junk box. My plan was to make two more boards with resistors from Ultrohm, but in that case I was one of the two unlucky receivers of humidity sensitive WW.

The first LTZ measured about 7.16V and the second 7.13V (the third I haven´t tested yet). As 7.16 and 7.13 was close to 5/7 of 10V I saw a chance to test an idea I had to use the LT5400. So I added first a divider from about 7.16 to 7.14 buffered with an op and added another op with the LT5400 with 10k x2 + 100k x2. See attached schematic. As op-amp I used an OPA2188 as I had some in my junkbox. As I use a prototype board I have connected the LT5400 with just thin wires (AWG30).

The prototype board is mounted in a Hammond alu-box and that box is mounted in a Prema alu-box from Reichelt (about 160x100x56mm if I remember correct). In the bottom of the Prema box I mounted a 40x40mm cheap peltier and on the peltier the Hammond box. So far I have only used the peltier to test the TC of the 10V out. From 20C to 40C it changed about -2ppm so about -0.1ppm/C.

The box have three Pomona 3770 binding posts 0V, 7.14286 and 10V. And yes the 7.14286 actually was that after I trimmed the 10V to 10.0000V. I only have 6 digit DMMs so that is a problem.

From July last year to September this year I have powered up the LTZ about 1 hour every 2-3 week. So it haven´t been on very much. I attach a graph showing the difference to one of my SVR-boards that are powered continuous. As the temperature during the tests have varied from about 18 to 27C I have made a slight first and second order temperature compensation of the data.
From september I have had the LTZ powered continuous. As can be seen the output have started to drift downwards. The first year the drift was about +0.7ppm but of course this can be the SVR drifting down. Now with the downward drift the question is if it is the LTZ or some other part drifting. I have an 10k NTC in the box and the interior is about 3C above room. As I have only a 6 digit DMM I just can say that the outputs are 9.99997V and 7.14284V so about the same ratio (from the LT5400). One reason the LT5400 is on the last op-amp is that it was easier to have the 10V and 7.14V out. Otherwise it isn´t good from a noise stand point. 

Another mistake I have done is to use a trimpotentiometer in series with the 250ohm input to the first opamps. The 250ohm and 90kohm are 8E16 WW from the junkbox.

Other notes. The OPA2188 can´t handle capacitive loads so a redesign of the output is on the list. The box is also susceptible to EMI. A simple test with a loop from a signal generator moved the output. If I some time will take me time I should make a program to run my signal generator together with a DMM all the way from 0.15-2000MHz. Just a quick check with 10dBm out and 80%AM and some frequencies from 10 to 1800MHz showed that both the LTZ, SVR-boards and the famous 2ppm from Ebay showed terrible sensitivities to the signals. 1800MHz (mobile) was far from worst. One source of error for me are when I do tests of OCXO´s at 10MHz especially if they have square wave signal out.

The LTZ-box is powered with 12V from a lab-supply and takes about 20mA at 23C room temperature                                       

Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on December 12, 2016, 09:21:51 am
Does anyone know how temperature stable the two 70k ohm collector pull-ups in the ltz1000 reference designs need to be?

The reference circuit without the heater stabilisation uses a single 30k, and the 3458A board chose two 75k from memory - so I wonder how critical the temp-stability of the current is across these transistors needs to be?

Edit - Another thought - will not the pn junction in the compensating bjt and the temp-sense bjt, be around 2mv/C - and mostly independent of current? On that basis the changes in current due to temperature affects on the pull-up resistance shouldn't really matter.

I was looking for 70k resistors from the Vishay S-series, but neither element14 nor mouser stock them. Then I wondered if these really needed to be tempco stable.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 2N3055 on December 12, 2016, 09:56:41 am
Datasheet for ltz1000 has info.. For a100 ppm change in those two resistors, 0,2 and 0.3 ppm change in ref voltage... Influence is resistor tempco divided with 300-500.. So I guess not so critical...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on December 12, 2016, 12:47:06 pm
Does anyone know how temperature stable the two 70k ohm collector pull-ups in the ltz1000 reference designs need to be?

The reference circuit without the heater stabilisation uses a single 30k, and the 3458A board chose two 75k from memory - so I wonder how critical the temp-stability of the current is across these transistors needs to be?

Edit - Another thought - will not the pn junction in the compensating bjt and the temp-sense bjt, be around 2mv/C - and mostly independent of current? On that basis the changes in current due to temperature affects on the pull-up resistance shouldn't really matter.

I was looking for 70k resistors from the Vishay S-series, but neither element14 nor mouser stock them. Then I wondered if these really needed to be tempco stable.

Don't waste your money on expensive Vishay MBF resistors, especially not for the 70k ones.
Several people measured their influence, consistently.

R2 influences by 1/250, R3 by < 1/1000, only. That's the reason, why HP in the 3458A used Thin Film.

R4 and R5 (12..15k / 1k) affect the most (+/- 1/75), but the overall T.C. can be trimmed to near zero by changing the compensation resistor.

Therefore, PWW resistors @ <= 5ppm/K are fully sufficient.

Also, do not waste any more time on re-thinking again the whole stuff, what we have already discussed many, many times.
This circuit really bears no miracle any more, i think.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on December 12, 2016, 01:12:36 pm
On another note: Has anyone on this forum actually build a working PWM-circuit which convert the 7.2V from a LTZ to 10V? Ive seen Diligent Minds simulating one suitable circuit on Page 24.
I dont want to talk about pros/cons regarding PWM vs. Resistor dividers, just results.
Also: Does the active filter design, which is used by Datron 4910/Fluke 5700A/Diligent Minds have an actual name?
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on December 12, 2016, 03:57:01 pm
R4 and R5 (12..15k / 1k) affect the most (+/- 1/75), but the overall T.C. can be trimmed to near zero by changing the compensation resistor.

Yes but if I remember correctly (this thread is too just big) Andreas did some experimenting on this and the result is that the compensation resistor has similar effect on Vout as the divider with the disadvantage that you cannot use anymore TC tracking resistor for nulling temperature effects on Vout.

The most cost/effective way is still to have two good stable resistors for the divider with similar TC and don't use any temperature compensation resistor for LTZ1000.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 12, 2016, 04:41:33 pm
How much the temperature set point influences the output voltage depends on the TC of the circuit without temperature stabilization (but still high temperature). This can be quite different between samples and also depends on other details, like the value for the "70K" resistor (R2) and the zener current. In principle there could be the option to tune the unregulated TC (via currents or possible series resistor) to get a small TC to start with, so that temperature regulation is not that critical any more. In this case the two temperature setting resistors could be much lower sensitivity  - up to the point that thin film ones could work. However the down side is, that one would need extra measurements and an individually matched resistor and thus would have more lead time and not every LTZ1000 might have a suitable operation point.

The 400 K compensation resistor in the DS is a different thing: it is like more compensating an possible effect of heater power. AFAIR the data from Andreas showed that this compensation is not working that good, as the residual TC is more linear and the "400 K" resistor gives nonlinear (e.g. square root like) adjustments.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 12, 2016, 07:28:34 pm
The 400 K compensation resistor in the DS is a different thing: it is like more compensating an possible effect of heater power. AFAIR the data from Andreas showed that this compensation is not working that good, as the residual TC is more linear and the "400 K" resistor gives nonlinear (e.g. square root like) adjustments.

Hello,

I also would only trim small deviations caused by LTZ1000 itself with R9.
The outer resistors are not on the same temperature as the heater and the temperature sensing transistor.
So a too large tempco will cause issues if you do not have a constant room temperature.
But as Frank already said PWW resistors with 3-5ppm/K are fine.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on December 15, 2016, 05:16:31 am
In principle there could be the option to tune the unregulated TC (via currents or possible series resistor) to get a small TC to start with, so that temperature regulation is not that critical any more. In this case the two temperature setting resistors could be much lower sensitivity  - up to the point that thin film ones could work.
Following this line of thinking for a bit,
 
The datasheet reference design for "Adjusting Temperature Coefficient in Unstabilized Applications" calls for a 200ohm trimmer.

Since the trimmer works as an in-series divider with the 120ohm to feed the zener voltage-drop into the inverting input of the op-amp - it is probably very tempco sensitive itself.

Vishay make a BMF 200ohm trimpot, Y4053200R000J0L, which has max tempco +-10ppm/C.  I'm wondering if that would be good enough? And if not, then what component the original app note authors might have been thinking of- when they were considering the circuit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 15, 2016, 04:22:18 pm
For precision trimming one should initially use a pot, than measure the value and replace the pot with a suitable fixed resistor or resistor combination. The resistor for TC trimming in series to the zener is usually only contributing a relatively small amount to the voltage, like 10 Ohms times 5 mA = 50 mV. So even a 100 ppm change in that resistor will be something like 5 µV or 1 ppm of the total voltage.  A larger resistor could be a problem though.
Some adjustment could be via the 70 K resistor too: with a range of 50 K to 100 K one cold change the TC by about 15 mV/300 K = 50 µV/K or 8 ppm/K. Not much, but it could be enough for fine tuning or when you start with a "good" sample.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 15, 2016, 09:15:46 pm
Vishay make a BMF 200ohm trimpot, Y4053200R000J0L, which has max tempco +-10ppm/C.  I'm wondering if that would be good enough? And if not, then what component the original app note authors might have been thinking of- when they were considering the circuit.

Helllo,

dont forget that the cirquit without temperature regulation has  around 50 ppm/K.
And a 100 Ohms resistor will only contribute around 10% to the overall voltage or T.C.
So all in all you will get a better value than the 50 ppm/K.
Perhaps in the range of 1 ppm/K.
But not the 0.05 ppm/K of the heated cirquit.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on December 15, 2016, 09:43:37 pm
When a manufacturer specifies tempco for a precision resistor or trimpot (eg +- 10ppm/C )  - does that represent the expected range across different component samples?

Or is it the tempco change that cannot be controlled for when used in circuit - or over the lifetime of the component?

If it's the first scenario - then the tempco for the 200 ohm trimpot should be able to be trimmed/cancelled out against tempco changes from the zener and the pn junction of the sense transistor.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 15, 2016, 09:52:12 pm
Hello,

ok you are right.

most of the T.C. (except Hysteresis) is more or less repeatable.

The other problem is temperature tracking between the trimpot and the zener (which heats by around 35 mW)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 16, 2016, 08:44:18 am
Trimmpots have the additional problem that the mechanical wiper could introduce some kind of hysteresis or similar problems. So if possible one avoids trimmers in circuits that are planed to be long time stable. Normal thin film resistors are usually more stable and reliable than good trimmers. It just takes some extra work - not a really problem in a hobby project.

The purpose of TC trimming would be to come down from the initial 50 ppm/K TC of the unregulated (e.g. unheated) reference - already reducing the TC from 50 to 5 ppm/K would reduce the sensitivity to the temperature set-point divider by a factor of 10. The aim would be a low TC at the later regulated temperature - so the test / adjustment would be with a modulated heater.

The idea of trimming all the way to < 0.5 ppm/K  and than use the reference without a heater is not that attractive, as there is also a second order TC, so the low TC would be valid only for a small temperature range.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on December 18, 2016, 06:24:54 pm
When a manufacturer specifies tempco for a precision resistor or trimpot (eg +- 10 ppm/C )  - does that represent the expected range across different component samples?

This specification means that for a given component, the TC can be anywhere within the range given, this does not mean that the TC of the component will vary between + and - 10 PPM/°C (for your example) over its operating range.   The TC 'curve' can be linear or nonlinear with temperature, in many cases it is nonlinear, it will change some within its operating temperature range.  This characteristic depends on the material used in the component, for resistors there are quite a few different types of elements made from metal alloys and so-called plastic elements such as the cermet types.  The method of manufacture will also affect the TC 'curve', in their 'raw' form (this is before they are made into a component), the TC tends to be of a fixed characteristic, alloys such as Evanohm will have a fixed TCR that does not vary with normal use.  The manufacturing process of the component can affect the 'finished' TC in various ways, stress applied to the resistive element will cause the TCR to 'appear' to change but the actual TCR of the element does not change itself, stress causes change in the resistance which at the terminals appears to be TCR but it isn't and stress is usually a nonlinear function.

A cermet trimmer always has a +/- TCR range, it can be either + or - and the TCR tends to be less than linear, typical cermet trimmers have a TCR of +/- 200 PPM/°C (as an example) meaning that the actual TCR of the trimmer in your hand can be anywhere within that range (-25, +50, -100, +150, -200, ect.) but they will all have a similar  TCR 'curve'.  Wire wound trimmers generally have the lowest TCR and the most linear TC of all trimmer types but there are wide variances within the various trimmers available.  There is only one WW trimmer on the market which has very low and stable characteristics and is military qualified, it is made by Bourns and costs around $10 each, this one has the best long term stability of any trimmer on the market.

Virtually all passive components have TCs and few have linear curves over temperature.

Data sheets may show a TC 'curve' with temperature, this will tell you if the TC is linear or not, linear TC can be compensated for relatively easily, non-linear not so easily.  Some resistors will have a low TCR but very non-linear, in some cases, the 'curve' is quite lumpy and varies up and down with temperature, others are hyperbolic, ellipsoid or linear.  In some cases, a PWW resistor can have different TCRs above and below the reference temperature, I have one or two spools of wire like that.  All of the newer wire I have are single TCR over temperature, in effect linear.  Most PWW manufacturers have non-linear TCR curves with increasing TCR at the temperature extremes.  In general stress cannot be completely removed although with time it tends to slowly decrease.

Be careful of PPM measurements made with DVMs and ADCs, they can affect the actual readings in unexpected ways unlike a resistance bridge which essentially measures at a null point with extremely high impedance, DVMs and ADC converters do not have that advantage and also have active circuitry at their inputs which can affect the readings.  They can produce a non-linear (parallel) error into the readings, it is generally small but an error just the same.  While I use DVMs, for critical high accuracy readings a resistance bridge is the only accepted method.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 31, 2016, 05:27:59 pm
Hello,

now I have long thought about the 7->10V transfer.
- heated oven for the resistors or a temperature compensated solution
- separate cirquit or on PCB
- etc. etc.

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1074698/#msg1074698 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1074698/#msg1074698)
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1074850/#msg1074850 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1074850/#msg1074850)

The solution that convinces me most is based on the LT5400-3 idea from Lars:

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1081104/#msg1081104 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1081104/#msg1081104)

Since my references are battery powered I do not want to use a additional heater.
So the solution will be temperature compensated.
For a easy adjustment I want to measure the temperature with a little controller.
(still not shure if a PIC12F683 with 10 bit ADC will be sufficient or if I will need a PIC24FV16KA301 with 12 Bit).
The adjustment of the T.C. (and eventually ageing drift) will be done with a LTC1257 12 Bit DAC with VREF taken from 10V output.

The principle cirquit is shown below.
The 20K/50K divider (R2,R3) is built from LT5400-3
R4 (0.1% max 15ppm/K between 511K and 1 Meg)
gives the gain for the first adjustment stage.
R5 + R6 do the raw adjustment. R6 consists of 2 resistors in series.
R7 sets the gain for the fine adjustment.
R8 + R9 do the fine adjustment. R9 again 2 resistors in series.
R11 sets the gain for the adjustment range of the DAC.
With the configuration shown the range is around + 12 / -4 ppm
for temperature adjustment and some ageing drift
(LTZ usually drifts down so compensation has more room for the + direction).
The 12 bit DAC resolution gives about 40nV/LSB @ 10V.
So switching between 2 steps is below resolution of a 8.5 digit DMM.
Power consumption will be 4-5mA @ 14V so 56-70mW instead of 300-500mW with a heated solution.
I plan to do this as sub-print on the AUX-connector of my LTZ1047B design.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 31, 2016, 07:02:55 pm
It depends on the sensor used and the analog front end if the 10 Bit ADC is good enough. Normally the DAC for the output should be higher resolution, as much of the adjustment range will be used to set the correct absolute value and only a part of it to compensate for temperature effects.

The power for a heated version very much depends on insulation. So it should be possible to get below the 300-500 mW. But usually it will be more than with a compensation solution.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on December 31, 2016, 07:25:41 pm
Might be worth looking at the Atmel parts. I've found them a bit easier to work with, because of the Arduino tools.
http://www.atmel.com/Images/Atmel-2548-8-bit-AVR-Microcontroller-Battery-Management-ATmega406_Datasheet.pdf (http://www.atmel.com/Images/Atmel-2548-8-bit-AVR-Microcontroller-Battery-Management-ATmega406_Datasheet.pdf)

This part is designed as a Li-ion battery controller.
Things I like:
 - on-chip voltage regulator
 - 12-bit ADCs

I've found the Arduino tools a bit more accessible than the Microchip stuff.

Using a null detector, you can set the output of the controller circuit to match precisely the 7.x output of t he lTZ1000A. Then, it should be possible to calculate the 10V value and get a result accurate the the linearity of the DAC. Plus, the output can always be trimmed byt tweaking a bit.   

Going with an off-chip regulator opens up a few more possibilities.

As all the LTZ circuits seem to predate modern microcontrollers, there could be some opportunities for improvement using some software. One thing, ideally the microcontroller would be suspended once the DAC voltage is set.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on December 31, 2016, 08:29:01 pm
My idea:
Assuming the LTC1043 is inherently stable over time: Zenervoltage 7,15V * 2 / 3 * 2 = 9,533V, so were talking about 0,5Vdiff instead of 3Vdiff from Zenervoltage to 10V. Then throw a highly stable resistor divider + age-correction-DAC against it or a PWM-divider (not that easy) to get 10V. All highly insulated in an oven  + lead-battery-pack + battery-charger-stuff (so it can travel by plane with varying ambient temperature and avoiding LTZ-hysteresis-problems, without those Lithium-battery-restrictions).

Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on December 31, 2016, 10:53:41 pm
The LTC1043 is not restricted to standard ratios. The clock can be overriden by an external source. So we could use it to digitally trim the reference.


Datasheet: http://cds.linear.com/docs/en/datasheet/1043fa.pdf (http://cds.linear.com/docs/en/datasheet/1043fa.pdf)

The best reference is on page 13, where  they show a frequency to voltage converter with an accuracy of .005%, which is about 5 digits of precision. So we would need to stack two of them, and eliminate pretty much all noise in the first stage.

The first stage should get us to 10V +/-1mV. Then, the second stage would have to kick in 4 more digits to get us 100nV trimming. The trick is, getting the noise in the first stage into that sub microvolt range. Definitely worth further investigation.



Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on January 01, 2017, 10:19:56 pm
Never looked at it that way, thanks for the idea! I dont really understand your 2-stage-approach, can you explain it in more detail? Since for a 7 to 10V converter im only interested in absolute stability, while avoiding resistors and having a simple means of adjusting the ratio for age drift of the LTZ1000. Since im not familiar with frequency-generator-topologies: What would be a fitting low cost solution for a 10KHz square signal generator with high stability and resolution (sub-Hz)? Im thinking about PPL/DDS/digital-counter-topology coupled with a sufficiently stable oscillator. 

Of course all in a well isolated oven, so temperature/hysteresis-problems dont concern me.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on January 02, 2017, 12:33:12 am
Looking at the LTC1043 datasheet, their most precise example is .005%, about 5 digits. Therefore, we can only correct the 10V level to maybe 10.000000, if we only use the DAC to adjust the last 100mV.

However, if we stack the second channel on top of this, we can get another 5 digits. The first DAC might have a 3V range, and the second DAC a 3mV range.  That does mean that we are reliant on a stable resistor divider. It should be possible to autocal the ratio using the overlap bits. Then, the major error would come from nonlinearities in the DACs.

The two DACs will overlap by a couple of bits. I think this is how the Datron unit works, and I have seen it in an Advantest unit.

I would use a simple microcontroller to set the frequency. Might also be useful to have a null detector, so the DAC could first null against the reference voltage, and then output the precise 10V.

This is all very tricky at 8.5 digits - but modern DACs and micros make it much easier.
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on January 10, 2017, 05:52:21 am
Are there other ways to guarantee zener startup - apart from using a 1n4148 on the op-amp output to force it to source and not sink - as the reference circuit does it?

I've built a few zener references and most have no problems starting don't require anything after the op-amp output. Experimenting a bit by removing it though - shows that the ltz1000 reference circuit is a bit finicky and sometimes fails to start.

Did I see mentioned somewhere the possibility of using a low value pull-up resistor to +VE on the ref-output which would then bias the non-inverting input?

Would that be problematic in coupling noise from +VE onto the ref output?

I wonder about biasing it and then turning the bias off after a short time, perhaps with transistor + charging capacitor.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on January 10, 2017, 11:19:51 am
Someone remind me to post my experiences with the LTZ1000 in about 10 month. I had a design, few hundred of these were built into some equipments, and my NDA will be over by then.

NDA expired? ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 10, 2017, 11:27:58 am
+1 :) Always fun to see what such references are used for. I see somebody was reading thru.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on January 10, 2017, 12:03:47 pm
You can write a book just making some copy paste from this thread ...

Inviato dal mio Nexus 6P utilizzando Tapatalk

Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on January 10, 2017, 03:41:14 pm
I today received this little board, okay it didn't receive I had to collect it from the toll. It was named to be a LTZ1000 reference. The curious fact is, that the IC that used to be the reference has absolut no marking on it, but the circuit indicates a LTZ like style schematic.
Does anybody know something about such a board? It seems to be part of some test gear, beside the Linear Technology label and the date code 10/84 there is a mirrored "Superman" icon on top of the pcb. On the backside is another date code 46-84 and an icon that seems to be a growing sun?
I guess the first thing to do is to reverse engineer the schematic before powering up the beast.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=94719;image)

I think this is a reversed Z like "Repus Renez" that reversed is "Super Zener" ... full story here:

  http://analogfootsteps.blogspot.it/2014/03/pranking-prankster-jim-williams-and.html (http://analogfootsteps.blogspot.it/2014/03/pranking-prankster-jim-williams-and.html)

ok I think now I know everything about this "can" (just kidding).
Title: Re: Ultra Precision Reference LTZ1000
Post by: dr.diesel on January 11, 2017, 08:43:47 pm
Probably a good place to ask this question vs starting a new thread.

When modding the 3458A oven temp with a 100K resistor (in parallel with the 15K), is the 1PPM/C Vishay Foils adequate for the task?
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on January 11, 2017, 11:27:51 pm
It is more than adequate, its impact is only about 1/6th of the original reistor. Even if you go with a 5ppm/K resistor thats ok. You need a new calibration (=adjustment) after the mod.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 21, 2017, 03:53:25 pm
Hello,

update from my measurements on LTZ#3-LTZ#6 for 3-9 kHrs of operation
see also:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1021549/#msg1021549 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1021549/#msg1021549)


here the updated table with averaged drift from all measurements and the charts:

I recorded (weekly) readings to determine ageing drift against my ADCs and against LTZ#2 with two 6.5 digit DMMs in 100 mV range.

Evaluation is from day 128 (after all adjustments done) to day 371 so around 9 kHrs.
The readings indicate all below 2 uV / kHr or below 2 ppm/year compared to my measurement setup.

LTZ#2 drifts about -1.57ppm/year.
the ADCs drift also in the range of 1-2 ppm over one year with some seasonal changes.
All in all there is not much difference in LMS slope between the (absolute) ADC readings and the DMM differential reading.

LTZ4 has developped to the lowest drifter (positive drift against LTZ#2, so canceling the negative drift of LTZ#2 partly).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on February 27, 2017, 09:21:54 pm
i think i might have interpreted the LTZ1000 circuit wrongly, but i am not too sure. could anyone give my schematic a sanity check?
(the purple resistors are suppose to be thermally coupled)

** updated
i made alot of mistakes woops ...
redrawn to andreas' version.

i am guessing this version should be fine?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on February 28, 2017, 01:05:52 pm
The capacitor C7 is wrong - it gives too much load to the output of the OP. R13 is also unusual - it won't help, but also won't hurt very much. It only makes sense if an extra cap for improved tolerance to capacitive loading is added.

It is a little odd to use three resistors in series to set the temperature: this resistor should be low drift so it is odd to use three expensive resistors if not needed. If for some reason a fine adjustment is wanted, the more obvious way would be to adjust the other side resistor of the divider with a parallel one: this way would could still use just one resistor and add the second one only if really needed.

Similar R7 and R19 are a little strange: there is no need to have exactly 70 K for that resistance. So 68 K or 75 K would be perfectly fine, even 30 K or 100 K should work too. More resistors only adds costs, size and solder joints.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on March 09, 2017, 04:54:58 pm
What is the best way for averaging 4 LTZ1000 in one output?

I tested 3 LTZ1000 with "just a resistor" as per datasheet but it leads to more instability than benefits.
I can register many random jumps up to half ppm and much more noise on my 3458a.
Test where made with 200 ohms and 4K ohms resitors.
The latter one was much better but still more noisier and unstable than just one LTZ1000.

So after those tests my idea is to buffer each single reference, and than connect the buffered output
as explained in the Datron 4910 manual (200 ohm per channel + 50 ohm before output).

Will it be better or in any case I must I expect a "stable" result with just the resistor method?

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 09, 2017, 05:02:52 pm
Hello,

for the just resistor method I could imagine that the current regulators for the zener influence each other.
So I would do a buffering before averaging.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 09, 2017, 07:17:47 pm
The standard LTZ1000 output is already low impedance - so kind of buffered. So there is no need to add an extra buffer before combining via resistors. So just a resistor each and than followed by a capacitor to ground for filtering (just because you can at essentially no downside). After that a buffer is kind of needed.

Combining the references might need some extra care at the ground side. The layout is important here, not so much for the noise, but for stability and the TC.

If the single refs have different levels of noise, different resistors would be needed to get the lowest noise - though long time stability would prefer same resistance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: fluxamp on March 11, 2017, 03:01:31 pm
finally got around to finish my dual ltz reference. the board implements a slightly modified version of Andreas' circuit (to accommodate the parts I had lying around). currently, only the datasheet components are populated, though. the first picture shows an intermediate version that still lacks the buffer (lower right) and the foam around the ltz

now it's off to the lab corner for burn-in next to the LM399 reference  :=\ still got to figure out what connector to use for the temperature sensors of each reference...
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 11, 2017, 03:09:55 pm
Neat build, just few points. BNCs might not be that good if you chance every last microvolt due to thermal EMFs and usually brass outer shell.
Also I'd trim pins of LTZ much shorter, almost flush to the board surface. Having them that long might cause more harm than good, as even with foam you can't avoid air drafts 100%.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 11, 2017, 03:12:14 pm
Hello,

I guess the buffer is a LT1010 type?

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: fluxamp on March 11, 2017, 03:30:03 pm
Neat build, just few points. BNCs might not be that good if you chance every last microvolt due to thermal EMFs and usually brass outer shell.
Also I'd trim pins of LTZ much shorter, almost flush to the board surface. Having them that long might cause more harm than good, as even with foam you can't avoid air drafts 100%.

thanks. this is for a proof of concept, hence the BNC. the last microvolt doesn't matter for this application. but I'll keep your advice in mind for the next one  :)

I guess the buffer is a LT1010 type?

yes, it's the buffer from the appendix of AN86.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Gyro on March 11, 2017, 08:37:28 pm
now it's off to the lab corner for burn-in next to the LM399 reference  :=\

That's the way we catch spiders in our house (the glass) - it looks rather appropriate!  ;D
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 11, 2017, 09:24:11 pm
now it's off to the lab corner for burn-in next to the LM399 reference  :=\

That's the way we catch spiders in our house (the glass) - it looks rather appropriate!  ;D

Huh it has 8 legs!!!!
Title: Re: Ultra Precision Reference LTZ1000
Post by: casinada on March 16, 2017, 04:25:58 pm
Paul Rako has an article on the LTZ1000:
http://electronicdesign.com/analog/what-s-all-ltz1000-stuff-anyway (http://electronicdesign.com/analog/what-s-all-ltz1000-stuff-anyway)

He goes on to note that the LTZ1000 is pretty much the only game in town, “National/TI obsoleted the LM199, so the LTZ1000 is the only replacement in the industry that I know of. It has quite a following, too, with one guy in Europe making a very cool looking PCB layout with slots (Fig. 2).”

Doesn't Illya aka "Tin" live in Taiwan?  :-//
Title: Re: Ultra Precision Reference LTZ1000
Post by: ManateeMafia on March 16, 2017, 08:01:56 pm
Around 2011-2013 I spotted a table of voltage references listed by Paul Rako in a magazine enumerating all known good references ... - ADI, National and LTC were listed.
A lot of ADI stuff was listed but the LTZ1000(A) from LTC was missing as high end reference ... well I wrote the man and his answer was he was only a webmaster for a certain semiconductor company - nothing more, although we knew the man from many technical webinars ... - so his selective memory was at that time not aware of the LTZ1000(A)
Times have changed since a certain semiconductor company has acquired LTC ... ?

:-)

Flinstone

And he also didn't own this equipment http://www.edn.com/electronics-blogs/designing-ideas/4311838/The-home-lab-of-Paul-Rako (http://www.edn.com/electronics-blogs/designing-ideas/4311838/The-home-lab-of-Paul-Rako)   :-DD

I am sure that certain semiconductor company is now offering its employees a new flavor of Kool-Aid.

@TiN
 :-+ for the recognition
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 18, 2017, 07:08:04 pm
I do live in Taiwan, but originally I'm from Ukraine, which is mm, sorta Europe :)

To stay on topic, I was on a business trip last week. That means gear at home is unattended. Not to waste precious digits, I hooked recent setup with Keithley 7168 scanner to bank of my LTZ1000 references, output connected to both HP 3458A's and whole thing was collecting data for a week. Whole bank powered by Keithley 2400 at +11VDC.

Both 3458A's are within 0.5ppm apart, so I just averaged reading from both of meters and presented it as final sample. All references scanned in sequence with 10 seconds soak time between switching  channels. Let's see the data. My main goal on this was to see if Keithley 7168 scanner can be used for sub-ppm level accuracy measurements.

One of channel ref was not happy (ch3), it's freshly built one, so will need to check on it later. Other one, channel 4 is crazy too, going all over the joint. But five other LTZs are happily running in subppm region, which is good start.

(https://xdevs.com/doc/xDevs.com/KX/kxref_avg32_1.png) (https://xdevs.com/doc/xDevs.com/KX/kxref_avg32.png)

Here's averaged data with simple median of 32. CH7 bright red reference is HP A9 board, rest are my KX LTZ boards (both patched A01 PCB version and B01). I'll have to take stuff apart to give more details what is what, as some of them are LTZ1000A, other LTZ1000, and different opamps/resistors combo's too.
But hey, CH2 lime reference seem to be extra noisy, isn't it?

Reduce median filter to 2:

(https://xdevs.com/doc/xDevs.com/KX/kxref_avg2_1.png) (https://xdevs.com/doc/xDevs.com/KX/kxref_avg2.png)

There is our good old jumper.  :bullshit: So now this is 3rd PCB on which same chip was installed, and it's safe to confirm that jumps are coming from the flakey LTZ itself, not the related circuitry around it. As side note, this data shows that properly working LTZ1000-based refs and behaving 3458A can achieve ~0.8ppm stability in mid-term, even without battery power or controlled temperature setup. Ambient temperature on 7 day graph log vary from +26C to +23C.

I'm happy with Keithley 7168, wish I'd have two of them now.  ^-^

RAW data and realtime page (https://xdevs.com/nvs_ltz1/).
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on March 19, 2017, 08:12:14 pm
Hei TiN, why don't you attach the little jumper to your noise meter? Just curious to see what is noise on in when not jumping.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CalMachine on March 20, 2017, 12:35:24 am
I'm about to join the most prestigious club  :-+  Just waiting on getting the z202 resistors from Vishay and I should have everything!  I would like to practice my soldering skills before I have at it, though.

Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on March 20, 2017, 02:49:48 pm
I'm about to join the most prestigious club  :-+  Just waiting on getting the z202 resistors from Vishay and I should have everything!  I would like to practice my soldering skills before I have at it, though.

I recognize those pcb :-)
Title: Re: Ultra Precision Reference LTZ1000
Post by: CalMachine on March 20, 2017, 03:56:15 pm
I'm about to join the most prestigious club  :-+  Just waiting on getting the z202 resistors from Vishay and I should have everything!  I would like to practice my soldering skills before I have at it, though.

I recognize those pcb :-)

Hehe  ;D  Thank you so much again for sending me your extras. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: VK5RC on April 04, 2017, 10:55:09 pm
@calmachine - please show what you did and why you did it that way.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CalMachine on April 05, 2017, 01:21:34 am
@calmachine - please show what you did and why you did it that way.

Will do!  Could be multiple weeks though....  :--  I first touched base with them on March 20th with the my order, and have yet to get prices / lead time.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 05, 2017, 09:07:48 pm
Whole bank powered by Keithley 2400 at +11VDC.


Hello Illya,

Is 11V not a bit marginal?

- depends of course also on thermal isolation and environment temperature.

at least on my cirquit with LTC2057 the dropout of the current regulator begins shortly after UBat falls below 11 V.

With best regards

Andreas

Edit: sorry was a wrong picture. now corrected.
Red: voltage over 120R
green: supply voltage
yellow: current regulator output (= gate of BF245C in my cirquit)
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 06, 2017, 08:45:36 pm
Quote
Hello,

I don´t know where I have seen the circuit from Lars.
It was a LT5400 with 2*100K in parallel and 2*10K in series.
So actually a 7:5 divider.

This together with a TL431 based heater could give a good basis for a 7->10V transfer.
See bottom of page:
http://www.techlib.com/electronics/ovenckts.htm (http://www.techlib.com/electronics/ovenckts.htm)

with best regards

Andreas

Lars found that 7:5 is possible with LT5400-3 but I found that 13:9 is possible with LT5400-8 (2x 9k in parallel and 2x 1k in series) which is much closer to 10V.

6,95V * 7:5 = 9,73V comparing to 6,95V * 13:9 = 10,0389V
Title: Re: Ultra Precision Reference LTZ1000
Post by: try on April 07, 2017, 12:58:40 pm
To get the divider you have to put his two combinations in series:

(1k+1k) / [ (1k+1k) + 9k||9k ] =
2k / ( 2k + 4,5k) =  2 / 6,5 = 4 / 13
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 07, 2017, 05:22:29 pm
Be careful using diffused chip resistor paks for precision voltage boosters - they are quite noisy compared to PWW.  If you're going from 7V to ~10V that noise will get gained up also.  Being SMT devices they are prone to mechanical stress pickup from the board, be warned.

Also note that if you use a '5400, you won't get a tight TCR ratio match across -two- or more packages.  You must do all your tight-tolerance divider ratios with just the 4 resistors provided in -one- single  package in order to keep a tight TCR.

Generally there are much better devices for use around LTZ circuits: For instance talk to Edwin - he will make you some PWW for the exact values you need at no extra cost.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 07, 2017, 06:46:30 pm
Quote
Hello Branadic - can you explain me how you obtain with 9k||9k + (1k+1k) (= 2.25) a ratio of 13:9 ... ? Perhaps I am overlooking something ... !

Thanks
Butterfly

You have a non-inverting amplifier, so the calculation is 6,95V * (1+ 2k/4.5k) = 6,95V * (1 + 4k/9k) = 6,95V * (9k/9k + 4k/9k) = 6,95V * 13/9 = 10,0388V
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on April 07, 2017, 06:52:59 pm
Be careful using diffused chip resistor paks for precision voltage boosters - they are quite noisy compared to PWW.  If you're going from 7V to ~10V that noise will get gained up also.  Being SMT devices they are prone to mechanical stress pickup from the board, be warned.

How noisy are they? LT says <-55db (dBuVrms/VDC 1 decade) for LT5400. Are that really bad for a 7-10V LTZ amp?
Agree that mitigating stress or checking the result in your design is important.

Also note that if you use a '5400, you won't get a tight TCR ratio match across -two- or more packages.  You must do all your tight-tolerance divider ratios with just the 4 resistors provided in -one- single  package in order to keep a tight TCR.
This is important!

Generally there are much better devices for use around LTZ circuits: For instance talk to Edwin - he will make you some PWW for the exact values you need at no extra cost.
What stability over a year can you get with Edwins WW for a 7-10V amp? My bad experience with Edwins resistors really says the opposite. I run a comparison of the LT5400-3 at 10 to 7V over a year and it was stable within about one ppm at 23C and about 40%RH difference.

Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on April 07, 2017, 07:01:18 pm
For the LTZ1000 that often is 7.1-7.2v the LT5400-3 is suited.
The LT5400-8 is more suited for the LM399 that is specified with a typical 6.95v.
I have a couple of LM399 and LT5400-8 exactly for this purpose but I haven't done tests on them yet. Maybe because I have found a simple temperature  compensated AD587JQ normally is as good or better with much less current draw for a DIY 10V reference.

Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 07, 2017, 07:16:07 pm
Quote
For the LTZ1000 that often is 7.1-7.2v the LT5400-3 is suited.
The LT5400-8 is more suited for the LM399 that is specified with a typical 6.95v.

You're right, that is exactly the way to go.

Quote
I have a couple of LM399 and LT5400-8 exactly for this purpose but I haven't done tests on them yet. Maybe because I have found a simple temperature  compensated AD587JQ normally is as good or better with much less current draw for a DIY 10V reference.

I'd love to see how that works and compares to other setups, even though there are references like AD587JQ.
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on April 07, 2017, 09:01:36 pm
I've just measured my 3458A reference board (the only bit of a 3458A I own sadly); the voltage across the 111ohm zener current setting resistor and Q1 Vbe is 399mV which surprised me as I was expecting it to be nearer 600mV. Is this typical?

399mV means the zener current is 3.58mA; Q1's collector current is 89uA given the 74.2k resistor. 399mV Vbe @ 89uA Ic implies a reverse saturation current of approx 12E-12A which seems rather large - does it imply that Q1 may be damaged?

The reference seems to be stable enough with an ouput of 7.06V but I haven't tested it to any degree as yet. The board was powered at 18V and was drawing approx 33mA.

The reference is marked 1826-1860 with a date code of 9051. The voltage across the heater was 8V giving 264mW of heater power; room temperature was 20C so I'm not sure if it is an LTZ1000 or an LTZ1000A given that 264mW seems to be half way between the data sheet graphs @ 75C above ambient - so which is it likely to be?

[EDIT] Forgot to subtract the zener and LT1013 supply currents in the heater power calculation, so heater power actually nearer 230mW. That isn't far off the 200mW shown in the datasheet for an LTZ1000A @75C above ambient
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 08, 2017, 12:14:19 am
Lars:
Try running an '5400 resistor pak for a voltage booster for the newer high-res 32 bit ADC's and you'll see what I mean.  Compare that to PWW.  You'll be doing more work on noise low-pass bandwidth reduction especially if you use these on an ADC input - which generally means you're pushing the noise down to a lower freq., (not really eliminates it over longer time frames)  That resistor noise spec by LT (and for Vishay films in general) is generally very optimistic, and when you press them on the issue - well it turns out those noise specs are more theoretical in nature, and probably measured on an un-mounted device (just sitting in a test jig or wafer prober, which is not -your- PCB and thermal flow).  That complete package of device mounted to a PCB changes the story.

Unless you are careful with the mount of the '5400 pak, you can easily build a board that picks up every air draft and thermal stress / vibration change in the neighborhood.  You'll have to test in your application - don't assume every spec is as-advertised.

We use PWW resistors from Pettis, GR etc. and have predicted results - if you're worried about humidity, you use a decent vacuum-deposited coating, hermetic enclosure, silica bag,  etc.   For us and what we need, in an industrial environment the PWW is a good, profitable & robust solution when dealing with vibration, sudden air drafts etc.  We send modules from low-humidity North America to the jungles of Thailand - plastic packages and all - and if you plan for it it's not a problem.  It does take planning though.

You'll find that humidity is more of a concern if you leave your box switched off for a long time - and it's certainly on a longer time scale to see effects (weeks).  Keep your precision devices in an always-on, slightly warm enclosure and humidity effects will be mitigated.   At least that's what we tend to see.

If a humidity test is called for we'll use a saturated salt solution to keep the device in a known, saturated atmosphere at known humidity over 3 ~ 6 months, etc. with power on and power off - and you'll learn more about your circuit that way.

If your application needed a smaller size, wasn't prone to vibration effects and you could live with more noise - then a '5400 pak could work for you if used very carefully.  Every situation needs an appropriate solution to meet the customer's needs.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on April 08, 2017, 01:40:51 am
I was thinking of do a 4 ltz1000 on one module.

PROS:
- compact PCB (more easier to hovenize)
- use only one 13K/1K divider
- feed the 70K and 12K/1K resistors with an averaged 7V (less drifty and less noisier) that maybe should even improve stability
- lower noise reference of 4 combined ltz1000
- slightly cheaper than 4 LTZ1000 modules

CONS:
- all your eggs are in one 12K/1K divider
- will be more hard to trim for tempco
- loose possibility to select the best LTZ1000 module
- single point of failure

Does anyone ever tried or want to discuss?

Inviato dal mio Nexus 6P utilizzando Tapatalk

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 08, 2017, 06:46:31 am
Hello,

From the last 4 built references I have
1 with large popcorn noise
1 with detectable popcorn noise
and only 2 which are without detectable popcorn noise.

From ageing drift there are also 2 good and 2 not so good devices.

So if you put all in 1 cirquit all will be bad.
With 4 different devices you will have the chance for 1 excellent device.

You need more samples so that you can select.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on April 08, 2017, 06:54:04 am
I've just measured my 3458A reference board (the only bit of a 3458A I own sadly); the voltage across the 111ohm zener current setting resistor and Q1 Vbe is 399mV which surprised me as I was expecting it to be nearer 600mV. Is this typical?

...

[EDIT] Forgot to subtract the zener and LT1013 supply currents in the heater power calculation, so heater power actually nearer 230mW. That isn't far off the 200mW shown in the datasheet for an LTZ1000A @75C above ambient

Surely is that typical for a diode, due to its -2mV/°C coefficient.

75°C above RT gives about -150mV lower forward voltage.

The rest of the currents also seems reasonable, so your reference is fine, very probably.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 08, 2017, 08:05:42 am
With reference chips it is a good idea to still have access to the individual voltages. This way one can see if some parts are drifting more than others and also check if some have higher noise. Depending on the noise levels one might decide to give the better units a higher weight.

The transistor currents are not that critical, especially not for the noise. Also the average voltage would be available only after a buffer - so possible some extra drift / noise there. So having a lower noise voltage source for this gives essentially no improvement on the overall noise. The advantage of using the individual reference is that there will be no drift coupling, and even if one reference totally fails, the remaining ones would be still as good as before.  A similar thing applies to the 13K/1K divider - even if the drift of different units would compensate to a small degree this would still also work for the overall voltages.

A shared divider saves a little, but it also introduces a single point of failure and failure of one unit (for whatever reason) would cause a shift in all the temperatures. So I would definitely prefer separate dividers. Having 4 separate dividers also gives some averaging over there drift, so there is some (though not really much) return in precision for the extra costs.

There is still something to having the references all close together, as this can help to bring the lower side of the output voltages together.  For the positive circuit the ground (reference -) connections can be kind of tricky. It might need averaging resistors for this side too, even if they are small.

Compared to the standard circuit a few points might be worth a thought:
1) A way to measure the voltage of the temperature setting resistors might be useful. This might only take something like a jumper and output connector for optional access. Modern DMMs might be more stable than the divider.
2) As a short at the output can upset the heater, it might be a good idea to have a kind of supervision, to prevent excessive heating. This would be less of a problem with an averages reference as this essentially needs a buffer, but the separate outputs would be still sensitive.
3) The temperature regulation loop in nonlinear: heater power is proportional to the square of the current. Thus the quality of control depends on the power level and is getting lower at the low end. So it might be a good idea to make the loop at least a little more linear to allow good operation to lower levels of heater power. It would also reduce the upsets on transients, as power spikes would be limited.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on April 08, 2017, 08:40:07 am
Lars:
Try running an '5400 resistor pak for a voltage booster for the newer high-res 32 bit ADC's and you'll see what I mean.  Compare that to PWW.  You'll be doing more work on noise low-pass bandwidth reduction especially if you use these on an ADC input - which generally means you're pushing the noise down to a lower freq., (not really eliminates it over longer time frames)  That resistor noise spec by LT (and for Vishay films in general) is generally very optimistic, and when you press them on the issue - well it turns out those noise specs are more theoretical in nature, and probably measured on an un-mounted device (just sitting in a test jig or wafer prober, which is not -your- PCB and thermal flow).  That complete package of device mounted to a PCB changes the story.

At the position where the LT5400 would be used (7 to 10V gain stage), noise can easily be filtered, also given the relatively high source impedance of that noise source. So that should not be a concern. For an A/D application, that is different, as this is usually broader in frequency band. Not so here, it is DC essentially.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 08, 2017, 09:42:18 am
The excess noise of noisy resistors tend to have a significant 1/f contribution. So filtering is not really practical. I do not know the standard (and thus the bandwidth) by which it is measured, but -55 dB does not sound very low noise this would be something like a 12 µV of noise at 7 V. This sounds like a lot compared to something like 1.2 µV peak to peak or 0.2 µV RMS for the LTZ1000 and 0.1-10 Hz frequency band.

Filtering in the very low frequency band might be more in the semi digital domain: so using a low noise wire wound divider as a first approximation and if a second, divider might give a lower drift at the expense of higher noise, this could be measured in comparison to do correction an a very lang time scale (e.g. hours or longer),  maybe with something like a digital trimming.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on April 08, 2017, 11:19:50 am
First of, the standard referenced (MIL 202, M308) in the data sheet is not covering the tradiational 1/f noise frequency range (which is from DC to some ten Hz). The frequency range covered is geometrically centered arround 1KHz and is 1kHz wide. Also, the -55dB figure, as per spec, is defined as the ratio of the DC voltage applied accross the resistor, measured in V, to a RMS noise voltage, measured in uV. So we are talking about appr. 13nV RMS excess noise here.
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on April 08, 2017, 02:28:21 pm
I've just measured my 3458A reference board (the only bit of a 3458A I own sadly); the voltage across the 111ohm zener current setting resistor and Q1 Vbe is 399mV which surprised me as I was expecting it to be nearer 600mV. Is this typical?

...

[EDIT] Forgot to subtract the zener and LT1013 supply currents in the heater power calculation, so heater power actually nearer 230mW. That isn't far off the 200mW shown in the datasheet for an LTZ1000A @75C above ambient

Surely is that typical for a diode, due to its -2mV/°C coefficient.

75°C above RT gives about -150mV lower forward voltage.

The rest of the currents also seems reasonable, so your reference is fine, very probably.

Frank

Thank you - I don't know how I managed to overlook that.

Do you agree that the reference will be an LTZ1000A? Only I'd got the idea that originally HP used the LTZ1000 and by the time they switched to the LTZ1000A they'd stopped marking them with their own part number. I've very likely got this completely wrong though.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on April 08, 2017, 02:44:53 pm
Thank you - I don't know how I managed to overlook that.

Do you agree that the reference will be an LTZ1000A? Only I'd got the idea that originally HP used the LTZ1000 and by the time they switched to the LTZ1000A they'd stopped marking them with their own part number. I've very likely got this completely wrong though.

It is an LTZ1000A, as far as I know, and nobody else found the non A version in any HP3458A references.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 08, 2017, 06:01:54 pm
First of, the standard referenced (MIL 202, M308) in the data sheet is not covering the tradiational 1/f noise frequency range (which is from DC to some ten Hz). The frequency range covered is geometrically centered arround 1KHz and is 1kHz wide. Also, the -55dB figure, as per spec, is defined as the ratio of the DC voltage applied accross the resistor, measured in V, to a RMS noise voltage, measured in uV. So we are talking about appr. 13nV RMS excess noise here.

Therein lies the problem with Datasheets and sketchy noise specs - and trying to filter out the noise introduced by LT5400 into an otherwise precision circuit.

The 1/F noise is the problem - If you've ever tried this: You build a 7-10V voltage booster with a clever application of LT5400.  You realize it's a little too noisy for your ADC system. You low-pass filter your 10V output say to 5Hz, thinking you'll get rid of noise...Then you test everything and realize you got some noise energy at 1Hz and below.  So you dink around with more filtering, say 0.5Hz.  Now you realize you've got more noise down below .1Hz, and maybe even a bigger problem....and so on.  Then you realize what a rat-hole that 1/f noise is doing to you.

It is fairly difficult to get rid of that noise and have your Vref stable for measurements over longer and longer time frames.  Just speaking from experience here.

At some point you realize it was easier to just go with some good PWW's, or if your customer demands it a custom metal film ratio set for your boost amp divider.  It is always better to -avoid noise when you can- rather than try to remove it from a signal later. At least that's what we try for.

The next thing you realize is: Do you really need 10V for your application?  :)  But that is a story for another day.

Couple of other "Gotcha's" on LT5400 paks - just a general head's up if you haven't used these before:

1)  The only thing going for them is pretty good TCR ratio matching.    The resistance absolute value (20%) and TCR is absolute garbage compared to real precision resistors - these are designed to only be used as ratio groups.  Be careful of that if your amplifier feedback circuit also depends on a total -absolute- value (including individual TCR of around 8ppm) of the divider as well as the divider -ratio- itself.

Note that the TCR ratio of LT5400 isn't anything that can't be done with good wire-matched PWW that are thermally tied together.  Or a good film resistor ratio set.  The advantage of using real resistors here is you also get good control over the absolute resistance value AND much better control over individual TCR AND much better mechanical stress forgiveness.  Your application may or may not need those characteristics.

2) The withstanding voltage of LT5400 is surprisingly low.  Remember these are IC style, small diffused resistors.  Be warned if you are using these as an input-signal divider; you might need surge protection -ahead- of the resistor pak.  These are not very forgiving of an over-voltage stress.

3)  These resistors - being small- have a surprising crosstalk especially on adjacent units.  Be aware of that if you have any signal with higher dv/dt or sensitive AC signals - like for instance if you're using these to build a differential / instrument amp, etc.  It's best to test on your own board before you believe anything on that datasheet.

4) Mounting a LT5400 is not a hand-soldering job.  For minimal package stress these want to be properly reflowed and watch out for solder paste thickness - if you can get them to "float" slightly off the PCB that can help.  The thermal pad is critical on the back side but remember this is a small capacitor to each resistor element also.  Lead-Free solder can introduce different stress characteristics over regular solder - make sure to test your board out mechanically so you know what the effects are.

Lots of things to watch out for with those 5400's.  They might be a good fit for some applications but for us they've always been somewhat disappointing and never helped the profit margin over other quality resistors.  Your mileage may vary.

They are smaller though. <Grin>
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on April 08, 2017, 11:37:49 pm
I appreciate that you brougth up the issue with 1/f noise with the 5400, especially as it is nowhere mentioned in the data sheet, the noise spec in there is certainly not of help. Using the 5400, I will check on this in my application.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 09, 2017, 09:41:30 am
I wonder if there are spice noise models for the different resistor technologies available, so that you can make a theoretical investigation on how the resistors behave in a real circuit application with different opamps.

@ Edwin or any other: Do you have real noise measurements on your resistors? I don't like the universal statement "Wirewound resistors don't exibit 1/f noise". This might be true for the wire, but a resistor is more than just the wire. Thanks.
How do Edwins resistor compare to UPF, UPW and all the other (ultra-) precision resistors?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 09, 2017, 01:18:05 pm
There is an articlew with some measurements on resistor excess noise for some resistor types:
https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiXrOrfupfTAhXCvxQKHXGmBdgQFggoMAA&url=https%3A%2F%2Fdcc.ligo.org%2Fpublic%2F0002%2FT0900200%2F001%2Fcurrent_noise.pdf&usg=AFQjCNELohORkodPhFRGcCVkUfrvgjFiCw (https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&cad=rja&uact=8&ved=0ahUKEwiXrOrfupfTAhXCvxQKHXGmBdgQFggoMAA&url=https%3A%2F%2Fdcc.ligo.org%2Fpublic%2F0002%2FT0900200%2F001%2Fcurrent_noise.pdf&usg=AFQjCNELohORkodPhFRGcCVkUfrvgjFiCw)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 09, 2017, 05:12:52 pm
Thanks Kleinstein. Sounds like a tradeoff between TC, noise and price of the resistor. RC55Y are cheap and tend to have low noise, as published by the linked article, but as Andreas found they have large aging drift.

(https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/?action=dlattach;attach=147753)

Vishay S102K are more expensive, have low noise as indicated by the article, but we don't have measurements on real TC available.
For UPW50, Econister, UP805 (Edwin Pettis) and Z201 we have TC measurements made by Andreas, but no noise investigation.  :-//

So I still hope that someone with 1k or 10k of the mentioned resistor types can measure noise to compare them to the publication to get rid of this lag.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 09, 2017, 05:37:22 pm
The excess noise of wire wound resistors is considered very low, so usually not a problem at all. The same is true for the foil resistors, even though the noise can be slightly higher. With thin film resistors it seems to depend on the type and also size. Some are not that bad, but some are. Even some carbon resistors seem to be better than there reputation.

A doubt there is much need to measure noise of WW resistors - this would be a rather difficult task. It might be interesting with thin film resistors like the LT5400.

Measuring the excess noise would need 4 approximately equal resistors and the suitable amplifier circuit and data collection part, somewhat similar to that used for low frequency. The LT5400 with 4 equal resistors might be a good candidate.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 09, 2017, 06:06:34 pm
The noise data of RN73 (nichrome on ceramic) are looking also promissing, they are cheap and available in different packages (0405, 0603 and 0805). Would be interesting to see, how they compare in TC measurement and if there is a way of proper mounting, to get rid of CTE mismatch when mounting to pcb.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on April 09, 2017, 08:30:44 pm
Mounting is an interesting question. If you use a larger package - 0805 - you have more mass to overcome forces from the PCB. Also, slots at each end of the device, and under the device, will further reduce the ability of the PCB to strain the resistor.  An interesting question for the next version of reference voltage sources. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 09, 2017, 09:03:49 pm
RC55Y are cheap and tend to have low noise, as published by the linked article, but as Andreas found they have large aging drift.

Hello,

I have only examined 1 sample of RC55Y. It could also be a "outlier" or "production fault".
(similar to USR2#1 sample on the table)
Even from the best resistors you get from time to time a "drifter".

But since T.C. was also >3 ppm/K (as expected from the data sheet with 15ppm/K)
 I didn´t want to spend my time on further samples for RCY55.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on April 09, 2017, 10:07:25 pm
@Kleinstein @Andreas

Yes having 4 LTZ in one board is deftly a bad idea because you cannot separate the good
apples from bad ones and temperature compensation adjustments will be more difficult to do.

So my definitive project will be to design a voltage reference made of 4 LTZ1000 reference
modules + one mother board.

Each LTZ1000 module will have the classical LTZ1000 circuit (plus Datron heater caps) implemented
with two LT1006 and buffered output (LTC2057). I'm not planing to do any EMI mitigation on the
LTZ1000 modules.

I'll keep the idea of having the "single instance" of 12K/1K divider on the mother board.
This will save few cents and will permit also to experiment with pwm controlled temperature set
point (that is where I'd like to end with).

Motherboard other than temperature set point will do the averaging of the 4 LTZ modules.
Averaged output will be buffered again. Mother board will also implement the power supply stage,
that will lover voltage to 13V (coming form a battery bank or from another power supply).
A few components will be added on the last buffer and on the power supply stage to do a little bit of
EMI filtering.

That should keep me busy for a fair amount of time.




Title: Re: Ultra Precision Reference LTZ1000
Post by: CalMachine on April 09, 2017, 10:53:59 pm
@Kleinstein @Andreas

Yes having 4 LTZ in one board is deftly a bad idea because you cannot separate the good
apples from bad ones and temperature compensation adjustments will be more difficult to do.

So my definitive project will be to design a voltage reference made of 4 LTZ1000 reference
modules + one mother board.

Each LTZ1000 module will have the classical LTZ1000 circuit (plus Datron heater caps) implemented
with two LT1006 and buffered output (LTC2057). I'm not planing to do any EMI mitigation on the
LTZ1000 modules.

I'll keep the idea of having the "single instance" of 12K/1K divider on the mother board.
This will save few cents and will permit also to experiment with pwm controlled temperature set
point (that is where I'd like to end with).

Motherboard other than temperature set point will do the averaging of the 4 LTZ modules.
Averaged output will be buffered again. Mother board will also implement the power supply stage,
that will lover voltage to 13V (coming form a battery bank or from another power supply).
A few components will be added on the last buffer and on the power supply stage to do a little bit of
EMI filtering.

That should keep me busy for a fair amount of time.

This is very similar to what I plan on doing soon.   :-+

I also want to try to do something using the 2DW23X zeners.
Title: Re: Ultra Precision Reference LTZ1000
Post by: lukier on April 10, 2017, 12:44:40 am
So my definitive project will be to design a voltage reference made of 4 LTZ1000 reference
modules + one mother board.

I'm planning something similar, a poor-man's DIY mini Fluke 734A, four pluggable modules, each with 10V and 10K.

I've collected most of the critical parts in the last months:

The overall idea is to design small 3458A like ref board with just LTZ1000 basic circuit, all through hole, just one SMD - unbelievably tiny LMT70YFQT temp sensor just under the LTZ1000 and the whole thing using two S5637-ND connectors to connect to module's base PCB and enclosed in some ABS 3D printed case to prevent air flow (and insulate a bit).

But my analog-fu is not good enough yet to go from there. Each module base board would carry this ref board + 7V->10V step up that I need to think about (DigilentMind's MCU with multiple PWM idea looks nice on paper, need to test it), the 10K reference resistor maybe with a small heater to keep it stable and then I was thinking about etching flat flex out of Pyralux to connect the signals from the board to the binding posts, like in 732B.

But there are even more things where I need to learn more and test various concepts, maybe the volt-nut elders here will be able to help:
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 10, 2017, 04:19:22 am
Sounds like enough work for next 3-5 years, that's for sure. LTZ1000-based circuit deceivingly simple at unprepared eye, but quickly morph into great time-vampire project, as you get your feet wet. And you can't escape it afterwards! I fell into this trap 4 years ago, and still no end. Memo for "don't-become-voltnut" members - do not build LTZ circuits  ;D

Maybe you can use just one step-up 7V-10V module, instead of per module. That way you can save some BOM and time, as this circuit is equally difficult, if not more difficult than LTZ REF itself, if goal also not to compromise LTZ's own stability performance.

As for me, I'm tweaking PID (https://xdevs.com/vk5rc_ltz_tc/) for new bigger TEC box, which can fit VK5RC's KX reference. So far no good, need more work. Big chamber slows things a LOT. :D

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 10, 2017, 04:38:15 am

I'll keep the idea of having the "single instance" of 12K/1K divider on the mother board.
This will save few cents and will permit also to experiment with pwm controlled temperature set
point (that is where I'd like to end with).

Motherboard other than temperature set point will do the averaging of the 4 LTZ modules.


Hello,

I would make the option of placing the 12/1K divider also locally on the sub boards.
(in case there is some influence between the individual references over the set point).

I still do not get what is the idea behind a common heater set point.
Do you want to trim the output voltage by setting the temperature (around 50 ppm/K)

Putting all outputs to a averaged one is a good idea.
But how do you do the star ground concept + kelvin sensing so that the heater currents do not influence the output voltage?
Without individual (galvanic isolated) power supplies this will be a demanding task.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 10, 2017, 06:31:00 am
I wonder if I could use small signal latching relay, such as TQ2-L2-5VDC that is used on some of the Keithley scanner cards to switch the output between 7V and 10V to see the drift of the 7V->10V step up. With careful thermal planning and routing both lines similarly (placement, junctions) it shouldn't be an issue?

how much insulation - I bought some Spacetherm offcuts so I might use that, but I've read here that overinsulating LTZ1000 is detrimental. In 732B they insulate the whole lot, but I guess it is because LTFLU doesn't have a heater and they heat the whole lot. Spacetherm still might come handy to insulate VHP202Z coupled to small heating resistor.
Hello,

I also use the TQ2-L2 5V relays in my relay multiplexer for the daily measurements.
Since the coil is mostly unpowered there should not be much issue with thermals when using a metal housing.
A contact cleaning routine (like on some instruments on switch on) could be a good idea when you are using it not every day.

I do not have fear with over insulation. Most of the heat goes out by the package over the package pins and the PCB. The main effect of isolation is lesser noise from thermal effects.
If your heater falls out of regulation you will get 50 ppm/K response on the output. (which is hard to ignore).
So if you test your cirquit 5-10 deg C above your max environment temperature you should have enough headroom.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: VK5RC on April 10, 2017, 09:34:56 am
Sounds like enough work for next 3-5 years, that's for sure. LTZ1000-based circuit deceivingly simple at unprepared eye, but quickly morph into great time-vampire project, as you get your feet wet. And you can't escape it afterwards! I fell into this trap 4 years ago, and still no end. Memo for "don't-become-voltnut" members - do not build LTZ circuits  ;D

Maybe you can use just one step-up 7V-10V module, instead of per module. That way you can save some BOM and time, as this circuit is equally difficult, if not more difficult than LTZ REF itself, if goal also not to compromise LTZ's own stability performance.

As for me, I'm tweaking PID (https://xdevs.com/vk5rc_ltz_tc/) for new bigger TEC box, which can fit VK5RC's KX reference. So far no good, need more work. Big chamber slows things a LOT. :D
TiN Thanks for publishing the work, :-+.  I was hoping for the reference to have a bit more of a 'time-lag'.   It seems to change its internal temperature pretty quickly :--
Oh well - need to think of version 2!!
Rob
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 10, 2017, 10:09:12 am
And it ran out of temperature headroom (https://xdevs.com/vk5rc_ltz_tc/) once reached +42.86 °C temperature (PCB) / +41.3 °C (TEC BOX), woohoo.  :scared:
As reminder for others, VK5RC's KX reference module have 12.0K/1K temperature setpoint. Based on this I'd recommend keeping ambient below +30C for this setup, to be on a safe side.

I'd say 12K/1K bit too low for travel reference, as for example here in summer ambient can be around +32-36°C, and it's not even considering more warm countries like AU,Africa,etc.

+3°C over that gives figure +128ppm, which translates into ~+42.7 ppm/K of LTZ positive zener tempco without temperature oven running. This just stresses again on fact, that LTZ1000 performance is vitally depends on internal oven stability.  :-BROKE

"Time-lag" is about 300 seconds between my TEC box and KX module temperature sensor. I've reset PID parameters, hopefully will get smoother temperature ramp next days.

DSV-data (https://xdevs.com/datashort/vkltz_tcr_nplc100_tin.csv) for those who play with numbers at home.  :-/O
Title: Re: Ultra Precision Reference LTZ1000
Post by: lukier on April 10, 2017, 10:22:32 am
Sounds like enough work for next 3-5 years, that's for sure. LTZ1000-based circuit deceivingly simple at unprepared eye, but quickly morph into great time-vampire project, as you get your feet wet. And you can't escape it afterwards! I fell into this trap 4 years ago, and still no end. Memo for "don't-become-voltnut" members - do not build LTZ circuits  ;D

Yes, this is definitely one of these projects :) And maybe it's a good thing, as voltnuttery is so expensive so it is good to spread it over 3 years. Recently this kind of shopping spree peaked (eBay resistors + Digikey), as I want to build the small reference boards relatively quickly so they can age in some shoebox with a linear PSU for the next year or two while I learn more, test various concepts for the power supply and 7->10 step up and save enough for 3458A :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on April 10, 2017, 12:38:14 pm
I still do not get what is the idea behind a common heater set point.
Do you want to trim the output voltage by setting the temperature (around 50 ppm/K).

The idea is to substitute this 12K/1K signal with a 4 pwm controlled signal in the future
so basically the mother board will be used mainly for checking if everything works.
I accept your advice to add other 3 other 12K/1K positions in case one is not stable
enough.

What i'd like to have is a complete PWM driven temperature set point.

1. it's should be more stable than the resistor divider in the long term
2. you can use it for trimming output of each of the single module
3. maybe you can use it for implementing some minimal temperature compensation

But how do you do the star ground concept + kelvin sensing so that the heater currents do
not influence the output voltage?
Without individual (galvanic isolated) power supplies this will be a demanding task.

High side of each LTZ1000 module is will be buffered, so when connected for averaging it should
not influence each other. My plan is to stick together all four zener kelvin connection on the
lower side. This seems to me exactly how Datron 4910 is made. If possible I'd like to avoid
the 4 (or 5) insulated power supply for this iteration. Does will work? Don't know.

Consider I plan to have different grounding pin for heater, opamps, zener and kelvin
connection on each LTZ1000 module.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 10, 2017, 03:44:01 pm
The output of the normal LTZ1000 circuit is already buffered. So there is no need to have another buffer before averaging. Even if a LTZ2057 will not add much offset,  it will add a little noise and also possible EMI problems - so it is worth avoiding it if you don't need it.

However there are usually no separate drive and sense lines - so the connectors can get critical (need low R) if low resistors are used for averaging. Connecting the negative sides can be more tricky - one option would be separated supplies or alternatively averaging resistors as well. This would require a buffer for the negative side as well and the negative side would be slightly different from the power supply GND. Depending on the application this might be acceptable or slightly inconvenient.

The positive side buffer might already be more than just a buffer - some of the 7 to 10 V circuits have a high input impedance and might directly connect here.

For the temperature set-point I would be careful with a PWM generated voltage - any failure here could lead to over temperature and there would also be possible noise coming in this way. It might be enough to have the option to measure the actual divider ratio (that is have an output) and allow for some initial calibration measurements with a slightly shifted temperature. A possible drift of the set-point could than be corrected numerical. E.g. you know the LTZs TC with respect to the set temperature (around 50 ppm/K, individually measured) and the measured shift in set temperature (or set voltage).

So the modules could be just normal ref. circuits with just extra connections to have access to the divider and enough sensing lines. No need to use separate LT1006s - the dual LT1013 is just fine. For the individual voltages something like series resistors might be enough protection against something like a short or excess caps. Output supervision might be an option - thus to turn of the heater if the output voltage is much too low.

I don't think it is a good idea to have the temperature sensor close the reference, this area has temperature gradients and extra traces add heat paths. The more suitable place would be the resistors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 10, 2017, 05:25:52 pm
My plan is to stick together all four zener kelvin connection on the
lower side. ....
Does will work? Don't know.

Consider I plan to have different grounding pin for heater, opamps, zener and kelvin
connection on each LTZ1000 module.

Hello,

It´s hard for me to understand how you will do that.
You can either connect the heater+zener currents at the power supply or the kelvin sensing pins.
But not both at the same time without getting ground loops and influencing voltage drops.
Of course you can use sense force OP-Amps for the zener grounds or true differential sensing for each zener.
But this will need additional efforts.

I am also not convinced that a PWM-ratio is easier than a resistor ratio.
It is only different.

Of course you are right that the long term stability should be better.
On the other side you have to
- filter out the PWM-noise with non-perfect filters.
- correct the ratio for T.C. anyway since the rise and fall times of your switches are temperature dependant.
- so carefully select the PWM-frequency between both issues

minor effects: (at least for the LTZ setpoint).
- regard input voltage dependant R,on of the switches that will influence INL linearity.
- use switches with low charge injection
...

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on April 11, 2017, 10:52:29 am
Quote from: Andreas
It´s hard for me to understand how you will do that.

I think this is a polite way for you tell me that I need to take more attention to this problem I may overlooked  ;)

Quote from: Kleinstein
Connecting the negative sides can be more tricky ... or alternatively averaging resistors as well.

OK let see if I understand you both guys.

PIN 7 of LTZ1000 will be a little bit over the GND and each of the LTZ1000 GND point will be a little different
than the others. If I connect this four pins together I get strange things to happens due to some current flowing
in other paths than "expected" (ground loops).

This means that I need to use an op-amp to cancel out this "offset" and lower everything to a common GND
point (this point than can be used as the LO side of the reference). This 4 current cancellation op-amp must have a
negative rail to push everything down.

Is this correct?

This meas also that special care must be taken to have also the 120 resistor GND side to almost on the same GND level.

Quote from: Andreas
I am also not convinced that a PWM-ratio is easier than a resistor ratio. It is only different.

Never told is easy (especially for me). What I was thinking is that the thermal regulation should be a little bit
forgiving so if you can only get it stable to 10ppm (I think) it will be perfectly acceptable. How much is hard to
get it I still have to investigate. Thermal lag may also fix a non perfect pwm filtering if it don't screw the
thermal regulation circuit.

Quote from: Kleinstein
The output of the normal LTZ1000 circuit is already buffered.

Yes but I want to isolate LTZ1000 from capacitative load problems (had a lot of problems in past that I want
to avoid). Than I'd like also to have independent channels for sporadic itercomparison. Don't know if this can
be done with simple resistive averaging.

Quote from: Kleinstein
For the temperature set-point I would be careful with a PWM generated voltage - any failure here could lead to over temperature and there would also be possible noise coming in this way. It might be enough to have the option to measure the actual divider ratio (that is have an output) and allow for some initial calibration measurements with a slightly shifted temperature.

That's nice. Maybe the best is still to use the 13K/1K divider and than add a fine adjustment by PWM.
Measure divider ratio time by time (any 6.5 digits multimeter should be sufficient for this) and digital
compensate for its drift.

Considering that we need just few hundred ppm margin to compensate for divider TC and log term drift
this should be easier to do than a 100% PWM signal. This will also ensure that you will not cook the
reference in case PWM circuit fails (PWM only contribute to a very limited amount on the temperature
set poit). Maybe also a 10/12 bit DAC should be enough stable for the same adjustment purpose.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 11, 2017, 12:10:58 pm
The outputs for the individual references might want an extra buffer, but for averaging the 4 reference signals inside one does not need a buffer before the resistors to get the average voltage.

If it just to measure the 4 individual references, one could use a resistor or RL combination to isolate the single references from a possible external capacitive load. Just connecting a DMM might not mind an 1-10K resistor in series.

It is only to drive larger loads, like KV divider that one would need a true buffered output, but this would also prefer to have separate drive and sense terminals, not just buffered with 2 terminals, but more like 4 terminal.

Having 4 OPs for current cancellation at the negative side, is just one option, but this also is a lot of effort and it adds the noise and offset of that OP. Depending on the rest of the circuit, there are other options: one would be using 4 resistors to average the negative sides of the refs as well. This is like controlled ground loops. The downside of this is that one would need a kind  of buffer at the low side as well.

To to anything at the GND level one very likely will need a kind of negative supply (could be a virtual GND) anyway. Having a negative supply available would also give a few more Options for the OPs used in the reference circuit (e.g. LT1097 instead of LT1013).
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on April 11, 2017, 09:21:45 pm
Thanks Kleinstein and Andreas for your considerations, I think I made my mind to where to try go.
I'll share my progress in next days.
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on April 14, 2017, 11:23:22 am
About RC55Y mentioned in an earlier post.

I once tested 10 samples of 1kohm 15ppm/K from Farnell mounted on FR4 boards without power. The first two months the drift was up to 30ppm but after that for a couple of years the drift was about 5ppm/year. The humidity sensitivity were about 25-35ppm for an RH variation of 40% at around 23C. Temperature coefficient varied between about +10 to -15ppm/K. Actually four of the ten samples were at about -15ppm/K. No sample were within +-5ppm/K!

/Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on April 14, 2017, 11:35:17 am
I did a first try to measure noise on the LT5400-8 as I had a sample mounted on a SO to DIP adapter (FR4 board). As I had no available low noise amplifier I measured with my best DMM at home that is a HP3456A with 0.1uv resolution. I made a bridge out of the LT5400-8 with 1+1k in one arm and 10+10k in the other. As I expected I couldn´t see any difference with 0 or 10VDC applied except the offset DC. At 1PLC I had about 1uVp-p at 10PLC 0.3uVp-p and at 100PLC 0.1uVp-p (last digit).

My setup was probably not the best (see picture). Cheap 1 meter long unshielded banana cables, some silver plated and others even nickel plated.

Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on April 14, 2017, 11:40:55 am
I have to ask a question related to 1/f noise and resistors for the LTZ1000 standard design that might be important and that I don´t remember to have seen an answer for.
 
From the LTZ datasheet I see that the zener noise at 1 Hz is about 60nV/sqrt-Hz. My question is how much noise (sqrt-Hz at 1Hz) is needed on the respective resistors R1-R5 to get the same amount out as the LTZ?

In another way: how much is the noise attenuated from each resistor to the output. With just a brief check my guess is that the worst one is the 1kohm that seems to be attenuated only about seven times? But as the 1kohm only has 0.5VDC the 1/f noise should not be high even with a thin film SMD like ERA6, PCF0805, RG2012 or RN73 from what I see in the papers from Seifert (in previous link by Kleinstein in post 1919) and Maerki (ETH)??
https://people.phys.ethz.ch/~pmaerki/public/resistor_flicker_noise/20130723a_white_paper_resistor_flicker_noise.pdf

Another question is if 1 Hz noise and DC voltage (eg thermal EMFs) from the resistors have the same attenuations?
Sorry for being a bit lazy and not setting up a simulation but somebody might already have the information or be quicker than me to get a result?

Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 14, 2017, 01:33:32 pm
Mhm,

my low noise amplifier uses normal metal film resistors.
(1K as input resistor for the high pass).
The noise floor is a factor 5-10 below the noise of a LTZ1000.

And most of the noise comes from the leakage current of the input capacitor.
So I think we do not need to worry about the LTZ cirquit resistors.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 14, 2017, 01:58:56 pm
The resistor excess noise only appears if there is a significant (DC) voltage at the resistors. In the low noise amplifier, there will be essentially no DC voltage on the resistors at the sensitive part. So there is no problem at all.

This is different for the LTZ1000 circuit or an amplifier to scale from 7 V to 10 V. However in the LTZ1000 circuit noise from the resistors will like drift of the resistors attenuated. I agree with the first estimate that the 1 K resistor noise would be attenuated least, by about a factor of 7. Also the still low voltage can keep the noise contribution low.
Chances are the 70 K resistors could give more contribution, despite of an attenuation by a factor of about 200.

So resistor excess noise will not be a problem in the reference circuit itself. It is more of a potential problem with a scaling amplifier.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 14, 2017, 04:06:25 pm
A couple of notes here RE: Resistor noise in LTZ circuit:

Just because you can't see much excess resistor1/f noise on the Vref output doesn't mean it's not there circulating across the LTZ crystal lattice.  You want any noise in that LTZ substrate as low as possible - even its own Zener will make noise, but as you watch that die over 5~10 years you can see the effects of the die's crystal lattice approaching a truly relaxed state - and even the Zener noise will typically diminish to a much lower value than when it was an infant.  Sometimes not, but usually.  Stress on the die means there are bonds changing position, and that means electron pathways changing position, created and destroyed, etc.  Edwin had a good analogy with water flow:  It's like rocks tumbling and moving around in a small stream:  You can hear the water noise when the stream flows over rocks, but you can't hear the water's noise if the stream flows over a smooth muddy channel.  Same idea applies here, on an electron charge carrier level.

The more current noise you have flowing across the lattice, the less likely it will become stable over time - or it won't become as stable as possible I should say.  That's why we use PWW around an LTZ circuit whenever possible and practical, and that's why the datasheet recommends their use.  ANY other resistor type (unless we invent new physics at some point) will always add excess noise across that LTZ and thus decrease stability - and that's the same reason we don't use an AZ amp as the current driver, with its very high current noise injected into the substrate.

We're just trying to give that LTZ the best possible chance of becoming stabilized with low drift and lowest output noise.  It will take time for everything to stabilize.

The 70k's are the main contributors here.  Even though the absolute value of 70k is not too critical, you really want the lowest noise possible across that LTZ for best long term stability.

RE:7V to 10V booster output:  Yes, you really have to be careful here as any gain error or noise will get boosted up.  And as pointed out: You can't average out or low-pass filter 1/f noise very well - you just get noise energy at lower freq. The goal here is to not generate any noise if you don't have to - in the real world that means generate the least possible noise. 

For use with high rez ADC's and DAC's though you're generally NOT trying to make 10V...you really want a lower voltage as a reference point for more modern chips...usually no more than 5V.  So a lot of times for real applications we're dividing the Vref output DOWN and buffering - which is a little easier. 


Title: Re: Ultra Precision Reference LTZ1000
Post by: enut11 on April 18, 2017, 07:31:07 am
Hi All
I now have most of the parts to construct my first LTZ1000 project. All that is missing is the LTZ chip. The main resistors are all Edwin Pettis supplied Type 802 and the PCB is from @mimmus78.

I came across this chip listing on eBay:
http://www.ebay.com.au/itm/401303985615?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT (http://www.ebay.com.au/itm/401303985615?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT)

Is this a good deal at $55US or too risky? If no good, what source of LTZ100ACH would you recommend?
enut11
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on April 18, 2017, 08:02:24 am
Heads up, you can buy straight from Linear Tech site, with a debit/credit card.

And contrary to other reports, there is no minimum $250 purchase order (that's for a trade/commercial order).

For LTZ1000CH#PBF I paid $42.85 USD.

There is a USD $54 shipping charge to Aust however. For that reason I ended up getting 2x ltz1000 and 2x lm399.

For me, knowing the provenance of the refs was worth the money, given the time I ended up putting into them.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 18, 2017, 08:15:08 am
enut11
That is 100% fake.

Second the comment to buy directly from LT, they are happy to sell you even 1pcs. Or at least from reputable retailer. Digikey has some in stock.
I'll be getting 3-4 chips this week, could chime in 2 for you if you want. Shipping from TW would be 15-20$, I think.
Title: Re: Ultra Precision Reference LTZ1000
Post by: enut11 on April 18, 2017, 09:30:47 am
Thanks gents for helping me avoid a big mistake.

TiN, I would like to take you up on your offer. I will PM you.
enut11
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on April 20, 2017, 04:42:10 pm
Going back to grounding, isn't Figure I2 from AN-86 the WRONG way to do Kelvin Sensing?   You see, Zener (and other) currents create a voltage drop across the Zener-Force trace resistance (red marks in attached).  This makes current want to flow in the Kelvin sense connection (green arrow) which defeats its purpose.
(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=309675)

So, what's the proper way to implement Kelvin sensing?  One way would be to buffer the Kelvin point, but then you'd need a negative supply.  A more practical implementation might be to treat the junction of R5, R1 and Pin 7 as a Kelvin star node and use that as your Kelvin Sense and as a star point for return currents from e.g. resistive divider of a 7V to 10V output converter as shown in second attachment.   Comments?  How do you all do it?
(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=309677)
Title: Re: Ultra Precision Reference LTZ1000
Post by: 2N3055 on April 20, 2017, 05:01:13 pm
Output of LZ1000 is taken from pins 3 and 7.. It is combination of zener and transistor that is used...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on April 20, 2017, 05:29:31 pm
I'm not sure why AN-86 appears to suggest creating a ground loop.  The "7V Positive Reference Circuit" in the data sheet is clearer.
Title: Re: Ultra Precision Reference LTZ1000
Post by: pitagoras on April 20, 2017, 06:12:24 pm
Is there a reference design PCB for this "normal" positive 7V reference?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Micke on April 21, 2017, 06:58:22 am
On the Eval. board for AD5781, they connect ground to the resistive divider directly to pin 7 on LTZ1000.
I have done like this on my first LTZ1000 design, I have not experienced any drawbacks yet...  :)
They also have a RC filter between unbuffered 7V and OP-amps with 1.5k and 10µF, quite big capacitance! I thought of doing like this but reduced the cap to 100nF instead, I was afraid that tiniest leakage current of the cap would introduce errors. I was thinking of though if having 10µF use a solid wet tantalum.
Schematic AD5781 Eval board with LTZ1000: https://ez.analog.com/servlet/JiveServlet/download/13219-2-41351/EVAL-AD5791SDZ_LTZ1000A.pdf
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on April 21, 2017, 09:22:45 am
Well, the true ground point should be at the output of the unit. Now for a PCB, one could have that at pin 7, for a unit in a box with e.g. binding posts, things look different. It should be at the negative output binding post. It needs to be set in a way that the change in current through the related wire from pin 7 to the output (load effects, temperature changes / related copper wire drifts and current accross) is sufficently low. The output impedance of a 732B e.g. is 0.1mOhm, as a side comment. So 10mA load at the output causes 1ppm change in voltage. It musst be assured, if that e.g. is the goal, that any return current from that binding post to pin 7 is not generating a ground shift.
The filter capacitor should be a lowest leakage foil capacitor, and the input resistor could be higher, provided the bias current (change again) of the opamp is low, the capacitor will anyway filter resistor noise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Micke on April 21, 2017, 11:02:41 am
I did at least not drive the output current via pin 7 of LTZ1000... I do have built in the PCB in a metal box with 2 pair of binding posts (Buffered 7V with LTC2057 and 10V with LTC2057) , the output negatives are done with separate 0,75mm² cables directly to incoming ground on the PCB. I have done load tests, for example loading the 10V output with 10mA, the output drops 7,6ppm... not great result, but most likely I will not load the outputs that much   :)
But I realize now I should have done like your good explanation, have the output ground as the common ground point... 
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on April 22, 2017, 04:50:00 pm
What you think about using LT1037 to buffer LTZ1000 output with a LTC2057 to zero out offset (same circuit as shown in LTC2057 datasheet).
I'd like to use it in my 4 TLZ1000 reference as "Ultralow Noise Composite Amplifier"

The problem I see is that LT1037 has a little much input bias current than just LTC2057.
This should be not much a problem as this input bias/offset current seems to be constant from 20°C and up ... I think you will get some nA difference from 25° to 45°c that is the internal temperature of the reference.
What will be the influence on the LTZ1000 of this nA bias current offset?

Also LT1028 is interesting, but input bias current is not linear over the temperature range.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 22, 2017, 06:56:48 pm
The standard LTZ1000 circuit can deliver quite some current. The OP is delivering the current and the zener connection is used for sensing. The variants with an extra transistor as emitter follower can even deliver higher currents if needed. This goes up to the point of providing force/sense connections to compensate wire resistance.

The problem why sometimes buffering for the output is desired is, that if the load to the output is so high that the voltage drops, this shifts the temperature set point to a higher value and thus can easily cause the heater to turn on all the way. This thermal stress can cause a shift in observed voltage, e.g. due to thermal hysteresis. In theory one could add an extra protection against this: so limit or turn of the heater, if the reference voltage drops by more than something in the mV range  (enough to allow a cold start).

So there is no really problem for the ref circuit to drive even a much higher input current in the mA range, if this internal. Current spikes from the LTC2057 would be the greater concern. So it is a good idea to have an RC (maybe LC) filter in series, at least for that OP. Without extra filtering, the white noise of the LTZ1000 is way higher than that of the LT1037 - so if would make sense to have at least some filtering here as well.

The LT1037 is not unity stable, the LT1007 is the unity gain stable version.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on April 23, 2017, 12:28:38 am
Thanks Kleinstein, I understand this now.
By this buffer I want to obtain short circuit proof circuit, and a more easier way to sum up the four cells without much interferences and current loops one each other.
LTC2057 will be only used to zero out the offset. His spark noise should not came out directly and I was considering RC filtering both at the inputs that at the output of it.

What op amp to use as current cancelling?
For this I'm considering again LTC2057, this time it will be tied up to a very low impedance to ground node, I was thinking in this case I can ignore those sparks.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 23, 2017, 07:38:12 am
Current canceling usually should not use an AZ OP - definitely not a high current noise one like the LT2057. More like a normal precision one, like LT1013 (if single supply is needed), OP07, LT1097 or maybe OPA141. In some areas even an TLC271 or LM358 might do the job. Having a small DC error here is not that critical. More of the error will likely be due to the resistors anyway.

Just for averaging, there is no need to have a buffer. The LTZ1000 circuit has no problem driving the rather constant maybe 10-100 µA needed for a resistive combiner. An important principle in a precision circuit is not to use many precision parts, but to have a circuit that does not critically depend on many parts. So it is more like having a minimum number of amplifiers in the signal path. So one would rarely have something like only a buffer - so it is a little like going back and learning from old times when an OP was expensive and not that good. No OP can beat a piece of copper wire when it comes to drift and noise. There can be still quite a few parts in not so critical areas, like protection, current canceling and the power supply or monitoring.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on April 23, 2017, 09:45:47 am
Why would the current cancelling Opamp's Vos drift not have the same impact on output drift as in the buffer amp (amplification factor, if any, left aside)?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 23, 2017, 11:43:36 am
There are different ways of doing current canceling / combining the negative side. It depends on the solution chosen of cause:
Using a kind of buffer or virtual ground for the whole circuit would have a large impact of the OPs offset. In this case a really good OP is needed, and the LT2057 might be acceptable.

A second, similar option is using resistors to combine the low side voltage too and than use a buffer with optional force/sense function. Here too a good OP is needed.

If one uses classical current canceling - thus sending a constant current of the right size to the GND point, the OPs offset is even less important. It is attenuated by a factor set by the resistor used to set the current and the resistance of the ground loop - so usually something around 100-1000, maybe more. However the resistors used in the compensation circuit also contribute, likely more than the OP.

An other option is using a virtual ground only for the main current ("120 Ohms " resistor) and keep the transistor to sense the ground. In this case the drift / noise of the OP used is attenuated by a factor of about 10. So drift is less important by that factor. One can combine this with current canceling for the 100 µA at the transistor if really needed.

So my idea was about using the last option of current canceling by current sources, as this should give the best results.
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on April 23, 2017, 03:59:40 pm
The standard LTZ1000 circuit can deliver quite some current. The OP is delivering the current and the zener connection is used for sensing. The variants with an extra transistor as emitter follower can even deliver higher currents if needed. This goes up to the point of providing force/sense connections to compensate wire resistance.  <clip>
If you pull several mA from the Pos output, where/how do you set up a return current path such that it does not corrupt the output with a I*R voltage drop?  Do you guys buffer the ground and use force/sense connections?  Or just have one massively heavy-duty ground connection at R5, R1, Pin 7 super-node?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 23, 2017, 06:42:48 pm
With an additional current source to provide the approximate current needed by LTZ1000 Zener and the divider for the temperature set point, the positive side of the zener can act like a low input-current sense connection. The OP (usually LT1013) will act as the forcing output.

This is similar to return current compensation on the negative side. However the negative side might be a little easier with only about 100 µA from the transistor used for sensing.

However the more normal situation is to have an only very moderate load current, so that just a single ground point and low impedance connection. The really troublesome part is only the possible change in load current. The more predictable part of the load current could be added locally at the load.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chris_11 on May 01, 2017, 08:03:27 am
Did anyone try to force the LTZ1000 PCB temperature with a TEC? The TEC would be linear controlled to avoid switching noise. My plan is to use a PCB temperature setting close to typical ambient I.e. 22 centigrade and use a LTZ1000A with only about 45-50 dice temp. The thermal voltage between the dice and Kovar leads and again between the Kovar leads and the PCB copper is a contributor to the stability. That's the main reason for the hood over the LTZ1000 in the HP3458A. The only cure is to keep the differential temps at the Kovar to copper interface at the PCB as stable as possible.

Christian
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 01, 2017, 08:14:24 am
Hello,

and how do you keep humidity from condensing at 22 deg C?

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: chris_11 on May 01, 2017, 02:41:11 pm
Keep it sealed and put a dryer bag inside. For condesation on a 22 centigrade surface the humidity and temp would need to be high. Definitely not metrology grade environment.
Ovenized only means temp higher than worst case ambient. Then the LTZ1000 has to run even higher with higher aging/drift. And the oven draws always max. power which needs big batteries for a transport standard. TEC should be relativ efficient when the environment is close to the set temp.
My idea is to run everything from a 12V SLA without any DC-DC. For transport with cigarette lighter plug in for recharge.   
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 01, 2017, 03:05:07 pm
Hmm,

to keep the PCB of the LTZ down to 22 deg C the TEC has to be lower than 22 deg C.
Assume 17 deg C. -> In my "Lab" a dew point temperature of 17 deg C is not unusual in summer.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on May 03, 2017, 09:31:25 am
@MisterDiodes, Edwin Pettis: What would you suggest as a costeffective and good LTZ1000 -> 10V schematic which can be adjusted for drift?

I would assume the circuit from the Linear AN86 page 46 (LTC1150 + LT1010) with a PWW-resistor-network from Mr. Pettis + low resistance Bourns 3250W trimmpot/Hex-switch which connects PTF56-resistors. The whole thing, including the LTZ1000 of course, temperature stabilized by a PID-controller like the ADN8834.
But maybe there are better solutions?
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on May 05, 2017, 04:56:05 pm
Circuit for stable 7V to 10V conversion?  That all depends on your final application.  The first question to ask:  Do you really need 10V?  Why?  How quiet does that Vref  need to be?  If you're trying for <5ppm / yr drift, do you even have a way to measure for that accurately?  If you do, that would mean you already have multiple calibrated references on hand.

7V to 10V accurate conversion is not a trivial problem, and is harder than building the LTZ circuit - for instance:

A 732a/b comes to mind as a good design example... :) depending on how much drift and how often you need to adjust.  That's basically what you're talking about, at an extreme level.  If you need a very stable 10V, just buy a 732'.... You won't make anything near as good as that for the price (used or new), especially if your time is worth anything.  Depending on the definition of "good" of course.

A PWW pot with PWW resistors will make an acceptable, economical boost unit for an LTZ.  Talk to Edwin, and he'll make you a set of ratio resistors.  Use a quality Bourns PWW pot for adjustment.  How well you build it from there is up to you, and that could take an infinite number of forms - depending on what you need.

It also depends on what load you're driving - how many mA, op-amp selection, output sourcing + sinking requirements, current limiting,  hysterisis, temp. span power cycling, vibration, thermal flow, etc etc. etc.  The design parameters list is very, very long and is impossible to answer here.

You also have to decide:  If you're driving an ADC Vref input, pay attention to the drive current required.  That's a gotcha on newer fast ADC's.

I wouldn't worry about ovenizing if this your first project.  Build your device to not need an oven first, and see if you really need one.  Add the oven later and see where it degrades performance.   If you don't have a way to really measure down to low PPM accurately, you won't even see if the oven is doing anything for you.

Those PWW wrapped around an amp will get you started on a simple 10V boost circuit.  It won't be 732a/b level, but maybe you don't need that?

If it were me, I'd attenuate the LTZ output down to 5V or 2.5V...much more useful for ADC / DAC work, and you're not gaining up the noise. For an accurate, stable, very low drift 10V do it right and get some working 731's or 732's first... otherwise you won't have a good way to verify a DIY circuit.

EDIT: Somewhere here Dr. Frank has has a published design for his 7V to 10V Vboost circuit.  I don't have time right now to look up the link but that will get you started.   Also:  If you're going to all the work to make a 10V converter, just have Edwin make you an LTZ resistor set - further reducing the need for a noisy, complex oven system. That will make for a quieter LTZ circuit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on May 05, 2017, 10:04:57 pm
Lets be honest here: the nut in voltnut has its reason  :-DD I frankly dont need an ultrastable reference, im just interested in the technology/necessary skill to build them. My problem is indeed that i dont own a 3458A to even judge my selfbuild reference (>3,5k€) and 732-references are likely >1k€ here in germany, if they even appear on ebay. My 6.5 digit DMM 34465A is at the moment all i have, but of course i aim for better equipment.

At the moment i have a LTZ-reference based on TiN KX-board, connected to a zener-to-10V-converterboard based on Andreas suggestion: PTF56-resistors, LTC2057, 12-Bit-DAC to trimm it nicely to 10V with about 5µVpp noise, according to the 34465A. But since the 7V-10V-converter consists of a lot of those resistors i dont have great confidence in its drift and want to change the design to a 2-resistor-OP Amp-design like you mentioned. I will search for the design approach of Dr. Frank like you mentioned and have a look at it.
Im not really interested in using the reference with an ADC, since discrete ADCs like the LT2400 or LTC2508-32 dont come even close to the specifications of the Multi-Slope-Designs used in 8.5 Digit DMMs...also i simply lack the necessary amount of skill and experience to get the reference-voltage to the ADC without introducing those nasty errors because of the ADC-input-current-peaks (like mentioned in the LTC2508-32-DS).

The 732B-oven-controller really isnt that special, im wondering why you say that such an oven contributes to the noise? I thought the only downside of oven-stabilized-designs are the additional thermo-emf-voltages caused by the temperature-differences between oven and measuring-DMM at ambient temperature?

All in all, i would still have to build 3 or more references for intercomparison reasons, to get the necessary amount of confidence and the ability to judge inidividual drift and errors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on May 06, 2017, 04:24:21 am
Well, if this is mostly due to educational purposes, why dont you try different approaches with the three samples you want to build. Use different techniques/parts, options have been described here. To judge the results though, while intercomparison will give you a clue whats going on, in the end you need some type of starting point and end point reference, everything inbetween could still be relative, that way you limit the effort to have external comparision to precise reference sources (as you dont have your own calibrated one) but still know what you get.
Title: Re: Ultra Precision Reference LTZ1000
Post by: rigrunner on May 10, 2017, 11:18:38 pm
I've had the parts to build this for a while and have finally found a little time to put it together.

This board was courtesy of Svangool - thanks Sjef  :-+

I'll find somewhere safe to leave it for a while and let it burn in.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on May 11, 2017, 12:09:19 pm
I've had the parts to build this for a while and have finally found a little time to put it together.

Any reason why you thermally coupled also the 70K resistors other than the divider?
Title: Re: Ultra Precision Reference LTZ1000
Post by: rigrunner on May 11, 2017, 02:27:51 pm
Any reason why you thermally coupled also the 70K resistors other than the divider?

No great rationale other than they are in parallel feeding q1 and q2 on the LTZ and i didn't think it would hurt to couple them.
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on May 23, 2017, 04:37:46 pm
After reading the thread “How do you measure drifts of the order of 1ppm/year?
  https://www.eevblog.com/forum/metrology/how-do-you-measure-drifts-of-the-order-of-1ppmyear/msg1198288/#msg1198288 (https://www.eevblog.com/forum/metrology/how-do-you-measure-drifts-of-the-order-of-1ppmyear/msg1198288/#msg1198288)   I am curious what maximum long-term stability the LTZ1000 really have. The datasheet just say some typical value. If I buy an LTZ1000 from Linear or Digikey what can I expect as maximum drift (with reasonable confidence) if I go for the design in the datasheet but set for 45C with 12k:1k? Assume perfect other components.  Say that I let it be powered for 3 months and calibrate it after that. What will be a reasonable uncertainty spec for 1 year? 1-2-5-10ppm? I can´t find a lot of data for a not selected LTZ1000. DCV standards like Datron 4910 and Fluke 7000 series probably have selected LTZ. Assuming I don´t have the possibility to select my LTZ it would have been nice to have more data from others on non-selected units. Spreadbury´s paper seems to be from a batch of 24 non-selected LTZ but probably from the same batch (and 28 years ago).  As Spreadbury says it seems that every 10 degrees C seems to halve the drift but for me the statistics are to low and I am not sure this rule applies here as little as for voltage references from Analog Devices. If this was true, a reference at 95C would have 32 times higher drift than a reference at 45C. Even from Spreadbury´s paper the variance seems to be high and his data are extrapolated as I understand it. The other paper Dr.Frank mentions by Pickering, Fluke, Metron, etc. I can´t find on the internet.

Another paper I have found and that confuses me due to the large drift of the Fluke 7000 series: In Andrei Pokalitov´s very interesting thesis “Development of National Standard for Voltage Unit Based on Solid-State References” he has followed 10 Fluke 7000-series modules and from what I see the average drift the first year is -2.3ppm (between -1.4 and -3.8ppm/year for a single module) that is far more than the -0.8ppm/year I found in the user manual from Fluke and also the figure Dr.Frank probably refer to in the thread for the LTZ1000 drift. Also the stability specification in the manual is 1.8ppm for 1 year. Even after 3 years the drift Pokatilov saw was in average -1.3ppm/year and the single modules varied between -1.0 and -2.2ppm/year.
After about 1 year one module (Z5) of the ten makes a jump that shifts the average about 0.3ppm so my conclusion is that the LTZ in Z5 made a jump of about 3ppm! In another chart, another module (Z12) seems to make a jump and also shifts drift rate.

So what to believe about LTZ1000 reasonable maximum stability over a year at 45C internal?
What conclusion can I do if I intercompare three newly bought LTZ1000?

Of course I know you can do a lot of other mistakes in the LTZ design but consider only the new bought LTZ. From the above could 5ppm for a year be a reasonable spec (with the same confidence as I see from eg DMM manufacturers) from the above or am I totally wrong?

Lars

Ps. Ok sending out this question only hoping to get a good discussion.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 23, 2017, 07:26:11 pm
Hello Lars,

in the datasheet there is no upper limit for the drift.
And so it is not predictable for a single device.

They cannot look at the purity / crystal defects of every
single device which might influence the ageing.

As I observe increasing popcorn noise on newer devices (references)
it might also be that after the tsunami in Japan (Tepco)
the puirty of silicon is no longer the same.
It might of course also be that I now have better instruments to detect popcorn noise.

And final even when you have built the LTZ you never know if the drift itself will be stable or even decreasing.
Each "event" like (temperature) shock or short cirquit might start a new ageing cycle with different ageing speed.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 23, 2017, 07:55:26 pm
Andreas, most of the wafer silicon comes from Wacker Chemie, very probably outside Japan. Wafer production also should not have any conjunction to the Japanese Tsunami and Earthquakes.
LTZ1000 production is in California, so also no connection.
It's always possible, that one batch is bad, but that's old, large analogue structures, so not that probable.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 23, 2017, 07:59:44 pm
Hello Frank,

afaik there are only 3 large scale producers on the world for single crystal silicon.
one in Japan
one in the US
and of course Wacker Chemie in Burghausen.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on May 23, 2017, 08:17:50 pm
Doubling the drift rate every 10 K of higher temperature is a rough rule of thumb for many thermally activated processes (also works for biological processes like milk getting old). However I am not to sure if it actually 10 K for the LTZ1000, it could be 7 K or 12 K for doubling. In addition the initial phase can be a superposition of effects going up and down and partially compensating. So it might be a good idea to have some burn in, so that only the slowest process is dominating. After that there should be drift in one direction only if there are not other processes coming in (like radiation damage, hysteresis form temperature cycle).

A low temperature also slows down this initial burn in - so it is a 2 sided thing to go for only 45 C. So it might even be better to do a 2 (or more) step burn in: first at a higher temperature and only after that at the final temperature.

As there is a certain chance to get a bad reference, it is difficult to give an upper limit on drift / stability without an individual test / burn in. The chances are low, but there are a few bad ones, that are not detected at the manufacturer. So without an individual test, there will be a few outliers. Not sure about the fractions accepted by DMM manufacturers, but I would expect tighter specs there. The lower temperature will only improve long time drift, but not the chance for rare outliers. It might even make it slower to find a bad one and it slows down the initial burn in.

Even with tested good samples, it really helps to wait for after the initial burn in. Especially the very first part (e.g. first 100 hours)  is not that well defined. Often testing would include that initial burn in phase anyway.

Chances get much better to guarantee a certain limit if 2 refs are used and compared. With 2 refs one should be able to detect any sudden jumps (that will not happen in both) and it is also very unlikely that 2 units will have the same unusually high drift rate. So those rare bad units could be detected with a good certainty at least (one still does not know which unit is bad), but at least is warned to need recalibration.

Comparing 3 units over a reasonable time should give an indication if there a bad ref and which one i would likely be. However there is little to tell about the final long term drift (e.g. years 2-..), as chances are that the units will show a similar long term drift. Only with different temperatures there might be something, but likely not enough statistics.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on May 24, 2017, 02:45:23 pm
The ball park 10K for an increase of 2 in aging is driven essentially by the Arrhenius law. Details on the web. However, re. the Fluke 7000, the drift is not only given by the LTZ1000, but also by the gain-defining amplifiers in the amp stage. Vishay non-hermetic resistors have been used here, and these seem to be higher drift than the hermetic foil or WW resistors one could use (and Fluke used elsewhere on their non-Wavetek references) , even though due to statistical (distribution of drift rates over several resistors) the demonsstrated drift is less than one would expect from a single resistor of the type used (the spec value is actually not that good; there are better non-hermetic resistors available than the one used; on paper at least).
Title: Re: Ultra Precision Reference LTZ1000
Post by: rigrunner on May 30, 2017, 11:51:57 pm
My LTZ has been powered on for > 350 hours now so time to log some data and see how it is doing.
Logging is with Datron 1271 on 10V range set to 8.5 digits resolution, one measurement taken every 30 seconds.
LTZ is powered at 15V from a basic 7815 supply.



Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on June 03, 2017, 04:09:22 am
LTZ1000 non A chip microscope images

I had an old LTZ1000 chip that I knew I would not use so I sacrificed if for the advancement of our knowledge.

It uses a similar air entrained epoxy as the LTZ1000A. This must be a low stress attachment. I believe DiligentMinds noted that the LTZ1000A has an extra thermal interface material under the chip.

In the images you can see that the LTZ1000A sits higher above the TO-5 header than the LTZ1000 chip.
The chip was very clean and we had a good microscope so we took a few images.
There is a little detail inside the Super Zener symbol I had not noticed before.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on June 03, 2017, 04:16:53 am
More fun with a microscope and a digital camera.
LT1088
The LT1088 True RMS sensor uses a similar chip to the LTZ1000. The hermetic package will open cleanly with a 200 watt soldering iron applied to the lid.
The LT1088 operation is detailed in Linear Technology Application note 22.

With the lid off you can clearly see the two chips with the OTT die attachment process.
Extra credit for the person who identifies the very special lens used for the “LT1088 hermetic package.jpg” image.
The die has heater rings that are similar to the LTZ1000. It uses 4 of the 8 transistors (diodes) in the middle of the die to sense die temperature. It does not look like there is a Zener in the middle of the die.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Muxr on June 03, 2017, 04:29:18 am
Great photos. I want that machine they use for attaching pins to the die. Imagine the dead bug possibilities!
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on June 03, 2017, 05:08:12 am
If you used a 16 pin ceramic package similar to this you would have space for an LTZ1000 die (if you could get one), a LT1013 die and a Vishay MTR hybrid resistor network. Now your entire LTZ1000 system is in a hermetically sealed package. It would only cost you a few thousand per package! And you could regulate the package temperature with a TEC for minimum power.

But then there would be nothing left to tweak. What's the fun in that?

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on June 03, 2017, 11:51:34 am
This ceramic packages are available of the shelf, no problem. LT1013-Die is available at least at Texas Instruments... LTZ1000 is somewhat more difficult to get as bare die at least in small quantities. So maybe you have to buy a complete wafer.
However, this is only half of the truth. The more expensive part is the assembly, the die attachement and the developement of the processes and their installations. Nothing you would do with manuel pick and place apparatus or bonding machines.
At the end of the process you need to solder the metal cap to the ceramic package using vacuum and/or inert gas and AuSn solder preforms. Additional costs are for the tools.

Conclusion: Interesting way to go, but not worth the money you have to invest unless you have a big budget and no other idea how to spend it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on June 03, 2017, 12:38:04 pm
Thank you, chuckb, for great LT1088 teardown. Probably they used same or similar process when making LTZs, LT1088s. I wanted to play with that chip for a while already, but not managed to find resources yet.

Hermetic packages for LTZ ref, even while it make no financial sense (probably running cost of such project is more than getting LHe PVJS), at least we can have great fun speculating about it.

On more practical note, I travelled with one of my LTZ1000CH based modules to a friend, and reference output of the module was within -0.8ppm of my measurement average after 1 month of 24/7 operation. Measurement was taken by friend's 3458A, which I got repaired and calibrated (https://www.eevblog.com/forum/metrology/repair-yes-another-little-3458a-repair-log/) to my references last year November. So even with quick setup it was reassuring to see <2ppm data from different references on term of 8 months. But the interesting thing was once I connected Fluke 8846A parallel to 3458A and LTZ output, readings jumped to down -16ppm! All usual settings were done on meter, manual 10V range, NPLC100, High-Z input impedance. Even switching 8846A input terminals to rear (essentially disconnecting LTZ from input) still corrupted output at -11ppm. Huh? Only hard power off with rear mechanical switch "fixed" the output back to expected level.

Connecting 34401A in parallel with exact same cables powered from same mains breaker did not change LTZ output even a ppm. Same with my K2002, no effect. Only 8846A caused this. LTZ module was powered by battery at all times. So another thing to watch out hooking multiple DMMs to direct zener output without buffering.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on June 05, 2017, 11:54:22 am
Volt-nut candies has arrived.

In case somebody forgot how genuine LTZ reference looks like, here the close-ups.

(https://xdevs.com/doc/xDevs.com/KX/REFX/ltzc_1.jpg) (https://xdevs.com/doc/xDevs.com/KX/REFX/ltzc.jpg) (https://xdevs.com/doc/xDevs.com/KX/REFX/ltzd_1.jpg) (https://xdevs.com/doc/xDevs.com/KX/REFX/ltzd.jpg)

Bonus shot, compared to LTZ1000CH from 1990:

(https://xdevs.com/doc/xDevs.com/KX/REFX/ltze_1.jpg) (https://xdevs.com/doc/xDevs.com/KX/REFX/ltze.jpg) (https://xdevs.com/doc/xDevs.com/KX/REFX/ltzf_1.jpg) (https://xdevs.com/doc/xDevs.com/KX/REFX/ltzf.jpg)

P.S. No problems ordering just 2pcs qty each type directly from LTC website ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on June 13, 2017, 02:23:19 am
Extra credit for the person who identifies the very special lens used for the “LT1088 hermetic package.jpg” image.
The 1X in the lower right corner was supplied by the 200mm f/5.6 Medical Nikkor lens. It's a slick lens with a built in ring flash.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on June 13, 2017, 04:13:53 am
Extra credit for the person who identifies the very special lens used for the “LT1088 hermetic package.jpg” image.
The 1X in the lower right corner was supplied by the 200mm f/5.6 Medical Nikkor lens. It's a slick lens with a built in ring flash.

That's a nice lens.  :-+ I was looking to buy one few years ago, but they still fetch pretty penny, so I stay happy with my Sigma 150mm f/2.8 macro.
Title: Re: Ultra Precision Reference LTZ1000
Post by: borghese on June 21, 2017, 03:35:49 pm
I'm going to make my first LTZ based board. Has anyone
tried the thermal performance with board thickness 32mil and copper weight of 2 oz? What is your opinion?
Best regards
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on June 21, 2017, 04:01:35 pm
There is a limited advantage in having a thicker Cu in getting the ring more effective. However it would need even thinner lines to bring the signals out.  Usually the layout should be in a way that wire / board trace resistance should not be significant.
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on June 22, 2017, 12:41:56 pm
Does anyone ground the metal can of the LTZ? 
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on June 22, 2017, 01:58:53 pm
I have guard pour on my board, however, its not connected to the can.
Title: Re: Ultra Precision Reference LTZ1000
Post by: schmitt trigger on June 22, 2017, 02:21:39 pm
Chuck;
thanks for the naked-IC-porn photos!  ^-^

It definitively shows that you have substantial experience in the field.

To me these photos epitomize the Linear Tech spirit: an extreme attention to the most minute details, to obtain the very best analog performance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on June 30, 2017, 09:52:58 pm
I had stability problems with my LTZ1000 build so I thought I'd do some long-term data logging and see if it settled down.  I initially decided to monitor it with both meter and data logger.  Here are the results.  Both set for 100 PLC.  Temperature is from a LM35 sensor that sits 2cm above the aluminum case that holds the LTZ1000 (and provides ~1.5K additional heating above true ambient).   All I can say is Keysight sure doesn't make meters like HP did!(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=328198;image)
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on July 01, 2017, 04:06:04 am
Good information. I love my 34970a.
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on July 01, 2017, 10:08:52 pm
I guess this is a good example of what people have said in this thread:  You can't use a meter with a '399 voltage reference to measure the performance of a LTZ1000.   I'm just surprised the 34465a made such a good thermometer!  Even when temperature is stable between the 16 - 21 hour mark, there's a great deal of noise that made me wonder if my LTZ1000 was operating correctly.  But in view of the 34970a measurements, it seems fine.

Do others with 6.5 digit meters experience similar issues?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on July 02, 2017, 01:56:55 pm
I guess this is a good example of what people have said in this thread:  You can't use a meter with a '399 voltage reference to measure the performance of a LTZ1000.   I'm just surprised the 34465a made such a good thermometer!  Even when temperature is stable between the 16 - 21 hour mark, there's a great deal of noise that made me wonder if my LTZ1000 was operating correctly.  But in view of the 34970a measurements, it seems fine.

Do others with 6.5 digit meters experience similar issues?

What issue do you mean?
I think you let yourself fool by the different visual appearances of both graphs, which are at first differently formatted, e.g. the thicker line width for the 34970A.
Then, both instruments feature different resolutions over GPIB, i.e. 100nV for the 34465A, and 1uV only for the 34970A.
If you look closer at the short-term noise, the 34465A varies about 3uVpp, and so does the 34390A. The finer resolution of the 465A gives a more fluttery appearance.

Also, the time resolution of the 34490A measurement seems to be much lower, than the 34465As, maybe there's an additional running-average filter, which additionally reduces the apparent noise.

I made a comparison between the 34465A, 34470A and the 3458A, using a stable 10V reference (5442A), equivalent to the LTZ1000:
https://www.eevblog.com/forum/testgear/keysight's-new-34465a-(6-5-digit)-and-34470a-(7-5-digit)-bench-multimeters/msg889217/#msg889217 (https://www.eevblog.com/forum/testgear/keysight's-new-34465a-(6-5-digit)-and-34470a-(7-5-digit)-bench-multimeters/msg889217/#msg889217)

which indicates, that concerning noise, the 34470A performs similar to the 3458A, only due to the LTZ1000A based references, whereas the 34465A (which has identical hardware as the '470A, otherwise), shows more noise due to its LM399 reference.

Latter is valid for all LM399 based DMMs, as the 34401A and your 34390, which share the identical DMM circuit.
The 34465A/470A are very similar to, or based on the 34410/411 design. (Same Multislope IV architecture, many identical crucial components)

Therefore, the Keysight instrument are very probably made as good as under the former brands.


In the end, you made a trivial conclusion, that you can't really evaluate an LTZ1000 by an LM399 based instrument, that applies to to your 34970A as well.

You did not describe, how you have set up your instruments. The temperature sensor measures the LTZ1000s temperature, but obviously neither the real room temperature, nor the instruments individual temperatures.
Probably, you have stacked them, 34465A on top of the 34970A, so that the 465A is heated additionally by the 970A.
Both instruments are specified to have a T.C. of about 5ppm/°C. So the change of 10uV or 1.4 ppm for the 34465A, in face of the 2°C change RT (?) change, or much more, if you really stacked the instruments, is very well inside specification.

That might explain the seemingly better temperature stability of the 34970A.
Therefore you should have a better / more temperature stable experimental setup, before you draw the wrong conclusions.

Btw.: I also measured the 16h stability and noise of my 34401A, using the same 10V reference. That looks quite similar to your measurements on the 34970A:
https://www.eevblog.com/forum/testgear/hp34401-measurement-of-linearity/msg358701/#msg358701 (https://www.eevblog.com/forum/testgear/hp34401-measurement-of-linearity/msg358701/#msg358701)

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: HighVoltage on July 02, 2017, 09:07:08 pm
I had stability problems with my LTZ1000 build so I thought I'd do some long-term data logging and see if it settled down.  I initially decided to monitor it with both meter and data logger.  Here are the results.  Both set for 100 PLC.  Temperature is from a LM35 sensor that sits 2cm above the aluminum case that holds the LTZ1000 (and provides ~1.5K additional heating above true ambient).   All I can say is Keysight sure doesn't make meters like HP did!

What cables did you use to connect the 34465A and the 34970A
Picture please of your setup?
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on July 03, 2017, 09:58:35 pm
Thank you Dr. Frank for your comments.
There are indeed two data sets acquired simultaneously and later imported and manipulated within Excel.  34465A data was free-running (auto-zero ON, NPLC = 100) while the 34970A Data Acquisition unit was scanning ~30 channels every two minutes with a two second delay after each relay switch event.  34970A also set to 100 NPLC.  Data records may also have ~60 seconds of time skew as the meters were started and stopped manually and normalized to the same time scale within Excel.  And yes, I did thin the 34465A lines and add a data point so I could could try and understand if 34465 apparent finer resolution was an artifact of internal meter filtering or true ADC step size.

I agree I was somewhat fooled by the higher sample rate and resolution of the 34465A.  During the period of steady temperature, I took this to be purely noise whereas the 34970A data looked to be the expected bit toggling when the measured value is near the threshold of an ADC step; superimposed noise being on order of 1 uV.

By way of background, my initial LTZ1000 build was with LTC2057 choppers and I had noise, drift, and jumps in output voltage.  Adding capacitors all over the place seemed to help, but when I'd run simulations with the added capacitors, loop stability was compromised to the point where I couldn't understand why physical hardware didn't break into oscillation.  I then replaced LTC2057's with LT1677's (I didn't know about the LT1006 at the time).  That made a huge difference in noise but I still had the drift and jumps in output voltage like the 34465A plot I originally posted.

I was therefore astonished when I collected the 34970A data-  Voltage jumps are gone.  Voltage drift highly correlated with temperature gone.   Perhaps I drew the wrong conclusion?  Attached are pictures of meter setup and connections to LTZ.  34970A connections are soldered to shielded Cat-6 cables (1 nF capacitor feed-thru's into boxs - there are two LTZ's side-by-side).  Temperature sensor is black TO-92 over left box.  34465A are EX-hook to RG-58 coax in Test Setup photo.   I originally stacked the 34465A on top of the 34970A with a 5 cm space between, but every now and then I'd get voltage "spikes" in the 34465A data which I correlated to relay switching events within the 34970A, so I moved them apart.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on July 04, 2017, 10:40:07 am
Thank you Dr. Frank for your comments.
There are indeed two data sets acquired simultaneously and later imported and manipulated within Excel.  34465A data was free-running (auto-zero ON, NPLC = 100) while the 34970A Data Acquisition unit was scanning ~30 channels every two minutes with a two second delay after each relay switch event.  34970A also set to 100 NPLC.  Data records may also have ~60 seconds of time skew as the meters were started and stopped manually and normalized to the same time scale within Excel.  And yes, I did thin the 34465A lines and add a data point so I could could try and understand if 34465 apparent finer resolution was an artifact of internal meter filtering or true ADC step size.

I agree I was somewhat fooled by the higher sample rate and resolution of the 34465A.  During the period of steady temperature, I took this to be purely noise whereas the 34970A data looked to be the expected bit toggling when the measured value is near the threshold of an ADC step; superimposed noise being on order of 1 uV.

By way of background, my initial LTZ1000 build was with LTC2057 choppers and I had noise, drift, and jumps in output voltage.  Adding capacitors all over the place seemed to help, but when I'd run simulations with the added capacitors, loop stability was compromised to the point where I couldn't understand why physical hardware didn't break into oscillation.  I then replaced LTC2057's with LT1677's (I didn't know about the LT1006 at the time).  That made a huge difference in noise but I still had the drift and jumps in output voltage like the 34465A plot I originally posted.

I was therefore astonished when I collected the 34970A data-  Voltage jumps are gone.  Voltage drift highly correlated with temperature gone.   Perhaps I drew the wrong conclusion?  Attached are pictures of meter setup and connections to LTZ.  34970A connections are soldered to shielded Cat-6 cables (1 nF capacitor feed-thru's into boxs - there are two LTZ's side-by-side).  Temperature sensor is black TO-92 over left box.  34465A are EX-hook to RG-58 coax in Test Setup photo.   I originally stacked the 34465A on top of the 34970A with a 5 cm space between, but every now and then I'd get voltage "spikes" in the 34465A data which I correlated to relay switching events within the 34970A, so I moved them apart.

Sorry to say, but your setup is really a mess, especially in aspect of low thermal voltage connections.
No wonder you're measuring this temperature dependent voltage on the 34465A, that is probably not the instruments T.C., but the e.m.f. of these totally inappropriate clamps, in comparison to the twisted pair soldered Cu cables which are used for the 34970A. You may at first also use soldered, twisted pair Cu cable for connection the 34465A.
These feed-through capacitors used as the voltage output of the reference are also not the best pick for low e.m.f.

Please replace all of that stuff with good CuTe jacks, where you have the choice of connecting with good cables (Cu with Au plated connectors) towards the 34465A, or clamping blank Cu cables with the jacks' screws.
I even had big problems on my analogue / DC precision measurements with my (10 times more stable) 3458A, when room temperature changed a few °C, so I moved the whole lab down to the basement.
Only there, at about 0.1°C stable environmental temperature, I was able to make measurements in the sub-ppm region, as you tried to do here, also.

Check for switch mode PSUs in your room, these mostly create these spikes you're seeing.
Use the additional capacitors from Andreas design, which requires an additional bodge at one point for stability.
 Adding only two 100nF capacitors, in parallel to the 120 and 1k precision resistor already improved my old LTZ reference greatly.

The shielding by your boxes looks nicely, but is probably not effective, as the external disturbances enter either via the supply, or the output. Both sides are not appropriately connected to any guard, as your PSU, as well as your DMMs don't have a guard. Maybe connecting to ground may help a bit, but in the end, that shielding is mostly useless, compared to the effects of e.mf. generation.

So I recommend that you at first completely revise your assembly before attempting to make precision measurements.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 04, 2017, 07:11:10 pm

 Adding only two 100nF capacitors, in parallel to the 120 and 1k precision resistor already improved my old LTZ reference greatly.


Hello,

of course you get the best benefit of those 2 capacitors when soldering directly to the corresponding (base+emitter) pins of the LTZ1000.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on July 06, 2017, 10:25:46 am
Dr. Frank-  I soldered Cat-6 to LTZ proto and screwed meter end into Gold dual banana and wrapped meter side with rag.  I'll admit, it's a bit quieter but I also severed the connection to six AD588's under test (Al enclosure at back left of my previous post attachment).  See picture attached present meter connection and LTZ readings following temperature quite nicely.  I further plan to 1) put a LM35 in the banana socket of the 34465A connector to read meter ambient temperature and 2) surround LTX prototypes with copper and aluminum plates for supplemental RF and thermal shielding.  Stay tuned for results...

A few things I forgot to mention before:
* Thanks for pointing me to your excellent review of the then new Keysight meters
* I've looked at and agree my 34465A is within spec assuming the "Non ACAL Temp Coeff" applied within +/- 2C (see Note 7 Keysight datasheet)

Please explain why capacitor feed-thrus are bad from emf viewpoint.  I admit to having a RF-noisy shop.  Even turning on the Hakko soldering iron will cause a noticeable shift of measured voltage (uV to 10'2 of uV).  These feed-thrus are directly soldered to PCB inside enclosure and are mounted upon a (hopefully) isothermal aluminum cover plate.  Surely this is better than standard connectors whose pins are held by plastic.  And unlike standard connectors, feed-thrus provide double-digit attenuation above 10 MHz (assumed 50 Ohm measurement).  What do you recommend?  CuTe jacks will have far greater RF leakage into the metal box.

Regarding shielding, left LTZ is powered by analog rectified and LM317-based regulator in its own metal box about a meter away.  It's shielded cable is tied to its box which is connected to PE (Earth) of the AC mains.  That's why the shield wire is pulled aside on the LTZ end (to eliminate ground loop).  The right LTZ proto is powered via black jack from battery with linear PSU keeping battery in float condition.   Right LTZ also has BNC jacks for zener voltage measurement whereby the shields of the coax were actively driven at guard voltage.  Because I didn't have Triax cable to meter, this picked up noise and was abandoned.  Therefore each LTZ has separate floating supply.  Ground of each LTZ has single-point connection to case.  Case is connected to shields of Cat-6 cable back to data logger where shields are tied to the PE screw of the 34970A data logger.  All voltage measurements are differential via twisted-pairs within Cat-6 cable.

Regarding 100nF capacitors, my SPICE analysis shows this compromises phase margin.  See attached where the Green traces depict the Bode Plot amplitude and phase of the Zener side of the regulator.   Note gain peaking of LTZ transistor stage at 550 kHz (red trace) with 100nF B-E capacitor.  I 'll show analysis circuit in another post (getting late).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on July 06, 2017, 03:36:45 pm
The feedthrough caps use ceramics and often a kind of kovar alloy to avoid high thermal mismatch. However these kovar like alloys tend to have a relatively high sebecke coefficient and thus higher thermal EMF. However it depends on the thermal design around the caps. There are 2 ways to avoid large errors: one is thermal coupling to the case on both sides (inside and also outside). The other is having a symmetric design, thus having a similar design for the Ref. GND too.

For the power supply the caps are a good idea.

Depending on the LTZ1000 circuit used, the circuit might not like to much capacitance at the output.
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on July 06, 2017, 06:03:21 pm
Thanks, Kleinstein.  Since these are just resin sealed, not hermetically sealed, I thought lead to be just tinned copper wire.  But I can't find this specified on the product page or in their brochures at http://eis.apitech.com/resin-sealed-bolt-in-filters.aspx (http://eis.apitech.com/resin-sealed-bolt-in-filters.aspx)   How could I tell for sure?
(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=329628)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on July 06, 2017, 07:16:13 pm
One could check for thermal EMF, when creating a thermal gradient around the feed through. So solder blank copper wired to both ends and measure the voltage. Than use something like the fingers or a soldering iron to create thermal gradients at the feed through. If it is copper only, there should be only a low voltage of maybe a few 10 µV. With a different material and some 10 K temperature difference it would be more in the 100-400 µV range.

Even with just copper (or other wires for thermocouples) wires one sometimes checks them, by moving a hot spot along the wire.  With a sensitive meter one could even detect areas that a more heavily bend than other (annealed) wire.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on July 06, 2017, 07:17:10 pm
A magnet will quickly inform you if the lead material is KOVAR.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on July 06, 2017, 07:46:31 pm


Please explain why capacitor feed-thrus are bad from emf viewpoint.  I admit to having a RF-noisy shop.  Even turning on the Hakko soldering iron will cause a noticeable shift of measured voltage (uV to 10'2 of uV).  These feed-thrus are directly soldered to PCB inside enclosure and are mounted upon a (hopefully) isothermal aluminum cover plate.  Surely this is better than standard connectors whose pins are held by plastic.  And unlike standard connectors, feed-thrus provide double-digit attenuation above 10 MHz (assumed 50 Ohm measurement).  What do you recommend?  CuTe jacks will have far greater RF leakage into the metal box.

Regarding shielding, left LTZ is powered by analog rectified and LM317-based regulator in its own metal box about a meter away.  It's shielded cable is tied to its box which is connected to PE (Earth) of the AC mains.  That's why the shield wire is pulled aside on the LTZ end (to eliminate ground loop).  The right LTZ proto is powered via black jack from battery with linear PSU keeping battery in float condition.   Right LTZ also has BNC jacks for zener voltage measurement whereby the shields of the coax were actively driven at guard voltage.  Because I didn't have Triax cable to meter, this picked up noise and was abandoned.  Therefore each LTZ has separate floating supply.  Ground of each LTZ has single-point connection to case.  Case is connected to shields of Cat-6 cable back to data logger where shields are tied to the PE screw of the 34970A data logger.  All voltage measurements are differential via twisted-pairs within Cat-6 cable.

Regarding 100nF capacitors, my SPICE analysis shows this compromises phase margin.  See attached where the Green traces depict the Bode Plot amplitude and phase of the Zener side of the regulator.   Note gain peaking of LTZ transistor stage at 550 kHz (red trace) with 100nF B-E capacitor.  I 'll show analysis circuit in another post (getting late).

Kleinstein already answered this question.
There are simply too many probable dissimilar metals and too many junctions involved.. better keep it simple, so not to loose the overview over the signal path.
Have a look in the LTZ 1000 datasheet, or the National Semiconductor application note for the LM199, both warn explicitly of thermal junctions, and simply to reduce the number of junctions.. that is the biggest problem in your setup.

Frankly speaking, I'm completely confused about your CAT 6 cable in series with the feed through capacitors plus clamped jacks, and so on.
Clamping the wrong metals, or oxydized metals also makes nice unpredictable thermocouples.


If think hat you have put too much focus on the shielding in comparison to e.m.f.s, that's true also for the absolute values of the different disturbance voltages.

I have seen similar shifts as you, then I used a big ferrite on the externally located DC supply cables, then these two 100nF, at least, maybe a simple grounding of the metal case, and now, no shift any more, even a switch mode LED light creates only minute changes on the the order of one ppm, instead of several ten ppm.
Maybe it's no good idea to ground the supply directly to mains earth. (I don't that, neither)

That's all a bit of vodoo, and fiddling around with the shielding (also keep it simple) , until the reference was nearly immune against RF or mains spikes.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on July 08, 2017, 02:45:08 pm
A magnet will quickly inform you if the lead material is KOVAR.
Thanks for the tip!  For the 1nF capacitor-only feedthroughs I'm using, there is NO magnetic attraction.  And when I scrape the leads, I see the Cu color.  With a LC type, the magnet IS attracted to the body, but not the leads.  I suspect magnet was attracted to ferrite bead inside, but it could also have been the ceramic capacitor.  High-K ceramic capacitors (Type II & III) are ferromagnetic.   They also have piezoelectric and microphonic characteristics which could superimpose noise onto the reference output.   So if you want to use these bolt-in filters to keep RF out of your LTZ, make sure it has a (Type I) low-value NPO or COG capacitor within.
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on July 08, 2017, 11:23:10 pm
Regarding 100nF capacitors, my SPICE analysis shows this compromises phase margin.  See attached where the Green traces depict the Bode Plot amplitude and phase of the Zener side of the regulator.   Note gain peaking of LTZ transistor stage at 550 kHz (red trace) with 100nF B-E capacitor.  I 'll show analysis circuit in another post (getting late).
I take this comment back.  If one uses a 22nF capacitor on Pin 5 to Ground instead of the 2nF shown in the Positive Reference Circuit on Page 6 of the data sheet, the current regulator loop crosses over much lower at 25 kHz and results in plenty of gain and phase margin against the effects of the 100nF B-E capacitor.  OK, now that I understand this, I'll try it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on July 09, 2017, 08:59:42 am
A large capacitor at the OPs input to GND can compromise the higher frequency noise. Some of the data-sheet circuits use 22 nF, some use 2 nF. Form the higher frequency noise performance I would prefer the smaller capacitor. In the low frequency range the lower transistor noise is effective instead of that of the OP.

A capacitor at the transistor B-E is aimed against RF noise - so even smaller than 100 nF capacitors should have a significant effect - so 1 nF could be enough. In addition to lowering phase reserve the capacitor could also increase the higher frequency noise. Even if not oscillating poor phase reserve can amplify some of the OPs noise. An extra cap in parallel to the zener might help to compensate for some of the negative effects. Usually the better way would be to keep out RF signal at the first place. So have a RF tight case and proper filtering at the supply and some (e.g. ferrite beat) at the output.

In the original circuit also capacitive loading to the output is a possible problem and this problem can add to the effect of the capacitor at the transistor. So an additional cap at the transistor is expected to make the circuit more sensitive to capacitive loading.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Vtile on July 11, 2017, 04:20:05 pm
It is propably mentioned and maybe even analysed in many times in this enormaus 80-pages thread. How good is LTZ1000s stability without the inbuild heater unit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 11, 2017, 07:06:53 pm
around 50 ppm/deg C (with the standard datasheet cirquit)
with a extra resistor you can get somewhat better.
Title: Re: Ultra Precision Reference LTZ1000
Post by: orin on July 12, 2017, 05:07:11 am
FWIW:

I got the PCB from OSHPark (SvanGool version) and built one up with Edwin Pettis's resistors.

I dialed in my Fluke 343A (which is nowhere near as stable) to match the LTZ output and recorded the difference for 60 hours or so on an Agilent 34461A.  Resulting screenshot is attached.

Enjoy.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 12, 2017, 05:32:05 am
Hello,

You will need more references to decide if its the 343 or the 34461A which is drifting ...

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: orin on July 12, 2017, 06:05:04 am
Hello,

You will need more references to decide if its the 343 or the 34461A which is drifting ...

with best regards

Andreas


It's about what I'd expect for the 343A.  It was only spec'd to 3ppm/deg C.

I'm more concerned with eliminating the glitches which are likely RFI from WIFI or cellphones.
Title: Re: Ultra Precision Reference LTZ1000
Post by: VK5RC on July 29, 2017, 11:27:20 am
Beginnings of an experiment with several LTZs (x6)
- TiNs Kx boards - OshPark vB03 - thanks TiN (and SvanGool for uploading)
- Foam lined metal boxes x2 - metal (grounded) dividers between each reference (hard to see in pictures)
- Each reference has own linear low noise PSU 18v to 15V, TPS7A4901 regulator, linear PSU in metal box hard against reference metal box
- LM7805 supply for temp sensors
- 18V supply from linear LM7818 supply - transformer at some distance ~1m.
- LTZ1000. four As. , two Cs,  one of the C from 1990 from a fellow Aus volt-nut (retired) EEVbloger - Thanks lowimpendance
- Mostly TE UPW50 resistors - one set of Mr Pettis'
- Op Amps  LT1006 x4 ,  LT 2057 x2
- Terminals, Pomona 3770
- cabling twisted solid core copper, ferrite on LTZ output wires (Wurth)
- LTZ mounted low and flush to the board - foam only supports for the boards - see TiNs results with one of my other LTZ references.

Currently they are settling in - the more I look the more I find EMI is a very significant issue.
EMI culprits identified to date
 - LED light transformer (SMPSU - the work of the devil!!)
 - Uniteruptable AC power supply (also SMPSU) supplying the DC power supply.
 - most of my lab other gear, even an HP E3644A - connecting a laptop-GPIB (Prologix) - esp if mains powered.

In the next month or so I hope to investigate this to get some data to guide correction.

I find that all of this gear appears to Lower the readings displayed by the 3458, some as much as 60uV . I have not found any interference that 'raises' the  voltage as displayed.

I would be interested to hear if others have similar findings.

PS Later when in 'serious' use  - boxes will be further thermally insulated.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 29, 2017, 03:44:42 pm

I find that all of this gear appears to Lower the readings displayed by the 3458, some as much as 60uV . I have not found any interference that 'raises' the  voltage as displayed.

I would be interested to hear if others have similar findings.

Hello,

yes that is typical for EMI.
The reason is that the EMI is rectified on the input/output protection diodes and thus gives a negative offset.

As I knew this already before from my LM399 references I did already some countermeasures on my first design.
(Battery supply to keep mains line EMI out and output filtering).

But obviously not enough so I had to fix this in the 2nd revision: (Caution R19 is needed to avoid oscillating).
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=52101 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=52101)

(later improvements are mainly thermal management + different resistors).

In my case the USB cables for my ADCs are the main EMI source.
It also helps somewhat if you place all your gear on a metal plate.

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on July 31, 2017, 01:11:54 am
VK5RC,
Yes, you found out exactly what happens when measuring low ppm, and I've written about this many times.  No switcher power supply nearby, no motors, no clicking unshielded relays / solenoids, no nearby RF transmitters (WiFi, cell phones, bluetooth etc), no PWM LED lights, try to minimize any AZ chopper op-amps (or add serious bypass and shielding - watch out for chopper freq noise on power rails), even no DMM for some measures - that's why we keep a fleet of analog null meters in the cal room when nulling to 732's + KVD - that will give you less error band than a single 3458a.  That's also why we switch over to 24V battery bus halogen incand. or DC LED lighting when going after best quality measure.  Halogen incandescent emit some IR, but much better color index than LED's of course.   We have several DC halogen lamps with cold (IR trap) filters that get a lot of use, and only use halogen + cold fiber illuminators on the microscopes and cameras (LED's don't have the color rendering quality we need for wafer test & inspection).  The concept here is you try not to generate thermal noise or thermal / photo oscillators with your pure DC lighting.   And you certainly don't shine a PWM-flickering LED lamp at your circuit when trying to get a voltage measure...You find out what parts are photo-sensitive to that PWM freq.

If you're in a clean room you make sure all the ground straps are in place on the Tyvek butterball suit, and test that every time you step out of the airlock.  Of course the table, floor and walls are anti-static, and generally we keep the area right at 60~65% RH (micro-misters overhead supplied with DI water) and generally 20°C in the cal & testing rooms, but it may get warmer on the production floor.  Anti-Stat generator fans of course but not too close to the DUT, and those are shut down just before testing starts.

Don't forget what's on the other side of the walls also.  We keep a clear area of about 15'~ 20' all directions from DUT (incl. above and below), and isolated grounds.  Fiber only for command / control, avoid all USB connections even if isolated.  Typically inner room test area has has steel + copper screen liner and shields most external RF.

It's also handy to have a supply of extra Mu-metal and copper shielding foil on hand for difficult setups.

You can't over-do keeping your test area quiet.  Every PN junction in your precision circuit wants to become a radio  or photo or mechanical stress receiver / rectifier at the worst time.
Title: Re: Ultra Precision Reference LTZ1000
Post by: VK5RC on July 31, 2017, 12:23:58 pm
Thanks Andreas and MisterDiodes,
I have had just a little experience with EMI with my Amateur radio work - but they are generally far less sensitive.
I thought I had sorted ground issues - mmmmmm. I am not sure I can come at my 'volt-nuttery' having its own room at home.
Re 'EMI' from light/heat sources ; in preparation for Earth Moon Earth contact (on hold at present) I built a G4DDK Ultra low noise pre-amp for 1.2GHz (~0.3dB NF 37dB gain) and was able to measure the RF (at 1.2GHz) noise differences from 'cold sky' to a 'warm' tree nearby and to the sun and was within 0.5dB of what I should have measured (by calculation)
Thanks again for the advice and direction.
Robert
Title: Re: Ultra Precision Reference LTZ1000
Post by: Do Ma on August 22, 2017, 09:26:08 am
Hey all.
I want to built up a LTZ1000 reference with 16 LTZ1000 modules. The single LTZ1000 modules (the pcb design for this I do myself) works fine . But i got a tempco problem when I connect the moduls parallel. ( Connect them to sum point with a 100Ohm Vishay Resistor. I check the noise with 2 modules and I see the noise is going down 1/sqrt(n) (measurement with Fluke8508A 8 1/2digits)
Have somebody experience with this parallel connecting?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 22, 2017, 11:10:38 am
Welcome to forum, that is a very solid first post.  ^-^

I had no problems with 2 modules when I tried, however used higher value resistor (VHD100 10K+10K) and voltage of my modules were close (~40 uV apart).
What exactly issue you have, can share more details? Also blockdiagram of all connections and perhaps few photos would be great illustration.

Did you check for ground loops and power supply connections? Since you can't have direct zener kelvin connection in such setup, unwanted thermocouple junctions could be included as result, visible as "excessive tempco" at your DMM.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 22, 2017, 01:03:33 pm
Keithley 2000 is reading temperature sensor? Hard to guess anything from the graph photo, other than something is terribly wrong :). Meter GPIB 3 shows -5.5ppm deviation, and meter GPIB 4 shows almost -10ppm deviation. That tells me grounding/current loops/connection issues.

Zener voltage reading by SMA connectors? SMA is not good for low thermals, as connector package is usually gold plated brass. You want only copper/copper connections with minimal amount of junctions (best is single twisted wire direct from zener to DMM binding posts) to get accurate microvolt-level measurements.

Also I can't see which resistors are used. You want 13K/1K and 120R to be most stable.
What is your single module measured tempco? Should be better than 0.1ppm/K for properly working reference.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Do Ma on August 22, 2017, 01:12:12 pm
Yes I think it is the grounding too but how to realize that with 16 moduls.
The single modul tempco is lower than 0.1 ppm. I got this problem only with more moduls.
keithley 2000 is reading temperatur and the fluke meassure one single module and the sum point (the single modul is much better in single configuration)
I can change the sma connectors in triax connector this is implemented. Also the settings are 13K/1K and 120R
Title: Re: Ultra Precision Reference LTZ1000
Post by: The Soulman on August 22, 2017, 01:38:44 pm
Zener voltage reading by SMA connectors? SMA is not good for low thermals, as connector package is usually gold plated brass. You want only copper/copper connections with minimal amount of junctions (best is single twisted wire direct from zener to DMM binding posts) to get accurate microvolt-level measurements.

Ok not the best, but realistically what thermal-gradient do you expect there to be on that connector?
And how does the base metal of the connector matter as all connections are made on the same gold surface? When mating the two (assume crimped )connectors it would be copper-gold-gold-copper?

My gut tells me to be more concerned in areas where larger thermal-gradients do exist such as the connection to the kovar legs of the heated reference and to the oxidized binding posts of some warm ancient dmm.  :box:

Not that I'm a expert, just asking to learn something.  :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 22, 2017, 02:01:44 pm
Here some pictures from the prototype. The setpoint is 13K / 1K

Unfortunately they are not visible. (at least for me)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 22, 2017, 02:13:31 pm
Hello,

all I get is this:

perhaps it would be better if you upload (smaller sized) pictures here directly in the board.
So they will be also visible after half a year or later.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 22, 2017, 02:15:28 pm
Or my ftp (link in sub), I'll repost :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Do Ma on August 22, 2017, 02:41:11 pm
Here more pictures
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 22, 2017, 03:39:45 pm
Try to resize photos less, details are barely visible.
Regarding the schematics, what is the purpose of R12 (3.3K to ground, parallel to 1K of oven setpoint network)?.
Resistor network at buffer amplifier can be a problem as well. What was the idea to have it there?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on August 22, 2017, 04:02:53 pm
For isolated supply simple DC-DC-converters + LT3042 should do the trick: eliminating ground loops and providing low noise supplies for the modules.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Do Ma on August 23, 2017, 06:24:20 am
With the potentionmeter at the buffer we wanted to trim the single voltages at the same level. It only was a test and yes it is possible to trim them at for example 7.5V
I will change the pcb layout and check grounding again. Also I'll check isolated supply for the modules and test it. I will give feedback again.

Thanks a lot!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on August 23, 2017, 03:59:41 pm
There is no need to trim / scale the reference modules to about the same voltage. With larger resistors for averaging there is not that much current flow, even if they are some 100 mV apart. It is only that the resistors stability gets more important when the differences get larger. However an extra scaling stage would likely add the same error of even more. Just for averaging there is no need to have an extra buffer - the output of the standard LTZ1000 circuit is already capable of driving several mA - so well enough  for something like a 1-10 K resistor.

Combining several LTC2057 OPs in one circuit could also cause trouble with one OP demodulating the noise produced by other OPs. The more reliable way is to stay with the LT1013, even in the SO8 version if needed.

The LTC2057 might be suitable to buffer the voltages behind the combining resistors.
Using combining resistors (and another buffer) at the ground side too could be an alternative to have isolated supplies. Buffering the negative side might need a kind of negative supply, though usually not -15 V, - 5 V or -3 V would be enough.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on September 15, 2017, 02:58:54 pm
In the corner of the LTZ1000 chip you will find the initials
MG
CN

CN is for Carl Nelson. He worked with Dobkin on the LM399 and he designed the LTZ1000.

He talks about some of that work here -
http://www.electronicdesign.com/analog/interview-analog-guru-carl-nelson (http://www.electronicdesign.com/analog/interview-analog-guru-carl-nelson)

Two interesting sections -
"Ten years later (after the LM399 - cb), we began thinking about how to take the next step toward “God’s own reference.”  We made the decision to design a heated chip that had only the basic reference parts on it, comprising a Zener diode, a temperature-compensating transistor, a temperature-sensing transistor, and a heater. That way, we could optimize the layout to be sure all the devices were at exactly the same temperature, even with the heater running at full power. The user could crank up the Zener diode current to get extremely low noise. That became the LTZ1000, and it was the only game in town for very high-end DVMs (digital voltmeters) and NIST (National Institute of Standards and Technology) transfer standards. I have heard scientists used it to calibrate the Large Hadron Collider. Yet even that part has drift and noise residues. The goal is to make a part so good that you can’t measure it, so the work goes on."

"One place that Spice breaks down is thermal interactions on the chip. I have designed quite a few high-current regulators, so I tend to think of any current below 100 mA as being thermally benign. Yet one of my recent designs had a thermal runaway problem in a 20-mA bias loop because it was all jammed into a tiny space. Spice never saw it coming.
I am now developing a method to do thermal modeling in Spice that takes into account each transistor’s temperature. It’s rudimentary, but it works, and lets you see die temperature unfold in front of you as time proceeds. I plan to include it in a macromodel of the LTZ1000 heated voltage reference, so customers can do thermal modeling as well as electrical. The Spice folks are choking on their lunch when they see this, but I think it’s the wave of the future."

Another comment by Mr Nelson -
http://www.electronicdesign.com/analog/what-s-all-ltz1000-stuff-anyway (http://www.electronicdesign.com/analog/what-s-all-ltz1000-stuff-anyway)

"Brisebois explains, “The simple loop circuits will work at low noise, but not low tempco. By far the most popular circuit is the full ‘7V Positive Reference Circuit’ (Fig 3). One useful thing to understand (it took me 15 years) about the LTZ1000 is that pin 4 is the p-substrate. All the other pins operate above that (which is why you want the heater a diode-drop up) ... except for the mysterious case of pins 6 and 7, which operate 0.6V below the substrate.” Carl Nelson, the LTZ1000 designer, notes he did this to allow for a true subsurface Kelvin connection to the bottom of the Zener, reducing its resistance."
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 15, 2017, 03:17:49 pm
Very thank you, tear to the eye are that interview and these people contributions.   :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on September 15, 2017, 07:50:26 pm
Does anyone know when that spice model for the LTZ1000 might become available? is there a partial model anywhere yet?

I have used a 2N5089 in my simple model, possibly still too large an assumed size, and hfe much too high, anyone think of a smaller, lower hfe transistor I could use instead?

Title: Re: Ultra Precision Reference LTZ1000
Post by: Vtile on September 15, 2017, 08:46:02 pm
Hello it is me again, asking silly questions. Why all the LTZ1000s are seated down to PCB and not top of nice teflon(ish) standoff like used in many some hi-performance OPs with TO-99 cans.

Edit. PS. Another silly question (I have plenty of them) why LTZ1000s are seated to PCB at all and not thermally sealed container with only as non-thermally-conducting leads as possible.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on September 15, 2017, 09:49:59 pm
To keep the pads and leads at the same temperature you need some insulation on the solder side of the PCB as well as some insulation to keep out draughts on the top. Too much insulation and the control loop cannot control the die temperature though.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vtile on September 15, 2017, 10:17:36 pm
Hmm.... Too much insulation.. So what is the optimal amount of insulation? ... I suppose the amount that correspond to positive slope of the optimal heating power. Too weird, time to get some sleep.  :o I also have silly question as how there is no convection introduced drift inside the enormous free space inside of the can, are those vacuum?
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on September 15, 2017, 10:56:35 pm
Hmm.... Too much insulation.. So what is the optimal amount of insulation? ... I suppose the amount that correspond to positive slope of the optimal heating power. Too weird, time to get some sleep.  :o I also have silly question as how there is no convection introduced drift inside the enormous free space inside of the can, are those vacuum?

They are filled with dried air.  There is some thought the chip can maintain better thermal stability if allowed to draw more heater power. However, air currents around the leads, top and bottom cause thermal fluctuations.  Maybe some open cell foam to dampen air currents yet allow it to "breath" is a good compromise.

I did a video showing just a bit of air around the legs will affect the output;
https://www.youtube.com/watch?v=sYhQBudCLiU (https://www.youtube.com/watch?v=sYhQBudCLiU)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vtile on September 15, 2017, 11:44:19 pm
Interesting so there is better thermal stability when the can is upside down? As there is microclimate inside the can and when the system is not in equilibrium (oven driver is heating or cooling to compensate) there should be convection as there is molecules.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on September 16, 2017, 03:45:07 am
hmmm after re-reading the vicinity of this post
The most thorough analysis of LTZ1000: http://bbs.38hot.net/forum.php?mod=viewthread&tid=88278 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=88278) (use google translate)
and also parts of the 38hot.net, it appears that many of the DIY or prototype pics i saw in many threads do not use the "pre-compensation" resistor which is indicated for unstabilized application (extra resistor above pin3), but since it does reduce TC, why dont heated builds include them too?
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on September 16, 2017, 06:03:42 am
That's an interesting question. As I read it, the goal is to select that resistor such that the zener diode has a zero temperature coefficient. Of course, that is a bit redundant with the heated substrate. However  I wonder if that would eliminate some  of the variability associated with things like orientation, or temperature differentials associated with the legs. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on September 16, 2017, 06:49:36 am
As the legs are KOVAR alloy to seal properly to the glass inserts around each pin you are stuck with the 8 thermocouples to contend with, the bias 400K resistor and or the series compensation resistor "above" the zener can compensate for temperature variations of the die, but cannot compensate any thermocouple effects.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 16, 2017, 09:37:40 am
hmmm after re-reading the vicinity of this post
The most thorough analysis of LTZ1000: http://bbs.38hot.net/forum.php?mod=viewthread&tid=88278 (http://bbs.38hot.net/forum.php?mod=viewthread&tid=88278) (use google translate)
and also parts of the 38hot.net, it appears that many of the DIY or prototype pics i saw in many threads do not use the "pre-compensation" resistor which is indicated for unstabilized application (extra resistor above pin3), but since it does reduce TC, why dont heated builds include them too?

The resistor above to adjust the TC to zero has the big disadvantage that it effectively increases the zener resistance and this way makes the circuit more sensitive to resistor changes, e.g. with the 120 Ohms, or the 70 K from the voltage loop. So it is usually making things worse in a heated application. The LTZ goes the way of having a reasonably low unheated TC (e.g. 50 ppm/K), but having a super stable temperature (like 0.001 K).

Too much insulation can reduce the effectivity of the temperature control, as the usual circuit is made for higher power and does not correct for the square voltage - power relation at the heater. So loop gain (and thus the ability control the temperature) goes down as the heater power goes down. If used with very good thermal insulation, a modified temperature control part might be helpful to keep the temperature as stable as with higher power. The heater loop still running with the nonlinear heater indicates that the temperature control loop is still not that much optimized.

Keeping the leads short helps to reduce temperature dependent resistance of the wires. For keeping the solder joints at the same temperature and thus avoiding thermal EMF longer leads would be more of an advantage if isolation against air currents is used. So the best length for the wires is not an easy question - it more like experience showed that shorter leads usually work better.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on September 16, 2017, 03:24:03 pm
That raises two questions.

1) Would a small (3mm) insulating standoff be a good idea? This standoff would eliminate any cooling due to air flow. The longer leads would, as noted, reduce heat losses through the legs.

2) Was balancing the zener current part of the original design idea, eliminated when LT found that it did not help once the diode temperature was stabilized? Maybe they thought   that an oven was not necessary in some applications. The Geller reference is an unheated design that is set to the zero on the temperature curve.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on September 16, 2017, 05:18:34 pm
That raises two questions.

1) Would a small (3mm) insulating standoff be a good idea? This standoff would eliminate any cooling due to air flow. The longer leads would, as noted, reduce heat losses through the legs.

2) Was balancing the zener current part of the original design idea, eliminated when LT found that it did not help once the diode temperature was stabilized? Maybe they thought   that an oven was not necessary in some applications. The Geller reference is an unheated design that is set to the zero on the temperature curve.

The LTZ is a power in / power out device first.  A stable voltage output is the by-product.  You must have -some- thermal heat flow out of the LTZ otherwise the heater won't be able to regulate.  So you protect the LTZ from air drafts, but not necessarily insulate it.  You want some heat flow down those leads, normally.  By the same token you don't normally ovenize the LTZ itself unless you're heating the die externally - but really what we've seen in every case we tried: the on-die heater does a (much) better job.

If you over insulate the LTZ you get a wobbly output and see the heater go out of regulation - you don't ever want to see that heater current dropping low or close to zero.  The voodoo slots you see on some designs sometimes allow an un-balanced air draft to develop and you never want that either.  We don't use slots or crop circles in our designs; we've never had the need for that.  Some specific application might want that if there is an external heat source issue that needs to be mitigated, but it won't be required from the LTZ itself.

Not all applications require the manufacturing expense or extra power required for a heater.  Not a lot of real applications even need an LTZ.  If you're needing an LTZ in some design, by definition everything downstream is probably going to be very, very expensive anyway.  Just changing the LTZ Vref voltage to another absolute value in a very stable, low noise way is usually much harder to achieve than the basic LTZ circuit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kennylxix on September 17, 2017, 01:54:35 am
Hi. I was wondering if anyone has any spare pcbs for the ltz1000 reference board?  I've got the ltz1000 on the way but can't afford to have 3 boards made (I take care of my disabled mother full time so money is perpetually tight)
I'm happy to pay a reasonable amount plus shipping.
Thanks!
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on September 17, 2017, 02:25:47 am
I have two extra extra of the latest B03 version.  Send me a PM. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on September 18, 2017, 03:17:23 am
this post is stemming from the "new adventures" found in the new thread by manateemafia MX reference

due to a lack of an actual ability to see inside an enclosure, i resort to femm4.2 to try out some disspation simulation. it appears copper clad PCB may leak alot more heat than needed?
in my crude simulation, the LTZ sit inside a 30mm foam ball, which is sliced thru by a PCB. the left n right half are different PCB. right half is full thick 1.6mm PCB 2oz, left is suppose to mimic slotting and 1oz copper. and for the fun of it, the edge is mated to the outer box. a funny carbon box inside a foam skin.

(since femm4.2 does not have all the materials, most of the chosen materials nearly matches PCB, silicon, copper, ABS, etc.)

the femm have a plot function, which seem to describe a steeper temp isolation (lower plot) for the modified left side (pic T-grad.gif) vs the right side (upper plot).

while it is true everything inside a project box will be heat up, however if in the case of a LTZ (non-A) if we assume it can be foam isolated to increase the thermal resistance to 400C/W just like an A version, wont it be a boon?

but as i try to math it out, a KOVAR pin/leg about 2mm long x 21mil, can have its thermal resistance estimated at approx 520C/W. for 8pins = about 65C/W. so for the stated stable thermal resistance inside LTZ pdf (=80C/W), the pins alone is the single most leaky "heat channel" (for all the pins to get 80C/W, they need to be at least 96mil long). this imply the LTZ heater need to work alot more harder pushing out heat to short pins, so in theory if the pin landing no longer need to be heated as vigorously by ramping up thermal resistance, should the zener voltage become more stable?
mass of LTZ1000 ~ 1g
mass of 3cm foam ~ 0.02g
mass of 1.6mm FR4 400mil diam ~ 1.6g ??

due to my above assumptions, since the 8 pins carry a heavy thermal influence, wont this require more attention to remove more thermal mass around the pin landing? so that the LTZ only try to adjust/compensate its own temperature and not the entire PCB?
(rename **.txt to **.FEH to use in femm)
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on September 18, 2017, 10:47:50 am
@3roomlab-  Very interesting model results!  Thanks for sharing.

Do you have individual copper traces connected to each pin in model (if so, what width per pin?) or do all pins connect to solid 1 oz or 2 oz copper plane on both sides of PCB?  Or only one side?   Also, when you say "edge is mated to the outer box", do you mean the top/bottom copper planes are thermally connected to box?  Or just the PCB substrate?
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on September 18, 2017, 04:00:50 pm
2.gif does confuse me, I am not sure what has been plotted there, it looks like the insulation keeps cooler than the surrounding air to me, so it must be plotting something different to what I expect? also any copper layers will not be 100% fill.

Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on September 18, 2017, 04:31:31 pm
Not that it can't be done for just fun, we've never seen a serious attempt at thermal simulation that comes very close to any -real life- LTZ module design.  All in all the LTZ can itself is pretty forgiving but you do run into other issues when trying to run any accurate thermal sim.  Typically you don't read too much into the thermal sim results for any LTZ design.

For instance, the various combinations we deal with:  Are you connecting the LTZ to inner trace or outer? Copper weight? Number layers?? Ground planes??  What PCB material (FR-4, High Stab Rodgers, ??)? Size of board??  Board mounting method to shield box?? Soldermask, and what type?  Conformal coating and what type? Air draft shield around LTZ and what type / material / thermal flow??  Solder mass at each joint?  Ambient temp around LTZ?  Component distances from LTZ and what is their thermal dissipation, component lead length and bend radii, number of bends, emmisivity. PWW or Metal Foils resistor cans or combo?  Distance to board connectors, and what is connected to each board connector, number of connectors, wire gauge solid or stranded??  Ambient temp of shield box?  Overall thermal mass and time lag?  Is the interior of the box purged with CO2 or Nitrogen or Air or ????  What is the LTZ board mounted to and how does that structure act thermally?

And so on.

All of those elements play at least some small role in exactly how every LTZ finds it's unique & stable operating point, but the on board heater does a pretty good job of isolating the LTZ die from the rest of the world.  We've never seen voodoo slots do anything helpful, at least in our tests, and neither does the very successful HP3458a Vref module, for decades.  A (much) more accurate thermal investigation would involve just building some real designs and comparing sim theory vs. real-life reality (remember reality wins every time) - you'd get a better feel for what's going on, and gain more knowledge faster - at least that's what we've seen.

Have fun though!


Title: Re: Ultra Precision Reference LTZ1000
Post by: zhtoor on September 18, 2017, 07:01:57 pm
For instance, the various combinations we deal with:  Are you connecting the LTZ to inner trace or outer? Copper weight? Number layers?? Ground planes??  What PCB material (FR-4, High Stab Rodgers, ??)? Size of board??  Board mounting method to shield box?? Soldermask, and what type?  Conformal coating and what type? Air draft shield around LTZ and what type / material / thermal flow??  Solder mass at each joint?  Ambient temp around LTZ?  Component distances from LTZ and what is their thermal dissipation, component lead length and bend radii, number of bends, emmisivity. PWW or Metal Foils resistor cans or combo?  Distance to board connectors, and what is connected to each board connector, number of connectors, wire gauge solid or stranded??  Ambient temp of shield box?  Overall thermal mass and time lag?  Is the interior of the box purged with CO2 or Nitrogen or Air or ????  What is the LTZ board mounted to and how does that structure act thermally?

hello,

that essentially means the reference system as a *WHOLE* has to be simulated from
a thermal point of view keeping in mind thermal sources and sinks reasonably accurately,
which i suspect should be pretty difficult (albeit possible).

regards.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on September 18, 2017, 08:33:49 pm
yea im jus fiddling around femm for fun, but it is very helpful cos even a FLIR wont see thru thermals like this.

the trace are connected to pin (see pic 11), on 1 side. for edge box mating, all materials meet the "box". i also tried to simulate solder, but the effect is too small to see near the LTZ, however, a large blob outside have a interesting effect (pic 101)
in 2.gif, i exaggerated the sphere foam to 100x less conductive to magnify the effect of the heat going thru the PCB.

i also tried a simulation with long kovar pins going sideways. comparatively, copper trace need to be very small to match the same thermal resistance of KOVAR, by the time i am able to get a 3C difference using 10mW as heat source on 1 pin (300C/W?), the copper ends up being 11mil wide @ 16m-ohm x360mil long. resistance wise, this copper trace is about 16mohm, the kovar is about 20mohm. so in terms of the experiment andreas did regarding seating height, it is low seating with joint temperature controlled by LTZ or extremely well insulated joints further out (over 1000C/w). the blob of solder also have a interesting "heat capacitor/buffer effect" see 102.gif.

then i try a combination of slot and sink (see 100.gif), creating a deliberate temperature "short circuit to ground", the effect is also very interesting. 100.gif is 4 dots, 1 of which have a copper trace running to the left edge leaking heat into FR4 around it. it passes thru slots and another copper sinker

(TBH, i have no idea what im doing fiddling with these)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vtile on September 18, 2017, 08:53:32 pm
Now when you are at it, what about those connection whiskers hanging between the wafer and the legs. Cool is that some dedicated simulation program or DIY?
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on September 19, 2017, 12:35:16 am
Now when you are at it, what about those connection whiskers hanging between the wafer and the legs. Cool is that some dedicated simulation program or DIY?

i got the idea of the side section from a pic here (photo by eevblog member chuckb)
(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=189496;image)
i assumed the whiskers dont do much.

the program is by these ppl
http://www.femm.info/wiki/DavidMeeker (http://www.femm.info/wiki/DavidMeeker)
free to use
http://www.femm.info/wiki/HomePage (http://www.femm.info/wiki/HomePage)

edit : after some more thinking about many things misterdiodes said and the results posted by our hardworking andreas with his many many many many versions of LTZ, it seems to me that if an "uncontrolled" power source drives the LTZ, the fluctuations in power consumption = fluctuations in ppm = small thermal variations, what if the LTZ is supplied with accurate CV and CC = constant power = a fixed thermal leakage? or it has already been done in such a way?
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on September 19, 2017, 04:13:02 pm
The LTZ -when the heater is working and holding the die temperature steady - is not going to respond much to reasonable (small) supply voltage variation.  The Vref output voltage is itself overwhelmingly set by the zener junction and it's transistor driving the '1013 current source - and that Vref voltage will be different for every individual die, but very stable.  Small  supply voltage changes and even a Voffset drift of the '1013 current driver do not have any major effect on Vref.

That's the beauty of the circuit.  Elegantly simple, pristine analog circuit yet very, very effective and stable.  Every element you need to be ultra-stable is already in that LTZ can, and out of your control for the most part.  The rest of the components are relatively forgiving, as long as you watch out for air drafts, EMI problems, etc.

Sometimes we use a linear voltage pre-regulator just ahead of LTZ as an additional noise suppression technique for our particular situation, but that isn't really needed for a lot of applications.

That's what I meant in my post above:  The on-die heater does a very good job of isolating the die from the rest of the world AS LONG as it can regulate temperature properly - that is the foundation on which everything else is built.  It is a heater only, not a cooler.  Therefore you have to keep the die a bit warmer than the variable temperature surroundings, and there -must- be some thermal flow -out- of the LTZ, at least in a controlled way.  As long as you understand that, then you understand why you can't over-insulate the LTZ or run it too cold - which means too close to ambient temperature (heater ratio resistors too low).  The die must must be held at some higher headroom temperature difference between all of its surroundings.  That means you look at your application requirements and set your heater resistor ratio based on the expected high temperature of the local environment.

In other words:  Let the on-die heater system do it's job however it needs to, use good fundamental design rules (compact board, star reference points, keep an eye on trace voltage drops, thermals, shielding, etc.) and then (most) everything falls into place to give you a very stable Vref output.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 19, 2017, 08:03:41 pm
i got the idea of the side section from a pic here (photo by eevblog member chuckb)

now you can improve your simulation model according to the real world issues:

- different length and number of bond wires
  (the chip is most likely not symmetrically cooled by the bond wires.)

- chip not exactly centered

- different temperatures of the on-chip thermo-couples
  Aluminium to Gold bond wire to Kovar Pin

the only thing that can be influenced is trying to keep the pin to PCB connections (Kovar to lead to copper) at the same temperature. But I am not really shure what is better cutouts or not. Long or short leads. We had a long discussion with the LM399 thermal photos. My impression was that a certain thermal mass is necessary to keep the pins all at the same temperature.
(And perhaps some slots at a 1-2 cm distance to keep other heat sources away).

  We've never seen voodoo slots do anything helpful, at least in our tests, and neither does the very successful HP3458a Vref module, for decades.

Mhm,
- the venerable Datron calibrators use slots (even with flex cirquit) around the LTZ in its 4000 series.
- Agilent (HP) now also uses slots in the 34470A reference cirquit. (have they learned something during last 30 years?)

The LTZ -when the heater is working and holding the die temperature steady - is not going to respond much to reasonable (small) supply voltage variation. 

Ok for small variations in the 100mV range this plays no role.
But -0.4ppm/V variation is something where I do not want to have a unstabilized power supply.
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg842662/#msg842662 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg842662/#msg842662)

And even with a linear regulator you have to take care that it is not too close at the LTZ1000 if you want to have less than 0.1 ppm/V. (or you can use isolation slots between voltage regulator and LTZ to improve the PSRR).

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg846835/#msg846835 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg846835/#msg846835)
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg935102/#msg935102 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg935102/#msg935102)

With best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on September 19, 2017, 09:39:00 pm
In our experience, voodoo slots have never done anything helpful except when you want to build a sensitive vibration detector out of an LTZ  :-DD.  There might be applications where a slot is required to suit some design.    I would never add them just for looks though.  Never seen slots on a 3458a Vref., and on an early test where we made the same board design with and without slots (5 boards each) we could see slots did nothing positive, at least for what we are doing.  Except the slotted board had vibration problems unless we padded the mounting.

We use slots only very, very carefully and only when we know they are required - If you get something flapping around loose in the breeze on a production circuit you'll always find out about it - in a bad way.  Like when you find out your circuit is picking up the lumbering freight train down the road and you can tell it has loaded cars or not....<yes, that has happened>  So if you add the slots do it only if you -know- for sure you need them - and then I would look at a vibration isolation mechanical mounting system.

Notice in my previous post I said "small" power supply deviations were allowed.  You don't want the LTZ's power source dancing around too much, and use a pre-regulator as required.

Yes, I should have been more clear: We don't put the linear regulators on the same board as the LTZ...the LTZ is always on it's own module for what we do, and that lets us do burn-in on tester jigs ahead of time while the rest of the system undergoes separate testing.



Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 20, 2017, 04:26:23 am
I wouldn't use 34470A design as a very good example of LTZ design for purpose of long-term stability/reference standard role.
Title: Re: Ultra Precision Reference LTZ1000
Post by: pigrew on September 20, 2017, 05:15:25 am
Do slots help reduce die strain (due to TCE mismatches)?

Or is the die attach somewhat flexible reducing strain effects?

For example, the LTC6655 suggests cutouts around its package.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Micke on September 20, 2017, 07:09:01 am
MisterDiodes,

I really enjoy your posts and have learned a lot, but I have a question...  :)
I understand you burn in the LTZ1000 assemblies for like a year, but do you do any temperature cycling, or are they just powered in room temperature?

I have built 3 LTZ1000:
2 LTZ1000A  Burn in time so far almost 5000h
1 LTZ1000   Burn in time 3000h, on this I tried some temperature chock treatment, with just the LTZ1000 soldered on the PCB, I heated the PCB to +125C and put it in the freezer for a while and then cycled this like 5 times. But I have read that maybe this was to extreme, I should have instead slowly narrowed down the temperature span.
But anyhow, so far the LTZ1000 (non-A) shows less power cycling hysteresis than the LTZ1000A, I read it should be the opposite, LTZ1000A should have less power cycling hysteresis. Could this be that the LTZ1000A just need even more burn in time?
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on September 20, 2017, 10:49:35 am
I wouldn't use 34470A design as a very good example of LTZ design for purpose of long-term stability/reference standard role.
I value your opinion.  Can you please explain why?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 20, 2017, 04:14:35 pm
The LTC6655 and similar SMD parts are much more sensitive to board stress. For this reason they might need some slots or even a U form cut. The To-99 if the LTZ is rather insensitive to board stress. The metal case and open air bond wires keeps stress away from the chip itself - especially if soldered with a little spacing to the board.

I the reference circuit is on a small board by itself, there will be not much stress anyway - so no real need for extra stress reduction - just make sure not to have a poor connection to the main board part that causes massive stress and temperature gradients.

For the temperature gradient the copper layout is more important than cuts in the FR4 - much of the heat flow is through the copper.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on September 20, 2017, 05:02:53 pm
A couple of thoughts below, and remember this comes from experience building profitable circuits in a production environment, and where customers pay for reliability and 24/7/365 operation, OR where the device might go into shutdown for an hour, a day or a month or more.  For us, failure in the field is NOT an option (at least in spirit), and if there is a field failure we take that very seriously and try to improve the product so that particular product failure -never- happens again.  A hobbyist may or may not choose to do it this way depending on what the application goal is.  I have to just keep it to the highlights here, I can't give you an exact recipe.  Use the information at your own risk, since your situation may call for a different procedure.

RE: Burn in procedure:  Yes there are many temperature cycles that go into burn in, which is a combination of a long steady run, and then a period of thermal cycles, etc.  We throw everything at the LTZ and it had better work within spec after every trip thru the thermal chamber.  This is usually a good way to weed out bad performers on other areas of the board too.

You have to realize that if your product is shipped air freight in an unheated airplane cargo area, it's going to get very cold.  Or if it goes to somewhere like a hot customs inspection area and sits for a week its going to get very hot.  The customer doesn't care - they need it to work out of the box, and we provide guidelines for a minimum stabilization time before guaranteed specs are met after shipping.  Hint: it's not really the extreme temperatures that causes real issues, it's the -rate of change- of temperature that can cause surprises on your Vref., so that is something we test for on every device to meet customer design requirements.  Sometimes you see something break with a small 30°C shock test, and it might have worked fine before over a slow 100°C ramp.  Everything around the LTZ has to remain in a working condition after every thermal cycle, no matter what we throw at it in our test design.  Our test will include the customer requirements plus another safety factor to make -absolutely sure- it works to specification at customer site - with a comfortable margin for error.

We test at the whole range -65°C to 150°C for storage, and that can be over a day or some weeks, and then there is the actual operating temp range which varies by customer design requirement.  We never use the non A version, only the LTZ1000A (same as most 3458a's, which we find overall is more stable over the long term, at least in our tests) and yes there is a small power cycle hysteresis but that should be well under 0.5ppm on a stable LTZ, and most of the time we need to hit a 2ppm or 4ppm stable operational window - so we're not trying to replicate a Fluke 732.

We do develop a stabilization time procedure for the customer so they know when it should be back in spec after a power down of say 15 minutes, 1hr, 12hr, 24hr and 30+ days.  It should recover typically within a couple hours or a day or two, sometimes longer...but even then it should stay within the guaranteed 24hr drift rate spec.  Like any precision equipment if it has been powered off for a long time, you expect to power it on and let lit stabilize for some time before it goes back to work and settles back to "in spec" condition.

It just depends on the design requirements, and usually each customer has a very specific need.  Our job is to deliver customer satisfaction - because happy customers are the very best variety.

RE: Keysight 34470a as design inspiration - That's not really a metrology grade instrument.  The Keysight sales guy brought in an early model to demo, and the stupid thing drifted more in 4 hours than an old reliable 3456a drifts in a month.  It could be better now, but look at the specs - be careful when they start listing accuracy in % rather than PPM and compare 24V 10V range accuracy to a 3458a...and let me know which one is much more stable.  Plus those danged PLayskool child-safe recessed banana plugs tells you right there they aren't paying attention to low-thermal design goals (I know they are trying to sell to the safety-spec market but that is not the metrology market).  I know the 34470 is not a replacement for the 3458 and is at a price point to match - but the new design techniques don't inspire anything from a low-ppm tool point of view.  They may have some of those problems worked out but we sent the salesman out the door with his stuff...he didn't sell us on any of newer, cheaper DMMs.  Our fleet tends to stay at the 3456a / 3458a style for lower drift.  In the long term the 3458a's don't cost much to own (for the accuracy provided) since they are usually very reliable - and if you get it under the extended warranty.

RE: Slots on LTC6655... That package is SMT, and is prone to every circuit board stress / flex problem known - which really shows up on the trimmed die resistors as increased noise.  Not a low ppm-style part - that's like a toy compared to LTZ, but not every design needs an LTZ either. Sometimes even slots aren't enough for that package, but use what the design calls for, and in this case slots help and are recommended.  But comparing a '6655 package to an LTZ is like comparing apples and oranges - the LTZ is much more insulated from PCB mechanical stresses.

The other thing to watch out for with slots - be careful that adding slots doesn't increase trace length so much that now you've increased EMI / current loop antenna effects.  If you try to help too much in one area you wind up with decreased performance in another area.

Have fun!

PS EDIT:  Also look at something like a Datron 4808 calibrator 10V accuracy spec in both long and short term (apparently with a slotted LTZ, I haven't seen this in person) and tell me if that's really different from a standard 3458a...and then compare it to a High Stab 3458a with 02 option (exact same board as any 3458a still no slots, just a rather well performing selected LTZ).  Is the calibrator LTZ Vref design really more stable overall than what is really the basic LTZ datasheet circuit in the 3458a?







Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on September 20, 2017, 07:24:48 pm
now you can improve your simulation model according to the real world issues:
- different length and number of bond wires
  (the chip is most likely not symmetrically cooled by the bond wires.)
- chip not exactly centered


after a few more fiddly diddly
here is what the FEMM thinks of the 3 bond wires vs 1 bond wire. ~ approx 38uW diff (0.05C?). pic TT6/7
uniformity of connection to LTZ island TT8.gif, the bottom side lacking copper fingers = higher temperature. diff in top side island and bottom side island is approx 1C

**update
i corrected the W/mK error for plan view. hard rubber mimic nearly FR4 0.8mm thick, lead liquid actually mimics very close to a copper pour back planed 0.8mm FR4. all 1oz.
now with this, the thermal leak presented by a trace looks more corrected. so the simulation for using small widths connected to the +10C source (LTZ) and using it as "resistor" to keep the opposing temperatures "far" from each other. (pic P1)
the center ground plane appears to keep uniformity very well, the right most temperature point is simply a +10C point on bare FR4 for show
as seen on the LTZ model 3 traces, the top trace 10mil by FEMM contour calculation, the leak is 26uW. left trace is a 6mil 400mil long to a fatter 50mil, leak is 24uW. bottom trace is 50mil straight from the +10C pin, leak is 40uW. so as we can see, the 6mil is gving good resistance. of course i think to consider uW leak level is overkill, but i think by varying the length it can help to keep all the pin temperatures uniform, which will need extreme fine temperature measurement. but on the other hand, after introducing an outer ring of thermal impedance, by introducing a small fat ground plane inside the LTZ island under or top side, without varying the trace lengths, the centre island can have its own uniform temperature by self regulation (P2 pic)
** addition
by applying the new W/mK to side view. and go with a tiny copper spreader and use the hot pin as a "preheater". we might force the cooler pins to within 0.1C (in theory). or even crazier, put the LTZ on a tiny ALU sub-board for LED. on ALU, the simulation show the temp diff is now under 0.1C for sure (in theory).
(now what improvements would we expect if these are applied to LM399?)[/size]


new update **
a little imp sprung to mind after thinking about misterdiodes mention of heaters. so i modified the simulation to have some 0603 resistors heat the legs. assuming you can heat at a good rate (simulation suggests 10mW per vicinity of a pin), it appears it could be possible to bring all the pins to 0.02C of tolerance from each other.
simulated are A001.gif / A003.gif
only topside heater and or top and bottom heated.

and A002.gif is an overkill heater layout of 16x 0603 heaters in 4 series strings of 4. assuming 12V supply and total heating of 80mW, each 0603 (5mW) needs to be about 1.8k. or we could use all 1k and operate a variable CV to regulate the actual mW output. (i noticed i made an error in 1 of the materials, but still the model still allows us to see the behavior of the temperature balance)
on a top only possibility, and to create a larger thermal mass, it is likely possible to stack on larger resistor sizes @ 0805
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on September 20, 2017, 09:54:20 pm
For anyone who's forgotten, Dave Jones did a teardown of the 34470a here:

https://www.youtube.com/watch?v=_QpApuKdcqQ (https://www.youtube.com/watch?v=_QpApuKdcqQ)

About 14:15 in you'll see the LTZ Vref board construction, and notice they are going for a much lower price point with the SMT components.  Nothing but penny resistors in there, and SMT caps.  This board will be very prone to mechanical vibration pickup, but they do have that somewhat isolating plastic clip that might help (or make things worse).  There are slots around the LTZ and a slot to isolate the heat from the heater transistor.  Still 15k over 1k heater ratio.

At 16:00 you can see the removed bypass cap (or whatever they were trying to do that didn't pan out - or maybe test points) under the LTZ.

But the accuracy / stability of the entire meter suffers due in part to this design and has relatively fairly low 24hr accuracy.  This is a good example of what happens when designers go the cheap route - this is one reason why a 3458a runs circles around the cheaper DMM's (for low ppm stability / accuracy spec).

ON THE OTHER hand it also shows how forgiving the LTZ is even when used in a somewhat lower price point application.  If you consider about $3900 cheap for this 7.5 digit DMM.  Even at that price we found a better value and better accuracy in a used 8.5 digit 3458a, but that's what we need.  Other users will have different needs.

It would be interesting to see if anyone has made a better-quality LTZ board for this meter, and did that help overall performance?
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on September 20, 2017, 10:04:49 pm
I think the greater limiting factor with the 34470 is the tempco from all the surrounding components and not the reference board itself.  I suspect, the LTZ is simply overkill in the 34470 and the meter as a whole just cant gain a significant benefit from it, other than perhaps long term drift.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 20, 2017, 11:19:20 pm
Dr.Frank did good detailed summary on this design in Dave's video discussion thread. Somebody at PC can surely find link to it and post here. SMD esistors could be still VPG foils , but I never see VPGs BMF with such style, they are usually light-blue or encapsulated in epoxy. Either way SMT assembly not great for stress and vibration. Also those MLCC's there are great microphones, and vibration sensors from meter's fan. :) Piezoelectricity is reason why I used only film caps on my reference, even though they cost few $ a piece.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on September 21, 2017, 01:32:42 am
The resistors on the board in question are film, not foil, for one thing if they were going to foil they would have used the larger non-SMT package, this looks like a cost cutting design in just about every way.  The noise is likely to be higher than if they had used foil or PWW resistors and you are supposed to use film capacitors not low cost crappy SMT ceramics, no this is not a high performance Vref board compared to the 3458A's or other similar versions, this design barely manages to get near the 'claimed' 7.5 digit performance, the specs are not great by any comparison.  An old 3456A would give this bird a run for its money for stability and long term accuracy.  The newer DVMs are of questionable design compared to the earlier generations.
Title: Re: Ultra Precision Reference LTZ1000
Post by: lowimpedance on September 21, 2017, 03:26:19 am
PS EDIT:  Also look at something like a Datron 4808 calibrator 10V accuracy spec in both long and short term (apparently with a slotted LTZ, I haven't seen this in person)
It indeed has slots, see this old post for a few pictures of it.
https://www.eevblog.com/forum/testgear/datron-voltage-reference-pcb-module-pics/msg813331/#msg813331 (https://www.eevblog.com/forum/testgear/datron-voltage-reference-pcb-module-pics/msg813331/#msg813331)
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on September 21, 2017, 04:21:14 am
...and after all the time spent on those floppy slots, for no net gain on the instrument daily / yearly drift rate or noise over the slotless design.    The advantage on the 3458a compact module style is the small board size - If the LTZ is mounted on a larger board then stress reduction slots might add some benefit as long as trace length isn't compromised and as long as weird draft flows don't develop, etc.  OR if you have to deal with a heat source coming in from a certain direction, then of course you need to tweak the design as required.

The other weak area on the 34470a LTZ module design is that cheap header connector - if those header sockets are allowed to freely float like that they will tend to wear and go intermittent as the gold wears away on the contact pins - we've seen failures like that especially after a header connector gets loose while traveling on FedEx somewhere, and then both the header pins and sockets need replacement.

I agree with Edwin:  There is not a lot on the new cheap(er) meters that inspires confidence in the design expertise of the product engineering team at Keysight (or elsewhere) these days - even on a non-metrology grade instrument.  Of course it is not a replacement for a 3458a and never promised to be, but it's a shame they cut corners to that extent on a meter that still sells for almost $4k.  If it was a cheaper meter yes it's understandable.

Of course you get faster readings and a whiz-bang display in a smaller, lighter footprint, but at the end of the day we still need low drift and good stability - for what we do at least.  These meters tend to fall way short compared to what you can buy on the used market for about the same cost that works much better if you need better stability.  You also get good quality low thermal binding posts on the better quality meters, and if you're doing low ppm measures: that's an important consideration.

It just depends on what you need.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on September 22, 2017, 08:17:33 pm
Another glaring rookie goof up in the 34470A video, the designers placed the LTZ module right over the clock oscillator on the main board, are they serious?   It is sitting right on top of the crystal, gee what could go wrong there?
Title: Re: Ultra Precision Reference LTZ1000
Post by: technogeeky on September 22, 2017, 08:41:12 pm
Another glaring rookie goof up in the 34470A video, the designers placed the LTZ module right over the clock oscillator on the main board, are they serious?   It is sitting right on top of the crystal, gee what could go wrong there?

You're probably going to feel a bit silly, but: that's not a crystal. It's a resistor.

From the pictures here (https://www.flickr.com/photos/eevblog/16765926266/in/photostream/), we can see that that component is populated (but not labelled on the silkscreen) on the 34470A (board 34465-xxxx):

(https://farm9.staticflickr.com/8721/16765926266_c0b941ba70_c.jpg) (https://flic.kr/p/rxxKLf)

And it is silkscreened but unpopulated on the other board (board 34460-xxxx):

(https://farm8.staticflickr.com/7606/16584505777_058021b678_c.jpg) (https://flic.kr/p/rgvVLM)

I only investigated because it seemed so boneheaded to put a crystal (usually controlling a digital system) right next to an analog reference, so I was curious to see it. Turns out, nope! Just a precision resistor.


Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on September 22, 2017, 09:48:40 pm
Interesting, in the video Dave identifies that can as a crystal, you can't read what is written on it unfortunately.  Unless it is identified on the schematic as a resistor I can only go by Dave's commentary that it is a crystal.  So we have a bit of a mystery here, what is it a resistor or a crystal?
Title: Re: Ultra Precision Reference LTZ1000
Post by: technogeeky on September 22, 2017, 10:46:49 pm
Interesting, in the video Dave identifies that can as a crystal, you can't read what is written on it unfortunately.  Unless it is identified on the schematic as a resistor I can only go by Dave's commentary that it is a crystal.  So we have a bit of a mystery here, what is it a resistor or a crystal?

It's a resistor. That's why I linked the photo of the 2nd board: it's R324 (unpopulated on that board). I can't read what is on the part, but text wise it looks very much like a Vishay metallized (oil filled?) resistor. But we can be 100%certain that it's the same part/location as on the unpopulated board.

Also, a crystal in an instrument like this would probably be a 4-pin crystal. (And it is: it's a tiny 4-pin one, 106.25 MHz, to the bottom-left of the Lattice chip).

So Dave just made a mistake in speaking, no biggie.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CalMachine on September 22, 2017, 10:50:28 pm
(https://farm8.staticflickr.com/7288/16171849053_4f27951155_b.jpg) (https://flic.kr/p/qD3XiF)
Keysight 34470A Multimeter Teardown (https://flic.kr/p/qD3XiF) by Dave Jones (https://www.flickr.com/photos/eevblog/), on Flickr
Title: Re: Ultra Precision Reference LTZ1000
Post by: AG7CK on September 22, 2017, 11:45:08 pm
It has been mentioned several places on the forum: It is the autocal reference resistor.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 23, 2017, 05:51:01 am
Probably comes from LTFLU-based KI 7510 price? :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on September 23, 2017, 05:23:29 pm
This is getting off topic now, but in answer to your question:

In the US, it's more like a little over $4k per meter when you get the warranty, shipping, sales tax (depending on what state) and TruVolt software stuff turned on.  Z540 cal goes on top of that.  The lower price doesn't include the advanced software license - at least not when we got the sales demo and the written quote from Keysight.

Note the "Typical Configured" price of over $3800:
http://www.keysight.com/en/pd-2520154-pn-34470A/digital-multimeter-7-digit-performance-truevolt-dmm?cc=US&lc=eng (http://www.keysight.com/en/pd-2520154-pn-34470A/digital-multimeter-7-digit-performance-truevolt-dmm?cc=US&lc=eng)

And again - at least when we patiently waded thru the sales demo in 2015, this meter -was not- nearly as stable in 6.5 digit mode as an LM399-based 3456a, which you can get for maybe around $300 (or somewhere around that) on eBay (a basic 3456a cal runs about $100 or $175 for Z540).  In fact the demo 34470a not only drifted faster in four hours as did a 3456a drifts in a month (new '56a spec was 8ppm/day, older ones we have all measure at < 4ppm per month and are 1ppm or less per day), the 34470a drifted faster in four hours than all FIVE 3456a's 30 day spec in the same room.  And of course against the 3458a's there is no contest, but the 34470a is not in competition with that one.  Tell me again why you'd want this meter if you're after good stability over even 24hrs - and why is it a an example of a good Vref module design technique?  At any price??

Here's a real sample in the lab:  In comparison to a used, working Z540 calibrated 3458a that we've got a total of about $4300 invested after first year (24hr hr spec of 0.5ppm plus .05ppm of range on 10VDC range - which is what about all quality LTZ -based devices are capable of, with or without voodoo slots on the Vref module)...and on 34470a you get 8ppm + 2ppm (10DCV range) per 24 hrs (see datasheet):

http://www.keysight.com/en/pd-2520154-pn-34470A/digital-multimeter-7-digit-performance-truevolt-dmm?cc=US&lc=eng (http://www.keysight.com/en/pd-2520154-pn-34470A/digital-multimeter-7-digit-performance-truevolt-dmm?cc=US&lc=eng)

Also note that 34470a input bias current is "<30pA"...So we'll take that as meaning up to 29.9pA, which means you're not going to be throwing out your decent analog null meter anytime soon (Keithley 155's / Fluke 845's are < 200fA and even well below that if they are dialed in carefully).

So the disappointing question I'm left with is this:  If you're Keysight, and you have all the design and development work done on a perfectly good working 3458a LTZ module where you already have lots of inventory - and at this point your Vref cost is really only the BOM parts cost - why on Earth do you try to design a medicore, cheap-ass LTZ Vref to build a 7.5 digit meter with only medicore stability?  There wasn't say $10~$15 (volume cost for better resistors and caps) left over in the budget to use a PROVEN GOOD LTZ module design you already own that requires no engineering dev work?  Software will never compensate for higher drift rates on an LTZ module - In other words your LTZ-based device is never going to be more stable than the Vref module itself.

Maybe the rest of the meter is so dismal that they can't get better than even 2 or 4ppm per day drift (which is still not that great). Maybe they just gave up trying at some point.

Again - people might not need the high stability and they like the smaller size / faster reading per second of 34470a.  And that's what they should get.  The 34470a serves as a good example of "Build to a price point" LTZ module technique that gets you relative medicore stability performance.  You get what you pay for, and sometimes if you pay less for an older, much more stable unit - you're getting more.  IF real stability and good quality binding posts are more important to you than the fluffy display - then 34470a is not a really a good choice for a lot of low-ppm measures.
Title: Re: Ultra Precision Reference LTZ1000
Post by: VK5RC on September 24, 2017, 04:20:54 am
I just had a 'naughty' thought, perhaps they did try the 3458's LTZ module in the 34470 and perhaps it worked a bit too well!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on September 24, 2017, 04:30:00 am
Possibly, they had to use a LTZ circuit, cheapened as it is, because a LM399's noise was probably just a little too much even for selected units and they were trying to hit a 'usable' 7.5 digit claim, even though the specs don't support real 7.5 digit performance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 24, 2017, 07:45:22 pm
Not all cheap resistor are settling to a stable value - some continue drifting in one direction (like up with most carbon resistors). Even with relatively poor resistors the LTZ1000 reference is relatively stable.

So TC of the 34470 is likely more from the rest of the circuit. This could be resistors or not perfectly matching FET on resistance in a few places. The reading coming back with an ACAL confirms the reference itself it not the problem. It would be only after ACAL that you get mainly drift of the reference circuit, and very little from the rest of the meter.
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on September 25, 2017, 04:53:45 am
The Keysight plastic carrier does not do anything for LTZ1000 heat loss due to conduction on the FR-4 of the reference PCB, which has variable airflow directly across it?
I don't know the 3458a mechanical but the ref pcb seems out of direct airflow, in the corner. I see a duct to ensure that.

Let's cool the heater.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 25, 2017, 06:19:53 pm
I won't expect the temperature control loop to get unstable (in the sense of start oscillation) with too much isolation. It is more like running out of regulation because self heating from the zener current. So a higher set point temperature would be needed. With the resistor as heater and thus a square law heater, the thermal loop gain will go down with lower power. So the loop will get more sluggish and less accurate at lower power / more isolation.

Besides the thermocouple effects at the Kovar pins, also the TC of the pin resistance could be a factor. Here some extra thermal isolation on the board would help, but is limited due to the copper connections.
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on September 30, 2017, 05:51:00 pm
LTZ1000ACH ship dates, Digi-Key keeps pushing them back from Sept. to mid November now. LT store says "consult factory". Which one of you is hoarding them.

I used to gripe about LT prices being a bit higher and their field engineers told me they are a smaller fab and always have stock, it's part of the cost.
To me it is important to have availability for sole-sourced parts, so I understood.

But not today, perhaps these parts have a long burn-in or are on allocation now.
I truly hope AD didn't mess things up.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on September 30, 2017, 08:40:10 pm
LTZ1000ACH ship dates, Digi-Key keeps pushing them back from Sept. to mid November now. LT store says "consult factory". Which one of you is hoarding them.

I used to gripe about LT prices being a bit higher and their field engineers told me they are a smaller fab and always have stock, it's part of the cost.
To me it is important to have availability for sole-sourced parts, so I understood.

But not today, perhaps these parts have a long burn-in or are on allocation now.
I truly hope AD didn't mess things up.

Ive had one on back-order from Digikey for about 2 months.  The ETA has not changed and is still said to ship later next week.  So I suspect they simply ran out, then back-orders depleted their next stock shipment.  Digikey does not seem to stock many of these, never seen their stock more than about 70.  And I'm sure Digikey and other large company's will get first dibs on any stock from LT before the direct on-line store.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 30, 2017, 08:55:45 pm
No problem with the non-A version, they stock 106. So why you want to go for the A version?

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on October 01, 2017, 12:15:28 am
I see a lot of struggle with thermal design alone, for the LTZ1000. An 84 page thread with 571,940 views and I didn't see a thermal model or mechanical configuration solidified.

It's difficult to do thermal design when conduction, convection, and radiation heat losses are unknown.
The LTZ1000 datasheet (http://cds.linear.com/docs/en/datasheet/1000afe.pdf) offers one number, ?JA for us to work with.
Graphs G04,G05,G06 show about 30-40% heater power required for the "A" compared to non-A version (but no mention of can configuration; on a PCB, free air, cap on top etc.)

I think the A's higher thermal resistance 400°C/W vs 80°C/W as a "Matryoshka doll" approach insulating the die from the case greatly lowers heater power requirements which might lower the Kovar TC effects due to a smaller temperature gradient. And the cap/insulation delta T. I'm not sure, it's my speculation.
Ultimately I think the thermal design is more forgiving for the A part.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on October 01, 2017, 12:42:46 am
Part of the problem is that the stability goal of these designs is such that it may be difficult to simulate the system. In particular, the PCB traces may have quite an influence.

The voltage temperature coefficient for copper to Kovar is 40 microvolts per degree Celsius. As we are looking for sub-microvolt stability, and assuming that the temperature at the can end is consistent, that means we want the temperature of the critical pads to vary by less than .01 C.

That said, top and bottom caps seem to do a lot of the work. Plus, getting some separation from other components will help. Also suggests that flush mount is best, as it will reduce the temperature difference across the leads. Second up would be making sure that the sensitive pins have a similar thermal path - which suggests thin traces connected to the critical pins. There's also the issue of the external resistors, which may be quite a lot more sensitive to temperature shifts.



Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on October 01, 2017, 09:22:57 pm
I agree, top and bottom covers are beneficial but I wonder about the reference IC-PCB interface.

Talking about one temperature gradient- between the Kovar leads and the PCB.
Silicon-gold-Kovar-solder-ENIG-copper; Don't know if this gives the usual quoted 35-40?uV/°C and are people using low EMF solder here.

For the Agilent 34470a implementation (above pics) I think it's not optimal to insulate the LTZ case but have the PCB exposed to forced air, as the FR-4 acting as a heatsink. Voodoo slots would lower conduction heat losses from the LTZ leads, but not evenly across all pins.

My analogy is standing bare foot in cold water, and you have a winter jacket on.
Your core is nice and warm but a large temperature gradient down to your feet.

I think you need to enclose (insulate) the LTZ (on both PCB sides) and as much of the ref PCB around it as possible to get isothermal IC connections. So the temp gradient occurs away mostly on the PCB copper traces leading to the ref IC pads. Or maybe not.
Part of the fun here is learning a new microcosm. I think I will add the connecting TC's and try Spice sims when I get a chance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on October 01, 2017, 10:49:26 pm
The analogy is slightly different - we're talking about your feet being in separate buckets of cold water. If they are not at the same temperature, you start getting the 40uV per degree C of the Kovar working against you. Everything else in the path is either at the same temperature (gold wires in the can) or relatively thin such that the temperature delta is small (the kovar - solder - copper layers at the PCB interface).

So our challenge is, getting the critical PCB pads at the same temperature.
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on October 02, 2017, 04:26:52 am
I understand your point. This thermal IR image from TiN's KX Ref at xdev.com (https://xdevs.com/article/kx-ref/) shows the main (~12°C) temperature gradient from top (IC case) to bottom (PCB). I wrongly thought that was something to minimize as I realized LT's intent to cancel out thermal EMF's, the Seebeck pairs:
pin 3, 7 cancel
pin 4, 5 cancel
pin 7, 6 cancel
pin 6, 8 cancel

Between pins it would be voodoo slots and differing copper traces making pads unequal temperature. That would cause large errors if I'm understanding this correctly now.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on October 02, 2017, 05:17:03 am
That's it exactly.

If the pads are reasonably well insulated from the rest of the board and have good thermal conductivity between them, then short legs should work best. That approach assumes that the pads have a materially higher temperature than the rest of the system.

If the pads are not well insulated, then longer legs will help keep the temperature more even at the kovar-PCB junction. TiN's picture seems to show a degree or two caused by the package, even with quite long Kovar legs.

The Datron approach seems to be short legs; a big insulator on the back; and slots. A ground plane inside the can pinout, populated with through-plated holes, would increase the thermal conductivity between the pins. I'd bet that, with a good insulator on the back, this would be better than slots. When these things were being designed, that was not an option.

Kleinstein's copper cap is less thermally efficient, but should help with even distribution of temperature.

And the big nono is unbalanced copper coming out of the pads.

As noted elsewhere, the 3458a reference works well. You see there long, thin traces and insulating caps that cover both sides of the board. The LTZ1000 also sits well clear of any other device, and the separate board does not hurt.

The 34470A design appears to implement some of these ideas.
https://youtu.be/_QpApuKdcqQ?t=887


Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on October 02, 2017, 11:08:57 pm
Theoretically, 0.36°C temperature difference between two LTZ pads (pins 3,7) Kovar generates 14uV which is 2ppm error, me thinks.
If this is correct, then some PCB designs out there are aggravating this by not having symmetrical copper traces leading away from the pads. The payoff from guard bands, copper pours, star-connections etc may get lost.


Looking at Keysight 34470-26503 REV 003 ref. PCB; Along with others, I'm not impressed...

Underside has extra "pads" at LTZ pins 3, 7; I think the idea is to thermally balance those pads.
You'd not put a bypass cap there- no solder mask and detrimental to long term drift as discussed earlier in this thread.

But star connection on pin 3 but not pin 7. Strange. Three ferrite beads for EMI but skinny traces to GND.

I sketched a partial schematic and could not make sense of it. Labels on the backside make it difficult.
U1 LT1013 pin 5 and pin 2 have RC between them? Must be going crazy, that's between the heater and ref op-amp.
{used wrong LT1013 pinout SOIC vs DIP}


{pic is crop of Dave's teardown pic.}
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on October 02, 2017, 11:57:37 pm
Keep in mind that the SMD version of the LT1013 has a non standard pin out. Pin 5 is an output and pin 2 is the negative supply for the chip.  They had to do this to fit the die inside a standard SMD package. It has caused me no end of problems...
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on October 03, 2017, 01:12:12 am
The mixed-up design ideas is something you see when the design engineer and the layout engineer are not talking. For a 7.5 digit DMM, 2uV is only 2 counts. There's likely more noise than that in the rest of the system. If there's a new 8.5 digit coming, then maybe some of this gets fixed. On the other hand, the cover area is quite large and may be enough to keep the temperatures even despite the thermal path.
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on October 03, 2017, 03:44:18 am
I did have the wrong LT1013 pinout (DIP vs SOIC); Now 34470-26503 schematic looks vanilla except for the FB's.
I'm surprised at the cost reduction with what looks like Yageo 0603's and three precision 1206 's. Not sure who uses Helvetica font on their 1206's. Stackpole maybe.
If Agilent broke the piggy bank, using three Vishay VFCP smt foil (http://www.vishaypg.com/docs/63106/VFCP.pdf) adds ~$30 cost.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 03, 2017, 09:12:26 am
A temperature difference between the pins is not good, but it only the change in the temperature difference that would cause trouble. The constant part would be just an other small addition to the reference voltage (even with very low noise).

One can expect the temperature differences to be about proportional to the heater power and thus about proportional to the temperature difference of the reference to environment. If the assumed 0.36 K difference is at a ref to air difference of 20 K, the 2 ppm effect would occur over a 20 K span. Thus it would be a contribution to the TC of 0.1 ppm/K.  HP tends to use a higher temperature for the LTZ1000 - thus the effect would be even smaller.  So the additional error is in the range of the normal TC.

If made on purpose and well sized it could even be a good alternative to the kind of afterthought 400 K resistor to compensate residual TC of the non A version. With a FEM simulation (or a few iterative steps or pure luck) it sounds plausible to find such a suitable layout / thermal design.

The rather cheap SMT resistors might be the bigger issue, e.g. due to humidity effects on the board.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 03, 2017, 09:35:58 am
Hi floobydust,
would you mind publishing your schematic here?

Thanks
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on October 03, 2017, 08:41:13 pm
Here is my schematic of the Keysight 34470-26503 REV 003 reference PCB, from Dave's teardown pics.

Connector J1 pinout I could not see traces and the labels are in the way. Surely some errors there. If people let me know I will update it.


Comparing to HP3458a (https://xdevs.com/fix/hp3458a/#a9pcba) reference, I notice:

Collector resistors 74k25 -> 75k3 (look like vanilla 1%'ers)
Zener resistor 111R-> 100R
GND balance resistor 2k76-> 4k22

Heater base drive 499R-> 511R
Heater ratio still 15k/1k
Heater monitor V at transistor instead of op-amp
Using dual diode BAS28 (https://assets.nexperia.com/documents/data-sheet/BAS28.pdf)
No temp slope comp resistor for non-A LTZ but support for TO-126 heater transistor
Addition of three ferrite chip beads

UPDATE 2020-12-26: schematic corrections and updated to Rev. 2 based on info from thread about 34470a LTZ1000 reference PC board clones:
https://www.eevblog.com/forum/metrology/buyers-beware-misleading-34470a-reference-modules-(clones)-on-ebay/msg3383376/#msg3383376 (https://www.eevblog.com/forum/metrology/buyers-beware-misleading-34470a-reference-modules-(clones)-on-ebay/msg3383376/#msg3383376)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 04, 2017, 02:08:36 pm
My estimate below shows, that a temperature gradient between the pins should not be that critical. It would take more than about 0.3 K of difference to make the error larger than the "normal" 0.05 ppm/K TC of the LTZ1000 circuit. This should not be that difficult with a symmetric layout. An extra heater would be kind of overkill. If at some extra copper to improve the coupling between the pins should be all it takes.

Today the thermal performance can be simulated if needed, and it is reasonable repeatable. This might make is even possible to replace the 400 K compensation resistor with an intentional temperature gradient. However I am not sure the needed gradient is easy to obtain - it might need a significant asymmetry.
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on October 04, 2017, 08:56:20 pm
Kovar delta-T of 0.1 K gives 4uV or 0.6ppm at 7.1846089V ref. Does that seem correct?
To me it looks critical, keeping all the pins at the same temperature throughout varying ambient temperature. I hear you can cal it out as a fixed offset, but the danger is if the pin-pin temperature gradient ever changes magnitude, due to changing heat loss/gain across the PCB.

34470a having fan airflow across the ref. PCB either will either swamp that or make it worse, as I think the fan is variable speed. The voodoo slots insulate in three areas but are not symmetrical, and LTZ pin 3 is at the PCB edge.


3roomlab, from TiN's IR pic, I see radiant heat transfer from the underside of the LTZ to the PCB, so the PCB pads are heated by both (short leads) conduction and radiation from the ref. IC. The challenge seems to be keeping symmetrical heat loss around the full circle. I did not see the glass as part of your thermal model. Is it in there.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 04, 2017, 09:46:41 pm
My estimate below shows, that a temperature gradient between the pins should not be that critical. It would take more than about 0.3 K of difference to make the error larger than the "normal" 0.05 ppm/K TC of the LTZ1000 circuit.

I think it is much more critical than that what you can estimate.
My PSRR experiment shows for a battery voltage between 14 and 18.5V a temperature difference of 1.5 deg C measured near the voltage regulator (LT1763) which is a couple of cm away from the LTZ.

On the NTC near the LTZ1000 you can see practically no change from the voltage regulator heating. (only some ambient temperature changes).
So the temperature on the LTZ pins is nearly not affected by the voltage regulator heating.

But: the change on LTZ output is repeatable around 3uV (nearly 0.5 ppm or 0.1 ppm/V) difference between 14 and 18.5V at the voltage regulator input.

So what really counts are measurement values. (We still have not enough).

with best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on October 04, 2017, 10:39:46 pm
The third heat source is the heater transistor- in your circuit, is it supplied pre or post voltage reg? I could see it's dissipation also increase with higher Vcc, if pre-Vreg.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on October 04, 2017, 11:11:03 pm
The heater has to be behind the regulator, as the LTZ1000 is very sensitive to operating temperature.

The 3uV is going to be from differential thermal EMFs. We are talking about really small differences, but they need attention. This explains why  you see slots between the power section and the LTZ on some of these boards. That new Keysight reference seems to have a lot of good ideas in it, questions around final execution notwithstanding.

At the end of the day, we are niggling over very small things. But they add up, so eliminating everything possible that we can hit through layout is a good idea.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chickenHeadKnob on October 05, 2017, 01:27:17 am

3roomlab, from TiN's IR pic, I see radiant heat transfer from the underside of the LTZ to the PCB, so the PCB pads are heated by both (short leads) conduction and radiation from the ref. IC. The challenge seems to be keeping symmetrical heat loss around the full circle. I did not see the glass as part of your thermal model. Is it in there.

I believe that is a mirror reflection artifact from the copper ring on TiN's kx board, copper is an excellent IR reflector. Using teflon as a substitute for FR4 in simulation is suspect, as I expect pure teflon is a much better thermal insulator.
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on October 05, 2017, 02:01:31 am
Found a nice article in
"http://www.electronicdesign.com/analog/what-s-all-ltz1000-stuff-anyway"

about LTZ1000's, TiN's KX-design, and plenty of background information and references to basic articles.

Particularly interesting for me in this context, the thermal image of the temperature antistress distribution.

Thanks again to TiN  :-+

(edit: yes, i know, well known infos for some ;) )
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 05, 2017, 04:40:13 am
The third heat source is the heater transistor- in your circuit, is it supplied pre or post voltage reg? I could see it's dissipation also increase with higher Vcc, if pre-Vreg.

the schematic is here:
https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=189655 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=189655)

So all is supplied from the 14V voltage regulator LT1763 to reduce battery voltage dependency.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on October 05, 2017, 04:58:38 am
The third heat source is the heater transistor- in your circuit, is it supplied pre or post voltage reg? I could see it's dissipation also increase with higher Vcc, if pre-Vreg.

the schematic is here:
https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=189655 (https://www.eevblog.com/forum/projects/ultra-precision-reference-ltz1000/?action=dlattach;attach=189655)

So all is supplied from the 14V voltage regulator LT1763 to reduce battery voltage dependency.

with best regards

Andreas

what is the ball park power consumption (entire circuit powered) of this 14V variant 1) approx at start up? and 2) when stable?
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on October 05, 2017, 06:02:47 am
it is substitute with teflon. in FEMM there is glass from 0.8 to over 4 W/m.K. nobody know what is LTZ type  :-DD

Schott (http://www.us.schott.com/epackaging/english/overview/technologies/gtms/index.html) uses borosilicate glass 8250 (hard) with Kovar. Corning seems to have discontinued their semi glass line. Some data pg 22 (http://www.schott.com/d/epackaging/a67ecd2e-f020-465b-954e-932148c624cf/1.0/schott-hermetic-packaging-and-sealing-technology_eng.pdf)
Datasheet with thermal conductivity data for 8250 glass (http://www.us.schott.com/tubing/media/selector/datasheets/english/schott-tubing_datasheet_glass-8250_english.pdf) at 90°C = 1.2W/mK.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 05, 2017, 03:54:29 pm
Bottom "heat" pattern is definately IR reflection on the gold plated circular shape.

I since I didn't build any LTZs lately, must not resist the urge to build few more, this time bit different, and more traditional design to discuss about.  :popcorn:

PNG-schematics (https://xdevs.com/doc/xDevs.com/FX/schematics_f00.png)

 :bullshit:
Title: Re: Ultra Precision Reference LTZ1000
Post by: dr.diesel on October 05, 2017, 04:08:15 pm
I since I didn't build any LTZs lately, must not resist the urge to build few more, this time bit different, and more traditional design to discuss about.  :popcorn:

WooHoo!

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 05, 2017, 05:17:16 pm
Bottom "heat" pattern is definately IR reflection on the gold plated circular shape.

I since I didn't build any LTZs lately, must not resist the urge to build few more, this time bit different, and more traditional design to discuss about.  :popcorn:

PNG-schematics (https://xdevs.com/doc/xDevs.com/FX/schematics_f00.png)

 :bullshit:
The LTZ1000 part looks very conventional. I somewhat doubt one would really need 0.2 ppm/K resistors. The important parameter on the resistors should be long term stability, not the TC. Of cause they usually come together, but not always. Just for the TC the resistors look better than needed. Due to the high current output a transistor the LT1013's output might be a good idea, though not absolutely needed.


For the voltage regular, one usually needs the capacitors just at the input and output of the regulator, even close by. So even just a ferrite bead as shown could make the regulator oscillate. Extra inductive filtering should be on the input side and maybe after the first set of capacitors at the output. If you really want the LTC2057 in the circuit, I would use a separate regulator (even if just an 78L15), as the 2057 would be a significant source of RF noise. One might also want some filtering between the LTZ reference an an AZ op at its output.

The 7 to 10 V circuit shown does not look like it would tolerate capacitive loading and could compensate for voltage drop at the GND side. Not sure with this, as the drawing is a little confusing. The resistors in the 7 to 10 V part are way more critical (e.g. a factor 100) than in the LTZ1000 part. So one should also have an direct output at the 7 V level so one could at least check for long time drift of the resistor ratio.
The divider might also need resistors for trimming, if exactly 10 V are intended.
Due to the errors expected from the resistors in the 7 to 10 V stage one might consider a good conventional OP instead of a AZ type. This might need slightly lower resistor values however.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 05, 2017, 05:23:46 pm
what is the ball park power consumption (entire circuit powered) of this 14V variant 1) approx at start up? and 2) when stable?

The battery current of LTZ#3-#6 at room temperature is listed here:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560)

The power up duration is only several 100 ms so it is negligible. You can calculate the value from the heater resistor in the data sheet.
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg832030/#msg832030 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg832030/#msg832030)

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 05, 2017, 09:52:22 pm
I'm back in the LTZ club again.  :-+ I had some issue with the yellow resisitors used in the cirrcuit, the 120R resistor measure high resistance after a while. That's why I dropped all of them out of my circuit.

Within the last two days I received a bunch of goodies, a resistor from Frank to repair my LT-LTZ000 board, resistors from Rhopoint, LTZ1047B boards including batterie monitor from Andreas and some material like LTZ1000 and capacitors for repairing my Keithley 181 (which is now working again) from Digikey. A lot of stuff to assemble the next weeks. However, the resistors in my first LTZ1047 are replaced and I have to observe if the LTZ took any damage. The LT-LTZ1000 is now repaired, but needs some minor changes as it differs from datasheet circuit.

I also received the mysterious reference from Philipp, which I'm pretty much sure it is an arrangement of 4x LTx99 together with some OP07, but I'm still reverse engineering the circuit. News about it in the corresponding thread. And I received some wonderful standoffs from Emmanuel. Thank you very much, thanks to all of you guys. I really enjoy your contacts.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on October 06, 2017, 02:09:01 am
On the new TiN design:

1) How about a series pass FET on the output? Good way to keep everything safe.

2) The Fluke resistor pack is a bit of a rarity. If we can get the output voltage close, how about fine-tuning it with a DIP switch and a resistor pack? Tolerance and stability is not so critical in these last bits. 8 bits might not be enough - but it seems that 16 would do. Probably 16 switches, and resistor values selected such that there's a bit of overlap.
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on October 06, 2017, 02:53:22 am

2) The Fluke resistor pack is a bit of a rarity. If we can get the output voltage close, how about fine-tuning it with a DIP switch and a resistor pack? Tolerance and stability is not so critical in these last bits. 8 bits might not be enough - but it seems that 16 would do. Probably 16 switches, and resistor values selected such that there's a bit of overlap.

Don't know where to get that at all. That's why I would prefer the ability to use a precision resistor-cascade with low resistance and -trimmer as last stage like in Dr.Frank's design.

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 06, 2017, 04:49:13 am
2) The Fluke resistor pack is a bit of a rarity.

Lucky for me, greed has no limits here (https://xdevs.com/article/res_f8846a/). However it's optional, one can use "simple" VHD200 R10/R11 + trim resistor R9.

Full disclaimer before this get out of hands, this reference is one off design for specific purpose to put inside the Fluke battery pack (hence the name, "Fluke eXperimental") and use as a transportable standard for 3458A/5700A. So input protection, output protection and trimming will be implemented once I start PCB design to see how it all goes.  LTZ's resistors will have option for PTH PWWs from Edwin as well. 0.2ppm VPGs right now in schematics are just reused from old KX design.

As result, I have no means to make this design commonly repeatable like the older one, however design files will be public once performance is verified (think 2019).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on October 06, 2017, 09:29:41 am
"Before this gets out of hand" ...i thought thats why we gathered here  :-DD

Anyway: Does anyone know if SO8-Package LT1013 contribute more drift in the long term compared to the DIP-package? Because of maybe humidity dependence and pcb-lenght-variation due to temperature/humidity-changes and therefore mechanical stress on the LT1013-package.

Also: It would be nice if every LTZ1000-board in a bank would have its isolated supply which is dead quiet, like its done in Fluke 7001-modules https://www.eevblog.com/forum/metrology/teardown-voltage-standards/msg902910/#msg902910 (https://www.eevblog.com/forum/metrology/teardown-voltage-standards/msg902910/#msg902910) Are there any suggestions how to accomplish this or ready made solutions? Maybe standard transformer + LT3042 already suffices?
Interestingly Fluke 732B and 734 doesnt feature the claimed quiet isolated dc/dc-converter (Fluke 7001) which would enable mains powered Fluke 7001-modules to be directly compared to a JJA. So how are Fluke 732B/A compared to a JJA, during battery operation or mains powered?  ???
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 06, 2017, 04:41:51 pm
SO8 suspected not that much from humidity but from mechanical stress directly from the board due to much shorter pins.

I was happy with results on my isolated supply for nV head (X1801) using LT3439, standard CTX02 trafo and LT3042+3092 on the output. However for this current LTZ ref it's not going to be used due to extra power waste (battery life) and no real need (standard should have enough juice to work few days without mains).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 06, 2017, 05:21:50 pm
The DIP LT1013 is slightly better than SO8, mainly due to board stress. However both should be good enough, since one a small fraction (around 1/200) of the OPs dirft will appear at the output.

It is not he LTZ1000 circuit that needs a separate supply, but it can be the part around it. It can sometimes save you an extra OP for separate force sense lines.

If there are batteries in the circuit anyway for transport, one can use them for calibration of critical measurements too. So there is a limited need for a highly isolated supply.
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on October 06, 2017, 06:01:25 pm
As far as I know the Vishay resistors TiN have in the schematic (Z202 and HZ) are not 0.2ppm/C but according to the datasheet +-2ppm/C. The 0.2ppm/C specified as typical more seems to be the variation of the temperature coefficient over the whole temperature range??

As the Z202 specified for the two most critical positions (1k and 12.5k) are epoxy I would be even more worried for humidity than temperature that to some extent can be compensated. I have not tested Z202 but the old S102 definitely, from both my own measurements and also Vishay app notes, are humidity sensitive up to about 1ppm/%RH. This is also in the same region I have measured for WW like 8E16 and also SMD0805 like RN73, ERA 6A and PCF0805. The sensitivity varies both between same value resistors and also between different values. Lower values seem to be less sensitive.

The long term drift for WW I have tested are low maybe 1-2ppm/year compared to the SMDs that are more 5-20ppm/year after the first months.

This is for no load or very light loads at normal lab temperatures and mounted on FR4 boards.

Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 07, 2017, 07:15:35 pm
Updated schematics to F01.

* Power nets update, LDO output is +11V due to input power is +12V pack. R15 changed to 110K accordingly.
* Added optional C22
* Guard nets around LTZ driven by R16-R17 network
* Temp sensor IC powered from isolated +5V/IGND
* Added filter RCR R18,C24,R19 between 7V out and chopper input.
* Output gain amp replaced to ADA4522-2, with second amp used as output buffer/sense.

(https://xdevs.com/doc/xDevs.com/FX/schematics_f01_1.png) (https://xdevs.com/doc/xDevs.com/FX/schematics_f01.png)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 07, 2017, 07:37:01 pm
Hello,

- C7 will make U6A instable
- C22 does not help much without a additional resistor between C22/U2A and R1.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on October 07, 2017, 07:55:49 pm
A couple of small comments around the output buffer.

1) The 2N3904 is a bit noisy for the output transistor (6dB specification). You could use a low-noise part, typically around 2dB, instead. Or maybe even a series pass FET, as per the Fluek 732.

2) You need to get something to deliver negative feedback into  the output amp. Otherwise, the output voltage will slam up to near rail when the output connector is disconnected. A reasonably high value resistor should do it, maybe 10k.

Also - these resistors may all need to be low-noise parts.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 07, 2017, 09:24:04 pm
The filters around the voltage regulator will likely make it oscillate. The regulator needs the caps directly at the input and output. The filter at the output of the regulator does not make any sense. Extra inductive filtering might be a good idea at the output and maybe for the negative supply side.

The R18 / R19 resistors should probably be higher value. The ADA4552 does not need such a low impedance.

Usually there is no need to have separate OPs for the 7 to 10 V amplification and the output driver with drive and sense for the positive side. Both can be done with a single precision OP and maybe a second lower grade one to do current compensation for the sense input. Provisions for missing sense connection is a good idea - this could be a resistor with an additional diode for protection.
The output amplifier should be made tolerant to capacitive loads (e.g. extra capacitive feedback).

The noise of the driving transistors (2n3904) is not a problem as they are inside an OPs loop.

An output with separate force and sense only makes sense if there are force and sense for the negative side too. This also includes the ground point of the divider that sets the gain. One might want to use the second half of the 4522 for the negative side - however this would need a different supply (e.g. a negative).

The guard lines make more sense if closer to the right voltage. So either R3 or R16 should be adjusted.
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on October 07, 2017, 10:11:51 pm
TiN, if you are open to some observations on your FX reference.
I would apply EMI filtering and bypass capacitors differently. Unless I am misunderstanding things which frequently happens. Very difficult to know all subtleties and wisdom applied.

Having bypass caps grounded to multiple places is not what I would do, because they end up effectively in series, connecting nodes at high frequencies.
Ground for C1, C3 not at U2A pin 4; FB3 would ensure U2A rails are noisy at RF.
Ground for C10, C11, C12 different than C8, C16; shunting FB2.
FA2 looks bypassed; C17 comes first after the Vreg. for stability. If worried about RF from the Vreg, I would place FA2 downstream of C17.

I would break up rails+gnd with FB or inductors into islands, so no intermingling bypass cap grounds, and PVIN filtered to U6, Q2.
I'd draw a pic but it's Thanksgiving long weekend up here.

Running off a battery, I would add a polyfuse so D28 and PCB traces do not burn up if wrong polarity, or perhaps use a series Schottky.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on October 07, 2017, 11:05:02 pm
1) The 2N3904 is a bit noisy for the output transistor (6dB specification). You could use a low-noise part, typically around 2dB, instead. Or maybe even a series pass FET, as per the Fluek 732.

I really wouldn't worry about it. A typical 2N3904 has an en of 1.35 nVrms /sqrt(Hz) at 10 mA, realistically the bandwidth the reference is going to be used in is probably only 25Hz, so that's a 6.75 nV rms contribution to a 10V output. Even taken as peak that's a mere 1.05 ppb, or if you prefer -167 dB. It's going to be swamped by the intrinsic reference noise at around 2uVptp/sqrt(Hz), 48 dB higher.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 08, 2017, 12:24:08 pm
I wanted to get started on PCB, hence excessive different ground nets, to see how to separate on routing first. Sorry if that cause confusion.
Added first idea for placement. LTZ top left, LDO and heater transistor bottom left, 7V->10V top right and output pass transistor bottom right.
Board size arbitrary atm, need to check metal cases that can be reused. Fluke SIP is bend to right angle, to save on Z-height.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 08, 2017, 12:46:14 pm
The 7 to 10 V amplifier part and output buffer need a major change. Especially getting separate force and sense wires for the negative side will likely need a big change to the circuit (maybe including the power supply). So it is still way to early for layout.

Getting the ground right is also important - nothing to decide afterwards how it best fits the layout. It also depends on the output stage - one might even end up better having the LTZ1000 circuit for a negative polarity.

The heater transistor is not such a bad heat source. The only really bad thing about it is that it is so localized, as a distributed heat source it also has positive effects - up to the point of stabilizing the temperature of the whole board. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on October 08, 2017, 03:37:53 pm
If this is a really new project, would it be better outside this LTZ1000 mega threat, even maybe projects?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 08, 2017, 03:44:05 pm
It's in good place here, as just another iteration of LTZ module with 10V output.
Also I'm bit lost why negative sense would be helpful, as it's essentially battery powered source.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on October 08, 2017, 06:45:13 pm
Negative sense compensates for the drop in voltage accros the negative output. While the output amplifier senses at the positive output post, the negative output post is not sensed.
Assume the negative line is 10mOhms and you draw 1mA then you have 1ppm of error through the load. If the load is always high impedance (3458A), then this load offset error would of course not occure.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on October 09, 2017, 06:33:18 pm
Quick and simple question, when buffering the LTZ1000 reference, with say an LTC1150, should a series resistor be added to prevent excessive loading should there be a problem with the buffer?  Like 10K or so?  Or is this generally not necessary or desirable?

I have a LTC1150/LT1010 buffer built that works quite well, but I'm not sure if I should worry about the possible loading of the LTC1150 in the off or no-power state.  Such as turn on or if there was some fault with the buffer.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 09, 2017, 07:23:22 pm
A series resistor and a capacitor at the input side of the buffer to ground is a good idea for several reasons:
It works as a filter and thus would reduce the higher frequency noise a little. The LT1013 and LTZ zener are usually more noisy than a 10 K resistor. The added noise of the 10 K are not that bad at low frequency. One could ague that maybe 5 K might be better, but 10 K is a reasonable value.

Not powered the buffer circuit might be so much of a load (at least until the supply caps are charged) and might even get damaged from a powerful voltage source without a resistor or similar. The load might be to much for the LTZ circuit and could cause it to turn the heater too high.

The AZ amplifier has some current spikes that contain RF frequencies and thus might upset the reference a little. If paranoid even more than just simple RC filtering might be good.

A resistor (especially if suitable for sufficient voltage) at the input of the buffer might also offer some protection against ESD.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 09, 2017, 07:42:58 pm
Kleinstein, ap, floobydust, martinr33
Thank you for feedback. I've updated output stage as discussed.

PNG-schematics FX Rev.02 (https://xdevs.com/doc/xDevs.com/FX/schematics_f02.png)

Also I've dig into stashes and got enough parts to build some crude prototype. Sanity check in LTSpice before we go blowing stuff up:

(https://xdevs.com/doc/xDevs.com/FX/ltspice_pa.png) (https://xdevs.com/doc/xDevs.com/FX/ltz_fx_output7v_10v.asc)

Few hours later...to my surprise it even worked right off the bed.
Critical resistors used are custom VPG VHD200 (20K/7.663K, measured <1ppm/K TCR (https://xdevs.com/vpg_tcr_rms2/)), and trim S102K 330R + PTF 30R.
Rest are random PTF's. KX LTZ output connected to opamp ADA4522-4 input via 3.01K-1uF-3.01K network. Current drawn from reference is <300nA.
Output transistors are NPN+PNP pair STD830CP40 (http://www.st.com/content/ccc/resource/technical/document/datasheet/c4/80/89/70/76/ca/4b/9c/CD00236358.pdf/files/CD00236358.pdf/jcr:content/translations/en.CD00236358.pdf).

(https://xdevs.com/doc/xDevs.com/FX/fx_out_buf_1.jpg) (https://xdevs.com/doc/xDevs.com/FX/fx_out_buf.jpg) (https://xdevs.com/doc/xDevs.com/FX/proto_outstg_1.jpg) (https://xdevs.com/doc/xDevs.com/FX/proto_outstg.jpg)

Currently I've hooked it to 3458A to log some stability/noise ballpark.

FX output stage with ADA4522-4 and KX channel 6 ref, which is +7.13665V output. Simulation values very well match to real output value.

Live measurement data:

(https://xdevs.com/doc/xDevs.com/FX/fxpa_noise_2h.png) (https://xdevs.com/fx_test_proto1/)

Last year data from Fluke 732B vs another 3458A, 24 hour, NPLC 100 to comparison:

(https://xdevs.com/doc/xDevs.com/FX/732b_noise_24h.png)

Also output is trimmed (R3 on LTSpice schematics) using S102K 330ohm + PTF56 30 ohm 50ppm/K. Per calculation shift of this resistance network to 100ppm will cause output to change 1.3ppm.

I'm pretty happy with the result, given it has zero shielding, no air drafts protection.

Both LTZ reference and prototype amp powered from Fluke 792A battery pack (+12.5/-12.5V SLA).
This is where this build will eventually go, to make it a transportable 10V standard to use for 3458A/5700A calibrations.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 09, 2017, 08:03:17 pm
The shown output stage should get extra compensation / local feedback at the OPs. This would be a small capacitor (e.g. 100 pF range) from the OPs output to the inverting input. R8 is should be a little larger for this. This should reduce ringing and sensitivity to capacitive load.

With a different output stage at the negative side one might be able to get away with a much lower negative supply, maybe down to 0.5 V.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 09, 2017, 08:13:16 pm
I've tried load output with 5Kohm and 47uF cap, that shown just as 0.4ppm shift. 1uF load worked fine as well.

Opamp and BJTs powered directly from battery rails, no LDO. Will see how much margin is there before if go out of regulation. Per opamp DS with 1mA load it should be better than 100mV from rail voltage.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on October 09, 2017, 08:14:32 pm
I usually design in one other component to limit potential damage to the LTZ1000A chip. Depending on expected operating temperature, I add a series voltage dropping Zener at the collector of the heater transistor. This limits the peak chip temperature rise. Other people have mentioned that if the LTZ1000A chip gets somewhere over 100 deg C it will affect aging. Over 150 deg C can cause permanent damage.

My last design needed to work in a warm environment so I ran the chip at 95 deg C. After it warmed up (in a cool environment on the bench) I think I had 8 volts to the heater. With a 15 V power supply I had a 4V Zener in series with the collector of the heater transistor. The warm up time was a longer than normal. However, when I was checking operation on the bench I did not have to worry about my test probe slipping, shorting out the wrong node and overheating the chip.

When starting up a new design I use a separate PS for the heater voltage and I start with something like 5V till I verify that I have the PCB design correct. I increase the 1k ohm heater transistor base resistor to 10k on some low temperature designs to prevent a sneak path for heater current during warm up.

Adding a series voltage dropping Zener to the collector of the heater transistor is good insurance. The voltage dropping Zener may also help aging in a reference that has frequent power cycles. There will be less peak stress on the chip as it warms up. With 13V across a 300 ohm heater there will be 560 mW of heat on the chip until it reaches operating temperature where it needs around 100mW (65 deg C chip, LTZ1000A) to maintain temperature.

The non A version of the chip may require full heater voltage for correct operation.
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on October 10, 2017, 01:41:30 am
I think it's a good idea to limit the heater output.

The LTZ (http://cds.linear.com/docs/en/datasheet/1000afe.pdf) heater resistor has a spread of more than 2:1; 200-420ohms with 300 ohms nominal.
Then factor in the "A" needs 1/5 the heater power of the non-A and you could have way too much... gain...heat...

Could you move the zener (led?) between from LT1013 op-amp (-) input to heater transistor emitter, to voltage-limit the LT1013's output.
It's just zener's heat has to be kept away from the ref amp and LTZ. Or use current-sense perhaps.


note the datasheet heater graphs, unknown physical configuration- free air, on a pcb etc.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on October 10, 2017, 02:12:04 am
You could use a device between the heater transistor emitter and the (-) input of the op amp but I don't like to do it that way.  I try to limit the wiring going directly to the op amp inputs. They are just another EMI antenna connected into a very very sensitive node. An LED or a glass Zener may generate current when exposed to light or have leakage currents that will disrupt this sensitive circuit node.

A resistor or an Zener on the heater transistor collector can be located far away in the corner of the pcb where the heat does not influence operation.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on October 10, 2017, 06:43:14 am
You could use a device between the heater transistor emitter and the (-) input of the op amp but I don't like to do it that way.  I try to limit the wiring going directly to the op amp inputs. They are just another EMI antenna connected into a very very sensitive node. An LED or a glass Zener may generate current when exposed to light or have leakage currents that will disrupt this sensitive circuit node.

A resistor or an Zener on the heater transistor collector can be located far away in the corner of the pcb where the heat does not influence operation.

Whilst agreeing with the heat flow issue, surely a raised potential at the heater emitter will reduce the parasitic diode leakage?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 10, 2017, 11:33:49 am
Zener diodes have leakage well below the nominal voltage. So it is not a good idea to modify anything at the OPs input side. Limiting with a zener diode in series with the transistors collector is good (if the supply is reasonable stable). This will also spread out the power that otherwise would be all at the transistor.

Another option would be at the transistors base towards ground, so limiting the maximum output voltage to the heater. Here a VBE multiplier (transistor + pot)  might be an option. A power limit decreasing with high temperature is nothing bad.

Due to the spread in heater resistance and different thermal insulation / set temperature one might have to adjust the maximum heater voltage individually.

The higher temperature gain for the heater in the A version is not a real problem. Due to the square law with the resistor, the change in power for a change in voltage is also lower. So the gain is not that much higher.

@TiN: the ouput driver looks like it is only marginally stable. Even if it does not oscillate with 47 µF at the output this is not really guarantied. Capacitance from the outputs towards the circuit ground could cause trouble. Small extra caps at the OPs should help so that caps at the outputs could be used as a measure against EMI.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 10, 2017, 12:11:50 pm
I'd say that large capacitance is rather extreme and unusual. Added provisions for C39,C40,R32 if that what you mean.

Also overnight span with deliberate temperature changes from +25.6 to +31 didn't reveal visible correlations, and output still in 0.4ppm window.  :=\
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 10, 2017, 12:46:43 pm
C39,C40 and R32 is what I meant with extra compensation.

The caps C41-C44 look a little unusual, just two caps from the transistors collector toward the power ground would be the more normal way.

One point someone already mentioned before is that is might be a good idea to have a resistor or diode between the force and sense pins. This way the voltage would not increase very much if the sense connection is lost for some reason.

less than 0.4 ppm variation over a 6 K temperature range is very good, given that some of this is likely noise and maybe still some initial drift. It won't be super good for the LTZ1000 alone, but it is for the amplifier.

One could get a small negative supply from just a diodes drop or two. This could save you the second battery pack. With RR Ops a single 12 V supply might be just sufficient, though a little more (like 14 V) would make things easier.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on October 10, 2017, 01:14:18 pm
Whilst agreeing with the heat flow issue, surely a raised potential at the heater emitter will reduce the parasitic diode leakage?

I measured the leakage current of the parasitic diodes inside the LTZ chip several years ago. The leakage was less than 1 pa at 15 V bias. So the internal parasitic diodes shown on the LTZ data sheet are very good, low leakage diodes.

External Zeners or normal diodes have to be carefully designed in to prevent leakage currents or EMI demodulation issues.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 10, 2017, 01:31:26 pm
Second battery pack is available regardless, as I still intend to keep original function of the power pack to provide +11/-11V to F792A, once such need occur. This LTZ design is effort to make it more useful, instead of having just a large box with batteries sitting around, doing nothing. Also floating 10V ref in lab can be useful for bridge/null metering purposes, as I have no means to invest into real 732A/732B. Another challenge is how to fanout this circuit output to the external world. Adding 4 binding posts would be non-trivial due to triple shielding shells.

I'll also have to implement under-voltage shut-off circuit, to prevent LTZ+amplifier draining batteries too much, but that's outside of this thread scope.
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on October 11, 2017, 12:26:02 am
Zener diodes have leakage well below the nominal voltage. So it is not a good idea to modify anything at the OPs input side...

Yes the heater control op-amp inputs are very sensitive; definitely no zener there to limit the heater power.
The impedances at about 10k and 70k I thought moderate, but the gain is extremely high.
1uA there causes about 7-17mW/500mW power shift.

I used KO4BB SPICE model for the LTZ1000A heater. (http://www.ko4bb.com/getsimple/index.php?id=a-spice-model-for-the-ltz1000-heater)  The heater transistor is run common emitter though.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 19, 2017, 04:04:40 pm
Interesting to know, for some reason Rhopoint has changed the specification for their 8G16D resistors from ±3ppm/°C to ±5ppm/°C.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vtile on October 19, 2017, 11:20:10 pm
Since the heater/oven seems to be one of the achilles (as lazy reader of these electron splitting threads, which are really interesting. :) ) of the LTZ1000, why everybody is doing analog controller of the oven. Put it digital and run it through MPC or even digital PID....?  :o
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 19, 2017, 11:30:57 pm
It's very sensitive and digital more likely to inject more noise into the system, than not :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vtile on October 19, 2017, 11:38:09 pm
It's very sensitive and digital more likely to inject more noise into the system, than not :)
So digital chip designers still failing to deliver?  >:D ;)



PS. If someone is digital chip designer, take above as friendly teasing.  :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 20, 2017, 04:42:19 am
Interesting to know, for some reason Rhopoint has changed the specification for their 8G16D resistors from ±3ppm/°C to ±5ppm/°C.

-branadic-
Hello,

I have seen that on the web-page. (from one week to another).
But if you look at the data sheet the 5ppm/K were always the "standard" tempco.

If you look at a very old data sheet of 8E16 (not the 8G16) they have stated
5 ppm max for -55...125 deg C
3 ppm typ for 0..85 deg C

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 20, 2017, 07:42:46 am
Since the heater/oven seems to be one of the achilles (as lazy reader of these electron splitting threads, which are really interesting. :) ) of the LTZ1000, why everybody is doing analog controller of the oven. Put it digital and run it through MPC or even digital PID....?  :o
The temperature regulation in the LTZ1000 chip is still on a time scale that is easy to handle in an analog way. The analog PI regulator circuit is actually working very well. The A version still uses the same regulator setup and they do not compensate for the nonlinear heater function. So if really needed there would be still some room for even better regulation in the analog domain. However the current system seems to be well good enough and very fast regulation is not needed.  It would be demanding to get the same performance with a digital regulator: the on chip thermal loop is rather fast (up to the kHz range) and really low noise.

A digital regulator is attractive with large thermal systems (e.g. for the whole circuit or larger), because this will include longer time constants in the minutes range, that can get difficult in the analog domain. For such slow systems one also tends to aim for relatively fast reaction and thus a closely tuned regulator that a digital system can provide. For the fast LTZ1000 heater nobody cares if thermal stabilization needs 20 seconds instead of a possible maybe 1 second.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on October 20, 2017, 10:53:01 am
Someone remind me to post my experiences with the LTZ1000 in about 10 month. I had a design, few hundred of these were built into some equipments, and my NDA will be over by then.

Reminder, spill the beans.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 20, 2017, 07:33:44 pm
Since the heater/oven seems to be one of the achilles (as lazy reader of these electron splitting threads, which are really interesting. :) ) of the LTZ1000, why everybody is doing analog controller of the oven. Put it digital and run it through MPC or even digital PID....?  :o
Mhm,

you are aware that the 0.05 ppm/K correspond to 2uV/K change at the temperature sensor?
Would be a very interesting digital controller design to get the readings fast enough with a much lower resolution/noise floor.

And thermal time constant of the A-Version is damned fast.
When I measure the Zener voltage with a temperature setpoint step with 10NPLC
it is in steady state within 2 readings. (less than 800ms).

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on October 20, 2017, 10:22:18 pm

... you are aware that the 0.05 ppm/K correspond to 2uV/K change at the temperature sensor?


Andreas,

I think you forgot a decimal. 1ppm of 7.15v = 5.1uV, so 0.05ppm would be 0.255uV/K
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vtile on October 20, 2017, 11:09:26 pm
Well isn't the 0.05 ppm same than 50 ppb so for 7.15 Volts the 0.05 ppm would be equal to 50 ppb and as: 7.15 V * 10^-9 * 50 = 357.5 nV (/ K)
 
My throw did get out of hand yesterday it seems.

Edit. 7.5 V corrected to 7.15V
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on October 20, 2017, 11:16:39 pm
^ Need to scale 7.15 to 10 for a true ppm comparison.  7.15/10 = 0.715.  357.5nV*0.715 = 255nV for 0.05ppm based of 10.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 20, 2017, 11:21:43 pm

... you are aware that the 0.05 ppm/K correspond to 2uV/K change at the temperature sensor?


Andreas,

I think you forgot a decimal. 1ppm of 7.15v = 5.1uV, so 0.05ppm would be 0.255uV/K

You have  to calculate differently.
The RefAmp w/o the oven has a T.C. of about 50ppm/K.
A 0.05ppm change in the reference voltage is therefore equivalent to 1mK change in the oven temperature.
The sensing element, i.e. the base- emitter diode has about -2.1mV/K sensitivity, so 1mK is equivalent to a change of 2.1uV.

B.t.w.: Has anybody fully calculated, how the oven works, especially,  on which transistor fundamentals it's stability is based on? (Like Early voltage, temperature voltage Ut, and so on)
We have some theoretics-only guys here in this forum, participating also in this thread,  so that would be great, as such a model would give an idea about the dependency of the oven set point, and the stability parameters of the oven circuit, drift over time , and regulation stability.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vtile on October 20, 2017, 11:24:29 pm
^ Need to scale 7.15 to 10 for a true ppm comparison.  7.15/10 = 0.715.  357.5nV*0.175 = 255nV for 0.05ppm based of 10.
Ah, there were invisible 10. :) I were a bit confused a moment why 255nV "error".

Edit. After Dr.Franks post.
I have not calculated anything else than above. I'm only armchair theorist here at these subjects, so bear with me. :P

While I haven't done any calculations and I will not do so in the future. I'm pretty confident that control system is not linear in microscopic level it is kept and that the control values would have to be dynamically changed for different parts of control window to get optimal stability and control over the system. Analog propably not, digital maybe, especially since you could use all the computer software to analyse the control problem in hand and parametrice the controller from there.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Awesome14 on October 21, 2017, 09:27:57 am
When I wanted to build a LTZ1000 ref, I just called LT and asked how to do it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 21, 2017, 10:13:40 am
For the temperature sensing transistor it is V_BE at a given current around 100 µA that matters. The early voltage can have a slight effect on the gain of the transistor and thus the voltage gain the OP sees. For the stability of the temperature this would be a second order effect.  V_BE changes by some 2.1 mV/K, but the transistor with the 70 K already gives gain and thus the collector voltage already has a TC of around 500 mV/K.

So getting a good temperature reading is not that difficult, though it likely would need more than a µC internal ADC. The more tricky part for an digital regulator would be the output: The heater is good for something like 100 K temperature rise and should be adjusted fine to the 0.1 mK level. That would be something like a 20 bit DAC.  Not really attractive if half an LT1013 can do it as well (likely lower noise, but a little slower) and with much less EMI problems.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 21, 2017, 11:27:40 am
For the temperature sensing transistor it is V_BE at a given current around 100 µA that matters. The early voltage can have a slight effect on the gain of the transistor and thus the voltage gain the OP sees. For the stability of the temperature this would be a second order effect.  V_BE changes by some 2.1 mV/K, but the transistor with the 70 K already gives gain and thus the collector voltage already has a TC of around 500 mV/K.

So getting a good temperature reading is not that difficult, though it likely would need more than a µC internal ADC. The more tricky part for an digital regulator would be the output: The heater is good for something like 100 K temperature rise and should be adjusted fine to the 0.1 mK level. That would be something like a 20 bit DAC.  Not really attractive if half an LT1013 can do it as well (likely lower noise, but a little slower) and with much less EMI problems.

Kleinstein,

when I mentioned these 'theorists-only guy' in this thread, I exactly meant you.. maybe you were able to calculate this circuit correctly and fully... by means of the Ebers-Moll model, for example.

The oven circuit is more tricky.
Your estimate is probably correct, in that the T.C. of the collector voltage is much higher than the Ube usually would be (-2.1mV/K), but this Ube of the oven sensor does not change in this circuit, as you describe.

It is nearly constant, determined by the reference voltage Uref, like so: Ube = Uref(20°C) * (T-20°C) * alpha * R5/(R4+R5), with alpha being the T.C. of the RefAmp, about +50ppm/K.

So, how did you calculate these 500mV/K, and can you provide a complete calculation for this whole circuit, please?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on October 21, 2017, 01:51:15 pm
It is nearly constant, determined by the reference voltage Uref, like so: Ube = Uref(20°C) * (T-20°C) * alpha * R5/(R4+R5), with alpha being the T.C. of the RefAmp, about +50ppm/K.

Kleinstein is describing the open loop behaviour. Obviously you don't see this change when the circuit is closed loop .

Quote
So, how did you calculate these 500mV/K, and can you provide a complete calculation for this whole circuit, please?

Frank

The -500mV/K is just VBE change with temperature -2.1mV/K times the transistor's gain as a common emitter amplifier RC/Re where RC = 70k and Re is 26.1mV*/IC = 261R, so gain = 268. And 268 * -2.1mV = -563 mV/K.

* That figure is for 25C, the proper figure can be had from kT/q, with T for the operating temperature, k = Boltzmann's constant and q = fundamental electron charge.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 21, 2017, 01:53:14 pm
V_BE changes by some 2.1 mV/K, but the transistor with the 70 K already gives gain and thus the collector voltage already has a TC of around 500 mV/K.

You want to cheat. That what you want to describe is not the digital way.

If you do it the "true" digital way you will diode connect the transistor (shorting collector and basis) with a pull up resistor.
So you have only the temperature of -2mV/K.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on October 21, 2017, 03:09:37 pm
Andreas is correct in that a true digital way would be measuring the V_BE directly and not the amplified signal relative to the set-point from the divider. However I am afraid this is kind of difficult, as there are not many high res. ADCs that can directly use the 7.0x V reference voltage.  This might give a way to get rid of the 2 more critical resistors for the temperature set point. Except maybe for that divider drift I see no need to improve much on the temperature regulator. There is no real need to have a faster reaction as there are usually no large temperature fluctuations on the very fast scale.

While a digital temperature control it not really useful, there might be a chance that the set point divider could be checked with a high quality ADC, especially if such an ADC is present in the system anyway. This would be a way to detect and maybe digitally correct for long term drift of the divider. So maybe of you really want to cut costs on the two resistors in a low cost 7 digit meter.

In principle chances are good that the analog regulator could be tuned to a faster reaction if needed. The standard version uses the same circuit for the normal and A version and it does not correct for the nonlinear heater - so there is definitely some room for a faster control. However I doubt this would make a big difference, as the critical part is more like drift over months and not a small contribution to noise in the 1-1000 Hz range.  If at all it would be likely the low power region that could profit and allow better performance when just at the edge before the temperature regulator drops out of regulation. For normal use my feeling it that it is not worth the effort - maybe for the few cases when the whole circuit is in an oven and thus can / should constantly run at a low heater power. In this case the change can also be rather simple: higher gain and a rather low limit to the heater power.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zhtoor on October 21, 2017, 03:17:12 pm
or maybe deriving the heater power from the already available 7v in the main zener reference
and implement a pwm heater controller using this derived voltage to drive the heater, pwm control being
affected by digital circuitry with set point coming in from the sensor transistor in the chip in the form of
a target pulse width.

regards.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on October 21, 2017, 06:53:45 pm
Turning things around a bit, according to the datasheet, a 7 Ohm change in R3 (the 70k heater setpoint resistor) causes a 0.2ppm shift in output, or about 2uV. Therefore, with a small series resistor, I could adjust the output of the LTZ1000 with some precision. For example, to move 100uV, I would add 350 ohms. Seems like this might be an easy way to trim the reference to have fewer digits (i.e. get more trailing zeros).

Also, I am not so sure that heater stability is a problem. I'm more concerned about the unheated parts.
Title: Re: Ultra Precision Reference LTZ1000
Post by: tszaboo on October 24, 2017, 12:11:59 pm
Someone remind me to post my experiences with the LTZ1000 in about 10 month. I had a design, few hundred of these were built into some equipments, and my NDA will be over by then.

Reminder, spill the beans.
All right, but no specifics. Dont even ask for them, I consider them the IP of my previous employer.

I give you a story instead.
So I was designing high end battery testing equipment. The largest electric car manufacturer, (back in the day, not anymore) was using our system for testing the chemistry and they wanted much better voltage accuracy. Few PPM region. You need this, because open circuit state of charge calculation is very voltage dependent, and errors accumulate etc,etc. So they asked for an improved precision of our system.
We are talking about a big noisy system, which can supply 50A into each battery, and gets hot, even though it is water cooled. Not really the ideal, quiet, nice environment for voltage references. We narrowed it down to the LTZ1000 and the LM399 for the voltage reference, or integrating something into our system (management said no to this before you could finish a sentence). The LM399 was obsolete at that time, even from Linear, I think they were changing to the lead free process, but dont quote me on that.

So  I gathered all the circuit information, reverse engineering and pictures that I could, and designed a circuit. And immediately realized how stupid I am because Pin Configuration: BOTTOM VIEW. DOH! Funny enough, if you solder the LTZ1000 on the bottom side it works.
The final circuit is the one from the datasheet. It is on a small board with SMD components (except the opamp and the LTZ), carefully selected 5 PPM/K (max) thin film resistors (1206), SMD substitutes for the diode and transistor. Onboard voltage regulator, is a 7815, nothing fancy. Just place it to the other side of the PCB. And I didnt use any fancy swastika milling or anything like that. There was some to separate the 2N3904 and the VREG, and the resistors, but that's it. Maybe total of 40mm milling, on a credit card sized board. There was also an EEPROM onboard, to store the calibrated values. It went into a small plastic box (since there are big fans in the device) and it attaches to the base board with two nice gold plated board to board .1 inch header. I also placed the 4 critical resistors in close proximity. Thin film, no magic routing, no magic opamp upgrade, no magic low noise voltage regulator.
It worked out beautifully. We couldnt measure reliably the tempco, it was some 0.3ppm for the assembly. After a year we recorded some 2 ppm drift. (Both measurements were done with freshly calibrated 3458A). Inside the system it also worked as it should, making measurements, that are comparable to the 3458A, only faster. Bear in mind that we had to work in a single range, around 4 volt, since we were measuring Li-ion batteries, and nothing more.
Subsequently it was designed into a product, that was selling in larger volumes. Production ramped up. We had a lengthy burn-in process, I think it was at least 2-3 weeks. So I made a PCB holding and powering 5 of these. The output went into a switch matrix that went into the 3458A. Thinking about using a generic purpose relay card to do this? Well, forget it. Normal relays heat up when on, and the contacts will act like thermocouples. So let's design our own switch card.
Calibration setup looked like this: there was a stack of 30 LTZ1000 boards sitting on the base board. All went into another stack of relay cards. That went into the 3458a. Computer controls everything, python. 1000 NPLC voltage reading from the DMM. That is 20 seconds for one reading. One measurement is not measurement. I think we did some 15-30ish measurement of each card, throw away highs and lows, and average the rest. Confidence had to be high. All in the office, done by an engineer. Just making the test setup is expensive. Custom boards designed, firmware written, only to speed up production.
And then the calibration procedure started with an unskippable 30 minutes wait. Before that, there was an earlier setup, where each board was individually connected by hand. So that was about 16 board/day throughput for the calibration phase. Expensive? Well, 16 of these went into machines with "you cannot afford it" price tags, so no. We had a lot more assembly and building to do on each tester.

And that is my story. It has been a great ride! Maybe once I will go back to design precision analog, I definitely miss it sometimes.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 24, 2017, 01:24:20 pm
Thanks for the story  :-+. So essentially you needed low-noise stable reference, and stability was just to get away without frequent (expensive) calibrations. Guess nothing wrong in using LTZ in that perspective, since customer pays.
Measuring tempco to ~0.1ppm or wee bit better is not a problem if one to use large (20C+) temperature delta (gracefully).
Title: Re: Ultra Precision Reference LTZ1000
Post by: tszaboo on October 24, 2017, 02:19:38 pm
Yes, stability was very important. And also the tempco had to be better than the reference we used. The 0.5PPM/K would have been enough. I think the final specification called for 30ppm full error (tempco+drift of Vref and AFE total) in a single voltage range, for a year, but the second system was a lot better than spec. The LTZ was used to correct the errors of the Vref driving the ADC, sort of background calibration.

You know, I would've liked to measure every last parameter of the circuit. But, you know how it is. I did a set of tests to prove that it is better than the required specification. This, when they are waiting to launch production, maybe in overtime, not having the right tools in the lab. I've used cooling packs to verify the tempco, on an overnight measurement, because during the day everything was too noisy. Once it was done, it is hard to convince management to spend more resources to say: OK, but how much better than spec is it? No, they are not interested in bragging rights.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 24, 2017, 02:27:04 pm
Yea, getting job done and getting paid is little bit different than getting voltnut hobby fed. I'd be curious what ADC was used , LTC 240x series? We see many members here will LTZ refs, but only few like Andreas to have next step actually using REF to do measurements.
Title: Re: Ultra Precision Reference LTZ1000
Post by: tszaboo on October 24, 2017, 02:47:06 pm
The old system was using a 24 bit multichannel delta sigma from TI. ADS12xx. In normal operation, the system took samples much faster than these few SPS measurements, and it uses digital magic, oversampling, filtering and continuous calibration to achieve the good samples.

The AFE I designed was using a 18 bit SAR from LT. We got 20-21 effective bits from that part after all the digital filtering (typical INL of 0.5ppm). Again, the system was running a 0.1ms control loop on these values, to make the main feature of the device (battery tester). But the real magic usually is between the DUT and the ADC.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 24, 2017, 03:31:49 pm
OK, thanks :) I've got the idea.
Title: Re: Ultra Precision Reference LTZ1000
Post by: EEVblog on October 25, 2017, 10:56:09 pm
Below is a link to the HP Journal that highlighted the 3458A which would have appeared soon after product introduction. Again it makes no claim for designing the LTZ.
http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1989-04.pdf (http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1989-04.pdf)   ... “

Wow, tons of cool stuff in that, and lots of names  :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on October 26, 2017, 05:52:13 pm
I can also vouch for the LTZ being available to everyone before 3458a was even on the market - I was there on the fab line.  Our company was working with LT on some die production issues of the LTZ and similar references, and I remember HP and other manufacture's feedback on a higher insulating epoxy bond attach, better wire bond attach and other improvements that made the "A" version of the LTZ a much better device for production than the first non-"A" version.  HP was building on experience gained from the 3456a and the LM399, as was LT.  The LTZ was absolutely NOT HP's design, but HP's (and other's) feedback did help to improve the device later.  That's when there was collaboration going on between the designers, various suppliers and the manufacturing fab lines.
'
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on October 26, 2017, 05:54:29 pm
2.   It uses Vishay epoxy S102 resistors (!). HP used their TaN technology for the resistors elsewhere in the 3458A and I believe that they would have recognised that only one resistor in the LTZ circuit needed to have absolute stability, the others are all ratio defined which would be excellent built with their TaN film.

I don't recall this subtlety of the LTZ circuit being discussed before.  i.e. the ratio of R3 to R2.   One of my LTZ builds used 68.1K in series with 2K to form the 70K resistors for R2 and R3.  Wondering how critical the exact resistance had to be, I shorted out the 2K portion of R3.  Output voltage increased 150 uV from 7.11835V to 7.11850V.  I removed the short across R3's 2K and shorted out the 2K portion of R2.  Output voltage increased 850 uV.  So far, so good. My calculated sensitivity of output voltage WRT R3 is -0.074 ppm voltage per +100 ppm change in R3 and -0.42 ppm voltage per +100 ppm change in R2 which is consistent with JanAF's (and others) sensitivity of -0.07 and -0.4 ppm/100ppm for R3 and R2 respectively.

Here's the surprise-  When I shorted out both 2K portions of R2 and R3, the voltage returned to the original 7.11835V.  In other words, decreasing both R2 and R3 by the same 2.85% had no effect on output voltage.   This implies the ratio of R2 to R3 to be far more important than absolute value.   Comments?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 26, 2017, 07:13:55 pm
Hello,

interesting finding: so you should keep both collector currents at the same value.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on October 26, 2017, 08:02:40 pm
I had to do a quick check on my prototype LTZ1000 box that still have jumpers to lower the original R2 and R3 69.8kohm by paralleling 6.8M.

What I see is:
a rise of 320uV for paralleling R2
a rise of 50uV for paralleling R3
a rise of 370uV for paralleling both R2 and R3

Buffered 7V output quickly measured with a Keithley 2000.

Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 26, 2017, 08:18:29 pm
Hmm,

this result sounds more logical.

By the way Lars: you know how to display one more digit on the K2000?
https://www.eevblog.com/forum/metrology/getting-one-more-digit-from-a-6-5-digit-meter-without-using-gpib/msg1300529/#msg1300529 (https://www.eevblog.com/forum/metrology/getting-one-more-digit-from-a-6-5-digit-meter-without-using-gpib/msg1300529/#msg1300529)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: lars on October 26, 2017, 08:23:18 pm
Hmm,

this result sounds more logical.

By the way Lars: you know how to display one more digit on the K2000?
https://www.eevblog.com/forum/metrology/getting-one-more-digit-from-a-6-5-digit-meter-without-using-gpib/msg1300529/#msg1300529 (https://www.eevblog.com/forum/metrology/getting-one-more-digit-from-a-6-5-digit-meter-without-using-gpib/msg1300529/#msg1300529)

with best regards

Andreas


Yes I have seen that. But normally, if I need an extra digit I use GPIB and averaging in software. For this test I didn´t care.

Lars
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on October 27, 2017, 02:09:58 am
I had to do a quick check on my prototype LTZ1000 box that still have jumpers to lower the original R2 and R3 69.8kohm by paralleling 6.8M.

What I see is:
a rise of 320uV for paralleling R2
a rise of 50uV for paralleling R3
a rise of 370uV for paralleling both R2 and R3

Buffered 7V output quickly measured with a Keithley 2000.

Lars

Thanks for checking this.  I did measurement on a different unit (nominal 7.13692V) and got:
    R3 (70.1K --> 68.1K)   +100 uV
    R2 (70.1K --> 68.1K)   +880 uV
    Both decreased            +990 uV
Conclusion- I screwed something up in my initial test.  Will have to take that one apart and try again...

@Flinstone-  What did you mean by "the others are all ratio defined"?  I assume R1 is the "only one resistor in the LTZ circuit needed to have absolute stability" and clearly the R4/R5 ratio defines the operating temperature (absolute value not important).  So what's the other ratio if it's not R2/R3?
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on October 27, 2017, 08:30:34 am
The one resistor is the current setting resistor.

The temperature setting resistor con be calibrated.
Just measure the 7V zener out with a 6.5 multimeter and what exit from the divider. If you keep this ratio constant with a pot you are done, you don't need super extra stable resistor.

The 70K resistor have very high suppression ratio and even higher if you use 100K ohm.

So you end up with one resitor.

Hope I'm not wrong.

@Flinstone-  What did you mean by "the others are all ratio defined"?  I assume R1 is the "only one resistor in the LTZ circuit needed to have absolute stability" and clearly the R4/R5 ratio defines the operating temperature (absolute value not important).  So what's the other ratio if it's not R2/R3?

That's secret proprietary information...  I'm certain Flinstone has been asked not to repeat this...  It is very similar to my design-- only *one* high stability resistor (in terms of absolute value) is needed.  There are enough clues in this thread to figure this out on your own...
Title: Five new kids on the block - Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 30, 2017, 03:32:52 pm
I have assembled and tested my 5 new LTZ1000 reference boards.

They all are based on Andreas schematic, providing additional EMI filtering for great immunity against RF and mains disturbances.
The single sided layout, gathers all possible thermo-couples on the bottom side, and accepts through hole components only, PWW as well as MBF precision resistors.
Star points for +Uref and - Uref separate the different currents of the reference amplifier and the supply currents. All capacitors are WIMA foil type.

All modules are set to nominal 45°C oven temperature, by a 12k/1k divider.

4 of the circuits (LTZ #1 .. #4) are completely mounted inside a tuner box, and an interior styrofoam isolation, latter being intended mostly for cancelling any air draughts, and equalizing the interior temperature. It is planned to mount these 4 modules inside an outer metal box, including isolated PSUs. Inside the small compartment of the tuner boxes, there's room for a small and simple 12V stabilizer.

The fifth box (LTZ #5) is built on a PCB from Andreas (thanks again), which contains a tuner box on the top side, and is enclosed in an outer aluminum case. Maybe later I like to add a battery supply for use as a Travelling Standard.

These non-A type LTZ1000 allow a trimming of the temperature coefficient by an appropriate choice of R9.

Both the reference voltage, and the amplified 10.000V are fed to CuTe jacks (Pomona), so that the 10.000V can be re-adjusted at any time by measuring the known ratio between both potentials. Any good 6 1/2 digit DMM should be good for a few ppm precise 10.000V output.

These two blue resistors which provide the 7.2 -> 10V stepUp, are BMF type from AE, and the precision NTC measures their temperature in situ, for a possible correction of the 10V / Uref ratio.


The T.C. measurement of the 10V/Uref ratio just of today reveals a value of < 0.1ppm/K, although I did not (yet) determine and match the BMFs T.C.s in any way.

Edit 21.4.2018: Update schematic for correct OpAmp LTC1052.
C7, C8 chopper capacitors are tied to GND for the 1052.
The MAX420 and the 7650 require to connect them to Cret, pin 5.
Title: Results from the Prototype - Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 30, 2017, 03:34:36 pm
The new boards are an improved and miniaturized version of my prototype board, which actually went live in 2005 already.
The prototype layout contained several errors, and I reversed the heater supply, pin 1+2, so I discovered these substrate diodes, and LT changed their datasheet for the first time, afterwards.

The first measurements showed noise of  1ppm peak to peak, mainly caused by the 34401A I used.
But there were many spikes and also longer glitches.
The spikes were picked up from the noisy environment, and some of them caused the oven regulator to step out, which caused these ~ 30sec long glitches.

I made a lot of experiments especially on REF_1 (7.176..V), including accidently shorting the direct output, which caused big permanent shift effects. I could remove this hysteresis by temperature cycling.

After 12 years of nearly permanent operation, these references read 7.176 212V and 7.147 957V, so that's an average annual drift of < 0.8ppm / year. Currently they both show about - 0.6ppm/year.

I later moved my whole metrology equipment to our basement, where temperature changes during the experiments are as low as a few tenths of a °C, and the EMI disturbance is quite low,
as all switch mode power supplies are banned from this room, apart from the supplies in the measuring P.C.s
Recently, I replaced a 'stinker', inside one of the P.C.s.
At least the snubber network inside its PSU failed, creating a lot of disturbance.

The output voltages of the new modules now show no spikes, nor any glitches any more, as the 28h stability measurement (out of the box) on LTZ #5 demonstrates, thanks to better shielding, and due to the additional blocking capacitors, designed in by Andreas.
The measured noise is about 10 times lower than with the 34401A and the prototypes, between 0.025 and 0.050 ppm (rms).

This LTZ #5 is already trimmed to about 0.020ppm/K, so all apparent voltage changes are most probably caused by the 3458A only.

The warm-up time of the whole LTZ assembly to < 1ppm is about 15 minutes.

The change of the internal temperature of the 3458A is clearly visible in the measurement.
The big dip of -0.5ppm after 21.5 hours was caused by my wife when she opened the window, and so unintentionally determined the T.C. of my 3458A, i.e. +0.4ppm/K.

I measured the oven temperature of the prototype REF_1, by fast sampling of the base-emitter voltage of the transistor inside the reference amplifier.
As its collector current is constant, this U(BE) is a direct measure of the oven temperature, it's changing by quite precisely -2.1mV/K (see AoE).
The first reading of U(be) after powering on represents room temperature (about 22°C), the last and stable reading represents the oven temperature.

The U(BE) of the oven regulation transistor cannot be used for that purpose, as this voltage is fixed by the 12k/1k divider.

The diagram shows the self heating effect. As the LTZ1000 is very well insulated, upside down in a double styrofoam enclosure, this 10K temperature rise would be typical for the A version also.

The stabilized oven temperature is about 51°C, and between 50..54°C for the new modules.

The U(BE) of the new modules were measured with the 34465A, sampling each 1 msec.

I also measured the collector-emitter voltage of the oven sensor transistor, which shows the typical 7ms time constant of the 100nF/70kOhm in the beginning and about 500mV/K sensitivity of the sensor output.

The compilation of the reference amplifier change over temperature shows a nice linear T.C. of +55ppm/K
Title: Determination of the T.C.s - Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 30, 2017, 03:39:20 pm
How to measure the T.C. of the modules on the order of 0.05ppm/K , when the reference DMM, the 3458A itself has a 10 times higher T.C.?

The bootstrap solution is to first keep the temperature of the 3458A to within 0.1°C constant, and to monitor its internal temperature. Then the modules temperature will be changed by 10°C by forced heating or cooling, inside an isolated (beer) box.
The difference of the interior and the environmental temperature is constantly at about 6.5 ... 7.5°C.

This reverses the situation of the confidence in these measurements, so that the change on the module output voltage is now 10 time higher than possible changes caused by the 3458A.

This will give figures like the initial measurement on the LTZ #5.
During forced cooling, there occurs a shift of the output voltage, which is most probably due to thermal imbalances, causing air drafts and thermal e.m.f.s
As soon as the cooling / heating source is remove, all these inhomogeneity vanishes, and the output shows the regular T.C. change on the equilibrium path.

This is definitely no sign of hysteresis, as start and end point clearly converge into the same output value.

The first measurement with no R9 assembled, gives about -0.060ppm/K.
All modules have the LTZ1000 with its legs left long, and all module show an initial negative T.C.
I determined the individual T.C.s of all the precision resistors R1 .. R5, and matched the 5 sets to about equal resulting T.C. of -0.05ppm/K. I used the attenuation factors for each resistor from 5 different experiments, as given in the table.
The resulting T.C.s of the complete modules were higher than this caluculated T.C., up to -0.3ppm/K.
R9 will always add a positive T.C., so it is possible to trim the T.C.s to near zero, as shown for LTZ#1, using the box method.
The thermal cycle loops look more complicated, but in the end also deliver a nearly linear T.C. behavior.
Title: Summary of test results - Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 30, 2017, 03:41:16 pm
In the last (bootstrap) step, I used an already trimmed module to determine the T.C.s of the other modules with better stability and confidence.
I used the DCV RATIO mode of the 3458A to measure the relative changes of each of two modules.
This eliminates the T.C. dependency of the 3458A.
Now, the reference module is kept constant to a few tenths of °C, and the DUT module is again changed by 10°C, which gives a confidence ratio of 100.
The measurement of all parameters is displayed in the first diagram. The resulting T.C. (box) for
LTZ#5 is about 0.020ppm/K, and U-shaped, by averaging away the reference noise, which is much bigger in magnitude, than the change due to the T.C..

It's really not practical to trim the T.C. further. Over a 18..28°C laboratory temperature range the absolute change is about +/-0.1ppm, completely sufficient for a travelling standard also.

The summary for all 5 modules is given in the table, which also includes their noise, measured against the 3458A at NPLC 100, over 1h, therefore including short- and midterm variations.
LTZ #1 is remarkably low-noise, whereas LTZ #4 has nearly double the noise.


In retrospect, the 3458A simplifies these delicate T.C. measurements, by its own low noise level.
Its own T.C. is not that much better, than other bench DMMs, so a stable environmental temperature is required with all these instruments, or an already trimmed reference module.


Next step will be, to monitor the timely drift of all the modules.

LTZ #5 already is running since March, and showing quite high -2ppm of drift since then.
This will decrease by next year, and hopefully I'll find several modules with lower drift, perhaps with a positive one also.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 30, 2017, 03:42:12 pm
Yey. Unveil the tempco on us  :D
Title: Re: Ultra Precision Reference LTZ1000
Post by: dr.diesel on October 30, 2017, 05:21:47 pm
Digesting, thanks for write-up Dr.Frank!
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 30, 2017, 06:56:36 pm
I would exercise caution with box method on tempco match, as I see not always linear behavior (granted that I run bit wider DUT exercise from +20C to +55C).

Did you do any selection for resistors to determine similar direction TCR, or you just base on LTZ attenuation factors for resistance stability? What are their spec, 3ppm/K?

Thank you for detailed write up, appreciate the effort.

I think we getting enough participants to do a big round robin for LTZ refs in 2018? I'll definitely have new design travel ref for it (10V).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 30, 2017, 10:52:59 pm
I would exercise caution with box method on tempco match, as I see not always linear behavior (granted that I run bit wider DUT exercise from +20C to +55C).

Did you do any selection for resistors to determine similar direction TCR, or you just base on LTZ attenuation factors for resistance stability? What are their spec, 3ppm/K?

Thank you for detailed write up, appreciate the effort.

I think we getting enough participants to do a big round robin for LTZ refs in 2018? I'll definitely have new design travel ref for it (10V).

The LTZ #5 shows a slight U-shape behavior, whereas the other 4 references, #1 ... #4 are mostly linear, like the LTZ #1 I have shown.
The T.C. is buried so deeply in the zener noise, that it's pretty hard to make any reasonable T.C. determination below 0.02ppm/K.. therefore I find the box method quite appropriate.
It's also sufficient, if one assumes an absolute drift goal over 18..28°C.
In this case, the LTZ#5 would be within +/-0.1ppm, and this is also pretty darn close to the physical limits of analogue DCV measurements.

All commercial references claim a T.C. of minimum 0.04ppm/K, if I remember correctly, so 0.02ppm/k is ridiculously low.

The TCs of all PWW resistors are written down in the table, including the sign of their T.C.s

As I simply bought these resistors (econistors from G.R.) from the stock, w/o any further specification limits, or special matching, I had to use, whatever was delivered.

These were specified 3ppm/k typical, 5ppm/K maximum, similar to Vishays BMFs.
The 120 Ohm resistors showed some strange hysteretic behavior, as reported elsewhere in the forum, but all others were mostly linear and well below the maximum value.

As discussed quite often, the attenuation factors take care that the resistor stabilities are not so important, and it additionally turned out, that the intrinsic T.C. of the LTZ1000 seems to have superior influence.
In the end my design goals were completely fulfilled, that is an annual drift rate below 1ppm, and a low T.C. so that this does not carry no weight in uncertainty, compared to the timely drift, and compared to reasonable limits in DCV measurements in an amateur metrology lab.

Frankly speaking, I designed the modules in first instance to a good cost/performance relationship (about 100€ BOM cost), avoiding any over-engineering, like using Vishay hermetical VHPs (I could barely resist!), or voodoo-stuff w/o any proven benefit (e.g. these slits).

Yes, we may plan a chain comparison on a high metrological level.. I assume thsee modules also deliver sufficient uncertainty w/o battery backup.. and I might throw in one of my VHP202Z 10k resistors.

Let's see, what happens in the upcoming year, looking forward to the new S.I., kg, and Volt / Ohm.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: pitagoras on November 09, 2017, 02:45:30 am
Hello,
I'm entering the game with a standard +7V design.   :scared:
Only difference is separated heater/ref power (as A9 does).
Resistors are Rhopoint econistors for this first build. A second board will probably wear Edwins. Both will use ACH.
For R4 I could only get 2x25k so pcb has this provision for two parallel resistors.
While pcb is being made, I'll be probably building a tec box and some controller.
I'll be reporting news!


Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on November 09, 2017, 10:23:16 am
Did someone tested LTZ1000 at 20mA for long term consequences?
I suppose it needs also a higher temperature set point than usual ... maybe at lest 13K/1K resitor for the non A version.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 09, 2017, 10:37:07 am
Why would you want that? Drift rate will be horrible in long-term. :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on November 09, 2017, 11:07:07 am
Well I'm just thinking at this message of few posts ago. If it does not accelerate burn in and he tell us that "You can safely bias the LTZ1000(A) with 20mA" I suppose it does not harm too much too. So I'm asking if someone tested at 20mA.

Hi forum members,

Bob Dobkin answered one of my follow-up questions:

[Me]:

About the Zener current of the LTZ1000-- I think you said it can take more than 5mA, but is it helpful to use more Zener current during the burn-in or would I end up with more long term drift in this case, and if more current is helpful, then how much is safe?

[Bob Dobkin]:

You can safely bias the LTZ1000(A) with 20mA. However, I do not think that will further accelerate the burn-in process.

I think three things take effect during the burn in. The first, is annealing of the aluminum metal. With this annealing, there is a resistance change in the aluminum. Secondly, the interface between the aluminum and the silicon changes. Also there are stress changes that anneal out.

None of these is particularly current sensitive.

====================================

It took him a while to answer this, but I'm glad he did... Wow, he must be super-busy!

Later,
Ken
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on November 09, 2017, 03:22:14 pm
There is a slight chance that aging might be a little faster at a high current. One will definitely need a higher temperature set-point at a higher current as there will be more self heating. So not a good idea with the A version.

At higher current, the resistance on the AL traces on the chip, the pins and the board get more important. So chances are drift and TC will be worse. Higher power will also give more driving force for convection type thermal noise.

The main possible advantage with a higher current would be slightly lower noise, about 1/2 the noise voltage at 4 times the current would be a first guess. However the low frequency part can be different with less advantage.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on November 09, 2017, 04:01:12 pm
So Kleinstein maybe the 5mA is just the balance of all the factors: self heating, TC and internal resistance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on November 09, 2017, 04:19:22 pm
The main reason for using a higher current is the lower noise level, and maybe to a certain degree a lower zener resistance. Most other aspects like self heating, influence of lead resistance, internal resistance would prefer a lower current. Also the unheated TC of the reference is expected to get slightly better at lower current, though the effect is likely small - the TC zero crossing for the unheated chip would be at rather low currents (my guess would be in the 0.1-1 mA range, but also depends on the "70 K" resistors).

So it is a little like low current for good long term stability and higher current for lower noise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 09, 2017, 10:40:15 pm
As promised, a quick look at the performance of one of my new LTZ1000s, it's named LTZ #3.

This module is programmed for output of the LTZ1000 voltage, and also trimmed to 10V, label +Ref_buf and 10.00000V in the schematic.
The 20h stability of the LTZ direct output (7.131364V) is shown in the first diagram.
(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=368584;image)

Main contribution for drift in the beginning comes from the 3458A, which needed 5h to stabilize completely. The LTZ #3 mostly stays within a window of +/- 0.1ppm, otherwise.

The 1h noise @ NPLC50 is about 0.045ppm rms.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=368586;image)

These diagrams, and all which will follow, are prepared directly from the raw data, so there is not a single dip or glitch, thanks to the tuner box, and Andreas additional caps.

The T.C. of the LTZ1000 is about -0.025ppm.
In the window, I have marked the thermal equilibrium parts of the curve, again.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=368588;image)

Then I've measured the T.C. of the divider, that are 4k over 10k BMF resistors from Alpha Electronics.
I just used the DCV RATIO function of the 3458A, measuring both voltage outputs.
I had some luck, the resistors seem to have a very close T.C., so the overall ratio T.C. is about +0.06ppm/K.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=368590;image)
(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=368592;image)

In the end, the 14h stability of the 10V output, vs. the 3458A is demonstrated. Latter was stable to +/- 0.1°C.
The module at first was sitting directly on top of the 3458A (~25°C), but I put a box underneath, so it cooled down a few degrees. So, there's again a non-equilibrium step visible, which quickly (20min.) returns to the initial value.
These frequent dips in temperature are probably caused by the thermostat in the basement, as we are heading winter, and the heating is already running, until about 11 p.m., when these dips vanish.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=368594;image)

1h noise is  again about 0,043ppm.

So, these relatively cheap BMFs perform very well, as I already found out with my precision Hamon divider.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on November 11, 2017, 05:52:59 pm
Dr. Frank,
Do you have a way to test your LTZ's against something other than one 3458a?  I see that you've produced data, but normally we would never just use another single LTZ to measure against (aka 3458a).  For instance if you measure an LTZ circuit with just a single 3458a, in essence you're comparing only the drift of one LTZ die to other LTZ dies, using basically the same circuit for all Vref's.  The drift trend direction will tend to be the same, and you can possibly convince yourself into much better results if you're -only- looking at inter-comparing LTZ die.

At least you know you don't have a completely mucked up circuit module, but it is still wise to use other test methods if possible.  That's hard to do with an LTZ since that's already at close to the top of the food chain.

It would be interesting to see how the results compare to more than one reference technology to test against - for instance we use multiple cal'd 732's, KVD's, nullmeters & multiple 3458a's to measure a Vref accurately... You'll raise confidence and lower uncertainty of any LTZ  absolute value measure /  long term drift assessment that way - which is the whole point if you're down in the low ppm range.

Just another example: more tools ===>  happier Volt-Nut!!
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on November 11, 2017, 06:25:24 pm
Also, be careful using 3458a automatic ratio mode at low PPM - that can introduce more uncertainty.  You can still do ratio measures, but for lowest ppm uncertainty you'll generally take manual measures and calculate the ratio from those results (Or using a low thermal scanner switch setup, etc.)- Better yet if you can do a manual transfer measurements from a cal'd 732 (for instance) for best result if you're after low traceable uncertainty.  Explained here:

http://literature.cdn.keysight.com/litweb/pdf/5992-1058EN.pdf (http://literature.cdn.keysight.com/litweb/pdf/5992-1058EN.pdf)

Getting true a absolute value measure at low traceable uncertainty isn't trivial on a high performance LTZ - if that's what you're after.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zhtoor on November 11, 2017, 06:46:46 pm
Dr. Frank,
Do you have a way to test your LTZ's against something other than one 3458a?  I see that you've produced data, but normally we would never just use another single LTZ to measure against (aka 3458a).  For instance if you measure an LTZ circuit with just a single 3458a, in essence you're comparing only the drift of one LTZ die to other LTZ dies, using basically the same circuit for all Vref's.  The drift trend direction will tend to be the same, and you can possibly convince yourself into much better results if you're -only- looking at inter-comparing LTZ die.

At least you know you don't have a completely mucked up circuit module, but it is still wise to use other test methods if possible.  That's hard to do with an LTZ since that's already at close to the top of the food chain.

It would be interesting to see how the results compare to more than one reference technology to test against - for instance we use multiple cal'd 732's, KVD's, nullmeters & multiple 3458a's to measure a Vref accurately... You'll raise confidence and lower uncertainty of any LTZ  absolute value measure /  long term drift assessment that way - which is the whole point if you're down in the low ppm range.

Just another example: more tools ===>  happier Volt-Nut!!

hello,

short of testing against a JJA, would a set of weston cells make a viable choice to test LTZ1000's against?

regards.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 11, 2017, 07:19:27 pm
There was a question about overdriving LTZ with high current. Well, I got some practical data, using jumper chip as a specimen, since I don't care much about it's long-term stability.
Graph data:

LTZ unit with "default" resistor and current (https://xdevs.com/doc/xDevs.com/KX/ltz_orig.png).
Same LTZ with 60 ohm current resistor (https://xdevs.com/doc/xDevs.com/KX/ltz_10ma.png). - that's about 10 mA zener current.
Same LTZ with 40 ohm current resistor (https://xdevs.com/doc/xDevs.com/KX/ltz_15ma_test.png) - that's about 15 mA zener current. Output jumped +855 ppm as result.
Difference in output between 60 ohm and 40 ohm current resistors (https://xdevs.com/doc/xDevs.com/KX/ltz_10ma_15ma_jump.png).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on November 11, 2017, 07:53:19 pm
Zhtoor....

The Weston cell has long passed into history as a voltage standard, while you might get a Weston Cell calibrated at NIST to .04 PPM, that comes with a long list of limits, that is only valid at the time of measurement, any movement of the cell, even gently will invalidate that measurement and increase the uncertainty, not to mention the cost is in the thousands of dollars, they are very fragile and have significant temperature coefficients, you would get a better measurement comparing two LTZs against each other.  However, for a valid and accurate reading, they must be compared to a certified 732A (preferably two or more), otherwise you are just comparing drift rates between the LTZs.  The 3458A is a very good transfer standard, used to compare a LTZ against a 732A you can get sub PPM uncertainty if done correctly but the 3458A by itself is not a standard.

A functioning Weston Cell might give you a reference that is possibly good to perhaps 10 PPM or 20 PPM with a uncertainty of a few PPM if handled very carefully, that would have to be done on site to minimize uncertainty, you could probably get away with using a very good 731B in this case, an old one with a very good drift history.  You can't draw any significant current from it, you don't want to leave it connected to a meter for any longer than necessary and you want the temperature to be reasonably steady.  Way more trouble than a LTZ Vref, even one that isn't performing top notch.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zhtoor on November 11, 2017, 08:14:06 pm
Zhtoor....

The Weston cell has long passed into history as a voltage standard, while you might get a Weston Cell calibrated at NIST to .04 PPM, that comes with a long list of limits, that is only valid at the time of measurement, any movement of the cell, even gently will invalidate that measurement and increase the uncertainty, not to mention the cost is in the thousands of dollars, they are very fragile and have significant temperature coefficients, you would get a better measurement comparing two LTZs against each other.  However, for a valid and accurate reading, they must be compared to a certified 732A (preferably two or more), otherwise you are just comparing drift rates between the LTZs.  The 3458A is a very good transfer standard, used to compare a LTZ against a 732A you can get sub PPM uncertainty if done correctly but the 3458A by itself is not a standard.

A functioning Weston Cell might give you a reference that is possibly good to perhaps 10 PPM or 20 PPM with a uncertainty of a few PPM if handled very carefully, that would have to be done on site to minimize uncertainty, you could probably get away with using a very good 731B in this case, an old one with a very good drift history.  You can't draw any significant current from it, you don't want to leave it connected to a meter for any longer than necessary and you want the temperature to be reasonably steady.  Way more trouble than a LTZ Vref, even one that isn't performing top notch.

thanks and almost agreed.

i was talking about characterizing the long term *drift* performance of LTZ1000's by comparing to other *types* of standards,
like LTFLU based, SZA263 based, 1N829A based, JJA based or *maybe* Weston Cell based, assuming different technologies drift differently.
inadequacies of Weston Cells are abundant, but, noise performance and drift is not one of them (in a tightly controlled temperature).

best regards.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 11, 2017, 08:51:11 pm
Dr. Frank,
Do you have a way to test your LTZ's against something other than one 3458a?  I see that you've produced data, but normally we would never just use another single LTZ to measure against (aka 3458a).  For instance if you measure an LTZ circuit with just a single 3458a, in essence you're comparing only the drift of one LTZ die to other LTZ dies, using basically the same circuit for all Vref's.  The drift trend direction will tend to be the same, and you can possibly convince yourself into much better results if you're -only- looking at inter-comparing LTZ die.

At least you know you don't have a completely mucked up circuit module, but it is still wise to use other test methods if possible.  That's hard to do with an LTZ since that's already at close to the top of the food chain.

It would be interesting to see how the results compare to more than one reference technology to test against - for instance we use multiple cal'd 732's, KVD's, nullmeters & multiple 3458a's to measure a Vref accurately... You'll raise confidence and lower uncertainty of any LTZ  absolute value measure /  long term drift assessment that way - which is the whole point if you're down in the low ppm range.

Just another example: more tools ===>  happier Volt-Nut!!

Hello Mr. Diodes,
your first question and remark is legitimate.
Yes, over the last years, I use the 3458A as a comparator and its LTZ1000A @ 65°C for the baseline reference, plus a Fluke 5442A, plus these two prototype LTZ1000 references.
The LTZs have been running for 12 years now, whereas the 3458A and the 5442A were only switched on when used.
So, the LTZs should have the typical -0.8ppm / year drift, the 3458A a fraction of that drift, down to zero drift, as the references typically do not drift when unpowered. Same goes for the 5442A, which should typically  have a positive drift over time.

Starting in 2009, I compared these 4 references regularly, and their relative drifts were as expected, i.e. the 5442A upwards, both LTZs downwards, relative to the 3458A.
The total relative drift per year between the 5442A and both LTZs was less than 1ppm, which was my stability goal.

That's the poor mans way of maintaining Volt, as I don't want to calibrate the standards by a metrology lab, or by usage of commercial instruments, like a 732A.
Btw.: The 100 year-drift of Le Grand K, the kg prototype, was identified by the very same principle.


I doubt, that a KVD or a Null Detector give any advantage over the 3458A as a comparator..

During that time, I had the chance to 'zero' the absolute Volt in my lab, at first when I got the 5442A, then by a comparison to a recently calibrated 8508A, and latest, when I got two brand new 34465A from KS, which agreed within 1ppm to my baseline.

That's all no regular calibration, that's crystal clear.
But for an amateur grade lab, there is high  probability, that these artefact calibration points, together with the frequent relative drift measurements, provide good enough accuracy at about a few ppm.
I don't want to say uncertainty, as this would require or imply regular calibration methods by a proven chain  from official metrology labs.

And I also want to emphasize, that I do not want to dig into the tenths of ppm region, where all these nice officially accepted standards rule.

The addition of up to five new LTZ1000 may improve the drift statistics, although they will also have a probable negative drift.. so SZA263 based references are lacking.

Anyhow, my current group of 4 references, with their underlying history will be sufficient to measure the drift behaviour of the new references, and that's the most important feature.

Now that I have some more compact LTZs, whith proven low T.C., I can send them to a friendly volt-nuts companion, who might punch another nail in my baseline.

Frank

PS: I also added a Hamon divider for 100:1 and 10:1 transfers (DIY), a 5450A, and recently a 845AR to my lab, and these redundant instruments  increased my confidence and insight a lot, over the bare uncertainty of the 3458A.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on November 11, 2017, 09:12:48 pm
There was a question about overdriving LTZ with high current. Well, I got some practical data, using jumper chip as a specimen, since I don't care much about it's long-term stability.
Graph data:

LTZ unit with "default" resistor and current (https://xdevs.com/doc/xDevs.com/KX/ltz_orig.png).
Same LTZ with 60 ohm current resistor (https://xdevs.com/doc/xDevs.com/KX/ltz_10ma.png). - that's about 10 mA zener current.
Same LTZ with 40 ohm current resistor (https://xdevs.com/doc/xDevs.com/KX/ltz_15ma_test.png) - that's about 15 mA zener current. Output jumped +855 ppm as result.
Difference in output between 60 ohm and 40 ohm current resistors (https://xdevs.com/doc/xDevs.com/KX/ltz_10ma_15ma_jump.png).
Hmmm, it is a shame that the jumps did not stop, but it definitely seemed at first glance to be improved, at 15mA your jumpy specimin seems to have a much lower tempco, that stands out to me. Some stuff I have read is that at low currents a zener will jump like that, so it is just a mild die fault then? any experts know something that they are allowed to say? no NDA's in the way that is.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on November 12, 2017, 04:55:09 pm
Agilent, in Service Note 3458A-18A, states that unpowered LTZ1000 references can lose their ageing characteristic if stored unpowered, leading to an error of up to 15 ppm. Running the meter for 6 weeks apparently solves this problem. They don't say how long the unpowered period is. Dr. Frank's evidence would suggest that annual checking is enough. Or maybe, this problem is limited to very few units.
Plus, the 3458a operating temperature is higher, which raises the question of how a higher operating temp changes things in this regard.

Dr. Frank's numbers suggest that he, at least, does not have this problem. 15ppm would show up in that simple comparison to a new meter.




The internal reference assembly used in the 3458A are aged (stabilized under a powered-up state) and
monitored for appropriate DCV time drift for use in the 3458A. Initially, virtually all references drift
at rates too high for use in the 3458A. However, the rate of drift decreases with time and the future
drift performance of the reference assembly can be accurately predicted with a high level of certainty.
If the reference assemblies are powered down for an extended period of time (such as being stored in a
stock bin) the references revert back toward their “pre-aged state”. As a result the initial drift rate for
the DCV reference may be high enough that the DCV function may be “out of specification” prior to
the first calibration/adjustment interval (90 days or 1 year).

Some of our references used in recent production have been stored in a stock bin long enough to
exhibit this drift problem. The error associated with this long-term drift issue will cause a gain error
for all voltage, resistance and current measurements. This error is expected to be less than 15 ppm of
the reading.
Operation of the 3458A for six weeks is sufficient for these references to stabilize under a powered-up
state. Adjustment/calibration of the instrument after this initial six week operating period will
eliminate this issue and the reference will be sufficiently stable to remain within specification until the
next regular scheduled adjustment/calibration event.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 12, 2017, 06:22:36 pm
Agilent, in Service Note 3458A-18A, states that unpowered LTZ1000 references can lose their ageing characteristic if stored unpowered, leading to an error of up to 15 ppm. Running the meter for 6 weeks apparently solves this problem. They don't say how long the unpowered period is. Dr. Frank's evidence would suggest that annual checking is enough. Or maybe, this problem is limited to very few units.
Plus, the 3458a operating temperature is higher, which raises the question of how a higher operating temp changes things in this regard.

Dr. Frank's numbers suggest that he, at least, does not have this problem. 15ppm would show up in that simple comparison to a new meter.




The internal reference assembly used in the 3458A are aged (stabilized under a powered-up state) and
monitored for appropriate DCV time drift for use in the 3458A. Initially, virtually all references drift
at rates too high for use in the 3458A. However, the rate of drift decreases with time and the future
drift performance of the reference assembly can be accurately predicted with a high level of certainty.
If the reference assemblies are powered down for an extended period of time (such as being stored in a
stock bin) the references revert back toward their “pre-aged state”. As a result the initial drift rate for
the DCV reference may be high enough that the DCV function may be “out of specification” prior to
the first calibration/adjustment interval (90 days or 1 year).

Some of our references used in recent production have been stored in a stock bin long enough to
exhibit this drift problem. The error associated with this long-term drift issue will cause a gain error
for all voltage, resistance and current measurements. This error is expected to be less than 15 ppm of
the reading.
Operation of the 3458A for six weeks is sufficient for these references to stabilize under a powered-up
state. Adjustment/calibration of the instrument after this initial six week operating period will
eliminate this issue and the reference will be sufficiently stable to remain within specification until the
next regular scheduled adjustment/calibration event.

This applies to the hp LTZ1000A circuit, which runs at about 90°C.
This implies a much higher drift rate, but also a hysteresis, or creep effect.
What I have seen on my LTZ1000 references, that both chips do not show noteworthy hysteresis, if the oven temperature is not that high, so 65°C as intended will give a small hysteresis, and 45°C, as in Pickerings design of the Datron 4910 or the 7001 references, will give no hysteresis.

So, that's another reason, why I have pimped my 3458A reference to about 65°C.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 12, 2017, 06:25:32 pm
I tested for this once too, did not see the effect, however I run both of my meters pimped too (100K VPG resistor over stock 15K one).
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on November 12, 2017, 07:39:12 pm
I've moved one to the lower temperature as well. I figure if it gets hot enough to be a problem, I won't be using the meter that day!

I guess these were designed before the long-term characteristics of the LTZ1000 were fully understood. The design does seem to run unnecessarily hot, and I wonder if that gets in the way of long-term stability.


An interesting observation about these meters is that there seems to be no airflow over much other than the power supplies. There's nothing to clean off of the boards. The shielding seems designed that way. So I am thinking that the inguard boards are sufficiently low power that there's minimal self-heating going on. Maybe 10 - 12 Celsius, judging by the internal temperature measurement. Even running in a rack, the enclosure would have to be really hot to cause problem with the reference. In practice, I would be worried about the power supplies if the meter got hot enough to cause a problem.



Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 13, 2017, 12:10:13 am
As it was covered many times, HP deliberately designed meter to fit +50C operation temperature range, for applications like production, where meters sit packed in the hot rack.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on November 13, 2017, 02:08:08 am
Max operating temperature according to the apc is 55C (storage up to 75C). With a 15 degree internal rise, the reference would have to be certain to operate at 70 celsius. 90 celsius allows for an extra 20 degrees of guardband, which would only make sense if the operating temperature was hard to predict or manage. But HP certainly knew the characteristics of these parts.

Plus, at that time, nobody would have known about the issues with operating the LTZ1000 at the raised temperature.

Also, operating at 55C (which is really hot, rack or not), the lifetime of the capacitors subject to high ripple currents would have been awful.

Bottom line is, we can safely drop the operating temperature of the LTZ1000 to 65C, and the meter may still be OK at 55C operating temperature.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 13, 2017, 08:08:44 am
Max operating temperature according to the apc is 55C (storage up to 75C). With a 15 degree internal rise, the reference would have to be certain to operate at 70 celsius. 90 celsius allows for an extra 20 degrees of guardband, which would only make sense if the operating temperature was hard to predict or manage. But HP certainly knew the characteristics of these parts.

Plus, at that time, nobody would have known about the issues with operating the LTZ1000 at the raised temperature.

Also, operating at 55C (which is really hot, rack or not), the lifetime of the capacitors subject to high ripple currents would have been awful.

Bottom line is, we can safely drop the operating temperature of the LTZ1000 to 65C, and the meter may still be OK at 55C operating temperature.

Your statements are utterly wrong and dangerous!   :-- :-- :--

You should have read the correct facts from experienced users beforehand, as you have to take into account more sources of temperature rise.

The minimum temperature rises are:
+13°C between room and internal temperature, due to instrument self heating
+10°C self heating of the A version
+5°C heater regulation margin

Therefore, this modified 65°C oven temperature limits operation to 37°C ambient!!

Then, you have to take into account additionally:
+5.. +10°C contamination of fan
+5.. +10°C usage inside a 19" rack
10°C production variation of LTZ1000 regarding oven set temperature.

So, in total, you might easily have 40°C temperature difference between ambient and oven temperature, that's why hp initially set that to about 95°C.

At last, I recommend this modification to 65°C oven temperature only by carefully monitoring the internal temperature, which must stay below 45°C.

I further recommend a max. ambient operating temperature of 35°C, operation on desktop, not in a rack, and frequent cleaning of the fan.


Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: tszaboo on November 13, 2017, 09:52:10 am
Not to mention, the internal temperature is avaliable as a GPIB command from the 3458A.
So if you want to use it as a high end, accurate, desktop meter maybe used for calibration, 1000 NPLC, you can always just request the internal temperature.

The script I've used for calibration did a (3458A) self calibration every time the internal temperature changed by 1 degrees.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on November 13, 2017, 04:19:49 pm
For best accuracy one should have the filter clean on the 3458 anyway. With a clogged filter the airflow is reduced and thus different temperature gradients are established. For this reason a temperature regulated fan is not a good idea in a design where the airflow is directly across sensitive parts. It could be if the sensitive part would be fully protected from the airflow, and airflow dependent temperature gradients.

Reducing the temperature for the reference slows down the drift and settling of the reference. So when cold it also takes longer for the reference to settle. So after something like 2 years the higher temperature reference might be more stable, as it can be more settled. A lower temperature is not always an advantage.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on November 14, 2017, 08:57:58 pm
A new LTZ design is in town, this time made by Analog Devices / Linear Technology themself for AD5791 and with all the things you can think of such as slots, BMF resistors, ...

(http://www.analog.com/-/media/images/analog-dialogue/en/volume-51/number-3/articles/high-precision-voltage-source/139436_fig_08.jpg)

Source (http://www.analog.com/en/analog-dialogue/articles/high-precision-voltage-source.html)

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on November 15, 2017, 02:28:35 am
Didn't the previous eval board have the LTZ on it: https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg828843/#msg828843 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg828843/#msg828843)
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on November 15, 2017, 04:34:26 am
Yes the AD5791 demo board has always had a place for LTZ1000 to be installed, for many years.  If you look at the datasheet they never really mention the VRef to use with that chip, nor do they mention the fact that the "low noise" figures quoted aren't for low freq / DC - and watch how the spec'd noise units change at low frequency.  Lots of red flags.  At the time the chip came out AD had no Vref to even come close to driving that Dac to full potential, so they quietly just put the competitors (LT) Vref part on the demo board.  Some of the boards have the LTZ layout upside down, I guess people sometimes don't catch the TOP SIDE vs BOTTOM SIDE pinout view on the LTZ datatsheet.  It happens.

The demo board I have in front of me also has a non-descript connector for "Vref input" with no description of how important that is if you want the full DAC specs...like any old voltage source will do.  A 7805 should work fine, right?

As with all diffused IC resistors the DAC noise is pretty high - if you're trying to use this chip to make some sort of an adjustable -DC- voltage source, I wouldn't do that if low noise is important to you.  The chip is very sensitive to board stress also.  It didn't impress anyone very much at the lab.
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on November 15, 2017, 09:15:50 am
Some guy on http://bbs.38hot.net/ (http://bbs.38hot.net/) made working kits of the AN86 suggested by Jim Williams: http://bbs.38hot.net/thread-29599-1-1.html (http://bbs.38hot.net/thread-29599-1-1.html) But it seems he doesnt produce kits anymore. Maybe someone here has aquired such a kit or knows about the thread?
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on November 18, 2017, 11:31:01 pm
You raise a really important point: I need to put a label on the  unit that indicates that it is modified for low temperature operation.

And yes, I missed the extra 10 degrees of latitude recommended for the A version. I may end up testing that next summer, as temperatures rise. I'll be watching to see if my reference appears to drift as we cross the 37C threshhold.

Something else: I need to dig into  the unit again, but it looks like the airflow design is mostly to keep the power supplies cool. There seems to be little flow over the other boards. In photos online, the units do seem to be very clean inside, and even the filters don't appear that dirty.

And finally - the deeper air filter on the older units does seem to let them run a lot quieter than the new filters, which are right on top of the fan. 

Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on November 19, 2017, 06:08:59 pm
... and this one:

https://www.youtube.com/watch?v=_UyUHz9qpEQ (https://www.youtube.com/watch?v=_UyUHz9qpEQ)
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on November 19, 2017, 10:34:04 pm
In last video they measured noise in the 1uV range with 3458a? Isn't the meter contribution the great part of the noise?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 20, 2017, 04:57:37 am
3458A was set to fast NPLC, so it's hard to say. :)

Meawhile, jumper LTZ driven with 15mA still alive and kicking. With some heavy averaging it can even seem to be almost normal:

(https://xdevs.com/doc/xDevs.com/KX/ltz_jumpy.png)

There are step temperature excursions, stable at levels to 0.005C with points +21C, +50C, +30C and +24C.

CSV-data (https://xdevs.com/datashort/kx_707_10ma_tec_test2_nplc100.csv) in case somebody wants.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on November 20, 2017, 10:33:16 am
3458A was set to fast NPLC, so it's hard to say. :)

No they say it's in 10 seconds aperture for the noise test ... the fast aperture was for checking INL.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 20, 2017, 10:34:26 am
No, 10 seconds was window aperture to capture 0.1Hz-10Hz noise.
There is no 10 second aperture in 3458A :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on November 20, 2017, 01:04:25 pm
I think we are trying to say the same thing.
They say 10 seconds ... so it should be 600 (or 500) NPLC.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 20, 2017, 02:05:53 pm
Then you will get one sample, from which there is zero information about noise.
What they say is aperture of the sampling window was defined as 10 seconds worth of samples (whatever it was, NPLC1 or 10, etc).
So we are talking about different concept.
Title: Re: Ultra Precision Reference LTZ1000
Post by: bopcph on November 20, 2017, 05:05:53 pm
I would say that 60 sec. is absolute minimum if you want to measure down to 0.1 Hz
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on November 20, 2017, 07:35:02 pm
To get the 0.1 Hz to 10 Hz peak to peak noise, the closest thing would be sampling with 10 Hz (thus likely 2 or 3 PLC with AZ active) and taking samples over a 10 s window. For more accurate values one needs to repeat and average the peak to peak values. Alternative would be using something like 1 PLC sampling for a longer time (e.g. 60 s) and than get the noise spectrum and calculate the peak to peak value from the spectrum - this may not correctly care for popcorn noise however.

To get little noise from the references used the noise test is likely at about 0 output. This also allows to use the 100 mV range of the DMM to get low noise from there.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 20, 2017, 08:11:34 pm
Hello,

For noise testing you will need a low noise amplifier to get out of the DMM noise.
And a 10 Hz sampling is by far not enough from Shannon theorem for a 10 Hz bandwidth.

So the best is usually a factor 10000 amplifier and a medium sensitive scope (2 mV/div)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on November 21, 2017, 09:35:37 am
Kleinstein: yes it seems they used 1NPLC.
The chart (seems to) have a span of 10.5 seconds (cannot read it) ... and in the upper corner there is printed "105 samples" so this round up to 1NPLC.
Never though you can run the ADC at 0V to zero out noise of the references.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on November 28, 2017, 11:11:23 pm
Question regarding the 400K temperature compensation resistor and use on the LTZ1000A.   I know this part is said not to be used or needed for the A part, but if used will it or could it cause any long term harm?  Reason I'm asking, I found both of my LTZ1000A's KX boards have negative T/C, #1 is about -0.08ppm/K and #2 is about 0.1ppm/K.  I found by using a 390K TC resistor on the #2 reference the TC is below 0.05ppm/K now.  10 to 40deg C test only drifted down 8uV.  That's just under 0.04ppm/K.  So I'm really inclined to  leave it in now.  Started with 1M, then 470K, then 390K and each time seeing an improvement.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on November 29, 2017, 02:06:58 am
Tried a 300K and ended up with the magic number.  I cant improve on this, not with the equipment I have.

(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/C4321020-7389-4CB3-A5CC-5EAAA647609C.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/C4321020-7389-4CB3-A5CC-5EAAA647609C.jpg.html)

I placed the reference in the refrigerator for a few hours to stabilize at 4.8 Deg C, started my plot when it warmed up to 5.0 Deg C, I let it warm up slowly at first, until about 18 Deg C, then turned on the oven to warm the internal temp to 39.6 Deg C (maxed out, normally set to 35.0).  I cant see any real change now, + or - 2.5uV is within the noise of the 34465a.
(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/EE77516D-6E70-4B26-9FCB-D15977051CBD.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/EE77516D-6E70-4B26-9FCB-D15977051CBD.jpg.html)

The 34465A is null'd at 7.161554v, 10 NLPC, 10v manual range, 10M input Z, math averaging 50 readings (med filter).  Hack or not I'm a happy camper now. Going to let it cook here overnight and see how it holds, then repeat the temp cycle in reverse tomorrow.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on November 29, 2017, 05:14:15 am
That sure is interesting.

My initial hypothesis is that the temperature coefficient of the 390k resistor is offsetting the net temperature coefficient of the other sensitive resistors in the circuit. That's an interesting technique that could give a DMM better temperature stability. Also suggests that the temperature coefficient of the resistor is more important than the value, although your testing indicates a sensible progression.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 29, 2017, 07:33:07 am
for improper PC layout (in the area of ground currents).

I would not sign that: even with the same layout I had a initial stray between +0.015 and -0.23 ppm with different LTZ1000A references.
Lead length of the LTZ1000A also plays a role if you look somewhat earlier in the thread.

What I finde somewhat strange: I could only increase the T.C. value with the resistor. (from negative to positive).
Perhaps you should make another measurement with 2 references and measuring the difference in 100mV range.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on November 29, 2017, 08:50:53 am
I cant see any real change now, + or - 2.5uV is within the noise of the 34465a.

Then, you don't need your oven anymore?  ;D
Title: Re: Ultra Precision Reference LTZ1000
Post by: AG7CK on November 29, 2017, 11:58:06 am
The 400k resistor is in the datasheet. So it does not imo sound credible to associate it primarily with PCB layout design considerations.

The datasheet reads on page 1: "LTZ1000A uses a proprietary die attach method to provide significantly higher thermal resistance than the LTZ1000".

I do believe this is the key to understanding why LT in the "7V Positive Reference Circuit" on page 7 writes that the 400k "PROVIDES TC COMPENSATION, DELETE FOR LTZ1000A".

Imo the 400k resistor is part of the "cybernetics" of the thermal-electrical control system that the LTZ1000 is.

My hypothesis is:

The primary control system of LTZ1000 is the oven. An equilibrium parameter (Vbe, left transistor) from this oven is transferred to the voltage reference circuit (Vbe, right transistor) via heat (yes - heat). [The two transistors are supposed to be "identical", and the ("received") Vbe of the right transistor is the main control parameter of the reference).]

Due to leakage or for some other reason, [my guess is that] this transfer can be improved on by introducing an electrical current transfer from the heater voltage at point (1) via the 400k resistor to R1 (which is part of the reference setting circuit). So an element of electrical control is added to the heat flow control (for the lower thermal resistance LTZ1000 only. For the LTZ1000A they seemingly has found that it is not needed).

This would also explain why Andreas could only tweak the TC more positive: Current flows from the heater positive side point(1) to R1 - and the higher the oven heater voltage, the higher the current.

I will try to upload a figure, and then edit the post if I find it necessary. I think there are several smart people here that soon will elaborate on this hypothesis or prove me wrong.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on November 29, 2017, 02:47:07 pm
The 400 K resistor is a first approximation to compensate the residual TC of a typical LTZ1000 (non A) circuit. I don't think there is a really deeper thought behind it, just a way to do a small adjustment of the TC towards a more positive value. Depending on the actual reference, layout, thermal setup and temperature range a value different from 400 K (e.g. 270 K to 1 M) might be better. The TC of the resistor is not at all important, that would be only second order may be reducing the curvature if an PTC is used.

Andrea's measurements also showed that the contribution from the 400 K resistor is nonlinear, as it is following the heater voltage and thus about the square root of the heater power. So compensation is really good only for a small temperature range.

The A version seem to give lowet TC without the compensation and thus does not need the extra resistor. If the TC turns out to be too negative it can still be used, but it would be a surprise if 400 K turns out to be the right values. I would more expect higher values.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on November 29, 2017, 02:50:01 pm
I cant see any real change now, + or - 2.5uV is within the noise of the 34465a.

Then, you don't need your oven anymore?  ;D

Not so much for the LTZ, but I'm also going to have a 10v buffer placed in the oven as well.  Even though I have a custom VHD200 network coming for the 10v buffer which should also minimize temp sensitivity, I want to keep everything temp stable ;D

I have been fighting the negative TC with my two references for months.  At first I thought it may be the lead length as I placed the LTZ1000A about 1.5mm above the board, but unlike for Andreas, dropping it to the board and trimming the leads did nothing for me.  Now I am very satisfied, Ill post the overnight plot and a reverse (from 40 Deg C to 15 Deg C ) plot a bit later today. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on November 29, 2017, 03:17:54 pm
The 400k resistor is in the datasheet. So it does not imo sound credible to associate it primarily with PCB layout design considerations.

The datasheet reads on page 1: "LTZ1000A uses a proprietary die attach method to provide significantly higher thermal resistance than the LTZ1000".

I do believe this is the key to understanding why LT in the "7V Positive Reference Circuit" on page 7 writes that the 400k "PROVIDES TC COMPENSATION, DELETE FOR LTZ1000A".

Imo the 400k resistor is part of the "cybernetics" of the thermal-electrical control system that the LTZ1000 is.

My hypothesis is:

The primary control system of LTZ1000 is the oven. An equilibrium parameter (Vbe, left transistor) from this oven is transferred to the voltage reference circuit (Vbe, right transistor) via heat (yes - heat). [The two transistors are supposed to be "identical", and the ("received") Vbe of the right transistor is the main control parameter of the reference).]

Due to leakage or for some other reason, [my guess is that] this transfer can be improved on by introducing an electrical current transfer from the heater voltage at point (1) via the 400k resistor to R1 (which is part of the reference setting circuit). So an element of electrical control is added to the heat flow control (for the lower thermal resistance LTZ1000 only. For the LTZ1000A they seemingly has found that it is not needed).

This would also explain why Andreas could only tweak the TC more positive: Current flows from the heater positive side point(1) to R1 - and the higher the oven heater voltage, the higher the current.

I will try to upload a figure, and then edit the post if I find it necessary. I think there are several smart people here that soon will elaborate on this hypothesis or prove me wrong.
Nice ... this call for an experiment.

I expect TC to diminish when the "ambient" temperature is very near to the regulation limit.

The less power is needed to heat the reference die, the less gradient there will be, the lesser TC it will have.

It will be helpful to put on a chart, heater power used and "ambient temperature" with reference V delta (or calculated TC).
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on November 30, 2017, 01:27:23 am
Turned the oven off and put some frozen cool packs on the reference enclosure, plot from 39.6 Deg C to 12.8 Deg C internal oven temp, I cant detect any noticeable TC drift with the LTZ1000A now.  Before adding the 300K tempco resistor I saw a very pronounced negative TC and it was 100% repeatable.  The very slight downward drift over 5 hours here is the 34465A as the room warmed up slightly.  The 34465A will drift downward several uV per Deg C increase.  The slight fluctuations where mostly caused by me moving around close by and disturbing the air around the meter.  Id say its darn near flat from 5 to 40 Deg C.  Its now beyond my capability to measure.

(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/BD87AA8D-D0A7-4277-8FAF-4D85232F9339.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/BD87AA8D-D0A7-4277-8FAF-4D85232F9339.jpg.html)

The 34465A is null'd at 7.161552v, 10 NLPC, 10v manual range, 10M input Z, math averaging 10 readings (fast filter).
(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/8DD0EF6E-E1FD-44CE-AE95-8752CF767634.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/8DD0EF6E-E1FD-44CE-AE95-8752CF767634.jpg.html)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 30, 2017, 04:49:03 am
...
Imo the 400k resistor is part of the "cybernetics" of the thermal-electrical control system that the LTZ1000 is.
...
Nice ... this call for an experiment.
...

Well, off you go.

Ask and you shall receive :) Here are three test results of my latest FX LTZ1000A reference, which follows the datasheet schematics with LT1013ACN.

(https://xdevs.com/doc/xDevs.com/FX/pcb/fxref_1.jpg) (https://xdevs.com/doc/xDevs.com/FX/pcb/fxref.jpg) (https://xdevs.com/doc/xDevs.com/FX/pcb/fxrbot_1.jpg) (https://xdevs.com/doc/xDevs.com/FX/pcb/fxrbot.jpg)

Setup of DUT (not the sample shown on photo above): LTZ1000ACH, 51 week 2016, 1K AE XB BMF, 15K AE XB BMF, two S102 in parallel to get 132R.
Third unit module running tempco test, graceful ramp +20c to +50c, with help of Keithley 2510 and YSI 44006.

LTZ section powered from +11V, sourced by low-noise LT3042 LDO. Input power delivered from Keithley 2400, set at +12V with 105mA compliance.

Output measured by three meters, pair of 3458A and Keithley 2002 (GPIB 4).

(https://xdevs.com/doc/xDevs.com/FX/test/fx3_tc1_1.png) (https://xdevs.com/fx3_test1_tec/)

This module provided initial TC -0.25 ppm/K. No compensation resistor populated (R13 position).

For Test 2 additional compensation resistor was added, 390K&Omega; 5% 1206 on R13 position.

(https://xdevs.com/doc/xDevs.com/FX/test/fx3_tc2_1.png) (https://xdevs.com/fx3_test2_tec/)

Much better now!

Retest with 331K&Omega; R13 resistor:

(https://xdevs.com/doc/xDevs.com/FX/test/fx3_tc3_1.png) (https://xdevs.com/fx3_test3_tec/)

If judge by temperature ramp down curve, then tempco is <0.02ppm/K with this resistor setup. (0.5 ppm change over 25K delta).
Pay attention on the left ppm vertical scale of the graphs, it's not the same between the tests.

Also this is non-aged reference, 0 hours burn-in. I started TC test first thing after assembly.

CSV-file with all data (https://xdevs.com/datashort/fx3_tec_test1_nplc100.csv) for those who want to play with own plotting/analysis.

As bonus, one can see the 2002 noise performance (20 NPLC, default DFILTER 10 ON, LINE SYNC) compared to 3458A (NPLC100)  :-DMM
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on November 30, 2017, 04:36:13 pm
The measured TC of TiNs reference looks rather constant, thus a nearly perfect linear temperature - voltage relation. The compensation however is nonlinear as the heater voltage is about proportional to the square root of the heater power and thus the square root of set temperature minus actual temperature minus self heating. One can see the rather curved relationship with the compensation resistor. At high temperatures the compensation has too much effect. I wonder if it might be wort using a different type of TC compensation, that is more linear. I first idea might be a PT1000/PT100 in series to R2, maybe with a second resistor in parallel to reduce/adjust the strength.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on November 30, 2017, 05:27:39 pm
Well yes initial TC is linear ... but this is the LTZ1000A not the LTZ1000.
Still convinced that LTZ1000 operated at near temperature regulation limit should exhibit less TC ... maybe I check this, this night.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on December 01, 2017, 12:34:44 am
for improper PC layout (in the area of ground currents).

I would not sign that: even with the same layout I had a initial stray between +0.015 and -0.23 ppm with different LTZ1000A references.
Lead length of the LTZ1000A also plays a role if you look somewhat earlier in the thread.

What I finde somewhat strange: I could only increase the T.C. value with the resistor. (from negative to positive).
Perhaps you should make another measurement with 2 references and measuring the difference in 100mV range.

With best regards

Andreas

Done, used my second LTZ1000A KX ref to null the DUT, this left ~20mV to null in the 3465A.  Used 100mV range, 100NLPC with math filter set to fast (10 readings), AZ on and 10M Ohm Z. Sweep from 10.6 deg C to 40.0 deg C shows less than 2.5uV deviation or ~0.35ppm.  There is no real curve or slope, its seems to average right down the middle, no non-linearity seen.  So over a 29.6 deg span that comes to ~0.01ppm? It appears to be simply flat across any temp I would ever expect this box to be used in.  Maybe I need to send this one over to TiN for better testing.

(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/ACF0163C-DD81-48B2-A8D1-E673B250E476.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/ACF0163C-DD81-48B2-A8D1-E673B250E476.jpg.html)

(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/DD420BC0-C088-480D-8054-D72E50C9EBF7.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/DD420BC0-C088-480D-8054-D72E50C9EBF7.jpg.html)
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on December 01, 2017, 12:35:24 am
So I run my tests with my heated LTZ1000 (non A - no compensation).
Results are opposite to what I expected, than more I approach the upper limit of the heater, than more TC increase in a non linear way.
I have to think at this.


VOUT        T       TC
========    ==     ====
7.0880010   25   
7.0880035   30     0.07
7.0880065   35     0.08
7.0880115   40     0.14
7.0880155   42.3   0.24
7.0880175   43.3   0.28
7.0880210   44.4   0.45




Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 01, 2017, 04:57:36 am
Thermographs of the FX reference, LTZ1000A with 1K/15K setpoint, powered by +11VDC. Large size clickable.  :-DMM

(https://xdevs.com/doc/xDevs.com/FX/thermal/fx1_thermal_1.jpg) (https://xdevs.com/doc/xDevs.com/FX/thermal/fx1_thermal.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 01, 2017, 07:52:29 am
  There is no real curve or slope, its seems to average right down the middle, no non-linearity seen.  So over a 29.6 deg span that comes to ~0.01ppm? It appears to be simply flat across any temp I would ever expect this box to be used in. 

Hello,

seems to be only noise (perhaps by thermal EMF).
Did you cover your inputs to the DMM with a cloth?

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 01, 2017, 10:33:01 am
Measuring a LTZ1000 referenz with an 34465 or similar meter is mainly measuring noise and drift of the meter internal LM399 reference. Even with a better meter it is a combination of both references, so something like two LTZ1000 circuits.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on December 01, 2017, 11:58:29 am
So I run my tests with my heated LTZ1000 (non A - no compensation).
Results are opposite to what I expected, than more I approach the upper limit of the heater, than more TC increase in a non linear way.
I have to think at this.

...


Well, maybe you should have read before, what I have measured recently..
The T.C. seems to rise as soon as you approach the oven temperature by some margin.

It is also quite convenient to draw the output deviation over the temperature, then you can see directly, what's going on, and you may draw a box around the curve for determining the boxed T.C.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 01, 2017, 12:30:41 pm
Indeed, output/temp graphs might be easier to grasp:

(http://xdevs.com/doc/xDevs.com/FX/test/fx3_ref_curve.png)
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on December 01, 2017, 01:37:21 pm
  There is no real curve or slope, its seems to average right down the middle, no non-linearity seen.  So over a 29.6 deg span that comes to ~0.01ppm? It appears to be simply flat across any temp I would ever expect this box to be used in. 

Hello,

seems to be only noise (perhaps by thermal EMF).
Did you cover your inputs to the DMM with a cloth?

with best regards

Andreas

I did not, the test was done just as the photo above shows. The real problem is as Kleinstein points out, trying to measure a LTZ1000 reference with an LM399 based meter.  At this point I can only confirm my references seem to be performing well and possibly far better than the meter I have to measure them with.  At least the drift I was able to see before installing the 300K TC resistor appears to be gone now.  It's as good as I can get it, going to have to send it off for any further evaluations at this point.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 01, 2017, 02:24:46 pm
Hello,

let´s do the math:

In 10V range a 1 ppm drift of the LM399 reference will give you 1 ppm drift (7uV) of the 7V reading at constant input.
In 100mV range a 1 ppm drift of the LM399 reference at 20 mV input will give you 1 ppm drift (20nV) of the 20mV reading.

So even when you loose more than 1 ppm due to the scaling resistors in the 100mV range, the relative measurement will be better than the absolute measurement in 10V range.

with best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: beanflying on December 02, 2017, 01:23:40 am
This thread is truly epic, I think I have digested and understood 'some' of the first 10 pages  :-\

Not sure why but I am also having flashbacks to the most boring Uni lecturer I had to tolerate in 2 hours sessions for Probability and Sadistics  |O
Title: Re: Ultra Precision Reference LTZ1000
Post by: Zucca on December 04, 2017, 02:31:13 pm
This thread is truly epic, I think I have digested and understood 'some' of the first 10 pages  :-\

I think some of us need an "Ultra Precision Reference LTZ1000 for beginner..." you could probably make 10 YT Video on this.
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on December 05, 2017, 12:01:36 pm
Thermographs of the FX reference, LTZ1000A with 1K/15K setpoint, powered by +11VDC. Large size clickable.  :-DMM

(https://xdevs.com/doc/xDevs.com/FX/thermal/fx1_thermal_1.jpg) (https://xdevs.com/doc/xDevs.com/FX/thermal/fx1_thermal.jpg)
@TiN-  Very nice thermographs!   Is the board laying horizontal?  If so, I'm surprised at the 3K temperature difference surrounding the LTZ pins.  Had you expected this?  On your thermograph of the back side, frame IR000740, it looks like three pins are cooler than the rest.  Is this due to different amounts of solder, thicker traces on these pins, different emissivity, or something else?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 05, 2017, 03:33:59 pm
  Had you expected this?

Hello,

if you look at the chip photo: there are different numbers of bond wires connected to some pins.
(different thermal resistance).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on December 05, 2017, 05:08:21 pm
I'm the opinion that because of different emission factors of the different materials the results shouldn't be overrated. For a quality statement some coating with known emission coefficient is essential.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on December 05, 2017, 06:13:00 pm
All I wanted to say is, take it only as a nice colorful picture but nothing more, even though TiN has marked several points with temperatures. These temperatures are not valid or reallity unless each point of the measurement was corrected for its individual emission coefficient or the complete board coated with a coating of known emission coefficent. There are a lot of people out there and I'm sure also on this board that don't know the difficulties on thermogaphics and take that pictures as representing reallity. No, it isn't!

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 05, 2017, 06:19:21 pm
Much of the thermal gradients would be stable and thus would not change that much. It is mainly the part of the thermal gradients that does change, that could be trouble. Sources for this is the changing heater power of the  LTZ and the heater transistor and to a smaller degree the diode. Another factor it heat loss from convection, if the instrument is tilted.
Temperature differences between the critical pins (mainly  pins 3 , 7 and 6) can add thermal EMF, that can add to the final TC.
The tricky part is finding a good balance between thermal gradients that would favor thin long lines and low copper resistance that would favor thick copper.

With the thermal camera reading emissivity can be a factor - especially readings on metallic surface are not real. So the small gradients close to the hot LTZ1000 might not be all real, but could include environmental radiation and also heat flow by convection if the board is tilted. It still is nice to look at the thermals.

From below the temperature around the LTZ looks really nice and even. At least one of the two slightly colder pins is the rather thick ground connection and thus not a surprise. The other could be due to the lines going there too. Things will change with additional cover anyway. The more telling thermal picture would be from below, with the cap on the top side mounted.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on December 05, 2017, 06:41:37 pm
Just as helpful thought, not bashing TiN's work at all:

The photos are an estimate of what's going on, but not close to reality unless you have a proper constant-emissive coating designed for real thermal testing.  We don't for an instant take the temperature annotation to mean anything for an absolute measure of temperature.

That being said what you do see here that on such a large board you get big temperature gradients from one end to the other.  Hopefully they don't change too much but that depends on enclosure and environment.  On a much smaller Vref module you'll get a board hopefully in equilibrium at about one temperature around the Vref components (and reacts much less to changing environment), and that's normally what you want for production.

On the other hand, the other thing we don't know about this board is how it works in an enclosure - you really have to look at the entire final system as a whole.  It may be that the temperature evens out inside the enclosure - an IR photo of the -bare- board could be misleading. What counts is how does it work in the final enclosure system, and we'll see that on the final TC testing of the finished system - and it could be that everything works out just fine and within LTZ specs.

TiN:  Where is the air-draft cover on the LTZ top and bottom?  Or will this be part of the enclosure system??

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on December 05, 2017, 06:50:37 pm
Quote
That being said what you do see here that on such a large board you get big temperature gradients from one end to the other

That is a typical misinterpretation I was warning about. Your interpretation implies a constant emission coefficient of the solder mask along the complete board, but this is not the case and depends on several aspects such as thickness of the solder mask, copper density underneath, the compound iself, reflections of the surrounding, ...

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on December 05, 2017, 07:02:33 pm
Regardless of the thermal photo, you don't need a thermal photo to know that this board is going to have a significant thermal gradient from one end to the other, that is not an interpretation due to the image.  Small board is better than large board in nearly all cases.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zhtoor on December 05, 2017, 07:54:34 pm
Regardless of the thermal photo, you don't need a thermal photo to know that this board is going to have a significant thermal gradient from one end to the other, that is not an interpretation due to the image.  Small board is better than large board in nearly all cases.

maybe somebody tries this to reduce thermal gradients across the ref board.
ie; 3-dimensional pcb construction.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 06, 2017, 04:43:21 am
Quote
Where is the air-draft cover on the LTZ top and bottom?  Or will this be part of the enclosure system??
They will be installed for final tests. All these above are indeed just colorful pictures to get some rough idea of things, not aiming for any kind of accurate thermal test, can't agree more :)

I still need to assemble two remaining refs with 10V stage. There was no intention to make this board isothermal, however to reduce hotspot area board will be thermally coupled to metal base of the enclosure (except LTZ1000 area, of course).  Kelvin connection for 7V voltage output is taken at inner layer traces, not surface trace.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on December 07, 2017, 03:57:36 am
It may be that the temperature evens out inside the enclosure

im curious, do you purposely design your boards to maximise thermal "even-ness" (excluding the LTZ area)?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 07, 2017, 04:49:19 am
It's easier to try keep temperature same across the parts to limit the root cause for issues, instead of battling with temperature compensation and other wizardry to fix the consequences.
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 10, 2017, 08:46:01 pm
Does anyone speak French?  Is there a way to automatically translate French captions into English?

https://youtu.be/SVXdSIp9stc
Title: Re: Ultra Precision Reference LTZ1000
Post by: plesa on December 10, 2017, 10:18:46 pm
Does anyone speak French?  Is there a way to automatically translate French captions into English?

https://youtu.be/SVXdSIp9stc

Yes, enable subtitles and in settings select auto-translate to English. It is not 100%.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on December 10, 2017, 10:57:45 pm
Does anyone speak French?  Is there a way to automatically translate French captions into English?

https://youtu.be/SVXdSIp9stc

Yes, enable subtitles and in settings select auto-translate to English. It is not 100%.

I hope its not 100%, otherwise we have all been doing it wrong.

Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on December 11, 2017, 12:32:51 am
Yes, that at precisely 01:12:53 -54 it's my telling too, that's where i'm totaly understand him ... 
:-DD :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: beanflying on December 11, 2017, 12:48:51 am
I don't speak or read french but it made more sense untranslated  :o

Somewhere in the first 10 minutes the auto translate dropped the "F" bomb  :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: Grapsus on December 11, 2017, 05:14:58 am
Does anyone speak French?  Is there a way to automatically translate French captions into English?

https://youtu.be/SVXdSIp9stc

I do, feel free to ask if you don't trust the automatic translation at some point. Also Jipihorn, the guy who made this video is a member of this forum...
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 13, 2017, 11:39:01 pm
I've been taking a swing at making my own LTZ board, based on the schematics of Andreas and Dr. Frank:

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg249123/#msg249123 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg249123/#msg249123)

https://www.eevblog.com/forum/metrology/mx-reference/msg1297126/#msg1297126 (https://www.eevblog.com/forum/metrology/mx-reference/msg1297126/#msg1297126)

I had a few questions:

Question 1: Frank uses very wide traces for +Vz and -Vz coming out of the LTZ1000, to reduce ohmic losses in the traces.  However, my understanding is that once the LTZ1000 is insulated (e.g. in a bit of foam), the majority of the heat egress is through the copper traces.  Here I've tried out a layout which takes the opposite approach: use skinny traces to minimize the heat egress.  My understanding is that the down-side of this approach is that R1 can be considered to have two parts: the 120R resistor, and the trace leading to it, and the trace leading to it has the poor temperature coefficient of copper.  My question is, how can I develop an intuition about which side of this trade-off is better, optimizing the tempco of R1 via fat traces, or minimizing heat egress via skinny traces?

Question 2: I had two ideas for the thermal treatment of R1 through R5.  Either include those resistors inside of the foam which insulates the LTZ1000, effectively creating a tiny oven, or do your best to totally isolate them from the heat of the LTZ1000.  I'm not sure which is the better approach, and I've attached sketches of both approaches.  Keeping them in the oven would raise the temperature of the resistors, which isn't ideal if the the flat spot on their tempco curve is near room temperature (like with Vishay foils), but they would effectively be in a (pseudo) temperature-regulated environment, so maybe that doesn't matter so much?

The thermal isolation idea I have in mind is to laser-cut some rings of EVA foam (marked on the board with silk-screened zones).  The inner ring would be a "hat" with a lid which isolates the LTZ1000.  Then there would be an air gap (with a few ventilation holes in the board), followed by an outer ring of foam, which would be an open-topped column, and the inside face would be lined with a thermal reflector (aluminum or copper foil).  The idea would be to insulate the LTZ1000 (reducing its total heat output via copper trace conduction, convection, and radiation), then have a "chimney" which creates a thermally isolated zone -- thermal radiation is bounced / absorbed by the outer foam ring, and convected away before it can reach R1 - R5.  Thoughts?

Additional notes:

- I've used a 4-layer design, where the outer layers form an EMI shield, joined by via stitching.

- The grey box outline surrounding the board indicates the inner dimensions of a Hammond 1590B diecast case.

I would love to get any feedback on this layout.  I'm reaching into (personally) unexplored territory with this board layout, so if there things which strike you as obviously wrong, I probably don't see them, so please point them out!

edit: "EVA foam", not "EPA foam"

edit2: Hmm, perhaps the convection holes around the foam are hurting more than helping?  They would cool off the LTZ, forcing it to draw more power and just raise the temperature inside of the 1590B enclosure?

edit3: see this thread for the latest boards: https://www.eevblog.com/forum/metrology/px-reference/ (https://www.eevblog.com/forum/metrology/px-reference/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 14, 2017, 04:20:45 am
I'd get rid of the voodoo holes around the LTZ, and bypassing your question 1 would focus on getting board with uniform temperature gradients around all critical components (resistors/LTZ). If you have small temperature variation over the board, it doesn't really matter, if traces are skinny or fat. Also you don't want to load unbuffered LTZ output to maintain best accuracy, so in typical setup with Gohm DCV impedance or null-meter those resistive losses don't matter.

For Q2, I'd bias toward getting resistors somewhat decoupled, as temperature accelerate aging and drift of the resistor element. Possible benefit may be more for non-hermetic types in epoxy packages, like Edwin's PWW/VPG Z's to smooth humidity impact a bit, but your PCB shows footprints for HZ. Also using HZ for 70K bias resistors is overkill, you can just have 3-5ppm/K in there without measurable difference :).

Overall, your board looks cute  ^-^
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 14, 2017, 05:48:43 am


Hello,

Q1: what you really want is to have uniform temperature at the (critical) pins. And no air flow around the leads.
The KOVAR pins have 39uV/K against copper.
On a heated device you get easily temperature differences of several K between pins.
So I would use equal trace widths for the sense pins.
In this regard your star point (too) near at the ground pin is somewhat counter productive.

Q2: we are all in a learning phase: so why not try out. But be shure to have enough boards to compare the statistics.
It shurely also depends on the resistors (EPOXY) used. Humidity is the main factor.
I have large differences between e.g. vishay S102 / Z201 / 8G16 / UPW50 / UP805 resistors regarding humidity.
And the "sweet spot" of the vishay resistors does only exist in the manufacturers phantasy.
Unfortunately resistors cannot read data sheets.

- I've used a 4-layer design, where the outer layers form an EMI shield, joined by via stitching.

the problem with 4 layer design is that the (critical) components are not between the outer layers.

The cirquit diagram is not drawn correct (ok I am also guilty). C11 C12 belong to the base-emitter junctions of the LTZ1000 and not to protect the resistors. So also the placement of these critical components is wrong.

I have intentionally used SMD X7R for these capacitors to get nearer to the LTZ pins. (you could also use Panasonic ECHU Film capacitors nowadays to reduce microphonic effects).

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 14, 2017, 06:41:32 am
TiN, Andreas, thank you for your feedback!

Andreas, I have updated the schematic to reflect the intent of C11 / C12 -- is this correct?  (attached)

Update: whoops, totally fudged C12.  updating coming momentarily...

Edit: fixed C12.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on December 14, 2017, 07:04:54 pm
Just a few thoughts for Cellular, based on past experience:

1. I would lose the voodoo holes and crop circles.  At least in our tests those are not really helpful in most cases and will actually cause more thermal gradients on the board and make LTZ traces longer than required.  What has really worked much better for us is to let the board heat naturally and evenly in a stable way - any thermal gradients on the board you want to stay steady at equilibrium.  Excess copper around the LTZ tends to make the board react more to changing ambient conditions, which you don't want.

2.  For Vref boards we never use more than one mounting / screw hole.  The moment you add more than exactly one mechanical screw hold-down on a board you've just created a stress riser between the board and it's housing.  If you need more than one screw hold-down, the hold-downs should be compliant (use rubber washers, flex-plastic posts, etc.).  Ideally the Vref board has a minimal mechanical attachment to anything around it, and it should be absolutely free to assume any size it wants to be over time without fighting against the enclosure.

3.  There is a difference between Air Draft protection on the LTZ and Foam "Insulation".  Air Draft protection you need around the leads top and bottom  (and keep those leads short for A version).  You don't necessarily want or need foam thermal insulation around the LTZ because you do need at least some steady thermal flow out of the device for the on-chip heater to stay stable.  If you're using skinny traces and foam insulation you can easily run into a condition where the LTZ is over-insulated - and the end result is a wobbly Vref.  Keep an eye on that.

4. Keep all your current loop areas small. Remember that copper on the board does exactly nothing for low freq mag fields, so the board always goes into a good enclosure shielding system - for wherever this is going to be used.

Again: A very good starting place for LTZ design is to look at the 3458a LTZ Vref board as inspiration, proven over hundreds of thousands of units.  The final result of that board is basically any real drift you'll see is from the LTZ die itself, which is beyond your control - and that's about as good as it gets.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 14, 2017, 07:14:28 pm

Andreas, I have updated the schematic to reflect the intent of C11 / C12 -- is this correct?  (attached)

Hello,

it shows the intention.
-> the more essential is the correct placing in layout.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on December 14, 2017, 07:44:29 pm
Related to MisterDiodes comments above, recently I did some tests with my reference wrapped in open cell foam and unwrapped inside a metal enclosure.  I found less TC drift with the reference board not being wrapped in foam.  So I came up with another low stress mounting idea.  Cut some slots in some felt strips and slid the board into position.  There is a small amount of play to insure there is no stress on the board.

Also like MisterDiodes mentions, my A chip is dropped to the board and I have small closed cell foam caps for the underside of the board and the can itself.  I going to alter this and make a foam ring to shield the pins from the board to the can only with the can exposed above the foam ring.

(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/52521448-72B9-4E6D-8F97-346848D5799B.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/52521448-72B9-4E6D-8F97-346848D5799B.jpg.html)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 14, 2017, 08:14:48 pm
The traces towards R1 (usually 120 Ohms) is in dead a difficult question. One has to find a kind of compromise between thermal layout and trance resistance.
One thing one can do is to have the traces wider where the temperature gradient is small. So have a relatively thin trace near the reference and a thicker one near the resistor, where thermal properties are less important. Copper resistance near the LTZ is less important than copper resistance away from the chip. Also not every bit of copper resistance is bad - the 400 K compensation resistor suggests that the normal reference circuit will have a certain typical TC and the correct amount of TC added to the resistors could even be an improvement over the 400 K resistor.

The difficult pin on the LTZ1000 is the ground  and to a lesser extend the +7 V pin, as here are several connections going off.  At least the 70 K resistors can share a common trace - likely also with the 13 K/1 K divider. The tricky ones are the 1 K and 120 Ohms resistors to the GND pin.

One does not need super thin traces - the more important thing is a balance in thermal design, so about equal heat flow to all pins. So in areas where several lines run in parallel they should be thinner than the other ones. The idea behind extra copper near the LTZ is to have thermal coupling between the pins and the lines towards the pins - this extra copper only makes sense if used correct. If not well balanced it can do more harm than good.
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 15, 2017, 08:57:52 am
Thanks so much for the feedback and discussion, all!

Here's an alternate, simpler, denser idea on a 50x50mm 2-sided board.

edit: a couple of slight routing tweaks

edit2: oshpark ordering link: https://oshpark.com/shared_projects/FH6nJLus (https://oshpark.com/shared_projects/FH6nJLus)

edit3: github link: https://github.com/pepaslabs/px-ref (https://github.com/pepaslabs/px-ref)

edit4: see this thread for the latest boards: https://www.eevblog.com/forum/metrology/px-reference/ (https://www.eevblog.com/forum/metrology/px-reference/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 15, 2017, 11:15:14 am
Such a productivity. I took me 3 years to get from KX to FX, and you cooking them like hot buns non-stop.  :D
I'd say make all variants, and then try a futile comparison between the different designs. With good amount of luck, we could see the different stability after 3-5 years of measurements.  ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on December 15, 2017, 11:43:38 am
I'm just watching your very interesting developments right now.
But i can tell, that my constantly with pure 4s 18650 driven kx is very stable, as i can see with my 34461a.  :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on December 15, 2017, 12:01:23 pm
I had a few questions:

Question 1: Frank uses very wide traces for +Vz and -Vz coming out of the LTZ1000, to reduce ohmic losses in the traces.  However, my understanding is that once the LTZ1000 is insulated (e.g. in a bit of foam), the majority of the heat egress is through the copper traces.  Here I've tried out a layout which takes the opposite approach: use skinny traces to minimize the heat egress.  My understanding is that the down-side of this approach is that R1 can be considered to have two parts: the 120R resistor, and the trace leading to it, and the trace leading to it has the poor temperature coefficient of copper.  My question is, how can I develop an intuition about which side of this trade-off is better, optimizing the tempco of R1 via fat traces, or minimizing heat egress via skinny traces?


Main idea for these broad traces is having very good thermal conductivity, so that the solder joints of the LTZ1000 pins 3 +4 are approximately on the same temperature as the corresponding solder joints of +Ref and -Ref.
The +Ref PCB track carries the zener current of 4mA, whereas the -Ref track carries about 200µA only, i.e. both collector currents. Evidently, I did not balance both tracks in terms of voltage difference across these paths. So I doubt, that it will make any difference, if you use smaller tracks.

Anyhow, as I have a single sided board, the number of solder joints / thermocouples is reduced to a minimum, and these are pairwise symmetric from the LTZ1000 footpoint to the outer jacks, so cancelling each other.
As all these solder joints are located on one horizontal plane, that should help to equalize the temperature difference between all of them.

2 layers or even 4 layers create much more potential thermocouples (i.e. by the vias), and these are additionally distributed over different planes, like the top side, where you will definitely have a different temperature than on the bottom side.

So I think, that your 4 layer approach is not so good regarding thermal aspects, and also over-engineered, and too costly.
Keep things simple!

Regarding the resistors R1 (120 Ohm) , R4 / R5 (12k / 1k) , and R2 (70k), I arranged them around the LTZ1000, so that the lowest resistor value is closest to the LTZ, providing lowest parasitic track resistance. The influence on the T.C. of the 120 Oh resistor should be quite low.
I think, that's the optimum way, and you should again avoid additional layers.

Question 2: I had two ideas for the thermal treatment of R1 through R5.  Either include those resistors inside of the foam which insulates the LTZ1000, effectively creating a tiny oven, or do your best to totally isolate them from the heat of the LTZ1000.  I'm not sure which is the better approach, and I've attached sketches of both approaches.  Keeping them in the oven would raise the temperature of the resistors, which isn't ideal if the the flat spot on their tempco curve is near room temperature (like with Vishay foils), but they would effectively be in a (pseudo) temperature-regulated environment, so maybe that doesn't matter so much?

The thermal isolation idea I have in mind is to laser-cut some rings of EVA foam (marked on the board with silk-screened zones).  The inner ring would be a "hat" with a lid which isolates the LTZ1000.  Then there would be an air gap (with a few ventilation holes in the board), followed by an outer ring of foam, which would be an open-topped column, and the inside face would be lined with a thermal reflector (aluminum or copper foil).  The idea would be to insulate the LTZ1000 (reducing its total heat output via copper trace conduction, convection, and radiation), then have a "chimney" which creates a thermally isolated zone -- thermal radiation is bounced / absorbed by the outer foam ring, and convected away before it can reach R1 - R5.  Thoughts?

Additional notes:

- I've used a 4-layer design, where the outer layers form an EMI shield, joined by via stitching.

- The grey box outline surrounding the board indicates the inner dimensions of a Hammond 1590B diecast case.

I would love to get any feedback on this layout.  I'm reaching into (personally) unexplored territory with this board layout, so if there things which strike you as obviously wrong, I probably don't see them, so please point them out!

edit: "EVA foam", not "EPA foam"

edit2: Hmm, perhaps the convection holes around the foam are hurting more than helping?  They would cool off the LTZ, forcing it to draw more power and just raise the temperature inside of the 1590B enclosure?

That's all too complicated and over-engineered, again!

I have enclosed the PCB inside a styrofoam box, and omitted the Styrofoam cap on top of the LTZ1000.
This box suppresses any air draught from outside, and lets the whole interior warm up to about 7°C above ambient temperature.
So a certain amount of heat is flowing through this enclosure, to guarantee stability of the oven regulator, but reduces also the oven power for the non-A version.
That's about 16mA @ 12V, 22°C

It was possible to reduce the overall T.C. to near zero by the nominal 400k resistor (R10), so I would not waste any thoughts about an additional oven for the resistors, or a convoluted isolation.

Same goes for the ground plane layer, for EMC suppression, that's also not necessary.
As you have a pure DC application, such a layer makes no sense at all, as the EMC disturbance comes from outside (mains, switch mode PSU, etc.)

Therefore, a simple tuner box all around the PCB is much more effective, as all of my measurements demonstrate. (I.e. not a single glitch anymore, during nearly 100h of measurement)

My approach delivers very good results, like more complicated ones (e.g. from TiN) obviously do also.

You might go ahead with your design, but you'll never get better results, as these existing designs are optimized already.
And I don't see any idea or ansatz in your proposal, why / how this would give any better results.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 15, 2017, 01:53:47 pm
Dr. Frank saved us all all that typing,  :-+, cannot agree more. I can only speak for my own designs, the implementation and approach was driven mostly by the end use goal purpose, not the attempt to improve already working solution (reference board that is). In the end we are limited by performance of the zener itself + performance of the measurement equipment + environment isolation (EMI, temperature, humidity) that is.

So "Keithley experimental" design was targeted for compact size, with wide input supply for easy integration within other equipment, providing direct LTZ output voltage. Recent "FX" design was targeted around getting stable output with 10V stange, so LTZ section was even more simplified, using 1013 opamps and using PTF56 70K resistors instead of fancy BMFs. Those are decision I made during the design, rest are just playing around to make PCB look nice.  ^-^ I'm still waiting for multi-LTZ design from someoone, in attempt to reduce output noise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on December 15, 2017, 02:12:46 pm
CM, I like your V2 board a lot, if you have some boards made, Ill buy one and build it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: tszaboo on December 15, 2017, 02:38:14 pm

So I think, that your 4 layer approach is not so good regarding thermal aspects, and also over-engineered, and too costly.
Keep things simple!
I shall disagree. My design was 4 layer, inner layers were ground. Having these two layers ment that the thermal aspects are much easier to handle. Remember that copper conducts heat 400 times better than FR4. Having a solid ground plane means solving thermal issues and equalizing the thermals for components. You not only need to match the leads of the LTZ1000, but you have a bunch of resistors. Keeping them in pair (and SMD in my case) means that they are much better coupled thermally.

And the cost of the PCB is quite irrelevant when you make more than 1. The LTZ was about 35EUR, last time I've checked, and the PCB is a fraction of this cost.
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 15, 2017, 03:24:08 pm
CM, I like your V2 board a lot, if you have some boards made, Ill buy one and build it.

Drat, I have already placed my order for the second version, else I would have included a board for you.

Here's the oshpark links if you want to place your own order:

complex version 1: https://oshpark.com/shared_projects/mkNWJ591 (https://oshpark.com/shared_projects/mkNWJ591)

simple version 2: https://oshpark.com/shared_projects/FH6nJLus (https://oshpark.com/shared_projects/FH6nJLus)

I'll put it all up on github later today.

Edit: The cap footprints should fit any film cap with 0.2" lead spacing (e.g. WIMA MKS2 (via mouser), or Kemet R82 (digikey)).  The R1-R3 footprints should fit any foil resistor (Vishay with 0.15" or AE with 0.2" lead spacing), and the R4/R5 divider footprint is intended for a Vishay foil divider.  R1-R5 will fit hermetic or not.

edit: see this thread for the latest boards: https://www.eevblog.com/forum/metrology/px-reference/ (https://www.eevblog.com/forum/metrology/px-reference/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on December 15, 2017, 03:36:05 pm

So I think, that your 4 layer approach is not so good regarding thermal aspects, and also over-engineered, and too costly.
Keep things simple!
I shall disagree. My design was 4 layer, inner layers were ground. Having these two layers ment that the thermal aspects are much easier to handle. Remember that copper conducts heat 400 times better than FR4. Having a solid ground plane means solving thermal issues and equalizing the thermals for components. You not only need to match the leads of the LTZ1000, but you have a bunch of resistors. Keeping them in pair (and SMD in my case) means that they are much better coupled thermally.

And the cost of the PCB is quite irrelevant when you make more than 1. The LTZ was about 35EUR, last time I've checked, and the PCB is a fraction of this cost.

You're right, that one GND layer might help equalizing temperature differences.

But that's not the aspect, which I highlighted, I clearly focused on the increased number of  thermocouples.. and your description of your 'mysterious' (not published) design does not explain, why this should have less number of thermocouples. Also, it's not convincing, that these SMD components are well coupled to this thermal plane, as there's PCB material in between..

From you and other contributors in this thread, I'm simply missing any proof for the relevance of such proposed "improvements", let it be practical measurements, or profound theoretical calculations.

As long as this is not available, I regard these ideas simply as vodoo stuff, or over-engineering.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 15, 2017, 03:49:52 pm
BOOM! Gauntlet thrown! Bring on the designs!
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on December 15, 2017, 04:10:55 pm
Regarding thermal insulation around the chip itself, I'm able to see what Andreas and others have been saying first hand.  Too much thermal insulation definitely has a negative impact of the chips ability to self regulate its temp.  Despite being happy with the TC and stability of my reference, out of curiosity (after all, I'm only doing this to learn and for fun) I decided to ditch the closed cell foam hat for the chip and make a skirt to only shield air currents from the pins.  I saw a smoother, more linear TC curve that became positive over 32 deg C and had to adjust my TC resistor to a higher value, from 300K to 330K.

The foam is only slightly smaller in diameter to the can, so the foam will not make contact with the pins, its just thicker than the cans height above the board, the inner edge can be gently tucked just under the can.
(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/1367FAC2-5FC7-417B-B544-425AD6FD278B.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/1367FAC2-5FC7-417B-B544-425AD6FD278B.jpg.html)

Ill collect proper data and post a good TC plot later today, but here is a screen shot of my first 40 to 15 deg C sweep;
(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/A0AF629E-D848-4303-9F53-0141C0798BE1.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/A0AF629E-D848-4303-9F53-0141C0798BE1.jpg.html)

The negative spike the the end is from me getting close to take the photo.  So from 40 deg C start, slight voltage increase, about 1uV around 33 deg C, then slight dip about 27 deg C then flat from 25 to 15 Deg C.
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 15, 2017, 06:22:22 pm
kj7e, I was thinking of trying the exact same thing -- thanks for the field report!
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on December 15, 2017, 09:26:01 pm
that black foam is usually conductive, just hope no fragments break off in a few years and change things under the LTZ can.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on December 15, 2017, 10:40:18 pm
that black foam is usually conductive, just hope no fragments break off in a few years and change things under the LTZ can.

I checked before using this foam, not able to detect any conductivity.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dr.diesel on December 15, 2017, 10:49:27 pm
I checked before using this foam, not able to detect any conductivity.

Humidity might also toss a wrench with respect to the foam, especially considering it's slightly compressed under the LTZ.
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on December 16, 2017, 04:00:26 am
An Interview with “Analog Guru” Carl Nelson, Sept. 13, 2017
http://www.electronicdesign.com/analog/interview-analog-guru-carl-nelson (http://www.electronicdesign.com/analog/interview-analog-guru-carl-nelson)

"...I am now developing a method to do thermal modeling in Spice that takes into account each transistor’s temperature. It’s rudimentary, but it works, and lets you see die temperature unfold in front of you as time proceeds. I plan to include it in a macromodel of the LTZ1000 heated voltage reference, so customers can do thermal modeling as well as electrical. The Spice folks are choking on their lunch when they see this, but I think it’s the wave of the future."
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 16, 2017, 09:48:37 am
Thermal modeling is nothing new. I remember an old article about thermal modeling OP for low offsets - that was nearly 20 years ago. However the normal spice simulations don't include it. Much of the design of such old chips is using symmetry to get low thermal gradients - so I don't think this will make a big difference for the LTZ chip itself. You can't change the chip anyway.

Humidity should not be a problem so close to the LTZ chip, as the temperature is higher than the normal air temperature. It is more that the high temperature could be a problem for the foam, accelerating aging. Quite a lot of foam foam from the 1960's does not look that good today and at something like 60 C aging could be 10 times faster than normal.
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 16, 2017, 11:39:58 am
I recreated Dr. Frank's board layout (https://www.eevblog.com/forum/metrology/mx-reference/msg1297126/#msg1297126 (https://www.eevblog.com/forum/metrology/mx-reference/msg1297126/#msg1297126)) in kicad and published the design on OSHPark, so that others could order a copy of the board if they want recreate his setup.  (Dr. Frank, I hope you don't mind!)

I imported the jpg of his board into kicad and tried to match it as closely as possible.  I hope I got it right!

The board dimensions are just shy of 80x50mm.

Modifications:

- The precision resistor footprints include 0.15" (Vishay) and 0.2" (AE) lead spacing.

Edit: OSHPark order link: https://oshpark.com/shared_projects/aF98MB4w (https://oshpark.com/shared_projects/aF98MB4w)

Edit2: github link: https://github.com/pepaslabs/dr-frank-ltz1000 (https://github.com/pepaslabs/dr-frank-ltz1000)

Edit3: Hmm, Frank's design actually has the copper on the back-side.  oops...

Edit4: Moved the copper traces to the back side, and used copper traces for the two jumper links.  New OSHPark link: https://oshpark.com/shared_projects/RFzngdpy (https://oshpark.com/shared_projects/RFzngdpy)

Edit5: Omitted D3 (thanks Frank!), corrected value of R5 (thanks CalMachine!).  New OSHPark link: https://oshpark.com/shared_projects/gl2aXmlh (https://oshpark.com/shared_projects/gl2aXmlh)

Edit6: Just a reminder: BC639 has a different footprint (emitter-collector-base) than 2N3904 (emitter-base-collector).

Edit7: Correcting the silkscreen to show LTC1052 rather than MAX420.  Also using larger pads for the TO-99 footprint.  OSHPark: https://oshpark.com/shared_projects/dGYcQAgn (https://oshpark.com/shared_projects/dGYcQAgn)
Title: Re: Ultra Precision Reference LTZ1000
Post by: dr.diesel on December 16, 2017, 12:20:32 pm
Humidity should not be a problem so close to the LTZ chip, as the temperature is higher than the normal air temperature. It is more that the high temperature could be a problem for the foam, accelerating aging. Quite a lot of foam foam from the 1960's does not look that good today and at something like 60 C aging could be 10 times faster than normal.

I was thinking in more of an on/off situation like many's 3458A, but you're right on kj7e's case with it hot 24-7.

But I think the foam aging is a better point, as it ages it will slowly drop strength/push/compression against the LTZ can.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on December 16, 2017, 01:49:00 pm
I recreated Dr. Frank's board layout (https://www.eevblog.com/forum/metrology/mx-reference/msg1297126/#msg1297126 (https://www.eevblog.com/forum/metrology/mx-reference/msg1297126/#msg1297126)) in kicad and published the design on OSHPark, so that others could order a copy of the board if they want recreate his setup.  (Dr. Frank, I hope you don't mind!)

I imported the jpg of his board into kicad and tried to match it as closely as possible.  I hope I got it right!

The board dimensions are just shy of 80x50mm.

Modifications:

- The precision resistor footprints include 0.15" (Vishay) and 0.2" (AE) lead spacing.

edit: OSHPark order link: https://oshpark.com/shared_projects/aF98MB4w (https://oshpark.com/shared_projects/aF98MB4w)

edit2: github link: https://github.com/pepaslabs/dr-frank-ltz1000 (https://github.com/pepaslabs/dr-frank-ltz1000)

edit3: hmm, Frank's design actually has the copper on the back-side.  oops...

edit4: moved the copper traces to the back side, and used copper traces for the two jumper links.  new OSHPark link: https://oshpark.com/shared_projects/RFzngdpy (https://oshpark.com/shared_projects/RFzngdpy)

Really cute!
If you like to improve the circuit  and simplify the PCB a bit, then you might skip D3, as it's not necessary to have two diodes in series.
That might even disturb the T.C. compensation, so I did not use that either.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on December 16, 2017, 03:02:30 pm
Humidity should not be a problem so close to the LTZ chip, as the temperature is higher than the normal air temperature. It is more that the high temperature could be a problem for the foam, accelerating aging. Quite a lot of foam foam from the 1960's does not look that good today and at something like 60 C aging could be 10 times faster than normal.

I was thinking in more of an on/off situation like many's 3458A, but you're right on kj7e's case with it hot 24-7.

But I think the foam aging is a better point, as it ages it will slowly drop strength/push/compression against the LTZ can.

Yeah, I'm going to radius the inside edge so there is minimal contact with the can itself.  I'm finding out (as I'm sure may of the old players already know) simple seems to work the best.
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 16, 2017, 05:50:19 pm
If you like to improve the circuit  and simplify the PCB a bit, then you might skip D3, as it's not necessary to have two diodes in series.
That might even disturb the T.C. compensation, so I did not use that either.

Thanks!  I've removed D3.

Also thanks to CalMachine for pointing out that both R4 and R5 were labeled 12k!
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 17, 2017, 09:51:42 am
I decided to round out this bunch of boards with a clone of the A9 reference board used in the HP 3458A.

I reproduced this just from some of TiN's hi-res photos, so some of the dimensions might not line up perfectly (I'm pretty confident about the placement of the components (which are on grid), but I'm unsure of the exact diameter and position of the mounting holes.  If TiN could weigh in with some official dimensions, I'll update the design). -- This has been fixed in v2 of the board.

A huge thanks to TiN for the incredible depth of information he posts to xdevs.com!

Modifications:

HP included some footprints for non-Vishay versions of the 15k, 1k, and 111R resistors, but they're never used.  I eliminated those to allow a bit more room to accommodate hermetically sealed versions of these resistors, as well as a footprint for a Vishay divider (e.g. VHD200).

This board is slightly shorter than the official board, which allows it to fit within a 50x50mm area (the cheapest pricing tier for many PCB manufacturers).

OSHPark link: https://oshpark.com/shared_projects/fXEO68Tb (https://oshpark.com/shared_projects/fXEO68Tb)

github link: https://github.com/pepaslabs/hp-03458-66509-clone (https://github.com/pepaslabs/hp-03458-66509-clone)

edit: the through-board connectors are Molex 22-17-2052: https://www.mouser.com/ProductDetail/Molex/22-17-2052/?qs=sGAEpiMZZMs%252bGHln7q6pm%252bS0pk2Wo0XxllCQVBT5EJg%3D (https://www.mouser.com/ProductDetail/Molex/22-17-2052/?qs=sGAEpiMZZMs%252bGHln7q6pm%252bS0pk2Wo0XxllCQVBT5EJg%3D)

edit2: v2 of the board has various alignment fixes and hermetic options for R413 and R415.  OSHPark link: https://oshpark.com/shared_projects/jP5xkfJy (https://oshpark.com/shared_projects/jP5xkfJy)
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 17, 2017, 09:53:36 am
For comparison, here are some of TiN's reference photos of the A9 board.

edit: Thanks again to TiN for publishing these!  See https://xdevs.com/article/volt_xfer/ and https://xdevs.com/fix/hp3458a/#a9pcba
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 17, 2017, 02:36:44 pm
Keeping links to related articles would be nice too.  :P

I think will be much faster for someone else who has A9 to take measurements for mount hole dimensions, as I'm currently on vacation in the windy city. :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 17, 2017, 06:49:22 pm
Ah, sorry, I should have thought to link to the articles.  I'll update the post.  Enjoy your vacation!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on December 17, 2017, 09:50:27 pm

There is a disagreement going on about R418 (a 2K67 resistor from -15V to ground)-- and what is it's purpose.  I say it's not needed, others say "oh yes it is".  If anyone can, please test your meter with and without this to see if it makes any difference-- if it doesn't, (test temp tracking also)-- then leave it out.


It's R419, and its purpose is quite obvious.. it draws -5.6mA out of GND, exactly compensating all currents into GND from the reference circuit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on December 17, 2017, 10:00:44 pm
There is a disagreement going on about R418 (a 2K67 resistor from -15V to ground)-- and what is it's purpose.  I say it's not needed, others say "oh yes it is".  If anyone can, please test your meter with and without this to see if it makes any difference-- if it doesn't, (test temp tracking also)-- then leave it out.
I think you mean R419 - and I can't see any purpose for this resistor on the unused -15V rail on the A9 ref board. I believe it may have been used on the factory test rigs used to calibrate or pass/fail the A9 boards for some purpose or other. But perhaps just a stupid afterthought left in the design...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 17, 2017, 10:27:39 pm
Having a resistor in series with the zener at the positive side is a two sided thing. The idea of such a resistor is to reduce the raw TC (without temperature stabilization) of the voltage reference part. However this will also make the resistor and the current setting resistor more important. Sensitivity of the current setting resistor will be up by about a factor of 3 and the extra resistor should be similar critical. So the added resistor only works if really good resistors are used. More for the understanding of the residual TC is might be interesting to see of the added resistor would make a big change to the compensation resistor - this might give hints if the residual TC is more due to not so good temperature control or effects of the pins / layout.

There is somewhat limited gain from spending a lot of money on the resistors - at some point, using a second LTZ reference might be the more efficient way, maybe even used with just PTF type resistors. Inside a meter or with access to a good meter, it might even be worth having access to the divided voltage for the temperature set-point. In theory drift of the divider could be corrected if measured without too much distortion (this might not be easy). With access to the temperature set-point one could consider a controlled way of startup procedure to reduce thermal hysteresis.

Only about 0.5% of the OPs drift and low frequency noise will be at the output. Thus the OP should not be that critical, and there is not that much choices of better OPs. There may be option if single supply is not needed, but than the startup sequence of the positive and negative reference might become important.  The 1 M resistor setting the response speed for the temperature control is not at all critical, it's working in combination with a cap of usually high tolerance and the regulator speed is not that tight adjusted. LT suggest the same control for the LTZ1000A and no adaption is made to the actual thermal setup or the nonlinear heater - so who cares about a +-10% or even more tolerance here.

I agree that the nominal 400 K resistor for TC compensation is a kind of bodge: The residual TC before correction seems to be about constant (e.g. the effect is linear in temperature) . However the correction follows about a square root of the set temperature - actual temperature - self heating. Thus it will get kind of nonlinear if the temperature is too close to the set point. So the compensation will not work that well with a low temperature setting. It might need individual adjustments, depending on the layout and thermal setting and maybe individual units.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on December 17, 2017, 11:31:27 pm
It's R419, and its purpose is quite obvious.. it draws -5.6mA out of GND, exactly compensating all currents into GND from the reference circuit.

OK, you got me!  Thanks for the correction-- yes, when I zoom in on my very low resolution copy of the schematic, it does say R419, and not R418.  Oops!

Well, this is one of the theories that I have heard as to it's purpose, but I have never seen any experimental results proving such a claim.  If this is true (and R419 is indeed necessary), then the value would have to be adjusted if we choose a better op-amp that might have a different quiescent current than the LT1013.

Experimental result?
Instead of measuring the currents, you can do a simple calculation beforehand, using typical or even maximum current values:
Zener current ~ 0.40V (@90°C) /111Ohm = 3.6mA
collector currents ~ 2x(7.2V (typ.) -0.4V) / 74.25k = 183µA
divider current ~ 7.2V /16k =450µA
LT1013 supply = 2 x 0.5mA (max. value) = 1mA

Sum~5.2mA versus 15V/2.67kOhm = 5.6mA

Evidently, these currents nearly cancel, leaving the analogue ground supply 'A', pin J400 (4) with some 100µA, depending on sample variation. I can't overlook, where on the main analogue board, or on the A/D board the Ref GND is married with analogue GND, but very probably, it's not buffered, in contrast to the +7V Ref signal.
On the A/D board, at least there's R168 (?), a 10k2 resistor, sinking -1.2mA out of Ref GND (it's labelled ZR_LO2 there).
And on the analogue board, the potential of Ref_GND can be measured by the DCV input multiplexer also..

In the resistor reference current circuit, you'll also find a similar compensation resistor, that's R311 (9k09) which sinks 2mA from analogue ground, balancing the reference currents through resistors RP300A .. C..


Back to the LTZ circuit... a current of 5.6mA over GND would create a potential difference of about 100µV over only 20mOhm, or on the order of 15ppm.. So if the connector would change its resistance by that amount, that would create a well measurable error.

I bet, that removing this 2k67 resistor would shift the calibration remarkably. (Would be the experimental proof, that I won't do for obvious reasons)

Fluke uses active current cancellation circuits in their 732B, and as far as I remember, in their reference circuits for their calibrators also. The purpose is the same, very obviously.


By the way, my 3458A showed a clearly visible -0.5ppm shift, after returning it from a volt-nuts meeting two years ago, that's been 2x200km ride by car, with some vibration, although I got a very comfortable French car, with smooth suspension.
 
I directly thougt that the connector of the reference had changed its contact resistance towards smaller values.. and I also thought, that sending these instruments to hp for calibration, that it would always give some shift by the transport itself.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on December 17, 2017, 11:50:08 pm
You get a bunch of engineers together and they have to start redesigning things. What Fun! Here is my contribution.

I think the A9 PCB layout could be better. TiN took several IR images of the electronics in the 3458A.
https://www.eevblog.com/forum/repair/repair-old-rusty-hp-3458a/msg808569/#msg808569 (https://www.eevblog.com/forum/repair/repair-old-rusty-hp-3458a/msg808569/#msg808569)

The last image shows that the R419 and the heater transistor are the hottest things on the PCB. And they are located right next to the Kovar pins of the LTZ1000A. The Image even shows a strong thermal gradient right across the pins. 

These high temperature parts will contribute to warm up drift and increase the temp co of the reference. As ambient temperature changes the pass transistor temperature changes so the thermal gradient across the LTZ1000A pins will change so the Temf of the Kovar pins will change.

These parts could be arranged better. They should be on the opposite end of the pcb from the LTZ1000A.



Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on December 18, 2017, 02:22:05 am
Here is my guess for all the current balancing resistors.

The offset voltage caused by the ground current could simply be nulled out during calibration. However, if it is caused by the voltage drop in a copper trace on the PCB then that offset voltage has a 4000 ppm / deg C drift. So you have to do what you can to minimize the offsets caused by current flowing in copper traces.

You also have the problem of unstable resistances in connectors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: pitagoras on December 18, 2017, 03:20:09 am
I've shared my board at OSHPARK too, if anyone is interested.

https://oshpark.com/shared_projects/DmMENXtg

It was going to be PX but it has been taken  :)

So it has become QX, much better for the logo  :P 
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on December 18, 2017, 05:09:44 am
Digilent:

It doesn't matter if you believe me or not re: '2057 input chopper noise.  You're welcome to pay my client for the documentation - otherwise just pay no attention.  Consider the free advice clue as worth exactly what you paid for it. That's as far as I can go on a public forum.

What does matter is LT specifically recommends against a '2057 for various reasons, unnecessary excess noise across the Zener is one of them.  These are the people that manufacture the part.  I would guess they have some knowledge of what works and what doesn't, and they handle a lot more design feedback from volume manufactures.  They have about zero economic reason to even sell LTZ's in small orders, so be glad they even do that.  The fact that they even discuss design know-how is an added bonus.

For the gazillionth time:  It is true that other amps will work as the LTZ current driver, but the "1013 is hands down the best amp to use for the right mix of current and voltage noise.  It is tailor- made to be the LTZ's companion.  That is the part to use, and that is the part they will stand behind on datasheet specs.  When you talk to LT apps engineering, that's what they tell you - at least that's what I've gotten on more than one occasion when I ask about "upgrading" to a chopper amp.  There is just no reason to do that.  Remember you're using the amp as a CURRENT driver, and the zener + transistor stability will overwhelm whatever small Voffset you've got on the '1013.

Check your specs - we've never seen an hfe on the the LTZ transistors as low as 50.  Typical is 200, the range is 80 to 450.  A small Voffset on the current driver amp is not going to result in significant Vref change.

There are lots and lots of older "standard" 3458a's that work just fine to "002" high stability option specs - we have several that don't drift a ppm per year.  That means the board design is not the main contributor to drift - it's the LTZ die itself (and scope of normal drift variation part to part), and that is far beyond anyone's "hand tuned" control.

Go ahead, try it - remove the ground current cancellation resistor on that 3458a Vref board and let me know what happens as the ambient temperature changes....and let me know if it's not pretty smart to use a sub-penny carbon resistor (fancier types not required here) to reduce ground current at the module header pins....  I really don't see designers flailing around: I see a smart, well thought out design that produced the most successful DMM in history - and a DMM that has outsold and out-lasted every competitor design over time.  Am I wrong?

If there were a better way to do it we'd have it after 30+ years.  You're more than welcome to produce a better Vref replacement that works in production.  Hopefully Keysight will be able to at some point...
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 18, 2017, 06:08:32 am
Update the HP A9 reference board clone (03458-66509):

I figured out how to scale and align TiN's images (see https://xdevs.com/article/volt_xfer/) on top of kicad screenshots (using gimp) and dialed in all of the dimensions.  They match up pretty closely!  (see attached overlays).

Also, I've managed to squeeze in room for hermetic footprints on R413 and R415.  The footprints are backwards compatible, so you can populate this board with original HP components, or upgrade the critical  resistors to hermetic packages.

This version of the board is intended to mimic the original board as closely as possible, with the option of upgrading the resistors, but in a future version I'd like to explore diverging from the original design a bit, perhaps with the "R60" mentioned above, etc.

I was a bit surprised to find that the LTZ isn't perfectly centered between the two mounting holes.  I decided to err on the side of reproducing HP's error.

v2 OSHPark link: https://oshpark.com/shared_projects/jP5xkfJy

github: https://github.com/pepaslabs/hp-03458-66509-clone
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on December 18, 2017, 07:44:02 am


Well, if this is being done for the reasons that you state-- and what you are saying sounds reasonable, then why are they bothering when it's an offset, and as long as the offset does not change then it doesn't matter?  Why in the heck would they use a very noisy carbon-film type resistor for this.  There is really something goofy going on here-- I think somebody was desperately plastering band-aids all over this design-- with the hope of being able to "fix" a number of issues-- instead of just re-engineering the whole circuit and layout.  The whole design looks as though they were flailing about without really understanding what they were doing.  Those engineers are no longer at HP (or Agilent, or Keysight) anymore-- so we may never know what the hell they were up to.  I guarantee you this-- I could design a much better Vref replacement for the 3458A than factory; and if I can do it, then why don't THEY do it?


Hu, Carbon?
In the BOM, R419 is specified TF (usually Thin Film), TC100.

And on my A9 board, it really looks like a Thin Film resistor, not at all like a carbon type.
(and it's definitely 1%, brown ring, also visible on other boards. Carbon resistors are 10% at best)

Again, the whole reference circuit is not directly fed into the A/D circuit, but is routed over at least three connectors, which might well change their resistance.

In the Fluke 5440 and 5720, they treat this GND star point and supply current problem much nicer, just lay both schematics side-by-side.

That's also the reason, why I  designed a big star point into my latest design as a stand-alone 7 / 10V reference, but I would also have some trouble with GND, if I would use my modules inside another circuit.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on December 18, 2017, 10:15:19 am
Man, so many new open source LTZ1000-boards, but no LTZ1000A available....  :-DD
Maybe we can gather all open source LTZ1000-boards in a new thread/post?

Special thanks to cellularmitosis, who apparently needs no sleep and produces a new board every few days.  ;D
Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on December 18, 2017, 11:04:58 am
A seller on AliExpress is offering this LTZ1000 board (no affiliation):

https://www.aliexpress.com/item/Ltz1000-ltz1000a-PCB-circuit-board-thickness-1-0mm-size-62mm-62mm/32829991789.html (https://www.aliexpress.com/item/Ltz1000-ltz1000a-PCB-circuit-board-thickness-1-0mm-size-62mm-62mm/32829991789.html)

(https://ae01.alicdn.com/kf/HTB1M2hjXyoaPuJjSsplq6zg7XXaY/Ltz1000-ltz1000a-PCB-leiterplatten-dicke-1-0mm-gr-e-62mm-62mm.jpg_640x640.jpg)

And there is a seller which is selling LTZ1000ACH, but I'm not sure if I would buy them (no affiliation):

https://www.aliexpress.com/item/5PCS-LOT-LTZ1000ACH-LTZ1000/32757679028.html (https://www.aliexpress.com/item/5PCS-LOT-LTZ1000ACH-LTZ1000/32757679028.html)
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on December 19, 2017, 12:38:21 am
Update the HP A9 reference board clone (03458-66509):

I figured out how to scale and align TiN's images (see https://xdevs.com/article/volt_xfer/) on top of kicad screenshots (using gimp) and dialed in all of the dimensions.  They match up pretty closely!  (see attached overlays).

Also, I've managed to squeeze in room for hermetic footprints on R413 and R415.  The footprints are backwards compatible, so you can populate this board with original HP components, or upgrade the critical  resistors to hermetic packages.

This version of the board is intended to mimic the original board as closely as possible, with the option of upgrading the resistors, but in a future version I'd like to explore diverging from the original design a bit, perhaps with the "R60" mentioned above, etc.

I was a bit surprised to find that the LTZ isn't perfectly centered between the two mounting holes.  I decided to err on the side of reproducing HP's error.

v2 OSHPark link: https://oshpark.com/shared_projects/jP5xkfJy

github: https://github.com/pepaslabs/hp-03458-66509-clone

Nice I think I will use it to build and age a A9 replacement for my 3458a. The one actually inside is friend of TiN little jumpy.
Title: Re: Five new kids on the block - Ultra Precision Reference LTZ1000
Post by: 3roomlab on December 19, 2017, 01:33:39 am
I have assembled and tested my 5 new LTZ1000 reference boards.

They all are based on Andreas schematic, providing additional EMI filtering for great immunity against RF and mains disturbances.

ive been playing with eagle, i wonder, has anyone been succesful in totally laying this entirely on 1 side? i must say i have no success.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on December 19, 2017, 01:52:12 am
And there is a seller which is selling LTZ1000ACH, but I'm not sure if I would buy them (no affiliation):

https://www.aliexpress.com/item/5PCS-LOT-LTZ1000ACH-LTZ1000/32757679028.html (https://www.aliexpress.com/item/5PCS-LOT-LTZ1000ACH-LTZ1000/32757679028.html)

I wouldn't touch them with a bargepole. Straight off the bat no manufacturers logo and no date code.
Title: Re: Five new kids on the block - Ultra Precision Reference LTZ1000
Post by: cellularmitosis on December 19, 2017, 05:32:44 am
I have assembled and tested my 5 new LTZ1000 reference boards.

They all are based on Andreas schematic, providing additional EMI filtering for great immunity against RF and mains disturbances.

ive been playing with eagle, i wonder, has anyone been succesful in totally laying this entirely on 1 side? i must say i have no success.

Dr. Frank has!  https://www.eevblog.com/forum/metrology/mx-reference/msg1297126/#msg1297126 (https://www.eevblog.com/forum/metrology/mx-reference/msg1297126/#msg1297126)

edit: actually he used two jumper wires, so *almost* entirely on one side.  I put a copy of his design on OSHPark: https://oshpark.com/shared_projects/gl2aXmlh (https://oshpark.com/shared_projects/gl2aXmlh)
Title: Re: Ultra Precision Reference LTZ1000
Post by: borghese on December 19, 2017, 05:37:39 pm
You have to load the appropriate DRU file for 1 layer; for example "Multi-CB_1L_125um-Tracks_OL35um.dru". File attached, just rename from TXT to DRU
Regards
Title: Re: Five new kids on the block - Ultra Precision Reference LTZ1000
Post by: 3roomlab on December 21, 2017, 01:11:26 pm
I have assembled and tested my 5 new LTZ1000 reference boards.

They all are based on Andreas schematic, providing additional EMI filtering for great immunity against RF and mains disturbances.

ive been playing with eagle, i wonder, has anyone been succesful in totally laying this entirely on 1 side? i must say i have no success.

Dr. Frank has!  https://www.eevblog.com/forum/metrology/mx-reference/msg1297126/#msg1297126 (https://www.eevblog.com/forum/metrology/mx-reference/msg1297126/#msg1297126)

edit: actually he used two jumper wires, so *almost* entirely on one side.  I put a copy of his design on OSHPark: https://oshpark.com/shared_projects/gl2aXmlh (https://oshpark.com/shared_projects/gl2aXmlh)

i know he did, i quoted his post in my question. i should re-word the Qn as : did anyone else have success in a strictly 1 layer layout w/o using jumpers?

this is my whimsical layout which i did for fun and somewhat curiosity
https://3.bp.blogspot.com/-fUTVzhfdWqY/Wjuw9s3vnXI/AAAAAAAAC30/BwFihqLtVVcEBqPCOMeiwlxS7IgqzYitQCLcBGAs/s1600/LTZ1k_11%2Bcopy.gif (https://3.bp.blogspot.com/-fUTVzhfdWqY/Wjuw9s3vnXI/AAAAAAAAC30/BwFihqLtVVcEBqPCOMeiwlxS7IgqzYitQCLcBGAs/s1600/LTZ1k_11%2Bcopy.gif)
i included the "RR0" which on LTZ pdf page6, is for finding an unstabilized TC compensation (but now i think it is a useless inclusion :/). the idea is to do the construction manhattan style, so no leads will be visible on the rear. the size is based on a IP67 plastic box 100x68mm. i dont suppose i have seen anybody create their favourite project box as a piece of component?

in my version, i had to use ground plane to connect capacitors :( (i also have to "jump" VREF to the 2nd op amp). which lead me to think, since capacitors do not really need to track temperatures and influence overall tempco, it should be possible to flip all the capacitors to the flipside of the PCB and have them out of the way of all the resistors on the front side.



*update
well i wasnt quite satisfied, and i think i managed to really fit all into 1 layer.

https://2.bp.blogspot.com/-ggDXXGuKW-A/Wjvgm3jeewI/AAAAAAAAC4I/rGwKasaRdf8qRVw13cVOsFrf3OUn19GxgCLcBGAs/s1600/LTZ1k_11B%2Bcopy.gif (https://2.bp.blogspot.com/-ggDXXGuKW-A/Wjvgm3jeewI/AAAAAAAAC4I/rGwKasaRdf8qRVw13cVOsFrf3OUn19GxgCLcBGAs/s1600/LTZ1k_11B%2Bcopy.gif)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on December 21, 2017, 03:39:00 pm
The gain of the temperature compensation transistor reduces to about 50 when the base and collector are at the same voltage (which is where this circuit biases the transistor)-- so the high hfe listed in the data sheet is misleading. 

Isn't this the condition in which I measured 200 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg862127/#msg862127)?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 21, 2017, 04:05:30 pm
For the sensitivity to the OP it is not Hfe that matters, but the voltage gain of the transistor stage. This is about 6.5 V / (kT/e) or about 200, depending on the temperature. The early effect might reduce this gain a little, but not that much. The input side is rather low impedance and the collector side is usually much higher impedance - so the actual Hfe does not matter as long as it's in a reasonable range and not much below 1.


Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 21, 2017, 05:04:05 pm
3roomlab, or cellularmitosis should make single-layer LTZ ref with large pads, so we can order metallized ceramic board to make hermetic LTZ ref :).
Put some VAR resistors, get kovar tubes for feedthru copper pins and seal it all in vacuum or argon filled tube. 

Likely there would be no difference in performance, but it would look neat. Maybe toss an orange LED or two on the base to give it warm fuzzy glow too  :popcorn: .
Title: Re: Ultra Precision Reference LTZ1000
Post by: beanflying on December 22, 2017, 02:21:48 am
3roomlab, or cellularmitosis should make single-layer LTZ ref with large pads, so we can order metallized ceramic board to make hermetic LTZ ref :).
Put some VAR resistors, get kovar tubes for feedthru copper pins and seal it all in vacuum or argon filled tube. 

Likely there would be no difference in performance, but it would look neat. Maybe toss an orange LED or two on the base to give it warm fuzzy glow too  :popcorn: .

I would prefer a 5 digit Nixie voltmeter on the front please  :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on December 28, 2017, 07:19:26 pm
Prema Semiconductor used a slightly different circuit to power the LTZ1000 from 12V in Prema 6048. I found two circuit diagrams with slighlty different resistor values in two different manuals. Would be interesting to see what they finally assembled.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on December 28, 2017, 09:50:19 pm
i dont know if my eyes are playing tricks ... but what does the red resistor do?
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on December 28, 2017, 11:29:34 pm
Not an expert here, but in ref PCB layouts, there's two grounds- the high-current heater return and the reference (-).
They are separated to minimize any heater-induced I2R voltage drop across ground from shifting the 0V reference point and causing uV offset error.

Your PREMA schematic just seems to use one symbol though, as some CADD software cannot understand two ground (nets) that are connected together at the PSU central grounding point. I don't have a 6048 or 6047 PCB to look at both sides.

The 10R resistor between them is usually to avoid big trouble if one ground is open circuited, and to lower Q for any RF picked up between the two ground traces.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on December 29, 2017, 03:50:11 am
Not an expert here, but in ref PCB layouts, there's two grounds- the high-current heater return and the reference (-).
They are separated to minimize any heater-induced I2R voltage drop across ground from shifting the 0V reference point and causing uV offset error.

Your PREMA schematic just seems to use one symbol though, as some CADD software cannot understand two ground (nets) that are connected together at the PSU central grounding point. I don't have a 6048 or 6047 PCB to look at both sides.

The 10R resistor between them is usually to avoid big trouble if one ground is open circuited, and to lower Q for any RF picked up between the two ground traces.

i could not get my head around it. so i dump something into FEMM 4.2 to visualize it
pic1 describes the approx currents and the 10R between the 2 sides, each with its own 0v (cyan)
pic2 is the same currents, but all traces are approx 6mil (no 10R)
pic3 same again, left side is approx 200mil trace, right is 6mil trace (no 10R)
pic4 is 6mil only 1 GND (no heater GND)

the simulation idea behind 6mil and 200mil trace comes from saturn PCB
6mil 1 oz PCB 1 inch long loaded @ 0.1mA returns a potential diff of about 0.011v
230mil 1oz PCB 1 inch long loaded @ 5mA returns a potential diff of about 0.011v (2oz PCB will only need about 150mil wide)
esp for VREF end, i wonder how much of these traces should be balanced between sourcing and draining. it would be a crazy matching exercise, this reminds me of that zero ohm thread, trying to find the zero current point inside a thick copper piece.

i also assume that the GND return current posing the most problem is the heater as the current varies with changing temperature.

but since swapping these around in simulation for GND, it appears as long as all returns appear at exactly the same star point, it doesnt seem to need a 2nd heater return? what did i miss? (assume the left side GND is the master)
maybe the better question is, since pin 3 potential is referenced to the GND thru R1, how could a seperated heater return create a more stable GND point since it is the only GND? if GND shifts, wouldnt VREF also shift and result in no change? (i assume a low noise LDO is on board and the V supply is always "constant")


i went a little further in FEMM 4.2 simulation. the animated gifs alternate between 2 diff current returns. however the more i look at these, i seem to confuse myself more

assuming zero volts is the black hole, it prevents a current return disturbance on the right from affecting the 1 on the left.
(https://4.bp.blogspot.com/-0ruzKkOHybo/WkbNuyCn9fI/AAAAAAAAC6w/hxs_l9LoFHw90m6VdKDS9js_pm1oUQpEQCLcBGAs/s640/c1c2.gif)

i need to emphasize, i am assuming by simulations.

this is with/without the 10R linker. i am unsure what to make of it.
(https://2.bp.blogspot.com/-WkybrkN7s6Q/Wkak3TCx9oI/AAAAAAAAC50/WgRoHpYwN-YPURROS8Pa3kIyz3n_gSzNACLcBGAs/s640/b14b15.gif)

i can assume since all GND labels are not really zero, what does come close to a full negation? huge capacitor as sinker?
(https://4.bp.blogspot.com/-yUBU4N76jFE/Wka_F7BRsWI/AAAAAAAAC6g/4yfXCavP_6M7uvANhyhAFiLM5I0v5_ttQCLcBGAs/s640/b27b28.gif)

(the txt file needs to be renamed *.FEC for use in FEMM 4.2)
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on December 30, 2017, 08:41:34 pm
Colourful sims, what I expect for showing the electric field in copper PCB traces. Learned about the "river mouth" being something to consider.

My theory for the Prema 10R resistor - it does nothing at DC as the PCB trace resistance is comparatively low, unless for open-circuit protection on the Kelvin zener (-).
Or, it's to fool the CAD software. But at high frequencies, RF, the twin trace inductance is now at play and I suspect that another reason for it.

Copy pasta from http://www.electronicdesign.com/analog/what-s-all-ltz1000-stuff-anyway (http://www.electronicdesign.com/analog/what-s-all-ltz1000-stuff-anyway):

"Some folks put a dummy resistor in the schematic to separate those grounds into different nets. However, Mark Thoren, staff scientist at Linear Technology says, "Dummy resistors separating 'grounds' are a recipe for disaster, and I see disasters related to this practice all the time. One of the first things to look for when reviewing a customer's schematics is multiple ground symbols without a good reason for them."

'Do be aware of the return currents causing drift problems. [Carl] Nelson comments, “Current out of pin 7 is about 6.5 V/R2 + 6.5 V/R3 = 186 uA. Current out of R5 is about 550 uA.  Current from R1 (same as the Zener current) is about 4 mA.  These currents should be routed separately to the low side of the reference output. If a single trace is used, and the trace resistance is 0.4R , voltage drop in the trace will be 1.9 mV. Copper has a thermal coefficient of 0.0038/°C, which generates 7 uV/°C in the trace, equal to about 1 ppm/°C in the reference.  This is about 20 times higher than the expected drift of the part’s design intent.”
Title: Re: Ultra Precision Reference LTZ1000
Post by: guenthert on January 01, 2018, 03:42:46 pm
Copper has a thermal coefficient of 0.0038/°C, which generates 7 uV/°C in the trace, equal to about 1 ppm/°C in the reference.  This is about 20 times higher than the expected drift of the part’s design intent.”
There he lost me.  What "thermal coefficient" is meant?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 01, 2018, 05:13:54 pm
If a single trace is used, and the trace resistance is 0.4R
How long are your traces?
I usually use minimum 24 mils which have 0.9R per meter with 1 oz copper.
Usually you should use Kelvin sensing for the zener voltage.
Within the resistor loops you have at least a reduction factor of 100 for the resistance changes.

There he lost me.  What "thermal coefficient" is meant?
0.385%/K is the thermal resistance change of pure metals like copper, platinum etc.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 01, 2018, 09:37:52 pm
Happy New 2018 to all voltnuts. Wish you all guys short LTZ lead-times and smooth stable voltages.
Little present on my LTZ data. I had my references turned off for few weeks, and just in mid-December I put them all back in new box and powered backup.
Since then all 8 references are scanned non-stop using HP 3458A and Keithley 7168 nV scanner card.

So far:

(https://xdevs.com/doc/xDevs.com/FX/nvs_dec.png) (https://xdevs.com/nvs_december17/)

Modules:

Channel 1: KX 7V LTZ1000 reference.
Channel 2: KX 7V LTZ1000 reference.
Channel 3: KX 7V LTZ1000 reference.
Channel 4: HP 3458A STD A9 reference
Channel 5: xDevs.com FX 10V reference prototype.
Channel 6: KX 7V LTZ1000 reference prototype.
Channel 7: KX 7V LTZ1000 reference prototype.
Channel 8: xDevs.com FX 10V reference prototype.

P.S. Over last year I got 8M of pageviews (https://xdevs.com/article/ny2018/), which is amazing to me, given the narrow niche of my projects.  :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 01, 2018, 10:18:21 pm
Looks like the 3458 got an extra 0.2 to 0.3 ppm shift by Christmas. At least all the curves seem to shift in parallel - so the more likely cause would be the meter.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on January 01, 2018, 11:59:44 pm
Looks like the 3458 got an extra 0.2 to 0.3 ppm shift by Christmas. At least all the curves seem to shift in parallel - so the more likely cause would be the meter.
I think the meter shift seems to track temperature ... It's hard to say for me with all this faded colored dots. I'm daltonic, so it's even harder for me ...

This almost demonstrate (what Frank keeps saying) that at lowerish temperature there is not zener histeresys.

The 3458a was always on during this time?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 02, 2018, 02:51:32 am
I think that was shift caused by ACAL DCV, triggered by temperature change.
The meter and setup was moved 2 days to another room prior the log start.

Room is freely moving ambient, no airconditioning, zero airflow around the references box.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 02, 2018, 09:44:55 am
ACAL causing the shift sounds very plausible.

The different refs seem to show quite different initial drift from recovering from the time off. It might be interesting if this somehow correlates with temperature setting or A and non A versions.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on January 02, 2018, 11:23:14 am
I think that was shift caused by ACAL DCV, triggered by temperature change.
The meter and setup was moved 2 days to another room prior the log start.

Room is freely moving ambient, no airconditioning, zero airflow around the references box.

Happy New Year, Illya!

Very interesting experiment..

Could you please assign the oven temperatures of the 8 different references, and maybe their initial reference values?
 
Especially CH2 and CH3 need over a week or so to stabilize from a ~2ppm change..
I assume, these references which need long time to stabilize, run at higher oven temperatures?

After a power interruption, even after several days, all of my 8 LTZ1000 references, which run at 45..55 and at 60°C (inside my 3458A), stabilize to their initial value within < 0.2ppm after a few hours, latest, and stay there.

I'm just sending a friendly volt-nuts colleague one of my LTZ references in cold condition, and I'm really curious about the round-trip comparisons of the reference voltage, at first after a few days at his location, and then on return in my lab.
This round-trip will collect possible shifts due to vibrations also, like my 3458A encountered on the last volt-nuts gathering two years ago.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on January 02, 2018, 02:04:38 pm
I think that was shift caused by ACAL DCV, triggered by temperature change.
The meter and setup was moved 2 days to another room prior the log start.

Room is freely moving ambient, no airconditioning, zero airflow around the references box.

Happy New Year, Illya!

Very interesting experiment..

Could you please assign the oven temperatures of the 8 different references, and maybe their initial reference values?
 
Especially CH2 and CH3 need over a week or so to stabilize from a ~2ppm change..
I assume, these references which need long time to stabilize, run at higher oven temperatures?

After a power interruption, even after several days, all of my 8 LTZ1000 references, which run at 45..55 and at 60°C (inside my 3458A), stabilize to their initial value within < 0.2ppm after a few hours, latest, and stay there.

I'm just sending a friendly volt-nuts colleague one of my LTZ references in cold condition, and I'm really curious about the round-trip comparisons of the reference voltage, at first after a few days at his location, and then on return in my lab.
This round-trip will collect possible shifts due to vibrations also, like my 3458A encountered on the last volt-nuts gathering two years ago.

Frank
Also resistors type could be interesting ...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 02, 2018, 02:14:16 pm
This round-trip will collect possible shifts due to vibrations also, like my 3458A encountered on the last volt-nuts gathering two years ago.

Ups,
now I´m feeling guilty:
https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg840100/#msg840100 (https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg840100/#msg840100)

(https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/?action=dlattach;attach=192976)

So we should do the next meeting at your location?

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on January 02, 2018, 05:14:34 pm
On TiN's fantastic - and live - data logging set!

We're seeing a lot about the meter here, at these levels of resolution. I think we need a calculation to take out the temperature variance of the 3458a. It looks like it is around 0.5ppm per degree K (that's just from eyeballing the drop on December 24). I think that this is more significant than the drift on at least some of the references. Note how much larger it is for the 10V references over the 7.xV references.

As the chart stands, references that have a temperature coefficient that matches the 3458a look rather better than they should.

Once the temperature coefficient is established, it is probably better not to do autocals.

There's also the question of drift in the 3458a ADC.  I know that TiN has looked at this, but for long-term logging, this is also a factor.

Here's a quick correlation analysis, checking each reference against the recorded temperature:

ch1   ch2           ch3           ch4           ch5           ch6           ch7   ch8          k16v   k10v
59%   -84%   -81%   -83%   -70%   -23%   91%   -65%   2%   99%

Channel 7 most closely tracks the temperature of the 3458a, assuming a positive temperature coefficient for the meter. If the meter has a negative tempco, then references 2,3,4 are closer. Therefore, if the 3458a was at a constant temperature, one of these three may well be the best reference from a stability point of view. That is, of course, assuming no material drift in the meter.

Put another way - we are looking for the "golden reference" which is stable over both  temperature and  time. Even more golden would be stability across the dimension of space - which would make it easy to ship.

My experience is that the 732a is a really good example of such a reference. Probably why it is still around. Although it is about 100x heavier than these references, and really does not like going dark.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 02, 2018, 06:33:22 pm
Quote
So we should do the next meeting at your location?

with best regards

Andreas

I'm in with a calibrated Keithley 2002, our 3458A, our calibrated Prema 5017 SC, hopefully with my till then calibrated private Prema 5017 SC and some LTZ1000 and LM399 based references.  :-+

The nice thing is with Andreas PC software for 3458A, the GPIB adapter I can bring along and the ambient sensor module we are able to monitore live data together with ambient properties (temperature, humidity, dew point and pressure).

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on January 02, 2018, 07:27:52 pm

Ups,
now I´m feeling guilty:

So we should do the next meeting at your location?

with best regards

Andreas


Hello Andreas,

no need at all to feel guilty.. The 3458A is not a standard!

This shift was an interesting experiment.. and covered by the other 3 references @ home..
For the next time, I need an algorithm for detecting and valuating such drifts and drops inside such a reference group for proper calculation of the expected mean value..

Didn't somebody mention recently, that calibrated 3458As encounter a shift of up to 5ppm, just by transportation?
So I wonder, how transporting instruments like these might work at all.

In the end, it was a really nice meeting, and I propose to repeat it this year, maybe here, near Frankfurt where 2..3 other well-known volt-nuts from this area may also be willing to participate.

Frank

PS: Two references are just on their way to a round trip via dhl, so I'm very curious, how their measured values can be reproduced afterwards.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 02, 2018, 08:22:28 pm
Dr.Frank,
I will take bank apart once I get back Taiwan next week, and will list all configurations (opamps, resistors, LTZ type) per each channel. Two of KX modules are with AUGAT socket for zener.  :)

martinr33, my 3458As have no measureable tempco, but before you go into gossip theory, do not forget that all references are connected to meter thru scanner card, NOT directly. And I did not measure impact of the scanner JFETs on tempco/drift yet ;) Also all modules, except A9 had thermal stress at start from wiring connections (not using any connectors at KX outputs, only direct solder copper twisted pairs between scanner and board). FX 10V modules had zero aging at all, with fresh LTZ chips.

I periodically was checking drift and stability of the meter, it's still accurate and stable. In fact, just before leaving to vacation, I had calibrated two KX LTZ1000CH's refs from CalMachine and shipped to him.

Assigned value: KX1 module (large input power binding posts): 7.141467 VDC , https://xdevs.com/ckx1_test5_tc/
Assigned value: KX2 module (smaller input power binding posts): 7.157411 VDC , https://xdevs.com/ckx2_test10_tc/ 

These modules arrived to CalMachine, but since he's too lazy shy busy, he just got few hours on each module, using his calibrated (i think <30 days ago) 3458A. Here is his data:

CSV-data (https://xdevs.com/doc/xDevs.com/CalMachine/backcal/cmkx_post_final_test_nplc100.csv).

Plots:

(https://xdevs.com/doc/xDevs.com/CalMachine/backcal/KX1_Log1.JPG)

(https://xdevs.com/doc/xDevs.com/CalMachine/backcal/KX2_Log1.JPG)

So output deviation fits my expectation of 2ppm DCV at my lab accuracy, with good margin:

KX1 module 7.157411 VDC (xDevs lab) vs 7.157415 VDC (CalMachine lab), +0.56 ppm off.
KX2 module 7.141467 VDC (xDevs lab) vs 7.141472 VDC (CalMachine lab), +0.70 ppm off.

Not that bad, given international air shipping in winter and different calibration source (my 3458As calibrated vs 732B (cal August 2016 by Tektronix USA) in January/February 2017). CalMachine's meter calibrated by Keysight. :) Also CalMachine's temp is lower, I calibrated values at +24C, not 20. So tempco may contribute another 0.2ppm error.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on January 02, 2018, 09:05:16 pm
What I am missing here, then, is why did the autocal cause an obvious shift in the reading if the meters are stable over time and temperature?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 02, 2018, 09:10:56 pm
What I am missing here, then, is why did the autocal cause an obvious shift in the reading if the meters are stable over time and temperature?
I think reply is obvious if you consider own meter's noise from it's own LTZ and front end/ADC which is about observed 0.2ppm minimum. ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on January 02, 2018, 09:22:26 pm
What I am missing here, then, is why did the autocal cause an obvious shift in the reading if the meters are stable over time and temperature?
I think reply is obvious if you consider own meter's noise from it's own LTZ and front end/ADC which is about observed 0.2ppm minimum. ;)

On second look - that dip cannot be an autocal, as it takes way too long to get to the new level. . Autocal should show up as a discontinuity in the readings, not a slope covering multiple datapoints.

So something else made that dip happen.

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 02, 2018, 09:29:35 pm
snip.
Yup, AVG100 moving filter :). Sorry about that. Together with the way D3.is plots graphs averaged line is rendered as continuous slope. You can pull CSV from my site and check yourself in RAW points.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on January 02, 2018, 10:18:07 pm

So something else made that dip happen.
[/quote]Yup, AVG100 moving filter :). Sorry about that. Together with the way D3.is plots graphs averaged line is rendered as continuous slope. You can pull CSV from my site and check yourself in RAW points.
[/quote]

OK, now I found it - about a 1.3uV drop (13 counts, .13ppm) at 23/12/2017-17:52:45

Why would you do an autocal in response to temperature changes if the meter is not affected by temperature? Seems that that add unnecessary uncertainty.




Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 02, 2018, 10:36:23 pm
Looking in a different way on the data the autocal effect comes more visible. However, CH6 seems to be quite uneffected by changes in temperature.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 03, 2018, 06:26:42 am
Why would you do an autocal in response to temperature changes if the meter is not affected by temperature? Seems that that add unnecessary uncertainty.

Because of two reasons:
* I had implemented ACAL code in python app before actual tempco test for DCV 10V range was done.
* ACAL is used also for resistance tests, for which I did not done full characterisation yet. I will get back to this once my Fluke SL935 standard come back.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 03, 2018, 08:05:44 pm
PS: Two references are just on their way to a round trip via dhl, so I'm very curious, how their measured values can be reproduced afterwards.
Hello Frank,

I never had issues with my LTZ1000A references when transporting them (hot) to calibration and back.
But I would perhaps do a "drop test" several times before I give it into mail.

The only issue I had was with a LM399 reference after transport for first calibration.
After that I mentioned that the readings with my ADCs on LM399#2 have shifted about 4 PPM (30uV).
The only explanation I could find is that I had not put any Top/Bottom marking onto the card box which I have used to keep air drafts away.
So the orientation of the LM399 within the box was not clear before and after the calibration.
And I could reproduce the shift by tilting the reference in different orientations.
So I learned it is essential to check the references before/after transportation.

LM399 also seem to be sensitive to tilting for several days when being heated. Reported here:
https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg1014749/#msg1014749 (https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg1014749/#msg1014749)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on January 04, 2018, 01:33:19 pm
I couldnt find a more fitting topic, so i hijack this thread to ask: Which setup do you use to measure your references on the long run, to calculate drift and compare them?

I think a good technique is to sequentially connect each zener-reference against each other in opposition, this will leave a voltage <200mV so one can use a simple DMM in 200mV-Range, compared to just measuring each zener-reference after another while using the expensive 3458A in 10V-Range. And when switching the polarity of the references during measurement one could average thermal-emf-errors which might occur.
Heres a good article about it: https://www.researchgate.net/publication/228900801_Complete_Characterization_of_a_Low_Thermal_Scanner_for_Automatic_Voltage_Measurement (https://www.researchgate.net/publication/228900801_Complete_Characterization_of_a_Low_Thermal_Scanner_for_Automatic_Voltage_Measurement)

But i still dont understand if a cheaper DMM in the 200mV-range would affect the drift-measurement or if the selfdrift of the DMM-selfdrift would cancel out during the long-time measurement. Maybe someone can point out how its done?

Also: I still would need a good reference with a known low drift to calculate the absolute drift of each of my LTZ1000A-references, is that correct?

Also it surprised me that in the Data Proof scanners 160/320 the wires are internally soldered to the Pomona-jacks, instead of copper spade lugs/copper-wires being used throughout the whole device like i would have expected: https://doc.xdevs.com/doc/Data_proof/img/bot_open.jpg (https://doc.xdevs.com/doc/Data_proof/img/bot_open.jpg)

Since i have a Keithley 705-scanner mainframe and there are no <1µV cards available with the necessary type-c-contact-relays to copy the circuit in Figure 1c of the Article, i think about building myself a fitting card based on OptoFets (no contact life limitation). Of course i would characterize the resulting thermal emf with my Keithley 181 Nanovoltmeter.   

These questions emerged because i now have my 7x LTZ1000A-reference which i want to measure.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 04, 2018, 01:46:15 pm
If you doesn't have a high quality meter, using one reference to subtract from the other is a real option. It still relies on that one reference to be good.

I would not switch the reference polarities, as the extra switches tend to cause more trouble than good. At least the modern meters tend to be about as good as reversing the polarity, when it comes to offsets. The low voltage range will only con tribute a little to the overall voltage, so it's (gain-) drift would usually not be that important.

Soldered connections are generally not a problem - thermal EMFs only develops if there is a temperature difference across the different materials.

Optofets can be a little tricky for low volts DC, as there is some self heating. So they are not per se DC accurate. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 04, 2018, 04:07:41 pm
Which setup do you use to measure your references on the long run, to calculate drift and compare them?

Hello,

for the first: I try to get as many calibrations as possible from calibrated equipment. In best case I have the calibration report so that I can narrow down the uncertainity of the calibration points after some years.

2nd: I do dayly intercomparisons of my ADCs (ADC13 is one of the most stable) and known good references.
So I can detect unusual drifts. E.g. the jump on LTZ#1 by -1.9 ppm on day ~820 (green dots) due to a short on the unbuffered output.
I use a relay scanner with latching signal relays for this. (low heat generation). After each switching I wait some time to let the thermals settle.

But i still dont understand if a cheaper DMM in the 200mV-range would affect the drift-measurement or if the selfdrift of the DMM-selfdrift would cancel out during the long-time measurement. Maybe someone can point out how its done?

Also: I still would need a good reference with a known low drift to calculate the absolute drift of each of my LTZ1000A-references, is that correct?

lets do the math: 
- 30 ppm error in 10V range are 300 uV.   
- 50 ppm error in 100mV range only 5 uV.  (assuming that the error is larger in the 100mV range against the native 10V range).
And yes you will need a well aged known good reference so that you can do differential measurements.
LTZ1000 references tend all to drift down over time.

So I use my well aged LTZ#2 as reference for the new references LTZ#3-#6 to do weekly ageing measurements.
Several ADC´s measure the absolute value and 2 DMMs in 100mV range the difference to LTZ#2.

These questions emerged because i now have my 7x LTZ1000A-reference which i want to measure.
Welcome to the club.
Before starting with ageing experiments I would fully characterize the references as good as I can.
(Tempco, variation of power supply, EMI sensitivity (changes when using battery supply, or laying the hand over cables, mobile phone ...), tilting, ....).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 04, 2018, 07:15:24 pm
I do have the first data (6.5 hours) of my LTZ1000#1 (one of three references based on Andreas LTZ1048B battery powered boards with battery monitor, LTZ1000 none-A and Rhopoint 8G16A resistors with 12k:1k for temperature setpoint). Measurement will be running until tomorrow.

MEAN: 7.1490899458 V
STD: 267.55 nV

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on January 05, 2018, 01:49:23 pm
Thanks for all the suggestions. I still need to get the Rhopoint-resistors and have smd-resistors installed at the moment to i could test the references at least after building. I still need to evaluate my scanner-setup and maybe might buy a cheap Keithley 2000, which will then monitor the references on the long run, which are compared in opposition to each other and to a known reference.
Each KX-reference will be placed in a Hammond-case, together with a LT3042-regulator, input-filter and an output-buffer. This should lead to robust references which can age undisturbed.
The tempco-test will of course also be done once i have all references assembled.
I dont want to use my 3458A for long-run-measurements since i need it for many other measurements.

So much to do...

Need to find the post about output buffers, i think it was mentioned that the internal protection diodes of the OP-amp could be activated during a short on the buffered output?
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on January 05, 2018, 02:51:02 pm
Each KX-reference will be placed in a Hammond-case, together with a LT3042-regulator, input-filter and an output-buffer.

Have a look at LT1763 too.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on January 05, 2018, 03:24:30 pm
I already have the LT3042 and fitting boards, but thanks for the suggestion. Of course the LTZ1000 doesnt need such a good regulator, but hey.
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on January 05, 2018, 04:00:47 pm
Need to find the post about output buffers, i think it was mentioned that the internal protection diodes of the OP-amp could be activated during a short on the buffered output?

I used Andreas’ output buffer:

https://www.eevblog.com/forum/metrology/px-reference/msg1386669/#msg1386669 (https://www.eevblog.com/forum/metrology/px-reference/msg1386669/#msg1386669)

https://github.com/pepaslabs/px-ref/blob/master/kicad/releases/v2.2/basic-ltz1000.pdf (https://github.com/pepaslabs/px-ref/blob/master/kicad/releases/v2.2/basic-ltz1000.pdf)

Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on January 05, 2018, 05:25:04 pm
Hi cellular,
osh park will send me your boards v2.2 in a couple of days.  :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on January 05, 2018, 05:32:58 pm
Cellular -
Just be aware of the (very low) output drive current of a '2057, these are usually never meant to be used directly as an output buffer... If you need any drive current at all you probably want a simple, cheap, low noise emitter follower / current limit circuit in your output buffer feedback loop.  See the Fluke 732b schematic for inspiration.

Otherwise that chopper noise can feed thru to your Vref output once you start drawing real current, and you'll start seeing offset errors also as the output current draw goes up past a mA or two.  This effect is -not- listed on the datasheet directly. 

It just depends on what your application, and just something to keep an eye on.  It will probably work OK as-is if you're only driving DMM inputs, but be aware of what happens if you try to drive (for instance) a higher speed ADC / DAC Vref input that needs real current flow.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 05, 2018, 07:15:39 pm
Just be aware of the (very low) output drive current of a '2057,

You mix that up with a LTC1050.
Short cirquit current on LTC2057 is above 30 mA (sourcing).

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on January 05, 2018, 07:43:25 pm
Andreas:
"Short circuit" current means you have zero voltage output signal - which doesn't apply here.  A signal of "Zero" is useless.  That spec is more to calculate overload protection for the amp.

You will begin to see increased chopper noise and Voffset loading errors at around 2 or 3mA out from a '2057 - LT apps recommends to keep the output current draw on those choppers as low as possible for best performance -  < 1~2mA preferred, and certainly <<<< 5mA.  The less current the better in terms of noise performance.

Look at the topology of how the demodulator section works on the output side of any chopper amp, and you'll realize why you can't pull much current and keep output noise low.

That's why chopper amps will normally have some sort of follower amp or transistor drive stage if you want to supply any real current flow.

Like I said - if you're just driving a DMM input section then a bare-naked chopper amp output can work - but if you need some current flow you normally have some sort of boost follower.

Cheapest, most reliable and lowest noise solution is usually a transistor follower - and a larger area transistor can add a very negligible amount of noise.

You'll see LT1010's in some of the app-note literature but those are pretty noisy (especially at frequencies you weren't planning on) - even within the chopper amp feedback loop you see much more noise added to the output than you probably want - depending on what you're doing, of course.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on January 05, 2018, 09:11:39 pm
So basically like the output buffer of the Datron 4910 (Fluke 732B doesnt show full schematics): https://doc.xdevs.com/doc/Datron/4910_4911/4910%20c20090120%20%5B8%5D.pdf Page2
But instead of the OP27 i would take a zero-drift-op-amp to not compromise the drift of my reference, is that correct? I just dont understand why they inserted C123 and D102.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on January 05, 2018, 09:29:09 pm
I already have the LT3042 and fitting boards, but thanks for the suggestion. Of course the LTZ1000 doesnt need such a good regulator, but hey.

This is a nice article about a low noise voltage regulator made by Peter Märki, ETH Zurich.
I've attached it to this post, but it can be found online here:
https://people.phys.ethz.ch/~pmaerki/voltage_regulator_2013_0.02/

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 05, 2018, 09:40:43 pm
Even if the OP could deliver enough current it could be a good idea to limit the power consumption of a precision amplifier and thus use a separate driver stage. Heat loss from the chip can lead to chip internal temperature gradients and thus extra offsets, even with an AZ OP.

The noise of the current driver would not be such a big issue, as it would be inside the loop. It would be only at higher frequencies that the noise will coming from the driver. If higher frequency (e.g. kHz range) is an issue one might even consider a kind of compound amplifier instead of just a current driver, since there is quite some higher frequency noise from the LTC2057.

The Datron output amplifier includes some filtering. So it is not just a buffer. Here there is no need to replace the OP27 with another AZ OP. It would be more like changing to an JFET based OP to get less input bias. D102 is just for level shifting. So the output can go to higher voltage.
C123 is setting the cross over between the LTC1052 and the OP27 to a rather low frequency (around 0.5 Hz).

I would more like look at the compound amplifier in the LTC2057 data-sheet, or just use the two transistors for the current limited emitter follower.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on January 05, 2018, 10:19:38 pm
So basically like the output buffer of the Datron 4910 (Fluke 732B doesnt show full schematics): https://doc.xdevs.com/doc/Datron/4910_4911/4910%20c20090120%20%5B8%5D.pdf Page2
But instead of the OP27 i would take a zero-drift-op-amp to not compromise the drift of my reference, is that correct? I just dont understand why they inserted C123 and D102.

Echo - Just for a concept example, if you get the Fluke 732b manual at Xdevs site, go to page 113 - and everything you want to know is mounted right at the business end of the output terminals. Current boost and limiter functions are provided by 2 X 2N3904's...  These transistors are buffering the output of the final low-drift op-amp, and offering current limit as well.  On the Fluke 732b current is limited to around 12mA max for safety (short circuit at the output terminals causes no harm) - which is set by the 22 Ohm R1.  As you try to draw more current, the voltage developed on R1 turns on Q1, and as Q1 starts to conduct - that in turn begins to shut down Q2.  The signal 10V High Output Stage comes from an op-amp stage and it's output resistor-isolated from the Q1 & Q2 follower / limiter.

The output terminals will see around 1ppm voltage error as you approach 12mA according to specs, but in actual use the error is typically (much) less than that.

This transistor buffer current boost + limiter design is very common for DC driver designs, and when you use large area transistors you're looking at only a couple nV/rtHz noise added (if that).  Which is generally less than most op-amps and a whole lot cheaper and more reliable.  Sometimes you'll see additional diode drops or zener are in the current limiter driver line (from op-amp to follower) to raise the base-driver operating point headroom on the output driver / limiter - this also has the effect of making the current limit cut-off point more defined with slightly less voltage error, and sometimes puts the op-amp output level in a more quiet place relative to power supply rails.  It does add a little more noise though.

There are lots of variations to this type of output buffer circuit.

If you're driving a fast ADC  or DAC typically you'll need an op-amp behind the '2057 to get some push-pull current flow at higher freqs.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on January 05, 2018, 11:11:15 pm
Thanks for the info and description.
The buffer should only act as a short circuit/overload-protector so the LTZ1000 behind it wont be harmed, since ive read that some people here had the misfortune of shorting the LTZ-output and thereby ruining the established smooth drift.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 06, 2018, 06:03:51 pm
I now have more data of my LTZ1000(non-A)#1. Obviously the TC is 0.28255ppm/K or 2.02µV/K in the observed change in ambient temperature. I have a 402k compensation resistor installed. What is your suggestion, increasing or decreasing the resistor value and by what amount? Is there some rule of thumbs?

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 06, 2018, 06:41:38 pm
Hello,

for the non-A I do not really have a receipe.
But I think the principal direction should be the same as here for the A-Version:

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg999857/#msg999857 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg999857/#msg999857)

So to decrease the T.C. by 80 ppm you will have to leave out the 400 K resistor.
Probably on the non-A version the effect from heater is larger than on the A-Version.
A estimate could be sqrt(400 K/W / 80 K/W) so a factor 2.3 more than on the A-Version.

But: 0.8 deg C room temperature change seems to be too little for me to really differ between LTZ T.C. and instrument T.C.
I would do at least a 20 deg C temperature change for the LTZ at constant conditions of the instrument.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 06, 2018, 07:02:32 pm
Thanks Andreas,

so I need to go into the climate chamber with my LM399 and my LTZ1000 as soon as it is available. Don't have a working temperature box at home :(

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 06, 2018, 07:12:11 pm
Conrad has:

https://www.conrad.de/de/kuehlbox-thermoelektrisch-g30-dc-12-v-rot-grau-29-l-eeknrel-mobicool-1423217.html (https://www.conrad.de/de/kuehlbox-thermoelektrisch-g30-dc-12-v-rot-grau-29-l-eeknrel-mobicool-1423217.html)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 06, 2018, 07:18:19 pm
Sorry was a 12V only version:

So at home this one is better if you do not want to outsource the beer from the fridge.

https://www.conrad.de/de/kuehlbox-thermoelektrisch-v26-12230-12-v-230-v-rot-25-l-eeka-mobicool-1423216.html (https://www.conrad.de/de/kuehlbox-thermoelektrisch-v26-12230-12-v-230-v-rot-25-l-eeka-mobicool-1423216.html)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 06, 2018, 08:26:49 pm
What temperature slope do you suggest? Up to 5K/min are possible with the chamber we have at work.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 06, 2018, 09:46:46 pm
Hello branadic,

for practical reasons I usually use 0.12K/minute.
-> one measurement cycle over 30 deg C with rest time at minimum and maximum needs and some overlap around 13-15 hrs. = 1 day

I have already used 0.03 or 0.05K/minute for final measurements especially when the thermal mass is larger.
Then the measurement usually is splitted into a warm and a cold phase on different days.

Maximum rate I used is around 0.3K/minute but only for smaller temperature changes (+/- 5 to +/-7 K).

If you have a too large slope then you will have additional "measurement dependant hysteresis" because the temperature sensor has not the same temperature as your zener/resistors.

Consider also: maximum slope in my "lab" is around 2K per hour (or 0.03K per minute).
So if you have the time you should choose that what you expect in later use.
For the same reason I put the reference into a shoe box so that I do not have large air drafts (similar to later use).

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 06, 2018, 09:57:08 pm
5 K / min is already relatively fast for testing a precision reference. A realistic speed would be more like less than 1 K / min.

The effect of the compensation resistor is approximately linear in 1/R.  As the correction is coming from the heater, it depends on the thermal setup. Due to the resistive heater the change in heater voltage also depends on the heater power and  thus the set temperature.

For the A version the thermal coupling is thermal resistance is larger, but the higher set temperature and lower heater power tend to have an opposite effect. Due to the large number of influences it is hard to predict how strong the effect of the compensating resistor is. The best bet is more like a measurement of the TC with and without the 400K. If needed one can then calculate the suitable resistor.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on January 06, 2018, 11:43:13 pm
Regarding the TC resistor and the LTZ1000A, all three of mine showed about 0.1 ppm / K negative TC without the TC resistor.  The 400K value is just a ballpark starting point it seems.  I found one needed 330K, one 390K and one 470K to achieve similar end results.  All three show the same behavior with the TC resistor in place, the TC slides downward slightly from 10deg C to about the 24deg C point, then it will level off or show a slight positive TC around about 28deg C and onward. The TC dropped from the 0.1 ppm / K to less than 0.05 ppm / K.  I have been testing from 10deg C to 50deg C with a very crude manual slope control (but it works).  I have seen too aggressive temp slope gives false results as not all of the parts on the reference board have had time to thermally stabilize.  If the temp is increased from 25 to 35 deg C, in say 10 min (1 K / min), my references will show a more positive TC while warming, then settle down in value after the temp has stabilized.  I have seen much better/stable results with a less aggressive slope, around 10 K / hour or more.

I use a small portable cooler as like in the link above but the air movement inside is too disruptive.  I found I can avoid this by using some frozen cold packs, place everything inside and let it cool to about 8 deg C, then remove the ice packs and start taking measurements as it slowly warms from 10deg C to near room temp (takes about 2 hours).  Then I use some large wirewound resistors in the cooler and my lab supply to gently warm from there, starting off at about 5 watts which gets me to about 30 deg C, then increase the wattage by 5 watts every 5 deg C.  Its crude, but it works.

(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/0958091C-39B0-442D-BB74-A2418ABBD2FF.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/0958091C-39B0-442D-BB74-A2418ABBD2FF.jpg.html)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TheSteve on January 08, 2018, 05:12:19 am
All kinds of boring and unoriginal - I just boxed an HP 3458A A9 ref board.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 08, 2018, 06:14:03 am
Oh wow, the 7480T is the first multimeter with the input jacks for high and low arranged in a horizontal way instead of vertical that I see.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: TheSteve on January 08, 2018, 06:19:12 am
Oh wow, the 7480T is the first multimeter with the input jacks for high and low arranged in a horizontal way instead of vertical that I see.

-branadic-

Yep, just to force you to really focus when making connections so you get them right. They are also not in a .75 x .75 arrangement so I can't use a shorting block that would fit many of the Keithley and Keysight meters.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 2N3055 on January 08, 2018, 06:23:30 am
What is it, 20x20mm ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 08, 2018, 06:43:41 am
Oh wow, the 7480T is the first multimeter with the input jacks for high and low arranged in a horizontal way instead of vertical that I see.

-branadic-

Yep, just to force you to really focus when making connections so you get them right.

but at least they are more likely at the same temperature.
I ever wondered how one could make a precision instrument with connectors at different temperature levels.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TheSteve on January 08, 2018, 07:30:24 am
What is it, 20x20mm ?

It fits a standard dual banana just fine for measuring voltage or 2 wire resistance. It looks to be 19.05x25mm.

but at least they are more likely at the same temperature.
I ever wondered how one could make a precision instrument with connectors at different temperature levels.

with best regards

Andreas

I had never considered that before - maybe that was what they had in mind.
Title: Re: Ultra Precision Reference LTZ1000...DIY Voltage Standard
Post by: Insatman on January 18, 2018, 08:14:35 am
I recently built a battery backed voltage standard.  Four references are included.  The primary reference is a LTZ1000 scaled to 10V.   There are three secondary references.  First sec ref is based on three LM199s which are averaged and then scaled to 10V.  2nd sec ref is an LT1021BCN8-10.  This was the best Single chip 10V reference type I have tested so far.   Third sec reference is the infamous VRE305AD.  This 5V reference has stellar specification which unfortunately it does not quite meet.  But it is still a pretty good reference, just quite pricey for the performance level.

The chassis uses two 12V, 7ah batteries in series to power the references.   A LM319 pre-regulator drops the voltage from ~24 to 19VDC.  It is then filtered to remove battery charger noise.  The 19 volts are then fed to the two reference modules where a LT3080ET regulator drops the voltage to 15V.   The primary regulator module contains the LTZ1000 reference on a custom circuit board.  Originally I planned on using the KX reference board.  But...after two failed attempts I designed my own board.   

The secondary module contains the LM199x3, LT1021 and VRE305 references, all sharing the same 15V rail.   Both modules are enclosed in a cast Aluminum enclosure within the steel enclosure of the voltage reference chassis.   

Schematics, photos and data are attached.  I will need more than one post for all the attachments...sorry.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on January 18, 2018, 08:20:38 am
More PDFs for my prior post on DIY LTZ1000 Reference

Note the data also includes an modified MV-106 and a DIY LM399 reference
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on January 18, 2018, 08:22:59 am
Final PDF for DIY LTZ1000 Vref
Title: Re: Ultra Precision Reference LTZ1000
Post by: borghese on January 18, 2018, 11:20:36 am
I think that OPA177 is not specified for input voltages of about 0.5 Volts; it is better to use the LT1013 or LT1006
Best regards
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 26, 2018, 07:42:12 pm
My triple set is almost ready. Board is the LTZ1048B including BMON (battery monitor and battery charger) and battery pack (12x AA NiMH) by Andreas. It currently delivers only the buffered zener voltage, but VSMP 10k is already installed and VSMP 25k is on my desk to boost the voltage to 10V after I do have an idea about its drift and aging. This is probably the most professional complete solution for the LTZ I know. Thanks Andreas.  :-+

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on January 26, 2018, 09:10:36 pm
Very cool screws!!
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 26, 2018, 09:23:34 pm
Only a few stainless steel screws. The panels were designed with Schaeffer Frontpanel Designer and laser cutted by a friend of mine. The back panel does contain Pomona 3770 binding posts. Back panel will be finished soon, but I need some spacer as D-Sub25 connector is not flush with the circuit board edge.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 27, 2018, 04:59:43 am
Hello,

Only a few stainless steel screws. The panels were designed with Schaeffer Frontpanel Designer and laser cutted by a friend of mine. The back panel does contain Pomona 3770 binding posts.

Really good looking panels against my "hand crafted" ones.

but I need some spacer as D-Sub25 connector is not flush with the circuit board edge.


Why don´t you leave the D-Sub connector off (like Frank) or replace the connector with a different one?
There are only 4 pins of interest used on the D-Sub connector:
2 for the internal temperature sensor.
2 for the unbuffered LTZ-output.
But I think for the later that it harms more (I had many accidents with unbuffered outputs) than is useful to have it outside the reference. Except if you use the 7->10V transfer option on the buffered output.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 27, 2018, 08:27:16 am
Back panel will be finished soon, but I need some spacer as D-Sub25 connector is not flush with the circuit board edge.
Hello,

the intention was that the D-Sub front is in flush with the front plate.
But that works only with the original thickness of the front plate from the housing.
I also did not want to fix the D-Sub to the front plate to avoid mechanical stress to the PCB.
The PCB is already fixed from the BMON-side (back) so I wanted to leave the front side floating to avoid stress on the PCB.
So using Pomona connectors on the front side is a step in the right direction.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 27, 2018, 11:36:06 am
Well, I could replace the D-Sub25 angled pcb type by a panel mounted one for wire soldering to be compatible to your solution. This way the existing backpanels can be used without modification, there is no additional board stress and spacers are obsolete.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on January 27, 2018, 11:57:31 am
Board is the LTZ1048B including BMON (battery monitor and battery charger) and battery pack (12x AA NiMH) by Andreas.

I looked around here in the Forum, but I wasn't able to find something, which describes this LTZ1048B board in detail.  :-//
Could you post a link please? Thanks.

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 27, 2018, 02:00:32 pm
It's the board shown here (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg825587/#msg825587) and there is also some schematic within this thread. The BMON is described here (https://www.mikrocontroller.net/articles/Batteriewächter).

-branadic-

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 27, 2018, 07:24:24 pm
A nice back can charm as well.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on January 30, 2018, 04:12:01 am
I thought it might be fun for someone to take a look on some random numbers.

It's HP A9 STD-reference (https://xdevs.com/article/volt_xfer/), powered by different sources, different times in the year, with uncontrolled ambient conditions (typical +21 to +27c), measured by two (https://xdevs.com/fix/hp3458a/) different HP 3458A (https://xdevs.com/fix/hp3458a_u2/) (calibrated off same source, though) and with Keithley 7168 JFET nanovolt scanner (https://xdevs.com/review/kei7168/) in between.

(https://xdevs.com/doc/xDevs.com/xfer_volt/ltzxfer.png)

This very same reference I used March 2016 to calibrate my 3458A first time.

(https://xdevs.com/doc/xDevs.com/xfer_volt/img/chamber_1.jpg)

Original data, taken prior to shipping

(https://xdevs.com/doc/xDevs.com/xfer_volt/vref_start.png) (https://xdevs.com/vtx_ltz1_t1/)

Even with all involved, I'm impressed with the peak-peak number and data.  :box:

Sample size is non-existent, but if one to judge from this single unit, then theory of having standard A9 3458A reference achieving ~2ppm/year stability might have some real possibility.

If one to count from first measurement after shipment (May 20, 2016), 7.184609 vs last measurement (January 11, 2018), 7.184636 VDC, change is +3.76ppm over 601 days, that is +2.3 ppm/year. Which is bold statement already, as own meters drift is on similar scale, so it's hard to tell who is who.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 02, 2018, 03:37:21 pm
Well, I think I need lower noise low noise amplifier. Finally got around and started test I wanted to do for very long time. Here's some interesting data for discussion.

Test setup: MDO4054C scope + Pipelie's 1:10000 pre-amplifier from low-noise thread, so 1mV on amplifier output is equal to 100nV.
DUT:  Modified KX reference board, LTZ1000CH random chip. It's running with standard 120 ohm VHP100 and 75K PTF56 resistor.
Power supply for reference: Agilent E3649A, +15VDC.

(https://xdevs.com/doc/xDevs.com/KX/ltz_test1.png)

Shown graph reveals ~270nV/pk-pk noise on 0.1Hz-10Hz band.
Output voltage is 7.0751391 V.

Own preamplifier + scope noise floor is around 110nV pk-pk.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on February 02, 2018, 04:14:24 pm
Having 260 nV noise from the reference + amplifier compared to 110 nV from just the amplifier is not a problem. To a good approximation one can compensate for the amplifiers own noise up to the point where the source noise is slightly lower than the amplifiers noise.
For looking at the noise data the RMS values are usually more practical than peak to peak values as these show much lower fluctuations.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Magnificent Bastard on February 02, 2018, 04:35:12 pm
Shown graph reveals ~270nV/pk-pk noise on 0.1Hz-10Hz band.
Output voltage is 7.0751391 V.
Own preamplifier + scope noise floor is around 110nV pk-pk.

I think you got very lucky, and have an LTZ1000 that has exceptionally low noise.  Better keep that one!
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 02, 2018, 04:51:05 pm
There is nothing special about this chip ;).

Kleinstein
Well, that is my concern. I want to bump zener current 4-6 times to get in ballpark of 100nV/pkpk noise. To be more confident in noise that would require <50 nV/pk-pk capable amplifier.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TheSteve on February 02, 2018, 06:03:59 pm
It feels very cold in this thread...  >:D
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 02, 2018, 08:42:27 pm
I think you got very lucky, and have an LTZ1000 that has exceptionally low noise.  Better keep that one!
Hello,

my crystal ball sees a smoking dewar with LN2 around the board.

Otherwise there would be something fishy with that LTZ1000.
The stray in noise is usually not that high.

with best regards

@Illya: photos please

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: CalMachine on February 02, 2018, 09:28:26 pm
It feels very cold in this thread...  >:D

Put some full-length pants on  :popcorn:
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 03, 2018, 12:30:40 am


Hello,

my crystal ball sees a smoking dewar with LN2 around the board.
@Illya: photos please

Andreas

:) Yes, this is LTZ chip cooled down to 77K.
I don't have any worthy meters at work, just an agilent 34970A, so here is live log:
https://xdevs.com/cltz_test1/.
Its just an indication, as noise and stability in data just shows now good is LM399 in 34970A. LTZ chamber temperature measured with Type K TC and MAX31855 converter, tied to RPi by SPI bus.

Just checking if whole idea have any means to it, before investing into making 24/7 operation capable cryocooled LTZ reference. One of things I am not sure is how stable temperatures would stay, due to oxygen and air creep into dewar.
Heater drive on LTZ is disconnected ofc.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on February 03, 2018, 04:34:00 pm
Did you submerge the whole board in LN²? Since i know you have the money and are crazy enough to give it a thought: You could also buy a "Superconductor Technologies Superfilter" on ebay which contains a stirling-engine capable of producing LN² and can run indefinitely.

https://www.ebay.com/sch/i.html?_odkw=super+filter&_osacat=12576&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xsuperfilter.TRS0&_nkw=superfilter&_sacat=12576 (https://www.ebay.com/sch/i.html?_odkw=super+filter&_osacat=12576&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0.Xsuperfilter.TRS0&_nkw=superfilter&_sacat=12576)
http://benkrasnow.blogspot.de/2008/08/diy-liquid-nitrogen-generator.html (http://benkrasnow.blogspot.de/2008/08/diy-liquid-nitrogen-generator.html) Here the stirling engine is shown and used.

Time to build that ultra low drift/noise 3458B.  ;D
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on February 03, 2018, 04:50:27 pm
Did you submerge the whole board in LN²? Since i know you have the money and are crazy enough to give it a thought: You could also buy a "Superconductor Technologies Superfilter" on ebay which contains a stirling-engine capable of producing LN² and can run indefinitely.

One would just make a board that clamps directly to the cryocooler's cold finger and surround the whole assembly with a vacuum flask and evacuate it, that is, you can cut out the intermediary LN2.

That just leaves the tiny problem of how to make a good low thermal emf connection across a ~230 K thermal difference.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on February 03, 2018, 05:01:33 pm
I dont know how stable you can regulate the cold-finger-temperature. Im just surprised that the whole LTZ-assembly still works at 77K and that the ref-voltage is still in the 7V-range.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on February 03, 2018, 05:38:55 pm
I dont know how stable you can regulate the cold-finger-temperature.

Good question. I know it's good enough to not add noise to microwave amplifiers that are being cryocooled specifically to get low noise (That's where most of the 2nd hand cryocoolers come from).
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on February 04, 2018, 02:19:48 pm
TiN
Great LN2 Experiment!
I extrapolated some temp control resistor values for you at the very cold temperatures. See attached PDF. This is based on the -55C to +125 deg C characterization that I did a few years ago.

Given a 7.0751 V zener -
For a -150 deg C control point the nominal 13k value for R4 should be 6.075k ohms. This would yield 1.0 V on pin 6 of the chip.
For a -175 deg C control point R4 would be 5.738k ohms. This would be 1.05 V on pin 6.

The 120 ohm resistor probably had 0.96 V across it so you would have been running 8 ma for this test. This is a guess because the Vbe of the Q1 does not match theory at this time. This is because of the internal Zener kelvin connections.

Good luck!
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 04, 2018, 05:18:59 pm
Cryocooler they say...

(https://xdevs.com/doc/STI/img/sti_ov_1.jpg)

Not sure if she'll be alright, need to have my friend to test it. Anyone got software for these STI RX 850 boxes?
My biggest concern would be mechanical decoupling (these motors produce quite a vibration during operation) of LTZ reference module and insulation against environment (condensing air on the reference assembly wouldn't be desired experience).

chuckb
I doubt that LTZ curve stays linear on these extreme temperatures.
I can measure some points. Resistors and board are outside, at ambient temperature, only LTZ chip is chilled.

Also using LTZ's own oven likely to be pointless, as heat flux removal ability of liquid nitrogen is many hundreds watts per volume that I have here now.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on February 04, 2018, 06:41:52 pm
Maybe LN² between the coldfinger and LTZ to transport the heat to the coldfinger, while a steel mesh in the LN² would dampen vibrations sufficiently? And a regulated heater in the LN² to carefully regulate the LN²-temperature since the colfinger-temp will vary alot i assume.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on February 04, 2018, 06:44:29 pm
I was thinking of an earlier experiment where you put a pcb inside a copper cylinder and submerged it in Nitrogen. But I don't remember the details.

I would love to see the chip node voltages. For the temperature, remove the divider resistors and short the base (pin 6) to the collector ( pin 8 ) . The 70k resistor will be the 100ua current source.
 
Looks like the Lakeshore Silicon temp sensors stay linear down to around 30 deg K. See attached. Of course that will be an issue when you progress to Liquid Helium!

Running the heater should work fine. The Liquid Nitrogen is still isolated by the steel package. Using an LTZ1000A would work even better with the extra thermal and stress isolation of the special chip mounting. You will probably need the heater to get to 0.001 deg C temp stability and repeatability.

What is the control temperature of the cryocoolers?

Great experiment!
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on February 04, 2018, 07:14:10 pm
TiN, this is the right step to PJVS ...

Inviato dal mio ONEPLUS A5010 utilizzando Tapatalk

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on February 04, 2018, 09:45:50 pm
The special feature of the LTZ1000 is the good heater and temperature reading. For a LN temperature reference is would be more something like the LTFLU / SZA263 - however I don't know if the intrinsic TC is still that low at LN temperature.

Anyway I son't think this is really practical, as there is quite some effort in LN und cooling / warming to room temperature is quite some stress for the parts.  Ideally one would get a JJ reference. At least squids are possible at LN temperature - so one could get a squid + coil based current reference. A squid can also make is nice low voltage amplifier and current sensor.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 05, 2018, 02:10:32 am
 
The special feature of the LTZ1000 is the good heater and temperature reading. For a LN temperature reference is would be more something like the LTFLU / SZA263 - however I don't know if the intrinsic TC is still that low at LN temperature.
I'd stick with LTZ, just because it's commercially available. Such experiments are likely to cause few chips to be dead/permanently shifted/corrupted anyway.

Quote
Anyway I son't think this is really practical, as there is quite some effort in LN und cooling / warming to room temperature is quite some stress for the parts.
As unpractical as having multiple 8.5-digit meters and more than 10 LTZ1000-based references at home. We use decaliters of LN2 daily in the lab, so it's no big deal to leave 30L dewar in corner running something for few weeks.

Quote
Ideally one would get a JJ reference. At least squids are possible at LN temperature - so one could get a squid + coil based current reference. A squid can also make is nice low voltage amplifier and current sensor.
Ideally. As soon these things go from mid-5-digit $$ costs to 4-digit, I'll break a bank and get one. Before that, we stuck with little unpractical experiments for fun.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 21, 2018, 12:18:28 pm
LN2 slowly evaporated from the dewar over last week, so I've got interesting curve of LTZ tempco w/o heater (measured by 2001).
Interesting "island of stability" at around -130 C, before the tempco reverses.

Total 38MB log CSV with over 6 days of data (http://d:\_cal\ramon_event\cryoltz4_2001_nplc100_tin.csv).

Also chuckb's guess about

Quote
The 120 ohm resistor probably had 0.96 V across it so you would have been running 8 ma for this test.
is very correct, when chip was at LN2 temp, voltage over 120R was 0.963V .
Title: Re: Ultra Precision Reference LTZ1000
Post by: zhtoor on February 21, 2018, 01:01:04 pm
LN2 slowly evaporated from the dewar over last week, so I've got interesting curve of LTZ tempco w/o heater (measured by 2001).
Interesting "island of stability" at around -130 C, before the tempco reverses.

Total 38MB log CSV with over 6 days of data (http://d:\_cal\ramon_event\cryoltz4_2001_nplc100_tin.csv).

Also chuckb's guess about

Quote
The 120 ohm resistor probably had 0.96 V across it so you would have been running 8 ma for this test.
is very correct, when chip was at LN2 temp, voltage over 120R was 0.963V .

hello,

what happened between -1 and +5 degC ?

regards.

-zia
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 21, 2018, 01:18:17 pm
I think condensed water melt and leaked :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on February 21, 2018, 03:14:50 pm
I wonder if you can alter the zener current enough to push the zero TC point over to -78C (dry ice temperature).  Very interesting!
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 21, 2018, 04:25:36 pm
Getting to DICE temps is no better than going to LN2 anyway. I don't miss using DICE, having cold acetone slurry and other nasty and messy stuff (used DICE few times to cool CPUs/GPUs). LN2/single-stage CC is so much easier once you solve air going into dewar. :)
Anyway, all of that is offtopic here. I'll try with heater on and LN2 again, once have more time.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on February 21, 2018, 04:28:12 pm
I wonder if you can alter the zener current enough to push the zero TC point over to -78C (dry ice temperature).  Very interesting!
Remember that's not the curve for a LTZ at a stable current.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on February 21, 2018, 05:55:05 pm
There are a few techniques used to change the zero TC point of the LTZ1000.

Janaf and others experimented with this back around post #1144-1176 (2015)

Change the  Q2   Q1 collector resistor to 5.6M ohms or add a 20 ohm resistor between the top of the zener and the 7v circuit node. This resistor is identified by R60 on this forum. This was shown on the LTZ data sheet and used in the Datron 4910 Voltage reference. 
So increasing R2 from 68k to 5.6 Meg raised the Zero TC point (with unstabilized current) from -130 deg C to 40 deg C. The same happens with adding R60 and increasing its value from 0 to 20 ohms.

The R2 impact will be nonlinear but R60 is linear so we can do an estimate.

The goal of -78 deg C is 30% of the way between -130 deg C and 40 deg C, so you could try an R60 value of 6 ohms to minimize the basic temp co with dry ice.

I would shoot for a chip temp of -60 deg C and run the heater so you have 0.001 deg C chip stability. That would take an R60 value of 8 ohms.
This is all guesswork you understand!

For TiN a Q2 collector resistance of 39k like Datron would lower the Zero TC point to an unknown cooler temperature.

corrected a few values
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on March 10, 2018, 02:43:45 pm
Well, I think I need lower noise low noise amplifier. Finally got around and started test I wanted to do for very long time. Here's some interesting data for discussion.

Test setup: MDO4054C scope + Pipelie's 1:10000 pre-amplifier from low-noise thread, so 1mV on amplifier output is equal to 100nV.
DUT:  Modified KX reference board, LTZ1000CH random chip. It's running with standard 120 ohm VHP100 and 75K PTF56 resistor.
Power supply for reference: Agilent E3649A, +15VDC.

Shown graph reveals ~270nV/pk-pk noise on 0.1Hz-10Hz band.
Output voltage is 7.0751391 V.

Own preamplifier + scope noise floor is around 110nV pk-pk.

TiN
You achieved very low noise here at 77K and 8 ma. Can you check the noise of this same LTZ setup under normal conditions (40 deg C, 4 ma)? The noise will of course be much higher at room temperature. But, how high? I would expect the noise increase caused by the current reduction (8 ma to 4 ma) to be 1.4 times. Then the remaining noise increase would be cause by the temperature change. It looks like the noise reduction from cooling may be substantial. I would like to quantify it.
What would life be like without numbers!

The only other place I have seen information on Zener noise vs temperature is in the LM399 data sheet. See attached.

Keep moving the State of the Art forward for us. :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 10, 2018, 03:54:56 pm
I tested 10mA before (different LTZ module and different chip) and reduction on noise was less than I expected, about 20% only. I think I posted data before.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on March 10, 2018, 09:08:08 pm
I tested 10mA before (different LTZ module and different chip) and reduction on noise was less than I expected, about 20% only. I think I posted data before.

I remember seeing that so I dug it up.

There was a question about overdriving LTZ with high current. Well, I got some practical data, using jumper chip as a specimen, since I don't care much about it's long-term stability.

The noise was evaluated with a 3458A which will not have the low noise floor like your dedicated tester. Or was there some other testing that I missed?

Also it would be best to evaluate the same chip that was tested at 77K so we know if the that Zener is SPECIAL.

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 12, 2018, 04:08:28 am
I'll come back to more tests later on, the story of cryoLTZ not finished yet.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on March 27, 2018, 03:06:22 am
Thermal resistance of the LTZ1000 non A package.

The data sheet has confusing (for me) information for the non A LTZ1000. The Electrical Characteristics table lists a thermal resistance of 80 deg K / watt. The last graph of the Typical Performance Characteristics indicates an 80 deg K rise with 0.5 watts of heater power or a thermal resistance of 160 deg K / watt. What is the correct value?

Has anybody performed testing to clarify this?
Thanks
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on March 27, 2018, 03:38:01 am
@chuckb-  I ran into that too.  See https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1043115/#msg1043115 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1043115/#msg1043115) and the next few responses.  Correct thermal resistance for the non-A part is about 160 K/W according to data sheet typical curves.   While I have not verified this, the 160 K/W compares nicely with the 150 K/W of other devices in a TO-5 package (e.g. LT1012) which would presumably have the same die attach and therefore similar thermal resistance as the non-A LTZ1000.   I suspect the 80 K/W in the data sheet is a typo.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on March 29, 2018, 01:25:52 pm
Damned, now a portion of the worst case happened - Dilligentminds removed posts, hurting quote-integrity of this thread. :-/

Title: Re: Ultra Precision Reference LTZ1000
Post by: BravoV on March 29, 2018, 01:33:36 pm
Damned, now a portion of the worst case happened - Dilligentminds removed posts, hurting quote-integrity of this thread. :-/

Lesson learned, at least for me, use quote next time and save the posted images too if its important.

Also personally, I don't trust people who used external hosting for their images posted here in this forum, as I have the feeling that in their mind once they want to leave, all they need is just delete their posts and disable/terminate the images posted externally.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 29, 2018, 01:51:06 pm
Quote
I don't trust people who used external hosting
.
Goes both ways, I don't trust putting data, photos and files to some oompa-lumpa web-hosting server nobody knows where and hoping it will be around in 10 years from now.  :--
If I decide to have my content withdrawn, it's still my content and right to do so.   :blah:
Title: Re: Ultra Precision Reference LTZ1000
Post by: BravoV on March 29, 2018, 02:17:26 pm
Quote
I don't trust people who used external hosting
.
Goes both ways, I don't trust putting data, photos and files to some oompa-lumpa web-hosting server nobody knows where and hoping it will be around in 10 years from now.  :--

If I decide to have my content withdrawn, it's still my content and right to do so.   :blah:

Two ways ? Not always, as you're definitely with an agenda and surely not sincere sharing your posts here and still riding EEVBlog to gain popularity. That is one way.  ;)

Just still curious why you haven't officially announce your own forum/web/portal/video blog ? I guess when the time comes one day, all your posts will suddenly gone from here, all images gone, hence its not sincere sharing as you're thinking you have the power with just one click to make it all gone from here.  Again, this is one way too. ;)

Also probably that coincides with the timing of official launching of the "Tin Metrology" xdevs.com portal soon ? But good for you and your ambition, wish you luck.  :-+

No doubt, all your posts is yours, but still I have the right to save local copy once you posted "publicly", and also I have the right to re-post in the internet too if someone needs it, without any catch, this, two ways.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 29, 2018, 02:28:24 pm
Go ahead, save it all, more backups the better. Just don't forget credits and all, so other readers know the source originator.
I also lost you on "official announce" part, links are in my profile and under each post sub, how more official can it be. There is no official launching anything, that I know about either.  :-//

Suggest we kill the offtopic on these good points and discuss LTZ designs instead.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BravoV on March 29, 2018, 02:40:36 pm
Agree, no more, I stopped here.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ArthurDent on March 29, 2018, 03:00:03 pm
I have started collecting precision resistors and other parts to build a LTZ1000 reference and ordered the KX boards from OSHPARK and would like to comment on the company.

When the boards arrived there was a problem and I emailed them and got an instant reply. They went above and beyond anything I expected to completely correct the problem. I am very impressed at their level of service and the quality of their produced boards.  I know occasionally we all hear about something we buy not living up to the claims about the product but I feel we also should comment on the great service and products we receive from companies like OSHPARK.  I’m impressed.
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on March 30, 2018, 10:57:52 am
OT
Dilligentminds removed posts, hurting quote-integrity of this thread. :-/
DiligentMinds contributed some great ideas and insights to this thread.   Does anyone have a backup of this thread from before his posts were removed?   I heard once you put something out on the internet, it's always out there... but where?
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on March 30, 2018, 02:11:54 pm
OT
Dilligentminds removed posts, hurting quote-integrity of this thread. :-/
DiligentMinds contributed some great ideas and insights to this thread.   Does anyone have a backup of this thread from before his posts were removed?   I heard once you put something out on the internet, it's always out there... but where?

OT:

Play arround a little with WaybackMachine
https://archive.org/web/ (https://archive.org/web/)
like this:
https://web.archive.org/web/20180217033926/https://www.eevblog.com/forum/index.php (https://web.archive.org/web/20180217033926/https://www.eevblog.com/forum/index.php)

or google cache.

€: Gradually one should start at suitable place in the forum its own thread with topic to Dilligentminds.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 05, 2018, 02:58:59 am
I've laid out this LTZ1000 based 10V voltage reference board.   The circuit takes 18-24 VDC input (regulated) and produces a 10.0000 Volt output into high impedance.   This is an iteration of an earlier design so I know it works.  I'm trying to improve things a bit with the new layout and addition of some filtering.   

Some notes:
1)  The resistors with 4 terminals are just resistors with thru-holes set up for 0.150 or 0.4 inch spacing.  I'm using DipTrace for the layout  and by setting up the schematic this way it ensures I connect all the pads.
2)  The S1 connection is to separate the grounds so when I do the ground plane fill, those pads are not included.   I just install a jumper to connect them at a single point.
3)  The ferrites used are single turn intended for high-frequency noise suppression.   They are about the size of a 1/2W resistor and have near zero DC resistance.
4)  The board size is 2x3".  This is necessary to fit in my particular application.
5)  The space around the LTZ1000 will allow for a small Styrofoam hollow cube to be double-stick taped to the board providing some insulation and preventing air currents from affecting the LTZ1000
6)  The board will be housed in a cast aluminum enclosure lined with foam.

See attached pictures.

Anyone have a comments or suggestions before I commit to making these boards?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 05, 2018, 04:32:32 am
Anyone have a comments or suggestions before I commit to making these boards?

- I would place D4 directly to the input to prevent C17 blowing in case of reverse polarity.
  Additional bonus: L1+L2 see directly a capacitor (C15) giving a PI filter.

- Is U4 really stable with 10nF load? -> I would add a "capacitive loading isolation cirquit"
  See R21+C22 in my cirquit (R21 has to be adapted to the OP-Amp type and may be up to 100 Ohms).

- I am missing the EMI capacitors at the most sensitive pins of the cirquit
  (C11+C12 in my design placed directly between base + emitter pins of the LTZ IC)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 05, 2018, 04:39:30 am
Anyone have a comments or suggestions before I commit to making these boards?

- I would place D4 directly to the input to prevent C17 blowing in case of reverse polarity.
  Additional bonus: L1+L2 see directly a capacitor (C15) giving a PI filter.

- Is U4 really stable with 10nF load? -> I would add a "capacitive loading isolation cirquit"
  See R21+C22 in my cirquit (R21 has to be adapted to the OP-Amp type and may be up to 100 Ohms).

- I am missing the EMI capacitors at the most sensitive pins of the cirquit
  (C11+C12 in my design placed directly between base + emitter pins of the LTZ IC)

with best regards

Andreas

Moving the diode is a good idea.  I will try and modify the layout.

The OPA177FP op-amp is stable seeing 10nF directly, but a resistor will fit in the location of L3 just in case.  It's actually the same pad spacing.

I thought about putting caps there before but never saw it implemented, so I was reluctant.  I will see if I can fit them in the layout.  I'm assuming you are using film capacitors there?

Thanks...........Insatman
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 05, 2018, 05:08:39 am

I thought about putting caps there before but never saw it implemented, so I was reluctant.  I will see if I can fit them in the layout.  I'm assuming you are using film capacitors there?


Hello,

I have to admit that I am using X7R capacitors to get them really close to the pins.
(one is 0603 in the middle of the LTZ-pins the other 0805)
But of course film capacitors (e.g. SMD ECHU type) are also possible.

with best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 05, 2018, 06:10:00 am
Ok...I implemented all the suggestions.  On the new caps, I used two.  A 100nF film located some ways away from the LTZ1000 and an SMD 1206 33nF COG capacitor located very close to the chip on the underside of the board.   I happen to have quite a few of those in stock at the moment.   Both the board and schematic are updated.

Thanks Andreas.

Insatman.
Title: Re: Ultra Precision Reference LTZ1000
Post by: montemcguire on April 05, 2018, 07:20:45 am
I have to admit that I am using X7R capacitors to get them really close to the pins.
(one is 0603 in the middle of the LTZ-pins the other 0805)
But of course film capacitors (e.g. SMD ECHU type) are also possible.

with best regards

Andreas

You can now get 10nF C0G capacitors in an 0603 case. Many are 25V parts, but TDK has a 100V part in that size as well. So, you don't have to suffer the vagaries of X7R, unless you really want the 'voltage squish' and real component losses of X7R. Time marches on, and parts keep getting smaller!

Best Regards
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 05, 2018, 07:45:56 am

You can now get 10nF C0G capacitors in an 0603 case. Many are 25V parts, but TDK has a 100V part in that size as well. So, you don't have to suffer the vagaries of X7R, unless you really want the 'voltage squish' and real component losses of X7R. Time marches on, and parts keep getting smaller!

Best Regards

Jeez...1206 parts are hard enough to solder...0603 is a nightmare.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 05, 2018, 03:11:19 pm
Changing L3 to a resistor would ruin the low output impedance. The trick when makting the OPs output more tolerant to capacitive drive it to have the DC feedback from the output (thus behind L3 or resistor) and the fast feedback via a capacitor directly from the OP.  Just the extra cap and L3 instead of the usual resistor could also work reasonable.

Some here may not like the one rather thick line going to the LTZ1000, because of possible thermal gradients. I am not sure it matters.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 05, 2018, 03:36:42 pm
Build the circuit how you need to, but keep in mind LT/AD does not recommend adding those extra EMI caps, and in our tests normally they are not required, or desired - Especially SMT ceramics always run the risk of adding mechanical noise.  The solution is to look at what your EMI source really is, and see if that can't be corrected.

I suggest you might want to test your circuit in your enclosure FIRST to see if they are actually needed at your location, with your test setup.  Add the extra caps -only- as required.  If your circuit operates normally without them, you're good.

The noise spec you're looking for as defined by LT is if you look at many 10 second periods of your output, you should see an -average- PEAK noise of < 1.2uV averaged across all periods of observation.   It is normal to see an occasional peak noise pulse of perhaps over 2uV on occasion, but that is considered perfectly normal and well within bounds.

As Kleinstein noted, normally all traces to the LTZ should have somewhat equal thermal impedance, otherwise you may have created a thermal EMF at the device leads even with the cap over the LTZ.  If the thermal EMF is stable you might be OK but the uneven traces might cause problems if any airflow in that area.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 06, 2018, 04:22:02 am
Changing L3 to a resistor would ruin the low output impedance. The trick when makting the OPs output more tolerant to capacitive drive it to have the DC feedback from the output (thus behind L3 or resistor) and the fast feedback via a capacitor directly from the OP.  Just the extra cap and L3 instead of the usual resistor could also work reasonable.

Some here may not like the one rather thick line going to the LTZ1000, because of possible thermal gradients. I am not sure it matters.

I modified the layout slightly to make all the traces the same width...but not the same length.  Note that I intend to cover the LTZ1000 with a small cube of hollowed out styrofoam which also cover about 1/4" of the PCB around the device.  the bottom of the board will also have about 1/8" of foam in that same area.   This both prevents air currents from reaching the device and lowers the input power required by the heater to maintain temperature.  Furthermore, the finished board will be enclosed in a cast aluminum enclosure lined with thin foam on the inside.  So no air currents are expected.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 06, 2018, 04:27:48 am
Build the circuit how you need to, but keep in mind LT/AD does not recommend adding those extra EMI caps, and in our tests normally they are not required, or desired - Especially SMT ceramics always run the risk of adding mechanical noise.  The solution is to look at what your EMI source really is, and see if that can't be corrected.

I suggest you might want to test your circuit in your enclosure FIRST to see if they are actually needed at your location, with your test setup.  Add the extra caps -only- as required.  If your circuit operates normally without them, you're good.

The noise spec you're looking for as defined by LT is if you look at many 10 second periods of your output, you should see an -average- PEAK noise of < 1.2uV averaged across all periods of observation.   It is normal to see an occasional peak noise pulse of perhaps over 2uV on occasion, but that is considered perfectly normal and well within bounds.

As Kleinstein noted, normally all traces to the LTZ should have somewhat equal thermal impedance, otherwise you may have created a thermal EMF at the device leads even with the cap over the LTZ.  If the thermal EMF is stable you might be OK but the uneven traces might cause problems if any airflow in that area.

I added those caps due to Andreas recommendation...someone I have come to respect in this area of expertise.   In parallel with this effort I am also building a 10K:1 amplifier to measure the noise you mention in your specification. see https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg1471764/#msg1471764. (https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg1471764/#msg1471764.) 

I can add the EMI caps if necessary.   Attached are the latest schematics and PCB layouts.   Note I also added some additional SMD caps on the input and output connectors...why not...I don't have to use them.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on April 06, 2018, 05:12:27 am
I believe the latest guidance for C2 is 22nF. The Linear Tech datasheet calls out the incorrect value for this capacitor on the positive 7V regulator schematic. The capacitor value on the schematic for the negative 7V regulator is correct.

For safety during development, I like to have a 5V zener in series with the collector of Q1 to limit the maximum heater voltage to 10V. This can prevent permanent damage to the LTZ1000A chip if there is a problem during the development process. The Zener is not needed if you use the non A version of the chip.

Good luck!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 06, 2018, 05:21:34 am
I believe the latest guidance for C2 is 22nF. The Linear Tech datasheet calls out the incorrect value for this capacitor on the positive 7V regulator schematic. The capacitor value on the schematic for the negative 7V regulator is correct.

For safety during development, I like to have a 5V zener in series with the collector of Q1 to limit the maximum heater voltage to 10V. This can prevent permanent damage to the LTZ1000A chip if there is a problem during the development process. The Zener is not needed if you use the non A version of the chip.

Good luck!

Thanks for the update on C2.  My PCB can accommodate that value easily.  I will update my schematic.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 06, 2018, 09:49:39 am
The last diagram shown  an odd connection at the lower end of R10.


The ferrite at the output of the 10 V amplifier would add to DC output resistance. Normally feedback should be all the way from the output - could be down to the connector. In addition some local feedback via a capacitor might help a little with more tolerance to output capacitance. Even if an OP data-sheet says that the OP is stable with 1 nF or maybe 10 nF at the output, this only means it is not oscillating. Added capacitance usually still degrades the output and makes is more prone to ringing / oscillation. For an external output it would be a good idea to have to usual isolation with resistor to have a more capacitive tolerant output.

Those EMF caps Andreas suggested were part of more changes and just adding the caps, but without the other changes will reduce stability and likely make the circuit more sensitive to capacitive load.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 06, 2018, 10:39:02 am
The last diagram shown  an odd connection at the lower end of R10.


The ferrite at the output of the 10 V amplifier would add to DC output resistance. Normally feedback should be all the way from the output - could be down to the connector. In addition some local feedback via a capacitor might help a little with more tolerance to output capacitance. Even if an OP data-sheet says that the OP is stable with 1 nF or maybe 10 nF at the output, this only means it is not oscillating. Added capacitance usually still degrades the output and makes is more prone to ringing / oscillation. For an external output it would be a good idea to have to usual isolation with resistor to have a more capacitive tolerant output.

Those EMF caps Andreas suggested were part of more changes and just adding the caps, but without the other changes will reduce stability and likely make the circuit more sensitive to capacitive load.

You caught an error in the schematic with R10...thanks.

As for the ferrites I use they have a thick wire going through them.  The resistance is very very low, probably less than a PCB trace of equal length.

As for the caps on the op-amp output, there is a lot of debate around this.   I have always used 10nF on my voltage references.   In this thread it has been suggested to add them using a series resistor for op-amp stability.  I am reluctant to add resistance.  So...I decided to put the pads in the PCB and decide down the road to add the capacitance or not based on experience. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on April 06, 2018, 05:34:33 pm
Insatman, I strongly suggest you look at the Vref circuits in HP (Keysight), et al, Linear Tech originated the LTZ1000 over 30 years ago and their published schematic has stood the test of time (sans typos).  A bunch of bypass capacitors are neither necessary or wise, if your circuit needs such band aids, it is because you are doing something wrong or trying to compensate for external EMI and it is a well know fact that you always clean up noise at the source first before trying to do it in your circuitry.

MisterDiodes manufactures LTZ based references for industrial use in environments none of you are likely to encounter, he knows what he is talking about and I concur completely with his advice.  You are certainly welcome to ignore it but be advised it is not the best course to pursue.  The 3458A has utilized the LTZ circuit since conception without all the excessive capacitors and it certainly appears to be working just fine.  I suggest you implement the original circuit as is, if you find that you have have EMI problems then take the proper steps to eliminate the interference externally before modifying the LTZ circuit.

The first good step is using a steel enclosure not aluminum.  Keep noisy equipment such as laptops as far away as possible, that includes any circuitry with clocks in them and their associated cabling (such as ADCs or DACs), LED lighting or CCFL lighting (or standard fluorescent).  Incandescent or Halogen work just fine here.  This advice is all time proven and verified by many independent sources over the years.

If you have any questions about the operation of the LTZ circuit, the best place to go for advice is the engineers at Linear Technology, they will be most happy to answer them, for some reason, that course of action does not seem to be very popular on this forum.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 06, 2018, 06:27:58 pm
Yes, I've built a couple  :-DD 

Insatman:  Build your box however you want, just understand -  What happens by adding an "EMI" cap directly across an analog PN junction on a precision substrate, is you can potentially develop a situation where you convert a small voltage spike into what can be a larger current spike on the LTZ (when you count various inductive effects in the leads, etc) - and you don't want to "ring the bell" on your LTZ chip, at least as little as possible.

You're output might look a little cleaner but you may not like effects on the substrate crystal lattice over time.  This can show up as an affected long term drift rate, which may or may not be noticeable if you build just a few Vrefs.

The LTZ zener will add it's own noise of course but we want to try not to add any -more- current noise.

As Edwin pointed out:  There is absolutely nothing inside the LTZ circuit that should be creating much noise, except for the LTZ Zener itself.  Especially when you use PWW resistors.

Best engineering practice is to mitigate EMI noise elsewhere or add shielding if possible - that's only why I suggested you try the circuit as per LTZ datasheet first.  It _should_ be fine.  You can always add an extra spike filter farther downstream, away from the LTZ directly.

Or just use the "EMI caps" if you find there is no other way for your application if your test setup is just too noisy.  Andreas was using the extra "EMI caps" because he said that's where he got best results for his test setup - your test setup might be different and not require them.

As I just posted on the "shielded chamber" thread, it's handy to have some of these around to test with your Vref (like you see in every good low-noise app note):

https://bascousa.com/1-2-gallon-metal-paint-can.html

Or even standard drawn steel electrical boxes come in handy too.

Aluminum boxes won't do much shielding at low freq H-field.





 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 06, 2018, 07:39:53 pm
Yes, I've built a couple  :-DD 
If I would be evil: I would say "glad to be not your customer". But since I'm not, I have never said that.

Of course there is one strategy to ignore EMI. And live like 30 years ago without high speed internet, cable TV, mobiles, WIFI and do not forget to ban the keyless entry FOB for your car. And also prevent your neighbours from using such "devils things" if you are living in a urban region. So today we have the complete frequency range from about 150kHz to 5GHz.

Insatman, I strongly suggest you look at the Vref circuits in HP (Keysight), et al, Linear Tech

By the way the EMI capacitors are adopted from the DATRON reference cirquit. So no invention from me.
https://doc.xdevs.com/doc/Datron/4910_4911/4910%20Reference%20Assembly%20c20090208%20%5B1%5D.pdf

Of course a metal housing helps against direct radiation. And a tinnned steel housing somewhat against magnetic fields.
(thats why I normally use a double shielded strategy).
But are you really using a transformer with shield between primary and secondary winding
like better instruments (3458A) do with their shield + guard stragegy?
And your paint can does only help if there is no antenna (ground strap or signal strap) looking out of the CAN.

The easiest way to look if you are affected by EMI is to measure the heater voltage on your oscilloscope (with AC-coupling in a sensitive range). If you have randomly (typically negative large (up to several 10mV)) spikes on the heater output besides the normal regulation noise then its time to improve EMI measures. Of course you can also see the spikes on the VREF output, but with much smaller amplitude so you will need a appropriate LNA for the scope.
So it is always good to have a option besides shielding.

with best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on April 06, 2018, 10:05:19 pm
"If I would be evil: I would say "glad to be not your customer". But since I'm not, I have never said that."  Really Andreas?  You know absolutely nothing about his designs and the fact that he sells to demanding industrial customers says a lot about it.  They are not sitting in a comfortable calibration lab, they are in industrial environments, anything but comfortable.  If you were his customer (which you probably couldn't afford) at least you would have a high quality reference in your hands.  Think about that.

I'm curious, why did you think we were talking about you in particular, we made no mention of anybody?
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 06, 2018, 11:04:40 pm
Yes, I've built a couple  :-DD 
If I would be evil: I would say "glad to be not your customer". But since I'm not, I have never said that.

Of course there is one strategy to ignore EMI. And live like 30 years ago without high speed internet, cable TV, mobiles, WIFI and do not forget to ban the keyless entry FOB for your car. And also prevent your neighbours from using such "devils things" if you are living in a urban region. So today we have the complete frequency range from about 150kHz to 5GHz.

Andreas

<Sigh> I never knew this thread would turn unpleasant, and I can't remember why spending time to post seemed to be a good idea.  I have no concern or argument if anyone adds "EMI" caps or not...If it makes you happy, knock yourself out!  I just thought it would be helpful to know why you might want to check first to see if it's really required or not before adding extra parts.  That was my intention, and maybe that wasn't clear enough.

Datron?  Maybe if they had stuck to the datasheet, they might still be around! :) (Kidding)

5GHz?  That's all?? - Andreas, sometimes in on the production line your device will be in a very quiet place, no clocks over 10 or 100kHz allowed.  Other times your device will be sitting next to a 100Ghz- capable test jig with 6 high current servo drives and about 25 various solenoids, pressure regulators, etc. An EMI nightmare, but the standard circuit LTZ's shields are holding against the onslaught (without any extra parts) and the Vref is steady, test data is all good.   And one day the customer will call and complain he's got 1Hz noise on his test data, and they swore it seemed like it was the LTZ.   Do we start adding caps?  No, we first track down the problem...it turns out it's high freq all right, an 80GHz signal being cycled on and off at 1Hz on the test jig running near a measure signal.  The real solution was to re-route one of the measurement cables to the back side of a steel support leg (the tech had taken apart the machine and put the cables back in the wrong position) - end of problem.  Sometimes it's that simple, sometimes not.

If we couldn't have found the problem and the only solution was to alter the LTZ circuit then of course it's a good idea to do whatever needs to be done.  If the customer needs a customized solution and we need to alter the basic LTZ circuit for some reason, then of course we would do that - whatever it takes.  We have to keep the customer happy, because if they aren't - well we don't get paid.  That's a pretty tight feedback loop to let us know how we're doing.

Do we really use screened and shielded transformers?  Yup!  Its a great idea!  We have them made at one of the same facilities that makes transformers for Keysight, and a lot of other high end test equipment... It's amazing what is done on transformers for equipment like a 3458a that is never shown on the schematic.  You're right - we -are- bombarded by EMI more and more every day, and keeping the noise out of the precision systems is very important.

You can do the same "quiet" transformer power supply techniques at home by building your own or looking at "Medical" screened transformers (usually toroid).  These will typically be a single screen but really help reduce capacitive coupling between windings on a toroid.  For hobby use even the low cost Signal transformer standard Split Bobbin E-Frame types are really pretty good at power line noise reduction - they won't have screens but the split bobbin keeps interwinding capacitance pretty low (because the windings aren't on top of each other like on a toroid), and you can add your own steel box cover as needed (or as required).  Really not a bad solution and not too expensive either.

Peace out!



Title: Re: Ultra Precision Reference LTZ1000
Post by: zhtoor on April 06, 2018, 11:48:52 pm
@MrDiodes

Dear Sir,

it has been a privilege to be getting advice from an experienced person like you,
and i don't think that i can thank you enough for that.

i am most grateful and best regards.

-zia
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 07, 2018, 12:20:56 am
...Now I remembered why I posted... Thanks and same to you.

And really - the world is bad enough right now.  EEvblog should be about camaraderie and good, fun discussion - please let's just keep it at that level.

If you disagree with me that's fine, but I'll look forward to common ground another day.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 07, 2018, 12:25:53 am
...and I was hoping someone would get the "common ground" joke [rimshot]

I'll just show myself out now :)

Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on April 07, 2018, 12:47:54 am
...and I was hoping someone would get the "common ground" joke [rimshot]

I'll just show myself out now :)

Where did you bootstrap that 'joke' from?

Here's your coat, I've already got mine... :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on April 07, 2018, 12:55:25 am
If you have any questions about the operation of the LTZ circuit, the best place to go for advice is the engineers at Linear Technology, they will be most happy to answer them, for some reason, that course of action does not seem to be very popular on this forum.

That's probably because the folks here are either amateurs, who don't have a relationship with Linear Technology Analog Devices, therefore probably don't have the first clue how to get in touch with one of their application engineers, or professionals working on hobby projects who feel some reluctance to exploit 'professional' resources for a private project.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on April 07, 2018, 01:17:42 am
This so describes everyone here;

    You Might Be an Engineer if...

    you see a good design and still have to change it.
    you still own a slide rule and you know how to use it.
    your family haven't the foggiest idea what you do at work.
    in college you thought Spring Break was metal fatigue failure.
    you have modified your can-opener to be microprocessor driven.
    you are better with a Karnaugh map than you are with a street map.
    you think "cuddling" is simply an unproductive application of heat exchange
    you have owned a calculator with no equal key and know what RPN stands for.
    you make four sets of drawings (with seven revisions) before making a bird bath.
    you have trouble writing anything unless the paper has horizontal and vertical lines.
    your ideal evening consists of fast-forwarding through the latest sci-fi movie looking for technical inaccuracies.
    you think the value of a book is directly proportionate to the amount of tables, charts and graphs it contains.

Thanks to all who have offered their insight and experience, for one, its helped me out a bunch.  My LTZ1000 project is done and now off to others for testing and comparison.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 07, 2018, 02:33:32 am

And really - the world is bad enough right now.  EEvblog should be about camaraderie and good, fun discussion - please let's just keep it at that level.

If you disagree with me that's fine, but I'll look forward to common ground another day.

Thanks for the advice and I agree with you statement concerning what EEvBlog should be about.   All too often on the internet people have thin skins and good discussion turns into something unproductive.

A step back...My goal in this design is to make a PCB with lots of options, giving me the best chance for an improved LTZ1000 reference.   My present reference does not seem to perform as well as I'd like.  It was built largely to the original published Linear Tech circuit complete with typos.   There are some differences like the 10nF on the scaling op-amp output.   see https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1403374/#msg1403374 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1403374/#msg1403374) for the original post describing my first effort.

My reference will be battery powered using the hardware described in the above referenced post.  Nothing digital is in this box, unless you want to count what I describe next as digital.   The only large noise source is my poor choice of switch mode battery chargers which can be turned off prior to making measurements...although I tend to forget to do so when logging the voltages daily.   These switching based chargers need replacement or modification....they are the largest source of noise in my little E-lab....something to add to my already long list of things to do. 

I do have extensive experience with EMI noise, shielding and suppression.  In my career, I was on a team that designed and built several EMP and lighting generators for a variety of customers, both governments and private industry.   Imagine designing control and instrumentation electronics to be housed on an EMP generator?   

By using the EEvBlog "hive mind" I was trying to get everyone's input on the LTZ1000 circuit.  This way I could design a PCB that would ultimately yield a good design after some experimentation.  In that process, I would learn what works and what does't.  After all, isn't that one of the prime motivations for this hobby...learning?    At this point I think the present PCB design is versatile enough to serve my purpose.

This forum is a valuable source of information and camaraderie for me in my retirement years.  This hobby helps me keep my mind from rotting away and allows me to explore areas of electronics I wasn't able to pursue earlier in life.  An example is the LTZ1000 circuit.   My previously built 3x LM199 voltage reference is more than good enough really for my lab....but...the LTZ1000 is supposed to be better and I want to build one that actually is as good as I can make it.   

 
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on April 07, 2018, 03:07:29 am
I fear this may have simply been a joke which was lost in translation, or a simple difference of opinion with no ill-will attached.  Andreas, MisterDiodes, Edwin, Kleinstein Dr. Frank, TiN, and many others have been dedicated contributors to this forum, with data, designs, feedback, and advice.  I am very grateful to you all.   :clap:
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 07, 2018, 04:32:31 am
Quote from: MisterDiodes
I never knew this thread would turn unpleasant, and I can't remember why spending time to post seemed to be a good idea.  I have no concern or argument if anyone adds "EMI" caps or not...If it makes you happy, knock yourself out!  I just thought it would be helpful to know why you might want to check first to see if it's really required or not before adding extra parts.  That was my intention, and maybe that wasn't clear enough.

Don't let it get under the skin, your input is valued here. Nowadays more people seem to expect everything presented for them on the plate, with theory and instructions and explanations that even 5 year old can read. And when you give just a hint you get bashed for not breaking your NDAs and business agreements, with puzzled faces. After all can't please all, there will be always unhappy fella (too expensive, too difficult, too hard to buy parts, no schematics posted, no test result posted, whatever..) :).

On my refs (KX with chopper amp and SMT parts, FX with traditional 1013 and THT parts) I saw no positive effects of any additional caps (when modified one of the boards, including additional resistors as Dr.Frank was quite convincing). So as result I did not implement them, keeping design simpler, by the books. I saw no spikes or jumps when good LTZ chip used and proper measurement setup, power source and wiring are used. And my homelab is not some EMI-shielded faraday cage, just a standard apartment with LED lights, monitors, desktop confuser w/o case and bunch of other crap turned on.

Using extra caps or other design changes because of Datron or another company used it before, without rationale why should not be a reason for design engineer to do same in own build. Datron refs even have voodoo slots and VPG networks too, but as we already know, plain 3458A ref works just fine without any of that, providing tempco and stability better than majority of the LTZ builds over these 90 pages.

And approach not to generate EMI instead of patching circuits around to suppress it is the industry standard for decades already. Take any RF equipment, and ask a question, why so many expensive custom made shields around everything, especially around active circuits? Heck, even standard consumer stuff like PC VGA cards, motherboards and peripherals, being as low cost as possible, still usually have ground planes on the edge with via stitching and shielded connectors to reduce emitted EM. Otherwise lot of that stuff would not pass certification and might have trouble selling :). 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 07, 2018, 03:38:26 pm
Hello,

@MisterDiodes:
every time I recommend the EMI-capacitors you shoot agaist them.
Telling the fairy-tale that they will do harm to the poor LTZ (like choppers et al).
Creating unnecessary FUD for the new-comers.
As a professional I wouldn´d do that with any official prove. (which is still missing).
If it should have been a joke then it is hard to understand for a non native speaker.

@TIN:
If you have no problems in your environment then of course you are free not to implement any measures.
Perhaps the multi-layer design implements some parasitic (small) capacitors
which are sufficient for your environment. (would be worth to examine).

Others here in the forum (also in the KX thread) have problems
"with some small unexplained glitches"
https://www.eevblog.com/forum/metrology/kx-reference/msg1213344/#msg1213344 (https://www.eevblog.com/forum/metrology/kx-reference/msg1213344/#msg1213344)
which could be either a problem of the meter or the reference.

Others have "impact at the end comes from touching" [the DMM]
https://www.eevblog.com/forum/metrology/kx-reference/msg1298271/#msg1298271 (https://www.eevblog.com/forum/metrology/kx-reference/msg1298271/#msg1298271)
Which is also still unclear.

Does it really help those members telling they should do "better shielding" (how?)
Ups forgot to mention they need a special transformer too...

Better shielding + transformer are several 10$.
EMI-capacitors are some cents.

just my 2ct

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 07, 2018, 04:14:50 pm
I don't use special transformers, but the battery power for critical measurements.
If anyone have problems with my design, I'd like to see feedback from those people, otherwise it's just a guesswork.
Using DMM as the measure of reference (is it reference? to me even those people you linked are not so sure ;) ) spikes is somewhat far-fetched.

Same would be saying ref have a problem when observing shift few ppm by connecting noisy DMM like F8846A.  :=\
Film SMT capacitors are not some cents, but that is (together with 10$ for shielding) IMO irrelevant, as it is not commercial product, but a learning tool.
Also in your design it is not just two capacitors, but other modifications required as well, to make it all working properly.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 07, 2018, 05:53:18 pm
Andreas:

It's OK if you don't understand the structure of a crystal lattice and aging effects, and some of the factors that might make that worse - or better.  That's well beyond the scope of what I can show you here.  I'll give you a hint below though.

From my experience after building hundreds of LTZ's, we've never needed to alter the basic LTZ circuit.  Ever.  Yes we've added shielding and Yes on the test bench we take pains to keep everything as quiet as possible.  For units going into the field they include more ruggedized shielding techniques and that works in every situation we've encountered.  Like how it works on 3458a. The reason we can't always add CPU's to the circuit for DAC controls is we're in a situation where WE can't be the ones making noise, and that's why sometimes pure analog is the way to go.  Sometimes an assist with a CPU / FPGA is a good way.  It just depends on application.

If you had to alter the circuit for your use, that's one thing - but I know from experience that doesn't apply everywhere.  It doesn't apply to 3458a, it doesn't seem to apply to TiN's circuits, it doesn't apply to our circuits, LT/AD doesn't need or recommend they be used, etc.  Now of course there might be -some- effect on YOUR board or test setup where the altered circuit got better results - but that doesn't mean it applies in -every- case, does it?  If someone is having trouble, and adding the caps helps - then Yay!.  But I suspect the problem really might lie elsewhere.

I would invite you to look at a new Re-Spin of an LTZ application, now that AD owns the Company - Look at the LTZ circuit here, and in this case you want a low noise Vref to show off the 20 bit AD5791 DAC they're selling - see page 20:

http://www.analog.com/media/en/technical-documentation/user-guides/eval-ad5791sdz-ug-1152.pdf (http://www.analog.com/media/en/technical-documentation/user-guides/eval-ad5791sdz-ug-1152.pdf)

After a chat with AD, I'm told there are some typos that will be corrected on the next doc release...But the note on C44 refers to C13 C12, The note about R30 should be R48, and the note re: U3, U4 should refer to U1, U2.

The deviation from the LTZ1000 datasheet is they use SMT parts (board picks up vibration and stress changes), the '1013 is swapped for an AD4077-2 (Basically newer gen precision OP07) because AD wanted to showcase some of their own brand.  The AD4077 current driver likes an extra cap compensation, and the usual 22nF cap has been upped to 100nf - otherwise the circuit topology is just really a basic LTZ.

Notice the RC between the LTZ and the 10V boost.  That a good place to remove a little noise and isolate the LTZ from any downstream activity / current noise.

Notice the 15k over 1k heater resistor ratio.  They went with this "Hotter" ratio because on an bare naked board they liked the warmer run temp of the LTZ - it would resist casual air drafts better.  This may cause slightly lower long term drift but that is not the goal here.

Something else to notice is the standard resistors used for 10V boost:  Because this circuit is feeding a DAC you'd like to have a little OVER +-10V cardinal output on this Vref, which means as designed you want the LTZ with a minimum 7.14VDC using the 25k/10k boost ratio.  Since AD owns LTZ part, they can pick and choose the LTZ demo chips to make sure the LTZ demo board  reference output has enough headroom to let the output of the '5791 output run to +-10VDC full scale (The AD guy was pretty sure on this when I pointed that out, but he is going to check).

Andreas (BIG CLUE):  After 36 years of LT / AD manufacturing LTZ chips and getting customer feedback, please take a look at that schematic topology and let me know how many low impedance caps you see straddling any single PN junction on the LTZ?.  How many chopper amps are used?  What could be the reason for that "Fairy Tale" ??

Now back to a real test:  I haven't tested this board on my bench, but my colleague tried one of these new LTZ ref boards on his '5791 demo, and wanted to double check these test results - and he does have access to a .1 to 10Hz LNA (Jim Williams Wet Tant style):

http://www.analog.com/en/analog-dialogue/articles/high-precision-voltage-source.html (http://www.analog.com/en/analog-dialogue/articles/high-precision-voltage-source.html)

So I emailed him last night to see how the results went.  In general his comments were positive.  Testing the noise at the output of the LTZ was typical <<1.2uV p-p, and the '5791 output was fairly close to the published test report IF you pay attention:

A) Gotta add the goofy little afterthought foam LTZ draft cover in the kit. Looks like you're on your own for covering the bottom side (AD says they are changing that on next rev).

B) He couldn't do it with the USB cable from a laptop to the demo controller card - he used an isolated cable from a desktop PC box  located on the floor a little farther away.  The output of the DAC got cleaner when you unplug the digital controller cable, as expected.

C) The Keithley switcher power supply added a little more noise to the output (not a total disaster), but switching to batts or Protek 303 linear (transformer) supply worked fine.

D) This circuit didn't like the soldering iron cycling on and off on the same outlet strip, nor did it like the LED desk lamp.

E) BUT: Putting the circuit and LNA amp in a leftover Xmas Cookie tin got very good results, and after that the desk lamp was fine.

F) If he set the board on a soft foam bleacher pad, the board quit reacting to every mechanical noise on the test bench (Noise pickup from SMT caps).  Without the pad, if he flipped a switch or tapped a pencil on the bench, that would show up on the output.

G) He saw more noise on the '5791 output at full scale - he was getting more like 4 or 5uV (or 7uV on occasion) peak.  The datasheet DAC spec's 1.1uV added noise but that's at mid-scale, at 90%+ full scale you'll see more noise.

EDIT:  He noticed that if you averaged the peaks from several 10 sec periods the peak noise could be called ~4uV peak.  So he was able to get in the same ballpark as published results.

I realize that not everyone has access to LT / AD apps engineering.  I realize people like to play.

Again:  My only suggestion is - If you're finding that adding caps helps your circuit, you might sniff around a bit to find out what the true cause of the problem might be.

The standard circuit topology -should- work fine, and I suggest if you're having trouble with a modified circuit:  Try stripping it back to the standard circuit and that might help you troubleshoot where the real problem is.  You might find that correcting a thermal / noise issue will work as well or better as adding extra caps - and that in turn might give your LTZ the very best chance at aging gracefully.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 07, 2018, 09:22:22 pm
One other suggestion while you play with Vrefs, and a head's up if you're just starting out:

Sometimes there's an "uncertainty principle" involved in measuring the LTZ (or any precision Vref) circuit nodes proper while the circuit is running:  If you probe the circuit nodes with a meter or scope, that can change the thermal balance of the LTZ enough that you're suddenly looking at a different LTZ circuit operating point when the probe is in the circuit.  Especially probing the traces anywhere near the LTZ can suck enough heat out - or add enough capacitance - that suddenly your LTZ will show a shifted Vref output, or sometimes add a bit of oscillation.  The LTZ gets cooler, then adds more heat, then your probe heats up a little and suddenly less heater power needed, etc.  That can show up on the output as a wobble.  Sometimes it's fine; you'll see the Vref output glitch and then re-stabilize a short time after the probe goes in or out of circuit.

Even if you attach a measuring access wire or trace to a circuit node (and even a very fine wire) or try to get a measure from a component lead -  that becomes part of the thermal balance, and that may or may not have an effect.  Lower mass probes can work better here, or sometimes a longer stainless steel probe needle will help (less heat flow), and try to keep your warm paws away from the circuit as much as possible!

So it's a good idea to keep an eye on your Vref absolute value if you're trying to read for example the Vbe of the heater sense transistor.   Try to grab your "hot" measures in a way where the Vref output doesn't change (much) during the measure, with your probe in or out of circuit.

Otherwise you might be chasing a "phantom" signal.


Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 08, 2018, 10:25:01 am
Hello Voltnuts,
                      I have attached schematics of the EV-LTZ1000-REFZ carrier board as well HiRes photo of the actual board and R48 can be found here: http://www.vishaypg.com/docs/63109/vfcd1505.pdf (http://www.vishaypg.com/docs/63109/vfcd1505.pdf)

Best regards
Fred Flinstone


Hmmmm....why the 1N270 Diode is being used in this board rather than the 1n4148 used before.   Data sheet attached.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zhtoor on April 08, 2018, 11:48:01 am
Hello Voltnuts,
                      I have attached schematics of the EV-LTZ1000-REFZ carrier board as well HiRes photo of the actual board and R48 can be found here: http://www.vishaypg.com/docs/63109/vfcd1505.pdf (http://www.vishaypg.com/docs/63109/vfcd1505.pdf)

Best regards
Fred Flinstone

Hmmmm....why the 1N270 Diode is being used in this board rather than the 1n4148 used before.   Data sheet attached.

interesting... maybe MisterDiodes can explain this. (lower Vf maybe Ge vs Si)

-zia
Title: DRe: Ultra Precision Reference LTZ1000
Post by: martinr33 on April 08, 2018, 12:02:46 pm
The small SMT 0.1 uf capacitors on the board look like X7R material, because they appear brown. These devices are microphonic - x7r has piezoelectric properties.

Replacing them with C0G parts would likely eliminate the mechanical sensitivity.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on April 08, 2018, 01:48:59 pm
Hmmmm....why the 1N270 Diode is being used in this board rather than the 1n4148 used before.   Data sheet attached.

One immediate thought is that these evaluation boards tend to be used lying around in the open on the bench. The 1N4148 has a clear glass case, the 1N270 is opaque. One hopes the implication of this is obvious in present company.

Beyond that I'm not sure that there's anything in it - the two places a diode is used are both the kind of place where almost any old signal diode will do. Ge Vf tempco is about -2.5mV/°K versus Si's of -2.1mV/°K, so nothing helpful going on there. Vf is lower, but it's not as if this circuit is scrabbling to find the odd 0.3V. Junction capacitance is much the same.

In fact, unless I've missed something, the 1N4148 and 1N270 are about as similar as it's possible to get while using a different semiconductor material except one's black and one's clear.
Title: Re: DRe: Ultra Precision Reference LTZ1000
Post by: Cerebus on April 08, 2018, 01:52:55 pm
The small SMT 0.1 uf capacitors on the board look like X7R material, because they appear brown. These devices are microphonic - x7r has piezoelectric properties.

Replacing them with C0G parts would likely eliminate the mechanical sensitivity.

In point of fact they have X8R dielectrics, the TDK part number (C1608X8R1E104K) is called out in the eval. board documentation.
Title: Re: Ultra Precision Reference LTZ1000
Post by: zhtoor on April 08, 2018, 01:54:54 pm
Hmmmm....why the 1N270 Diode is being used in this board rather than the 1n4148 used before.   Data sheet attached.

One immediate thought is that these evaluation boards tend to be used lying around in the open on the bench. The 1N4148 has a clear glass case, the 1N270 is opaque. One hopes the implication of this is obvious in present company.

Beyond that I'm not sure that there's anything in it - the two places a diode is used are both the kind of place where almost any old signal diode will do. Ge Vf tempco is about -2.5mV/°K versus Si's of -2.1mV/°K, so nothing helpful going on there. Vf is lower, but it's not as if this circuit is scrabbling to find the odd 0.3V. Junction capacitance is much the same.

In fact, unless I've missed something, the 1N4148 and 1N270 are about as similar as it's possible to get while using a different semiconductor material except one's black and one's clear.

no 1n4148 opaque equivalent in silicon? why germanium? gold-bonded at that (supposedly lower noise)

-zia
Title: Re: Ultra Precision Reference LTZ1000
Post by: blackdog on April 08, 2018, 02:24:34 pm
Hi,


I cant see why there is a 1N270 and not a 1N4148, the diode is in the feedbackloop, so normaly you can forget about the properties of this diode.
But.. i'am never to old to learn  :-DD

Kind regards,
Bram
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on April 08, 2018, 04:35:39 pm
Here's a link to an article on piezoelectric effects in MLCC devices.

http://www.kemet.com/Lists/TechnicalArticles/Attachments/88/2006%2007%20ArrowAsiaTimes%20-%20MLC%20Noise.pdf (http://www.kemet.com/Lists/TechnicalArticles/Attachments/88/2006%2007%20ArrowAsiaTimes%20-%20MLC%20Noise.pdf)

x8R is a nice dielectric, but  does make the design vibration and shock sensitive. Replacing those caps with C0G devices will help with the mechanical sensitivity.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 08, 2018, 06:47:21 pm
I posted that schematic of the AD5791 just as an example of how the standard LTZ1000 topology works for noise - the point being is that even a fairly casual, less than perfect design should easily get you in the ballpark of <1.2uV noise, even on a bare board.  This is not the best design if you're going for low long term drift on higher precision system, and that was not the goal of the demo board.  This is designed just as a quiet, stable-enough-for-a-demo voltage source that can demonstrate low noise in the few uV range even after boosting to ~10V.

By the way that demo board LTZ Vref was a cut & paste from another piece of in-house gear at LT/AD where they needed a low noise source, my rep says, and that is Rev 0.  He says that they have another rev drawing coming up from the docs department.  I suspect some of the parts on the BOM are there because there aren't critical and are what they had in stock (see below about diodes).

If you were to buy a Vref from me, all critical parts in the analog section would be Thru hole, because vibration noise is a P.I.T.A. and where our modules go they have to be vibration-resistant.  If you need very low TC we might talk about a chopper amp for the VBoost section (after the RC to isolate the LTZ from chopper noise), and we'd use PWW resistors when required.  If the customer has other needs then we go from there.

We would also consider air draft shields very important around the LTZ and we also especially look at the traces and component leads around Pin 6 on the LTZ.  Since whatever you connect to Pin 6 is also part of the very sensitive thermal balance on the Temp sense transistor.  All the pins on the LTZ are critical, but Pin 6 can cause a fair amount of trouble.  If you suck heat out of that base junction, you're un-intentionally changing Vbe, and well...you kiss heat stability goodbye.   The other pins are sensitive too.

When the LTZ tells you to shield the LTZ from air drafts, by extension that also means the traces and leads directly connected TO the LTZ might be causing trouble if they see air drafts. 

Like I keep saying: LTZ is a Power In / Power Out device.  Get the power flow stable and a stable Vref is the by-product.  That means all the thermal circuits have to be stable.  Generally we won't ever run an LTZ on a bare board except for burn in or initial testing...when it's going to work it is always in a shielded enclosure.  At least that's how we -always- use them.

The ADA4077-2 amp is just a newer gen OP-07 (and closest thing AD had to an LT1013, for the sales dept.).  Even that is not the most perfect amp to use since it is not spec'd for low current noise at 10Hz.  The LT1013 is spec'd for low current AND low voltage noise @ <10Hz, AND comes in a DIP.  The LT1013 IS -the- amp to use with the LTZ because it was designed with that exact LTZ application in mind.  There has never been any true upgrade for it.

The diode is not super critical.  It is only there to ensure that the LT1013 (or other amp) would start the current loop.  On the newer process LT1013's often you don't even need the diode because they can make sure the Voffset is slightly shifted.  Sometimes you can run an LTZ without the diode at all and there's enough Voffset when the amp powers on that the current loop starts and settles in a stable condition.  Without the diode you run the risk of the current loop starting in its second stable condition, where current = 0 for this circuit - which is a perfectly valid operating point also. 

In fact if you go back to very early prototype 3458a's, I think there are might be a few of those Vrefs around without the diode - but LT learned pretty early on what can happen if a 3458a powers up with a Vref sitting at 0 volts.  Oops.

SO:  You need that diode to guarantee startup across all temperatures, and that's about it.  I don't think diodes optics plays a huge role but that would be something to look at.  Once the LTZ Vref goes into an enclosure that should NOT be an issue at all.

The diode on the heater line is just a safety prevent reverse bias on the substrate.  It is not critical in operation, but it should always be there during power supply power up / down.

Remember the LTZ circuit needs a quiet CURRENT driver for its Zener, and the Voffset of the loop is not too important.  The gain of the transistor and Zener is so large and overwhelms any small Voffset drift in the current loop amp - it doesn't really have a huge effect on the final Vref output.  It's more important to keep current noise very low.

That's why LTZ's never need or want a chopper amp in the current loop, and that's why LT/AD doesn't recommend using chopper amps there, even though they would be more than happy to sell you a million or two choppers.



Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on April 08, 2018, 07:17:45 pm
I found the LTZ1000A was many times more sensitize to air currents around the pins, top and bottom than air over or around the can.  My best results where with the chip just above the board and with the leads shielded from air currents, but with the can exposed.

(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/5DC85501-1846-4BC1-ADB4-92E4A7F09E6B.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/5DC85501-1846-4BC1-ADB4-92E4A7F09E6B.jpg.html)

(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/AED09ACB-83C7-49BA-B620-A4C8C7EA1A10.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/AED09ACB-83C7-49BA-B620-A4C8C7EA1A10.jpg.html)

(http://i241.photobucket.com/albums/ff146/wsmc551/Elecronics/6EE25DF3-145D-454B-8D62-1E7F63FA7480.jpg) (http://s241.photobucket.com/user/wsmc551/media/Elecronics/6EE25DF3-145D-454B-8D62-1E7F63FA7480.jpg.html)

As an unintended benefit, the PCB traces are also protected from air currents near the chip.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ArthurDent on April 08, 2018, 08:06:24 pm
There is a reason that the 1N270 (and other Ge) diodes are painted black. Years ago I followed the instructions of an article that described removing the black paint from a common Ge diode and using it for a photo sensor in a flash meter for photography. The diode with the paint removed was placed under a frosted plastic dome removed from an old neon panel lamp. When the flash went off the diode (which formed half of a voltage divider) conducted proportional to the intensity of the flash and then a regular diode connected the voltage to a capacitor used as a sample-and-hold circuit with an IGFET to display the voltage on an analog meter with the scale calibrated in aperture values.

As far as using Ge vs Si diodes within a feedback loop, the Ge would have lower voltage drop but I’m not sure if that is the reason or how it would matter.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 08, 2018, 08:51:17 pm
The voltage drop of the diode in the current loop really makes no difference. The current driver amp will always drive it's output to bring its input pins into balance - so a silicon or germanium diode doesn't really matter.  You just need to create a voltage drop in the loop to guarantee the current amp will start the loop flowing in the correct direction at power up.

The need for LTZ air draft protection is clearly shown on the datasheet, in fact there are couple sample output noise plots showing the difference between no air draft shield vs air draft shield.  This has always been a key requirement of the LTZ since Day One.  Typically you cap the top and bottom but protecting the pins is most important.  If you OVER insulate the LTZ system that can create problems as well, since the heater is depending on heat flow -out- of the chip to maintain regulation.  The heater can only add heat - the system depends on at least a little heat flow out of of the device pins to maintain regulation if it gets too warm.  Normally you want that to not happen, and normally it stays in good control.  That's why you always pick your heater ratio resistors to run the chip at a comfortable temperature margin over ambient.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 08, 2018, 09:28:13 pm
..On some of the 3458a's there was also a high value resistor from V+ going to the Vref line - and that was an additional startup aid to trickle a little current into the current loop before the current amp really started.  According to LT that shouldn't be needed on newer process LT1013's - but often nobody wants to change a working LTZ circuit so that resistor is still included. The regular datasheet circuit doesn't show it these days, the older sheets did have that.

I remembered something else:  With that ADA4077 there may be a "sweet spot" where if if its operating output is raised a certain offset from the rails that made for a bit lower output noise.  The ADA4077 also needs an extra comp cap on the output.

At one time that was another reason for the 1N4148 on the LT1013 - it raised the normal amp output drive level  to a "sweet spot" where you see a bit lower noise on the amp output.  LT says you probably don't need it but they suggest using a regular Si diode in that location to cover all bases for best performance. OK!
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 09, 2018, 04:10:06 am
Perhaps attached chart might be interesting to some in this thread.
After some greedy bidding on recent Wavetek 7000 bits and pieces I got myself one 7000 cell (based on LTZ1000CH and TaN statistical resistor network to provide 10V) and 7000S switch modules.

My friend Todd hooked it up to K2400 to power with +12V, and we get next log, showing conditioning procedure over the 10V output:

(https://xdevs.com/doc/Wavetek/7000/test/w7000_10v_cold_1.png) (https://xdevs.com/doc/Wavetek/7000/test/w7000_10v_cold.png)

Now it settled to about -8 ppm.

(https://xdevs.com/doc/Wavetek/7000/test/w7000_10v_cold_zoom.png).

Peak-to-peak wobble is about 1ppm, which is a LOT for LTZ1000-based ref. Maybe this was the reason why Fluke killed 7000 series ref?  :-//

Cover unit with the blanket...

(https://xdevs.com/doc/Wavetek/7000/test/w7000_10v_cold_covered.png)

Aha :) Another reminder to air drafts not allowed when talking <ppm noise resolution.  :-BROKE

Article and reverse engineering of the module is planned for future projects.
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on April 09, 2018, 08:05:31 am
Quote
Article and reverse engineering of the module is planned for future projects.
Wow! This will be a hit!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on April 09, 2018, 10:05:56 am
You never fail to amaze TiN.  :) But im more interested in the used DCDC-converter which boasts with very high isolation, than the hysteresis-elimination technique used.

Wavetek 7000 DC reference testing from eBay at MM lab: https://www.youtube.com/watch?v=WNEbZkN77Go (https://www.youtube.com/watch?v=WNEbZkN77Go)

Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on April 09, 2018, 05:12:21 pm
Perhaps attached chart might be interesting to some in this thread.
After some greedy bidding on recent Wavetek 7000 bits and pieces I got myself one 7000 cell (based on LTZ1000CH and TaN statistical resistor network to provide 10V) and 7000S switch modules.

Oh, goody. I'll be very interested to see how these settle out across several cycles of the conditioning process. That is, I'm interested in how close the end values of several conditioning procedures are to each other.

Can I please suggest that this gets its own thread/topic rather than being tacked on as a subsidiary to this, already overlong, thread.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 11, 2018, 10:54:08 am
Is it just me, or Analog devices does not allow to buy LTZ1000 from website anymore? Once I click "Purchase" it redirects me to ecommerce cart site, but does not add anything into cart.
I tried both ACH and CH, still same. If add other parts, like opamp - no problem.  :palm: :scared:
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on April 11, 2018, 11:09:26 am
Is it just me, or Analog devices does not allow to buy LTZ1000 from website anymore? Once I click "Purchase" it redirects me to ecommerce cart site, but does not add anything into cart.
I tried both ACH and CH, still same. If add other parts, like opamp - no problem.  :palm: :scared:

Possibly a glitch in the transition to the Analog Devices website? If I were you I'd drop them a line and ask.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on April 11, 2018, 10:38:12 pm
Is it just me, or Analog devices does not allow to buy LTZ1000 from website anymore? Once I click "Purchase" it redirects me to ecommerce cart site, but does not add anything into cart.
I tried both ACH and CH, still same. If add other parts, like opamp - no problem.  :palm: :scared:

I tried and get the same, actually no I get worse - if I choose any sample, like LM399A which I gladly sample for free, I am given the red carpet treatment... https://shoppingcart.analog.com/ and my old Linear email and password works fine.

The same LM399 and I click Purchase (or indeed the LTZ1000 which has never been available for sample so I can only click Purchase)... it takes me to https://checkout.na3.netsuite.com/app/center/nlvisitor.nl/... and requires a login. I've tried both my old AD and Linear logins with no joy. The email password reset isn't working either.  :(

So my advice is to load up with all the AD and LT samples for free while they sort it out...  ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: eurofox on April 12, 2018, 03:29:35 am
Is it just me, or Analog devices does not allow to buy LTZ1000 from website anymore? Once I click "Purchase" it redirects me to ecommerce cart site, but does not add anything into cart.
I tried both ACH and CH, still same. If add other parts, like opamp - no problem.  :palm: :scared:

I tried and get the same, actually no I get worse - if I choose any sample, like LM399A which I gladly sample for free, I am given the red carpet treatment... https://shoppingcart.analog.com/ and my old Linear email and password works fine.

The same LM399 and I click Purchase (or indeed the LTZ1000 which has never been available for sample so I can only click Purchase)... it takes me to https://checkout.na3.netsuite.com/app/center/nlvisitor.nl/... and requires a login. I've tried both my old AD and Linear logins with no joy. The email password reset isn't working either.  :(

So my advice is to load up with all the AD and LT samples for free while they sort it out...  ;)

You guy's must be on a black list because I can buy without problem, I just try it!

 :-DD :-DD :-DD :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: SvanGool on April 12, 2018, 08:59:33 am
None of my linear or AD accounts worked either. But if you register new and just add the item to your purchase order, you can purchase. The only thing I had is that minimum UPS shipping cost for two LZ1000ACH to The Netherlands (Europe) is USD 54, which diverted me back to Digikey  :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 12, 2018, 10:23:04 am
Purchase button still broken, even with new account. But if I use "Enter the Order" and then manually type in LTZ into order list - it finds chips and seems like I can add into ordering system.
Ugh...  :rant:
Title: Re: Ultra Precision Reference LTZ1000
Post by: pitagoras on April 13, 2018, 01:43:33 am
Looks like some random page migration strategy is taking place.  :--

Here: http://www.analog.com/en/products/analog-functions/voltage-references/shunt-voltage-references/ltz1000.html#product-samplebuy (http://www.analog.com/en/products/analog-functions/voltage-references/shunt-voltage-references/ltz1000.html#product-samplebuy)
I only see options to buy >=100.
Clicking purchase, though, I get redirected to some http://shopping.na3.netsuite.com/ (http://shopping.na3.netsuite.com/) page where one can add one by one going to "continue shopping".
ACH appears as backorder and CH as available (image attached).
I didn't have Analog account and my linear account got migrated (they sent me an email). When they migrated the account I observed what TiN says: purchase getting redirected to some list of distributors (I don't remember the details, weeks ago).

If they only were prone to hire at least one software guy  :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 17, 2018, 02:11:43 am
Attached is a chart showing my present LTZ1000 voltage over time compared to three other references.   It has the worst temperature dependence...yet it should be superior.  The unit is housed in a cast aluminum box lined with foam.  The LTZ1000 is also enclosed in a small hollow Styrofoam block on the PCB.   Schematic is attached.   
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on April 17, 2018, 03:08:53 am
Several things may contribute to this performance.

The OPA177 is not a rail to rail op amp. The data sheet indicates some level of performance at 1V above the negative rail. Based on my previous measurements the input voltage to U3 will be 0.4 to 0.5V. The input voltage of U1 will be around 0.6V. These voltages seem to low for reliable performance from this otherwise fine op amp. A single opamp similar to the LT1013 will work fine here. I don't have a model number for you off hand.

The R5 resistor is listed at 12k. That seems to low of a value to me for a LTZ1000A. It may work with a LTZ1000 non A in a cool environment. You may be running out of heater authority during warm ambient conditions.

The R8 392k Temp Co resistor usually has to be selected based on the particular circuit layout and other magic. Have you had an opportunity to optimize this value?

Hope this helps.

update
P.S. With a 0.6ppm / deg C, the temp co tracking of R11 and R12 in the output amplifier also may be an issue. Monitoring the heater voltage and the raw 7v zener voltage could help isolate the real issue.

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 17, 2018, 04:10:04 am
OOM heater would render in much higher TC result, but yes, 12K/1K is bad idea for typical conditions.
Using trimmer in critical TC path is big no-no. Output buffer 7V-10V section is way more critical for matched resistors than LTZ ref itself.
Return currents can be also cause issues. Without seeing the board or accurate data result it is not possible to tell better.

Quote from: chuckb
selected based on the particular circuit layout and other magic.
:-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 17, 2018, 07:08:26 am
Several things may contribute to this performance.

The OPA177 is not a rail to rail op amp. The data sheet indicates some level of performance at 1V above the negative rail. Based on my previous measurements the input voltage to U3 will be 0.4 to 0.5V. The input voltage of U1 will be around 0.6V. These voltages seem to low for reliable performance from this otherwise fine op amp. A single opamp similar to the LT1013 will work fine here. I don't have a model number for you off hand.

The R5 resistor is listed at 12k. That seems to low of a value to me for a LTZ1000A. It may work with a LTZ1000 non A in a cool environment. You may be running out of heater authority during warm ambient conditions.

The R8 392k Temp Co resistor usually has to be selected based on the particular circuit layout and other magic. Have you had an opportunity to optimize this value?

Hope this helps.

update
P.S. With a 0.6ppm / deg C, the temp co tracking of R11 and R12 in the output amplifier also may be an issue. Monitoring the heater voltage and the raw 7v zener voltage could help isolate the real issue.

I already have plans to replace the OPA177 with the LT1013 for the two op-amps servicing the LTZ1000 directly.  I will use the OPA177 just for the output scaling.   I have a 13K resistor on order to replace the 12K resistor on my next LTZ1000 build.   Is there any guide on what value of resistor value gives what heater temperature?

I recognize that my resistors used on the scaling op-amp are likely a problem, but honestly I have a hard time acquiring decent resistors here in Philippines.  Ebay and Digikey are basically my only sources.   Finding three terminal resistor on Ebay with the correct ratio has been an exercise in frustration.

As for the 392K resistor, this is the closest value to the 400K resistor recommended in the LT datasheet for the LTZ1000.   Any guidance as to how to optimize this resistor is appreciated.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 17, 2018, 10:18:10 am
Did you talk to Edwin here on forums to get proper resistors. Using expensive VPG does not give you any measurable benefit in correctly designed and built LTZ ref.

Also you asking questions that were explained and tested many times even in this very thread, leave alone threads about my reference design. I know typing a question is much easier than taking time to read all the pages here, but you will get much clearer picture in the result.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 17, 2018, 11:00:43 am
Did you talk to Edwin here on forums to get proper resistors. Using expensive VPG does not give you any measurable benefit in correctly designed and built LTZ ref.

Also you asking questions that were explained and tested many times even in this very thread, leave alone threads about my reference design. I know typing a question is much easier than taking time to read all the pages here, but you will get much clearer picture in the result.

VPG?

I'll go read more of this very long thread.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on April 17, 2018, 12:19:27 pm
VPG = Vishay Precision Group = Bulk Metal Foil Resistors
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on April 17, 2018, 01:19:57 pm
The 400K TC resistor value is just a starting point.  You have to perform your own tests in order to determine the correct value to achieve the 0.05ppm/K or minimum TC drift.  In one case I needed to use 300K resistor and another a 680K.  I was able to do better than 0.05ppm/K with multiple builds, but it took considerable time and testing to get there.

Some of my testing here;
https://www.eevblog.com/forum/metrology/kx-reference/msg1369941/#msg1369941 (https://www.eevblog.com/forum/metrology/kx-reference/msg1369941/#msg1369941)

Also check this thread for information on sources for LTZ1000(a) resistors;
https://www.eevblog.com/forum/metrology/resistor-set-for-ltz1000-positive-standard-7v-circuit/ (https://www.eevblog.com/forum/metrology/resistor-set-for-ltz1000-positive-standard-7v-circuit/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: MisterDiodes on April 17, 2018, 04:20:07 pm
Insatman:  As others have noted, an LT1013 will do everything you want it to do for a LTZ amp.  You don't really need expensive resistors around the LTZ, since the LTZ is more forgiving to resistor drift than something like a 7V-10V boost circuit - You just want decent resistors, and the heater ratio pair is most important. PWW are perfectly fine and the preferred choice, and Edwin will give you a deal on an LTZ set, too.

Yes, do some reading, but for sure read page 5 of the LTZ1000 datasheet regarding the difference between the A and Non A version:

The LTZ1000A should be set about 10°C higher than the LTZ1000. This is because normal operating power dissipation in the LTZ1000A causes a temperature rise of about 10°C.

Your heater ratio of 12k over 1k is really pretty low, even if you were using Non-A.  You always want the HEATER circuit to control the die temp, NOT the ZENER.  We always use a range of 13k to 15k over 1k for our needs with LTZ1000A, I know some here use 12.5k / 1k.  The cooler you get on your heater ratio means you have to keep a cooler ambient on your LTZ - and if that heater goes out of regulation (or if the Zener starts controlling die temp) you will have a guaranteed crappy Vref.

Also with the A version you normally don't need the 400k (or whatever value you empirically test).  If you think you must use that, I suggest you get the circuit running within spec FIRST, and then only add that extra resistor as required - and after you learn how the circuit works.  As the circuit ages you might find that resistor isn't helping LTZ1000a TC as much 5 or 10 years from now - and that's why LT recommends against it for A version.  It's your party though, do what you need to for your goal.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 18, 2018, 02:10:02 am
The 400K TC resistor value is just a starting point.  You have to perform your own tests in order to determine the correct value to achieve the 0.05ppm/K or minimum TC drift.  In one case I needed to use 300K resistor and another a 680K.  I was able to do better than 0.05ppm/K with multiple builds, but it took considerable time and testing to get there.

Some of my testing here;
https://www.eevblog.com/forum/metrology/kx-reference/msg1369941/#msg1369941 (https://www.eevblog.com/forum/metrology/kx-reference/msg1369941/#msg1369941)

Also check this thread for information on sources for LTZ1000(a) resistors;
https://www.eevblog.com/forum/metrology/resistor-set-for-ltz1000-positive-standard-7v-circuit/ (https://www.eevblog.com/forum/metrology/resistor-set-for-ltz1000-positive-standard-7v-circuit/)

thankyou so much for the references.  Saved me hours of trying to get through over 1000 posts on this thread
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 18, 2018, 02:15:05 am
Insatman:  As others have noted, an LT1013 will do everything you want it to do for a LTZ amp.  You don't really need expensive resistors around the LTZ, since the LTZ is more forgiving to resistor drift than something like a 7V-10V boost circuit - You just want decent resistors, and the heater ratio pair is most important. PWW are perfectly fine and the preferred choice, and Edwin will give you a deal on an LTZ set, too.

Yes, do some reading, but for sure read page 5 of the LTZ1000 datasheet regarding the difference between the A and Non A version:

The LTZ1000A should be set about 10°C higher than the LTZ1000. This is because normal operating power dissipation in the LTZ1000A causes a temperature rise of about 10°C.

Your heater ratio of 12k over 1k is really pretty low, even if you were using Non-A.  You always want the HEATER circuit to control the die temp, NOT the ZENER.  We always use a range of 13k to 15k over 1k for our needs with LTZ1000A, I know some here use 12.5k / 1k.  The cooler you get on your heater ratio means you have to keep a cooler ambient on your LTZ - and if that heater goes out of regulation (or if the Zener starts controlling die temp) you will have a guaranteed crappy Vref.

Also with the A version you normally don't need the 400k (or whatever value you empirically test).  If you think you must use that, I suggest you get the circuit running within spec FIRST, and then only add that extra resistor as required - and after you learn how the circuit works.  As the circuit ages you might find that resistor isn't helping LTZ1000a TC as much 5 or 10 years from now - and that's why LT recommends against it for A version.  It's your party though, do what you need to for your goal.

Thanks for the guidance on the ratio resistors.  Originally I used 12K because it was available and I could not find a 13K at that time.  I have a 13K resistor on order for weeks now...still waiting.  I suspected that cheaper resistors would work in some places and I do realize that the scaling stage is the most important.   I think my current problem is the op-amp used for the LTZ and have a plan to switch to the LT1013 for that service.   I will be building two boards up when all the parts and PCBs arrive.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on April 18, 2018, 02:40:51 am
I had really good results using a Vishay VHD200 resistor divider network in my 7 to 10v buffer, but it took 6 months to get it and it was not cheap  :scared:

More info on the buffer here;
https://www.eevblog.com/forum/metrology/ltz1000-10v-buffer/ (https://www.eevblog.com/forum/metrology/ltz1000-10v-buffer/)

I found the temp set divider resistors to be somewhat more critical than the 120 ohm resistor, so I would still use the lowest TC parts you can get here.  In mine, I used 13K/1K, as others have mentioned beware of using anything lower than 13:1 to retain thermal stability.  Also, send Edwin Pettis a note and get a complete set of his PWW parts:  https://www.eevblog.com/forum/profile/?u=96921 (https://www.eevblog.com/forum/profile/?u=96921)  His prices are extremely reasonable compared to Vishay and you wont have to wait forever.

Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on April 18, 2018, 05:29:32 am
Texas Components seems to have a 3 to 4 week turn-around time, but their VHD200's are definitely pricey (about $48 if I recall).
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on April 18, 2018, 01:30:59 pm
Texas Components seems to have a 3 to 4 week turn-around time, but their VHD200's are definitely pricey (about $48 if I recall).

Not if you order 0.1ppm TCR with 0.001 match, I went overboard and ordered the highest spec they would sell me for the 25K2/10K.  That little bugger was more than twice that and they sure took their time to make it.  Unfortunately I had calculated that value for another LTZ1000A chip which I ended up not using due to some strange behavior I saw, so I had to make some adjustments in the trimming section.  The standard 13K/1K VHD200 with 0.01 match I used for the LTZ voltage divider was about  $43.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 18, 2018, 05:04:44 pm
The compensating "400 K" resistor is only working well over a small range, as the compensation is nonlinear, especially with a low set temperature and thus low heater power.  For this reason the suitable value also depends on the thermal setup and the set temperature /  heater power. The lower the set temperature the higher the value for the resistor. Also the thermal setup will have an influence- so inside a case the best value will be different from the bare board.

I would really question spending much more on the resistors than on the LTZ reference. If one really needs more, a 2nd layer of temperature regulation or a 2 nd LTZ1000 might be more economic than using resistors that don't make a difference. The good point about the LTZ1000 is that it is not that sensitive to the resistors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 19, 2018, 07:41:06 am
I think I killed an LTZ1000ACH.  I have no idea how/why it died.   It was working for months and recently i posted data here about it's temperature coefficient and got a lot of advise on improvement.  In an attempt test two of the suggestions:
1)  I un-powered the board.
2)  Changed R5 from 12K to 13.7K (i just got a Zfoil 13.7K on Ebay recently).
3)  Changed U1/U3 from OPA177FP to ADA4522 op-amps (in DIP adapters).
4)  Upon power up the output went to positive rail or about 14V.

I did a visual check and removed U4 to check the output of the LTZ directly...it was about 13.8V
I tried replacing the ADA4522 opamps with LT1006 units but same result.

Before I throw away a $50 reference I thought I'd post a schematic with various voltages measured and see if I'm just being stupid.
The heater does not appear to be getting any power.   Maybe the Zener is open circuit?

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 19, 2018, 09:10:53 am
Which 4522 you used? Maybe you got confused the single and dual package versions? :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on April 19, 2018, 09:20:33 am
Which 4522 you used? Maybe you got confused the single and dual package versions? :)

4522-1  single package.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on April 19, 2018, 02:09:58 pm
The heater looks OK. If it was broken, I would expect to see a voltage differential across it. The problem is, U1 is only pushing 20mV, insufficient to turn on Q1.

Next step, check the voltage on the inverting input of U1. If it is not the same as the voltage on the non-infringement input, there is a problem with the op amp circuit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on April 19, 2018, 02:18:32 pm
Replace the LTZ1000 with two NPNs and Zener. Then You will make sure if Your LTZ is dead.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ArthurDent on April 19, 2018, 02:24:49 pm
Hard to guess without actually having the board in front of us but a possibility could be a problem with the new op amp/adapter wiring. Can you set up a test board to see if the op amps in the adapters do work as op amps.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Galaxyrise on April 19, 2018, 03:20:43 pm
I find that pin6 voltage of 19mV to be inconsistent with the other measurements:
  * With the ref output at 13.9V, if the voltage divider is working it should be around 945mV 
  * The pin 8->7 voltage of 0.652 suggests the transistor is conducting, (though not as much as I'd expect with a base voltage of 0.9V). 
  * The heater control opamp is at its minumum output, suggesting its IN- is greater than IN+

The readings on the refamp side would suggest a dead zener to me, I can't otherwise justify that voltage drop across the zener.

Something I did after damaging a couple LTZ modules was to build up a fake LTZ using discrete transistors and a diode soldered on to some CAT5 that I could plug/solder in place of a real LTZ.  If the circuit was working with the "fake", then I'd put in a real LTZ.  Before putting in a new LTZ, maybe put in a fake one to verify the circuit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 19, 2018, 04:06:24 pm
The LTZ circuit is kind of sensitive to a wrong output:
too low (e.g. to much load) and the heater will go too high
too high (e.g. oscillating, transients during turn on) and the transistor below the zener can see excessive base current that destroys it. Also the zener might break from over-current, though less likely.

AZ OP might take some time to get working when turned on. One more reason I would be suspicious about using an AZ OP. In addition there is absolutely no need for a low drift OP. Drift of the OP is attenuated by a factor of about 200. So anything better than 50 µV/K would be OK.

The kind of dummy LTZ is a good idea to test a new circuit.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 19, 2018, 10:01:08 pm
Hello,

I always use a dummy LTZ when trying a new layout or a new OP-Amp to see if there are oscillations or other issues.
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg829328/#msg829328 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg829328/#msg829328)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: CraigD73 on May 13, 2018, 03:17:34 am
Just starting a LTZ1000A project. After many hours of reading some great posts on the forum I have a fair grasp of what is needed.

I could still use a couple of recommendations for the +12V power supply regulator and OP amp to use for the ordinal 7-10V converter.   I assume one would want a regulator with low noise and low TC.  For the OP amp I was thinking about the zero drift devices with low input offset.  But I am not up to date on who has the best parts in these areas.

What about a switching regulator to allow 5V or Li battery power?  They have switching noise which I believe could be mitigated.  Don't think I would put the switcher on the same board and it could be followed by a linear.  Battery power does have some appeal.

I am not really a voltnut but I would like to to the best I can as a learning experience.  Most likely not going to use the extra pricey .005% resistors just the Vishay low TC .01% foils.

I have had an LTZ1000A running on a test board for about two weeks now.  Built the board to burn-in the LTZ1000 and for something to play with.  The little cube next to the board is a pseudo-LTZ1000 built with a zener, heater resistor and a couple of transistors potted in some foam.  It worked but I forgot about the Vbe and used a 7.5V so it makes and 8.1V.  It was also some what unstable because of thermal lag.  The resistors are just junk box .1% MF's and while I did pay attention the Kelvin paths I didn't optimize the layout at all.  I was actually going to hand wire or island mill some copper clad but at the last minute I decided to send it to JLC PCB in China along with a 3GHz prescaler board for my HP34401A counter.  The quality and delivery were really great, received 10 pcs in 5 days all for $2.00 US.

The references reads 7.0707V on my HP 6.5 digit  HP34401A.  This is some what lower than what others are are reporting but still within the specification.   

Title: Re: Ultra Precision Reference LTZ1000
Post by: try on May 21, 2018, 05:45:05 pm
Hello craig73,


I am not really a voltnut but I would like to to the best I can as a learning experience.  Most likely not going to use the extra pricey .005% resistors just the Vishay low TC .01% foils.

why do you intend to use 0.01% or even 0.005% ones?
They should not provide any advantage for the output voltage of the reference in terms of temperature or long-term stability over the simple ones in 0.1% precision.

I see two trimmers on your board. What do you use them for?
The picture is a nice one but a wiring diagramm might show a reason for the relatively low voltage on the output.
It could be interesting where you diverge from the original wiring in the data sheet.

Regards
try
Title: Re: Ultra Precision Reference LTZ1000
Post by: CraigD73 on May 21, 2018, 07:39:53 pm
I am new to all this and not in any way an expert.  What I have gleaned reading lots of posts the two critical areas of the circuit are the divider used to set the heater temp and the resistor used to set the Zener current.  For the divider, the ratio rather than the resistor values is the important parameter,  it needs to have the best TC and long term drift characteristics. There is some debate as to exactly what ratio to use, seems to depend on your view of long term drift of the device vs max environmental usage temp.  The 120 ohm Zener current sensing resistor also needs a good TC and long term stability but it value depends on what Zener current you wish to use, this seems to be a noise vs long term stability issue.  Not knowing enough I am just going to stay with the recommended values.  For the three critical resistors your choices seem to be WW or metal foil.   Not looked too much at the WW resistors but have looked at the Vishay Z201 and VSMP smt metal foils.   Their sweet spot seems to be in .01%, they don't offer much at lower precision.   A normal .1% film resistor is going to have way worse TC and drift than the Vishay foil resistors.  Going to .005% or .001% adds a lot to the cost.  Still need to look at WW resistors.   A custom Vishay .01% VSMP runs about $13 so it's not a killer for the three critical resistors.   Vishay can make almost any value by programming shunts included on the raw stock material.

One of the trimmers is used for the 7-10V converter -- didn't want to select resistors.  The other trimmer is on the heater divider to play with the temps but will be fixed in the final design.  The board uses normal 1% resistors and not built to be an accurate reference, it's just for exploration and burn-in.
Craig
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on May 21, 2018, 07:58:23 pm
The board picture shows a LT1179  quad OP, that is rather slow. This can interfere with the LTZ1000 voltage loop and even make it oscillate. If you have a single supply the LT1013 is usually the best choice for the OP: accurate enough and single supply and not a chopper that can produce etwa trouble.  So for the LTZ1000 ref. + 7 to 10 V amplifier it usually takes an LT1013 and a single chopper OP or high precision BJT based one (e.g. OP177).

For the temperature setting divider, a very high quality thin film resistor array may be an option - though it is hard to find suitable ones in small quantity.
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on May 21, 2018, 08:35:52 pm
I am new to all this and not in any way an expert.  What I have gleaned reading lots of posts the two critical areas of the circuit are the divider used to set the heater temp and the resistor used to set the Zener current.  For the divider, the ratio rather than the resistor values is the important parameter,  it needs to have the best TC and long term drift characteristics. There is some debate as to exactly what ratio to use, seems to depend on your view of long term drift of the device vs max environmental usage temp.  The 120 ohm Zener current sensing resistor also needs a good TC and long term stability but it value depends on what Zener current you wish to use, this seems to be a noise vs long term stability issue.  Not knowing enough I am just going to stay with the recommended values.  For the three critical resistors your choices seem to be WW or metal foil.   Not looked too much at the WW resistors but have looked at the Vishay Z201 and VSMP smt metal foils.   Their sweet spot seems to be in .01%, they don't offer much at lower precision.   A normal .1% film resistor is going to have way worse TC and drift than the Vishay foil resistors.  Going to .005% or .001% adds a lot to the cost.  Still need to look at WW resistors.   A custom Vishay .01% VSMP runs about $13 so it's not a killer for the three critical resistors.   Vishay can make almost any value by programming shunts included on the raw stock material.

One of the trimmers is used for the 7-10V converter -- didn't want to select resistors.  The other trimmer is on the heater divider to play with the temps but will be fixed in the final design.  The board uses normal 1% resistors and not built to be an accurate reference, it's just for exploration and burn-in.
Craig

Hi Craig,

It turns out that the datasheet's ranking of which resistor is more important seems to be a bit off (one of the 70k resistors is actually more important than the 120R resistor).  See https://www.eevblog.com/forum/metrology/resistor-set-for-ltz1000-positive-standard-7v-circuit/msg1386014/#msg1386014 (https://www.eevblog.com/forum/metrology/resistor-set-for-ltz1000-positive-standard-7v-circuit/msg1386014/#msg1386014)
Title: Re: Ultra Precision Reference LTZ1000
Post by: CraigD73 on May 21, 2018, 08:38:40 pm
Yup --the LT1179 is all I had in my parts stock -- will have to order some LT1013's
Craig
Title: Re: Ultra Precision Reference LTZ1000
Post by: try on May 21, 2018, 09:35:56 pm
I am new to all this and not in any way an expert.  What I have gleaned reading lots of posts the two critical areas of the circuit are the divider used to set the heater temp and the resistor used to set the Zener current.  For the divider, the ratio rather than the resistor values is the important parameter,  it needs to have the best TC and long term drift characteristics. There is some debate as to exactly what ratio to use, seems to depend on your view of long term drift of the device vs max environmental usage temp.  The

Forget the useless debate.  ;)
It is the maximum environmental usage temp that puts a floor under the operating temperature. If you want the reference to be stable with varying ambient temperature the heat regulation has to work properly. Give it some headroom by fixing the regulator temperature adequately above. Even with the heater disconnected, you have a temperature increase. In my case of the "non-A"-version it was like 3-7 degrees celsius if I remember correctly.
There is a really helpful description how to measure that temperature posted by doc Frank somewhere.
That description discloses the real operating temperature of your reference.
The precision of that measurement depends on two things:
1. Your LTZ, being off, having adapted ambient temperature.
2. Your multimeter being fast when measuring the initial Ube-voltage relating to ambient temperature.

Once you found that temperature figure you can calculate how to change the operating temperature taking into account the individual Ube of your LTZ in question.
...
Quote
Not looked too much at the WW resistors but have looked at the Vishay Z201 and VSMP smt metal foils.   Their sweet spot seems to be in .01%, they don't offer much at lower precision.
In case of the VSMP the table in the datasheet looks like the absolute resistor value determines the possible precision and TC.
If you need 120 Ohm you have no choice and the resistor does not get better if you order it in 0.005%.
I have the impression that everybody is using through-the-hole resistors for the divider instead of SMD ones.

Your possible options are:
1. Using simple metal film resistors (p.e. Yageo MF).
I used them in my prototype and was rewarded with a shaky output  of a couple of ppms up and down upon temp variations of +- 5 degrees celsius in my room.  :palm:
2. Using something slightly better, like PTF56. At least the spec sheet shows better figures than the standard Yageo metall film resistors. I replaced the 120 Ohm and the divider and my prototype looked stable then.
3. Use metal foil or WW resistors. Examples: Vishay S102, GR's "econistor" sold by Rhopoint or the often quoted "Ultrohm Plus" manufactured by fellow member Edwin Pettis.
4. Use something special with good tracking ratios:
      a) poor man's tracking solution: try to couple your resistors thermally with copper foil (see pictures from Andreas, p.e.)
      b) LT-5400 can be used for a certain divider ratio
      c) Vishay 300144 + 300145 and their Z-variant offer you a divider product manufactured according to your specs
5. Expensive solution with high impress factor: Order your resistors or your divider in an hermetically closed housing. (see pictures from tin). Doc Frank did the calulation, conclusion: This luxury does not improve the performance. But if it makes you sleep better, why not? ^-^

Quote
A normal .1% film resistor is going to have way worse TC and drift than the Vishay foil resistors.  Going to .005% or .001% adds a lot to the cost.  Still need to look at WW resistors.   A custom Vishay .01% VSMP runs about $13 so it's not a killer for the three critical resistors.   Vishay can make almost any value by programming shunts included on the raw stock material.
Yes, but the precision (.1%) is not the determining factor. You get Vishay S102 in 1% and all standard foil properties apply regardless of precision. The only difference with 1% is that the laser cutting the resistor templates stops cutting earlier.
Quote
One of the trimmers is used for the 7-10V converter -- didn't want to select resistors.  The other trimmer is on the heater divider to play with the temps but will be fixed in the final design.  The board uses normal 1% resistors and not built to be an accurate reference, it's just for exploration and burn-in.
Craig
Out of the data sheet for a simple trimmer in 10K:
General offer ±250 ppm/℃ (±100ppm/℃ is available if    => 250ppm through the wiper!  :--
Pettis recommends Bourns 3250 and 3290 (expensive, but. mil-grade)
Fellow member branadic used one of those Vishay Models: 533, 534 or 535 (still expensive)

Regards
try
Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on May 21, 2018, 09:46:33 pm
Quote
This luxury does not improve the performance.

Are you sure about that?  I was under the impression that non-hermetic vishays had something like 1ppm per % relative humidity.  That’s at least a 20ppm swing from season to season, which is quite a bit larger error than what you will see from temperature fluctuations in your lab.

Granted, with the error attenuation of the LTZ circuit, this should be a relatively minor effect on the output, but I wouldn’t say that it doesn’t improve performance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: RandallMcRee on May 21, 2018, 10:13:39 pm

Quote
  b) LT-5400 can be used for a certain divider ratio 

THe LT5400 is not recommended in this application (ref Mister Diodes who claimed that this came from LT app engineers). I did try it and got bad results. I moved to a Vishay divider set.

Presumably in the LTZ circuit, there is too much current to eliminate self-heating.
Title: Re: Ultra Precision Reference LTZ1000
Post by: try on May 21, 2018, 10:21:15 pm
Hi cellularmitosis,

Quote
This luxury does not improve the performance.

Are you sure about that?  I was under the impression that non-hermetic vishays had something like 1ppm per % relative humidity.  That’s at least a 20ppm swing from season to season, which is quite a bit larger error than what you will see from temperature fluctuations in your lab.
Roughly the same. Say 0,05ppm/K * ( (28-15) K ) =0,65 ppm (I have no exact figure of the TC!)
20ppm resistance variation translates into 0,52 ppm (if I have set up my spreadsheet on voltage sensitivity correctly)

At least this is cyclical and does not cause an unidirectional trend.
Quote

Granted, with the error attenuation of the LTZ circuit, this should be a relatively minor effect on the output, but I wouldn’t say that it doesn’t improve performance.

No, I am not sure because I only looked at the long-term drift effect of the hermetic enclosure. The drift reduction does not play a role because the zener drift dominates if I got doc Frank's statements correctly.

I am not aware of your impression as I ignored the humidity aspect of it!
My environment varies roughly from 40% to 60% only.
I assume Lars Walenius or branadic could contribute here.
Do you have any findings?

Regards
try
Title: Re: Ultra Precision Reference LTZ1000
Post by: try on May 21, 2018, 10:30:09 pm
Hi RandallMcRee,


Quote
  b) LT-5400 can be used for a certain divider ratio 

THe LT5400 is not recommended in this application (ref Mister Diodes who claimed that this came from LT app engineers). I did try it and got bad results. I moved to a Vishay divider set.

Presumably in the LTZ circuit, there is too much current to eliminate self-heating.

Could you quantify your bad results somehow? What might be considered a bad result for Andreas could be a good one for me, p.e. :)
Where do you use the LT5400? To set the temperature or for the voltage raise from 7V to 10V?

Title: Re: Ultra Precision Reference LTZ1000
Post by: RandallMcRee on May 22, 2018, 12:43:53 am
Hi RandallMcRee,


Quote
  b) LT-5400 can be used for a certain divider ratio 

THe LT5400 is not recommended in this application (ref Mister Diodes who claimed that this came from LT app engineers). I did try it and got bad results. I moved to a Vishay divider set.

Presumably in the LTZ circuit, there is too much current to eliminate self-heating.

Could you quantify your bad results somehow? What might be considered a bad result for Andreas could be a good one for me, p.e. :)
Where do you use the LT5400? To set the temperature or for the voltage raise from 7V to 10V?

Was specifically referring to R4/R5 ratio set.
7v-10v (opamp gain setting) is fine. OPamp gain set is what the LT5400 was designed for.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CraigD73 on May 22, 2018, 07:46:12 am
Ok, I just did a quick test on the sensitivity of R2 the 70K for the Zener.   Added a ~70meg in parallel with the 70K which by my calculations reduced the value by about .1% (1000ppm), I see no change in output voltage on my 6-1/2 digit HP DVM.  That is not to say it didn't change but I can't see it.   Should be fairly easy to get std cost .1% or even 1% with 50ppm TC's.

Guess I will need to start the hunt for an 8-1/2 digit meter.

If I get time I will chedk to see what it takes to see a change in the output.    Got to be a little careful I don't want to smoke something.

Craig
Title: Re: Ultra Precision Reference LTZ1000
Post by: try on May 22, 2018, 11:02:59 am
Hello CraigD73,

Ok, I just did a quick test on the sensitivity of R2 the 70K for the Zener.   Added a ~70meg in parallel with the 70K which by my calculations reduced the value by about .1% (1000ppm), I see no change in output voltage on my 6-1/2 digit HP DVM.  That is not to say it didn't change but I can't see it.   Should be fairly easy to get std cost .1% or even 1% with 50ppm TC's.

Guess I will need to start the hunt for an 8-1/2 digit meter.
This is not necessary.
Your 1000ppm change of R3 should yield a 3ppm change in output voltage.
According to measurements from lymex rather 4ppm. There is a table around in this thread that compiled the sensitivies measured by different forum members.
I don't have access to my own measurements right now unfortunately.

Maybe the contact failed?
Try 10M Ohm instead.
The effect can be seen on a 6,5-digit multimeter.

Regards
try
Title: Re: Ultra Precision Reference LTZ1000
Post by: CraigD73 on May 23, 2018, 02:10:24 am

Did another test on R2, by paralleling my 71.5K resistor with a 10 Meg.  I see about 200uV rise  in the Vz which seems to calculate out to .39 PPM for a 100 PPM (.01%) change in resistance.   A little more than what the data sheet indicates but not way out of wack.   I am somewhat limited by the lack of voltage measurement capability with a 6.5 digit meter but its not orders magnitude off.   Here are my numbers -- someone can check my math.
R2  = 71.5V   (1%)
R2 ||  10Meg  (5%)  =  70992.4
Vz @ 71.5K = 7.07056  Vz @ 70.993K  = 7.07076   Delta V = +200uV  (good enough for first order approximation)

Think I will stick with the a 69.8K .1% Panasonic or TE  a +/-10PPM TC MF at about a buck.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on May 23, 2018, 02:15:31 am
You want the lowest TC parts here, the exact value is not very critical.  So if you find a 3ppm/C TC 1% resistor go with it every time rather than a 0.005% 20ppm/C TC part.
Title: Re: Ultra Precision Reference LTZ1000
Post by: try on May 23, 2018, 09:00:44 am
Hi CraigD73,


 someone can check my math.
R2  = 71.5kV   (1%)

Your math is OK.
By the way, I measured a sensitivity of 0,4ppm as well in my prototype board.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MegaVolt on May 23, 2018, 11:33:56 am
Guess I will need to start the hunt for an 8-1/2 digit meter.
This is not necessary.
...
3ppm change in output voltage.
...
The effect can be seen on a 6,5-digit multimeter.
34465 6,5-digit multimeter. 24 hour error = 13ppm

How can they measure changes in 3 ppm?
Title: Re: Ultra Precision Reference LTZ1000
Post by: try on May 23, 2018, 01:10:44 pm
Hello Megavolt,

that measurement does not take 24 hours.
You measure the voltage, that might take some seconds.
The multimeter does not jump 13ppm when you are measuring with the parallel resistor a few seconds later.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MegaVolt on May 23, 2018, 01:32:13 pm
measuring with the parallel resistor a few seconds later.
I was not attentive :( It was about jumping relative measurements in a short time.

Thank you corrected.
Title: Re: Ultra Precision Reference LTZ1000
Post by: keen101 on June 19, 2018, 06:27:46 am
So, i know this is many years too late,  and maybe there is zero Interest in this anymore, but there were many people who had wanted an LTZ1000 board way back when i posted my HP/Agilent Clone on my blog several years back (wordpress.com/2013/02/12/hpagilent-03458-66509-7v-dc-reference-clone/).

Since so many had asked me for one,  i finally made a few boards and put them on ebay. It seems no one wants one anymore,  so maybe it was a waste of time, and if so, oh well, still a neat little board I'm proud of.

Here is the ebay link if anyone is interested.  Thanks. (https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F113011267007 (https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F113011267007)).
Title: Re: Ultra Precision Reference LTZ1000
Post by: TheSteve on June 19, 2018, 06:51:56 am
I think the problem may be that your price is a little bit too high. You can buy original 3458A A9 ref boards for less quite often on ebay and they use the LTZ1000ACH.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 19, 2018, 08:16:09 am
Nice board, but the price is way too high.
Also, it's lacking some information, like oven temperature set point.. is it still 95°C (15k/1k divider), or did you adapt it to the non-A version (at least 10°C less), and for metrology application, i.e. smallest possible expected drift, like 13k/1k and 65°C?

Frank

PS: And the module should have been trimmed for lowest T.C.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on June 19, 2018, 08:39:21 am
About 130€ BOM and you want 350$. Price is way to high and would only be okay if it would already have a long-term-burn-in and calibration data so one can use it directly in a used 3458A for example.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on June 19, 2018, 08:50:15 am
Based on eBay listing photos, sadly 15K/1K is used with CH chip.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on June 19, 2018, 11:51:55 am
I think the problem may be that your price is a little bit too high. You can buy original 3458A A9 ref boards for less quite often on ebay and they use the LTZ1000ACH.

Also on a $350 ticket item a description that includes a phrase like "The chip has been tested and appears to be working correctly in circuit, but has not been burned in for even better stability." doesn't exactly inspire confidence. Someone who's going to fork out $350 wants a guarantee that the board is working and meets specifications, which for an item like the A9 board includes a drift test over at least several months. That is the value add and that is what justifies a price that is significantly above the BOM cost.
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on June 19, 2018, 02:34:22 pm
From ebay item's description:

'LTZ1000 heat compensated chip standard (which often goes bad)'

prove it
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on June 19, 2018, 05:04:50 pm
I would not expect a lot of failing LTZ ref modules in the 3458. They are supposed to be well tested and burned in. So the bad ones with excessive drift or significant popcorn noise (which might often come together) should be sorted out. There still seem to be rare cases with HP refs. to show popcorn noise, but I am afraid the chances are higher with the untested replacement boards.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on June 19, 2018, 05:52:08 pm
I think that there would be some interest in the bare board from this group. That might be a way to recover your investment. You might also find some buyers for the completed board, at a price that lets you recover the parts cost.

Thanks for doing this, I know that it isn't meeting your expectations but it is nice to have this piece of engineering done. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: VK5RC on July 02, 2018, 08:05:44 am
If I recall correctly - somewhere in this post - somebody gave mentioned a good quality socket that could be used to temporarily fit an LTZ - to try and sort some 'good ones' without a full board each.
Does any one recall the detail of the socket/source etc or did I imagine it?  :-//
Title: Re: Ultra Precision Reference LTZ1000
Post by: SvanGool on July 02, 2018, 09:07:07 am
This one maybe? : https://www.eevblog.com/forum/metrology/px-reference/msg1381836/#msg1381836 (https://www.eevblog.com/forum/metrology/px-reference/msg1381836/#msg1381836) by TiN
Title: Re: Ultra Precision Reference LTZ1000
Post by: VK5RC on July 02, 2018, 09:55:29 am
Thanks, my Google fu is improving, I think it is this one.   https://www.digikey.com.au/product-detail/en/te-connectivity-amp-connectors/8058-1G32/1-1437508-6-ND/2259044 (https://www.digikey.com.au/product-detail/en/te-connectivity-amp-connectors/8058-1G32/1-1437508-6-ND/2259044) 

Thanks to BU508A in this post.  https://www.eevblog.com/forum/metrology/kx-reference/msg1274394/#msg1274394. (https://www.eevblog.com/forum/metrology/kx-reference/msg1274394/#msg1274394.) reply#136
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 16, 2018, 12:33:44 pm
Since I received a few vintage LTZ1000 samples from lowimpedance and need some boards for comparison I decided to use the design of Dr. Frank. I modified his design to fit into a Hammond 1455C1201 case and added LT1763 (SO8) voltage regulator, giving 12V. This is how it currently looks like. The 3 blocks to the right indicate the place for Pomona 3770 binding posts.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Haasje93 on September 18, 2018, 10:31:26 am
It looks really nice! :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on September 18, 2018, 12:18:52 pm
Hello,
the loose power supply GND cable must NOT be connected to the negative reference star point, but instead to the jack farther right.
I'd recommend to separate the power supply thermally and shileding-wise.

I see no basic deviation to my LTZ design, so far, so the rest is ok.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 18, 2018, 04:38:48 pm
+1 for the thermal isolation between LT1763 and LTZ.
(thats why I will do a re-design of my B-revision)
In your case it might be less urgent if you have a stabilized external supply instead of battery.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 18, 2018, 07:37:50 pm
Thanks for the feedback. Changed the loose wire to JP2, added a thermal slot between regulator and reference ciruit and changed two MKS 100nF to MKP2 100nF. Attached the almost final state of the board.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 19, 2018, 06:01:10 pm
I will order some boards within the next days. Someone out there who wants a few boards of this layout as well?

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: BradC on September 19, 2018, 11:39:06 pm
I will order some boards within the next days. Someone out there who wants a few boards of this layout as well?

-branadic-

I'll put my hand up for one please.
Title: Re: Ultra Precision Reference LTZ1000
Post by: GregDunn on September 20, 2018, 12:57:51 am
Are you selling boards only, or boards with the LTZ1000?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 20, 2018, 05:57:16 am
Boards only...
For orders please write me a short pm with how many boards you need. I will close this offering by the end of next week and order the boards in the necessary quantities.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 20, 2018, 04:53:04 pm
Wow, didn't expect such a response. I think I will order at Elecrow and pcb cost will be in the order of $2 per board or less depending on the final quantity plus shipping cost (Airmail) plus shipping to you guys (simple envelope to keep cost down). Thus I changed the outer form to a rectangle of size 120 x 50mm². PCB color will be black with immersion gold, single layer board.
Attached is the final schematic.
Please send me an official email adress with the PN too. Thanks.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 20, 2018, 05:18:31 pm
The pot for gain adjustment in the final stage is a little odd. Normally one avoids using such low ohms pots, as the wiper contact may not be that reliable.  The more normal way is to have something like 10-100 Ohms in parallel to a 10 K pot with 5-100 K in series.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 20, 2018, 05:51:24 pm
Since this board is working for Frank and since I had the chance to measure one of his reference boards I wouldn't complain ;)

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: seec on September 21, 2018, 10:45:35 am
is it a fake?
https://ru.aliexpress.com/store/product/LTZ1000ACH/1200151_32372123768.html
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 21, 2018, 12:27:27 pm
Does not look genuine to me

- LT-logo is missing
- printing is not correctly aligned to Pin 8 marker.

So in best case it is refurbished and re-marked.
see also:

http://volt-nuts.febo.narkive.com/FIfiYHU5/ltz1000ach-and-ltz1000ch-in-china (http://volt-nuts.febo.narkive.com/FIfiYHU5/ltz1000ach-and-ltz1000ch-in-china)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: try on September 21, 2018, 01:04:42 pm
Hello Kleinstein,

The pot for gain adjustment in the final stage is a little odd. Normally one avoids using such low ohms pots, as the wiper contact may not be that reliable.  The more normal way is to have something like 10-100 Ohms in parallel to a 10 K pot with 5-100 K in series.

as far as I know every wiper contact can fail. Is there a particular issue with low ohm pots?

Obviously your proposal does not fit Frank's trimming scheme where he is basically trimming in series needing an option for a low ohm variation at the end of the trimming chain.
Could you propose a complete trimming scheme for the divider regardless of the layout available on the PCB?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 21, 2018, 08:13:59 pm
One week left to sign up for the board. Currently there are 45 boards on the order list. Currently there are 130 boards on the order list.

6x branadic
3x SvanGool
3x BradC
4x eplpwr
3x Sprock
2x FredTW
2x Haasje93
1x retroware
2x dhillman
5x try
2x flittle
10x bck
5x F64098
2x RandallMcRee
10x MiDi
5x e61_phil
2x Le_Bassiste
5x quarks
2x Macbeth (3)
5x meandeev
5x martinr33 (10/20)
3x Hermann W
3x mikron
2x Harfner
3x pansku
2x Carrington
2x mweymarn
3x Vbemultiplier
6x vmiceli
5x ap
3x sixtimesseven
2x AlfBaz
5x FriedLogic
2x guenthert (need email address)
2x Vgkid
3x borghese


-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on September 22, 2018, 10:42:27 pm
My attempt:
LTZ1000-PCB Designed by Dr Frank and
LT1763-Low-Noise-Supply designed by Cellularmitosis

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=528830;image)

Both PCBs are made available as OSHW by Cellularmitosis (big thanks  :-+ ) and can be bought here or via any other pcb-manufacturer with the gerber-files:

https://oshpark.com/shared_projects/dGYcQAgn (https://oshpark.com/shared_projects/dGYcQAgn) LTZ-Board
https://oshpark.com/shared_projects/uVr4yDgz (https://oshpark.com/shared_projects/uVr4yDgz) LT1763-Board

Why i did it that way:

LTZ1000 is directly buffered via LTC1052 since i dont use the 7->10V-function for the references at the moment,
LTZ1000 protected from airflow by green lemonjuice-cap,
an EMI-Filter BNX002-01 is used at the power supply input https://www.murata.com/en-eu/api/pdfdownloadapi?cate=luNoiseSupprFilteBlockType&partno=BNX002-01, (https://www.murata.com/en-eu/api/pdfdownloadapi?cate=luNoiseSupprFilteBlockType&partno=BNX002-01,)
a double sided copper-clad-board at the pomona-jacks should equalize thermal differences pretty well,
the LT1763 is located further from the LTZ1000-PCB, so it doesnt affect it by temperature variation due to varying input voltage,
TEKO 393-case is afterwards stuffed again with paper towel shreds to reduce airflow,
Resistors by Edwin Pettis

Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on September 23, 2018, 08:14:10 pm
Wow, didn't expect such a response. I think I will order at Elecrow and pcb cost will be in the order of $2 per board or less depending on the final quantity plus shipping cost (Airmail) plus shipping to you guys (simple envelope to keep cost down). Thus I changed the outer form to a rectangle of size 120 x 50mm². PCB color will be black with immersion gold, single layer board.
Attached is the final schematic.
Please send me an official email adress with the PN too. Thanks.

Anyone interested in group buy of precision resistor set?

Edit:

LTZ1000 Precision resistors group buy meeting point (https://www.eevblog.com/forum/buysellwanted/group-buy-ltz1000-precision-resistor-set-(for-branadic-10v-pcb)/msg1846061/#msg1846061)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on September 23, 2018, 10:37:55 pm
I am very honored by all these experiments!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Hermann W on September 24, 2018, 08:25:07 pm
@Branadic: There is a little mistake in the circuit diagram. It is not the regulator LT1763-3.3, but LT1763 without -3.3
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 24, 2018, 08:42:54 pm
Sure it's the adjustable version, but I used the library of the fixed version. Pinout matches.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: pansku on September 25, 2018, 08:43:40 am
@branadic Pm sent  :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 28, 2018, 06:00:46 am
The call ends today, last minute orders are welcome:

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1840139/#msg1840139 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1840139/#msg1840139)

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: AlfBaz on September 28, 2018, 06:13:42 am
PM sent, hopefully I didn't miss the boat
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on September 28, 2018, 10:39:58 am
Pm sent.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 28, 2018, 06:01:13 pm
The call is now closed. I ordered 150 boards. So this is a total of $139.50 + shipping $36.97 + import turnover tax to Germany + shipping cost to each of you. Inside EU this is about 1.45€ and international probably 3.70€.

Can't say anything about turnover taxes by now, but each board is about $1.17 + taxes + shipping, I think that is fine for all of you?
Production time 4-7 days plus 3-7 business days for shipping to me.

I still need some email addresses before I can start to write all of you for detailed information on how to pay me (invoice or PayPal).

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Hermann W on September 29, 2018, 06:46:17 pm
@branadic: thank you for the personal Email.
Looking at the 10V-divider I suppose it is not correct. R12=6k and R13=2k333.. So UR13 is 2,8V (not 2,688V :bullshit:) and there is no space for R14 and R15. R13 has to be a little bit smaller.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on September 29, 2018, 09:26:31 pm
@branadic: thank you for the personal Email.
Looking at the 10V-divider I suppose it is not correct. R12=6k and R13=2k333.. So UR13 is 2,8V (not 2,688V :bullshit:) and there is no space for R14 and R15. R13 has to be a little bit smaller.

Hermann, you misunderstand. I was scratching my head and then realised you are working out the resistors in parallel.  :-DD

This is not the case - it's just the PCB footprints giving you the option of axial wirewound or metal foil resistors. One or the other. Also the R12 vs R12A placement looks like it requires a jumper depending on what type of resistor you go with. It has to be said branadics placement of the component labels on the PCB leave a lot to be desired  :palm: But reading the schematic and layout it can be worked out.

I'm not sure why there is a difference between the values of wirewound vs metal foils - I guess I have to find Dr. Franks original reasoning?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 29, 2018, 09:49:01 pm
Quote
It has to be said branadics placement of the component labels on the PCB leave a lot to be desired  :palm:

It has to be said, that I got the Eagle files from Dr. Frank, added the voltage regulator and slightly changed the position of some components to make the board fit into the Hammond case. I didn't change components label or values, they where given as it.  :-//

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on September 29, 2018, 10:39:42 pm
It has to be said, that I got the Eagle files from Dr. Frank, added the voltage regulator and slightly changed the position of some components to make the board fit into the Hammond case. I didn't change components label or values, they where given as it.  :-//

Yes, but the .pdf board layout you provided in your email does not include the (human readable) silkscreen, it does contain all kinds of meta-data labels that are all over the place and overlapping and should not be part of the gerbers (I hope).

Just look at Echo88's Dr. Frank board a few posts above - proper silkscreen.

At the end of the day it doesn't matter providing the board is electrically sound. I'm not complaining, it's a first spin that we all jumped on afterall  ;)

ETA: I see the fancy PCB is actually Cellularmitosis version of Dr. Franks. So he perhaps tidied it up and added the silkscreen? I do apologise!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Hermann W on September 29, 2018, 11:19:06 pm
I was scratching my head and then realised you are working out the resistors in parallel.
Ok, I take the circuit diagram how it was. Now i had to laugh too  :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: mweymarn on October 02, 2018, 03:21:40 pm
All,

fyi - Digikey appears to have the LTZ1000A back in stock. At the moment they show 288 pieces available...

Regards,
Martin
Title: Announcement: Special offer for Ultrohm Plus
Post by: MiDi on October 05, 2018, 10:35:16 pm
Special offer for pww resistors Ultrohm Plus from Edwin till 2018-10-21 (https://www.eevblog.com/forum/buysellwanted/group-buy-ltz1000-precision-resistor-set-(for-branadic-10v-pcb)/msg1872767/#msg1872767)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 06, 2018, 08:48:25 am
Order has been updated to: In production. That took quite long.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: BradC on October 08, 2018, 08:11:21 am
Quick question.
So I re-read this entire thread (and a few others) looking for answers to these questions and can't seem to find anything other than vague subjective handwaving. So I'll ask a couple of questions and hopefully not trigger WW3.

LTZ1000 vs LTZ1000A. I'm under the impression that the standard LTZ1000 is actually likely to age / drift slower if it's run at a low enough temperature (ie with a 12.5k/1k divider). Are there really any real-world advantages to the A model other than power consumption (says he who has just taken delivery of some A units)?

Chopper amps as buffers. There are a number of posts dotted through several threads indicating that if you follow an LTZ1000 with a chopper it might be advantageous to stick an RC network in between to insulate the zener against the chopper input current pulses. My gut reaction is that sounds entirely reasonable and I'm struggling to see a downside. Has anyone done it? What sort of magnitude RC network might one look at if someone was mad enough to hack one into an existing design?

Title: Re: Ultra Precision Reference LTZ1000
Post by: chekhov on October 08, 2018, 01:31:06 pm

Chopper amps as buffers. There are a number of posts dotted through several threads indicating that if you follow an LTZ1000 with a chopper it might be advantageous to stick an RC network in between to insulate the zener against the chopper input current pulses. My gut reaction is that sounds entirely reasonable and I'm struggling to see a downside. Has anyone done it? What sort of magnitude RC network might one look at if someone was mad enough to hack one into an existing design?

Not an answer, but a quick hint - I've seen this thing in TiN's article - 'Project 792X - 10V "FX" reference'(https://xdevs.com/article/792x/ (https://xdevs.com/article/792x/)), look for "RC network R7C1 and R11C3"
There is no deep observations regarding particular component values, put probably it was mentioned somewhere else or deduced from opamp specs.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Magnificent Bastard on October 08, 2018, 07:46:57 pm
Quick question.
So I re-read this entire thread (and a few others) looking for answers to these questions and can't seem to find anything other than vague subjective handwaving. So I'll ask a couple of questions and hopefully not trigger WW3.

LTZ1000 vs LTZ1000A. I'm under the impression that the standard LTZ1000 is actually likely to age / drift slower if it's run at a low enough temperature (ie with a 12.5k/1k divider). Are there really any real-world advantages to the A model other than power consumption (says he who has just taken delivery of some A units)?

Chopper amps as buffers. There are a number of posts dotted through several threads indicating that if you follow an LTZ1000 with a chopper it might be advantageous to stick an RC network in between to insulate the zener against the chopper input current pulses. My gut reaction is that sounds entirely reasonable and I'm struggling to see a downside. Has anyone done it? What sort of magnitude RC network might one look at if someone was mad enough to hack one into an existing design?

Quote from: DiligentMinds (Private Communication)
Quote from: John R. Pickering (Private Communication)

Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 09, 2018, 05:02:55 pm


  • The 'A' version is the same die, but with a die attach method that is thermally insulating.  This helps a lot if you are running your reference on battery power-- it will save around 20% energy vs. the non-'A' part if run at the same die temperature.  LT (now ADI) applications engineers have said that the 'A' version has less hysteresis through power cycles.  Since the non-'A' version can be run at 10oC lower die temperature, the 20% energy savings is dubious.  The leads on the 'A' version will be cooler-- so that is a big plus in managing thermal EMFs between the Kovar leads and the copper board traces-- (the idea is that you want to keep all of these junctions balanced and at the same temperature).  Because of the die-attach method used in the 'A' version, it is advisable to have a high-temp (125oC) burn-in period where the entire burn-in period is 15-minutes ON and 15-minutes OFF.  This exercises the die-attach so that spurious jumps are suppressed.  This burn-in process must be followed by a conditioning process (like the Pickering Patent).  Because it uses a (more or less) ordinary die attach method, the non-'A' version does not require this special burn-in procedure-- but it still needs a 90-day (or so) burn-in (always ON) to 'settle' before calibration.



All my LTZ1000 run at about -measured- 50...54°C (12k/1k), and each circuit consumes in total about 25mA.
The PCB and the device are  inside an insulated box, so that assembly heats up to about 10°C above ambient.
At 22°C R.T., that makes about 20°C difference to heat up for the LTZ1000. From the datasheet diagram, that's about 100mW or 20mA heating power @ 240 Ohm heater resistance, which gives exactly these 25mA, when including OpAmps and reference supply.
I did not -yet- check for LTZ1000A, but the same calculation yields: 12.5k/1k => 62°C, about 30°C difference (due to higher thermal insulation) => 80mW, 18mA heater power, which would give 2mA less current consumption only (23mA in total).  Maybe somebody else can confirm that value for the LTZ1000A.
The only advantage of the A version would be a warm-up time of <1sec, compared to 20..30sec for the non-A version.

I still do not recommend such a 'burn-in', as it will only introduce big hysteresis, as measured and proven by Pickering, hp in their drift - AN18A, and by my own measurements.
Even if one applies the Pickering method, it's really difficult to get to the virgin state, if ever possible.
I would estimate, that the theoretical relaxation process by burn-in is minor compared to the hysteresis effect, so better never excessively heat the LTZ1000 / A device, neither by soldering (no short leads either), nor by 'burn-in'.

Anyhow, nobody knows -up to now- how LT tests the finalized LTZ1000/A devices.
As it's specified for -55/+125°C operating temperature, maybe they test it 100% for both temperatures at the final tester, although the datasheet implies testing parameters at 25°C only.
That might leave the finished device in an unknown hysteretic state, and some devices will stay there indefinitely, others may drift towards their virgin state.

So the initial drift of several ppm/ x months may arise from such a final test over temperature, but not being the 'real' annual drift.

I have encountered initial drifts between zero and -2.5ppm / yr. for all of my seven LTZ1000 / 50°C references, either after assembly, or after erratically over-heating and re-conditioning.
After that time, all seem to approach the typical -0.8ppm/year, or less.

So I again recommend to just leave them alone, as burn-in may do more harm than will really / practically / measurably improve the long-term drift.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 09, 2018, 06:13:23 pm
Hello,


All my LTZ1000 run at about -measured- 50...54°C (12k/1k), and each circuit consumes in total about 25mA.
The PCB and the device are  inside an insulated box, so that assembly heats up to about 10°C above ambient.
At 22°C R.T., that makes about 20°C difference to heat up for the LTZ1000. From the datasheet diagram, that's about 100mW or 20mA heating power @ 240 Ohm heater resistance, which gives exactly these 25mA, when including OpAmps and reference supply.
I did not -yet- check for LTZ1000A, but the same calculation yields: 12.5k/1k => 62°C, about 30°C difference (due to higher thermal insulation) => 80mW, 18mA heater power, which would give 2mA less current consumption only (23mA in total).  Maybe somebody else can confirm that value for the LTZ1000A.


the current consumption of my LTC2057 buffered devices is listed here:
(20-24 mA including a LT1763 voltage regulator which should be well below 1 mA)

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560)

For ageing: I think it depends more on the individual device or datecode than on the "A" or non A version.
But since we do not have enough samples and a JJA at hand we will never know.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 09, 2018, 06:18:20 pm

...as measured and proven by Pickering, hp in their drift - AN18A,

Would you please link the publications/pdfs you are refering to? Thanks.  :-+

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on October 09, 2018, 06:45:22 pm
Anyhow, nobody knows -up to know- how LT tests the finalized LTZ1000/A devices.
As it's specified for -55/+125°C operating temperature, maybe they test it 100% for both temperatures at the final tester, although the datasheet implies testing parameters at 25°C only.

Quote
Note 2: All testing is done at 25°C. Pulse testing is used for LTZ1000A to
minimize temperature rise during testing. LTZ1000 and LTZ1000A devices
are QA tested at –55°C and 125°C.

Whatever QA testing means  :-//
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 09, 2018, 07:26:33 pm
Whatever QA testing means  :-//
Usually: you take from each lot a number of samples and test them.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 09, 2018, 07:59:05 pm
Hello,


the current consumption of my LTC2057 buffered devices is listed here:
(20-24 mA including a LT1763 voltage regulator which should be well below 1 mA)

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560)

For ageing: I think it depends more on the individual device or datecode than on the "A" or non A version.
But since we do not have enough samples and a JJA at hand we will never know.

with best regards

Andreas

Andreas,
thank you very much for your hints, which support my rough estimations.
Therefore, the LTZ1000A really has no big advantage regarding power consumption over the non-A device.

Regarding ageing, I think it's possible to make at least a well educated guess, even w/o a JJA.

If you have a history, and a big enough amount of LTZ1000, you can identify these minute deviations.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 09, 2018, 08:09:04 pm
Whatever QA testing means  :-//
Usually: you take from each lot a number of samples and test them.

There's different philosophies, or requirements on testing, which I have seen at different manufacturers at their production lines...

If you have commercial grade devices, you would only take some random samples and test them to the limits (e.g. over temperature), and rely on predictive statistics.
If you have high grade devices, like military, or critical automotive parts (e.g. non-volatile memory), you would really test them 100% (each device) at the limit temperatures.

I don't know, how serious LT takes the expensive LTZ1000, but I could imagine that because of the price tag, they really test it to 100%.

Maybe we should contact them, which tests they really perform on the devices.
And maybe they are not really aware of the pitfall of such handling.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 09, 2018, 08:45:39 pm

...as measured and proven by Pickering, hp in their drift - AN18A,

Would you please link the publications/pdfs you are refering to? Thanks.  :-+

-branadic-

I refer to the patent of Pickering, and his explanations on the 7001 reference.
AN18a should be well known, so I don't put a link here. You just have to extract from that AN18a, that the 3458A may basically suffer from hysteresis, if left unpowered (which is not included in the specifications).

branadic, when you have measured my LTZ #3 last January, it was quite cold, below 0°C, during the transport. You see the graph before, and after this ring comparison, and over the following year after initialization, referenced to my home 3458A and 5442A. Latter seem to be constant within < 1ppm.
This #3 reference made a hysteretic jump of about +1ppm, due to the low temperatures, which is obviously a permanent, and constant one.
You also see two baseline points for the 3458A, the first is from acbern, the 2nd is taken recently at the Hannover Maker Faire, using this same #3 compared to the PTB 3458A.
The ring comparison before/after the transport to the Maker Faire shows no change, in contrast.

This event, and several others, support my own experience with hysteresis behaviour of the LTZ1000 device, at sub-ppm level, even w/o JJA.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on October 10, 2018, 12:05:42 am
So... ife we could add a little bit of logic to the 3458a to deliver that ramping waveform to the LTZ1000A on startup, it would improve the drift on the 3458a?

I think that the circuit could be noise-free - it would have a "suicide mode" that cut all power once the warmup was completed. There would certainly be some digital noise in the window. Problem is, it is 4 hours long which seems a bit much for day to day operation. but is the spec for true precision.

Or maybe the 3458a devices were selected for low hysteresis.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 12, 2018, 09:33:41 am
UPDATE: Got the info today, that the boards have been shipped on Wednesday, October 10, 2018. What should I say, they today already received at my location. Attached is a picture on how they looked like, before they where shipped.

Time to send out some mails this weekend.

-branadic-

EDIT: Just for sanity check. Everyone should have received an email with all the further details. Hopefully we will see some pictures of assembled LTZ-boards soon.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on October 13, 2018, 06:53:29 pm
Received email , monies will be sent.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 13, 2018, 08:44:57 pm
All extra boards are sold.  :-+

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 14, 2018, 10:01:01 am
Hello,

when I see the effort I would rather make something with a small processor and a DAC (LT1257).
similar to the cirquit here:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg844021/#msg844021 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg844021/#msg844021)

In any case I would use a relay to disconnect the hysteresis cirquit after the full time.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on October 16, 2018, 11:41:43 pm
First impression of branadics (Dr. Franks) design - could not wait and bodged test-pcb together - thank you very much!

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=550286)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 17, 2018, 06:52:35 am
Wonderful, hope it is alive  :-+

BTW: The second bunch with boards went to the post office this morning and should receive their owners within the next days.
Thanks to all those of you sending a beer or two extra.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 17, 2018, 07:36:08 am
First impression of branadics (Dr. Franks) design - could not wait and bodged test-pcb together - thank you very much!

But why do you use IC-sockets in a precision cirquit?
I had horrible drifts (several ppms) in my LM399#3 until I removed the sockets.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: borghese on October 17, 2018, 09:01:53 am
Boards arrived
High resolution image https://islandlabs.eu/_media/Black%20Boards.jpg
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on October 17, 2018, 10:02:21 am
Short test was successful  :-+

But my heart went into my boots after power it on  :o

The output of +REFbuf was sitting at ~6.9V for a felt eternity until it suddenly went to stable ~7.10V  :phew:

Is this expected behaviour?

I triple checked everything before power it on and went step by step through initial operation:

1) supply check (only components for this installed)
2) chopper check (simple zener & for safety 330Ohm heater resistor installed, missing LT1013 & LTZ1000)
3) final test with all components

But why do you use IC-sockets in a precision cirquit?
I had horrible drifts (several ppms) in my LM399#3 until I removed the sockets.

I knew someone would ask that  8)
This pcb is just to practice and for testing purposes.
In the productive units there will be no sockets and no jellybean (0815) resistors wacked together  ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: dkozel on October 17, 2018, 10:25:53 am
Has anyone created a bill of materials from the schematic? If not I'll do that tonight and post it up here.

Many thanks to branadic and MIDI!
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on October 17, 2018, 10:42:39 am
Got BOM with schematics & layout from branadic, ask him.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 17, 2018, 04:09:15 pm
The output of +REFbuf was sitting at ~6.9V for a felt eternity until it suddenly went to stable ~7.10V  :phew:

Is this expected behaviour?


No,

except if you count eternity in micro-seconds.
Here a cold-start of my LTZ#5

blue: 14V power supply after regulator (switching on is done via "on"-Pin of the LT1763)
yellow: zener voltage (unbuffered) but the buffered output follows within ms (2nd picture)
green: heater voltage (stable after ~400 ms)
red: zener current (voltage on 120 ohms resistor).

When I zoom in for the zener voltage the output is stable (within some mV) after 200 ms.

with best regards

Andreas




Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 17, 2018, 04:39:35 pm


The output of +REFbuf was sitting at ~6.9V for a felt eternity until it suddenly went to stable ~7.10V  :phew:

Is this expected behaviour?



That depends. And you have to be precise.
The A version is instantly on , < 1 sec for the oven, seems that branadic uses one.
The non A takes between 10 to 30sec  to stabilize. Last year, I have published several warm up graphs.
So which version do you use? That's not visible on your picture.

And there's a 50ppm/K T.C., so it also depends on the oven set point.

For that you have to check the warm up directly at the reference, then at the chopper output.
Latter may also take some time to operate correctly, but also less than 1s.

If you determine the proper time scales where things happen , 'felt eternity' is useless, it's much easier to track potential failure.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 17, 2018, 06:24:57 pm
Forgot to mention: mine is a LTZ1000A version

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 17, 2018, 06:52:44 pm
Quote
The A version is instantly on , < 1 sec for the oven, seems that branadic uses one.

You mean Andreas ;)

Quote
So which version do you use? That's not visible on your picture.

He's using LTZ1000CH, so "longer" warm-up time to live with.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 17, 2018, 08:03:35 pm
branadic,
sorry, that I confused Andreas and you.

Currently being on an engineering meeting in Dresden, that seems to take its toll. Skål.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on October 17, 2018, 11:36:01 pm
Apologies for my unprecision on this ultra precision thread  ::)

Updated picture of first impression to better resolution.

It is a non A with 12k, so ~45° heater set point.

Attached are the shots for startup - Houston we have a problem!

Powersupply goes to 12V and then drops to ~10V before going to 12V again when heater reduced power.
At same time the REFbuf (dark blue) of chopper steps to the correct value - naturally as 10V supply do not allow for 10V output and REFBuf is to low.
 :wtf:

Checked all traces and connections on PS lines, all well below an Ohm.
Measured input voltage at jack on power up -> constant @15V.
Load is ok, ~50mA initial to ~20mA steady state.

LT1763 damaged?
Oscillation? Possible, but has to be quite low in amplitude, there is nothing in the plots.
Is missing local decoupling for chopper intended?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 18, 2018, 08:45:26 am
I can only guess about the LT1763 circuit.. but it seems to be not OK.

Did you use the variable version (not any of the fixed ones)?

Does the device heat up extensively on power on? => 50mA at warm up is perfectly fine for the LTZ1000 circuit, settles to ~25mA.
P.D. is 150mW, maybe that's too much???

As it's an LDO, stability may be an issue, test for oscillation and check stabilization caps.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on October 18, 2018, 12:00:03 pm
Ordered LT1763IS8PBF from voelkner aka conrad, should be adj. version - see attachments.

Will do further investigation likely this evening...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on October 18, 2018, 08:01:58 pm
Has anyone created a bill of materials from the schematic? If not I'll do that tonight and post it up here.

Many thanks to branadic and MIDI!

It would be great if you have curated a decent one.

Of the important ICs besides the LTZ1000/A my own BOM of actual manufacturer part numbers with the correct foot prints is:

LT1763CS8#PBF
LT1013ACN8#PBF
LTC1052CN8#PBF     (certainly not MAX420)

Correct me if I'm wrong?

I've had trouble with the 70K MF resistors not fitting perfectly. It looks like Cellularmitosis version of the board fixed this with the extra pads. Bent leads it is. Mustn't grumble.

A BOM of preferred caps would be good too if you've done it  :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on October 18, 2018, 08:52:06 pm
Thank you branadic  (and Dr.Frank) :-+

Got my boards today, just a test fit for the most important parts...
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on October 18, 2018, 09:46:06 pm
Short update to the PS issue, will give details tomorrow.

It was oscillation (1Vpp@200kHz) between my SMPS and LT1763 - with linear PS everything is fine.

A quick look at the datasheet gives ~30dB ripple rejection @200kHz, so 1Vpp should turn into 30mVpp at the output - nope: there is ~50mVpp at FB-Pin (should be ~3mV).

This reminds me of something stated in datasheet of LT3045 - if I remember correctly:
The input cap in conjunction with SMPS should be placed a good portion away from the linear regulator to avoid interference - now I have seen why!

And here things are even worse, the regulator screwed up completly  :popcorn:
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 18, 2018, 10:39:50 pm
Good that you found the reason. For me it's a complete no go to combine precision circuits and SMPS. However, I suggest reading AN101 by Linear Technology for  using switchers and LDOs.

I'm currently soldering my boards. Some components arrived today. Could finish two boards by now, but it's to late to power them up. Another 3 boards are presoldered and another 5 are preassembled. Still waiting for some parts.

Please keep an eye on C7, C8 and C9, they should be soldered as far as possible from the edge, so the board fit's without problems to the case. Further you have to bend Q1 somewhat. Cut the contacts of the DC jack after soldering. If you consider that points the board fits without problems into the first slot of the Hammond case. However, I recommend to use some Kapton/Polyimid tape for the edge, before you slide the boards powered into the case. Solder maks is not a reliable isolation.

All capacitors are MKS2 (Wima) except C7 and C8, this are MKP2 (Wima). For the NTC choose whatever you prefer, it's up to you.

Pictures coming soon as well as drawing for the case.

-branadic-

Edit: All boards, except 6 which have been reserved for one use, have been shipped.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on October 19, 2018, 10:02:43 pm
Good that you found the reason. For me it's a complete no go to combine precision circuits and SMPS. However, I suggest reading AN101 by Linear Technology for  using switchers and LDOs.

Yes, it was a lesson learned, even for initial operation I will avoid SMPS in future :horse:
Ultra precision circuits and SMPS are tough to combine while maintaining the precision, but e.g. keithley did in DMM7510 ;)
Thanks for AN101, it was a good bed reading to get an idea of realistic numbers.

Hopefully last OT post, here are the promised details of investigation on LT1763 screw up (follow up of 2375 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1900076/#msg1900076), 2383 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1901735/#msg1901735) & 2388 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1903772/#msg1903772)).

The temperature of LT1763 was measured with thermocouple with pcb upside down in free air @15V supply:
room temp: 21.4°C
max @warm up: 30.9°C (dT 9.5°C) - certainly not in equilibrium
min @steady state: 28.5°C (dT 7.1°C)

The reference is GND at power jack for all measurements:

1. Screw up on warm up due to resonance between SMPS and LT1763.
    LT1763 dropped from 12V to 10V output with 15V input and ripple of 1Vpp@200kHz.
    Same result with 16V supply, so this seems to be an issue, or is it a feature (expected behaviour)?

2. Apparently normal operation at steady state with expected 12V output - input ripple is reduced to 0.76Vpp.

3. Same at steady state with closeup of 12V ripple: 0.76Vpp/0.076Vpp gives attenuation of 10 (20dB), Datasheet states ~30db@200kHz - so it is a bit off.
    Interestingly the feedback has 40mVpp ripple, but should have only 1/10th of 12V ripple (7.6mVpp).
    There is a lot of current flowing between SMPS and input cap and as the probes are referenced to GND at power jack, there is a bit of voltage drop between GND at power jack and GND at LT1763 output involved.
    But luckily we can get the voltage drop due to excessive current from -Ref line, which is ~20mVpp, so ~20mVpp remaining at feedback.
    Should be in the ballpark as there was no appropriate probing possible (normal GND leads at probes).
   
4. Added 0.5m leads to SMPS - resonance has gone and turned into expected ripple for SMPS (down to 1/10th at ~100mVpp).
    Output now is 12V on warm up & steady state.
    So I had the luck to hit the resonance point of the system with choosen leads :box: :bullshit:
   
5. For comparison: same with linear PSU  :=\
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on October 20, 2018, 09:46:54 am
Yes, it was a lesson learned, even for initial operation I will avoid SMPS in future :horse:

Imho it's not about SMPS, it's about loopback compensation. A linear PSU is no different in this regard.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on October 20, 2018, 08:16:26 pm
Is the LT1763 input capacitor C12 1uF/25V being an 0805 MLCC under specified? The data sheet calls for anything between 1uF-10uF, but this IC is usually used for <=5V (at least it's fixed versions are in that range). Perhaps a cap closer to 10uF would be better for the higher input voltages?

Any old MLCC capacitor could present a drastically lower capacitance at input voltages as large as 15-18V.

See Temperature and Voltage Variation of Ceramic Capacitors, or Why Your 4.7µF Capacitor Becomes a 0.33µF Capacitor (https://www.maximintegrated.com/en/app-notes/index.mvp/id/5527)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 20, 2018, 09:13:47 pm
I use 0805 1µF X7R/50V capacitors. If you are afraid you can bodge a MKS2 1µF cap instead.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on October 21, 2018, 10:49:27 am
Any old MLCC capacitor could present a drastically lower capacitance at input voltages as large as 15-18V.

I don't think it's  about age. It's about dielectric material and volumetric capacitance (bigger caps of small size tend to have more dc bias problems). The only way to know possible variation is (apart from measuring) to refer to datasheet or simulator. Big vendors like murata, kemet, avx provide dc bias curves. The effect can be very pronounced even at voltages below 5V.

Although, there is an aging effect as well: https://www.murata.com/support/faqs/products/capacitor/mlcc/char/0006 (https://www.murata.com/support/faqs/products/capacitor/mlcc/char/0006)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on October 21, 2018, 12:52:43 pm
Any old MLCC capacitor could present a drastically lower capacitance at input voltages as large as 15-18V.

I don't think it's  about age. It's about dielectric material and volumetric capacitance (bigger caps of small size tend to have more dc bias problems). The only way to know possible variation is (apart from measuring) to refer to datasheet or simulator. Big vendors like murata, kemet, avx provide dc bias curves. The effect can be very pronounced even at voltages below 5V.

Although, there is an aging effect as well: https://www.murata.com/support/faqs/products/capacitor/mlcc/char/0006 (https://www.murata.com/support/faqs/products/capacitor/mlcc/char/0006)

<Chuckle> In idiomatic English "Any old x" is just an emphatic way of saying "Any x" possibly with a side suggestion that it's not new, novel, or in any way special.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 22, 2018, 08:51:30 pm
Since one user didn't answer by now there are 5 boards left for the community. So for those of you that have been late, here is your last chance to participate. Simply write me a PN with your email address and postal address for further details + shipping and how many boards you need.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 24, 2018, 06:39:16 pm
Sorry to say that, but all boards have been sold.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on October 25, 2018, 08:16:12 am
I'm curious why LM399 and ltz1000 are not bypassed by a cap? Neither directly, nor with an RC-filter. Is this because of potential problems (with, e.g., leakage current, or opamp's input bias) or because this is not really needed?
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on October 25, 2018, 09:14:24 am
I know at least one dmm with LM399 that uses a bypass cap, think it was 0.33uF.
For LTZ1000 there is a hot discussion about bypassing (https://www.eevblog.com/forum/metrology/mx-reference/msg1297826/#msg1297826).
If used good caps e.g. MKP there is no issue with leakage.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BradC on October 25, 2018, 01:42:09 pm
Sorry to say that, but all boards have been sold.

You say that like its a bad thing.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 25, 2018, 06:27:32 pm
I'm curious why LM399 and ltz1000 are not bypassed by a cap? Neither directly, nor with an RC-filter. Is this because of potential problems (with, e.g., leakage current, or opamp's input bias) or because this is not really needed?

Hello,

Most designs are rather old. So mobile phones, WIFI etc. did not play a role.
On LM399 a 100nF cap improves massively EMI behaviour.
Leakage is negligible compared to 1 Ohms output impedance.

On the datasheet cirquit of the LTZ1000 you will get a instable output without further components.
(so use either Dr. Franks (branadic PCB) or my design to improve behaviour).

When you look at the Fluke 732B specification it is a 0.18V/m specification without being out of tolerance.
Industry standard requires to withstand 10V/m so you will need a shielded RF cabinet to operate a Fluke 732B according to spec.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 27, 2018, 06:27:35 pm
Little volt nut meeting with 9x LTZ references and 2x AD587 references on Keithley2002 and K3458A and lot of good discussion today in Stuttgart, together with some homework for the next meeting.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on October 27, 2018, 07:10:44 pm
What's the name of the power supply on the photo? (the one below Keithleys).
Title: Re: Ultra Precision Reference LTZ1000
Post by: 2N3055 on October 27, 2018, 07:22:29 pm
What's the name of the power supply on the photo? (the one below Keithleys).

Looks like Hameg HM8143
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 27, 2018, 08:45:29 pm
What's the name of the power supply on the photo? (the one below Keithleys).

Looks like Hameg HM8143

Exact, it's a HM8143.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: casinada on October 27, 2018, 09:40:12 pm
After all the effort on expensive multi-meters and nice voltage references, do the cables make sense?  :-//
Title: Re: Ultra Precision Reference LTZ1000
Post by: ManateeMafia on October 27, 2018, 11:13:10 pm
Looks like you have plenty of data collection going on there.

A couple of questions:
1. Do you have a gold standard reference? One that has been recently calibrated or measured against a calibrated source?
2. Do you plan on shipping a reference around for measurements against house standards?
3. The 2182A is the best meter there for series-opposition measurements. Is there a plan to create a special cable for it so you can make measurements against the others?
4. Do any of you have access to a Data Proof scanner?
5. Will the measurements be compared between line power and battery operation?

Good luck. I am sure more will want to join you by your next meeting.
BTW, I thought meetings in Germany included beer. I see no evidence of such.  :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 28, 2018, 10:11:41 am
Looks like you have plenty of data collection going on there.

A couple of questions:
1. Do you have a gold standard reference? One that has been recently calibrated or measured against a calibrated source?
2. Do you plan on shipping a reference around for measurements against house standards?
5. Will the measurements be compared between line power and battery operation?

Hello,

yes around 12.2 Mb raw .csv data. It will need some time to evaluate all.
1. the 3458A was recently calibrated at Keysight Böblingen, so we are within 90 days specs.
2. I plan to ship (within EU) my AD587LW#02 after having a shippable read out interface. (but this will be part of a new thread).
5. My references are only specified for battery operation.
    Branadics reference LTZ1000#3 has been tested for both without and with line power.
    (I can not see any significant difference before and after the glitch due to connecting).

Some impressions:
My LTZ#4 on HP3458A some minutes: Standard deviation 0.2 uV
A bit more noisy the travel standard AD587LW#02: Standard deviation 0.6 uV (offtopic here)
Branadics LTZ1000#3 (10V option unadjusted) battery and line powered (after the glitch)

with best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 28, 2018, 12:25:32 pm
Quote
After all the effort on expensive multi-meters and nice voltage references, do the cables make sense?  :-//

You are right, good cables are important. But to be honest, 100€ and more for a ready to go 1m PTFE cable with gold-plated spade lugs or simple Multi Contact (former Staubli) connectors are half the budget of a LTZ reference und pretty expensive. I'm still searching for an economic solution or a source for good twisted pair, shielded PTFE cable. This is what I took for homework to be done until next meeting.  :P

Quote
2. Do you plan on shipping a reference around for measurements against house standards?
3. The 2182A is the best meter there for series-opposition measurements. Is there a plan to create a special cable for it so you can make measurements against the others?
4. Do any of you have access to a Data Proof scanner?

Good luck. I am sure more will want to join you by your next meeting.
BTW, I thought meetings in Germany included beer. I see no evidence of such.

2. The maximum I think of is an intercomparison within Germany where I can travel to.
3. Well, the 2182A needs some calibration first, but yes the plan is to use it in further measurements. Cables are already at hand for it.
4. No, I don't have a Data Proof scanner. I once had a Prema 2080, but sold it by stupidity once I got my Prema 5017 SC, that was before we bought the K3458A.

No drinks in the lab which is full of expensive gear and electronics. Since Andreas had to drive, beer was prohibited :) But we had coffee instead.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 28, 2018, 07:16:47 pm
Sorry, those cables and laptops next to sensitive equipment bothers me enough to leave this post here..  :bullshit:
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 28, 2018, 08:05:27 pm
Sorry TiN, but not everyone can wastefully spend money like you do. This is fine for you, but please don't complain that not everybody is in your situation. Somewhat more social competences would even be good for you and is more worth then money ;)

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: GregDunn on October 28, 2018, 08:59:35 pm
Beer + calibrated references + expensive DMMs = the European equivalent of "Hey, y'all, watch this"?   :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: lukier on October 28, 2018, 09:13:11 pm
You are right, good cables are important. But to be honest, 100€ and more for a ready to go 1m PTFE cable with gold-plated spade lugs or simple Multi Contact (former Staubli) connectors are half the budget of a LTZ reference und pretty expensive. I'm still searching for an economic solution or a source for good twisted pair, shielded PTFE cable. This is what I took for homework to be done until next meeting.  :P

You don't need to spend 100€/m. Well maybe off the shelf Fluke cables cost that much, but things can be DIY-ed for much less, not to mention that Cat6 ethernet cable would be probably good enough.

If the group in Germany is big enough one could do a group buy a 150m reel and split the cost:
https://www.mouser.co.uk/ProductDetail/Belden-Wire-Cable/8719-060500?qs=sGAEpiMZZMs5%2f3jTaGtq4K0qP2YKd7fbUuidhOjrEF0%3d (https://www.mouser.co.uk/ProductDetail/Belden-Wire-Cable/8719-060500?qs=sGAEpiMZZMs5%2f3jTaGtq4K0qP2YKd7fbUuidhOjrEF0%3d)

From time to time one can find off-cuts on eBay like I did recently:
https://www.ebay.com/itm/192406299624 (https://www.ebay.com/itm/192406299624)

All in all I've paid 88.02 GBP for 17m (too much), so ~5.17 GBP/m. One would need < 3m for a DIY Fluke 5440A-7003 (based on this cable), so ~12.5 GBP,  4.56 GBP for two Pomona 1825-6 and few quid more for copper spades and thermal shrink tubes. That is probably < 25 GBP for a set of 3 cables almost identical to what Fluke uses for 732B. Not pure copper, not PTFE, but good enough for Fluke it seems. See the photo (I'm waiting for guard Pomonas from Mouser). This is some heavy cable, should be good enough up to 10A as well.

I have some 4 wire PTFE coming my way from eBay (again off-cuts) for high resistance / low current stuff. It is also around 5-6 GBP/m (all in all, shipping, taxes). I'll share more when it gets here and I'll make some leads.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 28, 2018, 09:14:58 pm
Beer + calibrated references + expensive DMMs = the European equivalent of "Hey, y'all, watch this"?   :-DD

The DMMs are not private, but part of the calibrated equipment at my work. So we can use it to compare our homebrew stuff to get the volt at home. What else do you want?

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on October 28, 2018, 09:22:54 pm
How does transportation affect precision? Are ltz1000 sensitive to vibrations and (big) change of temperature?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on October 28, 2018, 09:32:13 pm
Quote
vYou don't need to spend 100€/m. Well maybe off the shelf Fluke cables cost that much, but things can be DIY-ed for much less, not to mention that Cat6 ethernet cable would be probably good enough.

Thanks for sharing.

At least the reference design by Andreas uses a battery pack to power them during transportation. The inguard with the resistors and reference is thermally isolated with cotton wool.
To reduce temperature effects I had them in a "cooling" bag during transportation and thus good isolated from ambient temperature.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 28, 2018, 09:45:00 pm
How does transportation affect precision? Are ltz1000 sensitive to vibrations and (big) change of temperature?

Hello,

since I transport my LTZs hot they are less affected by temperature.

I also check them before and after transport against my 24 Bit ADCs.
Up to now no issue found outside the stability of my ADCs (around 0.25 ppm std dev).

So it is more risk to transport a LTZ1000 or  a complete 3458A in cold state in winter.
(see reports of Frank here e.g.)
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1882325/#msg1882325 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1882325/#msg1882325)


with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 28, 2018, 10:46:30 pm
Folks, please calm down!

The quality of these leads maybe not so good, but volt-nuts meetings should be appreciated, anyhow.
Especially, if the scope of this comparison is still to be analysed.

A German engineering meeting w/o beer, that's another serious story.. that has to be improved! Illya, what's your favorite booze?

In the company, we recently had our international engineering meeting from our 10 development sites, from 4 different continents (Australia has no Engineering anymore, sorry Dave), and German beer was the most important feature.

I also can add, at the latest volt-nuts meeting @ Andreas and with branadic , I carried my 3458A.

Afterwards, due to the transport, it showed a jump of -0.5ppm. It was not that cold at all, like the latest LTZ comparison last year, of two of my LTZ1000 (unheated), so most probaly, that simply was caused by vibration.

I was able to definitely identify that by comparison to the home-residing references (2x LTZ1000, 1x 5442A)

Anyhow, (cold) transportation and vibration is not yet examined well, inside this thread..

Andreas' approach are heated references, mine are potentially unheated ones, during transport.

Pitiful, we did not do that complete ring-comparison yet.

There are a lot of people here in Germany and EU to organize LTZ1000 and 10k Ohm exchange, but somehow there's no real drive to just do it, by DHL, or personally...

Instead of moaning at each other, maybe we could organize something international, even using quality references, as LTZs and VHPs.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on October 28, 2018, 11:50:03 pm
It looks like you guys all had some fun. Besides, I've always found the "teflon coated pure copper cable with crimped lugs mating with purest tellurium copper posts" a bit like audiophool wankery. I mean it also requires the environment to be totally sterile, no draughts, changes of temp, and just so the Seebeck effect is cancelled out after plugging leads in a mere 2 seconds vs 30 seconds (totally made up) with inferior brass posts and connections?

Ok, if you are in a factory calibration situation like a US army post, drilling through 10's or 100's per day, then a fast connection get the job done, shift it, move on to next job is the order of the day. The grunt will not care so expensive low thermal leads are easily justified here.

But in your own lab or a get together?? Just needs some time to settle.

I am also only a 6.5 digit nut.  :-DD

Title: Re: Ultra Precision Reference LTZ1000
Post by: GregDunn on October 29, 2018, 12:05:59 am
A German engineering meeting w/o beer, that's another serious story.. that has to be improved! Illya, what's your favorite booze?

In the company, we recently had our international engineering meeting from our 10 development sites, from 4 different continents (Australia has no Engineering anymore, sorry Dave), and German beer was the most important feature.

I'll have to settle for raising a virtual toast from my end - but give me time to visit the nearest Hofbräuhaus and collect some nice Oktoberfest brew before the next volt-nut meeting so I can celebrate accordingly!
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on October 29, 2018, 04:19:18 am
Quote from: Dr.Frank
The quality of these leads maybe not so good, but volt-nuts meetings should be appreciated, anyhow.

Indeed, the more meetings the better.  :-+ I still remember lots of fun during my 1 week meet-up in US 2 years ago, we should make it happen again in 2019 with US nuts.
My comment was just a hint on areas to improve, perhaps it was lost in language/cultural differentials. No need spend hundreds of dollars/euros/pounds to get CAT6e shielded cable and benefit the low-thermal connections to the 3458A's posts, and get rid of those laptops full of switching power supplies. I design computer hardware for living, so I know how much crap does this stuff emit for RFI/EMI first hand :). Little improvements and care like that pay off by better confidence in results.
Or maybe I played with nanovoltmeters too much, where using even different copper cable is well visible...  :phew:

Quote from: Dr.Frank
There are a lot of people here in Germany and EU to organize LTZ1000 and 10k Ohm exchange, but somehow there's no real drive to just do it, by DHL, or personally...
Instead of moaning at each other, maybe we could organize something international, even using quality references, as LTZs and VHPs.

I'd love to get some refs rotated (or DMMs, as my calibrator is already happy and in order). But I fear we'll run into same issue as USA Cal club thread members, with undefined procedures and lack of data transparency. Often amount of work to even perform single reference transfer round-trip in terms of careful math, environment effect accounting and drift prediction is underestimated. While that's all fine for 6.5digits, getting numbers up to 8.5d level is whole other story, outside of this thread topic.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on October 29, 2018, 05:37:19 pm
You are right, good cables are important. But to be honest, 100€ and more for a ready to go 1m PTFE cable with gold-plated spade lugs or simple Multi Contact (former Staubli) connectors are half the budget of a LTZ reference und pretty expensive. I'm still searching for an economic solution or a source for good twisted pair, shielded PTFE cable. This is what I took for homework to be done until next meeting.  :P

ab-precision (https://www.ab-precision.de/products/accessories/) has fully assembled low emf, diy-kits and 2/4 wire teflon cable - everything a low-emf heart desires  ;) (not affiliated)

A year ago I got a pair of self-made 2/4wire ptfe low emf (45/50Eur) from german ebay-seller sd-trader (http://www.ebay.de/usr/sd-trader?_trksid=p2057872.m2749.l2754), but at the moment there are no items...

(https://i.ebayimg.com/images/i/162719846724-0-0/s-l140/p.jpg)

Low EMF comes at a price, even the Pomona 3770 are quite expensive: ~15$ each  :o
Title: Re: Ultra Precision Reference LTZ1000
Post by: MikeP on October 29, 2018, 07:31:23 pm
 Regarding cheap CuTe connectors - FUREZ. This is a recommendation of some metrological  specialist. I used this and can confirm good quality.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on October 29, 2018, 08:42:24 pm
Those Furez-connectors: https://www.douglasconnection.com/Furez-Products_c20.htm (https://www.douglasconnection.com/Furez-Products_c20.htm)
look rather good, but lack the possibilty to directly be crimped on copper wires and have a big thermal mass.
I rather stay with the spade-lug-version mentioned by MiDi.
Title: Re: Ultra Precision Reference LTZ1000
Post by: VK5RC on October 30, 2018, 11:05:23 am
The Aussie volt-nuts did a reference shuffle about a year ago, certainly a lot of lessons were learnt. In my set up, a laptop in the lab anywhere is pretty bad, 10-20uV change, esp if connected by gpib, more so if running on the charger.
The travel of the references - probably a mixture of road and air- I think also wasn't good.
For my longer term (11 months to date) reference measurements, 9  KZ  LTZs, one old 3458 ref board and a Fluke 731b.
I have used exclusively one (and only one actual cable) of Pomona's low emf shielded cables - I have been very happy with the consistency of the results.
6 of DrFranks LTZs are in the pipeline, 3 using a 'quick and dirty' mixture of vishay (120Rs) & TEs , and 3 awaiting some Edwin goodness!
Title: Re: Ultra Precision Reference LTZ1000
Post by: MikeP on November 02, 2018, 07:55:36 pm
but lack the possibilty to directly be crimped on copper wires

 No. This connectors can be crimped very well. In addition, e >:Dbay offers this brand very inexpensive.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on November 02, 2018, 08:34:12 pm
Must have overlooked the crimp-type-ones and only did see the ones with the tightening screws. Indeed, they look price-wise not bad compared to the standard Pomona 3770-binding posts:

https://www.ebay.com/itm/Furez-TST-W30AG-Silver-Plated-Copper-Banana-Plug-Speaker-Connectors-Crimp-Solder/142938936767?hash=item2147d315bf:g:ZlQAAOSwfLpbnEgS:rk:17:pf:0 (https://www.ebay.com/itm/Furez-TST-W30AG-Silver-Plated-Copper-Banana-Plug-Speaker-Connectors-Crimp-Solder/142938936767?hash=item2147d315bf:g:ZlQAAOSwfLpbnEgS:rk:17:pf:0)
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on November 03, 2018, 11:34:52 pm
Silver oxidizes fairly quickly in air which I assume would be terrible for thermal EMFs. If you are going to have to clean them before every use why not stick to unplated copper?

Do Furez do gold plated copper plugs?
Title: Re: Ultra Precision Reference LTZ1000
Post by: ManateeMafia on November 04, 2018, 01:12:35 am
I have some of these https://www.douglasconnection.com/Furez-TSTWP30NP-Bare-Copper-Banana-Plug-Connectors-Pair-FZTSTWP30NP.htm (https://www.douglasconnection.com/Furez-TSTWP30NP-Bare-Copper-Banana-Plug-Connectors-Pair-FZTSTWP30NP.htm) I use for a Keithley 181 cable.

They are nice but do scratch easily if the binding posts are not clean.

Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on November 04, 2018, 02:58:43 pm
What is a resin printer such as Anycubic Photon worth for? Exact, for printing LTZ caps. Did that today.

Offer: I also printed those HP/A/K LTZ1000 caps, but they don't fit to this board or any other board I have. The one who writes me a PN first can get those two caps for postage cost only. Will also add the bottom cap, that I print the next days.

Attention: Please check your LTZ boards for short circuits. Someone reported a pretty big short on one of his boards. I haven't checked all the boards, just packaged them and sent them out.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on November 04, 2018, 08:45:15 pm
BTW, I wonder why lt1013 is used and not, say, LT1001 . LT1001 has lower offset. Sorry if this was discussed before.

Is LT1001 auto-zero op-amp? This could explain why people don't use it. The datasheet doesn't mention this.
Title: Re: Ultra Precision Reference LTZ1000
Post by: borghese on November 04, 2018, 09:29:18 pm
The minimum input voltage of LT1001 is > 1 Volt; in normal LTZ circuit the voltage is about 0.5 Volt.
NO, the LT1001 is not Auto-zero OP. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: borghese on November 04, 2018, 09:32:25 pm
Quote
What is a resin printer such as Anycubic Photon worth for? Exact, for printing LTZ caps. Did that today.
Hello
Can you share the CAD files?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on November 04, 2018, 10:07:39 pm
Quote
What is a resin printer such as Anycubic Photon worth for? Exact, for printing LTZ caps. Did that today.
Hello
Can you share the CAD files?

Which one do you mean, the HP/A/K? They can be found here:

https://xdevs.com/doc/HP_Agilent_Keysight/3458A/cad/a9_cap_top.STEP
https://xdevs.com/doc/HP_Agilent_Keysight/3458A/cad/a9_cap_bot.STEP

Or do you mean the one I designed?

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: borghese on November 04, 2018, 10:58:27 pm
The one you designed.
Thank you in advance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on November 05, 2018, 06:15:48 pm
The caps are given away. Congrats to the new owner.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: dkozel on November 05, 2018, 10:42:57 pm
borghese, there's a zip attached to branadic's previous post. I don't have an stp file viewer, but it's almost certainly his caps.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on November 06, 2018, 01:43:49 am
To exe, reply 2430, the LT1013 was specifically designed to work with the LTZ circuitry, the LT1006 is very similar to the LT1013 being a single op-amp but is not exactly identical.  The LT1013 (from LT) is still the best op-amp to use with the LTZ circuits.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on November 06, 2018, 04:05:26 pm
The LT1013 is single supply, so it can work well at the low (e.g. around 500 mV) input level, without a negative supply. The single equivalent is the Lt1006 (the lt1005 is an obsolete regulator).

The LT1001 is other wise OK , but not single supply and would thus need an extra negative supply and provisions to get a defined start-up sequence. It might still be OK for the negative reference circuit, but even there during startup the common mode voltage can be quite close to the negative side.

Also the OPs are not that critical to the performance, so no need for a really high performance OP. Just from the data-sheet performance even an LM358 could work reasonable, though I would still prefer the LT1013, but no real need to get one of the better grades. Just like with the resistors the drift from the OP is attenuated by a factor of some 200.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 06, 2018, 07:45:39 pm
Hello,

the LT1013 has better open loop gain (against LT1001)
This is essential especially for the zener current regulator.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on November 07, 2018, 03:00:35 pm
Attached are the cad files for front and real panel of the Hammond case.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Fastah on November 07, 2018, 06:38:57 pm
Sorry to say that, but all boards have been sold.

-branadic-

Hi
I'm interested for 3-5 boards. Are you planning to make more boards for sale here on forum?

Thank you
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on November 07, 2018, 09:26:24 pm
In short? No :)

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on November 08, 2018, 08:40:53 am
the LT1013 has better open loop gain (against LT1001)
This is essential especially for the zener current regulator.

Why is this essential? To reduce noise?

Just from the data-sheet performance even an LM358 could work reasonable, though I would still prefer the LT1013, but no real need to get one of the better grades. Just like with the resistors the drift from the OP is attenuated by a factor of some 200.

Could you please elaborate how offset is attenuated? I thought offset only amplifies as we upconvert 6.95V to 10V.

PS thanks guys for sharing. Love your research, die shots, etc :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on November 08, 2018, 05:57:01 pm
The error signal from the LTZ1000 is first amplified by the transistor inside the LTZ1000. This transistor has a voltage gain of around 200. The OPs only see the amplified error signal. So compare the effects at the transistor base the OPs offset and noise is effectively attenuated by that factor of 200.

So an 1 mV offset form the OP would result in some 5 µV extra voltage shift for the whole circuit.
The amplification be the transistor also adds to the loop gain. So even if the OP would have a gain of only 100K the total loop gain would be at some 20 millions and would thus only contribute some 0.3 µV to the 7 V output. So I don't think the amplifiers gain should be that important.

The main point's for the LT1013 are that it is well behaved on start up, e.g. with the supply still low, does not show phase reversal and has low enough current noise to work with some 70 K input resistance. Noise is well good enough.
Title: Re: Ultra Precision Reference LTZ1000
Post by: VK5RC on November 12, 2018, 09:17:18 am
A photo of the 1st 3 DrFranks pcb  ltz10000A, with vishay s102 120ohm, TEs others, x3 tps7a4901 low noise psu . Having a little warm up.
Thanks DrFrank et al!

Later I will have some data about the effect of an 800km road trip on a 3458 (for calibration)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on November 12, 2018, 05:43:46 pm
Be careful with the unbuffered reference output, prevent shorts by accident.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: VK5RC on November 12, 2018, 07:53:23 pm
I have a procedure to reduce that risk, the ltz's hot is the last connected and the first disconnected.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 14, 2018, 05:00:53 am
Perhaps interesting dataset for somebody curious about how freshly built LTZ ref behave when first powered on, and how initial days of settle look like.

(https://xdevs.com/doc/xDevs.com/FX/build10/ltzf_nov18_1.png) (https://xdevs.com/doc/xDevs.com/FX/build10/ltzf_nov18.png)

Four meters used for sampling:
* 3458A with Keithley 7168 nV-scanner card (ch1-ch8)
* 3458A (drifty ADC) on black HPC chart.
* K2002 (K4 chart)
* second K2002 (K6 chart) measuring my 24/7 792X as main 10V reference (LTZ FX based)

No aircon, so bit higher ambient temps than usual 24c
From November 7 I restart logging, and ran ACAL DCV on 3458A drifty. You can see it's ADC drift on first 2 days as ~+2ppm a day.
But to my great surprise drift on ADC become <0.1ppm a day afterwards. I'm running multiple ACALs now every day. CAL72? value also show similar data.
I don't believe in self-fixing 3458 ADCs, but never know. Meter was left running for about a month, drifting.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on November 15, 2018, 07:45:13 pm
So, you have a jumper and two drifter out of 8 new build LTZ1000 references? Or did the other references had time before this measurement to burn in?

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on November 16, 2018, 01:07:16 am
Jumper is same LTZ1000A chip from eBay 3458 A9 (https://xdevs.com/article/ltz_tale1/).
CH1(2) reference had few days runtime before. CH2-CH8 are all first power on (not counting few minutes long test runs). K2002-6 is my 24/7 10V FX reference (uninterrupted power since Feb'18).

I'll need to check CH6 and CH8 units though.

Here I rearrange data to use last yesterday value as 0ppm reference (https://xdevs.com/nvsf_nov18/). It's bit easier to see settling time on difference channels.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on December 03, 2018, 06:07:05 pm
One reference fully assembled and running on 3458A since 400h with 10V boost installed. Another 5 references only buffered are almost ready to go and 4 references are still waiting for their LTZ resistors to arrive. What about the other boards that have been spread over the whole world?

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Sprock on December 04, 2018, 09:21:52 am
Hello all,
Resitors still in Frankfurt / Germany.
regards Sprock
Title: Re: Ultra Precision Reference LTZ1000
Post by: BradC on December 04, 2018, 09:44:38 am
What about the other boards that have been spread over the whole world?

Sitting in a big box with other lonely parts. Resistors have been sitting in a USPS facility in Sanfransico for a week now. They should get here before Christmas, just in time for the festive pause hopefully resulting in some assembly in the new year.
Title: Re: Ultra Precision Reference LTZ1000
Post by: pansku on December 04, 2018, 10:04:18 am
What about the other boards that have been spread over the whole world?

Waiting for parts and the ability to use my right hand for soldering *sigh*
Title: Re: Ultra Precision Reference LTZ1000
Post by: SvanGool on December 04, 2018, 11:45:27 am
@Sprock:

Nice card guides, may I ask where you got those?
I assume you are using a bigger enclosure than the Hammond 1455C1210, not (I like the direct ref option you still maintained)?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Sprock on December 04, 2018, 02:00:31 pm
Hi
@ SvanGool,

guides are from scrapp box. The original is from Phönix Type FLP/SKBD.
Yes, you are right the case is bigger. It is the 1455 J 1210  instead of C.
No, all 3 boards will get different boxes. Only one in the black aluminium
with board guide.
regards
Sprock
Title: Re: Ultra Precision Reference LTZ1000
Post by: SvanGool on December 04, 2018, 02:12:54 pm
Thanks !

Mouser has them: https://www.mouser.de/ProductDetail/Phoenix-Contact/2204121 (https://www.mouser.de/ProductDetail/Phoenix-Contact/2204121?qs=sGAEpiMZZMuvJlO0BgfYbLt982FZ9m5S) (but not on stock)
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on December 05, 2018, 08:51:38 pm
One reference fully assembled and running on 3458A since 400h with 10V boost installed. Another 5 references only buffered are almost ready to go and 4 references are still waiting for their LTZ resistors to arrive. What about the other boards that have been spread over the whole world?

-branadic-

Mine is still in the box waiting for resistors (group buy on eevblog).

Nice boxes you have. What are they and where did you get them? Are they on Digi-key?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Haasje93 on December 05, 2018, 09:40:53 pm
Hi!

On page 93 is your awnser. But i have here the link for the cases on Digikey.
https://www.digikey.com/products/en?keywords=1455C1201 (https://www.digikey.com/products/en?keywords=1455C1201)

Regards,
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on December 05, 2018, 09:59:54 pm
Exactly, Hammond 1455C1201 is what the board is designed for. I had a colleague milling the frontpanels for me. The files for them are available a few posts above.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: dkozel on December 06, 2018, 11:39:14 pm
I've ordered the long lead time items but have to finish selecting the last few more basic bits and get them ordered. I've been distracted with figuring out how I'm going to measure these once they're assembled. I don't want to miss the burn-in and do want to measure the three I'm building simultaneously.

I've started testing and warm-up of a pair of 3458A multimeters that I've borrowed (Thread (https://www.eevblog.com/forum/metrology/testing-working-3458as/)). Along side that I've been looking at different scanner options and managed to find a nice deal here on the forum for a Keithley 7001 with 7011-S cards. They're spec'd for <500nV offset voltage, so >10x worse than TiN's 7168 cards, but I imagine >10x easier to get too. ;) I look forward to the day they aren't good enough for my needs.

Still need to get some cables together, but the last few pages of this thread as well as the various other low EMF threads have been useful there.

Branadic, quick question for you, do the LTZs have >4.2 mm of vertical clearance when in the Hammond case? I'm considering socketing the LTZs if it will work. Also, do you have any plans for how you're using the thermistor? I'm wondering if it's thermally a terrible idea to drill a small hole in the LTZ plastic covers (thanks for the models) and placing the thermistor in direct contact with the case. I have to imagine the thermal transfer would be minimal, but...  :-//

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 07, 2018, 08:25:59 am
There is no real need to measure temperature of the LTZ1000 itself. The temperature sensor is on the chip and the temperature is very well regulated - down to the mK range.

Temperature is more effecting the resistors and maybe thermal EMF from the contacts LTZ to copper. Another point is the change in heater power that might effect the reference.

So a temperature sensor would be better placed at the case or at the resistors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on December 07, 2018, 10:08:07 pm
Quote
Branadic, quick question for you, do the LTZs have >4.2 mm of vertical clearance when in the Hammond case? I'm considering socketing the LTZs if it will work. Also, do you have any plans for how you're using the thermistor? I'm wondering if it's thermally a terrible idea to drill a small hole in the LTZ plastic covers (thanks for the models) and placing the thermistor in direct contact with the case. I have to imagine the thermal transfer would be minimal, but...  :-//

There is for sure enough space inside the Hammond case above the LTZ, but do me a favor and don't use a socket for your reference. I do have a minimal gap between board and LTZ to avoid any stress transfer between them.
The temperature sensor be it a thermistor or a platinum sensor can be used to measure temperature dependance of the whole circuit to verify everthings works a treat. And as Kleinstein already stated, it's not the temperature of the LTZ you want to monitor, but all the other components such as the resistors.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: VK5RC on December 09, 2018, 06:13:02 am
Received some of Mr Pettis' resistors during the week so finished stage 2 of a x6 DrFrank's PCB based Ltz Reference Bank
It is located above TiNs KZ PCB reference bank (plus one old 3458 LTZ reference board alone)
(The 'code' next to each output refers to
   A or C  - LTZ1000 A or C,   
   1 or 2  - op amp LT1013=1 or 2057=2
   Resistors V =vishay. , U= TE's UPW series, P=Pettis Engineering
All have 2 stage linear PSUs
     1st common rail LM38xx,
      2nd stage each LTZ has its own TPS7A4901 ultra low noise in a separate box
All connected to mains UPS
Pomona 3770 posts for Ref 4-15

My Thanks to EEVBlog VoltNuts esp TiN, DrFrank, Edwin Pettis just to name a few.
Robert
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 09, 2018, 08:15:40 am
Hello,

Looks like a serious ageing test.  :clap:

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: VK5RC on December 09, 2018, 09:16:02 am
Thanks, references 1 to 9 and `3458` have been almost always switched on since Aug 2017. Reference 8 up until Sept was doing brilliantly but then dropped about 8uV. But now is pretty consistent again - within 1-2uV
My results also may be effected by the 800km road trip my old 3458 went on, for calibration in September - all in spec - so no adjustment. The results before and after cal don't appear to have a consistent trend.
One I get a few months of data from the new references , I read every few weeks I will publish here.
Robert
Title: Re: Ultra Precision Reference LTZ1000
Post by: ha110ween on January 11, 2019, 03:38:43 am
Hi!

I bulid my LTZ1000A Reference based on Dr.Frank's PCB,and the LT1763 Supply designed by Cellularmitosis.

The Resistors ratio is 12K4:1K.
Keep the long leads of LTZ1000A and protected from airflow by a foamed plastic block.

The plastic box is temporary, I'll replace it with metal shell later.
I put a layer of aluminium foil on the outside of the plastic box to reduce EMI interference.

I'll do some tests later.

Thanks to Dr.Frank,Andreas,branadic,Cellularmitosis,TiN and others.
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on January 11, 2019, 04:57:52 am
@ha110ween

Nice Job. Thank you for sharing, and welcome to the forum.  :-+

Some information about 10V 'divider' konfiguration and what type of binding posts you use would be nice, after some days of settle down maybe also some logged data.

I like it.  :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: ha110ween on January 11, 2019, 06:10:56 am
@ha110ween

Nice Job. Thank you for sharing, and welcome to the forum.  :-+

Some information about 10V 'divider' konfiguration and what type of binding posts you use would be nice, after some days of settle down maybe also some logged data.

I like it.  :)

Hi hwj-d,

Thank you :D

The output of the Zener is 7.08840v,so the resistors are (18+250+10K):25K.

The posts were removed from my old instruments.

I have a Keysight 34465A and a Fluke 2638A Data Acquisition Unit,I'll use that to record drift data.


Title: Re: Ultra Precision Reference LTZ1000
Post by: Inverted18650 on January 11, 2019, 07:23:02 pm
Would building this into a custom copper box enclosure be better or worse than building into an aluminum box? Would a solid copper box aid at all in reducing outside emf from the circuit? Please and thank you in advance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on January 11, 2019, 08:40:00 pm
Would building this into a custom copper box enclosure be better or worse than building into an aluminum box? Would a solid copper box aid at all in reducing outside emf from the circuit? Please and thank you in advance.

A steel box would be best for EMI, Aluminum and Copper would provide good RFI shielding but not much for EMI.
Title: Re: Ultra Precision Reference LTZ1000
Post by: eplpwr on January 12, 2019, 10:49:51 am
What about the other boards that have been spread over the whole world?

As many others: waiting for resistors ... I'm in the last batch for Edwins resistors. The other day I got a mail from Texas Components that they had misplaced my special order from half a year ago, and had produced exactly none of the ordered resistors (some strange story about not beeing able to mfg resistors with 0.125" spacing).

Regarding the Vishays, my alternative is to buy Z201 and test them for tempco, which will cause further delays.

Precision takes time.  :=\
Title: Re: Ultra Precision Reference LTZ1000
Post by: beanflying on January 13, 2019, 12:25:42 am
What about the other boards that have been spread over the whole world?

As many others: waiting for resistors ... I'm in the last batch for Edwins resistors. The other day I got a mail from Texas Components that they had misplaced my special order from half a year ago, and had produced exactly none of the ordered resistors (some strange story about not beeing able to mfg resistors with 0.125" spacing).

Regarding the Vishays, my alternative is to buy Z201 and test them for tempco, which will cause further delays.

Precision takes time.  :=\

Not at all happy with Texas Components and custom Vishay delivery times lost orders and email excuses :horse:
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 15, 2019, 01:56:58 pm
Here is one unit based on the previously shown board. It uses Rhopoint 8G16D resistors with 1k:12k for temperature setting at the LTZ1000CH (manufactured in 2018) and 4k (2x 2k) + 10k UPW50 resistors plus a 20ohm 64W pot with 22ohm resistor in parallel to one branch of the pot for the 10V boost circuit.
The voltage reference was adjusted to the corrected readings (reads 9,9999945V instead of 10,000000V with respect to the calibration report) on our 3458A (still within 90day specs). It will now take the big trip overseas in its double thermally insulated package to reach its new owner. Hopefully it does a good job there.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: AG7CK on January 16, 2019, 03:24:34 am
The graph is imo very well laid out and easy to read. If possible, I would like to know what program / software was used for the multi-graph template?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on January 16, 2019, 06:50:56 am
The answer is GNU Octave / Matlab.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: meandeev on January 27, 2019, 05:33:29 pm
branadic demanded photos some time ago:

here are my first two references, at this time without insulation/housing. For a first test i populated the first one with a LTZ from a broken HP3458-reference with strange high 7,245V and the second one with a new LTZ bought at Digikey. Both are compared with a KVD and a Null-meter (it is a clone of the one in Conrad Hoffmans calibration lab article) against a Voltagestandard-Reference and each other.

Title: Re: Ultra Precision Reference LTZ1000
Post by: ha110ween on January 28, 2019, 03:04:44 am
Hi,

I have measured my LTZ1000 References(Dr.Frank 's PCB) with my 34465A.
The data was loged by RPi_LogNut through the LAN port.

The python code of the DMM setup like below:
Code: [Select]
inst.write("CONF:VOLT:DC 10,MIN")

inst.write("VOLT:IMP:AUTO ON")
inst.write("VOLT:ZERO:AUTO ON")
inst.write("VOLT:NULL:STAT OFF")

inst.write("TRIG:SOUR IMM")
inst.write("TRIG:COUN 1")
inst.write("TRIG:DEL:AUTO OFF")

inst.write("DISP OFF")

The data is not averaged and the temperature(red line) is readed from the DMM internal sensor.
The python code is:
Code: [Select]
Temperature = inst.ask("SYST:TEMP?")
The drift  is caused mainly by the LM399 or the resistor networks of the 34465A,so the T.C. of the 35565A is about 0.5ppm/°C(Non ACAL).

I will measure the T.C. of my three LTZ1000 References later.

Thanks.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 29, 2019, 11:39:30 am
What should be a tolerance for non-precise resistors please? I just do not have 1% resistors in all nominals and wonder if I can use resistors with tolerance 5%? I am talking about R9, R10, R11, R6, R8 etc.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 29, 2019, 10:05:07 pm
The extra resistors at the temperature regulator (e.g. base, 400 K nominal, 1 M and 10 K) are not critical in there value / tolerance. The 1 M and 10 K set the frequency response - so no real need to be more accurate than the capacitor.  The 400 K resistors is used to compensate for some residual TC - the best value depends on the temperature, thermal insulation and reference chip. The best value could be considerable away from 400 K (e.g. 270 K - 1 M). Especially if a small resistor is used, it should be stable and thus more like 1% grade.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Macbeth on January 29, 2019, 10:14:17 pm
branadic demanded photos some time ago:

here are my first two references, at this time without insulation/housing. For a first test i populated the first one with a LTZ from a broken HP3458-reference with strange high 7,245V and the second one with a new LTZ bought at Digikey. Both are compared with a KVD and a Null-meter (it is a clone of the one in Conrad Hoffmans calibration lab article) against a Voltagestandard-Reference and each other.

Both those LTZ's are the ACH version and so you shouldn't need the 400k resistors as they are for the CH version AFAIK.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on January 30, 2019, 12:12:04 am
branadic demanded photos some time ago:

here are my first two references, at this time without insulation/housing. For a first test i populated the first one with a LTZ from a broken HP3458-reference with strange high 7,245V and the second one with a new LTZ bought at Digikey. Both are compared with a KVD and a Null-meter (it is a clone of the one in Conrad Hoffmans calibration lab article) against a Voltagestandard-Reference and each other.

Both those LTZ's are the ACH version and so you shouldn't need the 400k resistors as they are for the CH version AFAIK.

Even the 'A' can benefit from TC fine tuning.  Also, 400k for the TC resistor is just a place to start and the optimal value can be above or below this.  I think I found one of my 'A's needed 680K, while another needed 300K.

See here; https://www.eevblog.com/forum/metrology/kx-reference/msg1369941/#msg1369941 (https://www.eevblog.com/forum/metrology/kx-reference/msg1369941/#msg1369941)
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 30, 2019, 10:10:35 am
branadic demanded photos some time ago:

here are my first two references, at this time without insulation/housing. For a first test i populated the first one with a LTZ from a broken HP3458-reference with strange high 7,245V and the second one with a new LTZ bought at Digikey. Both are compared with a KVD and a Null-meter (it is a clone of the one in Conrad Hoffmans calibration lab article) against a Voltagestandard-Reference and each other.

Both those LTZ's are the ACH version and so you shouldn't need the 400k resistors as they are for the CH version AFAIK.

Even the 'A' can benefit from TC fine tuning.  Also, 400k for the TC resistor is just a place to start and the optimal value can be above or below this.  I think I found one of my 'A's needed 680K, while another needed 300K.

See here; https://www.eevblog.com/forum/metrology/kx-reference/msg1369941/#msg1369941 (https://www.eevblog.com/forum/metrology/kx-reference/msg1369941/#msg1369941)

Interesting.
Pardon my ignorance, but how did you come up with the TC resistor values? Purely empirical?
I have a non-A LTZ1000 and thinking what values I should start from.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on January 30, 2019, 11:25:21 am


Interesting.
Pardon my ignorance, but how did you come up with the TC resistor values? Purely empirical?
I have a non-A LTZ1000 and thinking what values I should start from.

I have published an elaborate description of my setup, and also how I measured and iteratively trimmed the T.C. of the assembly:

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1336573/#msg1336573 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1336573/#msg1336573)

See the small table in my 4th thread.
I always started without R9 (= inf.). Any resistor in between 240k and 1M will increase the T.C., so you can only trim reference assembly with an initially negative T.C.
I did not check for the A version, it's initial T.C. , maybe its sign might be different, but I assume that the increase of the T.C. by decreasing value of R9 will be the same.

That bootstrap method I have used the measure the T.C. can probably also be done with a LM399 based DMM.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on January 30, 2019, 04:13:27 pm
branadic demanded photos some time ago:

here are my first two references, at this time without insulation/housing. For a first test i populated the first one with a LTZ from a broken HP3458-reference with strange high 7,245V and the second one with a new LTZ bought at Digikey. Both are compared with a KVD and a Null-meter (it is a clone of the one in Conrad Hoffmans calibration lab article) against a Voltagestandard-Reference and each other.

Both those LTZ's are the ACH version and so you shouldn't need the 400k resistors as they are for the CH version AFAIK.

Even the 'A' can benefit from TC fine tuning.  Also, 400k for the TC resistor is just a place to start and the optimal value can be above or below this.  I think I found one of my 'A's needed 680K, while another needed 300K.

See here; https://www.eevblog.com/forum/metrology/kx-reference/msg1369941/#msg1369941 (https://www.eevblog.com/forum/metrology/kx-reference/msg1369941/#msg1369941)

Interesting.
Pardon my ignorance, but how did you come up with the TC resistor values? Purely empirical?
I have a non-A LTZ1000 and thinking what values I should start from.

Very much the same way Dr. Frank explains. But basically built an environmental chamber out of an ice chest to chill and warm the reference while monitoring the temperature and voltage deviation with a 7.5 dig DMM.  Repeated the tests many times over a few weeks.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Sprock on January 30, 2019, 05:43:33 pm
Hello
my heater is an old ion. (Bügeleisen)
Do not take it too serious.

Just a fast solution for me. :-)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 30, 2019, 08:31:16 pm


Interesting.
Pardon my ignorance, but how did you come up with the TC resistor values? Purely empirical?
I have a non-A LTZ1000 and thinking what values I should start from.

Hello,
I would start with R9 = infinite.
you can trim T.C. up by +40 ppb/K for each 1 Meg resistor in parallel for R9 on a LTZ1000A.

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg907048/#msg907048 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg907048/#msg907048)

Hello
my heater is an old ion. (Bügeleisen)
Do not take it too serious.

Just a fast solution for me. :-)

Interesting trimming bolt on the side  :-DD

best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 30, 2019, 09:15:08 pm
The TC compensation used the heater voltage. This means the strength depends on the used power level and set temperature. So the +40 ppb/K is only a ball part number. The actual number depends on the heater level and thus set temperature and insulation (e.g. cap).  A lower set temperature is expected to give less heater power and thus more change in voltage to compensate for temperature changes at a given thermal setup. The tendency should be a larger resistor for a lower set temperature.
Rather close to the set temperature things can get quite nonlinear - making TC compensation difficult.

Testing / selecting R9 should be done with the final thermal setup (especially cap over LTZ) and set temperature.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 31, 2019, 01:55:35 pm

Hello,
I would start with R9 = infinite.
you can trim T.C. up by +40 ppb/K for each 1 Meg resistor in parallel for R9 on a LTZ1000A.



Thank you
The below is very helpful:

Quote
For R9 = 1 Meg I get a T.C. increasement of around +0.04ppm/K
100K give around +0.4ppm/K over 20 deg C.

I feel like to need to read all 100 pages of this thread.  |O
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 31, 2019, 07:36:28 pm
I feel like to need to read all 100 pages of this thread.  |O


Otherwise you do not know that shortening the legs of a LTZ1000A also increases the T.C.
I recommend to start with long legs and shorten as necessary.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 01, 2019, 12:39:59 am
Quote
that shortening the legs of a LTZ1000A also increases the T.C.

Hmm, you have a link to data on this? I didn't see a difference in my boards.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 01, 2019, 08:04:08 pm
Hello Illya,

its all within this thread for my samples:

LTZ#3
Long legs -80 ppb/K
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg881955/#msg881955 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg881955/#msg881955)

Half shorted legs -40 ppb/K
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg924793/#msg924793 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg924793/#msg924793)

2-3 mm remaining legs -22 ppb/K
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg928435/#msg928435 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg928435/#msg928435)


LTZ #4
Long legs -230 ppb/K
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg882026/#msg882026 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg882026/#msg882026)

short legs -95 ppb/K
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg905152/#msg905152 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg905152/#msg905152)

so the last mm seems to change more than shortening by half.

Summary table
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg935102/#msg935102 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg935102/#msg935102)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: DC1MC on February 01, 2019, 09:17:36 pm
Woah, this legs thing it's really woodoo magic  :o !!!

 DC1MC
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 01, 2019, 10:13:10 pm
Andreas
I'm lost with your posts now, as you contradicting yourself in here  :-//.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 02, 2019, 06:12:42 am
Hello,

sorry I do not see what you mean.
I think it is a straight forward observation:
the shorter the legs the more less negative the T.C. (so T.C. increases).

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 02, 2019, 12:00:06 pm
Per your results, going from -80 ppb/K to -22 ppb/K and from -230 ppb/K to -95 ppm/K means TC is decreased (less impact on output voltage from temperature), not increased.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 2N3055 on February 02, 2019, 12:05:45 pm
Per your results, going from -80 ppb/K to -22 ppb/K and from -230 ppb/K to -95 ppm/K means TC is decreased (less impact on output voltage from temperature), not increased.

It decreased in absolute value (mathematically) , but it increased in value (as in it was less negative)....
Terminology gap.

EDIT: Spellchecker typo. Value decreased, it didn't die ...  :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 02, 2019, 12:29:03 pm
Yup. I'm going by usual convention of zero TC = no change, ignoring the sign.
Title: Re: Ultra Precision Reference LTZ1000
Post by: GregDunn on February 05, 2019, 01:11:47 am
Freshly arrived from across the pond, thanks to branadic for this nice little package.  Aged LTZ1000 with log of voltage vs. time, measured at 10.000002 VDC.

Obviously, I don't have a DMM good enough to check the LSDs; but this newly repaired HP3490A seems to think it's pretty close at 5.5 digits worth of precision.  This is after 4 hours of warmup; I'm now in the process of letting some other DMMs settle so I can cross-check them with it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: AG7CK on February 05, 2019, 02:02:48 pm
I like this "no voodoo" clean simple functional 10V box based on the green PCB from recent posts and a "classic" DIY-electronics style enclosure.

If Branadic or someone else has one more for sale or will produce these characterized plug-and-play reference units for other members, I would also like to buy one or be put in a queue for future purchase. Thanks.

Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on February 07, 2019, 12:33:54 pm
My board is almost done. Still waiting for precision resistors to arrive...
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on February 11, 2019, 01:09:40 am
My #1 branadic / Dr. Frank

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=649011)

Did quick check on noise for 7V & 10V with linear bench PSU:
Noise floor 10min: ~115nVpp (https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg1428673/#msg1428673)

7V buffered
10min: 2.3µVpp
12s best: 1.5µVpp
12s typ: 1.7µVpp
12s worst: 2.1µVpp

10V
10min: 3.2µVpp
12s best: 2.0µVpp
12s typ: 2.3µVpp
12s worst: 2.8µVpp
Title: Re: Ultra Precision Reference LTZ1000
Post by: Magnificent Bastard on February 11, 2019, 02:08:11 am
You might get even better noise readings if you add an air-draft excluder to the top and bottom of the LTZ1000.
Title: Re: Ultra Precision Reference LTZ1000
Post by: RandallMcRee on February 11, 2019, 04:55:32 pm

I suspect that you have some unidentified noise source.

Both of my DrFrank boards (sorry for not posting!) showed ~0.9uV of noise. There were two different LTZs, one from Arrow, one from Mouser, A and non-A.

Certainly air drafts, etc. are a possibility. My noise floor is similar to yours.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on February 11, 2019, 11:37:30 pm
Thanks for the suggestions, seems it is worth to investigate.  :-+
First thought was: ok, it is in spec, but bit on high side (DS: 1.2µVpp typ, 2µVpp max).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 12, 2019, 03:50:11 pm
I'm very pleased that Mr. Pettis' resistors fit well on the PCB, that looks really nice, also in the final enclosure.

I also suggest more thermal isolation, as that noise level is a bit high, but dependent on the sample.
That measurement is also dependent on the bandwidth under observation, so identical methods and BW limits should be obeyed.

For a more practical use, you may determine StDev with your 'new' 3458A, at NPLC 100, so you may get 100..200nV rms only, that's equivalent to maybe < 1Hz BW.

And you might measure and trim its T.C. 8) (if not already done?)
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on February 18, 2019, 01:02:05 am
Seems it was a misunderstanding what was measured (clarified in the post):
I measured 7V after buffer and the noise added by the LTC1052 is quite high (DS: 1.5µVpp typ, 7Vdirect -> 7Vbuf: ~0.7µVpp), did not realized that it adds so much noise...

Battery powered 0.1-10Hz noise:
7V buffered: ~1.7µVpp (12s, typ) - same with linear bench psu
7V direct: ~1µVpp (12s, typ)

Seems it is in the ballpark of other users  :-DMM

There was no measurable difference in noise with or without air-draft excluder in 0.1-10Hz range for this unit, but maybe it affects noise below 0.1Hz  :-//

TC compensation leads to next project: thermal chamber
Or even two for direct comparison of temperature stabilized one against DUT?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on February 19, 2019, 10:19:26 am
Your results are generally consistent with mine.  Typical 0.1Hz to 10Hz noise is around 0.8 to 1.4uV with a noise floor of the 10K:1 amp used around 150nV.   
Title: Re: Ultra Precision Reference LTZ1000
Post by: GregDunn on February 28, 2019, 06:40:00 pm
I've been using my reference to check calibration of my DMMs (particularly newly repaired ones) and as such I have had to move the output cables around to connect to different units.

Something I've seen happen: when removing and re-connecting cables, sometimes the reference output will drop to about 2.9VDC and stick there.  Cycling power to the reference brings it back immediately.  I've been careful to ground myself before touching the reference's case and not touch the bare leads but it happened anyway.

Is this a characteristic of the LTC1052 going into protection mode?  The datasheet only talks about overload recovery and doesn't address any sort of latch-up considerations...
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 01, 2019, 10:37:58 pm
Haven't observed something similar yet, neither on your reference nor on mine.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on March 01, 2019, 10:57:28 pm
From the LTC1052 data sheet.

Note 2: Connecting any terminal to voltages greater than V+, or less than
V–, may cause destructive latch-up. It is recommended that no sources
operating from external supplies be applied prior to power-up of the
LTC1052/LTC7652.


It usually takes several ma to induce SCR latchup. Is there a transorb on the output to protect against ESD causing latchup? Or it may just be a bad Op-amp.
Title: Re: Ultra Precision Reference LTZ1000
Post by: GregDunn on March 02, 2019, 12:49:23 am
Hmmm... I hope switching on/off a DMM connected to the reference output isn't a potential issue because I've done that a couple of times.  Shouldn't be...

I've left it open circuit for now, and checked the output a few times in the last couple of days, but haven't seen it happen again.  The output seems in spec at the moment.

Title: Re: Ultra Precision Reference LTZ1000
Post by: ArthurDent on March 02, 2019, 03:19:00 am
I'm using a different opamp but I also connected a transistor to buffer the opamp output and protect it in case I did something stupid. Where the transistor is inside the feedback loop it has no effect on the output accuracy. Only needed to add 3 components.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 02, 2019, 05:41:52 am

It usually takes several ma to induce SCR latchup.

But this can happen if you use some types of switchmode power supplies with capacitors between input mains line and output.
(not fully galvanic isolated).

You should mention latchup as usually the power supply current increases and the OP-Amp will get hot in this case.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 24, 2019, 10:48:31 pm
Hello,

I built 2 LTZ1000 (non A) devices. (12K heater setpoint)
So now we can do a direct comparison of startup-times


Here a cold-start of my LTZ#5

blue: 14V power supply after regulator (switching on is done via "on"-Pin of the LT1763)
yellow: zener voltage (unbuffered) but the buffered output follows within ms (2nd picture)
green: heater voltage (stable after ~400 ms)
red: zener current (voltage on 120 ohms resistor).

When I zoom in for the zener voltage the output is stable (within some mV) after 200 ms.


First picture Here on LTZ1000 #7 with LT1013A (CERDIP) as OP-Amp

blue: 14V power supply after regulator (switching on is done via "on"-Pin of the LT1763)
red: zener current (voltage on 120 ohms resistor).
green: Voltage on Gate of FET BF245C (output current regulator)
yellow: heater voltage (stable after 90 seconds!)


2nd picture:

blue: 14V power supply after regulator (switching on is done via "on"-Pin of the LT1763)
red: zener current (voltage on 120 ohms resistor).
green: Voltage on Gate of FET BF245C (output current regulator)
yellow: unbuffered zener voltage (not much change after 30 ms)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 25, 2019, 07:44:29 am
Hello,

I built 2 LTZ1000 (non A) devices. (12K heater setpoint)
So now we can do a direct comparison of startup-times




First picture Here on LTZ1000 #7 with LT1013A (CERDIP) as OP-Amp

..
red: zener current (voltage on 120 ohms resistor).
...
with best regards

Andreas

Hello Andreas,

could you please determine more precisely (in mV) the voltage difference across the 120 Ohm resistor, between start @ 10.22msec, and later, when oven has stabilized, @ 30..90sec? What was your room temperature?

From these numbers it's possible to determine the real oven temperature quite precisely.

Thanks!
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 25, 2019, 10:10:54 pm
Hello Frank,

good Idea.

but since this measurement was only made to have a look at all regulator cirquits (for oscillations) I did neither measure the PCB temperature (which might be different from room temperature) nor pay attention to use shielded probes for all channels.
But I will repeat the UR1 measurement with a better setup the next days.

Today I am measuring T.C. (with long legs) of the LTZ#7.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 27, 2019, 10:37:38 pm
Hello,

today I repeated the power-on measurement of UR1 on the new LTZ1000 devices:

LTZ7:
start with 24.7 deg C PCB-temperature (NTC populated on PCB) and about 24 deg C room temperature.
I increased the resolution by adding a 400 mV offset so I could use the +/-500mV range and 16 Bits ADC-resolution.

result
start with 523 mV end with 468mV = 55.2 mV difference or 27.6 deg C above 24.7 deg c = 52.3 deg C operating temperature if I calculated it right.

T.C. measurement shows linear T.C. -57 ppb/K up to 40 deg C environment temperature.

LTZ8:
start with 24.6 deg C PCB-temperature

result
start with 533 mV end with 478 mV = 54.5 mV difference or 27.2 deg C above 24.6 deg C = 51.8 deg C operating temperature.

But when I look at the T.C. measurement of LTZ8 it seems that the heater regulation gets instable above 33 deg C environment temperature.
Linear T.C. up to 32 deg C is around -26 ppb/K.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 28, 2019, 10:28:36 pm
Hello,

just some measurement values in comparison:

LTZ#7 is populated with a LT1013A in CERDIP for the basis cirquit
LTZ#8 is populated with 2*LTC2057
Both LTZ1000 (non A) with datecode 1443
temperature setpoint = 12K
the output buffer is LTC2057.

on #8 I will try to increase the temperature setpoint to see if the non-linearity can be shifted above 40 deg C
33 deg C is too marginal for my "lab" as this temperature is reached in summer.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 28, 2019, 11:36:13 pm
Hello,

today I repeated the power-on measurement of UR1 on the new LTZ1000 devices:

LTZ7:
start with 24.7 deg C PCB-temperature (NTC populated on PCB) and about 24 deg C room temperature.
I increased the resolution by adding a 400 mV offset so I could use the +/-500mV range and 16 Bits ADC-resolution.

result
start with 523 mV end with 468mV = 55.2 mV difference or 27.6 deg C above 24.7 deg c = 52.3 deg C operating temperature if I calculated it right.

T.C. measurement shows linear T.C. -57 ppb/K up to 40 deg C environment temperature.

LTZ8:
start with 24.6 deg C PCB-temperature

result
start with 533 mV end with 478 mV = 54.5 mV difference or 27.2 deg C above 24.6 deg C = 51.8 deg C operating temperature.

But when I look at the T.C. measurement of LTZ8 it seems that the heater regulation gets instable above 33 deg C environment temperature.
Linear T.C. up to 32 deg C is around -26 ppb/K.

with best regards

Andreas

Hello Andreas,
thank you for these measurements.
I also found 50..52°C on all of my 7 LTZ1000 / 12k/1k references.
I also found similar T.C. figures like you.
My interpretation concerning the 'instability' above 33°C R.T. is, that the visible increase in your last diagram is not necessarily a sign that the oven regulation gets unstable, that is to my opinion an increasing T.C. of higher order, which depends on the degree of compensation. for the -52ppb/K, that anomaly is not visible.

52°C is high enough to have about 38°C R.T. before the margin for the oven control is too small.. All of my newer LTZs can be operated at  up to 40°C in that sense, but their individual T.C. compensations, and the resulting reference voltage deviations at higher temperature, limit the usable temperature between 35°C to 40°C.
(At the May meeting, we should have a look on the variety of graphs of my T.C. measurements, difficult to describe here)

That also depends on the thermal packaging. My electronics package heats up 7.5°C above R.T., and I have no additional isolation around the LTZ1000. That means, 40°C R.T.  gives 47.5°C inner temperature, and that is barely 5°C regulation margin, so that's the tightest upper limit.

In the end, 12k/1k ~ 52°C oven, is good and safe for each sample, intended for the nominal cal lab of 18..28°C.
(Aren't the 732s specified in a similar manner?)*
Above that, the behavior of each compensated circuit has to be determined.

Frank

*Yes, the 732B is specified for T.C. <= 0.04ppm/K in 15..35°C. Oven temperature is about 45°C
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 29, 2019, 10:28:04 pm
Hello,

I have additional thermal isolation around the LTZ (to reduce air current induced noise) and need more than the usual 18 to 28 deg C range.

So I tried increasing the setpoint by adding a PTF56 resistor with 25K2 in parallel to the 1K setpoint resistor.

the ratio changed from 13:1 to 13.476:1 and starting from 7.10881 V output voltage base voltage decreased by 19.1 mV or +9.5 deg C setpoint change.
Output voltage increased by +2.99 mV so + 420 ppm or 44.1 ppm/K  (unheated) raw T.C. of the LTZ.

The non-linearity above 33 deg C disappeared (was shifted above 42 deg C).
Average T.C. -30 ppb/K

q.e.d.

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: dkozel on March 30, 2019, 01:49:32 pm
It's taken longer than I'd hoped to get to this point, but just about everything is soldered up. Trying to figure out some unit tests before adding the LTZ, but hoping to add those later today.

(https://i.imgur.com/l95IksM.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 31, 2019, 11:35:30 am
Thanks, but there must be much more references out there as far as I remember.

Found this, looks like they put together what is published in this thread (plastic caps, design ideas, ...)

https://islandlabs.eu/ltz1000.html

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: jlmoon on March 31, 2019, 04:23:55 pm
Aren't these the A Version? 
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on March 31, 2019, 06:15:00 pm
Thanks, but there must be much more references out there as far as I remember.

Found this, looks like they put together what is published in this thread (plastic caps, design ideas, ...)

https://islandlabs.eu/ltz1000.html

-branadic-

I have two of those. One A one non A. The non A aged > 10000 hours the A now about 3-4k. 213 is A, 136 is not. Temp was  23C +-10C over the time.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 02, 2019, 09:12:45 pm
Hello,

bad surprise (at least for me).

while shortening the legs on 2 of my LTZ1000A samples increased the T.C. this time with LTZ1000 (non-A) the T.C. decreased.

On LTZ#7 I had with long legs -57 ppb/K. I shortened the legs by ~7mm and wanted to get into the +/-20ppb/K range.
Instead I got -138 ppb/K making T.C. even worse as before.

Similar picture on LTZ#8: long legs +25K2 in parallel gave -30ppb/K (so near target). So I shorted only by ~5 mm.
Instead of zero I got -45 ppb/K.

Anyone with similar experiences for LTZ1000/LTZ1000A?

with best regards

Andreas


Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 02, 2019, 09:26:56 pm
I just finished my boxes. The refs are isolated in RF boxes with some capacitors on Vin then those boxes are soldered shut(two spots to make sure shielding is continous. Those boxes are put into some Hammond boxes with a wire soldered to the RF box for earth connection and closed up. My reading offsets dropped by 50%. Was -40uV from nominal, down to -20uV.
Title: Re: Ultra Precision Reference LTZ1000
Post by: RandallMcRee on April 02, 2019, 11:14:15 pm
I just finished my boxes. The refs are isolated in RF boxes with some capacitors on Vin then those boxes are soldered shut(two spots to make sure shielding is continous. Those boxes are put into some Hammond boxes with a wire soldered to the RF box for earth connection and closed up. My reading offsets dropped by 50%. Was -40uV from nominal, down to -20uV.

Sealed? No ventilation? I've read in this very thread (somewhere, can'f find it now--sorry!) that no ventilation is bad because the LTZ1000 will lose regulation at some point...
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 02, 2019, 11:22:05 pm
I just finished my boxes. The refs are isolated in RF boxes with some capacitors on Vin then those boxes are soldered shut(two spots to make sure shielding is continous. Those boxes are put into some Hammond boxes with a wire soldered to the RF box for earth connection and closed up. My reading offsets dropped by 50%. Was -40uV from nominal, down to -20uV.

Sealed? No ventilation? I've read in this very thread (somewhere, can'f find it now--sorry!) that no ventilation is bad because the LTZ1000 will lose regulation at some point...

No, they're not hermetically sealed, just shielded from noise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on April 03, 2019, 01:40:34 am

Sealed? No ventilation? I've read in this very thread (somewhere, can'f find it now--sorry!) that no ventilation is bad because the LTZ1000 will lose regulation at some point...

you must be talking about misterdiodes post.

it was actually a discussion about LTZ power disspation as heat, and restricting it with thermal isolation. as heat can get into LTZ, the idea was to have high thermal isolation. to which misterdiodes commented, if the isolation is too high, the LTZ heater regulation will go nuts.

if you simulate on femm, it is so easy for thermal conduction to over ride all the insulation done. from FR4 or some plastic box to air, the insulation advantage could be around 10x (in W/mk terms). but from FR4 to copper, the conductive advantage is more than 100x 30x. so for most designs, the copper trace can easily out conduct heat around isolation slots. the isolation gain becomes more apparent when the "moat" is large enough. but all this is only important if the environment temperature fluctuates. so if everyone puts their LTZ in Franks basement, I think the results will be very nice and striaght. but for everyone else, they need to buy a wine chiller or something.
which is very nicely done by Mr Jorn, which I always always love to repost as example.
https://www.eevblog.com/forum/metrology/dmm-adc-noise-comparison-testing-project/450/ (https://www.eevblog.com/forum/metrology/dmm-adc-noise-comparison-testing-project/450/)

in the CERN document about ADC 7717 (2017 pdf), they spoke of regulating the temperature of the entire LTZ circuit including the 7717 ADC so that this fluctuation is stopped. but I think they did not go with it because they said it in the document, it consume too much power. they are not nuts enough, otherwise, what is a few watts. <-- I think I misread this one, wanted to re read the pdf, cant find it. strange it stuck in my mind.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Magnificent Bastard on April 03, 2019, 05:04:55 pm
"[CERN] ... are not nuts enough, otherwise, what is a few watts."
:-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on April 03, 2019, 06:41:34 pm
I've been using my reference to check calibration of my DMMs (particularly newly repaired ones) and as such I have had to move the output cables around to connect to different units.

Something I've seen happen: when removing and re-connecting cables, sometimes the reference output will drop to about 2.9VDC and stick there.  Cycling power to the reference brings it back immediately.  I've been careful to ground myself before touching the reference's case and not touch the bare leads but it happened anyway.

Is this a characteristic of the LTC1052 going into protection mode?  The datasheet only talks about overload recovery and doesn't address any sort of latch-up considerations...

Today I had same issue on my #2, but it happend without changing anything.
There were 2 DMMs connected to 10V output for couple of hours when the output got stuck at a couple of volts.
After power cycling everything seems to be fine again.
 :wtf:
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 03, 2019, 06:54:03 pm
I have my 9x LTZ1000 references running for almost 1000h and haven't observed something similar by now.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: GregDunn on April 03, 2019, 07:46:55 pm
I've left mine running continuously since it arrived (though without a load) and it's only happened a couple of times.  I just went downstairs to check the output a few minutes ago and it's rock solid at 10.0000V.  The only thing I can think of is that hooking it to a live circuit instead of a DMM may have transferred a "floating" voltage to the output and upset the buffer - but that's mere speculation.

Maybe I should leave one of my 8800As powered up and monitoring it for a while, just for the sake of completeness.
Title: Re: Ultra Precision Reference LTZ1000
Post by: pelule on April 03, 2019, 07:55:46 pm
description sounds like a soft latcht-up. Is there any pin which may high (even short time) a pin higher/lower voltage than a supply voltage.
/pelule
Title: Re: Ultra Precision Reference LTZ1000
Post by: GregDunn on April 03, 2019, 08:36:43 pm
The supply on mine is 15V - the only way I see that a higher voltage could be applied to any part of the circuit would be a stray voltage applied to the output terminals.  I'm not saying it doesn't happen, but it would need to be an issue with an AC-powered piece of gear, either improperly grounded or having a static charge accumulating at the input...  I pretty much only connect it to my Fluke, HP and Keithley bench DMMs.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 03, 2019, 09:14:32 pm
I just finished my boxes. The refs are isolated in RF boxes with some capacitors on Vin then those boxes are soldered shut(two spots to make sure shielding is continous. Those boxes are put into some Hammond boxes with a wire soldered to the RF box for earth connection and closed up. My reading offsets dropped by 50%. Was -40uV from nominal, down to -20uV.

Hello,

do you have a cirquit diagram of those references?

do you supply them by a switchmode power supply.
Is there any switch mode power supply (or LED lamp) near the cirquit?
What happens with battery supply?

In principle I see two possible issues:
- either instability due too much capacitive loading if the output has no measure for isolating capacitive loads.
- or instability due to EMI/switchmode supplies.

Sealed? No ventilation? I've read in this very thread (somewhere, can'f find it now--sorry!) that no ventilation is bad because the LTZ1000 will lose regulation at some point...

but not at room temperature. Most of the heat is transported by the component leads and by the copper on the PCB. So the chance of over isolation is very small.
I suggest to do a measurement of T.C. then you can see where the regulation begins to be weak (non-linear) and when it is completely failing (with 40-50 ppm/K).

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 04, 2019, 12:01:54 am
I just finished my boxes. The refs are isolated in RF boxes with some capacitors on Vin then those boxes are soldered shut(two spots to make sure shielding is continous. Those boxes are put into some Hammond boxes with a wire soldered to the RF box for earth connection and closed up. My reading offsets dropped by 50%. Was -40uV from nominal, down to -20uV.

Hello,

do you have a cirquit diagram of those references?

do you supply them by a switchmode power supply.
Is there any switch mode power supply (or LED lamp) near the cirquit?
What happens with battery supply?

In principle I see two possible issues:
- either instability due too much capacitive loading if the output has no measure for isolating capacitive loads.
- or instability due to EMI/switchmode supplies.

Sealed? No ventilation? I've read in this very thread (somewhere, can'f find it now--sorry!) that no ventilation is bad because the LTZ1000 will lose regulation at some point...

but not at room temperature. Most of the heat is transported by the component leads and by the copper on the PCB. So the chance of over isolation is very small.
I suggest to do a measurement of T.C. then you can see where the regulation begins to be weak (non-linear) and when it is completely failing (with 40-50 ppm/K).

with best regards

Andreas

He sent me full schematics and parts lists for both. I've attached the buffered output section which is what I use to watch it. I've been powering them with a DP832 that they sit on top of and ALL the lighting is LED lighting.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on April 04, 2019, 12:37:58 am
So if I read this right, your reference is outputting 10V +/- whatever the multiplied deviation on the LTZ1000 is from 7.14V? Not a bad way to go, as long as you know the voltage. No pots to drift (I like things a little over 10V, rather than a little under).
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 04, 2019, 01:09:54 am
These output about 3-4 uV under raw zener output. 213 is ~7.090466V. I was considering adding a 10V buffered output but I'm not that worried about it now.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 04, 2019, 04:53:36 am
He sent me full schematics and parts lists for both. I've attached the buffered output section which is what I use to watch it. I've been powering them with a DP832 that they sit on top of and ALL the lighting is LED lighting.

And where are the capacitors that you added?
Only on power supply or also on output?

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 04, 2019, 05:34:02 am
He sent me full schematics and parts lists for both. I've attached the buffered output section which is what I use to watch it. I've been powering them with a DP832 that they sit on top of and ALL the lighting is LED lighting.

And where are the capacitors that you added?
Only on power supply or also on output?

with best regards

Andreas

I only added the capacitors to the input of the circuit across the feed throughs. So inside the hammond box but outside the RF box. I should also mention I mistakenly purchased mini banana plugs for the output so my testing has only been done with poorly fitting leads with the boxes. New standard banana jacks and new end plates are on their way and I'll start logging consistently again.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 04, 2019, 09:02:45 pm
I only added the capacitors to the input of the circuit across the feed throughs.

So no capacitor at the output and no ferrite or something like that -> it is most likely conducted EMI.
You can check this if the output changes by moving wires or holding the isolated wires by hand.
If the output changes then it is 100% EMI.

Unfortunately the output buffer will get instable with large capacitive loads according to my simulation.
So you could try 1 to 5 nF at the output or a R/C low pass with 47R - 100R and 100nF at the output.
In this case you will have to switch the DMM to > 10 GOhm mode.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 04, 2019, 09:33:32 pm
I only added the capacitors to the input of the circuit across the feed throughs.

So no capacitor at the output and no ferrite or something like that -> it is most likely conducted EMI.
You can check this if the output changes by moving wires or holding the isolated wires by hand.
If the output changes then it is 100% EMI.

Unfortunately the output buffer will get instable with large capacitive loads according to my simulation.
So you could try 1 to 5 nF at the output or a R/C low pass with 47R - 100R and 100nF at the output.
In this case you will have to switch the DMM to > 10 GOhm mode.

with best regards

Andreas

Even at 2s(minimum integration time for 7.5D) I only see the lsd change with twisted 1 meter long leads. The output leads are twisted to the glass isolated pass through, then twisted again to the binding posts. The meter leads are also twisted from the box to the meter. The only change I saw from  no box to RF and aluminum box is the 20uV offset change. I assume this is from better thermal isolation though, no breezes and more gradual temperature changes.

I'll swap the end plates to move to standard bananas and monitor for another 36 hours to see if any other changes took place. The ltz1000A board was ±0.4ppm  and the ltz1000 was ±2pm but the 1000 was bothered more by my kids during the day so those readings weren't great. I can't actually grab the soldered wires any more but I don't remember having issues with that before. Once I get new data I'll see if it seems to need these alterations.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on April 05, 2019, 01:40:16 am
Test your reference with the lid on and off, see if the change is immediate with the absence of the lid.  You could have a switching mode supply somewhere near (or not even that near) which is causing RFI/EMI and the chopper amp is rectifying affecting your output.  I just about went crazy with this exact same issue.  The steel Tekno boxes will work very well to shield both RFI/EMI.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 05, 2019, 09:40:55 pm
Hello,

modifications on my new LTZ1000 (non A) references:

LTZ#7 calculating around 40 ppb for each 1 Meg Resistor for R9 gave 3 in parallel so 330K to compensate for 120 (138) ppb.
LTZ#8 calculating also around 40 ppb gave a 910 K resistor for R9 to compensate for 45 ppb.

Measurement Result:
LTZ#7 gave +62 ppb/K in average. So in realty we had +67 ppb/1 Meg resistor.
LTZ#8 gave -5 ppb/K in average. So this has around +36 ppb / 1 Meg resistor.

Measures:
LTZ#7 changed R9 = 510K instead of 330K and soldered the inner housing which was only loose up to now to ease component changes.
LTZ#8 I am unshure wether I should change R9 = 820 K instead of 910K.
(here I am already within my usual +/- 20 ppb/K target).

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 07, 2019, 09:03:54 pm
Hello,

further modifications:

LTZ#7: now with R9 = 510K and inner housing soldered as planned.  -> -10 ppm/K over 18-38 deg C
LTZ#8: As I had to solder the inner housing I also changed R9 = 820K -> +10 ppm/K in average.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on April 08, 2019, 11:10:02 pm
Not quite the same level of detail as Andreas, but I've been logging one of my LTZ1000A's over the past year.  Its surprisingly stable, according to my Simpson 8.5" needle 260, its not budged at all  :-DD

(https://oi241.photobucket.com/albums/ff146/wsmc551/Elecronics/IMG_8726.jpg) (https://s241.photobucket.com/user/wsmc551/media/Elecronics/IMG_8726.jpg.html)

Who needs an 8588A anyway.


On a serious note, I found this the best solution to simply monitor the output while it cooks for long term aging.  Need something to show the output is at least present, and its very energy efficient  :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on April 09, 2019, 12:53:37 pm
When a company I worked for acquired Sola Electric, a colleague of mine found Joseph Sola's Simpson 260.  Joseph Sola patented improvements to the Ferroresonent Transformer, a.k.a. Constant Voltage Transformer in the late 1930's.  His Simpson 260 had a very low serial number, single digit or teens, IIRC.

Relevance-  Interesting how mankind used to be able to measure voltage without a precision reference!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 09, 2019, 09:20:52 pm
Hello,

LTZ#7 in final adjust state with R9 = 475K
Between 18 and 38 deg C the average linear T.C. is -2 ppb/K
Box T.C. is 0.92 ppm/20 deg C so 46 ppb/K in the limited temperature range.

Above 38 deg C the T.C. increases so the overall box T.C. is 66 ppb/K.
For my needs the reference has to work to about 33 deg C so there is also some reserve.

I will have to re-test the power consumption as the temperature setpoint has changed.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on April 10, 2019, 12:27:18 am
Is it 33°C environmental, or internal temperature?

Your cabinet upstairs is getting really hot in summer, isn't it?  :palm:

basement is much better!  ;D

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 10, 2019, 04:45:05 am
Hello Frank,

unfortunately the range 18 deg (winter) to 33 deg (last summer) 
environmental temperature is that what I have as "normal" in my "lab".
And that with up to 6-7 deg C change over one day.

So I am really envious on your lab in basement.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 10, 2019, 05:56:35 am
That's not too bad, it's 10C to 38C here. Up to 18C change in a day. Looking at getting a mini split put in so I can keep it MUCH cooler and stable.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on April 10, 2019, 08:54:32 am
Andreas,

so what is the temperature rise from environmental to internal temperature?

If I remember right, mine is about 7°C , or so. I did not isolate the LTZ1000 against the PCB, but have a styrofoam layer completely around the PCB

Couldn't you arrange a small lab place at the level of your houses entrance?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 10, 2019, 06:30:43 pm
so what is the temperature rise from environmental to internal temperature?

Hello,

Of course the difference depends on environmental temperature
(as the heater power decreases with environment temperature increase).

Attached you find some temperatures of the measurement above.

Environment (of LTZ) temperature (measured on top of the aluminium housing of LTZ#7)
PCB temperature measured inside LTZ#7
Heater temperature of the heat spreader (aluminium sheet) below the aluminium housing of the reference within the car cooling box.
ADC25 temperature (the temperature of the measurement system outside the car cooling box).

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: bsw_m on April 16, 2019, 12:15:08 pm
Arrived 2 sets of precision metal foil resistors for LTZ1000
The manufacturer promises very good characteristics of these resistors. So will check it.
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on April 16, 2019, 01:46:09 pm
@ bsw_m

could You write approximate prices of these devices ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: bsw_m on April 16, 2019, 03:12:10 pm
Price is not so high. Write pm.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 16, 2019, 09:16:16 pm
Price is not so high. Write pm.

Is this a special secret or can you share price, source and specs to everyone?

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: bsw_m on April 17, 2019, 04:30:26 am
Price is not so high. Write pm.

Is this a special secret or can you share price, source and specs to everyone?

-branadic-

I think it will make sense after testing
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on April 17, 2019, 05:50:10 am
Are these hermetic? They don't look so.
Title: Re: Ultra Precision Reference LTZ1000
Post by: bsw_m on April 17, 2019, 07:22:26 am
Are these hermetic? They don't look so.

The resistor body consists of 2 parts, which are hermetically glued together.
I would probably describe them as semi hermetic.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on April 17, 2019, 09:03:24 am
What's the size?
Title: Re: Ultra Precision Reference LTZ1000
Post by: bsw_m on April 17, 2019, 09:58:03 am
What's the size?

18.5x15.5x6.5 millimeters. Pin pitch 2.5mm
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 18, 2019, 03:48:00 am
I have an LTZ1000A and right now I'm seeing random fluctuations at times. It'll run around 7.0903935V but I'm starting to see dips, sometimes suddenly, to 7.0903514V or ..611V, ..750V. These seem pretty extreme and way off the average. Is this thing dead, or is it my meter? I'm really considering buying another 7.5D to compare against because it seems odd to see these types of jumps especially with 100s integration times. Current is steady, and the ambient temperature is not changing that much. Maybe 10C over the course of today but many drastic dips. It has until now been very stable but also until today or yesterday my average was closer to 7.0904300V. That was a sudden change over about 4 readings and it has been low since but my other reference also suffered the same drop which makes me suspect the meter.  :-//
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 18, 2019, 04:15:43 am
And for those of us who don't have magic Palantir the meter is?
Sorry, but photos of setup, wiring and power source are mandatory for ppm healing by internet..  :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 18, 2019, 04:49:36 am
And for those of us who don't have magic Palantir the meter is?
Sorry, but photos of setup, wiring and power source are mandatory for ppm healing by internet..  :)

So here is the setup and what binding posts and cables I'm using. In case it's hard to see... The Rigol DP832 is feeding both refs with 14V(readback is off, output is calibrated). The red one(1000A) has Pomona 3770 binding posts(copper/gold) and using Pomona 5291A copper/gold retractable banana plug cables straight into the Prema 5017SC. Inside the hammond boxes are teko boxes and inside those are the references, insulated from the boxes by non conductive foam.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on April 18, 2019, 05:03:28 am
One thing that you may wish to observe is the Pomona cable/binding post combination. The cable plug insulation shells are spring loaded. I saw it happen that when inserted into the 3770 posts, the springs slowly pushed the plugs out of the posts. One would expect they don't, given this is same vendor.
What comes in mind secondly is external EMI interference. That is harder to trace though.
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 18, 2019, 05:16:53 am
One thing that you may wish to observe is the Pomona cable/binding post combination. The cable plug insulation shells are spring loaded. I saw it happen that when inserted into the 3770 posts, the springs slowly pushed the plugs out of the posts. One would expect they don't, given this is same vendor.
What comes in mind secondly is external EMI interference. That is harder to trace though.

I just checked and the cables are still firmly in the binding posts. As for EMI, the Teko box is isolated from everything except for the green input banana jack. I have tried that earthed(not just to power supply ground) and it seemed to help some with noise(Can get 7-10 samples within a couple hundred nanovolts) but for some reason my kids have issues not playing with that cable so I do not have it connected right now. Also no, my kids have not been touching it since this started. The meter case is all earthed so it's fairly well insulated from outside noise. The cables and things could pick up some noise but I'd expect that to be more consistent since conditions don't change that much where these are really significant changes and it's not just 1 sample, it's 3-4 before it starts to return to normal.
Title: Re: Ultra Precision Reference LTZ1000
Post by: kj7e on April 18, 2019, 05:26:47 am
Are you willing to send your reference out?  If so, I could stick it on my DMM7510 for a few days and see if its your environment or the reference itself.
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 18, 2019, 05:39:28 am
Are you willing to send your reference out?  If so, I could stick it on my DMM7510 for a few days and see if its your environment or the reference itself.

If nobody else has any ideas and it continues to spike like this I'd appreciate someone else checking it out so I might PM you about that.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on April 18, 2019, 09:04:24 am
Are you willing to send your reference out?  If so, I could stick it on my DMM7510 for a few days and see if its your environment or the reference itself.

If nobody else has any ideas and it continues to spike like this I'd appreciate someone else checking it out so I might PM you about that.

Hello,
if I understand correctly, you have 2 PCBs ordered from that external company, which probably copied TiNs design (or whatever).
And both PCBs show these downward dips of several ppm?
time constants of these dips are several seconds, up to 30sec?
(Sorry, but proper scaling is missing in your diagrams)

Then these references really suffer from external EMI disturbances, as discussed intensively before, in this thread!

TiNs design is mostly a copy of the original LT schematic, and this is by design susceptible to EMI.

I have seen such dips also in both of my prototype LTZ1000 references, I think I already have published these old measurements somewhere here.. and these look very similar.

You can try to isolate your PCB by a steel box, or whatever you like, but EMI enters via power supply, or output jacks, no chance..
Even some of TiNs measurements (some unfiltered ones) on his own references show such dips.

The improvement for this problem is, either to use the Datron solution (for standalone reference 4910), implemented by Andreas.

Or you try adding 2 x 100nF foil capacitors in parallel to the 1k and 120 Ohm  resistors, which will short these EMI spikes, which affect the sensitive BE diodes in either transistors of the LTZ1000, and will unlatch the oven regulation .

This simple measure improved my mentioned references a lot.

Anyhow, get rid of any SMPSUs in your lab!

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 18, 2019, 04:01:58 pm
Are you willing to send your reference out?  If so, I could stick it on my DMM7510 for a few days and see if its your environment or the reference itself.

If nobody else has any ideas and it continues to spike like this I'd appreciate someone else checking it out so I might PM you about that.

Hello,
if I understand correctly, you have 2 PCBs ordered from that external company, which probably copied TiNs design (or whatever).
And both PCBs show these downward dips of several ppm?
time constants of these dips are several seconds, up to 30sec?
(Sorry, but proper scaling is missing in your diagrams)

Then these references really suffer from external EMI disturbances, as discussed intensively before, in this thread!

TiNs design is mostly a copy of the original LT schematic, and this is by design susceptible to EMI.

I have seen such dips also in both of my prototype LTZ1000 references, I think I already have published these old measurements somewhere here.. and these look very similar.

You can try to isolate your PCB by a steel box, or whatever you like, but EMI enters via power supply, or output jacks, no chance..
Even some of TiNs measurements (some unfiltered ones) on his own references show such dips.

The improvement for this problem is, either to use the Datron solution (for standalone reference 4910), implemented by Andreas.

Or you try adding 2 x 100nF foil capacitors in parallel to the 1k and 120 Ohm  resistors, which will short these EMI spikes, which affect the sensitive BE diodes in either transistors of the LTZ1000, and will unlatch the oven regulation .

This simple measure improved my mentioned references a lot.

Anyhow, get rid of any SMPSUs in your lab!

Frank

The biggest spikes are roughly 7ppm. I don't have any smpsu except in the PC's which are about 3 meters away. The spikes took place with only the logging PC, the meter and the power supply on. All the lab equipment is on it's own mains circuit with its own battery backup. I put a 2uF metallized polypropylene capacitor(Kemet C4G, 850VDC) across the PS output shortly after my last post. The reason I wasn't suspecting EMI is that I haven't seen this behavior in the month of continuous logging. If it continues, or happens again, I will add the 100nF foil caps across R7/R10. Thanks for the tip.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 18, 2019, 04:12:10 pm
Theory about reference picking noise from power supply is easy to check - connect reference to +12V battery, like old one from car/motorcycle and log for few days.
Properly working ref should have stability within 0.2ppm. To remove DMM out of equation - use two references and connect them in opposition, so your Prema would only measure difference between REF1 and REF2 on most sensitive DCV range (100mV?).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on April 18, 2019, 06:43:19 pm
No, no and no, putting capacitors across semiconductor junctions only transforms voltage spikes into current spikes and the microscopic matrices does not like that at all, it can even create cracks eventually but mostly decreases long term stability and increases noise.  That is the last thing you want being fed into a reference zener, we have addressed this point before earlier in this thread.

Regarding the Linear Technology reference design, it is just that, it is a starting point from which the design engineer uses to refine, tweak and improve the design for their specific purpose.  Authors have often pointed out that app notes are not finished complete designs but starting points that you have to finish for your own specific use.  To wit, shielding a sensitive circuit from interference is something that you have to take care of and putting capacitors in the wrong places is not a fix, shielding requires the proper enclosure(s), often copper (or maybe aluminum) inside steel and sometimes mu metal around components, aluminum is not particularly effective in shielding on its own, I believe we also talked about this earlier.  Improper construction techniques only adds to the problems and this includes connections to the outside world.  Removing noise generating sources to farther away also reduces the garbage being injected into sensitive equipment, sometimes moving them further away won't work either if they're really noisy.....rule of thumb......always take care of noise at its source.

If you want a reference that provides the best possible long term stability then you're going to have to invest in doing things the right way and stop taking shortcuts that will affect long term stability even if you can't measure it today.
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 18, 2019, 07:19:06 pm
No, no and no, putting capacitors across semiconductor junctions only transforms voltage spikes into current spikes and the microscopic matrices does not like that at all, it can even create cracks eventually but mostly decreases long term stability and increases noise.  That is the last thing you want being fed into a reference zener, we have addressed this point before earlier in this thread.

Regarding the Linear Technology reference design, it is just that, it is a starting point from which the design engineer uses to refine, tweak and improve the design for their specific purpose.  Authors have often pointed out that app notes are not finished complete designs but starting points that you have to finish for your own specific use.  To wit, shielding a sensitive circuit from interference is something that you have to take care of and putting capacitors in the wrong places is not a fix, shielding requires the proper enclosure(s), often copper (or maybe aluminum) inside steel and sometimes mu metal around components, aluminum is not particularly effective in shielding on its own, I believe we also talked about this earlier.  Improper construction techniques only adds to the problems and this includes connections to the outside world.  Removing noise generating sources to farther away also reduces the garbage being injected into sensitive equipment, sometimes moving them further away won't work either if they're really noisy.....rule of thumb......always take care of noise at its source.

If you want a reference that provides the best possible long term stability then you're going to have to invest in doing things the right way and stop taking shortcuts that will affect long term stability even if you can't measure it today.

As far as I know the Teko 273 tin plated steel boxes are made for RFI and EMI noise so I'm not sure if that's a shortcut? Do you have another suggestion? I'll go back and read up on the capacitors.

Theory about reference picking noise from power supply is easy to check - connect reference to +12V battery, like old one from car/motorcycle and log for few days.
Properly working ref should have stability within 0.2ppm. To remove DMM out of equation - use two references and connect them in opposition, so your Prema would only measure difference between REF1 and REF2 on most sensitive DCV range (100mV?).

I have run it on a battery and it was .14ppm better but as of now I'm just trying to get a basic idea of it running(looking for issues like these) so a power supply is easier. Although that was when I was just running them in a cardboard box waiting for other boxes to arrive so it's not really good data which is why I've deleted all but 1 of those logs per ref. After I've logged for a few more days, assuming it looks stable, I'll switch back to battery and log a week, then try measuring using both refs.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on April 18, 2019, 10:04:09 pm
Is your Teko case well grounded?  As far as being steel, that is a good first step.  If you are still experiencing excessive noise on your reference output, then the EMI is likely being conducted by the cabling to and/or from the power supply or DVM/scope.  The noise can be coming from the power supply (also conducted through from the power line) or the EMI is being radiated by something nearby.  Since you say that you did not notice these glitches in the previous month then something has changed since, something you added in the room perhaps or something new generating noise on the power line.  Sometimes large appliances such as refrigerators will generate power line hash or transmitters for instance.

The LTZ circuit is incapable of generating such noise itself aside from little 1/f noise spikes so when experiencing unusual noise on the output of the LTZ circuit look for outside sources and do no try to band aid the problem by putting capacitors where they don't belong.

If the spikes are still present on the output of the reference when operating on a battery, you've just eliminated one source, the line operated power supply.  Since you say there was only a 0.14PPM drop in noise then that is mostly just 'normal' noise your power supply is generating, then you need to look for the source of the spikes, start turning things off and seeing if the spikes go away.  What kind of lighting do you have, that is another wideband noise source if it isn't incandescent or Halogen.
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 19, 2019, 02:27:43 am
The case is well grounded but on a hunch I decided to check the input shorted with a gold plated copper shorting plug. This is what I got and may well be what I'm seeing. Integration time is 10 seconds so this is only slightly over an hour but I still think it's pretty revealing. I guess I need to start a repair thread.  :-// :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 19, 2019, 04:28:26 am
I have to admit, I'm in Edwin's camp here on LTZ vs caps discussion. 3458A's A9 don't use magic caps either, for what it's worth (yes, not great design for long stability otherwise).
More often than not spikes and other instability is caused by measurement gear or wiring or environment (EMI/RFI/power coupling) than reference itself. Trying to make reference more robust against external world influence is kinda going backwards.

maginnovision.
If your references are indeed based on my design, I can only remind that my KX calibration/testing programme (https://xdevs.com/article/kx_calserv/) is still applies to these, if you willing to have 2nd set of eyes and dataset for reference.
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 19, 2019, 05:46:37 am
Well I fixed the meter and now I'm roughly 2 uV from the ideal 7.0904622V varying +/- 3-4uV(max 7.090463, min 7.090456) over last hour or so without earth connected. Not bad if it continues like this since the meter is +/- that many uV with a short. I'll have to get a meter that doesn't use an lm399 at some point to really check stability or send it to one of you. I guess I could try my 1072, I don't know if that's more or less stable than an lm399. Thanks for all the suggestions and offers to double check.
Title: Re: Ultra Precision Reference LTZ1000
Post by: bsw_m on April 19, 2019, 07:35:25 am
I can not wait and perform dirty test for 13k/1k divider:
Applied from calibrator 7.000000V to input of divider and measured output by 6.5digit voltmeter. Measured output voltage from divider is 0.499988V with ambient temperature 24 Celsius. Then warmed divider to 60 Celsius, output voltage the same. Voltage changed to 0.499987V when temperature rise the 75 Celsius. When the temperature dropped to 24 Celsius output voltage is 0.499988V
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 19, 2019, 08:34:18 am
Quote
No, no and no, putting capacitors across semiconductor junctions only transforms voltage spikes into current spikes and the microscopic matrices does not like that at all, it can even create cracks eventually but mostly decreases long term stability and increases noise.  That is the last thing you want being fed into a reference zener, we have addressed this point before earlier in this thread.

Unless I haven't read a few scientific publications presenting real world correlations of latice structure of silicon vs. current spikes I put this into the drawer "myths, fairy tales and fake news". Even though it sounds reasonable it's not truth in the same moment.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on April 19, 2019, 08:35:44 am
All you need is g..gle:
The Belorussian precision foil resistors:
http://www.ajax.by/rpf-2.html (http://www.ajax.by/rpf-2.html)
http://www.ajax.by/rezist.html (http://www.ajax.by/rezist.html)
http://www.ajax.by/rez_set.html (http://www.ajax.by/rez_set.html)

Update:
The "RFP-2 datasheet" with tempco measurement details:
http://www.atkp.narod.ru/PDF/RFP_2passport.pdf (http://www.atkp.narod.ru/PDF/RFP_2passport.pdf)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on April 19, 2019, 08:38:41 am
I have to admit, I'm in Edwin's camp here on LTZ vs caps discussion. 3458A's A9 don't use magic caps either, for what it's worth (yes, not great design for long stability otherwise).
More often than not spikes and other instability is caused by measurement gear or wiring or environment (EMI/RFI/power coupling) than reference itself. Trying to make reference more robust against external world influence is kinda going backwards.



Hello Illya,

you compare A9 board, which sits double shielded inside the 3458A, to 'our' standalone reference application, which all are definitely exposed to external EMI.

That comparison is not feasible, as it's definitely a different use case for the LTZ circuit.

Datron, as one of only two designers and suppliers of an LTZ based 10V reference (e.g. 4910) definitely has applied several components for hardening the circuit against external EMI. One feature are one or two 100nF parallel to the BE of the temperature sensing transistor, the other is an additional RC filter at the 1013 opamp for the reference amplifier.
I assume, that you still have that 7000 reference, maybe you can have a reverse engineering look inside that circuit, and I bet you will find similar circuit (as Mr. Pickering was working for Datron, as well as on the 7000, afaik).

Your argument, NOT to make the LTZ circuit more robust against EMI ('going backwards') is kind of strange, what do you propose, instead?


I can only contribute my own experimental experience, that these additional components really suppress external EMI pulses, but w/o any degradation of the long term drift.
All of my 7 LTZ circuits show an annual drift of less than 2ppm from start, and less than 1ppm after an initial run-in time of about half a year, despite all having these capacitors fitted.


The claims of Mr. Pettis, aka MisterDiodes, are not plausible to me, because he/they did never give any experimental proof for their claims, neither any detailed description, how/where their LTZ circuits were used, i.e. whether inside a hermetically shielded environment, or as a standalone application.
Also, any links to scientific papers about such supposed 'lattice degradation' are missing.
Therefore, I still consider Mr. Pettis objections to this case as being baseless, irrelevant and even misleading.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: bsw_m on April 19, 2019, 08:46:23 am
http://www.ajax.by/rpf-2.html (http://www.ajax.by/rpf-2.html)
http://www.ajax.by/rezist.html (http://www.ajax.by/rezist.html)
http://www.ajax.by/rez_set.html (http://www.ajax.by/rez_set.html)

Yes, it is they.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 19, 2019, 01:50:44 pm
My approach is rather to keep ref circuit with minimal support parts necessary. Shielding is important for ref like LTZ, with or without additional circuitry. Double shielding like in 3458A is not so special. If we found time and money to build multiple LTZ boards, going that last step to ensure happy environment for it isn't unexpected.
Even Fluke recognize this as normal with much more robust 732 and suggest doing critical measurements only on floating battery power.

Going by experimental data, my own results with 7000 are questionable, it produce some wierd data so I don't have confidence that overcomplicated 7000 design is actually good.

Adding caps feels like taking cheap 10ppm/K resistor, putting it in oven and calling result 0.1 ppm/K standard. Valid approach for low cost applications but it does not cancel resistor own errors, and we rely on assumption of oven stability instead of inherent resistive element quality. Maybe wrong analogy, but hope I shared the idea.

After all I never intended KX modules as finished product, it have zero protection and quite beginner unfriendly. Having direct unbuffered LTZ output to external world isn't good idea either. Adding output amp with bipolar discrete stage like on my FX design resolves many if not all of the issues from external loads. My main LTZ ref is triple shielded and on battery power.

My final note would be : the more designs, the better :) Let's not just focus on saying design A or design B is worse or better, as either approach has own design quirks.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on April 19, 2019, 07:41:38 pm
After all I never intended KX modules as finished product

I knew it  :-DD
you must be happy so many people are "mysteriously" hooked onto an unfinished design
now they have to throw it away
no wait, take out the LTZ, the LTZ is innocent !  :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on April 19, 2019, 07:48:41 pm
If anyone's objections are baseless, irrelevant and misleading it is your comments, if you think that all research is published, you're very wrong, a great deal of research at semi fabs are private and well guarded from snoopers such as the competition and covered by NDAs as anyone would expect.  What gets published is probably only 10% of the real research and if you think Universities are a prime source, think again.  Your sources are very much limited in scope so don't assume you know everything because it has been 'published'.

Do you really think your puny efforts at measurements could detect such things as micro-crystalline changes over any period of time?  Don't make me laugh, some of these fab companies have tens of millions of dollars of the best equipment you can buy, way out of your league, so don't try to blow smoke up every's asses with your ignorance.  You can't verify anything like that, you have no way of verifying it and in such case you have no grounds for making such nonsensical unsupported statements.

The best way to protect a sensitive voltage reference circuit is to remove the external sources of noise and if necessary (which is most of the time) properly shield the enclosure with the correct materials.  Since you have no way of seeing what those capacitors are really doing to the LTZ you have no right to claim that nothing is happening at the crystalline level as it the case.  You already know that thermal excursions can affect the LTZ, whether up or down in temperature, it definitely produces a measurable change in the output when the LTZ has been kept at one temperature and then changed to a different temperature.....that is evidence of changes to the crystal matrix.  That is why you should set the temperature of the LTZ and then leave it alone.  Thermal shock is one example. physical shock is another, try dropping an LTZ on the floor and see what happens to the voltage, small change again.  There is a whole list of things that can affect the output voltage of the LTZ zener, to deny that current pulses from capacitors can't do that is plain silly.  It is just that some affects can be easier to measure than others, thermal shock probably being the easiest to detect.

Just because you can't measure it, don't claim it doesn't exist because someone else is likely able to measure it with the right equipment.

Since you're associated with an University, why don't you try reaching out to one of the German semi fabs and ask them about it and see just how much they'll tell you on the subject.  Let me know how successful you were.......

Oh, by the way, it is well known that capacitors convert voltage pulses into current pulses or has that bit of theory slipped past?
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on April 20, 2019, 10:09:58 am
Mr Pettis, while Frank and me and probably many others here agree that preventing the RF disturbance from even entering the board is the correct answer to the problem described rather than applying two brute force 100nF caps accross the 120R/1k resistors, and while we vaguely remember that RF voltages applied to capacitors result in a current from the source and through the capacitor and while we concurr that current spikes through junctions (as well as voltage spikes across junctions) may have an impact on these junctions (up to being distructive), would you shed some light based on your very special knowledge, unavailable to us, how an RF signal induced into the circuitry arround said LTZ pins and shorted at these pins would create a related current through that junction, while an RF voltage applied to the junction and not shorted by a capacitor would not create a related current through the junction, and why it would not rather be the other way round.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on April 20, 2019, 07:22:11 pm
Dear Adrian & Mr. Pettis,
I'd like to continue this dispute later, but meanwhile I wish you a peaceful Happy Easter!
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Magnificent Bastard on April 20, 2019, 11:48:52 pm
Dear Adrian & Mr. Pettis,
I'd like to continue this dispute later, but meanwhile I wish you a peaceful Happy Easter!
Frank

I suggest single shot pistols at 25 paces, at dawn...
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on April 21, 2019, 12:22:28 am
Dear Adrian & Mr. Pettis,
I'd like to continue this dispute later, but meanwhile I wish you a peaceful Happy Easter!
Frank

I suggest single shot pistols at 25 paces, at dawn...

Hmm - might want to consider using a few capacitors to supress the noise a bit. Oh wait.....
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on April 21, 2019, 04:16:07 pm
Thanks guys, quite amusing, I think we can all agree to cease the overly hostile rhetoric, it really isn't necessary.

We get it, you would like hard copy backup for tech you don't have access to, we all would, unfortunately there is a lot of tech out there which is highly secretive and covered by very strict NDAs that you really don't want to break.  We are privy to only the barest amount of details necessary for our work that intermingles with their needs, details are not generally part of it and even if they were we couldn't spill them.   They don't even want their own people to know too much, very very few know about the whole picture, everyone is pigeon holed, they know their part of the puzzle and little more.  I would love to know more details myself, it is fascinating but that isn't going to happen.  If we say anything it is all that we can or may know except that what information we have is backed by by solid research we know to be proven.

So please don't get mad at us for the limited way we can say anything, on the other hand, if you would prefer we just say nothing when subjects come up and pretend we don't know anything we can do that too.  We really don't want to get anybody mad.  I will be away from here for a few days so don't expect a response right away.

Kind regards.
Title: Re: Ultra Precision Reference LTZ1000
Post by: guenthert on April 21, 2019, 05:36:29 pm
[..]
Datron, as one of only two designers and suppliers of an LTZ based 10V reference (e.g. 4910) definitely has applied several components for hardening the circuit against external EMI. One feature are one or two 100nF parallel to the BE of the temperature sensing transistor, the other is an additional RC filter at the 1013 opamp for the reference amplifier.
[..]
I too noticed quite a few capacitors in the Datron 4910 schematic, but are those truly to suppress external EMI?  Since the 4910 uses a PWM scheme as voltage divider, I suspect there will be a fair share of EMI being produced internally.

Further and unrelated, I wonder whether old schematics are simply not quite sufficient anymore in terms of EMI suppression.  Back in the eighties and before, one was typically concerned with the 50/60Hz from the power grid and perhaps a few to a hundred MHz from nearby radio stations.  The latter was probably safely ignored in DC circuits.  These days a major component of house-hold (and hobbyist-lab) EMI are from SMPS, including those in now all-prevalent LED lamps.  At typically 40kHz to 400kHz, I fear they can't as easily be ignored.  And while one could attempt to rid oneself (and the neighbors ;-} of LED lamps, I don't want to feed my PC from a linear power supply (like the earliest micro computers were -- how heavy is a 600W 110V toroid?  Oh, just 6kg and $60 -- I did expect it to be much worse).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 21, 2019, 06:49:26 pm
Even those 100 MHz from FM radio or some 800 MHz from a mobile phone can be a problem for a "DC" circuit. It usually would not damage the chips, but the RF signal can be demodulated and cause some extra "noise". Especially the pulsed signal from GSM / Dect phones can cause quite some audible signals in audio equipment. The problem with the really high frequencies is that there the circuit diagram is not enough anymore - here the layout also has quite some influence. Not many capacitors still act like a cap in the GHz range.

The emissions from a SMPS are 2 - fold: one is ripple at the low end, where the OPs may still have some PSRR. The 2 nd point are the much higher frequencies from hard switching and ringing - these can extend to 10-100 MHz range. There are ways to keep the RF out, e.g. with a closed RF box and proper filters (e.g. feed through caps). Ideally the emissions to air from a SMPS should be weaker than the radio signals, not to interfere with radio receptions. It's only the supply that may carry more.

LTZ1000 circuit from the DS may not be the best solution to withstand EMI, but it is well tested and changes are not easy. I would not be too much worried about damaging the reference from EMI with the changed circuit. The changes tend to not change that much here and most of the EMI is more like a small signal added that causes a problem as long as it's present. With ESD the original circuit is also not really good. The possible problem is more with the changes effecting the turn on or turn off case - the loop is kind of tricky and could temporarily cause too much current if not properly starting. This can also be a problem with alternative OPs to the LT1013 - the steady state is easy, but turn on / off can be tricky and is not always well defined in the data-sheets or spice models.

For the zener or transistor I won't expect real crystal damage so easy. A more common problem with zeners (especially not burried ones) are hot electrons causing floating charges inside an oxide, a little like an unintended floating gate FET like in an EPROM. Thermal transients could effect the glue.
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on April 21, 2019, 07:09:18 pm
Therefore you may see a lot of ferrite beads and small chokes here and there in the today's schematics..
Title: Re: Ultra Precision Reference LTZ1000
Post by: TheSteve on April 21, 2019, 09:38:56 pm
RF can cause all kinds of anomalies. I know if I transmit with 100 watts or greater around 7 MHz it will cause my 3458A's to generate a fault that requires a power cycle. Lower/higher power levels and other RF frequencies can cause errors in the readings. In my case the antenna is located on a tower outside, not super close to the references.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on April 22, 2019, 08:09:56 pm
As a former tv & radio service tech working for around 4 years (and practicing my hobby ham radio) close to a big AM medium wave transmitter facility I can approve that it makes sense to keep RF out of ANY ELECTRONICS, even non-receiver-type. Any PN junction can be a rectifier.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on April 28, 2019, 11:25:55 am
Ok, here's my reply to the statements of Mr.Pettis and his alter ego MisterDiodes.

I'd like to point out, that the eevblog is an 'open' forum. Especially in this thread many capable engineers, physicists, technicians and DIYer have contributed many new ideas, schematics, layouts, publications, calculations, limit estimations, test measurements, everything for free, in a copy-able, and most importantly, verifiable manner. I very much appreciate all these great and profound contributions here, and in this sense also the offer of custom specific resistor sets for a reasonable price, from Mr. Pettis.

In the different physics communities, usually all theoretical and experimental publications are freely accessible, papers maybe at a cost, but the openness is a fundamental necessity of this science. Each new theory or experiment requires critical and open reviews, pros and cons, before these new findings are taken for granted. There's also a strict principle, what you can't measure, replicate, or explain properly, simply does not exist in reality. Example: The infamous Cold Fusion experiment of Fleischmann and Pons.

I'm having the mindset of both of these worlds, therefore I absolutely dislike any entry here, which makes a claim without any verifiable and open facts, as of one of the above mentioned items.
Hiding oneself behind references to NDA, unknown, mysterious and frightening companies and hidden documents, and especially omitting ANY quantitative or qualitative detail about the claim, are no arguments for truth or existence of such, either.


In fact, such an argumentation technique fatally reminds me of all these quacksalvers like Solar Roadways, Solus Graphene Heater, Fontus Self Filling Water Bottle, Batteroo / Batterizer, and Theranos as best example for claiming an at first glance evident idea, but then secretly hiding details about supposed machines and tests, and sooner or later being debunked due to missing basic principles.

Mr. Pettis ratings and wordings about serious and profound contributions here in this thread, like 'being puny', 'ignorance', 'unsupported statements', and alike, are a bad substitute for arguments.

Proposals like 'remove the external sources of noise', or 'preventing the RF disturbance' are simply unrealistic. That's possible maybe in an anechoic RF chamber, or in an application where the circuit is not accessible from outside, like in the 3458A.
But this is not the use case of any of the references like 731, 732, 7000, 4910, and of all the DIY LTZ 1000 based references.

All these are used in lower grade cal labs, but also in more or less noisy environments, like in the ordinary houses of the forum contributors, which are likely polluted by RF spikes originating from coffee machines, dish washer, cell phone, WLAN, lighting and PC SMPSUs, and from the 'dirty' mains network.
Therefore the DIY references have to be shielded, that's very obviously necessary. But instead of repeating again and again that common place, would anybody please give a detailed description and practical demonstration, how to 'properly' immunize the circuit further from the exterior noise.

The  design by Datron / Andreas is already proven to efficiently mitigate this problem.
I also cannot recognize a 'brute force 100nF caps' method. Adrian, please explain in detail, what you mean by this.
It's a common technique in commercial electronics to use a lot of 'EMC capacitors' to mitigate EMC irradiation.
Especially in a DC application like the LTZ1000 circuit, such filters are beneficial, as long the circuits are stable.

The sparse hint from Mr. Pettis that EMC pulses are transformed into current spikes (of what magnitude, please?), which in turn shall damage the 'microscopic matrices', does not convince at all.
Maybe the doped silicon crystal  is meant, but the binding energies are on the order of eV, whereas the energy involved in irradiated emission is very probably many magnitudes lower than that, so any deterioration by this suggested mechanism is extremely unlikely, or the magnitude of measurable impact is extremely low.
Also, here we are talking about over 30 years old big, bipolar chip structures, being much less sensitive to supposed 'excessive' electric fields or currents, compared to modern small scale field effect structures.

Please, check all of your own LTZ 1000 applications critically concerning EMC irradiation, present your results here, and bring up some practical ideas and alternative product designs, how to solve that problem differently.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: ap on April 29, 2019, 07:20:27 am
Re. the brute force capacitor: normally when you work on coupled noise that you were not able to prevent from entering a circuitry you try to fight it with tunes means. E. g. we had to do this against demodulated disturbances comming from mobile phones. Based on research on that topic by a big phone company (which we took as given and that finally helped) the most efficient way was to use a specific capacitance value in a specific form factor. Both had an influence on attenuation (in a nutshell, form factor defined parasitoc inductance; resonance effect). Now not knowing what noise source causes the disturbances here in the LTZ design resulted in using high value, kind of 'catch-all' capacitors. Not that efficent at higher frequencies, but covering a broad frequency spectrum. Thats what I call brute force. Others may call this differently.

The other thing is: The lattice distruction theory using caps is not logic in this application. Every ac voltage across an impedance causes a current. If the voltage is essentially shorted by the cap (as it seems to be as the cap helped), most of the current is now flowing through the capacitor, and the voltage accross it (and accross the junction in parallel) is lower than without the capacitor as the capacitor presents an AC short (thats why it is used). So the junction is seeing a lower AC voltage (ideally close to zero) with capacitor than without, so the lattice should also be less affected by the disturbance. In this way of using the capacitor, the voltage is also transferred in a current (as the claim was), but the current generated through the capacitor is not through the lattice/junction, and any potential current through the junction, caused by the noise voltage applied, is reducted as the voltage is reduced /shorted.
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on April 29, 2019, 08:16:00 am
..the most efficient way was to use a specific capacitance value in a specific form factor. Both had an influence on attenuation (in a nutshell, form factor defined parasitoc inductance; resonance effect). ..
A pretty important point. Experts do know well, but general public sometimes does not, that for every small chunk of freq spectra you want to block you may need a special value or a type of capacitor (or a combination of Ls and Cs).

The usual quality foil 100+nF capacitors people use here do not work at SW/VHF/UHF/GSM/Wifi/3G/5G/etc frequencies well, thus you get almost no attenuation.

Even people here are concerned on piezoelectrics of ceramics caps, you can hardly block >10MHz frequencies without using ceramics (smd, or special materials and forms for >1GHz).

And even with leadless smd ceramics, you have to use a parallel combination of several values, usually 3 in 1:100 ratio, to cover a larger chunk of spectra, for example 100pF||10nF||1uF, etc., with the lower value cap placed closer to the EMI source.
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on April 29, 2019, 10:51:58 am
And even with leadless smd ceramics, you have to use a parallel combination of several values, usually 3 in 1:100 ratio

I always wondered how such "multistage" bypassing is designed. What I learned is that just paralleling caps is asking for trouble if not done properly due to resonance effects. Does this 1:100 ratio help to avoid resonant peaks? How to validate the performance?
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on April 29, 2019, 11:50:58 am
When you start to look at the frequency characteristics of various capacitors you may see their impedance creates a specific rather narrow attenuation pattern ("V" shaped impedance vs. freq). The 1:100 ratio (advised by ADI for example) usually covers the typical attenuation BW of the capacitors used in such a combination (ie 3 partially overlapping "V"s). The actual combination has to be planned somehow, as it has no sense to combine a 100pF ceramics with 1uF foil, etc. The best verification of the BW of the blocking effect of a capacitors combination is a measurement, as usual.

For example the smd capacitor's V shaped impedance (https://www.avx.com/docs/techinfo/CeramicCapacitors/parasitc.pdf (https://www.avx.com/docs/techinfo/CeramicCapacitors/parasitc.pdf)) below.

While the X7R 1206 10nF will block "best" say from 20-200MHz, the 10nF Wima MKS2 will block "best" from  12-28MHz.
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on April 29, 2019, 12:41:57 pm
The actual combination has to be planned somehow, as it has no sense to combine a 100pF ceramics with 1uF foil, etc. The best verification of the BW of the blocking effect of a capacitors combination is a measurement, as usual.

yeah, that's the thing, it's very easy to make things *much worse* just by paralleling caps because they form. This was a big surprise to me, many people still not aware :). I'm attaching a picture from Renesas's AN1325, which I think is completely wrong. Doing so because it's a common pitfall cultivated by many sources. The resulting impedance is not a sum of individual impedances on the plot (even this part is shown wrongly on it).

It's not that easy to find info on the subject, so I just post one link here: https://www.edn.com/electronics-blogs/living-analog/4460969/Bypass-Capacitor-Resonances- (https://www.edn.com/electronics-blogs/living-analog/4460969/Bypass-Capacitor-Resonances-) . A good starter into the subject.

Anyway, point taken. It seem the only way to verify performance is to do measurements. Too bad because it's not that easy as this needs to be done on the actual board. I wonder if measurements can be performed with just a signal generator, oscilloscope, and a piece of coax cable (+ maybe 50ohm resistors for termination). Since we are talking about many tens of MHz, I expect proper measurements to be challenging. At least with equipment I have :). (Sorry for going offtopic)
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on April 29, 2019, 01:06:15 pm
Ok, the initial topic has been on blocking EMI fields such you not get them into the LTZ. The moral of my post above is to show the 100nF Wima (aka "brute force blocking") will hardly block till 10MHz and that is the point.
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on April 29, 2019, 02:16:11 pm
And here is an online simulation program for modelling impedance, esr, s-params, and creating the Spice model of the various types of capacitors

http://ksim.kemet.com/ (http://ksim.kemet.com/)


Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on April 29, 2019, 02:27:05 pm
the 100nF Wima (aka "brute force blocking") will hardly block till 10MHz and that is the point.

Do you mean it will not block above 10MHz? I'd say it will not work above a few MHz....
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on April 29, 2019, 03:28:23 pm
FYI - here is a simulation with 3 blocking capacitors at an "rail", where the 50ohm EMI source is loosely coupled via 10pF capacitor to the rail, the rail itself is 1k resistive impedance (ie LTZ pin).

The Spice capacitor's Models were generated by KEMET's online app, the values of the parasitics were taken at the frequencies with cap's lowest impedance.

The subcircuits Names are actual partnumbers.

Not an optimal approach, but you may try with S-parameters as a homework.. :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on April 29, 2019, 07:25:03 pm
And measuring/reproducing suggested e.g. by Dr. Frank is what we should try to become able to do, instead of fishing in dirty water.

I guess not many people here around have a shielded, anechoic basement, a collection of current clamps and a signal generator able to do sub 1 Hz AM or other stuff which would be preferred to tickle our valuable voltage standards. I would like to suggest figuring out forum standards (IDS - International Dave Standard? :-DD) to disturb voltage references and become able to put some value to the supression of the influence when trying to harden them. More like "Raspberry Pi with rpitx with some capacitors to shield/plus/minus and a metal plate of size x*y below it" (tekbox lisn thrown in here or there) or "travelling piezo lighter" testing instead of "Frankonia tin box with €300.000 R&S stack next to it." If we find some empty lab to confirm findings, the better!

Wouldn't that be a great topic for the Metrology meeting?

Best regards,

Hendrik
Title: Re: Ultra Precision Reference LTZ1000
Post by: eplpwr on April 29, 2019, 08:22:32 pm
Good evening (in my TZ)!  ;)

I'm in the process of buildung a number of LTZ boards - just waiting for some Ultrohm resistors ... Also, I want to be set up to measure the boards voltage from power on and onwards - got me a Keithley 7002 w/ 7011-S for that purpose. And some 3458A, DMM7510, 34470A usw ... standard voltnuttery.  :)

Regarding encapsulation I've got som nice Mu-metal boxes from Russia. Inside these I plan to make an alumin(i)um oven box, home CNC style. Qestion is: should the alu chassis parts 1) touch the componens for best thermal equilibrum , 2) have a small distance filled by isolating material like Sil-Pad to be "softer on the compinents", or 3) have an air gap of - say - 0.5 mm to allow all components their "freedom of movement"?

If physical stress was unimportant, I would go for the direct contact, but the more I read, the more I see components wishing to expand/shrink at their own pace.

Recommendations most welcome!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on April 30, 2019, 07:50:39 am
Do you have a link to those mu-metal-boxes?
The aluminiumbox doesnt need to be thermally coupled to the LTZ-board as no component generates so much heat, that it needs to be cooled. Also you generally want a good thermal insulation of the LTZ-board to the case and mechanical flexibility of the board to avoid strain-induced offset-voltage.
I suggest following AN159 on shielding box construction, for generally good shielding: https://www.analog.com/media/en/technical-documentation/application-notes/an159fa.pdf (https://www.analog.com/media/en/technical-documentation/application-notes/an159fa.pdf) Page 7.
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on April 30, 2019, 08:41:47 am
OT: One can also, generally speaking, exaggerate. If that goes so far as to create a certain monoculture of opinion, our Forum Jewel has lost. In my opinion, the limit here is to represent what is technically reasonable without taking other opinions to absurdity from the outset. The learning effect for all the fellow readers is to justify this difference and not to prevent it. And this learning effect is the meaning of the whole, even above technical correctness, because it is only in the ensuing discourse that it becomes accessible at all.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on April 30, 2019, 06:55:49 pm

For example the smd capacitor's V shaped impedance (https://www.avx.com/docs/techinfo/CeramicCapacitors/parasitc.pdf (https://www.avx.com/docs/techinfo/CeramicCapacitors/parasitc.pdf)) below.

While the X7R 1206 10nF will block "best" say from 20-200MHz, the 10nF Wima MKS2 will block "best" from  12-28MHz.

Yeah, this is a very good point. I found it a hard way that one 10nF cap not equal to another 10nF cap. Or in other words depends on type/make/manufacturer.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on May 01, 2019, 12:35:17 am
we need the "jaxbird analyzer"
was any of you using it ?
https://www.eevblog.com/forum/projects/impedance-analyzer-build-and-experiments/?all (https://www.eevblog.com/forum/projects/impedance-analyzer-build-and-experiments/?all)
Title: Re: Ultra Precision Reference LTZ1000
Post by: eplpwr on May 01, 2019, 10:51:43 am
Do you have a link to those mu-metal-boxes?

Here you go:
https://www.ebay.com/itm/Mu-metal-nickel-iron-alloys-shielding-case-for-transformers/282939791744?hash=item41e0869980:g:S4cAAOSwt51auf2g (https://www.ebay.com/itm/Mu-metal-nickel-iron-alloys-shielding-case-for-transformers/282939791744?hash=item41e0869980:g:S4cAAOSwt51auf2g)

Rather small since they are made for transformers; not a box in the generic sense. I like the pre-made holes since I've read that Mu-metal may need re-annealing after being formed or machined.

The aluminiumbox doesnt need to be thermally coupled to the LTZ-board as no component generates so much heat, that it needs to be cooled. Also you generally want a good thermal insulation of the LTZ-board to the case and mechanical flexibility of the board to avoid strain-induced offset-voltage.
I suggest following AN159 on shielding box construction, for generally good shielding: https://www.analog.com/media/en/technical-documentation/application-notes/an159fa.pdf (https://www.analog.com/media/en/technical-documentation/application-notes/an159fa.pdf) Page 7.

I guess I was somewhat unclear regarding the purpose of my aluminium "box" - it is to be a heated oven. I'm planning to custom-machine an aluminium slab to fully encapsulate a voltage reference, a heater of some sorts (like the '723-based version described in another thread) and possibly a step-up/-down board to get a specific voltage like 5V or 10V as output. Thus, my goal is to maximize thermal transfer to each component and have a large, hopefully isothermal, mass containing all the electronics. In practice, it will be at least three "slabs" that make up the whole enclosure, I'm thinking a top part with MOSFET heaters, a middle part with heater control and Vref, and a bottom part with MOSFET heaters again. I'm aware that a fully custom encapsulation will mean that every dimension, specifically for resistors, will be unique so there will be a need to machine new parts if I change from WW to BMF, for example. Circulating air is supposedly a bad thing, so I'm planning on very narrow encapsulation of the components (say, 1mm). My question is if it's good to leave it like that - with an air gap surrounding each component - or try to actually make thermal contact using some method?

I had some thoughts of other materials, like Ag or Cu, but I've read that machining is very difficult and would require casting. Since I've worked with aluminium before with good results I'll stick with that - I have a couple of CNC machines so I won't have to rely on my unsteady hands.

Hopefully, I've explained what I'm aiming for in understandable terms.  8)
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 01, 2019, 12:29:02 pm
There is no need to machine a custom aluminium case as simple aluminium square profile will do the job. You should put your effort more into the circuit design and components characterization.
If you don't know where to start take a look at videos like
Rebuilding Fluke SL935 resistance standard prototype (https://www.youtube.com/watch?v=qBthxNMv9N4)
and you can see the oven construction and how 732B is constructed and designed, also read the circuit diagrams on it. This will give you a brief idea how they made it.
The best solutions is the one that was shown to be working with low effort and a one others can duplicate to reproduce the results made with it.
If you would ask me, it's not worth the effort machining a custom aluminium case, even though it's a nice project from the perspective of CNC machining. :)

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on May 01, 2019, 04:03:33 pm
we need the "jaxbird analyzer"
was any of you using it ?
https://www.eevblog.com/forum/projects/impedance-analyzer-build-and-experiments/?all (https://www.eevblog.com/forum/projects/impedance-analyzer-build-and-experiments/?all)

It's too low freq (500kHz). I used to use a signal generator and oscilloscope to do this. Basic arrangements are described here: https://meettechniek.info/passive/capacitance.html (https://meettechniek.info/passive/capacitance.html) .

I did even simpler than that: I just connected oscilloscope to signal gen. Then I shunted the output and observed signal amplitude vs frequency. At some point amplitude stops falling. Afaik this is the resonant frequency of the capacitor and it cannot be used anywhere closer or above this frequency.  The amplitude should tell the ESR, as capacitor is essentially a voltage divider with 50Ohm signal gen. But I'm not 100% sure if this is a right arrangement because there was not termination, etc. This also does not give information about signal phase.

Probably, a better approach is just open the datasheet and see impedance curve. For smd caps reputable manufacturers prive this info. But this project doesn't use smd components :).

I also considered buying this: https://www.sdr-kits.net/introducing-DG8SAQ-VNWA3 (https://www.sdr-kits.net/introducing-DG8SAQ-VNWA3) . But a bit too pricey.
Title: Re: Ultra Precision Reference LTZ1000
Post by: FriedLogic on May 01, 2019, 11:44:51 pm
Hi,

I think that the real issue that Edwin and MisterDiodes were referring to is the general approach of putting any capacitor on the IC pin to kind of clamp down on the noise there instead of stopping it getting to the IC in the first place. 'Optimising' the capacitors might only make that aspect of things worse.


The other thing is: The lattice distruction theory using caps is not logic in this application. Every ac voltage across an impedance causes a current. If the voltage is essentially shorted by the cap (as it seems to be as the cap helped), most of the current is now flowing through the capacitor, and the voltage accross it (and accross the junction in parallel) is lower than without the capacitor as the capacitor presents an AC short (thats why it is used). So the junction is seeing a lower AC voltage (ideally close to zero) with capacitor than without, so the lattice should also be less affected by the disturbance. In this way of using the capacitor, the voltage is also transferred in a current (as the claim was), but the current generated through the capacitor is not through the lattice/junction, and any potential current through the junction, caused by the noise voltage applied, is reducted as the voltage is reduced /shorted.

That assumes that the noise is coming into the IC on the pin that has the capacitor on it, which may not be the case.

Now the extent to which any if this might affect the IC in a specific case is another question. Using capacitors like this may not be ideal, but it's possible that in some cases it does not have major negative effects - and references which see very little noise anyway may be one case.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on May 02, 2019, 07:26:34 am
It is definitely better to keep out RF interference from the whole circuit - this also needs the right caps. However this is more like a separate topic better not discussed in this already long thread. It not only applies to the reference bus other circuits too.

It may sill be a good idea to have the circuit tolerant to some RF, so it is not upset so much. Here extra caps may help - however they should be more likely rather small as it's only the really higher frequencies that matter. From external shielding the RF power should be low enough that possible damage to the chip due to RF should not be an issue.
The problem with a cap just added base to emitter is that it also interferes with the stability of the control loop. Even if not oscillating is can cause a problem during turn on / turn off.  AFAIK the control loop is already in the normal form not unconditionally stable - adding extra caps only makes thinks worse and might cause significant overshoot in turn on or with an external short.  A problem with EMI is also that it can depend on details of the layout / parasitic inductance - so even a measurement is only valid for the one board and the DMM side to detect interference might also be susceptible.
Title: Re: Ultra Precision Reference LTZ1000
Post by: bsw_m on May 03, 2019, 12:11:33 pm
First TCR test for resitors from Ajax: https://xdevs.com/ajax_tcr_test1_may19/
So 10kOhm (blue line) - this is old broken resistive element from resistor.

P.S.
I began to receive a lot of questions in a personal, related to the price of resistors and their acquisition.
I do not sell these resistors. You can write directly to the manufacturer: e-mail: rezist@ajax.by
But, if you have any problems when interacting with the manufacturer, I can theoretically assist in placing an order and purchasing resistors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Pipelie on May 03, 2019, 03:12:50 pm
First TCR test for resitors from Ajax: https://xdevs.com/ajax_tcr_test1_may19/
So 10kOhm (blue line) - this is old broken resistive element from resistor.

P.S.
I began to receive a lot of questions in a personal, related to the price of resistors and their acquisition.
I do not sell these resistors. You can write directly to the manufacturer: e-mail: rezist@ajax.by
But, if you have any problems when interacting with the manufacturer, I can theoretically assist in placing an order and purchasing resistors.

FYI, here is the TCR result of TiN's data.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Pipelie on May 03, 2019, 03:28:33 pm
some results from the TCR measurements I did recently,  for comparison :popcorn:.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Pipelie on May 03, 2019, 03:30:28 pm
continue...
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on May 21, 2019, 05:28:49 pm
Update the HP A9 reference board clone (03458-66509):


does anybody know what to call the (gold plated?) J400/401 part in digikey? or know the part ref name/model? (the thru hole socket thingy)
*mmm ty @ MB (the post after this), I later saw CM post #2060. which had the link  Molex 22-17-2052
https://octopart.com/search?q=Molex%2022-17-2052
Title: Re: Ultra Precision Reference LTZ1000
Post by: Magnificent Bastard on May 21, 2019, 06:15:10 pm
Update the HP A9 reference board clone (03458-66509):


does anybody know what to call the (gold plated?) J400/401 part in digikey? or know the part ref name/model? (the thru hole socket thingy)

I believe these are made by Molex (see attached PDF).

-MB
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on May 22, 2019, 10:53:02 am
I was playing around with the outline of 03458-66509
I just realized the LTZ is not really sitting in the middle of the 2 screw hole
I checked on other photos and it seem to be "not an error" ?
the plastic cap however looks symmetrical ... hey whats going on  :-DD
Im tempted to put it straight in layout  :P
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 22, 2019, 07:28:32 pm
Hello,

perhaps it has to do with the Pin8-marker (nose) on the LTZ-package?

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on May 22, 2019, 11:47:26 pm
Hello,

perhaps it has to do with the Pin8-marker (nose) on the LTZ-package?

with best regards

Andreas

to have the screw avoid the tab, the LTZ needs to be really way out approx 3-4mm more (blue X is original position). right now its about 1mm off. if the LTZ is turned, it sits center. I dont think we will get what the original story is about this 1 haha
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on June 17, 2019, 06:17:29 pm
I know 6 1/2 DMM should not be used to track LTZ1000, but given that I do not have any better one yet, what are the best settings used for monitoring LTZ1000 (or LM399)? Currently, I have it set-up as follows:

1) Filter on (Moving average, count - 100, window 2%)
2) NPLC: 12 (maximum) 

What do you think?


Thanks
Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on June 17, 2019, 06:37:19 pm
Reading a reference with a DMM will give a result that depends on the ratio of the external and meter internal reference. 6.5 digit meters tend to have something like an LM399 reference, so one would mainly see the noise of that reference.
A few Fluke meters have an  SZA263 / LTFLU based reference, even with only 6.5 digits. So this case may not be so bad.

What setting works best depends on the meter. It also sets which frequency range is seen most. Digital filtering can to a large part also be done later. So using less digital filtering will give more data an one can decide afterwords how much averaging is suitable.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on June 17, 2019, 06:49:45 pm
I know 6 1/2 DMM should not be used to track LTZ1000, but given that I do not have any better one yet

Ideally you would want two LTZ1000 references and then monitor difference between them using 100mV (or whatever minimal range there is) with DMM. This will give you magnitude less error from DMM's own reference. You can ship then one of the references to somebody with calibrated high-end setup, to provide you accurate voltage of the reference. This way you can cheaply obtain ppm-level accuracy and resolution on your LTZ1000 boards, without spending thousands for 8.5-digit DMM.
Title: Re: Ultra Precision Reference LTZ1000
Post by: bsdphk on June 17, 2019, 07:32:57 pm
No: Ideally you would have three references and 3 DVMs, so you can do 3-cornered-hat style modelling.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on June 17, 2019, 08:14:56 pm
I know 6 1/2 DMM should not be used to track LTZ1000, but given that I do not have any better one yet

Ideally you would want two LTZ1000 references and then monitor difference between them using 100mV (or whatever minimal range there is) with DMM. This will give you magnitude less error from DMM's own reference. You can ship then one of the references to somebody with calibrated high-end setup, to provide you accurate voltage of the reference. This way you can cheaply obtain ppm-level accuracy and resolution on your LTZ1000 boards, without spending thousands for 8.5-digit DMM.


 :palm: :palm: :palm:

Ok, its time to place yet another Digi-key order
How long do you think the reference has to be burned in on the battery power before calibrating it with 8 1/2 DMM?
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on June 17, 2019, 08:15:37 pm
What setting works best depends on the meter.


I have Keithley DMM6500
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on June 17, 2019, 08:22:44 pm
burned in on the battery power before calibrating it with 8 1/2 DMM?

Depends on the reference, really, and resistors used. Usually community here determined 1000 hours is reasonably low number. Some reference examples drift even years after assembly. Some calm down and settle within a month. It is always good idea to build more units than you need, cherry pick the "golden" ones for your use, and then share the rest to community Cal Clubs :popcorn:.
For real good calibration at cardinal point, you would not even use 8 1/2 DMM , but something like verified other reference (F732 and alike) and nullmeter such as Keithley 155 or Fluke 845.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on June 28, 2019, 09:27:54 am
The build has been completed.
Now the reference will be burning for a few months. By the way, is there any advantage using batteries vs a PSU? I understand that batteries produce noise by the chemical reaction. Unfortunately, the PSU is not much better. I do not have a dedicated lab so during the day there are all kinds of intereference introduced via the PSU through mains supply during the day. At night it's much better. What's the best choice please? Any recommendations?
I went through AN124, but the cost of the circuit (Vishay XTV138M030P0A alone is £340+ and its not available) is absurd. FYG - NASA had some issues with this type of capacitor. There were tantalum wet slug capacitor failures in the Apollo telescope mount charger battery regulator modules.


Another question I have is on the temp oven. I have branadic's board fitting into the Hammond case and its not designed for oven.
What kind of inaccuracy may be introduced if I do not keep LTZ1000 in the oven at contract temp?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on June 28, 2019, 10:02:17 am
LTZ1000 circuit itself does not require external oven to reach its typical performance ~0.05 ppm/K. Battery is preferred because it avoids risk of ground loops during measurement, but its not needed for burn-in or aging. Decent linear power supply like those old HP ones would be sufficient.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on June 28, 2019, 10:23:38 am
LTZ1000 circuit itself does not require external oven to reach its typical performance ~0.05 ppm/K.

That's helpful - thank you

Quote
Battery is preferred because it avoids risk of ground loops during measurement, but its not needed for burn-in or aging. Decent linear power supply like those old HP ones would be sufficient.


OK, I need 15V input (LT1763 can take it up to 20V and then dropping it down to 12V). What battery are you using please? I have 1800mAh 18.5V 5S Graphene battery, but it would not be enough I suppose. How is the battery charged? Swapping for another one?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Hermann W on June 28, 2019, 12:22:47 pm
what battery are you using please?
For aging, I take a simple plug-in power supply. For measurements I use a linear power supply and for transfer a tool battery. Because the battery can have up to 21V, I have built a small adapter with 78L15. This battery (1.5Ah) lasts for 2 days but there are bigger ones.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on June 28, 2019, 12:38:00 pm
For my LTFLU-1 prototype I have made something similiar with Li-Ion batteries from Makita:

(https://i.imgur.com/Qb3TYaA.jpg)

The advantage is: you can get a cheap chinese version of these sockets on ebay,
rip out the electronics and put in some nice LDO.

Example:
https://www.ebay.com/itm/283470670352 (https://www.ebay.com/itm/283470670352)

BU508A
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on June 28, 2019, 12:38:24 pm
what battery are you using please?
For aging, I take a simple plug-in power supply. For measurements I use a linear power supply and for transfer a tool battery. Because the battery can have up to 21V, I have built a small adapter with 78L15. This battery (1.5Ah) lasts for 2 days but there are bigger ones.

I have a 15V 4A PSU for SkyRC MC3000 charging device, but I think p-p is more like millivolts.
The battery you have on the photo is from a power tool? 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Hermann W on June 28, 2019, 02:29:23 pm
The battery you have on the photo is from a power tool?
Yes, a cheap one from the hardware store. They have nominal 18V. That means 5 LiIon with a maximum of 21V after charging. The voltage regulator with the matching capacitors filters a lot.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on June 29, 2019, 05:14:01 am
I know 6 1/2 DMM should not be used to track LTZ1000, but given that I do not have any better one yet, what are the best settings used for monitoring LTZ1000 (or LM399)? Currently, I have it set-up as follows:

1) Filter on (Moving average, count - 100, window 2%)
2) NPLC: 12 (maximum) 

What do you think?


Thanks
Alex

I am curious
when should 1 use moving average and when to use repeating average in this case? I am biased to use repeating because the result/data can be used for other math in spreadsheet.
If I collect the data in moving average, the plot is already displayed/calculated as a trend and I cannot use it for Stddev calculation or alan-variance, am I right?

and since the time scale of LTZ1000 shifting ppm is in hours days weeks and months, and the limit (is that the limit?) of the machine is 12NPLC, shouldnt the data be collected as repeating in order to process a longer trend period in spreadsheet? eg : 1000 nplc math?

(sanity check : I have not been sampling much and may have forgotten some things)
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on June 29, 2019, 08:20:28 am
If you turn off the filter and use the fewest NPLC that gives you 6.5 digits, you can do all the processing in your spreadsheet.

Conversely, at these settings the display is pretty useless.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on June 29, 2019, 08:50:13 am
Another question - did anyone use LT3045-A Ultralow-noise (<0.8µVrms) LDO to feed 12V to LTZ1000?
Is there any disadvantages?
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on July 13, 2019, 07:01:46 am
Another question - did anyone use LT3045-A Ultralow-noise (<0.8µVrms) LDO to feed 12V to LTZ1000?
Is there any disadvantages?
I believe TiN did in his FX reference, he used the lower current version LT3042. LT3042 and LT3045 require very careful layout design, not doing so would basically degrade or invalidate its performance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: pansku on July 20, 2019, 06:28:18 pm
Just finished building 2 units with the Dr. Frank PCB  :phew:

I'm only on page 20 on this subject, but I got the impression that these should be powered on for about a month continously to burn in? As I'm limited to just a Keithley 2015 before we get some 3458A's to the lab I work in, is the correct way to do this by measuring the difference between 2 units on mV range and when they don't drift against each other that much, then I'll start trimming to desired output? After that time we should have the HPAK meters, put the boxes in a weather cabinet, run from lets say from 15 to 35 degrees °C and trim the 400k resistor? And lastly finish the project by having them calibrated against 732B(?) at the company cal lab.

Does that sound like a solid plan? I'm currently using 13k/1k and non-A LTZ1000. These references are going to end up in homelab with high'ish oven set point as the tempereture can reach around 30°C on the hottest summerdays inside.

Obligatory picture  ;D
Don't mind the missing power jack for now. I'll grab it later with the Hammond boxes when I'll order some more components to other projects.

(https://i.imgur.com/kh0vLQi.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on July 20, 2019, 07:07:39 pm
As I'm limited to just a Keithley 2015 before we get some 3458A's to the lab I work in, is the correct way to do this by measuring the difference between 2 units on mV range and when they don't drift against each other that much, then I'll start trimming to desired output? After that time we should have the HPAK meters, put the boxes in a weather cabinet, run from lets say from 15 to 35 degrees °C and trim the 400k resistor? And lastly finish the project by having them calibrated against 732B(?) at the company cal lab.

Drift should be measured against trusted reference.
Two drifting references could have nearly same drifting rate...
If the TC is unknown/untrimmed this could appear as drift, unless you measure them at constant temperature against each other.
A month of burn in should decrease the drift to acceptable rate.
It depends how accurate you want to trim the output to 10V...
Finally you have to determine value with precision reference - 732B should be good enough  ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 20, 2019, 07:21:59 pm
Hello,

additional to the points of MiDi:
Trimming the T.C. will affect output voltage. -> you will have to do this first.

Fortunately you can do T.C. measuring of the both references against each other (in 100mV Range of your DMM) as soon as the first large drift has gone.

not all references are stable after 1 kHr.
my LTZ#8 still drifts with  ~0.5 ppm/kHr against my stable LTZ#2 after 2 kHrs.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: pansku on July 20, 2019, 07:35:20 pm
Drift should be measured against trusted reference.
Two drifting references could have nearly same drifting rate...
If the TC is unknown/untrimmed this could appear as drift, unless you measure them at constant temperature against each other.
A month of burn in should decrease the drift to acceptable rate.
It depends how accurate you want to trim the output to 10V...
Finally you have to determine value with precision reference - 732B should be good enough  ;)

Hello,

additional to the points of MiDi:
Trimming the T.C. will affect output voltage. -> you will have to do this first.

Fortunately you can do T.C. measuring of the both references against each other (in 100mV Range of your DMM) as soon as the first large drift has gone.

not all references are stable after 1 kHr.
my LTZ#8 still drifts with  ~0.5 ppm/kHr against my stable LTZ#2 after 2 kHrs.

with best regards

Andreas


Thanks for the info. Too bad I only have access to LM399 based instruments atm as the cal lab is too busy to lend me a 8508A and a transfer standard  :-DD But hey, can't complain if they can provide me with a traceable calibration for free.

Seems like I have a lot more research to do while waiting for them to stabilize. This project and the tester build I get to participate at work (   ;)  ) will surely provide a valuable lesson in precision electronics measurements.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on July 21, 2019, 07:26:40 am
pansku
You are on the right track, other than using LTZ1000CH. I found ACH easier to work with, and more linear in TC (before you trim them to <0.05ppm/K).
Avoid using connectors out of the LTZ boards to reduce risk of thermal EMF issues ;) But what do I know...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on July 21, 2019, 09:11:37 am
Just finished building 2 units with the Dr. Frank PCB  :phew:

I'm only on page 20 on this subject, but I got the impression that these should be powered on for about a month continously to burn in? As I'm limited to just a Keithley 2015 before we get some 3458A's to the lab I work in, is the correct way to do this by measuring the difference between 2 units on mV range and when they don't drift against each other that much, then I'll start trimming to desired output? After that time we should have the HPAK meters, put the boxes in a weather cabinet, run from lets say from 15 to 35 degrees °C and trim the 400k resistor? And lastly finish the project by having them calibrated against 732B(?) at the company cal lab.

Does that sound like a solid plan? I'm currently using 13k/1k and non-A LTZ1000. These references are going to end up in homelab with high'ish oven set point as the tempereture can reach around 30°C on the hottest summerdays inside.

Obligatory picture  ;D
Don't mind the missing power jack for now. I'll grab it later with the Hammond boxes when I'll order some more components to other projects.


Glad to see another new born pair of references.. welcome in the club.

These non -A references are quite fine, but you've set their oven temperature to probably 60..65°C, instead of using 12k/1k for 50..55°C.
Therefore you can expect a typical drift rate of about -2ppm/year, after the initial higher rate drift phase of 3..6 months.
Note: A 'burn-In' would mean that you'd run the LTZ1000 or LTZ1000A at elevated room temperatures, say over 120°C to let interior epoxy / silicon crystal anneal or create sped-up drift of exterior components.
(This process might be necessary on the A version.)

That's not necessary at all, because the LTZ1000 simply will show an initial drift of about -1..-3ppm/ 3 months, and then the drift will change to the typical rates mentioned above.

So you can directly build the completed tuner box , thermal isolation and Jacks and start trimming the overall T.C., as the references voltages will change during that process.

Your 6 1/2 digit meter is quite fine for tracking the initial drift, if you don't let it run continuously.. any reference which is not powered, will probably drift at nearly zero rate, especially when it's already aged.
So you will compare in the end 3 different references with 3 different drift rates.. in the beginning you LTZs will also differ, but might show the same rate later.

Later on, your new LTZ references will take over as fix points, hopefully you can transfer absolute readings into your lab by comparison.

The T.C. trimming process by bootstrapping is a bit more difficult using a LM399 based instrument, so you need to take care for constant environmental temperature.. Have you got basements in houses in Finland?

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: pansku on July 21, 2019, 12:14:15 pm

Glad to see another new born pair of references.. welcome in the club.

These non -A references are quite fine, but you've set their oven temperature to probably 60..65°C, instead of using 12k/1k for 50..55°C.
Therefore you can expect a typical drift rate of about -2ppm/year, after the initial higher rate drift phase of 3..6 months.
Note: A 'burn-In' would mean that you'd run the LTZ1000 or LTZ1000A at elevated room temperatures, say over 120°C to let interior epoxy / silicon crystal anneal or create sped-up drift of exterior components.
(This process might be necessary on the A version.)

That's not necessary at all, because the LTZ1000 simply will show an initial drift of about -1..-3ppm/ 3 months, and then the drift will change to the typical rates mentioned above.

So you can directly build the completed tuner box , thermal isolation and Jacks and start trimming the overall T.C., as the references voltages will change during that process.

Your 6 1/2 digit meter is quite fine for tracking the initial drift, if you don't let it run continuously.. any reference which is not powered, will probably drift at nearly zero rate, especially when it's already aged.
So you will compare in the end 3 different references with 3 different drift rates.. in the beginning you LTZs will also differ, but might show the same rate later.

Later on, your new LTZ references will take over as fix points, hopefully you can transfer absolute readings into your lab by comparison.

The T.C. trimming process by bootstrapping is a bit more difficult using a LM399 based instrument, so you need to take care for constant environmental temperature.. Have you got basements in houses in Finland?

Frank

Hi Frank,

Unfortunately the ambient conditions are really poor at the moment. I live in a student apartment with no basement available, even worse it is high up in southwest-side so one of the hottest places in the old building during summer. Typically outdoor tempereture +2...3°C unless I'm running a portable ac which in turn can create a worst case temperure delta of almost 10°C between day and night  |O

Fortunately I work part time in a power electronics RnD lab so I do have access to stuff like weather cabinets and, in a bit over a month, a pair of 3458A's  :-+ I will propably leave these boxes running somewhere in that building to age because all the linear power supplies I have at my tiny 25m² apartment make a lot of audible noise.

Technically speaking I could use the cabinets (-40° to +130°C with humidity adjustment) for burn in (not the aging I spoke of earlier with the wrong term). The lab at work is at a pretty constant tempereture. Those could maybe be used for TC trimming with the Keithley?

I still have one more PCB left and I'll try sneak in a order from VPG at work. That would allow me to build one more unit with 12k/1k and using possibly VHP101 resistors for the booster (and maybe even for rest of the critical parts) at almost no cost to me. I think I'll have to gather some experience with these first.
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on July 21, 2019, 03:08:44 pm
These non -A references are quite fine, but you've set their oven temperature to probably 60..65°C, instead of using 12k/1k for 50..55°C.

Isn't it the other way around? The A is better isolated and will heat up itself a little bit more. Therefore, you will need a higher heater temperature on the A type.


@pansku: I have also problems with my room temperature. I bought a small thermal chamber and a camping cooling box. At the moment I'm only using the thermal chamber to have stable 23°C and put the DUT and the reference into it. The meter isn't that crucial because it only compares the two references.
My plan is to control the camping box to fixed 23°C and use the thermal chamber for different temperatures to measure TCs.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on July 25, 2019, 06:10:39 am
These non -A references are quite fine, but you've set their oven temperature to probably 60..65°C, instead of using 12k/1k for 50..55°C.

Isn't it the other way around? The A is better isolated and will heat up itself a little bit more. Therefore, you will need a higher heater temperature on the A type.
How can one calculate the ratio to temperature yield for the LTZ1000? Is there any documentation on that? I remember on the voltnut board someone said they posted a chart here on the eevblog forum but I could not find it
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on July 25, 2019, 06:12:59 am
Has anyone tried to place a big thick copper plate, on the bottom of an LTZ1000 PCB? With thermal non conductive insulation. The goal would be to equalize and eliminate the temperature gradients, only thing I don't know if the thermal insulator would cause any noise/leakage on its own.

The better option being a ceramic PCB of course, like in the modern Fluke DMMs. The best option would be a multilayer ceramic PCB.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on July 25, 2019, 06:46:57 am
If you have a single sided PCB, that'll be a good idea thermally-wise, but that may cause short circuit.
Another technique would be to have a thermal isolation all around the bottom layer, e.g. by styrofoam... see my mechanical / thermal design around page 67, or so.

Best solution is to have a broad circular copper ring around the LTZ1000 on the top layer, when all its electrical connections are on the bottom layer.
See John Pickerings design inside the Wavetek / Fluke 7000 reference.

Btw. alll these other slots are nonsense.

Frank

Title: Re: Ultra Precision Reference LTZ1000
Post by: MegaVolt on July 25, 2019, 08:06:24 am
Tell me a mistake in my reasoning
A typical circuit stabilizes the current through the zener diode.
If we, knowing this current, add a precise resistor in series with the Zener diode, then we can get 10 V out by applying only 1 exact resistor.
Where am I wrong?
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on July 25, 2019, 08:12:45 am
Best solution is to have a broad circular copper ring around the LTZ1000 on the top layer, when all its electrical connections are on the bottom layer.
Will do thanks!

Actually, what would be interesting is machining a small copper ring, with a thickness of 4 mm and diameter just around the LTZ, and soldering it, top and bottom, while routing the connections on the inner layers, might be overkill, PCB can be 4 - 6 layers
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on July 25, 2019, 10:23:30 am
If we, knowing this current, add a precise resistor in series with the Zener diode, then we can get 10 V out by applying only 1 exact resistor.
Where am I wrong?

Where/how to get such resistor? :). Making a stable precision resistor of a non-standard value seems to be quite a challenge.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MegaVolt on July 25, 2019, 11:03:35 am
Quote
Where/how to get such resistor? :). Making a stable precision resistor of a non-standard value seems to be quite a challenge.
Creating a divider requires two exact resistors. In my opinion one exact resistor is cheaper than two.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on July 25, 2019, 11:44:51 am
Tell me a mistake in my reasoning
A typical circuit stabilizes the current through the zener diode.
If we, knowing this current, add a precise resistor in series with the Zener diode, then we can get 10 V out by applying only 1 exact resistor.
Where am I wrong?
With LM399 or other zener diodes you can exactly do that (bootstrap).
For LTZ1000 the circuitry is totally different and not applicable in this way.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on July 25, 2019, 11:51:23 am
A set of 2 resistors with matching TC is often cheaper than one resistor with good absolute TC at the same level.

Anyway the current through the zener is not as constant as the voltage. The current depends on one resistor (usually 120 Ohms) and the actual die temperature.

If it is about reducing the number of resistors, one could in theory combine the 7 to 10 V step with the divider for the temperature setting. This adds another OP and a little bit (but not that much) of extra drift and noise from that OP. So it's not the usual way.

The LM399 circuit may be combined to use the 7 to 10 V step to also provide the current, but this still needs to very stable resistors as a pair. Just for the current to the LM399 less accurate resistors are sufficient.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MegaVolt on July 25, 2019, 11:54:11 am
For LTZ1000 the circuitry is totally different and not applicable in this way.
What will hurt? What is the physical phenomenon?
Title: Re: Ultra Precision Reference LTZ1000
Post by: MegaVolt on July 25, 2019, 11:57:56 am
A set of 2 resistors with matching TC is often cheaper than one resistor with good absolute TC at the same level.
Thank!

Quote
If it is about reducing the number of resistors, one could in theory combine the 7 to 10 V step with the divider for the temperature setting. This adds another OP and a little bit (but not that much) of extra drift and noise from that OP. So it's not the usual way.
Maybe you have a diagram of this idea? I do not quite understand how temperature setting is related to output voltage?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on July 25, 2019, 01:31:55 pm
The temperature setting is not related to the voltage, but there are already 2 highly stable resistors that could be extended to a third. So 3 resistors in a row to get the  500 mV , 7 V and 10 V.  It's more like a theoretical option - not really practical.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on July 26, 2019, 06:08:49 am
We know that SZA263 was a buried zener on one die and a silicon diode on a second die, mounted on some ceramic substrate, while LTFLU are two identical transistors with one used as a more or less ordinary zener. So the question is, how could a buried zener based refamp with the transistor integrated on one die plus the onboard heater perform? So the question in more detail is:

Has someone tried to use LTZ as a LTFLU like refamp with the LTFLU circuitry aorund? This could be done by using zener diode and Q2. Therefore connect pin 3 and 7 and there is your LTFLU like refamp on pin 4, 3+7, 6 and 8. So the already shown LTFLU circuit could be used to make a references, starting with 3mA through the zener (R12) and a simplified version of R7 divider. The remaining part of Q1 could be used as a temperature sensing diode. R13 is individual selected for a specific oven temperature.

(https://www.eevblog.com/forum/metrology/the-ltflu-(aka-sza263)-reference-zener-diode-circuit/?action=dlattach;attach=268725;image)

What could be the advantage? R7 divider is still critical, but no extra gain stage for 7V --> 10V is required, thus lower noise of the 10V? Demands on oven stability are decreased? However, the oven is small and onboard so could be well regulated?
What are your thoughts?

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on July 26, 2019, 07:38:41 am
One can not wire the zener and transistor the other way round in the LTZ - they are already connected through the base and there is the substrate with more parasitic "diodes".

The LTFLU / SZA circuit is somewhat related, but for a different use. It essentially needs to make a higher voltage reference, more like 10 V. There is a way a round with an extra amplifier just for the collector current, but that would be more unusual.
There was a slight advantage of this configuration in the old days before good OPs, as one could directly get a 10 V or other higher reference. However the performance of the transistor to sense the voltage divider is limited. One is not really free to chose the transistor current for the amplification, but usually has to choose it to get a low TC. To get low noise it may take relatively low values for the divider R7, as there can be quite some base current (and thus current noise).

The LTZ circuit looks odd at first sight with the transistor at the low side, but it has some good points, as the transistor current can come directly from the 7 V level and only some 0.5 V for the current setting resistor is also not that bad. The circuit may get clearer if one considers it as a kind of bridge with the zener and R1 on one side and  V_BE and R2 at the other side.

There are quite a few modern OPs with less noise than the LTZ1000, so an extra OP for the 7 to 10 V stage is not a problem.
So the LTZ1000 internal circuit is good as it is - with the exception that the TC without the oven is relatively high and can thus not be trimmed to 0 by the transistor current. This is where the LTFLU is a little better.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on July 26, 2019, 10:41:10 am
As far as i understood the LTZ1000 datasheet page 6 shows how to trim the TC for unstabilized applications.

On the other hand, running a LTZ1000 or LTFLU reference at a temperature where the TC curve exhibits a maximum or minimum may not be very desirable. It results in a "noise rectifier", since minor variations of temperature will not average out any more in the reference output. Better leave a small linear TC.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on July 26, 2019, 12:04:00 pm
Adding a linear contribution does not help the rectifying action of a square law curve. So the nonlinear shape may be less visible if there is a linear background, the nonlinear part is still there.

The bigger "noise rectifying" effect is likely with the temperature regulation, due to the square law heater with a resistor. If well shielded it should not matter, but in a noisy environment and close to the drop out limit (low set temperature) there may be some effect of noise / variations in the temperature to shift the actual temperature a little lower. One could at least approximately correct the heater curve and this way get slightly better regulation close to the edge. However it's only s small improvement - though at moderate effort.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on July 26, 2019, 01:02:32 pm
We know that SZA263 was a buried zener on one die and a silicon diode on a second die, mounted on some ceramic substrate, while LTFLU are two identical transistors with one used as a more or less ordinary zener. So the question is, how could a buried zener based refamp with the transistor integrated on one die plus the onboard heater perform? So the question in more detail is:

Has someone tried to use LTZ as a LTFLU like refamp with the LTFLU circuitry aorund? This could be done by using zener diode and Q2. Therefore connect pin 3 and 7 and there is your LTFLU like refamp on pin 4, 3+7, 6 and 8. So the already shown LTFLU circuit could be used to make a references, starting with 3mA through the zener (R12) and a simplified version of R7 divider. The remaining part of Q1 could be used as a temperature sensing diode. R13 is individual selected for a specific oven temperature.



What could be the advantage? R7 divider is still critical, but no extra gain stage for 7V --> 10V is required, thus lower noise of the 10V? Demands on oven stability are decreased? However, the oven is small and onboard so could be well regulated?
What are your thoughts?

-branadic-

Theoretically, that might work, but will probably damage Q1, due to restriction:

"Pin 4: Substrate and Zener Negative. Must have a higher
positive value than Pin 7. If Q1 is zenered (about 7V) a
permanent degradation in beta will result."

If Q1 zeners already <7V, this will not work.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on July 26, 2019, 01:55:53 pm

If Q1 zeners already <7V, this will not work.


If you look at the Absolute Maximum Ratings then Q1/Q2 must not be reverse biased above 2V.

A normal transistor is specced at 5 V  maximum reverse bias and will zener around 7-8V.
(and usually is a good noise generator in this mode).

So the chance that Q1 does not zener above 3-4V is very little.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Insatman on July 29, 2019, 10:07:47 am
Just a fun photo.

I walked into my little lab today and took a snapshot of volt nut fantasy.   It's a LTZ1000 based reference that has been burning in for around 18 months since it's last tweak.  The truth is this number on my old fluke 8505A varies by up to +/-30uv at times.  But the reference is in a cardboard box, powered by a cheap walwart and has unshieled leads going to the meter.   Not to bad considering.   I have a better housed primary reference.  This was one of three boards I built and the best was selected for my reference chassis.
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on July 29, 2019, 10:45:48 pm

Long term stability of +/-30uv is only 6ppm,  that is nothing to sneeze at.  Nice job!
Title: Re: Ultra Precision Reference LTZ1000
Post by: F64098 on August 03, 2019, 04:07:00 pm
Hello everybody,

after waiting a long time for all that good stuff to arrive, i finished my first two boards yesterday.

Inspired by the boards of branadic and Dr. Franks schematic i made my own board, adding a double RC-filter at the input of the LTC1052
and move the power supply to a separate board (not built yet).
The PCB fits into a TEKO 394 housing and it's enough space left for the power supply and maybe a heater regulator for the whole housing.
As you can see, in spite of everything, i forgot to order the LTC1052  :palm:
R14 will be measured and ordered after the burn-in period. The yellow jumpers can be used to connect the floating copper planes to top or bottom ground.
The boards are nearly without errors, all parts are fitting well and they are functionally. Just the drill holes for the two types of transistors are both a little bit to small.
Unfortunately one of the LTZ1000 seems to be defective. Zener and heater are good, but the junction of the two emitters / Pin 7 has a problem.
On both 70k-resistors i measure too much voltage compared to the running board. It seems, both transistors can't drive any current. Is that a known error?
Bought them as "used but tested" on ebay a while ago, but used them yesterday the first time.
I plan to build another two boards. Is it advisable to look for non-A LTZ 1000?

Best regards

Frank


Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on August 04, 2019, 06:21:34 am
Are this resistors from Edwin G. Pettis? I didn't got my payed sets since february from him :rant:
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on August 04, 2019, 07:44:24 am
I have questions about bc369.

1) What is special about it?

2) It seems it's not bc369 in the circuit, is it? bc369 seems to be to-92.
Title: Re: Ultra Precision Reference LTZ1000
Post by: F64098 on August 04, 2019, 09:38:10 am
Are this resistors from Edwin G. Pettis?

Yes, ordered last year as a "Halloween offer".

Quote
I didn't got my payed sets since february from him :rant:

Be patient, they are really handmade and i also had to wait 5 months.

Best regards

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: F64098 on August 04, 2019, 09:41:55 am
I have questions about bc369.

1) What is special about it?

Nothing. Just a simple cheap PNP from my standard distributor.

Quote
2) It seems it's not bc369 in the circuit, is it? bc369 seems to be to-92.

I made the layout for TO-92 and TO-126 just for experimental purpose. I used the BD176, because there is a tiny little layout error for the TO-92 8)

Best regards

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 04, 2019, 10:39:56 am
why PNP?
The standard positive cirquit uses a NPN

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: F64098 on August 04, 2019, 11:38:25 am
 :palm:
I confused the "original" BC639 with the BC369.
But i used a NPN-Transistor and soldered in a BD176.
The layout is already corrected (bigger holes) and the TO-92 pins are gone...

Best regards

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: beanflying on August 04, 2019, 12:03:59 pm
Still waiting patiently for a few sets from Edwin too. Hope he is slaving over a bobbin winder and not on Summer holidays  ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 04, 2019, 01:00:36 pm
But i used a NPN-Transistor and soldered in a BD176.

According to my datasheets the BD176 is a PNP with BD175 as NPN complement.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: F64098 on August 04, 2019, 02:30:18 pm
 :-DD

Okay, i think my license to solder is finally lost...
Time to join the Supervised Thinking.

Changed the transistor to a 100% REAL NPN and look, both units perform _slightly_ better...
But on the other hand,  this embarrassing mistake saved both LTZs from being grilled by a defectice 1kOhm setpoint resistor.
Handled them all with maximum care and bent them with a special tool but one of them is really dead.

Best regards

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on August 04, 2019, 02:56:13 pm
Still waiting patiently for a few sets from Edwin too. Hope he is slaving over a bobbin winder and not on Summer holidays  ;)

hmmm I have been wondering for some time
did anyone have load life specs for his resistors? xx ppm yy C @ zzzz hrs 90min on 30min off ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on August 04, 2019, 04:13:14 pm
How are the Edwin's resistors manufactured? Any details on that? Is the resistive wire enamel coated? Bifilar winding (low L)? For such a resistance like 70k/12k you would need a pretty long and thin wire to wind on that small core, imho..
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on August 04, 2019, 06:19:41 pm
How are the Edwin's resistors manufactured? Any details on that? Is the resistive wire enamel coated? Bifilar winding (low L)? For such a resistance like 70k/12k you would need a pretty long and thin wire to wind on that small core, imho..


Have a read here (https://www.eevblog.com/forum/metrology/x-ray-images-of-precision-resistors/).

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on August 04, 2019, 06:58:21 pm
did anyone have load life specs for his resistors? xx ppm yy C @ zzzz hrs 90min on 30min off ?

the datasheet is here:
https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg463479/#msg463479 (https://www.eevblog.com/forum/metrology/t-c-measurements-on-precision-resistors/msg463479/#msg463479)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on August 04, 2019, 06:59:51 pm
...
Handled them all with maximum care and bent them with a special tool but one of them is really dead.
Hm, those nice views.  :scared:
Title: Re: Ultra Precision Reference LTZ1000
Post by: MegaVolt on August 05, 2019, 08:14:58 am
Inspired by the boards of branadic and Dr. Franks schematic i made my own board, adding a double RC-filter at the input of the LTC1052
and move the power supply to a separate board (not built yet).
Can you share the circuit on which the printed circuit board is made. Very interesting wiring.
Title: Re: Ultra Precision Reference LTZ1000
Post by: F64098 on August 05, 2019, 12:53:26 pm
I have no own schematic, just used Dr. Frank's schematic and added the two R/C-filters.
The two OPs got also their own R/C-filters from 10Ohms/10µF/100nF for their power supplies.

Best regards

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Qmavam on August 24, 2019, 09:31:11 pm
A couple days ago I got up at 2:45am to make sure I was awake to bid at 3:17am on an LTZ1000ACH.
When I saw it the price was $1.25, When I got up it had increased to $3.25.
With 15 seconds left I bid $4.00, I was over bid at $4.50, But I had time to put in a $5.00 bid.
It sold for $5.50.
 Boy, do I feel stupid.

 It was coming from China, don't know if it was any good.
But I would have paid $6.00 to find out! :-)
  Mikek

PS. I don't even know what I would with it!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Magnificent Bastard on August 24, 2019, 10:09:02 pm
A couple days ago I got up at 2:45am to make sure I was awake to bid at 3:17am on an LTZ1000ACH.
When I saw it the price was $1.25, When I got up it had increased to $3.25.
With 15 seconds left I bid $4.00, I was over bid at $4.50, But I had time to put in a $5.00 bid.
It sold for $5.50.
 Boy, do I feel stupid.

 It was coming from China, don't know if it was any good.
But I would have paid $6.00 to find out! :-)
  Mikek

PS. I don't even know what I would with it!

I think someone did you a favor.  REAL {and in-spec} LTZs go for a lot more than $6.  This was probably a FAKE device.  If you want a REAL LTZ, get some samples from analog devices.
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on August 24, 2019, 11:28:22 pm
Yea, if you're getting one for $6 you could be VERY lucky. I'd suspect you're getting a total fake, or a damaged one instead.
Title: Re: Ultra Precision Reference LTZ1000
Post by: feedback.loop on August 26, 2019, 11:43:49 pm
Let's get the logic straight. It was an auction. The fact that it ended with $5.50 does not mean that the part was fake. It may be a fake, but using the end price as a confirmation is not logical.
Title: Re: Ultra Precision Reference LTZ1000
Post by: GigaJoe on August 27, 2019, 12:28:53 am
100% fake ...
auction's  image:
https://pasteboard.co/IuyosXD.jpg
pin orientation,  fonts, printing ...
Title: Re: Ultra Precision Reference LTZ1000
Post by: ckocagil on August 27, 2019, 02:04:08 am
Does anyone know what happened to the cheap LTZ1000s from China? I searched all over taobao but can't find any cheaper than $45-50 which is nearly what you'd pay for a brand new one. Did this well dry up?
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on August 29, 2019, 01:25:52 pm
a 2005 report about investigation of vref noise in metrology zeners and JVS (using allan variance)
zeners tested Motorolas, Linears LTZ, waveteks
and motorolas have lower noise floor?

Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on August 29, 2019, 05:28:03 pm
Just my view of this article -

Fifteen years ago I was talking to a participant of the North American Intercomparison of the 10V standards. Every few years Fluke F732B standards were shipped all over the country, each lab determines what they think the voltage is. Those results are sent to the pivot lab for analysis. The four GOLDEN Fluke 732Bs used in the intercomparison were probably the same F732Bs with Motorola chip that were used in this test. The Acknowledgments section says as much.

The comment by a participant was "those four F732Bs are the best that Fluke ever made". While I'm sure that the results of Dr Witt and Dr Tang evaluation are accurate (I have met both of the gentlemen and toured their labs) they may not be representative of real world production parts.

BR
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on August 29, 2019, 05:43:48 pm
Can you explain what you mean by "not real world production units"? Are they cheating like using the four references as one? When they write "Motorola", it isn't Motorola? Or somebody outside Fluke reworked the devices?

Anyway it appears like even ultra precision references are not the real winners. I mean 3 ppb white noise at 1000 s sampling 15 years ago leaves a lot of space. Would like to know what the best ones a capable of nowadays.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on August 29, 2019, 06:07:08 pm
If I understand the article right the data in the histogram are for the low frequency limit due to 1/f noise, so the very low frequency noise  (e.g.  < 0.01 Hz), or the minimum / asymptotic value for the Allan variance. This is not just comparing the pure Zener references, but the full 10 V references: the Motorola ref. (SZA263) are older Fluke 732B, the Linear ref. should be newer Fluke 732B with LTFLU and the wavetec refes should be LTZ1000 based.
Especially the lowest frequency noise can very well also depend on the quality of the temperature control and 7 to 10 V circuit. There is also a good chance that the refs used are not just of the shelf ones, but possibly selected ones. I would more consider it a comparison the the 10 V refs., not just the zeners.

The higher frequency noise (e.g. 0.1 -10 Hz) could be different - in the article the sample LTFLU had lower white noise but more 1/f noise than the SZA263 sample.
Title: Re: Ultra Precision Reference LTZ1000
Post by: RandallMcRee on August 29, 2019, 07:56:28 pm
Can you explain what you mean by "not real world production units"? Are they cheating like using the four references as one? When they write "Motorola", it isn't Motorola? Or somebody outside Fluke reworked the devices?

. . .
Regards, Dieter

I'm not chuckb but what he says seems pretty clear: "not production units" is referring to the fact that those four went through a special selection process. Hence, as we all know from statistics class *not* randomly selected and thus not representative of a sample. E.g. to spell it out I can't buy one from digikey and be guaranteed to get that result. But maybe I could buy 100, and put them through a selection process, etc.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on August 29, 2019, 08:01:45 pm
Can you explain what you mean by "not real world production units"? Are they cheating like using the four references as one? When they write "Motorola", it isn't Motorola? Or somebody outside Fluke reworked the devices?

Anyway it appears like even ultra precision references are not the real winners. I mean 3 ppb white noise at 1000 s sampling 15 years ago leaves a lot of space. Would like to know what the best ones a capable of nowadays.

Regards, Dieter

The impression I had was that Fluke selected the very best units from the normal production for their own internal use and for special tests. So these are probably the best 0.1% of units produced. Some parameter like flicker noise might be 2x better than normal for some units. Of course some parameters (long term drift) can not be determined accurately at the factory during the few months they have them. There are probably some production units that are just as good as the units in the article. It's just statistics.

The Allan Deviations of my five Fluke 732A units are around 40nV for 100-1000 sec (Morotola SZA263). 
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on August 29, 2019, 09:31:34 pm
Zlymex showed a table of voltage reference specs, where the 732B had 0.06 ppm noise as compared to the 732A with 0.1 ppm noise.
https://www.eevblog.com/forum/metrology/teardown-voltage-standards/msg902849/#msg902849 (https://www.eevblog.com/forum/metrology/teardown-voltage-standards/msg902849/#msg902849)
When you start from the 732A Allan deviations and calculate 40 nV * 0.6 then you roughly get the numbers of the paper.

In Zlymex's table the 732B is listed as "LTFLU-1" while in the paper they say "five 732B instruments fitted with Motorola reference/amplifiers". Does this mean the noise difference is not attributable to the references M or L? Somehow i don't get it.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on August 29, 2019, 09:46:59 pm
If a lot of the reference noise is white noise...   would it not be reduced by using a filter of some kind on the reference?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on August 30, 2019, 06:34:29 am
Zlymex showed a table of voltage reference specs, where the 732B had 0.06 ppm noise as compared to the 732A with 0.1 ppm noise.
https://www.eevblog.com/forum/metrology/teardown-voltage-standards/msg902849/#msg902849 (https://www.eevblog.com/forum/metrology/teardown-voltage-standards/msg902849/#msg902849)
When you start from the 732A Allan deviations and calculate 40 nV * 0.6 then you roughly get the numbers of the paper.

In Zlymex's table the 732B is listed as "LTFLU-1" while in the paper they say "five 732B instruments fitted with Motorola reference/amplifiers". Does this mean the noise difference is not attributable to the references M or L? Somehow i don't get it.

Regards, Dieter

AFAIK there are older 732B with Motorola Ref. and newer 732B with LTFLU. Its also possible there was a missprinp and the Motorola units were actually 732A units.
The SZA263 is long obsolete - likely the reason Fluke got the LTFLU as a replacement.
Noise is not the primary concern, it is more about the long term drift.

Noise filtering  is tricky, as at the very low level capacitor leakage, DA and temperature effects can cause more trouble than good at the very low frequencies. In many uses a DMM or similar would be used that does low pass filtering anyway. In many cases one would case about noise at some .01-.1 Hz  Though even if only white noise, filtering would be tricky, with huge caps (100s of µF of polypropylene (better PTFE) caps).
Title: Re: Ultra Precision Reference LTZ1000
Post by: truser on September 09, 2019, 11:59:37 am
Bright thoughts to all!

Have the technology stopped improving over the past 20+ years or did something more accurate than the great-grandfather LTZ1000 (which have already been discontinued (for unknown reasons) from production) or so?

And...

Maybe someone will advise modern amplifiers (instead of LT1013) for a reference voltage source?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 09, 2019, 12:18:05 pm
So far there is no newer replacement for the LTZ1000.

The LT1013 is still be best bet for the reference circuit. The LT1013 is well good enough and not too expensive  - no need for experiments there.
Title: Re: Ultra Precision Reference LTZ1000
Post by: razvan784 on September 10, 2019, 10:04:00 am
Where are you getting these rumors that the LTZ1000 is discontinued? :palm:
It clearly states "In Production" on the Analog Devices (which bought Linear Technology) website: https://www.analog.com/en/products/ltz1000.html (https://www.analog.com/en/products/ltz1000.html)
It may be old, but there is no real need for a replacement -- it's a very good design, with no obvious flaws, and it's a Zener after all, you can't really improve much on basic physical phenomena.
There are currently only two ultra-stable, ultra-low-noise references in integrated circuit form: the LTZ1000 and the LTFLU1, the latter being a custom design for Fluke (now also Keithley, they are under the same parent corporation) and not available for general sale. And as I said, there is really no need for more, there is not much one can improve about them.
You can do the math on how much the LT1013 offset voltage, bias current, open-loop gain and noise affect the reference voltage and you will probably find it's also adequate for the job.
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on September 10, 2019, 01:38:10 pm
Is there any comparison on the performance of the LTZ1000 made in say 80ties/90ties and the latest silicon (especially after the merge LT+ADI)?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 10, 2019, 02:49:40 pm
Is there any comparison on the performance of the LTZ1000 made in say 80ties/90ties and the latest silicon (especially after the merge LT+ADI)?

Well, more or less, but still ongoing: https://www.eevblog.com/forum/metrology/vintage-ltz1000-from-1986-nib- (https://www.eevblog.com/forum/metrology/vintage-ltz1000-from-1986-nib-)!/

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on September 10, 2019, 05:16:17 pm
“O Metrologists," imo said, "the task I have designated you to perform is this. I want you to tell me" ......... "The Answer."

      The Answer?     The Answer to what?

"LTZ1000s!" urged imo. "The ultimate question of 80s/90s LTZ1000s compared to post merger ADI/LT LTZ1000s and everything!"


      <long pause>


      Tricky


"But can you do it?"


      <long pause>


      Yes.......... We can do it.

"There is an answer?" said imo with breathless excitement.

      Yes.   LTZ1000s and Everything. There is an answer. But, We'll have to think about it.

“How long?”.

      Seven and a half million minutes

"Seven and a half million minutes...!” imo cried. "That's nearly 14.27 years!

      Yes, We said we’d have to think about it, and take rather a lot of measurements didn’t we?
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on September 10, 2019, 05:50:51 pm
Hopefully there have been advances in manufacturing and materials over 30-40 years?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kjelt on September 10, 2019, 05:56:22 pm
Hopefully there have been advances in manufacturing and materials over 30-40 years?
Yes!................. but not on precision ultra low noise zenerdiodes  :o
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on September 10, 2019, 08:35:44 pm

Perhaps it is time to switch to AC?  :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: dr.diesel on September 10, 2019, 11:55:09 pm
Hopefully there have been advances in manufacturing and materials over 30-40 years?
Yes!................. but not on precision ultra low noise zenerdiodes  :o

Perhaps no need/market for it?  Or maybe companies that require that performance have rolled their own, Intel maybe as an example?
Title: Re: Ultra Precision Reference LTZ1000
Post by: mrflibble on September 11, 2019, 05:22:29 am
      Yes.   LTZ1000s and Everything. There is an answer. But, We'll have to think about it.

“How long?”.

      Seven and a half million minutes

"Seven and a half million minutes...!” imo cried. "That's nearly 14.27 years!

      Yes, We said we’d have to think about it, and take rather a lot of measurements didn’t we?

I'm surprised ArthurDent hasn't made an appearance yet.  ;D
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on September 11, 2019, 06:20:30 am
Kleinstein wrote an answer about reference noise filtering and i did a little experiment to get some numbers.

Took an 18 KOhm resistor to charge a 650 uF film capacitor we had to 10 V by our AD587 reference and then left it connected with a 3.3 MOhm resistor over night, watching with HP 3456A. Such capacitors are currently offered at ebay for 44 € per unit. After connection of the 3.3 MOhm resistor the voltage dropped slowly, in total about 70 or 80 ppm. But in the morning the voltage drop recovered and ended up as only 23 ppm.
It means that HP 3456A input parallel with that capacitor exhibits a current of 70 pA at 10 V, corresponding to 143 GOhm. Probably this is the input current of the HP3456A, so with a good OpAmp this may be much lower.

Regards, Dieter

PS: I can imagine that the capacitor may produce unwanted effects under temperature change but that's another step.
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on September 11, 2019, 06:31:59 am
What about this circuit? (values on the schematic are arbitrary).
[attachimg=1]

I saw it in AoE. The idea is upper capacitor has zero DC voltage accross it, so leakage doesn't matter. As a result, you can use  even electrolytic cap (so it is claimed).
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on September 11, 2019, 07:00:02 am
No, you want the capacitor to serve as a reference during the filter time constant. Sorry, but i guess the dirt effects will be much worse with electrolytic caps. Probably you won't even reach a time constant of 35 minutes due to self discharge.
Now i remember we have some gold supercaps that i could try as well. But then the problem will be charge balancing to reach 10 V. As Kleinstein wrote, it's not something simple.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on September 11, 2019, 12:33:07 pm
Kleinstein wrote an answer about reference noise filtering and i did a little experiment to get some numbers.

Took an 18 KOhm resistor to charge a 650 uF film capacitor we had to 10 V by our AD587 reference and then left it connected with a 3.3 MOhm resistor over night, watching with HP 3456A. Such capacitors are currently offered at ebay for 44 € per unit. After connection of the 3.3 MOhm resistor the voltage dropped slowly, in total about 70 or 80 ppm. But in the morning the voltage drop recovered and ended up as only 23 ppm.
It means that HP 3456A input parallel with that capacitor exhibits a current of 70 pA at 10 V, corresponding to 143 GOhm. Probably this is the input current of the HP3456A, so with a good OpAmp this may be much lower.

Regards, Dieter

PS: I can imagine that the capacitor may produce unwanted effects under temperature change but that's another step.


Interesting experiment.

You could also compensate the 70pA DMM current with some kind of current source, to balance things out.   The enormous time constant would likely "eat" any noise produced by the current source.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on September 11, 2019, 03:00:59 pm
Kleinstein wrote an answer about reference noise filtering and i did a little experiment to get some numbers.

Took an 18 KOhm resistor to charge a 650 uF film capacitor we had to 10 V by our AD587 reference and then left it connected with a 3.3 MOhm resistor over night, watching with HP 3456A. Such capacitors are currently offered at ebay for 44 € per unit. After connection of the 3.3 MOhm resistor the voltage dropped slowly, in total about 70 or 80 ppm. But in the morning the voltage drop recovered and ended up as only 23 ppm.
It means that HP 3456A input parallel with that capacitor exhibits a current of 70 pA at 10 V, corresponding to 143 GOhm. Probably this is the input current of the HP3456A, so with a good OpAmp this may be much lower.

Regards, Dieter

PS: I can imagine that the capacitor may produce unwanted effects under temperature change but that's another step.

in some older posting by mr blackdog, he did a guarded capacitor, ie capacitor sitting on a guard voltage which sits on another capacitor to gnd. the guard rail provides all the leakage the gnded capacitor needs, while the AC goes thru 2 capacitors to ground, the precision rail is suppose to see zero leakage to the guard rail because the potential is nearly the same.
it is complex, but it looks like you can make as big a filter as you want as long as you can wait for the charge up.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on September 11, 2019, 03:17:02 pm
Probably this is the circuit exe showed above with two capacitors, the lower one meant to be the helper (guard). Still there is one critical capacitor that needs to have reference quality up to a certain time scale. It is the one which holds the main voltage and the other one is more or less decoration, like the electrical drive in a hybrid SUV. Maybe i am wrong, but somebody needs to show the numbers.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 11, 2019, 03:40:17 pm
Leakage is just one problem with a low pass filter. Another is dielectric absorption, that may requires hours to weeks (with electrolytic caps) for settling.  Capacitors also react to temperature changes and possibly also air pressure changes, which can add low frequency noise. Instead of using two $44 capacitors, I would prefer a second reference chip.

It also depends a lot in how the reference is used. Most DMMs act as a low pass filter. Filtering would in this case not help very much (it still can with some DMMs).

The 2 capacitor circuit helps against leakage, but only to a limited extend against dielectric absorption and one needs 2 caps of twice the size.
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on September 11, 2019, 04:21:07 pm
Fyi - I've seen somewhere Mickle(T) did a measurement of the current coming out of the DMM's inputs (tens pA till nA as a short pulses pos/neg during AZ etc., about 10 DMMs, as I can remember). Thus the direct measurement of the voltage at the capacitor might be somehow influenced by that current..
PS: re above 2 caps filter - do the electrolytic (and tantalum) capacitors need a "minimum polarization voltage" in order to work properly??
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on September 11, 2019, 05:02:04 pm
Yes, somebody should write a clear statement that building analog storage devices with time constants of minutes or hours in 2019 is complete retro. Let the DVM run, take averages and use those numbers. For example i plotted the Allan deviation of my AD4522 preamplifier and found that it has a broad minimum of 3 nV at about 30 to 60 seconds. Nobody would do this exercise in the analog domain.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on September 12, 2019, 01:02:43 pm
Of course analog filters with long time constants are retro - but they are still cool!
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 17, 2019, 02:42:33 am
Wonder what that might be...

(https://xdevs.com/doc/xDevs.com/QVR/img/qvr_eevblog.jpg)

6-layers of ceramic substrate...
Price?  If you have to ask, you can't afford it ...  :scared:
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on September 17, 2019, 03:07:58 am
3458a ovenized quad reference board?

Does it support the Pickering patent?
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 17, 2019, 01:02:27 pm
What patent? Oven oscillator at startup? No, I am little sceptical that it helps much anyway.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on September 17, 2019, 03:21:12 pm
Yes - the Pickering patent claims to significantly reduce LTZ1000 drift after a power off period.

https://patents.google.com/patent/US5369245A/en

"An electronic component is conditioned to remove distortion in a temperature response characteristic due to a temperature hysteresis effect, by subjecting the component to a controlled temperature variation prior to operation of the component at a given temperature. "
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on September 17, 2019, 07:32:27 pm
Wonder what that might be...

(https://xdevs.com/doc/xDevs.com/QVR/img/qvr_eevblog.jpg)

6-layers of ceramic substrate...
Price?  If you have to ask, you can't afford it ...  :scared:
I guess it's just one more iteration of this other ...(https://uploads.tapatalk-cdn.com/20190917/b96ee5c23d67b959cacba2352ae2d88f.jpg)

Inviato dal mio ONEPLUS A5010 utilizzando Tapatalk

Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 18, 2019, 03:19:41 am
I'm bit lost how your board assembles together? How are the results? I see PCB made in May 2019?
And unconnected copper pads bugging me  :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on September 18, 2019, 03:41:04 pm
They assemble one o top of the other.

The board have pin 1 and pin 2 swapped on both LTZ1000 ... Kicad played some bad trick when it lost the symbols reconnecting it in reverse order when I reassigned it. Anyway I managed to not notice the problem despite the many times I have checked the schematics. I had to bodge some fix that fortunately seems to have no much impact on thermal design.

The board had also some filtering if you wanted to use autozero opamp for the LTZ reference. This seems to cause more problems so I just reverted to original LTZ circuit bypassing filtering.

Once fixed board I had to build a TEK mini thermal chamber to properly test TC ... and this has taken me some more time.

Averaged reference seems pretty stable and also TC looks ok ... you'll never know how it works until you do not put inside the 3458a.
Then the project was suspended because I was busy moving to a new house ... things are moving slow now.

The upper board hosts the two LTZs.
The bottom board hosts connection to 3458a, averaging/buffering circuit, and virtual ground generator for second zener.

There are some unconnected copper pour (both sides) just aiming to improve temperature equalization around the board, don't know how it improves ...

Virtual ground is used for second zener, referencing pin 7 of first LTZ.

I used only one divider shared between the two LTZ for temperature setting, "powered" from the averaged/buffered reference. Sensing of the averaged buffered out reference is done at the 3458a connector pin, so what it goes to the divider can suffer from some copper TC. I made some raw calculation and the effect should be very minimal.

PS: Routing the board trying to keep EMF balanced was a hell of work ... I can see why you selected ceramic substrate.
Title: Re: Ultra Precision Reference LTZ1000
Post by: feedback.loop on September 19, 2019, 01:54:50 am
Pins 1 and 2 are the heater. Does it matter which way around they are connected?
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on September 19, 2019, 04:47:16 am
It is very important to have the correct polarity and both pins have to be >= the voltage at pin 4.
The substrate diodes are drawn in the block diagram in Datasheet.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on September 19, 2019, 06:28:29 am
Swapping pin1 and pin2 of the heater was my first fail about 15 years ago, on my prototype.

That way I discovered the internal diode across these pins, and in turn caused the first revision A of the LT datasheet, where you should now see this diode.

Simply don't swap pin1 and pin2 !


Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 20, 2019, 06:13:23 am
Received PCBs. Sex on a stick!

Assembling first board (by hand as usual):

(https://xdevs.com/doc/xDevs.com/QVR/img/qvr_ref_wip.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kjelt on September 20, 2019, 08:13:37 am
Hi TiN,
Looks awesome (and expensive  :) ).
What is your goal? A 9,5 digit accuracy so a stable last digit ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: syau on September 20, 2019, 10:15:16 am

3458B  :scared:
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 20, 2019, 11:47:28 am
And first board is now online! Need to trim and measure each cell performance, before I start tests on combined output.

No smoke, no sparks, everything worked from first try so far. Board eats ~115 mA from +18V rail and some mA from -15V rail.

(https://xdevs.com/doc/xDevs.com/QVR/img/qvr_first_1.jpg) (https://xdevs.com/doc/xDevs.com/QVR/img/qvr_first.jpg)

Also next photo gives some idea how many expensive resistors did I sort to find a match for 1 quad board.

(https://xdevs.com/doc/xDevs.com/QVR/img/qvr_bmf_1.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 20, 2019, 12:32:57 pm
I don't see a real need to match the resistors for a board with multiple references in parallel. It can help to match the LTZ1000 chips, to have a reasonable equal voltage so that the averaging resistors get even less important.
There could be some adjustment needed for current compensation if used.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on September 20, 2019, 01:51:00 pm
Obfuscated parts, hidden collector resistors, a link leading to nirvana...
A Thriller :popcorn:
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 20, 2019, 02:07:33 pm
My 3rd 3458A is not golden, so need to goldify it myself.  :-DD
Main goal to get <0.2 uVpk-pk noise, so I can avoid need of external 10V reference for calibrations.
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on September 20, 2019, 02:32:23 pm
TiN what's the cost of the board? Looks like >$500 to me...
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 20, 2019, 03:20:03 pm
Total cost in parts for one board is about $3k.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kosmic on September 20, 2019, 04:55:35 pm
Really nice board Illya, thank you for posting.

Starting to look like a Valhalla 2720gs  ^-^
Title: Re: Ultra Precision Reference LTZ1000
Post by: antintedo on September 20, 2019, 05:32:05 pm
If I squint really hard I can see OPA2140A and ADA4522-2. How is my eyesight?
Edit: that does not look like $3k worth of resistors and ICs, is the PCB $1.5k per piece?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kjelt on September 20, 2019, 08:04:16 pm
Total cost in parts for one board is about $3k.

You were meaning it literally, not kidding  :)

My 3rd 3458A is not golden, so need to goldify it myself.  :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: Theboel on September 20, 2019, 10:36:44 pm
@ Tin
Just wondering to lowering the overall cost maybe You sell for the unmatched resistor.  :D :D :D :D
not a disc price but cut the waiting time
Title: Re: Ultra Precision Reference LTZ1000
Post by: 2N3055 on September 20, 2019, 10:57:15 pm
If I squint really hard I can see OPA2140A and ADA4522-2. How is my eyesight?
Edit: that does not look like $3k worth of resistors and ICs, is the PCB $1.5k per piece?
That is probably total cost of all resistors and parts from which he selected ones that he put on the boards.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on September 21, 2019, 12:58:23 am
My 3rd 3458A is not golden, so need to goldify it myself.  :-DD
Main goal to get <0.2 uVpk-pk noise, so I can avoid need of external 10V reference for calibrations.

what if you lower the temperature of the entire 3458a? then maybe have a LTZ heater at 30C?
https://www.eevblog.com/forum/metrology/dmm-adc-noise-comparison-testing-project/450/ (https://www.eevblog.com/forum/metrology/dmm-adc-noise-comparison-testing-project/450/)

dont know what is the set point of jorns LTZ, maybe 65C ?
that post, jorns stdev = 0.37uV @ 18C, is this better than most DMM/LTZ?  :-// and its a 34470a
maybe a cooler LTZ with smaller R1 ... 10mA ? but looking at some other posts, it seems to indicate that the noise of LTZ is not smallest at higher current. i cannot remember the post, after 3mA, noise increases?
did you try your select LTZ at different R1 and see if each has a low noise at a different current? I am wondering if each LTZ noise is exactly the same at exact same current, which i think is not true. that could mean sort by noise instead of Vz? but i dont know ... never build one of these before ...

i always have a thinking that stability can be mitigated by removing temperature problems (that is after reading all the wonderful tempco experiments of cos)
but noise? can noise be mitigated by tweaking temperature as well?

kill the mad cow tempco, murder the humidity, now .... what do we do with the noise ...
i did see some articles about cooling to reduce 1/f noise ... but i dont know. im sure its not the LN type of cooling, i think electronics are not specially made for LN. esp when there is humidity around
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on September 21, 2019, 08:40:47 am
My answer would be a very serious study of LTFLU, which also has four zeners inside. Appearently it can be used at 4x 3 mA current. But that belongs to the LTFLU thread. I will also try a low impedance capacitive 7V -> 10V stage to improve noise. Yet another thread. I will also try to use a TEC "oven" at 23°C (with desiccant inside) in order to keep noise and aging down. Made a small, high efficiency TEC controller to run from battery. There are lots of interesting details.

I think TiNs approach is more about engineering. Rapid results! To whom it matters: Recently i found that OPA189/OPA2189 has about 5 times less current noise than ADA4522 (in the specs). Maybe it's a new generation of chips, similar to AD4528. If i have the calc right at 50 KOhm input impedance total noise will be roughly the same as a OPA140.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 21, 2019, 09:35:35 am
For the LTZ1000 circuit itself the OPs noise and drift is not that critical. It is attenuated by about a factor of 200. So the LT1013 is still well good enough and no need to worry about AZ spikes.  The interesting point of this 4 reference circuit would be how to combine the outputs: the low side (GND) could probably use individual current compensation. For the high side with averaging resistors it would likely need a buffer amplifier, and this would likely be an AZ type, like ADA4528, AD8628, LTC2057 or OPA189.

With so much extra power, one may have to check the thermals inside the 3458. Worst case by getting a -5 V rail for the current compensation and possibly powering the LTZ1000 heater from some 8 V rail.

Normally using 4 reference should about half the noise. So the expected noise level should be more like 0.6 µV_pp (.1-10 Hz), maybe a little less with selected LTZ1000. A little of the 10 Hz end may be removed by filtering, but not that much. However the relevant bandwidth would be more like 0.01 - 1 Hz anyway. With 13K/1K dividers and LTZ1000A the temperature is already relatively low - this also helps keeping the power for the heaters low.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on September 26, 2019, 08:36:14 pm
So this is noise of my dual LTZ A9 board (700nV to 800nV p2p) ... time to order a couple of 50 ohm resistor and check how it performs at high current.

Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on September 27, 2019, 09:45:30 am
So this is noise of my dual LTZ A9 board (700nV to 800nV p2p)

What do you use as an amplifier?
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on September 27, 2019, 10:33:47 am
I guess it is the one from the DIY-LNA-Thread (https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg1336848/#msg1336848) with 0.1-10Hz and x10k amplification.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on September 27, 2019, 12:59:16 pm
Yep this one

I guess it is the one from the DIY-LNA-Thread (https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg1336848/#msg1336848) with 0.1-10Hz and x10k amplification.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on September 28, 2019, 11:34:01 am
And this is the board "slap together" ... not nice as Tin ones but it seems to works. Since one week it tracks sub ppm the other 3 LTZ I built. I'm considering to put everything in one pcb instead of having it stacked.

(https://i.ibb.co/txbWpWy/IMG-20190928-131755.jpg) (https://ibb.co/mXHM5MQ)

(https://i.ibb.co/drMKJBW/IMG-20190928-131737.jpg) (https://ibb.co/JKtkFnB)

(https://i.ibb.co/sFKrDZt/IMG-20190928-131719.jpg) (https://ibb.co/64H5pkN)
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 28, 2019, 11:54:37 am
Wow those leads are long :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on September 28, 2019, 04:11:26 pm
Wow those leads are long :)

They will be cut when on the final pcb board ;-)
Title: Re: Ultra Precision Reference LTZ1000
Post by: antintedo on September 28, 2019, 05:18:07 pm
Speaking of 3458A mods, maybe consider not using those Molex connectors and solder wires instead? Apparently they can cause issues: https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1377590/#msg1377590 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1377590/#msg1377590)
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on September 28, 2019, 08:17:03 pm
Once I tested what was effect of moving/removing the A9 board from 3458A and I didn't measured any shift. But this is just my unit and it doesn't prove or disprove anything ... maybe one day I'll test also effect of removing the current compensation resistor.

Anyway I'm not going to solder the board on 3458a ... this seems too much violence to such an instrument.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on September 29, 2019, 08:38:41 am
On August 23, i showed a possible solution in the LTFLU thread:

https://www.eevblog.com/forum/metrology/the-ltflu-(aka-sza263)-reference-zener-diode-circuit/375/ (https://www.eevblog.com/forum/metrology/the-ltflu-(aka-sza263)-reference-zener-diode-circuit/375/)

That is a IP66 (waterproof) case and it takes my LTFLU reference board including a sensirion humidity sensor and a 5 g desiccant bag. The image also shows how to make a thermal clamp for the interface cable, in order to create a thermal "nirwana" inside the case.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on September 29, 2019, 04:47:30 pm
I need to send my LTZ1000 (non-A version) board to somebody to fine tune it. Can anyone help please? I am fine sending it worldwide, but the UK would be the perfect destination. I do not have equipment to set it up properly.
What's the best way to post LTZ1000? Running in the temperature chamber or …?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on September 29, 2019, 08:21:11 pm
Would you mind telling or showing more details, like PCB,mechanical and thermal design, choice of resistors?
If prerequisites are ok, I offer to do the T.C. trimming, and determination of output voltage(s)

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: mimmus78 on September 30, 2019, 09:50:44 am
On August 23, i showed a possible solution in the LTFLU thread:

https://www.eevblog.com/forum/metrology/the-ltflu-(aka-sza263)-reference-zener-diode-circuit/375/ (https://www.eevblog.com/forum/metrology/the-ltflu-(aka-sza263)-reference-zener-diode-circuit/375/)

That is a IP66 (waterproof) case and it takes my LTFLU reference board including a sensirion humidity sensor and a 5 g desiccant bag. The image also shows how to make a thermal clamp for the interface cable, in order to create a thermal "nirwana" inside the case.

Regards, Dieter

Well consider I have stacked design mainly for this reason ... everything is heat producer is on the top board, and this is connected to bottom board by solid copper wires. The molex connectors are on the bottom PCB where no relevant heat is produced.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on September 30, 2019, 04:15:21 pm
Yes, i guess you want to run the LTZ1000 using its heater.
Anyway, now that i learned how to compensate reference amplfier residual TC using a temperature measurement circuit (like https://www.eevblog.com/forum/metrology/the-ltflu-(aka-sza263)-reference-zener-diode-circuit/msg2578746/#msg2578746 (https://www.eevblog.com/forum/metrology/the-ltflu-(aka-sza263)-reference-zener-diode-circuit/msg2578746/#msg2578746)), i am wondering how the LTZ1000 would perform at room temperature, i mean in a TEC "oven".

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on September 30, 2019, 04:35:19 pm

My understanding is that it is very difficult to balance an LTZ1000 for zero TC at room temperature.

Of course, that makes it an interesting intellectual challenge!
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on September 30, 2019, 06:05:57 pm
Did you ask a question?
Have a look at the schematic! The same extraction/measurement of chip temperature works for the LTZ1000. It's even better since you have an independent transistor as temperature sensor. Once you have the temperature signal, you can use it to raise or lower the temperature coefficient as you like. This works much better than the usual 400 KOhm resistor, because that signal isn't temperature but heater power.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 30, 2019, 06:37:59 pm
For compensation of the residual TC, the chip internal transistor is not useful. The internal regulation keeps it at essentially constant temperature.
The residual TC is not so much because of the internal temperature regulation not working well. It is more because of effects on the resistors, thermal EMF and an effect of the heater power in the reference part.

It would need something like an external temperature sensor, or as used in the standard circuit use the heater voltage as an approximation.
An external temperature sensor (e.g. diode or PT1000) may be better than the 400K (R9) resistor from the data-sheet, that uses the heater as an approximation for the external temperature. AT least what I sow here in this thread looks more like a linear TC than a direct correlation with heater current (more like square root of heater power).
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on September 30, 2019, 07:37:56 pm
Sorry, this time you missed it completely. This is about the residual TC without using the on chip heater, but using a TEC "oven" at room temperature instead. And don't tell me that an external temperature sensor will work better than an on chip sensor.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on September 30, 2019, 07:51:39 pm
Did you ask a question?
Have a look at the schematic! The same extraction/measurement of chip temperature works for the LTZ1000. It's even better since you have an independent transistor as temperature sensor. Once you have the temperature signal, you can use it to raise or lower the temperature coefficient as you like. This works much better than the usual 400 KOhm resistor, because that signal isn't temperature but heater power.

Regards, Dieter

Consider how the LFTLU is made relatively temperature insensitive by a combination of choice of zener current and use of the built in transistor as a compensation device.  That scheme is hard to replicate on the LTZ1000, it seems to me, because its pass transistor isn't connected the same way as LTFLU.

I do like the idea of keeping the LTZ1000 in a controlled temperature environment, using its own heater transistor to measure the temperature.  Just the fact of keeping all the other components and the board itself at a stable temperature has to be an overall win.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 30, 2019, 08:25:21 pm
The TC to start with at the LTZ1000 is rather high. So it is quite difficult to reduce the TC without using a critical high stability resistor.
There could be chance that this may work at a reduced current (e.g. 0.5 mA). Less current should reduce the TC and the fine tune could than be possible with the transistor current. However this comes at the price of higher noise and I don't know how aging changes at lower current.

Even if still using the internal heater, a reduce TC to start with would reduce the importance of the set point resistors.
Ideally there would be a LTZ1000B with lower TC to start with, e.g. from a reduced voltage zener (e.g. 6.7 V total reference).
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on October 01, 2019, 01:17:33 am
Would you mind telling or showing more details, like PCB,mechanical and thermal design, choice of resistors?
If prerequisites are ok, I offer to do the T.C. trimming, and determination of output voltage(s)

Frank

This is the board I have - your design :)  The resistors are Vishay. The two critical resistors are hermetically sealed.
Here is another link - https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg2514555/#msg2514555 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg2514555/#msg2514555)
Very much appreciate your assistance.

(https://i.imgur.com/whJ6qBe.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 01, 2019, 08:15:09 am
Would you mind telling or showing more details, like PCB,mechanical and thermal design, choice of resistors?
If prerequisites are ok, I offer to do the T.C. trimming, and determination of output voltage(s)

Frank

This is the board I have - your design :)  The resistors are Vishay. The two critical resistors are hermetically sealed.

Very much appreciate your assistance.


Well, fine,  :-+, so I'm familiar with that board, at least.
So what is the T.C. of these resistors, the Vishay and the other ones?
Did you determine these T.C.s?

How is the PCB assembled, or is this the current state?

It's not feasible to trim this naked PCB, as the mechanical/thermal assembly also influences the T.C.
Also be aware, that the trimmed 10V output has to be re-trimmed, because T.C. trimming by this nominal 200k resistor changes the LTZ1000 output voltage.

My offer persists, if you would have made a proper assembly.
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on October 01, 2019, 09:05:18 am
Would you mind telling or showing more details, like PCB,mechanical and thermal design, choice of resistors?
If prerequisites are ok, I offer to do the T.C. trimming, and determination of output voltage(s)

Frank

This is the board I have - your design :)  The resistors are Vishay. The two critical resistors are hermetically sealed.

Very much appreciate your assistance.


Well, fine,  :-+, so I'm familiar with that board, at least.
So what is the T.C. of these resistors, the Vishay and the other ones?
Did you determine these T.C.s?

How is the PCB assembled, or is this the current state?

It's not feasible to trim this naked PCB, as the mechanical/thermal assembly also influences the T.C.
Also be aware, that the trimmed 10V output has to be re-trimmed, because T.C. trimming by this nominal 200k resistor changes the LTZ1000 output voltage.

My offer persists, if you would have made a proper assembly.
Frank

Non-critical resistors are 0.01% 5ppm 0.5W Vishay SFERNICE Foil resistors T.C +/-5ppm/C
Critical resistors are 0.01% 0.3W RADIAL Vishay Metal Foil seal resistors (VH102K and VHD200 used as a single resistor) - I think these have T.C. +/- 1ppm/C and 2ppm/C respectively.

The board was assembled by hand. Resistors and LTZ1000 was soldered with an extra care trying not to overheat these components.
I left long legs for LTZ1000 - not sure if it was the right decision. It's been a long debate here about the legs length and TCR.
 
Currently, the board is in the Hammond enclosure (LTZ1000 has been isolated for air drafts) running 1500h+
No, I did not determined the T.C.

Thank you once again.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 01, 2019, 11:01:55 am


Non-critical resistors are 0.01% 5ppm 0.5W Vishay SFERNICE Foil resistors T.C +/-5ppm/C
Critical resistors are 0.01% 0.3W RADIAL Vishay Metal Foil seal resistors (VH102K and VHD200 used as a single resistor) - I think these have T.C. +/- 1ppm/C and 2ppm/C respectively.

The board was assembled by hand. Resistors and LTZ1000 was soldered with an extra care trying not to overheat these components.
I left long legs for LTZ1000 - not sure if it was the right decision. It's been a long debate here about the legs length and TCR.
 
Currently, the board is in the Hammond enclosure (LTZ1000 has been isolated for air drafts) running 1500h+
No, I did not determined the T.C.

Thank you once again.

Well,  I also left the legs long... successful.

Everything sounds good, maybe you have a picture of the completed device, including power supply.

Anyhow, if nobody else in your country (UK?) gives an offer, you may send it to me.. just send me a PM to clarify details.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on October 01, 2019, 12:33:11 pm
Non-critical resistors are 0.01% 5ppm 0.5W Vishay SFERNICE Foil resistors T.C +/-5ppm/C
Critical resistors are 0.01% 0.3W RADIAL Vishay Metal Foil seal resistors (VH102K and VHD200 used as a single resistor) - I think these have T.C. +/- 1ppm/C and 2ppm/C respectively.

The most critical resistors are the boost resistors for 7->10V.
Their tracking TCR and drift are only attenuated ~3x, whereas all other are >=100x.
The Datasheet seems to be wrong for the relevance of the impact of resistor changes. (https://github.com/pepaslabs/ltz1000-info)

Put your money wisely  ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on October 01, 2019, 04:00:23 pm


Non-critical resistors are 0.01% 5ppm 0.5W Vishay SFERNICE Foil resistors T.C +/-5ppm/C
Critical resistors are 0.01% 0.3W RADIAL Vishay Metal Foil seal resistors (VH102K and VHD200 used as a single resistor) - I think these have T.C. +/- 1ppm/C and 2ppm/C respectively.

The board was assembled by hand. Resistors and LTZ1000 was soldered with an extra care trying not to overheat these components.
I left long legs for LTZ1000 - not sure if it was the right decision. It's been a long debate here about the legs length and TCR.
 
Currently, the board is in the Hammond enclosure (LTZ1000 has been isolated for air drafts) running 1500h+
No, I did not determined the T.C.

Thank you once again.

Well,  I also left the legs long... successful.

Everything sounds good, maybe you have a picture of the completed device, including power supply.

Anyhow, if nobody else in your country (UK?) gives an offer, you may send it to me.. just send me a PM to clarify details.

Frank

Thank you
PM sent
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on October 03, 2019, 03:12:46 am
Does anyone have a spare LTZ1000 PCB? I would favour a board based on a design by Dr Frank and branadic?
Please send me a PM
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on October 04, 2019, 03:01:55 pm
I'd also like advice on source for a PCB either from member here or from online board house that has a design.  I, sadly don't have 4 LTZ1000 but only two older 2001 and 2004 LTZ1000ACH.  Is there anyone that has some PCB's ready that I could purchase?  This seems to be the best route to a nice precision reference vs just buying one (and it's good learning experience for this computer scientist).  You guys have put so much effort into this and hats off  :clap: I want in please?  Wow TIN that PCB looks sweet!  I hope you'll post some stats and graphs from it.  After going through hand selecting that many resistors to make your quad... perhaps you've got enough decent resistors left over for a single board set you could part with?

Best Regards,

Bill
Title: Re: Ultra Precision Reference LTZ1000
Post by: RandallMcRee on October 04, 2019, 03:35:43 pm
Your wish is our command:
https://github.com/pepaslabs/px-ref (https://github.com/pepaslabs/px-ref)

Notice that there is a link in the readme to OSH boards, under Purchase. I have built six and they work well.

BTW your older LTZ1000A are fine, like fine wine, it seems.

addendum: The PX board is the work of Mr. Pepas; as you can see from the github url and the readme therein. I just thought I should publicly acknowledge that this is all his (and others!) great work and we are grateful for it!
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on October 04, 2019, 06:23:15 pm
There is Dr. Frank's recreation as well
https://github.com/pepaslabs/dr-frank-ltz1000
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 06, 2019, 06:30:34 am
Mhm,

do you think that the capacity does not change within 37 days with room temperature?
If you pull the plates of a capacitor apart (e.g. rising temperature) the voltage will increase.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Magnificent Bastard on October 07, 2019, 04:41:05 pm
being distracted by the thread https://www.eevblog.com/forum/metrology/forum-crowd-project-simple-10v-ltz1000-plugnplay-box-(with-1k10k-hermetic)/ (https://www.eevblog.com/forum/metrology/forum-crowd-project-simple-10v-ltz1000-plugnplay-box-(with-1k10k-hermetic)/)
i took a peek at the ordering site, and noticed the ROHS and temp range confusion

i just have to ask everyone here

when you bought your LTZ1000 CH/ACH
did you know it was a
1) 0~70C unit? (ROHS complaint)
2) or a -55~+125C unit ? (non ROHS complaint)

digikey/mouser list their as -55~+125C and it is ROHS complaint. there is apparently no such unit on ADI website.

This is a "moot" point.  Since this is an internally heated device, there is an upper and lower bound on the ambient temperature anyway for proper operation.
Title: Re: Ultra Precision Reference LTZ1000
Post by: essele on November 15, 2019, 04:55:54 pm
I thought I'd post my exploits with building a battery-backed LTZ1000 reference unit ... this has been done with a huge amount of input from this forum -- so a massive thanks to just about everyone! I'm sure there are a long list of things I've done wrong, a few I've worked out myself, and probably hundreds I'm not aware of ... any improvements would really be welcome.

This is a board based on the 10V one from Dr Frank, and using a (very slightly) modified version from the one that Cellularmitosis posted (and hosts on GitHub.)

The reference board is contained in the Teko 393 tuner enclosure which you can see in the middle of the outer enclosure. I used modelling foam which should be a good insulator to build the internal compartments.

The power supply board, which is really meant to keep the batteries charged, is based on a tps7a4901 along with another LDO 3.3v regulator to supply the front panel. The batteries are charged in parallel pairs using MCP73831's powered from isolated DC/DC converters, all powered from a mains AC/DC converter.

The batteries should last three or four days for the reference, and the AVR uses an average of 0.5mA in non-alarm mode, and 1.5mA in alarm mode, so that will last for weeks (it has a separate battery.)

[attachimg=1]

The rear panel is a PCB which I only used since it's easier than trying to cut holes in anything else.

[attachimg=2]

The front panel is also a PCB, but has an atmega328p on the back along with a couple of resistor dividers for the analog inputs, two rear-mount LED's, and a small SMD piezo sounder. This keeps an eye on whether external power is connected or not, flashes the LED's to show battery levels when charging, and then alarms if the battery level starts to get low ... it also gives you a helpful set of tones when mains is applied or removed (yes, I had fun with that!)

[attachimg=3]

I've made up a few reference boards with different resistor sets on (this one is Sfernice 2ppm ones from eBay, but I also have a 5ppm version, and one with Edwins PWW's), so my intent is to build out a few more enclosures ... but I've got a few lessons learned from this one to include...

- The LiPo chargers get a bit warm, so I will see if I can move them to the other side of the board so they are closer to the vent holes ... this isn't really an issue since it's only really a problem if the batteries are particularly low (I could also reduce the charging current, but it's only 170mA at the moment anyway.)

- I get some blips when turning power on or off ... they can be in excess of 10uV ... I'm not sure if this is related to changes in the 12V power supply or some kind of noise. I need to do some more experiments ... interestingly there aren't showing up since everything is in the enclosure??

- I used a simple header and crimp connector on the front panel with no polarisation, and 16.8v on one pin ... yes - one dead avr. Some polarisation needed, would probably switch to an IDC one with a box (also saves the crimping!)

- There are no power switches, so nothing can be switched off ... so to turn off the alarm once the battery gets low (assuming you don't want to plug the power in) is a big disassembly job. I think a couple of rear mounted slide switches on the front panel with cut-outs should work -- one for the 12V supply to the ref, the other to turn off the AVR.

- I soldered the wires onto the Pomona 3770 jacks ... it didn't go particularly well, will probably need to redo them ... do others solder, or use crimp terminals?

And finally, I can't really measure the stability of any of the references yet ... my 34470A seems to be awful, it wanders all over the place (well 1-2ppm in the space of a day, lots of noise at the start of any temp increase), on ratio mode (which hopefully eliminates any issues with the meter) with a Datron 4000A it seems much more steady, with only a very minor temperature based delta ... but I have no idea which of them is the cause yet. I have a Prema 6048 which is away for calibration with Keysight, but they are taking an eternity, I think it's the first one they've had. Next project is a switching unit, so I can do some sensible data gathering from multiple devices.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on November 15, 2019, 05:11:11 pm
It looks very nice  :-+
Are there (invisible) earth connections directly screwed on all parts of metal case?
If not, you should add them for safety.
Title: Re: Ultra Precision Reference LTZ1000
Post by: essele on November 15, 2019, 06:05:49 pm
It looks very nice  :-+
Are there (invisible) earth connections directly screwed on all parts of metal case?
If not, you should add them for safety.


Thanks -- I missed that off of my list of lessons learned ... the rear panel actually has a copper pour and through hole plating on the four main fixings and one of the fixings for the power supply board, so that was supposed to do the trick, however it's not working. I'm not sure why yet ... I was just enjoying the thing being in one piece for a while before I dismantle it again!

Actually I hadn't really considered the top and bottom panels (which are separate) ... so maybe this isn't a good case choice, they do a single piece version which I think has the same dimensions, just may be more challenging for assembly.

EDIT -- so I mounted the back panel the wrong way around -- sigh, and so the plated hole that supposed to line up with the earthed stand-off doesn't ... I'll need to switch that around, but still doesn't solve the top and bottom issue. And actually the IEC socket fixings are earthed, so they would have been a better place to put the through hole plating (which I didn't!)
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on November 15, 2019, 06:32:56 pm
And actually the IEC socket fixings are earthed, so they would have been a better place to put the through hole plating (which I didn't!)

That would have been my next suggestion  ;)
I am not shure if the earth connections for the sides are appropriate, I guess not.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on November 15, 2019, 07:54:41 pm

- I soldered the wires onto the Pomona 3770 jacks ... it didn't go particularly well, will probably need to redo them ... do others solder, or use crimp terminals?


Very nice! Well done mate
Pomona 3770-0 - I use these ones too for my LTZ1000 project and I solder wires to them. Make sure you have the correct heat temp and they absorb a lot of heat.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on November 15, 2019, 09:05:04 pm
It is really hard to measure the performance of a good reference. For example, you could use a 3458a, but it doesn't have the stability of a dedicated 10V reference, so it is hard to tell what you are looking at.

If you build a second unit, the delta between them can give you some ideas.
Title: Re: Ultra Precision Reference LTZ1000
Post by: essele on November 29, 2019, 09:19:52 am
Ok, so I finally got my Prema 6048 back from Keysight, all calibrated and happy.

I'm still working on my USB switching unit, so I've just done some overnight measurements comparing the 34470A and the 6048 measuring the reference from the posts above.

The top orange line is the measurement from the 34470A and the blue line is the 6048. The lower orange line is the temperature ... I pretty much melted the BME280 when trying to get the bloody thing to solder onto my board, so I'm not entirely convinced about the absolute temp, relative seems to be ok though.

The scale for the main measurements is ((v/first_v)-1)*1000000. So this should show ppm deviation from the original reading in each case.

You can see the 34470A is a bit all over the place (well, from +0.4ppm to -1.2ppm) although still easily within its 24h spec, it does show the marked different to the 6048 which is sitting in +/- 0.3ppm range.

The 34470A is in 100PLC, AZ on, fixed 10V range, no filter. Powered on for weeks.
The 6048 is on 20s sampling (8.5 digit), 20V range, no filter. Powered on for about 90mins at the start, so may still be warming.

Measurements are in a loop with no other delays, so that works out at approximately 1 measurement every 24 seconds.

Clearly there isn't enough information in this to make any concrete assertions, and the data set is a bit too short, but I thought it was an interesting initial set of data.

I should be able to get the switching going in the next few hours, then the intention is to sample two LTZ1000's and a Datron 4000A on both DMMs.
Title: Re: Ultra Precision Reference LTZ1000
Post by: HighVoltage on November 30, 2019, 09:48:22 am
Very interesting, essele!

The 34470A has some known flaws.
My biggest complaint was the ACAL drift.
Actually the 7 1/2 digit 34470A is much worst than the 6 1/2 digit 34465A, even worst than some of my older 34401A.

Keysight is working on a solution....
https://www.eevblog.com/forum/metrology/keysight-34470a-calibration-and-acal-problems/ (https://www.eevblog.com/forum/metrology/keysight-34470a-calibration-and-acal-problems/)

Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on November 30, 2019, 05:49:28 pm
That looks pretty good! I wish Keysight could handle the 8017. I'm guessing the lack of english manual is why they "can't". In fact the only place I know of that can is Prema which means paying 350$ return shipping alone. Does it get more stable at higher integration times or nearly the same output?
Title: Re: Ultra Precision Reference LTZ1000
Post by: essele on November 30, 2019, 06:30:53 pm
I’ve now got my usb switch working but I saw some very strange behaviour.

I was switching between two 10v refs, and reading one 20s reading from the Prema each time ... the readings slowly converged, very weird ... I initially suspected my switch (since I built it!) but after some testing it looks like there is some kind of filtering going on in the Prema (despite the digital filter being off) ... it really does look like a rolling average.

It seems to be related to the number of readings and not elapsed time, so I now run it in 4s continuous mode for 20s before switching to a 20s single reading and it seems much better.

I’ve just rehoused the second reference in a similar case as above (but v2 with some improvements) and I’m about to kick off a new set of measurements, I will try some variations of the above and longer integration times as well as it seems a bit more jittery than the single measurement above.
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on November 30, 2019, 06:42:18 pm
Which of the LTZ1000 reference PCB do you think is the most evolved and includes ability to do the 7V to 10V?  Or... do you think the 7.x to 10V is better done outside the reference container or inside it?  It seems a stable 7.x volt reference with boost to 10V trimmed output is the ideal. From your experience what do you suggest?

Bill
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on November 30, 2019, 07:16:59 pm
I’ve now got my usb switch working but I saw some very strange behaviour.

I was switching between two 10v refs, and reading one 20s reading from the Prema each time ... the readings slowly converged, very weird ... I initially suspected my switch (since I built it!) but after some testing it looks like there is some kind of filtering going on in the Prema (despite the digital filter being off) ... it really does look like a rolling average.

It seems to be related to the number of readings and not elapsed time, so I now run it in 4s continuous mode for 20s before switching to a 20s single reading and it seems much better.

I’ve just rehoused the second reference in a similar case as above (but v2 with some improvements) and I’m about to kick off a new set of measurements, I will try some variations of the above and longer integration times as well as it seems a bit more jittery than the single measurement above.

If it runs like the others then yes the filter includes a rolling average of 10(or more) readings. Ideally you should watch one for a time, then switch over.

I haven't looked but if you can force a trigger that resets the average and starts anew.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on November 30, 2019, 07:19:51 pm
The LTZ1000 reference is usually more stable than the 7 to 10 V step. So it makes absolutely sense to also have a 7 V output, not just 10 V. The 10 V stability is mainly dependent on the 7 to 10 V step. For the 7 to 10 V step there are several possibly option besides the choice of very stable resistors - so this would be better a separate thread.

In most cases there is no problem to have the 7 to 10 V step in the same container. It can make things even a little easier and could save on an extra buffer or wire compensation.
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on November 30, 2019, 08:56:59 pm
Here are my aged babies I want to build with.  They're the oldest ones I could find available.  My hope is they're more stable now and aged already.

Essele that's a beautiful build you put together there!  What batteries did you use there?


Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on November 30, 2019, 09:36:29 pm
(Zener based) References only age over temperature (~Arrhenius), but practically not over time at R.T.
Therefore, just fire them up and monitor, how they perform.
50°C oven ~ -1..2ppm/year, doubles each 10°C. In continuous working mode, drift rate usually decreases over time, until Random Walk is main drift phenomenon.
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: essele on November 30, 2019, 09:40:19 pm
Hi notfaded1,

Thanks - I’m pretty pleased with them (there are two now!)

The batteries are from HobbyKing...

https://hobbyking.com/en_us/turnigy-2000mah-1s-1c-lipoly-w-2-pin-jst-ph-connector.html

... the first time I used them they were quite a bit cheaper, I do think it would be better to use a 4S pack now, but I’m still struggling to find an easy way of charging a pack. I also still need to look at the noise created when charging as there are a variety of switched mode supplies in there.
Title: Re: Ultra Precision Reference LTZ1000
Post by: essele on December 01, 2019, 10:53:10 am
Some more data...

I’ve switched to running at 20s integration times for 200 seconds before then grabbing a reading, this seems a much better approach, the filter is hopefully then not ‘contaminated’ with old readings.

The manual for other Prema’s suggests setting the integration time will clear the filter, so I think more experimenting is needed here as I’m fairly sure that’s not what I was seeing.

So here is a graph for overnight ... the orange and blue lines are the Prema readings for two LTZ1000’s and the grey and yellow are the 34470A.

After an initial settling down the two references seem to track each other pretty well for both meters — my interpretation is that the Prema has a negative temp coefficient and the 34470A has a positive - and I can’t really tell what’s going on with the LTZ’s other than they seem to be reasonably well matched. Does that seem like a reasonable interpretation?

I’m going to add a Datron 4000A into the mix and probably the 7v outputs as well (once I make up some more cables), although at close to 4mins per sample it’s going to reduce the data points a fair amount.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on December 01, 2019, 04:16:14 pm
The wrong foam could remove parts of the magic smoke, not as in "all magic smoke", more like local depletion. White foam doesn't increase my trust.
Title: Re: Ultra Precision Reference LTZ1000
Post by: essele on December 04, 2019, 10:19:14 pm
Final graph for the moment ... I'm going to need to find/build a temperature chamber now!

So I've swapped all the dodgy test leads with gold plated Pomona double banana plugs and used copper test lead wire, this seems to have stabilised the 34470A quite a bit.

The attached graph is the 7v and 10v of reference 1, and the 10v of reference 2 ... I did run a test with a Datron 4000A but I was still experimenting with the Prema so it's not particularly useful, I'll need to do it again at some point (it had quite a few spurious multi-ppm jumps though!)

Very roughly the Prema seems to have a -0.2ppm/C temperature coefficient, and the 34470A seems to have a +0.3ppm/C, although clearly as I don't know the reference coefficients they could be better or worse than that, hence the need for the temperature chamber.

Confusingly the 7v output (dark blue, and grey) seems to be better on the Prema and worse on the 34470. I will run some analysis on the numbers when I get some time.

I have discovered a few things about the Prema as well ... I'll start another thread on that shortly .. basically it's not as granular as the manual suggests and relies on averaging unless you get to the top end of the integration times. So 4s for example (on 20V range), which is supposed to be 7.5 digits, the first reading after a filter clear is always a multiple of 5uV from any other first-reading. The included graph is with 80s integration times .. which seems to be ok.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 11, 2019, 05:29:54 am
Working on my LTZ1000 reference :) I spent quite a bit tweaking the schematic and getting it nice

[attach=1]
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 11, 2019, 05:52:24 am
C9 is wrong
C11+C12  too
Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 11, 2019, 06:13:55 am
Thanks, you're quite right, I haven't double checked the values yet.

[attach=1]
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on December 15, 2019, 08:14:44 am
Yes, have been using a similar preamplifier for our HP 3456A, yet with lower gain (100x). Since the HP 3456A has a native resolution of 100nV, the preamplifier gave me a resolution of 1 nV. Our Fluke 8600 has a resolution of 10 uV, so 100x would result in 100 nV resolution, still about 0,01 ppm of 10 V. So i am not sure you need 10 000x. When using an OpAmp at 80 dB gain i would select a device with more than 120 dB open loop gain. And you may want chopper amplifiers with input filters in order to get a stable null.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on December 15, 2019, 08:23:11 am
Which Null-/nV-Meter has input current in fA range?
Usually they are in the pA range, in contrast to electrometers which need to be in the low fA range.
For measuring to the uV you want a front-end with low 1/f voltage noise and a very low TC including T-EMF.
LMC662 or other fA input bias current op amps have quite high 1/f voltage noise and TC.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 15, 2019, 03:04:58 pm
A DIY nullmeter is off topic in this thread, that is very long already. It may still be an interesting topic for a different thread.
The null-meters usually have a higher input current, more like pA to nA. It depends if the aim is more lowest voltage noise (e.g. nV range and below) or low input current, possibly to the single digit pA or possible also below. With a floating supply (e.g. batteries) it only take 1 amplifier at the input.  The rest is more like a low power ADC and LCD to keep the power consumption down.  For low bandwidth measurements digital filtering can also have advantages, like an FIR type response. So it may be an interesting project, but not in this thread.

Back to topic with the LTZ1000 reference: does the divider to set the temperature have to be  1K and some 12.5 K to 14 K  or is it possible to use higher resistance, like 2 K and 25 K.  I ask because it could than be possible to use a resistor array for the divider. A ratio of 1 : 13  (voltage divider to 1/14) could be made from 8 equal resistors, also in a way to use 2 arrays of 4 resistors without need for very good matching.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 28, 2019, 08:58:00 pm
Hmm,

did anyone already recognize that the Package of the LTZ1000 (non A) has connection to the chip?

Today I measured 0.477V between housing and cirquit ground which is nearly the same as R1 = 0.465V = Pin 4 of the LTZ1000.
Resistance between Pin 4 and housing is around 65 Ohms (both directions).
So it seems that the housing is high ohmic connected to substrate.
I could also draw ~5mA between housing and ground in mA-Mode of the DMM.
(of course the output voltage changed immediately).

I had expected that the housing is connected to pin 7 (most negative point) but not at a voltage somewhere in between.
So you have to take care not to make a short cirquit via the housing.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on December 29, 2019, 01:44:36 am
@Kleinstein.....

Why do you think multiple resistors are needed in the temperature setting divider?  ±0.1% with low TCR is all that is needed, anything more is not only overkill but quite unnecessary.  The temperature setting does not require that precise of setting for the chip temperature, ±0.1% is already a fraction of a degree, and the on chip temperature isn't that accurate according to spec, what more do you need?  Stability is not dependent on tolerance, only resistor stability and even there it isn't all that tight.  Most multi-resistor chips that offer very low TCR tend to be more expensive than a couple of ±0.1% resistors,  PWW or film.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 29, 2019, 11:54:50 am
Temperature setting does only need a divider.  Using 8 equal resistors from an array may still be an attractive option and the price can be competitive: The ones I had in mind are NOMCA/NOMCT or 2xMORN with 8 x 5 K as a lower cost option (some $4) and 2xLT5400 (2x some $8), but 10 K. The absolute TCR may not be that good, but the matching usually is. The more problematic parameter with individual resistors is the long time drift anyway, not so much the TCR. Naturally data on long time drift are tricky so the TCR get more attention as the long time stable resistors usually are also low TCR.

No need for high accuracy, so no need for the higher grades with even better matching. The easy to reach combinations and thus temperature settings are limited. 1:13 looks like the most practical to reach and one can get it with combining always 2 resistors in pairs, so that one can also use 2 arrays of 4. The main downside is the higher impedance, especially with the LT5400.

It makes sense to have the case connected to the substrate. This is kind of the normal case if the chip is soldered to the case. Thus planar BJTs usually have the collector at the case / back tap. JFETs tend to have the gate (which is the substrate) at the case.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 13, 2020, 09:43:43 pm
Hello,

I had a strange "ageing effect" on my LTZ#2 which I cannot completely explain.
The 9 year old battery pack was now rather weak.
And last week I also forgot to recharge over night.
So it happened that during two of my daily automated measurements that LTZ#2 was switched off by the battery monitor.
That is no problem for a absolute measurement.
But I am also doing difference measurements between two references as sanity ckeck for my ADCs.
The ADCs have a unbuffered LTC1043 2:1 divider at the input.
To protect the references in case of failures I have two 4,7K resistors between the references and the LTC1043 2:1 divider.
The voltage is checked to be within 1 mV against the expected target value. If the voltage is ok two relais contact short the 4K7 resistors to reduce noise.
But if one of the references is switched off there is a path with about 10K between the active and the switched off voltage reference. So the switched off reference is back-supplied by about 0.5 mA from the resistors and the input protection diode of the LTC1043.

In my opinion this should be no problem but on the measurement after exchange of the battery pack with a new one I recognized that the output voltage had increased by about 3.1ppm. (see day 2200)
Interestingly that is the opposite direction which I usually get when shorting the unbuffered output of the LTZ. (see day 1250)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 14, 2020, 08:35:57 am
I also would not expect back-feeding the LTZ1000 circuit with a limited current (less than the zener current)  to be a problem.
How does the change compare to a simple power down and thus thermal hysteresis ?

Shortening a LTZ1000 ref circuit is different: removing the output upsets the temperature regulation and would turn on the heater full power. The damage / change could than be from over-temperature. Discharging some caps could be another problem - though I would not expect this to cause damage.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on January 14, 2020, 09:25:45 am
Andreas, your graph shows several years of data with two events, right? The more visible -5.5 ppm step happened in 2017, but you are now talking about the +3 ppm step at the end of the curve. This time the event seems to revert some of the previous aging. Could this be an effect of handling the devices? Are you regularly handling the devices or do you keep them in a "don't touch" corner?

Would be interesting to see the curve after some more years. This business really requires patience.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on January 14, 2020, 09:33:10 am
Hello Andreas,

when you overheated the LTZ1000 circuit at day 1250, you probably introduced a permanent hysteresis, which is of the type that does not slowly drift back by itself. The decrease of the output after overheating is the correct direction, anyhow.
Now, as the oven failed after years, the LTZ maybe simply jumped back in direction to the initial state, i.e. before day 1250.
That's also the correct direction, because if you cool down the LTZ1000, like below room temperature, or even below 0°C, its value will always go upwards.

The non-A version is more likely to show such hysteresis, whereas the A version often shows short dips, when not initially pre-treated correctly.

Maybe you remember, that John R. Pickering exactly does this in his 7000 reference, cycling the oven between room temperature and maybe 20..30°C above the set oven temperature of about 50°C, to get rid of any hysteresis.

I also don't think that it has anything to do with the back fed current.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 14, 2020, 07:57:47 pm
Could this be an effect of handling the devices? Are you regularly handling the devices or do you keep them in a "don't touch" corner?

Ok, I did not tell the complete story:
Usually my LTZ#1 + LTZ#2 references are running 24/7 on my measurement table and are only measured once per day with a wired relay multiplexer.
Once a week I also do a manual comparison against LTZ#3-LTZ#8.
1-2 times a year I try to get a calibration either from a friendly volt-nut or when the calibration guy at work calibrates stuff at our location with his Fluke 5520A.

The last successful automated measurement was on tuesday.
On wednesday + thursday the battery of LTZ#2 was down during measurement in the morning.
On friday I transported some of my references to calibration with the Fluke (unfortunately no measurement in the morning).
At work after 2 hours temperature settling I recognized that the battery voltage was unusual low on LTZ#2 (14.8V) although I had charged in the morning before transport.
At home doing the daily measurement after recharging I finally found out that against tuesday the voltage had increased by +22uV.
With the reading of the Fluke 5520A (with a 34401A in 100mV range as zero-voltmeter) I also get 22uV increased voltage difference between LTZ#1 and LTZ#2. So the +3.1 ppm shift was before calibration. (either the battery flat or the transport to calibration).

But on previous transports I never had any voltage shift on my powered LTZ references.

How does the change compare to a simple power down and thus thermal hysteresis ?

Shortening a LTZ1000 ref circuit is different:
With a simple power down I never have a voltage shift that I can measure (noise limit is around 2uV with 2:1 divider).
The setpoint temperature of around 52 deg C is rather low so that there is also low hysteresis between room temperature and powered LTZ.
After the shorting of the unbuffered output (see day 1250) it is of course different. In this case I could reduce the initial hysteresis by several power downs from a initial much higher value to around -5 ppm.

Hello Andreas,

when you overheated the LTZ1000 circuit at day 1250, you probably introduced a permanent hysteresis, which is of the type that does not slowly drift back by itself. The decrease of the output after overheating is the correct direction, anyhow.
Now, as the oven failed after years, the LTZ maybe simply jumped back in direction to the initial state, i.e. before day 1250.
That's also the correct direction, because if you cool down the LTZ1000, like below room temperature, or even below 0°C, its value will always go upwards.

I also don't think that it has anything to do with the back fed current.

Hello Frank,

I think that is the correct Idea. I usually had only short power interruptions of some minutes for tests.
Now with the battery flat the power outage might have been for 2 half days giving more time to relax into the previous direction.
Should switch off the device for a longer time to see what happens.

I also think that there is no correlation with any back fed current (since it is in same direction as normal current and much lower).

At the moment I make a longer measurement (~18 hours) to check if the Allan deviation behaves unusual.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on January 15, 2020, 03:15:27 am
I wonder if something happened as the battery voltage fell. It didn't just "go flat" ?
Have to try run a reference undervoltaged, where the zener is starved and off and see if the op-amp oscillates or misbehaves or latches up. From LT1013 datasheet: (https://www.analog.com/media/en/technical-documentation/data-sheets/LT1013-LT1014.pdf)
"...There is one circumstance, however, under which the phase reversal protection circuitry does not function: when the other op amp on the LT1013, or one specific amplifier of the other three on the LT1014, is driven hard into negative saturation at the output."

So it shares an internal common bias, they are not totally independent op-amps.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 15, 2020, 05:26:05 am
I wonder if something happened as the battery voltage fell. It didn't just "go flat" ?
In my case the LT1763 voltage regulator (set to 14V) is switched off at 13.8V by the battery monitor.
Switching on happens at 15V (hysteresis).

So it shares an internal common bias, they are not totally independent op-amps.
Didn´t know that. Interesting.
But so far I have tested switch on / off behavior by replacing the battery monitor with a frequency generator.
(the scope pictures are somewhere in this thread: no oscillations).

Edit: the scope pictures are beginning from here:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg832030/#msg832030 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg832030/#msg832030)

With best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 15, 2020, 07:08:22 am
I wonder if something happened as the battery voltage fell. It didn't just "go flat" ?
Have to try run a reference undervoltaged, where the zener is starved and off and see if the op-amp oscillates or misbehaves or latches up. From LT1013 datasheet: (https://www.analog.com/media/en/technical-documentation/data-sheets/LT1013-LT1014.pdf)
"...There is one circumstance, however, under which the phase reversal protection circuitry does not function: when the other op amp on the LT1013, or one specific amplifier of the other three on the LT1014, is driven hard into negative saturation at the output."

So it shares an internal common bias, they are not totally independent op-amps.
A good find, but I doubt this would be a problem here. The OPs work with one side at some 0.5 V, never higher than one diode drop. So there should be no need to even rely on the phase reversal protection.
Oscillation when the supply to the OP is too low may become an issue, but this would drive the OPs output close to the positive output. The FB loop is a little tricky, and could oscillate when the OP gets to slow or with extra delays from saturation recovery. However in this case there is not much power to drive too much zener current, so even if it starts oscillating it should not damage the reference.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on January 15, 2020, 09:59:59 am
From LT1013 datasheet: (https://www.analog.com/media/en/technical-documentation/data-sheets/LT1013-LT1014.pdf)
"...There is one circumstance, however, under which the phase reversal protection circuitry does not function: when the other op amp on the LT1013, or one specific amplifier of the other three on the LT1014, is driven hard into negative saturation at the output."

So it shares an internal common bias, they are not totally independent op-amps.

Interesting, and it underscores something that I have learned over the years:

Read the data sheet from beginning to end, do not merely skim it for the characteristics that you are looking for.
Things to  particularly watch out for are caveats that undermine the headline features (e.g. current noise on op amps with impressive 'headline' noise figures) and things related to substrate connections (e.g. a small footnote saying "never let pin x become reverse biased relative to pin y"). I've seen people come a cropper more than once from missing some vital bit of information that was under their noses if they had only bothered to look.
Title: Re: LTZ1000 questions
Post by: Crossphased on January 26, 2020, 12:44:32 pm
Hi guys,
I have two questions regarding the circuit for an LTZ1000A. I just finished putting together my first board using the LTZ. I've read lots of forum posts, and pored through the datasheet to understand it better. One thing I noticed is this voltage reference can be damaged if incorrect voltages are applied to its pins. Before I insert the LTZ into the board, are there some known voltages I can check each pin for, to make sure the surrounding circuit is operating properly?

*EDIT removed a question I was able to figure out
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on January 26, 2020, 04:27:28 pm
A complete answer to your question is difficult. Maybe you can first make a LTZ1000 substitute from discrete parts plus some wires? It's a minor effort but may save your real LTZ1000s life.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 26, 2020, 04:47:04 pm
A substitute for the voltage loop part is relatively simple (transistor + Zener)
For the heater loop, one could limit the heater voltage (e.g. at the base of the heater driver transistor), so that no excessive power is applied. This could be part of the normal circuit, not just for the initial test.

Another point is checking the circuit once more.  I known trap for the young players is the unusual pin-out of the LT1013 in SO8 case.   
Title: Re: Ultra Precision Reference LTZ1000
Post by: Crossphased on January 26, 2020, 07:48:22 pm
Great thanks very much guys, will make a substitute LTZ from discrete components- good idea!
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 27, 2020, 06:30:59 pm
Quick temperature oven question.
I have the following temperature graph meaning there is about 0.6C fluctuation. I wonder if this is due to the oven not being properly insulated?

EDIT: The amplitude is 0.3C (max 35.1, 34.75 min). I have TE Connectivity GA10K3A1A 3976K NTC +/- 0.1C. The oven should stabilise to 0.1C
Title: Re: Ultra Precision Reference LTZ1000
Post by: Vgkid on January 27, 2020, 06:47:18 pm
If that scale is in minutes, and from initial turn on. Give it time to stabilize.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 27, 2020, 06:50:03 pm
Thank you. The problem is that it’s not stabilising.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 27, 2020, 06:53:17 pm
It looks like a regulator that is rather close to oscillation. Much added insulation will change the system and thus have different parameters for the controller.  It may still stabilize over a long time, but it would be better to optimize the regulator tuning.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 27, 2020, 07:01:25 pm
I wonder if this is due to the oven not being properly insulated?
I fear that the NTC for the temperature controller is too far from the heat source.

Thats why I typically use 2 temperature sensors.
One for the heater and one for the point of interest.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 27, 2020, 07:13:30 pm
I wonder if this is due to the oven not being properly insulated?
I fear that the NTC for the temperature controller is too far from the heat source.

Thats why I typically use 2 temperature sensors.
One for the heater and one for the point of interest.

With best regards

Andreas

Hi Andreas,

Interesting point. I have a metal enclosure and two NTC sensors (I specified the type two posts above) - One sensor is attached to the centre of the enclosure (metal part) and another sensor is also in the middle measuring the air. Is this a wrong approach?

Thanks
Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 27, 2020, 07:16:54 pm
Much added insulation will change the system and thus have different parameters for the controller. 

Yeah. I have lost  |O insulation material and now have to order a new one. Any recommendation on insulation please?
I think insulation is a must. Otherwise  the metal enclosure is losing heat very quickly and it takes time to heat up the oven (four 10W resistors). Hence 0.3C oscillation
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on January 27, 2020, 07:20:11 pm
The period looks like 160 seconds or 2.7 minutes?
I've seen temperature graphs with that long of a time-constant due to the lab HVAC cycling. Make sure there is no draft or airflow from a vent influencing your test. You can put a piece of cardboard over it to see if that makes a difference.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 27, 2020, 07:23:54 pm
The period looks like 160 seconds or 2.7 minutes?
I've seen temperature graphs with that long of a time-constant due to the lab HVAC cycling. Make sure there is no draft or airflow from a vent influencing your test. You can put a piece of cardboard over it to see if that makes a difference.

There is no aircon. However, you are correct there is a temp change / draft. It comes back to a proper insulation
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on January 27, 2020, 07:45:07 pm
Yeah. I have lost  |O insulation material and now have to order a new one. Any recommendation on insulation please?
Aerogel
https://en.wikipedia.org/wiki/Aerogel
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on January 27, 2020, 07:53:24 pm
What kind of controller are you using? Oscillation is typical for an on-off controller. A linear "PI" controller will also behave like that when using excessive gain factors. Also the P and the I gain need to be near a certain ratio for fast settling time.
A well adjusted linear controller will show small/slow changes of heater output and even smaller changes of temperature. As Andreas wrote, a good oven needs a sensor close to the heater, with no air gap in between. My LTFLU oven keeps that "fast" sensor to within +/- 0.5 milliK over 24 hours, using an Arroyo TecSource 5235 as controller. The Arroyo PDF manuals are quite instructive.

Regards, Dieter

Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 27, 2020, 08:42:34 pm
Solved!

Attaching one NTC directly to the heater (inside the box to the wall against the source) source and putting another NTC in the middle of the box solved the problem. Thank you Andreas!

Now the heater is having an output of 210 mA rather than going from 400mA down to zero and back to 400mA. The inside temperature is now 34.6 (needs fine-tuning) within 0.1C

Title: Re: Ultra Precision Reference LTZ1000
Post by: Hermann W on January 29, 2020, 11:18:36 am
I wonder if this is due to the oven not being properly insulated?
I fear that the NTC for the temperature controller is too far from the heat source.

Thats why I typically use 2 temperature sensors.
One for the heater and one for the point of interest.
There are many ways to get to the goal. But that's not a classic control technique. The actual value must be measured at the point to be regulated. Otherwise the actual value does not correspond to the setpoint. The heater may be constant, but not the test object. The example shows quite clearly that the control parameters have a too high gain - as Kleinstein said.
What kind of controller is used? Temperature control works quite well with a PI controller. The integration time constant must then be chosen to be the same as the control system time constant.
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on January 29, 2020, 01:37:13 pm
How are your 2 thermistors wired, plz?
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on January 29, 2020, 01:40:22 pm
As far as i understand, once you have a rock-solid heater temperature control loop, you can stack another control loop on top, this time using the DUTs temperature sensor.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Hermann W on January 29, 2020, 02:00:18 pm
As far as i understand, once you have a rock-solid heater temperature control loop, you can stack another control loop on top, this time using the DUTs temperature sensor.
This is a common way when the manipulated variable (heating) requires separate control. This is not really necessary for temperature control.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Hermann W on January 29, 2020, 02:21:44 pm
Now i know what a rocksolid heater is. This is a good example. I once did that for my wood boiler. The internal regulation was for the position of the air throttle and the external regulation for the exhaust gas temperature.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 29, 2020, 09:32:32 pm
How are your 2 thermistors wired, plz?

In my ageing box for references one NTC is on the PCB in the middle of all voltage references.
(left in the middle of the PCB)

The other is in the middle of the top heater foil (with the red wires).
The bottom heater foil (below the PCB) is in series with the top heater foil so it needs no extra NTC.

The heater is controlled by a simple P-Controller (fast) from the heat spreader NTC.
The slow contol loop with the NTC on the PCB is a I-Controller with some anti windup limitations when the current temperature is far away from setpoint. The I-Controller output gives a Offset which is added to the setpoint for the P-Controller.

Since there is some self-heating due to many references the Offset is negative (I-Out in deg C)

here a log of the heat-up phase:

Time                                         T-PCB  T-HTR   14V      17V      24V      I-Out   P-Out (hex from 0x0000 to 0x2400 or 0..10000 dez)
08:21:01;D7   0  0 9999.9 H9; 38.21; 31.79; 13881; 16974; 24006; -4.18; P2400;   
08:22:01;D7   0 12    0.0 D7; 39.34; 39.41; 13881; 16981; 24012; -4.18; P2400; 
08:23:01;D7@  1 12    0.0 D7; 40.87; 45.15; 13874; 16974; 24033; -4.18; P2400;   
08:24:01;D7@  2 12    0.0 D7; 42.55; 49.58; 13867; 16988; 24053; -4.18; P2400;   
08:25:01;D7@  3 12    0.0 D7; 44.15; 51.91; 13860; 17021; 24593; -4.18; P2400;   
08:26:01;D7@  4 12    0.0 D7; 45.24; 51.88; 13860; 16981; 24087; -4.18; P2400;   
08:27:01;D7@  5 12    0.0 D7; 46.16; 51.91; 13847; 17028; 24600; -4.18; P2400;   
08:28:01;D7@  6 12    0.0 D7; 47.02; 51.91; 13847; 17028; 24600; -4.18; P2400;   
08:29:01;D7@  7 12    0.0 D7; 47.77; 51.88; 13840; 17028; 24094; -4.18; P2400;   
08:30:01;D7@  8 12    0.0 D7; 48.45; 51.91; 13827; 17028; 24600; -4.18; P2400;   
08:31:01;D7@  9 12    0.0 D7; 49.06; 51.79; 13827; 17028; 24600; -4.18; P0000; 
08:32:01;D7@ 10 12    0.0 D7; 49.44; 50.55; 13820; 17028; 24600; -4.18; P0000;   
08:33:01;D7@ 11 12    0.0 D7; 49.71; 49.49; 13820; 17028; 24600; -4.18; P0000; 
08:34:01;D7@ 12 12    0.0 D7; 49.85; 48.49; 13813; 17028; 24600; -4.18; P0000;   
08:35:01;A4   0  0    0.1 A4; 49.98; 47.63; 13820; 17028; 24600; -4.18; P0000;   
08:36:01;A5   0  0    0.1 A5; 50.01; 46.86; 13813; 17028; 24593; -4.18; P0000;   
08:37:01;A6   0  0    0.1 A6; 50.03; 46.12; 13820; 17035; 24593; -4.18; P0000;   
08:38:01;A7   0  0    0.1 A7; 49.96; 45.49; 13813; 17035; 24593; -4.18; P0133;
08:39:01;B4   0  0    0.1 B4; 49.94; 45.17; 13820; 17035; 24600; -4.18; P0257;   
08:40:01;B5   0  0    0.1 B5; 49.92; 45.06; 13820; 17035; 24600; -4.15; P02bf;   
08:41:01;B6   0  0    0.1 B6; 49.92; 45.01; 13806; 17035; 24593; -4.13; P0302; 
08:42:01;B7   0  0    0.1 B7; 49.87; 44.99; 13820; 17035; 24593; -4.08; P0330; 
08:43:01;C4   0  0    0.1 C4; 49.85; 45.01; 13813; 17028; 24593; -4.03; P0343;   
08:44:01;C5   0  0    0.1 C5; 49.87; 45.03; 13820; 17028; 24593; -3.99; P035c;
08:45:01;C6   0  0    0.1 C6; 49.85; 45.03; 13813; 17028; 24593; -3.94; P0383; 
08:46:01;C7   0  0    0.1 C7; 49.87; 45.10; 13813; 17028; 24600; -3.90; P0373;
08:47:01;D4   0  0    0.1 D4; 49.87; 45.10; 13813; 17035; 24600; -3.86; P039a; 
08:48:01;D5   0  0    0.1 D5; 49.87; 45.15; 13813; 17035; 24600; -3.81; P0397;
08:49:01;D6   0  0    0.1 D6; 49.87; 45.19; 13813; 17021; 24600; -3.77; P0395; 
08:50:01;D7   0  0    0.1 D7; 49.89; 45.21; 13820; 17035; 24593; -3.73; P03a7;   
08:51:01;E4   0  0    0.1 E4; 49.92; 45.26; 13806; 17028; 24593; -3.71; P039e; 
08:52:01;E5   0  0    0.1 E5; 49.92; 45.28; 13813; 17028; 24600; -3.68; P03a2; 
08:53:01;E6   0  0    0.1 E6; 49.94; 45.31; 13813; 17035; 24593; -3.66; P03a7; 
08:54:01;E7   0  0    0.1 E7; 49.96; 45.31; 13813; 17035; 24600; -3.65; P03b9; 
08:55:01;F4   0  0    0.1 F4; 49.96; 45.37; 13813; 17035; 24587; -3.63; P0387;
08:56:01;F5   0  0    0.1 F5; 50.01; 45.35; 13813; 17035; 24607; -3.64; P03a7; 
08:57:01;F6   0  0    0.1 F6; 50.01; 45.40; 13813; 17021; 24600; -3.64; P037b;   
08:58:01;F7   0  0    0.1 F7; 50.05; 45.37; 13806; 17035; 24593; -3.66; P038e; 
08:59:01;G4   0  0    0.1 G4; 50.03; 45.37; 13813; 17028; 24593; -3.67; P037e;
09:00:01;G5   0  0    0.1 G5; 50.05; 45.35; 13813; 17035; 24600; -3.68; P038a;
09:01:01;G6   0  0    0.1 G6; 50.07; 45.37; 13813; 17035; 24593; -3.71; P0366; 
09:02:01;G7   0  0    0.1 G7; 50.07; 45.35; 13813; 17035; 24593; -3.73; P0364;
09:03:01;H4   0  0    0.1 H4; 50.10; 45.33; 13813; 17028; 24600; -3.76; P0362;
09:04:01;H5   0  0    0.1 H5; 50.10; 45.31; 13813; 17028; 24600; -3.80; P0359; 
09:05:01;H6   0  0    0.1 H6; 50.07; 45.28; 13813; 17035; 24600; -3.82; P0350;   

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on January 29, 2020, 09:45:31 pm
@Andreas: has your thermostat got "digital" control (2xRth+MCU) then?
I've been looking for some 2xRth+(1-2x)opamp "linear" version I will add directly on the 10V Vref board.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 29, 2020, 10:26:52 pm
Hello

yes it is a PIC24FV301 with 12 Bit ADC where the NTCs and the 100 Hz PWM heater output is connected.
It is only used as dumb measurement machine, multiplexer controller and heater actuator (with overtemperature limitation).

The actual control loop is on the connected PC.
Every 10 seconds the P-controller part is calculated.
The I-controller only all 60 seconds.
The long time constants and especially the anti-windup strategy are difficult in analog domain.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on January 30, 2020, 12:23:40 am
But volt-nuts would rather avoid digital+pwm close to their lovely reference :) Therefore the idea with analog PI even it would be difficult (we do it not because it is easy..).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 30, 2020, 05:36:45 am
Hello,

yes you are right, I only use it for those ugly AD586, LTC1236 and LT1027 references for pre-ageing.
But 100 Hz PWM will be canceled out by most integrating instruments with mains suppression.

The principle can also be used in a analog controller. A inner P-Controller for the heater. And the setpoint with a offset from a I-Controller (where you have carefully limit the output signal range to avoid very long settling times).

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 30, 2020, 01:56:41 pm
What kind of controller is used? Temperature control works quite well with a PI controller.

A simple P-Controller.
However, the problem is not in controller, but in placement of NTCs.
I had to place one NTC right next to the source and I failed - this gave me oscillation 
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 30, 2020, 04:13:46 pm
Made a stupid mistake last night while burning the midnight oil - applied +15V to the buffer output +10.000000V (Dr Frank's PCB).
Now both the BUF and BUF 10.000000V outputs are dead. VREF on the LTZ1000 is giving me 7.08823V (just like before this accident). So I guess LTC1052 was killed?  |O

I paid the price for staying very late  >:(
Title: Re: Ultra Precision Reference LTZ1000
Post by: guenthert on January 31, 2020, 05:19:28 pm
But volt-nuts would rather avoid digital+pwm close to their lovely reference :) Therefore the idea with analog PI even it would be difficult (we do it not because it is easy..).
Whoa, that's a slippery slope there, ending with batteries, potentiometers and galvanometers like it's 1899. 

Just because PWM is easy for the uController, there doesn't have to be a high (EMI indcucing) current PWM to the heater.  Nothing stops you from adding a cap or two before the series pass transistor (assuming a sufficiently capable transistor of course) ...
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on January 31, 2020, 06:30:04 pm
But volt-nuts would rather avoid digital+pwm close to their lovely reference :) Therefore the idea with analog PI even it would be difficult (we do it not because it is easy..).
Whoa, that's a slippery slope there, ending with batteries, potentiometers and galvanometers like it's 1899. 
Edit: It took me 2 hours to wire and simulate :)
Added the temperature difference between the heated case and board.
The TIP121 has to be thermally isolated from the case  :-[
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 31, 2020, 07:46:10 pm
Nothing stops you from adding a cap or two before the series pass transistor (assuming a sufficiently capable transistor of course) ...
Ok I forgot to mention that I use a rather slow automotive power stage (BTS432) which is optimized to EMI with turn on/off times around 100 us.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on February 01, 2020, 09:11:45 am
Sure, the simulation of the thermostated box for the Vref is off topic here, therefore I stop with the below picture - I've moved the thermistor (the heater one) a bit off the heater - I get a nice oscillation :)

PS: added a version with 2x TIP121 as the heaters with added white phonon noise :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on February 05, 2020, 12:00:30 pm
I wonder if this is due to the oven not being properly insulated?
I fear that the NTC for the temperature controller is too far from the heat source.

Thats why I typically use 2 temperature sensors.
One for the heater and one for the point of interest.

With best regards

Andreas

Hi Andreas,

I managed to obtain temperature stabilisation between 34.81C to 34.93C which is within around 0.1C.
I used two NTCs - one attached right next to the heating resistor and one is next to LTZ1000A.
I am using 2  x TE Connectivity GA10K3A1A (+/-0.1C tolerance, B value tolerance 0.5%).
Do you think this is sufficient? The enclosure is covered in one layer of insulation. I think I have to work more on insulation putting the second layer.

Thanks
Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on February 16, 2020, 09:26:23 am
I can see from time to time these spikes (marked in red in the photo). This is a new ltz1000ach ageing, but the measurements were taken (a) in the temperature oven (b) in the shielded enclosure (c) powered by a battery pack. The only thing which comes to my mind are cables. I’m using ordinary 22AGW cables rather than shielded ones. However, from the DMM I’m running banana to BNC shielded cable with hooks at the end.

What do others think? Where these spikes are coming from? What cables are you using for your boards please (links to Digi-Key would be appreciated)
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on February 16, 2020, 09:32:53 am
Your DMM6500 Vref is an LM399.. Popcorn?
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on February 16, 2020, 09:42:31 am
@alex-sh
Looks like typical popcorn noise. That's the LTZ itself. Should decrease over the months, but should be observed. My LTZ are reasonably quiet after 18 months.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on February 16, 2020, 09:48:06 am
There are several possible reasons for just a single out-layer. One possibly source could be EMI (e.g. mobile phone sending a rather strong sync signal once in a while,  radar).  Popcorn noise of the DMM reference would usually look different and would not be visible near zero.

With just a relatively low impedance reference to a DMM the cables are not that critical - a poor choice could give some thermal EMF, but this is more a problem with the connectors that the cable itself.  BNC connectors may not be the best choice for DC.

What is exactly measured ? It does not look like directly reading the 7 V with the DMM. This would not make that much sense anyway as the DMM internal reference would dominate.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on February 16, 2020, 10:09:26 am
You seem to have 1.5 uV drift in 10 minutes, which is a lot and may indicate there is something else going on besides ageing. Or is the plot in hours?

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on February 16, 2020, 11:22:51 am
The Vref based on a selected LM399AH inside the DMM6500 may walk (random walk) 5uV p-p at constant temp.
Edit: added "AH"
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 16, 2020, 11:51:28 am
What do others think?

... you need more meters.
otherwise you cannot distinguish wether it is from the LTZ or from the meter.

my K2000 also has from time to time (at certain temperatures) some popcorn noise.
Of course there can also be many other reasons like EMI from mains into the reference or the meter.

of course popcorn noise (at least short duration events) from the reference can also be measured with a 1/f (0.1-10 Hz) amplifier

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on February 16, 2020, 12:37:47 pm
You seem to have 1.5 uV drift in 10 minutes, which is a lot and may indicate there is something else going on besides ageing. Or is the plot in hours?

Regards, Dieter
Minutes. Looks like a relative fresh assembled new kit to me.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on February 16, 2020, 02:47:15 pm
I can see from time to time these spikes (marked in red in the photo). This is a new ltz1000ach ageing, but the measurements were taken (a) in the temperature oven (b) in the shielded enclosure (c) powered by a battery pack. The only thing which comes to my mind are cables. I’m using ordinary 22AGW cables rather than shielded ones. However, from the DMM I’m running banana to BNC shielded cable with hooks at the end.

What do others think? Where these spikes are coming from? What cables are you using for your boards please (links to Digi-Key would be appreciated)

Alex,
I assume you are using the same PCB and circuit like your already running LTZ1000 reference board?
Have you ever observed these spikes on this non-A version reference with this DMM?
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on February 16, 2020, 03:40:35 pm
You seem to have 1.5 uV drift in 10 minutes, which is a lot and may indicate there is something else going on besides ageing. Or is the plot in hours?

Regards, Dieter
Minutes. Looks like a relative fresh assembled new kit to me.

It's correct. It is minutes and this has been assembled recently. This is LTZ1000ACH
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on February 16, 2020, 03:53:41 pm
I can see from time to time these spikes (marked in red in the photo). This is a new ltz1000ach ageing, but the measurements were taken (a) in the temperature oven (b) in the shielded enclosure (c) powered by a battery pack. The only thing which comes to my mind are cables. I’m using ordinary 22AGW cables rather than shielded ones. However, from the DMM I’m running banana to BNC shielded cable with hooks at the end.

What do others think? Where these spikes are coming from? What cables are you using for your boards please (links to Digi-Key would be appreciated)

Alex,
I assume you are using the same PCB and circuit like your already running LTZ1000 reference board?
Have you ever observed these spikes on this non-A version reference with this DMM?
Frank


Hallo Dr Frank,

No, this is a different PCB producing a buffered 7.1V. This is the LTZ1000ACH
The idea is to have several LTZ1000 and LTZ1000ACH and then I can monitor the drift against the recently calibrated ones.
Unfortunately, my gear is too useless to monitor
I was conducting some tests with the temperature oven when I noticed this peak noise. I cannot remember observing it with a non-A version.

However, I must admit that the reference has not been aged yet. It probably has to sit on the PSU for months before doing any tests

Thanks
Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on February 16, 2020, 03:56:41 pm
What do others think?

... you need more meters.
otherwise you cannot distinguish wether it is from the LTZ or from the meter.


I completely agree with you.
However, we are looking into an expensive territory.
I can do ratio measurement on my DMM between a calibrated LTZ1000 and a new LTZ1000 (after aging it).
Or maybe you can advise on how to measure it properly without spending $$$ for the equipment?
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on February 16, 2020, 04:15:46 pm
The Vref based on a selected LM399AH inside the DMM6500 may walk (random walk) 5uV p-p at constant temp.
Edit: added "AH"

Afaik the reference inside is SZA263 .
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on February 16, 2020, 05:40:19 pm
Something to compare. This is 10V PX LTZ-CH, now ca. 20 month at 15V. Such a peek happens ca. 1/month last 6 month.
Weather is quite stormy, last 2h.

Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on February 16, 2020, 06:17:08 pm
Something to compare. This is 10V PX LTZ-CH, now ca. 20 month at 15V. Such a peek happens ca. 1/month last 6 month.
Weather is quite stormy, last 2h.

So it is a 20 months old Vref? 31uV p-t-p!!!
Do you think it has been caused by a storm? I remember reading a thread where MisterDiodes mentioned that LTZ1000 was picking up a train several blocks away.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Conrad Hoffman on February 16, 2020, 07:44:35 pm
I don't know if this applies to buried zeners but a friend used to build commercial instruments with voltage references. He selected his TC zeners based on noise. The zeners with the lowest noise were also the most stable over time. This was in the days of 1N82x types. I believe popcorn noise is the result of defects in the crystal lattice and I'd be surprised if it improved over time. Naturally at the level we're talking here, noise can sneak in from anywhere and everywhere! As for that LT1052 failure some posts above, I always found they were quite fragile and managed to pop more than a couple. They also aren't very good at driving their own feedback network, preventing the use of low values for low noise. Regardless, the zero drift makes up for everything else.
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on February 16, 2020, 07:51:52 pm
Something to compare. This is 10V PX LTZ-CH, now ca. 20 month at 15V. Such a peek happens ca. 1/month last 6 month.
Weather is quite stormy, last 2h.

So it is a 20 months old Vref? 31uV p-t-p!!!
Do you think it has been caused by a storm? I remember reading a thread where MisterDiodes mentioned that LTZ1000 was picking up a train several blocks away.
This PtP is the single popcorn peak. Std Dev under this circumstances with 10V upward regulation is 1.77µV, without popcorn <1.5µV for this 10V-PX, without upward regulation <1.3µV.
Think about, this DMM6500 isn't better. The PtP limit of this meter itself isn't better than ~ 10 to 12µV. Below that, you are looking to the limit of your 6.5 meter, not the DUT.  ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on February 16, 2020, 08:14:14 pm
The Vref based on a selected LM399AH inside the DMM6500 may walk (random walk) 5uV p-p at constant temp.
Edit: added "AH"

Afaik the reference inside is SZA263 .

IMHO DMM7510 has got LTFLU (SZA263?).
DMM6500 has got LM399AH voltage reference with Keithley marking - https://xdevs.com/review/dmm6500/
Title: Re: Ultra Precision Reference LTZ1000
Post by: hwj-d on February 16, 2020, 08:18:18 pm
Because of the "storm". Maybe the quickly falling air pressure caused the slight upward trend that can be seen at the end of the curve.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on February 16, 2020, 08:36:09 pm
The Vref based on a selected LM399AH inside the DMM6500 may walk (random walk) 5uV p-p at constant temp.
Edit: added "AH"

Afaik the reference inside is SZA263 .

IMHO DMM7510 has got LTFLU (SZA263?).
DMM6500 has got LM399AH voltage reference with Keithley marking - https://xdevs.com/review/dmm6500/

The 7510 has the LTFLU-1 inside.
(https://farm9.static.flickr.com/8817/17082267821_ae439ef7b4_b.jpg)

Source:
https://hiveminer.com/Tags/dmm7510,pcb (https://hiveminer.com/Tags/dmm7510,pcb)

The SZA263 has been produced by Motorola and is obsolete since a very long time (back in the 1980's I think).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on February 17, 2020, 12:35:00 am
Yes Motorola originated this part and a whole laundry list of zener based references, some of which live on in various newer reincarnations such as the LTFLU (you might call it the grandchild).  There were several pages of data sheets on various reference zeners and reference amplifiers (aka the SZA263 that eventually morphed into the LTFLU).

Besides the many zener references such as the 1N82xA series, 1N4565-1N4580, 1N3154/A, 1N4775/A, 1N4780/A, series1N935A/B/C, 1N216xA series and 1N941/A-1N945/A series
The precision ref zener series MZ605, MZ610, MZ620 and MZ640
Amplifying regulator diodes, MCA1911 - MCA2234
Low voltage zeners, MZ2360/61

Plus a host of house numbered variations like the SZA263.

Today, the LTFLU is only sourced by Linear Tech and sold only to Fluke, any of these that show up on the flea bays are either from recycled/resold equipment or fakes.  How the LTFLU 'legally' found its way inside a TEK piece of gear is up for speculation, perhaps a quiet agreement between TEK/Fluke/LT but Fluke was the only buyer of these that I had heard of.

Yes I'm aware that ADI took over LT but it is still LT making these parts, ADI doesn't make them.  No I didn't like the take over, I think ADI is messing LT up.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on February 17, 2020, 03:25:51 am
The Danaher Corporation bought Fluke in 1998. Then Fluke was spun off as part of Fortive a few years ago. Danaher also bought Tektronics in 2007 and Keithley in 2010. So Fluke, Keithley and Tektronics were all related for awhile. So at one point they may have shared their best technology like the LTFLU.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on February 17, 2020, 04:11:47 am
Interesting, that may have been a viable situation although I'd bet Fluke wasn't too happy about it, never know about these corporate dealings, insanity lives for these <laughing>.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on February 17, 2020, 10:05:04 am
Wondering if the LTFLU is orderable as a replacement from Keithley/Tektronix :-/O
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 18, 2020, 12:38:55 am
Buying LTFLU without matching resistors is feat with little benefit vs "usual" LTZ.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Conrad Hoffman on February 18, 2020, 12:44:40 am
I was able to improve the thermal performance of my Fluke 731A by tweaking the resistors. The old cardboard box and light bulb trick. It took a few days but was well worth it. That leads me to believe it would work with any of 'em.
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on February 18, 2020, 01:06:59 am
Buying LTFLU without matching resistors is feat with little benefit vs "usual" LTZ.

Speaking of this I was wondering... I recently (for the heck of it) picked up an F8842A.  Can I use it to make a decent voltage reference to help with comparing to my new 3458?  I'm already planning on two LTZ1000A's and have the LTZ's but what about using the resistor network from the F8842A with it's reference zener?  I saw someone else did this and boosted the output to make 10V reference.  I was hoping to do something similar.  No one's figured out how to use these resistor networks from an F8842A with an LTZ have they?  Or is that out of the question because they're all matched and you couldn't make it work?  That's the first thing that came to mind... wow a well aged resistor network... with the right ratios could be golden with an old aged LTZ1000A... maybe I'm dreaming?

To add to this... I've kinda come to the conclusion that making or remaking some refs makes more sense than buying old (maybe not working) 732A.  It's a little let down I'd think to pay that much then be stuck trying to take that old foam apart inside and then being afraid of messing up the way it's put together if it doesn't work right.  I can see replacing the batteries and some minor on the edges repairs but tearing into the guts doesn't look like it's for the faint at heart?  I may get one anyhow and try... I'm looking in other places now vs. just Ebay.  I found the 3458 that way.

I'd almost rather sleuth for a 732B I think.  The search for the 3458 was long but maybe it's worth the wait vs. one of your types of teardowns to try and fix an A.

What do you cut out the PCB section with without tearing it up so you have clean cut?  Some kind of dremel or saw of some kind?

Thanks,

Bill
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 18, 2020, 03:51:26 am
Yes and no. With 732A/B/C you get much more than just a reference chip and some resistors. There is far more attention to make everything rugged, battery backed-up and robust enough for everyday use and transport, which is a project on its own, compared to just LTZ module. I've bought 732A some time ago, and it had jumping SZA263 chip. Thread: https://www.eevblog.com/forum/metrology/fluke-732a-with-popcorn-noise-sza/ (https://www.eevblog.com/forum/metrology/fluke-732a-with-popcorn-noise-sza/)

Since I didn't care about history, I've butchered original SZA chip, replaced it with SZA263 from donor 8842A, and... jumps are gone... yay.... but noise is 20 times worse now... That made me think 8840/8842A's get worse bin of SZA chips. Now I got 5440B reference board, where I can steal two SZA263's and matching PWW resistors to transplant it into 732A to make it useful... But that project sits abandoned since September. I'll revisit it some day.

With LTZ it's easier and cheaper (time wise) to get all parts and get it going. You don't need to dick around resistors and matching, unlike SZA/LTFLU. In worst case if you buy bad 732A, you get nice project box with oven, battery power, low thermal posts where you can put LTZ1000A circuit inside and have fancy looking DIY REF for your lab. ;) One of the benefits that SZA/LTFLU have - you can use same resistors to scale output voltage to 10V directly, instead of additional active components in case of LTZ. Making sub-ppm stable 10V out of 7V is much more difficult task than ultra-stable 7V.
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on February 20, 2020, 01:25:06 am
Making sub-ppm stable 10V out of 7V is much more difficult task than ultra-stable 7V.
Yes and isn't this just what you need to compare with your 3458(s) right?  Maybe not to calibrate with but at least to compare and see how they agree... see what's drifting and which are staying more the same as a group giving some confidence.  I suppose either way measuring both the default 7V stable reference and the boosted 10V would be a good idea anyhow.  Perhaps your unboosted 7V reference is pretty stable but something happened with your boost resistors drifting and now your 10V is off because the boost part of the circuit changed?  I'm thinking this because I'm at the point of ordering PCB's and resistors vs. only looking for 732A/B.  I really like the red FX PCB btw... bummed I missed out on the FX reference.  How did you get so many Fluke-custom hermetic film resistor network P/N 2464707?  Ironically I think the company that makes them is just south of where I work... I think they're in Tempe, AZ.

Bill
Title: Re: Ultra Precision Reference LTZ1000
Post by: Villain on February 20, 2020, 03:20:44 pm
Hi,

i have a quick side question. Is it possible to buy a LTZ1000 reference board fully assembled somewhere? Or from someone on the forum? I would pay an appropriate price obviously.

Regards,

Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: Grandchuck on February 20, 2020, 05:50:56 pm
https://www.mouser.com/ProductDetail/Analog-Devices/EV-LTZ1000-REFZ?qs=1mbolxNpo8fB2m%252Bgl85yGA%3D%3D (https://www.mouser.com/ProductDetail/Analog-Devices/EV-LTZ1000-REFZ?qs=1mbolxNpo8fB2m%252Bgl85yGA%3D%3D)

Mouser ... $450
Title: Re: Ultra Precision Reference LTZ1000
Post by: Villain on February 20, 2020, 06:14:42 pm
Oh very interesting, thank you
Title: Re: Ultra Precision Reference LTZ1000
Post by: Edwin G. Pettis on February 20, 2020, 06:26:58 pm
As expected, the ADI implementation of the LTZ1000 circuits are flawed, they do not conform to the original design and does not produce the original specifications.  I would not recommend buying this board if you really want a good LTZ1000 reference.  They don't know what they're doing yet, they have no experience with this design and should have kept to the original design of LT.  They used the wrong resistors too....I know you were expecting me to say it but it is a fact none the less.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Villain on February 20, 2020, 06:45:40 pm
Yeah had a quick look at the design. I must say that i am too lazy to build one myself though, its time consuming..

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 20, 2020, 07:40:56 pm
Another possibility:

http://www.friedrich-messtechnik.de/index.php/unsere-produkte/32-uncategorised/71-esn-2010 (http://www.friedrich-messtechnik.de/index.php/unsere-produkte/32-uncategorised/71-esn-2010)

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on February 20, 2020, 07:53:37 pm
Another possibility:

http://www.friedrich-messtechnik.de/index.php/unsere-produkte/32-uncategorised/71-esn-2010 (http://www.friedrich-messtechnik.de/index.php/unsere-produkte/32-uncategorised/71-esn-2010)

With best regards

Andreas

Any idea how much it costs?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 20, 2020, 07:54:40 pm
Another possibility:

https://islandlabs.eu/ltz1000-images.html or https://isolalab.com/

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Villain on February 20, 2020, 07:58:10 pm
I contacted them already, found it an hour or so ago too.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 20, 2020, 08:06:47 pm
Another possibility:

http://www.friedrich-messtechnik.de/index.php/unsere-produkte/32-uncategorised/71-esn-2010 (http://www.friedrich-messtechnik.de/index.php/unsere-produkte/32-uncategorised/71-esn-2010)

With best regards

Andreas

Any idea how much it costs?

I only found it by accident when looking for LTZ1000. So I have no idea.

With best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Villain on February 20, 2020, 08:13:45 pm
I will let you all know the price when they respond.

edit: IslandLabs guys say 245 eur for LTZ1000ACH board

edit2: the friedrich-messtechnik guy said they only sell to companies
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on February 20, 2020, 08:36:10 pm
Having bought two from island labs I will say they seem to be good quality. When purchased you get data on aging, noise, current calibration, bom, and schematics. They're also fairly helpful with questions and offer 1 free calibration(I forget the time span).

Attached a couple of pictures I took last year of the LTZ1000A board. If I have time I'll take more detailed ones later of both but since they're in two boxes and one is soldered I don't have time just now.
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on February 23, 2020, 07:00:47 am
It just wouldn't be fun not build some of my own... I am interested in converting this into a non-LTZ reference though.  That's why I asked about best way to safely cut PCB's... IDK about tin snips but I know it's been done.  It's in a working 8842A now.  Somehow the reference might be more fun than the old MM to me I think.

Bill
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on February 23, 2020, 07:07:04 am
It just wouldn't be fun not build some of my own... I am interested in converting this into a non-LTZ reference though.  That's why I asked about best way to safely cut PCB's... IDK about tin snips but I know it's been done.  It's in a working 8842A now.  Somehow the reference might be more fun than the old MM to me I think.

Bill
Didn't you build an enclosed 10V reference with this method @Micke?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Micke on February 23, 2020, 09:30:11 am
Yepp, I had a 8842A DMM beyond rescue...
I just used a hacksaw to cut out RefAmp, thought of using Dremel as well, but thought that hacksaw would generate less vibrations, and easier make a straight cut.
Could have made RefAmp board even smaller, but wanted to be on the safe side, and to have somewhere to put mounting screws...
I soldered power +/- 15V directly on Op-amp pins U702 on the secondary side. For Ground, I used the via holes just under the text "C103" (think shield was soldered in these holes originally)
I am not very impressed by the stability though, typical run with FLUKE 8846A below (PLC100), SZA263 in metal box with lid on, powered 24/7 for weeks:
* Min  10.00005V
* Max 10.00010V
* Avg 10.00007V
* SD 7,6µV
* 40000 # samples
So a span of 5ppm between Max and Min, did expect better actually!
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on February 23, 2020, 12:02:00 pm
Quote
So a span of 5ppm between Max and Min, did expect better actually!
SZA263 is a zener with a transistor on the chip. You cannot expect "LTZ1000 stability" unless the module is ovenised, imho.
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on February 23, 2020, 01:19:48 pm
[...]
* Min  10.00005V
* Max 10.00010V
* Avg 10.00007V
* SD 7,6µV
* 40000 # samples
So a span of 5ppm between Max and Min, did expect better actually!

5ppm over several weeks is not too shabby?  Is the area temperature controlled?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Micke on February 23, 2020, 07:04:09 pm
[...]
* Min  10.00005V
* Max 10.00010V
* Avg 10.00007V
* SD 7,6µV
* 40000 # samples
So a span of 5ppm between Max and Min, did expect better actually!

5ppm over several weeks is not too shabby?  Is the area temperature controlled?

Did not record start/stop time, but 40000 samples at PLC100 is unfortunately only like 22h
Yeah, did not expect LTZ1000 performance, but I am pretty sure the SZA263 drift more than my AD581LH (need to find the notes from the measurenents... ;) )
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on February 24, 2020, 04:26:39 am
I've finally started logging voltage and temp together. I'm using 1 array of 10 DS18B20's to measure ambient, 1 array of 5 for each of 2 meters. The placement for the arrays for the meters is essentially placed between the ADC and the reference. Is that the best place to measure the internal temp, or should it be more central to the analog board?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 28, 2020, 06:18:59 pm
Hi,

I tested Analog Discovery 2 spectrum analyzer function together with pipelies LNA (0.1 ... 10Hz) and found that this is a decent setup, without the need of a boat anchor on the desk. Thought that could be of interest for you guys. As an example I measured LNA with shorted input, a 9V battery and one of my LTZ references.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on February 28, 2020, 07:06:41 pm

[...]  together with pipelies LNA (0.1 ... 10Hz)  [...]


What is the "pipelies LNA" ?
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on February 28, 2020, 07:58:31 pm
Quote
What is the "pipelies LNA" ?

https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg1005460/#msg1005460 (https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg1005460/#msg1005460)
https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg1401067/#msg1401067 (https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg1401067/#msg1401067)
https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/?action=dlattach;attach=385141 (https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/?action=dlattach;attach=385141)

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 04, 2020, 12:15:56 pm
I always wondered how the noise spectrum of my LTZ references would look like. Sure we can use DMM readings to get a raw idea, but even the 1/f region is always hard to get. Now that I have one of those nice Digital Spectrum Analyzers (Advantest R9211) or as they are also called Dynamic Signal Analyzers or FFT Analyzers, I was acutally able to create such a nice noise plot today.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on April 04, 2020, 12:26:39 pm
I always wondered how the noise spectrum of my LTZ references would look like. Sure we can use DMM readings to get a raw idea, but even the 1/f region is always hard to get. Now that I have one of those nice Digital Spectrum Analyzers (Advantest R9211) or as they are also called Dynamic Signal Analyzers or FFT Analyzers, I was acutally able to create such a nice noise plot today.

-branadic-

That is very cool!  -  what is the noise floor of an instrument like that?

Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on April 04, 2020, 01:34:56 pm
Hi,

I tested Analog Discovery 2 spectrum analyzer function together with pipelies LNA (0.1 ... 10Hz) and found that this is a decent setup, without the need of a boat anchor on the desk. Thought that could be of interest for you guys. As an example I measured LNA with shorted input, a 9V battery and one of my LTZ references.

-branadic-

An LTZ1000 with no flicker noise?   :-//
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 04, 2020, 01:36:20 pm
Mhm,

I can explain the 50 Hz peak in the spectrum: your cookies box isnt tight enough.
But where do the 60 Hz come from? (Screen frequency of the instrument?)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Castorp on April 04, 2020, 04:26:53 pm
Looks just like the LTZ1000 spectra I've measured many times in different ways.  :-+

My 89441A does produce 60 Hz internally, and sometimes it does show in the measurements.

Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on April 16, 2020, 10:25:41 pm
My precision resistors are coming pretty soon I found out today!  I just got these for the binding posts on my references.  I'm hoping these will help some.
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 18, 2020, 09:59:39 pm
Has anybody used Grafana to visualize data while logging? I'm doing this but I'm currently using a single right hand y axis for temps but the Internal temps are pretty far from Ambient. Does anybody know how to add a second Y axis? You can see the issue I have and maybe you can understand why I'd like dual scales to get more detail even if it may not be all that necessary. If you have any tips please share!

EDIT: http://172.119.228.219:3000/dashboard/snapshot/F3ptvJ1tIbHtU7X4roRV3Qlm0h5WboFv?orgId=1 (http://172.119.228.219:3000/dashboard/snapshot/F3ptvJ1tIbHtU7X4roRV3Qlm0h5WboFv?orgId=1) Here is a link to a snapshot, since not everyone is using a 4k monitor.
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on April 19, 2020, 07:00:26 am
I used relative ppm instead of volt for the Y scaling in Grafana. Two Y Axis will have different scalings and the reference voltages are hard to compare.
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 19, 2020, 07:06:06 am
I used relative ppm instead of volt for the Y scaling in Grafana. Two Y Axis will have different scalings and the reference voltages are hard to compare.

That's on my list. I had some trouble getting the C++ interface for influxdb working right and since it's running I'm just going to let it go and get back to it after the ~7 days it logs(it logs to a CSV file, and a more verbose log as well as influx). Did you do that through math IN grafana or by passing the ppm data?
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on April 19, 2020, 07:14:53 am
I stored raw data in influxdb (using Python) and calculated everything in Grafana, but one have to be careful with the queries on big sets of data. I killed my server several times (I have several million entries in influxdb)
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 19, 2020, 09:19:07 am
I stored raw data in influxdb (using Python) and calculated everything in Grafana, but one have to be careful with the queries on big sets of data. I killed my server several times (I have several million entries in influxdb)

Would you be able to share how you do that? I'm having trouble calculating the mean and then using that to convert to PPM. The results always end up returning null.
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on April 19, 2020, 11:25:02 am
Imho you can’t mix aggregate and non-aggregate data in a query. Therefore, I used a constant in the query. I know it is very ugly, sorry. If you find a good solution to calculate each point together with the mean of all points it would be very nice to know.
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on April 19, 2020, 11:31:01 am
Imho you can’t mix aggregate and non-aggregate data in a query. Therefore, I used a constant in the query. I know it is very ugly, sorry. If you find a good solution to calculate each point together with the mean of all points it would be very nice to know.

You can, in Oracle at least  (Oracle Analytics).   Other databases probably have something similar.  Look for the OVER clause.
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on April 19, 2020, 11:36:23 am
I was taking about influxdb
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on April 19, 2020, 01:24:18 pm
I was taking about influxdb

Is it possible to export the data and process it further in a different DB, where you don't need the high flow performance?
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 19, 2020, 03:11:20 pm
Well I attempted both select mean("reading") as "mean"... And it worked but all nulls. I also tried select mean("reading') into "autogen"."mean"... Both cases they create "mean" and it's correctly populated but when using it in math like I said it just returns null for every data point. Maybe I'll try tracking the mean in my program and continuously updating it and then attempting to use the most recent one for the math. In my program I also have it perform 43 readings to stabilize(using a scanner) before logging so perhaps that's another place to get my mean value from, then I'll be able to have 1 constant mean value for every reading point. I'll try some things in a few days when it's finished. If nothing else a hard constant isn't that bad.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 20, 2020, 02:25:06 am
I've swapped reference in experimental 3458A to explore the low-noise theories. It went with few trap pitfalls, but meter is running now and logging first data.
Click on image to see livestream recording (2.5 hours).

(https://xdevs.com/doc/xDevs.com/QVR/img/qvr_swap_1.jpg) (https://www.youtube.com/watch?v=Qp2dPAz7Q-g)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on April 20, 2020, 05:01:13 am
Hello Illya,

I am missing some kind of air shield for the LTZ1000s to get "real low noise"

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: maginnovision on April 20, 2020, 03:13:27 pm
https://snapshot.raintank.io/dashboard/snapshot/1bEqz2W4r5htRG56dgdJ7j2xl5qnrNEd

I set it up so that I take the first 100 readings and calculate a mean with that to calculate ppm values. That single mean value is logged once per reading. In this case one problem is plainly visible. While those 100 readings were taken the temperature was rising but as logging started the temperature started to drop. I'll have to try a running mean next. It does look better with both readings and temps but I still would like a second temp scale for the ambient temp. This is ok until I can see if that's possible.
Title: Re: Ultra Precision Reference LTZ1000
Post by: nnills on April 21, 2020, 08:32:43 am
I must say it is a beautiful board you made there @TiN ! One question I have is why you spend your money on a ceramic Rogers material. Is it to reduce mechanical stress due to thermal expansion?
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on April 26, 2020, 10:56:13 pm
Ok I don't want to start major debate but I know many of you here have built multiples of different designs here.  I have my LTZ1000's, I now have 4 sets of precision ww resistors for the important ones (this was what took a while).  There are two PCB designs that can be ordered I found on github online.  Dr. Franks design and cellularmitosis little board.  Are there any other options I have?  I was thinking of trying a few so two isn't a lot of variations.  I'll have to order multiple PCB's anyhow from any FAB but that's not my concern because I'm sure any extras someone will want.  Does anyone have any others I can try?

BTW I watched the livestream video of you installing the 4 LTZ board TiN... pretty wild stuff.  I'm not going to try that.  Nice fix BTW.  I'll need a couple more 3458's before I try something like that I think :P

Thanks,

Bill
Title: Re: Ultra Precision Reference LTZ1000
Post by: SvanGool on April 26, 2020, 11:54:08 pm
Another one: TIN's singe LTZ1000 board https://oshpark.com/shared_projects/HfKcqjV3 (https://oshpark.com/shared_projects/HfKcqjV3)
Description here: https://xdevs.com/article/kx-ref (https://xdevs.com/article/kx-ref)
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on April 29, 2020, 11:16:39 am
@branadic

I was very interested to see your LNA  + AD2 vs. proper-DSA spectrum comparison.

Did you figure out what the shortcomings of the LNA + AD2 route were? It would be great to figure out a light way of getting good spectra instead of having to use a boat-anchor...

TIA, Alan
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 29, 2020, 11:29:05 am
Well, the biggest shortcoming is, that you need an LNA, right? There are LNAs for several ranges such as 0.1Hz - 10Hz or 10Hz - 100kHz. What it would need is an LNA for the complete range 100mHz to 100kHz instead. There are several solutions out there such as DC-1MHz or commercial gear like Stanford Research SR560, but they are expensive. Couldn't find a proper DIY solution for the 100mHz - 100kHz range yet.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on April 29, 2020, 01:34:33 pm
I was wondering whether you had any thoughts about the apparent lack of 1/f noise using that set-up - somehow down to the AD2 or the FFT settings?

Alan
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on April 29, 2020, 04:12:19 pm
The LNA from Pipelie uses an AZ OP (or 2) and thus has essentially no 1/f noise, at least with a short. With a actual voltage there would be noise from the coupling cap if an electrolytic cap is used. I am not sure if the noise show for the battery is more from the battery or possibly from the coupling cap.

The downside of the usual AZ OPs is the limited bandwidth, especially if the first stage is used with a high gain. So 0.1 Hz to 100 kHz could become tricky. However 0.1 Hz to some 10 KHz may be realistic for such a setup without an intentional filter for the upper limit.

Similar one may be able to extend the lower limit a little below 0.1 Hz with a larger capacitor - however things are limited there. It is not just the cross over frequency, but also current noise (which gets visible as 1/f noise with a very larger resistance instead of a larger cap) and also dielectric absorption, so that electrolytic caps need really long settling before using it for slow processes.

For measuring down to really low frequencies the way to go would be using 2 reference and measuring the difference with a DC coupled amplifier, at least for the initial stage, possibly all the way with a DC compensation.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on April 29, 2020, 05:13:51 pm
Just for inspiration one could have a look at the schematic of SR560:

https://doc.xdevs.com/docs/Standford Research Systems/SR560/Stanford_Research_SR560.pdf (https://doc.xdevs.com/docs/Standford Research Systems/SR560/Stanford_Research_SR560.pdf)

and build something similar to it, maybe with reduced functionality and more modern parts available such as MMBF5103 for the JFET, that was tested to have very low 1/f noise:

http://www.angelfire.com/az3/dimitri/images/AX_Dec2018_pp56-58.pdf (http://www.angelfire.com/az3/dimitri/images/AX_Dec2018_pp56-58.pdf)

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: alanambrose on May 02, 2020, 06:08:29 pm
Interesting, following the links I see the NPD5564 pair in the original SR560 is now replaced with a LSK389B pair which is available from Linear (and some other channels) for about $6. Maybe this is drifting off the original subject though...
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on May 03, 2020, 01:00:17 pm
What it would need is an LNA for the complete range 100mHz to 100kHz instead. There are several solutions out there such as DC-1MHz or commercial gear like Stanford Research SR560, but they are expensive. Couldn't find a proper DIY solution for the 100mHz - 100kHz range yet.
I know it gets a bit off topic...

For 0.1Hz to 100kHz Andreas 0.1 to 10Hz LNA (https://www.eevblog.com/forum/metrology/diy-low-frenquency-noise-meter/msg1148584/#msg1148584) could be suitable with some modifications.
With e.g. another LT1037 in second stage and tweaking the lowpass filters to get the cutoff frequency to 100kHz it should do the job and is affordable - I did similar modification a while back for other application.

AN159 10Hz to 100kHz/1MHz (https://www.analog.com/media/en/technical-documentation/application-notes/an159fa.pdf) (Layout files (https://www.analog.com/media/en/reference-design-documentation/design-integration-files/AN159_Layout_Files.zip)) might be an option.
Downside is its limitation with low cutoff at 10Hz (1/f corner ~100Hz), so one needs at least second LNA for 0.1 to 10Hz and combine them - not so easy and not so cheap.

If I got it right the SR560 has quite high noise figure at low impedances, it seems better suited for higher source impedances (maybe > 1k \$\Omega\$)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 03, 2020, 04:26:23 pm
Hello,

I initially had a 2nd LT1037 on the output stage.
The result was massive oscillations.
(The reason for the LT1012 in the second stage).
So obviously you will have to do some additional
shielding between stages with 2 * LT1037.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on May 08, 2020, 04:46:22 pm
Anyone seen these before?  I bought a couple just to test out and alter a little.  Some of the parts look ok and some could use replacing but you don't see completed boards very often even if missing the LTZ.

Bill
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on May 09, 2020, 11:52:38 am
Anyone seen these before?  I bought a couple just to test out and alter a little.  Some of the parts look ok and some could use replacing but you don't see completed boards very often even if missing the LTZ.

Bill

Where did you get them?
Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on May 09, 2020, 12:02:32 pm
Anyone seen these before?  I bought a couple just to test out and alter a little.  Some of the parts look ok and some could use replacing but you don't see completed boards very often even if missing the LTZ.

Bill

Where did you get them?

I assume, here:

https://www.ebay.com/itm/333584715972 (https://www.ebay.com/itm/333584715972)
Title: Re: Ultra Precision Reference LTZ1000
Post by: picburner on May 09, 2020, 02:06:59 pm
You are all really terrible.... I could not resist and I also took a couple :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on May 11, 2020, 04:23:03 pm
Yep that's where I bought them from @BU508A!  Didn't take long for you guys to buy them all up!   :-DD

I knew this was coming... complete units using new LTZ (I ordered one of these too to try):
https://www.ebay.com/itm/1-Customized-Ultra-Precision-Voltage-Reference-Board-LTZ1000ACH-LTZ1000CH/333594628743 (https://www.ebay.com/itm/1-Customized-Ultra-Precision-Voltage-Reference-Board-LTZ1000ACH-LTZ1000CH/333594628743)

I'm going to add some of my seasoned aged LTZ's to the other bare boards and see if I can improve on the aging time a little.  I've got some PWW to try instead as well.

Bill
Title: Re: Ultra Precision Reference LTZ1000
Post by: picburner on May 11, 2020, 05:23:06 pm
If it can be useful to someone, in the attachment, there is the schematic that the seller has used.
Title: Re: Ultra Precision Reference LTZ1000
Post by: chuckb on May 14, 2020, 10:53:10 pm
Noopy provided links to his microscopic views of the LTZ1000 chip here -
https://www.richis-lab.de/REF03.htm (https://www.richis-lab.de/REF03.htm)

In one of the images you could see light coming from the circular Zener junction. That’s very cool. So, I had to explore that.

I made a little pcb with a tall socket for the LTZ1000. It also had selectable bias currents and operating temperature.

My friend Jim has a great collection of top-of-the-line microscopes. He coupled his new Nikon Z6 to the Nikon Metaphot Metallurgical microscope for the following images.
Thanks Jim!

As you would expect, as the current increased the light increased.
Changing the chip temperature from 50 deg C to 95 deg C at 4ma bias made no noticeable change in the light.

For one image Jim minimized all ambient light so we could capture the full 360 circle of light from the breakdown. Half of the light is hidden behind the trace on the top layer.
Title: Re: Ultra Precision Reference LTZ1000
Post by: CalMachine on May 14, 2020, 11:03:51 pm
For one image Jim minimized all ambient light so we could capture the full 360 circle of light from the breakdown. Half of the light is hidden behind the trace on the top layer.


:wtf:


 :scared:
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on May 14, 2020, 11:11:01 pm
Interesting how the light appears in "dots" like stars in a nebula.

Guess this is due to imperfections, so some parts of the junction breaks down more than others?

You can imagine how such a process could be electrically noisy...

It would be awesome to record that light with some kind of photodetector and "listen" to it - is the light output noisy like the zener current?

Title: Re: Ultra Precision Reference LTZ1000
Post by: Magnificent Bastard on May 15, 2020, 05:02:11 am
Interesting how the light appears in "dots" like stars in a nebula.

Guess this is due to imperfections, so some parts of the junction breaks down more than others?

You can imagine how such a process could be electrically noisy...

It would be awesome to record that light with some kind of photodetector and "listen" to it - is the light output noisy like the zener current?

Also, what might prove interesting is to hit the junction with a LASER-- and watch what happens with the 1/f noise and voltage output.  I've been wanting to do this for a long time, but it seems @chuckb beat me to it, and is pretty much ready to do this test!
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on May 15, 2020, 09:21:27 am
Interesting how the light appears in "dots" like stars in a nebula.

Guess this is due to imperfections, so some parts of the junction breaks down more than others?

You can imagine how such a process could be electrically noisy...

It would be awesome to record that light with some kind of photodetector and "listen" to it - is the light output noisy like the zener current?

I can also imagine the light may show some fluctuations. Changes are these may correlate with noise in the voltage.

I don't think this is a kind of junction break-down. The more likely mechanism is that the zener diode in the avalanche regime produces hot electrons and some of these can get to the surface oxide / interface. Relaxation of the electrons there can happen with light at some suitable states (similar to color centers). 

Normally the idea behind the buried zener is to avoid this effect by keeping the hot electron from reaching the surface. The second point is that they do less harm in the burried zener: this part can still work but is not so visible.
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on May 15, 2020, 11:44:14 am
Interesting how the light appears in "dots" like stars in a nebula.

Guess this is due to imperfections, so some parts of the junction breaks down more than others?

You can imagine how such a process could be electrically noisy...

It would be awesome to record that light with some kind of photodetector and "listen" to it - is the light output noisy like the zener current?

I can also imagine the light may show some fluctuations. Changes are these may correlate with noise in the voltage.

I don't think this is a kind of junction break-down. The more likely mechanism is that the zener diode in the avalanche regime produces hot electrons and some of these can get to the surface oxide / interface. Relaxation of the electrons there can happen with light at some suitable states (similar to color centers). 

Normally the idea behind the buried zener is to avoid this effect by keeping the hot electron from reaching the surface. The second point is that they do less harm in the burried zener: this part can still work but is not so visible.

If the mechanism is due to electrons relaxing and "going back to bed", perhaps taking a spectrum of the light would show something interesting?  (confirming the material, perhaps, and thereby proving the hypothesis?)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Noopy on May 19, 2020, 05:40:53 am
Interesting how the light appears in "dots" like stars in a nebula.

Guess this is due to imperfections, so some parts of the junction breaks down more than others?

You can imagine how such a process could be electrically noisy...

It would be awesome to record that light with some kind of photodetector and "listen" to it - is the light output noisy like the zener current?

I can also imagine the light may show some fluctuations. Changes are these may correlate with noise in the voltage.

I don't think this is a kind of junction break-down. The more likely mechanism is that the zener diode in the avalanche regime produces hot electrons and some of these can get to the surface oxide / interface. Relaxation of the electrons there can happen with light at some suitable states (similar to color centers). 

Normally the idea behind the buried zener is to avoid this effect by keeping the hot electron from reaching the surface. The second point is that they do less harm in the burried zener: this part can still work but is not so visible.

Are you sure?
I´m no expert regarding semiconductor physics but in my understanding z-diodes with this voltage rating work at least to some extend in avalanche breakdown.
In avalanche breakdown accelerated electrons hit other electrons setting them free on a not exactly defined energy level. If the energy level is in the range of visible light their recombination can emit visible light.
This recombination will perfectly happen in the junction area. In my view most of the recombination will happen there.
Correct me if I´m wrong.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on May 19, 2020, 07:03:04 am
A agree one the way the zener is supposed to work. However I doubt that one would see light from the buried junction. This would be rather deep inside the silicon so only very little of that light can escape. The normal avalanche process  should also not produce light as the energy from the hot electron is used to generate new pairs. The normal recombination in silicon is without any light and if any it would be in the IR range (~ 1 µm). It would be only if a hot electron recombines or excites some defect in some way.

It usually takes some defects so that an indirect semiconductor like silicon can emit light. The logical position would be the surface or just inside the oxide. My estimate is that the way to the surface should be easier for a hot electron than for visible light. This would be different if the light is in the NIR range.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Noopy on May 19, 2020, 10:14:37 am
However I doubt that one would see light from the buried junction. This would be rather deep inside the silicon so only very little of that light can escape.

I´m not sure about this.
A view days ago I tried to use a big KD501 transistor as a photovoltaic cell.
(https://richis-lab.de/Bipolar02.htm (https://richis-lab.de/Bipolar02.htm))
Across the base-emitter-junction I got the same current as across the base-collector-junction. It seems there wasn´t significant light reduction.


The normal avalanche process  should also not produce light as the energy from the hot electron is used to generate new pairs. The normal recombination in silicon is without any light and if any it would be in the IR range (~ 1 µm). It would be only if a hot electron recombines or excites some defect in some way.

I agree with you that hot electrons generate new pairs but some of them will recombinate. Otherwise you will get a real breakdown with 0V and destruction of the junction. (I´m not absolutely sure about the last sentence but that would be my interpretation.)
The hot electrons can have a higher energy than you will see while normal current flow in the semiconductor. With "normal" current flow and "normal" recombination you don´t see any light. I agree with that. But in my view there is recombination of hot electrons.


I tried to take a "maximum tilted" picture but you can´t really say where the light is generated:

(https://richis-lab.de/images/REF01/01_11b.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on May 19, 2020, 11:58:35 am
How deeply is a buried zener buried? May be the layer above it is thin-enough to be transparrent to the light? May be photons from inner layer somehow re-emmiter from the outer layer? (purelly guessing here, I have zero knowledge about semiconductors)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Simon_RL on May 19, 2020, 12:20:14 pm
Hi All,
Please don’t laugh at me for this question. I am a newbie to electronics and have developed a strong interest in metrology. I want to build a voltage reference based on the LTZ1000a and unfortunately I haven’t got the knowledge to design my own circuit yet. Basically I need a reference for a few experiments I want to do as part of my learning process. I have been hunting for a good circuit and came across this circuit board on AliExpress. If some one can please provide feedback on this circuit and advise if it is any good it would greatly appreciate. Unfortunately there isn’t a schematic, but there are clear pictures of the board and silk screen. If this is no good and someone could please pint me in the direction of a good design I would really appreciate it.

https://m.aliexpress.com/item/4000615209128.html?spm=a2g0n.wishlist-amp.item.4000615209128&aff_trace_key=&aff_platform=msite&m_page_id=2033amp-vGQRqGHv_FhCn8pzRV1uSQ1589885700140&browser_id=fcbdcf015c134b0ca64ebcab0b0f18c2&is_c=Y

Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on May 19, 2020, 01:11:22 pm
Hi,

welcome to the volt-nuts section.  :)

Hi All,
Please don’t laugh at me for this question. I am a newbie to electronics and have developed a strong interest in metrology. I want to build a voltage reference based on the LTZ1000a and unfortunately I haven’t got the knowledge to design my own circuit yet. Basically I need a reference for a few experiments I want to do as part of my learning process. I have been hunting for a good circuit and came across this circuit board on AliExpress. If some one can please provide feedback on this circuit and advise if it is any good it would greatly appreciate. Unfortunately there isn’t a schematic, but there are clear pictures of the board and silk screen. If this is no good and someone could please pint me in the direction of a good design I would really appreciate it.

https://m.aliexpress.com/item/4000615209128.html?spm=a2g0n.wishlist-amp.item.4000615209128&aff_trace_key=&aff_platform=msite&m_page_id=2033amp-vGQRqGHv_FhCn8pzRV1uSQ1589885700140&browser_id=fcbdcf015c134b0ca64ebcab0b0f18c2&is_c=Y (https://m.aliexpress.com/item/4000615209128.html?spm=a2g0n.wishlist-amp.item.4000615209128&aff_trace_key=&aff_platform=msite&m_page_id=2033amp-vGQRqGHv_FhCn8pzRV1uSQ1589885700140&browser_id=fcbdcf015c134b0ca64ebcab0b0f18c2&is_c=Y)

I strongly recommend to read this thread from the beginning. You'll find a lot of useful information and designs of a good LTZ1000 based reference.
Here are some examples:

LTZ1000 based on the design of Dr. Frank:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/ (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1837169/#msg1837169)
https://github.com/pepaslabs/dr-frank-ltz1000 (https://github.com/pepaslabs/dr-frank-ltz1000)

TiN's KX-reference:
https://xdevs.com/article/kx-ref/ (https://xdevs.com/article/kx-ref/)

MX reference from user ManateeMafia
https://www.eevblog.com/forum/metrology/mx-reference/ (https://www.eevblog.com/forum/metrology/mx-reference/)

Lot of work lies in front of you.  :-/O   ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Simon_RL on May 19, 2020, 01:58:05 pm
Hi,

welcome to the volt-nuts section.  :)

Hi All,
Please don’t laugh at me for this question. I am a newbie to electronics and have developed a strong interest in metrology. I want to build a voltage reference based on the LTZ1000a and unfortunately I haven’t got the knowledge to design my own circuit yet. Basically I need a reference for a few experiments I want to do as part of my learning process. I have been hunting for a good circuit and came across this circuit board on AliExpress. If some one can please provide feedback on this circuit and advise if it is any good it would greatly appreciate. Unfortunately there isn’t a schematic, but there are clear pictures of the board and silk screen. If this is no good and someone could please pint me in the direction of a good design I would really appreciate it.

https://m.aliexpress.com/item/4000615209128.html?spm=a2g0n.wishlist-amp.item.4000615209128&aff_trace_key=&aff_platform=msite&m_page_id=2033amp-vGQRqGHv_FhCn8pzRV1uSQ1589885700140&browser_id=fcbdcf015c134b0ca64ebcab0b0f18c2&is_c=Y (https://m.aliexpress.com/item/4000615209128.html?spm=a2g0n.wishlist-amp.item.4000615209128&aff_trace_key=&aff_platform=msite&m_page_id=2033amp-vGQRqGHv_FhCn8pzRV1uSQ1589885700140&browser_id=fcbdcf015c134b0ca64ebcab0b0f18c2&is_c=Y)

I strongly recommend to read this thread from the beginning. You'll find a lot of useful information and designs of a good LTZ1000 based reference.
Here are some examples:

LTZ1000 based on the design of Dr. Frank:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/ (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/)
https://github.com/pepaslabs/dr-frank-ltz1000 (https://github.com/pepaslabs/dr-frank-ltz1000)

TiN's KX-reference:
https://xdevs.com/article/kx-ref/ (https://xdevs.com/article/kx-ref/)

MX reference from user ManateeMafia
https://www.eevblog.com/forum/metrology/mx-reference/ (https://www.eevblog.com/forum/metrology/mx-reference/)

Lot of work lies in front of you.  :-/O   ;)

Thanks Heaps BU508A. Very much appreciate your assistance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on May 19, 2020, 04:47:43 pm
However I doubt that one would see light from the buried junction. This would be rather deep inside the silicon so only very little of that light can escape.

I´m not sure about this.
A view days ago I tried to use a big KD501 transistor as a photovoltaic cell.
(https://richis-lab.de/Bipolar02.htm (https://richis-lab.de/Bipolar02.htm))
Across the base-emitter-junction I got the same current as across the base-collector-junction. It seems there wasn´t significant light reduction.


The normal avalanche process  should also not produce light as the energy from the hot electron is used to generate new pairs. The normal recombination in silicon is without any light and if any it would be in the IR range (~ 1 µm). It would be only if a hot electron recombines or excites some defect in some way.

I agree with you that hot electrons generate new pairs but some of them will recombinate. Otherwise you will get a real breakdown with 0V and destruction of the junction. (I´m not absolutely sure about the last sentence but that would be my interpretation.)
The hot electrons can have a higher energy than you will see while normal current flow in the semiconductor. With "normal" current flow and "normal" recombination you don´t see any light. I agree with that. But in my view there is recombination of hot electrons.


I tried to take a "maximum tilted" picture but you can´t really say where the light is generated:

(https://richis-lab.de/images/REF01/01_11b.jpg)

Several things to note here:

1) If the emission is happening underneath an oxide layer, let us remember that we call the silicon dioxide we encounter on an everyday basis "glass". No problems with light getting through centimetres of glass, let alone microns or 100s of nanometers.

2) The assumption made so far is that silicon is the emission candidate. What if it's the dopant? Several common dopants are very strongly associated with visible emission bands (common: arsenic, phosphorous, less common: gallium). There is, admittedly, very little dopant but we're seeing very little light.

3) The assumption that the material is "too thick" for emissions to make their way out.  Remember that we are in the 100s - 1000s of nanometres territory here. At that scale one's assumptions brought from the normal scale world about opacity are quite likely to be wrong.

This diagram of the structure of the buried Zener from the LM399 might be instructive at this stage. It looks to me like the emission is happening well away from the region where the 'buried' junction action is supposed to be going on, perhaps between the outer ring of P- diffusion and the N- substrate or between the cathode and the surface part of the anode P- diffusion.

[attachimg=1]
Title: Re: Ultra Precision Reference LTZ1000
Post by: Noopy on May 19, 2020, 05:17:43 pm
...

Several things to note here:

1) If the emission is happening underneath an oxide layer, let us remember that we call the silicon dioxide we encounter on an everyday basis "glass". No problems with light getting through centimetres of glass, let alone microns or 100s of nanometers.

2) The assumption made so far is that silicon is the emission candidate. What if it's the dopant? Several common dopants are very strongly associated with visible emission bands (common: arsenic, phosphorous, less common: gallium). There is, admittedly, very little dopant but we're seeing very little light.

3) The assumption that the material is "too thick" for emissions to make their way out.  Remember that we are in the 100s - 1000s of nanometres territory here. At that scale one's assumptions brought from the normal scale world about opacity are quite likely to be wrong.

This diagram of the structure of the buried Zener from the LM399 might be instructive at this stage. It looks to me like the emission is happening well away from the region where the 'buried' junction action is supposed to be going on, perhaps between the outer ring of P- diffusion and the N- substrate or between the cathode and the surface part of the anode P- diffusion.

(Attachment Link)


I agree with you in most points except the last one. Be aware that the round thing in the middle of the LTZ1000 is a buried zener and a transistor.

I took also a picture of the transistor working in breakdown:

(https://richis-lab.de/images/REF01/01_12.jpg)

=> The z-diode has to be around the transistor.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on May 19, 2020, 10:47:51 pm

I agree with you in most points except the last one. Be aware that the round thing in the middle of the LTZ1000 is a buried zener and a transistor.

I took also a picture of the traor working in breakdown:

(https://richis-lab.de/images/REF01/01_12.jpg)

=> The z-diode has to be around the transistor.

Even with my very limited understanding of silicon fabrication I don't believe that is right. The circular structure fits every diagram of a buried zener that I've ever seen, and the structures further out (outside the central region) look much more like what I understand a bipolar transistor to look like on a die. There are more than the two shown in the schematic (I can see 4 things that definitely look like transistors, perhaps even eight), but it is quite common for multiple transistors to be paralleled 'on chip' into a single transistor to allow for thermal balancing, dealing with thermal gradients and the like - exactly what one might expect on a chip like the LTZ1000.

I'd be deeply grateful if someone who is actually properly qualified at decoding dies shots would produce an annotated version of one of the many LTZ1000 die shots kicking about marking out the actual transistors, their CBE connections and so on.
Title: Re: Ultra Precision Reference LTZ1000
Post by: splin on May 19, 2020, 11:33:05 pm
Can you buy 'reasonably priced' germanium microscope optics to allow an IR camera to be used to show where currents flow and the current densities?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Noopy on May 20, 2020, 07:57:41 am
Even with my very limited understanding of silicon fabrication I don't believe that is right. The circular structure fits every diagram of a buried zener that I've ever seen, and the structures further out (outside the central region) look much more like what I understand a bipolar transistor to look like on a die. There are more than the two shown in the schematic (I can see 4 things that definitely look like transistors, perhaps even eight), but it is quite common for multiple transistors to be paralleled 'on chip' into a single transistor to allow for thermal balancing, dealing with thermal gradients and the like - exactly what one might expect on a chip like the LTZ1000.

I'd be deeply grateful if someone who is actually properly qualified at decoding dies shots would produce an annotated version of one of the many LTZ1000 die shots kicking about marking out the actual transistors, their CBE connections and so on.

Well looking in detail at my own assumptions I have to admit you are right. But I´m right, too.  ;D

(https://richis-lab.de/images/REF01/01_02x.jpg)
(https://richis-lab.de/images/REF01/01_04.jpg)
(https://richis-lab.de/images/REF01/01_04x.jpg)

The z-diode is designed as descriped in the LM399 diagram. It is connected with the red metal (cathode) and the black metal (anode).
The transistor Q1 is already there with it´s emitter connected to the blue metal in the center. The base is a part of the z-diode (red). The collector is connected from the edge (white).

So there is a transistor which is surrounded by the z-diode but it´s already in the z-diode structure.

The "avalanche lights" confirm this: You can see the base-emitter-junction on the edge of the middle circle whereas the z-diode-junction is buried under the surrounding ring.

Q2 consists of four transistors surrounding the z-diode and Q1 (grey, yellow, blue).

 :-+


Can you buy 'reasonably priced' germanium microscope optics to allow an IR camera to be used to show where currents flow and the current densities?

I´m afraid such an optic is unaffordable...  :'(
Title: Re: Ultra Precision Reference LTZ1000
Post by: magic on May 20, 2020, 09:48:39 am
Our friends at Foveon produced a marketing graphic which illustrates light penetration through silicon.
[attachimg=1]

It is my vague recollection that the depth of base and emitter diffusions in a typical "medium voltage" monolithic bipolar process is a few microns, emitters of course being shallower than bases.

I'd be deeply grateful if someone who is actually properly qualified at decoding dies shots would produce an annotated version of one of the many LTZ1000 die shots kicking about marking out the actual transistors, their CBE connections and so on.
There was some speculation and links to semi-helpful sources in Noopy's original LTZ teardown thread. As an improperly qualified hobbyist I think I had figured it out at one point. See if my old posts make any sense to you.

edit
Another source, this time with concrete numbers. If I read it right, 36% of red/orange light (as seen on Noopy's photos) should be able to pass through a few microns of silicon.
https://www.pveducation.org/pvcdrom/materials/optical-properties-of-silicon (https://www.pveducation.org/pvcdrom/materials/optical-properties-of-silicon)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on May 20, 2020, 02:43:28 pm
(https://richis-lab.de/images/REF01/01_02x.jpg)
(https://richis-lab.de/images/REF01/01_04x.jpg)

The z-diode is designed as descriped in the LM399 diagram. It is connected with the red metal (cathode) and the black metal (anode).
The transistor Q1 is already there with it´s emitter connected to the blue metal in the center. The base is a part of the z-diode (red). The collector is connected from the edge (white).

So there is a transistor which is surrounded by the z-diode but it´s already in the z-diode structure.

The "avalanche lights" confirm this: You can see the base-emitter-junction on the edge of the middle circle whereas the z-diode-junction is buried under the surrounding ring.

Q2 consists of four transistors surrounding the z-diode and Q1 (grey, yellow, blue).

 :-+

Looking at a larger picture with the bonding wires I can see:

Red connects to pin 3 - Zener cathode
Black connects to pin 4 - Q1 base/Zener anode
White connects to pin 5 - Q1 collector
Yellow connects to pin 6 - Q2 base
Blue connects to pin 7 - Q1/Q2 emitters
Grey connects to pin 8 - Q2 collector

So, the Black trace connects to the Q1 base/Zener anode and Red is the Zener cathode, not as stated "The base is a part of the z-diode (red)." So the base connection is the outer circle.

My head now officially hurts from sitting here for 15 minutes trying to imagine exactly what the 3D structure of Q1/the Zener actually looks like and I'm still not there. Fortunately shopping calls so I've an excuse to give up, at least for the time being.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Noopy on May 20, 2020, 05:30:54 pm
Looking at a larger picture with the bonding wires I can see:

Red connects to pin 3 - Zener cathode
Black connects to pin 4 - Q1 base/Zener anode
White connects to pin 5 - Q1 collector
Yellow connects to pin 6 - Q2 base
Blue connects to pin 7 - Q1/Q2 emitters
Grey connects to pin 8 - Q2 collector

So, the Black trace connects to the Q1 base/Zener anode and Red is the Zener cathode, not as stated "The base is a part of the z-diode (red)." So the base connection is the outer circle.

My head now officially hurts from sitting here for 15 minutes trying to imagine exactly what the 3D structure of Q1/the Zener actually looks like and I'm still not there. Fortunately shopping calls so I've an excuse to give up, at least for the time being.

Damn! I´m wrong. You are right.  :-+
You got me on a wrong track.
If I´m not wrong again my first statement was actually right: In the middle circle there is a zener with a transistor inside it. zener and Q1 share some parts but there is more inside the LTZ1000 than you can see in the datasheet of the LM399.

Title: Re: Ultra Precision Reference LTZ1000
Post by: magic on May 23, 2020, 09:07:21 am
I took another look at that thing and this is my best guess of what the internal structure might be, assuming they use the standard noncomplementary bipolar process.

[attachimg=1]

D1 uses the buried zener construction described in Linear AN82, but with a central hole to contain Q1. The anode consists of two P diffusions of different depth, breadth and strenght. The cathode is a strong and shallow N diffusion which fully covers the area of highest P concentration where breakdown voltage is lowest and actual breakdown will occur. This active part of the junction is located a few microns beneath the surface.

Q1 is a standard vertical NPN (top to bottom: EBC). Base is the same silicon as D1 anode, providing the necessary connection which is nowhere to be found on the surface. There is a thin, cross-shaped disturbance visible on the surface which is probably caused by a buried layer diffusion below. Such diffusion could connect Q1 collector to the four contacts surrounding the reference diode structure which are all wired to pin 5. Alternatively, D1 anode could have no hole and Q1 collector would be the N silicon which surrounds D1 anode, but then Q1 would have considerable base width and probably poor beta.

It is known that D1 anode is connected to the substrate and, according to designer Carl Nelson, there exists a subsurface Kelvin connection to the bottom of D1. I presume it all means that the anode is not isolated from the substrate by the buried layer, except for the aforementioned four thin lines. Between the lines, the buried layer is empty and the anode connects with the substrate.

A second similar ring of deep P diffusion is located outside, to isolate D1/Q1 from other transistors. This ring also is penetrated by the buried layer Q1 collector links. On its surface there is a metal connection to pin 4.

Q2 consists of four standard vertical NPNs placed around the reference structure and wired in parallel.

Comments, questions and arguments are welcome :popcorn:
Title: Re: Ultra Precision Reference LTZ1000
Post by: Noopy on May 23, 2020, 03:33:00 pm
I took another look at that thing and this is my best guess of what the internal structure might be, assuming they use the standard noncomplementary bipolar process.

(Attachment Link)

D1 uses the buried zener construction described in Linear AN82, but with a central hole to contain Q1. The anode consists of two P diffusions of different depth, breadth and strenght. The cathode is a strong and shallow N diffusion which fully covers the area of highest P concentration where breakdown voltage is lowest and actual breakdown will occur. This active part of the junction is located a few microns beneath the surface.

Q1 is a standard vertical NPN (top to bottom: EBC). Base is the same silicon as D1 anode, providing the necessary connection which is nowhere to be found on the surface. There is a thin, cross-shaped disturbance visible on the surface which is probably caused by a buried layer diffusion below. Such diffusion could connect Q1 collector to the four contacts surrounding the reference diode structure which are all wired to pin 5. Alternatively, D1 anode could have no hole and Q1 collector would be the N silicon which surrounds D1 anode, but then Q1 would have considerable base width and probably poor beta.

It is known that D1 anode is connected to the substrate and, according to designer Carl Nelson, there exists a subsurface Kelvin connection to the bottom of D1. I presume it all means that the anode is not isolated from the substrate by the buried layer, except for the aforementioned four thin lines. Between the lines, the buried layer is empty and the anode connects with the substrate.

A second similar ring of deep P diffusion is located outside, to isolate D1/Q1 from other transistors. This ring also is penetrated by the buried layer Q1 collector links. On its surface there is a metal connection to pin 4.

Q2 consists of four standard vertical NPNs placed around the reference structure and wired in parallel.

Comments, questions and arguments are welcome :popcorn:

Chapeau! Good explanation, good picture, very nice!  :-+ :-+ :-+
Sound reasonable!  :-+

...how did you paint this?


Title: Re: Ultra Precision Reference LTZ1000
Post by: magic on May 23, 2020, 06:01:06 pm
...how did you paint this?
A few circles, rectangles and 45° rotations to get one quarter of the top surface, then mirror to get a full half, then perspective transformation. All functions available in gimp, I'm sure other advanced image editors like Photoshop could do it too.
The cross section is just a few ellipses drawn on a new layer which restricted them to the bottom half of the frame. That's cheating; frankly, the base diffusion should have a flat bottom over most of its area ::)
It actually is pretty simple in retrospect but I spent an hour learning how to operate that crazy software.
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on May 23, 2020, 06:06:40 pm
A vector drawing application like Adobe Illustrator, or Inkscape in the open source world, would be perfect for that kind of work!

Photoshop will work, but it has to be flogged to go there, kicking, screaming, and protesting the whole way...  (It has only rudimentary vector drawing capabilities).  I have never tried the Gimp but I imagine it doesn't major on vector drawing eiter.   Photoshop is to Illustrator what Gimp is to Inkscape, I believe.
Title: Re: Ultra Precision Reference LTZ1000
Post by: magic on May 23, 2020, 07:08:57 pm
I used zero vector graphics capabilities and drew it like in Microsoft Paint :D

Yes, I know. But vector graphics would be yet another even more specialized software to learn. Raster editors are more versatile; everything I did today I will probably want to do to a photograph or some bitmap graphic downloaded from the Internet another day. In the past I used Gimp to alter schematics in PNG format, try that with a vector editor :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on May 24, 2020, 11:21:34 am
wow, I was under impression that the picture was made in a chip design CAD.
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on May 24, 2020, 11:26:08 am
I used zero vector graphics capabilities and drew it like in Microsoft Paint :D

Yes, I know. But vector graphics would be yet another even more specialized software to learn. Raster editors are more versatile; everything I did today I will probably want to do to a photograph or some bitmap graphic downloaded from the Internet another day. In the past I used Gimp to alter schematics in PNG format, try that with a vector editor :)

I hear you.  These applications have big learning curves.  But there are really only those two fundamental types...    if we ignore 3D for now!  :D
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on May 24, 2020, 01:20:52 pm
Here's a paper describing light emission from a silicon avalanche diode. Fantastic to see those pictures.

https://aip.scitation.org/doi/10.1063/1.4931056
Title: Re: Ultra Precision Reference LTZ1000
Post by: magic on May 25, 2020, 09:46:45 am
wow, I was under impression that the picture was made in a chip design CAD.
No. I'm not a professional designer, just spent too much time staring at analog ICs :P

The drawing is to be taken with a grain of salt. It may be wrong altogether and various minor details are certainly wrong.

It's completely not to scale, in real world the deep diffusions are almost half-spherical because the dopant doesn't care which direction to diffuse, the concentration of dopant steadily decreases as it diffuses further away from the point of application which I didn't bother trying to show, the shallow diffusions ought to have flat bottoms because the "point" of application is not a single point or line but a wide 2D area, possibly other things...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Noopy on June 01, 2020, 08:43:00 pm
However I doubt that one would see light from the buried junction. This would be rather deep inside the silicon so only very little of that light can escape.

I´m not sure about this.
A view days ago I tried to use a big KD501 transistor as a photovoltaic cell.
(https://richis-lab.de/Bipolar02.htm (https://richis-lab.de/Bipolar02.htm))
Across the base-emitter-junction I got the same current as across the base-collector-junction. It seems there wasn´t significant light reduction.


The normal avalanche process  should also not produce light as the energy from the hot electron is used to generate new pairs. The normal recombination in silicon is without any light and if any it would be in the IR range (~ 1 µm). It would be only if a hot electron recombines or excites some defect in some way.

I agree with you that hot electrons generate new pairs but some of them will recombinate. Otherwise you will get a real breakdown with 0V and destruction of the junction. (I´m not absolutely sure about the last sentence but that would be my interpretation.)
The hot electrons can have a higher energy than you will see while normal current flow in the semiconductor. With "normal" current flow and "normal" recombination you don´t see any light. I agree with that. But in my view there is recombination of hot electrons.


I tried to take a "maximum tilted" picture but you can´t really say where the light is generated:

(https://richis-lab.de/images/REF01/01_11b.jpg)


Hi all!

We talked about the avalanche breakdown light in the LTZ1000 and whether it is generated in the pn-junction. If so the light dots would stand for irregularities in the zener-junction.
Kleinstein suggested that the light dots occur in the upper layer at impurities outside the zener-junction.

Coincidentally I got a BUX22. What is the similarity between the LTZ1000 and the monster BUX22?
The BUX22 has some minor but visible defects in the base-emitter-junction:

(https://richis-lab.de/images/transistoren/07x17.jpg)

And the glowing occurs first next to the defects not on top of the defects. In my view that means that the avalanche breakdown glowing occurs first at points where there are irregularities in the pn-junction (higher electrical field force).
q.e.d.


Whole story here:

https://richis-lab.de/Bipolar07.htm (https://richis-lab.de/Bipolar07.htm)

 :popcorn:
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 03, 2020, 07:30:16 am
1. I don't think that this project would belong into this thread, please delete and continue with your other one, you already opened.
2. Concerning the LTZ1000, why do you want to reinvent the wheel, again?
Maybe you should define precisely your requirements concerning stability figures and noise immunity, before discussing cosmetic aspects like the form factor, and (again) over-engineering the components used. Better than A9 and compact designs are already available.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on June 03, 2020, 09:06:00 am
Point 1 is well made, but how is re-using the A9 "reinventing the wheel", quite the opposite surely, and there's nothing cosmetic about form factors.

A form factor is a basic utilitarian part of a specification - there's a world of difference between a portable instrument and one intended for rack mounting. Form factor is probably point one on any outline specification for any product, so much so that the form factor implicitly or explicitly defines whole categories of products. Nobody wants a toilet that doesn't fit the implicit form factor, or a 50 cm mobile phone, or a 2.5 m long 'luxury' car.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on June 03, 2020, 07:07:35 pm
1. I don't think that this project would belong into this thread, please delete and continue with your other one, you already opened.
2. Concerning the LTZ1000, why do you want to reinvent the wheel, again?
Maybe you should define precisely your requirements concerning stability figures and noise immunity, before discussing cosmetic aspects like the form factor, and (again) over-engineering the components used. Better than A9 and compact designs are already available.

Frank
Not the A9 from a 3458A, but an LTZ1000 reference in a A9 form factor, electrically compatible (better resistors, lower running temperature, better layout). What do you mean by reinventing the wheel? One can never have enough LTZ1000 projects or references. I haven't built one yet, why shouldn't I? I don't want to use an existing one, I don't like the form factor and the layout of the existing ones, simple as that, they are awesome piece of engineering don't get me wrong, I'm don't doubt the performance one bit, but don't fit my philosophy and needs. All the requirements are around the form factor, if compromises need to be made, they will be made to fit the form factor. Completely agree on the requirements, this is high level, not well thought yet. Considering VHD200 as overkill for an LTZ1000 project in my opinion is questionable, I certainly don't agree with it. We don't have to continue discussing, as this indeed does not fit the LTZ1000 thread, you are very welcome to jump on the other thread :)

Point 1 is well made, but how is re-using the A9 "reinventing the wheel", quite the opposite surely, and there's nothing cosmetic about form factors.

A form factor is a basic utilitarian part of a specification - there's a world of difference between a portable instrument and one intended for rack mounting. Form factor is probably point one on any outline specification for any product, so much so that the form factor implicitly or explicitly defines whole categories of products. Nobody wants a toilet that doesn't fit the implicit form factor, or a 50 cm mobile phone, or a 2.5 m long 'luxury' car.
I wholeheartedly agree with this, thanks a lot
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on June 18, 2020, 08:14:51 am
Here is some data on an LTZ1000 ref I've been playing with, this does not look very good does it? |O
Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on June 18, 2020, 08:34:28 am
Here is some data on an LTZ1000 ref I've been playing with, this does not look very good does it? |O

Any RF sources nearby? Neonlights on the ceiling? If you have a spectrum analyzer, please check of any unwanted RF.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on June 18, 2020, 08:40:05 am
It is hard to tell how good the LTZ1000 reference is. With a DMM reading the DC voltage one sees a combination of the external and DMM internal reference. With the DMM7510 this is the LTFLU and LTZ1000 combined. Depending on the DMM setting one may also have some extra contributions from the DMM (the DMM7510 has relatively high noise at 100 PLC - seems to be some odd Keithley specific thing).

So some 1.8 µV peak to peak is about the value one would expect. Naturally the noise reading show quite some variations. A reliable noise reading takes quite some times, so more like the median over some 10 intervals with some 100-1000 readings.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on June 18, 2020, 09:00:39 am
The DMM7510 isnt capable of displaying the actual LTZ-noise, for that youll need a 0.1-10Hz-LNA.
Id suggest to use batteries instead of a powersupply for such measurements.
Also the graph-function is limited by the 4LSB-noise, maybe it gives out more resolution via GPIB which can be used to produce a better/smoother diagram?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 18, 2020, 09:38:33 am
Here is some data on an LTZ1000 ref I've been playing with, this does not look very good does it? |O

Frankly speaking, your whole set-up, including the cables, is not looking good at all.

I also do not know, what's inside the aluminum sheet, or what your LTZ reference you're actually using.
Anyhow, you're always comparing the LTZ versus your DMM, so the noise is always a combination of both.
Your instrument should perform noise-wise nearly as good as a 3458A, the whole setup seems to have too few resolution, at least the rms noise for an LTZ is on the order of  200nVrms or 0.03ppm only.. maybe you also use Standard Deviation for measuring the noise.That 1.7µV pp is not optimal, but on the order of what to expect.

If you want to have stable measurements, you're really dealing with sub-ppm stability - what a properly built LTZ can deliver, you have first to set up everything in a stable way, not that Flying Dutchman approach..  these loosely hanging, un-shielded cables with inappropriate connection jacks are simply acting like antennas, and by themselves create a lot of other disturbances.

If your actual LTZ circuit (?) is built from the original LT schematic, then it's not inert at all against E.M.C., so the hint for SMPSUs from others, is the crucial point here.

Maybe you understand now, that 'better' components, layout, and so on are not the key points.. maybe you just do the basics first.

I will append a picture how the stability diagram will look like.


Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on June 18, 2020, 10:24:09 am
Here is some data on an LTZ1000 ref I've been playing with, this does not look very good does it? |O

Any RF sources nearby? Neonlights on the ceiling? If you have a spectrum analyzer, please check of any unwanted RF.
Yes! The thing on the wall just next to it is a low energy Bluetooth device measuring temperature  |O
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on June 18, 2020, 10:26:23 am
It is hard to tell how good the LTZ1000 reference is. With a DMM reading the DC voltage one sees a combination of the external and DMM internal reference. With the DMM7510 this is the LTFLU and LTZ1000 combined. Depending on the DMM setting one may also have some extra contributions from the DMM (the DMM7510 has relatively high noise at 100 PLC - seems to be some odd Keithley specific thing).

So some 1.8 µV peak to peak is about the value one would expect. Naturally the noise reading show quite some variations. A reliable noise reading takes quite some times, so more like the median over some 10 intervals with some 100-1000 readings.
Yes I know that :-+ This is not a serious measurement, just a sanity check. Three or more multimeters (DMM7510 and 3458A) sampling the reference is what I had in mind for the serious measurement, and proper cables and shielding.

The reference used here is an old and unmodified A9 board from an 3458A. DMM7510 is what I had conveniently located near the power supply.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 18, 2020, 12:10:04 pm
Yes I know that :-+ This is not a serious measurement, just a sanity check. Three or more multimeters (DMM7510 and 3458A) sampling the reference is what I had in mind for the serious measurement, and proper cables and shielding.

The reference used here is an old and unmodified A9 board from an 3458A. DMM7510 is what I had conveniently located near the power supply.

That's a too elaborated approach, which will create new problems.
 
Parallel measurement with several DMMs is unnecessary, complicated, and will give big interference noise from one DMM to the other.
We had this failure recently, during our MM 2020 already, so do not repeat the same mistake.

Keep everything simple, i.e. one good DMM, make a clean setup, do the basic shielding, and then you're done.

Frank
https://www.eevblog.com/forum/metrology/volt-nut-meeting-2019-in-stuttgartgermany/msg3091382/#msg3091382 (https://www.eevblog.com/forum/metrology/volt-nut-meeting-2019-in-stuttgartgermany/msg3091382/#msg3091382)
Title: Re: Ultra Precision Reference LTZ1000
Post by: ramon on June 18, 2020, 04:28:44 pm
Am I the only one that doesn't see any problem?

   niner_007  ->  ΔY = 1.73uVpp  (unkown interval)
   Dr. Frank  ->  ΔY = 1.33uVpp  (** 1 hour interval)

   (** assuming 7V absolute value, and +/- 0.95ppm Δ)

So results doesn't seem too bad considering power cables, and board and DMM placement.
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on June 18, 2020, 04:39:38 pm
Looks like a very good result to me too, but I'm not a voltnut.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on June 18, 2020, 04:51:03 pm
Yes I know that :-+ This is not a serious measurement, just a sanity check. Three or more multimeters (DMM7510 and 3458A) sampling the reference is what I had in mind for the serious measurement, and proper cables and shielding.

The reference used here is an old and unmodified A9 board from an 3458A. DMM7510 is what I had conveniently located near the power supply.

That's a too elaborated approach, which will create new problems.
 
Parallel measurement with several DMMs is unnecessary, complicated, and will give big interference noise from one DMM to the other.
We had this failure recently, during our MM 2020 already, so do not repeat the same mistake.

Keep everything simple, i.e. one good DMM, make a clean setup, do the basic shielding, and then you're done.

Frank
https://www.eevblog.com/forum/metrology/volt-nut-meeting-2019-in-stuttgartgermany/msg3091382/#msg3091382 (https://www.eevblog.com/forum/metrology/volt-nut-meeting-2019-in-stuttgartgermany/msg3091382/#msg3091382)
Not paralleled, I was thinking of switched across 3 or more DMMs with a scanner
Title: Re: Ultra Precision Reference LTZ1000
Post by: MegaVolt on June 18, 2020, 07:06:40 pm
For comparison: I get 850 nV RMS for 1000 samples with NPLC = 5 for direct measurement of Fluke 732a vs DMM7510.
And just 300 nV RMS noise when measuring one Fluke 732a against another a range of 0.1 in the same conditions. And this is completely not caring about shielding using the most ordinary wires from a multimeter.

From this we can conclude that the direct measurement of a good reference voltage source directly against the DMM7510 does not make any sense. Because we only measure the noise of the multimeter :(
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 18, 2020, 09:03:20 pm
Am I the only one that doesn't see any problem?

   niner_007  ->  ΔY = 1.73uVpp  (unkown interval)
   Dr. Frank  ->  ΔY = 1.33uVpp  (** 1 hour interval)

   (** assuming 7V absolute value, and +/- 0.95ppm Δ)

So results doesn't seem too bad considering power cables, and board and DMM placement.

Hi folks,
That discussion is quite interesting now.  :-+

The LTZ is specified as 1.2µVpp noise, which is mathematically equivalent to 420nVrms.
The measurement from niner_007 shows 2µVpp or 700nvrms, if you look more carefully at the cursor position, which is definitely too high, and indicates additional noise.

Typical LTZs compared against a 3458A, or also against a 7510 (which has an LTFLU reference inside!?) only show 150..300nVrms.
A 732A should measure even lower.
Please have a look into the 'DMM noise' measurement campaign, we did a few years ago. You will get a good estimate of the noise figures of the different DMMs.
Maybe the 7510 is more noisy for other reasons, (I don't like the limitation to NPLC 5), I do not remember that precisely any more:
https://www.eevblog.com/forum/metrology/dmm-adc-noise-comparison-testing-project/ (https://www.eevblog.com/forum/metrology/dmm-adc-noise-comparison-testing-project/)


These values depend on the settings, the equipment and the environment, and then also on the quality of the LTZ / DUT and the reference inside the DMM.
So to get comparable results:

1. Averaging time of the DMM: use NPLC 100, or 1.6 .. 2 sec averaging/sampling time for one data point
2. Always use statistics: Take 16 datapoints of NPLC100, note average and StD.
The StD is also equivalent to the rms noise value, on this time scale.
With more and longer averaging data, especially the StD, will be biased by timely or temperature drift effects, or from other noise sources like Popcorn noise.
3. You may distinguish the different noise or (in-) stability effects described above by using Allan Deviation statistics
4. Digitization error/noise: For sub-ppm measurements, at least 0.1ppm resolution @ 10V is required, but the 7510 seems to have 0.5µV only
5. Use a DMM with an equivalently noisy internal reference, like another LTZ1000, or an LTFLU. The real noise figure of the DUT is then about 1/SQRT(2) of the StD
6. Avoid or mitigate external disturbance, like E.M.C. and temperature change, which will both falsify / contribute to the StD value.
7. For precise determination of the absolute value of the DUT, use low e.m.f. cables, and reverse the leads at the DUT to cancel these.

On our MM2020 meeting, we discussed this data evaluation deeply.
Many measurements on the different LTZ1000 circuits (~22EA) showed 500nVrms, or more StD. That was a clear indicator that something was wrong, and these measurements should have been discarded at once.
In the end we identified the root cause(s), so that we could reduce our disagreement of uncertainty between our reference groups from 2ppm to about 0.5ppm.

Scanning the DUT with different DMMs seems like a good idea, but the scanner itself will introduce a lot of e.m.f. errors / noise, or you invest $$$ in a nV scanner.
Notice again, that we're discussing sub-ppm absolute values also.
The other way round, i.e. scanning several LTZs with one DMM, also depends on the quality of the scanner.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: MiDi on June 19, 2020, 04:51:33 am
The LTZ is specified as 1.2µVpp noise, which is mathematically equivalent to 420nVrms.

Usually the rough conversion from peak to peak noise to rms is by dividing by 6.
That would give ~200nVrms for LTZ1000.
Could you please explain the difference?

https://youtu.be/-KcODSYXiZA (https://youtu.be/-KcODSYXiZA)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 19, 2020, 07:09:32 am
The LTZ is specified as 1.2µVpp noise, which is mathematically equivalent to 420nVrms.

Usually the rough conversion from peak to peak noise to rms is by dividing by 6.
That would give ~200nVrms for LTZ1000.
Could you please explain the difference?

https://youtu.be/-KcODSYXiZA (https://youtu.be/-KcODSYXiZA)

The conversion depends on the actual noise waveform, that's  missing in this video also.
If you have sinusoidal noise, instead of that Gaussian noise, then the rms value would be: Upp/(2*SQRT(2)).
For simplicity, I take this as an upper estimate, if a peak-peak value is given.
Btw.: Zener noise is mostly not Gaussian, that's why you can't filter it well.

I prefer the  direct StD measurement over p-p, because that quantity is better defined, or better established in error/stability calculus. DMMs mostly calculate this value.

Also, the formula for the StD is nearly the same as the rms calculation for a random waveform, so giving an estimate for the rms noise for a short observation time.
This will only be the case, if the mean value, i.e. the DC component is zero. That's the reason, why longer observation times will give wrong StD values concerning noise, as drifts will give a non-zero average.

Coming from frequency stability calculation, the Allan Deviation calculus is the best and most accepted method to measure and separate the different noise types  / stability figures.
peak-peak values are also not used there. In the DMM noise project, we had successfully established the Allan Deviation also for voltage noise characterization.

PS: This problem with different types of noise vs. conversion factors of rms <=> pp is briefly mentioned here:
https://www.analog.com/media/en/training-seminars/tutorials/MT-048.pdf (https://www.analog.com/media/en/training-seminars/tutorials/MT-048.pdf)

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on June 19, 2020, 07:24:34 am
Measuring the RMS value usually gives less scattering values compared to the peak to peak numbers. For good peak to peak numbers it would take several test intervals (e.g. 100-1000 points each) and than take some mean.

There can still be some justification of the peak to peak value if one has a large contribution of popcorn (random telegraph) noise. In this case the simple approximate factor 6 does no longer apply.
For the actual use the worst case and thus the peak to peak value may be more relevant.
With more noise source (here at least the external reference and the meter internal reference) the noise gets more normal, so that one can better use RMS and the simple statistics.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on June 19, 2020, 09:56:18 am

Typical LTZs compared against a 3458A, or also against a 7510 (which has an LTFLU reference inside!?) only show 150..300nVrms.


Yes, the DMM7510 has a LTFLU inside.
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg2922618/#msg2922618 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg2922618/#msg2922618)
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on June 19, 2020, 10:37:21 pm
Results seems to be about the same for me on the DMM7510, 100 sample averaging filter, and 15NPLC
Title: Re: Ultra Precision Reference LTZ1000
Post by: dr.diesel on June 19, 2020, 11:07:57 pm
15NPLC

In regards to the lowest noise region of the 7510, from the user manual:

Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on June 20, 2020, 03:39:55 am
Yeah, I mean to try that, I remember the discussion about the weird DMM7510 noise in the DMM noise thread, I have better meters, this one was the closest :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Grandchuck on June 20, 2020, 05:22:36 pm
On our MM2020 meeting, we discussed this data evaluation deeply.
Many measurements on the different LTZ1000 circuits (~22EA) showed 500nVrms, or more StD. That was a clear indicator that something was wrong, and these measurements should have been discarded at once.
In the end we identified the root cause(s), so that we could reduce our disagreement of uncertainty between our reference groups from 2ppm to about 0.5ppm.

Frank
[/quote]

What kinds of issues were identified as root causes?  I will guess that EMI is/was a factor.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on June 20, 2020, 06:22:01 pm
Quote
What kinds of issues were identified as root causes?  I will guess that EMI is/was a factor.

Turned out to be a simple issue with one button in the wrong place. Guard button on K3458A was in "low" position and not in "open". Guard of the cable was connected to case of the reference and Guard jack of K3458A, but on GND on K2002. This created a Guard loop, which created the differences.
I was able to recreate this problem today. Having multiple meters in parallel can then influence the readings.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on June 20, 2020, 06:42:37 pm

A "Guard Loop" - there's a new one! :D
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 20, 2020, 07:31:33 pm

What kinds of issues were identified as root causes?  I will guess that EMI is/was a factor.

The 2nd definite effect were two 3458A in parallel. They were not triggered synchronously, therefore the charge injection of one would every time influence the readings of the other, and vice versa.

The StD value was extremely high, in the µV range, instead of 150..250nV, as usual.
Shows, that StD can be used as a sanity check, provided you have comparable or identical situation.
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on June 20, 2020, 07:53:02 pm

What kinds of issues were identified as root causes?  I will guess that EMI is/was a factor.

The 2nd definite effect were two 3458A in parallel. They were not triggered synchronously, therefore the charge injection of one would every time influence the readings of the other, and vice versa.

The StD value was extremely high, in the µV range, instead of 150..250nV, as usual.
Shows, that StD can be used as a sanity check, provided you have comparable or identical situation.
Frank

Interesting.  I have tried 4DMM in parallel but they were all triggered in sync via GPIB, that might be why I didn't see any particular problems with that method.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on June 21, 2020, 01:08:35 am
Over 1 hr of data, 2.0189uVpp, 394nV std
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on June 21, 2020, 03:46:57 pm

What kinds of issues were identified as root causes?  I will guess that EMI is/was a factor.

The 2nd definite effect were two 3458A in parallel. They were not triggered synchronously, therefore the charge injection of one would every time influence the readings of the other, and vice versa.

The StD value was extremely high, in the µV range, instead of 150..250nV, as usual.
Shows, that StD can be used as a sanity check, provided you have comparable or identical situation.
Frank

Std. Dev. of 1 µV would mean ~6µVpp. If you further assume 6nApp from the 3458A that would lead to an output impedance of 1k.

I think the GUARD loop is much more likely to explain the high std. dev.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on June 21, 2020, 08:44:47 pm
How do you synchronize multiple 3458A in parallel, that’s not possible is it? Why not scan the inputs with a scanner? What’s paralleling giving you? nV scanner are available, relays with low EMF are also available or can be constructed
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on June 21, 2020, 08:55:21 pm
How do you synchronize multiple 3458A in parallel, that’s not possible is it?

External Trigger, GPIB GET (That's what I'm using most of the time)


Why not scan the inputs with a scanner? What’s paralleling giving you? nV scanner are available, relays with low EMF are also available or can be constructed

Sometimes you want to compare if some disturbance was caused by the DMM or the source. And in these cases you want to integrate over the exact same point in time. INL comparisions are such an example.

Reasonable scanners are also not available to everyone.
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on June 21, 2020, 09:32:31 pm
The conversion depends on the actual noise waveform, that's  missing in this video also.
If you have sinusoidal noise, instead of that Gaussian noise, then the rms value would be: Upp/(2*SQRT(2)).

Sorry, for beeing that late with my comment. But this is a fundamental topic and worth to discuss it deeper, I think.

In the video, they're talking about noise which creates a bell curve in the histogram and that is it what matters. The distribution is important not the signal over time. If you take all the values of your sinewave and mix the order of the values it will result in the same RMS value. Therefore, it doesn't make sense to talk about sinusoidal noise. It is more important how the shape of the histogram looks like.

The histogram of a sinewave might make sense as a worst case, because the highest abundance is at the maxima (makes absolute sense if have a look at the derivative), but that is a very unlikely shape for noise.


The 1/f (pink) noise means that there isn't only uncorrelated noise (white), but also some correlated noise. Which means the values you measure are dependend from the past (finite correlation length).

It is also wrong to say, that a gaussian histogram indicates white noise. The histogram is just the probaility density function and 1/f has also a bell shape.


@Frank: I'm absolutely sure that everything from that is known by you, I just want to make it more clear, that the signal over time is less important than the appearing values.


Edit: The standard formula for the standard deviation will give also the correct numbers, if you feed in a sinewave. There is no need to differentiate here.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on June 22, 2020, 07:14:36 pm

The 1/f (pink) noise means that there isn't only uncorrelated noise (white), but also some correlated noise. Which means the values you measure are dependend from the past (finite correlation length).

It is also wrong to say, that a gaussian histogram indicates white noise. The histogram is just the probaility density function and 1/f has also a bell shape.
With 1/f noise it depends on the details. One may have a bell shaped histogram, but the histogram can also look quite different (e.g. with dominant popcorn noise - which also gives an approximately 1/f spectrum). If the 1/f part is more like some random walk the measured histogram may also look different from the gauss bell curve. It is possible to a bell shaped histogram with 1/f noise, but this is not always the case.

The histogram and frequency spectrum are kind of complementary. So one would need to look at both - there is no way to convert one to the other.
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on June 25, 2020, 10:24:26 am
I played with some simulated random walks. To evaluate "how wrong" 6x the standard deviation compared to the "real" peak to peak value is, I created 1000 random walks. Every walk was a million steps long. I calculated the standard deviation and the peak to peak value for every walk and compared them.

The mean ratio of 6x std. dev / pp was 1.38 (+/- 0.19). Which means you will almost ever overestimate the peak to peak value by taking 6x the standard deviation in the case of a random walk.

Btw.: The standard error of the standard deviation is S/sqrt(2(n-1)) which means you will already have 0.18 sigma (relative to a standard deviation of 1) if you only take 16 measurments with your 3458A.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on June 25, 2020, 02:17:44 pm
What happens to the stdev/pp ratio for real (shorter) measurement series?

For example in my current observation of two LTFLU 10 V references i see a stdev = 0,029 ppm of the daily averages, so times 6 gives an expected pp of 0,174 ppm. After 38 days i have an observed pp of 0,11 ppm (minimum -0,065 ppm, maximum 0,046 ppm). So that gives a ratio of about 1.6 (overestimation of pp by 6x formula). In this case the factor seems to be more like 4 instead of 6.

Maybe this case is not a random walk, but something else. Maybe air pressure changes.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on June 25, 2020, 03:27:11 pm
Popcorn noise can give a rather low ratio for peak to peak values relative to RMS value.
Some periodic background (e.g. day / night temperature or pressure variations could also give a small ratio).
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on June 25, 2020, 03:37:45 pm
What happens to the stdev/pp ratio for real (shorter) measurement series?

For example in my current observation of two LTFLU 10 V references i see a stdev = 0,029 ppm of the daily averages, so times 6 gives an expected pp of 0,174 ppm. After 38 days i have an observed pp of 0,11 ppm (minimum -0,065 ppm, maximum 0,046 ppm). So that gives a ratio of about 1.6 (overestimation of pp by 6x formula). In this case the factor seems to be more like 4 instead of 6.

Maybe this case is not a random walk, but something else. Maybe air pressure changes.

Regards, Dieter

Maybe it was a bit misleading to say "Seems to me, that there is no need to take values lower than 6 to estimate the pp noise" (Therefore, I deleted that sentence in the post above). What I wanted to say was: 6 is already conservative. It is most likely less than 6x std. dev. (6 / 1.38 = 4.34)
Title: Re: Ultra Precision Reference LTZ1000
Post by: mrflibble on June 25, 2020, 03:52:56 pm
I played with some simulated random walks. To evaluate "how wrong" 6x the standard deviation compared to the "real" peak to peak value is, I created 1000 random walks. Every walk was a million steps long. I calculated the standard deviation and the peak to peak value for every walk and compared them.

Quick note regarding peak-to-peak value of a simulated random walk.
You may also want to try:
- do random walk of N steps, storing each location x[n] at step number n.
- sort all x[n]
- for maximum, take sorted list entry at index floor(0.95*N)
- for minimum, take sorted list entry at index floor(0.05*N)

Notation: x[n]is location at step number n, assuming start position x[0]=0.
Adjust the (0.05, 0.95) constants to taste.

Similar story for the mean value. Since you sorted that list already, you might as well take the median, so x[ floor(N/2) ].

PS: request from those of us who do find this sort of thing interesting, but are a but strapped for time... I did not read the entire thread today, so I'm sorry if I missed the context that would have made it obvious... But: for walk_example_1 and walk_example_2, I couldn't get the information of what it was. I.e, is this a single trial of N=1E6 steps. (yes). Or is this the sum of all M=1E3 trial runs. (No). To be sure it was a single trial the image filenames actually were more informative. That  and eyeballing the number of bins ~ 50. And eyeballing the area of the histograms .... "mmmh, if I put this blob here and that blob there I get an about level line around the count of ... 20000. Okay. About 50 * about 20000 equals about 1E6. Check, it is a single trial. Or you could just put that information in the plot title. Just a suggestion. I am as guilty of forgetting to do this as the next person. Reason I started doing proper annotation, titles and whatnot even in my own projects that never see the light of day: yeeeaaaars from now my future self will thank my current self for making it easy to follow what the hell I was doing at the time. ;)

Oh yeah, random other note: (PPS? :P ) If you want to solve for the expectation value of the (min,max) values of a random walk you can use the infinity-norm of the x-vector, where again x[0] is start, and X[N] is end position. So in this case x is an (N+1) dimensional vector. max(x) == inf-norm(x). Using that you can solve for min,max analytically. Or do it the proper aka lazy way and just solve for max, then do some handwaving and claim symmetry relation between min & max.

Something similar can be done for the (0.05*N, 0.95*N) values, but that might get too involved for a quick experiment. If interested, lookup "order statistics".

Related linkies:
https://en.wikipedia.org/wiki/Norm_(mathematics)#Maximum_norm_(special_case_of:_infinity_norm,_uniform_norm,_or_supremum_norm)
https://en.wikipedia.org/wiki/Order_statistic
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on June 25, 2020, 04:01:49 pm
@mrflibble: Thanks for the hints. I already played with the sorted "path" to estimate only 99.73% (6 sigma) for peak to peak. But the difference is so small that I didn't cover it in the first post. 95% would only be equal to 2 sigma -> factor 4 instead of 6.

You're absolutely right with the shown examples. I promise to make better titles in the future ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on June 27, 2020, 05:37:55 pm
When i was thinking about my data and about this difference between peak-to-peak expected from single point standard deviation and observed peak-to-peak values, maybe this is caused by looking at the difference of two reference voltages.

I guess the rare peak values of one reference will "collide" with the rare peak values of opposite polarity of the other reference even more rarely. So one would see 1.4 * the RMS of one reference but only 1 * the peak-to-peak values of one reference. Such a model could explain my observation until now. Maybe the expected higher peaks will appear after taking a very long data series with hundreds of points.
In other low noise tests where one device (meter) is much better than the other (DUT), the proposed factor 6 should hold better.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on June 27, 2020, 06:54:26 pm
Hi Dieter,

I'm not sure if you had that in mind, but I think your example is something like two normal distributions (one for every reference) which have similiar properties. Therefore, I made two distributions with the same µ and sigma (0 and 1). It seems to me, that the ratio between peak to peak and the standard deviation hasn't changed. (And I think that was expected because of the central limit theorem)

Best regards
Philipp
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on June 27, 2020, 08:53:38 pm
Yes, that's what is expected, except i was wondering how long it will take to observe those peaks. And somehow i think it should depend on bandwidth. I could try what i get when looking at 24 * 38 hourly averages instead of 38 daily averages.
Maybe i should just be patient and wait for the first 2000 hours as everybody else.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Grandchuck on September 20, 2020, 03:15:39 pm
There was a very interesting post by TiN on April 20 regarding his design and development of a reference board for one of his 3458As:

"I've swapped reference in experimental 3458A to explore the low-noise theories. It went with few trap pitfalls, but meter is running now and logging first data."

How is that experiment proceeding?  Any results that can be shared yet?
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on September 21, 2020, 03:59:24 pm
There was a very interesting post by TiN on April 20 regarding his design and development of a reference board for one of his 3458As:

"I've swapped reference in experimental 3458A to explore the low-noise theories. It went with few trap pitfalls, but meter is running now and logging first data."

How is that experiment proceeding?  Any results that can be shared yet?
Is this the board with 4 LTZ1000's on it?  If so that did look interesting to see what kind of data it produced.

Bill
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on September 21, 2020, 05:02:49 pm
So far noise data aligns with expectations on QVR ref.

Battery power:

(https://xdevs.com/doc/xDevs.com/QVR/test_noise_qvr2b/xDevs_noise003.png)

SMU power:

(https://xdevs.com/doc/xDevs.com/QVR/test_noise_qvr2/xqvr2_test1028.png)

But once installed in 3458A it brings havoc, most likely due to huge power consumption (190mA +15V, 20mA -15V) and heat dumped next to resistance current source circuits and DC preamp. Half of the ranges of DCV and resistance are ruined after transplantation.  >:D
I did not expect it to be easy plug and play project anyway, more problem to see, better learning to get ..

Calibration report (https://xdevs.com/doc/HP_Agilent_Keysight/3458C/cal/XCR_XDEVS_3458CQ_GPIB11_PRECAL_MAY_31_2020.pdf).

I want to try with ref sitting externally to meter and with different power/compensation schemes, but had no time to do that yet.  :palm:

To remind - single goal of that design is to provide lowest noise 7V reference possible, NOT the ultra-stable or battery powered DC standard. In fact I'd expect annual stability be much worse than usual 2ppm/year that even standard 03458-66509 can do after oven mod.  :popcorn:
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 21, 2020, 05:41:54 pm
Why does it take so much power ? I would expect way less than 50 mA for a LTZ1000 reference circuit.

Not directly related to high precision, but what would be the minimum current needed ? I would expect some 3 mA for the zener (a little less than normal) some 0.5 mA for the OPs and transistor currents and than the heater, depending on the environmental temperature. For power conserving one could have the heater control transistor(s) not at the far edge of the board, but close to the LTZ to also help heating. At low current the transistor has more power than the resistive heater.
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on September 21, 2020, 07:13:55 pm
Despite the power and heat it's just such a neat idea... perhaps you could extend the connections for the PCB outside the case and build a little case for it so it can stabilize in there.  It seems you really don't have to fool the 3458A at all since it boots with it inside.   :-+  I'd be curious to know if not having the regular reference inside the case at all would have any effect the opposite way ie. not hot enough???  One things for sure... it was one of the coolest looking reference pcb's I've seen in while.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Grandchuck on September 21, 2020, 08:28:08 pm
Why does it take so much power ? I would expect way less than 50 mA for a LTZ1000 reference circuit.


Four LTZ1000s.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on September 22, 2020, 03:34:28 am
Why does it take so much power ? I would expect way less than 50 mA for a LTZ1000 reference circuit.

Not directly related to high precision, but what would be the minimum current needed ? I would expect some 3 mA for the zener (a little less than normal) some 0.5 mA for the OPs and transistor currents and than the heater, depending on the environmental temperature. For power conserving one could have the heater control transistor(s) not at the far edge of the board, but close to the LTZ to also help heating. At low current the transistor has more power than the resistive heater.
A lot more than that, I measured an LTZ1000 board, taken directly from a 3458A, using 30mA at 11V, maybe the heater temperature being higher could explained it, but it seems the heater circuit uses a lot of power
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on September 22, 2020, 07:37:13 am
The A9 board from the 3458 is known to run at a rather high temperature. Still 30 mA is quite a bit, as the heater power goes up with the square of the current. TiNs is at nearly 50 mA per LTZ1000 so higher than that. Is that because of more heat loss through the board ? With a highly conductive board I would definitely prefer the A version.

Another part could be the heater resistance. There is quite some tolerance range in the data-sheet. A lower resistance heater would naturally need more current. So not all chips would be the same. The variations in the heater resistance should also effect the value for the "400K " TC compensation resistor. So not such a surprise that the datasheet example 400 K does not fit all.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on September 22, 2020, 08:51:07 am
TiNs 4 boards use about 170mA in total for heating, i.e. 42mA each LTZ.
I don't remember, which type he used (A, non A), and which oven temperature.

I recently assembled my first two LTZ1000A references at about 52°C (12k/1k) inside a thermally isolated tuner box, LTZs again not individually isolated, and each consumes 18mA @ 12V in total only. All my non A references at the same oven temperature consume about 23mA in total.

So I really wonder, what the hybrid of TiN is doing ...
Probably a completely different type of reference, off from the LTZ1000, is needed to really achieve lower noise in the 3458A.

Frank

PS: At 36:22min in his video you can see, that he uses the A version, and 13k/1K oven setting, i.e. about 70°C.
42mA is far too high, but maybe the stabilizer and averaging circuits consume a noteworthy part of that.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on September 22, 2020, 08:58:58 am
Does the reference board have a temperature sensor? In order to reduce power consumption one could wrap the board to protect it from the fan air flow. An easy test, and then you know whether it's the heaters. Later one can think about whether it's a problem for low thermal EMF to leave the whole board running hot.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Pipelie on September 22, 2020, 09:38:00 am
@TiN
time to wake up and reveal the answer!

As far as I know, to achieve ultra low noise, TiN isn't just put 4 LTZ in parallel he also increase the Iz of LTZ significantly. :popcorn:
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on September 22, 2020, 10:02:30 am
@TiN
time to wake up and reveal the answer!

As far as I know, to achieve ultra low noise, TiN isn't just put 4 LTZ in parallel he also increase the Iz of LTZ significantly. :popcorn:
Probably not... if Illya has dimensioned the neg. currents correctly, to exactly compensate the reference currents,
then each Iz should be about 4mA.
PS: In the video, 120 Ohm are probably used for the zener current, that gives typically less than 4mA Iz

190mA minus 20mA then gives  about170mA for the 4 heater currents, plus the summing OpAmp. It's that easy.
The oven temperature can be measured by digitizing the startup voltage of the BE diode of the reference transistor.
This changes by -2mV/K, so its difference between cold and hot state gives quite precisely the final oven temperature.
A pity, that nobody else determines the real oven temperatures.
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on September 22, 2020, 06:25:04 pm
So I really wonder, what the hybrid of TiN is doing ...

I fear the ceramics together with short legs is doing a good cooling job ...

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: KT88 on September 22, 2020, 07:23:40 pm
Quote
I fear the ceramics together with short legs is doing a good cooling job ...
...but may cause some mechanical strain on the other hand side...
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on September 23, 2020, 07:08:03 am
So I really wonder, what the hybrid of TiN is doing ...

I fear the ceramics together with short legs is doing a good cooling job ...

with best regards

Andreas
I do wonder if a ceramic PCB is a sensible approach for an LTZ1000 reference, when the reference is doing the temperature stabilization, typically Fluke et all use a ceramic PCB, with a non heated reference, or with the heater heating the entire ceramic PCB, no? Maybe not much better can be done from what was already achieved here, prior, with standard PCB construction. Would be interesting to see thermal pictures of the ceramic PCB, I think someone has posted them before.
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 23, 2020, 07:32:13 am
It's Rogers, not a ceramic PCB, so thermal conductivity is expected not to be that great compared to real ceramics.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 05, 2020, 03:08:53 pm
I would like to summarize about the newly built two LTZ1000As, which are the first ones to me, after 7 non-A types. At first, these references will be powered from a common linear 12V supply, that are about 11.5V for the circuit.

To mitigate random 'jumpers' and for pre-ageing of the die cast, both LTZ chips got a high temperature Burn-In. I can't disclose any details.
I only assembled the reference and a buffer amplifier, w/o 10V amplification. The output got a  ferrite core to suppress external noise.
The mechanical assembly is similar to the previous 5 LTZ1000 CH. For thermal insulation, I salvaged 3mm thin Polystyrol from Doner Kebab boxes, which is readily available, and can be cut much more nicely with a scalpel, and also saves some space.
Its purpose is to mitigate fast thermal changes and create an isothermal chamber inside the tuner box to mitigate thermal e.m.f.  for the whole assembly, but not only for the LTZ chip, like the plastic caps do in the hp3458A reference. The legs of the A chips were not cut short at all.

Temperature difference between ambient and internal is about 2°C, due to the 400K/W thermal resistivity, whereas the non A chips create 7°C difference.
All my references use a 12k/1k divider. By choosing 100µs sampling interval on my 34465A, I precisely measured 53.0 and 51.6°C oven temperatures. The chip is heated up within 3 seconds, and the supply current is 18mA only.
Initially, I also experimented with 12.5k/1k to account for the 10°C self heating of the A type. This gives 10°C higher oven temperatures, i.e. between 60..65°C. A 13k/1k divider probably gives over 70°C, in contrast to the data sheet.
Therefore, the 12k/1k gives best drift performance of < 1ppm/yr., similar to any other standard references like 732X and Datron 7000.

I measured the 12h stability of both references, also to determine some noise parameters (1h and 10min.). The first measurement started at power on and indicates that the whole assembly needs about 15min for stabilization to < 0.1ppm of nominal.

The stability is mostly at +/- 0.1ppmpp, at certain 1h time frames even +/-  0.05ppmpp or 0.028 ppmrms, which seems to be less than the other LTZs.
The references probably need some further settling time to deliver better short term stability.

As you can see, I used mixed types of PWW (econistor from G.R.) and BMF (FLCY from AE) resistors, but did not determine any T.C.s upfront.
The overall T.C.s were 0.02 and 0.03 ppm/K respectively, w/o any additional compensation resistor R9.
The measurement for LTZ#7 with 51,6°C oven temperature is quite interesting, as at about 40°C internal temperature the oven regulation fails, i.e. the low T.C. of the regulated oven develops abruptly into the +50ppm/K of the unregulated reference. This confirms that the self heating is about 11°C.

'A' types at nominal 50°C oven temperature can be used up to about 38°C room temperature 'only', but this is no disadvantage in a standard lab environment between 18..28°C.

Frank.
Title: Re: Ultra Precision Reference LTZ1000
Post by: babysitter on October 05, 2020, 06:45:56 pm
Hm, do I glimpse a bit of inspiration from my box? :)
How did you wire the ferrite toroid - common mode choke? source material?

BR
Hendi
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 05, 2020, 08:11:31 pm
All my references use a 12k/1k divider.

Hello Frank,

You simply had luck that the voltage of the LTZ (7.1V) is more at the lower end of the tolerance.
With 7.3V zener voltage the oven would fall out of regulation already at 30 deg C.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 05, 2020, 10:27:07 pm
Hm, do I glimpse a bit of inspiration from my box? :)
How did you wire the ferrite toroid - common mode choke? source material?

BR
Hendi

Hello Hendi ,
yes of course  ;)
it's wound common mode, like a CAN bus choke, and it's the cheapest lacquered TDK ferrite (B64290L38X830) I got from voelkner/Conrad, about 1.8µH, or so.

best wishes to Aschebersch!

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 05, 2020, 10:34:14 pm
All my references use a 12k/1k divider.

Hello Frank,

You simply had luck that the voltage of the LTZ (7.1V) is more at the lower end of the tolerance.
With 7.3V zener voltage the oven would fall out of regulation already at 30 deg C.

with best regards

Andreas

Hello Andreas,
I figure out what you're referring to, i.e. higher reference voltage gives lower oven temperature, 200mV more give about 8°C less.. theoretically.. as I can't discover this systematicity in the data I've summarized. The UBE of the temperature sensing transistor will also vary, and therefore, it's not out-and-out that 7.3V reference voltage really gives about 42°C.

And it's no luck at all, because, I determine the final oven temperature for each of my references.  ;D
If I'd find a too low oven set point, I could assemble a 12.5k/1k divider as well.. a simple, variable, fine tuning circuit for the oven temperature, as well for the T.C. would be great.

Have you done that measurement on your references as well, especially on the one with 7.3V?
Your 34401A can also do the job!  :-+

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: openloop on October 08, 2020, 10:55:48 pm
You guys, it seems, have a lot of references sitting around...   ;D

Have you tried to do a Battle Royale between them?  :box:

Like take 3 of those, power them from separate batteries, tie 0 terminals together so they form a Benz-like star, let them warmup, of course.

Now voltages between tips should be less than 100mV (1V, if you're unlucky). In that range even my humble 34401As are precise enough (like 60nV stddev).
Take two DMMs (3 for sanity checks) and log the voltages between neighboring tips (with simultaneous triggering) for several hours.

Now you have 3 rows of data (third is the difference between first two, if only 2 DMMs used). 
Now, estimate the variances. Each of those 3 variances is a sum of 2 corresponding variances of your references.
Now you have 3 unknowns and 3 equations so you can solve for individual variances!
Maybe rotate the setup and redo to see if repeatable.

Thus you can find the quietest reference of all.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on October 09, 2020, 07:59:41 am
Many of those self built references have issues with their outputs: Since they have OpAmp output pins directly or almost directly connected to the binding posts, eventually connected with some meters of cable, they are sensitive to RF and to capacitive loads. Often hobbyists found it difficult to wire more than one reference and more than one voltmeter in one circuit. With a more robust reference output circuit that would not be a problem at all and the proposed difference measurement would be the way to go.

When drawing the Keithley 213 4x DAC schematic i saw how to implement a stable output circuit that includes and drives a 100 uF buffer cap.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: MegaVolt on October 09, 2020, 10:25:26 am
When drawing the Keithley 213 4x DAC schematic i saw how to implement a stable output circuit that includes and drives a 100 uF buffer cap.
Will you share your find with us?
Title: Re: Ultra Precision Reference LTZ1000
Post by: openloop on October 09, 2020, 12:19:23 pm
Dieter,

Quote
Often hobbyists found it difficult to wire more than one reference and more than one voltmeter in one circuit.

Because references are independently battery powered and connected in only one point there are no ground loops or some such.
In my case, two DMMs are well grounded and were connected to the circuit with two 15cm long twisted pairs.

Worked fine.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on October 09, 2020, 01:37:40 pm
OK, here is the Keithley DAC output section i mentioned. A similar buffer with output filter including a large buffer cap can be used for a lab voltage reference with binding post interface.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: openloop on October 09, 2020, 01:47:41 pm
After thinking about it some more, I must admit, there is asymmetry in the connection of 2 DMMs. That's one of the reasons why I mentioned rotating the setup.
In my case though, outputs are driven by LTC2057s and they seem can handle capacitive load of 2 DMMs just fine.

Technically, variance measurement does not require simultaneous acquisition.  One can collect variance data for for each pair separately and then solve the equations.
But that makes the problem of how long to run the experiment even more acute. Because it's not clear at what time scale LTZ1000 can be considered ergodic enough.
You know, running into a "Black Swan" problem.
In my case, one of those happened when on one of the references buffer LTC2057 went bad: suddenly started drawing non-trivial amount of bias current...
Title: Re: Ultra Precision Reference LTZ1000
Post by: e61_phil on October 09, 2020, 02:42:53 pm
You have to keep in mind, that the inputs of the DMM aren't perfectly the same. The HI input is really high-impedant, but the LO input is normally connected to the whole GND of the floating electronics (higher leakage and much more capacitance).

A couple of weeks ago, I made some experiments with my SR1010-1k and the 3458A. I applied 10V to 10 resistors of the SR1010-1k in series (4W connection sourced by Fluke 5440B). In the first experiment I connected the 3458A LO to the lowest resistor (also LO from the 5440B) and the 3458A HI to the middle of the chain. After that I reversed the connectors on the 3458A and I measured a difference of a couple of µV. Unfortunately, that made it impossible to make the linearity test I was intended to do.
I also played around with the Guard, but that didn't improve much.

What I just wanted to say: You really need proper low impedant output for such difference measurements.
Title: Re: Ultra Precision Reference LTZ1000
Post by: rigrunner on October 12, 2020, 11:10:30 pm
I would like to summarize about the newly built two LTZ1000As, which are the first ones to me, after 7 non-A types. At first, these references will be powered from a common linear 12V supply, that are about 11.5V for the circuit.

Nice to see the boards in use  :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 14, 2020, 04:59:51 am

it's wound common mode, like a CAN bus choke, and it's the cheapest lacquered TDK ferrite (B64290L38X830) I got from voelkner/Conrad, about 1.8µH, or so.

Hello Frank,

so 1 winding on each side? (cannot see it exactly on the photo).

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: doktor pyta on October 14, 2020, 09:10:55 pm
https://www.changpuak.ch/electronics/Arduino-Shield-BHUMI.php (https://www.changpuak.ch/electronics/Arduino-Shield-BHUMI.php)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on October 14, 2020, 09:14:50 pm

it's wound common mode, like a CAN bus choke, and it's the cheapest lacquered TDK ferrite (B64290L38X830) I got from voelkner/Conrad, about 1.8µH, or so.

Hello Frank,

so 1 winding on each side? (cannot see it exactly on the photo).

with best regards

Andreas
yes, quite randomly.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on October 14, 2020, 09:46:35 pm
https://www.changpuak.ch/electronics/Arduino-Shield-BHUMI.php (https://www.changpuak.ch/electronics/Arduino-Shield-BHUMI.php)

Its a pity.
All those costly parts and then the temperature setpoint with 11:1 (below room temperature).
And a switchmode supply.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: openloop on October 25, 2020, 12:51:18 am
Quote
All those costly parts and then the temperature setpoint with 11:1 (below room temperature).

I've crunched some numbers, for the fun of it.

And, according to two dudes named Ebers and Moll, to keep temperature the same as for 12:1 ratio, for 11:1 R3 needs to be 13K7  :o

I do not know what consequences of increasing collector current to .5mA will be. Will the whole thing stay in regulation? Will somewhat increased self-heating of the temperature sensing transistor screw things? Will the additional voltage drop on pin7 be noticeable?

On another hand, dividers can be made out of them cool LT5400s ...  8)
Title: Re: Ultra Precision Reference LTZ1000
Post by: uski on October 26, 2020, 05:00:51 am
Hi,

Did anyone hear about a group buy of LTZ1000A ?
It is out of stock anywhere but AD sells directly for $54.50 each for a pack of 20.

Any other way to get my hands on one ?
If someone wants to make a group buy I'd happily order one.

Or if multiple are interested maybe we could get a group buy going ?

Thanks
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 22, 2020, 07:43:49 pm
Hello,

I finally have adjusted the T.C. of my LTZ#9 (LTZ1000 non A version)

first measurement on 03.11.2020 without R9: gives -128 ppb /K
from my rule of thumb (derrived from the LTZ1000A measurements) that each 1 Meg resistor compensates  +40 ppb/K
So I tried a 330K resistor.

measurement on 06.11.2020 shows clearly some over-compensation giving +31 ppb/K
So it seems on the LTZ1000 (non A) I have to calculate with 53 ppb/K for each 1 Meg resistor.

The first measurements with 402K  (e.g. 10.11.2020) where somewhat drifting so I had to wait until the measurements stabilized.
(perhaps I shouldnt have used a cheap 1% metal film resistor)

Now on 21.11.2020 the final result is 1 ppb/K in average. But of course due to the non linearity introduced by the temperature compensation there is some "Box T.C." of around 45 ppb/K over the temperature range of 12-38 deg C measured on top of the housing of the LTZ.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on November 23, 2020, 08:11:37 am
The drift only looks bad because the scaling of the graph changes. In absolute numbers the curve without the resistor looks similar. One can also see that the resistor only has a really small effect on the voltage. So drift of the compensation resistor (even with cheap 1% resistors) should not be an issue.
The visible drift and hysteresis is more from the other resistors. Chances are this is still in the early hours for the parts and thus still in the initial drift after soldering / cleaning.

The compensation is nonlinear. So the right size of the compensation resistor would depend on the heater power / set temperature and likely also the thermal design.  With a higher set temperature and thus more heater power the heater voltage will change less with temperature and thus a smaller compensation resistor is expected. Similar more isolation could prefer a smaller resistor.
I would expect the right compensation resistor to be about inverse proportional to the heater voltage at a fixed temperature.
Title: Re: Ultra Precision Reference LTZ1000
Post by: openloop on November 26, 2020, 03:03:24 am
Andreas,

What is the time scale of your temperature sweeping graphs?
I mean, what is the total elapsed time?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 26, 2020, 05:33:19 am
Hello,

Setpoint temperature ramp speed is 0.12 deg C / minute.
(Actual temperature at the top of the aluminium housing of the PCB follows more ore less).
I usually start from 25 deg C down to cold, ramp up to hot and do another cold phase until minimum reaching 25 deg again.
In this case I did another hot phase and switched off the cooler during last phase.

Attached a different graph over time from first and last measurement.
So total time takes 1500 - 1900 minutes (so 25 - 30 hours) in this case.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on November 26, 2020, 08:34:40 am
Hello Andreas,

we recently had a discussion about the temperature slope the other day. Even though I use 0.1K/min for the slope, which is the minimum that my Arroyo 5305 can do automatically, this is still to large to reach thermal equilibrium across the board and components. TiN uses a maximum slope of 0.02K/min and a minimum slope of about 0.0084K/min, so we are talking about a factor of 10 smaller value. This is achieved by a software controlled temperature profile and available here:

https://xdevs.com/guide/teckit (https://xdevs.com/guide/teckit)

GitHub repository:
https://github.com/tin-/teckit (https://github.com/tin-/teckit)

My explaination of the "open eye" (or hystersis if you want to call it like that) in your but also my measurements is, that thermal resistance and capacitance come into play if the slope is too fast. Thus, run up and run down are different. Solution, decrease the slope.

One thing that I don't like about the standard datasheet circuit of LTZ is, that tc-compensation and amplification to 10V are correlated and not independent from each other. This (let's call it) issue was solved in a commercial product of a voltage reference though.

By the way: I found two documents related to pre-aging of LTZ1000 provided by Cern:

1101699_V1_Burn_in_of_LTZ1000.pdf  (https://www.eserviceinfo.com/downloadsm/126908/CERN_1101699%20V1%20Burn%20in%20of%20LTZ1000.html)

1070495_V1_HPM_equipment_description_DS22bit.pdf  (https://www.eserviceinfo.com/downloadsm/117047/.%20Rare%20and%20Ancient%20Equipment_1070495%20V1%20HPM%20equipment%20description%20DS22bit.html)

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on November 26, 2020, 08:54:17 pm
Hello branadic,

you are right (at least for a normal lab).

But in my case in summer I have up to 2 deg C / hour temperature rising. (from 22 deg to 33 deg C in a few hours).
So testing at 7.2 deg C / hour is only testing something like the "worst case".

On the other side: my battery pack within the LTZs limits the test time to a maximum of ~2 days.
So setting the ramp speed to below 0.05 deg C / minute is not really a option.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 01, 2020, 12:01:47 am
Hey folks, I finished the layout of my LTZ1000 reference module. It is built around an 3458A reference form factor. 6 layers, uses mostly through hole parts, the divider is VHD200, the other sensitive resistors are VHP202Z, I also use MKP capacitors, and plan on using the free space for a few LMT70 temperature sensors, a USB interface and microcontroller for tracing and calibration.

I appreciate any feedback on the layout, specially around grounding.

P.S. each cell in the picture is 1mm, so that makes the thickest trace 1mm, an the thinnest trace 0.4mm.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 01, 2020, 05:47:31 am
Hello,

for me it looks like you have to populate the LTZ on the bottom side of the PCB.
Is this intended?

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 01, 2020, 06:04:20 am
it is not meant to be populated on the bottom, perhaps orientation is not visible well
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 01, 2020, 06:10:50 am
I'm wondering if there is any concern in routing sensitive signal path in the inner layers, or whether it should always be routed on the top or bottom. Maybe surface contamination on the inner layers can't be as well controlled as on the top layer or bottom layers, which can receive a good cleaning at any time, hmm? Or am I overthinking.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 01, 2020, 07:28:19 am
perhaps orientation is not visible well
ok my fault.
I expected the nose on the top side of the PCB.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 01, 2020, 07:58:59 am
I'm wondering if there is any concern in routing sensitive signal path in the inner layers, or whether it should always be routed on the top or bottom. Maybe surface contamination on the inner layers can't be as well controlled as on the top layer or bottom layers, which can receive a good cleaning at any time, hmm? Or am I overthinking.

The traces are to a large part protected by the solder-mask. So surface leakage is mainly at the solder joints, and these have to on the outer layer anyway. The circuit is not that high in  impedance for most parts - so leakage is not very critical, it is not about pA currents.
The layout looks nearly like 1 layer, so there is essentially no need or advantage to go with 4 or more layers. 2 layers should be good enough. More layers add to possible mechanical stress in the board.

The traces are relatively wide and this way give quite some heat conduction paths around the LTZ1000.
The ground star point is a tricky part. Electrical is may be still OK with the relatively thick path to LTZ1000. Thermally this is not a good solution.  The alternative solution is to have the critical low side sense directly from the pin of the LTZ1000 and keep the rest separate with thinner traces.  It depends on the circuit around the reference (and off the board) how the ground connection should be.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Noopy on December 01, 2020, 07:45:05 pm
Any LTZ1000-fans here?  ;D

By popular request I have "designed" a LTZ1000 coffee cup:

https://www.redbubble.com/de/i/tasse/Referenzspannungsquelle-LTZ1000-von-Richis-Lab/63614214.9Q0AD (https://www.redbubble.com/de/i/tasse/Referenzspannungsquelle-LTZ1000-von-Richis-Lab/63614214.9Q0AD)

 8)

The LTZ1000 clock looks quite interesting...  ;D
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 02, 2020, 05:16:31 am
I'm wondering if there is any concern in routing sensitive signal path in the inner layers, or whether it should always be routed on the top or bottom. Maybe surface contamination on the inner layers can't be as well controlled as on the top layer or bottom layers, which can receive a good cleaning at any time, hmm? Or am I overthinking.

2 layers should be good enough. More layers add to possible mechanical stress in the board.
What’s the mechanism by which that would happen? That seems surprising to me. I went for more layers just for layout neatness. This is not meant to be efficient economically, I am using VHD200 after all, which is overkill for an LTZ1000 design with its high ppm attenuation factor.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 02, 2020, 08:04:31 am
Mr. Kleinstein, made few updates, how's this? Replaced SMD diodes with thru hole diodes. Added ground plane for VCC and AGND. And made traces smaller. I think I could also add equalized "ballast" thermal pads for each trace around the LTZ1000 as well ala Datron. As is, does it lift your concern about thermals?

With the space I have, I don't know if better can be done  :'(
Title: Re: Ultra Precision Reference LTZ1000
Post by: d-smes on December 07, 2020, 03:00:31 pm
Six layer board?!
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 07, 2020, 09:34:23 pm
Yes, 6. As said, unless it has a negative effect, I have no problem with it. There is some digital circuitry planned that will need the extra layers.

Btw, my thermal design is not good, stay tuned for some updates.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 09, 2020, 05:59:59 am
For the non critical resistors, I use Vishay MBA0204, which is very similar to the one you listed. I think relief or cutouts around the mounting screws might make sense, but I think the way it's done in your picture might make the board prone to vibration.

I believe a plastic mounting cap can be made, such that the pressure will be put on the plastic no matter the pressure, not on the PCB, while still being tight. When I get to the CAD tool, I'll post pics when I have them. A much simpler solution might be a tiny piece of rubber top and bottom to the cap.
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on December 09, 2020, 06:23:48 am
I had thought of putting a copper pour as a big dot inside the LTZ pin's circle.
Somewhere I had modelled it in FEMM and it seemed to help keep all the pins isothermal. This pic is as far as I got debunking voodoo slots for myself, with FR-4 and 1oz cu. and air. The copper traces do not seem to conduct as much heat away but my simulation could be wrong. FEMM is not easy to use.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 09, 2020, 06:58:48 am
Are the L shapes copper pour?
Title: Re: Ultra Precision Reference LTZ1000
Post by: CDN_Torsten on December 09, 2020, 10:51:02 am
floobydust - I like your idea of a copper pour in the pin-circle.  This should offer some thermal equalization benefit...especially if done on all layers and then via stitched to thermally tie all layers together.  Getting the pour to 'hug' round each of the pads would help as well...

For your simulation - intuitively is doesn't feel completely right.  I would have expected the copper traces (and FR4) to conduct much more heat, and I would have expected the slots would be a much more distinct thermal barrier.

I fully agree with you that these simulations are very complex to set-up correctly.  I have worked with OpenFOAM and have felt the pain...

For your simulation, it feels like too coarse of a mesh was used in the simulation...this may be blurring the detailed thermal behaviour you are looking for.
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on December 09, 2020, 02:53:14 pm
For the non critical resistors, I use Vishay MBA0204, which is very similar to the one you listed. I think relief or cutouts around the mounting screws might make sense, but I think the way it's done in your picture might make the board prone to vibration.

I believe a plastic mounting cap can be made, such that the pressure will be put on the plastic no matter the pressure, not on the PCB, while still being tight. When I get to the CAD tool, I'll post pics when I have them. A much simpler solution might be a tiny piece of rubber top and bottom to the cap.

you are right, i tried some leaf spring equations and there might be issues

i made another doodle for fun.  some bottom copper pours are missing for viewing clarity. out of curiosity, i wanted to know the thermal resistance of the thermal ring. D = 11mm, 2oz Rt = (0.5pi.D/(380*0.002* 70e-6))/2 = 162C/W (too high?). by using a 1.5mm dia solid copper wire as a ring = (0.5pi.D/(380*cu area))/2 = 13 C/W . 6 layers? 162/6 = 27C/W ? this is like an unknown performance variable.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on December 09, 2020, 03:37:33 pm
Hey folks, I finished the layout of my LTZ1000 reference module. It is built around an 3458A reference form factor. 6 layers, uses mostly through hole parts, the divider is VHD200, the other sensitive resistors are VHP202Z, I also use MKP capacitors, and plan on using the free space for a few LMT70 temperature sensors, a USB interface and microcontroller for tracing and calibration.

I appreciate any feedback on the layout, specially around grounding.



OK, I can't resist any more to make some comments.

At first, this 6 layer board is a complete over-engineering, and mostly counter-productive.

These additional layers do more harm in terms of thermal-electric voltages, than simply using a single sided board only.
Latter would reduce the number of solder- and via- joints to the absolute minimum, would let you control them much better as you would have a single iso-thermal plane only, not randomly distributed over 6 planes.

Alternatively, you could place all analogue signal joints on one layer, and the supply voltages on a 2nd layer.
Please revise your star point concept for the two reference points, especially concerning the current flow from and into the different resistors around the LTZ1000.
I can not recognize at all, if these paths are all correctly Kelvin- sensing designed. Also, you should try to get a symmetrical layout for the reference pins.

These GND and Vcc shielding planes are useless, because it's a DC-application, but not an RF board.
In contrary, possible EMI disturbances will come from outside the board only, therefore an EMI shield (tuner box) all around the PCB would be more useful.

This could also serve as a shield against air draughts inside the 3458A. As often discussed before, the constant air flow inside the 3458A contradicts the data sheet recommendation to keep all solder joints away from this.

Maybe you also want to reduce the oven temperature to reasonable values, i.e. 12.5k/1k for 60..65°C.

The only proven measure to equalize the temperature gradients of the LTZ1000 is to apply a broad copper ring AROUND the chip.... the electrical connections to the LTZ have to be made on the opposite layer, of course.  This way it's done inside the Datron/Wavetek M7000 reference, which is the best LTZ1000 based 10V reference.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: notfaded1 on December 09, 2020, 08:41:56 pm
Like this one Dr. Frank?  :-+ :-+ :-+
Seems nice since they have LTZ1000 in them versus what's in our Flukes.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on December 09, 2020, 09:03:27 pm
No, it's the Datron 7001 module, ZLYMEX showed the interior, it has even two concentric copper rings around the LTZ, and all electrical connections on the bottom side:

https://www.eevblog.com/forum/metrology/teardown-voltage-standards/msg902910/#msg902910 (https://www.eevblog.com/forum/metrology/teardown-voltage-standards/msg902910/#msg902910)

https://www.eevblog.com/forum/metrology/teardown-voltage-standards/?action=dlattach;attach=211775;image (https://www.eevblog.com/forum/metrology/teardown-voltage-standards/?action=dlattach;attach=211775;image)

The earlier 4910 / 4911  share these LTZ1000 modules from the Datron 1281 / 1271 DMMs, also on display on that page, and these have these accidental slots around the LTZ, which later many have copied blindly.


Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on December 09, 2020, 10:21:17 pm
[...] The only proven measure to equalize the temperature gradients of the LTZ1000 is to apply a broad copper ring AROUND the chip.... the electrical connections to the LTZ have to be made on the opposite layer, of course.  [...]
Frank

Yes, the ring outside the pin circle and what about a dot inside? Thermally-coupling the warm and cool pads.
I understand a goal is to keep the LTZ1000 PCB pads all at the same temperature. For a two-layer board, I think this is not so practical due to the doubled-up traces for the Kelvin connections, leaving that pad cooler than the rest, along with any non-symmetry with other PCB traces fanning out from the LTZ also giving unequal heat transfer.

I see widely varying designs for a thermal ring, some close to the LTZ, others many cm away.

Having a copper-pour ring around the outside of the LTZ, once it's cut into segments I don't think it's as useful.
Because FR-4 thermal conductivity is poor, you don't get much heat transfer over the gap. I find that a PCB copper-pour with a cut or slice is no longer good at transferring electrons or heat, despite the mind being fooled and thinking it's all continuous.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 10, 2020, 07:06:19 am

OK, I can't resist any more to make some comments.

Frank
Thank you for the feedback Frank. Don't hesitate to share it, and I appreciate your feedback very much.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 10, 2020, 10:41:17 am
Not all pins at the LTZ1000 are equally important. The critical ones are the 2 with the kelvin connection to sense the output voltage. These two should have a similar temperature, if possible. Here it is not even every temperature difference that is really bad, just the change in the difference. The more constant part just add a few µV to the reference voltage.

I would be a bit careful with a 4 or 6 layer board, as this are layers glued together and this may cause internal stress between the layers. Normally 2 layers should be plenty for the LTZ1000 reference layout.

The rings around the reference can make sense. 2 separate thinner rings can make some sense and could be more effective in suppressing gradients. I still think this is more like a point that is done, because it can be done and is cheap - not really needed.

With connectors for the output I would more worry about heat flow around the connectors - these can also cause thermal EMF and there naturally is heat flow to the other side. It may make sense to have relatively thin traces at the connector for the critical signals.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 11, 2020, 02:14:39 am
I would be a bit careful with a 4 or 6 layer board, as this are layers glued together and this may cause internal stress between the layers. Normally 2 layers should be plenty for the LTZ1000 reference layout.
TiNs KX and FX designs are 4 layers, isn't stress a concern there too?
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on December 11, 2020, 03:14:53 am
Not all pins at the LTZ1000 are equally important. The critical ones are the 2 with the kelvin connection to sense the output voltage. These two should have a similar temperature, if possible. Here it is not even every temperature difference that is really bad, just the change in the difference. The more constant part just add a few µV to the reference voltage.

I would be a bit careful with a 4 or 6 layer board, as this are layers glued together and this may cause internal stress between the layers. Normally 2 layers should be plenty for the LTZ1000 reference layout.

The rings around the reference can make sense. 2 separate thinner rings can make some sense and could be more effective in suppressing gradients. I still think this is more like a point that is done, because it can be done and is cheap - not really needed.

With connectors for the output I would more worry about heat flow around the connectors - these can also cause thermal EMF and there naturally is heat flow to the other side. It may make sense to have relatively thin traces at the connector for the critical signals.

Sorry, I had questioned all this before in page 75 from 10/2017 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1316520/) and liked my idea to thermally couple the pads somewhat, like in pic (having troubles posting images tonight).
Agilent 34470a ref has oddball extra pads at pins 3,7. (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1315334/#msg1315334) You wouldn't put anything, like a capacitor there, it only makes to sense to me if they are for thermal EQ, or their PCB layout guy is not so great. 34470a has forced-air cooling so a steady draft across the ref PCB backside as well, then less of an issue for (pads) temperature difference compared to using a closed box for an enclosure. The 3458a has the cap/cover on BOTH sides of the pcb.

I'm not sold on the outside ring, it only can work if there are no cuts/slices and very hard to analyze with a thermal imaging cam and the emissivity of copper in the way. Although, there are a great many different rings designs out there.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on December 11, 2020, 05:40:02 am
The W7000 uses a > 2 layer design, so apparently it works just fine.
I cant remember if we had thermal pictures of ltzs with copper thermal rings around them to see how well it works and know only about the KX reference which is 4 layer and has large copper areas beneath its thin prepregs.
Considering that Copper/FR4 thermal conductivity difference is a factor of ~1100 i imagine the heat doesnt really care if theres a thermal conductor (copper ring) on the other side of a 1.5mm thick thermal insulator and happily continues to go where it wants along the traces.

Vishay recently released their THJP-product, a highly conductive thermal jumper, which may be suitable to thermally couple the ltz-legs. At 1€/piece its maybe worth a try. Maybe its not beneficial in the end, like slots around the LTZ.
Attached is an example design that uses THJP0612, which i incorporated into a prototype LTZ-pcb.
Tests still to be done, layout isnt ready yet.

https://www.eevblog.com/2020/11/14/eevblog-1347-smd-thermal-jumpers-could-be-game-changing/ (https://www.eevblog.com/2020/11/14/eevblog-1347-smd-thermal-jumpers-could-be-game-changing/)
https://www.vishay.com/docs/60157/thjp.pdf (https://www.vishay.com/docs/60157/thjp.pdf)
https://xdevs.com/doc/Wavetek/7000/img/w7000top.jpg (https://xdevs.com/doc/Wavetek/7000/img/w7000top.jpg) trace color indicates at least three layers
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on December 11, 2020, 06:08:39 am
I think multi-layer stuff is the new voodoo slots  :horse: . If design is done properly it will work good on 1 layer or on 6 layer. If design is not good, then no amount of layers will help it. Too my inexpirienced eye this PCB screenshot from 3roomlab tends toward bad design. I mean why we have mix of THT and SMT parts? No kelvin connection for sense from LTZ package. Mix of various trace thickness. Resistors oriented different ways towards LTZ package. Also if LTZ chip is not in same spot as in original 3458A then it will generate issues for stuff on A1.

Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on December 11, 2020, 06:51:34 am
Especially true if you don't want to cut the legs,,

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 11, 2020, 11:37:31 pm
3roomlab, are you planning to replace the reference in the 3458A? For me that answer is not quite, I just adopted the form factor. But nice to see others using the same form factor  :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 12, 2020, 12:25:24 am
I mean why we have mix of THT and SMT parts? No kelvin connection for sense from LTZ package.
Hehe, the last SMD part on my PCB is a tantalum cap, these are mostly low ESR in SMD.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 12, 2020, 09:30:08 am
The ring around the LTZ is there avoid uneven heat flow to different directions. It is not so much about heatflow to the inside, more about heat flow to the outside. The source of temperature differences between the pins 3 and 7 is more an asymmetric outside, not the chip itself. An additional wire can improve on this, but it is an odd part to place. Depending on the board used, the ring can be essentially for free.

The last layout from 3roomlab still has a mayor flaw with the ground connection: the output ground (pin 2 of J400) needs to be separate from the power ground (pin4 of J400) - at least to the star-ground, but much better directly to the LTZ1000.
Similar the +7 V output should ideally come directly from the LTZ1000.
The correct ground connection is way more important than any thermal details.

I see no problem mixing THT and SMD parts, especially not for low quantity and manual soldering.
The form factor and connectors for the A9 board may not be the best choice for a standalone reference, but it is also not that bad.
Having the reference in a similar position may still be a good idea (unless there is a really good reason against it), to really keep it exchangeable.
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on December 13, 2020, 02:26:54 am
I went through your calculations and had to stop part way. I just wanted to know what is the heat input to each pad, in order to calculate the temperature difference when people are not using symmetrical pcb traces to the Kelvin pins. The ring is a second aspect to look at - I feel cuts/slices in the copper scuttle the intent to equalize heat outflow.

Missing is the heat loss due to convection currents within the plastic cap and radiation, verses conduction losses to any foam insulation around the IC.
Missing is the bonding wire(s) heat transfer die to pin.
Missing are glass seals' thermal resistance; dimensions unknown. Schott (https://www.schott.com/epackaging/english/overview/products/index.html?highlighted_text=to+package) has nice TO glass.

Just the Kovar pins:
Using 17.3W/m-K, 2mm long (shortest pins), 0.5mm dia pins=2mm^2.
Kovar Rt = L/(k*A) = (2mm/1000)/(17.3*(0.2mm^2/1000^2) = 578°C/W/pin. There's 8 of them for 72.3°C/W total.
Using 17.3W/m-K, 12.5mm long, 0.5mm dia pins=2mm^2.
Kovar Rt = L/(k*A) = (12.5mm/1000)/(17.3*(0.2mm^2/1000^2) = 3,613°C/W/pin. There's 8 of them for 451.6°C/W total.

Reality check, one of TiN's KX thermal cam pics showed a can temperature 46.93°C and PCB temp of around 34.53°C. The LTZ has long pins, say 12.5mm or 1/2".
LTZ1000 θJA=80°C/W value did not jive with the datasheet graphs  :-//  LTZ1000A θJA=400°C/W matches graphs OK though. θJA=175°C/W matches the (non-A) curves, LM723 is 165°C/W. That is reasonable for the measured temperature.

Using 0.13W (top of my head) to the die heater on an LTZ1000A, my pin calculations say the thermal resistance of the pins is too high for that temperature gradient so I must be wrong.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 13, 2020, 05:48:49 am

Missing is the bonding wire(s) heat transfer die to pin.


And note: there are 3 bond wires on (heater) pin 1
and different lengths of 1 wire on the other pins.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Noopy on December 13, 2020, 07:42:45 am
(https://richis-lab.de/images/REF01/01_02.jpg)

https://richis-lab.de/REF03.htm (https://richis-lab.de/REF03.htm)

 :-/O :)

I could try to measure the lengths but is that really relevant?  ???
Title: Re: Ultra Precision Reference LTZ1000
Post by: floobydust on December 13, 2020, 11:08:07 pm
I think pin 7 has way more copper (trace thickness) and will run cooler than pin 3.
This was sort of leading me to try figure out and model the difference, by knowing heat input from the pins to pads.
For the bonding wire calc, my math:
32um (std size) AL wire x 2mm long Rt =0.002/(220*0.00080425mm^2) = 11,304°C/W each, or 1,130°C/W for all ten.
For the glass insulators, 0.5mm ID 2.2mm OD, 1.5mm L, Schott 8250
Rt = ln(2.2/0.5)/(2pi*1.5/1000*1.2) = 131°C/W each, or 16.4°C/W for all eight.
The glass is conducting the can's heat to the pins, glass is a much better insulator but also huge size compared to the bonding wires.

This ring stuff fools the mind so you think it's isothermal. The copper-pour border around the pcb edges are taking ambient air temp and conducting it under the cap. The copper slices leave thermal islands in the ring. We have no thermal imaging cam pics to verify. My thoughts anyway.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Noopy on December 14, 2020, 02:58:12 pm
I have taken some pictures of the "air impregnated polymer" die attach that is also used in the LTZ1000A.
I have posted the pictures here:

https://www.eevblog.com/forum/projects/ltz1000-nice-die-pictures/msg3369600/#msg3369600 (https://www.eevblog.com/forum/projects/ltz1000-nice-die-pictures/msg3369600/#msg3369600)

 :-/O
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on December 20, 2020, 04:07:52 am
With connectors for the output I would more worry about heat flow around the connectors - these can also cause thermal EMF and there naturally is heat flow to the other side. It may make sense to have relatively thin traces at the connector for the critical signals.
The neat thing about the 3458A form factor, if you use it outside the 3458A, you don't have to use the connector, and use wires directly to the PCB. Very versatile.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on January 08, 2021, 03:00:09 am
What could it be :D
Title: Re: Ultra Precision Reference LTZ1000
Post by: Haasje93 on January 08, 2021, 11:31:14 am
WOW! :-+
Your'e up to something.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Free_WiFi on January 18, 2021, 08:40:00 pm
Just a little bit of topic ...
On YouTube i saw a video where was clearly showed that's ltz1000 tend to heat-up intermittently .... like a blinking led.
Since the integrated heating oven of the ltz1000 is not linear,because it's tend to make some pwmming,thus i'm asking my self if
- the LTZ 1000 packaging is not already obsolete for our decade? (2021 and so on....).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on January 18, 2021, 09:09:38 pm
If build correctly the heater control is a linear PI regulator and does not oscillate. The control is slightly nonlinear (as the heater is a resistor) and the regulator usually works on the heater voltage (with a series diode). This is not ideal (the regulator gain changes with powert), but it can still work, as the thermal system has a rather short dead time. In theroy one could imporve on this, but usually no need for it. So why fix it if not broken.  It the regulator is oscillating there would be something broken to fix.
There is some special circuits to intentionally add some oscillation to remove hysteretic effects - though more like a very special case and only for the initial phase.
 

There is nothing wrong with the packaging: just a simple card box with aluminum for ESD shielding around the parts. The hermetic sealed parts need no special humidity control.
Title: Re: Ultra Precision Reference LTZ1000
Post by: ramon on January 19, 2021, 12:57:14 am
There could be some kind of package that allows hermetic sealing without needed Kovar leads.

And if Kovar is absolutely needed, someone would prefer SMT to allow mounting directly on a ceramic or special substrate.

Unless you air wire everything, and then you really connect the 'star point' directly into the leads instead of the PCB. But then you will need to do extra work reducing effect of air currents.

Current packaging need too many considerations (tricks?) regarding thermal, mechanical, electrical, etc ... efects. As a new package would have too.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on January 19, 2021, 08:18:16 am
If somebody wants to improve on thermal EMF, they can use the LTZ1000 in an oven. Then you can keep the opamps for zener current control and for temperature measurement at constant temperature as well. And maybe the 7V to 10V gain stage, too. That one will in general need an oven, anyway. Except you hand-select resistor sets for zero TC.
As far as i understand, one weak point of the LTZ1000 package is the missing 4-wire connection for the zener cathode. There should have been two pins with two separate bonding wires. One pin for current feed, the other for voltage sense. The star wiring should be on-chip, not behind a bond wire with its two wire bonds.

Regards, DIeter
Title: Re: Ultra Precision Reference LTZ1000
Post by: antintedo on January 19, 2021, 12:09:43 pm
There could be some kind of package that allows hermetic sealing without needed Kovar leads.

Copper to glass seals are possible, Vishay uses them for many hermetic resistors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on January 19, 2021, 07:04:47 pm
There could be some kind of package that allows hermetic sealing without needed Kovar leads.

Copper to glass seals are possible, Vishay uses them for many hermetic resistors.

Not directly there is always some Kovar involved.

From the VHZ datasheet:
"These parts are made with glass to metal seal enclosures employing Kovar eyelets which allow the copper leads to pass through the enclosure"

So basically this fact already proofs tht's LTZ1000 packaging is more like : Meeeeeh ..... VS Very Good!

So you like the "elephant feet" of the vishay resistors?
The LTZ package would double in size with those.
And heater power would also increase for a factor.

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: DenCraw on February 15, 2021, 10:12:40 am
the amount of knowledge here overwelmd me  a lot.
I want to ask if it is a good idea to put the reference voltage box inside a vacuum box with a Peltier cell
with a pwm controller with temperature sensors inside and outside the external box
in order to control the ambient temperature to 25 degrees.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on February 15, 2021, 10:16:17 am
the amount of knowledge here overwelmd me  a lot.
I want to ask if it is a good idea to put the reference voltage box inside a vacuum box with a Peltier cell
with a pwm controller with temperature sensors inside and outside the external box
in order to control the ambient temperature to 25 degrees.

TiN already had the idea with a Dewar flask (https://www.eevblog.com/forum/metrology/lm399-based-10-v-reference/msg828919/#msg828919) :)

https://en.wikipedia.org/wiki/Vacuum_flask (https://en.wikipedia.org/wiki/Vacuum_flask)
Title: Re: Ultra Precision Reference LTZ1000
Post by: DenCraw on February 15, 2021, 10:17:41 am
.. that was fast...
Title: Re: Ultra Precision Reference LTZ1000
Post by: 3roomlab on February 17, 2021, 09:54:52 am
put the reference voltage box inside a vacuum box with a Peltier cell

the INRIM "travelling" std 2017
Title: Re: Ultra Precision Reference LTZ1000
Post by: DenCraw on February 17, 2021, 10:26:02 am
Excellent!!!
that is what i was looking for!.
Here is my lousy experiment but with a LM399 and a
TEC1-12706,40mm x 40mm x 4mm,0~15.2V DC and 0~6A
Title: Re: Ultra Precision Reference LTZ1000
Post by: cowasaki on February 28, 2021, 07:02:33 pm
I have my reference in a plastic box wrapped in bubble wrap with a small heater pad which keeps the temperature between 34 and 36C constantly.

Connected to my Keithley 2100 I have been seeing 10.00000 for six months but today it dropped to 9.99999 and now 9.99998 I know that its just 20uV but as it was totally stable and suddenly dropping today I was wondering what sort of level of variability it should have with a 6.5 digit Keithley 2100?

My LTZ1000 board is powered from AC via a 12-0-12 transformer across both sides so 24v into a 7415 with a 2200uF/25V cap on the 15V side.  The 15V is good for 15.000
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on February 28, 2021, 07:19:21 pm
Hello,

when reading the spec: the uncertainity is 38 + 6 ppm in the 10V range so +/- 440uV for a 10 V reading.
So 20uV is a good result.

By the way: my K2000 has a tempco of 0.55 ppm/K environment temperature.
Besides this it suffers from some "pocorn" noise reading sometimes higher or lower around 1 ppm even at the same temperature.
But I fear: you will need much more DMMs to decide wether the DMM drifts or the reference.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on March 04, 2021, 02:34:27 am
LTZ at -260°C ? Coming soon  :-/O .

(https://xdevs.com/doc/xDevs.com/cryotest/cryoltz.jpg)
Title: Re: Ultra Precision Reference LTZ1000
Post by: DenCraw on March 04, 2021, 10:39:37 am
what if you use also a vacuum chamber...
Title: Re: Ultra Precision Reference LTZ1000
Post by: MegaVolt on March 04, 2021, 12:15:24 pm
LTZ at -260°C ? Coming soon  :-/O .
What for?
Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on March 04, 2021, 12:19:21 pm
LTZ at -260°C ? Coming soon  :-/O .
What for?

Because it is much cooler.
Title: Re: Ultra Precision Reference LTZ1000
Post by: MegaVolt on March 04, 2021, 12:22:51 pm
Because it is much cooler.
Cool and then hit with a hammer :))))
Title: Re: Ultra Precision Reference LTZ1000
Post by: exe on March 04, 2021, 03:41:54 pm
LTZ at -260°C ? Coming soon  :-/O .

I guess internal heater should be disabled...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on March 04, 2021, 03:43:52 pm
LTZ at -260°C ? Coming soon  :-/O .



Hello Illya,
Below about -15°C the LTZ1000 chip will pick up kind of non reversible hysteresis / shift / damage of its output voltage.
Even the 7000 can not handle this state any more by its de-'gaussing' method.

Therefore I'm curious, what's your intention (@liquid/pumped H2?) ... lower noise?

When I see this cryogenic apparatus, have you meanwhile bought a JJA, indeed?
 
Frank   
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 04, 2021, 07:26:32 pm
LTZ at -260°C ? Coming soon

and do not forget to measure 1/f noise and wideband noise.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 04, 2021, 08:01:45 pm
By the way:

I measured wideband noise on my buffered LTZ´s.
Mainly to see wether the EMI-capacitors C16-C19 have a bad influence on wideband noise.
(transferring some voltage regulator noise via the shield to the output of the LTZ).

I first thought that my AN83 LNA is defective because the noise was really low.
But in comparison with the other LTZ´s the trend is that my LTZ1000 based references with ADA4522 buffer have significantly lower noise than my LTZ1000A based references with LTC2057 output buffer. So who is the guilty: The LTZ variant (where I would estimate around 5-10% lower noise for the non-A Variant) or the buffer?

Any other experiences?

The 1/f noise has no correlation to A or non-A type.
And since my first 1/f noise measurements LTZ#3 now has increased 1/f jumps (some kind of very short popcorn noise).

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 04, 2021, 08:43:00 pm
The measured noise is quite a bit lower than the white noise specs in the LTZ1000 datasheet (some 40 nV/sqrt(Hz) in the graph for 4 mA zener current).

8 µV RMS for the 100 kHz BW corresponds to some 25 nV/sqrt(Hz) white noise.

If there is an extra buffer, one could easily add some higher frequency filtering it does not take that much in the kHz range. So the acural reference noise may not be that relevant. The buffer amplifier noise should be lowert than the measurend noise. However some of the AZ OP can show higher noise when used as a simple buffer (more higher frequency spikes going in to out and the other way round). The noise specs for the OPs are usually with a higher gain (e.g. > 10). So it may be worth to just check the noise of the buffers alone.

The higher frequency reference noise can effect some multislope or similar ADCs, as it can get mixed back to near DC and for some odd reason some DMMs don't include much filtering there, though it would be quite simple. Most other uses should not really care much about the higher freuquency noise.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 10, 2021, 07:46:22 pm
Hello,

I finally managed to summarize also some 1/f (0.1 .. 10 Hz) noise measurements.
As already mentioned there is no correlation to -A or non A type of LTZ.

I usually do 100 second measurements to catch more popcorn noise events.
But of course these have a little higher peak-peak noise than the standard 10 second measurements since more "rare" noise amplitudes are recorded.

LTZ#3 has moved into a "little jumper" over the time.
Where I have no explanation for it.
But also at the beginning the noise was not very low.

According to my calibration measurements LTZ#4 is the device with lowest drift over time.
Interestingly it is also one of the lower noise devices.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: SigurdR on March 28, 2021, 09:31:32 am
Interesting results!

Noise is actually increasing over the 5-year span.

Or is it the noise of the measurement apparatus that increases, I wonder, but I guess a reference measuurement is made to verify this is not the case.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 28, 2021, 06:44:07 pm
Noise is actually increasing over the 5-year span.

Or is it the noise of the measurement apparatus that increases, I wonder, but I guess a reference measuurement is made to verify this is not the case.

Mhm,

I have looked up the LTZ4 measurement:

Actually there is one change in measurement evaluation.
2016 I have generally used resolution enhancement from 16 to 20 Bit
instead of now (2021) using a 1 kHz FIR filter to reduce the oscilloscope bandwidth and noise.
The 20 Bit filtering effectively gives together with 50 kHz sample rate a low pass frequency somewhat below 200 Hz instead of 1 kHz.
But in average this reduces only the Vpp values by ~10nV so around 1%.
Another reason is that there is one "outlier" with 1.77uVpp in the 2021 measurements.

The other thing that I have changed is a EMI capacitor 100nF between output ground and power supply ground of the LTC2057 buffer on LTZ#3 to LTZ#6. I will to have check if there is a influence.

On the other side: Noise is statistical. You never get the same results so 0.1-0.2uVpp difference in 1.2uVpp values is not a "significant change".

The noise floor is of course checked before the measurement series started. I usually check that it is below 0.2 uVpp (leakage current of the input capacitor low enough with a 7-10V NiMh battery) and that the 50 Hz mains hum is not significantly high. (no mains transformer too near to the cookies box).

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: SilverSolder on March 28, 2021, 06:50:19 pm

Don't forget it is important to replace the cookie box frequently, necessitating a statistically significant consumption of cookies!   :-DD
Title: Re: Ultra Precision Reference LTZ1000
Post by: SigurdR on March 29, 2021, 08:32:28 am

You are thorough!

Checking the noise floor and calibrate out that level is a good thing to do.
When we calibrate our DVM for ex, we use Voltage/etc references. Is there such a thing as a noise reference? a noise reference that gives out a lot of noise specified within a given band width so we can use that to check our own noise measurement gear?

Indeed, noise is statistical in nature, and 0,1-0,2uV for a 1,2uVp-p is almost 10-20%. When I do my 20-20k noise measurements I am happy to be +-10% "correct". Lately, I try to do FFT noise measurements downto 0.1Hz, and it is not trivial to get accurate results!


Kind regards,
Sigurd

Noise is actually increasing over the 5-year span.

Or is it the noise of the measurement apparatus that increases, I wonder, but I guess a reference measuurement is made to verify this is not the case.

Mhm,

I have looked up the LTZ4 measurement:

Actually there is one change in measurement evaluation.
2016 I have generally used resolution enhancement from 16 to 20 Bit
instead of now (2021) using a 1 kHz FIR filter to reduce the oscilloscope bandwidth and noise.
The 20 Bit filtering effectively gives together with 50 kHz sample rate a low pass frequency somewhat below 200 Hz instead of 1 kHz.
But in average this reduces only the Vpp values by ~10nV so around 1%.
Another reason is that there is one "outlier" with 1.77uVpp in the 2021 measurements.

The other thing that I have changed is a EMI capacitor 100nF between output ground and power supply ground of the LTC2057 buffer on LTZ#3 to LTZ#6. I will to have check if there is a influence.

On the other side: Noise is statistical. You never get the same results so 0.1-0.2uVpp difference in 1.2uVpp values is not a "significant change".

The noise floor is of course checked before the measurement series started. I usually check that it is below 0.2 uVpp (leakage current of the input capacitor low enough with a 7-10V NiMh battery) and that the 50 Hz mains hum is not significantly high. (no mains transformer too near to the cookies box).

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 29, 2021, 09:26:08 am
I resistor is a kind of noise reference  60 ohms gives 1 nV/sqrt(Hz). There is however still the difficulty that any amplifier will have its own noise and usually also current noise.
The other usual option is to us a resitor or similar only as a white noise source to check the frequency band and than use a sine or similar signal to test the actual voltage gain.

There are some noise sources thoug the stability is often not so great to call it a reference and most are for the RF range. Some AWGs can generate pseudorandom noise that may be good enough, but the quality varies.

For the scattering character of noise, the directly measured peak to peak values are by nature scattering a lot. The RMS reading is usually much less scattering.
For getting the noise from a FFT it is normal that there is quite some scattering for the lower decade or so. So to get good noise reading down to 0.1 Hz it take more like 100-100 seconds, so one has averaging over several 10 scond windows.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on April 23, 2021, 11:14:03 pm
I took a little bit of a different take on my implementation of an LTZ1000 module. Instead of focusing so much on the 3458A reference module form factor, I do want a smaller module, as long as performance is not impacted, but size and form factor are unrestricted. Much inspiration and learning for the layout of TiN's FX ref, Dr. Frank's implementation, and the CERN ADC, excellent and invaluable information folks! Not done yet, but I realized I got lots of intuition on how to implement a better 3458A reference module as well from this. So I'll probably spawn a few form factors. Not done yet, and far from final layout, I'm trying different layouts.
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on April 24, 2021, 04:21:39 am
Using VHP resistors for 70kOhm bias resistors is waste of money. Also ditch the slots ;)
Suggest you to make smaller board, not bigger, it will be helpful for performance of the module, if the placement is good.
Title: Re: Ultra Precision Reference LTZ1000
Post by: niner_007 on April 24, 2021, 07:13:27 am
Using VHP resistors for 70kOhm bias resistors is waste of money. Also ditch the slots ;)
Suggest you to make smaller board, not bigger, it will be helpful for performance of the module, if the placement is good.
Datron loved the slots though, and they look cool 8)

The 70K resistors (and 120 resistor) are actually VHP101, these are the best resistors VPG can make, with a max absolute TCR of 0.4ppm within a 20C to 30C window (binned), you can get these binned from Vishay, but I am using the garden variety ones, so they are hardly fancy, just a mere 2ppm/C or 5ppm/C, don't remember. The VHD200 divider isn't your Digikey resistor order, it's binned by Vishay and comes from Vishay with a guaranteed maximum tracking TCR of 0.5ppm within a 20C to 30C window, anything higher than that they sell to digikey :-DD Part number is 303391 if anyone wants to order, for a cool $90 per resistor.

Just to sit down for a bit and think, super cool that Vishay can produce these, bin them and guarantee the spec, not your datasheet spec or marketing talk, or typical figures talk, where you never know what you'll be getting. You don't have to buy 50,000 and select 50 best ones. Wish Analog Devices offered something like that for the LTZ1000.
Title: Re: Ultra Precision Reference LTZ1000
Post by: mrk on May 08, 2021, 01:30:18 pm
Thought about replacing the voltage divider R4/R5 for the tempreature with a PWM divider. Hoping to get at least some advantages from that.
What do you think?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on May 08, 2021, 03:22:38 pm
A PWM divider could be resonable stable, but there is still some possible residual drift (different on/off times, leakage, switch resistance drift). The other challange is avoiding noise / ripple. The start phase may be a challange too. One may need a sparate startup sequence to avoid excessive overshoot apon start up.  A possible added point may be a better defined ramp up phase - up to the point of including special exursions to lower turn off/on hysteresis.

It sounds possible and interesting, but not necessary easy. Likely it would be about building a seprate PWM DAC first and see how good it works - no extra need for very high linearity, but low ripple and low drift.
Title: Re: Ultra Precision Reference LTZ1000
Post by: bsdphk on May 09, 2021, 05:36:55 pm
A PWM divider could be resonable stable, but there is still some possible residual drift (different on/off times, leakage, switch resistance drift).

Those are pretty much solved problems.  See Figure 7 on page 12 in HP Journal April 1989 (the 3458 issue) and the HP3245 which does precisely that with its PWM divider (as far as I have been able to tell.)
Title: Re: Ultra Precision Reference LTZ1000
Post by: bsdphk on May 09, 2021, 05:39:11 pm
I should add: The PWM facilities in good microcontrollers can easily be programmed to do the "balanced pulse" trick.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on May 09, 2021, 06:48:13 pm
A PWM divider could be resonable stable, but there is still some possible residual drift (different on/off times, leakage, switch resistance drift).

Those are pretty much solved problems.  See Figure 7 on page 12 in HP Journal April 1989 (the 3458 issue) and the HP3245 which does precisely that with its PWM divider (as far as I have been able to tell.)
The HP figure 7 solves a different point, that I thing would not apply to a constant PWM ouput anyway. The On/off time drift is usually quite small, unless the frequency is really high. So just make sure the frequency is no too hight. In the DMMs the small drift is part of the offset that is corrected by AZ mode together with other larger effects.
Also the PWM DACs in the something like the Fluke 5700 usually uses a zero adjustment from time to time. I has a few additional sources of drift and the switch time drift may not be the main issue.

Anyway the PWM DAC part is an interesting part but at least initially it would be not very LTZ1000 sprecific. This thread is long enough - so better start a new thread on a PWM DAC, there  are already a few, but the main part there is more linearity and ripple.
Because of the attenuation factor the error from the temperature set voltage one effect the result to a small fraction, so the demands may not be too extreme.
Title: Re: Ultra Precision Reference LTZ1000
Post by: KT88 on May 09, 2021, 11:14:40 pm
A PWM DAC would be nice for the gain stage that amplifies Vz to 10V as well.
But this would not only reguire high strability but also high resolution, if we want the 10V to be spot on...
I agree with Kleinstein that another thread for this deep rabbit hole makes more sense than keeeping it here.

Cheers

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: bsdphk on May 10, 2021, 05:42:01 am
The HP figure 7 solves a different point, that I thing would not apply to a constant PWM ouput anyway.

Implement your PWM DAC with two pins instead of one, one pulling up and one pulling down, and it solves the ailments you listed above (if you calibrate it).

Dont tell me it doesnt work: I've done it and it works.
Title: Re: Ultra Precision Reference LTZ1000
Post by: RoGeorge on May 10, 2021, 07:22:07 am
You mean like this?
https://www.eevblog.com/forum/projects/fun-circuit-to-play-with/ (https://www.eevblog.com/forum/projects/fun-circuit-to-play-with/)
Title: Re: Ultra Precision Reference LTZ1000
Post by: KT88 on May 10, 2021, 08:46:49 am
The moment two resistors combine two PWMs the resistor ratio matters again...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 10, 2021, 04:05:59 pm
Thought about replacing the voltage divider R4/R5 for the tempreature with a PWM divider. Hoping to get at least some advantages from that.
  • Cheaper?
  • Adjustable Tempreature
  • Higher stability?
What do you think?

I think that such questions should always be started from the (engineering) requirements and from design goals, not backwards from an anticipated solution... as this would be better and professionell engineering practice. Consequently, all the replies to your three questions so far did not give any concrete answer.

So, to answer your questions concretely: I think that a PWM would be a very bad approach in all of your categories.

At first stability: what stability requirements do you mean, like short term (noise), temperature, long term drift, or susceptibility to E.M.C. , pressure, humidity, vibration?

These 2 resistors theoretically contribute only by 1/75 .. 1/100 of their own stability figures, so the LTZ chip itself has paramount influence on mostly all these parameters; that has been measured / demonstrated in this lengthy thread many times. Practically, the residual T.C. of up to 0.3ppm/K, despite e.g. T.C. matching of the resistors, is not yet understood here, and is obviously not relevant, as the overall T.C. can easily be trimmed, down to <0.02ppm/K.
As the oven regulation and in turn the reference voltage is very sensitive to external noise, keyword voltage dips, for a PWM solution you'd need a very elaborate filtering, which would probably yield high cost and in the end worse noise figures than the passive divider solution.

Concerning cost, these Vishay hermetically sealed, oil filled, luxury resistors are not really necessary; much cheaper ones will do the job as well. These only have to fulfill certain minimum technical requirements regarding e.g. T.C. and timely drift.
Please, first make yourself aware of the BOM cost of these cheaper solutions, they are in the ballpark of < 20€ for two b.m.f. resistors, or even much less for other technologies, like e.g. TiN has presented on the discussion about the clone reference of the 34470A.

Concerning oven set point change, that question makes no sense at all to me.
Instead, what would be the purpose/application, or your design goal for that feature?

If you would start from the requirement "timely stability", you would know, that the lower the temperature, the better this parameter.
50°C oven temperature gives about -0.8ppm/year, each 10°C more will double that number. Therefore, simply chose a fixed, lowest possible oven temperature.
Changing the oven temperature will change the reference voltage by about +50ppm/K, which would violate the overall stability requirement as such.

If your feature goal would be to have an easy and cheap(er) possibility to make thermal cycling like in the Pickering patent, well that's also already done in the Fluke 7000 devices, so no need to re-invent the wheel by another complicated solution.

From all these aspects, I can not imagine at all, what would be the benefit of a PWM solution, other than over-engineering an already solved problem  :horse:, just like this other voodoo stuff here, as PCB meander cuts, fancy resistors, ceramic and multi layer PCBs and so on.

Frank

Title: Re: Ultra Precision Reference LTZ1000
Post by: Grandchuck on May 28, 2021, 07:49:19 pm
One of my LTZ1000 reference circuits failed.  The LTC1052 output was oscillating and the failure occurred when I placed the circuit in a homemade cooler/foam box to measure its temperature performance.  I assume a static charge destroyed the LTC1052.  After replacing that IC, all is back to normal.

The LTC1052 is a CMOS device and perhaps should not be placed in a foam box?  A partial schematic is included ... you might recognize the good work of Dr. Frank.
Title: Re: Ultra Precision Reference LTZ1000
Post by: guenthert on May 29, 2021, 01:27:33 am
It just might be because the LTC1052 is directly connected to the output.  I would have liked a transistor follower in between, also because zero-drift/chopper OpAmps tend to have feeble output drive capability.  Well, next time  ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 29, 2021, 10:20:49 am
Hello Grandchuck,
thank you for the flowers  ;D

Anyhow, the LTC1052 was selected because it is one of the few zero offset / chopper amps which also have very low input bias (~ pA) which I originally needed for a precision amplification by a divider with a higher impedance.
As lower impedance solutions (~ 20kΩ) for this divider are available meanwhile, this is not required any more.

All of my 7 references are thermally isolated internally, using styrofoam, but not a single LTC1052 or 2057 has been blown up, especially not by an ESD event which would have originated from the foam.
But it's correct, that the output is not protected at all against external ESD or EOS scenarios.. an additional transistor driver with current limiting would be an advantage .. next time..

I also measured the 0.1 ..10Hz noise directly, and confirmed that the LTC1052 - due to its low bias current - performs very badly in this category, i.e. in total generating 2 times the noise of the raw LTZ1000 output. Briefly, here are the ballpark numbers, at ~7.2V output levels: direct out: ~ 140nVrms, 2057: ~ 180nVrms, 1052: ~ 270nVrms.
These different noise figures are not apparent at all, if you measure the references with e.g. a 3458A at NPLC 100.

Anyhow, in a new design the LTC1052 will be replaced by an ADA4522-1, and for some of the existing references by means of an adaptor PCB... I will report the outcome of this improvement (?)

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Grandchuck on May 29, 2021, 01:14:16 pm
Hello Dr. Frank,

I have 3 iterations of your design and one of them (the one that failed) would occasionally latch up ... the output would drop to some low voltage.  This only happened when cables/connections were being changed/moved.  Power cycling always restored normal operation.  Some kind of clue there?

Please do share additional details as you can.  As always, it will be appreciated.

Grandchuck
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on May 29, 2021, 02:06:38 pm
Grandchuck

I had a similar issue on one out of nine references based on the redesign of Frank's schematic I made a few years back. After replacing the LTC1052 similar things never happened again. However, I added a 120R resistor in the feedback loop of the reference amplifier and in series with the diode to prevent any issues during startup, in case that would cause any trouble.

-branadic-

BTW: There was a component listed on Arrow, ADR1000AHZ, but for some reason they removed their listing. However, it can still be found in the cache https://webcache.googleusercontent.com/search?q=cache:snoBuWs4HP0J:https://www.arrow.com/en/products/adr1000ahz/analog-devices+&cd=2&hl=de&ct=clnk&gl=de (https://webcache.googleusercontent.com/search?q=cache:snoBuWs4HP0J:https://www.arrow.com/en/products/adr1000ahz/analog-devices+&cd=2&hl=de&ct=clnk&gl=de)
Title: Re: Ultra Precision Reference LTZ1000
Post by: cemelec on May 29, 2021, 05:10:12 pm
I've been following this topic for a while; but is there anywhere today (May 2021) that you can buy a LTZ1000 at a sensible price? Searching comes up with ridiculous pricing....
This part is of sufficiently high value that I don't trust Ebay or any Chinese supplier, if they have it,  - its well worth faking.

Here in the UK the distributors I trust don't have it.
Is it still in production? According to AD website yes, so why so hard to get one?

Another part I'm interested in, the AD5791 20 bit DAC, has the same problems

Charles
Title: Re: Ultra Precision Reference LTZ1000
Post by: Grandchuck on May 29, 2021, 05:20:30 pm
I have an order in for an LTZ1000CH @ $58 and the supplier has flagged it to be shipped 6/29/2021
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 29, 2021, 06:41:08 pm
Hello Dr. Frank,

I have 3 iterations of your design and one of them (the one that failed) would occasionally latch up ... the output would drop to some low voltage.  This only happened when cables/connections were being changed/moved.  Power cycling always restored normal operation.  Some kind of clue there?

Please do share additional details as you can.  As always, it will be appreciated.

Grandchuck

Grandchuck,

Well, I can't guess, which 'iteration' you have used, as my schematic has been used by several other people.
Myself, I only published one schematic and one single sided layout, which has been been working well so far.

Also, you did not tell, whether the 1052 amplifier, or the reference amplifier itself showed a latch-up behavior.

So sorry, but I can't give any hints on this sparse information.
Any further hint is welcome.

Frank

@ cemelec:
The LTZ1000 may be under allocation also. It was rumored to have a lead time of 25 weeks, or so.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Grandchuck on May 29, 2021, 07:50:17 pm
The three references differ in the resistors.  They all use the PC board based on your design and schematic.  One uses Edwin Pettis devices (wire wounds) in all the important locations, one uses some of those and some low ppm Vishay foil types, and one uses some odds and ends purchased from various ebay stores.  All three compare favorably with each other and with Tin's FX reference, but not THAT good :)  I honestly don't feel that my 3458A is as rock solid as some discussed here by the serious volt nuts.  I have seen the term "golden" used to refer to some 3458As.  Mine is perhaps silver.

The LTC1052 is the device that latches up.  It only happens on occasion.

I will probably try your replacement for the LTC1052; if and when you release the information. :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on June 08, 2021, 03:43:44 pm
Many, many Thanks to Andreas!  :-+
He donated me one of his x10000 noise amplifiers, so I also was able to make absolute noise measurements on my 10 LTZ1000 based references.
For each reference, I only have taken one 10sec long sample, and let the scope calculate the Peak and RMS noise, see example screen shots.

Prototypes Ref_1 and Ref_2 are based mainly on the original datasheet schematic, plus two blocking capacitors in parallel to the 120 and 1k resistors.
LTZ #5 is fully assembled on a PCB from Andreas, lacking those 2..3 ESD / angst capacitors, and it is battery powered.
LTZ # 1 - 4, 6, 7 are based on my design, i.e. also lacking these ESD capacitors.
LTZ # 1-4 feature a 10V amplification.
On the LTZ #3 I repeated the measurements with an AD4522, instead of the LTC1052.
LTZ #2 was battery powered only for this experiment; running on a PSU, I estimate about 10% higher noise figures.
The FLUKE 7000 is also operated on battery power.

Nearly all measurements were done inside a cooking pot, apart from the box for Ref_1 and Ref_2, which is too big.

I also added the 1h noise figures measured with my 3458A at 100 NPLC, i.e. that's a convolution of the noise of the DUT and the 3458A internal LTZ1000A.
That measurement indicates, that the noise of the references does not play a dominant role when using them as a calibration source at this aperture.

I will update this table, as soon as I change more and more buffers from 1052 to 4522.

 
Frank

Updated the table, now 4 modified references. Measurement on a 9V battery gives about 41nV rms for the amplifier
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 08, 2021, 05:28:30 pm
For each reference, I only have taken one 10sec long sample
Hello Frank,

since noise is very statistical I usually do at least 15 samples 10 sec long and calculate the average + std dev of uVpp and uV RMS.

When looking for popcorn noise I even use 100 sec long samples.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: The Bootloader on August 04, 2021, 07:12:20 am
Hi there,

I would like to build myself a LTZ1000A reference.

I am a bit lost among all the versions available.
If I quote the signature of our fellow inmate cellularmitosis (https://www.eevblog.com/forum/profile/?u=85975), there are :
KX (https://goo.gl/2oWc1q) FX (https://goo.gl/M4N5Qv) MX (https://goo.gl/VecvSY) CX (https://goo.gl/DCZCd4) PX (https://goo.gl/AycNNQ) Frank (https://goo.gl/ZYk359) A9 (https://goo.gl/F1NJkz) QX (https://goo.gl/DjwDrX)

It seems like KX is the original one, Frank is a popular one, and PX is a compact one.
The other ones are either specialized (made to fit within a specific instrument) or a bit unpopular (so I might have difficulties finding support if needed)

I was leaning toward PX (https://www.eevblog.com/forum/metrology/px-reference/), but it seems like TiN offers KX calibration (https://xdevs.com/article/kx_calserv/) which is a big deal to me, so I might do this one instead.

Any opinion ? It seems like a jungle, I want to enter this world, and would like guidance as to what is my best bet so I won't be frustrated to have built the "wrong one".

I already have a set of resistors from this group buy (https://www.eevblog.com/forum/metrology/group-buy-ltz1000a-precision-resistor-set-(econistor-8g16-precision-wirewound)/) (70Kx2, 1K, 120, 12.5K). Originally intended for Dr Frank board, but I think it can be used for any board as long as they fit physically.

Thanks :-+
Title: Re: Ultra Precision Reference LTZ1000
Post by: leighcorrigall on August 31, 2021, 08:07:42 pm
Hi KX-ref owners,

I am about to solder the critical resistors and LTZ1000ACH onto TiN's reference board. As this is my first build it would be great if someone could perform a 'sanity check' on the component positions. See attached. I have ensured there are no shorts and I tried my best to orient the components correctly based on reference pictures. The board was cleaned multiple times with a new toothbrush and fresh isopropyl alcohol.

Bismuth solder paste was used for all non-critical components thus far. The total soldering time was much less than 280 seconds. Approximately much less than 4 seconds per lead. Priority was given to the ease of mounting and as suggested by the original xDevs post.

Even though they are greatly excessive :horse:, I used the following critical resistors that were purchased from AVNET:
1x Y4078120R000T9L (120 Ω)
2x Y607270K0000T9L (70 kΩ)
1x Y5076V0169TT9L (1 kΩ / 13 kΩ)

This reference board will be used in combination with an output buffer stage (based on the FX-ref board) to obtain approximately 10 V.

Thanks for your help!
Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on August 31, 2021, 11:24:22 pm
Looks alright. 70k VHP resistors are indeed pure wasted gold :)
Title: Re: Ultra Precision Reference LTZ1000
Post by: MegaVolt on September 21, 2021, 02:52:27 pm
In the fresh LTSpice I found models for LTZ1000 and LTZ1000a from AD.
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on September 21, 2021, 04:46:22 pm
The diode model has got a tempco, it seems..
Title: Re: Ultra Precision Reference LTZ1000
Post by: magic on September 21, 2021, 06:29:35 pm
Most zener models in LTspice have TC.
The question is: is it accurate over current and temperature?

I tried to reproduce the s-shaped TC of compensated zener references with some built-in diode models and failed.
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on September 21, 2021, 08:15:42 pm
And finally the complete Vref source while changing ambient temp from 20C to 60C.
LTZ1000: You may see the heater current changes with ambient (from 27mA to 0mA) and the Vref's TC is -7.8uV/C within 20C to 55C ambient temperature range.
LTZ1000A: You may see the heater current changes with ambient (from 17mA to 0mA) and the Vref's TC is 0uV/C within 20C to 55C ambient temperature range.

PS: the previous sim of the TC of the LTZ1000A "zener diode only" showed +2.7mV/C.
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on September 21, 2021, 09:09:25 pm
Most zener models in LTspice have TC.
The question is: is it accurate over current and temperature?

I tried to reproduce the s-shaped TC of compensated zener references with some built-in diode models and failed.

The LTspice zener models usually lack a few parameters which are needed for creating S shape with some compensation.
Look at the first line in my above model of the "iMo6V9" zener. The numbers are rather guesses..
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on September 22, 2021, 05:34:16 am
The model is missing the resistors shown by John Pickering at Metrology Meeting 2021 too.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on September 22, 2021, 06:22:53 am
With highest numeric resolution the TC of the LTZ1000A Vref shows -3nV/C (20-55C amb).
A small (ie 8ohm) resistor in anode does not change TC much, the output voltage increases by a few mV.
There is also an ADI's "testing jig" in the model - showing the response of the Vref on the heater power (switching it on/off). See below.
I think this is not the last revision of the model..
Title: Re: Ultra Precision Reference LTZ1000
Post by: chris_11 on September 22, 2021, 07:06:21 am
To the LT1000 LTSpice model. You can set the start temperature with a .temp statement and get an idea of the conditions in that case.

To the LTC1052 "Latched" reference. Educated guess: The LTC1052 gets phase reversal with both inputs at GND and you get a stable situation with the circuit not starting up. If you prebias one input enough in the right direction it should start.

A CMOS IC latch up is usually a destructive event with the CMOS IC turning into a switched on Thyristor over its supply rails with no real current limit.

@branadic.  You can add the resistors external and see what changes.
Title: Re: Ultra Precision Reference LTZ1000
Post by: aronake on November 23, 2021, 04:41:22 pm
How do people get hold of the fancy sealed metal film resistors?

They are pretty much out of stock in all places I have seen.

Put an order and wait?
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on November 23, 2021, 04:58:51 pm
Try Texas Components. They are a Vishay licensee and are pretty quick. They don't carry the full range.

You will probably have to call them.
Title: Re: Ultra Precision Reference LTZ1000
Post by: syau on November 24, 2021, 10:17:17 am
After several email exchange with an “authorized” distributor in Shenzhen, I gave up and get a quote from ELcoPC LLC in the State for few set customized VHP/VHD series resistors.

It will take 5 months to get it deliveries even if under Express Line.
Title: Final Assembly of LTZ1000 modules
Post by: Dr. Frank on December 20, 2021, 07:32:09 pm
Hello,

maybe you remember my LTZ 1000 tuner box assemblies.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1354865;image)


Inside the tuner box, there's space for a simple linear regulator, like an LM317 based one.

Those boxes were all powered by transformer wall warts, which I salvaged from different devices. I use a 2.8VA, 15V, 180mA transformer as a replacement for the original ones, plus bridge rectifier and electrolytic capacitor for an unregulated DC output. Here's an old  transformer case from Nokia.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1354871;image)

It was always my intention to have a proper mechanical assembly for these tuner boxes, inside an outer case.
At first, here's the LTZ #5, solution copyright by Andreas, battery powered, where I added CuTe Pomona jacks for output, Guard (connected to isolated tuner box) and case ground.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1354877;image)

Those Pomona jacks are long enough to mechanically connect outer case and the tuner box, adding an isolating plastic plate, and plastic spacers, so that outer box and tuner boxes are electrically isolated from each other, and also avoiding long connection cables.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1354883;image)

On the rear side, the tuner boxes are screwed on to another plastic plate, using an electrical connection to the tuner boxes, serving as a common Guard.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1354889;image)

Then I added the Guard and Case Ground jacks, a simple 12V LM317 stabilizer, and connected all 4 modules in parallel.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1354895;image)

I would have of course preferred 4 isolated supplies.
This way, the 4 reference grounds differ by 50.. 250µV, because of differences on the supply cables, due to different oven supply currents. It's also not possible to connect any of these 4 reference grounds together (to make differential measurements), as this directly shifts the references outputs.

That's ok for me at the moment, as I regularly compare all of my 12 voltage references against each other, by absolute measurements of each by means of my 3458A.
Maybe somebody has an idea, to commonly supply several LTZs and properly interface the reference grounds. I currently have no idea, how this is done inside the Datron 4910.

Here's my Tower of References, where I maintain Volt and Ohm.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1354901;image)

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 20, 2021, 08:37:27 pm
The setup looks nice.  If there is an EMI problem, one may consider adding some common mode choke / ferrite ring just inside the reference boxes.

For the ground problem, one could consider seprate transformers. Some mains transformers come with 2 fully separate winding and thus could power 2 ref modules.

If a single supply is wanted, one could build a circuit to shift the low sides of 3 modules a litte (e.g. +-1 mV range), so that the reference low side is at the same level as the one unit taken as a master and common ground for the output. So the low side would be all from 1 box and the other low sides on the extra extra amplier / compensation part. Shifting the low side would take quite some current, though only at a low voltage.

An alternative would be to directly connect the reference gounds and make sure the negative supply leads get the same current as the positive side. This would add some current regulation / mirroring and maybe the voltage regulation. So more circuit,  but likely less extra noise and drift. The refrence modules should not provide a significant current, so I don't think one would have to treat that current separate.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on December 20, 2021, 08:50:43 pm
With a bipolar supply one can use ground current compensation similar to the HP 3458A reference module.
With our LTFLU references, in order to use a simple +15V supply without negative supply, i am using a silicon diode in the Gnd connection to simulate a negative supply of -0.7 V. Then one can use chopper amplifiers to equilibrate the Gnds using the Gnd sense lines from each reference.
Or use a transformer with multiple secondaries to get separate supplies for each reference.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 20, 2021, 09:08:40 pm
Ground current compensation is with the 3458 is a good idea: the actual reference current is constant and thus possible to compensate with a constant current, and the heater and OPs can use a separate ground.  It is still not clear if this works well with the existing boards.
Title: Re: Final Assembly of LTZ1000 modules
Post by: BU508A on December 20, 2021, 09:38:25 pm
I would have of course preferred 4 isolated supplies.
This way, the 4 reference grounds differ by 50.. 250µV, because of differences on the supply cables, due to different oven supply currents. It's also not possible to connect any of these 4 reference grounds together (to make differential measurements), as this directly shifts the references outputs.

That's ok for me at the moment, as I regularly compare all of my 12 voltage references against each other, by absolute measurements of each by means of my 3458A.
Maybe somebody has an idea, to commonly supply several LTZs and properly interface the reference grounds. I currently have no idea, how this is done inside the Datron 4910.

If you'd like to go with isolated supplies, I'd recommend two Talema toroidal transformers, e.g. the 70033K. It has 2x 15VAC output and 2x 3.5VA. It is available at Bürklin for ca. 17.50 EUR/unit plus shipping.
https://www.buerklin.com/de/Ringkern-Flachtransformator-7-VA-15-V-15-V-2x115-V-Talema-70033K/p/38C766 (https://www.buerklin.com/de/Ringkern-Flachtransformator-7-VA-15-V-15-V-2x115-V-Talema-70033K/p/38C766)

(https://res.cloudinary.com/rsc/image/upload/b_rgb:FFFFFF,c_pad,dpr_1.0,f_auto,h_843,q_auto,w_1500/c_pad,h_843,w_1500/F2239216-01?pgw=1&pgwact=1)

Sizes (LxWxH): 50mm x 50mm x 24mm (ca.)

Attached the datasheet
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on December 20, 2021, 09:45:46 pm
An input filter, two of those https://www.mpaudio.net/product-page/audio-grade-transformer-60va (https://www.mpaudio.net/product-page/audio-grade-transformer-60va) and a nice PCB with CMCs and some LT3042s, preferably with good layout that actually achieves the stated PSRR -> 4 independent isolated supplies.
Yes, those transformers have way too much power, but they are the only ones i could find with shielding.
Title: Re: Ultra Precision Reference LTZ1000
Post by: BU508A on December 20, 2021, 10:00:51 pm
If you really want to, you can have a custom toroidal transformer made, including a shield winding and four separate secondary windings.

Multi Circuit Boards is offering this service but it is not cheap.
https://www.multi-circuit-boards.eu/en/products/toroidal-transformers.html (https://www.multi-circuit-boards.eu/en/products/toroidal-transformers.html)
Title: Re: Final Assembly of LTZ1000 modules
Post by: Andreas on December 21, 2021, 06:12:27 am
I would have of course preferred 4 isolated supplies.

Hello,

that is why I prefer to use batteries during measurement.
Since the linear regulated DC wall plug adapters are now unobtanium due to regulations the 2nd best option is to use 4 AC wall plug adapters.
If you dont have enough old outdoor Christmas Light transformers still some AC adapters are available.
I would take 4 of these:
https://de.rs-online.com/web/p/steckernetzteile/1391764

with best regards
 
Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on December 21, 2021, 07:42:40 am
Bürklin also have these shielded 12 VA transformers with two secondaries:
https://www.buerklin.com/de/Universal-Transformator-12%C2%A0V%C2%B7A-10%C2%A0V-12%C2%A0V/p/35C100 (https://www.buerklin.com/de/Universal-Transformator-12%C2%A0V%C2%B7A-10%C2%A0V-12%C2%A0V/p/35C100)
The Schmidbauer part number is UNT01223012,
These transformers have a residual coupling of about 3 pF around the shield.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: RoadDog on February 19, 2022, 10:35:06 pm
Been looking at ideas and other peoples builds to figure out building some references the last few days.

The KX board looks pretty cool from the write up on XDevs.

How do I get the Vishay resistors? Digikey doesn’t stock them and I’m guessing VPG wants you to order them in bulk? Are there others I can use with the same performance?

I like the ability to just order three boards from OSHPARK and building three references on a proven design. Searching here I’ve found a lot of possible options and seen that folks have pooled money to purchase lots of resistors in the past. I’ve searched a lot here. Hard to sort through it all and the shortages only compound things





 


Title: Re: Ultra Precision Reference LTZ1000
Post by: TiN on February 20, 2022, 02:39:40 am
You can order resistors in 1 pcs from VPG, if you ok with waiting times 6-8 month (been always like that even before any modern shortages madness).

KX design is old and not the best (overpriced unnecessary 70kOhm VHPs, unbuffered unprotected output, chopper opamps).
I'd suggest looking at FX design (https://xdevs.com/article/792x/), which is more traditional and much more friendly and robust for general use.

But you gotta have LTZ or ADR chip first, without it not much can be built.
Title: Re: Ultra Precision Reference LTZ1000
Post by: RoadDog on February 20, 2022, 04:56:51 pm
But you gotta have LTZ or ADR chip first, without it not much can be built.

Does it have to be the ACH or can I use the LTZ1000CH?  I can find those. ACH is out until the end of August unless I want to take my chances with eBay or “quotes” from unauthorized dealers

I tried your cart trick for that ADR on the website. They’re backordered and looks like you have to buy 100 at a time. No more small quantities I think.

Cool build. Love how you just hack random parts from different Fluke products into something.

If I wanted to go that direction are there gerber files somewhere I can download to use at OSHPARK?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Ole on March 01, 2022, 02:04:38 pm
If I am not mistaken the only difference is the thermal resistance.
The LTZ1000 is at 80°C/W and the 1000A is at 400°C/W. (Source: https://www.analog.com/media/en/technical-documentation/data-sheets/LTZ1000.pdf (https://www.analog.com/media/en/technical-documentation/data-sheets/LTZ1000.pdf) )
I am still quite new to the field of electronic measurement but, if you are using an insulating material it should matter relatively little. You might need a bit more insulator though.

The LTZ1000CH#PBF does seem to be in stock at Analog Devices Website, and you can, once its availible again, purchase the 1000A aswell in 20-packs
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on March 03, 2022, 07:36:03 pm
Is there a single-supply op, like the lt1013, but with a 'normal' soic dual pinout?

I ordinarily use opa2277 with +-rails, but get start-up problems when the rail supplies are not sequenced - so I want to switch to single supply.

Most of the modern low noise ops are quite fast/jfet  >10MHz and probably more susceptible to emi. But with an Andreas/Dr Frank compensation capacitor (R/C=10k/10n), i suspect it may not matter.

I found op213, which looks interesting - probably overkill for ltz1000.

lt1013      0.55uVp2p 0.1-10Hz.   drift 2uV/C.   GBW ~= 800kHz-1MHz

op213.   120nV p2p 0.1-10Hz.  offset drift 0.8uV/C best grade. low noise, low drift, single supply op.  4-36V.  GBW 3.4MHz.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 03, 2022, 08:28:47 pm
The OPs drift and noise are attenuated quite a bit. So the OP does not absolutely be low dift and low noise.
The TLE2022 is possible, but not with the best performance.
There are quite a few FET based OPs that could work (e.g. TLC272 / TLC277 / OPA2196 ) - though not highes performance. Not all are super fast.

The ADR1000 DS suggsts the ADA4084 , though this one could be tricky with the input bias current changing just at around 0.5 V where it is used. So it would not be my choice.

The OP213 would also not be that good, as it has quite some current noise and the source impedance would be around 50 Kohms. So it would be more noisy than an LT1013 and maybe even LM358.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 03, 2022, 08:42:40 pm
Hello,

I´d probably go with the ADA4522-2. (because of higher Large-Signal Voltage Gain).
And of course it is not forbidden to put a weak pull up on the zener for start-up.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on March 03, 2022, 09:40:13 pm
hmmm. that's a bad miscalculation on my part. input bias current (leading to current noise) of op213 is high 600nA max, versus 15nA typ lt1013, versus 2-4nA typ opa2277.

It is interesting that bipolar ada4084 is recommended for ADR1000 despite 16MHz GBW.

Is there a reason not to consider jfet input? Bjt has better gain and lower flicker noise. But the datasheet specs of modern jfet are also very good - presumably due to extra complexity around the input stage.

For example, opa2140 (Input voltage range includes V– supply) - and using a compensation/bypass capacitor to slow things down/address emi.

I am using mc33172 right now as a test - basically equivalent to lm358. 
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on March 03, 2022, 09:42:43 pm
Quote
And of course it is not forbidden to put a weak pull up on the zener for start-up.

Ohhh. very interesting, this might be simplest solution. I was also considering the discrete jfet thing in the 34401a used with the lm399 to bias the startup, but its tending to too much complexity.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 03, 2022, 09:49:55 pm
An Az OP can be tricky for 2 reasons: one is the start up (there may be some delay, though usually not too bad) and the other is the the input current, that often includes short current spikes that can upset the reference.  So an AZ OP may look good from the drift and low frequency noise, but may still cause extra noise. An AZ OP may want some extra filtering and good supply decoupling. So it may not work well in an unmodified circuit. The change for the slightly unusual pinout of the LT1013 is likely easier.

The ADA4522 is very low voltage noise, but this comes with relatively high current noise and also likely with relatively large current spikes.
So the AZ OP of choice would be more a type more suitable for a higher impedance like LTC2058, OPA2187, NCS21912 or AD8639. Less heat from a lower supply current also helps. The choice of AZ OPs for higher voltage is somewhat limited.

I see no absolute reason not to use a JFET type. The OPA2145 or OPA2196 may be an option.
Even the MC33172 may still be not that bad - the OPs noise and dirft are attenuated by about a factor of 200. So the OPs noise would still be a small contribution.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Cerebus on March 03, 2022, 10:10:24 pm
Quote
And of course it is not forbidden to put a weak pull up on the zener for start-up.

Ohhh. very interesting, this might be simplest solution. I was also considering the discrete jfet thing in the 34401a used with the lm399 to bias the startup, but its tending to too much complexity.

On the schematics for the 34401A that I have the startup circuit for the LM399 is a pull-up via a diode (1/2 a BAV99) and then 1k resistor to the +5V rail. Where did you you see a JFET?
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on March 03, 2022, 10:20:41 pm


On the schematics for the 34401A that I have the startup circuit for the LM399 is a pull-up via a diode (1/2 a BAV99) and then 1k resistor to the +5V rail. Where did you you see a JFET?

You're right, 34401a is 1k bias to 5V.  I was thinking of this self-start for lm399, https://www.eevblog.com/forum/metrology/influence-of-resistors-in-lm399-reference-circuit/msg1212712/#msg1212712 (https://www.eevblog.com/forum/metrology/influence-of-resistors-in-lm399-reference-circuit/msg1212712/#msg1212712)
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on March 04, 2022, 12:43:20 am
Ok, went back to the dual supply opa2277. Then applied the 344401a zener startup method.   

3.3V rail -> mmbd4148 -> 1k as pullup.

It appears to work well. The 3.3V digital supply is not ideal, given potential capacitive coupling, but is sufficient for the moment.

The question now is - can the in-loop diode at the op output be eliminated? I don't think serves any other purpose except as a bias - and is a potential source of emi rectification?
 
Edit. seems to work fine, with in loop diode removed. edit2. now seems not to be 100%.. ok, lowering the resistance, to increase pullup, and better control over the op loading, and it seems reliable.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on March 04, 2022, 07:44:31 am
That diode you eliminated prevents the opamp from blocking startup. Startup will then depend somewhat on the opamp input and output characteristics. One can bypass the diode with a 10 nF cap to prevent RF rectification.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 04, 2022, 08:06:16 am
Hello,
with a dual supplied OP-Amp or a OP-amp which can go below 0.5V at the output there is always risk to forward bias the substrate diodes in the LTZ1000. I would not want to remove this diode.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on March 04, 2022, 10:28:22 pm
Hello,
with a dual supplied OP-Amp or a OP-amp which can go below 0.5V at the output there is always risk to forward bias the substrate diodes in the LTZ1000. I would not want to remove this diode.

with best regards

Andreas

Thanks, I think I agree.
Title: Re: Ultra Precision Reference LTZ1000
Post by: RoadRunner on March 07, 2022, 02:34:11 pm
Hello to all,

I am looking to make a reference board with LTZ1000. I wonder where do people find these impossible to find resistors?
If any one already have these resistors for sale, I would love to buy them.

Is there a group buy planned? Are there other people looking for them? May be we can plan a group buy.


Regards
Title: Re: Ultra Precision Reference LTZ1000
Post by: Ole on March 07, 2022, 03:57:28 pm
Currently cou could get the LTZ1000CH#PBF from mouser.com, but not the 1000A
If we could organize a group buy for the Resistors and/or for the 1000A (once it is availible again from analog.com or other vendors),
I would very much be interested to participate.

Edit: The resistors are mostly from http://www.vishaypg.com/foil-resistors/hermetically-sealed/ (http://www.vishaypg.com/foil-resistors/hermetically-sealed/) for the hermetically sealed ones.
And yes the ordering from Vishay is not the simplest. I haven´t placed a order with them yet.

Edit2: The datasheet specifies a 13k/1k divider, does anyone know the resulting temperature from the upper resistor across multiple values?

Ole
Title: Re: Ultra Precision Reference LTZ1000
Post by: maat on March 07, 2022, 06:48:27 pm
In Germany the Vishay distributor is BADER GmbH & Co. KG (https://www.bader.net/ (https://www.bader.net/)). Send them an email, be prepared for hefty prices and long wait times (14 Weeks or so).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 07, 2022, 07:46:20 pm
At least for the first test one does not need the absolute highest stability resistors.  E.g. Mouser has 1 K and 13 K resistors in the S102 version (plastic case metal foil).

Some of the divider ratios can also be obtained with resistor networks: e.g. 1:12.1 from a dual 10K/1K. This is at the lower temperature end, but may still be OK for the non A version. A smaller resistor for R2 can shift the temperature up a little if needed.
The 8 or more equal resistor networks can also do some rations like 1:12 and 1:15 and 1:14 (AFAIR) and maybe a fre more.
Title: Re: Ultra Precision Reference LTZ1000
Post by: martinr33 on March 07, 2022, 08:15:31 pm
I have had good results from these folks:

http://webdirect.texascomponents.com/SearchResults.asp?Cat=1842 (http://webdirect.texascomponents.com/SearchResults.asp?Cat=1842)

You have to call / email to get quotes, and they do have a small premium for single parts. They are a Vishay licensee. They also used to have VHP devices, but they do not show them on their web page which means they could have a supply problem. Also, if you call them, they may have parts not on the web site. Generally, I have had them ship in a couple of weeks.

Also:
https://www.ebay.com/itm/121777259014?hash=item1c5a7d8206:g:x8wAAOSwVL1WD3Em (https://www.ebay.com/itm/121777259014?hash=item1c5a7d8206:g:x8wAAOSwVL1WD3Em)
for example.



Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 07, 2022, 09:25:03 pm
Hello,

according to the datasheet:

"With the values given in the applications, temperature is normally 60°C."
From there you can extrapolate the resistors with the typical -2mV/deg C of the base emitter diode.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on March 07, 2022, 09:39:35 pm
Quote
The 8 or more equal resistor networks can also do some rations like 1:12 and 1:15 and 1:14 (AFAIR) and maybe a fre more.

And even more ratios: https://xdevs.com/guide/rnet_ratio/ just pick the one you need.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: Ole on March 07, 2022, 10:42:48 pm
"With the values given in the applications, temperature is normally 60°C."
From there you can extrapolate the resistors with the typical -2mV/deg C of the base emitter diode

I would presume that the average voltage across R4 and R5 would be 7,7V which would give UR5 with 13k on R4 a value of 550mV approximately.
Since I don´t yet know the normal UBE of Q2 nor the normal temperature, I am gonna presume a temperature of 20°C and 0.65V.
My target oven temperature is between 40°C and 50°C which would mean that the UBE of Q2 would be at 0.6V so a 1k/12k Divider should do the job.
Although I might want to add a spot for an SMD resistor besides each part of the divider os that I can adjust the temperature by addding higher resistance values in paralell.

Ole
Title: Re: Ultra Precision Reference LTZ1000
Post by: julian1 on March 08, 2022, 03:12:57 am
Are there any reports of improvement in low frequency noise (current leakage, da, acoustic pickup) with film versus c0g/x7r  - for the 22nF or 100nF compensation cap (if used)?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 08, 2022, 05:16:27 am

I would presume that the average voltage across R4 and R5 would be 7,7V

No the output voltage is 7.2 V per data sheet.

by the way I published all operating points of some of my references here:
https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560)

the 0.53x V give around 52 deg C heater temperature which is enough for about 40 deg C environment temperature.
Note that the "environment temperature" of the reference internal of a housing is higher than room temperature.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 08, 2022, 07:06:57 am
Are there any reports of improvement in low frequency noise (current leakage, da, acoustic pickup) with film versus c0g/x7r  - for the 22nF or 100nF compensation cap (if used)?
The usual choice is using film caps - this was at least before higher capacitance C0G were available. The reference is static and dielectric absorbtion would have essentially no effect.  By now the price for C0G caps even with 100 nF is at an acceptable level and there is no real need to take the risk with X7R or similar with possible acoustic pickup and leakage.   I don't think X7R was ever a good choice.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Ole on March 20, 2022, 12:44:40 pm
So I´ve worked on a version of the LTZ1000(A) Reference Voltage Circuit that gives +10V and -10V as output.
Most of the circuit originates from the datasheet, I just added the ouput stage.
Edit: The added file is for the Falstad Simulator, I hope that is works
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 20, 2022, 01:05:20 pm
So I´ve worked on a version of the LTZ1000(A) Reference Voltage Circuit that gives +10V and -10V as output.
Most of the circuit originates from the datasheet, I just added the ouput stage.
Edit: The added file is for the Falstad Simulator, I hope that is works
That circuit looks horrible:
The compensation for the temperature regulation is wrong in the main reference part.
The added part to generate the +-10 V is made would have poor performance. There is a good intention to get some kelvin sensing, but the difference ampfier would just add way too much drift, making things only worse.

The more practical way is to avoid the extra stage and use some compensation of the ground current to get a good apprixmation to kelvin sensing. Depending on the rest of the circuit / supply, one could also just have a seprate ground for the supply and output side, meeting at a star ground point near the LTZ1000 ground.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on March 20, 2022, 03:04:52 pm
Hello,

the scaling resistors are rather high-ohmic.
Depending on OP-Amp you may get high current noise.

No further comments as the schematic is near un-readable.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Ole on June 10, 2022, 06:34:01 am
I´ve got a question about R2 and R3:
Can the values of these resistors theoretically be reduced to approx. 50kOhms?
Also, I´ve heard somewhere that R2 and R3 can theoretically be 5ppm/°C as well.
Is that an option or rather not?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on June 10, 2022, 07:27:14 am
A different value for R2 and R3 is definitely an option. The data-sheet already has circuits with 30 K and 50 K as examples. There is also no real need to have the same value and type for R2 and R3 - the main reason is a simpler BOM. More current at the transistors gives slightly less temperature effect from the transistors (which is not good), but with only 50 K the differente is minute ( some 1% for the temperature sens and some 3 ppm/K for the unheated TC). On the upside the noise is marginally lower. A somewhat higher values (e.g. 100 K) would work as well, but chances are that there is not much difference. With a much different value (e.g. 300 K or 20 K ) one may have to adjust some of the capacitors too.

5 ppm/C, 10 ppm/C and maybe even 25 ppm/C would still be acceptable for the resistors. The relevant question is more the long term stability and a low TC is used as a overall parameter to judge resistor quality, as specs for the long term drift are rare and vague. The drift is attenuated by a factor of some 100 to 500. So 10 ppm/C for the resistor would lead to some 0.02 to 0.1 ppm/C for the voltage and thus likely only a small contribution. If the same resistor series is available in 2, 5 and 10 ppm/K grades it may not make a big difference to use the best selection there.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Ole on June 10, 2022, 08:15:10 am
The reason why I would differ from the ususal 70k value is because there are 50k SMD resistors with a near zero tempco,
and those are in stock. Theoretically one could place two resistors in series but that could introduce thermal EMF.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on June 10, 2022, 06:35:12 pm
I´ve got a question about R2 and R3:
Can the values of these resistors theoretically be reduced to approx. 50kOhms?
Also, I´ve heard somewhere that R2 and R3 can theoretically be 5ppm/°C as well.
Is that an option or rather not?

Hello,

50k is possible.

Keep in mind that this will increase the sensitivity of setpoint temperature resistor ratio changes (1K/12K5) by about 10%.
So about 1.1 ppm / 100 ppm instead of 1 ppm/100 ppm ratio change.
Measured values should be somewhere at the beginning of this thread when I made measurements on my LTZ1000A #1 and #2.

The 70K resistor changes have low influence on overall T.C. so put your money mainly on the setpoint temperature resistor ratio.

with best regards

Andreas

edit: see here:

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg436981/#msg436981 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg436981/#msg436981)

Title: Re: Ultra Precision Reference LTZ1000
Post by: cellularmitosis on August 13, 2022, 10:08:14 am
If we look at just the refamp portion of the 7V LTZ circuit, we have this:

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1564219;image)

This got me thinking, could we just add one additional resistor to produce 10V?  Has anyone tried this?

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1564225;image)
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on August 13, 2022, 10:22:17 am
The proposed circuit will work, yet it will be useless.
Ube of the transistor adds a -2 mV/K temperature coefficient. This is to compensate the TC of the zener, so it vanishes (mostly). Now you multiply that by 600R/120R = 5 and there will be a TC of -10 mV/K in 10 V = -1000 ppm/K.
Now you can argue the LTZ1000 has a near perfect oven, but still this won't work well. Unless you  find a way to compensate the TC once more, maybe using the temperature sensor inside the LTZ1000.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: KT88 on August 13, 2022, 01:42:24 pm
No. Vbe is changing slightly with temperature which results in a change of Iz. There is one resistance value where the temperature drift will be compensated. You find this application example in the DS for an unheated LTZ1000. If the resistance is increased the over all drift worsons…
Also with the heated device there will be slight changes in the zener current which will be exaggerated by the additional resistance.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on August 13, 2022, 02:35:44 pm
No, the resistor value for fine tuning TC is around 10 or at most 20 Ohms.
The intention of the proposed circuit was to raise the reference output to 10 V.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: KT88 on August 13, 2022, 02:58:21 pm
Increasing the resistor further than 20ohms would overcompensate the drift. You would need about 600 Ohms at 5mA Iz to get to 10V. That would mean you are overcompensating by 30 - 60x…
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on November 22, 2022, 08:37:31 am
I think I have a similar experience with my first LTZ1000A.
CORRECTION: As soon as the board is assembled, the buffered output is giving me 7.11793.
Exactly the same of the 10.0000V V Ref b. Resistance between pin 2 and pin 6 LTC1052 is around 16.2kOhm, but OpAm is not working.
Not sure what the problem is though.

I am not sure what happened as I was very careful assembling the reference...


 PS Any idea where to source LTC1052??? Its obsolete
      Any direct replacement? TLC2654ACP?


One of my LTZ1000 reference circuits failed.  The LTC1052 output was oscillating and the failure occurred when I placed the circuit in a homemade cooler/foam box to measure its temperature performance.  I assume a static charge destroyed the LTC1052.  After replacing that IC, all is back to normal.

The LTC1052 is a CMOS device and perhaps should not be placed in a foam box?  A partial schematic is included ... you might recognize the good work of Dr. Frank.
Title: Re: Ultra Precision Reference LTZ1000
Post by: blackdog on November 22, 2022, 09:29:28 am
Hi alex-sh,

Have you considered that your measuring leads are a capacitive load on your circuit?

Chopper opamps do not like capacitive loads, see the datasheet for more details.

Your NTC is hanging loose, it can never give a stable reading this way.

Kind regards,
Bram
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on November 22, 2022, 10:06:27 am





Hi alex-sh,

Have you considered that your measuring leads are a capacitive load on your circuit?

Chopper opamps do not like capacitive loads, see the datasheet for more details.

Your NTC is hanging loose, it can never give a stable reading this way.

Kind regards,
Bram

Hi,

No. I do not see the same behavior on other LTZ1000 modules with the same leads.
Why do you think NTC is a problem? I wanted it to be long enough to read a temp around LTZ1000A
Title: Re: Ultra Precision Reference LTZ1000
Post by: blackdog on November 22, 2022, 11:18:38 am
Hi Alex,

Stability
Just because another module seemed "stable" does not mean that other modules will then also be stable....
There is always component spread even if you use the same parts with the same schematic and circuit board.

It is up to the builder to figure out to what extent a schematic and setup is stable.

NTC temperature measurement
Ask yourself, what are you measuring at the position where that NTC is hanging?
Is the draft (there always is) coming from the direction of the LTZ1000's legs or from some other direction, does the circuit board stay horizontal or is it mounted vertically?

And also don't forget that the wires of the NTC are a fair part of determining the measured temperature.

Can you show "your" schematic here that you built on the circuit board?
You may have made minor modifications that could be important.
Of course with the component values you used that are on the circuit board.

Then it will be easier to help you identify the cause of the instability.

Kind regards,
Bram

Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on November 22, 2022, 12:33:32 pm

 PS Any idea where to source LTC1052??? Its obsolete
      Any direct replacement? TLC2654ACP?

The TLC2654 sees to be a little lower in noise and higher bias. The ICL7650 would be on the other side with lower bias, higher noise. The exact values can scatter.
For the amplifier from 7 to 10 V one may also change to another AZ OP amp that can withstande a 12-16 V supply, like LTC2057 or MCP6V51 or OPA189. These are lower voltage noise, but even higher bias and don't need external capacitors.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on November 22, 2022, 02:06:58 pm
Hi Alex,

Stability
Just because another module seemed "stable" does not mean that other modules will then also be stable....
There is always component spread even if you use the same parts with the same schematic and circuit board.

It is up to the builder to figure out to what extent a schematic and setup is stable.

NTC temperature measurement
Ask yourself, what are you measuring at the position where that NTC is hanging?
Is the draft (there always is) coming from the direction of the LTZ1000's legs or from some other direction, does the circuit board stay horizontal or is it mounted vertically?

And also don't forget that the wires of the NTC are a fair part of determining the measured temperature.

Can you show "your" schematic here that you built on the circuit board?
You may have made minor modifications that could be important.
Of course with the component values you used that are on the circuit board.

Then it will be easier to help you identify the cause of the instability.

Kind regards,
Bram



Hi,

Please see attached the schematic. This is a modified Dr Frank module. I have built several of these without any issues, but LTZ1000
This one is LTZ1000A with corresponding 1K/13k divider. Something is not working correctly on the LTC1052 side...

Regards
Alex
 
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on November 22, 2022, 02:07:44 pm
Ok, what would you recommend as a direct replacement?



Hi Alex,

Stability
Just because another module seemed "stable" does not mean that other modules will then also be stable....
There is always component spread even if you use the same parts with the same schematic and circuit board.

It is up to the builder to figure out to what extent a schematic and setup is stable.

NTC temperature measurement
Ask yourself, what are you measuring at the position where that NTC is hanging?
Is the draft (there always is) coming from the direction of the LTZ1000's legs or from some other direction, does the circuit board stay horizontal or is it mounted vertically?

And also don't forget that the wires of the NTC are a fair part of determining the measured temperature.

Can you show "your" schematic here that you built on the circuit board?
You may have made minor modifications that could be important.
Of course with the component values you used that are on the circuit board.

Then it will be easier to help you identify the cause of the instability.

Kind regards,
Bram



Hi,

Please see attached the schematic. This is a modified Dr Frank module. I have built several of these without any issues, but LTZ1000
This one is LTZ1000A with corresponding 1K/13k divider. Something is not working correctly on the LTC1052 side...

Regards
Alex
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on November 22, 2022, 02:10:56 pm
My LTZ1000A is covered to minimise any draft - both the head and the legs.
I am measuring the temperature of environment next to LTZ1000A module.
This is a horizontal board.

Schematic is attached to the previous post.





Hi Alex,

Stability
Just because another module seemed "stable" does not mean that other modules will then also be stable....
There is always component spread even if you use the same parts with the same schematic and circuit board.

It is up to the builder to figure out to what extent a schematic and setup is stable.

NTC temperature measurement
Ask yourself, what are you measuring at the position where that NTC is hanging?
Is the draft (there always is) coming from the direction of the LTZ1000's legs or from some other direction, does the circuit board stay horizontal or is it mounted vertically?

And also don't forget that the wires of the NTC are a fair part of determining the measured temperature.

Can you show "your" schematic here that you built on the circuit board?
You may have made minor modifications that could be important.
Of course with the component values you used that are on the circuit board.

Then it will be easier to help you identify the cause of the instability.

Kind regards,
Bram


EDITED: Solved! One of jumper wires had a bad connection and it was not noticeable at all. The lesson learnt - double and triple checking everything
Title: Re: Ultra Precision Reference LTZ1000
Post by: Villain on November 30, 2022, 06:46:00 pm
anyone know where to source ltz1000ach nowadays without 100 weeks lead time?
Title: Re: Ultra Precision Reference LTZ1000
Post by: arcnet on November 30, 2022, 10:14:56 pm
anyone know where to source ltz1000ach nowadays without 100 weeks lead time?

Buy some 03458-66509 or 03458-66519... More seriously: I don't know. Currently I'm offering my customers to get LM399-based references instead which will be replaced when the LTZ1000 or ADR1000/ADR1001 are available (again)...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Ole on December 01, 2022, 01:48:48 pm
Additionally the Vishay Precision Website (www.vishaypg.com (http://www.vishaypg.com)) is also unavailible
Title: Re: Ultra Precision Reference LTZ1000
Post by: quarks on December 07, 2022, 04:46:49 pm
anyone know where to source ltz1000ach nowadays without 100 weeks lead time?

Send me a PM I have some in stock
Title: Re: Ultra Precision Reference LTZ1000
Post by: The Bootloader on December 25, 2022, 11:12:01 am
I recently got 2 LTZ1000A, directly from Analog. The leadtime was insane, but at least I got them, and it rewarded to be patient... I am now looking for a nice reference design. Any suggestion as to which one I should build? I have noticed there are a few designs available.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Villain on December 25, 2022, 05:09:43 pm
I recently got 2 LTZ1000A, directly from Analog. The leadtime was insane, but at least I got them, and it rewarded to be patient... I am now looking for a nice reference design. Any suggestion as to which one I should build? I have noticed there are a few designs available.

If i would have two chips i would build one Dr Frank's and one TiN's design. Just to have some variety and maybe compare (comparing one with one is not much statistics to go with but oh well)

Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 25, 2022, 06:40:29 pm
Hello,

Cellularmitosis has published some PCBs of 7V LTZ designs on his GitHub.

E.g:
https://github.com/pepaslabs/dr-frank-ltz1000

https://github.com/pepaslabs/px-ref

The leadtime was insane.

I hope you have already ordered the necessary precision resistors.
Otherwise you might have to wait another 6-14 weeks.

The stability of those references also depends on mechanical design (air drafts)
and EMI disturbances (mobiles / LED lamps) in your environment.

Which design to choose is mainly dependant on your personal preferences.
- dual supply / single / battery powered supply
- 7V / 10V output
- your environment conditions

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Haasje93 on December 28, 2022, 02:01:46 pm
Hi,

I found mine LTZ1000 PCb and parts in a forgotten corner in my home lab, it's a shame i know.. :palm:
I am busy with completing the PCb and i have already made the housing.
I have a question about the LTZ1000, I have red that the LTZ must not be mounted directly against the PCB. There has to be some room between them, i have also red that you should protect the leads againt any drafts. I found a bag of teflon tubing, i figured that i can put a single piece of tube around every lead to protect it against drafts. What do you think?

Kind regards,
Christiaan
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on December 28, 2022, 03:32:52 pm
Hello,

I usually put some foam around the whole LTZ (including the leads)
And of course do not forget the soldering side of the PCB.

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg250759/#msg250759 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg250759/#msg250759)

Others use a plastic cap over the LTZ.

with best regards

Andreas



Title: Re: Ultra Precision Reference LTZ1000
Post by: branadic on December 29, 2022, 04:14:29 pm
There is also the simplified LTZ reference circuit based on W/F7000 available,that only needs one "better" resistor and is otherwise using resistor networks, no need to spend gold on expensive components with long lead-times.

-branadic-
Title: Re: Ultra Precision Reference LTZ1000
Post by: The Bootloader on January 07, 2023, 04:09:48 am
https://github.com/pepaslabs/dr-frank-ltz1000 (https://github.com/pepaslabs/dr-frank-ltz1000)

https://github.com/pepaslabs/px-ref (https://github.com/pepaslabs/px-ref)

Awesome, looks like two solid designs. Not sure yet which one I want.
I don't mind 7V or 10V, I think it does not make a big difference.
I would say, instead, that I would rather do whatever circuit performs the best.

I hope you have already ordered the necessary precision resistors.
Otherwise you might have to wait another 6-14 weeks.

Yes, thankfully, there was a group order (https://www.eevblog.com/forum/metrology/group-buy-ltz1000a-precision-resistor-set-(econistor-8g16-precision-wirewound)/) a few months back and I got 120, 1K, 12.5K, 2x70K. I regret (a lot) not getting more than one set, but heh, better than nothing and enough for one reference with typical circuits. They are not the famous VHP100 series, but should still perform well.

The stability of those references also depends on mechanical design (air drafts)
and EMI disturbances (mobiles / LED lamps) in your environment.

I plan to just put the damn thing into a block of foam. Brute force method :-DD

Which design to choose is mainly dependant on your personal preferences.
- dual supply / single / battery powered supply
- 7V / 10V output
- your environment conditions

What I would like is to get something like a Fluke 732A in terms of features. I would love to have something that can be AC powered, but also run on battery for up to a few days so I can move it around freely or even ship it (cal club heh?) and not worry about power outages.

Thank you so much Andreas for the valuable feedback. Helped me make progress in my thoughts about what I will build. Still not sure yet, I need to continue digging in the rabbit hole.

There is also the simplified LTZ reference circuit based on W/F7000 available,that only needs one "better" resistor and is otherwise using resistor networks, no need to spend gold on expensive components with long lead-times.

-branadic-

This one? https://xdevs.com/article/b7000/ (https://xdevs.com/article/b7000/)
Interesting design - it seems like it does require quite a bit more initial trimming than the other designs, but that allows for reduced TC with lower cost components.

Aaarg another design to consider building :scared:

Would be interesting to build one of the standard design, and one of this design to compare them. But sadly, with a sample size of only one LTZ per design type, I think I would be comparing the actual LTZs and not the designs.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 18, 2023, 07:30:15 am
anyone know where to source ltz1000ach nowadays without 100 weeks lead time?

Yes, it is a disaster.
Not just for LTZ1000
I have been waiting for LTC6655 in ceramic for months now.
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on January 18, 2023, 07:56:01 am
That's what I do for my references as well.
1. Put a plastic cap on top of LTZ1000. Ideally it should cover the LTZ1000 and leads. I do not solder LTZ1000 "on the board". It is slightly elevated above the board.
2. If not - cover LTZ1000 leads with a foam.
3. cover soldering pads on the other side of the PCB with foam.

Hello,

I usually put some foam around the whole LTZ (including the leads)
And of course do not forget the soldering side of the PCB.

https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg250759/#msg250759 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg250759/#msg250759)

Others use a plastic cap over the LTZ.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on January 18, 2023, 08:05:21 am
anyone know where to source ltz1000ach nowadays without 100 weeks lead time?
Yes, it is a disaster.
..
Could it be they are going to discontinue the LTZ1000? They source vendors till the stock is empty, the vendors are changing their designs to the ADR1000 or ADR1001 already. It has no sense to manufacture three almost identical references, especially the ones in metal..
Title: Re: Ultra Precision Reference LTZ1000
Post by: syau on January 18, 2023, 02:42:41 pm
anyone know where to source ltz1000ach nowadays without 100 weeks lead time?
Yes, it is a disaster.
..
Could it be they are going to discontinue the LTZ1000? They source vendors till the stock is empty, the vendors are changing their designs to the ADR1000 or ADR1001 already. It has no sense to manufacture three almost identical references, especially the ones in metal..

Did a Mouser back order on 22 Oct, received 11 Jan.
Title: Re: Ultra Precision Reference LTZ1000
Post by: RikV on February 06, 2023, 07:33:27 pm
Is the project documentation on the FXref (TiN) publicly available? On Hithub or something? I'd like to build one but I am unable to find the necessary documentation (especially the gerbers).
Title: Re: Ultra Precision Reference LTZ1000
Post by: Tj138waterboy on February 06, 2023, 07:50:48 pm
https://xdevs.com/article/792x/
Title: Re: Ultra Precision Reference LTZ1000
Post by: RikV on February 06, 2023, 08:51:35 pm
Tj138waterboy,
Due to my age, I may have bad eyes, but on xDev site I only find a schematic in .pdf format but no real project (ECAD-)documentation nor Gerber files. Could you point me to where these links are? Please?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Tj138waterboy on February 06, 2023, 09:42:59 pm
Unless im mistaken TIN is the only one to design and complete the FX version and probably would be the only person with the files but I reread previous threads and found this info. It appears you would be better off getting one of the many oshpark pcbs as the FX is multilayer.
Nope, due to high cost only 14pcs of these modules will exist in the world, sorry.

KX one is available on OSH Park for PCBs : https://oshpark.com/shared_projects/HfKcqjV3
(LTZ chips you can buy from ADI and resistors from Edwin Pettis here or VPG).
Title: Re: Ultra Precision Reference LTZ1000
Post by: RikV on February 06, 2023, 10:54:28 pm
Is the quote in your reply from TiN himself? this surprises me since he advised someone in this thread to build the Fx instead of KX since it was a "better design", in his own words.
Being 4-layer is no problem and not so excessively expensive in regard to the other components on the board. Anyway, OSHpark is not the only company to produce multilayers in small quentities and by far not the cheapest. But thanks for the effort.
Title: Re: Ultra Precision Reference LTZ1000
Post by: r6502 on February 07, 2023, 12:27:42 pm
@RikV

Have a look here:
xDevs.com KX LTZ1000-based DC Voltage reference design  (https://xdevs.com/article/kx-ref/)

somewhere in the middle of the article, there you can find what you're looking for: Gerber files packed in *.rar format.

Have fun to build it.

Guido
Title: Re: Ultra Precision Reference LTZ1000
Post by: syau on February 09, 2023, 12:19:17 am
@RikV

Have a look here:
xDevs.com KX LTZ1000-based DC Voltage reference design  (https://xdevs.com/article/kx-ref/)

somewhere in the middle of the article, there you can find what you're looking for: Gerber files packed in *.rar format.

Have fun to build it.

Guido

Think he is looking for KF gerber file instead of the KX
Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on February 21, 2023, 11:59:09 am






anyone know where to source ltz1000ach nowadays without 100 weeks lead time?
Yes, it is a disaster.
..
Could it be they are going to discontinue the LTZ1000? They source vendors till the stock is empty, the vendors are changing their designs to the ADR1000 or ADR1001 already. It has no sense to manufacture three almost identical references, especially the ones in metal..

Did a Mouser back order on 22 Oct, received 11 Jan.



This is pure luck.
Most metal can vref and precision resistors lead time is months.
I am trying to source Vishay VHD divider 10k/27.2k - lead time is 47 weeks!
Title: Re: Ultra Precision Reference LTZ1000
Post by: syau on February 22, 2023, 03:53:31 pm






anyone know where to source ltz1000ach nowadays without 100 weeks lead time?
Yes, it is a disaster.
..
Could it be they are going to discontinue the LTZ1000? They source vendors till the stock is empty, the vendors are changing their designs to the ADR1000 or ADR1001 already. It has no sense to manufacture three almost identical references, especially the ones in metal..

Did a Mouser back order on 22 Oct, received 11 Jan.



This is pure luck.
Most metal can vref and precision resistors lead time is months.
I am trying to source Vishay VHD divider 10k/27.2k - lead time is 47 weeks!

Did ordered some VHD and VHP in Oct 2021 using express service and received in Mar 2022

Price of VHD was around USD$40
Price of VHP was around USD$50~$80

Title: Re: Ultra Precision Reference LTZ1000
Post by: alex-sh on February 23, 2023, 10:23:12 pm






anyone know where to source ltz1000ach nowadays without 100 weeks lead time?
Yes, it is a disaster.
..
Could it be they are going to discontinue the LTZ1000? They source vendors till the stock is empty, the vendors are changing their designs to the ADR1000 or ADR1001 already. It has no sense to manufacture three almost identical references, especially the ones in metal..

Did a Mouser back order on 22 Oct, received 11 Jan.



This is pure luck.
Most metal can vref and precision resistors lead time is months.
I am trying to source Vishay VHD divider 10k/27.2k - lead time is 47 weeks!

Did ordered some VHD and VHP in Oct 2021 using express service and received in Mar 2022

Price of VHD was around USD$40
Price of VHP was around USD$50~$80

Try to order the same resistors now lol  |O
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on February 24, 2023, 09:42:54 pm
Aside from the rant:
When building a LTZ1000 there is no need for those unobtanium resistors. As far as i understand the most critical resistor is the 120 Ohm one that determines zener current. As the typical zener differential resistance of a LTZ1000 is about 7 Ohm, there is a suppression factor 1/17. And the voltage on that resistor is about 0.6 V, another factor 11 lower than the 7 V zener voltage.
Total suppression factor should be about 1/180. There were some tables posted with these suppression factors, also for the other resistors, but i don't remember in which thread.
If you use a 5 ppm/K resistor like UPW25, the extra TC caused by the resistor is 0.03 ppm/K max. Congratulations if your reference build achieves a TC that low. One can also characterize 5 ppm resistors to select some with a zero TC temperature in the 20 to 40 °C range. And put the board into a hermetic enclosure with desiccant..

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on February 25, 2023, 09:45:06 am
The most critical resistors are the 2 resistors to set the oven temperature. These only matter as a ratio and this can take into account some of the dirft (e.g. the square part of the TC that is often relatively consistent for resistors of the same series / type). Also the use of a resistor array is possible and attractive here. In theory one could have the option to measure the actual ratio (the set voltage) and this way at least detect long term drift if it happens for these 2 resistors.

The attenuation factors are good enough that the TC is usually not that relevant. The limited temperature range also leads to usually better than nominal TC for most resistors.
The need for good resistors is because of the drift with time. Data on the long term drift are however rare and not very reliable - this makes the choice difficult.
Looking at better than 10 ppm/K resistors is mainly in the hope that the lower TC resistors also have better long term stability.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on February 25, 2023, 10:30:45 am
If somebody wants long term stability, they should probably avoid custom made parts as those will be new. Better get parts that have been on shelf for some years.

I think a good LTZ1000 build should incorporate tuning of the LTZ1000 TC using an oven temperature scan and some means of amplifying or attenuating the amount of TC compensation by the transistor. Usually amplification is required. One method is a voltage divider made of a 10 or 20 Ohm resistor in series with the zener and that 120 Ohm resistor.  This can raise the compensation from "native" -2 mV/K / 7V = -285 ppm/K to -300 ppm/K or whatever is needed.
After this kind of fine tuning the oven stability becomes less critical. When building an array it should even be possible to use one external oven for all references.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on March 19, 2023, 10:28:55 am
In an LTZ1000 or ADR1000 reference one might parallel the two transistors in order to improve noise. One can still measure temperature from Ube. Anybody tried this?

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on March 19, 2023, 10:48:43 am
In an LTZ1000 or ADR1000 reference one might parallel the two transistors in order to improve noise. One can still measure temperature from Ube. Anybody tried this?

Regards, Dieter
Isn't most of the noise coming from the zener itself?
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on March 19, 2023, 05:54:41 pm
There is only one zener in the LTZ1000, but two transistors.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: MK on March 19, 2023, 06:56:24 pm
That is irrelevant, the transistors are going to be ~2-5nV root hz, the zener about 50-100nVroot hz, the transistor noise is almost irrelevant in any of the sensible designs in use
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on March 19, 2023, 08:34:59 pm
So, you did not try and you won't try.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: magic on March 19, 2023, 08:43:24 pm
Measure noise at pin 4, compare against pin 3.
If it's less, there is no point even thinking about it.

Something to consider:
LT1007 runs its input stage transistors at 120μA each and achieves 60nVpp typical noise voltage over 0.1~10Hz.
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on March 19, 2023, 09:21:05 pm
With the notorious 70K resistor the transistor in the LTZ1000 has a collector current of about 93 uA, so the base current will be less than 1 uA. Don't know what this means for the noise.
Anyway, with a reference one would not so much worry about noise but about long term stability. My understanding was the very low transistor currents were to protect the device from aging. But maybe that was fantasy.
Also i remember an argument about whether one should use a capacitor across the zener like proposed in the ADR1000 datasheet or whether it can cause accelerated aging of the zener.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on March 19, 2023, 09:36:53 pm
100 µA of collector current is a reasonable current to get low noise (e.g. 2-5 nV/root Hz range) from a BJT. The base current is only adding current noise, not helping with less voltage noise.
So there is a good chance to get rather low noise from the transitor with the standard 70 K resistors. This is at least for the white noise part, but the LT1007 example shows that also 1/f noise can be pretty low with a comparable current. For the comparison the actual transistor size may also matter and it is not that easy to compare.
100 µA of collector current is actually not that small. It is a perfectly OK choice for an 2N3904 used as an amplifier.


I don't see very much chance for aging from a little more current. The transistor operates with a very low voltage (collector at base level and thus some 0.6 V only). So no chance for realy hot electrons.
The current density is still pretty low to expect anthing of electromigration in the aluminum.
Title: Re: Ultra Precision Reference LTZ1000
Post by: aronake on April 17, 2023, 01:52:43 pm

-DatasheetLymexJanaf
R110.14-0.14
R20.30.4-0.4
R3 0.20.03-0.07
R4/R5 1.00.95+1.2




-   Datasheet   Lymex    Janaf       Aron
R1       1.0      0.14        -0.14     -0.15
R2       0.3      0.4          -0.4       -0.45
R3       0.2      0.03         -0.07    -0.065
R4/R5  1.0      0.95        +1.2       0.95

Adding my sensitivity measurements on this classic table. Done with base of reference design.

Some added observations

R1       Higher senstivity at lower ohm. -0.17 at 100 ohm
R2       Higher senstivity at lower ohm. -0.53 at 55K ohm
R3       Higher senstivity at lower ohm. -0.078 at 55K ohm
R4/R5   Lower senstivity at higher ratio. 0.66 at 15. 0.99 at 12.


Title: Re: Ultra Precision Reference LTZ1000
Post by: Dunckx on April 27, 2023, 04:10:24 pm
Mouser currently have 1153 LTZ1000A...for how long?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Martinn on May 07, 2023, 02:30:28 pm
Hi all,

having read through a good part of this thread, I'd like to build a few (1-3, depending on cost) LTZ1000 references as well. I don't usually do precision stuff, best I have right now is a recent DMM6500 6.5 digit bench DMM.
What I'd like to do is
- build 1-3 units (depends on resistor cost)
- let them run a few 100 hours
- bring them to the local cal lab for a precise measurement (and repeat that say every year cost permitting).

I have a few questions! It seems that the peak of this activity was the massive group buy https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1837169/#msg1837169 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg1837169/#msg1837169) of branadic's board in September 2018. I hope there's still someone around...

- Are the design files of this group buy (schematic/PCB in eagle for KiCad format) somewhere available?

- How useful in real life is the 10 V output (besides aesthetics and the extra callenge)? It seems this adds complexity, extra error sources (amplifier) and potentially lots of extra drift (boost divider).
Let's say I want to measure an unknown 5 V reference. I can either hook up the LTZ1000 7 V to the DMM6500 first to see where it stands or I can connect both unknown 5 V and LTZ 7 V to the DMM in ratio mode (not sure what's better).

- How important is an output buffer to the zener voltage? I'd connect mostly DMM inputs (10M) to the output and also the cal lab probably will do that. A buffer adds error sources and cost. AN86 https://www.analog.com/media/en/technical-documentation/application-notes/an86f.pdf (https://www.analog.com/media/en/technical-documentation/application-notes/an86f.pdf) p. 46 lists an LTC1150/LT1010 as possible buffer, but I don't think I need the large current drive and would feel better without chopper artifacts.

- What power supply scheme are you using? The branadic circuit has an LT1763 ultra low noise LDO on board, generating +12 V. As the supply would run continously, an abandoned linear lab supply is probably excessive. Switch mode wall wart too noisy. So a small mains transformer/rectifier might be OK (12 V rectified giving some 18 V)? Or pre-regulate to maybe 14 V to reduce power in the LTZ box?

- What about ground, earth and shielding? Guarding seems not necessary as everything is low impedance. A mains supply with unshielded transformer would AC couple the mains voltage to the output, so a 1 nF...1 uF capacitor from supply GND to Earth (PE) would make sense. This also rules out 2 pin supplies, as they don't have a PE connector. What about the LTZ1000 box itself? Connect to PE (how)? Connect (via capacitor) to supply GND? Anodized aluminium is a pretty good isolator, did anyone bother trying to properly contact the anodized housing parts?

- Precision resistors: I asked Edwin and he might be able to supply a set. Apart from that, are there any realistic sources? 70 k and 12.5 k seem pretty exotic values. I think this is the main killer for the entire build.

Thanks! Martin
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 07, 2023, 03:44:14 pm
Hello,

just some experiences / thoughts.
- you will need some kind of buffer (otherwise in case of a accidential (even very short) short cirquit the reference will age very fast and need some months to recover).
- I recommend either a ADA4522-1 or a LTC2057 as buffer (LT1010 is not needed).
- I would build at least 3 devices so you can decide which one is the worst of the group.
- few 100 hours is not always sufficient. I have 2 samples of LTZ which needed over one year to stabilize below 2 ppm/year.
- 10V output is useful for devices with artifact calibration like 3458A
- I am using battery supply (14-18V) and LT1763 (14V). The LT1763 should be far away from the rest of the cirquilt to improve PSRR.
- with the batteries completely within the metal housing the housing can be used as guard.
- keeping power losses constant helps to improve stability of the reference.
- the special resistor values are usually built to order.
- Besides Edwins I have also ordered Vishay from Powertron/Teltow or built from series connected UPW50 stock values (RS).

with best regards

Andreas

Title: Re: Ultra Precision Reference LTZ1000
Post by: Martinn on May 07, 2023, 04:26:05 pm
- I am using battery supply (14-18V) and LT1763 (14V). The LT1763 should be far away from the rest of the cirquilt to improve PSRR.

Just found https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg874560/#msg874560) this table where you listed the battery currents as around 20 mA.
So with 2 Ah batteries this give you around 100 h of runtime - 4 days. How do you handle that? Replace batteries every three days? Float charge the eneloop NiMH? Regularly top up the charge?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 07, 2023, 05:06:56 pm
Hello,

I use a 24V switchmode supply with a analog cc/cv (200mA/17.4V after diode) for charging (not during measurements).
100 hrs is a bit optimistic as the current is up to 30mA with buffer and the cells are
neither completely full at float voltage nor completely empty at under voltage switchoff (13.8V)

So I calculate maximum 50 hours operating time for a fresh set of batteries.

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Martinn on May 09, 2023, 05:18:54 pm
So I calculate maximum 50 hours operating time for a fresh set of batteries.

As I find adding a battery a major PITA - what do you think are the effects of switching off the reference (hysteresis)? Mostly I'd have it running (at home), probably biggest influence would be bringing the unit to my local calibration lab (I guess I can tell them to run the unit overnight before measuring).
Of course the battery option nicely solves the isolation problem.

Maybe it's not too relevant for me, I only have a 6.5 digit DMM, although performance is quite decent: I measured a 7 V reference (ADR1399 eval board), averaging gave 7 digits, standard deviation of 1.3 uV. Specified accuracy is much lower of course, but for comparisons or ratio measurements I guess it is not too bad.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on May 09, 2023, 05:57:09 pm
The LTZ1000 does show some hysteresist in heating cooling cycles.  So a short (e.g. 1 minute) power down can have an effect on the voltage and it may take weeks to recover from this. The details depend on the set temperature.  So battery supply makes some sense. A reasonable solution can be 2 inputs for power linked with diodes. So one can change from one power source to another without interuption or could have a slightly lower voltage battry back as a backup in case the mains supply is interrupted.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Martinn on May 09, 2023, 06:11:03 pm
What amount of change can one expect as hysteresis? Is this in the sub-ppm region or more?
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 09, 2023, 06:46:17 pm
Usually, you observe sub-ppm or no change. The LTZ1000 may show bigger effect than the LTZ1000A. I always shut off my 3458A, when it's not in use, and observe absolutely zero hysteresis, after the usual 2h warm up. I lowered it's oven temp to about 65..70°C, to reduce it's drift
Both types are very sensitive to storage temperatures below 10°C, and must not be stored < -10°C, which creates a lot of hysteresis to about +1..5ppm, in latter case this might disable the hysteresis removal process by J.R. Pickering, in his Fluke 7000. See description in manual.
I have no problem with all of my LTZ1000  references , all running at 45..55°C, when I transport them "cold" in summer time. There's virtually no hysteresis at all.
I have not heard of any such problems as well from the U.S. Cal Club.
Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on May 09, 2023, 06:52:09 pm
Of course it makes a difference whether you run the reference 20 K or 60K above ambient temperature.
During my current study of a LTZ array i am using an external oven in the 30 to 45 °C range and after one or two temperature sweeps up and down all references come back within fractions of a ppm. Then they do not exhibit hysteresis anymore.
Hysteresis may also stem from metal foil resistors used in those reference circuits.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Martinn on May 09, 2023, 07:08:14 pm
Sounds fine... I plan on running an LTZ1000A with 12.5k temperature setpoint in my office, no arctic travels (and the cal lab might be in extended walking distance), so I guess I can live without battery backup.
Makes me wonder if I could measure a 1 ppm step. DMM6500 has 10 uV least digit (1.4 ppm) and 1.3 uV std of the averaged readout (0.2 ppm).
For that I probably can't even look unevenly at the connectors, otherwise they'd introduce thermal voltages far above that.
Has anyone considered wearing thick insulated winter gloves when handling connectors to reduce their heating?

Hysteresis may also stem from metal foil resistors used in those reference circuits.
So let's hope Edwin can still fabricate the precision wirewound resistors necessary...
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 09, 2023, 07:20:29 pm
1. use a differential method, resolving down to 10nV.
You'll need at least 3 references, anyhow
2. use CuTe jacks and appropriate connectors like Au coated or pure copper lugs or 4mm plugs of similar metal composition.
3. induced e.m.f. voltages disappear usually after a few tens of seconds.
4. Always use a set of 10..16 readings, with statistics, so you can judge from the StD value, if you measured in a stable manner. 100..300nV StD @ 7.15V level is fine. That might not be achievable with an ordinary 6.5 digits DMM
5. always make a reversal measurement, to remove e.m.f., and determine the e.m.f. value
6. you might also use 12k/1k for 45..55°C, like in the venerable Fluke 7000
7. I made very good experience with standard values of PWW resistors from G.R. or BMF from AE. both came from rhopoint in UK
I use 1k, 12k, 2x 70k and 120 because of the reduced oven temperature,  compared to the bad hp design
Title: Re: Ultra Precision Reference LTZ1000
Post by: Martinn on May 09, 2023, 07:47:33 pm
CuTe jacks and cables: I was planning to use Pomona 3770 binding posts and also buy some low emf cables from Mouser (any hints...?)

3 references: Andreas already mentioned that. Makes sense, but current LTZ1000A price at mouser is near $100 and custom resistors on top... will in the end be as expensive as my 6.5 digit bench DMM.

Statistics: Definitely. One thing I really like with the DMM6500 is the graphical display - you immediately see if there's drift.
100 nV StD: Sorry, I don't (yet) have the 8.5 digit entry ticket for the inner voltnut circle... 1 uV is the best I can get (5 NPLC, 10x filter)!

12k/1k: I've read a couple of times this might get a bit tight at elevated room temperatures, that's why I assumed 12.5k.
Assuming a metal box (probably aluminium, although steel would be better for magnetic shielding) does it help to add some foam isolation inside over the entire PCB? I have seen some builds like that. This would probably reduce the margin for the LTZ heater (if the entire PCB would heat up inside its isolation)? Or just have some draft shield over the LTZ1000A within a otherwise non-insulated box?

Rhopoint UK: Thanks a lot - excellent hint! GR 8G16 seem to be actually available in many values (not 12.5k however)! No confirmation yet from Edwin, he was hinting at some wire sizes running out.

Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 09, 2023, 08:14:14 pm
your DMM will resolve 100nV in differential Mode, in it's 1V or 100mV at least
I use double shield, I.e. a tuner box with foam  and an outer aluminum box. 
Andreas uses a similar shield.
So I can use case ground and Guard. See my assembly of  the 4fold references.
I use old mc cables, and assembled shielded PTFE with either lugs or 4mm banana from mc
shielded PTFE gave a noise improvement especially for OHM measurements
Title: Re: Ultra Precision Reference LTZ1000
Post by: antintedo on May 10, 2023, 02:43:49 am
What amount of change can one expect as hysteresis? Is this in the sub-ppm region or more?

Long time ago I did a small experiment to determine the effects of shipping the reference unpowered in colder seasons, maybe it will be helpful. The effect seems to be <0.5ppm if the reference never saw low temperatures, slightly more if it did. Degaussing-like temperature swings seem to restore the original behavior after exposure to cold. Simply waiting was very slow, power cycles with cooling to ambient temp helped only a little. I tested two parts from the same batch with roughly similar behavior, here's one chart I found:

(https://i.imgur.com/tpgtyQy.png)

Lowering the oven temperature is a good idea but I haven't tested it. An extreme version of this idea would be putting the board inside a slightly cooled peltier oven and setting the LTZ to 25*C so the LTZ die never experiences significant swings in either direction. Perhaps it could allow shipping in near freezing temperatures, assuming the problem lies with temperature swings alone and not absolute temperatures as well.
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on May 10, 2023, 06:31:34 am
I've recently added 20V Li-Ion (external, 5x 18650 old recycled batteries) to myADR1001, it lasts 2 days powering the box (37mA), wired via a diode to the voltage regulator's input of my built in linear psu (thus the battery and/or AC could be on). It is advisable not only to avoid power-off, but also to avoid AC leakage via the transformer during a measurement (powered from the batteries during the measurement). Your meter may resolve sub uV values after some math, but with its LM399 (afaik) inside you will see the LM399 fluctuations (a random walk/jumps within 5-10uVpp).
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on May 10, 2023, 09:32:23 am
As a heater oven is less circuitry than the Peltier oven, i was aiming for 37 °C, assuming it would be safe.

There is a fan inside the incubator i am using as temperature chamber for my array study and the six LTZ1000 references started behaving like an ants circus once the TC fine tuning approached 0.1 ppm/K. So i put the array into a little plastic container inside the temperature chamber to protect it from air draft. Then it's temperature happened to rise by 4 °C. I know this from the residual nonlinear TC.

So, once making an external oven, using low temperatures is possible and safe with a peltier heater/cooler. And i will measure actual chip temperatures of the references. The built-in second transistor can be a G=5 amplifier, so the output voltage will be about 2.5 V with -10 mV/K. If i digitize this with a 12 bit ADC with 3.3 V Vref, temperature resolution approaches 0.1 °C.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000
Post by: Martinn on May 10, 2023, 12:30:20 pm
I've recently added 20V Li-Ion (external, 5x 18650 old recycled batteries)
I also considered that. However unless you have really well matched quality cells, you'd need an active balancer. Also Li-Ion does not like float charge, so some extra charge management is necessary.
Or slap in a bunch of alkaline AA? At least you can measure their state of charge easily. Or NiMH LSD (like Andreas) - but charging them propery is far from trivial and I guess extended float charging will damage the cells as well.

Main benefit I see is perfect galvanic isolation, no mains coupling problems.

ADR1001
Yes, this would be the other attractive option! Just wait another few months (end 23?), get a ADR1001 and be done with it. No resistor sourcing troubles...

your DMM will resolve 100nV in differential Mode, in it's 1V or 100mV at least
I use double shield, I.e. a tuner box with foam  and an outer aluminum box. 
Andreas uses a similar shield.
So I can use case ground and Guard. See my assembly of  the 4fold references.

Quad: I remember TiN's design. Could you post a link to yours? I wonder how you implemented the guard.
Just called the local calibration lab. They can measure (3458A) with an uncertainty of 10 ppm + 1.4 uV, about half an hour of labor. Cost sounds acceptable, but for multiple LTZs (and yearly) too much. So I'd calibrate probably just one and then do a comparison. The national lab (METAS) can do (much) better, for probably much higher cost.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 10, 2023, 03:18:06 pm
instead of 12k5/1k, use 10k/800 
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 10, 2023, 07:08:40 pm

Quad: I remember TiN's design. Could you post a link to yours? I wonder how you implemented the guard.
Just called the local calibration lab. They can measure (3458A) with an uncertainty of 10 ppm + 1.4 uV, about half an hour of labor. Cost sounds acceptable, but for multiple LTZs (and yearly) too much. So I'd calibrate probably just one and then do a comparison. The national lab (METAS) can do (much) better, for probably much higher cost.

Let me GOGLE it ("Guard") for you: https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg3886166/#msg3886166 (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg3886166/#msg3886166)

With a stable ensemble of 3 references, you would only need to send one of these for calibration, best < 1ppm uncertainty.
On return, you compare again, if the travelling standard has changed on its tour, and then you could calibrate the others on your own.
Hint: Adrian from AB Precision makes reasonable prices for volt-nuts, but w/o official certificate. 10ppm is quite mediocre, Adrian can do better.
Another hint: A 3458A is NOT a reference standard! Therefore such a "calibration" I cannot recommend.
The 3458A can be used as a transfer standard < 1ppm against another "true" reference.

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 12, 2023, 07:19:17 am
@ Martinn, another hint: purchase the LTZ1000, i.e. the non-A version.
It's cheaper, and you can use 45..55°C oven temperature, with foam insulation, even up to 35°C and more room temperature w/o a problem.
Please search for yourself, this time  https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg3263778/#msg3263778.. (https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/msg3263778/#msg3263778..) in this thread I have shown T.C. measurements on one of my LTZ1000A references, using 12k/1k as well, and demonstrated that these failed at an internal temperature of > 39°C. The thermal isolation provides another ~7K temperature difference, therefore a bit more than 30°C r.t. is feasible.
Anyhow, precision measurements should only be made between 18 .. 28°C

Frank
Title: Re: Ultra Precision Reference LTZ1000
Post by: Martinn on May 23, 2023, 06:06:43 pm
Please search for yourself, this time
I expected this type of comment - it was inevitable...
Actually all questions one might ask on LTZ1000 have probably been answered several times in the past 3200 posts. Unfortunately it is near impossible to find the answers, Google does not help (unless you know some magical key word) and ChatGPT unfortunately has no clue of EE.
So thanks a lot for answering anyway!

Regarding the non-A version: Would not the better thermal coupling of the non-A lead to longer stabilization times and reduce the immunity to external temperature deviations? Or is the temperature control (an I controller as I understand it?) good enough so it does not matter either way? Combined with your foam isolation, would that not result in a much longer stabilization time?

Guard: Interesting, first time I see this. It seems that precision DMMs (my 6.5 digit does not have a guard terminal) interpret "Guard" differently than in high impedance (e.g. pH probe) measurements: With those, you drive exactly one signal line guard to the level you measure it to be. In DMMs the guard seems to enclose the whole input section, not just one signal. That probably makes sense as they have an excellent isolation to PE (earth) and their guard can be driven to some convenient potential (e.g. LO input).

I have to say I am a bit demotivated by the lowish 10 ppm uncertainty I could get from my local cal lab. After all, setting up several LTZ1000 boards is quite a (expensive) effort. On the other hand, simply switching on my DMM6500 (still in cal) will give me a 32 ppm uncertainty reading a 7.2 V source.

- Martin
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 23, 2023, 06:28:23 pm
Hello,

Or is the temperature control (an I controller as I understand it?) good enough so it does not matter either way?

The I part of the controller is low compared to the thermal time constants.
And yes the "400K" resistor compensates the tempco for the non-A version.

I have to say I am a bit demotivated by the lowish 10 ppm uncertainty
Perhaps you should start with some LM399 references which are cheaper and after some run in time the ageing drift is comparable.
(you should only not tilt them since they are not fully symmetrically like LTZ1000)

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Martinn on May 23, 2023, 06:57:46 pm
Hello Andreas,
Perhaps you should start with some LM399 references which are cheaper and after some run in time the ageing drift is comparable.
(you should only not tilt them since they are not fully symmetrically like LTZ1000)
Well, I already have a DMM6500 which has a LM399 built in, possibly selected/pre-aged (?), so I don't see much benefit in adding another one. A somehow cool idea using the LTZ1000 would be to have a few-ppm accurate reference around, but for now I don't see an affordable way of getting a sufficiently accurate reference measurement. I will certainly not spend a few hundred Fr. for a Josephson opinion from the national lab.

Tilt sensitivity: This would apply to the ADR1399 also? I have an eval board of the LCC version, have to try this.
BTW I ran this ADR1399 module also on a DMM7500 I have limited access to, I saw some discrete steps (forgot the amplitude, but significantly above the standard deviation of both the DMM7500 and my DMM6500) I don't see on my 6500. I have seen comments that the LM399 can do this, however it's strange I don't see them measuring with my DMM6500. Maybe it was just some warmup hiccups of the 7500 as it sat unpowered in a shelf before.

- Martin
Title: Re: Ultra Precision Reference LTZ1000
Post by: Andreas on May 23, 2023, 07:19:43 pm
for tilting of ADR1399LS8 see here my measurements:
https://www.eevblog.com/forum/metrology/adr1399-reference/msg4598620/#msg4598620 (https://www.eevblog.com/forum/metrology/adr1399-reference/msg4598620/#msg4598620)

of course the results depends on thermal isolation. (will get worse with less isolation).

with best regards

Andreas
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on May 23, 2023, 07:32:50 pm
Without proper meter or other system to compare there is little value in having just 1 LTZ1000 reference. At least one could not check the aging of the LTZ1000 reference.
One could have luck with 2 LTZ refrence: one well aged and than look at the difference for a new one or with heating 1 of the 2 circuits.
It could really make sense to gain experience with LM399 or ADR1399 reference first.

The better isolation of the A version could effect the quality of the temperature regulation with a little more loop gain. I think the more relevant point is reducing stress the the chip from a kind of soft mounting and also less variations in the heater power.

The resistive heater has a square law and thus a loop gain going up with more heater power. AFAIK the residual TC of the non A version before the compensation with R9 is more linear and not getting clearly better with higher heater power or much worse when at low power. This indicates that the residual TC is not from insuficient loop gain in the temperature control loop, but more from thermal gradients inside the chip caused by the heater power / sensor not at the ideal position. The smaller thermal resistance means more variation in the heater power, though this difference alone is only about 2.5-5 fold  (the data are abit confusing showing a 5 fold ratio in the termal resistance data in the table, but closer to 2.5 fold in the power needed in the heating curves.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Dr. Frank on May 24, 2023, 08:39:10 am
Please search for yourself, this time
I expected this type of comment - it was inevitable...
Sorry, den Spruch konnte ich mir diesmal nicht verkneifen.  ;D


Regarding the non-A version: Would not the better thermal coupling of the non-A lead to longer stabilization times and reduce the immunity to external temperature deviations? Or is the temperature control (an I controller as I understand it?) good enough so it does not matter either way? Combined with your foam isolation, would that not result in a much longer stabilization time?

The LTZ1000A stabilizes its oven temperature within about 3 sec, the LTZ1000 requires about 30sec. I provided an overview table for all of my different references in this thread.. I don't repeat that sentence again..  8)
Thermal stabilization of the complete circuit, i.e. including the 5 precision resistors is virtually identical between A and and non-A version, i.e. within 1h.

 
Guard: Interesting, first time I see this. It seems that precision DMMs (my 6.5 digit does not have a guard terminal) interpret "Guard" differently than in high impedance (e.g. pH probe) measurements: With those, you drive exactly one signal line guard to the level you measure it to be. In DMMs the guard seems to enclose the whole input section, not just one signal. That probably makes sense as they have an excellent isolation to PE (earth) and their guard can be driven to some convenient potential (e.g. LO input).

Well, higher grade instruments have exactly the same guarding scheme, look how the HP3458A, Fluke 335, 720A, 752A are built.
It's not that complicated, and as it's a passive Guard in each case, this might not be as effective.
I see an improvement in noise immunity, anyhow.

I just upgraded my "cold" travelling reference LTZ #3, which has an LTZ1000 inside.
I tested it's warm-up behavior after a 56h off-time @ 21°C room temperature. It returns to its initial value to +/- 0.1 ppm within 1h, see first diagram.

In the longterm stability diagram, you can see two  hysteresis shifts due to low temperature storage (<0°C).
At the end, there was a temporary shift of + 0.3ppm directly after assembling LTZ#3 into its new outer case. After one week, its reference value returned to its recent one within 0.1ppm, as well after the 56h off time.

So it's ready for a comparison @ Adrian.

I have to say I am a bit demotivated by the lowish 10 ppm uncertainty I could get from my local cal lab. After all, setting up several LTZ1000 boards is quite a (expensive) effort. On the other hand, simply switching on my DMM6500 (still in cal) will give me a 32 ppm uncertainty reading a 7.2 V source.

- Martin

At first, build your LTZ reference. Then you might either ship it to Adrian for a volt-nuts level calibration, <1ppm "unofficial" uncertainty, or you might join our Cal-Club and make an exchange with either of us.  It's a rather simple procedure, I guess, although you're living in Switzerland. You need an anchor reference in your lab, to identify possible shifts during transport. That might be your DMM in first place. Another LM399 reference would be better.
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on May 27, 2023, 07:23:19 am
..I have to say I am a bit demotivated by the lowish 10 ppm uncertainty I could get from my local cal lab. After all, setting up several LTZ1000 boards is quite a (expensive) effort. On the other hand, simply switching on my DMM6500 (still in cal) will give me a 32 ppm uncertainty reading a 7.2 V source.
You have to distinguish between a "metrological business" and a "hobby measurement". From my experience the concrete people in the labs there are kind and helpful people, sometimes they are voltnuts too.
99.999% of the routine boring measurements they do daily are for the clients who need their 5.5-6.5digits meters "calibrated" - where it means they need an "official" confirmation on paper their meter is within a spec (for legal purposes). Thus their uncertainties have the "legal" component built in (to be on the "safe side" in case of a dispute). And also they make $$ with that activity, indeed. When you talk to them (to a certain lab person there) as a hobbyist who does not require "legal paper" and all those boring calibration activities around a meter and just wants to see a voltage/frequency once a year/two they will certainly help you. Again - the people there are mostly nice and kind, from my experience..  ;)
Title: Re: Ultra Precision Reference LTZ1000
Post by: DH7DN on May 29, 2023, 05:53:15 pm
"Hobby measurement" basically means everything and nothing at the same time.  ;D If you ask a hobbyist "How much confidence do you have in your measurements?", the answers might be very different - depending on who you ask: "Everything is in spec", "Equipment recently calibrated against a well-known standard with an uncertainty of ...", "10.0000000 V as you can see". I think Dr. Frank's description is pretty much on point.
Title: Re: Ultra Precision Reference LTZ1000
Post by: iMo on May 30, 2023, 07:20:51 am
A "hobby measurement" of a single Vref source in a professional metrology lab could be made with a better uncertainty compared with the "lab's official uncertainty" - I am pretty confident about that..
Title: Re: Ultra Precision Reference LTZ1000
Post by: Echo88 on July 30, 2023, 01:55:56 pm
Regarding paralleled LTZ1000 for lower noise:
Im working on a lower noise ADC-board variant for my HPM7177-version.
For that im thinking of using 4x LTZ1000 -> ~0.5µVpp or if i ever get these: 4x ADR1000 -> 0.25µVpp.
Question is how to best achieve the 4x averaging without errors considering the GND-sense-concept of the HPM7177.
What would be the best way:
-Average raw 7V and GND-sense of every ref with resistors, without buffer
-Average raw 7V and GND-sense of every ref with resistors following a OP-buffer like ADA4522 which has 117nVpp and is already on the BOM?

Im also unsure about startup and interference between refs due to the GND-sense connections.

I attached schematics that showcase the ideas with and without buffers.
So far i know only of the QVR from TiN which is a quad-LTZ/ADR-reference board, are there other known publications of paralleled LTZ/ADR-boards?

https://xdevs.com/article/qvref/ (https://xdevs.com/article/qvref/) 
https://www.analog.com/media/en/technical-documentation/data-sheets/ada4522-1_4522-2_4522-4.pdf (https://www.analog.com/media/en/technical-documentation/data-sheets/ada4522-1_4522-2_4522-4.pdf)
Title: Re: Ultra Precision Reference LTZ1000
Post by: dietert1 on July 30, 2023, 05:23:04 pm
In february i started making a 6x LTZ1000 array and opened a separate thread.
https://www.eevblog.com/forum/metrology/making-an-array-of-ltz1000/msg4771946/#msg4771946 (https://www.eevblog.com/forum/metrology/making-an-array-of-ltz1000/msg4771946/#msg4771946)
I tried to make the cells of the array as simple as possible and put everything onto a very small board that can later be used as one reference.
I omitted LTZ1000 heater control. This can work well inside an external oven after fine-tuning each cell for zero TC at the same oven temperature. Fine-tuning the TCs required a temperature chamber with programmable temperature and development of a reliable tuning scheme.

Regards, Dieter
Title: Re: Ultra Precision Reference LTZ1000 (of HP3458A)
Post by: Dr. Frank on December 19, 2023, 04:40:56 pm
I wanted to find out about the T.C. behavior of my HP3458A, i.e. what's the influence stemming from the T.C. of the reference board, and which one from the A/D converter assembly U180.
The specification "with ACAL" assigns 0.15ppm/K to the reference board, and "without ACAL" are 0.5ppm/K for the overall T.C., i.e. the sum of both.
This overall T.C. makes manual transfer and stability measurements over a longer time difficult, especially when measuring at sub ppm level.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1957482;image)

I pulled the reference board out of my 3458A, and assembled it into an aluminum box, with 18V supply for heater and reference circuit, reference output to KS34465A DMM, and a precision NTC, tied to the 75k resistors on the board, and to be measured by an HP34401A.
The oven temperature is lowered to about 70°C, by the 100k parallel to the 15k resistor.
Also notice, that the T.C.-correction resistor R417 = 200k is assembled, which should NOT be used for the A-version, and probably creates an unwanted T.C. of the board.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1957452;image)

The LTZ1000A on the reference board is in upright orientation inside the aluminum box, when latter is closed and placed with its bottom plate on the electrical heater.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1957458;image)

Such low TC measurements are quite delicate, and I was now missing another "silent" and stable DMM like the 3458A.
The KS34465A has an LM399 inside, quite noisy, and might drift too much.
So I used its RATIO function, and a FLUKE 7000 as a reference. This deletes temperature and time drifts of the DMM.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1957464;image)

The noise of the 34465A is mitigated by taking data each 0.1K, or each 30 sec.

The aluminum box was first cooled down to an inner temperature of < 18°C, and then during the slow warm-up, the whole assembly was nearly in thermal equilibrium, so the T.C. could be determined to about +0.95ppm/K (linear regression or box method)

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1957470;image)

For the regular operation temperature range inside the 3458A, usually 35..36°C in my lab, I heated the aluminum box to about 43°C, and let it slowly cool down.
This gave a T.C. of about + 0.11 ppm/K.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1957476;image)

So this T.C. of about +0.1ppm/K is well inside specification.

I intended to bring its T.C. to zero, by removing or changing R417, improve its long term drift by further reducing the oven temperature, and would have replaced the ceramic capacitors by film capacitors, to reduce possible noise generation.

As timely and temperature drift is very low anyhow, I finally left the reference board as it is, for now.

Title: Re: Ultra Precision Reference LTZ1000 (3458A measurements)
Post by: Dr. Frank on December 19, 2023, 04:42:13 pm
My HP3458A has shown an overall T.C. of about +0.42ppm/K, when my wife opened the basement window unintentionally:

[attach=1]

From monitoring the CAL? 72 parameter, I determined roughly the T.C. of the U180, which is about -0.32ppm/K
[attach=2]

So it was evident, that the T.C. of the reference board should add in the same direction, and is now confirmed to be about 0.1ppm/K

That overall T.C. of 0.42ppm/K may disturb my transfer measurements, which take about 40minutes for 13 voltages.

If I encounter a room temperature drift of only 0.5°C, due to the heat generation of the fluorescent lamp, and of the 100W from the operator, I already get a 0.2ppm shift. As the reference with 0.1ppm/K gives no real chance for improvement, compared to the 0.32ppm/K for U180, I have to take care, that the room temperature rise stays below 0.2°C over the session.

Btw.: using the known T.C. of U180, I was able to calculate the timely drift of U180, from monitoring CAL? 72 parameter.

[attach=3]

That gives about 1.5ppm over 4 years, or 0.001ppm/day. Therefore, my U180 chip is not affected by the Service Note 18.
Title: Re: Ultra Precision Reference LTZ1000 (of HP3458A)
Post by: aronake on December 19, 2023, 05:49:02 pm

For the regular operation temperature range onside the 3458A, usually 35..36°C in my lab, I heated the aluminum box to about 43°C, and let it slowly cool down.
This gave a T.C. of about + 1.1 ppm/K.


You later wrote:
"So this T.C. of about +0.1ppm/K is well inside specification."

There seems to be something I don't understand. Assuming the graph show PPM on y-axis and degree C in x-axis, it looks like 1.1 ppm/10 degrees which is the 0.1ppm/K later mentioned.

Or just a typo?
Title: Re: Ultra Precision Reference LTZ1000 (of HP3458A)
Post by: Dr. Frank on December 19, 2023, 05:56:33 pm

For the regular operation temperature range onside the 3458A, usually 35..36°C in my lab, I heated the aluminum box to about 43°C, and let it slowly cool down.
This gave a T.C. of about + 1.1 ppm/K.


You later wrote:
"So this T.C. of about +0.1ppm/K is well inside specification."

There seems to be something I don't understand. Assuming the graph show PPM on y-axis and degree C in x-axis, it looks like 1.1 ppm/10 degrees which is the 0.1ppm/K later mentioned.

Or just a typo?

Sorry, just a typo.
That happened, because I'm struggling today with adding / inserting the pictures. The first one is always deleted.
 Something is not working properly with the posting software, or I'm too confused today.
Title: Re: Ultra Precision Reference LTZ1000 (mitigation of TC in measurement session)
Post by: Dr. Frank on December 20, 2023, 11:30:45 am
My basement lab has a very constant room temperature w/o HVAC, and when the room is not occupied.
In winter, only the gas heating is running, so you see the regular night setback, and a nearly constant r.t. of about (21.2 +/- 0.2) over weeks.
This can be used to make unattended/automated stability measurements on a reference DUT with the 3458A directly.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1958100;image)

I made transfer measurements on November 1st, 16th and December 1st. These semi manual measurements always raise the r.t. by 0.5 .. 1°C, but may reach a constant temperature later on in the session.

So I have to take this change into consideration for the 13..14 volt transfers, taking about 30..40min, which by far exceeds the transfer specification of the 3458A.
For the session of Dec. 1st I powered my equipment on the night before, at 10 p.m., which raised the r.t. to 22.4°C.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1958106;image)

In my recording sheets, I write down date / session start time / initial room and / 3458A temperature / ACAL temperature / CAL? 72 / end time / end temperatures.

(https://www.eevblog.com/forum/metrology/ultra-precision-reference-ltz1000/?action=dlattach;attach=1958112;image)

I began the first transfer session for my 7 resistor references before, at 9:56, lasting 23 min., and raising the temperature to 22.6°C, which was stable afterwards, as I didn't move out of the lab. During the following voltage transfer measurement between 10:50 - 11:25, r.t. and TEMP? of the 3458A raised by 0.1°C only, which would give about 0.05ppm for this TC induced change. I always begin with LTZ #1, and re - measure it in the end, which really gives about -0.06ppm transfer repeatability, as expected.

On Dec 16th, I made the next transfer measurement, only on my voltage references, so the temperature change was +0.3°C, giving about 0.13ppm shift.
LTZ #1 was measured +0.17ppm high compared to the start of the session, so that fits well.

As the 3458As reference has a 0.1ppm/K T.C. only, I could do an ACAL DC in between, as soon as the TEMP? rises more than 0.1°C, or I could repeat the session when the r.t. has settled.

One important aspects has to be addressed:
I have to make absolute voltage measurements by means of the 3458A for these transfers, as I have to compare voltages on very different levels, i.e. @ 7.1V and 10V.
Making differential measurements only, would nearly avoid all such T.C. related shifts, but would require a stable precision divider like the FLUKE 720A, to differentially compare all references against the FLUKE 7000. That transfer method can be done with about 0.1 .. 0.2ppm uncertainty, so it's questionable, which method is best.
Title: Re: Ultra Precision Reference LTZ1000
Post by: aronake on December 20, 2023, 01:49:10 pm
My still not completely verified approach to separately measure TC of A3 and TC of LTZ1000 on 3458a has been to measure change in cal72 with temperature for A3 TC and change in measured voltage after ACAL for LTZ1000 TC. Technically I have done this by keeping voltage reference in TEC box and using the AC to change temperature in my "laboratory". TC of cal72 + TC of voltage measurement after ACAL has quite well matched total 3458a (with no ACAL) in my sample universe among the 5 3458a I have. Plan is to have this verified by making TC sweeps of the bare A9s as Dr Frank has done.

4 of the 3458a have a LTZ1000 TC of 0.05 to 0.12 PPM/C. The last one have 0.19 PPM/C. Idea is to dissect this out of spec A9 and measure TC on all resistors separately and then tune it to 0 TC.
Title: Re: Ultra Precision Reference LTZ1000 (mitigation of TC in measurement session)
Post by: guenthert on December 21, 2023, 09:21:18 am

[..]

One important aspects has to be addressed:
I have to make absolute voltage measurements by means of the 3458A for these transfers, as I have to compare voltages on very different levels, i.e. @ 7.1V and 10V.
Making differential measurements only, would nearly avoid all such T.C. related shifts, but would require a stable precision divider like the FLUKE 720A, to differentially compare all references against the FLUKE 7000. That transfer method can be done with about 0.1 .. 0.2ppm uncertainty, so it's questionable, which method is best.
   Clearly using the DMM for direct measurement is more convenient, faster and can be automated.  If the linearity of the DMM is known or can be verified, that will then be  preferred.  Since the divider might have itself a (small) temperature dependency, I'd think it can be used to its fullest potential only in temperature controlled environments.  You are already in a better position than most of us there.

    Perhaps best in your position would be to (occasionally, say every other year or so) verify the linearity of the DMM and use that for measurements of the DUT.  I've seen others attempt such, by measuring 1,2,...9,10V from a calibrator (assumed to have better linearity than the DMM under test) or ~1V from a string of resistors fed from a stable source (and adding the individual  measurements).  I can't help by wondering, whether that is sufficient. @Kleinstein hopefully can comment on this, but afaiu, the capacitor of the integrator in the ADC of many precision DMMs, like the 3458A, is charged only to some comparably small voltage (much less than 1V) repeatedly in order to avoid nonlineratiies due to the voltage depending varying capacity.  Then it might be more appropriate to test the linearity at smaller voltages, i.e. fractions of the maximum voltage of the capacitor of the integrator.  This probably belongs  in another thread though.
Title: Re: Ultra Precision Reference LTZ1000
Post by: Kleinstein on December 21, 2023, 11:02:51 am
4 of the 3458a have a LTZ1000 TC of 0.05 to 0.12 PPM/C. The last one have 0.19 PPM/C. Idea is to dissect this out of spec A9 and measure TC on all resistors separately and then tune it to 0 TC.

I don't think one would need to measure the TC of all resistors separate. Unsoldering would be quite some stress to the parts. The first cadidate to look at the the R9 (200K/400K) resistors used to trim the TC, that HP populated even with the A version that does not need it. Best case one gets away with just removing the resistor and maybe add a different (likely larger) value to do a fine trim. Though only a relatively small disturbance one would still loose the absolute voltage calibration (may not be that bad if one has 5 meters at hand). In this case the question would be if one also wants set the temperature lower. It has pros and cons, e.g. limiting the max environmental temperature and a phase of more possible drift from a new settling phase.

The 3458 is normally quite good with linearity and the 7 to 10 V step is not that large. One may reduce the effect a little by using the meter with both polarities and thus do the test with negative voltages too. Actually testing the INL of the 3458 to a meaningfull level is difficult and by nature only a spot check. For the use here maybe check if the 10 V ref. is the same as the sum of 2 "halves"  (with a divider and buffer). It is more be a check if there is a defect causing way out of spec INL.
The main candidate for nonlinearity in the 3458 is not so much the integration capacitor and if at all the dielectric absorbtion there and not a voltage dependent capacitance. The main candidates are thermal effects in the resistors (self heating causing a tiny U³ contribution) and settling effects at the integrator. Much of the INL is not expected to change very much over time and would thus not matter that much for looking at the drift, if the same meter is used for all tests.
Title: Re: Ultra Precision Reference LTZ1000
Post by: aronake on December 21, 2023, 04:03:51 pm
4 of the 3458a have a LTZ1000 TC of 0.05 to 0.12 PPM/C. The last one have 0.19 PPM/C. Idea is to dissect this out of spec A9 and measure TC on all resistors separately and then tune it to 0 TC.

I don't think one would need to measure the TC of all resistors separate.

Thanks for comments. This would absolutely not have anything with some kind of need to do, 100% out of curiosity. ;) I suspect the individual resistors to be quite bad from a TC perspective.  But lets see. I only intend to give on A9 this treatment, so very minimal statistical input. It would not surprise me if HP/Agilent/Keysights approach to making A9 boards is to use quite mediocre resistors then temperature sweep the A9 boards and with quite relaxed tolerance, which seems to be 0.15 PPM/C or maybe a little lower, discard these that was not good enough or replace the resistors and do a new temp scan.