Author Topic: Ultra Precision Reference LTZ1000  (Read 896454 times)

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Offline Jay_Diddy_B

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Re: Ultra Precision Reference LTZ1000
« Reply #100 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

 

Offline BravoV

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Re: Ultra Precision Reference LTZ1000
« Reply #101 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

Offline babysitter

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Re: Ultra Precision Reference LTZ1000
« Reply #102 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:
« Last Edit: March 17, 2013, 08:42:00 pm by babysitter »
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Offline saturation

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Re: Ultra Precision Reference LTZ1000
« Reply #103 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. 
Best Wishes,

 Saturation
 

Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #104 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=*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.
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Offline babysitter

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Re: Ultra Precision Reference LTZ1000
« Reply #105 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.

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Offline quarks

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Re: Ultra Precision Reference LTZ1000
« Reply #106 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
« Last Edit: March 27, 2013, 03:42:01 pm by quarks »
 

Offline babysitter

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Re: Ultra Precision Reference LTZ1000
« Reply #107 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.

 

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Offline free_electron

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Re: Ultra Precision Reference LTZ1000
« Reply #108 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...
Professional Electron Wrangler.
Any comments, or points of view expressed, are my own and not endorsed , induced or compensated by my employer(s).
 

Offline babysitter

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Re: Ultra Precision Reference LTZ1000
« Reply #109 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...



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Offline quarks

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Re: Ultra Precision Reference LTZ1000
« Reply #110 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/)
- stress relief cutouts around LTZ1000 (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)
« Last Edit: May 06, 2013, 06:55:00 pm by quarks »
 

Offline Hypernova

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Re: Ultra Precision Reference LTZ1000
« Reply #111 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.
 

Offline BravoV

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Re: Ultra Precision Reference LTZ1000
« Reply #112 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 ?  ???

Offline chickenHeadKnob

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Re: Ultra Precision Reference LTZ1000
« Reply #113 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.
 

Online amspire

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Re: Ultra Precision Reference LTZ1000
« Reply #114 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.
 

Offline quarks

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Re: Ultra Precision Reference LTZ1000
« Reply #115 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

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
« Last Edit: May 06, 2013, 12:19:53 pm by quarks »
 

Offline quarks

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Re: Ultra Precision Reference LTZ1000
« Reply #116 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.
« Last Edit: May 06, 2013, 12:12:37 pm by quarks »
 

Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #117 on: May 06, 2013, 01:24:58 pm »
Only LTC1051 was produced in hermetical sealed package:

LTC1051MJ8
LTC1051CJ8
LTC1051AMJ8
LTC1051ACJ8
Fluke 8050A | Prema 5000 | Prema 5017 SC | Advantest R6581D | GenRad 1434-G | Datron 4000A | Tek 2465A | VNWA2.x with TCXO upgrade and access to: Keysight 3458A, Keithley 2002, Prema 5017 SC, 34401A, 34410A, Keithley 2182A, HDO6054, Keysight 53230A and other goodies at work
 

Offline babysitter

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Re: Ultra Precision Reference LTZ1000
« Reply #118 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
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Offline quarks

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Re: Ultra Precision Reference LTZ1000
« Reply #119 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.
 

Offline quarks

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Re: Ultra Precision Reference LTZ1000
« Reply #120 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
 

Offline babysitter

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Re: Ultra Precision Reference LTZ1000
« Reply #121 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 :)
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Offline Rufus

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Re: Ultra Precision Reference LTZ1000
« Reply #122 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?
 

Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #123 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.
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Offline branadic

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Re: Ultra Precision Reference LTZ1000
« Reply #124 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

a single sided design.
Fluke 8050A | Prema 5000 | Prema 5017 SC | Advantest R6581D | GenRad 1434-G | Datron 4000A | Tek 2465A | VNWA2.x with TCXO upgrade and access to: Keysight 3458A, Keithley 2002, Prema 5017 SC, 34401A, 34410A, Keithley 2182A, HDO6054, Keysight 53230A and other goodies at work
 


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