USA Cal Club: Round 2

[cellularmitosis]

Ok, enough delays!  Time to start round 2 of the cal club.   

This round will use a 7V LTZ1000 board (PX-ref v2.4).

Good things about this round / improvements over last round:

• The ref is an LTZ1000, woohoo! 
• This particular LTZ chip shows lower-than-typical 1/f noise (see date code 9811 in this page)
• Reverse polarity protection (schottky on positive input)
• Output short protection (LTC2057 buffer)
• Standardized on a common set of connectors
• Low EMI sensitivity (ferrite common-mode chokes on supply and output)
• Steel TEKO case (provides some amount of magnetic shielding)
• Star-pattern shipping (should detect shipping-induced hysteresis)
• Light weight package (about 9 oz.) == cheap shipping (about $4)

Things which aren't ideal about this round:

• Due to a mishap I lost the ~3 months of ageing on the LTZ which I had intended to use for this round 
• ...which means I also lost Doug's (voltagestandard.com) measurement using his calibrated 3458A 
• This LTZ has only been ageing for a week (but has only moved 1 count on a Keithley 2015 in that time)
• Tempco of the ref hasn't been measured / adjusted via the 400k resistor

But you know what, it's never going to be perfect -- there will always be more tweaks to be made and work to be done.  Time to get the show on the road!

Shipping:

This time, we'll use a star-pattern: the ref will get shipped back to me at each leg of the round.  Hopefully we can use this technique to detect any hysteresis / drift picked up during shipping.

Shipping is going to be pretty cheap (about $4), so here's how I'll approach it: I'll include a return-shipping label for convenience, and if you want to drop me a few bucks in paypal, that's great.  If not, no big deal -- the shipping is going to be a relatively small amount of money anyway, so I'm not worried about it.

Certainly, if you have calibrated gear, I don't think you should worry about shipping -- you're doing the rest of us a big favor just by participating 

Participants:

I'm not sure I have a complete list of everyone who wanted to participate in this round, so please chime in if you don't see your name!

• Muxr
• technogeeky
• VintageNut
• vindoline
• Conrad Hoffman
• dr.diesel
• CalMachine
• CatalinaWOW
• kj7e
• bitseeker
• RandallMcRee
• nikonoid
• martinr33
• orin
• Vacuuminded
• Vgkid
• MaxFrister
• SirAlucard
• flittle
• hwj-d
• rhb
• ArthurDent
• edavid
• GEOelectronics
• TWMIV
• Svgeesus

...and I think I might be sending the ref to a few surprise guests internationally as a "thank you" for being excellent contributors to the forum 

I think I'll choose the shipping order using a random sort, which is equally fair / unfair for everyone 

[cellularmitosis]

Some additional detail about the ref:

Supply voltage:

Valid supply voltage range is from about 9.1V (the LTZ falls out of temperature regulation below this point) to 15V (max specified supply voltage for the LT1013).  Let's standardize on 12V for this round.

Supply connection:

The ref has a 2-pin 0.1" female header socket for the supply connection, and will ship with two "pigtails": one with banana plugs and another with croc-clips.

The pigtail connector has been colored silver on the positive lead.  The CAT5 wire is solid-color for negative and white/stripped for positive.  The banana plug heat-shrink is yellow for positive and black for negative.  The croc clips are red for positive and green for negative.

Output connection:

The output pigtail connection is made using a paired set of Mil-Max machine pin headers with solder-cup termination.  These are gold-plated beryllium copper.  With a wrap of tissue, etc, these should track thermally and present minimal thermal EMF.

https://www.digikey.com/product-detail/en/mill-max-manufacturing-corp/380-10-164-00-001000/ED10164-64-ND/474594

https://www.digikey.com/product-detail/en/mill-max-manufacturing-corp/329-43-164-41-540000/ED90338-ND/1869520

Two pigtails will be supplied for the output connection: one with a Pomona 4892 dual banana plug (gold-plated beryllium copper spring, brass body), and one with bare copper wires.

https://www.digikey.com/product-detail/en/pomona-electronics/4892-0/501-1553-ND/737021

[bitseeker]

Thanks for putting this together and kicking off a new round. Looking forward to it. What all do you want us to capture/upload/post about the ref when we receive it?

[Andreas]

Hello,

By the way: with single supply the LT1013 will go up to 30V so it is not the limitation.

It would be also a good idea to put a voltage regulator directly to the cirquit so that everyone has the same voltage (since PSRR is not infinite).

Rhats why I always use a LT1763 based regulator in my cirquits either on board or also off board with the little single sided PCB that I have already shown.

With best regards

Andreas

[dr.diesel]

As much as possible, we should standardize our testing method.  ie polling frequency, instrument setup, log file format etc.

That would make it much easier to compare/analyze results.

[Conrad Hoffman]

Cool! Looking forward to it.

[GEOelectronics]

Great idea.Count me in.
Located in Missouri, sort of i the middle of USA.
Have access to a factory calibrated  LTZ1000 anchored Keysight DMM.

George Dowell

[TiN]

I have created FTP section and account for data store, if anyone willing to use this way to interchange files.

FTP server: ftp.xdevs.com
Login: usac_run2
Password: same as login, case-sensitive
FTP mode: passive
No size limits.

I also suggest members to list what equipment to be used, and measurement conditions. 
Maybe group data by the "type", such as:

Type 1a: Direct measurement, uncalibrated equipment (unknown uncertainty, over calibration 1year cycle), e.g. ebay Keithley 2000, etc.
Type 1b: Direct measurement, calibrated equipment (in 1 year spec or better), e.g. HP 3458A, calibrated by Keysight in August 2017, etc. If uncertainty of calibration point can be published - even the better
Type 2: Differential measurement vs calibrated DC-standard (e.g. Fluke 732/Datron 491x) with null-meter connection. e.g. UCC2 ref vs Fluke 732A, null-meter HP 3458A on 100mV range.

cellularmitosis got himself into rabbit hole, but if he can maintain and update excel charts/datasheet on each spoke of the star result set, that would be really useful.
I felt like last club was somewhat black box to the outsiders, as there was no end result and no summary reports published? (could be that I missed them either, apologies if that's true).

[flittle]

I am not sure if this is the best place for this but for those that had bad luck on the UGSimple I think I have found a good solution.  I was messing with the GUI and I noticed that if I clicked find in between each read I could get successful sequential reads.  So I looked at their c++ sample and decided to try sending the same command over and over between each read.  It worked so I have it logging to stdout one line for each reading.

C:\Users\flittle\Downloads>uglogger 1 3000 -1 "F1R3A1H1"
uglogger - v0.1
by flittle
Testing write & read combination before logging....Write test good.
Read test good.
Begin logging to standard out every 3000ms Ctrl-C to stop.
7.50702
7.50703
7.50703
7.50703
7.50703
7.50704
^C
C:\Users\flittle\Downloads>uglogger 1 3000 -1 "F1R3A1H1" >data.txt
uglogger - v0.1
by flittle
Testing write & read combination before logging....Write test good.
Read test good.
Begin logging to standard out every 3000ms Ctrl-C to stop.
^C

If anyone is interested I can post the code and/or link to an exe.

if you look at their sample c++ i just put this in a loop to get it to read sequentially.

Code: [Select]


                proc = Gwrite(address, (char *)commands.str().c_str());
istringstream r(Gread(address));//read from device
double dr = 0.00;
r >> dr;
cout << dr << endl;
Sleep(readDelay);


please excuse my vc++ I am used to arduino these days.

[MisterDiodes]

Cellular: Just a friendly head's up - and not to be a wet blanket - but that LTZ you have is a mere infant and hasn't been under power near long enough to stabilize.  I'd suggest to wait a while to let it settle down before starting shipping - otherwise the first people to receive the unit probably won't be on the same sheet of music as the people who get it later on.  The fact that it's drifting about the same rate as your meter may or may not be very meaningful.  Trying to hurry along here isn't going to help the data at all.

Be careful of a '2057 used by itself as an output buffer...keep the current very low (<<2mA), say driving a meter input circuit only.  Otherwise its demodulater won't work well and you'll get errors.  For instance: If someone were to drive an ADC Ref input that would need another amp in between.  Or they should be careful trying to do a direct comparison with another Vref, etc.  AZ Choppers usually need another companion amp in their feedback loop if you're using it as a buffer - and that should be low noise.

Carry On!

[cellularmitosis]

What all do you want us to capture/upload/post about the ref when we receive it?

Nothing in particular -- I figure each individual will probably be interested in different things anyway, so we'll get a variety of measurements and perspectives.

By the way: with single supply the LT1013 will go up to 30V so it is not the limitation.

It would be also a good idea to put a voltage regulator directly to the cirquit so that everyone has the same voltage (since PSRR is not infinite).

Thats why I always use a LT1763 based regulator in my cirquits either on board or also off board with the little single sided PCB that I have already shown.

Ah, that's a good point: +/-15 == 30

I could include an off-board regulator as a "pigtail" -- that's a good idea.

As much as possible, we should standardize our testing method.  ie polling frequency, instrument setup, log file format etc.

Good idea!

Have access to a factory calibrated  LTZ1000 anchored Keysight DMM.

PS
Presently can competently test for
DCV microiVolts to kiloVolts
R.F. ULF to uW
Resistance to milli to TOhms
Capacitance and inductance
Pulse width and repetition rate.

 

I have created FTP section and account for data store, if anyone willing to use this way to interchange files.

cellularmitosis got himself into rabbit hole, but if he can maintain and update excel charts/datasheet on each spoke of the star result set, that would be really useful.
I felt like last club was somewhat black box to the outsiders, as there was no end result and no summary reports published? (could be that I missed them either, apologies if that's true).

Thanks!  And that's good feedback -- there wasn't ever really an overall analysis (I guess I lost interest because the same ref couldn't continued to be passed around)

If anyone is interested I can post the code and/or link to an exe.

if you look at their sample c++ i just put this in a loop to get it to read sequentially.

That's fantastic!  I know the UGSimple is currently the cheapest option for GPIB, and I'm sure a lot of metrology forum members would be interested in pursuing that further (myself included -- I also have a UGSimple unit).  I would love to see a "UGSimple hacks" thread!

Cellular: Just a friendly head's up - and not to be a wet blanket - but that LTZ you have is a mere infant and hasn't been under power near long enough to stabilize.  I'd suggest to wait a while to let it settle down before starting shipping - otherwise the first people to receive the unit probably won't be on the same sheet of music as the people who get it later on.  The fact that it's drifting about the same rate as your meter may or may not be very meaningful.  Trying to hurry along here isn't going to help the data at all.

Be careful of a '2057 used by itself as an output buffer...keep the current very low (<<2mA), say driving a meter input circuit only.  Otherwise its demodulater won't work well and you'll get errors.  For instance: If someone were to drive an ADC Ref input that would need another amp in between.  Or they should be careful trying to do a direct comparison with another Vref, etc.  AZ Choppers usually need another companion amp in their feedback loop if you're using it as a buffer - and that should be low noise.

Yeah, that's a totally valid criticism of this setup, and something I should probably highlight more for those unfamiliar with Vref ageing : at one week in, the ref is still in the steepest part of its ageing curve.

I intentionally went with an older chip, hoping that the new ageing curve I've kicked off by soldering it won't be as steep as the ageing curve of a brand new chip.  Maybe!

I debating between keeping everyone waiting for another couple of months, but then I thought "$4 in shipping is pretty cheap entertainment", so I thought I'd start up round 2 now and see if anyone was interested.

[hwj-d]

Hi Cellular,
very nice to see its going on now. Thank you so much.

I would throw in two simular devices, thats now under power, since I show it in the px-thread from the 8. of March, but not (temp-) calibrated except with my 34461a.

As an idea, I had implemented a lm35caz TO-92 each, that has +-0.5 to 1°C accuracy, connected to supply voltage. So we can measure the internal temp directly as voltage (multiplied with 100) with an extra wire.

Also I have laying around some pizerow's. That's the little things with wlan and bluetooth on board (to be switched off during the measurement), I also would throw in two of them. They are thin as two stamps, so it doesn't matter to send it in the package. If someone could write a script (have no time to do that for now) for interfacing, measuring, uploading to TiN, we have also a standardized protocol method, if that makes sense, as a first thought!

Maybe one can additionally circular in the USA, the other comes back to EU, and vice versa? I would send them to cellular at the first. Or one to Andreas? One to Cellular?
Whats your thoughts?

Thanks to all.
HW

[CatalinaWOW]

I would certainly appreciate guidance on the type of data to be collected.  I am only marginally a volt-nut and my personal interest is primarily in seeing roughly where my instruments lie.  But I am very willing to help in ways that I can.  Obviously with a population of long out of calibration instruments, without even access to the last calibration data I will not have a meaningful contribution to absolute accuracy, and any contribution I can make on drift will be difficult to tease out and only available after this loop has been around multiple times.

I can get what I believe to be meaningful noise data (including spectral cuts of various types), tempco data over a limited range of temperature.  I also have a couple of HP mux switches which I can set up to make successive closely timed measurements of multiple sources using the same instrument. 

What type of data would be most useful to the group?  I can guide my efforts in that direction.

[vindoline]

Looking forward to it CM! Thank you for organizing this again.

[sokoloff]

I would certainly appreciate guidance on the type of data to be collected.  I am only marginally a volt-nut and my personal interest is primarily in seeing roughly where my instruments lie.  But I am very willing to help in ways that I can.  Obviously with a population of long out of calibration instruments, without even access to the last calibration data I will not have a meaningful contribution to absolute accuracy, and any contribution I can make on drift will be difficult to tease out and only available after this loop has been around multiple times.

I can get what I believe to be meaningful noise data (including spectral cuts of various types), tempco data over a limited range of temperature.  I also have a couple of HP mux switches which I can set up to make successive closely timed measurements of multiple sources using the same instrument. 

What type of data would be most useful to the group?  I can guide my efforts in that direction.

I feel probably similarly to Catalina here. I'm at best a millivolt-nut (or volt-millinut perhaps?), but would love to get a sense of where my instruments lie as well as possibly contribute something back to the group (beyond just the obvious few bucks for shipping offsets).

If there's a semi-standard process to adhere to, all the better, as that gives me something to direct my efforts as well as to learn about why things are done that particular way.

[rhb]

I think I should point out that summer and winter are poor times to be shipping a voltage reference as they will likely be subjected to extreme temperatures in transit.  We're already at the point where the back of a truck could hit 135 F sitting in a freight yard for a few hours while coming and going from Austin.

We did a weekend move in July in Dallas from one location to another location about 15 miles away.  Not a single one of the workstations would boot on Monday morning until I went around and reseated all the connectors.

[hwj-d]

I've got my ltz1000's and opamp's from Digikey Thief-River-Falls in wintertime, they had nearly minus 20°C a that date coming with plain with unheated cargo space, and now, they are all defective, as we can see ...   

[kj7e]

For the nature of this project, long term burn-in, shipping temp and a unified standard of measurement may be out of scope.  The fact we have an LTZ1000 to send around is on order of magnitude better than the SVR-T from round one.  The limiting factor for many here is going to be their own gear, not the DUT.  Shipping and external environmentals cant be controlled.  A standard of measurement is hard to define since each has unique gear and logging ability.  I think the spirit of this is just to provide the best data you can and maybe learn where you can improve along the way.  Looking forward to contributing as I can.

[rhb]

I certainly want to participate.  But my brother in-law makes fine wines and they do not ship wine to Texas in the summer.  Jason had a mishap with the LTZ1000 and I thought it worth pointing out that waiting until the fall might be a good idea.  It would give the reference time to reequilibrate and would avoid the risk of subjecting it to additional thermal stress.

I intend  to contribute some passive references. i have a bunch of NOS WW II mil-spec stuff that should be very stable by now.

My eBay 34401A reported 5.00000 VDC +- 1 digit  on a DMMCHeck Plus recently calibrated to 1 ppm on an in cal 3458A.  The 34401A appears to have had its last cal in 1999.

There are strong fundamental physical grounds for thinking that aging drift  is asymptotic to zero after a sufficiently long period.  Proving this would require a lot of data spanning 20 years, so I'm not likely to be able to prove it except indirectly by comparing 34401A and 3456A measurements of  a precision reference and plotting measured values against last known cal.

[cellularmitosis]

For the nature of this project, long term burn-in, shipping temp and a unified standard of measurement may be out of scope.  The fact we have an LTZ1000 to send around is on order of magnitude better than the SVR-T from round one.  The limiting factor for many here is going to be their own gear, not the DUT.  Shipping and external environmentals cant be controlled.  A standard of measurement is hard to define since each has unique gear and logging ability.  I think the spirit of this is just to provide the best data you can and maybe learn where you can improve along the way.  Looking forward to contributing as I can.

 

But my brother in-law makes fine wines and they do not ship wine to Texas in the summer.  Jason had a mishap with the LTZ1000 and I thought it worth pointing out that waiting until the fall might be a good idea.  It would give the reference time to reequilibrate and would avoid the risk of subjecting it to additional thermal stress.

That's a valid point, and is certainly something I would plan around if I were paying $$$ for a "real" calibration.

Again, this round isn't "perfect", but its time we got the ball rolling again.  There will always be future rounds where we can dial this in further!

[Conrad Hoffman]

AFAIK, calibration lab techs don't get the summer off due to lack of business. It's also doubtful that sales and shipments of precision meters cease during mid winter and mid summer. The storage temperature range for the LTZ1000 is -65 to 150 C, so I doubt you could damage one. Didn't see a spec for metal foil resistors, but I'd be surprised if it was an issue. The big question is hysterisis of everything as you cycle the temperature and the only way to find out is to try it. Temperature and vibration in shipping is one reason I dislike trimpots. Too many change by tapping them, so they're certainly subject to changes during shipping.

[GerryBags]

Erm, hi, guys. I just thought something like this might help with shipping your LTZ. This info is for DHL, but most large courier companies will offer similar facilities.

http://www.dhl.co.uk/content/dam/downloads/g0/express/services/industry/dhl_express_temperature_sensitive_packaging_brochure_en.pdf

[GEOelectronics]

Fractional and even Ohm resistors-

Once, in a package from Russia, with some items totally not related to this group discussion, the seller included 2 boxes of 1/2% 200 ohm resistors with a note of thanks for the purchase. Each box contained several cardboard carriers with 25 resistors lined up in idividual precise slots.

At that time I checked them with the bench Simpson 260 and sure enough they were 200 Ohms. Checked several and they were all 200 Ohms. On the Simpson VOM all tested were remarkably the same, so next they were checked on the bench Simpson 463, a 3 1/2 digit .1% (I think) digital meter. There they were again, 200.0.

That's when I decided to put them away for a future project, aside from the usual resistor stash (I almost said TRASH!).

Reading this thread today prompted a second look at them, this time with updated equipment

Each sample tested read between 200.2 and 200.7 Ohms. A random sample of 10 tied in parallel read 20.0529. Interesting.

Next step was to figure out what combinations 10 or 20 of those could created if hooked together with clip leads, in various clusters of series/ parallel groups.

Simple calculated that from 1 to 10 in parallel would yield 10 different resistances, same # for series. So 20 different combinations divided over 2 groups of 10 resistors.

Next I tackled the possible combinations that utilized one set of series plus one set of parallel possibilities, in series. This yielded 100 combinations

I didn't even begin the possible combinations in parallel.

There are some very interesting numbers on that list, which include 22.22222, 33.33333, 66.66666 266.66666 along with many the normal whole numbers starting at 10.


This is where my research stalled (read: mind=boggled) and decided to ask the computer experts here if they can do a spreadsheet that would calculate all the possibilities of 20 ea. 200 Ohm resistors.

I can envision two smallish boards with two rows of 10 terminal each, one row on each side and the resistors soldered across the terminals ladder style or maybe criss-crossed so they would all be in series already.

Clip leads to do the dirty work, and a spread sheet for "programming" information.

If this or some similar would be of interest to the traveling calibration folks, I will donate 100 resistors to the cause, enough for 5 pairs.


George Dowell

[martinr33]

"This is where my research stalled (read: mind=boggled) and decided to ask the computer experts here if they can do a spreadsheet that would calculate all the possibilities of 20 ea. 200 Ohm resistors."

This sounds like it could be a big deal... with 20 resistors, there are 20 factorial ways of ordering them - although half of them are aliases. It is a neat question, especially if all the resistors have different values.


Then, you can take readings from 18 points in the line. So you could multiply by 18, (or 18^2 if you measure two points relative to each other, rather than one against ground).

That calculates out to 20!/2 *18 = 2.18 E19... this could take a while.

And then there are all the series-parallel combinations that you can think up.



 

[hwj-d]

AFAIK, calibration lab techs don't get the summer off due to lack of business. It's also doubtful that sales and shipments of precision meters cease during mid winter and mid summer. The storage temperature range for the LTZ1000 is -65 to 150 C, so I doubt you could damage one. Didn't see a spec for metal foil resistors, but I'd be surprised if it was an issue. The big question is hysterisis of everything as you cycle the temperature and the only way to find out is to try it. Temperature and vibration in shipping is one reason I dislike trimpots. Too many change by tapping them, so they're certainly subject to changes during shipping.

Of course, mine were indeed not damaged.