USA calibration club

[kj7e]

CM, I have a good contact here in CA for any custom Vishay parts if needed, jut be prepared to wait 15-17 weeks.

Thought someone would like to see this, just having some fun with the new Keithley DMM7510 and testing the prototype LTC1150/LT1010 10v buffer.  The VHD200 ratio set divider network I have on order for this is still two months out .

[cellularmitosis]

Wow, that meter is awesome!  Thanks for making the video -- really neat to get to see someone put it through its paces.  Also nice to see the sort of stability I'm (eventually) aiming for!

Thanks kj7e

[Vacuuminded]

Just spent some time catching up on this thread, wow lots of things in the pipes!

Was any resolution reached with the new noise issue?  I'm curious if that simple piece of electrical tape was the root cause!

Finally rounded up a small PC and am up and (I think) running with the NI GPIB card.  So far have procured one GPIB cable.  Now just to figure out what program(s) I need for logging and control, and start learning how to use them!  Hoping to be up to speed and ready before the reference makes it's way here!

Regards,
Chris

[nikonoid]

Chris, are you under UNIX or Windows on that PC?

[Edwin G. Pettis]

You don't need those over priced Vishay parts, you're not going to get an equivalent return for your money in performance.....unless you like spending more money than needed.

[Vacuuminded]

Chris, are you under UNIX or Windows on that PC?

Windows 7 Pro, 32 bit.

[cellularmitosis]

Hi Chris,

I haven't solved it yet.  This weekend I'm going to take one more shot at scrubbing the board (perhaps with acetone), then try replacing the caps, etc.  I was hoping to not have to replace components, as that might throw out whatever history we have thus far, but we'll see!

[Joe Geller]

The failure documented here is pretty typical of a chip / board destroyed by having been powered by reverse voltage.  The reason the chip appears to be okay is because when powered off board, the trim input is not being tested.

The AD587 was first trimmed to very near 10V by two resistors about the trimmer, to Vout regulated, and common respectively.  After hours or semiautomated testing, the series resistor for the Vishay compensating thermistor was determined.  The small correction current developed by this very fine correction was applied to the trim pin.  Hours of final testing and calibration followed.

So, I think what has happened is that internal trim circuit is damaged (destroyed).  The reason there may be some correlation to the jumper is that the jumper connects the trim.

Because the fine temperature trim was unique to each individual AD587, once an AD587 of a SVR-T board was destroyed, there was no repair.  So, it was okay to use the thermal epoxy to get good thermal coupling between the thermistor and thermistor series resistor to the board itself.

Another reason the chip might be showing some signs of life is that for SVR-T boards, the AD587 was preselected, generally for an uncorrected tempco of better than about 3 ppm/c.  After correction, the SVR-T board tempco was typically better than 0.3 ppm/c.  Without the internal damaged trim circuit, there apparently remains a pretty good "raw" output, which however, can no longer be trimmed because the trim circuit is damaged.

We never spent much time looking at reverse powered boards, because all of the passive off chip components were likely okay.  These boards just went in the trash.

I took the AD587 off of the board, placed it into a machine socket, and clipped 15V and the meter leads to it, and I am shocked at how stable and low noise the output is.  And this is without any capacitors or other circuitry at all!  Just the IC in a socket!

Here's ~20 minutes of data (attached).

EDIT: adding photo of connections

[cellularmitosis]

 

Very interesting!  Thanks for weighing in on this Joe.  (for those unfamiliar, Joe is the designer of the SVR-T)

Welp, it looks like it is time for this humble gang of volt nuts to graduate to heated zeners!   

I have several taobao LM399 boards on hand which we could start using immediately.  I also rush-ordered a set of LTZ1000 boards which I recently designed, which should arrive on Thursday, so we could start using one of those after Christmas.  And TiN's "FX" reference should be ready in February.

[Andreas]

(for those unfamiliar, Joe is the designer of the SVR-T)

Just to clarify (from that what I know).
The SVR was designed and sold by Joe.
The SVR-T cirquit was a further development of Lars (then also sold by Joe).

with best regards

Andreas

[nikonoid]

Joe, thank you for your comments on this.

My biggest challenge for the last run was not the tempco, but noise on 10V.

I attached is last log of 16 hours. It was logged at 10PLC, so some averaging is needed to cleanup the results (20 moving average).



Temperature by Voltage correlation graph from that run shows almost no temperature dependency. If it is there and masked by the noise, it is certainly nowhere near 3ppm/C.



What could possibly create a noise on the output? Could somehow the damaged trim circuit manifest itself as noise on voltage read?

Please let us know what you think.

[CatalinaWOW]

Sad to hear that the SVR-T board is probably toast (sort of).  This also gives us direction for any subsequent traveling standard.  The nature of its use is that it will be connected and disconnected many, many times by many people.  Which is a recipe for error no matter the skill level and intentions of those involved.  So we should probably incorporate idiot proofing to the extent possible.  Definitely a diode bridge on power inputs.  Outputs are tougher since protection techniques will generally compromise performance, but we can probably come up with some ideas.

This comment does not point fingers at any individual.  As I understand the data history the noise increase does not correspond to a setup change.  Perhaps the cause is a power spike, ESD or some variant of the purple plague.  So protection will not eliminate all possibility of damage or degradation, just reduce the chances.

There may also still be merit in circulating the SVR-T with trim circuit disconnected.  It appears that the device has pretty good performance on its own.

[cellularmitosis]

Yeah I should reiterate that I am not upset about this at all.  The big win is that this cal club has a lot of interest and participation, and a few broken eggs is no big deal at all.  And, I would much rather have a mishap early on than have it happen when years of calibration history are at stake.

Yeah, I don’t think it is toast, but rather I now need to use an external op amp for the offset trim and temperature compensation circuitry.  That will be an enjoyable design exercise!   However that also invalidates any history we have thus far, so this is a good time to make a break and switch to another reference.

In terms of the things we’ve learned so far, input protection is a good one.  Good binding posts and having everyone use the same cables are another big one.  A shielded enclosure is another.  In general, doing everything we can to make everyone’s setup as identical as possible. 

As you say, output protection is a trickier one, because a buffer inevitably introduces some amount of error,  it perhaps we can overcome the danger of exposing the unbuffered output by coming up with a ritual to follow.  In the airline industry, using checklists in time of emergency has revolutionized their safety records, and now doctors are starting to adapt that practice to avoid operating room mishaps (see the book “Checklist Manifesto”).  We might have a ritual where you always start by connecting the buffered output first, and then as the last step you swap one lead from the buffered to the unbuffered output post, to minimize the chance of an output short, etc.

[cellularmitosis]

Nikonoid, I like that temperature - voltage correlation graph.  I need to learn how to make those!

[nikonoid]

Chris, are you under UNIX or Windows on that PC?

Windows 7 Pro, 32 bit.

There is an existing ezGPIB tool. I created my own VisualStudio code. It is very ugly, since I did not have time to write it nicely. It covers some functions for Keithley 2002 and some for HP3458a. I might do a rewrite later when I get time. If you like a copy, let me know and I will it PM to you.

[nikonoid]

Nikonoid, I like that temperature - voltage correlation graph.  I need to learn how to make those!

Cellular, this is very easy. It is called XY plot or scatter plot. Excel, as well as any other platform, has them.
Since voltage is pretty noisy in a way that is not correlated to temperature, it is beneficial to run voltage readings though pretty heavy averaging filter before plotting it against temp. In Excel for each cell you can just average 20 previous:  R23 =AVERAGE(I4:I23)

You can even make Excel plot trend line for you and display formula for trend line. Slope coefficient will give you the best PPM/C approximation and R^2 will be indicative of the quality of correlation (100% excellent, 30% BAD).

[bitseeker]

Sad to hear that the SVR-T board is probably toast (sort of).  This also gives us direction for any subsequent traveling standard.  The nature of its use is that it will be connected and disconnected many, many times by many people.  Which is a recipe for error no matter the skill level and intentions of those involved.  So we should probably incorporate idiot proofing to the extent possible.  Definitely a diode bridge on power inputs.  Outputs are tougher since protection techniques will generally compromise performance, but we can probably come up with some ideas.

I'm bummed, too, about the news of the SVR-T. But I'm thankful that Joe could stop by to clear up the mystery.

This comment does not point fingers at any individual.  As I understand the data history the noise increase does not correspond to a setup change.  Perhaps the cause is a power spike, ESD or some variant of the purple plague.  So protection will not eliminate all possibility of damage or degradation, just reduce the chances.

Agreed. It's an opportunity to learn and make improvements.

There may also still be merit in circulating the SVR-T with trim circuit disconnected.  It appears that the device has pretty good performance on its own.

Interesting idea. Could a new trim circuit be made for it?

Yeah I should reiterate that I am not upset about this at all.  The big win is that this cal club has a lot of interest and participation, and a few broken eggs is no big deal at all.  And, I would much rather have a mishap early on than have it happen when years of calibration history are at stake.

It's still unfortunate that it occurred when you so generously made the SVR-T available to the club. It's true, though, that's it's good to shake out the issues early on, rather than after we've got years of history on record.

Yeah, I don’t think it is toast, but rather I now need to use an external op amp for the offset trim and temperature compensation circuitry.  That will be an enjoyable design exercise! However that also invalidates any history we have thus far, so this is a good time to make a break and switch to another reference.

That's good news if it can be put back in service with some external trim, even if only for a stationary reference that you can use for comparison.

In terms of the things we’ve learned so far, input protection is a good one.  Good binding posts and having everyone use the same cables are another big one.  A shielded enclosure is another.  In general, doing everything we can to make everyone’s setup as identical as possible.

Check.

...perhaps we can overcome the danger of exposing the unbuffered output by coming up with a ritual to follow.  In the airline industry, using checklists in time of emergency has revolutionized their safety records, and now doctors are starting to adapt that practice to avoid operating room mishaps (see the book “Checklist Manifesto”).  We might have a ritual where you always start by connecting the buffered output first, and then as the last step you swap one lead from the buffered to the unbuffered output post, to minimize the chance of an output short, etc.

In fact, airline pilots have checklists for standard operations, regardless how many times they've gone through the same procedures for takeoff, landing, etc. I'm happy to follow any checklists that will ensure the safety of the equipment as well as the consistency and quality of the data.

[CatalinaWOW]

Nikonoid, I like that temperature - voltage correlation graph.  I need to learn how to make those!

Cellular, this is very easy. It is called XY plot or scatter plot. Excel, as well as any other platform, has them.
Since voltage is pretty noisy in a way that is not correlated to temperature, it is beneficial to run voltage readings though pretty heavy averaging filter before plotting it against temp. In Excel for each cell you can just average 20 previous:  R23 =AVERAGE(I4:I23)

You can even make Excel plot trend line for you and display formula for trend line. Slope coefficient will give you the best PPM/C approximation and R^2 will be indicative of the quality of correlation (100% excellent, 30% BAD).

I would suggest taking averages centered around the point of interest.  R23=AVERAGE(I13:I33).  It doesn't matter when the mean is not moving, but if there is a slope to the data errors are reduced.  We are post processing the data so there is no concern about getting data out of the future.

[orin]

There may also still be merit in circulating the SVR-T with trim circuit disconnected.  It appears that the device has pretty good performance on its own.

Interesting idea. Could a new trim circuit be made for it?

My understanding of Joe's post is that it's the trim circuit on the chip itself that is damaged, so nothing can be done, other than running with the trim circuit disconnected and accepting the uncorrected tempco.

[bitseeker]

There may also still be merit in circulating the SVR-T with trim circuit disconnected.  It appears that the device has pretty good performance on its own.

Interesting idea. Could a new trim circuit be made for it?

My understanding of Joe's post is that it's the trim circuit on the chip itself that is damaged, so nothing can be done, other than running with the trim circuit disconnected and accepting the uncorrected tempco.

Yeah, that was my understanding as well. I was just wondering if an external trim of some sort was a possibility. Volt-noob questions.

[cellularmitosis]

YEah, I meant an external trim + tempco compensation

[TiN]

You can't be sure if rest of the chip is still meets the spec, as damage for trim circuit might affect other areas of the die, and now every time you get questionable data, you'll be asking yourself if it's your or the chip. I'd ditch the chip, or replace it and retrim properly, or better yet use multiple units of same reference design, so you can relate data between them to see if any single unit doing funny business. That is how I maintain confidence in ppm-level measurements using four 8.5d meters. If all of them show same data deviations, then I know it is coming from the DUT and not the meter.

[nikonoid]

Cellular, in respect to copper clips used in the kit, I just saw a very useful modification from Rob Renz. It should be pretty easy to do. Watch video below from 4:30 till 5:30.




Sent from my iPhone using Tapatalk

[cellularmitosis]

Oh that is really clever nikonoid!

[lars]

About the SVR and SVR-T:  I designed the temperature compensation for the SVR-T but credit really should go to Joe for all hours he spent to supply calibrated boards to the Volt nut community at a really low price! Of course I am proud of the simple compensation with two components that adds both first and second order temperature compensation to the AD587LQ

About the SVR-T that have circulated in US:

With a bare IC that is stable and only 61ppm off I really wonder if the IC have been reverse powered. I have once toasted an AD587LQ in an SVR-T. That IC only outputted 0.4V and the supply pin took a lot more current (around 10mA if I remember correct). After that incident I always have put a 1N5819 or similar in series with the 15V. The about 0.2V drop only gives a small part of a ppm different output voltage normally. I have chosen the 1N5819 as it can stand 40v reverse voltage, have a reasonable low voltage drop at 2mA and is cheap.

For me next step in testing would be the bare IC plus a 10Mohm resistor from the trim-pin 5. With the 10Mohm connected to the output (pin 6) the voltage should be about 170ppm lower and if stable I shouldn’t suspect the trim-pin of the IC. A further test would be to connect to ground (pin 4) and see if the voltage is about 400ppm higher.

If you put the IC back on the board without jumper and the output is still noisy another possibility for noise is the pin 8. This pin has about 4kohm resistance. A resistance to ground here of 4Gohm will offset the output about 1ppm. Maybe I should take away the capacitor as a test.

If the IC output isn’t noisy a possibility is to measure the about 7V from the trim circuit (without the jumper). Measure on the jumper pin, see if it is noisy. I guess the attenuation from the trim pin to output is about 20 times so the noise should not be more than about 20ppm p-p measured with the DMM.

Lars