High Precision Resistance Measurement - What would be best to use?

[Chipguy]

Hi all

I am wondering what best to get for measuring resistance with very high precision.
There are all the well known Keysight, Keithley, Fluke, Transmille etc. 8.5 digit multimeters that would be fine.
But is there something more special that has a lower price tag than the $10.000-ish tags these meters usually have?

Any ideas?

[tautech]

A nulling RLC bridge but they're slow.

How many digits do you want ?
6.5 enough ?

http://www.siglenteu.com/pdxx.aspx?id=2773&T=2&tid=37

[TiN]

What is the resistance? 0.001 ohm? 1000 megaohm? 10 kohm? Different values have different optimal tools.
And what is very high precision? 0.1%? 0.1 ppm? What one field consider "very high precision" is mediocre for other use...

Without knowing your question, answer would be from "handheld Fluke is the best" to "CCC bridge and QHR standard is the only way for very high precision"...

[Chipguy]

Let's say from 1 Ohm to 100 MOhm.
While the precision will vary for both, the very low and the very high resistances.
At 100 M Ohm I would not expect more than 6.5 digit performance.

The performance should be similar to the Keysight 3458A with 8.5 digits.

It seems there are only multimeters on the market, no dedicated resitance meters.

[Gyro]

At 100 M Ohm I would not expect more than 6.5 digit performance.

 

https://www.tek.com/document/handbook/low-level-measurements-handbook

[TiN]

Well, bridge like ESI 242D and older versions of this system.

There is one in unknown condition on bay now for 3K. If you get it, fix it, calibrate it, than you can get 3458A or better performance.

[Chipguy]

Well, bridge like ESI 242D and older versions of this system.
There is one in unknown condition on bay now for 3K. If you get it, fix it, calibrate it, than you can get 3458A or better performance.

Oh wow, that is something. Never paid any attention to these.

I was wondering what I could achieve building a resistance meter myself.
Using your LTZ1000 Reference design for a start would be a must. I also had a brief look at that "31 bit" ultra high precision ADC from TI.
However, as of now it is just an idea.

[montemcguire]

The minimum requirement for quality resistance measurement is four wire capability, so you do not have to worry much about the test leads. A good Kelvin clamp probe is not cheap, but absolutely necessary. The Keysight 11059A Kelvin probe is a small fortune, but it's nicely made and works well. I don't want to drive their prices up, but a used, well loved, and regularly calibrated HP 3456A can be a very low cost 6.5 digit meter, much nicer than much more expensive, modern 6.5 digit meters. I lucked into one from NASA that had been calibrated regularly for a few decades and it seems to be very accurate and stable. Plus, the 3456A reference does not have much hysteresis, so you don't have to leave it on all the time to get good accuracy. For matching resistors, all you care about is repeatability and resolution, and the 3456A does well there too. Anything better would have to be a 3458A or some sort of bridge, which I either can't afford or don't want to deal with.

[ap]

Hi all

I am wondering what best to get for measuring resistance with very high precision.
There are all the well known Keysight, Keithley, Fluke, Transmille etc. 8.5 digit multimeters that would be fine.
But is there something more special that has a lower price tag than the $10.000-ish tags these meters usually have?

Any ideas?

Well, first of, there are cost efficient options to the 3458A, such as e.g. the Solartron 7081 or the Datron 1271, maybe 1281.
The 242 bride is not really that precise, in relative mode yes, but in absolute mode it is hard (if not impossible with the data available) to generate a traceable uncertainty chain.
If you want to go beyond what the 3458A can achiev, you need a DCC, the 9975 e.g costs about 2.5k used. Staring from a 10k calibrated resistor, you can cover the 0.1 to 100k (6 decades!) range.
Beyond the SR1010 helps in transferring values.
So for low cost, my recommendation would be a 7081, a 10k Standard, and a 9975. Allows sub-ppm uncertainty. If cheaper is what you want, just the 7081. If you can spend more, replace the 7081 by a 1281.

[Edwin G. Pettis]

What utter nonsense....I have used, calibrated and repaired 242D systems since 1973!  I have consistently been able to calibrate a 242D to within 1 PPM from 100 ohms to 1 Megohm, slightly increasing to 2 PPM towards the top end of 11Megohms and gradually increasing to 5 PPM on the lowest range mainly due to resolution limitations.  They are completely traceable to primary standards with low uncertainty.  I don't know where you're getting your information but it either incorrect or those 242Ds you've fussed with were not properly calibrated.  My system 242D is fully traceable through the SR-104 with uncertainty as low as under 0.5 PPM against it.  The uncertainty does increase slightly the farther you go from the 10K range but it is still quite small.  A 3458A only comes close to a 242D at a 10K cardinal point if directly calibrated against an SR-104, beyond that, the 3458A is not as accurate as a 242D.  It does take skill and experience to achieve such performance.....and don't both quoting the manual to me, those are conservative specifications and the 242D is quite capable of better performance, I've got the years of experience to know so.  Each 242D system is a bit unique so quoting just how long a 242D will maintain that 1 PPM accuracy depends on each bridge.  If you're worried about it, a quick check against the SR-104 will take care of that.

If you are looking for good accuracy, an older 3456A will give you very good performance at a very good price point, a lot of bang for the buck.  Unless you can justify the cost or real need, instruments like the 242D and 3458A tend to be too costly for the hobbyist unless you have deep pockets, calibration is not cheap if you intend on keeping them at peak performance and you will find very few calibration shops that will calibrate an 242D to capability and not just spec, same thing goes for the 3458A.

I've got a 3456A sitting on my bench near the 242D, it is checked against the 242D/SR-104 and my Vref often, so far, it is holding calibration better than the 1 day spec of 10 PPM at 122 days since I calibrated against the Vref.....not too shabby for a 30+year old DVM.  I have not tweaked it because I'm curious what the drift will be for 6 months, just to compare it against manual specs.

[ManateeMafia]

Edwin,

If you ever found the spare time to spend with some volt-nuts, I would love to spend a day going over the 242D/E's capabilities. I would even ship a 242 just so yours won't risk getting damaged.

[babysitter]

I second the notion of buying a good dmm for everything, as you can use your investment for a wider (digital multimeter) range if there are no reasons like collecting behind.

You might start to like the DCV:DCV ratio mode and if you employ a (no ltz1000-class necessary) voltage reference and have some good resistors (consider ovenizing? Can be done for sub 10 euroish) for bridge-building you might save money and get reasonable fun for less.

BR
Hendrik

(Anyway, a slightly defective ESI DC801 is sitting on my bench. Does somebody have the schematic of the non-A, non-B, non-bigger-character-suffix? The meter inside is by the way a HP 37-419 null detector, so the schematic of this would be great!)

[doktor pyta]

What is ESI DC801 ?
Could You show a photo, please?

[TiN]

It's a 33% of the 242D, nullmeter and DC source.
I have 240C (bridge) and blown up RS925D (resistance decade) .

[ManateeMafia]

Beat me to it. It is on page 140 of 160 in the 242B manual.

[quarks]

several years ago I opened a similar topic, most likely there should still be some useful information in it

https://www.eevblog.com/forum/chat/help-wanted-low-and-high-ohm-measuremet/msg169139/#msg169139

[Chipguy]

several years ago I opened a similar topic, most likely there should still be some useful information in it
https://www.eevblog.com/forum/chat/help-wanted-low-and-high-ohm-measuremet/msg169139/#msg169139

Ahh interesting, thanks !
I did search for existing articles like that, but your headline does not contain the word "Resistor" or "Resistance". So it slipped under my search radar.
So I should also search again for "ohm" and "Ohms" in the headlines.

[Fludo]

You may want to look into LCR meters,  which have the ability to measure real and complex impedance at variable frequency.

[anymouse]

(Anyway, a slightly defective ESI DC801 is sitting on my bench. Does somebody have the schematic of the non-A, non-B, non-bigger-character-suffix? The meter inside is by the way a HP 37-419 null detector, so the schematic of this would be great!)

That Singer one?

Well, there is a HP 419A Null detector meter. If I remember correctly, the ESI 801 uses a building block of the HP 491a  for the chopper amplifier. So I would start with the service manual for the HP 419A, which is found easily online.

[ap]

What utter nonsense....I have used, calibrated and repaired 242D systems since 1973!  I have consistently been able to calibrate a 242D to within 1 PPM from 100 ohms to 1 Megohm, slightly increasing to 2 PPM towards the top end of 11Megohms and gradually increasing to 5 PPM on the lowest range mainly due to resolution limitations.  They are completely traceable to primary standards with low uncertainty.  I don't know where you're getting your information but it either incorrect or those 242Ds you've fussed with were not properly calibrated.  My system 242D is fully traceable through the SR-104 with uncertainty as low as under 0.5 PPM against it.  The uncertainty does increase slightly the farther you go from the 10K range but it is still quite small.  A 3458A only comes close to a 242D at a 10K cardinal point if directly calibrated against an SR-104, beyond that, the 3458A is not as accurate as a 242D.  It does take skill and experience to achieve such performance.....and don't both quoting the manual to me, those are conservative specifications and the 242D is quite capable of better performance, I've got the years of experience to know so.  Each 242D system is a bit unique so quoting just how long a 242D will maintain that 1 PPM accuracy depends on each bridge.  If you're worried about it, a quick check against the SR-104 will take care of that.

Well, the manual available to me states 10ppm absolute measurement uncertainty, worse in lower ranges. It does not mention temperature coefficient nor annual aging. The current 925 resistance decade manual (which may or may not apply to the one used in the older 242D bridge; it looks redesigned) states 20ppm abs. accuracy, 20ppm anual stability and between 3 and 20ppm/K temperature coefficient. If you take all this into account (again here, the 242D manual is not specific about the impact of these parameters on the actual overall bridge accuracy), it gets pretty mediocre (20ppm is about a factor 2 worse than the 3458A annual ohms aging for 1k to 100k values). Maybe there are other specifications somewhere, I did not find any back when I looked at the 242.
So while a typical 242D may be much better, in a metrology environment you can not rely on a typical behaviour (typical for what; which measured ohms value, for which ambient range...?). You have to demonstrate the error contributions of the various parameters, for which unsufficient data is available.  For personal use, it is a different story, everybody will have to decide for himself.
In comparision, a resistance bridge built up with a (self-calibrateable!) Fluke 720A (details about resistance bridge measurement setup see manual; Standard needed) is very well characterized, so using this is much more convenient and also results in better calculable uncertainties. At a comparable price. So therefore I felt the 242 would not be a good solution to me and due to missing information extremely hard to characterize.
I will leave it at that.

[try]

What utter nonsense....I have used, calibrated and repaired 242D systems since 1973!  I have consistently been able to calibrate a 242D to within 1 PPM from 100 ohms to 1 Megohm, slightly increasing to 2 PPM towards the top end of 11Megohms and gradually increasing to 5 PPM on the lowest range mainly due to resolution limitations.  They are completely traceable to primary standards with low uncertainty.  I don't know where you're getting your information but it either incorrect or those 242Ds you've fussed with were not properly calibrated.  My system 242D is fully traceable through the SR-104 with uncertainty as low as under 0.5 PPM against it.  The uncertainty does increase slightly the farther you go from the 10K range but it is still quite small.  A 3458A only comes close to a 242D at a 10K cardinal point if directly calibrated against an SR-104, beyond that, the 3458A is not as accurate as a 242D.  It does take skill and experience to achieve such performance.....and don't both quoting the manual to me, those are conservative specifications and the 242D is quite capable of better performance, I've got the years of experience to know so.  Each 242D system is a bit unique so quoting just how long a 242D will maintain that 1 PPM accuracy depends on each bridge.  If you're worried about it, a quick check against the SR-104 will take care of that.

If you are looking for good accuracy, an older 3456A will give you very good performance at a very good price point, a lot of bang for the buck.  Unless you can justify the cost or real need, instruments like the 242D and 3458A tend to be too costly for the hobbyist unless you have deep pockets, calibration is not cheap if you intend on keeping them at peak performance and you will find very few calibration shops that will calibrate an 242D to capability and not just spec, same thing goes for the 3458A.

I've got a 3456A sitting on my bench near the 242D, it is checked against the 242D/SR-104 and my Vref often, so far, it is holding calibration better than the 1 day spec of 10 PPM at 122 days since I calibrated against the Vref.....not too shabby for a 30+year old DVM.  I have not tweaked it because I'm curious what the drift will be for 6 months, just to compare it against manual specs.

Edwin,

initially I did not intend to spread the word about it you but with you bragging about your measurement abilities while simultaneously failing to meet the specs I think others should be aware of my negative purchase experience with you.

This is what I wrote to you 2/27/2018 20:19:

Hello Edwin,

I hope you are doing well!

Unfortunately I have an issue with your resistors, they are off specification.

In your email dated on Christmas Eve (12/24/2016 18:30) you stated:

...The two 10Ks were about -2 PPM and -6 PPM from nominal....

When measuring them with PTB at the maker fair on 8/27/2017 they were 10,000 441 and 10,000 397 kOhm.
As the 3458A they used this time hadn't been calibrated/adjusted* for some time I waited for a arrival of a friend.

Last Friday we both went to the university department he had worked for.
We had a 3458A in there, 5 years old and never calibrated since.
We measured 10,000 485 kOhm and 10,000 491 kOhm.
By comparing to a Vishay VHP in 10k my friend had measured at work with his annually calibrated 3458A we were able to determine that the 3458A at university was reading roughly 16ppm too high.

But even then, the real value of your resistors would rather measure an adjusted 10,000 325 kOhm and 10,000 331 kOhm.
I just measured them on my 34401A that I adjusted to PTB specs at the maker fair and they were both at 10,000 34 kOhm.

I have to assume that the two candidates have either never exhibited the resistances you indicated or that they drifted roughly 35 ppm in just nine months.


The following pictures shows one of the two 10k resistors specified 10ppm (your writing!) that I purchased from you at the  end of 2016. I just measured it. They are both way off spec.

Now I have to read in this thread that you have a 3456A on your bench which you could have used to verify the resistor you produced for me what you obviously not bothered to do for a client order in the 10ppm precision range.

Conclusion:
Please do not claim high precision. You are probably a good source for PWW resistors in the 0,1% or 0,01% class and are delivering a good service that you do not charge for by producing PWW resistors with resistances as per customer specification.
I always enjoyed reading your contributions and still do with a grain of salt but the former confidence is gone.

I hope that the bunch of knowledge you acquired will show up in your PWW products sometime in the future.
And as opposed to my last email to you where I hinted to you that I ordered and paid 10ppm class and received two classes below:
You can continue to ignore it - no problem.

Greetings from Germany
try

* The 3458A had been calibrated in the voltage ranges shortly before the fair but not in the Ohm ranges.

[TiN]

For metrology use it make more sense not to use RS925, but use external standard like SR104 and substitution operation for unknown Rx comparison.
Also it is uncommon to have large temperature excursions during measurement cycle to get that big impact on the TCR. Calibration and verification of 242 is also little simpler than KVD like 720A, from which you cannot draw current to obtain best accuracy.

[CalMachine]

What utter nonsense....I have used, calibrated and repaired 242D systems since 1973!  I have consistently been able to calibrate a 242D to within 1 PPM from 100 ohms to 1 Megohm, slightly increasing to 2 PPM towards the top end of 11Megohms and gradually increasing to 5 PPM on the lowest range mainly due to resolution limitations.  They are completely traceable to primary standards with low uncertainty.  I don't know where you're getting your information but it either incorrect or those 242Ds you've fussed with were not properly calibrated.  My system 242D is fully traceable through the SR-104 with uncertainty as low as under 0.5 PPM against it.  The uncertainty does increase slightly the farther you go from the 10K range but it is still quite small.  A 3458A only comes close to a 242D at a 10K cardinal point if directly calibrated against an SR-104, beyond that, the 3458A is not as accurate as a 242D.  It does take skill and experience to achieve such performance.....and don't both quoting the manual to me, those are conservative specifications and the 242D is quite capable of better performance, I've got the years of experience to know so.  Each 242D system is a bit unique so quoting just how long a 242D will maintain that 1 PPM accuracy depends on each bridge.  If you're worried about it, a quick check against the SR-104 will take care of that.

If you are looking for good accuracy, an older 3456A will give you very good performance at a very good price point, a lot of bang for the buck.  Unless you can justify the cost or real need, instruments like the 242D and 3458A tend to be too costly for the hobbyist unless you have deep pockets, calibration is not cheap if you intend on keeping them at peak performance and you will find very few calibration shops that will calibrate an 242D to capability and not just spec, same thing goes for the 3458A.

I've got a 3456A sitting on my bench near the 242D, it is checked against the 242D/SR-104 and my Vref often, so far, it is holding calibration better than the 1 day spec of 10 PPM at 122 days since I calibrated against the Vref.....not too shabby for a 30+year old DVM.  I have not tweaked it because I'm curious what the drift will be for 6 months, just to compare it against manual specs.

Edwin,

initially I did not intend to spread the word about it you but with you bragging about your measurement abilities while simultaneously failing to meet the specs I think others should be aware of my negative purchase experience with you.

This is what I wrote to you 2/27/2018 20:19:

Hello Edwin,

I hope you are doing well!

Unfortunately I have an issue with your resistors, they are off specification.

In your email dated on Christmas Eve (12/24/2016 18:30) you stated:

...The two 10Ks were about -2 PPM and -6 PPM from nominal....

When measuring them with PTB at the maker fair on 8/27/2017 they were 10,000 441 and 10,000 397 kOhm.
As the 3458A they used this time hadn't been calibrated/adjusted* for some time I waited for a arrival of a friend.

Last Friday we both went to the university department he had worked for.
We had a 3458A in there, 5 years old and never calibrated since.
We measured 10,000 485 kOhm and 10,000 491 kOhm.
By comparing to a Vishay VHP in 10k my friend had measured at work with his annually calibrated 3458A we were able to determine that the 3458A at university was reading roughly 16ppm too high.

But even then, the real value of your resistors would rather measure an adjusted 10,000 325 kOhm and 10,000 331 kOhm.
I just measured them on my 34401A that I adjusted to PTB specs at the maker fair and they were both at 10,000 34 kOhm.

I have to assume that the two candidates have either never exhibited the resistances you indicated or that they drifted roughly 35 ppm in just nine months.


The following pictures shows one of the two 10k resistors specified 10ppm (your writing!) that I purchased from you at the  end of 2016. I just measured it. They are both way off spec.

Now I have to read in this thread that you have a 3456A on your bench which you could have used to verify the resistor you produced for me what you obviously not bothered to do for a client order in the 10ppm precision range.

Conclusion:
Please do not claim high precision. You are probably a good source for PWW resistors in the 0,1% or 0,01% class and are delivering a good service that you do not charge for by producing PWW resistors with resistances as per customer specification.
I always enjoyed reading your contributions and still do with a grain of salt but the former confidence is gone.

I hope that the bunch of knowledge you acquired will show up in your PWW products sometime in the future.
And as opposed to my last email to you where I hinted to you that I ordered and paid 10ppm class and received two classes below:
You can continue to ignore it - no problem.

Greetings from Germany
try

* The 3458A had been calibrated in the voltage ranges shortly before the fair but not in the Ohm ranges.

Given the information you've provided.  I am highly inclined to think you cannot accurately discern 10 ppm in an absolute measurement...

[MisterDiodes]

Last Friday we both went to the university department he had worked for.
We had a 3458A in there, 5 years old and never calibrated since.
We measured 10,000 485 kOhm and 10,000 491 kOhm.
By comparing to a Vishay VHP in 10k my friend had measured at work with his annually calibrated 3458A we were able to determine that the 3458A at university was reading roughly 16ppm too high.

But even then, the real value of your resistors would rather measure an adjusted 10,000 325 kOhm and 10,000 331 kOhm.
I just measured them on my 34401A that I adjusted to PTB specs at the maker fair and they were both at 10,000 34 kOhm.


try

* The 3458A had been calibrated in the voltage ranges shortly before the fair but not in the Ohm ranges.

Try:

So what your saying is - You really don't have a way to measure the resistors on on any real calibrated equipment, you don't have access to a single true resistance standard, and after 9 months of shipping and unknown storage / weather conditions - tell us all exactly why would Edwin be concerned?  Even with your very rustic measuring technique you still are within 35ppm.  Or whatever hit or miss technique you've used.  Not bad.

Have you once looked at your uncertainty levels on each piece of equipment?  Really??  Do you have any equipment you've -actually- kept calibrated?  Or is it the usual story around here that goes like .."I bought this old meter cheap on eBay, it hasn't been calibrated, but I took it to a friend and measured against his uncalibrated equipment and was about the same because his cousin had a resistor once that looked pretty good on his meter, and I don't want to spend any money to cal my own equipment".   And so on.

We've ordered several hundred resistors from Edwin last year, at various tolerances, .001% and .01% mostly. We maintain fully calibrated 3458a, 3456a, 732s, SR-104's etc.   All equipment with drift history, etc.  Guess what?? Using multiple meters backed up by the SR-104, all his resistors were fine, a couple were damaged in shipping and 1 was slightly off spec.  He replaced the problem children at no cost.  No drama, no BS.

In the end?  We got 100% of what we ordered, in spec.  That's the typical experience we have, and we've had many more problems with other vendors.  We've got some Vishay Voodoo Magiacals we ordered that were supposed to be 10.1k .01% and we got 101.01 ohms instead.  How's that for out of spec??  It took about 3 months before they finally replaced those.

And guess what also?? All resistors drift over time.  Comes with the territory unless you buy a Reference Standard.  The thing you'll notice about Pettis resistors is they tend to drift the same way, and they will have the same TC (about) if you ask him for that.

Did you ever stop to think what that means: YOU MEASURED BOTH EDWIN'S RESISTORS AND THEY WERE BOTH THE SAME....After 9+ months or whatever???  And you're complaining??!! Really!!??

C'mon.

[TiN]

I had not that big qty to play with, but that dozen of Edwin resistors I got are indeed well within spec for both TCR (standard spec <3ppm/K) and absolute accuracy (using <180day calibrated standards and multiple maintained meters) even after shipping and soldering stresses.

So yes, I would not try to claim anything unless there is proven meter with known absolute accuracy. 3458A on it's own does not produce any accurate readings, unless it is calibrated and proven stable against known reference standard.

And while maker faire cool event and fun to play at, measurements at any public event like that, with uncontrolled environment conditions, people lurking around, airflow drafts everywhere is just an indication only, not a proper measurement that anyone can reference to.

[Chipguy]

So yes, I would not try to claim anything unless there is proven meter with known absolute accuracy. 3458A on it's own does not produce any accurate readings, unless it is calibrated and proven stable against known reference standard.

One of the possible plans is to have a 3458A for that purpose.
Calibrating the resistance to Keysight specs can only be done by the PTB here and costs around 1000 EUR.
I did not find another lab in Germany that could meet the Keysight specs. I fact the one I talked to does indeed send their Datron 127x to the PTB for calibration as well.

[Edwin G. Pettis]

Most interesting, I have been talking to Try about those two resistors (he doesn't mention he has bought quite a few other resistors from me without complaint).  I originally tried to talk him out of ordering ±10 PPM resistors and told him why it would have been better to go with ±25 PPM instead.  I'm a little surprised at such a big fuss, I only charged Try $26.38 each for those resistors and frankly, that is an heck of a bargain (apparently he doesn't).  I rather doubt you could order 10 PPM resistors from anybody else for that price or even close to it, just how much is Vishay charging these days for even ±0.005%.  As with any precision resistor, it is going to drift and the first year is always the biggest shift, even a 5 PPM drift or a bit less could drop a 10 PPM resistor out of tolerance even if it was initially within the specified 10 PPM.  That was one of the reasons I tried to convince Try to go for 25 PPM plus lower cost.  The order was originally placed November 6, 2016 and likely shipped in early December (I'd have to check the records for the exact date) so these resistors are bit older than a year now, not nine months.

Given the unknown state of the instruments and the fact that a Vishay VHP 10K does not qualify as a resistance standard (and what was it measured on?), such tight PPM measurement uncertainty and accuracy is questionable for measuring a resistor that accurately.  There is the possibility that the resistors have moved out of the initial ±10 PPM, it would be silly to claim otherwise, however without the measurements being done on a properly calibrated instrument, the claimed measurements themselves are questionable at that accuracy.  For that level of accuracy, a direct comparison to a calibrated SR-104 is the appropriate method.

Since I have been busy working, I have not had the time to reply to Try's last email (last Wednesday) yet.  Does he want to send the resistors back to me?  Does he want a partial refund for the difference between 10 PPM and 25 PPM pricing?  At this point I don't know what he wants, I was rather surprised to see his posting here before trying to reach a solution with me.  Given the accuracy requirements here, while I accept that Try believes the resistors are "way out of spec", unless they are measured on a known accurate instrument, I really cannot accept his figures at face value in this case.  I am more than willing to try and find a solution but when splitting PPM hairs, I really need something better to go on.

[ap]

One of the possible plans is to have a 3458A for that purpose.
Calibrating the resistance to Keysight specs can only be done by the PTB here and costs around 1000 EUR.
I did not find another lab in Germany that could meet the Keysight specs. I fact the one I talked to does indeed send their Datron 127x to the PTB for calibration as well.

What exactly do you mean / refer to by Keysight resistor spec, and what is so special about it that you claim only PTB is able to calibrate it?

[Chipguy]

What exactly do you mean / refer to by Keysight resistor spec, and what is so special about it that you claim only PTB is able to calibrate it?

Simple as that: All the other labs I called are using something like: HP 3458A, Fluke 8xxx or Datron 127x for resistance calibration.
You see the problem?

Those are good enough to calibrate a Keysight 34401A for instance. But not good enough to calibrate another 8.5 digit multimeter to full spec.
The PTB however has some other means to do that. I have no idea what they use though (yet).

[Henrik_V]

This?
https://www.ptb.de/cms/en/ptb/fachabteilungen/abt2/fb-26/ag-262/the-quantum-hall-resistance.html
plus lots of stable artifacts in 24/7 stirred baths, AC-bridges..    ...    ...    skilled operators

[Chipguy]

This?
https://www.ptb.de/cms/en/ptb/fachabteilungen/abt2/fb-26/ag-262/the-quantum-hall-resistance.html
plus lots of stable artifacts in 24/7 stirred baths, AC-bridges..    ...    ...    skilled operators

Hallo Henrik,
yes, perhaps this. At this time I really don't know.
They should have diagrams in high res for download somewhere. Those show the tracability chain and/or rough diagrams of how they calibrate stuff.
I know that because we got a lot of them on the walls in our calibration lab at work.

[Chipguy]

I think that is what I mean:

https://www.ptb.de/cms/fileadmin/internet/fachabteilungen/abteilung_2/Kal-Messm-Abt2_V12_2017.pdf

[ap]

Simple as that: All the other labs I called are using something like: HP 3458A, Fluke 8xxx or Datron 127x for resistance calibration.
You see the problem?

Those are good enough to calibrate a Keysight 34401A for instance. But not good enough to calibrate another 8.5 digit multimeter to full spec.
The PTB however has some other means to do that. I have no idea what they use though (yet).

Well, then you called the wrong companies. There are several companies out there that have resistance standards that are specified (DAkkS) to sub ppm level over most of the range and low digit ppm in the 1 and 10Mohm ranges and which are very well positioned to calibrate a 3458A with very good TURs. Go look into the DAkkS data base and you will find them.
The meters you mention are indeed (in conjunction with a transfer decade or so) not suitable to calibrate the resistance ranges of a 3458A. But one would normally use a 5720/5730/4808 for calibration anyhow, if one would not want to work manually with resistance standards (which is more time consuming and costly than just connecting a calibrator). See also Fluke white paper on how to calibrate a 3458A with the 5720/30. Using low uncertainty dedicated standards is certainly preferrable though from a TUR perspective.

[branadic]

... a couple were damaged in shipping and 1 was slightly off spec....

Doh, this increases confidence to a maximum. If they got broken by shipping, this looks like a very sensitve component and construction leading in unreliable components. If they get broken by shipping, how reliable will they be in their final application?
But as I've learned, some resistor manufacturer are the opinion, that it is out of their scope what happens after the components have left their factory. This is one possible perception, with the chance of bad reputation. Another opinion is to improve construction and processes, so that shipping will not harm the component. Even though we are talking about a comparable cheap precision component this shouldn't imply poor reliability but more sustainability. My opinion.

-branadic-

[Echo88]

You do know that some package drivers are able to break the most ruggedized and careful packed stuff right? Since we didnt see any pictures of the damages all that remains are your opinions.

[branadic]

Even then it's up to the manufacturer that the package content is save during transport. I did already understand that you as well as MisterDiodes are fanboys of E.G.P., nobody could overlook that

-branadic-

[MisterDiodes]

... a couple were damaged in shipping and 1 was slightly off spec....

Doh, this increases confidence to a maximum. If they got broken by shipping, this looks like a very sensitve component and construction leading in unreliable components. If they get broken by shipping, how reliable will they be in their final application?

-branadic-

Let's see you build hundreds of a high precision anything on a production basis and see if you hit 100% after your product pass thru the post office.

The shipping damage was cause by the box getting jammed on a post office conveyor and crushing the box - not that it was an unreliable component.  We're guessing the out-of-spec resistor probably was part of the crushing process also since the lead was kinked hard.  Even then it was out only .013% on a .01% resistor - Edwin fixed that one too, and we didn't expect that.  That's what I mean by "slightly off spec". He wanted to make sure that we got within .01%.  OK, cool!

The important part is that even with correcting shipping damage, we wound up with 100% of what we ordered a week or two later.  Does that make me a fan??  Of course!

All the other many shipments we've received are perfectly fine.

We've got hundreds of Edwin's  PWW's (and other mfrs including GR, Reidon, Vishay) running in the field for years in test equipment literally running 24/7/365 and let's see...exactly zero have ever needed to be replaced.  That's what I can tell you.   As with ANY high precision resistor, you treat it with much care until it is safely mounted on a board, and don't overstress / crimp / kink / pull hard on the leads.  Like you would treat ANY. Precision. Component.  Regardless of where it comes from. 

As long as it's not overloaded or crushed it will probably outlast your lifetime.

Weren't you the one that was complaining about one of Edwin's resistors, and Edwin offered to replace it for you at no cost, regardless of mishandling?   Did you get your replacement?

Do other manufacturers do that for a hobbyist?

[MisterDiodes]

And by the way....How many other resistor manufacturers spend ANY time participating in this forum, explaining processes, answering questions, patiently offering free advice and help - even to those who are NOT customers?

I don't know of any... Maybe there are but they sure don't make it known.

[Echo88]

@Branadick: Its much simpler: i dislike you because of your attitude and pissing on the leg of multiple people. You know: whining about TiN not publishing his equations for his resistor-TCR-measurement, whining about Edwin who hasnt written a book which contains all his relevant resistor manufacturing knowledge. A resistor broke during shipment, DOH, clearly a major disaster which could have prevented by Captain Branadick.

I remember fondly the case, in which you showed your project here with attached eagle files and when people asked for schematic-pictures instead of eagle-files (because not everyone has eagle or wants to install it) and you basically said: fuck all those who dont have eagle to view it. Thats how you are and thats how i see you.

[Edwin G. Pettis]

An update on this resistor situation, first the person who originally bought the resistors has not contacted me to complain or ask for replacements.  While there is apparent reason to say that two resistors are broken, the root cause has not been determined, the fact that they were intact when originally shipped is the only solidly known fact as yet and I believe they were also intact when the buyer received them since there was no communication about bad parts from him.  The X-rays of the two resistors were not revealing in any manner, they did not show what had happened.  While Branadic contacted me earlier to complain a lot, he has not contacted me about the offer I made here on the blog.

Branadic seems intent to only complain and throw innuendo out, making unsupported remarks, resorting to silly claims about 'safe' shipping containers (that by the way, would be cost prohibitive compared to the cost of the resistors, that should be obvious).  The boxes I use now are rated for 200lbs and are hardly considered flimsy.

The point everyone seems to be making here, is either accept my offer (actually, the original buyer should ask since he bought them) or shut up and stop making an ass of yourself.  Get over it, it is only a couple of resistors, you are not making any brownie points here.

[branadic]

and you basically said: fuck all those who dont have eagle to view it.

@ Echo88
If you quote me, please quote me correct

-branadic-

[Chipguy]

Oh dear... what  have I done   
I made people argue... over nothing          
How did I manage that     

[branadic]

Get over it, it is only a couple of resistors, you are not making any brownie points here.

I'm the opinion, that a serious manufactor would backorder failing parts, analyze them to find out what was causing the failure, to improve manufacturing processes. But the statement reflects the main attitude. People are paying for functional parts, that's the point.

-branadic-

[Edwin G. Pettis]

Since this is getting way off this thread......last time!

The resistors are in Germany, I'm in America, now how do you think I'm going to be able to analyse those resistors from thousands of miles away?  What do you mean 'backorder' failing parts?  If you want to send them back for me to examine, feel free to do so, I'll be glad to post my findings and rest assured they will be accurate as possible.  Again, I think that the person who ordered them originally really should be making any requests, not somebody who did not purchase them.  As I said before, I received no complaint from the original purchaser which tells me the resistors were okay when they were received, by inference, that says something happened to those resistors after they were delivered....not before as you seem to imply.  It looks like you just want to complain for the sake of complaining.

Evidence has been presented by other customers that there is nothing wrong with my manufacturing processes except in someone's mind.  You did not respond to my earlier offer, you still haven't responded and that tells me that you really aren't interested in it, just in whining about it.

Enough of this silliness, you obviously aren't interested in any of this so stop it.  Unless I hear directly from the original purchaser in this matter, I consider this to be closed and done with, you have no standing.

[anishkgt]

Well a diy Version such as the milli ohm meter by scullcom (https://www.barbouri.com/2016/10/09/milliohm-meter-version-1-5/) would be a cheaper choice for just resistance measurement.


Www.Georgehobby.wordpress.com

Equipments: DSO104z, Hakko FX888D, Brymen BM869s

[amspire]

Since this is getting way off this thread......last time!

The resistors are in Germany, I'm in America, now how do you think I'm going to be able to analyse those resistors from thousands of miles away? 

Edwin, I think you are totally correct. If someone has an issue with your resistors, they should be talking to you directly. On a forum, discussions about issues with a few resistors is just annoying noise because it does not help the rest of us in any useful way. If it is such a big an issue, I do not know why they have not been posted back to you so you can analyse them.

I really appreciate your posts. Not everyone agrees with everything you say, but that is exactly what this forum is for. People have different experiences, different ways of working and they come to different conclusions. What you posts do tend to include is lots of information and that is gold.

Richard

[kutte]

and you basically said: fuck all those who dont have eagle to view it.

@ Echo88
If you quote me, please quote me correct

-branadic-

the correct quotes:
https://www.eevblog.com/forum/projects/oshw-24bit-adc-measurement-system-for-voltage-references/msg973338/#msg973338
https://www.eevblog.com/forum/projects/oshw-24bit-adc-measurement-system-for-voltage-references/msg973639/#msg973639
Kutte

[retroware]

I've been trying to use a frankenstein ESI 242 (ESI 240c, ESI RS925 - the one without trimmers, a Fluke 5440 and a Keithley 155) in an attempt to accurately calibrate the relative resistance difference of each resistor in a 1K per step SR1010. My end goal is to use the SR1010 as a calibrated decade divider.

I've been having no problems getting short term (~1min) stable .1 ppm resolution readings. But, it takes about 10~15 minutes to check all 12 resistors. As a check, I go back and spot check a couple of the resistors after measuring all 12 and the reading has drifted about 1 ppm, usually in the same direction but not by the same amount.

My first guess is TC, my lab is in a house basement with typical air conditioning and the SR1010 is specified at 5ppm/C. I'd have no problem believing that I have at least a .5C swing in temperature but I need to get an accurate thermometer to be sure.

My question is short of building a carefully temperature controlled room is there any way to get tighter readings? Are there other causes for this drift I should be looking out for? I'm using twisted 20awg solid copper wire for my interconnects and I adjust for lead and yoke variations after every resistor. Or is this about the best  I should expect given my setup? I'd be particularly interested in hearing from others that own a ESI 240.

Also, given that I'm not going to upgrade my environment, is there some way to factor TC drift into my calibration short of characterizing the drift of each individual resistor? Or am I going to have to read through the 32 page forum topic on measuring TC of precision resistors? 

[ap]

I like your Frankenstein statement 
The 1010 is not really built for very precise voltage dividing. Also, the 242 temperature drift adds. So the 1ppm is not a surprise. The 1010 is intended e.g for 1:100 ohms transfers and is pretty good at that, as temporary drifts are compensated out (see theory section of 1010 in user manual). For stable voltage divisions, there are better solutions (720A...). What you can do is to apply the error propagation methods of GUM, to calculate the temperature drift related uncertainty. It would go a little far to go into details how to calculate. In a nutshell, use the divider formula, calculate the weighted drift impacts of each of the contributors and combine this. You could assume a worst case scenario, all resistors on each side of the divider drifting 0.5x 5ppm up, the others down, but thats pessimistic. RSS would be more realistic.

[amspire]

The cheapest way to get accurate readings is to buy some PT100 (100 ohms) or PT1000 (1K) Platinum temperature sensors.

For example, you can get +/- 0.1 degC accurate ones from Mouser for about $6. Sensors are available down to at least 0.03% accuracy.

Rt = R0 * (1 + A* t + B*t2 + C*(t-100)* t3)

Where:

Rt is the resistance at temperature t, R0 is the resistance at 0 °C, and
A= 3.9083 E-3
B = -5.775 E-7
C = -4.183 E -12 (below 0 °C), or
C = 0 (above 0 °C)

So at room temperatures, it is very close to 3.9083 ohms/degree for the PT1000. At 20 degC, the resistance is 1077.9 degC.

The thing is measuring produces heat so the sensor has to be in good thermal contact with the thing you are measuring. I guess you could do this in a temperature well by adding oil.

The PT1000 sounds better then the PT100 with the higher resistance, but the PT100 is less susceptible to noise. You can use 1V across the PT1000 (as long as it is in thermal contact) but the lower the voltage the better. If you have 6 digit meter, you could a 100K range to measure a PT1000 just to minimize the power dissipation.

[retroware]

The 1010 is not really built for very precise voltage dividing. Also, the 242 temperature drift adds. So the 1ppm is not a surprise. The 1010 is intended e.g for 1:100 ohms transfers and is pretty good at that, as temporary drifts are compensated out (see theory section of 1010 in user manual). For stable voltage divisions, there are better solutions (720A...). What you can do is to apply the error propagation methods of GUM, to calculate the temperature drift related uncertainty. It would go a little far to go into details how to calculate. In a nutshell, use the divider formula, calculate the weighted drift impacts of each of the contributors and combine this. You could assume a worst case scenario, all resistors on each side of the divider drifting 0.5x 5ppm up, the others down, but thats pessimistic. RSS would be more realistic.

I started down this path in hopes of calibrating my RV622 and RV722 KVDs. The ESI documentation specifically calls out the SR1010 for this purpose. But, as I'm finding out, getting an accurate read of each resistor value is proving to be a challenge.  I might try my hand at estimating the TC contributions using some of the techniques you mentioned.  Maybe things would still be good enough to calibrate a 1ppm linearity KVD such as the RV722.

After acquiring the 622 and 722 and trying to self calibrate them, I broke down and acquired a Fluke 720a which I know I can use to accurately calibrate the 622 and 722. But, I'd still like to see how far I could push this 'old school' method.

The cheapest way to get accurate readings is to buy some PT100 (100 ohms) or PT1000 (1K) Platinum temperature sensors.

Thanks for reminding me that I have such a sensor! Plus I already have a 3456 in the 'Frankenstein' stack just waiting to measure the value.  I think I'll directly mount the sensor to the SR1010 case to see how much temperature variation I'm getting over a period of time.

[Chipguy]

The PT1000 sounds better then the PT100 with the higher resistance, but the PT100 is less susceptible to noise. You can use 1V across the PT1000 (as long as it is in thermal contact) but the lower the voltage the better. If you have 6 digit meter, you could a 100K range to measure a PT1000 just to minimize the power dissipation.

I tried both and found that PT100 works better for me due to higher noise immunity.
Since a PT1000 (the ones I used) should be driven with max. 0.1mA I did not see any advantage compared to the PT100 driven at 1mA.

I have designed a programmable resistance decade that can "output" resistance values from 1 Ohm to 1.6 M Ohm with a resolution of at least 6 digits.
It was calibrated against a Datron 1271 end of 2017 and is currently doing burn in tests since it has been calibrated.
For what I can tell it's current deviation of it's originally calibrated values less than 0.001% (10 PPM).
However I can only do these checks with a DAkks calibrated 34401A. A more reliable result will be revealed once it is going back to the Lab for a meetup with the Datron 1271.

That decade can simulate all sorts of sensors, like PT100, Ni120, YSI400/700.
It can also simualte water/ salt solutions with temperature compensation (using a second programmable decade as slave to make the temperarure sensor simulation)
Currently working on customisation so you can define "My resistive something" using Excel/Calc, outputting the table to CSV, whack the USB stick into the decade box and import it.

So now you know why I am thinking about a high precision resistance meter.
I need something better than the 34401A but do not want to spend around 10K for that.

[retroware]

I'm going to second Edwin Pettis's comment regarding the 242 as being a pretty darn good device for accurate resistance measurements. While I don't have a SR104 to compare against, I did measure the resistance of my SR1010 in series mode against the RS925. The reading was 11ppm off from the expected nominal of 10K. This is for equipment that is probably 30+ years old.  Now of course, the resistors in both the RS925 and the SR1010 could have both drifted in the same direction and rate over that period of time but I'd be willing to bet that all of resistors in the system are still well within the stated 50ppm lifetime drift spec.

This thread also suggests that the RS925 ages well:

https://www.eevblog.com/forum/testgear/esi-rs925a-decade-resistance-standard-mini-teardown

In terms of cost, the two critical components are the RS925 and the 240C. If one is patient, one can probably get the pair for around $500.

[ManateeMafia]

If you are real patient, and quick, you can get a complete 242E for $300. At least that's what I heard.  At that price any one part needs to be functional to cover the cost.

[dacman]

The laboratory I work at was once NVLAP certified using the ESI 242D as an NVLAP standard (although we were also certified using a Guildline bridge and an MI bridge).  Also, several decades in the RS925D have adjustment trimmers for each step.  IET Labs sells an RS925 equivalent.  One use for the RS925D by itself is as an RTD 4-wire simulator.