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.