Best way to determine other 10K standard resistors base on one newly calibrated - Page 1
Forum section: electronics / general

author: aronake
author_rank: Frequent Contributor
timestamp: June 12, 2024, 05:28:11 pm
content: HiI plan to have one of my 1 ohm and 10K ohm standard resistors calibrated at government standards and calibration laboratory. They will do 10k at 3 milliohm and 1 ohm at 0.3 microohm uncertanity at 95% level. So pretty decent. The lab is 10 minute walk away from where I live.I would want to compare these to be calibrated standards as accurately as I can to other 1 ohm and 10k ohm standard resistors I have before I hand them in for calibration and after. How do I best do this?Tools at hand that may be relevant are a couple of 3458a with 2 having certified calibration but these expired 3 years ago, a Keithely 7510 (in calibration, but i doubt the quality of the calibration), a Fluke 732b, a couple of DIY 10V LTZ1000, a LTZ1000 modified Yokogawa 7651 current/voltage source (which is very stable), a Keithley 2450 SMU.My plan:- Measure all resistors with all 3458a and the 7510 in best possible settings. As the 3458a are pretty far from the uncertanity of the calibration lab, resistances measured will mostly be seen as ratios against the to be calibrated resistors.- Use the 732b as voltage source over the to be calibrated 10K vs all other 10K (one by one) and measure voltage over both and each resistor. I would think the 732b have current capability for this, but will check before I try.- Use the Yokogawa at some suitable voltage and do same measurement as for with 732b for the 1 ohm resistors. It may be that the higher current capability of the Keithley 2450 may be better, but I think the Yokogawa is sufficient. It is quite a bit more stableThen analyse all results that hopefully match quite well to determine absolute value of other resistors.Reason to do measurements both before and after is to see that nothing have happened with the standard resistors while they were away. Also to test the measurement methodology so I can quickly do everything once I get the measured resistors back.Do this sound good based on the tools I have or any suggestions how to do this better?Bonus question: To what uncertanity could I expect to measure other resistors based on the newly calibrated with the proposed or some other better way of doing it (existing tools being the constrain)? I would do the comparison measurements same or the day after the resistors have been measured by the calibration lab. So not much of time drift. I will obviously be very cautions when bringing them home and keep them at 23 degrees in a sealed box, and bring them into my home lab which will then be at 23 degrees. So most of uncertanity ought to come from measurement methodology and limitations.

author: Sensorcat
author_rank: Regular Contributor
timestamp: June 12, 2024, 07:30:25 pm
content: A thought on your bonus question: Do you already know the temperature at which the lab will do the calibration? In many calibration reports I have seen, the temperature is not necessarily 23°C, but only reasonably close, and the lab indicates the temperature at which the calibration was done, instead of maintaining exactly 23°C. This affects your plan to do the before-after comparison. Furthermore, doing the comparison one day after the calibration is not as good as doing it right after it, as drift starts fast and then fades out with time, such that the first day is already a large fraction of the drift you get over a 90-day period. You can see this in specs of some precision instruments with errors for 1h/1d/90d/1y etc.

author: bdunham7
author_rank: Super Contributor
timestamp: June 13, 2024, 02:52:22 am
content: Quote from: Sensorcat on June 12, 2024, 07:30:25 pmBut calibrating a precision resistor consists of just measuring it and recording the value. How would that affect drift?

author: aronake
author_rank: Frequent Contributor
timestamp: June 13, 2024, 03:27:37 am
content: Quote from: Sensorcat on June 12, 2024, 07:30:25 pmThanks for input.The 10K resistor have a TC of around 0.04 ppm / C and the 1ohm around 0.1 ppm / C. So i would not be too concerned about +/- 1 degree, but of course the lower the better.On drift, i would think in reality it is quite linear (or driven by evens like thermal shock, being dropped, overvoltage etc) and that it is growing much quicker in the beginning is mostly related to the statistic model used for drift. Also measure uncertanity will probably also be much bigger than 1 day drift. But still a good point in trying to do the comparison as soon as possible.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 13, 2024, 01:33:11 pm
content: I would suggest using a stable current source and measuring the voltage ratio of two resistors connected in series for two polarities of the current, using the ratio mode on the HP3458A.CheersAlex

author: aronake
author_rank: Frequent Contributor
timestamp: June 13, 2024, 02:17:44 pm
content: Quote from: Alex Nikitin on June 13, 2024, 01:33:11 pmGood suggestion! I did not think about the ratio mode, but was thinking to use rear connectors for one of the resistors. Ratio seems much better!

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 13, 2024, 03:42:45 pm
content: The 3458A is not the best instrument for resistance transfer measurements, due to its mediocre (unstable) current source, its cumbersome 4W measurement method and because the probing voltage level is too low in some ranges.The Datron 1281, and its successors, the FLUKE 8508 / 8558 / 8588 are much better, concerning stability and transfer uncertainty for higher resistance values..The 3458A is as well not specified at all for resistance transfers.Fluke characterized that for the HP3458A HFL version, i.e. (0.5 + 0.1) ppm for 10kOhm range, (0.1 + 0.1) ppm for the 100kOhm range.Anyhow, I regularly achieve about 0.2ppm Standard Deviation for my 10kOhm measurements, which is the real transfer uncertainty for my group of six 10KOhm resistors.. I can clearly demonstrate, that the transfer repeatability is on that order of magnitude, which is again an order of magnitude worse than the DCV transfer uncertainty. Therefore, another DCV method would be superior. It is required to do the whole transfer within 20..30minutes, and checking the room temperature and TEMP? for a < 0.2°C change.If you want to use the 3458A for 10K transfers, you need to follow my recommendations:- 4W measurements with shielded PTFE cable, use Guard on both sides- use OFFSET COMP- resistors must either be characterized for low T.C., or need to have an internal thermometer, to mathematically compensate for its T.C.otherwise, your transfer from the National lab to your home lab is quite worthless.- fixed 10kOhm range- APER 1 (not NPLC 50 or 100!)- DELAY 1- use statistics on 16 samples (1 min)- use MEAN as a valid 8-digit result and StD value for check of stability (StD <= 0.2ppm or 2mOhm required)For more precise transfers, use bridge configuration, or external current source.Frank

author: Overspeed
author_rank: Frequent Contributor
timestamp: June 13, 2024, 05:38:52 pm
content: Helloperhaps use a precision current generator home made as a current bridge with selected transistor and use your HP to measure the voltage ?I agree than the HP 3458 is not the best tool for resistance measurementRegardsOS

author: aronake
author_rank: Frequent Contributor
timestamp: June 13, 2024, 06:07:30 pm
content: I just did some test measurements with the 3458a ratio function. That seems to work very well. It is repeatable down to around 0.1 PPM when switching the order of which the ratio is measured.To my surprise, using my LTZ1000 tweaked Yokogawa 7651 gave more stable ratio measurements on the 3458a for the 2 X 10K measurements than using my 732b as current source. 10V / 20k = 0.5 mA which the 732b should be able to drive with very limited degradation. Its specified to have maximum 0.1 PPM voltage change when delivering 2 mA. I have seen when doing other test that the Yokogawa is very stable. This further confirm that. An obvious benefit that it is also possible to set voltage, so I can use that for the 1 ohm resistor too.

author: Alex Nikitin
author_rank: Super Contributor
timestamp: June 13, 2024, 06:28:03 pm
content: The ratio mode is probably the most powerful tool the HP3458A has. It works well even with the rates of 1:100 as the range switching allows for a good resolution on both inputs. For comparative measurements on resistors it only needs a short term stable current source with a polarity switch to counteract the thermoelectric errors and will give a very accurate and repeatable result.CheersAlex

author: Dr. Frank
author_rank: Super Contributor
timestamp: June 13, 2024, 07:05:53 pm
content: I suggest to first define the required level of transfer uncertainty, and afterwards chose the appropriate method.I guess, that the absolute measurement of 10kΩ with an hp3458A is fully sufficient @ 0.2ppm.Everything else is over Engineering. The stability of these reference resistors as well the uncertainty of the National lab are probably less stable.For 1Ω, a bridge method is more appropriate.It would be very interesting, if the other methods mentioned here, would have been supported with such transfer uncertainty figures from experience/measurements, like mine.

author: Sensorcat
author_rank: Regular Contributor
timestamp: June 14, 2024, 11:49:44 pm
content: Quote from: bdunham7 on June 13, 2024, 02:52:22 amBecause drift is a 'random walk'https://en.wikipedia.org/wiki/Random_walkkind of process. That means, after N steps, the expected value for the distance from start is proportional to sqrt(N). Result: The error rises fast immediately after calibration, then the increase in error slows down. The actual resistor value, of course, is not affected. The time when it was measured by the reference instrument (=calibration) counts, because that is the time for which knowing the (almost) exact value is assumed. Whether a calibration includes an adjustment or not does not matter in this regard. Example (Keithley 2001, 20V range, 1PLC, DFILT off, ppm accuracy):±(ppm of reading + ppm of range)24h: 3.2 + 0.3590d: 8 + 0.41y: 12 + 0.42y: 16 + 0.4

author: aronake
author_rank: Frequent Contributor
timestamp: June 18, 2024, 04:31:09 am
content: Quote from: Sensorcat on June 14, 2024, 11:49:44 pmMy thinking is that drift is quite abit away from a random walk, there is quite a component of drift. But as many other things that really are not random walks is often modelled as a random walk for convencience as statistics etc are then easier to apply.

author: aronake
author_rank: Frequent Contributor
timestamp: June 18, 2024, 04:34:27 am
content: Thanks for all good inputs here.Except for the obvious thing of just measuring resistance with a couple of 3458a, the ratio suggestion has been very helpful! Its the purest form of direct use of the strongest point of the 3458a, its linearity.

author: ivo
author_rank: Regular Contributor
timestamp: June 20, 2024, 09:02:19 am
content: Use the 732 / ltz1000 as a "current source" (or both, alternated), connect the STD and DUT resistors in series (do one set of measurements with STD on top, another with it below), and do a ratio measurement of the top 10V and mid point voltages with the 3458. If you have 3 other resistors to measure against the "new STD" that would be 2 x 2 x 3 measurements. Obviously only works for small currents (10ks). Your current source will work for low Rs