Moin, Moin Attila, first off, as you obviously descend from Northern Germany, and are currently located @ MPI Saarbrücken, I propose that you afterwards send me your 10kOhm standard for characterization, in my cool lab near Frankfurt. Out there it was up to 38°C, downstairs, only stable 22.4°C.
I think I’m able to determine its resistance @ 22°C with ppm uncertainty, and 0.2ppm StD @ 16 samples of APER 1.\ 1:1 transfer uncertainty is about 0.1 .. 0.2ppm. FLUKE has validated these characteristics in their 3458AHFL datasheet. I’m performing such stable and precise 4W, OCOMP measurements regularly with my 3458A, on 6 precision 10KOhm resistors, as well on a 1kOhm. I have read the whole thread.. sorry that I respond very late as I was locked out due to a wrong address. There are several pitfalls in your setup and with the basic principles of Offset Compensation methods in general for 10k and 100k Ohm range resistance measurements.\ There are a few guys who already have explained some of these effects on the eevblog forum, I cite two threads here: https://www.eevblog.com/forum/metrology/optimal-configuration-of-hp-3458a-to-measure-10k/msg1476308/#msg1476308 https://www.eevblog.com/forum/metrology/hp3458a-ocomp-delay-related-problems/msg1465111/#msg1465111 Here are several topics I’d like to explain briefly. 1. emf voltages and cables\ The Offset Compensation method (of 3458A or other long range DMMs) is intended to remove all emfs. \ Therefore, it’s not necessary at all to use low emf cables, jacks, aor resistors. Manganine has higher emfs compared to others, so no problem.\ The discussion here is misleading concerning the root cause of your noise and instability problems 2. PVC cables have too low an isolation resistance. For 10kOhm, these introduce errors on the order of ppms when you drill plus and minus, but 10ppms when measuring 100kOhm. 3. The 3458A, as well as other DMMs are quite susceptible to external noise in your lab. \ Therefore, you MUST use drilled 4W cables, which implies using PTFE.\ These MUST have a shield around, which is connected to GUARD of the DMM (not grounded), and best be connected to the case of your standard resistor. 4. You have to delete all noise sources in your lab, i.e. all switch mode power supplies in lamps, PSUs, chargers, etc.\ Also get rid of any wireless emitters.\ I assume, that is the main source of your instabilities 5. You need to do your measurements with the 3458A at a very constant room temperature. My basement lab is constant to +/- 0.2°C over a week or so. Therefore I can perform DCV measurements stable to 0.1ppm over 24h before I have to redo an ACAL. I did not yet try such Ohm stability measurements, but this mode is definitely much less stable. 6. The OCOMP switches the measuring current on and off, as explained in those two threads. This leads to polarization currents, or dielectric absorption, every time when when the current is switched. That leads to a lowering of the measurement by at least 1ppm for 10k and 5ppm for 100k, depending on the cables / isolation used. Therefore, a delay of 1 sec for 10k and 5sec for 100k is necessary. This has to be tested. Increase the delay from zero, until the measured value does not increase any more.\ 1k and lower, as well as 1M and higher should be made with small delay of 30msec, as no such effect arises. These are universal parameters, also valid for all other DMMs with a similar OCOMP function.\ The optimal setting of the 3458A can be found in the links. It’s basically APER 1, DELAY 1 in your case.\ usage of NPLC 50, instead is counter productive, as this only increases the measurement time unnecessarily. 7. use statistics, limited to 16 samples for one data point, see links.\ The mean value will meet the transfer uncertainty of 0.1ppm and stability \~ Standard Deviation of 0.2ppm.\ If you use much more samples, medium term instabilities kick in, which have nothing to do with your test problem.\ These are temperature and timely drifts of your DMM and of your DUT. Think of the Allan Deviation statistics, what it is about. 8. Characterize your 3458A for Time and T.C. stability of its resistance mode.\ The 40k resistor of my 3458A has < 0.3ppm/K T.C., and is stable to a few ppm over several years. I already have a VHP101 inside, maybe your old instrument is not as stable.\ Anyhow, the 3458A is no reference standard, therefore, you should make long term stability measurements in relation to another external reference (Volt, Ohm) Frank _______________________________________________ volt-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
