Hello Attila, I have understood all of your description, which ruled out a lot of possible sources of error, but what really disturbs me is this passage:
*The 10kΩ resistor takes ages to settle. I've been using APER 1, DELAY 1, ZERO ON, OCOMP ON and varied DELAY from 1 to 10. \ Between DELAY 1 and DELAY 10 is almost 10ppm of difference. To get below 0.1ppm I would need a DELAY value in the order of 20 to 30. \ While that works for me, it's bascially a no-go if I want to get the resistor calibrated. \ The two other resistors do not show such a settling.* For 10k, and shielded PTFE cables, APER 1 and DELAY 1..2 is all what you need to get stable and precise readings. If you still see deviations (in which direction?) when using even longer delays, then either your 3458A has a problem, or your resistor, i.e. the lacquer of the wire wound resistor, which I think is the construction of such Reichsanstalt type resistors, shows an odd polarization effect, or a heating effect, or.. \ Have you got a picture of your resistor, or of its interior? To rule out a problem with your 3458A, have you ever measured another stable 10k resistor this way?\ You only speak of “*The two other resistors”,* but I assume you mean the 100 and 1k ones? What happens, if you just switch OCOMP off, to get rid of any switching / polarization effects, and simply measure the 4W resistance with NPLC 10, Delay 30 msec? \ Do you see a constant increase or decrease of the resistance, until it settles? I don’t want to be obtrusive, but the fastest way to identify the problem, would be to send me your resistor for a try out, because my setup, instrument and environment guarantees that I would only see weird effects from the DUT. Frank _______________________________________________ volt-nuts mailing list -- [email protected] -- To unsubscribe send an email to [email protected] To unsubscribe, go to and follow the instructions there.
