Illya, That is a great idea. I will give it a try.
Thanks On Sat, Nov 18, 2017 at 4:47 AM, Illya Tsemenko <il...@xdevs.com> wrote: > Since you have 732A, testing should be easy enough. Calibrate faulty meter > for zero and DCV 10V to 732A, record CAL? 2,1 value. This is your LTZ > output. Then leave it running for few days to drift away and calibrate > again to same 732A. Check CAL? 2,1 again. Calculate the difference and if > it matches output drift (that 1.1ppm/day you mention) - you can be 80% sure > that A9 is a problem. Other 19% go to A1 and A3 circuits, as 7V is not used > directly in the meter, and there are still gain parts to get +12 and > -12VREF on A3 and 10Vish bipolar levels on A1. If your CAL? 2,1 stays same > (within 0.3ppm) then A9 is fine. > > > On November 18, 2017 12:59:53 PM GMT+08:00, Randy Evans < > randyevans2...@gmail.com> wrote: >> >> I just received an Agilent 3458A that has a problem with noise and a >> drifting voltage measurements. I am using two Fluke 732As to compare >> absolute voltage measurements over time against the Agilent and an HP >> 3458A. The HP unit has a new A3 ADC card and seems to be very stable and >> low noise, so is being used for comparison. I have been doing simultaneous >> absolute voltage measurements and DC Cal Constant measurements several >> times a day and then calculating the drift rates of the two units using the >> HP Service Note 18 procedure. >> >> >> >> The results indicate the Cal Constant drift rate of both units is very >> similar and within spec per Service Note 18. However, the absolute value >> measurements show the Agilent unit changing 1.1 ppm over a day whereas the >> HP unit is within a tenth of a ppm over a day. In my way of thinking the >> Cal Constant procedure assumes the voltage reference board in the 3458A is >> stable, hence the absolute value reading should remain essentially constant >> after each ACAL DCV, which is the case with the HP unit. Since the Agilent >> unit shows a steady drift in the absolute reading, this would indicate to >> me that the voltage reference board is likely the cause of the problem, and >> is also likely the cause of the noisy readings. If so, this is a >> “relatively” easy fix (I have several 3458A voltage reference boards, one >> of which has been continuously powered up for several years). >> >> >> >> The issue is that I have to make a decision to keep or return the Agilent. >> It has a cal seal on it and if I open the unit up to change the voltage >> reference board, I own it and can’t return it. I would appreciate an >> opinion from the members of the group as to what they think the odds are >> that the voltage reference board is the source of the problems with the >> Agilent 3458A. >> >> >> >> Thanks, >> >> >> >> Randy Evans >> >> _______________________________________________ volt-nuts mailing list -- volt-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
