I have been testing two 3458As against a known good Fluke 732A. Each 3458A was calibrated for DCV before the start of the measurements so they both started at the same point. I have been running a series of tests consisting of measuring the Cal Constant as detailed in Service Note 18 for each meter several times a day (to calculate the drift per the procedure in SN 18). I also measure the 732A voltage in each meter each time using NLPC 100 and NRDGS 100 and then recording the STDEV, MEAN, MAX, and MIN values. What I have observed is that the Cal Constant is acceptably low but the MEAN value per measurement is drifting up in one meter and drifting down in the other. The unit drifting down has a new A3 board installed and the unit drifting upward is an Agilent 3458A only a few years old so would not be expected to have a drifting A3 board. It was only calibrated 1 time per the internal REV number, so would have likely been re-calibrated if the A3 board was replaced.
My question is what is the likely cause of the drift in the MEAN voltage reading if the Cal Constant value is relatively constant? SN 18 says the drift rate of the Cal Constant is an indication of drift in the A3 AD board, but I believe it assumes the A9 voltage ref board has a constant value over time. If this is not true (e;g., the voltage ref is drifting), I think this would explain the drift in the voltage reading even though the Cal Constant is relatively constant. Any opinions on this? 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.