If you are confident that the 732A is stable to 0.1ppm then just run an acal afer a wek, and determnine what has driifted. Your A/D board, as can be seen with a drifty cal constant, or, els the A9 ref. Dont do a checl everyday. this hides information.
> Gesendet: Freitag, 01. Dezember 2017 um 19:49 Uhr > Von: "Randy Evans" <[email protected]> > An: "Discussion of precise voltage measurement" <[email protected]> > Betreff: Re: [volt-nuts] Drifting 3458As > > I am running the ACAL to check cal constant drift over several times a day > and over a 7 day period (per SN18). The varying times of the day are to > see how temperature sensitivity affects the cal constant drift since the > room temperature is not constant through the day but is relatively constant > at the same time of day each day; i.e., the furnace is off during the night > so mornings are about 5 degrees C cooler than the afternoon. Even after > ACAL, I am seeing up to an absolute difference of 3.5 uV on the 732A > voltage reading between the HP and Agilent 3458As, depending on the time of > day. I suspect the A9 board in the Agilent is the reason since the HP > 3458A reads much closer to the 732A value than the Agilent 3458A over > temperature. Based on long term comparisons with other 732As and a 732B, I > am confident the 732A is stable within 0.1uV. > > I am using an ebay A9 board in the Agilent 3458A for the current testing > since I suspect the original A9 board in the Agilent 3458A. I am > separately testing the original A9 board since I am not completely > confident in the ebay A9 board. I do not have enough data to draw a > conclusion yet about the original A9 board. My current concern is to see > if there is agreement that the A9 board is likely the culprit. > > Thanks, > > Randy Evans > > On Fri, Dec 1, 2017 at 1:58 AM, <[email protected]> wrote: > > > What you describe (A9 drift) would be the explanation. However question is > > how much you see. The A9 should not drift much in the intervals you talk > > about (days). > > Also, you should run the ACAL to determine the cal constant not several > > times a day but with several days inbetween, and then divide by number of > > days to determin drift > > Frequent ACAL may not give you good results (random fluctuations such as > > noise, temp... and their impact during cal gets higher the shorter the time > > between ACALs) > > > > > > > > > Gesendet: Donnerstag, 30. November 2017 um 07:40 Uhr > > > Von: "Randy Evans" <[email protected]> > > > An: "Discussion of precise voltage measurement" <[email protected]> > > > Betreff: [volt-nuts] Drifting 3458As > > > > > > 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 -- [email protected] > > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > > mailman/listinfo/volt-nuts > > > and follow the instructions there. > > > > > _______________________________________________ > > volt-nuts mailing list -- [email protected] > > To unsubscribe, go to https://www.febo.com/cgi-bin/ > > mailman/listinfo/volt-nuts > > and follow the instructions there. > > > _______________________________________________ > volt-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts > and follow the instructions there. > _______________________________________________ volt-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/volt-nuts and follow the instructions there.
