Electronics > Metrology

732A hysteresis

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retroware:
I few months back I purchased a Fluke 732A with unknown cal history for some at home volt-nuttery. I've had it powered on for several months and it appears to be stable. I've monitored its voltage with two different 3458s. One that was brand new 3 years ago and one that was within 1ppm of the new unit three years ago (both are option 002). Neither have been calibrated since. The 732A measures .8 ppm different between the two units today. I'm half tempted to be happy with that, but I'd really like to have the 732A properly calibrated.

I've spent some time looking for a lab within 8 hours of the Washington DC area that would calibrate this for a reasonable price and so far the closest is in New York which would require shipping and probably result in the batteries going dead in transit.

Has anyone done any tests to see what sort of hysteresis the 732A exhibits if the battery fails? At this time of year the temperature changes from shipping wouldn't be too dramatic - maybe in the 10 degrees C range.

Or does anyone know of a lab (not including NIST) that is capable of calibrating a 732A within driving distance of DC?

Bill158:
I have collected 6 ea. 732A references over the last 18 years.  I started with one unit and added each until 2009.  During the period I have had those I had had at least 4 power outages where all lost battery power and went completely cold.  The most recent was in October 2019 when we in Northern California had a infamous Pacific Gas & Electric company "public safety power shutoff" because of high winds and PG&E power lines causing wildfires.  I am sure you have heard of this.
I had collected a great deal of data over the years on this units using the NBS TN 430 method of "round robin" inter-comparisons.  After each cold start I have waited several days and then made the usual comparison measurements and found that all but one 732A had recovered to with in 0.2 ppm, usually less, of it's original inter-comparison value (in uVolts).  I did receive one unit that had some previous data with it from a last calibration in 2002 (hand written) 10.0000281 and then in 2005 from "DELPHI" 10.000062.  That was the last 732A I got in 2009.  As best as I could determine it was 2.8 ppm high with what data I had at the time as to the exact value of the "volt" which I had gotten from where I was working 5 years before.  But that "volt" was 2.3 ppm high when I sent a 732B I had recently obtained in 2015 and then into FLUKE for a 540Z calibration.  So my basic guess is that this 732A was at least 6 ppm or so high.  So the DELPHI lab may have gotten it correct at that time.  This one could have been cold for a long time before I got it.
So my experience seems to indicate that these 732As recover VERY nicely after power down cold starts.  I have several friends in the area, one of who has experienced the same thing in cold start recovery. 
Using a 3458A has never proven to be as accurate as you would want and expect.  But if that is as close as you can get for the time being, then so be it.
Bill

retroware:
Thanks Bill158 for the very helpful information. Given that my unit is currently uncalibrated I might run it through one or two restart from cold conditions and monitor the unit as it stabilizes.

wn1fju:
Dave:  You might consider sending the lab's 3458A back to Keysight if they offer a metrology-grade precision calibration.  I'm not convinced the original precision calibration was ever done at the time of purchase even though we paid for it. 

leighcorrigall:
Hello, retroware!

I recently purchased a Fluke 732A from a fellow EEVBlog member a month ago. I am the third owner and the unit has only been powered off twice that I am aware of. Labels on the unit indicate that it might have been manufactured in the early '90s. I have not bothered to open the lid because I do not have to for the time being.

The last time it was calibrated was in 2015:
2015-11-03, 10.00010198 V, 1.0180223 V, 1.0000035 V @ 21 °C
2015-12-01, 10.00010440 V, 1.0179920 V, 1.0000608 V @ 21 °C (I do not know why it was measured twice)

With a freshly calibrated DMM (September), I measured the following as of today:
2021-10-05, 10.0001116 V, 1.0180225 V, 1.0000059 V @ 25 °C (nulled before measurement on the 10 V range)

For the most important range, this equates to 0.14 ppm/a over the past 6 years without considering temperature coefficients. I got lucky with this unit because it has been well taken care of. The other ranges are not as stable, but they turned out well anyway. 2.55 ppm/a for the 1.018 V range and -4.43 ppm/a for the 1 V range. Looking at the specifications from the manual tells me that these values are well within the anticipated drift. These Flukes age like good wine but they need to be well maintained.

I would suggest finding a reliable DMM and having it calibrated, then use it to measure the Fluke. This is a cheaper alternative and gives you more flexibility. Replace the Fluke batteries. Do not tamper with the ovenized reference chamber unless you know what you are doing.

Good luck!  :D


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