Electronics > Metrology

Metrology Meeting in Stuttgart/Germany

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alm:
I had time to run one more test to continue the 3458A guard switch saga, which was to check if the same problem also occurs if I use a different voltage reference than the Fluke 7001. So now I used the same 3458A #1 DMM and cable, but I used a Fluke 732A running off mains power (it does not have batteries yet) instead of the Fluke 7001 running of battery I used for the previous experiments. I tried both with connecting the guard lead to the F732A guard terminal, which is isolated from the 10 V HI/LO terminals. Unsurprisingly the guard switch did not make a difference there, and the difference are way down in the noise (0.05 ppm). Note that the vertical scale spans 0.2 ppm here:


Then I connected the guard to the same terminal as the low input lead to the DMM (so 10 V LO when measuring positive polarity and 10 V HI when measuring negative polarity). Here I observed a very similar effect to what I saw on the F7001, -6 to -8 ppm for this meter. So clearly the effect isn't just that the setting upsets the F7001 output stage:


Error bars again indicate standard deviation, n >= 20.

alm:
branadic and I on short notice came up with the idea of a mini (or micro) metrology meet at branadic's place in Stuttgart. The goal was to compare and transfer our best representation of 10 V and 10 kOhm between our labs over the span of a bit over 24h with a few hours of sleep. branadic was also so kind to add a thermistor to my 10 kOhm reference that was sorely missing an internal thermistor (see picture). All raw data is available on xDevs.com and the preliminary analysis (without nice plots / summary tables and without proper uncertainty calculations) are here on Github in a Jupyter Notebook.

A full article on xDevs.com should follow soon.

branadic:
Fun it was, attached an image of the DUTs that we focused on.

-branadic-

branadic:
Since I'm currently in the process of comparing the volt with Frank facing some trouble with measurements performed on our 3458A, I remembered again similar trouble we had at MM2023, that were fixed once we applied the guarding scheme as described in HP AN-123.
So I thought it is worth mentioning here and drawing it in color, as it might be helpful to others, too.  :-//

-branadic-

Dr. Frank:
 Dr. branadic, did you already find the culprit?

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