[volt-nuts] 732A drift

[acbern at gmx.de]

Randy,

that is strange. two things come in mind that might be worth checking. first, is the mains frequency setting of the 3458a set to 60Hz (I assume you are in the US)? this is important to suppress mains ac disturbing the measurement.
secondly, have you connected guard? tsp cables would be best to use.

a general statment re. the 1V and 1.18V. they are much less stable than the 10V. My 732A e.g. has a drift of 0.2ppm/a. So I use a kelvin-varley divider if I need 1V. this is self calibrating, so you have maybe 0.1ppm worse accuracy. you could also use the 3458a linearity to re-characterize the 1v with reference to the 10V. That also gives you good accuracy. Also, I only have the 10V cal'ed on a regular basis to below 0.5ppm accuracy, that costs much less than haveing all three voltages cal'ed, which would not add any benefit anyway.

Adrian

> Gesendet: Samstag, 23. August 2014 um 05:16 Uhr
> Von: "Randy Evans" <randyevans2688 at gmail.com>
> An: "volt-nuts at febo.com" <volt-nuts at febo.com>
> Betreff: [volt-nuts] 732A drift
>
> I hope someone can help with a strange anomaly on either my 3458A or the
> 732A.  The 732A 10V output as measured on my 3458A seems relatively stable
> over time (it bounces around about +/-1 uV but is it the 732 or the 3458?).
>  However, the 1.000 VDC output drifts downward at a rate around 1-2 uV per
> second as soon as I plug the 3458A into the 732 output. If I remove the
> 3458A and connect it back up after a few 10s of seconds, the reading goes
> back to what it started at and then drifts downward again.  The 1.018V
> output also drifts downward but at a much slower rate and not as much.  Now
> the question is: is it the 732 or the 3458A?  I tried to see it on my
> Agilent 34401A DMM but it really doesn't have the resolution, but I do seem
> to see it on the 1.000VDC output.  If it is the 732A, what would cause it
> to drift downward like that?  Since the 3458A has an input impedance of
> >10Gohm on the 1 and 10 V ranges, I wouldn't think the 732 would even see
> the difference of whether the 3458A is connected of not, but it clearly
> makes a difference as to how long its connected and how long it's been
> disconnected.
> 
> Any one have any conjectures?
> 
> Also, what will turn on the "In Cal" light?  What does it mean if it
> doesn't come on?
> 
> Thanks,
> 
> Randy
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