[volt-nuts] 732A drift

Todd Micallef tmicallef at gmail.com
Sat Aug 23 05:13:00 EDT 2014


Randy,

I looked at the 3458a input impedance, and it is difficult to get the meter set to the FixedZ (10M) mode. However, the 100v range is 10M. It should default to HiZ on reset.

I forgot to mention to check the outputs and guard resistance to ground. One of my 732a had some foam baffling under the cover that had dry rotted. There was a lot of leakage to ground. 
I can't remember if the foam was on the older or newer versions of the 732a.

The cal light comes on with a short wire stuck in the hole and connected to a LO output terminal. I don't know, but maybe the battery charge led has to be off.

Todd

Sent from my iPad

> On Aug 23, 2014, at 1:16, Randy Evans <randyevans2688 at gmail.com> wrote:
> 
> 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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