[volt-nuts] 732A drift

J. L. Trantham jltran at att.net
Sat Aug 23 06:42:20 EDT 2014


The 'IN CAL' LED is turned on as Todd describes.  It goes off if power to
the unit is lost and, thus, calibration is lost.  It is not related to the
battery charge LED.

As I understand it, the units are designed to powered on 24/7/365 and are
'IN CAL' once they are powered up, stable (weeks, months?), and have been
calibrated by your reference lab.  Once power is lost, meaning lost AC and
batteries depleted, the 'IN CAL' light goes out and outputs are thereafter

Once you decide to get the 732A calibrated, you will need to find a way to
ship it to the reference lab and get it shipped back while continuously
powered, connecting an external battery pack to the connector on the back of
the battery pack.  The internal battery pack is likely to last only a few

There are at least two types of connectors for an external battery, two 5
way binding posts and a Hypertronics connector which is a small black
connector about 'dime' sized.  I can find the part number for the mating
connector if you need it.

I think the +/- 1 uV drift with the 10 V output and the 3458A are within
specs for both the 732A and 3458A.

Not sure what to think about the drift on the other readings unless there is
some sort of 'dirt' on the 1 V and 1.018 V binding posts and/or ground.

Good luck.


-----Original Message-----
From: volt-nuts-bounces at febo.com [mailto:volt-nuts-bounces at febo.com] On
Behalf Of Todd Micallef
Sent: Saturday, August 23, 2014 4:13 AM
To: Discussion of precise voltage measurement
Subject: Re: [volt-nuts] 732A drift


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.


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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