[volt-nuts] 732A drift

[Todd Micallef]

The output impedance of both the 1v outputs is ~1k ohm. I wonder if Randy could check the 3458a input impedance with a 10M ohm resistor and the 10v output of the 732a. 

I was thinking that the 732a needed a minimum battery voltage to allow the in cal led to turn on with the short to the Lo terminal. I guess I could try it on one of mine that is waiting for repair.


Todd

Sent from my iPad

> On Aug 23, 2014, at 6:42, "J. L. Trantham" <jltran at att.net> wrote:
> 
> Randy,
> 
> 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
> unreliable.
> 
> 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
> hours.
> 
> 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.
> 
> Joe
> 
> 
> 
> -----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
> 
> 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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