[volt-nuts] RE "new" 3458A

[Randy Evans]

The unit seems to be working so far except for one issue.  After doing an
ACAL, and making sure the Auto Zero is ON,  I short the input leads with a
copper wire shunt across the inputs and the reading is approximately
 -000.0023 mVDC.  That seems rather high.  I would expect the unit to short
the input leads internally and force a zero reading during the ACAL.
Anyone have any comments on this reading?

Thanks,

Randy


On Sat, Aug 16, 2014 at 3:37 PM, Richard Moore <richiem5683 at gmail.com>
wrote:

> Hi Randy -- sounds like your unit is in cal, based on your measurements of
> DCV and precision 10k resistor.
>
> Using autocal all is recommended before doing precision measurements, and
> I do that if it's been more than a day or two since last use. The autocal
> uses the internal Vref and an internal 10K resistor to do cal on everything
> else, so that tells you what the basic cal procedure is. I just got my 3458
> back from Loveland, and that's what they did for me -- warmed it up, then
> ran autocal, then measured everything against a Fluke 5700, aided by an HP
> 3325, and another 3458.
>
> It has been 5 years since I replaced the display board (no "exchange" deal
> was available then AFAIK, so I don't know what's changed) and also the
> NVRAM board, which was dead, with one with the Snap-cap RAM chips. I did
> those replacements, then sent it home for cal, which was complete, since
> all the RAM was new. Now after 5 years, the unit passed all incoming
> performance tests and was sent back to me without a cal process of any
> kind. This tells me that an old, well-aged Vref module is a good thing. The
> 10VDC test had changed by a bit under 5ppm, or roughly 1ppm/year.
>
> They have a cal deal -- use code 1.090 -- press them for it -- and that
> saved me 30% off the normal price. I think this deal lasts until
> mid-September, so my recent "cal" ended up at just under $400 including
> shipping. I'm not sure the deal is available on new or first-time cals; my
> unit was in their data bank.
>
> But this is a long way of saying I don't think you need to send it for cal
> -- just push Auto Cal and Enter and wait about 10 minutes and you should be
> good to go.
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