[time-nuts] Calibration procedures - what is normal?

Dr. David Kirkby (Kirkby Microwave Ltd) drkirkby at kirkbymicrowave.co.uk
Fri Feb 12 18:24:48 EST 2016


On 12 Feb 2016 21:12, "Joseph Gray" <jgray at zianet.com> wrote:
>
> I sent my HP 3457A in for cal. I should be getting it back next week.
> I won't mention where I sent it, but it wasn't Keysight (I don't like
> that name). I recently changed the SRAM battery and purposely did not
> save the cal constants.

You may have seen my recent post on the 3457A. I was tempted to do as you
done, on the assumption that Keysight would adjust the meter to give the
best possible accuracy rather than just leave something untouched if it was
within spec.  Someone warned me that if it caused errors at startup,  it
might be considered needing a repair rather than just calibration.

Did the meter indicate in any way that the cal constants were lost? A POST
error or similar?

> The service manual lists an entire sequence of procedures for
> calibrating this DMM, starting with storing values for zero and full
> scale into the SRAM. All of this is done via the front panel, by
> pushing buttons.

So does that mean it is something one could do oneself without accurate
standards?

> I just found out that this part of the procedure is not normally done
> (at least by the lab I sent the DMM to). With no pre-existing cal
> constants, the tech I spoke to was rather annoyed that he was having
> to spend the time doing the hookups and pushing buttons for each
> function and range to store the zero and full scale values. I was told
> this added an extra hour to the normal procedure.

Ouch.

I assume this means that your meter is probably calibrated more accurately
than it would have been had any settings left unchanged if they were in
spec.

I have just bought a battery and intend fitting it soon.  I might ask
Keysight about the constants.

I really can't understand why they don't put two battery holders and a
couple of diodes so a good battery in an one would be ok. Having to mess
around desoldering batteries and hooking up power supplies seems crazy to
me.

Dr David Kirkby
Managing Director
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3
6DT, United Kingdom
Registered in England and Wales as company number 08914892
http://www.kirkbymicrowave.co.uk/
Tel 07910 441670 / +44 7910 441670 (0900-2100 GMT)


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