[volt-nuts] 3457A - should I preserve SRAM contents, or purposely corrupt them by removing power?

Dr. David Kirkby (Kirkby Microwave Ltd) drkirkby at kirkbymicrowave.co.uk
Mon Jan 25 06:12:17 EST 2016

As noted in another thread, I want to replace a battery in a 3457A that has
not been replaced in at least 11 years. The instrument has not been
calibrated in that time either. At the time it was purchased from a dealer,
I was told it was within specification, but if I wanted it calibrated I
would need to pay. I never did have it calibrated, so have no historical
data about this. I've no idea when it was calibrated, and have no cal
certificate, so have no idea of the errors at the time of calibration.

I now want to change the battery, *and* send it to Keysight for calibration
- I have a healthy skepticism of 3rd party labs, so would rather pay more
and get the job done by Keysight.

I'm wondering if I would be better purposely removing the battery, and
putting a short across the SRAM so I ensure the contents are definitely
lost. My logic is that

1) If I send it to Keysight and the cal data is corrupt, they will set the
meter correct.

2) If sent to Keysight, with the cal data in tact, then if its within
specification they will not adjust it. So if the limit on some parameter is
1%, and the error is 0.5%, then it will not be adjusted. But if the SRAM is
corrupted, the error will be huge (if it will read at all), so it would
force Keysight to adjust it to the correct value. At that point the error
should be effectively zero given its a 6.5 digit multimeter, which means
the uncertainly in Keysight's measurements should be much lower than the
uncertainty of my meter.  So by corrupting the SRAM, I should get a meter
returned to me that is more accurately calibrated than if I take the
trouble to preserve the SRAM contents.

3) The adjustments are I believe software, so there's no risk that
adjusting potentiometers will cause drift to increase.

4) I don't have any historical data from cal certificates, so even if I a
range is in error by 0.5%, I can't make any attempt to estimate the drift
over time. Clearly if I had cal certificates over a period of years, I
maybe able to get some idea of how the instrument is drifting, so possibly
correct for that, if it is drifting in one direction.


Dr. David Kirkby Ph.D CEng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Althorne, Essex, CM3 6DT,
Registered in England and Wales, company number 08914892.
Tel: 07910 441670 / +44 7910 441670 (0900 to 2100 GMT only please)

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