Joe wrote:
If I want to buy a used 3457A, is it better to buy one "as-is" and send it
for calibration, or perhaps spend a bit more and get one already
calibrated?
I have no experience with the seller you are looking at, but in
general the chance of something you buy on ebay really being
calibrated with NIST traceability are so close to zero that it is not
even worth looking into. I recommend treating every ebay instrument
as needing calibration regardless of what the seller says. (Again, I
have no experience with the seller you are looking at.)
If you want to investigate whether there is any chance an instrument
is calibrated with NIST traceability, you need to (i) ask what lab
did the calibration, and when; (ii) ask what accreditation body
accredits the lab; (iii) get a copy of the lab's accreditation
documents; and (iv) get a copy of the calibration certificate for the
particular instrument. You would then review the accreditation
documents (in particular, the "scope of calibration") to make sure
they are in order and to see what uncertainty the lab is accredited
to for (in the case of a DMM) DC voltage, AC voltage, DC and AC
current, and resistance. (Somretimes you will find that a lab is
accredited, but not to the uncertainty necessary to calibrate the
instrument in question to the manufacturer's specifications.)
Do all of this *before you bid*.
If the seller will not tell you what lab did the cal, or you cannot
obtain the accreditation documents and instrument calibration
certificate, treat the instrument as needing calibration and value it
accordingly.
It appears that the seller in this case does its own
calibrations. If it is an accredited cal lab, it will be able to
supply the documents mentioned above. If not (most likely because it
is not accredited), treat the instrument as needing calibration and
value it accordingly.
Best regards,
Charles
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