[volt-nuts] HP 3457A

[Charles Steinmetz]

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