[volt-nuts] HP 3457A

[Orin Eman]

Well, lets discuss the 3456A I got from goldenrubi, calibrated.  They send
a calibration certificate which claims that their standards are traceable
to NIST.  I have no reason to doubt that.  The list of standards used is
reasonable for a 3456A.  The certificate claims "in tolerance" for
condition received and condition returned.  Not surprising if they cal'd
the unit before listing, then checked it before shipping.  (One of their
later listings now puts a $ value below which they don't check the cal
before shipping.  Fair enough, not worthwhile checking an instrument that
sold for $200.)

Now, how good is their cal?  It's within 10ppm of a Geller SVR-T at 10V.
Said SVR-T is within 3ppm of a new Agilent 34461A (and to be honest, given
the data on the cal certificate for the 34461A, I trust the SVR-T).  Given
the uncertainties involved, I cannot say the 3456A is within 24 hour
specs... but it is well within 90 day specs.

In fact, the two 3455A and 3456As currently in my possession are all mighty
close to 24 hour specs.  These old meters don't seem to drift much and if
cal'ed within 5 years or so, they should be fine for us amateurs.

However, Joe's 3478A does seem to be the exception to this rule.

Orin.



On Sat, Aug 10, 2013 at 8:10 PM, Charles Steinmetz <csteinmetz at yandex.com>wrote:

> 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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