[volt-nuts] HP 3457A

Mike S mikes at flatsurface.com
Mon Aug 12 15:07:03 EDT 2013


On 8/12/2013 2:23 PM, John Phillips wrote:
> A calibration indicates that the unit under test is withing manufactures
> specification. The equipment and procedure used has to be "good enough"
> (bad words in a cal lab) to have a high probability (nothing is 100%) of
> insuring the calibration documentation is valid. Things can  can be a
> little looser if you are calibrating a 1% meter with a 10 ppm meter but it
> does not work the other way around.

You can calibrate either way. You can't however, calibrate the 10 ppm 
meter so it's in spec using a 1% meter. That's different. Calibration 
merely means that it's documented how close it is to a reference, such 
as NIST, not that it's within the manufacturer's spec. The 10 ppm meter 
would end up with a 1%+ calibration - precise but not accurate. Not 
particularly useful, but valid. A good cal lab would do a calibration to 
specification, where the uncertainties place the 10 ppm meter within spec.

As I cited and someone else already quoted, calibration is the "property 
of a measurement result whereby the result can be related to a reference 
through a documented unbroken chain of calibrations, each
contributing to the measurement uncertainty." Nothing to do with making 
a device meet its specifications.

That's why an eBay seller can claim they'll do a "calibration traceable 
to NIST," because they're not claiming any particular accuracy. It's 
really not worth anything, unless they give specific uncertainties or 
claim calibration to manufacturer's specification.


More information about the volt-nuts mailing list