[volt-nuts] A Fluke 732A
Charles Steinmetz
csteinmetz at yandex.com
Sun Mar 9 13:16:32 EDT 2014
Thomas wrote:
>True the documentation is not there but does that matter in a
>majority of Volt-Nut applications.
If the documentation has not been done, there is no basis upon which
to make ANY claim about the accuracy of a calibration. Really, the
documentation IS the calibration. Having a voltage standard that is
exactly 10.000000v but not knowing for sure what the voltage or the
calibration uncertainty is, is no better than having a voltage
standard that is tens of uV off and not knowing for sure what the
voltage is. The documentation is the only way the adjustment becomes
useful -- now you know exactly how far you can have confidence in the
voltage. Indeed, a standard that is tens of uV off is a perfectly
fine standard as long as you know the uncertainty -- which you would
only if the documentation has been done. So yes, the documentation
is absolutely critical to any calibration, accredited or not. And no
commercial lab that puts in the extreme effort to document its
results to the 1 ppm level or better is going to pass on
accreditation, because it would seriously limit their business.
>And if you ship VS local calibration you may have documentation
>stating lower uncertainty, but a local cal may actually be more accurate.
There are mountains of data on 732As that get shipped to Fluke every
year, and there is no problem getting uncertainties at the 0.1 ppm
level back at the customer's facility. This is just a non-issue with
732As. (The same is true of humidity, and temperature as long as you
stay within 5C of the cal temperature.)
>I also think the number of JJA's is larger then most think. Just
>this week a couple labs added 10 Volt Programmable Josephson voltage standards
The number of JJAs deployed is not the issue -- lots of research
facilities have them, but they do not calibrate third-party
instruments. For someone wanting to get an instrument calibrated,
the question is, how many commercial calibration labs have them? And
the answer is, only a very, very few. As I said before, take a look
at the NVLAP lab certifications.
Best regards,
Charles
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