Dave wrote:
I see a lot of sellers selling things on ebay which are NIST tracable,
but I wonder what this means.
Let's asume I borrow a 3458A 8.5 digit DVM which has a valid (i.e.
non- goldenrubi ) NIST tracable calibration, and use the 3458A to
calibrate my 4.5 digit handheld DVM. If I work out all the
uncertainties, could I perform a NIST traceable calibration on a 6.5,
7.5 or even 8.5 digit meter using my handheld DVM?
No, you could not perform ANY traceable calibration with the 3458A
itself, much less with any instrument you had calibrated with the
3458A, because *you* are not accredited (i.e., your laboratory
procedures are not reviewed and audited by a competent third-party to
establish their reliability and, therefore, to create the link of
traceability between your USE of the traceable 3458A and a primary
voltage standard). Thus, the chain of traceability is broken at your
USE of the 3458A. You would have a tool with a traceable calibration
(the 3458A), but you could not perform traceable calibrations with it
unless you obtained accrditation for your home lab.
Equipment dealers and even some so-called "calibration labs" ignore
this fact and act as if using the traceable DMM to calibrate another
instrument can result in a traceable calibration, notwithstanding the
fact that the person/lab doing that calibration is not accredited
(this appears to be universal on ebay, but is common among used
equipment dealers everywhere). That is simply not
true. Traceability exists *only if* there is an unbroken chain of
*accredited* measurements between the calibrated instrument and a
primary standard.
Calibration is one thing. Traceable calibration is another thing
entirely, and virtually nothing you find on ebay is traceably
calibrated regardless of what the seller says (or thinks).
Best regards,
Charles
ps. For most products, Agilent uses different equipment to do the
different levels of calibrations. (I cannot speak specifically to
their VNA calibrations.)
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