[volt-nuts] HP 3457A

[Robert Atkinson]

Hi Charles,
I have to disagree on one point, You CAN do a TRACABLE calibration without any approval. What you can't do is  ACCREDITED  Calibration. Many labs are accredited but also offer un-accredited, tracable calibration at lower cost. An example is that production test equipment could be tracable but qualification test accredited. Accredition is normally driven by legislation or self-regenerating "quality" systems.
Of course if you cal a 4.5 digit meter against a tracable standard, the highest level you could reasonably sub-calibrate would be 3.5 digit or possibly 3200 count. This assumes the 4.5 digit has suitable accuracy and stability specifications, just because it has more digits does not mean it's more accurate ;-)
Somethings don't need to be tracable, a Fluke 720 K-V divider or Caesium frequency standard spring to mind.

Robert G8RPI




________________________________
 From: Charles Steinmetz <csteinmetz at yandex.com>
To: Discussion of precise voltage measurement <volt-nuts at febo.com> 
Sent: Monday, 12 August 2013, 17:21
Subject: Re: [volt-nuts] HP 3457A
 

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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