[Test-Equipment] STD Cells----NBS Monograph 84

[wolfbob]

I did not read the Monograph in detail but scanned it looking specifically
for any indication that the variations in the emf of an individual cell was
possibly random and if they had any clues as to the distribution of the
randomness. I found NOTHING that would indicate anything but a systematic
change in emf due to a number of factors (temperature, age, shock history,
etc).

I think the world has been misled by the FACT that the NIIS uses the average
of a number of cells to DEFINE the STANDARD volt. This is a definition. It
is a good definition as it solves some of the problems germane in
determining a fundamental standard. But we poor folk are not trying to
establish and maintain an ABSOLUTE standard, but trying to establish and
maintain a secondary standard that has a voltage stamped on it side and that
is that. Averaging a bunch of these is no more accurate than the value of
any one of the calibrated secondary standards. In fact the average is worse
as it is contaminated by your local differential measurement errors. Using a
number of standard cells is useful in determining if one is bad or changed
from its original, but the average is definitely not as accurate as what is
stamped on the side of a good cell.

Either that or I'm wrong...

I hope this discussion will bring out the experts (I am definitely nothing
but a cranky old fat man) and this forum can expand into one of measurement
methodology as well as the interests for the equipment to support that
methodology.

WBob


----- Original Message ----- 
From: "Tom Dawson" <wb3akd at earthlink.net>
To: <test-equipment at mailman.qth.net>
Sent: Tuesday, June 01, 2004 5:02 AM
Subject: [Test-Equipment] STD Cells----NBS Monograph 84


>
>
> Monograph 84 regarding all you ever wanted to know about Weston standard
> cells is at
>
>
> http://www.radio-science.com/std_cells/mono_84.pdf
>
>
> If you want it, download within the next couple of weeks because its about
> 6MB and consumes quite a bit of that site's storage.
>
>
> regards,
>
> Tom
>
>
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>