[volt-nuts] Eppley Standard Cell and What Is It?

[J. Forster]

If the Standard Cell has been shaken (in shipping) it needs to sit a long
time before being useful as a standard. Some types of cells really do not
like being inverted. It is designed to work into an open circuit....  ie:
potentiometric comparison.

The other item is abn Eppley Thermopile. The mpount is probably Spindler &
Hoyer, and it fits Zeiss standard profile optical benches, made of
aluminum or cast iron (most often).

Inside the can, there is a metal disk that should be painted with a very,
very flat black paint. The paint absorbs radiation from VUV to X-rays and
turns the radiation into heat. The rear of the disk has a myriad of tiny
thermocouples. The cold side goes to the case. The terminals are usually
solid Cu.

In use, it is usually read out w/ a nanovoltmeter. They are usually
calibrated in mV/W. You will likely need a fairly strong light to see much
voltage.

Since it is a calorimeter, it can be used to compare the power in two
optical lines of widely disparate wavelengths.

Best,

-John

=============




> I purchased an eBay item (190538109632) for the 'Standard Cell' that
> included another item.
>
> What is it?
>
> The 'Standard Cell' is an 'Eppley Laboratory Catalog Number 100 (SN
> 762058) Low Termperature Coefficient Standard of E. M. F.' that has
> written on it '1.01931 @ 20 degree C' with a date of what I think is
> '2-4-69' which I think means Feburary 4, 1969.
>
> Using my 'new' Solartron 7081, I read the voltage at 1.017844 +/- about 1
> uV.  If I have the math correct, that is a decrease of about 35 uV/yr
> which, I think, is about what is predicted for these cell's, assuming my
> 7081 is accurate.
>
> I also have another Eppley Standard Cell (SN 821855) that reads 1.018709
> but no date or prior reading on the unit.
>
> On another, unrelated note, I have been able to chase down the US branch
> of Ametek in Oak Ridge, TN, and they will be getting my 7081 back to send
> to England for calibration and 'service best effort', given that the meter
> ceased production in 1998 with end of support 2008.  TAT is about 4 weeks
> in England.
>
> Now, what is that other thing in the listing?
>
> Joe
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