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

[Chuck Harris]

As I understand it, an unsaturated cell that measures 1.0178V is many, many years
past being useful as a standard, as is any unsaturated cell that measures below
1.0183V.

Saturated cells are very rare outside of laboratory conditions, as inverting the cell
will ruin it.  Unsaturated cells can withstand the topsy turvy travel conditions
presented by shipping.

-Chuck Harris

J. L. Trantham wrote:
> Roy,
>
> The 'experts' are here on the list. From my reading, they have about a 50 uV/Yr
> expected decline in value, thus the need for periodic 'calibration'. I do not have a
> feel for useful life expectancy but the two I have are in good condition and only the
> latest one has a value on the front of '1.01931 @ 20 degrees C' with a date on the
> side of '2-4-69'. This AM, it measures 1.017894. However, the 7081 is not known to be
> accurate, yet.
>
> The other cell still measures 1.018709 this AM.
>
> So, it would appear that they will make a good standard but will need to be measured
> from time to time to generate a log of date, temperature, and value.
>
> I wonder how long it has to be 'still' before it is again stable?
>
> Joe
>
>
> ----- Original Message ----- From: "Roy Phillips" <phill.r1 at btinternet.com>
> To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
> Sent: Thursday, September 22, 2011 5:16 AM
> Subject: Re: [volt-nuts] Eppley Standard Cell and What Is It?
>
>
>> Joe
>> Interesting point regarding the "Standard Cell", I have one that was purchased some
>> 12 years ago made by Western. It must be well beyond its calibrated accuracy. It
>> currently reads 1.018679 volts according to my 3458A. It seems to be stable but
>> below its original labeled standard (label lost). Are they worth keeping ?
>> Roy
>>
>>
>> --------------------------------------------------
>> From: "J. L. Trantham" <jltran at att.net>
>> Sent: Thursday, September 22, 2011 2:37 AM
>> To: "Discussion of precise voltage measurement" <volt-nuts at febo.com>
>> Subject: [volt-nuts] Eppley Standard Cell and What Is It?
>>
>>> 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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>>
>>
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