[volt-nuts] Old muirhead weston cell.

Eldon Johansen eldon.johansen at gmail.com
Mon Sep 13 18:44:51 UTC 2010

I should have mentioned, It is a saturated cell.
Originally it was wrapped in aluminum foil and was held in place with a
half inch thick foam pad on either side in the volt meter.
i removed it from that and it held it in my hand on the way to work,
then let it sit on the counter for 6 hours before measuring it.
there wasn't but a 5C difference between here and work, it had sat here
a week, so i figured it would be in the ballpark.
I was more concerned about my standards reading a millivolt high than
the life of this cell. The vibration didn't help either. 
I thought for sure the old weston cells were supposed to be 1.0183xx

anyhow, thanks for the information. 

Eldon Johansen
Eldon.johansen at gmail.com

On Sun, 2010-09-12 at 22:11 -0600, Ed Palmer wrote:

> Did you remove it from a temperature-controlled enclosure?  If not, it's 
> an unsaturated cell and 1.019XX V is correct.  If yes, then it's a 
> saturated cell and the voltage is a little high.  I have a couple of 
> Muirhead saturated cells that are spec'ed at 1.01877 V @ 15 C and 
> 1.01859 V @ 20 C. 
> Ed
> Eldon Johansen wrote:
> > Hello, new guy here. 
> >
> > I recently acquired an old fluke 801 differential voltmeter, and removed
> > the Muirhead Weston cell from it.
> > I'm not sure if it is the original cell or not, I don't doubt it.
> >
> > In any case, it was mounted upside down for what had to be a number of
> > years, and there are several tiny balls of mercury loose.
> > Compounding this issue, it does not work right side up, past 30 degrees
> > from horizontal it is as if it turned off.
> > My thoughts are this is due to the mercury detaching from the platinum
> > wire, it works great lying flat on the table.
> >
> > In any case i took it to work last week and did some measurements,
> > however the best i could do at the time is verify that it is delivering
> > 1.0190 +/- .05mV volts.
> > (This was at 18 degrees Celsius)
> > I'm in the process of building an oil bath and temperature regulator for
> > it, and by that time i should be able to find the 732b at work and get a
> > more accurate measurement.
> >
> > My question is there any good reason why is it nearly half a millivolt
> > over what the old books say it should be?
> >
> > thanks, 
> >
> > Eldon Johansen
> > eldon.johansen at gmail.com
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