[volt-nuts] Old Weston cells

[Joseph Gray]

These are the type made to put in portable equipment. That should be the
unsaturated type, correct?

Joe Gray
W5JG



On Tue, Aug 27, 2013 at 12:08 AM, <pa4tim at gmail.com> wrote:

> Are you sure they are unsaturated ? Because most unsaturated cells last
> only 10-20 years (AFIK). Saturated cells last much longer but they should
> be kept at 30 degrees celcius for the correct value. On the other hand, as
> far as I know they do not survive if they are not kept vertical and most of
> the time they are not when they are kept outside their oven.
>
>
> I have 4 weston cells in a guildline cabinet with oven. I have the cal
> data for the first 10 years they have been used. After this time the oven
> was turned off , the lab was closed but all gear  stayed put on that same
> place over 30 years (the lab was turned into a server room but all the gear
> just stayed unused ) I made a graph from the data. Took a ruler and
> extended the lines. After a few months I had a change to measure them with
> a calibrated 6,5 digit meter and a year later a 7,5 digit meter and the
> values I found where plus/min a few uV on the lines. But more important the
> difference between the individual cells was spot on with my graph. So I use
> them as my house standard (I do not measure them direct. I set my 332 at
> 10V. A fluke 720 of ESI KV at the value the cell must have. Connect them
> both to a Fluke 845 and set the 332 so the meter reads zero. Then I check
> my 731 against the 332 the same way and leave them both connected this way
> for a few hours. If the meter is still at zero after that time I use the
> 332 for calibrating a meter.
>
>
> The only problem is the high Rout of a KV. So I use a buffer made of a
> LTC1052 and LT1010 after the KV  if the multimeter is a 10 M version. But I
> still wonder if that is needed. I tested it with some meters but did not
> notice a difference that was within the meters resolution.
>
>
> Fred, pa4tim
>
>
>
>
> Verzonden met Windows
>
>
>
> Van: Joseph Gray
> Verzonden: dinsdag 27 augustus 2013 06:26
> Aan: Discussion of precise voltage measurement
>
> I suspected that there was nothing to do to rejuvenate these old cells. I
> thought I'd ask anyway.
>
> Thanks.
>
> Joe Gray
> W5JG
>
>
>
> On Mon, Aug 26, 2013 at 9:16 PM, zbigniew169 <zbigniew169 at gmail.com>
> wrote:
>
> > All my knowledge regarding Weston Cells tells me that is not possible in
> > any way :-((
> >
> >
> > 2013/8/27 Joseph Gray <jgray at zianet.com>
> >
> > > I got my hands on a few very old, unsaturated cells. I figured that
> they
> > > would be no good after all this time. Just out of curiosity, I measured
> > > them on my 3457A, which hasn't been sent off for calibration yet.
> > >
> > > DMM was set to 3 V scale to keep the input impedance high. Room
> > temperature
> > > = 26 C.
> > >
> > > Cell #1 = 1.018288
> > > Cell #2 = 1.018236
> > > Cell #3 = 1.018224
> > >
> > > I read that when they get below 1.0183 V, they are no good. Is there
> any
> > > (easy) way to rejuvenate these cells?
> > >
> > > Joe Gray
> > > W5JG
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> >
> >
> > --
> > Zbyszek
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