[volt-nuts] Old Weston cells

[pa4tim at gmail.com]

yes then they are for sure unsaturated.



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Van: Joseph Gray
Verzonden: ‎dinsdag‎ ‎27‎ ‎augustus‎ ‎2013 ‎15‎:‎17
Aan: Discussion of precise voltage measurement

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
>
>
>
>
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>
>
>
> 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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