One for the Old-timers

I've got an electrochemical voltage reference cell. Its an Eppley Laboratories M51316 with a rated voltage of 1.0913V +/-0.1%. I've Googled to no avail.

1) Does anyone know what the chemistry of this thing is?

2) How many coulombs of charge can one expect to get out of this?

3) There's a small gas bubble near the cathode. From normal use or excessive current draw?

This was a part of an old Fluke 801 DC voltmeter (not worth saving). But the cell appears to be OK and will make a decent calibration check for my shop junk.

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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"Paul Hovnanian P.E." schreef in bericht news: snipped-for-privacy@hovnanian.com...

The obvious candidate is the Weston standard cell

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but that is supposed to produce 1.0183V. The gas bubble has probably been there since the cell was made.

The Clark cell has an appreciably higher output

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In theory it might be an unsaturated Weston cell, but the output voltage is still too low

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Bill Sloman, Nijmegen
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Bill Sloman

IIRC, some nasty stuff like cadmium and mercury. Here's some info:

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As little as possible! Use a buffer amplifier and disconnect it when not in use. Old galvo calibrators would allow a few uA when off balance, but only briefly and only once in a while.

Best regards, Spehro Pefhany

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"it\'s the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
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Spehro Pefhany

Or it might be rated for the room temperature of an unheated British laboratory.

The number of coulombs you can get out of one while still maintaining its accuracy is very small.

Cheers,

Phil Hobbs

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Phil Hobbs

That's what I figured. The Fluke has (had) a 'Cal' button that otherwise left this cell de-energized.

I figure its probably OK to connect this to something with 1M to 10M input impedance for the time it takes to check the reading. I can then check old low-Z analog stuff against that. I'm not running a cal-cert shop here. This thing was free, so I figure I'll put it to use without damaging it. That's my plan anyway.

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Paul Hovnanian	paul@hovnanian.com
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Paul Hovnanian P.E.

^^^^^^^ Typo. Should be 1.0193V. Damn lyzdexia must be kicking in.

That makes the Weston Cell a likely candidate.

I checked the label on the cell. It definitely says 1.0193 (not a screwed up '8') but its possible that Eppley typoed the 8 to a 9. Or the chemistry is slightly different.

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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=A0 =A0 =A0 =A0 =A0 =A0 ^^^^^^^

en

It could be an unsaturated Weston Cell - they are claimed drift up by up to 100uV per year, but apparently offered a better temperature coefficient. Fluke might have expected the customers to return the machine every year for recalibration, which would have allowed them to correct the drift before it got out of specification.

-- Bill Sloman, Nijmegen

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bill.sloman

But why? Aren't common, dirt-cheap voltage references available?

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a7yvm109gf5d1

They don't look as cool, and don't contain dangrous chemicals in a fragile glass housing.

Unfortunately, they're light sensitive so you can't shouldn't put it in an acrylic box and illuminate it with blue LEDs.

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Spehro Pefhany

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Well, the good ones aren't all that cheap, and they all cost more than something you've already got in a junked instrument.

Most of them draw appreciable current - which the Weston standard cell doesn't - and my guess would be that they are all noisier than a Weston standard cell.

-- Bill Sloman, Nijmegen

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bill.sloman

[snip]

I'm making a nice wood box for it to keep it from getting broken and spilling mercury/cadmium/etc all over. It'll look neat next to all the other antique stuff I've got.

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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