One for the Old-timers

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

The obvious candidate is the Weston standard cell

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

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

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

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

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

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.

^^^^^^^ 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.

=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

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

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.

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

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.