What is the best way to get 1.34 volts, low current to replace Hg Batt

I expect so. More worrying would be the day to day variations with prevailing atmospheric pressure. But I expect a zinc air cell might just about be OK given that photographers use them in vintage light meters. eg

Their other suggestion is Schottky diode in series with a silver-oxide cells but then you would have to worry about temperature coefficients.

Duracell have a reasonably nice treatment of these batteries, but you cannot get to it through their new improved Flashy website that takes aeons to load even on a T1 broadband connection.

I honestly doubt that oxygen starvation will be a problem for a zinc air cell being used as a reference voltage at very low currents unless the battery chamber is hermetically sealed.

Although mercury cells are banned for consumer gear are you certain that the required spare mercury cell or an approved functional equivalent is not available through Keithley (for a price).

Regards, Martin Brown

Robert Baer wrote in news:9dCdneyxhrN9dAzRnZ2dnUVZ snipped-for-privacy@posted.localnet:

as if an ordinary mercury battery was "reference-grade"....

I'm surprised that no IC manufacturer has designed a chip to do this with today's available 1.5v or 3v cells,or that some entreprenure hasn't made a tiny SMD circuit board to do it.

Google turned up this site;

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atmospheric pressure. But I expect a zinc air cell might just about be OK given that photographers use them in vintage light meters. eg

but then you would have to worry about temperature coefficients.

I expect that we could analyze this closely enough to determine that the original mercury cell wasn't ever *really* the perfect component, either.

:)

get to it through their new improved Flashy website that takes aeons to load even on a T1 broadband connection.

being used as a reference voltage at very low currents unless the battery chamber is hermetically sealed.

required spare mercury cell or an approved functional equivalent is not available through Keithley (for a price).

That is a good question for the OP.

Thanks for the info, Martin.

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OP here,

It turns out Keithley does have a fix for using a standard AA cell. It involves changing three resistor values, two of which are very difficult to get to. Plus, I am not sure if the standard AA cell is as stable as the Hg cell was. This cell provides the drive for the ohms measurement.

Thanks to all for the ideas. I still may consider making a power supply for this. The meter has three power supplies made up from industrial 9 volt batteries. It has

+/- 18 volts, +/- 9 volts, and the Hg 1.34 volt. All of these are independent and do not share a common ground.

Regards, tm

Maybe a small switcher with three windings and independent common points might be a consideration.

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Why not just design a small precision regulator?

Thanks, Rich

How are you going to keep it from running the battery down when it isn't needed?

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Looks like ON Semi already have one that could do the job:

Most batteries can stand 1uA loads for almost as long as their nominal shelf life - and some will live longer as a result. Tempco is nothing to write home about though.

Regards, Martin Brown