Poor Man's GSWC - gallium stabilized weston cell

[zhtoor]

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[Echo88]

If the other guys didnt say it often enough: Weston-Cells are not used anymore, because they are vastly inferior in every aspect to a standard LTZ1000-module:

-HAZMAT - its a cocktail of mercury and cadmium in a glass vial: nobody wants this stuff
-cant be transported without problems / nobody wants to transport this stuff
-temperature coefficient larger than a LTZ1000
-cant be loaded at all / necessitates complicated equipment

Even if somebody would donate me one, i wouldnt want to have it, because of the chemical gunk in the glass vial. Conrad also has thrown his away.

Now to the Gallium-Cell-idea: These cells are expensive as fuck (as far as i know, may be they cost way less in Pakistan, also they arent operating at their triple point) and arent contributing in any way more than a standard temperature controller.

[Kleinstein]

The standard cells prefer a lower temperature for long life. A good Pt RTD and large enough a container should be good enough. So I don't think it is a good idea.

[zhtoor]

(as far as i know, may be they cost way less in Pakistan, also they arent operating at their triple point) and arent contributing in any way more than a standard temperature controller.

hello,

gallium cell achieves a melt temperature variance of around +- 0.02 milli kelvins.
could you educate me to a competing electronically controlled "standard temperature controller" that achieves something similar?

regards.

[zhtoor]

If the other guys didnt say it often enough: Weston-Cells are not used anymore, because they are vastly inferior in every aspect to a standard LTZ1000-module:

-HAZMAT - its a cocktail of mercury and cadmium in a glass vial: nobody wants this stuff

hello again,

as far as haz-mat is concerned you probably already have CFL's all over the place which contain - guess what - mercury.

as far as LTZ1000 being superior in all respects, well one aspect would be the noise comparison, and the other i will let LT
tell you:-

please see attached file.

regards.

[Echo88]

Guess which amount of mercury a CCFL contains? Milligrams! You break the thing, open a window for a few hours and gone are the tiny amounts of mercury. Now try that with a Weston-Cell.

You also dont need 0.02 mK temperature stability. A analog/digital-pid fully suffices as a temperature controller for a voltage reference, like it is done in a 732B.

[Kleinstein]

The Weston cell is not suitable for every day or long term use, so having low noise is not really a feature one can practically use. Also the very high impedance amplifier needed for more than occasional use will add to the noise.

With a TC of some 20 ppm/C there is no need for a temperature more stable than lets say 10 mK over a short time. For a large and thus likely slow system to stabilize a digital controller may be more suitable than an old style analog version.

[tggzzz]

The Weston cell is not suitable for every day or long term use, so having low noise is not really a feature one can practically use.

I've used a saturated Weston cell to verify that a new-old meter (a Solartron 7081) was less noisy than an external reference voltage. The latter exhibits 15uV/1.5ppm popcorn noise.

Other than that, I agree with what you have said; I find my saturated cells make an amusing temperature sensor (for my sins I picked up 4 from a school that was closing down).