Poor Man's GSWC - gallium stabilized weston cell - Page 1
Forum section: electronics / general

author: zhtoor
author_rank: Frequent Contributor
timestamp: October 30, 2017, 01:06:50 pm
content: -

author: Echo88
author_rank: Frequent Contributor
timestamp: October 30, 2017, 03:34:55 pm
content: 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 equipmentEven 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.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 30, 2017, 03:37:56 pm
content: 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.

author: zhtoor
author_rank: Frequent Contributor
timestamp: October 30, 2017, 03:52:04 pm
content: Quote from: Echo88 on October 30, 2017, 03:34:55 pmhello,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.

author: zhtoor
author_rank: Frequent Contributor
timestamp: October 30, 2017, 04:03:36 pm
content: Quote from: Echo88 on October 30, 2017, 03:34:55 pmhello 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 LTtell you:-please see attached file.regards.

author: Echo88
author_rank: Frequent Contributor
timestamp: October 30, 2017, 04:14:16 pm
content: 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.

author: Kleinstein
author_rank: Super Contributor
timestamp: October 30, 2017, 04:39:11 pm
content: 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.

author: tggzzz
author_rank: Super Contributor
timestamp: October 30, 2017, 06:24:42 pm
content: Quote from: Kleinstein on October 30, 2017, 04:39:11 pmI'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).