Re: Ambient temperature control

On 2/07/2024 2:24 am, Phil Hobbs wrote:

On 2024-07-01 07:24, Martin Brown wrote:

On 01/07/2024 02:14, Don Y wrote:

Assuming you can keep a device in its "normal operating (temperature)
range", how advantageous is it (think MTBF) to drive that ambient
down?  And, is there a sweet spot (as there is a cost to lowering the
temperature)?

>
There can be for some high performance low level OPamps. Deliberately running them as cold as is allowed helps take the LF noise floor down and by more than you would predict from Johnson noise. ISTR there was a patent for doing this back in the 1980's. Prior to that they tended to heat the front end to obtain temperature stability and low drift.

 BITD you tended to get popcorn noise from ions migrating around the surface and in deposited (rather than thermal) oxide.  Cooling helped that a lot.  Nowadays processes are generally clean enough that you don't get a lot of mobile ions.

>
https://ppubs.uspto.gov/dirsearch-public/print/downloadPdf/4883957
>
Made possible with the advent of decent solid state TECs.

>
Also, is there any advantage to minimizing the hysteresis between
the ACTUAL operating temperature extremes in such a control strategy
(given that lower hysteresis usually comes at an increased cost)?

>
Depends how temperature sensitive the thing is that you are protecting. The example I recall they were aiming for medium term stable 6 sig fig measurements with the lowest possible noise.

 You don't want to use a thermostat with TECs anyway--they die very rapidly, especially the soft-solder ones (Laird/Melcor).

Anybody who tries to use bang-bang control with a TEC will run into that. TEC's are non-linear devices, and work best when the current through them doesn't vary much.
Sloman A.W., Buggs P., Molloy J., and Stewart D. “A microcontroller-based driver to stabilise the temperature of an optical stage to 1mK in the range 4C to 38C, using a Peltier heat pump and a thermistor sensor” Measurement Science and Technology, 7 1653-64 (1996)
used a TEC, and the product didn't die in the field, or not a least over the roughly ten years it was on the market. My boss had had a run in with bang-bang control of TECs in another (earlier) product, and that hadn't gone well, so we were well aware of the problem (and the paper does go into it, briefly).
--
Bill Sloman, Sydney
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