Electronics > Metrology

Making Do with What You Got/ Building a Thermal Stability Fixture

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--- Quote from: TiN on January 24, 2021, 11:29:00 pm ---It is not hard to build a makeshift oven styrofoam box (few resistors, simple temperature controller with relay) and put a ref in there. Total cost could be as low as $5-$10 and suitable to keep temperature stable.
Next step is active thermostat box with some ready-to-go controller, such as Arroyo (example) or ILX 5910B (one was sold for $80). Add some cheap chinese 40W TEC, heatsink, RTD from Digikey, cooler for hot side and getting stability better than 0.01°C become trivial for small device like A9 3458A reference.

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Excellent suggestion!
Coincidentally, I'm a participant in Mark Rober's 'Monthly Classroom' online course and have a project underway for just what TIN described: http://mthly.co/p/gXkRm2

There’s a photo attached of a little (150mm) aluminum box for the Thermal Stability Fixture now sporting a spiffy backpack that many will recognize as a CPU cooler salvaged from a long departed PC. The fin part is mounted on a thick aluminum plate (5mm) and between the fins and the plate is the Peltier junction. That clever device can get cold on one side and hot on the other--you can see where this is going--the other photos are of the inside warmer than the fins on the outside.

Next will be to add the thermal conductive layers around the Peltier to even out any surface imperfections and run a temperature test.

TiN:
Metal box? Metal is rather poor thermal insulator choice.  ^-^
Otherwise good start, just don't forget that Peltier device is NOT a cooler but a heatpump with poor efficiency.

P.s. I still see no point in unneccessary informational noise "Making Do with What You Got" in every thread title.  ;)

Kean:
You cant realiably measure the surface of unpainted aluminium via IR.  This is due to IR reflections of surrounding things from the metal surface.
You may also need to adjust the emissivity setting on your IR temperature gun.

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For temperature control--rather than using a relay and switching the Peltier on/off--I'm thinking that varying PWM in response to temperature changes might avoid the hysteresis issues with on/off and also eliminate whatever the relay opening might generate. The Peltier I'm using is listed on Amazon as a TEG, however reviews suggest that it is a TEC. In any case, it draws 1.5A with an applied 12VDC from a bench PSU, dropping to 5VDC under load.

In actual operation, the power for the Peltier would come from a source that doesn't make the reference useless from its contributed noise. Perhaps a battery backed by a charger that is turned off when the reference is being used.

Suggestions?

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--- Quote from: TiN on January 31, 2021, 06:40:44 pm ---Metal box? Metal is rather poor thermal insulator choice.  ^-^
Otherwise good start, just don't forget that Peltier device is NOT a cooler but a heatpump with poor efficiency.

P.s. I still see no point in unneccessary informational noise "Making Do with What You Got" in every thread title.  ;)

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There will be foam insulation inside the box--later possibly on the outside as well. The box has been hanging out on my work bench for over a year--it was to have been part of an educational experiment for a kids radio telescope to investigate HII spectra in our galaxy. COVID put that on hold.

Peltier junctions and efficiency don't even live in the same country. I am hoping that in practice Peltier will just be managing stability of temperature around variations in my lab, however I do not harbor high hopes. If anyone wants a really efficient heat transfer, check out 'ammonia refrigeration cycle'.

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