Jerome, All of the modern temperature calibration dry-wells that support both lower-than-ambient and higher-than-ambient set points, within the same well cavity, do so by changing the current direction through (typically) several Peltier junctions attached to a massive aluminum block. See Hart Scientific (Fluke) 9170 & 9171 Metrology Dry-Well Calibrators. The low and high set point temperature ranges are much more limited than say a resistive element type that would extent upward >600-1000 C due to the limitation of the Peltier junction. I routinely go from 0.0C to 100C (and back) in typical calibration procedures and there is no intentional current limiting ramp necessary other than staying within the power envelope of the device. You only need to make sure that thermal conduction on both sides on the junction device is adequately. In your case, forced air cooled heatsink on one side and a liquid heat exchanger on the other. With good design, you should be able to achieve a liquid coolant temperature range of -10C to +100C very easily. A good PID controller, home brew or a Watlow off ebay, will give you very nice set-point control and stability. Been there, done that. Regards... Don
________________________________ From: Jerome Peters <[email protected]> To: Discussion of precise time and frequency measurement <[email protected]> Sent: Thu, September 9, 2010 2:41:52 PM Subject: [time-nuts] Cycling of Peltier junction Does anybody know about using the same Peltier junction for both heating and cooling? I'm concerned about thermal/mechanical shock when changing the polarity back-n-forth between hot and cold. Maybe there needs to be a controlled ramp, if so then how do I figure out the rate? Why: I'm in the process of building a small environmental chamber for my home lab. The volume is ~30 liter, target temp range of 0C to 60C. For the cooling side I am using water circulation (radiator, pump, reservoir & water block) and Peltier junctions. At first I was planning to have two separate systems, one for heating and one for cooling, but then I got to thinking that using just the water and Peltier could be used for both. I will be using a PID for temp control, and two TEC1-12726 Peltier Qcmax(w)= ~240 △T =0j Regards, Jerome ----------------------------------------------------------------------------------- This email message is for the sole use of the intended recipient(s) and may contain confidential information. Any unauthorized review, use, disclosure or distribution is prohibited. If you are not the intended recipient, please contact the sender by reply email and destroy all copies of the original message. ----------------------------------------------------------------------------------- _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
