[time-nuts] Cycling of Peltier junction

Don @ True-Cal true-cal at swbell.net
Thu Sep 9 20:59:02 UTC 2010


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 <jpeters at nvidia.com>
To: Discussion of precise time and frequency measurement <time-nuts at febo.com>
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
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