[time-nuts] TECs in cooling below ambient

[ed breya]

Many years ago, I got some junker DP sensors - the chilled mirror type. 
I never did find any specific info on the model, or get around to 
figuring out the guts to run them. I can't recall if the support 
electronics were missing, or maybe potted, or if I just didn't want to 
reverse engineer them. I think I junked the non-usable parts, but may 
have saved some of the heads. I vaguely recall powering the TEC on one, 
and saw the dew show up on the mirror - very cool, so to speak. I always 
assumed they cycled the temperature over a narrow range once dew 
appeared, and used lock-in techniques to get a reliable optical signal 
telling the dew versus NOT dew condition, to home in on the temperature. 
Interestingly, the reason these were probably junked was that the little 
DC fans in the heads had all crapped out due to worn out bearings. Fans 
are so critical to many things, but are often the weakest link.

Ed