Question, Is it a mistake to try to set the desired "stable" temperature above the highest normal ambient? I assumed that way would be more in line with what the heater in the LTZ1000 was trying to do. If that is a bad idea, I can change settings, no problem.
The instability that TIN noted was due to untuned PID and also poor insulation, both are work-in-progress and should be working by the weekend. The sole purpose of the last test was to see whether the TEC was capable of holding temperature significantly above ambient under the worst of conditions. The cyclical instability was to be expected due to untuned PID; holding the box temperature 9C above ambient on average, was a positive result I thought.
Now, what about metal boxes? Starting from the DUT (probably an A9 board), it should be in metal box to reduce interference, right? Temperature sensor for the TEC controller inside the box with the DUT, or stuck on the metal plate, which? Metal box containing DUT in close thermal contact with the thick plate that mounts the TEC, right? Next, enclose DUT box and thick metal plate with insulation and leave the TEC and heatsink in open air with fan on heatsink, right? That all make sense.
This is where I have a problem. The boxes TIN and shodan describe are bigger than what I would like, and have open space inside and a fan to circulate heat. I would prefer a small unit that can be run 24/7 as a stable voltage reference whenever needed.
If the insulated DUT metal box is in thermal conductivity with the TEC, that box should be at a uniform temperature and the DUT inside heated by radiant energy from the box. The only job I see for a fan to do is move air around and that would take heat away from the DUT box in the configuration described above. If I missed something here, please set me straight.