I think I'm seeing a similar problem that y'all were when I use my heater circuit (which is I believe the same as your heater circuit, it's the one Kira and Kevin are using at the 40m). Our temperature readout circuits might be slightly different.
Basically when I have the heater on the board as my readout op amps, I get up to a few tenths of a volt jump in my temperature readout; however, even after moving this circuit to a different board and using a separate power supply, I'm getting about a millivolt shift. This is not good for <1K control. I'm also well within the limits of my power supplies, have voltage regulatorsbefore the OP amps, etc... I will try swapping out the OP amp as you did, but thought it was a pretty weird problem.
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After some extensive testing, the circuit appears to be working as expected. The only exception is the affect the temperature control circuit has on all other electronics connected to the +24V kepco power supply. The model number on our electronics rack is ATE 36-3M, and is a Size "B" Quarter Rack model, rated for "Approx 100 watts" of power, with max DC voltage of 36V and max current of 3 amps, according to Table 1.1 of the manual. Our current readings on the power supply show between 1 and 2.5 amps at 24 volts, with the current depending on the 0 to 1.5 amps the vaccan heater draws. So our max power output from the power supply is 60 watts, well within the power limits.
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