Heater voltage readings for the blue case LTZ1000 reference from TaoBao.
Screened cable connected to the heater electrodes, connected at the diode and the transistor emitter.
Allowed 30 - 60 minutes to stabilize.
Temperature is maybe 22 - 23 c. Can't find my Raytek.
Heater voltage at startup 8.4 volts. Holds there until ref hits temp, then drops quickly.
Test LTZ1000 heater voltage
Hanging in free air, no case 7.78 - 7.80. Blow on it, 7.95. This is why people put foam on the part.
Case only, no case heater 7.353 - millivolt movement over minute or two.
Case with case heater active 5.863 - millivolt movement over a minute or two
Case heater is about 1.4W (14V 0.1A)
Agree that the case heater doesn't have to be that precise. It is very helpful with all the other parts - there's no temp drift as long as the outside temp is less than the case setting. Plus, the EM shielding is good. Now, as I noted I am still at a suspect 6.5 digits. So this is still junior stuff.
When I pull the heater sense wire, i'll put some thermal goop back in. I'll have to trace the circuit out, see what it takes to calibrate the heater.