Summarizing heater trends from Wednesday, 6/9. Reiterating from post , I ran the CTC-100 temp controller's auto tune routine to adjust PID coefficients for the heater. I then set the setpoint to 123K (operating temperature); the controller takes in the workpiece temperature as feedback. The heating data for this period is attached.
It took under 30 minutes for the temperature to rise from 72K (current cooling limit) to within a degree of the setpoint, 123K. The power delivered to the heater (bottom plot of first attachment) stayed below 25W, the limit we hardcoded. The workpiece temperature rises smoothly and plateaus around the setpoint, without significant overshooting. The controller holds the setpoint temperature pretty well thereafter. The second attachment is zoomed in on the workpiece temperature alone.
This run served as a test of the temperature controller's stability at the desired setpoint. Moving forward, we will continue to improve the cooling capacity of the chamber guided by our model. Once we optimize how cold we can get, we now know the heater can hold us at the desired temperature setpoint.