What is the appropriate strategy for tuning a controller with Heat and Cold. The system has a considerable lag, 50 lbs mass, and must use full authority just to reach ramp rates. The heating is using resistive heaters under a platen, and LN2 for cooling through the platen. Since the whole thing is in a vacuum, there is no conduction, little radiation (except from the heaters to the bottom of the chamber wall). I have a Watlow Model 942. Max heating ramp rate is 2.5C/min; max cooling is 1.2C/min. I must not overshoot and must maintain temperatures from -40C to 100C within +/- 1C. I also have a variable heating load on the platen of 0 to 250 W. thanks roger

-- ROGER KNUTSON (knuts026@comcast.net), September 19, 2004