Duet 3 6HC - Dual Thermistor Heater Routine

CrashWidget

Hi-

I'm looking for some reccomendations on how to handle this bed heating situation.

Running 3/8 aluminum plate with silicone bed heater with internal thermistor. This works well for intial heating responds well to PID tuning. However, the linked thermistor to Duet3 control is attached to pad which is on the underside of 3/8" plate.

It takes about an extra minute for thermal flow to reach top print surface through plate. When starting prints the bottom of plate is at correct temperature but top of plate is not.

Is there a way to have another thermisor on top of plate control when print should start? Only start. For efficiency of pad heater i'd like to keep internal pad thermistor controlling the PID routine.

Any thoughts on how this could be accomplished?

  hmmm interesting, just getting used to this forum.  Nice touch code sniipit is automatic if tabbed in! cool feature

thanks,

Crash

Phaedrux

What some have done is use a thermistor embedded in the plate as the control sensor and then use the thermistor directly attached to the heating pad as a thermal exceed cutoff using M143 to watch that sensor.

Alternatively, you could just add a G4 S60 pause command in your temp setting gcode to wait an extra minute for temps to equalize.

dc42

You could use a while-loop and conditional Gcode to wait until the second thermistor is within a specified tolerance of the temperature that you set.

deckingman

@CrashWidget As above but actually, you'll find that overall heat up time will be drastically reduced (improved) if you move the thermistor - (ideally fit it into hole in the edge off the plate, close to the upper surface). The reason being that when the sensor is close to the heating element, there is a rapid rise in temperature at that point. The heating algorithm will "see" that high temperature and turn the heater off. Then there will be delay for it to cool before the heater turns on again. That on-off-on cycle repeats until the plate eventually reaches print temperature. If you move the sensor as I suggest, then you won't get that on-off-on cycle - the heater will simply turn fully on until the temperature gets close to the set point when the PWM will start.