Help with heated bed config



  • Hi all, I will try to make this as brief and to the point as I can.

    I have a large format printer, bed size is 610x610. It is heated with the appropriate sized silicone heater and is 240v. Where I am in need of guidance is the bed has 3 thermocouples fitted to it, one is for diagnostics. It makes sense to have multiple sensors on such a large bed but I can't figure out how to get the duet2 to accept both and I suppose take an average. I have the thermocouple daughterboard and although it has both sensors connected it is only operating off one. Not even sure what I am asking can be done, bu any help would be much appreciated.


  • Moderator

    @Hytek Unfortunately, there isn't currently a firmware settings that combines temperature sensor readings; each heater is essentially controlled by one temperature sensor.

    However, you can set up both sensors, and use conditional gcode in RRF 3.1.1 to decide on actions based on the temperature responses. Another option is to do as @dc42 suggest here https://forum.duet3d.com/post/129870 and use one temperature sensor embedded in the plate for temperature control, and configure the one in the heater as overheat protection using M143.

    Ian



  • Luckily you are using thermocouples. If you wire them all together the actual voltage signal will average out. So if you just take all the +ve leads and connect together on the same +ve terminal and take the -ve leads to the same -terminal it will average out the three sensor readings. Its a pretty old school trick.

    good luck.



  • Thanks for the replies.

    As a point of interest there was a third option I was playing around with. The heating is divided up into 3 sections (front, center & rear) each section has it's own heating wire pair and a thermocouple. This would give me the option to heat smaller areas if required. The things that discouraged me from this is A. more components, more to go wrong. B. can the controller handle balancing 2 or 3 zones adequately. C. when one or two zones are used the dormant zone might become a heat sponge.
    If anyone has any input on this it would be much appreciated.

    Thanks again



  • Not related to 3D printers but I regularly heat large metal tubes at work and use many heaters. Up to 40 on a system and each one controlled independently. Each heater does have an effect on the others but usually it is minimal.

    It might be a good idea to do that but it may also complicate the slicing setup.

    I’m not sure if that was helpful or not.



  • This was helpful. I'd actually forgotten about the complications dealing with the slicer software.



  • Just an update in case anyone else needs this info in the future.

    I took the option suggested by baird1fa and joined all 3 sets of sensor wires. I did have to reverse them at the plug as it was reading in reverse. So far it seems to be a stable option (only tested half a dozen times) & haven't yet tested it with a print. Need to sort out other issues first.

    Thanks again for all the help 🙂



  • @Hytek you are welcome. Also with TCs the red wire is the negative in type K. The yellow is positive. I’m glad an old school trick was helpful.


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