PT100 temperature sensor for heatbed?



  • Can we use PT100 for HeatBed? if yes how are wiring and bonding done typically in such scenarios?



  • @patil-rushal825 said in PT100 temperature sensor for heatbed?:

    Can we use PT100 for HeatBed? if yes how are wiring and bonding done typically in such scenarios?

    Yes you can - in fact I have. But it's overkill IMO. You don't really need the additional accuracy that a PT100 will give you, especially on a heated bed where the temperature can vary between the upper and lower surface. Better just to find what temperature works, regardless of how precise that temperature might be.

    You need to use the daughter board that Duet supply. I have found that PT100s seem to be a bit more prone to electrical noise than simple NTK thermistors.



  • i used a pt1000 for my heatbed. wiring was just connecting it up.



  • @deckingman Thank you. That would be helpful for me in my development work and another thing is that by bonding I meant physical bonding of the sensor to the heatbed? In the sense how it is done? Do you use silicon gel to bond with the heatbed?



  • @patil-rushal825 said in PT100 temperature sensor for heatbed?:

    @deckingman Thank you. That would be helpful for me in my development work and another thing is that by bonding I meant physical bonding of the sensor to the heatbed? In the sense how it is done? Do you use silicon gel to bond with the heatbed?

    Ahh, now positioning of the bed temperature sensor is something that is often overlooked. Quite often people buy silicone bed heaters that have a temperature sensor built in. This is a real bad idea IMO - especially if you use a reasonably thick aluminium build plate. If the sensor is surface mounted then what happens is this. The heater starts to heat, and the underside of the bed (i.e. the junction between the heater and the aluminium) rapidly reaches temperature so the heater cuts out (or the PID control reduces the PWM). But the heat hasn't had time to "permeate" through to the upper surface. The heater won't come on again until the temperature at the underside of the plate drops below the set point which can take a bit of time. Then the heater cuts back in but rapidly turns off and so the cycle repeats.

    So basically, if the thermistor is fitted to the underside of the aluminium plate, it will take longer for the upper surface of the plate to reach temperature because the heater will keep turning off prematurely. Or, you might try to start printing as soon as the temperature appears to be up to the correct value, when in fact the upper surface is still quite a bit cooler. The thicker the aluminium plate, the more pronounced this will be - on a 3mm plate it might not matter at all but with 10mm it most certainly is a problem. Been there, done that, got the Tee shirt.

    My solution was to drill a small (about 3mm for a small PT100) diameter hole in the edge of the bed, as close to the upper surface as possible without breaking through, and as deep as possible (I managed about 45mm). Then I simply inserted the sensor into the hole and clamped the leads to the bed frame to prevent the sensor from falling out.

    HTH



  • @deckingman Isn't there a risk of having the thermistor too far from the heat source to be an effective control loop?



  • @phaedrux said in PT100 temperature sensor for heatbed?:

    @deckingman Isn't there a risk of having the thermistor too far from the heat source to be an effective control loop?

    Quick answer - yes.
    Longer answer - there is also a risk that having it too close also screws up the control loop with respect to the bed surface temperature.
    On balance, having tried both, I get much better control having the sensor closer to the upper surface. Warm up time is faster and temperature is stable. The only thing I've noticed is that it tends to run about 1 degree hotter than the set point. If that was critical, I'd simply choose a 1 degree lower set point.

    Edit. When I said it warms up faster, I meant that the too surface of the plate reached temperature faster.


 

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