PT100 reading too high

  • Today I was printing with PETG @ 240°C and was getting no bed or layer adhesion so I stopped printing and had tea and when I came back and switched the printer on I noticed that the heater temperature was showing 52°C when it was more like 26°C or 28°C in the room.

    How can I correct this error or is it a case of one of the components has gone.

    I am using:

    Duet 0.8.5
    E3D V6 with Copper Heat Block
    PT100 with MAX31865

    Which is most likely to be the culprit and how do I narrow it down? If I put a 100ohm resistor in place of the PT 100 it should show 0°C and if I put around 140ohms it should show over 100°C right? if it shows correctly that would point to the PT100 or I guess I could just measure the resistance of the PT100 but I don't know what resistance it should show at 26°C but I reckon it should be about 110ohms.

  • pretty much on the money with the ohms; but check the wiring first.

  • OK so on my system it is easy to disconnect the pt100 and so I measured the resistance and it is sitting at 111ohms which is right about where I would expect it for the current temperature. I have found a 100ohm resistor and when plugged in in place of the pt100 it reads 2.6°C which probably accounts for the wiring between the effector and the board which is about 1.6m. So now I am stumped as they both seem pretty close to what they should be.

  • And now that I put it all back together its reading 30°C which is only about 3°C high compared to the bed temperature. Maybe a bit or tarnish on the connector or something, I will keep an eye on it.

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