Temp sensing acting strange all of a sudden

  • I suddenly started get temperature rising too slowly errors on one of my hot ends. All was fine on one print and the following print just a few minutes later had problems.

    At first I thought it was a PT100 acting up, but now I think it something else. I replaced the PT100 on that hot end and the problem didn't change. However when I switch the wires to the other channel on the PT100 board it reads as expected.

    Channel 1 and Channel 2 are reading the same sensor quite differently suddenly.

    At room temperature, channel 1 reads about 21 degrees C and channel 2 reads 16 degrees C.
    At 70 degrees C on channel 1, channel 2 is only reading about 52 degrees C.

    This obviously makes it look like it's heating slower than it is and the hot end is getting hotter than expected.

    How can I tell if this is a failed PT100 board vs. something else.


  • administrators

    Are you using a 2 wire or 4 wire connection? If 2 wire, how have you jumpered the terminal block pairs?

    A 100 ohm resistor connected across the terminals should give a reading close to 0C.

  • 2 wire. They are jumped. I measured the continuity between connector screws to verify. Both PT100's measure 108.1 ohms. Channel 1 is displaying 20.8 degrees and channel 2 is displaying 15.7 degrees. I'll dig out some other resistors to verify if needed but I've reconfigured the printer to use the 'good' sensor for my primary extruder so I can get some printing done.

    That's one thing I love about this board, it's easy to temporarily reconfigure this kind of stuff.


  • administrators

    It sounds like one of the channels is faulty then. Ask your supplier for a replacement.

  • I got curious so I collected some more data:

    Resistor Channel 1 Channel 2
    100 1.9 -1.6
    150 127 97.9
    220 335.7 207.5

    It seems really odd that this just happened out of the blue. It has been working perfectly since September then yesterday it just started doing this.


  • I got my new PT100 board. It corrected the problem.

    The old board will be back to you guys to look at shortly.


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