PT100 doesnt accept calibration

  • Hey Guys,
    atm iam upgrading our selfmade 3D Printer at work with a Duet2Ethernet.
    With this upgrade we wanna use a PT100 sensor, i got the pt100 daugtherboard and a new sensor.

    Ive tested the daugtherboard with the 100ohm resistor and got a measure about 0.2degree.
    Then i pluged in the Sensor (it was a 2 wire sensor) and i got real bad measure, at room temperature the sensor showed up about 90°.
    So i did the 4 wire upgrade with the sensor, with the hope to fix this fault.
    Now i got the 4 wires pluged in and the sensor shows about 40-70° at room temperature.

    So i tried to fix this with setting a "R" in the M305 in my config and it works, the sensor showed up 23°(thats okay) with a R370 but somehow if i shut down the printer and switch it back on the measure is freaking out again. The R370 is still in the config. i tried again and got about 22° with R320, switched off and on the printer
    same game, the pt100 is freaking out again and again.

    i checked the resistance from the cables near the duet up to the sensor and got a measure about 116ohm.
    i checked too to save the changes in the config correct.

    i just dont get it why the sensor is freaking out after every restart.

    hope u guys can figger out for what iam to blind for 😛
    best regreats

  • administrators

    If the resistor reads 0.2C but your PT100 sensor is reading 90C, then you have either an extremely bad connection to it or the sensor is faulty. Don't waste time trying to calibrate it, PT100 sensors do not need to be calibrated.

  • So i need a new sensor?
    where could be the bad Connection? should i try to Change the cables between the pt100 and the duet?
    are there any specific cables for this Connection?

  • administrators

    What resistance does the PT100 measure right at the sensor connections, without the extension cable that I presume you have between it and the Duet?

  • just checked that out, got a measure About 115ohm.
    thats to much isnt it? the sensor should have exactly 100ohm didnt it?

  • it depends at what themperature you were measuring it.
    115 Ohm is 40C. Normally i would say that is incorrect, but we are having a hot summer and depending on where you are that could be correct.

  • i got the bed Thermistor working already and that one and a normal roomthermometer are showing both about 22 degree

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