PT100 Wiring



  • Hey guys,

    I have wired a Wanhao D6 with a Duet 2 Wifi and I am new to wiring printers. My heater power and 2-wire PT100 hot-end sensor are wired using a shielded 4-wire cable. Going through Step 3.9 of the setup guide (Configuration: Check Heater Functionality), as soon as I enable heat to the hot-end, the temp reading spikes and then faults and cuts power.

    I was following a wiring write-up from someone who went through the same upgrade, and they noticed that the PT100 signal would go off the scale whenever the extruder stepper moved. They then re-wired the PT100 with it's own dedicated shielded wire. I didn't expect this would be an issue for a heater vs a stepper, but do you think this is an interference issue that can only be solved by dedicated shielded wiring for the PT100?

    Thanks for any help!
    Matt



  • The heater is usually driven by a PWM output and as such about as noisy as a stepper driver, infact more as the Trinamic stepper drivers output a fairly smooth sinusoidal signal to the motor.

    But I'd start by verifying the wiring is correct as it could be a short between the heater and the pt100.



  • @bearer ok thank you!


  • administrators

    If the temperature reading errors are caused by interference then it's possible to add capacitors to the PT100 daughterboard to suppress it, similar to the way it was done for older thermocouple daughter boards as described here https://forum.duet3d.com/topic/1270/thermocouple-issues/11. The capacitors should be connected between each of the two inner pins of the terminal block and the ground plane of the PCB.



  • @matteo2u
    @dc42

    Hi, sorry to answer so late: I had the luck to finally find out what was causing the same behaviour you experienced at least on the Printer I build!

    Make sure that there is NO direct metal contact between you stepper and temperature-sensor (my temperature-sensors came with braidedsteel-shielding which was connected to the same metalplate the stepper was sitting on), like was in my case because everything was made out of metal, the bracket for the filamentstepper, the hotend, and all else in one big unit…
    As soon as the stepperbracket was out of "nonconductive" plastic, even all devices sharing 1 PE (Earth) didn´t do anything anymore! (Make sure also the screws are not "connecting" stepper to other metal that is shared by your temperature-sensor)

    After that, everything works brilliant for me! Those steppers were just such noisy beasts, that they distorted all other signals… Their field seem to be so strong that via the shielding of the temperature-sensor they just blew that signal...

    Best, Lucas


  • administrators

    Glad you solved it. Yes, stepper motors are noisy. The belts can also generate static, which may cause static discharge to the motor terminals. For this reason we recommend that stepper motor bodies are grounded, either through the printer frame if it is metallic, or using a ground wire.


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