PT100 wiring interference fix (and loose connection fix)



  • Just to say was getting interference with PT100.

    Canbus 2 wire cable can be had for £3.50/meter and is double shielded with a handy ground core to attach to a ground pin on the duetwifi. Interference is no more.



  • What symptoms were displayed? Be careful with shielded wire, if not grounded properly you can create a ground loop and even worse turn the thing into an antenna emitting EMI



  • Thank you for your concern but it is grounded well. The symptoms were aberrant temperature readings sporadically using the e3d supplied 2 wire harness. Not extreme eg 2000 deg C, but you could see on the temp graph spikes that do not represent the actual temperature of the heater block. As a result heater faults were occurring, that did not occur when I was using a thermistor. Now they are not. And as a small benefit the rather thick stiff cable supports my umbilical to the head a little better.


  • administrators

    Small temperature spikes can be caused either by interference (usually from an adjacent stepper motor cable), or by a bad connection.



  • I can highly recommend the canbus cable its appears very suitable.



  • Out of curiosity did you try the 4 wire method of hooking up the sensor as detailed in the wiki page https://duet3d.com/wiki/Connecting_PT100_temperature_sensors

    I believe that the 4 wire method is primarily used to account for the wire resistance but I wonder if it is at all helpful with negating interference. My 4 wire setup is working well but that doesn't mean it would help with a situation like your with obvious interference.



  • No I didn't although I'm sure there is probably a method of twisting the wires which helps.



  • For info, I use 4 wire PT 100s and do get occasional interference spikes. Mostly when moving the Z axis so it may be interference caused by the Z motor. I've not yet got around to changing to screened cable but it's on my "to do" list.



  • deckingman thanks for the info, I will keep that in mind for future builds.



  • So I was still getting random temperature spikes after using the shielded cable. In the end I tracked it down to the plug fitted to the pt100 sensor by e3d. A loose connection was the culprit. I cut the plug off and soldered the solid core leads (dont bend 'em too much!) of the pt100 sensor to the shielded cable. Solid as a rock now.


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