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    Incorrect readings of the PT100 sensor

    Duet Hardware and wiring
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    • vapvap
      vapvap last edited by

      Everything was in order, but one day the PT100 sensor (Heater 1) of the 3D printer began to show the wrong temperature:

      0_1558475576732_Screenshot from 2019-05-21 22-51-00.png

      Can you please tell me how to fix this problem?

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      • A Former User
        A Former User last edited by

        Maybe this sounds a little silly, but you're sure its not correct? A fault somewhere could lead to excessive current flowing through the sensor turning into a heater.

        If it is wrong then config and wiring needs a checkup. Try moving it to another input. Measure the resistance of the sensor if you have a multimeter.

        vapvap 1 Reply Last reply Reply Quote 0
        • vapvap
          vapvap @Guest last edited by

          @bearer It's weird, but now the temperature has dropped ...
          (I just turned off the printer, and turned it on after an hour.)

          0_1558481925532_Screenshot from 2019-05-22 00-34-35.png

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          • dc42
            dc42 administrators last edited by

            If PT100 channels show the temperature higher than you expect, but not a spike to 2000C, then this usually means you have a bad connection in the PT100 wiring. In the 2-wire configuration, each additional ohm of wiring resistance increases the reading by around 2.5C.

            Duet WiFi hardware designer and firmware engineer
            Please do not ask me for Duet support via PM or email, use the forum
            http://www.escher3d.com, https://miscsolutions.wordpress.com

            vapvap 1 Reply Last reply Reply Quote 0
            • vapvap
              vapvap @dc42 last edited by

              @dc42 Does this mean that you recommend changing the wires to thicker ones?

              A Former User 1 Reply Last reply Reply Quote 0
              • A Former User
                A Former User last edited by

                No need to change the wires unless they are unusually thin or long. Just measure the resistance if in doubt, or calculate from wire thickness and length if you don't have a meter. If they cause an offset it can be compensated in the M305 config, but for common setups it should be negligible.

                The thickness of the wires are fixed and as such not responsible for the temporary increase in temperature.

                vapvap 1 Reply Last reply Reply Quote 0
                • vapvap
                  vapvap @Guest last edited by

                  @bearer In that case, what do you think, why did my sensor "double" the temperature? And what can I do to avoid this in the future?

                  dc42 1 Reply Last reply Reply Quote 0
                  • A Former User
                    A Former User last edited by

                    Pointless speculation beyond the suggestions offered initially to try and isolate the cause. Intermittent faults are inherently difficult to track down. Faulty wiring somewhere is the best bet.

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                    • A Former User
                      A Former User @vapvap last edited by A Former User

                      @vapvap said in Incorrect readings of the PT100 sensor:

                      @dc42 Does this mean that you recommend changing the wires to thicker ones?

                      I think IF you would need to change something on the wires AFTER you have measured and posted here the resistance of your 2-wire-setup... I think 4-wire-setup would/could help you more than thicker wires...

                      since the 4-wire-measurement-setup seems to have been invented (on that island with those strange brexit-people... just kidding) to cancel out resistance of wires, in a 4-wire-setup the thickness is for short distances and for this application neglectable -> thicker wires could help of course in a 2-wire setup if you are too lazy to have your measured resistance calced out of the way by the duet2... that written here I am one of those 4-wire guys (not from the beginning)
                      All of this is of course only true if your wires are not infinte thin with infinite resistance... 🙂

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                      • dc42
                        dc42 administrators @vapvap last edited by

                        @vapvap said in Incorrect readings of the PT100 sensor:

                        @bearer In that case, what do you think, why did my sensor "double" the temperature?

                        Probably because there is a bad connection in one of the connectors in your PT100 wiring. Most likely a bad crimp.

                        Duet WiFi hardware designer and firmware engineer
                        Please do not ask me for Duet support via PM or email, use the forum
                        http://www.escher3d.com, https://miscsolutions.wordpress.com

                        vapvap 1 Reply Last reply Reply Quote 0
                        • vapvap
                          vapvap @dc42 last edited by

                          @dc42
                          I changed the wires to those that were bundled with the PT100 sensor. But the result was even worse (temperature difference ~ 12°C).
                          Tell me please, what should be the correct resistance in the wires?
                          Regards.

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                          • dc42
                            dc42 administrators last edited by

                            The PT100 should have a resistance of 100 ohms at 0C and about 108 ohms at a typical room temperature. if you use a 2-wire connection then each 1 ohm of resistance in the wires or connectors will cause the reading to increase by about 2.5C.

                            Duet WiFi hardware designer and firmware engineer
                            Please do not ask me for Duet support via PM or email, use the forum
                            http://www.escher3d.com, https://miscsolutions.wordpress.com

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