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    PT100 - 3 or 4 wire?

    Duet Hardware and wiring
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    • dragonn
      dragonn last edited by

      Hi,
      I am looking for a duet board and have some questions. I want to print with material which require temp over 300C.
      I already have some experience with PT100 and thermocouple but with both I did have a big problem - when my part cooling fan was on and the PWM were lower then 100% it affects temperature reading, but I think this was because I put the amplifier boards on the x carriage.

      Think forward I want 3 or 4 wire PT100 to avoid problems with interfering something again. So I have two questions:

      • how to wire a 3 wire PT100 to the Daughter Board? Wiki doesn't say anything, I found only on github info that 3-wire PT100 are supported but no wiring diagram.
      • did someone seen a 4 wire PT100 in E3D cartridge size? I have only found 3-wire ones. I know I can cut the wires from a 2 wire sensor and make it like almost 4-wire, but I would prefer an out-of-box solution.
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      • dc42
        dc42 administrators last edited by

        I don't recommend using a 3-wire PT100 because it requires a modification to the PT100 daughter board. Use 2-wire or 4-wire.

        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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        • dragonn
          dragonn last edited by

          Oh that is good to know. But can how to modify the daughter board? Could be useful for someone else.
          Moving on have someone seen an 4-wire PT100 3x12mm?

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          • dc42
            dc42 administrators last edited by

            I suggest you use 2 wire and convert to 4 wires close to the sensor.

            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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            • Loffy770
              Loffy770 last edited by

              David, I have interest in this too as I did in the past try the PT100 with my Duet but due to the spiking to 2000 degree I went back to a termistor. My PT100 and board came with my Duet from you guys so its know parts.

              So if I understand you correct I could use the same PT100 cartridge if I basically solder on two leads on the original leads? And the join again at the PT100 board..? 2 to 4 to 2 again..

              Should I run the four leads from close to the extruder, through the cable chain all the way up to the board to avoid interference from the cables in the chain?

              Can I use a regular awg28 flat ribbon leads to add the extra two leads or do I need a specific cable like the original PT100 cable?

              Just trying to understand what it takes to get the PT100 to work correctly.

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              • Dougal1957
                Dougal1957 last edited by

                I can tell you how I did it I used a length of 24AWG Cat 6 cable and used 2 sets of twisted pair with the PT100 end commoner 2-1 but keep them separate at the PT100 Daughter board end (you may have to cut the traces on the daughter board to convert to 4 wire.

                It is the twist in the cable that helps to avoid the interference

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                • Mike
                  Mike last edited by

                  I've got an E3D 2-wire PT100 sensor that I use in a 4-wire configuration. Maybe it's just be, but I constantly found the cartridge to wire connector a weak link. I'd get endless heater error despite all my efforts at strain relief. It all went away after I changed the connectors to some very secure RC ones.

                  So my configuration is as follows - 4 wires from PT100 daughter board (I've used twisted pairs in a shielded LAN cable), soldered together by pairs at the cartridge connector. Works really well. Just make sure you don't run any high-current wires (like extruder heater ones) completely parallel with the signal wires. In my case, having the wires twisted and in a shielded sheath mitigates that.

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