PT100 - 3 or 4 wire?

  • 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.

  • administrators

    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.

  • 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?

  • administrators

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

  • 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.

  • 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

  • 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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