PT100 Wiring

  • I added the PT100 Board to my DuetWifi
    I have a two wire thermocouple.. the documentation says wire it into Termal 3 & 4
    the board is not labeled.. I cant find a wiring diagram
    which terminal is 3 & 4?

  • administrators

    Do you really mean you have a thermocouple, or do you have a PT100 sensor? Which documentation are you referring to?

  • I have a pt100 from e3d
    Trying to wire it into the pt100 duet board

    Referring to the duet wifi docum3ntation on the pt100

  • Hi Adam,

    Documentation is here You should get to it by clicking on the link in the documentation section at the top of this forum page.



  • administrators

    The documentation says:

    Each channel has a 4-position terminal block. We'll number the terminals 1, 2, 3 and 4 in order (it doesn't matter which end you start from, because PT100 sensors don't care about polarity). Terminals 1 and 4 supply current to the sensor, and the voltage developed across the sensor is measured between the terminals 2 and 3.

  • I used that same PT100 and soldered on the 4 wires as shown in Davids blog.

    The daughter board I got didn't seem to have the traces between the solder pads, so I just connected it as per instructions.

    After the auto tune function, it seems to be working extremely accurately, but I'll get some sort of contact thermometer to actually test the real temp at the extruder as well to be sure.

  • Still havent been able to get the PT100 working
    not sure what im doing wrong

    currentlyl reading on the machine says temp is 2000 degrees
    so that seems wrong. LOL

    This is the current setting for my heaters

    ; Heaters
    M143 S280 ; Set maximum heater temperature to 280C
    M301 H0 S1.00 P10 I0.1 D200 T0.4 W180 B30 ; Use PID on bed heater (may require further tuning)
    M305 P0 T100000 B4138 C0 R4700 L0 H0 ; Set thermistor + ADC parameters for heater 0
    M305 P1 T100000 B4138 C0 R4700 L0 H0 X201 ; Set thermistor + ADC parameters for heater 1 and remap it to channel 201

    I only have one hotend.

  • administrators

    Your wiring is incorrect. From the instructions:

    To connect a 2-wire PT100 sensor:

    Connect the PT100 wires to terminal 2 and 3
    On production PT100 daughter boards, you need to either bridge each pair of solder pads next to the terminal block, or add a wire between terminals 1 and 2, and another between terminals 3 and 4. On pre-production PT100 boards there is already a trace bridging each pair of solder pads.

    The only PT100 board I have is buried in my Delta printer, so I can't easily do a photo.

    You have the PT100 connected between terminals 1 and 2 (or 3 and 4 depending on which end you numbered them from).

    Also the first RTD is selected using X200 in the M305, not X201.

    HTH David

  • David,

    I think its better if you put a picture on the wiki for the 2 wire and the 4 wire config to make things clearer. Hopefully this image will help users out. This is for the production board, the jumpers are reversed for the pre-production boards.

  • Adamfilip,

    Note the wiring in the 2 wire config. You don't just choose the first two terminals. One of the wire has to connect to the terminals in the yellow box and the other to the red box. The jumper bridges the two terminals 1-2, and 3-4. If you are wiring to the first two terminals and have a jumper, they are shorted to each other. You should get a resistance measurement of around 110 ohms at ambient temperature between terminals 2 and 3 if everything is wired correctly. The reading may vary depending on the resistance of your wiring to the sensor. If you want more accurate readings, you can compensate for the wire resistance up to the sensor by using a 4-wire setup.

    I hope that clears things up.

  • administrators

    Thanks for the diagram. For some users it is probably easier to add a wire link between terminals 1-2 and another between terminals 3-4 rather than solder-bridge the pads.

  • Thanks guys, I appreciate the help
    I dont have a great knowledge in electronics so im figuring it out as I go.
    anything to spell it out in layman's terms is good for me LOL

    so i adjusted my setting to be

    ; Heaters
    M143 S280 ; Set maximum heater temperature to 280C
    M301 H0 S1.00 P10 I0.1 D200 T0.4 W180 B30 ; Use PID on bed heater (may require further tuning)
    M305 P0 T100000 B4138 C0 R4700 L0 H0 ; Set thermistor + ADC parameters for heater 0
    M305 P1 T100000 B4138 C0 R4700 L0 H0 X200 ; Set thermistor + ADC parameters for heater 1 and remap it to channel 200

    here is the revised pic of the wiring

    It now works.. reading 23 degrees currently.
    I do think that perhaps for the next run of these boards.. a standard 2 pin jumper replaces the solder tabs.
    im not terrible with soldering but i try to avoid doing it to PCB boards. for fear of screwing something up.


  • I used an online calculator and PT100 Resistance table to come up with these values

    M305 P1 T110.23 B-356.98 C0 R4700 L0 H0 X200

    anyone see any issue with the negative value?

  • Actually you don't need any of those parameters. I have none and it just works: M305 P1 X200

  • administrators


    As Alex says there is no need for the T B C R L H switches on M305 for a PT100 - they are for thermistors, the MAX chip we use for the PT100 does all that internally.

    Regarding the solder jumpers, David and I discussed this and came to the conclusion that adding wire jumpers (as you did), was easier that cutting solder jumpers if you have a 4 wire PT100, using a 2 pin jumper would have made the board footprint bigger.

  • Thanks for the Tip regarding the M305 P1 X200

  • This is a great thread, hope folks don't mind me adding a few bits of info I learned hooking up my pt100 for future reference if anyone searches on it.

    Consider using shielded cable if your PT100 wiring runs in a bundle with the hot end heater, stepper, servo, etc.. wires attached to hot end carriage.
    Ground the shielding wire. The PT100 daughter board appears to be very sensitive to inducted currents / EMI. It constantly read 2000 when the hot end heater kicked in. Once I ground the shield wires in the bundle, the sensor worked liked a charm.

    Use good low resistance wire, per the note in the page,
    Limit number of connectors and/or ensure connectors are properly crimped.
    I had two conenctors and 26 or 28 gauge wire in one section of my wire path to the PT100. The crimp of one connector on the small wire was not perfect and introduce additional resistance and raised the temp reading by 30-40 degrees C. Removed that connector and small wire and instead used 20 gauge wire directly into PT100 daughterboard. Temp is now with +/- 1 C of room temp.

  • Wow nice post. I was looking for info about exactly this. Wow perfect photos of the wire from 2-1 and 3-4. I wasn't getting the 'add wire' explanation. Could be nice to have that photo on the wiki. Nice job guys!

  • I'm trying to make the setup a bit easier and I was wondering if using this for a 2 cable PT100 sounds like a good or bad idea:

  • Just finished a video showing how to make a simple adapter that fits perfectly on the PT100 RTD Duet3D board.

    Hope you guys like it! Works like a charm!

  • Best cringe worthy video with an Exacto blade I have seen in a long while. I was anticipating a sliced finger every time he uses it in an unsafe manner. If you're going through all that trouble, just solder the damn jumpers and use the correct 2 pin molex KK connector.

  • administrators

    Nice job!

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