PT100 thermistor firmware



  • Hello,
    I am having a little trouble with my thermister settings for a PT100 from E3D. With the hotend turned off the temperature readings is reading about room temperature. When I heat up the hotend to 200 degrees it responds fine but when I put PLA filament in it is obviously way too hot as the filament just runs right out the nozzel and even burns, indicating that the temperature is well above 200 degrees.

    I am running a genuine E3D V6 with the Volcano block and a 12 volt 40 watt heater cartridge.
    Heater section of the fimware is as follows;

    ; Heaters
    M307 H0 B0 S1.00 ; Disable bang-bang mode for the bed heater and set PWM limit
    M305 P0 T100000 B4138 R4700 ; Set thermistor + ADC parameters for heater 0
    M143 H0 S120 ; Set temperature limit for heater 0 to 120C
    M305 P1 X200 ; Configure thermocouple for heater 1
    M143 H1 S310 ; Set temperature limit for heater 1 to 310C

    I'm not sure if this might be a contributing factor, the wiring runs approximately 85 inches from the hotend to the Duet board.
    I would assume the issue is in the firmware.
    If anybody has any similar issues or thoughts, I would love some input.

    Cheers,
    Leif


  • Moderator

    Have you done a PID tune for your hotend?

    https://duet3d.dozuki.com/Wiki/Tuning_the_heater_temperature_control

    Also, just to confirm, is your power supply 12v or 24v?



  • I am running 12 Volt. I have not yet done a PID tune as I was planning on doing that once I get the major issue fixed. When I do heat up the hot end there is a few degrees of fluctuation but nothing serious. How would the PID fix the issue of it being way to hot ( I'm guessing at least 100 degrees to much judging from the burning of the PLA) ?


  • Moderator

    I was thinking the PID tuning may help if your temps were fluctuating greatly. But if they are fairly steady, just not reading accurately, that obviously won't help.

    Do you have another way of checking the hotend temperature? Like another thermometer or thermocouple on a multimeter? Do you have a plain thermistor to swap to to test?

    Is your PT100 2, 3, or 4 wire? If it's a long run as you say, you should be running a 4 wire to eliminate any potential interference.

    What brand of PT100 sensor is it? Are you using the Duet daughter board?


  • administrators

    It's hard to think of any reason why a PT100 would read correctly at room temperature but under-read at elevated temperature, other than an intermittent short circuit in the wiring - although that would probably show up as sudden temperature jumps. My delta uses an E3D PT100, and I print at 200 to 205C indicated temperature.

    Are you sure that the PT100 is in good thermal contact with the heater block, and hasn't slipped out?

    If you are using the Duet3D PT100 daughter board, you could try the other channel just in case the converter chip is faulty.



  • Phaedrux
    Unfortunately I only have PT100's all original E3D so I can't swap for a different kind. I have put in a spare pt100 and it has the same problem so I can eliminate a faulty PT100. I am running a 2 wire system but will try a 4 wire. I will look for a independent thermometer so I can check it from a completely different source ( hard to find such thermometer)

    All PT100 are E3D and I am running the Duet Daughter board.

    dc42
    The PT100 is securely installed.
    I am going to try the 4 wire system and following the directions you laid out on David Crockers Blog. In the photo it is shown the doubling up of wires at the thermistor but it does not describe the hookup at the Daughter Board. Do I take out the jumpers and install the additional wires into slot 1 and 4 or leave the jumpers in?

    I have switched to the 2nd channel on the daughter board and now the temperature is much lower to the point where I must have the heat set at a minimum of 250 to extrude PLA, I suppose this points to interference from only having two wires. What do you think?


  • Moderator

    Take out the jumpers and install the wires. Pretty sure that's described in the blog post you mention.



  • @dc42
    In the spirit of science I am trying one change at a time. I connected the thermistor to the second input on the Daughter board and changed the firmware accordingly, I did not add the additional 2 wires. The temperature seems to be about right now as it prints nicely at 225 degrees. I suppose this indicates your suggestion that the converter chip is faulty. How do I go about fixing it as I will need the second channel soon once I have all the initial bugs worked out and add a second extruder?


  • administrators

    If the PT100 daughter board is still under warranty, ask for it to be replaced.

    You can test the accuracy of the daughter board using fixed resistors, with the help of a PT100 resistance chart - there are plenty of these on the web.



  • @dc42
    I have a warranty daughter board comming.
    Thanks for your help


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