Multiple temp sensors report open when using resistor



  • Hi there,
    I'm back...

    So I have two Duet 2 Wifi boards at my dispoal. The old one I need to return has had no issues with the temp sensors, while the new one I got to replace it is reporting both E0 and Bed Temp as 2000c.

    I am using a 100k E3D Thermistor, generic Chinese glass bead, and lastly a simple 100k Ohm resistor. All report at 2000c on the new board. They all report around the same ohms using a multimeter.

    Old board reports the temp accurately. Both running same firmware versions. Oddly it seems the old board will report -237c when I leave the sensor connection disconnected.

    Config is below:

    ; Heaters

    M308 S0 P"bedtemp" Y"thermistor" T100000 B4138 ; configure sensor 0 as thermistor on pin bedtemp

    M950 H0 C"bedheat" T0 ; create bed heater output on bedheat and map it to sensor 0

    M143 H0 S120 ; set temperature limit for heater 0 to 120C

    M307 H0 B1 S1.00 ; enable bang-bang mode for the bed heater and set PWM limit

    M140 H0 ; map heated bed to heater 0

    M308 S1 P"e0temp" Y"thermistor" T100000 B4138 ; configure sensor 1 as thermistor on pin e0temp

    M950 H1 C"e0heat" T1 ; create nozzle heater output on e0heat and map it to sensor 1

    M143 H1 S280 ; set temperature limit for heater 1 to 280C

    M307 H1 B0 S1.00 ; disable bang-bang mode for heater and set PWM limit


  • Moderator

    @firex726 -273 means open circuit (ie nothing connected), +2000 means short circuit (ie no resistance). Your config defines only two thermistors, on bedtemp and e0temp. The formatting of commands is for RepRapFirmware 3.

    Send M115 and post reply.to confirm firmware version. Check connection of thermistors to correct pins, and continuity of thermistor wiring with a multimeter. To test boards, I use resistors directly connected to a molex plug, which plug straight into the board.

    If it’s still not working, post the full config.g you’re actually using on the board.

    Ian



  • Good Morning,

    M115

    FIRMWARE_NAME: RepRapFirmware for Duet 2 WiFi/Ethernet FIRMWARE_VERSION: 2.05.1 ELECTRONICS: Duet WiFi 1.02 or later FIRMWARE_DATE: 2020-02-09b1

    The thermistors read around 113k ohms at the connector pins; and the resistors around 99.8k ohms.

    20200221_062954.jpg

    config.g


  • Moderator

    @firex726 If you’re only getting -273 or +2000, I would normally think this behaviour is because you’ve shorted the VSSA fuse.

    Edit: not the issue!

    Ian



  • I believe @droftarts was going down the correct path. Looks like you're running RRF 2.05.1 but the sensors/heaters excerpt you posted was for a RRF 3 config.

    Try replacing your heaters section with this.

    ; 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 T100000 B4725 C7.060000e-8 R4700 ; set thermistor + ADC parameters for heater 1
    M143 H1 S280                             ; set temperature limit for heater 1 to 280C
    

    Also 4138 for your bed thermistor is probably wrong.


  • Moderator

    @blt3dp said in Multiple temp sensors report open when using resistor:

    I believe @droftarts was going down the correct path. Looks like you're running RRF 2.05.1 but the sensors/heaters excerpt you posted was for a RRF 3 config.

    Ugh, quite right! Got distracted and forgot what I’d asked! @blt3dp See answer above!

    Ian



  • Yep, that looks to have fixed things... Now onto tuning.

    Thanks for everyone's help!


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