Duet 2 Wifi temperature sensor reads high. Two Questions



  • Hi all. I have a Duet 2 Wifi board controlling my 3D printer and it's been stellar until last weekend when the E0_TEMP sensor started reading about 30C too high. This prompted an investigation and it turns out the thermistor (the stock one that came with my E3D Titan Aero) is not damaged. It produces a correct reading when connected to E1_TEMP. I moved it there and redefined my tool and also moved to RRF 3.0 in the process. It seems fine now.

    I fried my last board, an MKS Gen 1.4 which was a RAMPS all-in-one that I cannot recall the name of, by shorting the heater to the thermistor during a nozzle swap. I have been very careful not to repeat that mistake with my precious Duet. Although, such mistakes should not cause long term harm to the board, I believe it was designed thoughtfully to make things like this less catastrophic if they do happen.

    My questions are: What could have happened to E0_TEMP? Should I be worried about anything else malfunctioning?

    Thanks!



  • Given that temperature is actually read by way of resistance, I'd say a connection somewhere was just beginning to go bad. As the resistance went up, the temp went up. Even the replugging you did during diagnostics might have "cleared" something.

    If it happens again, check the tighness of the connectors grabbing the pins, check the crimps, pinched wire that was almost but not quite cut through, things like that.


  • Moderator

    @orbajosbrother The quickest way to test the Duet thermistor input is to connect a known-value resistor, preferably one that matches the value it expects from config.g.

    For example, my bed thermistor setting is 'M305 P0 T100000 B3988 C0 R4700' (in RRF 2). A 100k ohm resistor reports 24.7C, a 10k ohm resistor reports 87.1C. I keep a couple handy for exactly this, it's a quick way to check config.g settings are correct and Duet is working correctly!
    0_1566297998327_IMG_4641.JPG

    Ian



  • @Danal said in Duet 2 Wifi temperature sensor reads high. Two Questions:

    Given that temperature is actually read by way of resistance, I'd say a connection somewhere was just beginning to go bad. As the resistance went up, the temp went up. Even the replugging you did during diagnostics might have "cleared" something.

    If it happens again, check the tighness of the connectors grabbing the pins, check the crimps, pinched wire that was almost but not quite cut through, things like that.

    Thanks for the ideas. All I did was move the thermistor to the next input. I moved it back and it went back to reporting an incorrect temp.



  • @droftarts this is a brilliant idea! I'll definitely do this. Thanks!



  • So I found some resistors, I did as @droftarts suggested. E0_TEMP reads way higher than E1_TEMP with the same resistor. I get ~82C with a 100k in E1_TEMP and 131C in E0_TEMP. Same test with the 10K resistor results in 61C in E0 and 24C in E1. Same firmware config for both:

    M308 S1 A"HotEnd" P"E0_TEMP" Y"thermistor" T100000 B4725 C7.060000e-8 R4700
    ;M308 S1 A"HotEnd" P"E1_TEMP" Y"thermistor" T100000 B4725 C7.060000e-8 R4700
    

    So something really has happened to my temperature sensor 😞


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