Negative temperature value on bed Duet 0.8.5

  • Hi
    I had already started to install and configure the duet 0.8.5 when I got my duet wifi, so I wanted to get that up and running before switching over to the wifi board. But I am stuck on getting a negative reading on the bed temperature with about -23.0 celsius. I have a keenove silicon pad for 230v with a NTC 100k thermistor already baked in the silicone pad. When placing a 10K resistor instead I get 25.0 celsius so thats ok for the board, and when measuring the thermistor resistance I get about 123K. So it seams ok but the value is negative (-23.6)
    Am i doing something wrong or do I have to change the thermistor table that the duet reads from?
    Any help would be much appreciated!

  • administrators

    You must tell RepRapFirmware that you are now using a 100k NTC thermistor for the heated bed instead of the default 10k NTC thermistor. You can do this by adding

    M305 P0 T100000 B4138

    to your config.g. Maybe you will have to use a different beta value, too, but that depends on your thermistor.

  • Hi chrishamm!
    And many thanks for reply! Had a feeling that it was something like that.
    The beta value is 25/50 3950K. where and how do I change that value (if I have to)?
    Best regards

  • administrators

    That's what the 'B' parameter is for. For your thermistor you'll have to use this line:

    M305 P0 T100000 B3950

  • Thank you so much Chrishamm for a beginners question, starting to understand the firmware.
    Happy weekend!

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