Help configuring termistors



  • Hi,

    i am configuring Duet... and i have issues with termistors of Nozzle, i need help to configure it:

    The line in config.g i must to set up is:

     M305 Px Rxxxx Txxxxxx Bxxxx; Example P1 R4700 T100000 B4388 Where...
      P1 --> Correspond to Thermistor that i have assigned to tool 1, my only extruder
      R   --> Is the value (in ohms) of the series resistor on the controller electronics, default 4700.
      T   --> Its the resistance at room temperature
      B  --> Its the resistance at working temperature.
     Sometimes he uses parameter C, I don't know when or why, in the wiki he says he has more precision ...
    

    Well, with this info, a multimeter and 1 termometer, i have do some test.

    • I have test 2 volcano thermistors, and 3 "normal" thermistor.... all 5 provided by Aliexpress.
    • i have do the test with boiling water, and oil at 187º... with these results

    .................-- Resistance at room T=27º-- -- Resistance Boiling water T=101º-- -- Resistance with oil (Not Boiling) T=187º--
    Normal1.......................92.8.......................................................4.8.............................................................0.30..................................
    Normal2.......................90.6.......................................................5.5.............................................................0.30..................................
    Normal3.......................90.7.......................................................4.9.............................................................0.28..................................
    Volcano1.......................94.4......................................................6.4.............................................................0.90..................................
    Volcano2.......................93.2.......................................................6.5.............................................................0.85..................................

    With these info.... how i can fill line M305 P1, something like this?

         M305 P1 R4700 T92000 B????; I could not measure B, reach 230 degrees
    

    Until now.... I am placing the value of B, for error test, I put a kitchen thermometer, in the heatblock, I assign a value to B, for example 3900, and I tell duet to heat up to 230 degrees, an average temperature that I usually use .. When Duet reaches 230 degrees, I look at the thermometer reading, and go up or below the value of B, depending on whether the thermometer reading is higher or lower than the Duet reading ....

    This system is error proof, and quite slow ...

    Is there any other method?

    Thank you





  • @aidar mmm... O think that these info, its usefull after o have ajusted thermistors... If Duet dont read the correct temperature... The autotunig its not usefull....

    Think



  • @peirof
    For fine tuning the thermistors the process you describe seems correct.

    1. Start with a approximately good setting; I just took the manufacturers rating, but one can look for examples online, or directly measure it as you did.
    2. Heat up until it stabilises; read the temp with a known good thermometer (I have a cooking thermometer one for this, I'm not actually sure of the 'good' part)
    3. Refine the settings (by educated guesswork based on the results), reboot, reheat and repeat until you get to the accuracy you want.

    I dont think there is any better method outside of proper lab with the appropriate test chambers etc. edit: I'm wrong; see below.

    At some point you have to decide your setup is 'accurate enough' and just get on with printing. In my experience there is no need to have uber-accuracy.


  • administrators

    Go to the RRF online configurator thermistors page, select custom thermistor. There you can enter 3 resistance vs temperature values.



  • the ones from the vulcano look like a B3950
    https://www.makeralot.com/download/Reprap-Hotend-Thermistor-NTC-3950-100K.pdf

    the normal ones appear to be a semitec 104-gt2
    https://www.mouser.de/datasheet/2/362/P18-NT-Thermistor-1535133.pdf (104NT-4 is a replacement thats suppose to have the same characteristics)



  • @dc42 in Heaters page? I cant see how put three resistance value... Ask for resistance at 25,B and C



  • 9e371b4c-8c1e-488c-9c80-10fb0a77d462-image.png



  • Hi.

    What its the fórmula, that transform measured resistente in to temperature...?

    I cant adjust temperature control... I hace try a lot of valours, and i d like see the fórmula, for know how affects variables


  • administrators

    @peirof, look up Steinhart-Hart thermistor model.



  • @dc42

    This Web... Can be used with Duet?

    Thermistor model


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