Any way to offset PT100 temp setting beside running more wires?



  • I've just installed an E3D PT100 and using their supplied wires, unfortunately the temp reading is around 8degrees higher than my bed thermistor at room temp.

    Is there any way to correct temp reading without running extra wires?


  • administrators

    Use thicker wires?

    To get an error of 8C you must have about 3 ohms resistance in the connections to the PT100. Perhaps you have a bad connection?



  • The offset feature is a great idea, I've taken to measuring the nozzle temp with K type thermocouple probe and thermal paste and using the offset to adjust to real nozzle temp.



  • @dc42 I've changed over to a different PT100 and am still getting a high (but lower reading), would it be possible to add an offset feature?



  • Its already there Brian add an R parameter to M305 for that pt100 which is the series resistor value, this effectively offsets it. I've been measuring nozzle temp then adjusting it on the fly to match:

    M305 P1 X201 R400 ; temp channel config, heater 1, PT100 sensor 2, offset

    A higher R value will raise the indicated temp, a lower one will lower it. Only small adjustments are necessary.


  • administrators

    If the error is caused by the PT100 resistance being out of tolerance (i.e. a bit more than 100 ohms), then adjusting the R parameter will correct for it - but it suggests you are using a very low-quality PT100 sensor. However, if the error is caused by additional resistance in your wiring or connectors, then correcting it using the R parameter will cause the PT100 to under-read somewhat at higher temperatures.



  • I bought one from Precision Piezo and it seems to be measuing the same value as my bed so i'm happy.

    DjDemonD I don't suppose you sell even longer ones? I need roughly 100mm more. Very large corexy build.

    dc42, shouldn't there be a leg/support/standoff with the daughter board? It seems a little fragile unsupported…



  • @totalitarian:

    dc42, shouldn't there be a leg/support/standoff with the daughter board? It seems a little fragile unsupported…

    Doesn't it come with a little plastic standoff that snaps into the hole on the daughter board and hole on the duet board? (My thermocouple daughter board came with something like this.)



  • @totalitarian:

    I bought one from Precision Piezo and it seems to be measuing the same value as my bed so i'm happy.

    DjDemonD I don't suppose you sell even longer ones? I need roughly 100mm more. Very large corexy build.

    dc42, shouldn't there be a leg/support/standoff with the daughter board? It seems a little fragile unsupported…

    I don't do a longer lead version but make a linesman's splice joint and solder it, with good quality wire and you can extend it. You can always compensate it a little using the R parameter as above.


  • administrators

    @totalitarian:

    dc42, shouldn't there be a leg/support/standoff with the daughter board? It seems a little fragile unsupported…

    Yes, a plastic standoff is included with each daughter board.



  • @DjDemonD:

    @totalitarian:

    I bought one from Precision Piezo and it seems to be measuing the same value as my bed so i'm happy.

    DjDemonD I don't suppose you sell even longer ones? I need roughly 100mm more. Very large corexy build.

    dc42, shouldn't there be a leg/support/standoff with the daughter board? It seems a little fragile unsupported…

    I don't do a longer lead version but make a linesman's splice joint and solder it, with good quality wire and you can extend it. You can always compensate it a little using the R parameter as above.

    Thanks, i'll give that a go.



  • @dc42:

    @totalitarian:

    dc42, shouldn't there be a leg/support/standoff with the daughter board? It seems a little fragile unsupported…

    Yes, a plastic standoff is included with each daughter board.

    I'll have to take a look, I never noticed a standoff with mine.


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