PT100 thermocouple with k8200

Discussion in 'General' started by Abrooksdavis, Apr 27, 2016.

  1. Abrooksdavis

    Abrooksdavis Member

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    Hi all. I have successfull wired up the PT100 thermocouple and amplifier board to my k8200 control board. I created a dedicated 5v out from the board for the amplifier and everything appears to work.

    I then modified the marlin firmware with the thermal tables associated with sensor 20 and updated configuration.h to reflect this.

    Im running into temperature issues however, as the thermocouple gives a reading of 34-35C at idle. This is about 10C too high. The 5v feeding the amplifier board has been confirmed as a stable 5v incase anyone was wondering.

    Since E3D states that the sensor 20 table will give accurate temperature curves for the PT100 thermocouple I do not understand why I am getting an incorrect temperature reading.

    Can anyone please advise?

    Regards
     
  2. paulandrews

    paulandrews New Member

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    From John Shanahan (Owner of Pyrosales) says:
    My suspicion is that he may have a 2 wire devices, so he is not compensating for the leadwire resistance which adds to the resistance of the PT100

     
  3. DarKHawK

    DarKHawK New Member

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    There is a 4.7k resistor and a capacitor that stop this working, there is no successful way to modify thermistortables.h with these. I unsoldered cap and resistor and it works perfectly using sensor 20 in thermistortables.h, obviously doing this means you need to add a 4.7k pullup resistor to standard sensor if you want to go back (or replace cap and resistor if you have the skill.)
     

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