Thermocouple breakout notes



  • I ordered the optional thermocouple breakout and just wanted to share notes that ended up in the Delta google group so they are here for Beta users. Thanks to David for posting the information so the real credit goes to him.

    David Crocker
    When you connect your thermocouple, if it has the usual white and green wires then the white one goes into the left hand terminal as you look into the terminal block from the wires. The thermocouple terminals labelled 1 are channel 100, so you need M305 P1 X100 in config.g to associate that thermocouple with heater 1, in place of the standard M305 P1 command.

    I'll try to post some pictures and a larger guide on this soon. For me, I think additional information is also good to share like theory of thermocouple operation, key install and wiring points, special emphasis on understanding cold junction details, as well as the super critical thermal connection but electrical isolation required at the sensing end.
    Far too often we see beginner users make massive mistakes and blow up entire boards and systems because of lack of understanding of these key issues.

    Also, the knowledge that the typical thermocouple requires no calibration if implemented correctly. Compared to a thermistor, you aren't worried about BETA values and other issues and tables. A K type thermocouple can be as accurate as 3C plus or minus between any 2 printers with zero calibration by the user. But it means following the rules.


  • administrators

    Thanks, Jeyguy. The notes at http://reprap.org/wiki/Using_thermocouples_with_the_Duet_and_RepRapFirmware may also be useful, although of course the wiring is much simpler using the daughter board.

    For anyone else thinking of trying a thermocouple, E3D now sells an insulated and encapsulated one that is the same size as their PT100 sensor. So it fits the modified E3Dv6 heater block that they also sell.


  • administrators

    For the benefit of others who come across this thread, there are now up to date instructions for wiring thermocouples and using the daughter board at https://duet3d.com/wiki/Connecting_thermocouples.



  • For using them (pt100) since one week i can just say great ! Really easy to plug and setup.


 

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