Thermocouple Interference when motors are enabled

apiazza2010

Hello,

I am working with a rather large 3d printer. I'm running several thermocouple band heaters that I run back to the duet3d board. The run length is approx. 52 feet (16 meters). What I am experiencing now is that once I enable the motors on machine, the thermocouple reading go to 2000 (wire short). I tried the following to try and figure out where my problem is.

I run a separate wire, away from all components, from the duet3d to the thermocouple. If the band heaters are not installed (floating in the air), the thermocouple reading is correct and steady. Once the band heaters are touching the machine (as installed), the reading goes haywire. This only happens with the motors energized.

Is the issue my motors leaking noise into the system. is there a way for me to isolate them?
They are powered by a different power supply then the duet3d, and everything is grounded to the machine ground.

My understanding is that if my thermocouples weren't isolated properly, I would see a short on the MAX chip at all times, yet I only see it with the motors energized.
My other idea was noise picked up on the long length of the wire, but the installed wire and the free hanging wire away from the gantry show the same effect.

My other idea was to use a Expansion Board 3HC and connect all the thermocouple daughterboards there, and then run CAN back to the machine, but that was because my first ideas was noise in the long thermocouple leads.

Thank you for any help

apiazza2010

@apiazza2010

Forgot to mention I am running a Duet 3 6XD board and Teknic Stepper/Driver combos for everything else.

Thank you

apiazza2010

@apiazza2010 Another option is to go to back to AD8495 and run them in the analog temp inputs, and then create a custom curve.

I'm not sure if that will work, but I can try.

Thanks

dc42

@apiazza2010 said in Thermocouple Interference when motors are enabled:

My understanding is that if my thermocouples weren't isolated properly, I would see a short on the MAX chip at all times

Not necessarily.

Have you checked that there is no continuity between the thermocouple wires and the case of the thermocouple?

Have you grounded (to Duet VIN ground or similar) the hot end metalwork that the thermocouples and heaters are embedded in?

Which version of the thermocouple board do you have: the one with LEDs on it, or the earlier one?

apiazza2010

@dc42 Thank you so much for all the help.
The daughterboard i have is the one with the led's.

I have unfortunately found out that the thermocouples are indeed grounded type. I think this is where my problem lies.