@OwenD We're doing a university WAAM research project, where there is some variation in settings during the print, and unfortunately we got no say in welder choice, so we're stuck with what we've got. For the most part the goal involves modifying the power supply, so our current welder gets the job done. Unfortunately I have not yet been able to find any welders that are able to do what we need them to do either. Apologies for being vague, there are details of the design I can't post on here.

Good find on the current sensor, I've been trying to look for hall effect sensors but I think I need to work on my googling!

I hadn't considered the signal noise yet. The noise is going to make it quite difficult to control, but I'll cross that bridge when I get to it with some kind of filtering. It will be easier to design once I see a waveform on a screen.
Why do you say unless welding quite large pieces? Is that in relation to the welding current? or the duty cycle of the welder?

@OwenD Thanks for the response! The M951 command looks like exactly the one. We want to control the current through the voltage without adjusting the height. We've designed a current limiter board, but we want to implement a closed loop controller on the gate voltage to adjust the current.
Goal is: put a voltage on the gate of a power transistor through a custom gate driver, pass the ground wire through a current transformer, transform that current to a voltage to read into the duet. Use that voltage and compare it to the expected voltage (therefore the current), and use a closed loop controller to adjust the gate voltage until the desired welding current is achieved.
Unsure about the electronics for now - there are a few potential solutions in the works. The key thing is to figure out whether we can implement a PID controller on the duet or whether it would require an external board. It says the default sample and correction frequency is 5Hz - do you know what the maximum frequency for this is?

Is it possible to set up a custom PID controller on the duet board? I know that you can run a heater PID but I want to control a custom power supply board, which is used to control the power supply of a MIG welder with a current feedback loop, and want to apply a PID on it. Is this possible directly on the duet or do I have to use an external controller?

also that screenshot was taken almost immediately after turning the board on, the readings have since gone up another degree or two which I presume is down to the board heating up, but that implies that the original issue isn't that it is picking up heat from the board

@dc42 thanks for the suggestion!
I connected wire links to both ports and they both gave readings. Previously the wire link hadn't worked so not sure what happened there!

They both gave readings still significantly above the true room temperature of the house (the thermistors are accurate based on other temp readings from my other printer etc)
These are similar readings to what I am getting from the thermocouple itself so not sure what is to blame!

Hmm
Thanks for the detailed explanation!
I have made sure that the wires are properly in the daughterboard ports and it didn't seem to change anything so I think they must have been fine before.

It sounds like my daughterboard may potentially be broken, as it sounds like a wire link should work!

Is there any way to test the daughterboard to see if it is the problem?

@OwenD thanks!
I actually ended up looking through the object model and finding that it stores the last message as an option

so I put into the resume part of the daemon.g that it should only resume if the last message to have been written was to say that the printer is too hot! then if that is true and its cold enough, it resumes the print and posts a new message (so that the last message changes again)

here is my final code:

;daemon.g

if (sensors.analog[1].lastReading > 25) && (state.status=="processing");when temp0 goes above 20 degrees and a print is in progress
		M117 "The right head is too hot! Starting Cooldown" ;write message
		M25 ;pause Print
		
if (sensors.analog[1].lastReading < 20) && (state.displayMessage == "The right head is too hot! Starting Cooldown") && (state.status == "paused") ;if the status is paused, the temp is below 20 and the last message was from the overheating command
	M117 "Cooldown Complete - Print Resumed" ; write message
	M24 ; resume print

Thanks for the help!

@OwenD that could work
variables aren't an option in this code yet if I'm not wrong, but potentially could you use one of the unused items in the object model as a replacement variable and switch it according to what was being done?

@T3P3Tony that makes sense. I think I just saw it online so very easily could have misunderstood! Unfortunately I don't. It may be a case of ordering a new thermocouple to identify the issue!

@T3P3Tony
It is less severe than it was for some reason. but it is now around 5 degrees out which is still pretty far out! I agree it is very strange.
I tried switching to the other thermocouple port and it is the same. What is the best way to test the port? I tried connecting a direct wire link, which apparently should give a room temp reading I think I read but it output 2000 degrees error

Unfortunately I don't have another thermocouple on hand to test!