Heater control

baird1fa

Hello, I'm using a duet 3 6HC for a rather strange application and I've run into an issue with the heater control.

I have an oven at work that is used for heating samples to 65C and also rock them back and forth. The original mechanism that was used for rocking them needed to be replaced with something that had more flexibility in the types of motion it could preform. So I decided that a stepper motor would be a better option than what was previously used. I tried to create a controller using an arduino but that just didn't work out. That is why I ended up with a duet in this application.

I'm running a single Nema 34 stepper with an external driver that I can use for speed and position control, and all that is working great, where I'm having issues is with the heater controller in the duet. I have run the auto tuner which takes about 10hours to run on this system and after wards I'm left with a temperature controller that overshoots and seems to maintain a 7-10 degree offset from the setpoint. I have had to then run the setpoint at 57C to maintain 65C. Would anyone be able to offer me some help with this?

3DPMicro

I havent dug into the Duet heater parameters but look at M304. You may have to manually adjust the PID. It's also possible it may error out (thermal runaway protection) if these values get too far out of range. The response rate is sluggish so you may try moving the probe closer to the heat source to help stability. Hopefully someone with a better understanding of the Duet heater control can chime in

Phaedrux

Can you tell us your firmware version and what values were generated with PID tuning? Are those values being loaded at startup?

baird1fa

@phaedrux

I'm using
Board: Duet 3 MB6HC (MB6HC)
DSF Version: 3.4.1
Firmware: RepRapFirmware for Duet 3 MB6HC 3.4.1 (2022-06-01)

and here are the heater parameters

; Heater model parameters
M307 H0 R0.032 K0.044:0.000 D1000.00 E1.35 S1.00 B0

These are in the config override.g and they are loaded at startup with the M501 command at the end of the config.g

Phaedrux

@baird1fa said in Heater control:

D1000.00

That seems like a very high dead time. Did you set it manually?

baird1fa

@phaedrux I was messing around with that because if I used the parameters that the system auto tuner calculated the Heater would fault because the temperature was rising too slowly and then give an expected value that was negative, and the actual value that was even more negative. I could try running the auto tuner again but it take 16 hours to complete on this system.