Bed heater PID

Deler

Hi,
I tried to find the answer to my question on the forum, but no luck.
I have silicon heater 220V controlled by SSR. Currently, it is working in Bang-bang mode. I want to use PID mode.
I have checked https://duet3d.dozuki.com/Wiki/Choosing_a_bed_heater#Section_Bed_heater_driven_using_a_Solid_State_Relay but it is not clear for me how to set PWM frequency to 10Hz.
can someone help me and tell me what parameters I need to use with M307

deckingman

@deler As long as you use B0 to disable bang bang mode, then the default PWM frequency for the bed heater (H0) is 10Hz so you don''t need specify. But for future reference, or if you use a heater other than H0, then use F10. It is documented here https://duet3d.dozuki.com/Wiki/Gcode#Section_M307_Set_or_report_heating_process_parameters

Deler

@deckingman Thank you. it is more clear now

Deler

Another question came to my mind, do I need to do any PID tuning? if yes how can I do that?

dc42

@deler said in Bed heater PID:

Another question came to my mind, do I need to do any PID tuning? if yes how can I do that?

Yes. Look up M303 on that same GCode wiki page.

Deler

@dc42 said in Bed heater PID:

@deler said in Bed heater PID:

Another question came to my mind, do I need to do any PID tuning? if yes how can I do that?

Yes. Look up M303 on that same GCode wiki page.

after the tunning, I got the following results
Heater 0 model: gain 207.8, time constant 143.4, dead time 4.4, max PWM 1.00, calibration voltage 12.2, mode PID, inverted no, frequency default

also, I got a warning: heater 0 appears to be over-powered. if left on at full power, its temperature is predicted to reach 232c.

is it normal?

deckingman

@deler said in Bed heater PID:

@dc42 said in Bed heater PID:

@deler said in Bed heater PID:

Another question came to my mind, do I need to do any PID tuning? if yes how can I do that?

Yes. Look up M303 on that same GCode wiki page.

after the tunning, I got the following results
Heater 0 model: gain 207.8, time constant 143.4, dead time 4.4, max PWM 1.00, calibration voltage 12.2, mode PID, inverted no, frequency default

also, I got a warning: heater 0 appears to be over-powered. if left on at full power, its temperature is predicted to reach 232c.

is it normal?

Yes. Head the warning and don't leave the printer unattended for lengthy periods of time. In the unlikely event that a Mosfet or your SSR failed closed, then your bed could reach a temperature of 232 deg C.

If you are concerened, then you can either use a lower powered heater or fit a thermal cut out switch.