Is there a way to adjust the overshoot temp limit of bed heater?



  • I Guys, I just wanted to know if there is a way to adjust the over temp limit for the bed heater? I use a 3/8 inch thick cast aluminum platten that's about 144 square inches. I think bang bang may be the way to go as autotune sets it up with PWM that takes forever to get to 60c. Bang Bang will get me there in about 2 1/2 min, however, overshoots about 17 degrees and faults. I really don't care so much about the overshoot and it does settle in OK. Any other ideas for setting to try in my special case?

    Thanks for the help!

    Werner


  • administrators

    So you can change the amount of overshoot that is allowed, and the length of time it is allowed for by using:

    https://duet3d.com/wiki/G-code#M570:_Configure_heater_fault_detection

    e.g.
    [c]M570 H0 P20 T25[/c]

    This will allow a 20 second excursion of 25C.

    Also you may be able to improve on the PID parameters generated so you get a better response but still have the more stable temperature benefits of PID check out:

    https://duet3d.com/wiki/Tuning_the_heater_temperature_control#Setting_the_model_parameters_manually



  • Thank so much for the great info Tony!! I really appreciate it! I am giving this another go today and will let you know how it turns out!

    Have a great day!

    Werner



  • Hi Guys, I spent today playing with my PID settings but not having much luck. First thing is if I try to use autotune for PID my system will initiate with heater on and then error out with "Auto tune canceled because temperature is not increasing" After messing around with it a while I was able to get it to run by manually turning on the bed heat for a minutes then shutting off and immediately running the autotune. however, the values are still way off with overruns of 20c+? The other thing is when I cycle my power for the printer it sets all my setting back to a default and bang-bang and that is after trying to save with M500?

    Any clues or ideas are greatly appreciated!

    Thanks for the help!

    Werner



  • For the last bit you need to put M501 at the end of your config.g to load what is saved from M500.


  • administrators

    Which firmware version are you using? The auto tune algorithm changed at version 1.18.



  • @Werner:

    Hi Guys, I spent today playing with my PID settings but not having much luck. First thing is if I try to use autotune for PID my system will initiate with heater on and then error out with "Auto tune canceled because temperature is not increasing" After messing around with it a while I was able to get it to run by manually turning on the bed heat for a minutes then shutting off and immediately running the autotune. however, the values are still way off with overruns of 20c+? The other thing is when I cycle my power for the printer it sets all my setting back to a default and bang-bang and that is after trying to save with M500?

    Any clues or ideas are greatly appreciated!

    Thanks for the help!

    Werner

    I was getting the same error trying to tune my bed. I think the default PWM of .5 is too low. Once I set the PWM higher, I could get the bed auto tune to run.


  • administrators

    @Werner:

    Hi Guys, I spent today playing with my PID settings but not having much luck. First thing is if I try to use autotune for PID my system will initiate with heater on and then error out with "Auto tune canceled because temperature is not increasing" After messing around with it a while I was able to get it to run by manually turning on the bed heat for a minutes then shutting off and immediately running the autotune. however, the values are still way off with overruns of 20c+? The other thing is when I cycle my power for the printer it sets all my setting back to a default and bang-bang and that is after trying to save with M500?

    Any clues or ideas are greatly appreciated!

    Thanks for the help!

    Werner

    It's already covered on the wiki at https://duet3d.com/wiki/Spurious_heater_faults_and_how_to_avoid_them#Faults_when_tuning.


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