How to get PID autotuned?

GaRv3 · 2 Jul 2018, 01:19

Hi,

I performed the PID autotune as described here: https://www.duet3d.com/wiki/Tuning_the_heater_temperature_control.

Unfortunately it does not seem to be very precise.
When heating up at the beginning, the hotend overshoots by more than 10°C.
When the part cooling fan kicks in after the first layer it usually drops more than 10°C below the set temperature. I even had a security shut down due to a "heater failure" which was probably only because of this, because the heater works just fine.
During the rest of the print it fluctuates between +/- 5°C off the set temperature.

The bed PID seems to be okay though (+/- 0.3°C).

Is there a way to have the autotuning run more cycles to improve repeatability?

number40fan · 7 Feb 2018, 04:30

Did you save the results with M500?

If so, do you have M501 at the bottom of your config.g file so that it can use the new settings you saved with the M500?

GaRv3 · 7 Feb 2018, 13:02

Well, I saved the settings using M500 and removed the existing M307 from my config.g but didn't load config-override.g with M501. To be honest, I thought config-override.g would be loaded automatically without calling M501.

Thank you for making this clear. I appended M501 to my config.g and will investigate if it works now.

GaRv3 · 2 Jul 2018, 14:31

I added M501 to the config.g and verified that the PID values are in config_override.g but the extruder heater still overshoots about 8°C when warming up.

And I got this again right after the fan kicked in:

Error: Heating fault on heater 1, temperature excursion exceeded 15.0°C
Resume-after-power-fail state saved

T3P3Tony · 7 Feb 2018, 14:38

try running the tuning with the part cooling fan on

GaRv3 · 7 Feb 2018, 15:34

Ok, I did this now.
Placed the nozzle some mm above the build plate and started the PID calibration with fan at 100%.

But some seconds after the second layer started and the fan kicked in:

Error: Heating fault on heater 1, temperature excursion exceeded 15.0°C
Resume-after-power-fail state saved

dc42 · 7 Feb 2018, 23:31

The fan is over-cooling the nozzle or the heater block. Here are some remedies:

1. Use M570 to increase the allowed temperature excursion. But this is treating the symptom rather than the cause.

2. Change your fan duct so that more air blows on the print and less on the nozzle and the heater block.

3. Put a silicone sock over the heater block.

GaRv3 · 14 Feb 2018, 09:54

I have lowered the fan duct even more and put a silicone sock over the heater block. Now I at least do not get errors any more.
Seems to be ok now.