Problem with fluctuation at high-ish temperatures

Avatar

By darookee 14 February 2017 15:43

Member · 49 comments

I'm trying out colorFab_XT which needs to be printed at around 240°C, until now I only needed about 220-225°C and these temperatures are stable.

When heating everything up the nozzle stays at 240°C but as soon as the print starts, the temperature will drop to 230-225°C. When pausing the print the temperature will recover after a short time and, when pausing the print long enough, will be stable throughout the rest of the print.

What can I do to get a stable temperature right from the beginning?

This is from my config{,-override}.g:

M305 P1 T100000 B4388 R4700 H0 L0
M307 H1 A244.3 C136.2 D12.3 S1.00 B0

The temperature drops with and without using a fan :-/

Avatar

By dc42 14 February 2017 16:38

Administrator · 2,297 comments

Your dead time value of 12.3 seconds is very high. Try 6 or 8 seconds. If the temperature starts oscillating, you've set it too low.


Duet WiFi hardware designer and firmware engineer
http://www.escher3d.com
https://miscsolutions.wordpress.com

Avatar

By darookee 14 February 2017 20:53

Member · 49 comments

Thanks! I set the dead time to 8 and started a print, it is now much more stable and drop much slower when the fan is turning on. May decreasing the dead time make it even more stable? Can I change the values while printing to test ist out?

The parameters of my M307 where written by M500 after successfully doing a PID tune - is there anything that may have gone wrong here?

Avatar

By dc42 14 February 2017 21:41

Administrator · 2,297 comments

The dead time measurement is the least accurate part of the PID tuning process. The value you get seems to vary somewhat with the M303 S parameter you use, which isn't right. So I'm looking at an improved way of measuring it in the next release.

Reducing the dead time further may help, but if you go too low then the temperature will oscillate. You can adjust it while you are printing, if you don't mind the possibility of ruining the print if it does oscillate..


Duet WiFi hardware designer and firmware engineer
http://www.escher3d.com
https://miscsolutions.wordpress.com