Duet3D Magnetic Filament Monitor Drifting Sensitivity



  • I've been using the Rotating Magnet Version of the Duet3D Filament Monitor for a few months with no real issues after initial tuning. My g-code is configure for a sensitivity of 24.90 mm / rev. (M591 D0 P3 C3 S1 R10:150 L24.90 E10.0) I've recently enclosed the printed that the monitor is installed on and now I'm getting multiple "too little movement" alarms during prints. The enclosure is definitely a lot warmed than when it was open, but i'm seeing measured sensitivity going from 25.2 to 29.9 mm / rev over 700-800 mm of filament . I don't think that thermal expansion of the wheel would be that dramatic. Any ideas where I should start troubleshooting? Thanks.



  • Maybe something to look for, how good is your hotend cooling fan? I use a MFM also and had issues with the standard mosquito cooling fan as too much heat in the cool side of the hotend was causing the filament to soften, bunch up and prevent proper extrusion.



  • I am also using a standard mosquito cooling fan. What did you replace it with?



  • @evan000 40mm fan, made a simple adapter.


  • administrators

    @evan000 how hot is the filament monitor board and enclosure getting?



  • @T3P3Tony The ambient temperature inside the enclosure is 37.7C (99.8F). The monitor PCB is 45.4C(113.8F). @mwolter The mosquito heat sink is at 62.5C (144.5F) with the fan at full. I'll give your fan mod a try. Thanks for that.



  • Ran a 12 hour print with the enclosure open and temperatures near the filament monitor reached 88F, and I had no issues. The ATTiny44a and the AS5601 on the monitor are both rated to 85C and 125C respectively. The temperatures I saw before are well with in the spec'd ranges. Might be that I have a bad board in the monitor or a bad connection in the wiring. Does the filament monitor board have a diagnostic mode?



  • Might be able to help as I ran into a similar issue with the magnetic filament monitor on a printer in an enclosure.

    The TL;DR is to make sure you have ample cooling (large enough fan) for the hot end heat sink.

    No matter what I did the MFM would report minimum extrusion errors and occasionally the filament would strip and the print would fail. Examining the filament would show the filament was collapsing itself on the cold side of the hot end. This was with a slice mosquito and the stock 35mm fan. Mounted a 40mm fan with an adapter and all the issues went away. Now the MFM shows within 75% to 125% when the enclosure is at 65c.

    So to break it down, it’s possible the MFM is right and it’s indicating a blockage.


  • administrators

    @evan000 itd does not have a diagnostic mode but reports some diagnostic information back to the Duet in every communication so when you run M591 you get to see the AGC value which indicates how well the hall effect sensor is reading the magnet. What is yours reporting when its working well, and what is it reporting when its having issues?



  • Been a crazy few weeks since I had an update on this issue. I gave the monitor unit a through check and it was fine. No issue with the magnet or the hall effect sensor. Turns out the issue was the extruder stepper motor. It was skipping steps here and there which caused the error buildup. Replaced the motor and just completed a 32 hour print with no issues. The filament monitor was performing correctly the whole time. Lesson learned for me, but I hope this helps anyone else having a similar issue. Thanks for the suggestions and the time.


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