Magnetic Sensor Declining percentage



  • I just received a replacement PCB with firmware v3 and I'm still having issues of a declining min percentage until I get a false trigger.
    I have a Duet Wifi running RP 2.05.1 and a Duet Magnetic Filament sensor 1.7a firmware v3.
    M591 D0 P3 C3 S1 R10:130 L24.5 E3.0
    It's mounted above a Titan Aero on a Modix Big 60 V3.

    It starts with a min 98% and goes down over time until it hits the minimum which I have set to 10%. If I hit pause and resume it resets back to 98%, It seems to do fine for the first hour and then progressively gets worse. Here is a snippet of what's happening. Notice some of the lines have the same measurements but the percentage still drops. Nothing is clogged or slipping. It prints great.

    8/10/2020, 4:29:44 PM: M591 D0: Duet3D magnetic filament monitor on input 3, enabled, sensitivity 24.50mm/rev, allow 10% to 130%, check every 3.0mm, version 3, mag 132 agc 88, measured sensitivity 24.37mm/rev, min 99% max 103% over 21.1mm
    8/10/2020, 4:30:04 PM: M591 D0: Duet3D magnetic filament monitor on input 3, enabled, sensitivity 24.50mm/rev, allow 10% to 130%, check every 3.0mm, version 3, mag 132 agc 88, measured sensitivity 24.42mm/rev, min 97% max 103% over 57.3mm
    8/10/2020, 4:30:51 PM: M591 D0: Duet3D magnetic filament monitor on input 3, enabled, sensitivity 24.50mm/rev, allow 10% to 130%, check every 3.0mm, version 3, mag 130 agc 88, measured sensitivity 24.44mm/rev, min 92% max 104% over 204.8mm
    8/10/2020, 4:53:31 PM: M591 D0: Duet3D magnetic filament monitor on input 3, enabled, sensitivity 24.50mm/rev, allow 10% to 130%, check every 3.0mm, version 3, mag 130 agc 88, measured sensitivity 24.44mm/rev, min 60% max 106% over 3796.2mm
    8/10/2020, 5:23:40 PM: M591 D0: Duet3D magnetic filament monitor on input 3, enabled, sensitivity 24.50mm/rev, allow 10% to 130%, check every 3.0mm, version 3, mag 130 agc 88, measured sensitivity 24.45mm/rev, min 60% max 106% over 8589.7mm
    8/10/2020, 5:47:32 PM: M591 D0: Duet3D magnetic filament monitor on input 3, enabled, sensitivity 24.50mm/rev, allow 10% to 130%, check every 3.0mm, version 3, mag 130 agc 88, measured sensitivity 24.46mm/rev, min 34% max 106% over 12391.9mm


  • Moderator

    @chickenwoman Can you post a picture of how the sensor is mounted on the Titan Aero? Is it just hanging on the Bowden tube, ie the sensor isn't physically mounted itself? Could the Bowden tube be loose in either the sensor or extruder? Do you use large retractions or pressure advance?

    It's possible that the sensor is actually showing an issue with extrusion, and that the filament is slipping (what filament are you printing?) or the extruder is skipping steps (particularly if using PA and your settings are too much for the motor). The only way I can think of to actually test this is to run a print with the hot end disconnected from the extruder, so the extruder is pushing filament through with no resistance. I think that would show if the sensor is reading correctly, though may not account for extruder motor skipping.

    Ian



  • I guess I don't understand how the sensor works. Is it measuring the total percentage loss from the start of the print to the end or does it measure when movement slows down but resets when it speeds back up? I don't understand how these two lines can read the same measurement but have two different percentage.

    8/10/2020, 4:30:51 PM: M591 D0: Duet3D magnetic filament monitor on input 3, enabled, sensitivity 24.50mm/rev, allow 10% to 130%, check every 3.0mm, version 3, mag 130 agc 88, measured sensitivity 24.44mm/rev, min 92% max 104% over 204.8mm
    8/10/2020, 4:53:31 PM: M591 D0: Duet3D magnetic filament monitor on input 3, enabled, sensitivity 24.50mm/rev, allow 10% to 130%, check every 3.0mm, version 3, mag 130 agc 88, measured sensitivity 24.44mm/rev, min 60% max 106% over 3796.2mm

    The sensor isn't physically mounted but the tube from the sensor fits tightly into the Titan and the tube that feeds the filament is mounted above. I don't see any signs of the tube moving during retraction. My retractions are 2mm and I'm using a .6 nozzle on a volcano. The Titan is a geared so I don't think it's missing steps. My prints are smooth with no signs of over under extrusion.IMG_3401 (1).JPG


  • administrators

    @chickenwoman said in Magnetic Sensor Declining percentage:

    does it measure when movement slows down but resets when it speeds back up

    It measures the detected movement and compares it with the commanded movement every 3mm. When you send M591 Dn it reports the minimum and maximum deviations seen to that point in the print.

    So in your case it looks like the minimum deviation gets worse over time. If nothing is physically slipping that effects print quality over a long print then it might be that the idler pressure is insufficient to ensure the filament does not slip on the hob internal to the filament monitor. Is it possible to access the back of the filament monitor so you can mark a line on the hob/case as a reference. (say vertically). then you can try moving the filament a known distance back and forwards through the monitor to see if you can generate slips


  • Moderator

    As this is a Titan Aero, have you checked the bearings on the large gear? They are notorious for failing and causing odd extrusion issues.



  • Sorry about taking so long to respond. So I think it may be slipping in the sensor. I've been experimenting with different filaments, they all have the same issue but the slicker ones are worse. What would you recommend doing next?


  • administrators

    @chickenwoman is it possible to confirm this using this method:

    access the back of the filament monitor so you can mark a line on the hob/case as a reference. (say vertically). then you can try moving the filament a known distance back and forwards through the monitor to see if you can generate slips


Log in to reply