Magnetic Filament Monitor measured sensitivity?

ShreddinPB

Hey guys, Im running a Duet 3 mini 5+ and have just added magnetic filament monitors to my extruders. I am trying to calibrate them and am getting very large numbers on the measured sensitivity.
My board is this
Board: Duet 3 Mini 5+ (Mini5plus)
Firmware: RepRapFirmware for Duet 3 Mini 5+ 3.2.2 (2021-02-11)
Duet WiFi Server Version: 1.25
This is whats in my config.g for setup, towards the end of the file
M591 D0 P3 C"io1.in" S1
M591 D1 P3 C"io2.in" S1

I started an hour print with the monitor deactivated to get the values since it would pause right away every time with the default values. After the print the monitor reports this:
Duet3D rotating magnet filament monitor v3 on pin io1.in, disabled, sensitivity 28.80mm/rev, allow 60% to 160%, check every 3.0mm, version 3, mag 129 agc 67, measured sensitivity 69621.64mm/rev, min -2188% max 11019% over 2583.6mm

I updated the config to include the other paramaters from the setup page
M591 D0 P3 C"io1.in" S1 R70:130 L24.8 E3.0
M591 D1 P3 C"io2.in" S1 R70:130 L24.8 E3.0

and now I am getting this..
Duet3D rotating magnet filament monitor v3 on pin io1.in, disabled, sensitivity 24.80mm/rev, allow 70% to 130%, check every 3.0mm, version 3, mag 128 agc 67, measured sensitivity -905650.31mm/rev, min 26701% max -28193% over 884.4mm

Whats going on here?
Thanks!

ShreddinPB

After the print finished in 48 minutes it reports this
Duet3D rotating magnet filament monitor v3 on pin io1.in, disabled, sensitivity 24.80mm/rev, allow 70% to 130%, check every 3.0mm, version 3, mag 129 agc 67, measured sensitivity -2657692.25mm/rev, min 78355% max -82735% over 2595.4mm

alankilian

@shreddinpb VERY strange readings there.

The one thing I see from your report is that the AGC value of 67 is below the minimum AGC value of 85 listed HERE.

To make sure the sensor is measuring correctly, check the 'mag' and 'agc' values in 
the M591 report for the magnetic sensor. 'agc' is automatic gain control, used to 
bring the signal magnitude from the Hall sensor in range. The maximum value 
available is 128. 'mag' is the magnitude of the signal from the Hall sensor element, 
after applying agc. Under normal conditions, 'agc' should be in the range 85 to 105 
and 'mag' won't change much. So 'mag' is less useful than 'agc'.

This would say your magnet is too close to your sensor and you should add a little shim like a few layers of paper between the circuitboard and the housing.

T3P3Tony

@alankilian 67 is fine, especially for the new version of the sensors. I will update the docs to mention that.

T3P3Tony

@shreddinpb how is the sensor mounted and can you confirm that the magnet assembly rotates freely when you move some filament through the sensor by hand (it can help to make a small mark on the back so it can be observed easily).

ShreddinPB

@t3p3tony They are both pretty close to the input side of the extruder, like 15mm. It does look like the magnet is not rotating, I put a sharpie mark on the exposed part of the shaft and push filament thru and it doesnt appear to rotate that shaft.. so I will take it apart and see whats going on.

ShreddinPB

@t3p3tony SO I had printed the pieces with my resin printer since its much more accurate than my fdm for small parts. It looked to me like the filament hole was so tight that it didnt allow the filament to be pushed by the spring loaded bearing and make good contact with the encoder wheel. I slightly drilled out the filament hole and that helped a lot but was still skipping some. I tried drilling the hole a little bigger and the filament guides shattered, resing cant be drilled as easily as PLA
On the gtihub there is only STLs of those parts that I see, does anyone have the source cad files so I could easily just enlarge the hole in cad and print a new one?

Nurgelrot

@shreddinpb had the same issue with mine initially. I ran a lot of PC/CF filament trough it that seems to have worn it in. The hole diameter as least for mine was only very slightly off. So if you make a new model that would be great but it doesn't have to much larger at all.

ShreddinPB

@t3p3tony Ok, I made my own and it seems to work now Here are my current values:
Duet3D rotating magnet filament monitor v3 on pin io1.in, disabled, sensitivity 24.80mm/rev, allow 70% to 130%, check every 3.0mm, version 3, mag 132 agc 62, measured sensitivity 24.92mm/rev, min 94% max 107% over 832.1mm

I enlarged the filament hole a little bit and smoothed out some edges for it so it cant get caught on any sharp edges, feeds easy and seems to allow the filament to bend a little to contact the encoder teeth better. I will share the Fusion 360 file and STL if you guys want it.

T3P3Tony

@shreddinpb please do share the files, thanks!

ShreddinPB

@t3p3tony
STL is uploaded to this site, I couldnt upload the fusion file as its not in the allowed file upload filter, I also didnt see zips allowed so I have a link to it on my drop box.

MFS_newBase.stl

https://www.dropbox.com/s/9e47vm6t26r3db4/MFS_newBase.f3d?dl=0