Rotating Magnet Filament Monitor

Rotating Magnet Filament Monitor

It accurately monitors filament movement and takes appropriate action in case of extrusion issues like filament run out, extruder skipping steps, etc.


The Duet3D Rotating Magnet Filament Monitor accurately senses filament movement. Connect it to a Duet 2 or Duet 3, and the controller will use the indicated movement to determine a wide range of extrusion issues, including:

  • Filament run out
  • Extruder skipping steps
  • Nozzle starting to jam (causing skipped steps or grinding)
  • Filament beginning to grind in the extruder

It does this so accurately because it is effectively an extruder in reverse. The filament movement rotates a custom machined hobbed magnet assembly; the magnet rotation is sensed and constantly reported to the Duet. This method has proven highly accurate across a wide range of filaments – frequently capable of pausing the print before a filament jam or other issues have already caused the print to fail.

Assembled Only

The monitor is only available wholly assembled and tested at this stage. However, Duet may offer it as a kit in the future.

It comes with a connector pack with the Molex-KK-style housings and crimps to connect the monitor to the Duet.


The filament monitor is easy to set up and calibrate to your filament: Setting up the rotating magnet filament monitor.