This value is called the extrusion multiplier, and its determination is what the thickness sensor is all about. So all the filament sensor does is measure the filament’s current diameter.

The full test rig has a motor-driven feed and takeup spools, and three sensors measuring across the filament in three different spots around the radius; the measurements are averaged together to ...

The feature we're going to talk about is the filament runout sensor. As you might imagine, this sensor tells the printer when it runs out of filament.