A forage harvester has an engine which is drivingly connected to a chopper cylinder via first drive belt, and to a first end of a drive shaft of a discharge accelerator. A method, in another embodiment, comprises creating an indentation in a protective coating of a magnetic head, the indentation having a dimension that, when the protective coating wears, is indicative of an amount of wear of the protective coating. Presence of gas in the fluid is determined from the velocity. The particle counter measures the number of particles contained in the liquid discharged from the collector with the series of liquid inputoutput operations.