Patent ID: 7024924

Claim:
A forage harvester with a chopping drum rotating about an axis and carrying a plurality of chopping blades, the forage harvester having means for feeding crop material across a counterblade mounted on a counterblade support and cooperating with the chopping blades to define a cutting gap and to cut the crop material into relatively short lengths as it passes across the gap, a sensor mounted at a protected location on one of the bottom of the counterblade and the rear of the counterblade and the counterblade support, the sensor operable to measure a parameter of oscillation of the counterblade, the sensor connected to a processing device which is operable to perform the steps of: a. making at least two measurements of the parameter of oscillation induced in said counterblade; b. comparing integrals of said parameter of oscillation at least two frequency bands of the measured signal or its maximum value for each of said two measurements, and; c. evaluating a change between said two measurements.