A refiner for beating a raw material supplied between a stator beating part and a rotor beating part, and discharging the beaten raw material, the refiner including a rotating shaft, the rotor beating part attached to the rotating shaft, a motor configured to drive the rotating shaft; and a motor control part configured to variably control a rotation of the motor. The rotation of the motor of the rotor beating part is controlled by the motor control part to beat the raw material.

A measurement system for monitoring a gap adjustment mechanism of a processing device which has oppositely positioned processing elements with a gap between them. The measurement system has a first measuring device to measure information describing a position of that processing element which is moved by at least one actuating unit of the gap adjustment mechanism for adjusting the size of the gap, and at least one second measuring device to measure information describing a position of the at least one actuating unit. The measurement system has a data processing device configurable to determine the condition of the gap adjustment mechanism based on the information describing the position of the processing element and the information describing the position of the at least one actuating unit. Additionally, a method for monitoring a condition of a gap adjustment mechanism of a processing device.