Beating gap sensor device for a refiner apparatus and calibration method

A method of calibration of a sensor device comprising a transducer, which is configured to generate a magnetic field, wherein the sensor device is configured to measure a beating gap between a first and a second refining disc of a refiner apparatus and is configured to be mounted in the first refining disc, wherein the sensor device comprises a magnetic pole, a coil assembly and a measuring head, which measuring head is configured to be set in a calibration position relative to the second refining disc for calibration of the sensor device in a calibration sequence, wherein the measuring head constitutes a portion of a sleeve arrangement in which the magnetic pole is accommodated, wherein the sleeve arrangement comprises the outer end comprising the non-magnetic material configured to abut the second refining disc for the calibration sequence, wherein a non-magnetic sleeve end of the sleeve arrangement forms a sleeve end surface facing a second grinding surface of the second refining disc, and wherein the non-magnetic sleeve end comprises stainless steel, and wherein the measuring head comprises an outer end made of a non-magnetic material configured to be positioned in abutment with the second refining disc in the calibration sequence, the method comprising:

• starting the calibration sequence;
• inducing an electric current into the coil assembly to generate a magnetic field around the magnetic pole for the calibration sequence;
• rotating the first and/or the second refiner disc about a rotary axis and moving them axially toward each other;
• and
• bringing the measuring head into abutment with the second refining disc for calibrating the sensor device.