APPARATUS FOR DETERMINING AT LEAST ONE STATUS VALUE OF ROTOR

PURPOSE: To detect the state quantity of a rotary body, for example, the temp. thereof by providing at least one surface region composed of a permanent magnet material on the rotary body and providing a Hall element so as to exert a magnetic field on its output voltage. CONSTITUTION: A ferrite magnet disc 3 is attached to the shaft 2 of a rotary body 1. A plurality of segments 6 are provided on the periphery of the disc 3 and the mutually adjacent segments 6 have different polarities. A Hall element 5 is provided in relation to the disc 3 and the output voltage UH of the element 5 cyclically receives the effect due to the magnetic field of the disc 3 during the rotation of the rotary body 1. For example, the output voltage UH (t) of the element 5 in the case of lower temp. T1 characterizing an initial state is larger than the output voltage in the case of higher temp. T2. This lowering of output voltage is caused by the weakening of a magnetic field at higher temp. Therefore, by comparing the difference output voltage of voltages Umax (T1), Umax (T2) with the corresponding stored characteristics, the temp. of the rotary body 1 is calculated.