Patent ID: 6850054

Claim:
A device for non-contacting sensing of the rotational state of a rotor, that is, at least one of the states rotational position, rotational direction, rotational path covered, and rotational speed, wherein the rotor ( 1 , 10 ) has an end surface ( 1 a + 1 b ) ( 1 e + 1 f ) facing in an axial direction or, alternatively, a part of an envelope surface ( 1 c + 1 d ) facing in an axial up to a radial direction, divided around a rotational turn into an electrically conductive part ( 1 a , 1 c , 1 e ) and an electrically non-conductive part ( 1 b , 1 d , 1 f ), the central angles of said two parts around the axis of rotation of the rotor together comprising 360°, and wherein the device comprises three electric coils ( 2 a , 2 b , 2 c ) stationarily attached close to and with the axes of the coils directed towards the rotational path of the conductive part of the rotor, preferably directed perpendicular to the surface plane of the conductive part of the rotor, which coils ( 2 ) are each electrically connected to a capacitor ( 3 ) for forming a closed parallel resonant circuit 4 , where the resonant circuits of the three coils are connected to a pulse member for starting resonant oscillations as well as to an electronic circuit which may evaluate and present the selected data of the rotational state, and wherein further the conductive part and the non-conductive part of the rotor each occupy a central angle within the range 180°±50°, preferably both 180°, and the three coils are so placed that the sum of the two smallest central angles between them exceeds, by at least 10°, the largest of the two central angles which are occupied by the conductive and non-conductive parts of the rotor, respectively, the coils being preferably uniformly distributed with all three central angles between them amounting to 120°, whereby, in all the rotational positions of the rotor, at least one resonant circuit is damped to a maximum extent and at least one resonant circuit is damped to a minimum extent, characterized in that the electric circuit for each of the pairs of coil ( 2 ) and capacitor ( 3 ), which shall form each of the parallel resonant circuits ( 4 ), in its non-working condition, when no resonant oscillations are to take place in it, is configured as an open circuit, and that it comprises a means ( 6 ), which is constructed to close the circuit into a functioning closed parallel resonant circuit, when a resonant oscillation is to be started in this circuit, and to break this circuit again into an open circuit, when resonant oscillations shall no longer take place in this circuit, wherein each of the resonant circuits ( 4 ) provides measurements used in calculations to compensate for variations in the distance between the respective coil ( 2 ) and the rotational path of the conductive part of the rotor ( 1 c ) for clearance in the bearing of the rotor.