Patent ID: 8203717

Claim:
A sensor for the determination of the rotational speed of a shaft ( 16 ), the sensor having a stationary part ( 20 ) and a part ( 22 ) co-rotating with the shaft ( 16 ), wherein the stationary part ( 20 ) has a laser light source ( 24 ), a first optical coupler ( 26 ), an optical detector ( 28 ) and an evaluation unit ( 30 ) which determines the rotational speed from the detector signals and the rotating part ( 22 ) has a light guide coil ( 32 ) which is rotationally fixedly connected to the shaft ( 16 ) and is wound concentrically to the shaft ( 16 ) with the ends ( 34 and 36 ) of the light guide coil ( 32 ) being guided to an end face so that, on the one hand, the light ( 40 ) of the light source ( 24 ) can be coupled into both ends ( 34 and 36 ) and two light components run around in opposite directions in the light guide coil ( 32 ) and, on the other hand, the light components can be decoupled from the to ends ( 34 and 36 ) for the superimposition of the light components on the detector ( 28 ) so that, on a rotation of the shaft ( 16 ), the detector signals can be detected while exploiting the Sagnac effect from the phase shift of the two light components running around in opposite directions which is dependent on the rotational speed, wherein a stationary reference light guide coil ( 123 ) is provided into which light can likewise be coupled for the obtaining of light components running around in opposite senses and these light components can be detected superimposed on a reference detector ( 128 ) so that the evaluation unit ( 30 ) can determine the rotational speed while taking account of the reference detector signals.