Patent ID: 7370540

Claim:
Rotation angle sensor, in particular for an electrical steering system of an industrial truck, comprising: two magnetic field sensor elements, a permanent magnet, a shaft, an evaluation unit, and a voltage monitoring unit, wherein: the two magnetic field sensitive sensor elements are arranged on orthogonal axes and the permanent magnet is attached to the shaft extending through the axis intersection point and the output signals X, Y of the sensor elements are given to the evaluation unit, which determines from the two output signals X, Y the rotation angle value by means of a function saved in the evaluation unit, characterized in that for a plurality of predetermined values of one of the output signals X or Y associated ideal values calculated from the geometrical relationship of the sensors ( 1 , 2 ) of the other output signal Y, X are saved in the evaluation unit ( 10 ), the measured values of the other output signal Y, X are compared with the ideal values and a warning or stop signal is created if the difference between the measured and ideal value reaches a predetermined amount, the voltage monitoring unit is connected to the output of each of the sensor elements, which determines whether the voltage supply adjacent to the sensor elements lies within a predetermined voltage band and the output of a sensor element is set to the zero potential if the supply voltage of the sensor element lies outside the predetermined voltage band.