22 and is attached by means of driver pins 36 at the shaft side coupling element 28 a reflective vane 38 in the form of a circular disc out of which an angular segment has been cut out is arranged coaxicily under the vane 38 there is a printed circuit board 40 on which the electronic circuit 42 is arranged furthermore on the printed circuit board 40 there are two sensors u 1 and u 2 for detecting the position of the vane 38 in the exemplary embodiment described here the sensors u 1 u 2 are electro optical sensors which both transmit and receive visible radiation the sensors can however also be realized as magnetic sensors reed switches ultrasonic sensors radio frequency sensors mechanical switches or comparable arrangements each sensor u 1 u 2 has both an emitter a for transmitting light and a detector b for detecting incident light in particular light reflected from the vane 38 and or ambient light the arrangement of the vane 38 and sensors u 1 u 2 is constructed such that if the vane 38 covers a sensor u 1 u 2 the radiation emitted by the emitter a of this sensor u 1 u 2 is reflected onto the detector b a circuit 42 which contains a read only memory 44 expediently in the form of an electrically erasable programable read only memory eeprom is connected to the sensors u 1 u 2 the memory 44 can however also be a ram rom eprom flash memory or any other type of memory if an eeprom is used as memory 44 the circuit 42 only requires four external inputs or outputs since an eeprom is a component which operates serially the said inputs and outputs being earth.