The present invention relates to a device and a method for safely monitoring the rotary motion of a shaft. The device comprises measuring means for recording a first and a second signal, wherein the first signal represents the motion characteristic of an angular position of a first reference point of...http://www.google.co.uk/patents/US6591217?utm_source=gb-gplus-sharePatent US6591217 - Method and device for detecting errors in the signals of a system for monitoring the rotation of a shaft
