Abstract: A device for providing signals corresponding to rotation of a body having a magnetic sensor with a sensing pole positioned proximate to a tone wheel rotated by the rotating body. A permanent magnet is attached to the sensing pole and a signal voltage having a frequency proportional to the speed of the rotating body is induced in a coil surrounding the sensing pole. The sensing pole is made of square loop magnetic material and is shaped and arranged to cause the magnetomotive force difference between its pole face and the tone wheel to decrease as the air gap length between them decreases, thus causing the normally large change in sensor output with air gap length variation to be substantially reduced.