Abstract: A variable reluctance sensor is disclosed as adapted for sensing the rate of revolution of a toothed wheel of magnetic material. The sensor has at least two magnets disposed side by side. One of the magnet has a first pole (e.g. S pole) disposed opposite the toothed wheel, and the other magnet has a second pole (e.g. N pole) disposed opposite the toothed wheel. The second pole of the first mentioned magnet and the first pole of the second magnet are both held against a magnetic core around which a coil is wound. As the teeth of the magnetic wheel successively travel past the magnets, they create magnetic fluxes oriented in opposite directions, which counteract each other in the core. Consequently, the total magnetic flux in the magnetic member varies more greatly than heretofore depending upon whether each magnet is opposed to any one tooth, or to the space between any two neighboring teeth, of the magnetic wheel.

Abstract: An electromagnetic power generating type rotation sensor has a magnetic pole which is divided into an inner magnetic pole piece and an outer magnetic pole piece (3a, 13a) located in a position close to an outer peripheral part or a side part of a magnetic rotator. The inner magnetic pole piece (3b, 13b) is located adjacent to the outer magnetic pole piece but inside the sensor so as not to be exposed to the external environment.