ROTATION SENSOR

PROBLEM TO BE SOLVED: To provide a rotation detecting sensor capable of stabilizing duty ratio when there is a great fluctuation of output. SOLUTION: This sensor is provided with a rotating plate 2 having magnetic path changing pieces 6a-6c stood thereon at predetermined intervals to one another along the circumferential direction of the rotating plane thereof, first to third bias magnets 13b-15b disposed to have predetermined orientations with respect to the rotating plate 2, and magnetic resistance elements 13a-15a for detecting the first to third bias magnets 13b-15b. A predetermined arrangement of a plurality of resistors R1-R4 constituting the magnetic resistance elements 13a-15a and electrical connections between the resistors R1-R4 constitute a circuit consisting of the resistors R1, R2 which provide waveform outputs on detection of the rotation and movement of the magnetic path changing pieces 6a-6c. An output circuit has an output signal whose output variation width is about third-fourths of that under normal conditions, and the output circuit is connected to a comparator which shapes waveforms according to a threshold voltage set such that a predetermined duty ratio is achieved.