A New Type of Magnetic Motion Sensor and Its Application

A new type of sensor capable of sensing the direction and velocity of motion of smooth surfaced metallic targets is described. The sensor consists of a small permanent magnet and a magnetic field sensor displaced from each other along the line of motion, each at a small fixed distance from the target surface. Operation is based on the motion dependent location, strength and polarity of magnetic field sources created within proximate target regions via their passage through the field of the magnet. The fields arising from these target regions are detected by the magnetic field sensors, typically Hall effect or magnetoresistive devices. With ferromagnetic targets, a non-volatile memory of the direction of last occurring motion is also provided. Utility of these sensing capabilities is illustrated by descriptions of applications for automatic turn signal canceling and antitheft devices, back-up alarm activation and for engine misfire detection via crankshaft speed variation.