Abstract: To prevent the adhesion or penetration of iron filings or other magnetically permeable material, thereby avoiding a short-circuit of the magnetic circuit and ensuring an accurate output signal, a membrane comprised of a non-magnetic material covers the bottom of a casing facing a rotor, and a protuberance of a length at least equal to the maximum air gap between the membrane and the rotor is integrally molded to a portion of the membrane.

Abstract: A road wheel speed sensor for use with an automotive vehicle supported on road wheels. A pulsating variation in magnetic flux is produced with rotation of one of the road wheels. A signal converter is provided for converting the pulsation magnetic flux variation into a rectangular pulse signal to switching a transistor on and off. The signal converter is connected through power and signal lines to a processor. The transistor has a base electrode for receipt of the rectangular pulse signal, an emitter electrode, and a collector electrode connected to the signal line. A first resistor is connected between the power line and the signal line. A second resistor is connected between the power line and the emitter electrode of the transistor. A third resistor is connected between the signal line and the ground. The processor calculates a speed of rotation of the road wheel in response to a voltage developed across the third resistor.