Sensor design and measuring principle of the wheel-speed sensor
A wheel-speed sensor consists of a silicon integrated circuit in the sensor head, which is hermetically sealed with overmolded plastic. Bosch wheel-speed sensor circuits use Hall technology, which incorporates the Hall-sensing element, signal amplifier and signal processing all on a single chip. The circuit is exposed to the changing magnetic field of the rotating encoder, which is either a multipole or a steel wheel. In case of a steel wheel application, a magnet placed inside the sensor is needed.
The Hall element generates an alternating voltage that is proportional to the changing magnetic field. The sinusodial voltage is processed by the circuit into an alternating digital output signal, and the wheel-speed information is transferred into load-independent rectangle current impulses. The frequency of the current pulses are directly proportional to the wheel speed. A detection of very low speed nearly up to stand-still (0.1 km/h) is possible.