Anti-lock Braking System(ABS) 13 B. WHEEL SPEED SENSOR (WSS) : Working principle: The Wheel speed sensor in vehicle is connected to a voltage source for operation (active sensor). It is used in conjunction with a Magnetic encoder and supplies a signal with constant amplitude pulses whose frequency varies with the wheel speed. It uses AMR Effect principle, it has a semiconductor chip with the electronic circuitry for supply and signal processing integrated on it. This chip is located within an almost completely insulated magnetic circuit consisting of permanent magnet and pole elements. The wheel speed sensor is mounted directly above the Magnetize encoder. The Magnetic Encoder is a strip with North, south magnetic poles on it. Magnetic encoder is fitted on half shaft bearing. The alternating teeth and gap that accompanies the wheel rotation induces differential magnetic flux density, thus leading to the variation in the voltage induced in the semiconductor chip. The signal conditioning circuit converts this voltage variation into constant amplitude current pulses. The frequency of these pulses depends up on the wheel speed. This measurement principle permits zero speed measurement Precise alignment and gap between the stator pole and the Magnetic encoder is vital. To obtain correct signal, the specified gap between the end of sensor and the Magnetic encoder must be maintained. Refer Repairs section for procedure to check air gap. Pin Out: Pin Details: PIN NO. DESCRIPTION 1 Wheel Speed Sensor Signal 2 Wheel Speed Sensor Power Precautions while handling wheel speed sensor 1. Storage temperature (- 40° C to + 50° C) should not be exceeded 2. Avoid free fall of the sensor 3. The sensor tip should not be scratched. 4. Sensor should not be exposed to strong magnetic field.
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