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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.