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BRAKES
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9.3. WHEEL SPEED SENSOR: (MONITORS
WHEEL SPEED)
Working principle:
DF30 is an Active wheel speed sensor, which
means it must be connected to a voltage source
for operation. It supplies a signal with constant
amplitude pulses whose frequency varies with the
wheel speed.
DF30 works on AMR principle (Anisotropic
Magneto-Resistance) It has a semiconductor chip
with the electronic circuitry for supply and signal
processing integrated on it (Commonly known as
ASIC – Application Specific Integrated Circuit)
ASIC is mounted on Step Holder with magnetic
circuit consisting of permanent magnet and
sensing elements and then it is completely
insulated/over moulded with Black Polyamide 612
GF33.
DF30 wheel speed sensor is mounted directly
above the magnetized encoder or steel tone
wheel. The magnetized encoder/steel tone wheel
is a ring with no’s of poles/teeth on it.
Magnetized encoder or Tone wheel is fitted on to
the bearing/wheel hub. The alternating poles/teeth
and gap that accompanies the wheel rotation
induces differential magnetic flux density, thus
leading to the variation in the voltage induced in
the ASIC. 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.
The distance between the sensor reading position
surface and the target wheel surface is defined as
the mechanical air gap (s_mechanic). It must be
ensured that the lowest position of the encoder’s
magnetic track/tone wheel tooth must be used as
reference dimension for maximum air gap. To
obtain correct signal, the specified gap between
the end of sensor & the toner ring must be
maintained according to project specific Air-Gap
report shared by BOSCH during development.
Example:
Front:
0.5 mm to 1.5 mm
Rear:
0.5 mm to 1.5 mm
Precautions while handling DF30 Wheel Speed
Sensor -
Temperature specifications:
Sensor head : (-40°C to +150°C) should not be
exceeded
Cable : (-40°C to +115°C) should not be
exceeded
Storage Life : From date of manufacture: 10 years
under following conditions
1. Permitted temperature range: (-40 °C to +50
°C).
Ambient humidity range: (5 up to 80 %RH).
2. The WSS is classified as an electrostatic
discharge sensitive device (ESDS) requiring
precautionary / protective measures in respect
of handling and processing as defined in the
corresponding
internationally
applicable
standards (e.g. IEC 61340-5-1 series).Precise
alignment and gap (1 mm) between the stator
pole and the Toner wheel is vital. To obtain
correct signal, the specified gap between the
end of sensor & the toner ring must be
maintained.
Avoid any physical damage to DF30 Wheel
Speed Sensor (e.g. Free fall, Sensor head
scratched/cracked, exposed to strong magnetic
field etc.) Repair of the product is not possible and
not allowed. The sensor shall not be
disassembled and reinstalled. Disassembly or
repair may cause damage to the sensor and lead
to a delayed malfunction of the sensor. Sensor
failure like missing signal may lead to break down
of safety related functions on system level.
BOSCH warranty is excluded in case of
reinstallation
of
disassembled
sensors.
Replacement of the product may only be
performed by technically qualified personnel.