Rain Sensor (page 2 of 2)

WIPERS AND WASHERS

DESCRIPTION AND OPERATION

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The rain sensor unit attaches to the optical unit via four clips which latch onto formed tags on the optical unit. Positive 
retention is achieved by two retaining clips which force the clips onto the tags. The retaining clips must be withdrawn 
to facilitate sensor removal.

The sensor provides information to the BCU, via the K bus, for the optimum wiper operation for the prevailing 
conditions to maintain the screen in a clear condition at all times. The rain sensor is an optical unit which operates on 
an infrared waveband. The sensor uses the principle of the laws of reflection on interfacing surfaces between 
materials with differing refraction indices.

Rain Sensor Functionality

A.  = Clean and dry windscreen; B.  = Wet and dirty windscreen

1 Windscreen - Outside surface
2 Optical unit
3 Transmitter diodes (100% light transmitted)
4 Rain sensor unit
5 Receiver diodes (100% received)

6 Water droplets/film
7 Receiver diodes (less than 100% light 

received)

8 Lost light

The rain sensor contains transmitter and receiver diodes which transmit and receive infrared light which is directed 
onto the windscreen via an optical unit. The light is directed at an angle so that the light is reflected 100% on the 
outside surface of the screen and is transmitted back into the optical unit. To receive a 100% reflection, the outer 
screen surface must be clean and dry.

M84 0421

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B