42
Convenience electronics
Rain detection function
The sensor's core elements are an LED and a photo
diode. The sensor's basic principle is that the light
emerging from the LED is partially reflected by the
surface of the windscreen and, bundled by the optical
element, hits the photo diode.
The degree to which the diode's light is reflected,
and therefore the volume of light which hits the photo
diode, changes if the windscreen is coated with water
droplets or a film of water. The greater the coating,
the less light is reflected due to light refraction.
The photo diode's output signal can therefore be used
to calculate the quantity of precipitation.
The rain detrctor response time, i.e. the time which
passes between the detection of precipitation and the
emission of the output signal to the wipers, is less than
20ms.
LED
Photo diode
Large quantity of light
= no rain
Reflection with a dry windscreen
Reflection with a wet windscreen
Small quantity of light
= rain
Optical element
S338_127
S338_128
S338_129
