Rain sensor, function - GF82.30-P-4103-02GA

Function 

Infrared light is radiated from the infrared transmitter unit (2) through the lens (1) to the windshield (4). The intensity of the light reflected at the windshield is measured by the infrared receiver (3) which is located at the other end of the lens.

• Dry windshield (picture A) 

  If the windshield is dry in the vicinity of the rain sensor (B38), almost all of the light is reflected: The infrared receiver unit (3) measures high light intensity.

• Wet windshield (picture B) 

  If the windshield is wet in the area of the reflection surface, part of the light is diffused out of the windshield glass. This reduces the intensity of the reflected light, the infrared receiver unit (3) measures a lower light intensity.

Fig 1: View Of Dry And Wet Windshields

Courtesy of MERCEDES-BENZ USA

The light intensity measured by the infrared receiver (3) is a measure for the degree of wetting of the windshield. The smaller the measured intensity the larger the moisture on the windshield.

Reading out rain sensor 

The rain sensor (B38) is connected as an interface to the interior CAN via the overhead control panel control unit (N70). The front signal acquisition and actuation module (SAM) (N10/1) transmits a request via CAN interior to the rain sensor (B38), which then responds to each request by notifying the front SAM of the degree of wetting at any given moment.