Rain Sensor: Description and Operation

GF54.21-D-6000H Rain/Light Sensor, Component Description

- with CODE (JA5) Light/rain sensor







B38/2 Rain/light sensor

Location
The rain/light sensor is located on the inside of the windshield under the DBE control unit (N70). The rain/light sensor is pressed and held against the windshield by a ring.

Task
The rain/light sensor detects the amount of moisture on the windshield and controls the intermittent wipe interval of the windshield wiper system and rear window wiper system.
The rain/light sensor also detects the intensity of the daylight in order to control the automatic functions of the exterior and interior lights.







Operation of rain sensor
1 Lens
2 Infrared (IR) transmitter unit
3 IR receiver
4 Windshield
A Windshield is dry
B Windshield is wet

The rain/light sensor is active when circuit 15 R is ON.
Infrared light is emitted from the IR transmitter unit and deflected onto the windshield via the lens. The intensity of the light reflected at the windshield is measured by the IR receiver unit which is located at the other end of the lens.
A distinction is made between the following:
- Windshield is dry
If the section of windshield around the rain/light sensor is dry, the light is almost completely reflected and the IR receiver unit measures a high light intensity.

- Windshield is wet
If the windshield is wet around the rain/light sensor, part of the light is diffused out of the windshield glass. This reduces the intensity of the reflected light and the IR receiver unit measures a lower light intensity.

The light intensity measured by the IR receiver unit is an indication of the quantity of water on the windshield. The smaller the measured intensity, the greater the degree of wetting of the windshield.

Operation of light sensor
The light sensor (photodiode) measures the intensity of the light falling on it from outside.
In the following cases, automatic driving light actuation is controlled via the rain/light sensor:
- Dusk
- Darkness
- Driving through tunnels
- Detected sensor fault

The above-mentioned switch-on conditions are considered separately and the driving lights are switched on when at least one of the conditions is met.

A detection of fog is not recognized. In fog the driving lights must continue to be switched on manually.

Reading out via rain/light sensor
The rain/light sensor is connected to the Controller Area Network bus class B (interior) (CAN-B) via the DBE control unit as the interface. All the information from the rain/light sensor is thus available for the windshield wiper system, the rear window wiper system and the automatic functions of the exterior and interior lights.