– Principle of Operation:
– Rain sensor operates on total internal reflection principle
– Infrared light shone at 45-degree angle on clear windshield area
– Wet glass scatters light, reducing reflection to sensor
– Used in professional satellite communications antennas for rain blower activation
– Prevents water droplets on antenna feed mylar cover
– Irrigation Sensors:
– Available in wireless and hard-wired versions
– Employ hygroscopic disks that swell in rain
– Some use tipping bucket or conductance probes for rainfall measurement
– Can suspend irrigation watering through electrical switch
– Some include freeze sensor to prevent operation in freezing temperatures
– Automotive Sensors:
– General Motors introduced automatic rain sensor in 1950s
– Cadillac experimented with water-sensitive switch for convertible tops
– Cadillac equipped cars in 1996 with rain sensors for wipers
– Tesla updated AP2.x cars to detect rain using onboard cameras
– Most vehicles with rain sensors have an “auto” position on control column
– Physics of Rain Sensor:
– Modern rain sensors rely on total internal reflection
– Infrared light beamed at 45-degree angle into windshield
– Dry glass reflects light due to critical angle of 42°
– Wet glass changes critical angle to around 60°
– System detects water, triggering windshield wipers
– See Also:
– List of sensors
– Rain gauge
A rain sensor or rain switch is a switching device activated by rainfall. There are two main applications for rain sensors. The first is a water conservation device connected to an automatic irrigation system that causes the system to shut down in the event of rainfall. The second is a device used to protect the interior of an automobile from rain and to support the automatic mode of windscreen wipers.
