What Is a Rain Sensor for a Windshield?

A rain sensor or rain switch is switching device actuated by rainfall. There are two main types of rain sensor. The first one 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. It is a small electronic device under the mirror. It automatically turns on the windshield as soon as it senses rain.

For our discussion, we focus on the automotive sensors. In 1958, the Cadillac Motor Car Division of General Motors experimented with a water-sensitive switch that triggered various electric motors to close the convertible top and raise the open windows of a specially built Eldorado Biarritz model in case of rain.

The first such device appears to have been used by General Motors for that same purpose. In a concept vehicle designated, "Le Sabre" and built seven years earlier in 1950-1951. For the 19556 model year, Cadillac once again introduced an automotive rain sensor this time to automatically trigger the windshield wipers and adjust their speed to conditions.

The most common modern rain sensors are based on the principle of total internal reflection. An infrared light is beamed at 45 degree angle into the windshield from the interior. If the glass is wet, less light makes it back to the sensor and the wipers turn on.

In the past, automakers tried to eliminate the wipers or control their speed automatically. Some of the schemes involved detecting the vibrations caused by individual raindrops hitting the windshield, applying special coatings that did not drops to form, or even ultrasonically vibrating the windshield to break up the droplets so they don't need to be wiped at all. But these systems were plagued by problems and either never made it to production or was quickly axed because they annoyed more drivers than they pleased.

However a new type of wiper system is starting to appear on cars that actually do a good job of detecting the amount of water on the windshield and controlling the wipers. One such system is made by TRW, Inc. TRW, Inc uses optical sensors to detect the moisture. The sensor is mounted in contact with the inside near the rear view mirror.

About The Author Auto Glass Outlet is locally owned and has been in the industry for over 20 years.Grown from a single-shop location into an auto glass industry leader in the Washington, DC metropolitan area, with multiple service locations and warehouses throughout the area.