The rain monitor is designed to act as a sensor detecting the start and end of precipitation. It is used as a status indicator or sensor for controlling downstream safety devices (control units) protecting windows, ventilation flaps, sunblinds, awnings, etc. The sensor area takes the form of a capacitor on glass-coated ceramic. Glass passivation ensures that the rain monitor is extremely environment-resistant as well as robust while offering good long-term stability and resistance to aggressive media.
Whenever precipitation strikes the rain monitor and wets the sensor surface, this changes the capacitance of the surface, so triggering a switching signal, i.e. wetting of the sensor surface signals the precipitation status "yes".
To protect the sensor surface from bedewing and icing-up, it is heated to an over temperature of approx. 2K.
When the sensor surface is wetted, it is adjusted to approx. 10K above the ambient temperature, so ensuring fast faster drying. Once it has dried, the device switches to the precipitation status "no".
You can find further information here:Ceramic rain monitor 5.4106.00.000