Moisture detector for vehicle windscreen

摘要

The invention relates to a device for detecting moisture on a window pane with a moisture sensor which has a measuring circuit (MS) with a light-emitting transmitter and a receiver transmitting a sensor signal and responding to the emitted light, and an evaluation device (AW) comprising a difference generator (D) for the sensor signal. A simple embodiment of the device and simple processing are achieved in that the measuring circuit (MS) has an integration stage for detecting the quantity of light falling on the receiver, and a comparator stage used to transmit a triggering signal when the amount of light integrated from a certain time onwards exceeds a predetermined threshold, the total amount of light consisting of the light of the transmitter and possible external light, and the amount of external light detected when the transmitter is switched off are measured at separate time intervals. The evaluation device (AW) has a timer (T) the numerical value of which, produced during the integration period until the triggering signal arrives, is detected. To determine a variable for the total quantity of light and for the quantity of external light, a reciprocal-value generator (KW) is provided for generating the reciprocal values of each numerical value, said reciprocal values being supplied to the difference generator (D) used to derive a signal for the effective quantity of light (NL) from the difference between the total quantity of light and the quantity of external light.