To prevent the corresponding relation between the waterdrop stuck quality on the surface of a front glass and the output signal level of a light receiving means from fluctuating by ambient temperature changes.
In this temperature compensating method, the waterdrop quantity stuck on the surface of a window glass is detected by a light emitting means 7 guiding light into the window glass and a light receiving means 8 receiving the light reflected in the window glass. A detecting circuit 14 and an amplifying circuit required for the light emitting means 7 and the light receiving means 8 respectively are used in common, analog switches 18a, 18b, 18d are time- division-processed by a time division process section 19, and the detecting circuit 14 and the amplifying circuit 15 are electrically connected to the light receiving element 12 of the light emitting means 7 or the light receiving element 16 of the light receiving means 8.
KOYAMA TADASHI
TSUNETOMO KEIJI
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