Method for stabilizing output of rain sensor and protection method therefor

摘要

In a rain sensor, comprising light emitting means (7) for guiding light into a window glass so as to undergo total internal reflection within said window glass; light receiving means (8) for receiving the light which has undergone total internal reflection within the window glass; and means for detecting the amount of water drops adhered or present upon said window glass so as to output a driving signal to a wiper driver apparatus (20), a difference signal corresponding to a difference between a preset reference value and an output signal of an amplifier circuit (17) of the light receiving means is fed back to the amplifier circuit (17), and an amplification factor of the amplifier circuit (17) is adjusted so as to maintain the output signal thereof at a constant value irrespective of the operation condition of the wiper, when electrical power is applied to the rain sensor 2. Furthermore, in a protecting method for the rain sensor (2), a driving current fed to light emitting element (10) is measured and converted into an ambient temperature, and a driving current supplied to the light emitting element (10) by the driver circuit (12) is stopped when the converted value exceeds a preset higher temperature, by turning a switch circuit (14) to OFF. <IMAGE>