G - Physics – 01 – N
Patent
G - Physics
01
N
G01N 21/41 (2006.01) B60S 1/08 (2006.01) G01N 21/43 (2006.01)
Patent
CA 2132393
ABSTRACT OF THE DISCLOSURE An optical detection system for detecting rain or other water droplets on the outer surface of a window and for detecting fog on the inner surface of such window with a single photo-detector is disclosed. The optical detection method and apparatus of the invention measures the accumulation of water droplets on the window by light refraction of a first light beam with such droplets to redirect a first light beam to the photo-detector. A masking device prevents such first light beam from reaching the photo-detector directly without refraction. As a result the rain measurement output signal of the photo-detector increases with an increasing accumulation of water droplets on the window. The fog accumulation is measured by a second light beam reflected off the inner surface of the window to the photo-detector so that the fog measurement output signal of the photo-detector decreases with increasing amounts of fog since such fog scatters and diffuses the light to reduce the amount of light reflected to the photo- detector. A third light source is focused directly on the photo-detector to bias it into an operating point of high sensitivity to infrared light and is connected in a negative feedback circuit from the output of the photo- detector amplifier. The photo-detector output is connected to a narrowband amplifier that is tuned to the frequency of an oscillator which pulses the first and second light sources at different times. As a result of this negative feedback, changes in the output signal of the photo-detector due to external factors such as temperature changes or aging of the light sources and photo-detector, as well as changes in the supply voltage and ambient light are cancelled so they do not produce errors in the measurement signals.
Smart & Biggar
Zimmerman H. Allen
LandOfFree
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