Optical sensor with self-monitoring of transparency of light aperture

摘要

An optical sensor with a transparent aperture (7) for installation inside a motor vehicle and operating via the windscreen has an integral detector for ensuring that its aperture is not obscured by dust particles etc. The sensor housing (2) accommodates a light-sensitive receiver (4) and a second receiver (6) which latter comprises the detector element within the dotted area (1) in association with a light source (3) and coupling element (9). A known proportion (5) of the total light flux from the source (3) is directed at the surface of the aperture (7) and the amount returning to the receiver (6) due to the obscurities (8) is an index of the aperture opacity.