| 摘要 |
A failure protected optical fluid monitor is disclosed that uses, in combination, a single prism paired systems of light sources and light detectors to determine whether or not liquid in a container is present at a predetermined level. A pair of light sources and coordinated photodetectors are fitted behind the flat end of a conical prism and each light source is adapted to direct a beam of light through the flat rear surface of the prism onto an angled face of prism. If a liquid is in contact with the conical surface of the prism, most of the light is refracted at the prism's surface and exits into the liquid. Under these conditions the light detector are not activated. If no liquid is in contact with the conical surface of the prism, the light beams will be totally internally reflected at both conical surfaces of the prism and will exit on the opposite sides of the prism from the light source parallel to its initial direction. Each light beam is then detected by a photodetector. The presence of light will cause the photoelectric sensor to pass a current. By using dual light sources with dual light sensors, it is possible to guard against an undetected liquid level change masked by failure of a single light source of detector.
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