Universal liquid level sensor employing fresnel coefficient based discrete fiber optic measurement technique
Murshid, Syed H.
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A compact and light weight liquid-level-measuring system based on fiber-optics sensor technology is presented as alternative to systems based on float gauges and other conventional level sensors for liquids that pose fire, corrosion and explosion hazards. These Fresnel reflection based fiber-optic sensors are inherently safer because they do not include electrical connections inside fuel/chemical tanks, and they exploit changes in internal reflection of guided electromagnetic modes as a result of contact between the outer surface of optical fiber and a liquid. Discrete changes in light transmission/reflection are used to indicate that liquid has come into contact with a suitably designed fiber optic probe at the output end of the fiber. This endeavor presents a quasi-continuous fiber optic level detection system that measures liquid level to within known increments of depth, by placing the probes of a number of such sensors at known depths in a tank where each probe effectively serves as a level switch. Due to the fiber optic nature of the design, the system can operate from cryogenic applications to boiling fluids. Experimental results for liquid nitrogen and water are presented.