The measurement of the relative density of homogeneous fluids by means of an optical technique

A sensor that uses an intensity modulated optical method to measure the relative density of homogeneous fluids is described. An optical fiber is used in a special way as a refractometer to measure the index of refraction. The method relies on the optical power loss exhibited by a fiber bent beyond a critical radius. For such a fiber the critical angle of reflection is a function of the density of the surrounding medium. The latter will therefore determine the amount of leakage, which can be measured and related to the value of relative density. The measuring technique has one basic drawback: errors can arise due to source intensity variations, variable losses in fibers and connectors, and changes in detector sensitivity. This drawback has been addressed by taking necessary precautions and by the use of a method of referencing.<
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