A fiber-optic density sensor for monitoring the state-of-charge of a lead acid battery

A fiber-optic technique for measuring relative density has been developed and successfully applied to the electrolyte of a lead-acid battery. The method relies on the optical power loss exhibited by fibers bent beyond a critical radius. For such fibers the loss depends on the refractive index of the surrounding medium, which is proportional to its specific gravity. The amount of leakage can be measured and related to the value of the specific gravity. The application of this technique has one main drawback: errors can arise from source intensity variations, variable losses in fibers and connectors, and sensitivity changes in the detectors.<
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