Optical-Type Hydrometer for Lead-Acid Batteries and its Applications

As the most widely used means to know the charged condition of a lead-acid battery, the method to measure the specific gravity of the electrolyte is adopted. Here we report in this paper on an optical-type sensor taking advantage of the fact that the sulfuric acid electrolyte has a certain definite refractive index in accordance with its specific gravity and the device applying such a principle. Several years ago, we had already developed a specific gravity meter based in the aforementioned principle for use to the stationary type lead-acid batteries. Said optical-type sensor is completely insulated from a electrolyte and obtains linear specific gravity values converted into at the standard temperature. It can be commonly inserted with the conventional vent plug. And various improvements have been made with regard to its reliability and precision in measuring, culminating in today's ±0.003 accuracy in performance.