MEASURING METHOD FOR HUMIDITY USING OPTICAL FIBER AND HYGROSCOPE

PURPOSE:To take a high-accuracy measurement by directly measuring the quantity of light absorbed by the natural oscillation of water molecules entering an optical fiber. CONSTITUTION:A light source 1 is connected to one terminal of the optical fiber 2 and a photodetector 3 is connected to the other terminal to constitute a hygroscope. Then, the quantity of light transmitted through the optical fiber 2 is measured and transmission loss when humidity is 0% is subtracted from the transmission loss of the optical fiber to calculate the quantity of absorbed light. The quantity of water in the optical fiber 2 varies while balanced with the atmosphere of the optical fiber 2, so the humidity in the atmosphere can be measured from the quantity of the absorption by the water in the optical fiber 2. This optical fiber 2 may be based upon plastic or glass, but water is easy to enter the plastic-based fiber and, for example, polymethyl methacrylate, polycarbonate, and their heavy hydrides are used suitably for the core of the optical fiber.