PURPOSE:To speedily and accurately detect water immersion by providing a couple of water-absorptive expansion materials with curved surface parts facing each other across coated optical fibers on an upper porous bottom plate which is charged in a casing. CONSTITUTION:The coated optical fibers 5 and 5a are arranged as shown by a chain A while arranged between a couple of pressure plates 24 and 25 whose coupling parts are combined with the water-absorptive expansion materials 26. Then a box type casing 20 that the coated optical fibers 5 and 5a penetrate is covered with a lid to form the water immersion sensor tool, which is arranged on the bottom part of a closure 6. When water enters the closure 6 in this state, the water is speedily absorbed by the upper porous bottom plate 23 through through holes of the bottom surface of the casing 20 and absorbed by the expansion materials 26. The expansion materials speedily expand by the water absorption to narrow down the gap between both the pressure plates 24 and 25, so the coated optical fibers 5 and 5a which are straight when not impregnated with water bend as shown by a chain line B to increase the transmission loss of light. For the purpose, this is detected to speedily and accurately grasp the water immersion in the closure 6.
展开▼
