PURPOSE: To improve the economy of a landslide detecting sensor using optical fiber.
CONSTITUTION: The light from a light source 4 is made incident on the near end 3b of an optical fiber 2 (laid along the location to be inspected) through a photocoupler 5. The incident light is returned to the near end 2b after it is totally reflected at the far end of the fiber 2 or returned by a photocoupler 5, branched by the photocoupler 5, and made incident on a photodetector 6 which detects the quantity of the light. When a landslide occurs, the landslide is detected, because the fiber 2 is bent or twisted and a lateral pressure or tension is applied to the fiber 2 and, as a result, the light transmission loss of the fiber 2 increases. In the case where the fiber 2 is disconnected due to the landslide, the light receiving level of the photodetector 6 drops and the landslide can be detected, because the light reflectivity at the disconnected point becomes extremely small in addition to an increase in transmission loss due to the bending, twisting, lateral pressure, tension, etc.
AIHARA SHUICHI
SASAKI HIROYUKI
KOSAKA YUZO
