| 摘要 |
PURPOSE:To accurately detect abnormality, by arranging a sensor made of a shape memory alloy for bending an optical fiber, when a set temp. is exceeded, to the predetermined part of the optical fiber and applying photoelectric conversion to the return light of a sent-out optical pulse to perform the processing of data before detecting the difference of said data from one at a normal time. CONSTITUTION:Sensors 3 each made of a pipe shaped shape memory alloy for generating transmission loss are arranged to plural predetermined parts of an optical fiber 2 for transmitting light. An optical pulse is sent to the optical fiber 2 and the return light thereof is received to be converted by a photoelectric converter element 55 and further converted by a logarithmic A/D converter element 56 to store the return light intensity IR to a distance L as reference wave form data alpha and the difference gamma' between the reference wave form data alpha and the data beta from a movement n-time altering wave form data beta' forming circuit 63 for discrimination is obtained by a difference circuit 64 and operated by a distance differentiation circuit 65 to obtain data delta' and, when the light source side intersecting point of a threshold value function eta and the data delta' is generated, abnormality is judged by a comparing judge circuit 67 and an abnormality detection signal and abnormality generated position data are outputted to a distance data output circuit 68.
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