| 摘要 |
PURPOSE:To facilitate the estimation of the point to be monitored, by providing a position display unit close to a light loss changing mechanism. CONSTITUTION:Light emitted from a central unit 1 receives a Rayleigh scattering at each point of an optical fiber 5 and the return light thereof is detected with a receiver 9. Light passing through position display units 12a-12c of the optical fiber 5 suffers a specific loss and losses 21a-21c are created on the return light due to the Rayleigh scattering from a farther optical fiber 5. Light passing through a light loss changing mechanisms 7a-7c suffers a loss due to a change in the state, which causes steps 22a-22c in the return light. This condition is shown on a display unit 12 and no change in the step 22b is observed. Thus, the mechanism 7b is determined to be OFF.
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