Nippon Telegraph and Telephone Corporation

Sumitomo Electric Industries, Limited

Takeshi Tsujimura

Shigeru Tanaka

Hiroaki Sano

Kinji Taguchi

Tetsuro Yabuta

Kazunori Katayama

Yuji Azuma

Masatoshi Shimizu

Kuniaki Tanaka

Koichi Yoshida

Terminals of upstream and downstream sides of an in-service line and a detour line are connected by optical couplers. An optical oscilloscope is connected to one optical coupler, and a chirped pulse light source is connected to the other optical coupler to thereby form dualized lines. The detour line includes an optical line length adjuster for compensating for the phase difference of optical transmission signals that occurs because of the optical line length difference with the in-service line. Pulse light in which an optical frequency is chirped is transmitted from the chirped pulse light source. The pulse light is branched by the second optical coupler, passes through the in-service line and the detour line, is multiplexed again by the first optical coupler, and is measured by the optical oscilloscope. While matching an arrival time of the pulse light, the optical line length is adjusted by the optical line length adjuster so as to minimize the size of upper and lower limits of an interference waveform generated in an upper part of the pulse light waveform or so as to make a frequency of an interference waveform become zero.

Method of switching optical path, and apparatus thereof

A method of measuring a length of a conduit comprises the steps of: supplying air into a conduit to insert a filamentary body into the conduit by flow of the air; detecting arrival of a forward end of the filamentary body at an outlet of the conduit; and measuring the length of the conduit from the length of the filamentary body inserted into the conduit. An apparatus for measuring a length of a conduit, comprises an air supply device for supplying air into the conduit; a filamentary body including a wire and a plurality of elastic large-diameter members attached to the wire; and a device for detecting that a forward end of the filamentary body arrives at an outlet end of the conduit, where the length of the conduit is measured from the length of the filamentary body inserted into the conduit.

Method and apparatus for measuring length of conduit and for diagnosing

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Ibaraki, Japan

Takeshi Tsujimura