| 摘要 |
PURPOSE:To easily discriminate whether a conduit exposed by excavation is a gas pipe on the spot. CONSTITUTION:When a transmitter 3 is driven by a signal generator 5, a sonic wave vibrated in the resonance frequency of a conduit 1 is transmitted to the conduit 1 for 1musec in a pulse like state. A part of the sonic wave in the transmitted transmission wave S1 transmits through the conduit 1 as a transmitted wave St. At sonic wave vibrated in frequency shifted by the frequency predetermined from the resonance frequency of the conduit 1 is also transmitted in the same way. The transmitted transmission wave S2 propagates through the surfaces and material of the conduit 1 and the transmission waves S1, S2 are received by a receiver 4. The reception signals are inputted to a signal analyser 7 through a signal amplifier 6 and the difference between two input results is taken by the signal analyser 7 and only the signal of the transmitted wave St transmitted through the conduit 1 is detected. At the same time, the time lag of the transmitted wave St is measured to calculate the sonic velocity in a medium 2. The medium 2 can be specified from the difference in sonic velocity. |
