PURPOSE: To directly and accurately measure a pipe line length without any measurement error due to gas temperature, gas component in the pipe line to be measured and unknown error factors, relating to an acoustic pipe line length measuring system. ;CONSTITUTION: A sound generating means 4 that sends pulse-like sound wave from one end of a to-be-measured pipe line 28 into it, a sound collector means 5 that, at one end of the to-be-measured pipe line 28, collector pulse-like sound waves reflected on the other end of the pipe line 28, and a sound wave length measuring equipment 3 that, based on the time period between the time when the pulse-like sound waves are sent and the one when they are collected and also based on a sound velocity value in the pipe length, measures the length of the pipe line 28, are provided. Between one end of the to-be-measured pipe line 28 and a measurement system, a detachable sound velocity calibration pipe 10, of a fixed length, that is entirely wound up in coil is provided, and by temporarily releasing a purge valve 14, the sound velocity calibration pipe 10 is filled with the gas in the to-be-measured pipe line 28, for obtaining the length of the pipe line.;COPYRIGHT: (C)1994,JPO&Japio
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