Leakage Prevention Guidebook - Bureau of Waterworks Tokyo ...

Fig.14Electronic leakage detectorAcousticElectronic leakage detectorFig.15Acoustic method3.3 Correlation methodIn the correlation method, the position of leakage is detected by using a correlation type leakage detector (a combinationof correlation analyzer, sensor, amplifier, wireless transmitter, etc.).Firstly we place sensors at two points (where exposed ground surface i.e. gate valve and fire hydrant), then obtain theleakage noise propagation time difference to both sensors with correlation leakage detector. The position of leakage iscalculated by the time lag, distance between sensors, and velocity of leaking sound transmitting through the pipe.Correlation method has a benefit that enables investigation regardless of noise of cities and depth of pipes buried,because if directly detects the noise of leakage from the pipelines. It has the excellent characteristic of being largely- 13 -