User's Manual

ZONESCAN net 18 / 56
Version 1.4
Figure 10 Graph selection for correlated leaks
Figure 11 Correlation Graph
Correlation is a mathematical method for comparing two time series signals
with one another.
A leakage noise is simultaneously recorded by two sensors at different
locations. The sound emitted by the leak spreads in the water pipe at a
defined sound velocity. If the acoustic event were to be brief and occur only
once, e.g., a blow with hammer, it would be simple to measure the arrival at
both receivers. In this case, one would only need to compare the arrival
times at the two receivers with one another. If these are the same, the
sound has traveled the same distance to the receivers, i.e., the sound
source lies in the middle of the pipe between the receivers.
If the arrival times are different, it is possible to calculate the distance to the
two receivers from the measured time difference. The sound arrives at the
closer sensor before the more distant sensor.
Correlation graph