5
Principle of Correlation
In the "classic" correlation process, two sensors are deployed on pipe fittings ("dry"
connection) or connected to hydrants ("wet" connection). The sensors are positioned either
side of the suspected leak position. Noise is created by the leak as it escapes from the pipe
under pressure. This noise is conducted in both directions away from the leak through the
pipe wall (as minute vibrations) and through the water column (as a pressure wave). The leak
noise travels at a constant velocity (V), which depends on the material and diameter of the
pipe, and arrives first at the sensor nearer the leak. The arrival time at each sensor is
registered. The difference (Td) between the two arrival times, combined with knowledge of the
pipe type and length, enables the leak position to be calculated by the correlator. Depending
on the environmental conditions, accuracy of leak pinpointing can be to within centimetres.
Principle of correlation: L = ½ (D-(VxTd))
Leak position
V x Td
L
L
D
