Instruction Manual

93
Principle of Leak Noise Correlator
Below is a brief description of the principle of
the leak noise correlator.
Before the leak location can be detected, the
following four conditions must be met:
① The sound from the location of the leak must
reach two or more pre-amplifiers.
② The material of the target pipe must be
known.
③ The diameter of the target pipe must be
known.
④ The distance between the pre-amplifiers
receiving the sound must be known.
If any of these conditions is not met, the leak
location cannot be detected.
— Calculation of leak location —
Assume that the leak location is near the red
pre-amplifier. The sound of water leakage from
the leak location is first obtained by the red
pre-amplifier. The sound propagates in both the
red and blue directions from the leak point. The
propagation speeds are identical. When the water
leakage sound arrives at the red pre-amplifier at
a given time, it has also traveled toward the blue
pre-amplifier by distance L, which is equal to the
distance from the leak location to the red
pre-amplifier. The leak noise then travels the
remaining distance N to reach the blue
pre-amplifier.
Therefore, an additional time equal N divided by
the sound velocity is required for the leak noise
to reach the blue pre-amplifier (this additional
time is called the "time difference"). Since the
time difference is found by calculating the
correlation coefficient, N can be calculated as
the product of the time difference and the sound
velocity.
If N is known, the distance from the leak
location to the red pre-amplifier can be
calculated as (D-N)/2 (note that D is known
because that is one of the preconditions).
The equation is expressed as follows.
D − N D − (V × T
d
)
L = =
2 2
where Td is the delay time (time difference)
Pre-amplifier
(blue)
Pre-amplifier
(red)
Leak location