Understanding Acoustic Emission Testing- Reading 1 Part B-A

■ Noise Logger
This logger is installed at fittings via a simple magnetic coupling, and is
battery powered with no maintenance requirement, and no problems for being
immersed in water.
The separation distance between loggers depend mainly on the pipe material,
with plastic pipes requiring closer spacing than metallic.
Each unit is intelligent and adapts itself to the environment. If no leak is
present, a radio signal is transmitted to indicate normal background
conditions. However, as soon as a leak is detected, the unit enters an alarm
state and transmits a radio signal to indicate a "leak condition". Signals are
received by a module that can be mounted in a patrolling vehicle, or can be
easily hand-held. This receiving module analyses and "homes in" on signals
to identify the location of units indicating a "leak condition", and thus the
approximate position of a likely leak.
Charlie Chong/ Fion Zhang
http://www.ndt.net/article/wcndt00/papers/idn183/idn183.htm