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 MIL-HDBK-1023/4
generators to locate faults in direct-buried electric cables by tracing the sound emitted from the
fault when the impulse generator causes it to arc.
Figure 9
Typical Acoustic Detector
b). The set is designed for use in all weather and can easily be carried by the operator
to any field location. A sturdy carrying case is provided for storing and transport.
c) In use, the operator places a pickup element on the ground and listens for the
characteristic pop or thump in the earphones, then moves along the line toward the location of
the loudest sound. The set has a calibrated sound intensity meter which is used to make a final
precise location of the point of maximum sound, which is directly over the fault. The meter is
often found to be more sensitive than the ear in detecting a very weak signal. The meter and a
solid-state amplifier are contained in a lightweight compact housing which can be carried by a
strap around the neck, leaving the hands free to operate the instrument.
d) An important feature of the detector is the impulse indicator. This is an entirely
separate system which detects the current pulse as it is applied to the faulted cable and gives a
visual signal to the operator. When the operator is at a distance from the impulse generator and
cannot see or hear it operating, the indicator ensures that the impulse generator is operating. In
addition, the indicator tells the operator exactly when to listen for the thump and watch the
meter. This is most useful in areas of high background noise. The impulse indicator, complete
with its magnetic antenna, is included in the main amplifier housing.
e) A simplified diagram showing how the acoustic detector is used to detect a fault is
shown in Figure 10.
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