These turbulences generate a
wide spectrum of noise including
ultrasound, due to the friction of
the gas molecules (air for example)
through the hole.
The human ear hears up to about
20 kHz.
Therefore, the human ear does not
hear the ultrasound from about
20 kHz to 100 kHz.
That is why, by using sensors sensitive
to these ultrasounds, associated to a
heterodyne technique often centred
around 40 kHz, it is possible to nd
and hear the leaks easily.
Why are ultrasonic waves easy to
nd with an ultrasound detector ?
They are highly directional, emitting
in a specic direction.
They generate a high intensity
ultrasound at their emission source,
which decreases rapidly when further
away from the source.
They can be heard by heterodyne
technique (high frequency signal
demodulation type here, ultrasound
inaudible to the human ear) in low
frequency signals (audible to man,
here at about -2.5 kHz)
They can be detected in a noisy envi-
ronment (non-ultrasound), because
they are properly ltered by the
detector.
This ultrasonic technology has the
advantage of being accessible to all
by its ease of use.
ultrasOniC teChniQue tO
FinD Gas leaKs COmPresseD air Or
Other Gases unDer Pressure / VaCuum
When a gas goes from a high pressure state (compressed in a pipe at 6 bars
for example) to a low pressure state (leak in a line, with external atmospheric
pressure), there is a phenomenon of depression, which creates turbulences.
Pschiiiit
Emitted
ultrasounds
P ATM
P INT
= 6 Bar
P INT
= 6 Bar
