2
BENEFIT
OF
ULTRASOUND
TECHNIQUE
TO
FIND
GAS
LEAK
(COMPRESSED
AIR
OR
OTHER
ELSE
GAS
IN
PRESSION
/
DEPRESSION)
W
HEN A GAS MOVE FROM A HIGH PRESSURE STATE
(
COMPRESSED AIR IN A PIPE AT
6
B
AR FOR EXAMPLE
)
TO A LOW
PRESSURE STATE
(
LEAK IN A PIPE FOR EXAMPLE
,
WITH EXTERNAL ATMOSPHERE PRESSURE
),
THERE IS A DEPRESSION
PHENOMENON WHICH CREATE A TURBULENCE
(
SEE FIG
1).
FIG
1
T
HIS TURBULENCE GENERATES A NOISE WITH LARGE FREQUENCY SPECTRUM WHICH CONTAINS THE ULTRASOUND
,
DUE TO THE
FRICTION OF THE MOLECULES
(
AIR FOR EXAMPLE
)
THROUGH THE ORIFICE
.
HUMAN HEARS CORRECTLY UP TO
20
K
H
Z
.
S
O
,
HUMAN DOES NOT HEAR THE ULTRASOUND WHICH ONLY START AT THIS
FREQUENCY
.
T
HIS IS WHY
,
BY USING VERY SENSITIVE ULTRASONIC DETECTOR AND HETERODYNE TECHNIQUE
,
OFTEN CENTERED AROUND
40
K
H
Z
,
IT IS POSSIBLE TO FIND AND LISTEN TO THE LEAK
,
EASILY
.
W
HY ULTRASONIC WAVES ARE EASY TO FIND WITH AN ULTRASONIC DETECTOR
?
-
T
HEY ARE VERY DIRECTIONAL
,
THEY EMIT IN A PRECISE DIRECTION
-
T
HEY GENERATE A STRONG ULTRASONIC INTENSITY NEAR THEIR EMISSION SOURCE
,
DECREASING QUICKLY WHEN
LEAVING AWAY FROM THE LEAK
-
T
HEY CAN BE EASILY HEARD THANKS TO HETERODYNE TECHNIQUE
(
DEMODULATION OF A HIGH FREQUENCY WAVE
(
HERE
,
ULTRASOUND NOT AUDIBLE FOR HUMAN
)
TO LOW FREQUENCY
(
AUDIBLE FOR HUMAN
))
-
T
HEY CAN BE DETECTED IN A NOISY INDUSTRIAL ENVIRONMENT
,
CORRECTLY FILTERED BY THE DETECTOR
☺
ULTRASOUND TECHNOLOGY HAS THE MAJOR ADVANTAGE TO BE EASY TO USE AND ACCESSIBLE TO EVERYONE
.
Pschittt !
P int= 6 Bar
P int= 6 Bar
P atm
Emitted ultrasound
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