40 Localization of Acoustic Emission Sources …
459
40.4.2 The Example Analysis
The AE sources location in the two cases of the lowest location precision is discussed:
the physical source is very close to one of the sensors (i.e. if the physical source is
far away from the center of the sensors array, then, the greater the time difference is,
and the higher the location error of AE source is, due to the velocity variation), the
most complicated and irregular parts of the detected component.
40.4.2.1 Location Analysis in Region of A2
In region of A2, the planar location array is composed of sensors 20
# (−5405, −
200), 21
# (−4729,1400), 22
# (−4054, −200), 23
# (−3378, 1290), and 24
# (−2703, −
200). The simulated source of Pencil lead breaks(PLBs) are implemented at the point
that is in the connection line of the sensor 20
# and sensor 22
# and 300 mm away
from the sensor 20
# , and its coordinates is (−4354, −200). The maximum sensors
space among the sensors array is about 2700 mm. In order to reduce the influence
of velocity variation and complicated transmission paths of sound wave due to the
wave transmitting through the longitudinal weld W1, sensor 21
# does not participate
in location calculation. According to Formulas (40.6), (40.7), (40.8) and (40.9), the
calculation results are obtained shown in Table 40.3.
When LUCY (or δ LUCY ) is relatively small, the corresponding sound velocity
value is defined as the ideal sound velocity value V i . It is indicated from Table 40.3
and Fig. 40.7 that 4200–4800 m/s is assigned to V i in order to control the relative
LUCY (δ LUCY ) and relative LE(δ LE ) below 5%.
When V u is less than V i , LUCY is less than LE; when V u is greater than V i,
LUCY is greater than LE. The change rule of relative δ LUCY and the δ LE is constant
with the change of sound velocity.
Therefore, although it is difficult to find the actual physical location of the AE
source, a proper value of V u can be selected by means of LUCY analysis to improve
the location accuracy.
From the sub-figure in Fig. 40.7b, it can be found that the location error in the xdirection (circumferential direction) is generally smaller than that in the y-direction
(longitudinal direction, the wave received the sensor should transmit through the
circumferential weld), indicating that the weld has obvious influence on the sound
velocity and AE location.
40.4.2.2 Location Analysis in Region of A1
Planar location is adopted in region of A1. The AST (Auto Sensor Test) function is
applied, each channel transmits 8 standard pulse signals with a frequency of 150 kHz
and a width of 5.2 ms successively as the simulated source, and the other channels
receive the signals for location analysis.
459
40.4.2 The Example Analysis
The AE sources location in the two cases of the lowest location precision is discussed:
the physical source is very close to one of the sensors (i.e. if the physical source is
far away from the center of the sensors array, then, the greater the time difference is,
and the higher the location error of AE source is, due to the velocity variation), the
most complicated and irregular parts of the detected component.
40.4.2.1 Location Analysis in Region of A2
In region of A2, the planar location array is composed of sensors 20
# (−5405, −
200), 21
# (−4729,1400), 22
# (−4054, −200), 23
# (−3378, 1290), and 24
# (−2703, −
200). The simulated source of Pencil lead breaks(PLBs) are implemented at the point
that is in the connection line of the sensor 20
# and sensor 22
# and 300 mm away
from the sensor 20
# , and its coordinates is (−4354, −200). The maximum sensors
space among the sensors array is about 2700 mm. In order to reduce the influence
of velocity variation and complicated transmission paths of sound wave due to the
wave transmitting through the longitudinal weld W1, sensor 21
# does not participate
in location calculation. According to Formulas (40.6), (40.7), (40.8) and (40.9), the
calculation results are obtained shown in Table 40.3.
When LUCY (or δ LUCY ) is relatively small, the corresponding sound velocity
value is defined as the ideal sound velocity value V i . It is indicated from Table 40.3
and Fig. 40.7 that 4200–4800 m/s is assigned to V i in order to control the relative
LUCY (δ LUCY ) and relative LE(δ LE ) below 5%.
When V u is less than V i , LUCY is less than LE; when V u is greater than V i,
LUCY is greater than LE. The change rule of relative δ LUCY and the δ LE is constant
with the change of sound velocity.
Therefore, although it is difficult to find the actual physical location of the AE
source, a proper value of V u can be selected by means of LUCY analysis to improve
the location accuracy.
From the sub-figure in Fig. 40.7b, it can be found that the location error in the xdirection (circumferential direction) is generally smaller than that in the y-direction
(longitudinal direction, the wave received the sensor should transmit through the
circumferential weld), indicating that the weld has obvious influence on the sound
velocity and AE location.
40.4.2.2 Location Analysis in Region of A1
Planar location is adopted in region of A1. The AST (Auto Sensor Test) function is
applied, each channel transmits 8 standard pulse signals with a frequency of 150 kHz
and a width of 5.2 ms successively as the simulated source, and the other channels
receive the signals for location analysis.