DFX-7
Ultrasonic Flaw Detector
87
Example of Surface or Transducer Noise
Noise
Blocked
The diagrams above illustrate a typical surface noise condition. Refer to the
Noise
diagram:
(A)
refers to the noise in front of the actual back wall signal
(C)
. Notice the
start position of the gate. As a result, the
DFX-7
is detecting on the noise
(A)
as
shown at point
(B)
. However, the true measurement should be taken at point
(C)
.
Given the start, threshold, and gain levels, the amplitude from the noise is sufficient
enough to cause the
DFX-7
to detect, or measure the noise rather than the true back
wall thickness
(C)
. Therefore, the
DFX-7
is making an incorrect reading at point
(B)
.
Now refer to the
Blocked
diagram. The horizontal line at the top of
(D)
, is
GATE1
.
The start of
GATE1
has been moved just beyond the noise
(A)
to block the noise and
detect on the correct signal
(C)
. Note: the
DFX-7
will only detect on signals that are
located inside the dimensions of
GATE1 (B)
. Therefore, the
DFX-7
cannot see
(A)
at
all, with respect to the starting point of
(B)
. Also notice, the position of the threshold
level with respect to the baseline
(D)
, which represents the sensitivity setting of the
threshold. Extreme sensitivity is indicated by the bottom of the range
(D)
at the
baseline, and less sensitivity indicated by the top of the range at
(D)
. Therefore, the
vertical height of
GATE1
from the baseline, is the threshold level. The threshold level
can be increased to decrease sensitivity, or visa versa.
If the threshold level was increased in the
Noise
diagram, so that the vertical position
of
GATE1
was higher than the amplitude of the noise
(A)
, the
DFX-7
would have
detected on the true back wall
(C)
. Alternatively, if the gain level was decreased, the
signal amplitude of the noise
(A)
would have decreased below the threshold level,
and the
DFX-7
would have also detected the true back wall
(C)
. This example brings
all the fine adjustments into consideration, and demonstrates the versatility of having
a fully functional scope rather than a basic digital thickness gauge.
The procedures to adjust all of the features associated with the
Gates
are outlined
below:
Содержание DFX-7
Страница 35: ...Dakota Ultrasonics 34 Note Sets where the detection will occur on the negative or positive going echoes...
Страница 219: ...Dakota Ultrasonics 82 10 Finally press the MEAS key to return to the measurement screen and begin taking readings...
Страница 308: ...171 APPENDIX B SETUP LIBRARY Num Name Comment 1 Gn AGC Velocity 1 Enter Custom Name 2 3 4 5 6...
