DFX-7
Ultrasonic Flaw Detector
79
7.5 Threshold
The
Threshold
is the level (sensitivity) of the signal amplitude required to trigger the
thickness reading. This level can be used in conjunction with the gain. Example:
suppose the user can visually see a potential flaw on the display, but the
DFX-7
is
not detecting on the flaw because the
Gain
is too low, or the
Threshold
to high. The
Threshold
level can be decreased (lower sensitivity) in order to detect signals with
lower amplitudes. This will allow the amplitude from the reflection of the flaw to reach
and exceed the
Threshold
level, and enable the
DFX-7
to detect on the flaw or
defect. This can also be accomplished by increasing the
Gain
, allowing the signal to
exceed the current
Threshold
level. Lowering the
Threshold
(increases sensitivity),
and raising the
Threshold
decreases the sensitivity respectively.
The
DFX-7
is equipped with 3 independent gates, each with an adjustable threshold
level. All three gates can be enabled in any of the pulse echo modes, and in echo-
echo verify mode, and the thresholds set at varying levels of sensitivity. The allows
the user to create a pseudo make-shift “time corrected gain” function, by increasing
the sensitivity of each gate at different thickness values. A visual example would be
an upside down stair case, where each step represented a separate gate, for a
specific thickness range.
The procedures to adjust the
Thresholds
are outlined below:
Adjusting the Thresholds using the Hot Menus
1) Press the
MEAS
key once to activate measure menu items. Press the
MEAS
key multiple times to move right and the
ESC
key multiple times to
move left, until the
THRESH(1-3)
cell is highlighted.