Dakota Ultrasonics DFX-7 plus MANUAL2 - Manual (Page 88)

Dakota Ultrasonics
84
pulse, or in the material, the gate can be moved to the right of the noise and block
the unwanted noise. Gates 2 and 3 will automatically start from the end of gate 1, or
from a detection found inside of the boundaries of gate 1. Therefore, we use a hold-
off delay as a start feature for gates 2 and 3. See Diagram 2.
Hold-Off: The hold-off is the starting point of the left side of gates 2 & 3, and is used
only if a detection is found inside the previous gate. It should be considered a delay
from the detection point of the previous gate. When the hold-off is off, or 0, the gate
will start at the point of detection from the previous gate. As the value of the hold-off
is increased, it is further delaying the start of the gate to the right of the detection of
the previous gate. Note: Although we’ve used the terminology of hold-off for gate 3,
it is actually a “hold-back” from the detection of the second echo. Therefore, as the
value is increased, the “hold-back” moves closer to the second detection. Just the
opposite of the operation of gate 2 hold-off. See diagram 2.
Width: The width determines the physical length of the gate. Therefore, the width –
start (hold-ff) equals the length of the gate, as the start (hold-off) value is not equal to
zero. If no detection is located inside the boundaries of a gate, the width value is
used to start the next available gate. Key point: When the width is activated for a
gate, giving it a value, the next available gate is also activated. Therefore, activating
width1 of gate1, activates gate2, and activating width2 of gate2, activates gate3.
See
diagram 2.
Thresh: The threshold controls the level of sensitivity of the signal amplitude
required to trigger a detection, or measurement. It is represented by the distance
from the baseline, and displayed as the vertical position of a gate. The further the
vertical position is from the baseline, the less sensitive the threshold is, and visa
versa. This allows the user to have further control over the size of the defects
considered critical, or the ability to get a detection, from the opposite surface, in very
attenuative materials. This feature is used in conjunction with gain. Increasing the
threshold has a similar effect of decreasing the gain, and visa versa.