Checkline DFX-7 - Manual (Page 34)

Dakota Ultrasonics
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9) Finally, press the MEAS key to return to the measurement screen.
4.4 Gates
The gates are an important part of any ultrasonic device, in this case a flaw detector.
The primary purpose of using a flaw detector is to “detect” and estimate the “size” of
of flaws according to calibrated reference standards or simulated defects. The gates
play an important role in this process, as without them a detection/measurement isn’t
possible. The height of a gate is also a threshold, or controls the level of sensitivity.
They can be adjusted to a specific reference height, based a predetermined reflector,
and set to act as an alarm during the inspection process.
The more flexible a gate is, the better the possibilities for the user to setup an
application. For example, a test block with a target size and depth is optimized on
the A-Scan display with a signal amplitude at 70% full screen height. The inspector
wants to know of any defects during the inspection that are greater than or equal in
size to the calibrated test specimen. A gate is then enabled and set to a reference
height of 70%. The width and range are adjusted to cover the range tested, and the
inspection is underway.
The DFX-7 is equipped with 2 fully independent gates. Each gate has a start and
stop or width, a threshold, a polarity switch, and a detect option. A gate can only
detect on reflections that occur inside the boundaries of the gate. Anything outside of
the start and range/width of the gate will be ignored. Both gates can be enabled and
set for different detects, polarities, and positioned anywhere on the A-Scan display
independent of one another. The following sections cover enabling and setting up
gates:
4.5 Activating and Setting Up a Gate