Dakota Ultrasonics DFX-8 plus MANUAL2 - Manual (Page 99)

DFX-8
Ultrasonic Thickness Gauge
95
mode button on the keypad. The DFX-8 has been programmed to identify the modes
available to a specific transducer.
When configuring the DFX-8 for specific thru paint applications, all of the scope
parameters will potentially be needed. The delay, range, gain (AGC), thresholds,
gates, and hold-offs will be subject to change. For this reason, they have all been
added to Hot Menu fields located directly beneath the A-Scan display for quick and
easy access. Note: Once the values of the fields have been changed or modified,
these changes must be saved to a setup location prior to powering the DFX-8 off.
Failure to do so will result in losing your changes. Refer to page 158 for
additional information on setups.
THRU-PAINT (INCORRECT) THRU-PAINT (CORRECT)
Refer to the incorrect diagram above. Point (A) represents the detection on the first
back wall echo. The true, second back wall, reflection should be detecting at point
(D). However, the hold-off (C) is setup incorrectly and the DFX-8 is detecting the ring
down noise of the transducer, on the first reflection, rather than the true second back
wall reflection shown at (D).
Before we look at the diagram with the correct configuration, let’s consider all of our
options on how to fix the problem beforehand. Our delay and Range will simply
change the view options of the screen – not needed in this example. Will a gain
(AGC) or threshold adjustment fix the problem? Unfortunately not. Why? Notice
the amplitude of the cycle just to the left of (B). If we tried to increase the threshold
level above the height of the cycle, we would lose our detection for both echoes
resulting in no reading at all. If we decrease our gain (AGC), reducing the signal
amplitudes, we would also lose our detection of both back wall echoes.
Notice that the amplitude of the cycle just to the left of (C). The amplitude of the
cycle, at (C), is less than the amplitude of the cycle at (B), in terms of overall height.
If we decreased our gain (AGC), we would lose the first cycle (C) long before losing
the second cycle (B). Therefore, adjusting the gain (AGC) or threshold levels will
not help us in this example. Our final option is adjusting the GATE2 hold-off, shown