Checkline DFX-7 - Manual (Page 90)

Dakota Ultrasonics
86
7.7 Gates
The DFX-7 is equipped with 3 gates, as explained in the previous section. One gate
is active at all times in every measurement mode, with the exception of coating
mode. These gates are full featured and completely adjustable. They can be fine
tuned by the user to accommodate a variety of application scenarios. Diagram 1 in
the previous section outlines the gates and features available for all measurement
modes. Refer to the previous section for additional information. These features are
described in more detail below:
Note: In order to adjust the gates they must be activated. The gates are
automatically activated depending upon the measurement mode selected. If a gate
is inactive, it will be grayed out in the hot and tabbed menus. The explanations that
follow, assume that the proper measurement mode has been selected. Refer to
page 41 for more information on selecting measurement modes.
Gate 1
Is used in all measurement modes, and has the following features assigned to it;
start, width, and threshold. A gate can be used to overcome a great deal of
application scenarios. Surface noise, for instance, close to the initial pulse can cause
the erroneous measurements as the transducer receives reflections from the noise.
By adjusting the start position of the gate, the noise can be blocked and eliminated.
This is typical in aluminum, stainless steel, and titanium. This can also be a function
of using a low frequency transducer, which are known to be inherently noisy off the
initial pulse. The start feature of the gate is also used in multiple echo modes to
control measurements between 2 or more echoes. As we saw in previous section,
the threshold can be used to control the sensitivity level, and used in combination
with the width, control the sensitivity over a specific range.
Gate 2 & 3
These gate options will most commonly be used for multiple echo measurement
modes, to measure between 2 or more echoes ( E-E and E-EV). They are also
handy to use in a stand pulse echo mode, to create a pseudo time corrected gain
feel. As the thickness of the material increases, the signal amplitude of the reflection
decreases. Why not just turn up the gain? Well, this is certainly something to
consider, but is not always the best answer. As the gain is increased, the noise level
is also increased. At some point, increasing the gain provides little or no benefit to
the quality of the signal, and the additional noise introduced makes things worse. By
activating another gate, optimizing the gain level, setting the thresholds, and
adjusting the widths of the gates to cover specific thickness ranges, a tough
application might not be so bad after all. These gates have the following features set
assigned to them; holdoff (delay), width, and threshold.