Dakota Ultrasonics CMX - Manual (Page 67)

CMX High Performance Material & Coating Thickness Gauge
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7.4 Gain
The gain, or amplification of the return echoes, can be adjusted in the CMX to
accommodate a variety of applications. The setting of the gain is crucial in order to
obtain valid readings during the measurement process. Too much gain may result in
erroneous measurements, by detecting on noise rather than the actual material back
wall itself. Not enough gain may result in intermittent detection. It may also result in
lack of detection on internal flaws, pits, or porosity. The gain can easily be compared
to the volume control of a home stereo system. If you turn it up too muc h, you can’t
hear the music clearly. If it’s turned down too much, you can’t hear it at all.
The CMX has three gain settings (VLOW, LOW, MED, HI, VHI). The gain range is
42dB – 50dB in 2dB increments. Note: The CMX has been optimized for the MED
gain setting for all common applications. It should be operated in this mode as
standard. However, some applications may require the lower or higher gain settings.
When? The low settings may be necessary for noisy or granular cast materials. How
do I know when to lower the gain? If the reading becomes sporadic and won’t settle
down or resolve on a thickness value, the user can assume that the material is either
very noisy aluminum, or granular cast iron. This would be a good time to change the
CMX to lower gain setting and see if the reading settles down and become stable.
How do I know when to increase the gain? Often times the user will be trying to
measure a material that is hard to penetrate or pass sound through. This may be
due to the material type, or overall thickness of the material. When a material is hard
to pass sound through because of the thickness or general make-up, it would be a
good time to consider switching the CMX into a higher gain setting. Another example
might be the need to i ncrease overall sensitivity for locating fine pits or flaws. In any
case, the selectable gain settings offer the user some additional options to resolve
and overcome application issues.
Note: When the echo-echo thru-paint measurement mode is selected, the manual
gain feature is disabled and grayed out in the menu items. In this mode, the CMX
switches to an automatic gain mode (AGC) that optimizes the gain setting
automatically in the hardware of the CMX.
The procedures to adjust the Gain are outlined below: