Checkline DFX-7 - Manual (Page 78)

Dakota Ultrasonics
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8) Press the OK key to set the speed and return to the DISP menu., followed
by pressing the MEAS key to begin the B-Scan process.
9) Finally, press the MEAS key to return to the measurement screen and begin
the scanning process.
7.4 Gain
The gain, or amplification of the return echoes, can be adjusted in the DFX-7 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 much, you can’t
hear the music clearly. If it’s turned down too much, you can’t hear it at all.
The DFX-7 has 110dB gain range, but has been limited to a 60dB gain range (-10 to
50 dB), for thickness gauge applications. The common starting point for standard
thickness gauge applications is 46dB. This feature is used to increase/decrease the
power or amplitude of the signal. When used in conjunction with the attenuator
feature, it has a limited overall gain range of -30dB to 70dB.
The gain can be adjusted to accommodate a variety of material types. Having this
feature available, provides the user with a great deal of flexibility. 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 DFX-7 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 increasing the DFX-7 to a higher gain setting. Another
example might be the need to increase overall sensitivity for locating fine pits or
flaws. In any case, the adjustable gain feature offers the user some additional
options to resolve and overcome application issues.