Dakota Ultrasonics CMX DL plus - Manual (Page 91)

CMX
DL+
High Performance Material & Coating Thickness Gauge
87
Example of Surface or Transducer Noise
Noise Blocked
The diagrams above illustrate a typical surface noise condition. Refer to the Noise
diagram: (A) refers to the noise in front of the actual back wall signal (C). Notice the
start position of the gate. As a result, the CMX
DL+
is detecting on the noise (A) as
shown at point (B). However, the true measurement should be taken at point (C).
Given the start, threshold, and gain levels, the amplitude from the noise is sufficient
enough to cause the CMX
DL+
to detect, or measure the noise rather than the true
back wall thickness (C). Therefore, the CMX
DL+
is making an incorrect reading at
point (B).
Now refer to the Blocked diagram. The horizontal line at the top of (D), is GATE1.
The start of GATE1 has been moved just beyond the noise (A) to block the noise and
detect on the correct signal (C). Note: the CMX
DL+
will only detect on signals that are
located inside the dimensions of GATE1 (B). Therefore, the CMX DL+ cannot see (A)
at all, with respect to the starting point of (B). Also notice, the position of the
threshold level with respect to the baseline (D), which represents the sensitivity
setting of the threshold. Extreme sensitivity is indicated by the bottom of the range
(D) at the baseline, and less sensitivity indicated by the top of the range at (D).
Therefore, the vertical height of GATE1 from the baseline, is the threshold level. The
threshold level can be increased to decrease sensitivity, or visa versa.
If the threshold level was increased in the Noise diagram, so that the vertical position
of GATE1 was higher than the amplitude of the noise (A), the CMX
DL+
would have
detected on the true back wall (C). Alternatively, if the gain le vel was decreased, the
signal amplitude of the noise (A) would have decreased below the threshold level,
and the CMX
DL+
would have also detected the true back wall (C). This example
brings all the fine adjustments into consideration, and demonstrates the versatility of
having a fully functional scope rather than a basic digital thickness gauge.