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10.6.2
Initial Gain
The initial gain sets an upper limit on receiver gain in the vicinity of the excitation
pulse (mode 1) or the interface echo (modes 2 and 3). By effectively making the
excitation pulse or interface echo smaller, the TDG curve allows for detection of
echoes occurring close to the pulse. The initial gain can be adjusted from 0 dB to the
maximum defined by the MAX GAIN setting.
The INIT GAIN setting is most critical in applications where minimum thickness
measurements must be optimized. This setting should always be set with the aid of a
reference standard representing that minimum. In cases where the minimum
thickness capability is less important than penetration, and scatter echoes are not a
problem, the initial gain can be set to be equal to the maximum gain.
The initial gain does the following:
•
Indicates the initial (time-dependent) receiver gain currently selected.
•
Amplifies echoes that are close to the main bang or interface echoes.
•
Starts at time zero and extends to:
•
The main bang blank in mode 1.
•
The end of the interface blank in modes 2 and 3.
10.6.3
TDG Slope
The TDG slope controls the rate at which the receiver gain slopes up from the initial
gain level to the maximum gain level. The TDG slope starts at the position of the MB
BLANK parameter in mode 1, and at the end of the IF BLANK parameter in mode 2
and mode 3. The TDG slope helps suppress reflections from grain structure or fibers.
Generally, the TDG slope should be set as high as possible in order for it to reach the
maximum gain as quickly as possible without causing the gage to hang up on
spurious signals. The slope can be set from 0.0 dB/µs to 39.95 dB/µs.
10.7 Main Bang Blank
The main bang blank is effectively a blank zone that protects the receiver from false
readings generated by the main bang. This blank or dead zone (up to 18 microseconds
from the excitation pulse) prevents the trailing edge echoes of the excitation pulse
from being detected as back-wall or interface echoes. The end of the main bang blank
indicates the point in time at which the gage begins to search for echoes.
Custom Setups for Single Element Transducers
DMTA-10022-01EN, Rev. C, January 2015
175
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