FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

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each waveform digitization the time position of the two largest
peaks, assumed to represent a front reference surface, and a flaw
or back reference surface. If the user has requested that peak
amplitude data be collected, it is assumed that he has gated out
the reference surfaces and so a single value corresponding to the
amplitude of the highest peak in the data is stored instead.
In some situations it may be useful to combine the 2 methods of
data acquistion, by collecting both amplitude and time-of-f1ight
values for each peak. This is done, however, at the cost of
increased data storage space requirements.
Data is stored on disk, from which it can be retrieved for
further processing and display. There are k types of displays
that the system can currently produce:
i) rf or video waveforms (A-scans),
ii) 2-dimensional sections through 3~dimensional arrays of
data (including B-scans and C-scans),
iii) modified C-scans
iv) true 3-dimensional displays created by converting timeof-flight
data into linear measurements.
3.1 Waveform Display
Figure 5 shows a display of the 4096 data points collected from
an rf signal which had been sampled at 20 Mhz. This type of
display is most useful for retaining a representative waveform
from a scan for the evaluation of noise levels, signal strength,
etc. at some later time.
3.2 2-Dimensional Sections
Amplitude or time-of-f1ight data collected from a 2-dimensional
rectilinear scan is generally stored, either implicitly or
explicitly, in a 3~ d imensional array as a function of scanning
bridge position. The common B- and C-scans can be thought of as
displaying subsets of this array in the form of sections or
slices normal to one of the 3 dimensions. For example, the Cscan
of Figure 6 is simply a slice made normal to the "amplitude
axis" in a peak amplitude data array. Similarly, a B-scan
results from making a slice through a time-of-f1ight data array,
normal to the scan increment axis.
However the display subsystem is not limited to standard B- and
C-scan modes. For any given data array, 3 different types of
sections can be displayed, with the thickness and location of
each under user control.