FIFTH CANADIAN CONFERENCE ON NONDESTRUCTIVE ... - IAEA

3.3 Modified C-Scans
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If a series of amplitude profiles are drawn on the same page or
screen, each offset from the previous one by a small horizontal
and vertical displacement, the effect is much like that of a 3dimensional
projection. This method of display is known as
modified C-scan, and can be thought of as all the possible Cscans
of the testpiece, stacked one on top of another in order of
increasing amplitude threshold.
Beam profiles, used to aid in the characterization of ultrasonic
transducers, are a common form of modified C—scan display.
Figure 7 is an example, showing the echo response of a 3.5 MHz
transducer to a 2 mm diameter target as a function of their
relative positions. It shows graphically the ultrasonic beam
strength of a transducer at various points within it's field.
3-Dimensional Time-of-F1ight Displays
Since the tirne-of-f1ight from a transducer to a reflector is
proportional to their separation, 3-dimensional reflector
coordinates can be calculated for a scan knowing only the
inspection geometry and the measured time-of-f1ight values.
These can then be displayed in 3-dimensional form using standard
perspective or parallel projections (9) as supplied by the Core
library (10). Figure 8 shows time-of-f1ight data for the
testpiece of Section 3.2 plotted in this way. By combining the
information from a complete set of B-scans into one image, it
shows not only the extent of defects, but also allows some
estimation of their depth.
Because of the general nature of the 3~dimensional projections
used, it is possible to view the object from any angle or
distance.
h. DISCUSSION
The most important criterion for the system, as well as the most
difficult one to satisfy, was that of flexibility. It has been
achieved, we feel, through the use of a modular ultrasonic
subsystem and by the incorporation of the DTR into the system.
In particular, the ability of the DTR to digitize a received
waveform allows almost any desired numerical algorithm to be
applied to the data, while the storage of results as numeric data
files simplifies the data processing task. The softwarecontrolled
display subsystem also aids flexibility,
by simplifying modification and improvement ot' the display routines).