T.O. 33B-1-15-55.1.3.3.1 B-Scan.This is a means of data presentation that provides a cross-sectional view of the test piece under the scan path of asearch unit. This requires a device that transfers the movement of the search unit to the sweep of the video displaywhile the distance/depth information from the ultrasonic beam is used to vertically position the sweep to indicate therelative positions of part surfaces and internal discontinuities. This method of presentation is rarely used.5.1.3.3.2 C-Scan.This is a means of data presentation, which provides a plan view of the material and discontinuities therein. This isaccomplished by coupling a selected (electronically gated) output of an A-scan presentation to a x-y recorder or a videodisplay. Discontinuities are indicated at positions corresponding to the actual x-y locations of the discontinuities in thepart (see Figure 5-6). Devices to track and relay search unit position to the recorder or display are required. The videodisplays, usually in color, are produced after the analog signal is converted to digital data. The display can be adjustedso that the colors represent different depths or thickness if several gates are used. Alternatively, the signal amplitude isdisplayed in various colors.Figure 5-6. Typical C-Scan Inspection and Presentation.5.1.3.4 RelationshipofAScanWaveformDisplaytoDistance.In a test part containing a discontinuity, ultrasonic energy is reflected as echoes from the discontinuity and the backsurface of the test part. Referring back to Data Presentation Method, there are three methods of data presentation usedfor ultrasonic inspection: A-scan, B-scan and C-scan. Notice the positions of the displayed signals on the cathode raytube (CRT) in relation to the actual positions of the test-part front surface, discontinuity, and back surface. Thedistance along the CRT base line is proportional to the distance to the discontinuity and back surface in the test part. InData Presentation Methods, there are three methods of data presentation used for ultrasonic inspection: A-scan, B-scanand C-scan. The signals on the CRT were adjusted to position the initial pulse, on the grid marked “0” and the backsurface signal on the grid marked “5”. The discontinuity then appeared just to the right of the grid marked “1”. Theadjustment of the signals on the CRT was accomplished by varying two controls on the instrument: the Sweep Delayand the Sweep Length or Range. The adjustment made each space between the vertical grid lines on the CRTequivalent to 1 inch in the test part. Further information on operation of the ultrasonic equipment is contained insection 5.2.
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