Most basic pulse echo ultrasonic instruments use:

• A. Automatic read-out equipment
• B. A B scan presentation
• C. A C scan presentation
• D. An A scan presentation

Answer: (D)

In pulse-echo ultrasonic testing, the simplest and most fundamental display is the A-scan. It shows echo amplitude as a function of time, with the horizontal axis representing the time after the pulse is emitted and the vertical axis representing echo strength. Since sound travels at a known speed in the material, those times can be converted to depths, giving a one-dimensional profile that shows the surface reflection and any subsurface reflectors or flaws along the beam path. This straightforward trace is what basic instruments deliver because it provides direct depth information without needing to build up an image.

B-scan and C-scan, by contrast, construct two-dimensional images by moving the probe or combining multiple scans to map cross-sections or plan views, which adds complexity and equipment requirements beyond the simplest display. Automatic read-out is more of a feature set than the fundamental display type.