Distance Amplitude Correction (DAC) is used to compensate echo height variations due to depth.

• A. Transfer
• B. Distance amplitude correction
• C. Attenuation
• D. Interpretation

Answer: (B)

Distance Amplitude Correction addresses how echo height changes with depth by applying a depth-based gain to the received signal. In ultrasonic testing, deeper reflectors naturally produce smaller echoes because the sound loses energy as it travels through the material (attenuation) and because the beam spreads over distance. If you relied on raw echo amplitudes, deeper flaws would look weaker simply due to their location, making it hard to compare flaw sizes across depths.

DAC uses a compensation curve that increases the displayed amplitude of echoes as depth increases, so a reflector of a given size produces a more uniform, comparable height on the display regardless of how deep it is. This normalization helps you detect and size flaws consistently from near to far, rather than being biased by depth.

The other terms describe related ideas but not the specific corrective technique. Attenuation is the general loss of signal strength with distance, which causes the depth-related variation DAC corrects. Transfer and interpretation refer to different parts of data handling or evaluative steps and do not denote the depth-based amplitude correction itself.