In UT sizing, what does a DAC curve relate?

• A. Distance Amplitude Correction; relates echo amplitude to flaw size as a function of depth.
• B. Direct Amplitude Calibration; calibrates amplitude.
• C. Dynamic Attenuation Coefficient; models attenuation vs depth.
• D. Data Analysis Constant; used for display brightness.

Answer: (A)

Depth-dependent attenuation affects how loud an echo appears, so a Distance Amplitude Correction curve is used to normalize that effect. The DAC curve provides a reference relationship between how far the reflector is from the transducer (depth) and how large the echo should be for a given flaw size. By plotting or using this curve, you can translate an observed echo height back into an estimated flaw size, accounting for the fact deeper flaws naturally produce smaller echoes. In practice, you compare the measured echo amplitude at its depth to the DAC curve to infer the flaw size. The other terms don’t describe this depth-related amplitude-to-size correction used in UT sizing.