What is the purpose of distance amplitude correction (DAC) in phased array testing?

Distance amplitude correction (DAC) is a critical aspect of phased array testing that addresses the inherent relationship between the distance a sound wave travels through a material and the amplitude of the signal that returns to the transducer. As sound waves propagate through a medium, various factors can lead to a reduction in the amplitude of the returned signals, primarily due to geometrical spreading and attenuation within the material.

The purpose of implementing DAC is to correct for these variations in signal amplitude with distance. By applying DAC, technicians can ensure that signals originating from different depths are compared on an equal basis, allowing for accurate detection of flaws regardless of their position in the material being tested. This correction enhances the reliability of the test results and improves the sensitivity of the system to detect potential defects that might otherwise be masked by variations in amplitude that are caused merely by the distance involved.

The other options focus on unrelated functions, such as time delays in signal processing, adjustments to focal depths, or determining effective apertures, which do not directly pertain to amplitude variation corrections over distance.