What can cause irrelevant indications on the ultrasonic display screen?

Irrelevant indications on the ultrasonic display screen can arise from a variety of factors that introduce unwanted signals or noise into the ultrasonic response. Contoured surfaces can create variations in sound wave propagation, leading to the scattering of ultrasonic signals and producing reflections that do not correspond to actual defects, thereby generating irrelevant indications.

Edge effects occur at the boundaries of the material being tested, where the change in geometry can alter wave behavior. This results in a phenomenon where reflections from the edges might mistakenly be interpreted as signals from flaws within the material, causing false indications.

Surface conditions, such as roughness, coatings, or dirt, also play a significant role in generating irrelevant indications. Any imperfection or anomaly on the surface can interfere with the transmission of ultrasonic waves, causing variations in the signal that do not relate to internal material characteristics.

Since each of these factors contributes to the generation of irrelevant indications, all of them collectively can lead to a misunderstanding of the actual condition of the material being inspected. Thus, the answer that encompasses all these causes captures the comprehensive nature of what might generate irrelevant indications on the ultrasonic display.