Which of the following is NOT a source of non-relevant ultrasonic signals?

• A. Surface Roughness of the Part
• B. Mode Conversion Within the Part
• C. Shape or Contour of the Part
• D. Electrical Noise From the Instrument

Answer: (D)

Non-relevant ultrasonic signals are echoes that come from features of the part or the inspection setup, not from a flaw. Surface roughness creates many small reflections from the surface that aren’t flaws. Mode conversion happens when the ultrasonic wave changes type at boundaries inside the material, producing additional echoes that aren’t related to a defect. The shape or contour of the part can cause edge reflections and scattering that mimic flaw signals. Electrical noise from the instrument, however, is not a reflection or echo produced by the part’s geometry or material—it’s noise from the equipment itself. While it can degrade the readout, it isn’t a non-relevant signal produced by the part, so it’s not considered a source of non-relevant ultrasonic signals.