Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing, UT

Dead Zone -The initial pulse is a technical necessity. It limits the detectability
of near-surface discontinuities. Reflectors in the dead zone, the nonresolvable
area immediately beneath the surface, cannot be detected. The
dead zone is a function of the width of the initial pulse which is influenced by
the probe type, test instrument discontinuities and quality of the interface.
This is done by ensuring that the peak from the Perspex insert appears
beyond the trailing edge of the initial pulse start. Excessive dead zones are
generally attributable to a probe with excessive ringing in the crystal.