During the inspection of rails using conventional ultrasonics probes a beam of ultrasonic energy is
transmitted into the rail. The reflected or scattered energy of the transmitted beam is then detected using a
collection of transducers. The amplitude of any reflections together with when they occur in time can provide
valuable information about the integrity of the rail. Since defects are not totally predictable, the energy is
transmitted at several different incident angles in order to maximise the Probability of Detecion (PoD) of any
detrimental features present in the rail. The refracted angles generally used are 0, 37 or 45 and 70°. In
addition, transducers are also positioned to look across the rail head for longitudinal defects such as vertical
split heads and shear defects as previously shown in Figure 34-5