To localize and determine the size of discontinuities in accordance with the pulse echo method
For ultrasonic tests according to the pulse echo method with perpendicular sound coupling, standard normal probes are used. The localisation of discontinuities is here carried out by reflection of the sound wave, with the time of flight of acting as a measure of the depth of the discontinuity. In contrast, an exact determination of size is usually problematic due to material attenuation and sound field characteristics. The size of discontinuities of large spatial extension can be determined by scanning. The size of small discontinuities is determined by comparison with idealised replacement reflectors from a distance-gain-size diagram. In the experiment, such a DGS diagram is to be produced using a test block with defined replacement reflectors (drilled holes of different size and depth).
In the DGS diagram, the echo amplitudes of the replacement reflectors are presented in relation to the amplitude of an infinitely extended reflector in the spacing zero and its distances x relative to the zero field length xN. For the series of the diagonally arranged, equal-sized replacement reflectors, a horizontal evaluation line was determined and entered using TGC (time gain control).