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

Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing

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– Distance Gain Size is a method of setting sensitivity or assessing the signal<br />

from an unknown reflector based on the theoretical response of a flatbottomed<br />

hole reflector perpendicular to the beam axis. (DGS does not size<br />

the flaw, but relate it with a equivalent reflector) The DGS system was<br />

introduced by Krautkramer in 1958 and is referred to in German as AVG. A<br />

schematic of a general DGS diagram is shown in the Figure. The Y-axis<br />

shows the Gain and X-axis shows the Distance from the probe. In a general<br />

DGS diagram the distance is shown in units of Near Field and the scale is<br />

logarithmic to cover a wide range.

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