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Sizing Techniques
DGS or AVG curves allow the operator to size defects based on a calculated response curve for a given transducer, material, and reflector size. In this case the upper line marks the echo amplitude corresponding to a 2 mm reflector at various depths, and the lower line represents an indication level 6 dB below that threshold.
Distance-Amplitude Correction (DAC) is used to plot the equivalent amplitude of echoes from reflectors of the same size but a different distances from the transducer. The purple curve indicates that all of the peaks represent similar reflectors, although echo amplitude varies due to material attenuation and beam spreading.
Time Varied Gain (TVG) varies receiver gain across the screen to compensate for the changes in echo amplitude from different size reflectors of different distances due to material attenuation and beam spreading. Equal size reflectors produce equal height indications regardless of depth.
Multiple Echeos, Amplitude Decreases with Distance
API software utilizes the American Petroleum Institute's recommended practice for measuring the height of an ID crack by analyzing the echo envelope generated by an angle beam transducer. Crack dimensions can be calculated from the width of the echo envelope.
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