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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

Preparatory Notes for ASNT NDT Level III Examination - Ultrasonic Testing

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FLAT Bottom Holes FBH<br />

■<br />

DGS/AVG<br />

DGS is a sizing technique that relates the amplitude of the echo from a<br />

reflector to that of a flat bottom hold at the same depth or distance. This is<br />

known as Equivalent Reflector Size or ERS. DGS is an acronym <strong>for</strong><br />

Distance/Gain/Size and is also known as AVG from its German name,<br />

Abstand Verstarkung Grosse. Traditionally this technique involved manually<br />

comparing echo amplitudes with printed curves, however contemporary<br />

digital flaw detectors can draw the curves following a calibration routine and<br />

automatically calculate the ERS of a gated peak. The generated curves are<br />

derived from the calculated beam spreading pattern of a given transducer,<br />

based on its frequency and element diameter using a single calibration point.<br />

Material attenuation and coupling variation in the calibration block and test<br />

specimen can be accounted <strong>for</strong>.<br />

http://www.olympus-ims.com/en/ndt-tutorials/flaw-detection/dgs-avg/

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