Defect Length Sizing using The 6dB Drop Technique

Using the #ACS_Group #Ultrasonic_Flaw_Detector in the #6dB_Drop_Technique:

1. When an indication is observed during scanning, the next step is normally to identify the probe position that produces the maximum reflected amplitude. Then using the controller on the ultrasonic flaw detector to adjust the gain so that the amplitude of this signal is at the 80% or 100% (±5%) FSH (Full-Screen Height).
Note: In this case, it would be about 76% FSH.

2. After the position with the maximum reflected amplitude has been determined, the probe is moved from left to right while noting the two points where the reflected amplitude drops to 50% at the edges. The distance between the probe center at each of those two points represents the length of the flaw.
Note: In this case, 76% FSH is dropped to about 38%.

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