Length -6 dB Drop
To measure the length of a defect, the -6 dB drop can be used.
- The part is scanned for indications
- When an indication is encountered, its signal is peaked and its amplitude recorded
- The probe is moved sideways until the first -6 dB point is encountered. Its position is marked on the part and recorded
- The probe is moved sideways in the opposite direction until the second -6 dB point is encountered. The position is marked on the part and recorded
- The length of the indication is the measured distance between the two -6 dB points
Since the indication can be of irregular shape, it is important to measure the length where it is at its widest.