Full Screen Height 

FSHFull Screen Height refers to the height of the display on a conventional flaw detector screen. The amplitude of an echo is described by how high it is relative to the height of the screen. An echo that reaches the top of the screen is said to be at FSH or 100% FSH.

The sensitivity of an ultrasonic inspection is often set by raising the amplitude of a signal from a reference reflector, such as a side-drilled hole, to a specified % FSH. 100% FSH is not generally used because as the probe is scanned backwards and forwards over the reflector, the signal may disappear off the top of the screen.  So 80% FSH is a common value, which allows the full signal to be seen whether it is slightly above or below this level.

The picture shows two echoes, one at 80% FSH and the other at 50% FSH.

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