Evaluation According To The Dgs Method; Using The Dgs For Measurements - GE USM 36 Series Technical Reference And Operating Manual

Evaluation according to the DGS method

5.21 Evaluation according to the
DGS method
The USM 36 offers the optional evaluation method DGS
(distance - gain - size).

Using the DGS for measurements

You can use the DGS mode to compare the reflecting
power of a natural flaw in the test object with that of a
theoretical flaw (circular disk-shaped equivalent reflec-
tor) at the same depth.
A T T E N T I O N
You are comparing the reflecting power of a
natural flaw with that of a theoretical flaw. No
definitive conclusions may be drawn about
the natural flaw (roughness, inclined posi-
tion, etc.).
The so-called DGS diagram forms the basis for this
comparison of the reflecting power. This diagram con-
sists of a set of curves showing the connection of three
influencing variables:
USM 36
● Distance D between the probe coupling face and the
circular disk-shaped equivalent reflector
● Difference in gain G between a circular disk-shaped
equivalent reflector and a reference reflector, e.g. an
infinitely large backwall
● Size S of the circular disk-shaped equivalent reflector
The influencing variable S remains constant for one
curve in each set of curves.
The advantage of the DGS method lies in the fact that
you can carry out reproducible evaluations of small dis-
continuities. This reproducibility is especially important,
e.g. whenever you want to carry out an acceptance test.
In addition to the influencing variables already men-
tioned, there are other factors affecting the curve shape:
● sound attenuation,
● transfer losses,
● amplitude correction value,
● probe.
Issue 2 (12/2013)
5 Operation
5-121