Validity Of The Dgs Method - GE USM 36 Series Technical Reference And Operating Manual

Evaluation according to the DGS method

Validity of the DGS method

Echo amplitude evaluations using the DGS method are
only reliable and reproducible under the following condi-
tions:
● In test objects showing sound attenuation character-
istics that cannot be neglected, the sound attenuation
coefficient must be determined and entered in the
DGS table. For this purpose, the sound attenuation
coefficient is measured in the test object itself or in a
reference test block made of identical material, with
known reference reflectors at various distances ac-
cording to the known methods and, afterwards, en-
tered in the DGS tables. The subsequently displayed
evaluation curve will then take the effective sound at-
tenuation into account, independently of the distance.
● The reference echo must come from the test object if
possible. If this is not possible, it should be ensured
that the reference block is made of the same material
as the test object.
USM 36
● The evaluation must be carried out using the same
probe that was used for recording the reference echo.
Another probe of the same type can be used after re-
cording a new reference echo.
● Echo amplitudes for reflector distances smaller than
half of the near-field length of the probe used are sub-
ject to considerable variations, for physical reasons,
due to the interference phenomena being effective in
this area. Evaluation results may therefore vary by
more than the usually permissible ±2 dB. Although a
DGS evaluation is possible, it is not recommended in
this case.
Issue 2 (12/2013)
5 Operation
5-123