Echo Evaluation Using Dac/Tcg - GE USM 36 Series Technical Reference And Operating Manual

5 Operation

Echo evaluation using DAC/TCG

To be able to evaluate a flaw echo by means of the
DAC, certain conditions must be met:
● The distance-amplitude correction curve has to be re-
corded beforehand.
● It only applies to the same probe that was used for re-
cording the curve. It is not allowed to use even anoth-
er probe of the same type!
● The curve only applies to the material corresponding
to the material of the reference block.
● All functions affecting the echo amplitude must be set
in the same way as they existed during the recording
of the curve. This applies especially to the parame-
ters voltage, frequency, rectification, material veloci-
ty, and reject.
5-102
Change in the probe delay with DAC/TCG
Generally, a change in the probe delay automatically
also affects the shape of the sound field. This means
that a new recording of the reference echo would be the-
oretically required. However, minor changes in the de-
lay line, typically occurring due to the wear of the delay
line, have no noticeable effect on the programmed dis-
tance laws.
A T T E N T I O N
A recorded DAC curve no longer applies if
the probe delay changes to a larger extent,
e.g. caused by adding or removing a delay
line after a DAC curve has been recorded.
The same applies to immersion testing: The
DAC curve must be recorded after setting up
the final water delay line.
Failure to do so may lead to evaluation er-
rors.
Issue 2 (12/2013)
Distance-amplitude correction (DAC)
USM 36