GE 37 400, Technical Reference And Operating Manual

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Distance-amplitude correction (DAC) 5 Operation
USM 36 Issue 2 (12/2013) 5-93
5.18 Distance-amplitude correction
(DAC)
The USM 36 has an optional DAC function for the echo
evaluation by means of the distance-amplitude correc-
tion (DAC).
Due to the angle of beam spread and the sound attenu-
ation in the material, the echo height of equally sized re-
flectors depends on the distance to the probe.
A distance-amplitude correction curve, recorded using
defined reference reflectors, is a graphical representa-
tion of these influencing factors.
If you use a reference block having artificial flaws to re-
cord a DAC curve, you can use this echo amplitude for
the evaluation of a flaw without any further corrections.
The reference block should be made of the same mate-
rial as the test object.
The time-corrected gain TCG increases the gain in dis-
tance sensitive mode so that all reference echoes reach
80 % screen height. The amplitude evaluation of echo
indications is made in relation to the first reference echo.
– Switch to the second operating level.
– Select the function group EVAL .
– Select the function EVAL MODE and choose
DAC/TCG .
– Switch back to the first operating level. The function
group DAC/TCG is now displayed there.
If a stored DAC curve exists, it becomes effective now.