Specifications

11. Using DAC/TCG
USN52 L Operating Manual Page 71
11.1 Description of DAC/TCG
The USN52 L is equipped with Time Corrected Gain (TCG) and
Distance Amplitude Curve (DAC) functions, located in the TCG
menu.
TCG adjusts the gain at different locations in the A-scan display,
corresponding to different material depths, to compensate for sig-
nal loss (or variation) due to attenuation, beam spread, or other
factors. TCG is typically used to display reflectors of equal size at
equal amplitudes, regardless of their depth in the test material.
Alternatively, the DAC function displays all echoes at their true
amplitude with no depth compensation. A Distance Amplitude
Curve, however, is superimposed on the A-scan.
Both TCG and DAC displays are illustrated in Section 11.2.
DAC/TCG can be programmed with up to 10 data points (material
depths). The dynamic range of the DAC/TCG function is 40 dB.
Maximum curve slope is 6 dB per microsecond. Successive data
points do not have to decrease in amplitude. That is, the DAC/
TCG curve does not have to have a constantly descending slope.
11.2 Using DAC/TCG
A DAC curve is programmed using a series of echo signals at
various depths covering the range of depths to be inspected in the
test material. Because near field and beam spread vary accord-
ing to transducer size and frequency, and materials vary in attenu-
ation and velocity, DAC/TCG must be programmed differently for
different applications.
Before programming a DAC/TCG curve, instrument parameters,
e.g. RANGE, MTL VEL, RECTIF, PULSER, etc., should be set
according to the requirements of the test. PULSER and RECTIF
functions, in particular, should not be changed after the DAC/TCG
curve has been programmed, because these parameters affect
signal amplitude and, therefore, the accuracy of inspection results.
Only one curve may be programmed at any given time. However,
when a data set is stored (MEM menu), the current DAC/TCG
curve and status (OFF, TCG, or DAC) will be stored with the data
set. When recalled, curve status will be the same as when it was
stored. For example, if TCG is active when a data set is stored, it
will be active when that data set is recalled.
11. Using DAC/TCG