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When displayed, the DAC curve visually represents a line of constant reflector peaks over a range of
material depths. A new feature of the instrument is a multiple-curve option that displays three dB offset
DAC curves simultaneously. Each curve represents constant reflector size at varying material depth.
Remember that in DAC mode, the only deviation from traditional display and operation is the
appearance of the DAC curve. All A-Scan echoes are displayed at their non-compensated height.
A DAC curve is programmed using a series of same-reflector echoes at various depths covering the
range of depths to be inspected in the test material. Because near field and beam spread vary according
to transducer size and frequency, and materials vary in attenuation and velocity, DAC must be
programmed differently for different applications. A DAC curve can be based on up to 16 data points
(material depths).These points are recorded from the DAC menu as described below.
Recording the DAC Curve
DAC Curve points are typically taken from a standard with equally sized reflectors (holes) located at
various material depths. The primary echo from each of these points (for up to a total of 16 echoes) are
recorded. When DAC is active, the instrument displays a curve that represents echo peaks for constant
reflectors at varying material depth.
Before starting to record a reference curve, the instrument must be correctly calibrated. To program the
DAC Curve:
1
Access the DAC menu by pressing
DAC
AVG
, then select the DAC submenu by pressing the menu key
below it.
2
Press
and
to select the PROGRAM item. Press the
key or turn the knob to
Trigger the DAC program. When DAC program is triggered, “DAC” and a digit number indicating the
point index appears on the top right corner of the display.
3
Couple the probe to the first reference point and adjust the gate so that it is broken by the
primary echo. If necessary, adjust the gain so that the echo crosses the gate and the highest peak in the
gate is at approximately 80% of full-screen height. The highest peak must not be higher than 100%
full-screen height. Note that you can press
or
to search the next echo very quickly.
4
While the gate is lined up over the first reference echo, Press
and
to select the
RECORD function press the
key to record the first DAC Curve point. Note that the largest echo to
cross the A-Gate will be treated as the reference echo. The gain value at which this point is recorded
becomes the “baseline” gain value.
5
Continue to record additional curve points up to a maximum of 16 points (note that at least one
DAC Curve points are required). As soon as you have recorded at least one curve reference points, your
DAC is already active.
6
When complete press
and
to select the FINISH and press
key, then follow
the on-screen prompts to exit the DAC program.
Note that you can change the DAC curve line type between CURVE and DIRECT.
The stored DAC curve points can be edited as described in next section.
Editing DAC Curve
After reference points are recorded, their values may be manually adjusted, or some points may be
manually deleted. To edit or delete points:
1
With the DAC menu accessed, select EDIT submenu.
2
Select EDIT function. Continue to press
key or turn the knob to start the EDIT process.
When DAC EDIT process is triggered, “DAC” and a digit number appear indicating the point index on the
top right corner of the display.
3
Press
or
to select the point to edit.
4
To adjust a point’s height-Select ADJUST function. Turn the knob clockwise or anticlockwise to
adjust the point’s echo height.
5
To delete a point – Select DELETE function. Continue to press
key or turn the knob to
delete that point from the DAC records.
