Specifications

10. Using the Flaw Alarm / Measurement Gate
USN52 L Operating Manual Page 69
10.3 Adjusting Gate Parameters
If the gate is enabled, the following parameters must be set based
on the requirements of the application:
a-THRESH - To assure activation of the flaw alarm and valid mea-
surement data the threshold must be set to a level that any signifi-
cant echo signal will violate.
a-START - The leading (left) edge of the gate bar must be posi-
tioned so that any flaw or measurement echo signal will occur to
its right in the A-scan display. For many applications, this will be as
close as possible to the acoustic zero point, i.e. the initial pulse
(main bang) or an interface echo.
a-WIDTH - The trailing (right) edge of the gate bar must be posi-
tioned so that any flaw or measurement echo signal will occur to
its left in the A-scan display. For many applications, this will be as
close as possible to the backwall echo.
To set the parameters of gate a, proceed as follows:
1. Calibrate the A-scan display by following the appropriate pro-
cedure in Chapter 9.
2. If necessary, switch to the upper menu level and A-scan dis-
play:
or
3. Select the GATE menu: or
4. Adjust threshold, a-THRESH, level:
Level is shown as percent of screen height and vertical posi-
tion of the gate bar.
5. Position the leading edge, a-START:
Position is shown in inches (mm) of test material and by hori-
zontal position in the A-scan display.
6. Set width, a-WIDTH, to cover the depth/thickness range to
be monitored:
Simultaneously pressing automatically sets leading and
trailing edges at 20% and 90% of current A-scan width, re-
spectively.
Width is shown in inches (mm) of test material and by the
length of the gate bar in the A-scan display.
NOTE: When used for flaw monitoring or 0 TO 1st thick-
ness measurement, a single gate bar (gate a ) is displayed.
If MEASURE is set to MULTECHO a second bar (gate b )
appears. Purpose and operation of gate b are described n
Chapter 13.