16
16
Digital Readout of Pulse Amplitude. The pulse amplitude should digitally appear in the upper
left corner of the display in terms of percent of full screen. If not, press the blue “FLAW/GATE”
button to make it appear.
7.3 CALIBRATION
7.3.1
“Calibration” On Reference Samples
Before actual use for inspection use, the Curlin-AIR must be adjusted so it will reliability detect
and trigger the ALARM (audible &/or visual) whenever the ultrasonic beam is scanned over the
minimum-size flaw that needs to be detected.
7.3.2
Reference Sample
A reference sample containing various known-sized flaws, including the minimum-size
tolerable flaw, needs to be constructed from the same type material to be inspected. THIS IS
VERY IMPORTANT! For foam-type samples, for instance, horizontally-oriented
delamination/split-type flaws can be simulated by first removing a circular flat bottomed “plug”
of the material, say, mid-line deep, from one surface. Then, an identical plug (or the same one
if it is intact) can be re-inserted into the initial plug, while leaving a very slight air gap between
the plug and the flat bottom of the hole. The plug surface should then be sanded, etc. to make
it flush with the overall material surface. Using this or a similarly effective method can create
various known-sized diameters, depths and locations (center of sample, near edge of sample,
etc.).
7.3.3
Curlin-AIR Adjustment On Reference Sample
Adjust the GAIN until the signal amplitude is about 75% of screen height (if possible). Next,
steadily hold the ultrasonic beam directly over the simulated minimum-sized tolerable flaw. A
substantial reduction in signal amplitude should be observed. Now adjust the FLAW GATE so
that the ALARM reliably triggers when the beam is held directly over the flaw.
7.3.4
Maximum Scan Speed Determination
Since the Curlin-AIR operates with a rapid firing of ultrasonic pulses, it technically cannot
“instantaneously” detect flaws. Therefore, some maximum scanning speed limit is determined
primarily by:
C
The pulse repetition rate (Curlin-AIR portable - max rate is 125Hz rate)
C
The size and shape of the minimum-tolerable flaw
C
The ultrasonic beam diameter
C
FLAW GATE alarm threshold level
C
The material itself.
To obtain a general feeling for the acceptable scanning speed limit, scan the beam back and
forth at slowly increasing speeds across the minimum-size tolerable flaw until the ALARM no
longer detects the flaw. The maximum scan speed used must be below this limit and be slow
enough to reliably detect the subject flaw. Maximum scan speeds can be slightly enhanced by
setting the FLAW GATE level “tight” (small amplitude variation from good to flaw condition).
7.3.5
Edge Effects
By placing a minimum-sized flaw at the edge of the reference sample, it is possible to
determine performance when the beam is scanned along the edge of the material. Generally,
calibration /performance along an edge holds quite well until the outside edge of the transducer
extends over the material edge. Actual “edge” performance
must be
determined for each
application. Many times the Curlin-AIR flaw response will need to be compensated for by
readjusting it for “edge inspection”. Frequently, “butting” the test material intimately against the
edge of another material whose surface is slightly higher can facilitate edge inspection
convenience and performance. This setup acts as mechanical scan lines guide along the
edge, plus greatly reduces the chance of any applicable ultrasonic beam “leakage” around the
edge.
