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so that it acts as a "curtain", i.e., there is enough material to cover the test site without blocking
the open end of the rubber focusing probe. This is usually the most effective method since it
uses three barriers: the rubber focusing probe, the gloved hand and the rag.
e. Barrier: When covering a large area, it is sometimes helpful to use some reflective material,
such as a welders curtain or a drop cloth, to act as a barrier. Place the material so that it acts
as a "wall" between the test area and the competing sounds. Sometimes the barrier is draped
from ceiling to floor, at other times, it is hung over railings.
Low level leaks
In ultrasonic inspection of leakage, the amplitude of the sound often depends upon the amount of turbu-
lence generated at the leak site. The greater the turbulence, the louder the signal, the less the turbu-
lence, the lower the intensity of the signal. When a leak rate is so low that it produces little, if any turbu-
lence that is "detectable", it is considered "below threshold". If a leak appears to be of this nature:
1. Build up the pressure (if possible) to create greater turbulence.
2. Utilize LIQUID LEAK AMPLIFIER. This patented method incorporates a UE Systems
product called LIQUID LEAK AMPLIFIER, or LLA for short. LLA is a uniquely formulated liquid
substance that has special chemical proper-ties. Used as an ultrasonic "bubble test, a small
amount of LLA is poured over a suspected leak site. It produces a thin film through which the
escaping gas will pass. When it comes in contact with a low flow of gas, it quickly forms a large
number of small "soda-like" bubbles that burst as soon as they form. This bursting effect pro-
duces an ultrasonic shock wave that is heard as a crackling sound in the headphones. In
many instances the bubbles will not be seen, but they will be heard. This method is capable of
obtaining successful leak checks in systems with leaks as low as 1x10-6 ml/sec.
NOTE: The size of the test area will determine the amplitude selection of the Tone Generator. If the item
to be tested is small, select the LOW position. For larger items, use the HIGH position.
3. Scan the test area with the Ultraprobe as outlined in LEAK DETECTION procedure. (i.e., start
with the sensitivity selection at 70 and proceed down).
When positioning the Tone Generator, place the transducer facing and close to the most crucial test
area. If a general area is to be checked, position the Tone Generator so that it will cover as wide an area
as possible by placing it in the "middle" of the test item.
How far will the sound travel? The Tone Generator is designed to cover approximately 113 m³ (4000
cubic feet) of uninterrupted space. This is slightly larger than the size of a tractor trailer. Placement is
dependent upon such variables as the size of the leak to be tested, the thickness of the test wall and the
type of material testing (i.e. is it sound absorbant or sound reflective?). Remember, you are dealing with
a high frequency, short wave signal. If the sound is expected to travel through a thick wall, place the
Tone Generator close to the test zone, if it is a thin metallic wall, move it farther back and use "low". For
uneven surfaces it may be necessary to use two people. One person will move the Tone Generator
slowly close to and around the test areas while another person scans with the
Ultraprobe on the other side.
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