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Shielding Techniques
Since ultrasound is a high frequency, short wave signal, it can usually be blocked or "shielded". NOTE:
Men using any method, be sure to follow your plant's or company's safety guidelines. Some common
techniques are:
1. Body: place your body between the test area and the competing sounds to act as a barrier
2. Clip Board: Position the clip board close to the leak area and angle it so that it acts as a barrier
between the test area and the competing sounds
3. Gloved Hand: (USE CAUTION) using a gloved hand, wrap the hand around the rubber
focusing probe tip so that the index finger and the thumb are close to the very end and place
the rest of the hand on the test site so that there is a complete barrier of the hand between the
test area and the background noise. Move the hand and instrument together over the various
test zones.
4. Wipe rag: This is the same method as the "gloved hand" method, only, in addition to the glove,
use a wipe rag to wrap around the rubber focusing probe tip. Hold the rag in the gloved hand
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.
5. 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.
6. FREQUENCY TUNING If there are situations where a signal may be difficult to isolate, it may
be helpful to utilize the Frequency tuning Dial. Point the Ultraprobe toward the test area and
gradually adjust the frequency tune dial until the weak signal appears to be clearer and then
follow the basic detection methods previously outlined.
