hydratight BoltScope Pro, Руководство по эксплуатации

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6.2 Transducer contact requirements
The goal is to transmit as much sonic energy as possible from the transducer into
the bolt, and to send that energy, to the greatest extent possible, down and back
the center of the bolt, as shown in Figure 1.
Figure 1 Sound path in a good bolt
Smooth, even surfaced bolt ends that seat the entire active surface of the
transducer with minimum gap are required for accurate signal transmission. Bolt
ends may need to be cleaned, ground, etc. to achieve the required surface.
Avoid:

Rough or irregular surface’s which prevent adequate contact with the
transducer. Irregular or rough surfaces can be filled with couplant, but energy
transmission will still be reduced and dispersed causing mode conversions to
occur from reflections off the side walls of the bolt, as shown at left of Figure
2.

Bolt ends not perpendicular to the axis of the bolt, as shown at right of Figure
2. Energy will be transmitted toward the side wall and reflect along the bolt,
yielding poor signal quality and possible measurement errors. Avoid
alignment errors exceeding 2 degrees.
Figure 2 Rough and angled transducer contact

Rusted, dirty, or thick paint-covered bolt ends. These coatings prevent sonic
energy from traveling between the transducer and the bolt. Very thin coating
or plating is acceptable.