DMTA-10055-01EN, Rev. A, February 2015
Appendix C
322
A-scan The most common waveform display format, plotting
signal amplitude versus distance. An A-Scan shows the
pulse travel time in the horizontal direction (left to right),
representing the corresponding sound paths, and the echo
amplitude in the vertical direction.
Attenuation The loss in acoustic energy that occurs between any two
points of travel. This loss may be due to absorption,
reflection, scattering, and other phenomena.
Backwall echo The echo received from the side of the test piece opposite
the side to which the transducer is coupled. This echo
represents the thickness of the test piece at that point.
Background noise Extraneous signals caused by sources within the ultrasonic
testing system and/or the material being tested.
Beam-index point
(BIP)
For an angle beam probe, the point where the sound
leaves the wedge and enters the specimen.
Cal. block velocity Material sound velocity for the calibration block.
Couplant A material (usually a liquid or gel) used between the
transducer and the test piece to eliminate air from this
space and facilitate the passage of sound waves into and
out of the specimen.
Critical defect Either the largest tolerable defect or the smallest
intolerable defect. The critical defect size is usually given
by a specification or code.
Cross talk An unwanted condition affecting dual element
transducers in which acoustic energy travels from the
transmitting crystal to the receiving crystal by routes other
than the intended path through the test piece.
Damping (control) A variable resistance across the pulser circuit output
which shapes the excitation pulse. Typically it is used to
change pulse characteristics to optimize either penetration
(low damping) or near-surface resolution (high damping).
Table 32 Glossary (continued)
Term Definition
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