ultrasonic energy the same as a mirror reflects light.
1.2.38
Refracted Waves
Waves that have undergone change of velocity and direction by passing from
one material to another material with different acoustical properties.
Refraction will occur wherever the angle of the incident wave to the
interface is other than perpendicular.
1.2.39
Rejectable Discontinuity (Defect)
Reflector large enough to produce a signal (decibel rating) that exceeds
the reject/repair line.
1.2.40
Resolution
Ability to clearly distinguish signals obtained from two reflective
surfaces with a minimum separation distance. Near-surface resolution is
the ability to clearly distinguish a signal from a reflector at a minimum
distance under the contact or near surface without interference from the
initial pulse signal. Far-surface resolution is the ability to clearly
distinguish signals from reflectors displaced at minimum distances from the
far or back surface when the sound beam is normal to that back surface.
1.2.41
Ringing
Excitation in a transducer due to the application of a short pulse of high
voltage.
1.2.42
Scanning
Procedure of moving the search unit or units along a test surface to obtain
complete inspection of the entire volume of a material being inspected.
Preliminary scanning refers to a somewhat common practice of rapidly
traversing a weld ultrasonically with a higher instrument gain or
sensitivity level than will be used for the evaluation. It gives the
operator an estimate of the welding quality and also makes all defects more
prominent and less likely to be missed.
1.2.43
Search Unit
Device containing a piezoelectric material used for introducing vibrations
into a material to be inspected or for receiving the vibrations reflected
from the material. The active element of the search unit is defined as the
effective transmitting area. Search units are also called transducers or
probes. They may be single or dual and contain one or two piezoelectric
elements, respectively, for transmission and reception. The single search
unit is sometimes enclosed in a transducer wheel or search unit wheel. The
search unit may be manually handled and placed in direct contact with the
material to be inspected or may be held in a fixture for immersion
techniques.
1.2.44
Sensitivity
Measure of the ultrasonic equipment's ability to detect discontinuities.
Quantitatively, it is the level of amplification of the receiver circuit in
the ultrasonic instrument necessary to produce the required indication on
the scope from the reference hole in the reference block. Also see
"Standard Reference Level."
SECTION 05091A
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