1.2.18
Examination
Within the context of this specification, examination is equivalent to the
word "inspection."
1.2.19
Gain Control
Circuitry designed into the ultrasonic system to vary reflection amplitude.
This control is usually calibrated in decibels. It is also called the
sensitivity control.
1.2.20
Gross
Background displacement of the trace on the CRT from the established
baseline due to the gain setting, the characteristics of the test
equipment, or the material under examination.
1.2.21
Hertz
One complete set of recurrent values of a periodic quantity comprises a
cycle. In other words, any one set of periodic variations starting at one
condition and returning once to the same condition is a cycle.
1.2.22
Immersion Techniques
Test methods in which the part to be tested and the search units are
immersed in water or other suitable liquid couplant. A mechanical device
is used to firmly hold and direct the wave angle of the search unit. The
search unit does not contact the item being inspected.
1.2.23
Indication
Visual presentation on the cathode ray screen resulting from a sound beam
reflection from a boundary surface or discontinuity.
1.2.24
Initial Pulse Indication
Usually called the "initial pulse". A signal on the CRT screen marking the
instant at which a voltage impulse is applied to the transmitting crystal.
Its rising edge is frequently invisible due to the time lag in the probe
shoe and the consequent necessity to ensure coincidence between the time
base zero and the instant at which the transmitter pulse actually enters
the material under test.
1.2.25
Linearity
Property of an instrument revealed by a linear change in reflected signal
or displacement. The vertical linearity is determined by plotting the
change in ratios of signal amplitude from two adjacent reflections from an
area of known size. The horizontal linearity is determined by plotting the
distance the signal is displaced along the sweep against the change in
material thickness or by noting the spacing of multiple back reflections.
1.2.26
Longitudinal or Compressional Waves
Simple compression-rare-fraction waves in which particle motion within a
material is linear and in the direction of wave propagation. Also called
straight beams, or compressional or normal waves.
SECTION 05091A
Page 7
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