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 by
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 refraction 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.
1.2.27
Longitudinal Wave Inspection
Ultrasonic technique, normally using straight beam methods, in which
longitudinal waves are the dominant form.
1.2.28
Mid-Screen Reflection
Reflection whose amplitude is equal to one-half the usable screen height on
the CRT.
1.2.29
Megahertz (MHz)
One million hertz per second frequency.
1.2.30
NDT Level I
An NDT Level I individual should be qualified to properly perform specific
calibrations, specific NDT, and specific evaluations for acceptance or
rejection determinations according to written instructions, and to record
results.
1.2.31
NDT Level II
An NDT Level II individual should be qualified to set up and calibrate
equipment and to interpret and evaluate results with respect to applicable
codes, standards, and specifications.
1.2.32
NDT Level III
An NDT Level III individual should be capable of establishing techniques
and procedures; interpreting codes, standards, specifications, and
procedures; and designating the particular NDT methods, techniques, and
procedures to be used.
SECTION 05092A
Page 8
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