Ultrasonic Flaw Detector DFD30
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Appendix II Terms
This Appendix has listed the terms concerning ultrasonic non-destructive inspection involved in the Instructions, a
good understanding of the exact meaning of these terms will be helpful for using the Instructions better.
1.
Pulse amplitude: voltage amplitude of a pulse signal. When type A display is used, normally it is the height from
time base to the pulse peak.
2.
Pulse length: duration of a pulse in term of time or no. of cycles.
3.
dB: the logarithmic expression of the ratio of two amplitudes or strengths.
4.
Sound impedance: ratio of sound voltage of acoustic wave to a particle’s vibration speed, normally it is
expressed by the product of density
p
times by velocity
c
of the media.
5.
Matching of sound impedance: coupling of two media equivalent to the sound impedance.
6.
Attenuation: the phenomenon that the sound voltage weakens gradually when an ultrasonic wave propagates in
the media as the propagation distance increases.
7.
Total attenuation: the weakening in sound voltage in special waveform for ultrasonic beams of any shape that is
caused jointly by scattering, absorbing and diffuse of acoustic beam, etc. as the propagation distance increases.
8.
Attenuation coefficient: loss of sound voltage in unit distance due to material scattering when the ultrasonic
wave is propagating in media, normally it is expressed by dB/cm.
9.
Defect: discontinuity whose size, shape, direction, position or nature will damage the effective use of a work
piece, or that doesn’t meet the specified acceptance standard.
10.
Type A display: a kind of way for expressing information where horizontal base (X axis) is used for expressing
distance or time, and the deflection which is vertical to the base (Y axis) is used to express the amplitude.
11.
Sending pulse: electric pulse added to the energy exchanger for producing ultrasonic wave.
12.
Time-base line: horizontal scan line expressing time or distance in type A display fluorescent screen.
13.
Scan: the repeated movement of the same style from electronic beams that runs cross the detector’s fluorescent
screen.
14.
Scan range: Max. pitch interval that can be displayed on the time base line of the fluorescent screen.
15.
Scan speed: ratio of cross axis to corresponding pitch interval on the fluorescent screen.
16.
Delayed scan: a kind of scanning way where the starting part of the time base will not show in type A or B
display.
17.
Horizontal linearity: the extent for the signal displayed on the time or distance axis of the ultrasonic detector’s
fluorescent screen to be proportional to the signal entered into the receiver (multiple echoes from the calibrated
time generator or from a plate whose thickness is known).
18.
Vertical linearity: the extent for the signal displayed on the time or distance axis of the ultrasonic detector’s
fluorescent screen to be proportional to the amplitude of signal entered into the receiver.
19.
Dynamic range: with constant gain adjustment, ratio of wave height of the max. to the min. reflection area that
can be identified on the ultrasonic detector fluorescent screen. It is normally expressed by dB.
20.
Repeating frequency of pulse: no. of pulses the pulse generator uses for exciting the probe’s wafer per second to
generate the ultrasonic wave.
21.
Inspection frequency: frequency of ultrasonic wave used during ultrasonic inspection. Normally it is 0.4 MHz
~15MHz.
