Ultrasonic Flaw Detection Terminology

Ultrasonic flaw detector is a portable industrial non-destructive testing instrument, which can quickly and conveniently, non-destructively and accurately detect, locate, evaluate and diagnose many kinds of defects (cracks, inclusions, folding, porosity, sand holes, etc.) inside the workpiece, and it can be used in the laboratory as well as in the engineering site. It is an essential testing instrument in the NDT industry.

Ultrasonic nondestructive testing has a lot of terminology, commonly used A-type display, transmit pulse, pulse amplitude, pulse width, echo, bottom echo, defective echo, interference echo, late echo, phantom echo, decibel, acoustic impedance, attenuation, defects, time baseline, scanning, scanning range, scanning speed, horizontal linearity, vertical linearity, dynamic range, pulse repetition frequency, detection frequency, echo frequency, Sensitivity, sensitivity margin, resolving power, gate, attenuator, signal-to-noise ratio, gain, distance amplitude curve (DAC), coupling, test block, standard test block, comparison test block, probe, piezoelectric material, wafer, acoustic isolation layer, straight probe, slant probe, probe incidence point, probe angle, probe leading edge, etc. Knowing exactly what these terms represent will help you to better utilize the instrument for flaw detection.

1.Type A Display.
A method of representing information in which distance or time is represented by a horizontal baseline (X-axis) and amplitude is represented by a deflection perpendicular to the baseline (Y-axis).

2.Emitted Pulse.
An electrical pulse added to a transducer in order to produce ultrasound.

3.Pulse Amplitude.
The voltage amplitude of the pulse signal. When an A-type display is used, it is usually the height from the time base line to the peak of the pulse.

4.Pulse Width.
The duration of the pulse expressed as a time or period value.

5.Echo.
The ultrasound signal reflected back from a reflector.

6.Bottom Echo.
Wave reflected from the bottom surface of the inspected part.
7.Defect Echo.
Echoes caused by internal or surface defects in the inspected part.
8.Interference Echo.
A variety of echoes that impede the evaluation of the results of flaw detection are called interference echoes. Including false reflections, internal reflections and reflections due to instrument noise, external interference and other reflections.

9.Late Echo.
An echo from the same reflector that arrives late because it traveled a different path or underwent a wave transition along the way.
10.Phantom Echo.
A non-realistic echo (ghost wave) that appears in a material with good sound transmission due to the high repetition frequency of the ultrasonic flaw detector.
11.Decibel.
The logarithmic representation of the ratio of two amplitudes or intensities. A comparison of two wave heights on a display is often expressed in decibels.
12.Acoustic Impedance.
The ratio of the sound pressure of a sound wave to the vibrational velocity of a mass, usually expressed as the product of the density p and the velocity c of the medium.
13.Attenuation.
The phenomenon in which ultrasonic waves propagate through a medium and the sound pressure gradually decreases as the distance traveled increases.
14.Defect.
A discontinuity of size, shape, orientation, location, or nature that would be detrimental to the effective use of the workpiece or that does not meet the requirements of specified acceptance criteria.
15.Time Baseline.
A horizontal scanning line in the Model A display fluorescent screen indicating time or distance.
16.Scan.
Repeated movement of the electron beam across the fluorescent screen of a flaw detector in the same pattern.

17.Scanning Range.
The loudest range that can be displayed on the baseline at the time of the fluorescent screen.
18.Scan Speed.
The ratio of the horizontal axis on the phosphor screen to the corresponding sound range.
19.Horizontal Linearity.
The degree to which the signal displayed on the time or distance axis of an ultrasonic flaw detector's fluorescent screen is proportional to the signal fed into the receiver (either through a calibrated time generator or multiple echoes from a plate of known thickness).
20.Vertical Linearity.
The degree to which the signal displayed on the time or distance axis of the ultrasonic flaw detector's fluorescent screen is proportional to the amplitude of the signal at the input receiver.
21.Dynamic Range.
The ratio of the maximum and minimum reflected area wave heights that can be resolved on the screen of an ultrasonic flaw detector when the gain adjustment is constant. Usually expressed in decibels.
22.Pulse Repetition Frequency.
The number of pulses per second at which the probe wafer is excited by the pulse generator in order to produce ultrasonic waves.
23.Detection Frequency.
The ultrasonic frequency used for ultrasonic detection, usually 0.5~15MHZ.
24.Echo Frequency.
The reciprocal of the time between peaks obtained by expanding the echo on the time axis.

25.Sensitivity.
A measure of the smallest ultrasonic signal that produces a recognizable indication on the fluorescent screen of an ultrasonic flaw detector.
26.Sensitivity Margin.
In ultrasonic flaw detection systems, the difference between the standard defect detection sensitivity expressed at a certain level and the maximum detection sensitivity.
27.Resolving Power.

The ability of an ultrasonic flaw detection system to discriminate between defects in the transverse direction.
28.Gate.
An electronic method of selecting a range of time for the purpose of monitoring the flaw detection signal or for further processing.
29.Attenuator.
A device that causes a quantitative change in signal voltage (sound pressure). The amount of attenuation is expressed in decibels.
30.Signal-to-Noise Ratio.
The ratio of the amplitude of the ultrasound signal to the amplitude of the maximum background noise. Usually expressed in decibels.
31.Gain.
The logarithmic form of the amount of voltage amplification of the ultrasonic flaw detector receiver amplifier. Expressed in decibels.
32.Coupling.
The action of conducting sound waves between the probe and the inspected part.

33.Distance Amplitude Curve (DAC)
A set of curves drawn from three parameters: the distance of a known reflector that produces an echo, the gain of the flaw detector, and the size of the reflector, according to specified conditions. In actual flaw detection, the equivalent size of the flaw can be estimated from this curve by the measured distance to the flaw and the gain value.
34.Test Block.
A specimen used to characterize the properties of an ultrasonic inspection system and the sensitivity of the flaw detection.
35.Standard test piece.
A specimen whose material, shape and dimensions have been certified by a competent authority. Used for performance testing and sensitivity adjustment of ultrasonic testing devices or systems.
36.Comparison test block.

The test block is used to adjust the sensitivity of the ultrasonic detection system or the sensitivity adjustment.
Adjust the sensitivity of the ultrasonic detection system or compare the size of the defect test piece. Generally made of materials with similar characteristics to the material being tested.
37.Probe.
Transmit or receive (or both transmit and receive) ultrasound energy electro-acoustic conversion device. The device generally consists of a trademark plug, housing, backing, piezoelectric element, protective film or block.
38.Piezoelectric Material.
Materials with the property of piezoelectric effect, such as quartz, barium titanate, lead zirconate titanate, etc.
39.Wafer.
The electro-acoustic conversion element in the ultrasound probe. Mainly made of quartz, barium titanate and lead zirconate titanate piezoelectric materials, the shape of the plane, curved surface.

40.Acoustic Insulation.

A highly absorbent spacer used in bicrystalline probes to divide the sound path.
41.Straight probe.
A probe used for vertical flaw detection, mainly for longitudinal wave testing.
42.Oblique Probe.
A probe used for oblique sounding, mainly for transverse waves.
43.Probe Incidence Point.
The point on a transverse or surface wave probe where the axis of the emitted beam passes through the bottom surface of the probe.
44.Probe Angle.
The value of the tangent of the refractive angle (K-value) in the steel of an oblique probe, expressed as an Arabic numeral.
45.Probe Leading Edge.
The length of the leading edge of the slant probe, which is the distance from the point of incidence to the leading edge of the probe.