Ultrasonic flaw detector terminology
- Pulse amplitude: the voltage amplitude of the pulse signal. When using A-type display, it is usually the height from the time baseline to the pulse peak.
- Pulse length: pulse duration expressed as time or period value.
- Decibel: The logarithmic expression of the ratio of two amplitudes or intensities.
- Acoustic impedance: the ratio of the sound pressure of the sound wave to the vibration speed of the particle, usually expressed by the product of the density p of the medium and the speed c.
- Acoustic impedance matching: coupling between two media with similar acoustic impedance.
- Attenuation: When ultrasonic waves propagate in a medium, the sound pressure gradually weakens as the propagation distance increases.
- Total attenuation: For any shape of ultrasonic beam, the sound pressure of a specific waveform increases with the propagation distance and is weakened due to scattering, absorption and sound beam diffusion.
- Attenuation coefficient: When ultrasonic waves propagate in media, the loss of sound pressure within unit distance due to material scattering is usually expressed in decibels per centimeter.
- Defect: A discontinuity of size, shape, orientation, location or nature that would impair the effective use of the workpiece or that does not meet the requirements of specified acceptance criteria.
- Type A display: An information representation method that uses a horizontal baseline (X-axis) to represent distance or time, and a deflection perpendicular to the baseline (Y-axis) to represent amplitude.
- Transmit pulse: an electrical pulse added to the transducer in order to generate ultrasonic waves.
- Time baseline: The horizontal scanning line representing time or distance on the A-type display screen.
- Scanning: The electron beam moves across the flaw detector’s fluorescent screen repeatedly in the same pattern.
- Scanning range: The maximum sound path that can be displayed on the baseline when using a fluorescent screen.
- Scanning speed: the ratio of the horizontal axis on the fluorescent screen to the corresponding sound path.
- Delay scan: In type A or type B display, the starting part of the time baseline is not displayed.
- Horizontal linearity: The degree to which the signal displayed on the time or distance axis of the ultrasonic flaw detector’s screen is directly proportional to the signal input to the receiver (through a corrected time generator or multiple echoes from a plate of known thickness).
- Vertical linearity: The degree to which the signal displayed on the time or distance axis of the ultrasonic flaw detector’s screen is directly proportional to the signal amplitude input to the receiver.
- Dynamic range: When the gain adjustment remains unchanged, the ratio of the maximum and minimum reflection area wave heights that can be distinguished on the fluorescent screen of the ultrasonic flaw detector. Usually expressed in decibels.
- Pulse repetition frequency: In order to generate ultrasonic waves, the number of pulses per second that the pulse generator excites the probe element.
- Detection frequency: The ultrasonic frequency used in ultrasonic testing. Typically 0.4 MHz ~15MHz.
- Echo frequency: The reciprocal of the peak interval time obtained by expanding the observation of the echo on the time axis.
- Sensitivity: A measure of the smallest ultrasonic signal that produces a discernible indication on the screen of an ultrasonic flaw detector.
- Sensitivity margin: In an ultrasonic flaw detection system, the difference between the standard flaw detection sensitivity expressed at a certain level and the maximum detection sensitivity.
- Resolution: The ability of an ultrasonic flaw detection system to distinguish two adjacent defects of a certain size that are closest to each other in the transverse, longitudinal or depth direction.
- Suppression: In ultrasonic flaw detectors, a control method is used to reduce or eliminate low-amplitude signals (electrical or material noise) to highlight larger signals.
- Gate: An electronic method that selects a period of time for monitoring flaw detection signals or for further processing.
- Attenuator: A device that quantitatively changes the signal voltage (sound pressure). Attenuation is expressed in decibels.
- Signal-to-noise ratio: The ratio of the ultrasound signal amplitude to the maximum background noise amplitude. Usually expressed in decibels.
- Blocking: The phenomenon of sensitivity reduction or failure caused by the receiver immediately after receiving the transmitted pulse or strong pulse signal.
- Gain: The logarithmic form of the voltage amplification of the ultrasonic flaw detector receiving amplifier. Expressed in decibels.
- Distance Amplitude Curve (DAC): According to the specified conditions, a set of curves drawn by three parameters: the distance of the known reflector that generates the echo, the gain of the flaw detector and the size of the reflector. During actual flaw detection, the equivalent size of the flaw can be estimated from this curve based on the measured flaw distance and gain value.
- Coupling: It plays the role of conducting sound waves between the probe and the object being tested.
- Test block: a sample used to identify the characteristics and flaw detection sensitivity of the ultrasonic testing system.
- Standard test block: a test block whose material, shape and size have been verified by the competent authority or authoritative organization. Used for performance testing and sensitivity adjustment of ultrasonic testing devices or systems.
- Comparison test block: a test block used to adjust the sensitivity of the ultrasonic testing system or compare the size of defects. Generally made of materials with similar properties to the material being inspected.
- Probe: an electroacoustic conversion device that emits or receives (or both emits and receives) ultrasonic energy. The device generally consists of a trademark, plug, housing, backing, piezoelectric element, protective film or wedge.
- Straight probe: A probe used for vertical flaw detection, mainly used for longitudinal wave flaw detection.
- Angle probe: A probe used for oblique flaw detection, mainly used for shear wave flaw detection.
