In the field of non-destructive testing, ultrasonic testing instruments are widely used in industrial production and equipment operation and maintenance due to their accurate and efficient defect detection capabilities. Its classification logic is clear, and the core performance parameters directly determine the detection quality.
1. Core classification
According to the sound source initiative
Active flaw Detector (acoustic emission type) - relying on the ultrasonic waves actively emitted by internal defects under the action of the inspected object under the action of external force, combined with external induced conditions to judge the defect situation, suitable for dynamic monitoring scenarios.
Passive flaw Detector, which emits ultrasonic waves by the instrument itself and judges the defect state through the echoes of defect reflection and refraction, is the most widely used type in ultrasonic flaw detection.
By Emitting Wave Continuity
Continuous wave flaw Detector - the probe emits a single frequency equal amplitude sine wave, amplitude modulation wave or frequency modulation wave, which is mostly used for specific penetration method detection.
Pulse wave flaw Detector - emitting periodic exponential attenuation pulse waves, focusing on reflection flaw detection, has become the most widely used type due to its strong adaptability.
By defect display method
A-type display flaw Detector - oscilloscope horizontal seat standard propagation time, longitudinal seat standard echo amplitude, can determine the defect depth, estimate the defect size, simple structure, low price, strong adaptability, but the display is not intuitive, inconvenient to record, only reflect the single point result of the flaw detection surface.
Type B display flaw Detector - flat image display, which can show the defect distribution and depth of the workpiece profile, and the intuitiveness is better than that of type A.
Type C display flaw Detector – also a flat image, showing the cross-section of the defect perpendicular to the beam axis, but not the defect depth.
Direct imaging flaw Detector - including ultrasound TV, holographic imaging, etc., can directly display the true shape and size of defects with the highest accuracy.
Press the sonic channel
Single-channel flaw Detector – single-probe operation for single-point inspection.
Multi-channel flaw Detector - multiple probes work alternately, adapting to automated multi-point flaw detection scenarios.
Among them, the A-type display pulse reflection ultrasonic flaw Detector has balanced comprehensive performance and is the most widely used type of various instruments.
2. Key performance parameters
The performance parameters of the instrument directly affect the detection accuracy and reliability, and the core parameters include eight categories.
Vertical linear
It refers to the degree proportional to the height of the phosphor screen signal and the input signal voltage, which determines the quantitative flaw detection quality (the size of the defect is judged by the height of the defect echo). During the test, the coupling state should be fixed, and the bottom wave of the test block should be used as the full scale, and the attenuator should record the wave height change.
Horizontal linearity (time baseline)
It reflects the uniformity of the scanning line speed and affects the accuracy of defect positioning (when the geometric method determines the defect location, the distance represented by the unit length of the scanning line must be consistent). The test is commonly used by the multiple reflection method, which is judged by the equal interval of the spacing of the multiple bottom waves of the test block.
Detection range
It refers to the maximum depth that the instrument can detect the workpiece (the minimum depth is determined by the blind spot), which is related to the transmitting power, scanning time, etc., and needs to be adjusted according to the actual detection needs.
dynamic range
Expressed as the amount of attenuation (dB) required to attenuate the echo height from 80% saturation to 1mm (or disappear), it reflects the instrument's ability to respond to echoes of different amplitudes.
sensitivity
Characterize the instrument's ability to detect even the smallest defects, expressed as the size of the artificial defect (e.g., flat-bottom hole diameter) and gain margin at a specific distance, and pass a standard test block test.
Discrimination
It refers to the ability to distinguish two adjacent defects in the far field, which is the comprehensive performance of the instrument and the probe, which needs to be judged by the separation of the specific reflected waves of the test block.
Blind spots
The area where the defect cannot be detected properly after the first pulse is expressed as the minimum distance at which the defect can be detected, also with the help of standard test block testing.
Operating frequency
Usually at 0.5~20MHz, high frequency sensitivity, good resolution but large attenuation, low frequency penetration but low accuracy, need to be selected according to the grain thickness of the tested material (fine grain selection high frequency, coarse grain selection low frequency).
In addition, the repetition rate of the transmitted pulse (50~100kHz, related to the detection distance) and attenuator characteristics (total attenuation, minimum adjustment level, accuracy) are also important parameters.
3. Summary
Ultrasonic testing instruments are clearly classified, different types are adapted to different testing needs, and the core performance parameters determine the detection accuracy. In practical applications, it is necessary to select the instrument type based on the detection target (such as dynamic monitoring, automatic flaw detection, defect accurate imaging, etc.), and reasonably adjust the working frequency, detection range and other parameters according to the characteristics of the inspected material and testing requirements to provide reliable support for industrial non-destructive testing.
