Application Cases

Experiment Name: Pulse Eddy Current Testing Experiment

Research Direction: As a type of non-destructive testing technology, pulse eddy current testing is based on the principle of electromagnetic induction and is used to detect defects in conductive materials. The principle of pulse eddy current testing is essentially the same as that of traditional eddy current testing, with differences lying in the excitation method and signal analysis approach. In the remanufacturing inspection of metal components, pulse eddy current testing plays a crucial role. Defects in metal materials, whether on the surface or hidden internally, can cause incalculable losses. Surface defects in metals are relatively easier to detect, while internal defects are more difficult to identify.

The National University of Defense Technology in China has conducted in-depth research on pulse eddy current testing technology, widely applying it to the assessment of metal surface and subsurface defect sizes, and accurately identifying different types of defects that may coexist. Pulse eddy current testing technology is also used in time-domain signal analysis, utilizing the output signals from pulse eddy current testing to determine crack widths. The research team from the National University of Defense Technology has developed a "spectral separation point" classification method, which can detect crack types through spectral information, enhancing the accuracy of pulse eddy current testing. This experiment aims to analyze the basic principles involved in pulse eddy current testing methods. Simulation models are used to compare the effects of defective and non-defective aluminum plate samples on the surrounding magnetic field. The impact of changes in the size and location of internal defects in aluminum plates on the output signal is analyzed, and the methods for signal extraction and processing mechanisms are studied.

Experiment Purpose: To investigate the relationship between defect location and depth and the characteristics of detection signals, providing arguments and groundwork for subsequent experiments.

Testing Equipment: Power amplifier, signal generator, data acquisition card, Hall sensor, computer, excitation coil, test sample.

Experiment Process: The pulse eddy current testing system consists of a hardware detection platform and a data analysis software platform. The hardware platform can generate, amplify, and collect signals, which can reflect the condition of metal defects; the software platform mainly completes the data acquisition program, the detection system interface, and the data analysis and processing process. The software platform realizes functions such as feature extraction, real-time display, and data storage. The hardware system is composed of a probe and a detection device, as shown in Figure 1-1. The system includes a signal generator, power amplifier, signal conditioning circuit, data acquisition card, and computer, among others.

In the pulse eddy current testing experiment, the waveform generator produces a square wave signal with adjustable frequency, amplitude, and duty cycle. The power amplifier can amplify the signal output from the waveform generator, with an amplification factor of 10. The amplified signal serves as the excitation source for the excitation coil. The alternating current generates a changing magnetic field. When the detection coil is close to the aluminum plate being tested, due to the effect of the alternating magnetic field, eddy currents will be induced in the aluminum plate sample. The eddy current field generated by the alternating magnetic field is also alternating, so a second magnetic field induced by the alternating eddy currents will be generated on the aluminum plate. The first magnetic field excited by the excitation coil and the second magnetic field induced by the eddy currents will form a combined magnetic field. The Hall sensor at the center of the probe's bottom surface can detect the changes in the superimposed magnetic field. In the signal conditioning module, the output signal from the Hall sensor is differenced with a 2.5V voltage, and then an amplification chip is used to amplify the differential signal. After this operation, the signal can be recognized by the data acquisition card and meets the dynamic input range. The data acquisition card is equipped with an A/D converter, which can convert the analog signal output from the probe into a digital signal and transmit it to the computer. The computer software controls the data acquisition card and analyzes the sampled signals. The pulse eddy current testing device is equipped with a host computer software platform based on LabVIEW, which can intuitively display various signals through the software interface and perform data processing on the signals. The signals are analyzed using Matlab programs to determine the relationship between signal characteristics and sample defects.

Figure 1-1: Schematic Diagram of Pulse Eddy Current Hardware Detection Experiment

Experimental Results: To establish a relationship between defect location and depth and signal characteristics, a sample model that allows flexible changes in defect location and depth is required. The aluminum plate samples introduced in the section can provide four defect locations: 2mm, 4mm, 6mm, and 8mm, which represent the distance of internal defects from the surface of the aluminum plate, as well as four defect depths: 2mm, 4mm, 6mm, and 8mm. Using the pulse eddy current testing platform to detect internal defects, the defect signal waveforms shown in Figure 1-2 can be obtained. When detecting two different internal defects, two different defect signal waveforms can be obtained, and Figure 1-3 shows a comparison of the positive peak parts of the waveforms. It can be seen that for different defect locations and depths, the signals detected by the detection platform are different, with the differences in the positive peaks being clearly visible.

Figure 1-2: Defect Signal Detection Waveform

Figure 1-3: Comparison of Peak Values of Different Defect Signals