Ultrasonic testing is the main means of non-destructive testing in the industry. Using the PCI-9846 digitizer of ADLINK Technology, the multi-channel ultrasonic detection system is designed. The system is controlled by computer, using USB interface to use the single-chip unified scheduling, will reflect After the ultrasonic signal is processed, it is transformed by a digitizer, and a software system is designed to display and analyze the data. The test results show that the system has the advantages of high detection precision, strong analytical function, stable and reliable operation, and is suitable for wide application in industrial automation detection.
I. OverviewIn the safety management of pressure vessels, regular inspection is a necessary means to prevent failure of pressure vessels, especially to prevent major accidents. Due to the characteristics of manufacturing and use of pressure vessels, cracks and voids are inevitable in the mechanical structure. Non-destructive testing of pressure vessels is of great significance in terms of porosity and weld defects. Ultrasonic testing is an important non-destructive testing technology. It has been widely used in industrial and high-tech industries due to its strong penetrating power, reliable and accurate detection.
In the early ultrasonic testing, the detection signal was detected by analog signals, and the results mainly depended on experience for analysis, and there were a series of problems such as poor consistency and poor accuracy. With the application of high-tech such as computer technology and signal processing technology, the research on the digitalization of ultrasonic detection has become more and more extensive, and digital acquisition and analysis have become the development trend of ultrasonic flaw detection equipment. In general, resolution is an important indicator of ultrasonic testing, which directly affects the accuracy of measurement, and the ability to detect small defects is stronger. Due to the improvement of material technology, the thickness of the pressure vessel shell is continuously reduced, which requires ultrasonic testing. The resolution is further improved. Ultrasonic testing is essentially measuring the time difference of the reflected waves on the two surfaces in the direction of the thickness of the material. The thickness of the material can be calculated by calculation. For small defects and thin walls, the resolution is mainly required to have higher ultrasonic detection. The detection frequency, which is bound to bring higher requirements for the subsequent signal sampling processing part. Therefore, according to the design requirements and the characteristics of ADLINK's PCI-9846 multi-channel high-speed digitizer, the PCI-9846 digitizer is selected as the core, and the four-channel ultrasonic detection system with relevant hardware and software design has high precision and analysis function. Strong and other advantages.
Second, system design and compositionThe ultrasonic detection system consists of computer, PCI-9846 digitizer, C8051F340 single chip microcomputer, power supply, transmitting circuit and program-controlled amplifier circuit. The overall structure is shown in Figure 1.
Figure 1 Ultrasonic inspection system block diagram
The measurement process is initiated by the computer, and the C8051F340 is controlled by the USB port. The related switch signal is generated by the single-chip microcomputer. The high-voltage narrow pulse is generated through the transmitting circuit, and the transmitting probe is excited to generate ultrasonic waves. The receiving probe completes the acoustic-electrical conversion and converts it into a receiving electrical signal. After being programmed by a computer, the PCI-9846 digitizer is used for sampling. The digitizer and computer use the PCI interface for data exchange, which is displayed and analyzed by the computer. The power circuit and the peripheral circuit of the single chip include a watchdog, a crystal oscillator, a reset circuit, and the like. According to the design requirements, it is required to have four probes to work at the same time.
2.1 Selection of digital devices
The digitizer is essentially an A/D device with the appropriate interface and software to become a stand-alone device that is widely used in signal acquisition and analysis. For this system, the signal acquisition part is required to have the following characteristics:
At the same time, it can receive 4 inputs and perform A/D conversion. In this system, as the workpiece travels on the assembly line and the processes are completed at the same time, it is necessary to simultaneously inspect the four main locations, and it is necessary to have four input digitizers in terms of effectiveness.
A higher sampling frequency is required. The ultrasonic wave propagates in the steel product nearly 10 times faster than the air. After the ultrasonic pulse is emitted, the receiving end performs thickness measurement according to the two rebound echoes. If the flaw detection is performed, the higher the frequency, the more processing value the collected signal has. According to the maturity level of the transmitting probe and the application requirements, the frequency of the ultrasonic wave is selected to be 5 MHz, and the sampling rate of 10 M is theoretically required, but in practice, the sampling rate is required to be 30 M or more.
Has a large cache. The A/D transformed data is sent to the computer for processing. The two use the PCI bus to exchange data. The system is a 4-channel simultaneous acquisition system. The sampled data is large, and the large-capacity storage can reduce the real-time processing of the computer. Claim.
Easy to develop and use. As a device that communicates with a computer, there should be corresponding drivers and multiple software support on the software.
Based on the above factors, the PCI-9846 digitizer from ADLINK is adopted in consideration of price and performance. The main reason is that the design cycle of the self-designed circuit is long, the drive development is difficult, and the cost is high. PCI-9846 digitizer [5] has four inputs to meet the requirements of the number of input terminals; each channel can reach the sampling rate of 40MS / s, can meet the requirements of digital processing; onboard 512MB of memory, can effectively alleviate equipment Asynchronous problems between interfaces, in addition, ADLINK also provides development drivers and development kits for Matlab, VC++, and .net, allowing users to directly focus on applications.
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