Research on Multi-channel Virtual Ultrasonic Testing System

Zhang Guangming Chen Ziqiang Liu Yanmin Wang Yuwen

Abstract: The multi-channel virtual ultrasonic testing system is composed of a computer, 3 PC plug-in cards (multi-channel ultrasonic transmit / receive card, ultrasonic image card and stepper motor drive card), focus probe and mechanical system, which can realize A, B, C Scanning imaging, data processing, defect location, qualitative and quantitative analysis. The introduction of computer technology, virtual instrument technology, signal and image processing technology into the field of ultrasonic nondestructive testing has broadened the application range of traditional ultrasonic testing. The system uses multi-channel scanning imaging, which greatly improves the detection efficiency of the system. Compared with the traditional ultrasonic imaging system, it has the advantages of high detection efficiency, high precision, strong function, small size, and parameters that can be adjusted by software.
Keywords: Ultrasonic Nondestructive Testing; Ultrasound Imaging; Virtual Instruments Chinese Library Classification Classification Number: TB55

Multi-Channel Virtual Ultrasonic Testing

Zhang Guangming Chen Ziqiang Liu Yanmin Wang Yuwen
(Xi′an Jiaotong University, Xi′an 710049, China)

Abstract: The multi-channel virtual ultrasonic testing system uses three PC cards. They consist of the multi-channel ultrasonic transmit ／ receive card, ultrasonic graphic card, and step motor drive card. The A, B, C scan and data processing can be implemented. Virtual instrument and signal image process technology are introduced for ultrasonic nondestructive testing (NDT), while the range of applicability for traditional ultrasonic testing is extended. Other improvements include test efficiecy, precision, and software for the adjustment of governing parameters.
Keywords: ultrasonic NDT; ultrasonic imaging; virtual instrument

Digital ultrasonic imaging nondestructive testing generally uses point probe scanning or phased array probes to form simulated ultrasound images, and then uses a special image card to convert them into digital images [1]. Because ultrasound images can intuitively reproduce the size and shape of internal defects in workpieces, digital ultrasound imaging technology is widely used in the field of non-destructive testing. However, this technology has the following problems, which restrict its application. (1) Point probe scanning is usually mechanical scanning, the scanning speed is slow, the imaging efficiency of the system is low, especially when detecting large workpieces. (2) The manufacturing cost of industrial phased array probes is high and the system is complicated. At present, such probes are rare in China. (3) There are two main types of traditional digital ultrasound imaging systems: one is developed based on the traditional ultrasonic flaw detector. When this type of system is applied, some test parameters such as attenuation, gain, and excitation repetition frequency that have a great influence on the test results 2. The excitation pulse width must be adjusted manually, which is not conducive to detection automation and intelligence; the other is based on the intelligent chip (CPU). Such system software is not powerful. In order to solve these problems, we researched and developed a multi-channel virtual ultrasonic testing system. The entire system is a plug-in virtual instrument, which can complete the sequential receiving, quantization, imaging, image processing and other functions of multiple focus probes. Almost all system parameters are adjusted by software, which greatly increases the flexibility of the system and makes the instrument virtual It's a big step towards a truly intelligent ultrasound imaging system.
1 System composition and working principle The multi-channel virtual ultrasonic testing system is composed of a computer, 3 PC plug-in cards (multi-channel ultrasonic transmit / receive card, ultrasonic image card and stepper motor drive card), multiple focus probes and mechanical system [2 ], The principle block diagram is shown in Figure 1. The mechanical system includes a precise three-dimensional scanning worktable, a multi-station automatic rotary table, a special fixture and a sink.

Figure 1 Schematic diagram of a multi-channel virtual ultrasonic testing system

The system works cooperatively under the control of a computer. First, the system is initialized; second, the computer controls the stepper motor to drive the precision three-dimensional workbench, which drives multiple probes to scan the workpiece. At each scanning position, the ultrasonic transmitting / receiving card continuously loads high-voltage excitation pulses on each focused probe at a repeated excitation frequency, completes the transmission of ultrasonic waves, and sequentially receives the echo signals generated by each probe, and at the same time data acquisition The circuit works, converts the analog ultrasonic signal into a digital signal, and then the computer processes and stores, displays, and prints the ultrasonic image, and finally analyzes the defects.
The traditional point probe scanning ultrasound imaging system is limited by the mechanical scanning speed. In the case of high scanning resolution, the detection efficiency is very low. For example, the ultrasonic non-destructive testing computer processing system developed earlier in this paper, when the scanning resolution is 0.177 mm, it takes about 40 min for C to scan a (45 × 45) mm2 workpiece. With a multi-channel virtual ultrasonic inspection system, C-scan imaging of the workpiece can be completed in 13 minutes using four-channel scanning. In the practical application of the factory, such a high scanning resolution is usually not needed. By appropriately reducing the scanning resolution and increasing the number of channels, the system can basically meet the requirements of online detection.
Figure 2 shows the scanning path of the traditional point probe, and Figure 3 shows the scanning path of the four-channel virtual ultrasonic testing system. When scanning according to the path of Fig. 3, the four probes used are clamped on the special fixture, dragged by the precision scanning workbench at the same time, and scanned according to the predetermined path. The initial position of the four probes can be adjusted according to the size of the workpiece. Figure 3 divides Figure 2 into four small areas, and the scanning area of ​​each probe is only 1/4 of the original one. This greatly reduces the mechanical scanning time and replaces it with electronic switching time. Since the electronic switching speed is much faster than the mechanical scanning speed, the electronic switching time is almost negligible. If you increase the number of channels, you can also double the detection efficiency. The system is designed for 16 channels and can hold 16 probes at a time. The number of probes used in actual inspection will be limited by the size of the workpiece and the outer diameter of the water-focusing probe.

Fig.2 Scanning path of traditional point probeFig.3 Scanning path of four-channel virtual ultrasonic testing system

The multi-channel virtual ultrasonic inspection system is not only very important for improving the inspection efficiency of large workpieces. For small workpieces, the imaging inspection of multiple workpieces can be completed by one scan during inspection, which can greatly improve the inspection efficiency.
2 System hardware design
2.1 Multi-channel ultrasonic transmitting / receiving card Multi-channel ultrasonic transmitting / receiving card is a key part of the whole system. It involves the detection efficiency and image quality of the system. It is composed of +600 V high-voltage power generation circuit, ultrasonic transmitter / receiver and Most of the multi-channel electronic switch 3 is composed of [3], and its functional block diagram is shown in Figure 4. The ultrasonic transmitter / receiver is equivalent to an ordinary ultrasonic flaw detector, but its volume is small, and the parameters are all adjusted by software. The multi-channel electronic switcher performs high-fidelity switching on the received signal and is controlled by the computer. The high-voltage excitation pulse generated by the ultrasonic transmitter / receiver is continuously loaded on each probe at the repeated excitation frequency. The multi-channel electronic switcher ensures that the weak received signals generated by each probe are sent to the receiving port of the ultrasonic transmitter / receiver in order without distortion .

Figure 4 The principle block diagram of multi-channel ultrasonic transmitter / receiver card

2.2 Ultrasound image card Ultrasound image card is another key part of the whole system, which involves image quality, data acquisition accuracy, speed, system functions, etc. In order to meet the actual needs, the card designed analog-to-digital conversion circuit, clock circuit, window control circuit, scan selection circuit, acoustic characteristic measurement circuit, data storage circuit and bus management circuit, etc. [2], where the A / D conversion rate is 40 MHz, with 8-bit resolution. In order to improve the data acquisition and storage speed, the system has designed a 256 kB internal memory. Its block diagram is shown in Figure 5. NAL.ECHO, Sync.trig, Delay.trig are signals from the multi-channel ultrasonic transmitter / receiver card. : NAL.ECHO is an analog ultrasonic signal, Sync.trig is a synchronization signal, and Delay.trig is a delayed sampling pulse signal.
2.3 Stepper motor drive card In order to improve the detection accuracy and efficiency of the system and facilitate automation and intelligence, the system uses a stepper motor to drive a three-dimensional precision workbench. The stepper motor drive card uses the data line and address line of the computer to form a flexible ring divider through the design of the interface circuit to realize the control of the stepper motor. Follow the system prompt to enter some information about the workpiece and its installation, the system can complete autofocus.

Disclaimer:

The copyright of all technical documents belongs to the original author and the original publishing house. Jianke is only to share and spread the essence of other people ’s technical research for direct use for learning and research. Please use it for other purposes without permission. If any legal problems occur, it is not our responsibility. If you have any questions, please contact us in time, and we will correct or delete them immediately.