1 Composition of traditional analog system The composition of the measurement system is shown in Figure 1 and Figure 2. In the traditional simulation system, the basic composition of the measuring station is: sensor group, data collector, single-chip or PLC control system, communication adapter and analog radio station. Signal transmission is generally divided into 2 groups, one group is the acquisition signal transmission, and the other is the measurement control station signal transmission. In the transmission process, you can use analog transmission, or modern digital radio transmission. To ensure the stable transmission of signals, it is generally required to use two sets of signal channels to transmit separately. In the transmission process, power supply interference and radiation interference of detection components such as ray sources must also be considered. For the signal acquisition system, if the analog signal collected by the data collector is directly transmitted through the analog radio station, the transmission accuracy and bandwidth are difficult to guarantee due to the impact of various field environments, even after the signal passes through the digital radio station Transmission, transmission accuracy and bandwidth cannot guarantee that real-time signals can be accepted by subsequent processing systems. The control part is generally realized by using a single chip microcomputer or PLC. The cost of single chip microcomputer and PLC may be low, but the problems of early development and mass production of single chip microcomputer are bothering system developers. In terms of control accuracy and system debugging, debugging of single-chip and PLC systems requires the support of specialized peripheral equipment and professional technicians. The control signal required for the operation of the remote measurement station is transmitted by the analog FM radio station, and the accuracy of the control signal is sometimes not guaranteed due to the influence of the site environment. The workload during system debugging and the human-machine interaction process during system operation are also extremely difficult to achieve, especially when the remote control station system fails, system repair and manual control pose difficulties for system development and application. Therefore, the traditional analog signal transmission system and some digital signal transmission systems have many shortcomings and unpredictable problems in the application process. 2 Digital system composition The composition of its measurement system is shown in Figure 3 and Figure 4. In the composition of the digital system, the analog signal is transmitted to the digital data collector through the sensor group, and is converted into a digital signal after filtering, amplification, analog-to-digital conversion, etc., and then passed to the control station of the measuring station. The control machine is wirelessly networked with the host computer through the WIFI wireless network port of Intel Corporation. By setting the host computer and the measurement station control machine separately, the measurement station control machine becomes a remote terminal of the main control machine to achieve complete remote control. . Through the wireless network, the real-time data and images collected by the measuring station control machine are transmitted to the main control machine. At the same time, the main control machine fully controls the measuring station control machine and controls other peripheral devices through the RS 232 port or USB port. If there is strong interference (such as X-ray interference) in the wireless signal transmission during the measurement process, you can use the wireless network to preview the working state of the machine. The measuring station controller collects real-time data and stores it. After the interference is removed, the useful signal is wirelessly transmitted to the main controller. While receiving the signal, the host computer controls the measuring station equipment to prepare for the next signal acquisition. After everything is ready, the acquisition system is turned on for the next work. Adding an intermediate storage link in this way improves the accuracy of digital signal transmission through all-digital wireless signal transmission, and also improves anti-jamming capability and control accuracy. 2.1 Composition of sensor group and digital signal collector The system can be applied to various existing detection technologies, that is, all systems that can convert the detection signal obtained by the sensor group into a digital signal through a signal collector. The system can not only complete the transfer of conventional signals (such as signals collected by sensor groups such as temperature, pressure, flow, etc.) and unconventional signals (cameras, various endoscopes, sonar signals, etc.), but also can be applied to non-destructive testing projects. In the field, digital signals used to transmit ultrasonic measurement signals and X-ray inspection images. For example, the ultrasonic probe signal, when the ultrasonic probe transducer converts the flaw detection echo into an electrical signal, the signal collector can be designed as a combination of signal amplification, filtering, tuning, analog-to-digital conversion and other functions. After the series setting becomes a digital signal, it enters the computer through the measuring station controller port for storage and transmission to complete the signal collection; and for the X-ray digital real-time imaging acquisition device-flat panel detector (FPD), if the flat panel detector can directly Output digital images, you can directly enter the computer storage and transmission through the data cable, through the measuring station control machine port; for the signal that needs to be converted, you can first convert it to a signal that can be collected by the measuring station control machine through a proprietary device, and then enter Computer storage and transmission. 2.2 Measuring station controller The control station of the measuring station is at the core of the whole measuring station, and it is extremely important for the normal operation of the measuring station and the stable signal transmission, so the selection must be careful. The performance of the measuring station controller must meet the following points: (1) With low power consumption and high efficiency, it is best to be directly driven by a standard battery pack; (2) The working temperature range must be wide, the heat dissipation is good, and it is suitable for occasions with large temperature changes; (3) Impact resistance, vibration resistance, suitable for various on-site environments; (4) The volume is moderate, which is particularly important for some mobile acquisition and measurement stations; (5) Possess digital wireless transmission capability and support wireless transmission protocol; (6) The system can be well compatible with the host computer, and can ensure smooth software docking; (7) There are abundant peripheral interfaces, which can perform data transmission and control with various signal collectors and industrial controller PLC and other equipment. Based on the above points and the current software trends, we should choose industrial controllers such as box-type industrial computers and single-chip computers that are widely used. This industrial computer has good interface performance, has a LAN interface, can support WIFI wireless transmission protocol, and has extended functions. It is better to use an industrial computer equipped with Windows XP Embedded system, so that the stable work and signal transmission of the measuring station can be better achieved. 2.3 Selection of communication adapter and communication protocol Considering the actual working environment on site, choosing a communication adapter and communication protocol reasonably is also important for whether it can be stable, efficient, and guarantee transmission accuracy. For the general measuring station and the host computer, because it is within the visible range, you can choose the current universal WIFI signal adapter. When the WIFI signal can be satisfied, if you need remote transmission control, you can add a wireless network router, connect it to the Internet WAN through the router, and after reasonable configuration, expand to long-distance transmission, multi-point transmission and control. For example, in the location detection of ice blockages in oil pipelines, the on-site staff, remote monitoring personnel, and media pressurization pump station personnel all need to understand the real-time detection status at the same time, and multi-point transmission and control can be well achieved through this system. If you can't guarantee a wide area network connection in the workplace, you can also add WIFI signal power amplifier or add an existing digital radio station, such as Motorola's GM series car radio, working in the VHF / UHF frequency band, wireless digital transmission (9-wire system) Standard serial RS 232 interface), or American MDS company's telemetry remote control series digital radio (using digital signal processing, error correction coding, software radio, digital modulation and demodulation and surface mount integrated design and other technologies, with high performance and high reliability The radio station can provide a standard 232 data port and can be directly connected to a computer, seismic data collector, RTU data terminal, GPS receiver, digital camera, etc.). 2.4 The choice of host computer When choosing the main control machine, we must consider the characteristics of the main control station working environment, data transmission and storage capabilities, data processing capabilities, peripheral expansion interfaces (connecting more post-processing professional equipment). For mobile master workstations, you can choose on-board computers or even laptop computers. For those who need powerful post-processing capabilities, you can choose computers with special requirements such as graphics workstations. For the occasions that require high-precision control of the measurement system or use in special control, you can choose the main control machine that can be connected to the special control system and can transmit the signal to the industrial computer of the measurement station through the wireless network. 3 Conclusion By applying the digital wireless network to the real-time detection system of non-destructive testing, the analog transmission of the original equipment can be converted to digital transmission. For the situation where there is no interference at the work site and the amount of data transmission is small, you can choose an industrial computer and a single-chip computer with a simple function and low cost. For multi-group signal acquisition, multiple signal acquisition devices and wireless network routers, wireless signal repeaters and other devices can be added to expand the device functions. For occasions where the on-site working environment is complex and the wireless signal interference is serious, the signal acquisition and storage can be performed first. After the end, the interference source is turned off, and then the wireless signal transmission of the measurement station and the main control station computer is performed in the set transmission mode. This system can also add wireless gateways to connect to the Internet wide area network for ultra-long-distance data transmission and control, and truly achieve safe, stable, and efficient remote control solutions. Internet technology and modern non-destructive testing technology are well combined and applied. Through the expansion of other functions, more powerful control functions and functions can also be achieved. The laboratory and production field application shows that: due to the use of all-digital wireless signal transmission, accurate and timely data transmission, high control accuracy, strong anti-interference ability, and the expected effect has been achieved.
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Application of digital wireless network in real-time testing system of nondestructive testing
In the transmission process of detection signals and control signals of today's wireless measurement and control workstations, one is traditional analog transmission, represented by FM-FM; the other is digital transmission, represented by PCM. The two methods have their own characteristics. Analog transmission is relatively simple to implement. It does not require a special control chip for data control. It has good real-time performance. The disadvantage is that the transmission accuracy is not high and it is susceptible to environmental interference. , Need to use a special intelligent control chip for data bit control. It is extremely difficult to ensure the synchronization of data bits when performing digital communication in the detection state, which has become the main bottleneck restricting the application of digital wireless communication engineering. The advantages are high transmission accuracy and good security, which is the future development direction of wireless communication. Especially in the modern nondestructive testing process, due to the harsh on-site working environment and many uncontrollable interference factors, the anti-interference ability of the signal is very important.