Abstract: Integrate the PLC control system with the existing GPRS wireless communication network technology. Through the GPRS network communication technology, ultra-remote and reliable data transmission across the country or even the world can be achieved, and the purposes of remote data analysis and remote control can be achieved. Since the 1990s, digital technology has achieved rapid development and has increasingly penetrated into various fields. In the 21st century, smart homes will become a new fashion for modern society and families. As a general industrial control computer PLC, for more than 30 years, both in terms of function and application field, there has been a leap from logic control to digital control, monomer control to motion control, process control to distributed control. Today ’s editable Program controller PLC is becoming the mainstream control equipment in the field of industrial control, playing an increasingly important role in the world. With the rapid development of PLC applications, various advanced control strategies have to face the remote control applications of different objects in large-span distributed locations, how to realize various field data transmission processing and remote control in large-scale distributed applications , Remote maintenance, etc. is a very real problem, one of the premises is the remote transmission of various data packets. In the past, some PLC application systems used wireless digital radio communication to achieve the purpose of remote control of PLC, but this solution still has some defects, mainly because its distribution range is still relatively limited, and as the communication distance increases, its Reliability is greatly affected. At present, the latest application trend is to integrate the PLC control system with the existing GPRS wireless communication network technology. Through the GPRS network communication technology, ultra-remote and reliable data transmission across the country or even the world can be achieved, thereby achieving remote data analysis processing and remote control purpose. China Mobile GPRS system can provide wide area wireless IP connection. Building a distributed PLC control system on the mobile communication company's GPRS service platform to realize the PLC's wireless data transmission has the advantages of making full use of the existing network, shortening the construction cycle and reducing construction costs, and the equipment is easy to install and maintain. After comparative analysis, we chose China Mobile's GPRS system as the data communication platform of the distributed PLC control system. 1. High reliability: Compared with SMS short message mode, GPRS DTU uses connection-oriented TCP protocol communication to avoid the loss of data packets and ensure reliable data transmission. The center can simultaneously transmit data with multiple monitoring points without interfering with each other. The GPRS network itself has a perfect frequency division multiplexing mechanism, and has a strong anti-jamming performance, completely avoiding the multi-machine frequency band "collision" of traditional digital radio stations. 2. Strong real-time performance: GPRS has the characteristics of real-time online, the data transmission delay is small, and supports multi-point simultaneous transmission, so the GPRS monitoring data center can quickly and real-time two-way communication between multiple monitoring points, which satisfies the system for data collection and transmission. Real-time requirements. At present, the actual data transmission rate of GPRS is about 30Kbps, which can fully meet the requirements of the system data transmission rate (≥10Kbps). 3. Wide monitoring range: The GPRS network has achieved nationwide coverage, unlimited capacity expansion, and unlimited access locations, which can meet the access requirements of mountainous areas, towns, and trans-regions. For PLC control systems distributed throughout the city / province, or nationwide, GPRS network is the ideal choice. 4. Low system construction cost: Since the GPRS public network platform is adopted, there is no need to construct a network, and only equipment needs to be installed, so the construction cost is low; network maintenance costs are also eliminated. 5. Low system operating cost: Adopt GPRS public network communication, billing at a uniform rate nationwide, eliminating expensive roaming fees, GPRS network can be charged according to the actual communication flow of data, (1 minute-3 minutes / 1K byte), you can also press The monthly subscription is not limited to traffic charges, thus achieving low-cost communication of the system. 6. The system's transmission capacity and capacity expansion performance are good: The monitoring center shall realize real-time connection with each PLC control site. The system requirements can meet the needs of sudden data transmission, and GPRS technology can well meet the needs of transmitting sudden data; because the system uses a mature TCP / IP communication architecture and has good expansion performance, a monitoring center can easily Support thousands of on-site PLC data communication. 7. Low GPRS transmission power consumption, suitable for field power supply environment: Although two-way communication with a data center thousands of miles away, GPRS data transmission equipment only needs to communicate with nearby mobile base stations when it is working. Its overall power consumption is comparable to an ordinary GSM mobile phone, and the average power consumption is only 200 milliseconds. Watts are smaller than traditional digital radio stations. Therefore, the GPRS transmission method is very suitable for use in the field using solar power or battery power. 1. On-site control / collection point: The on-site monitoring point is automatically controlled by the PLC and collects relevant information. It is connected to the GPRS DTU terminal through the RS232 or RS485 interface. The device information collected by the PLC processes the data through the GPRS DTU terminal, encapsulates the protocol and sends it to the GPRS wireless network. 2. Monitoring center: a) Public network access solution The server is connected to the Internet through a public network, such as ADSL dial-up / telecom dedicated line broadband Internet access, etc., applying for a fixed IP address on the public network; it can realize the application of small and medium-capacity systems. b) Private network access solution The server uses the DDN special line provided by the provincial mobile communication company, applies for a fixed IP address, and is connected to the GPRS network. Since the DDN dedicated line can provide higher bandwidth, when the number of on-site PLCs increases, the center can meet the demand without expanding the capacity, and can realize large-capacity system applications. After receiving the data from the GPRS network, the RADIUS server of the monitoring center first performs AAA authentication, and then transmits it to the computer host of the monitoring center. The system software is used to restore and display the data and perform data processing, which further enhances the security performance of the system data communication. 3. GPRS / GSM mobile data transmission network: The data collected by the PLC is simultaneously decoded and processed by the air interface function module of the GPRS / GSM network, converted into a data transmission format on the public network, transmitted through the GPRS wireless data network of China Mobile, and finally transmitted to the IP address of the monitoring center. Each on-site control point uses the ZSD3120 GPRS DTU transparent data transmission terminal of Chengdu Zhongshan Technology Co., Ltd. and is connected to the monitoring center through a mobile GPRS network. The GPRS DTU of each field control point uses the mobile communication company's GPRS general data card or APN special data card. At the same time, the monitoring center registers the GPRS terminal number of each point and associates with the field control point information for identification and maintenance processing. The monitoring center runs the monitoring system software and collects the relevant data of the on-site control points in real time. The system uses ZSD3120 GPRS DTU wireless transparent data transmission terminal. Based on China Mobile's GPRS network, the product has the characteristics of high performance, high reliability and strong anti-interference ability. It provides standard RS232 / RS485 interface and can directly communicate with PC, single-chip system, RTU measurement and control terminal, PLC, GPS receiver, data concentrator And other connections, with remote diagnosis, testing, and supervision functions to meet the data collection and control between various industry dispatch or control centers and many remote sites. 1. Built-in TCP / IP protocol stack, optimized for GPRS network 2. Provide two-way GPRS wireless data transmission function 3. Provide RS232 / RS485 / RS422 interface 4. Comply with ETSI GSM Phase 2+ standard 5. Support automatic heartbeat and keep permanent online 6. Transparent data transmission: Provide two-way 100K large-capacity data buffer for user's data equipment, support large data packet transmission 7. Automatic dial-up connection: DTU automatically dials up to connect to the Internet and connects to the network. It supports the user to initiate a command connection or remote wake-up connection 8. Provide SMS channel, built-in Unicode international encoding conversion table 9. Support remote SMS / phone wakeup 10. Real-time monitoring of network connection, automatic redial function when disconnected 11. The support center is a fixed IP or dynamic domain name 12. The heartbeat report interval can be set by the user 13. Support point-to-point, point-to-multipoint, multipoint-to-multipoint and other data transmission 14. Support APN data private network service 15. Flexible installation, easy to use and reliable 16. Support multiple data centers, automatic switching 17. Adapt to low temperature and high temperature working environment 18. EMC anti-interference design, suitable for applications in harsh electromagnetic environments 19. Composite watchdog technology, never crash 20. Low power consumption technology of the whole machine, online standby current <20mA Due to the particularity of remote control, the system needs extremely high system security and stability. Security protection is mainly to prevent intentional and unintentional breaks from inside and outside the system. Network security protection measures include channel encryption, source encryption, login protection, access protection, access protection, firewall, etc. Stability means that the system can run uninterrupted for 7 × 24 hours. Even if hardware and software failures occur, the system cannot be interrupted. The monitoring center can be accessed through the public network or to the mobile private network. The public network access method is relatively low in cost. Enterprises do not need to lease a dedicated line, but when using a dedicated data line to access, GPRS data transmission equipment must be certified by the Radius server. The entire data transmission process is encrypted and protected, and the security is relatively high, which can fully guarantee the speed and network service quality. 1. APN data private network mode: APN server is configured in the internal network of the enterprise, and the mobile terminal uses the APN data private network. Because the data private network is adopted, the server is isolated from the public Internet, which can effectively avoid illegal intrusion. 2. Use the uniqueness of the SIM card to authenticate and authorize the user ’s SIM phone number, bind the SIM card number and APN on the network side, and delineate the range in which the user can access a certain system, only the SIM card mobile phone belonging to the designated industry No. can access the dedicated APN. The mobile terminal and monitoring center use the special APN assigned by China Mobile for wireless network access. The SIM card number of the ordinary mobile phone cannot call the special APN. 3. Each GPRS data transmission device can be individually configured with a DTU ID number and password, and the application center authentication is performed when the monitoring center logs in. Other GPRS devices without the DTU ID number and password assigned by the center will not be able to log in to the system. The security of the system is further enhanced. 4. Data encryption: The entire data transmission process can be encrypted and protected. 5. Network access security identification mechanism: use firewall software to set network authentication and security precautions to ensure system security. The monitoring center adopts wired mode, and the current cost of renting static IP is about 800-1500 yuan / month. The collection point adopts GPRS wireless mode. Currently, there are two charging methods: monthly fee and data fee. The monthly fee is 0.01 yuan -0.03 yuan / KB, and the monthly fee is 20 yuan / month. There is 1024KB traffic. It is estimated that the cost will gradually reduce. For users, due to lower communication costs, they have enjoyed the benefits. In addition, because the access device can be moved, when the control point is moved, the device can be migrated and can continue to be used, which can protect the user's original investment.
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PLC distributed control system of GPRS network