Development of network technology for the most fir

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The development of automation control system network technology

1. Introduction since the new century, the speed of informatization has accelerated. In the automation control system, great changes have taken place not only in the networking of office automation system, intelligent building automation system, municipal, transportation, logistics, commerce, banking and other utility automation systems, but also in the discrete industrial automation dominated by mechanical manufacturing, especially in the process industrial automation, which has also made a gratifying step towards digitalization, networking and intelligence. Especially for the large-scale refining and chemical projects that have recently started construction or have been successfully commissioned, about 1/4 of FF (Foundation Fieldbus) and other fieldbus products have been adopted in the field layer of its automation control system, and the high-speed Ethernet mainstream network products have been basically adopted in the monitoring layer, so as to achieve complete decentralized control, highly centralized operation display and management step by step (15 devices in the whole plant are operated in one general control room), The digitalization of the system has made a qualitative leap, laying a solid foundation for the integration of management and control. This is a major breakthrough in traditional DCS. At the beginning of the Eleventh Five-Year Plan, it is necessary to look at the development history of network technology from the perspective of automatic control system, so as to review the old and know the new

2. Historical review

after the emergence of telegrams, etc., there was a communication network for information transmission. Especially after the emergence of microcomputers, computers with different functions or regions were connected. The digital communication technology was expanded from the general single machine (host to terminal) and multi machine communication to the computer network system. The automatic control system is a distributed computer local area network that can complete the measurement and control functions. Its development process is as follows:

2.1 DCS primary communication system in the 1970s

DCS decentralized control liquid metal system with the advantages of strong toughness, good elasticity and fast magnetization began to appear in the mid-1970s. This was completed by large enterprises in the absence of a unified network standard. The network has about nodes with a communication distance of about 1km. The main nodes are control stations and operation stations. The topology is mainly ring and bus type. Most of the communication media are coaxial cables, and some are twisted pair. The communication rate is within 1Mbps. There are communication cards and other special network components in the control station and operation station. Representative products in this period include tdc2000 DHW (data highway) bus and CENTUM f bus, both of which adopt token bus communication protocol. Data sharing has been operated according to the station number. At this time, all field instruments are analog instruments, and a few special equipment have serial ports such as rs-232/rs-422/rs-485, which can be linked with them. During this period, the communication procedures include synchronous data link procedure (SDLC), advanced data link procedure (HDLC) and ccittx 25, etc

2.2 in 1975, Ethernet was introduced.

1975, Xerox Corporation of the United States introduced Ethernet. Later, 3Com and other suppliers participated in the Ethernet local area network. The Ethernet local area network formed on this basis has been greatly developed in various general systems for sudden transaction processing. Ethernet uses carrier sense multiple access/conflict detection, i.e. csma/cd, for data communication

2.3 the iso/osi reference model and IEEE802 family standards, which began in 1980, are based on the above two technologies. In February, 1980, the IEEE Institute of electronic and electrical engineers established a committee (IEEE802 Committee for short) to formulate local standards. In 1983, the ISO international organization for standardization adopted the OSI (open system interconnection) reference model, namely the iso/osi reference model. On this basis, in 1985, the IEEE802 Committee established 9 sub committees (later increased to 13 committees) (22 sub committees), of which IEEE802.3 is responsible for csma/cd, and IEEE802.4 is responsible for token bus, 802.5 negative command ring (other sub committees are responsible for high-level interface, logic circuit control, wide area, broadband, optical fiber, data and voice integrated network, interoperable local area security, wireless local area, limited high-speed local area, cable TV, etc.). The work of these sub committees later formed ISO standards, and these standards are also collectively referred to as IEEE802 standards

2.4 TDC3000 network, the milestone of DCS communication network development in the middle and late 1980s

, Of course, during this period, the system scale of the updated network is expanding, using optical fiber, the communication distance is several times that of the original, the communication rate is increased to 10Mbps or higher, the station number is several times that of the original, the number of station characters is increased from 8 characters to 12 characters, and the concept of domain is formed. However, during this period, the field instruments are still dominated by analog instruments or Hart standard instruments, but the field instruments of remote i/o data communication type are increasing, which are different from PLC The capability of digital communication such as analyzer is enhanced. The interconnection of DCs from different manufacturers has been put on the agenda. Heterogeneous network interconnection in DCS is gradually realized, and TDC3000 network structure is the most typical. DHW (250kpbs) is connected to LCN (local control network) through Hg (data high-speed channel); The newly developed bus VCN (universal control network) equivalent to DHW is connected to LCN through Nim (network interface module). The LCN network can be connected to 645 modules with a communication rate of 5mbps. The coaxial cable is used with a communication distance of 300m (2000m for optical fiber communication). It is used for the interconnection of operation stations, application modules and historical module upper computer interfaces (CG) in the control room. It is connected to the control station through DHW and VCN and leads to the site. The LCN adopts a proprietary token passing protocol with error check. CG cooperates with the existing interface software cm50s and cm50n to ensure the connection with the upper computer and complete the functions of plant management and advanced control. The VCN has 63 modules (32 redundant devices), the communication rate is 5mbps, the electric axis cable is used, and the communication distance is 300m. It is connected to the control stations PM, APM, LM, etc. Ucn and LCN have referred to the IEEE802.4 communication model

2.5 PLC multi-layer communication, a rising star in the 1980s

plc programmable controller has been connected by a single controller into a small and medium-sized system in the 1980s. Before and after 1990, one or more PLCs were connected with one or more PCs (HMI man-machine interface and configuration software or SCADA software were installed in the operating station) through rs232/rs485 serial port. It uses ready-made network technology, In particular, DDE or OPC data exchange software technology and IEC standard configuration software have greatly improved the openness and availability of PLC system and become a model of low-cost automation. Now it has gradually transitioned to the industrial Ethernet based network at the beginning of the 21st century, and the CIP common industrial protocol led by Rockwell has been formed. The devicenet/controlnet/ethernet/ip three-tier communication network has been accepted by people, PLC has changed from poor communication function to leading in networking

2.5 the upsurge of Fieldbus in the 1990s is in the ascendant.

fieldbus technology has formed an upsurge of development in the 1990s. It meets the needs of field measurement and control in various industries and forms a situation of coexistence of multiple standards. It subdivides the bit level sensor bus that transmits data width, the device bus that transmits data width of byte level, and the fieldbus that transmits data width of data flow or function block level, FF hi/ff HSE is more suitable for process control, and PROFIBUS and device net are more suitable for discrete control. The foundation fieldbus FF hi adopts the 1, 2, 7 and user layers of the iso/osi communication model. It has withstood a long-term test in practical engineering in terms of field two-wire power supply, explosion-proof, electromagnetic interference prevention, lightning protection and redundancy, field control (PID single loop regulation, cascade regulation, selective regulation, ratio regulation and other conventional controls are completed on site), interoperability and interchangeability. Ffhi considers the characteristics of various equipment on the section and the characteristics of field transmission signals in terms of communication, which is a summary of years of relevant experience. The virtual communication relationship (VCR) of fieldbus devices is divided into three types: client/server type (c/s) for setting parameters or changing operation mode, publisher/subscriber type (p/s) for refreshing input and output of function blocks, report distribution type (s/s source point/receiver point) for event reports and trend reports, and object dictionary (OD) is used Equipment description language (DDL) and the application process of function blocks in the user layer, complete the tasks of measurement data acquisition and control loop of the automation system, and ensure interoperability. On the basis of seamless connection with FF Hi, FF HSE uses high speed Ethernet (hse:high speed Ethernet) to complete the network cots task of the central control room level 1 or the monitoring layer, and uses network products such as switches and tcp/vdp/ip protocols of the transmission layer and network layer to ensure the openness and interoperability of the system

the development of fieldbus technology is inseparable from the realization of digitalization, networking and intelligence of field instruments. At present, the production of field instruments such as transmitters used in process industry is that FF accounts for 10%, Hart accounts for 40%, and analog instruments account for 50%. Therefore, it is necessary to pay attention to the updating of field detection instruments and actuators in order to popularize fieldbus technology

2.6 E has a bright future.

the rise of interconnection (global wide area) before the 1990s, as well as the development of mobile communication, multimedia technology, personal computer and operating system network support functions, have a profound impact on the digital communication technology of automatic measurement and control system. Due to the popularity of interconnection and the rise of the network access industry, the prices of switches, hubs, category 5 twisted pair copper cables and other network products have dropped. The application technology of Ethernet and interconnection protocol clusters (including tcp/ip) has penetrated into various connected devices. The transmission mode has developed from baseband to carrier and broadband, and the network rate has increased from 10m to 100m and 1000Mbps. Therefore, industrial Ethernet fever has risen in the automatic measurement and control system, Because some people emphasize the certainty and real-time characteristics of automatic measurement and control system, they have transformed it on the basis of commercial Ethernet to form a variety of real-time ethers, but this is only a process, and the key is whether the cost performance can be recognized by users. In a word, the trend towards flattening the network of automatic measurement and control system to the end of E is obvious, but it will take time

2.7 which is right or wrong between FCS and DCS in the new century

the emergence of the fourth generation DCS adapts to the development of fieldbus technology and management and control integration technology in the early 21st century. At present, the 11 master control systems that have passed the hist interoperability test certification of the Fieldbus Foundation are the 4th generation DCS systems, and it is pointed out in the foundation fieldbus system engineering guide that all FF functions, including engineering, configuration, maintenance and operation display functions, should be integrated into a single seamless master system. Engineering, configuration, maintenance and operational performance shall be compatible and seamlessly integrated with traditional analog or discrete i/o, smart Hart and dedicated i/o, bus based i/o and FF systems. It is not recommended to use independent software tools, displays or programs that are only for FF and are incompatible with traditional systems. Thus, it has found a solution for FCS to replace DCS and other viewpoints, that is, the road of common integration, complementarity and win-win between DCs and FCS. This is the credit of network technology, because it can make such complex communication requirements perfectly realize the integration under the conditions of economic applicability

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