集散型计算机控制系统

Distribution control system一、A brief introduction of the distributed control systemDistributed control system, also called distributed control system, is a new computer control system for centralized control system. It is a centralized decentralized control system based on multi processor based, is currently in process control, especially in large and medium-sized production device to control the application of the most and the highest reliability control system. In the traditional process control introduction of computer technology, using software composed of various functional modules, instead of the past conventional instrument function, to realize the control of production process of pressure, temperature, liquid level, flow, composition and mechanical quantities such as parameters, and the screen of CRT display, communication applications linked network technology component system. The features of DCS field control station of distributed control, real-time data transmission through the cable sent to the control room operator station, realize the centralized monitoring and management, decentralized control, the control function, load and risk diversification.Distributed control system of information management is "set", "scattered" is to control function, DCS system can realize decentralized control and centralized monitoring and management can be realized. In the aspect of system function, DCS and centralized control systems are not very different, but in the realization of system functions methods are completely different. Centralized control system only needs a computer and the I / O devices and CRT, keyboard, printer, etc. peripheral equipment can be complete system functionality and DCS would normally have to by the four basic parts: the system network, I / O control station, operator station and engineer station. In DCS, the field I/O control station, operator station and engineer station is composed of independent computers, respectively, to complete data acquisition and control; monitoring, alarm and recording; system configuration, system management and other functions. These specific features of the computer are referred to as "nodes", and all of these nodes and through network system connected together, become a complete and unified system, in order to achieve decentralized control and centralized monitoring, centralized operation. DCS system is with the modern large-scale industrial production automation continued to rise and process control requirements of increasingly complex emerges as the times require comprehensive control system, it is the product of computer technology, system control technology, network communication technology and multimedia technology combined, can provide window friendly interface and powerful communication function. Is a sophisticated equipment to complete process control and management.二、The history of the development of distributed control systemDCS since its inception in 1975, has experienced thirty years of development. In thirty years, although DCS has not been a major change in the structure of thesystem, but after the continuous development and improvement, its function and performance have been greatly improved. In general, DCS is toward more open, more standardized, more products in the direction of development. As the field of process automation computer control system, the traditional DCS is only a narrow concept. If you thought that only the production process of the DCS automation system, it leads to the wrong conclusion, because now the computer control system has been greatly expanded. It not only includes the DCS in the past contains a variety of content, also drill down to the field of every measurement equipment, implementing agencies, to the development to the production management and enterprise management. Traditional DCS now only refers to this part of the production process control automation, and industrial automation system concept, should be targeted to enterprise wide solutions, namely total solution level. Only from this point of view put forward and solve problems, to really play the computer automation of its function.After entering ninety age, computer technology, more and more new technologies were applied to the DCS. PLC is a kind of logic control of electronic equipment is developed, which is mainly used to replace inflexible and cumbersome relay logic. After entering the field bus technology in the mid ninety's development is very rapid, that some people have to predict: FCS based on field bus control system will replace the DCS as the protagonist. But the field bus can not replace the DCS. The reasons are as follows:1.Low speed network characteristics of the 1 field bus, so that the number of meters each bus did not reach a rational number. In practical application, a H1 bus can only be installed about 8 instruments. As a result, the field bus save cable advantage is very limited.2.field bus standards are not unified, no one has an absolute advantage, the user can choose.3.field bus is still not well solve the intrinsic safe danger zone problem.三、The main technical overview of systemThe system mainly has the field control station (I/O station), data communication system, man-machine interface unit (operator station and engineer station of OPS ENS), power supply cabinet, etc.. The system has an open architecture that can provide multi open data interface. In the harsh industrial field hardware system with high reliability, convenient maintenance, advanced technology. Finished the bottom software platform with powerful processing function, and provide convenient configuration complex control system and user is special and advanced control algorithm of the support ability of independent development, easy configuration and easy to use. Support a variety of fieldbus standards in order to adapt to future expansion needs. The design of the system with self diagnosis function and diagnosis to the appropriate redundancy configuration module level, high reliability. The occurrence of either component fault in the system, will not affect the operation of the system. System parameters, alarm, self diagnose and other managementfunctions is highly concentrated in the CRT display and print to the printer, control system on the physical function and truly decentralized, utilization rate of at least 99.9% of the whole system; system mean time to failure of 100000 hours, the realization of the complete monitoring of nuclear power, thermal power, thermal power, petrochemical, chemical, metallurgy, building materials and many other fields. The concept of "domain". The large scale control system with high-speed real time redundant network is divided into several relatively independent system, a system composed of a domain, the domain sharing data management and operation, and each domain is a functional integrity of the DCS system, in order to better meet the user's use. The network structure reliability, openness and advanced. In the operating system layer, the redundancy of 100Mbps Ethernet; in the control layer, using redundant100Mbps Ethernet and ensure the system reliability; in the field of signal processing layer and 12mbps PROFIBUS bus connecting central control unit and the signal processing module. The structure of Client/Server standard.Some DCS operationlayer using Client/Server open structure and reliable operating system. Operating system with WINDOWS NT operating system; the control station adopts mature embedded real-time multi task operating system QNS control system to ensurereal-time, safety and reliability. Control configuration software standard. The control system uses IEC611313 standard configuration tools, can achieve any monitoring and control requirements. Scalable and scalable, secure economy.The level of DCS system and management of a total of four levels: 1) direct control level (process control level): process control level is the basis for the distributed control system (DCS), main functions include: process data acquisition, direct digital control, equipment monitoring, system test and diagnosis and implementation running is safe and reliable. At this level, the process control computer known as the scene control station, and all kinds of field device directly connected (such as instrumentation, actuator etc.). The implementation of continuous monitoring, control and batch control of control object. At the same time it up withthe second layer is connected to the computer, control and management of information receiving level, to transfer control device of the characteristics of information and the collected real-time data. 2) the process management level: at this level the process management computer to realize comprehensive monitoring equipment operating process, simulation screen display and control circuit configuration and parameter modification, for all building electromechanical equipment operation process optimization processing, report on the operation, trend chart display. To achieve the overall optimization within the unit can, and to generate commands to the lower level. In this layer, the main function is to optimize process control, adaptive control, loop real-time data to simulate the picture monitor. 3) hierarchical management level: set the parameters according to the characteristics of the coordinated control system of building automation, intelligent building of the electrical equipment, is the overall coordinator. It can plan the system structure and operation mode of scale control system of each unit in the use of energy, according to the situation of the users. This is what needs the high level of building automation system.4) property management: building property management level resides in thebuilding automation system of the highest level, the scope of its management is very wide, these functions are integrated into the software system, through a comprehensive plan, under different conditions, combined with a variety of conditions and energy allocation, in order to achieve the optimal solutions to these problems. In this level, the need to achieve the integration of intelligent building automation equipment and public security automation system.四、The characteristics of distributed control system(1) the high reliability of the DCS system to control the spread of the computer implementation, the system uses fault-tolerant design of the structure, so a computer malfunction will not cause the loss of other systems. In addition, due to relatively simple task undertaken by each computer system can according to need to achieve the function with specific structure and software of special computer, so that the reliability of each computer system has also been improved.(2) open DCS using open, standardization, modularization and serialization design, each computer system using the LAN communication, to achieve information transmission, when the need to change or expand the system functionality, will add computer conveniently connected into the network system of communication or from the network discharge, almost does not affect the work of other computer systems. (3) flexibility through the configuration software according to the different process of application objects were software and hardware configuration, which determine the measurement and control signals and inter connections, from the control algorithm library choose the appropriate control law and basic graphics from the graphics libraries call components required for various monitoring control and alarm screen, thus convenient to constitute the control system.(4) easy maintenance function single small or micro dedicated computer, with characteristics of simple and convenient maintenance, when a local or a computer failure can in does not affect the online replacement of the operation of the whole system, rapid troubleshooting.(5) through the communication network data transfer coordination between the various stations, sharing, and coordination of the whole information system, to complete the overall function and optimization of control system.(6) control function complete control algorithm rich, set continuous control, sequence control and batch control in one, advanced control cascade, feedforward and decoupling, adaptive and predictive control can be realized, and can easily add the special control algorithm required. Very flexible forms of DCS, managed by a dedicated computer station, operator station and engineer station, recording station, field control station and data acquisition station, etc., but also by the universal server, industrial control computer and a programmable controller. At the bottom of the process control level by the general decentralized field control station, data acquisition station, data acquisition and control, and through the data communications network transmission to the monitoring computer production level. Production control level centralized management of the data from the process control level, such asoptimizing calculation, statistics, fault diagnosis and alarm etc.. With the development of computer technology, DCS and higher performance according to need the computer equipment through the network connection to achieve more senior management functions, such as scheduling, storage management, energy management etc.五、Distributed and centralized system is differentDistributed control system (DCS), also called the distributed system, a new type of computer is compared with the centralized control system of the control system, which is a centralized control system based on the development and evolution of the. In the aspect of system function, DCS and centralized control systems are not very different, but in the realization of system functions methods are completely different. Firstly, the framework of DCS system network, it is the foundation and core of DCS. As the network of the system for real-time DCS, reliability and scalability, plays a decisive role, so the manufacturers have been careful in this area of design. For the DCS system network, it must meet the requirements of real-time transmission of information, is completed within defined time limits. Here said the "OK" time limit, is that in any case, information transmission can be completed within the time limit, and the time limit is under the control of the process of real time demand. Therefore, measure system network performance index and the network is not rate, which is often referred to as bits per second number (BPS), but the real-time network system, which can ensure the long time to complete the required information transmission. The network system also must be very reliable, in any case, the communication can not be interrupted, the network topology so most manufacturers of DCS were doublebus ring or dual star. In order to meet the system requirements, the maximum number of nodes in the system can access the network should be several times larger than the number of nodes actually used. In this way, one can always add new nodes, on the other hand, it can also make the system running on the network communication load lighter, to ensure the real-time and reliability of the system. In the actual operation of the system, each node of the Internet and the net is that may occur at any time, especially the operator station, so that network reconfiguration will often, and this operation must not affect the system's normal operation. Therefore, network system should have a strong online network reconfiguration functions.Secondly, this is a complete on-site I/O processing and Realization of direct digital control (DOS) function of network nodes. A general DCS to set the field I/O control station, I/O and control functions to share the entire system. This can be avoided due to the failure of a site caused by the failure of the whole system, improve the system reliability, the site also allows sharing of data acquisition and control functions, is conducive to improve the performance of the whole system. The DCS operator station is to deal with all the relevant operation interface (HMI-Human Machine or Interface operator interface) network node function.Network system is the DCS Engineer Station, it is to DCS off-line configuration, configuration and online system supervision, control, maintenance ofthe network node, its main function is to provide to the DCS configuration, configuration software tools (software) and in DCS run on-line real time monitoring DCS network each node operation, system engineer can through the engineer station timely adjustment of system configuration and some system parameters set, the DCS in the best working condition at any time. Different with the centralized control system, all DCS are required to have system configuration function, it can be said that no system configuration functions of the system can't be called DCS.。