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Introduction Since the reform and opening up, China has introduced internationally advanced concepts and technologies for water treatment automation control through projects such as foreign governments and World Bank loans. After more than 10 years of efforts, the distribution monitoring system composed of PLC has become the mainstream of water treatment automation. Experience has shown that such a control system is safe, reliable and economical for the water treatment industry. With the continuous improvement of the performance of PLC technology, the chemical and metallurgical industries that have traditionally adopted DCS systems are also arguing whether to use DCS or a hybrid system of DCS and PLC, or a problem of the entire PLC system. With the continuous penetration of the concept of networking and informatization into the field of automation, fieldbus technology has become a new starting point in the world of automation. Faced with the rise of field bus technology, automation control technology for water treatment should not be advanced. The answer is yes. The problem is that the dust of the fieldbus technical standard IEC61158 was settled in 1999. There are eight types of buses that become the IEC's current fieldbus technical standards. The situation that people expect from a field bus to dominate the world has not happened. IEC61158 gave the final choice to the user. How to use the field bus has become a problem that is being considered by technical personnel engaged in the automation of water treatment.
1. Some views on the application of fieldbus issues 1.1 Fieldbus is an inevitable trend in the development of automation technology A typical enterprise network information integration system can be divided into three layers: control network infranet, intranet intranet, and global information internet internet. As far as the enterprise control network is concerned, traditional automatic monitoring and information integration systems (including distributed control systems based on PC, PLC, and DCS products) are characterized by one-on-one connection between field devices and control stations. The so-called I/O connection method uses voltage and current analog signals for measurement and control. It is an analog and digital hybrid system. Its disadvantages are:
(1) Information integration capability is not strong. The management information obtained by the control station is limited, and a large amount of data such as equipment parameters, faults and fault records are difficult to obtain, and it is difficult to achieve information exchange and information sharing between devices and between the system and the outside world.
(2) The system is not open, and the integration is poor. There is a lack of interoperability and interchangeability between products of different manufacturers.
(3) Reliability is not easy to guarantee. It merely disperses control into several parts and fails to achieve a complete dispersion of dangers. The large number of I/O cabling installations not only increases the cost but also increases the unreliability of the system.
(4) The maintainability is not high. Due to incomplete information of on-site equipment, its online fault diagnosis, alarm, and recording functions are not strong. It is difficult to complete parameterization functions such as remote parameter setting and modification of field devices, which affects the maintainability of the system.
With the rapid development of computers, microprocessors, networks and other technologies, intelligent field devices with built-in CPUs integrate detection and control, enhancing on-site processing capabilities, and allowing control functions to be fully decentralized to the field. The fieldbus is located at the bottom of the production control and network structure and is a fully digital, bi-directional, multi-station serial communication data bus between the field device and the control room control system. The open and unified all-digital network communication technology realizes the interconnection of field devices and forms a field bus full distributed integrated network control system (FCS). FCS regards control stations, communicable smart field devices, and other information resources as nodes in the enterprise network, greatly increasing non-control information (management information), and thus allowing enterprises to move from process control to process management, which means building management and control integration for the company. Paved the way, to promote the process of enterprise network, but also to control the integration of the network and public data network, to achieve optimal production, supply and marketing has played a catalytic role. Therefore, FCS is an inevitable trend in the development of automation technology.
1.2 The application of fieldbus must focus on the development of control technology. It cannot be applied for the application at the present stage of rapid development of information technology. Our standpoint should be higher. It is necessary not only to consider the factors of the current market share, but also to make assessments and judgments from the perspective of technological development. The root cause of the IEC61158 standard having to adopt multiple bus standards is usually considered to be two:
The first is that there is no single standard that can meet the needs of different types and different levels of applications from a technical and economic perspective. Therefore, from the perspective of the market, there is no difference between the merits and demerits of different types of fieldbus; second, it is considered as purely commercial competition. the result of.
The author is more inclined to think that the latter is the most important reason. The bus can be divided into a bit bus (sensor actuator bus), a device bus, and an information bus in terms of a broad field bus. This division may not be bad, but the problem is that it cannot obscure the essential difference between modern fieldbus and classical fieldbus. From a technical point of view, various fieldbuses have different technical purposes because of their different backgrounds and applications.
For example, as a field communication bus key technology network communication technology, there are several kinds of field bus communication methods mainly based on three basic communication modes, ie, client/server type; master/slave type; producer/consumption Type. The first two of the three communication methods are one-to-one and peer-to-peer communication. The latter is a one-to-many communication method. They are different in real-time communication, efficiency, and network structure flexibility. In the current field bus, both single mode and multiple modes are combined to enhance their communication capabilities and meet different needs. For example, FF bus is a typical bus combining three basic communication modes. It applies to aperiodic communication and accurate periodic communication to improve the flexibility and security of the network structure.
In short, although different fieldbuses occupy a certain market share, they have technical characteristics. Therefore, from the perspective of the generalized bus, the user adopts different buses, ie, multi-level buses, according to different parts of the system, or selects a single bus when conditions are ripe, which is a problem that needs careful consideration.
1.3 Fieldbus does not exclude remote I/O, but it is only an expedient measure. It is an issue that DCS and PLC technology have already solved to send the bus to the remote I/O. In the IEC61158 standard, some field buses themselves are developed by the PLC control system. This is based on remote I/O bus technology. As mentioned earlier, PLCs (including DCS) plus distributed I/Os installed in the field are economically obvious, especially for some simple field devices, so the bus system does not exclude remote I/O. Never equals "field bus." The essential characteristic of the fieldbus system is the use of intelligent field devices with fieldbus communication capabilities. The network nodes formed by these communicable intelligent field devices not only have vertical (system) communication but also horizontal (inter-node) communication capabilities. . The concept of "live" refers not only to distance, but more importantly to intelligent devices that can communicate. If only remote I/O conversion is used, then the soul of fieldbus multiple information and rich diagnostic management control functions will be lost. Due to the fact that the current fieldbus is not rich in smart field devices, it is sometimes expedient to confuse remote I/O and fieldbus.
1.4 FCS and DCS and PLC should coexist instead of replace FCS. It is based on the traditional instrument control system and distributed control system. It is gradually developed using fieldbus technology. At present, a large number of analog instruments, DCS and PLC are still used. According to the current situation, it is impossible for fieldbus smart meters to completely replace analog instruments. FCS cannot completely replace DCS and PLC. There is a transition period.
China is still in the initial stage of development of fieldbus. The conditions for universal application of fieldbus are not yet mature, mainly due to the determination of standards and the support rate of products (mainly domestic products). Therefore, from the user's perspective, there is no need to worry too much. Water treatment automation in the transitional period can still insist on using a low-cost distributed network control system composed of PLC, but it should be more flexible on the group network, the number of control substations need not be too rigid, remote I/O should be better Applications to shorten the analog signal transmission path and maximize the digital communication distance.
To facilitate future development, it is best to use a PLC communication bus that supports multiple master-slave systems and has a wide support rate so that, when conditions permit, the distributed I/O access system is replaced by the communication interface of field devices. IEC61158 contains 8 types of fieldbus standards, in addition to other international or national standards of fieldbus, such as CAN, LonWorks and so on. This kind of multi-bus coexistence is an important feature of the transition period, which has also led to the development of fieldbus integration technology. The hardware and software integration technology and product development of the system and network has become a hot topic in today's automation field. Subject, some products have been successfully developed. Therefore, it is not necessary to worry about the compatibility of the communication protocol with the FCS system in the future.
1.5 Increased demand for information will drive the combination of fieldbus and Ethernet With the richness and application of various intelligent field device products and the deepening of industrial management automation, there is information that in the next few years, the estimated amount of information will increase again. 10 to 30 times. According to the needs of management and management, managers hope to obtain more real-time information, and through the establishment of an open information management system to achieve information exchange and sharing. Therefore, with the increase of intelligent instrumentation, the transmitted data will also tend to be complex, and the data transmitted in the future may not be satisfied with several bytes. The increasing demand for information will promote the development of fieldbus technology. Therefore, some people think that the extension of Ethernet to the bottom layer of the control system is inevitable, and it is also a problem that we should pay attention to when choosing a field bus.
1.6 The unification of fieldbus standards is inevitable. This prediction may be premature, but in any case from the user's point of view, a variety of bus lines is not a good thing. As mentioned before, since these fieldbuses use completely different communication protocols, to solve the mutual compatibility and interoperability problems between these different standard systems, the user's investment and use and maintenance complexity will inevitably increase. The unified TCP/IP protocol has made the rapid development of the Internet network and many advances in the Ethernet standard. This has given a glimmer of hope to the industrial community that has been plagued by the compatibility problems of different protocols. Many fieldbus organizations are working to develop Ethernet/IP. Technology, Ethernet is introduced into the underlying network with its inexpensive, high-speed and convenient features, which not only facilitates integration of the field layer, control layer, and management layer in the vertical plane, but also reduces the integration costs of different manufacturers at the horizontal level. Of course, there are still many technical problems to be solved (such as bus power supply, intrinsic safety, etc.) to make industrial Ethernet eventually become a unified bus standard, but it is not impossible.
2. Conclusion In summary, field bus technology adapts to the trend of control to intelligent, decentralized, networked, and standardized development. It is the foundation for establishing enterprise information network and realizing the integration of management and control. Therefore, it becomes a hot spot for the development of automation technology. However, the dispute over the interests of various buses has actually hindered and delayed the application of FCS technology in China. Faced with the situation of multi-bus convergence, as a user of field bus technologies and products, in the current transitional period, how to select a field bus should be a matter to be carefully considered. Some of the views discussed in this article are not necessarily correct. It is for this reason that the author recommends that the National Water Industry Management and Technology Research Center establish an organization like the LonWorks Fieldbus Collaboration Network of the Intelligent Building Technology Extension Center under the Ministry of Construction Science and Technology Committee, mainly responsible for tracking The development of field bus technology, information technology exchanges, and guidance to the industry for the promotion and application of this new technology, and on this basis formulate China's water treatment automation technology standards and norms, and promote the development of water treatment automation technology.
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Simple Analysis of Fieldbus Problems in Water Treatment Automation Application
Abstract: The traditional water treatment automation control system uses the PLC control system. At present, everyone thinks that the water treatment control system should also be advanced. Therefore, we decided to adopt the current field bus technology. The article will discuss with you how to deal with water treatment. Fieldbus technology is applied in automation.