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Some Thoughts on Fieldbus Issues in Water Treatment Automation Applications Author: Guo Fengwen, Nanjing Municipal Engineering Design and Research Institute Introduction Since the reform and opening up, China has introduced relatively advanced international concepts and technologies for water treatment automation control through projects such as foreign investments and World Bank loans. After more than 10 years of effort, the distributed control and monitoring system based on PLCs has become the mainstream in water treatment automation. Experience has shown that such control systems are safe, reliable, and cost-effective for the water treatment industry. As the performance of PLC technology continues to improve, the chemical and metallurgical industries, which have traditionally relied on DCS systems, are now debating whether to use DCS systems alone, a hybrid system of DCS and PLCs, or entirely PLC-based systems. As the concepts of networking and informatization continue to penetrate into the field of automation, fieldbus technology has become a new starting point for automation in the world today. With the rise of fieldbus technology, does water treatment automation control technology still need to evolve? The answer is yes. The issue is that in 1999, the fieldbus technology standard IEC61158 was finalized, with 8 different buses becoming the current IEC fieldbus standards; the situation in which one single fieldbus would dominate everything did not occur as people had hoped. IEC 61158 leaves the final decision to the user, and how to apply fieldbuses is a question that technicians working in water treatment automation are considering. 1 Some views on fieldbus issues in applications 1.1 Fieldbuses are an inevitable trend in the development of automation technology. A typical enterprise network information integration system can be divided into three layers: the control infrastructur, the enterprise intranet, and the global information Internet. Regarding the control networks in enterprises, traditional automation monitoring and information integration systems (including distributed control systems based on PC, PLC, and DCS products) are characterized by what is known as I/O connections, where there is a one-to-one link between field devices and control stations. Measurement and control are carried out using analog signals of voltage and current, making it an analog-digital hybrid system. Its disadvantages include: (1) weak information integration capabilities. The management information obtained by the control station is limited; a large amount of data, such as device parameters, fault information, and fault records, is difficult to obtain, making it hard to achieve information exchange and sharing between devices as well as between the system and the outside world. (2) The system is not open, has poor integrability, and there is a lack of interoperability and interchangeability among products from different manufacturers. (3) Reliability is difficult to guarantee. It only disperses control across several local areas, failing to achieve a thorough dispersion of the risk. The installation of a large number of I/O cables not only increases costs but also reduces the reliability of the system. (4) Low maintainability. Due to incomplete information on the field devices, their functions for online fault diagnosis, alarm generation, and recording are limited; it is difficult to carry out tasks such as remote parameter setting and modification of these devices, which affects the maintainability of the system. With the rapid development of technologies such as computers, microprocessors, and networks, intelligent field devices equipped with CPUs combine detection and control functions, enhancing on-site processing capabilities and allowing control functions to be handled entirely at the site. The field bus is located at the lower level of the production control and network architecture; it is a fully digital, bidirectional, multi-station serial communication data bus used between field devices and the control room systems. Open, unified fully digital network communication technology enables the interconnection of field devices, resulting in a field-bus-based fully distributed integrated network control system (FCS). FCS treats control stations, communicable intelligent field devices, and other information resources as nodes in the enterprise network, thereby increasing non-control information (management information). This facilitates the transition of enterprises from process control to process management, paving the way for integrated control and management within enterprises. It also promotes the networking of enterprises and contributes to the integration of control networks with public data networks, thus helping to achieve optimal performance in production, supply, and distribution. Therefore, FCS is an inevitable trend in the development of automation technology. 1.2 The application of field buses should be guided by the development of control technology; it should not be adopted merely for the sake of application. At this stage of rapid advancement in information technology, we should adopt a higher standard. It is not only necessary to consider current market share factors, but it is also advisable to make evaluations and judgments from the perspective of technological development. There are generally two reasons why the IEC 61158 standard had to adopt various types of bus standards: first, it is believed that no single standard can meet the needs of applications of different types and at different levels from both technical and economic perspectives; therefore, from a market perspective, there is no distinction between different categories of field buses in terms of superiority or inferiority ； The second is the view that it is purely the result of commercial competition. The author is more inclined to believe that the latter is the most important reason. From the perspective of generalized field buses, buses can be classified into bit buses (sensors and actuators buses), device buses, and information flow buses. Such a classification may not be bad, but the problem is that it cannot blur the essential difference between modern fieldbuses and classical fieldbuses. From a technical perspective, various fieldbuses differ technically due to their different development backgrounds and application purposes. For example, network communication technology, which is a key technique for field buses, is used in several existing field bus systems; the communication methods in these systems are based on three basic communication patterns, namely the client/server model ； Master/Slave ； Producer/consumer type. Of the three communication methods, the first two are one-to-one, point-to-point communications, while the latter is a one-to-many communication method; they differ in terms of real-time performance, efficiency, and the flexibility of the network structure. In current fieldbuses, there are those that use a single mode, as well as those that combine multiple modes to enhance their communication capabilities and meet various requirements. For example, the FF bus is a typical example of a bus that combines three basic communication modes, which are used respectively for communicating aperiodic data and periodically precise data, in order to improve the flexibility and security of the network structure. In short, although different fieldbuses hold a certain market share, they each have their own technical characteristics. Therefore, from the perspective of a general bus system, it is a matter that requires careful consideration whether to use different buses for various parts of the system, adopting a multi-level bus approach, or to opt for a single bus once the conditions are right. 1.3 Fieldbuses do not rule out remote I/O, but this is only a temporary solution. Delivering the bus to remote I/O is something that DCS and PLC technologies have already solved; in the IEC61158 standard, some fieldbuses themselves originated from PLC control systems and are based on remote I/O bus technology. As mentioned earlier, the economic advantage of using PLCs (including DCS) together with distributed I/O units installed on-site is evident, especially for some simple field devices. Therefore, bus systems do not rule out the use of remote I/O, but this does not equate to a \"field bus\". The essential characteristic of a fieldbus system is the use of intelligent field devices with fieldbus communication capabilities. The network nodes formed by these communicative intelligent field devices have the ability to communicate both vertically (with the system) and horizontally (between nodes). "The concept of \"on-site\" refers not only to distance but, more importantly, to intelligent devices that can communicate with each other. If only remote I/O conversion is used, the essence of fieldbus’s rich information and advanced diagnostic management functions is lost. Since the variety of intelligent field devices for field buses is still limited at present, mixing up remote I/O with field buses is sometimes merely a temporary solution. 1.4 FCS and DCS, PLC should currently coexist rather than replace each other. FCS evolved gradually based on traditional instrument control systems and distributed control systems, making use of fieldbus technology; to this day, a large number of analog instruments, DCS, and PLCs are still in use. Given the current situation, fieldbus-based smart instruments cannot completely replace analog instruments, and FCS cannot completely replace DCS and PLCs; there is a transitional period in this regard. Our country is still in the initial stage of developing fieldbuses, and the conditions for their widespread use are not yet ripe, mainly due to issues such as standard establishment and the level of support for relevant products (especially domestic ones). Therefore, from the user’s perspective, there is no need to rush. During the transition period, low-cost distributed network control systems based on PLCs can still be used for water treatment automation; however, the network structure should be more flexible, there is no need to be overly rigid regarding the number of control stations, and remote I/O should be utilized more effectively in order to shorten the transmission path for analog signals and extend the distance over which digital communication can take place. For future development, it is advisable to choose a PLC communication bus that supports multi-master/slave systems and enjoys wide adoption, so that, when conditions permit, the communication interfaces of field devices can be used in place of distributed I/O access systems. IEC 61158 covers 8 types of fieldbus standards; there are also other international or **standard fieldbuses, such as CAN and Lon Works. This coexistence of multiple buses is an important characteristic of the transition period, and it has contributed to the development of fieldbus integration technologies. The development of software and hardware integration techniques as well as related products for such systems and networks has become a hot topic in the field of automation today, with some products already having been successfully developed. Therefore, by using a PLC system now, there is no need to worry about compatibility issues with FCS systems regarding communication protocols in the future. 1.5 The increasing demand for information will drive the integration of fieldbuses and Ethernet. With the growing variety of intelligent field device products and their wider application, as well as the advancement of industrial management automation, it is estimated that the amount of information required will increase by another 10 to 30 times in the coming years. Managers, in order to meet the needs of business management, desire to obtain more real-time information, and they achieve information exchange and sharing by establishing open information management systems. Therefore, as instrumentation becomes more intelligent, the data transmitted will inevitably become more complex; in the future, the data transmitted may no longer be limited to just a few bytes. The increasing demand for information will drive the development of fieldbus technology; therefore, some believe that it is inevitable for Ethernet to extend to the lower layers of control systems, and this is an issue we should take into account when choosing fieldbuses. 1.6 The standardization of fieldbus standards is inevitable. This prediction may be premature, but from the user’s perspective, the coexistence of multiple buses is by no means a good thing. As mentioned earlier, since these fieldbuses use completely different communication protocols, addressing the issues of compatibility and interoperability between systems based on these various standards inevitably increases the costs for users as well as the complexity of operation and maintenance. The unified TCP/IP protocol, along with the rapid development of the Internet and various advancements in Ethernet standards, has brought hope to the industrial sector, which has long been plagued by compatibility issues related to different protocols. Many fieldbus organizations are working on developing Ethernet/IP technology. With its advantages of low cost, high speed, and ease of use, Ethernet is being incorporated into underlying networks; this not only facilitates integration at the field level, control level, and management level vertically but also reduces the integration costs across different manufacturers horizontally. Of course, there are still many technical issues to be resolved before industrial Ethernet can ultimately become a unified bus standard (such as bus power supply and inherent security), but it is not impossible. 2 Conclusion In summary, fieldbus technology aligns with the trend toward intelligent, decentralized, networked, and standardized control systems. It serves as the foundation for establishing enterprise information networks and achieving integrated management and control, which is why it has become a focal point in the development of automation technologies. However, the conflicts of interest among various buses have actually hindered and delayed the application of FCS technology in our country. Faced with the situation of multiple buses coexisting, for users of fieldbus technologies and products, how to choose a fieldbus during this current transition period is an issue that requires careful consideration. Some of the views expressed in this article may not be correct; for that reason, the author suggests that **research centers for the management and technology of the water industry establish an organization similar to the LonWorks fieldbus collaboration network under the Intelligent Building Technology Promotion Center affiliated with the Ministry of Construction. Such an organization would be responsible for keeping track of the development of fieldbus technologies, facilitating the exchange of information technology-related knowledge, guiding the industry in the adoption and application of these new technologies, and on this basis formulating standards and regulations for automation technologies in water treatment, thereby promoting the advancement of such technologies. References 1 Yu Changyou, et al. Evaluation and selection of different fieldbuses in IEC 61158. Electrical Automation, 2001, 23(2): 4–6. 2 Li Jia, et al. The adoption of Ethernet technology is an inevitable trend in the development of fieldbus technology. Automation Instruments, 2001, 22(5): 1–4. 3 Chang Hong, et al. Analysis of three basic communication modes in fieldbuses. Journal of Electrical Engineering Technology, 2001, 6: 19–21. 4 Guo Fengwen. Development trends in automation control technology for the water industry. China Water & Wastewater, 2001, 17(3): 32–35