Abstract: Distributed Control System (DCS) is a mature technology that dominates the field of industrial control today. However, with the maturity of Fieldbus Control System (FCS) technology, the rapid development of network technology, the continuous innovation of software technology, and the emergence of wireless linking technology, DCS faces many opportunities and challenges. This paper takes this as its starting point. Keywords: DCS, FCS, network technology, wireless connection technology 1 Introduction Process control, as an application of automation technology [5,15], has a history of development that can be traced back to ancient times, but its industrial application can only be counted from the 1920s. At that time, the process control system was a simple system, and the instruments were base-type and large in size. Around the time of World War II, various complex control systems were developed. In terms of controllers, unit combination instruments came into being. Pneumatic unit combination instruments (QDZ) and electric unit combination instruments (DDZ) became the mainstream of control instruments at that time. With the development of science and technology [4], in the 1970s, the emergence of microcomputers [4] brought a major breakthrough to process control. Digital computers entered the field of industrial control and produced the first generation of control systems: Computer Centralized Control System (CCS). The system replaced traditional analog instruments, enabling the use of more advanced control technologies and bringing about a qualitative leap in process control. However, since CCS control is directly oriented towards the controlled object, it does not form a control network system, concentrating control while also concentrating danger. In response to the shortcomings of CCS, a true industrial control network system DCS was developed within a few years. This system disperses danger while concentrating control, so it is widely used in today's industrial control field. However, today's technological development is even more rapid, and technologies such as FCS, network technology, and computer technology pose a great challenge to DCS. This article is a superficial understanding of DCS. 2 Current DCS structural characteristics and the technologies adopted 2.1 Hardware network layered structure A typical DCS network system can be divided into three levels: process control level, control management level, and production management level [4,16]. The first layer, the process control level, primarily uses PLCs (Programmable Logical Controllers) or I/O modules via fieldbus to provide basic control over field devices. The second layer is the control and management level, where a monitoring computer connects to the PLCs or I/O modules through an industrial control network to monitor the process equipment. The third layer is the production management level, which connects to the monitoring computer via a file server, management computer, and industrial LAN to access field information and manage production at the higher level. This system configuration significantly reduces the probability of damage to the entire system due to unreliability in a single part. Furthermore, the continuous maturation of various hardware and software technologies greatly improves the overall system reliability, making DCS the mainstream industrial automatic control system today. 2.2 Software characteristics Due to the special functions of DCS[3], its software system is different from the software we usually talk about. It has its own characteristics. As shown in Figure 1, it is a block diagram and working principle of general DCS software. From this, we can see that it fully reflects the hierarchical network structure of DCS. For us, a lot of work is concentrated on the engineer station, while the operator station, server station and field control station are generally implemented with their own dedicated software. We just need to learn how to use them. 2.3 Disadvantages of DCS As a relatively mature engineering technology, DCS has achieved great success worldwide. However, with the progress of the times and the emergence of various new technologies, people's requirements for DCS have become increasingly demanding. Therefore, today's DCS has some shortcomings, specifically [9]: ① The system wiring work is particularly heavy because each field device needs to be connected to the control room with a cable, which brings many inconveniences to the subsequent wiring and maintenance; ② Since the standard analog 4-20mA signal is used instead of digital signal for data transmission, the reliability of the signal and anti-interference are questionable; ③ There are problems when different DCSs are interconnected. That is to say, when we select different DCSs to connect in the same project, there are often some troubles in mutual communication, which brings difficulties to system integration. Therefore, we need to do some work on the interoperability of different DCSs. 3 Current main technologies affecting the development of DCS 3.1 Rapid development of fieldbus system Fieldbus system refers to a new type of control system. It is a new type of network integrated fully distributed control system formed under the drive of fieldbus technology development. Its main features are [1]: ① In terms of structure, it breaks the traditional system structure, puts the control unit into the field device, and adds the communication function of the field device. The field gearbox can communicate directly with the valve and other actuators. Therefore, the control system can directly complete the control on the field without relying on the computer in the control room, and realizes the thorough distributed control; ② In terms of technology, FCS is an open system with consistency and openness of relevant standards. Therefore, as long as the same standard is followed, various different devices can be interconnected. For users, they can organize products from different manufacturers according to their own needs and build the most economical and effective system suitable for themselves; ③ In terms of reliability, it has higher reliability due to the adoption of full digital signal communication and the intelligence and functional autonomy of the field device. It also brings many conveniences in wiring and maintenance. From the current global development perspective of fieldbuses, FCS has a history of over ten years, its technology is mature, and it has formed an international standard. There are also successful examples of its application in process control. Therefore, some believe that FCS will replace DCS and become the next generation of control systems. 3.2 The rapid development of network technology: The basic trend in the development of control networks is towards open and transparent communication protocols. However, the openness of various fieldbuses used in DCS is not complete. In comparison, Ethernet has advantages such as high transmission speed, low power consumption, ease of installation, and good compatibility. It also supports all popular TCP/IP network protocols, so it is widely used in commercial systems. In recent years, with the development and maturation of network technology, Ethernet has entered the control field, forming a new type of Ethernet control technology. The following is an analysis of the characteristics of industrial Ethernet. Traditional industrial Ethernet uses a random access protocol—Carrier Sense Multiple Access with Collision Detection (CSMA/CD)[2] to control media access. For control processes with strict response time requirements, collisions may occur. However, the fast switching Ethernet technology that has emerged in recent years uses full-duplex communication, which can completely avoid collisions in CSMA/CD and can easily implement a priority mechanism to ensure the maximum utilization of network bandwidth and the best real-time performance. Moreover, the network speed is constantly improving, from 10M to Fast Ethernet 100M and 1000M. GM-level Ethernet technology is also under research. Therefore, there is reason to believe that the future Ethernet can fully meet the real-time requirements of industrial control systems. 3.3 Wireless Linking Technology Wireless linking technology is commonly used for wireless data acquisition [12,18], but rarely for control engineering. However, as this technology matures and becomes more standardized, its widespread application in industrial control is also possible. In particular, Bluetooth technology is attracting attention [13]. Here is a brief introduction to the characteristics of this technology: it uses the 2.4 GHz ISM band and adopts FM modulation. The transmission rate of this technology is designed to be 1 MHz, and it uses time-division full-duplex communication. The current communication distance is 10-100 m. It is evident that the communication distance must be increased to apply it in the industrial control field. It is particularly worth mentioning that in reference [17], a pendulum control based on wireless linking has been successfully implemented in the laboratory, which lays the foundation for us to adopt this technology in the industrial control field. 3.4 The Development of Software Technology From an engineering perspective, with the significant improvement in hardware performance, how to effectively organize and utilize them and fully unleash their potential is a major issue facing engineering software engineers. Currently, various independent SCADA software packages are becoming increasingly mature and are being accepted by more users. Here, I would like to talk about the emerging soft connection technologies used in the industrial control field, such as ODBC, OLEDB, OPC, COM, etc. In particular, OPC (OLE For Process Control) technology [6,18] is an industrial standard that introduces COM into industrial processes. Devices that meet this standard can communicate with other OPC client programs. Its working method is shown in Figure 2. This technology establishes a set of interface specifications that meet the requirements of industrial control, seamlessly connecting field signals with SCADA, HMI and other software according to a unified standard. At the same time, it effectively separates hardware and application software. As long as the device has a server with an OPC interface, any client program that supports its interface can use a unified method to access data from devices from different manufacturers without having to repeatedly develop drivers. This greatly improves the interoperability and adaptability of the control system. 4 Future Development Trends of DCS As can be seen from the above analysis[19], various new technologies are constantly emerging in the field of industrial control. New control schemes and ideas pose a strong challenge to the traditional DCS control. However, on the other hand, these technologies provide more opportunities for the development of DCS. Therefore, DCS should keep pace with the times and constantly adopt the latest technologies and ideas to enrich and improve itself. This is to achieve "keeping up with the times". The following are some DCS development trends based on the above. 4.1 Make full use of fieldbus technology to further decentralize DCS. As can be seen from the above, FCS has many advantages, but in actual applications, there are very few complete FCS. The main reasons are: ① The cost of developing equipment with fieldbus interface is too high. For enterprises, it is too expensive to replace traditional instruments with bus instruments; ② Although fieldbus has formed a standard, there are too many standards (IEC has 8 standard buses), and various standards are mutually exclusive. It will take time to achieve complete unification; ③ DCS field control station configuration control has advantages for some complex processes and can configure advanced and complex control strategies, but FCS cannot compare with it. For us, we need to make use of the advanced nature of FCS technology and adapt to the objective reality. This requires integrating FCS technology into DCS and adopting structural transformation [3]. Specifically, the I/O modules in DCS are separated from the control cabinet and moved to the field to complete data acquisition and communication. Some simple controls are delegated to the field, while complex control strategies are still implemented by DCS. This forms a hybrid control system of DCS and FCS, which combines the advantages of both and is a viable control idea. 4.2 Further Introducing Industrial Control Networks into DCS to Fully Network It. DCS data communication networks are typical local area network (LAN) communications. Today's DCS systems all use industrial LAN technology to transmit real-time information and perform comprehensive system management. However, at the field level, communication with various field devices mostly uses fieldbus, which has a lower transmission rate than Ethernet, but its product price is much higher. In contrast, Ethernet equipment is inexpensive, has internationally unified standards, and has been developing for nearly 20 years. People have proposed many improvements to its topology, CSMA/CD protocol, and system protocol, fundamentally eliminating collisions and significantly improving signal transmission speed. On the other hand, the further penetration of Ethernet into the field level makes the entire system network easier to integrate. Therefore, introducing Ethernet technology into the industrial control field level is an important direction for the future development of DCS. 4.3 Introducing wireless connection technology into DCS system In the current DCS, the data acquisition equipment is connected to the control room by dedicated cables, which causes a lot of inconvenience in system wiring, wiring troubleshooting, and maintenance, thus limiting the scope of use and spatial distance of DCS. If we adopt the wireless connection network structure shown in Figure 3 [7], we can save the heavy wiring, reduce investment, and improve system performance. Although this technology is not very mature at present, "nothing is impossible, only unimaginable". Therefore, it is reasonable to believe that with its technological progress, wireless connection technology will play a great role in DCS. 5 Summary DCS technology has a history of nearly 30 years. In the past 30 years, it has made great contributions to the automation industry around the world. However, the emergence of anything is a process. It has its glorious peak and is accompanied by an inevitable end. In today's era of rapid development of human science and technology, this process is also shortening its cycle. DCS is no exception. Science and technology have made it glorious, but at the same time, it will also lead to its decline. However, from the perspective of today's industrial control field, the standardization dispute over fieldbuses remains unresolved, with various buses mutually exclusive, making it difficult to establish a unified international standard in the short term. Therefore, it will take time for FCS to completely replace DCS. This does not mean that DCS can rest easy; on the contrary, it should fully utilize FCS's advanced technologies to improve itself. In terms of network communication, the resolution of communication reliability and real-time performance provides ample room for its application in DCS. DCS should fully utilize this to build our future enterprise automation networks. From a software perspective, current DCS configuration software is already quite powerful. Therefore, future development should focus on improving soft connectivity—interoperability between various software (including DCS and other software)—to promote the standardization of DCS. As a newly emerging technology, wireless connectivity is still immature, but it represents a completely new approach. DCS should closely monitor its development and incorporate it into its systems when the technology matures. In conclusion, as a mature engineering technology, DCS should leverage its strengths and continuously adopt the latest technologies to improve its functionality and keep pace with the times in the face of numerous challenges. 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