DCS and ESD

Thread Content

DCS, namely the so-called distributed control system, or referred to as a distributed control system in some literature, is a new type of computer-based control system as opposed to centralized control systems; it has evolved from centralized control systems. In terms of system functionality, there is not much difference between DCS and centralized control systems; however, their approaches to implementing these functionalities are completely different. Firstly, the backbone of DCS is the system network, which serves as its foundation and core. Since the network plays a decisive role in the real-time performance, reliability, and scalability of the entire DCS system, manufacturers have invested considerable effort in its careful design. For the system network of DCS, it must meet real-time requirements, that is, to complete the transmission of information within a specified time limit. The time limit referred to as “determined” here means that information transmission can be completed within this time limit under any circumstances, and this time limit is determined based on the real-time requirements of the controlled process. Therefore, the indicator for measuring the performance of a system network is not the network’s speed, that is, the number of bits per second (bps), but rather the real-time performance of the system network, that is, how quickly it can ensure the transmission of the required information is completed. The system network must also be highly reliable; network communication must not be interrupted under any circumstances. Therefore, most manufacturers’ DCS systems employ network topologies such as dual-bus, ring, or dual-star configurations. To meet the requirements for system scalability, the maximum number of nodes that can be connected to the system network should be several times greater than the actual number of nodes in use. In this way, new nodes can be added at any time on the one hand, while on the other hand it allows the system network to operate with a lower communication load, thereby ensuring the real-time performance and reliability of the system. During the actual operation of the system, connections to and from the internet for various nodes can occur at any time, especially at the operator station. As a result, network reconfiguration takes place frequently, and such operations must not affect the normal functioning of the system. Therefore, the system’s network should possess strong capabilities for online network reconfiguration. Secondly, it is a network node that handles on-site I/O entirely and implements direct digital control (DOS) functionality. Typically, a field I/O control station is installed in a DCS system to handle the I/O and control functions of the entire system. This not only prevents the entire system from failing due to the failure of a single site, thereby improving system reliability, but also allows each site to share the tasks of data collection and control, which helps to enhance the performance of the entire system. The operator station of a DCS is a network node that handles all human-machine interface (HMI – Human Machine Interface or operator interface) functions related to operational control. The system network is the engineer station of the DCS; it is a network node used for offline configuration and setup of the DCS, as well as for online monitoring, control, and maintenance of the system. Its main functions are to provide software tools for configuring the DCS, and to monitor in real time the operation of various nodes on the DCS network while it is running. This allows system engineers to adjust the system configuration and various parameters promptly through the engineer station, ensuring that the DCS remains in its optimal operating condition at all times. Unlike centralized control systems, all DCS systems require a system configuration function; it can be said that a system without such a function cannot be called a DCS. Since its introduction in 1975, DCS has gone through more than two decades of development. Over these more than twenty years, although there have been no major changes in the architectural structure of DCS, its functions and performance have improved significantly through continuous development and refinement. Overall, DCS is moving toward being more open, more standardized, and more productized. As a computer control system in the field of production process automation, the traditional DCS is merely a narrow concept. If one assumes that DCS is merely an automation system for production processes, it will lead to incorrect conclusions, as the meaning of modern computer control systems has been **expanded**. These systems include not only everything that was once part of DCS, but also extend down to every measuring device and actuator on the factory floor, and up to production management and all aspects of business operations. In the traditional sense, DCS now refers only to the automation of the production process control aspect, whereas the concept of an industrial automation system should be viewed as a comprehensive solution for enterprises, that is, at the level of a total solution. Only by raising and solving problems from this perspective can computer automation truly fulfill its intended role. After entering the 1990s, computer technology advanced by leaps and bounds, and more new technologies were applied to DCS. A PLC is an electronic device developed for sequential logic control, primarily used to replace inflexible and bulky relay logic. Fieldbus technology developed at a rapid pace after the mid-1990s, to the point that some people predicted that FCS based on fieldbuses would replace DCS as the dominant control system.