PLCs and DCSs, as crucial control facilities in the field of automatic control, are increasingly widely used in various production control scenarios. In the large-scale manufacturing system, they have become indispensable control tools. Regarding the application of PLC and DCS systems, we often have the following questions: What are the differences and connections between PLCs and DCSs? What aspects require special attention when using them? What are the current bottlenecks restricting their technological development? To address these questions, e-works interviewed Associate Professor Yang Hong of South China University of Technology, who has many years of experience in PLC and DCS application research, to explore the mysteries of PLC and DCS development.
First, to do a good job, one must first have the right tools. We must clearly define the difference between PLCs and DCSs, even though they are both control tools, their actual functions are quite different. A Distributed Control System (DCS) integrates computer technology, control technology, communication technology, and CRT technology. It is mainly a control system for monitoring, controlling, operating, and managing production processes. A PLC, on the other hand, is a Programmable Logic Controller. The similarity between DCS and PLCs lies in the basic software configuration, but DCS is more powerful. For example, it can generate databases, historical data, graphics, reports, and control configurations. PLCs generally control relatively simple objects, while DCSs can control all equipment in an enterprise, becoming a central hub. In the battlefield of production control, one is the general, and the other is the commander; there is no direct control between them. PLCs can send signals to DCSs, and vice versa; they cooperate with each other, and their master-slave relationship mainly depends on the requirements of the equipment.
The development of PLCs has been rapid, bringing with it various technological challenges. When discussing how to overcome the current bottlenecks in PLC development, Professor Yang suggested that we should broaden our horizons and consider how to achieve a national-level, universal, common, and comprehensive PLC platform. A universal PLC platform, whether as an information technology product, a control technology product, or a backbone product for the integration of informatization and industrialization, should be a key focus. The platform includes three parts: R&D/design, manufacturing, and application. Specific product target requirements (system hardware and software) and functional requirements (universal technical indicators of hardware and software, and performance advancement and reliability indicators) for a universal PLC platform are given.
Looking back at the development of DCS, a crucial aspect of the division between different technological stages is the reliance on the increase in the number of bits in the microprocessor. Some have even suggested that each microprocessor upgrade corresponds to a new level of DCS technology. Professor Yang believes that DCS is a product of the high integration of computer technology, control technology, and network technology. DCS typically uses several controllers (process stations) to control numerous control points in a production process. These controllers are connected via a network and can exchange data. Computer operator stations connect to the controllers through the network, collect production data, and transmit operational instructions. Therefore, DCS technology inevitably evolves with the advancement of microprocessor technology to meet the needs of new systems.
In the fiercely competitive PLC and DCS market, foreign giants have long dominated, while domestic products have struggled to gain traction. In light of this situation, Professor Yang, based on the above points, offers the following suggestions for the domestic PLC market:
First, we need to build a national-level, universal, common, and comprehensive PLC platform.
Second, we should start with market segmentation and use software to drive hardware development.
Third, the development and ownership of common technologies should belong to the state, and the promotion methods can draw on foreign experience.
Finally, regarding the future development direction of the PLC and DCS market, Professor Yang made the following prediction: For a long time, PLCs have been the main battleground in the field of industrial control automation, providing highly reliable control solutions for various automated control devices, forming a three-way balance with DCS and industrial PCs. At the same time, PLCs are also facing challenges from other technological products, especially industrial PCs. This pattern will continue for a considerable period. For DCS systems, miniaturization, diversification, PC-based architecture, and openness are the main directions for future development. Currently, the market share of small DCS systems is gradually being shared with PLCs, industrial PCs, and FCS. In the future, small DCS systems may first integrate with these three systems, and "soft DCS" technology will first be developed in small DCS systems. PC-based control will be more widely used in small and medium-sized process control, and various DCS manufacturers will launch small DCS systems based on industrial PCs. Open DCS systems will extend both upwards and downwards, allowing field data from the production process to flow freely throughout the enterprise, achieving seamless integration of information technology and control technology, and developing towards the integration of measurement, control, and management.
