PC-based control is a hot topic in the field of industrial control today. A personal computer running PC-based control software in the background is connected to the I/O network through a communication network, which constitutes a PC-based control system.
As various sectors of industry and manufacturing continue to develop towards large-scale operations, the demand for automation is becoming increasingly widespread, and the requirements for automatic control systems are also becoming more stringent. Various automatic control systems have developed rapidly in response to this widespread demand. The well-known DCS and PLC systems are being deployed in large quantities in various equipment and automation system engineering projects every year. Due to the industrial and manufacturing sectors' demand for integrated electrical control, instrumentation control, and management, as well as the development of information technology and the need for highly integrated control systems, coupled with the increasing sophistication and widespread adoption of PC technology, which has improved its performance-price ratio, a very favorable condition and broad market prospect have been provided for the rapid development of a new type of automatic control system solution: PC-based control. This provides many users with an alternative automatic control system solution besides DCS and PLC.
1. The Development History of Computer Control Systems
Data acquisition systems were the earliest form of computer application to appear in process control systems, marking the first step in computer involvement in control. Computers process, transform, and analyze the acquired analog or digital signals through input channels, providing data for reference by on-site personnel, production supervisors, and designers.
Following computer-guided operation systems, the earliest computer-controlled closed-loop control system emerged due to improvements in computer performance, particularly in computing power and reliability: the Direct Digital Control (DDC) system. Its difference from the previous two computer control systems lies in that the computer directly controls the actuators via output. Early DDC systems primarily used computers to replace conventional analog PID controllers. Because of the time-sharing control method, a single computer could control dozens or even hundreds of control loops, resulting in economic efficiency. Furthermore, due to the strong computing power of computers, DDC could easily implement advanced control principles that were difficult for analog controllers to achieve, such as feedforward control, optimal control, adaptive control, and intelligent control. The main drawback of early computer control systems was that centralized control led to a concentration of risks.
With the widespread application of computers in industrial control, especially their improved performance and reliability, further improvements in production process automation and management have become possible. This not only requires computers to participate in control but also in management, leading to the emergence of Distributed Control Systems (DCS) in 1975. These systems typically consist of a management information layer, a supervisory control layer, and a direct control layer, all handled by computers. After three generations of DCS development, Field Control Systems (FCS) began to attract attention in the 1990s.
From the development trend of computer control systems, we can clearly see that with the continuous improvement of computer cost-effectiveness and the continuous development of network communication technology, the control capabilities of computers are constantly being enhanced, and the application scope is constantly expanding. From the initial data acquisition system to today's widely used DCS, FCS, and PLC systems, software structure, communication capabilities, ease of use, and unified configuration environment have become more important. We believe that a new control solution—PC-based control—will develop rapidly.
2PCBasedControl technology
PCBasedControl technology is a high-performance measurement and control technology that integrates PC technology, signal measurement and analysis technology, control technology, and communication technology. It is used for signal measurement, industrial process data acquisition and control, motion control, and communication control. It includes an industrial computer platform, function cards, and application software. By inserting various function cards and writing software, powerful data acquisition systems, communication controllers, and motion control systems can be formed.
PC-based control technology has the following main performance characteristics:
(1) The system has good openness. In terms of software, it can support various open protocols, such as OPC, DDE, COM/DCOM, 0LE, etc. In terms of hardware, it can not only support various motion control products, but also various fieldbus systems, such as DeviceNet, PR0FIBUS, etc. It can also be easily expanded through EtherNet.
(2) Real-time control capability: There are three main types of real-time performance based on PC control technology. One type is called Soft PLC, which uses its internal software to determine the scan cycle to achieve real-time control. This performance characteristic means that in addition to completing control tasks, the PC can also handle a large number of PC tasks. This is more suitable for systems with low requirements for real-time performance and response time. Another type is real-time performance with real-time extension, which generally uses the standard real-time extension solution provided by Windows NT/CE—VenturCOM, a solution for deterministic control tasks. The third type is called Hard Real-Time Engine, whose control is always at the highest priority, and other Windows tasks cannot interrupt the control task, thus providing the same execution and scan characteristics as PLC.
3. Conclusion
In conclusion, with the further improvement of PC technology and its performance-price ratio, especially the further popularization and development of industrial Ethernet technology, it is believed that PC-based control system solutions will develop rapidly and become an irreversible trend in the field of automation.
