I. INTRODUCTION
In modern industrial automation control system, PLC (Programmable Logic Controller), DCS (Distributed Control System) and FCS (Fieldbus Control System) are the Three commonly used control schemes. Each of them has unique working principle, functional characteristics and applicable scenarios, providing diversified solutions for industrial automation. In this paper, we will analyze and compare these three control systems in detail so that readers can better understand the differences and connections between them.
II.PLC control system
Definition and working principle
PLC control system is a kind of program control equipment, which controls the state of input/output (I/O) signals through pre-written programs, so as to realize the automatic control, monitoring and operation of on-site equipment.PLC is mainly composed of CPU module, input module, output module and programming device, and its working principle includes three phases of input signal acquisition, program execution and output control.
Functional characteristics
(1) Good real-time: PLC control system has good real-time performance, which can quickly respond to changes in the field environment and quickly realize the preset control strategy.
(2) High stability: The control algorithm of PLC control system is stable and not affected by external electromagnetic interference, temperature changes, power supply fluctuations and other factors to ensure system reliability.
(3) Flexibility: the program of PLC control system can be modified and updated at any time, and can adapt to different control conditions and control requirements.
(4) easy to program: PLC control system programming language is simple and easy to learn, program design, modification and debugging is convenient and fast.
(5) easy to expand: PLC control system hardware and software can be flexibly expanded, according to the requirements of the configuration of different input and output modules, communication modules and so on.
III. DCS control system
Definition and working principle
DCS control system, also known as centralized distribution control system, is a microprocessor-based, decentralized control functions, display operation centralized, taking into account the design principles of autonomous and comprehensive coordination of a new generation of instrumentation control system. It is mainly composed of process control level and process monitoring level, with communication network as the link of multi-level computer system, integrated computer (Computer), communication (Communication), display (CRT) and control (Control) and other 4C technology.
Features
(1) High reliability: DCS system structure using redundant design, a single device computer failure will not lead to the whole system disorder.
(2) Openness: the use of systematic, modular, standardized open platform, all interconnected computer systems can be achieved through Ethernet and other communications means of centralized interconnection and interconnection access.
(3) Flexible configuration: DCS system can add or reduce system modules according to the actual demand to realize flexible configuration.
(4) Modularized design: All core equipment adopts modularized design, including processor, power supply, I/O module, communication module and AI/AO module, etc., which improves the expandability and maintainability of the system.
IV. FCS Control System
Definition and working principle
FCS control system is the abbreviation of field bus control system, which is a new generation control system developed from DCS and PLC. It adopts field bus technology to connect intelligent field devices and automation system into a fully decentralized, bidirectional transmission, multi-branch structure communication network.
Features
(1) Field communication network: FCS adopts field bus technology to realize digital communication between intelligent field devices and automation systems.
(2)Device interconnection and interoperability: FCS supports interconnection and interoperability between devices produced by different manufacturers, which reduces system integration costs.
(3)Decentralized function blocks: FCS decentralizes control functions to individual field devices, improving system reliability and flexibility.
(4) Communication line power supply: FCS supports power supply for field devices through communication lines, simplifying system wiring.
V. Comparison of PLC, DCS and FCS control systems
Structure
PLC is mainly composed of CPU modules, input modules, output modules and programming devices; DCS is a multi-level computer system composed of process control level and process monitoring level with communication network as a link; FCS is developed from DCS and PLC, the use of fieldbus technology to achieve intelligent field devices and automation systems connected.
Functional characteristics
PLC has the characteristics of good real-time, high stability, flexibility, easy programming and easy expansion; DCS has the characteristics of high reliability, openness, flexible configuration and modular design; FCS has the characteristics of on-site communication network, equipment interconnection and interoperability, decentralized function blocks and communication line power supply.
Applicable Scenarios
PLC is suitable for small automated production lines and equipment control; DCS is suitable for large-scale industrial process control and management, such as chemical industry, electric power, metallurgy and other fields; FCS is more suitable for the need to realize the interconnection of field devices and interoperability of complex industrial automation systems.
VI. Summary
PLC, DCS and FCS control systems have their own characteristics and play an important role in the field of industrial automation. By comparing their structural composition, functional characteristics and applicable scenarios, we can choose the most suitable control program according to the actual needs. With the continuous development of industrial automation, these three control systems will continue to play an important role and continue to innovate and improve.