Concept, composition and characteristics of fieldbus control system
First：The concept of fieldbus control system (FCS)
Fieldbus control is a computer local area network for the automation control of industrial equipment. It relies on a micro-processing chip with detection, control, and communication capabilities, and digital instruments (equipment) achieve complete decentralized control in the field, and use these field scattered measurement and control equipment as a network node, and connect these points in the form of a bus. To form a fieldbus control system. It belongs to the lowest network system and is a network integrated fully distributed control system. It disperses all the functions of the original distributed DCS system field control machine at each network node. For this reason, the originally closed, dedicated system can be turned into an open, standard system. The interconnection of products of different manufacturers is an update of the DCS system, which greatly simplifies the system structure, reduces costs, better meets practical requirements, and improves the reliability of system operation. Fieldbus control systems of different communication protocols are generally connected to the fieldbus network segment through the PC interface board of the bus slot in the industrial PC.
Second：The composition of the fieldbus control system
Fieldbus control system consists of three parts: measurement system, control system, and management system. The hardware and software of the communication part are its most distinctive parts.
1. Fieldbus control system:
Its software is an important part of the system. The software of the control system includes configuration software, maintenance software, simulation software, equipment software and monitoring software. First choose to develop configuration software, control and operate the man-machine interface software MMI. Through the configuration software, the connection between the function blocks is completed, the function block parameters are selected, and the network configuration is performed. In the process of network operation, the system collects data, performs data processing and calculation in real time. Optimized control and logic control alarm, monitoring, display, report, etc.
2, Fieldbus measurement system:
It is characterized by multi-variable and high-performance measurement, so that the measuring instrument has more functions such as calculation ability. Due to the use of digital signals, it has high resolution, high accuracy, strong anti-interference and anti-distortion capabilities, and also has the status of instrument equipment Information, the processing process can be adjusted.
3, Equipment management system:
Can provide diagnostic information, management information, equipment operating status information (including smart meters) of the equipment itself and the process, and equipment manufacturing information provided by the manufacturer. For example, Fisher-Rosemoune company launched the AMS management system, which is installed in the host computer and completes the management functions. It can form a comprehensive management system information database for field equipment, and realize the reliability analysis and predictability of the equipment on this basis. maintain. Change the passive management mode to the predictable management and maintenance mode. AMS software is a T-shaped structure with on-site server as the platform. It supports modularization on the on-site server and provides users with a graphical interface with feature-rich application software.
4. Bus system computer service mode:
The client/server model is currently the more popular network computer service model. The server represents the data source (provider), and the application client represents the data consumer. It obtains data from the data source and performs further processing. The guest room machine runs on a PC or workstation. The server runs on a minicomputer or a mainframe, and it uses the intelligence, resources, and data of both parties to complete tasks.
5. Database:
It can store a large amount of relevant data and applications in an organized and dynamic manner, realize full sharing and cross-access of data, and has a high degree of independence. During the operation of industrial equipment, the parameters continuously change, the data volume is large, and the real-time operation and control requirements are very high. Therefore, a distributed and real-time database system that can be accessed and operated mutually is formed. The mature ones on the market are Orad, sybas, Informix, SQL Server in relational databases; Infoplus, PI, ONSPEC in real-time databases, etc.
6.The hardware and software of the network system:
Network system hardware includes: system management host, server, gateway, protocol converter, hub, user computer, etc. and underlying intelligent instruments. Network system software includes network operating software such as NetWarc, LAN Mangger, Vines, and server operating software such as Lenix, os/2, Window NT. Application software database, communication protocol, network management protocol, etc.
Third：The characteristics of fieldbus control system
1. Centralized management in function, decentralized control, decentralized horizontally and hierarchically vertical in structure.
2. It must have fast real-time response capability. For the local area network of industrial equipment, its main communication volume is process information and operation management information. The amount of information is not large, and the transmission rate is not high below 1MPS. The information transmission task is relatively simple but in fact When the response time is higher than 0.01-0.5S. The so-called real-time performance is the online real-time collection of process parameters in the process of network communication, real-time processing of system information, and rapid feedback to the system to complete process control, to meet the time limit requirements of process control. In addition to controlling the external equipment of the management computer system, it is also necessary to control the equipment of the management control system, and have the ability to handle random events. The actual operating system should ensure timely handling under abnormal conditions, ensure the completion of tasks, or complete the most important tasks, and require timely detection and correction of random errors, at least to ensure that the impact of errors is not expanded, and it should be capable of resisting incorrect operations and incorrect input information. ability.
