In order to meet the needs of market competition, industrial production in the global market has gradually formed a computer integrated manufacturing system in the pursuit of competitiveness. The computer integrated manufacturing system adopts the viewpoints of system integration and information integration to organize production. The market, production planning, manufacturing process, enterprise management, and after-sales service are regarded as the production process to be considered in a unified manner, and computer, automatic control, and network communication technologies are used. Realize the integrated automation of the entire process to improve production, processing, and management decisions. In order to achieve this goal, it is necessary to interconnect smart devices at the company's on-site control, process monitoring, business management, and market management to form an integrated automation network to achieve residential connectivity and data sharing at all levels. "."
To this end, companies must first establish a sound management network for various corporate resources so that all resources can be fully deployed, balanced, and controlled to maximize their capabilities. Second, there must be a close relationship between market, operations, production, and R&D. Collaboration chain.
Industrial control networks, as the basis of the integrated automation system for industrial enterprises, can be divided into three levels in terms of structure: management level, monitoring level, and field device level. As shown in Figure 1. Among them, the top-level enterprise management network is mainly used for the transmission of information on planning, sales, inventory, finance, personnel, and business management of enterprises. Generally, each terminal device on the management layer exchanges information by sending emails, downloading web pages, querying databases, printing documents, and reading computer programs on file servers. Data packets are usually long and the throughput is large. And the initiation of data communication is random and irregular, because it requires that the network must have a large bandwidth. The management network is mainly composed of Fast Ethernet (100M, 1G, 10G, etc.). The middle manufacturing execution layer network is mainly used for information transmission in monitoring, optimization, scheduling, etc. Its characteristic is that information transmission has a certain periodicity and real-time nature, and the data throughput is large, so the network is required to have a large bandwidth. It is composed of a private network such as a token network. Concentrating on this layer of network is mainly composed of a network segment with a high transmission rate (such as 10M, 100MEthernet, etc.).
The lowest-level field device layer network is connected with field devices such as transmitters and actuators to collect field data and send control data to the device. It has some special characteristics compared with the post and telecommunication technologies and other information network technologies that mainly aim at the transmission of information. Since the ultimate goal of industrial automation network communication is to generate or initiate the movement or conversion of matter or energy by passing measurement and control data and related information, this network communication technology has the following specialities:
1 Timeliness of data transmission and real-time response of the system: Usually, the response time of the manufacturing automation system is required to be 0.01 to 0.5s, and the response time of the process control system is 0.5 to 2S. The response time of the information network is 2-6S. Obviously, the real-time nature of industrial communication networks is much higher.
2 High reliability: Industrial communication networks emphasize the integrity of data transmission in industrial environments. For communication networks operating in harsh industrial production sites, it is necessary to address environmental adaptability issues including electromagnetic environment adaptability or electromagnetic compatibility EMC, Adaptability to climate and environment (to be temperature resistant, waterproof, dustproof), mechanical environment adaptability (shock resistance, vibration resistance). It should have intrinsically safe performance in explosive or flammable situations.
3 Industrial communication networks need to address the compatibility of products and systems of different vendors on the network and emphasize interoperability. Therefore, it is based on the ISO/OSI “reference model for open system interconnection†that modern communication systems are based on. The user layer addresses this complete open communication through standard function blocks and Device Description (DD) functions.
4 Bus power. The industrial field control network can not only transmit communication information but also can transmit working power for field devices. This is mainly due to the ease of cable laying and maintenance. At the same time, bus power supply can also reduce cables and reduce wiring costs.
5 Broadcast, multicast, and unicast communication methods: Industrial communication networks connect a single user (transmitter, actuator, controller, or control system, etc.) to a system. The communication method is often broadcast. Group mode or client/server based unicast mode. In an IT network, one autonomous system and another autonomous system establish a one-to-one approach only when they need to communicate.
6 The length of information transmitted between devices at the field control level is relatively small. The information includes measurement values, control quantities, operating positions of the switches and valves, alarm status, equipment resource and maintenance information, system configuration, parameter modification, zero point and span adjustment information, etc. of the production facility. Its length is generally relatively small, usually only a few bits or a few, ten or a few tens of bytes, and the throughput requirement for network transmission is not high.
Due to the above characteristics and particularities, the field device layer network is mainly composed of low-speed fieldbus networks (such as FF, Profibus, DeviceNet, etc.).
From: Network World
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