Application of the hottest Industrial Ethernet in

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The application of industrial ether in industry

1 Introduction

the transformation of demand produces industrial ether. In large-scale control systems, the real-time control network specially designed for the control system is mostly used, which is called fieldbus system (FCS). FCS is developed in accordance with intelligent field instruments. Its original intention is to replace 4 ~ 20mA analog transmission technology with digital communication. However, with the development of fieldbus technology and intelligent instrument management and control integration (instrument calibration, control configuration, diagnosis, alarm, recording), FCS has caused an unprecedented revolution in the field of control

in the field of factory automation and process automation, FCS has been the mainstream solution of field level communication system in the past ten years. However, with the continuous progress and development of technology, the traditional fieldbus has increasingly shown its own limitations. On the one hand, with the continuous improvement of the intelligence level of field equipment, the control becomes more and more decentralized. The intelligence distributed throughout the factory and some people get carsick when driving need to continuously exchange control data between equipment and between intelligent equipment and factory control layer, which makes the data exchange volume between field equipment increase rapidly; On the other hand, with the development of computer technology, enterprises hope to integrate the underlying production information into a unified plant wide information management system. Therefore, the enterprise's information management system needs to read the on-site production data and realize remote service and maintenance through the industrial communication network. Therefore, vertical consistency has also become a hot topic. Users hope that the management and field levels can use unified The communication scheme compatible with office automation technology can greatly simplify the structure of the factory control system and save the cost of system implementation and maintenance

based on this demand, Ethernet technology began to gradually penetrate from the information management layer of factories and enterprises to the bottom, and Ethernet technology began to be applied to the control level communication of factories. Ethernet has the advantages of high transmission speed, low consumption, easy installation and good compatibility. Because it supports almost all popular network interconnection protocols, it is widely used in commercial systems. However, the traditional Ethernet is designed for the fields with low real-time requirements such as office automation. It adopts the bus topology and multi access carrier sense collision detection (csma/cd) communication mode. In the occasions with high real-time requirements, the transmission process of important data will produce transmission delay, which is called the "uncertainty" of Ethernet. The research shows that the transmission delay of commercial Ethernet in industrial applications is between 2 ~ 30ms, which is one of the important reasons that affect the long-term inability of Ethernet to enter the field of process control. Therefore, the research on ether has engineering practical value, resulting in a new type of ether - Industrial ether

2 technical characteristics of industrial Ethernet

Industrial Ethernet generally means that it is technically compatible with commercial Ethernet (i.e. IEEE802.3 standard), but in product design, it can meet the needs of industrial sites in terms of material selection, product strength, applicability, real-time, interoperability, reliability, anti-interference and even intrinsic safety

2.1 real time and certainty

with the development of Fast Ethernet and switched Ethernet technology, it has brought new opportunities to solve the uncertainty of Ethernet, making this application possible. First of all, the communication rate of Ethernet has increased from 10m and 100m to 1000m and 10g today. With the same data throughput, the improvement of communication rate means that the network load is reduced and the network transmission delay is reduced, and the surface is wiped clean, that is, the probability of network collision is greatly reduced. Secondly, using the star network topology, the switch divides the network into several segments. Ethernet switch has the function of data storage and forwarding, so that the input and output data frames between ports can be buffered, and there will be no collision; At the same time, the switch can also filter the data transmitted on the network, so that the data transmission between nodes in each segment is limited to the local segment, without going through the trunk, and does not occupy the bandwidth of other segments, thus reducing the network load of all segments and trunk. Thirdly, full duplex communication enables two pairs of twisted pairs (or two optical fibers) between ports to receive and send message frames at the same time, without conflict. Therefore, using switched hub and full duplex communication can make the conflict domain on the network disappear (full duplex communication), or the collision probability is greatly reduced (half duplex), so the certainty and real-time of Ethernet communication are greatly improved

2.2 stability and reliability

another major problem of Ethernet entering the field of industrial control is that the connectors, hubs, switches and cables used by it are designed for the commercial field, and are not designed for the harsh industrial field environment (such as redundant DC power input, high temperature, low temperature, dust prevention, etc.), so commercial network products can not be used in the harsh industrial field environment with high reliability requirements

with the development of network technology, the above problems are being solved rapidly. In order to solve the problem that the network can work stably under extreme conditions in the field of uninterrupted industrial applications, synergetic microsystems in the United States and Hirschmann, jetter Ag and other companies in Germany have specially developed and produced rack rail hub and switch products, which are installed on the standard DIN rail and have redundant power supply. The connector adopts a solid DB-9 structure. In June, 2002, Taiwan's moxa technologies launched its industrial Ethernet product, moxa etherdevice server, which is specially designed to connect industrial devices with Ethernet interfaces in industrial applications (such as PLC, HMI, DCS systems, etc.)

the recently released IEEE802.3af standard also defines the bus power supply specification of Ethernet. In addition, in practical applications, optical fiber transmission can be used for the backbone, shielded twisted pair can be used for the connection of field equipment, and redundant network technology can also be used for important sections, so as to improve the anti-interference ability and reliability of the network

2.3 Industrial Ethernet protocol

because the industrial automation network control system is not only a communication system that completes data transmission, but also an automatic control system that completes control functions with the help of the network. In addition to completing data transmission, it often needs to rely on the transmitted data and instructions to perform some control calculation and operation functions, and multiple network nodes coordinate to complete automatic control tasks. Therefore, it needs to meet the requirements of open systems and interoperability conditions in high-level protocols and specifications such as applications and users

corresponding to the iso/osi seven layer communication model, the Ethernet technical specification only maps to the physical layer and data link layer, while the network layer and transport layer protocols above it are currently dominated by tcp/ip (transmission control/inter) protocols (which have become the "de facto" standard of the Ethernet upload layer and network layer). There are no technical regulations for higher levels, such as session layer, presentation layer, application layer, etc. At present, commercial computer devices access information transparently through application layer protocols such as FTP (File Transfer Protocol), telnet (Remote Login Protocol), SMTP (Simple Mail Transfer Protocol), HTTP (WWW protocol), SNMP (Simple Network Management Protocol). They now play a very important role in interconnection. However, the data structure and other characteristics defined by these protocols are not suitable for real-time communication between field devices in the field of industrial process control

in order to meet the application requirements of industrial field control system, we must establish a complete and effective communication service model based on ethernet+tcp/ip protocol, formulate an effective real-time communication service mechanism, coordinate the transmission services of real-time and non real-time information in industrial field control system, form the application layer and user layer protocols received by the majority of industrial control manufacturers and users, and then form an open standard. Therefore, various fieldbus organizations have introduced Ethernet into the high-speed part of their fieldbus system, and formed the industrial Ethernet protocol by using Ethernet and tcp/ip technology, as well as the original low-speed fieldbus application layer protocol

3 application of Ethernet based on tcp/ip in the field of industrial control

3.1 Ethernet based on tcp/ip

ethernet only has physical layer and link layer specifications, and it is usually applied in combination with tcp/ip and other platform independent protocols. The Ethernet we refer to actually refers to Ethernet based on tcp/ip protocol, that is, ethernet/ip. Ethernet/ip (Ethernet Industrial Protocol) is the abbreviation of Ethernet industrial protocol. It is an open industrial standard launched by Rockwell Automation

at present, Rockwell Automation Network generally adopts a three-layer network structure, that is, the system of equipment layer, control layer and information layer. In this system, data can flow in both directions, and data can be exchanged between layers. For a specific application, one or several layers can be selected, and there may be stacking between each layer. Its purpose is to adopt an open, flat network system that meets the needs of high-performance systems and reduces the overall system cost (including improving the network/equipment diagnosis ability, reducing wiring, installation, system debugging time, and improving error correction ability), as shown in Figure 1

Figure 1 Rockwell Automation Network three-tier system

3.2 application case

when selecting accessories, the experimental machine of Xizhou water plant of Guangzhou water supply company should pay attention to the suitability. PLC system is the PLC system of Rockwell company. The water intake pump station of Xizhou water plant is located on liuwuzhou island in the lower reaches of Dongjiang River, far away from the plant, and is more than ten kilometers away from Xizhou water plant. In order to meet the needs of production scheduling, the PLC system of liuwuzhou water intake pump station must communicate with the PLC system of Xizhou water plant, but there is no communication cable across the river to communicate with the outside. Therefore, liuwuzhou water intake pump station forms a wireless Ethernet network with Xizhou water plant through microwave communication. This wireless Ethernet realizes two functions: one is industrial Ethernet communication between PLC systems, which is used to transmit real-time production data; the other is production scheduling communication, which is used to transmit production monitoring images and IP data. In Xizhou water plant, we can not only understand the real-time production data of liuwuzhou water intake pump station in detail, but also receive the real-time image of liuwuzhou water intake pump station. The duty personnel of Xizhou water plant can also communicate with the duty personnel of Xintang water plant and liuwuzhou water intake pump station through IP to convey the production scheduling orders. The network structure of this wireless Ethernet is shown in Figure 2

With the continuous increase in the number of product varieties of wood products packaging boxes

Figure 2 Wireless Ethernet structure diagram of Xizhou water plant

4 development trend and Prospect of industrial Ethernet

at present, Ethernet has been widely used in the resource management layer and executive manufacturing layer of the integrated automation system of industrial enterprises, and shows the trend of downward extension and direct application in the industrial control field. In the future, industrial Ethernet will play a more and more important role in the interconnection and information integration between field devices in the integrated automation system of industrial enterprises

Industrial Ethernet technology shows the beauty of "one to the end" industrial control informatization, that is, it can be extended to the enterprise field device control layer, so it is generally considered to be the best solution for the future control network. Industrial Ethernet has become the leading edge technology in fieldbus. (end)

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