Abstract : In view of the difficulty of integration of information islands, the necessity and advantages of the Ethernet network entering the industrial control field are clarified. The problems existing in the application of the industrial Ethernet network in the field of control and its improvement measures are analyzed. Finally, the industry is discussed in conjunction with the engineering practice. The application and development prospects of Ethernet networks.
1. Introduction Ethernet management has been used in the field of process control due to its many advantages such as low cost, high communication speed and bandwidth, good compatibility, rich hardware and software resources, extensive technical support, and strong sustainable development potential. widely used. The facts prove that through some real-time communication enhancement measures and the design and implementation of high-reliability networks for industrial applications, Ethernet can meet the real-time requirements of industrial data communications and industrial site environment requirements, and can be directly applied to the industrial field equipment. Communication. Industrial Ethernet generally refers to technically compatible with commercial Ethernet (that is, IEEE802.3 standard), but in product design, material selection, product strength, applicability, and real-time performance can meet the needs of industrial sites. That is, Ethernet that satisfies the requirements of environment, reliability, security, and ease of installation. Ethernet is a local area network that uses the carrier sense multiple access method (CSMA/CD) with collision detection to access shared media according to the IEEE 802.3 standard. The protocol corresponds to the physical layer and data link layer in the ISO/OSI Layer 7 reference model. The transmission medium for Ethernet is coaxial cable, twisted pair, and optical fiber. The bus or star topology is adopted. The transmission rate is 10Mbps, 100Mbps, 1000Mbps or higher. In the field of office and business, Ethernet is the most common communication network. In recent years, with the rapid development of Ethernet technology, Ethernet technology has begun to be widely used in industrial control. It is a modern automatic control technology and information network technology. The combined products are the landmark technologies for the next generation of automation equipment and are powerful tools for transforming traditional industries. They are also the key directions for informatization to drive industrialization. The domestic demand for industrial Ethernet networks is increasing. Industrial Ethernet technology is needed to support projects in petroleum, chemical, metallurgy, electric power, machinery, transportation, building materials, building management, modern agriculture, and many new projects.
2. The advantages of Industrial Ethernet The fieldbus generated in the mid-1980s, connecting intelligent field devices and automation systems to all-digital, two-way transmission, and multi-branch communication control networks, to decentralize and control industrial control systems. The development of intelligentization and intelligence has become possible, resulting in major changes in the architecture and functional structure of industrial control systems. After many years of disputes and struggles, the fieldbus international standard IEC-61158 gave up its original intention of formulating a single fieldbus standard, and eventually released eight kinds of them (the third edition added two types after revision, and became ten types) International standard for type bus. This shows that each major bus has its own characteristics and cannot be replaced by each other. It has been recognized by the world's industrial control circles. On the other hand, with the development of Internet technology, the majority of industrial control experts, manufacturers, and users have come to realize that the reason why field buses cannot be unified is that apart from their technical characteristics and the conflicts of interest supported by companies behind them, Also because of the development of fieldbus, the particularity of automation networks was overemphasized, and the development of information technology was neglected, resulting in the slow development of fieldbus technology, products and applications. At the same time, the Ethernet technology that monopolizes the information network communication in the office automation field has been widely used by the middle and upper levels of the management and control layer of the process control field, due to its many advantages, whether it is a large multinational or a small and medium-sized automation company. In the field of industrial control, with the ever-increasing scale of control systems, geographical dispersion of physical devices such as controlled objects and measurement and control devices becomes more and more obvious, and centralized control systems cannot meet the requirements of development. Due to the introduction of the fieldbus technical standard IEC-61158, there is no truly unified technical standard. Therefore, major industrial control companies in the world are looking for other ways to solve the problem of scalability and compatibility, so they are now widely used in information networks. Ethernet has become the first target of choice.
Ethernet is the most popular and widely used communication technology today. It has many advantages such as low price, multiple transmission media options, high speed, easy networking applications, etc., and its operating experience is the most abundant, with a large number of installation and maintenance personnel. An ideal industrial communication network. First, Ethernet over TCP/IP is an open communication network. Devices from different vendors are easily interconnected. This feature is very suitable for solving the problems of compatibility and interoperability of devices from different manufacturers in the control system; secondly, low cost and easy networking are the advantages of Ethernet. Ethernet network cards are inexpensive, and Ethernet interfaces with computers and servers are very convenient. There are many Ethernet technicians, which can reduce the training and maintenance costs of enterprises. Third, Ethernet has a fairly high data transmission rate and can provide enough bandwidth. Moreover, the Ethernet resource sharing capability is strong. Using Ethernet as a field bus, it is easy to connect I/O data to the information system. Data can be easily shared with resources, application software, and databases on the information system in real time. Ethernet is easy to connect with the Internet. In any city or anywhere, even the telephone line can be used to monitor and control the production of the enterprise through the Internet. In addition, as the most widely used computer network technology, Ethernet has received extensive technical support. Almost all programming languages ​​support Ethernet application development and there are a variety of development tools to choose from.
With the development of the economy and the advancement of automated office information networks, integrated enterprise automation, management and control integration has become a must for the survival and development of enterprises. Ethernet can easily realize the advantages of seamless connection between office automation network and industrial control network. It can enable tight integration of e-commerce and industrial production control sites, realizing the integration of enterprise management and control in the true sense.
3. Main problems existing in the application of Ethernet to industrial sites 3.1 Poor real-time and uncertainties in information transmission Industrial control networks require high real-time performance and certainty. Ethernet adopts Carrier Sense Multiple Access with Collision Detection (CSMA/CD) and Binary Exponential Backoff (BEB), so it will inevitably lead to delay in information transmission because its time lag is random, which means that Ethernet is essentially The network is a non-deterministic network system. Therefore, for the control process with strict response time, there is the possibility of collision and the uncertainty of the response time, so that the information cannot be transmitted normally as required, and the real-time and determinism of data transmission required by the industrial control network cannot be satisfied. .
3.2 Poor reliability of Ethernet The equipment installed at the industrial site should have high reliability, that is, it can resist impact, vibration, corrosion, dust, water, and have better electromagnetic compatibility. The traditional Ethernet is mainly used in the field of office automation. Its connectors, hubs, switches, and cables are all designed for office applications. It has poor anti-interference ability and can not meet the harsh environment requirements of industrial sites.
3.3 The lack of application layer protocol applied to industrial control The Ethernet standard only defines the physical layer and data link layer of the ISO/OSI reference model. Even the addition of the TCP/IP protocol only provides the functions of the network layer and the transport layer. . Both devices must use the same language rules for normal communication, which means that they must also have a unified application layer protocol. At present, the application layer protocols used in the field of commercial computer communications are FTP (File Transfer Protocol), Telnet (Telnet Protocol), SMTP (Simple Mail Transfer Protocol), and HTTP (Hypertext Transfer Protocol). The data structures and other characteristics specified by these protocols do not meet the real-time communication requirements between industrial control field devices. Therefore, a unified application layer protocol applicable to the control field must be established.
1. Introduction Ethernet management has been used in the field of process control due to its many advantages such as low cost, high communication speed and bandwidth, good compatibility, rich hardware and software resources, extensive technical support, and strong sustainable development potential. widely used. The facts prove that through some real-time communication enhancement measures and the design and implementation of high-reliability networks for industrial applications, Ethernet can meet the real-time requirements of industrial data communications and industrial site environment requirements, and can be directly applied to the industrial field equipment. Communication. Industrial Ethernet generally refers to technically compatible with commercial Ethernet (that is, IEEE802.3 standard), but in product design, material selection, product strength, applicability, and real-time performance can meet the needs of industrial sites. That is, Ethernet that satisfies the requirements of environment, reliability, security, and ease of installation. Ethernet is a local area network that uses the carrier sense multiple access method (CSMA/CD) with collision detection to access shared media according to the IEEE 802.3 standard. The protocol corresponds to the physical layer and data link layer in the ISO/OSI Layer 7 reference model. The transmission medium for Ethernet is coaxial cable, twisted pair, and optical fiber. The bus or star topology is adopted. The transmission rate is 10Mbps, 100Mbps, 1000Mbps or higher. In the field of office and business, Ethernet is the most common communication network. In recent years, with the rapid development of Ethernet technology, Ethernet technology has begun to be widely used in industrial control. It is a modern automatic control technology and information network technology. The combined products are the landmark technologies for the next generation of automation equipment and are powerful tools for transforming traditional industries. They are also the key directions for informatization to drive industrialization. The domestic demand for industrial Ethernet networks is increasing. Industrial Ethernet technology is needed to support projects in petroleum, chemical, metallurgy, electric power, machinery, transportation, building materials, building management, modern agriculture, and many new projects.
2. The advantages of Industrial Ethernet The fieldbus generated in the mid-1980s, connecting intelligent field devices and automation systems to all-digital, two-way transmission, and multi-branch communication control networks, to decentralize and control industrial control systems. The development of intelligentization and intelligence has become possible, resulting in major changes in the architecture and functional structure of industrial control systems. After many years of disputes and struggles, the fieldbus international standard IEC-61158 gave up its original intention of formulating a single fieldbus standard, and eventually released eight kinds of them (the third edition added two types after revision, and became ten types) International standard for type bus. This shows that each major bus has its own characteristics and cannot be replaced by each other. It has been recognized by the world's industrial control circles. On the other hand, with the development of Internet technology, the majority of industrial control experts, manufacturers, and users have come to realize that the reason why field buses cannot be unified is that apart from their technical characteristics and the conflicts of interest supported by companies behind them, Also because of the development of fieldbus, the particularity of automation networks was overemphasized, and the development of information technology was neglected, resulting in the slow development of fieldbus technology, products and applications. At the same time, the Ethernet technology that monopolizes the information network communication in the office automation field has been widely used by the middle and upper levels of the management and control layer of the process control field, due to its many advantages, whether it is a large multinational or a small and medium-sized automation company. In the field of industrial control, with the ever-increasing scale of control systems, geographical dispersion of physical devices such as controlled objects and measurement and control devices becomes more and more obvious, and centralized control systems cannot meet the requirements of development. Due to the introduction of the fieldbus technical standard IEC-61158, there is no truly unified technical standard. Therefore, major industrial control companies in the world are looking for other ways to solve the problem of scalability and compatibility, so they are now widely used in information networks. Ethernet has become the first target of choice.
Ethernet is the most popular and widely used communication technology today. It has many advantages such as low price, multiple transmission media options, high speed, easy networking applications, etc., and its operating experience is the most abundant, with a large number of installation and maintenance personnel. An ideal industrial communication network. First, Ethernet over TCP/IP is an open communication network. Devices from different vendors are easily interconnected. This feature is very suitable for solving the problems of compatibility and interoperability of devices from different manufacturers in the control system; secondly, low cost and easy networking are the advantages of Ethernet. Ethernet network cards are inexpensive, and Ethernet interfaces with computers and servers are very convenient. There are many Ethernet technicians, which can reduce the training and maintenance costs of enterprises. Third, Ethernet has a fairly high data transmission rate and can provide enough bandwidth. Moreover, the Ethernet resource sharing capability is strong. Using Ethernet as a field bus, it is easy to connect I/O data to the information system. Data can be easily shared with resources, application software, and databases on the information system in real time. Ethernet is easy to connect with the Internet. In any city or anywhere, even the telephone line can be used to monitor and control the production of the enterprise through the Internet. In addition, as the most widely used computer network technology, Ethernet has received extensive technical support. Almost all programming languages ​​support Ethernet application development and there are a variety of development tools to choose from.
With the development of the economy and the advancement of automated office information networks, integrated enterprise automation, management and control integration has become a must for the survival and development of enterprises. Ethernet can easily realize the advantages of seamless connection between office automation network and industrial control network. It can enable tight integration of e-commerce and industrial production control sites, realizing the integration of enterprise management and control in the true sense.
3. Main problems existing in the application of Ethernet to industrial sites 3.1 Poor real-time and uncertainties in information transmission Industrial control networks require high real-time performance and certainty. Ethernet adopts Carrier Sense Multiple Access with Collision Detection (CSMA/CD) and Binary Exponential Backoff (BEB), so it will inevitably lead to delay in information transmission because its time lag is random, which means that Ethernet is essentially The network is a non-deterministic network system. Therefore, for the control process with strict response time, there is the possibility of collision and the uncertainty of the response time, so that the information cannot be transmitted normally as required, and the real-time and determinism of data transmission required by the industrial control network cannot be satisfied. .
3.2 Poor reliability of Ethernet The equipment installed at the industrial site should have high reliability, that is, it can resist impact, vibration, corrosion, dust, water, and have better electromagnetic compatibility. The traditional Ethernet is mainly used in the field of office automation. Its connectors, hubs, switches, and cables are all designed for office applications. It has poor anti-interference ability and can not meet the harsh environment requirements of industrial sites.
3.3 The lack of application layer protocol applied to industrial control The Ethernet standard only defines the physical layer and data link layer of the ISO/OSI reference model. Even the addition of the TCP/IP protocol only provides the functions of the network layer and the transport layer. . Both devices must use the same language rules for normal communication, which means that they must also have a unified application layer protocol. At present, the application layer protocols used in the field of commercial computer communications are FTP (File Transfer Protocol), Telnet (Telnet Protocol), SMTP (Simple Mail Transfer Protocol), and HTTP (Hypertext Transfer Protocol). The data structures and other characteristics specified by these protocols do not meet the real-time communication requirements between industrial control field devices. Therefore, a unified application layer protocol applicable to the control field must be established.