Fieldbus and Ethernet interconnection in an automation control system

In the past, the biggest obstacle to Ethernet entering the fieldbus system was the uncertainty of Ethernet, because Ethernet uses the CSMA/CD medium access control protocol at the data link layer. This protocol is extremely efficient under light load conditions, but In the case of heavy load, the protocol will retry the transmission after a random time pause in the event of a conflict, thus affecting the real-time nature of the data. This is not tolerable for industrial control networks where real-time requirements are critical, and the devices used in Ethernet, including connectors, hubs, switches, and cables, are designed for office applications. It does not meet the requirements of the harsh environment of the industrial site. There is also Ethernet anti-jamming performance is poor, does not have intrinsic safety performance, and can not supply power to the field instrument. However, with the development of technology, 100M Ethernet is now the mainstream, and 10 Gigabit Ethernet is also put into practical operation, and the development of switched Ethernet technology has fundamentally solved the randomness of transmission time caused by Ethernet collision. Bigger problem. And Ethernet equipment manufacturers are also developing equipment that meets industrial site requirements to meet the requirements. At the same time, it also has the following characteristics:

1. Ethernet is currently the most widely used computer network technology and is widely supported by technology. Almost all programming languages ​​support Ethernet application development, such as Java, Visual C++, Visual Basic, and more. These programming languages ​​have great development prospects due to their wide use and high attention from software developers. Therefore, if Ethernet is used as the field bus, a variety of development tools and development environments can be guaranteed.

2. Low cost. Because Ethernet is the most widely used, it is highly valued and widely supported by hardware developers and manufacturers. There are a variety of hardware products for users to choose from, and due to a wide range of applications, hardware prices are relatively low. At present, the price of Ethernet network card is only one tenth of the field bus such as Profibus and FF, and with the development of integrated circuit technology, its price will further decline [34].

3. The communication rate is high. At present, 100M Fast Ethernet has been widely used, 1000M Ethernet technology has gradually matured, and 10 Gigabit Ethernet has been put into use, and its speed is much faster than the current field bus. Ethernet can meet the higher bandwidth requirements.

4, rich in hardware and software resources. Since Ethernet has been used for many years, people have a lot of experience in the design and application of Ethernet, and they are also very familiar with its technology. A large amount of software resources and design experience can significantly reduce system development and training costs, which can significantly reduce the overall cost of the system and greatly accelerate the development and promotion of the system.

5. The potential for sustainable development is great. Due to the wide application of Ethernet, its development has been widely valued and a large amount of technical input. Moreover, in this era of rapid change of information, the survival and development of enterprises depend to a large extent on a fast and effective communication management network. The development of information technology and communication technology will be more rapid and mature, thus ensuring Ethernet. Technology continues to move forward.

Therefore, if the industrial control field adopts Ethernet as the communication network platform between field devices, it can avoid the fieldbus technology from being out of the mainstream of computer network technology, so that fieldbus technology and other network technologies can promote each other and develop together. And to ensure technical sustainability, there is no need for separate research input in technology upgrades. In the future, the industrial control network will inevitably develop to Figure 4.1.