As we all know, in enterprise information systems, Ethernet has become the de facto standard network, and industrial real-time control is an extension of traditional Ethernet, helping users build more open and integrated industrial automation and information networks. Industrial Ethernet technology, it is a combination of standard Ethernet and general industrial protocols. First of all, he met the real-time requirements of industrial automation. The CSMA/CD used in the original Ethernet could not meet the real-time requirements of the industry. At that time, it was mainly fieldbus and token ring network. With the improvement of technology, the switch was in real-time It has met all industrial application requirements from high-precision time synchronization (+-100ns), distributed servo control, discrete control, process control to safety systems, and supports on-site and remote monitoring, diagnosis and configuration; of course, EtherNet/IP The product can also use other standard Ethernet services such as HTTP, SNMP, etc.. This means that industrial automation and enterprise information systems are more directly integrated. For example, without additional programming, relevant personnel can easily configure, diagnose and monitor plant equipment through a web browser. In addition, EtherNet/IP also makes regulations from EMC and installation protection levels to ensure the strict industrial environment adaptability of EtherNet/IP products.
Characteristics of Industrial Ethernet Technology
Communication certainty and real-time
The biggest feature of an industrial control network different from an ordinary data network is that it must meet the real-time requirements of the control function, that is, the signal transmission must be fast enough and meet the certainty of the signal. Real-time control often requires accurate timing refresh of data for certain variables. Because EtherNet adopts the CSMA/CD method, when the network load is large, the uncertainty of network transmission cannot meet the real-time requirements of industrial control, so traditional Ethernet technology cannot meet the real-time requirements of the control system for accurate timing communication, and has been regarded as "Non-deterministic" networks. However, the development of Fast Ethernet and Switched Ethernet technology has brought new opportunities to solve the non-deterministic problem of Ethernet, making this application possible. First of all, the communication rate of EtherNet has increased from 10M and 100M to today's 1000M and 10G. With the same data throughput, the increase in communication rate means the reduction of network load and network transmission delay, that is, network collision The probability is greatly reduced. Secondly, using a star network topology, the switch divides the network into several network segments. The EtherNet switch has the functions of data storage and forwarding, so that the input and output data frames between the ports can be buffered and no collisions will occur. At the same time, the switch can also filter the data transmitted on the network to make each network segment The data transmission between nodes is only limited to the local network segment, without passing through the backbone network, and does not occupy the bandwidth of other network segments, thereby reducing the network load of all network segments and backbone networks. Third, full-duplex communication makes it possible to simultaneously receive and send message frames on two twisted pairs (or two optical fibers) between the ports without conflict. Therefore, the use of switching hubs and full-duplex communication can make the collision domain on the network no longer exist (full-duplex communication), or the collision probability is greatly reduced (half-duplex), so the determinism and real-time of EtherNet communication are greatly improved. improve.
Stability and reliability
Traditional EtherNet is not designed for industrial applications, and does not consider the adaptability needs of the industrial field environment. Because the mechanical, climate, and dust conditions at the industrial site are very harsh, higher requirements are placed on the industrial reliability of the equipment. In the factory environment, the industrial network must have good reliability, recoverability and maintainability. In order to solve the problem that the network can work stably under extreme conditions in the field of uninterrupted industrial applications, Maiwei has specially developed and produced industrial Ethernet switches installed on standard DIN rails, and supports redundant power supply.
The network security of industrial systems is another security issue that must be considered for industrial Ethernet applications. Industrial Ethernet can integrate the traditional three-layer network system of the enterprise, that is, the information management layer, the process monitoring layer, and the field equipment layer, so that the data transmission rate is faster, the real-time performance is higher, and it can be seamlessly integrated with the Internet. Realize the sharing of data and improve the operating efficiency of the factory. But at the same time, a series of network security issues have been raised. Industrial networks may be subject to network security threats including virus infection, illegal intrusion by hackers, and illegal operations. In general, a gateway or firewall can be used to isolate the industrial network from the external network, and the security management of the network can also be strengthened through multiple security mechanisms such as authority control and data encryption.
Bus power supply problem
Bus power supply (or bus feed) means that the cables connected to the field devices not only transmit data signals, but also provide working power to the field devices. The following methods can be adopted for power supply of field devices:
- On the basis of the current Ethernet standard, appropriately modify the technical specifications of the physical layer, modulate the Manchester signal of the Ethernet to a DC or low-frequency AC power supply, and then separate the two signals at the field device side.
- Do not change the current physical layer structure, but provide power for field devices through idle cables in the connection cables.