Industrial Ethernet application characteristics in the industrial field

- Aug 22, 2018-

I. Overview

As we all know, in enterprise information systems, Ethernet has become the de facto standard network. Industrial real-time control is an extension of traditional Ethernet, helping users to build more open and integrated industrial automation and information networks. Industrial Ethernet technology, which is a combination of standard Ethernet and general industrial protocols. First of all, he met the real-time requirements of industrial automation. The original Ethernet CSMA/CD could not meet the industrial real-time requirements. At that time, the fieldbus and token ring network were mainly used. With the improvement of technology, the switch was in real time. Aspects have met all industrial application requirements from high-precision time synchronization (+-100ns), distributed servo control, discrete control, process control to safety systems, and support on-site and remote monitoring, diagnostics and configuration; of course, EtherNet/IP Products 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 the need for additional programming, the relevant personnel can easily configure, diagnose and monitor plant equipment through a web browser. In addition, EtherNet/IP also specifies EMC and installation protection levels to ensure the strict industrial environment adaptability of EtherNet/IP products.

Second, the characteristics of industrial Ethernet technology

2.1 Communication certainty and real-time

The biggest characteristic of industrial control networks different from ordinary data networks is that they must meet the real-time requirements of control functions, that is, the signal transmission is fast enough and the signal certainty is satisfied. Real-time control often requires accurate timing refresh of data for certain variables. Since EtherNet adopts CSMA/CD mode and the network load is large, the uncertainty of network transmission cannot meet the real-time requirements of industrial control. Therefore, traditional Ethernet technology is difficult to meet the real-time requirements of accurate timing communication required by control systems. "non-deterministic" network. However, the development of Fast Ethernet and switched Ethernet technology has brought new opportunities to solve the problem of non-determinism of Ethernet, making this application possible. First, EtherNet's communication rate has increased from 10M, 100M to today's 1000M, 10G. In the case of the same data throughput, the increase of communication rate means the reduction of network load and the reduction of network transmission delay, that is, network collision. The probability is greatly reduced. Second, using a star network topology, the switch divides the network into several network segments. EtherNet switches have the functions of data storage and forwarding, so that the data frames input and output between ports can be buffered and no longer collide; at the same time, the switch can also filter the data transmitted on the network to make each network segment The transmission of data between nodes is limited to the local network segment, without going through the backbone network or occupying the bandwidth of other network segments, thereby reducing the network load of all network segments and backbone networks. Again, full-duplex communication allows two pairs of twisted pairs (or two fibers) to receive and transmit message frames simultaneously between 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), thus making the EtherNet communication deterministic and real-time greatly improve.

2.2 Stability and reliability

Traditional EtherNet is not designed for industrial applications and does not take into account the adaptability needs of the industrial field environment. Due to the extremely harsh conditions of machinery, climate, dust and other conditions on the industrial site, higher requirements are placed on the industrial reliability of the equipment. In a factory environment, industrial networks must have good reliability, recoverability, and maintainability. In order to solve the problem that the network can work stably under the extreme conditions in the field of uninterrupted industrial applications, Maiwei specializes in the development and production of industrial Ethernet switches installed on standard DIN rails and supports redundant power supply.

2.3 Security

Network security for 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, namely the information management layer, the process monitoring layer and the field device layer, so that the data transmission rate is faster, the real-time performance is higher, and the system can be seamlessly integrated with the Internet. Realize the sharing of data and improve the efficiency of the operation of the factory. But it also introduces a series of cyber security issues, industrial networks may be subject to network security threats including virus infection, hacker illegal intrusion and illegal operations. Under normal circumstances, the industrial network and the external network can be isolated by using a gateway or a firewall, and the security management of the network can be strengthened through various security mechanisms such as authority control and data encryption.

2.4 Bus Power Problems

Bus power (or bus feed) means that the cable connected to the field device not only transmits data signals, but also provides operating power to the field devices. The following methods can be used to power the field devices:

(1) Based on the current Ethernet standard, the physical specification of the physical layer is appropriately modified, and the Manchester signal of the Ethernet is modulated onto a DC or low frequency AC power supply, and the two signals are separated at the field device end.

(2) The field device is powered by the idle cable in the connecting cable without changing the structure of the current physical layer.

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