introduction
Ethernet refers to the baseband LAN specification created by Xerox and jointly developed by Xerox, Intel and DEC. It is the most common communication protocol standard used in existing LANs. The Ethernet network uses CSMA/CD (Carrier Sense Multiple Access and Collision Detection) technology and runs on multiple types of cables at 10M/S. Ethernet is similar to the IEEE802.3 family of standards.
Industrial Ethernet is an Ethernet technology used in industrial control. It is technically compatible with commercial Ethernet (ie IEEE802.3 standard). When designing products, the choice of materials, product strength, applicability and real-time, Interoperability, reliability, anti-interference, intrinsic safety and other aspects can meet the needs of industrial sites.
Ethernet was once considered a "non-deterministic" network. As the basis of information technology, it was developed for IT applications. Only limited applications can be obtained in the field of industrial control. This is due to:
The Medium Access Control (MAC) layer protocol of Ethernet uses Carrier Sense Multiple Access with Collision Detection (CSMA/CD). When the network load is heavy, the determinism of the network cannot meet the real-time requirements of industrial control.
Connectors, hubs, switches, and cables used in Ethernet are designed for office applications and do not meet the harsh environmental requirements of industrial sites;
In the factory environment, Ethernet anti-interference (EMI) performance is poor, if used in hazardous situations, Ethernet does not have intrinsic safety performance;
Ether-net cannot supply power to field devices via signal lines.
With the development and popularization of Internet technology, the increase of Ethernet transmission rate and the development of Ethernet switching technology, the above problems are rapidly being solved in Industrial Ethernet.
Key technologies for the application of Ethernet to industrial sites
(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, 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 system. "non-deterministic" network.
Industrial Ethernet has taken the following measures to make this problem basically solved:
Increase network bandwidth with Fast Ethernet
The communication rate of Ethernet has increased from 10, 100 Mb/s to 1, 10 Gb/s today. In the case of the same data throughput, the increase of the communication rate means that the network load is reduced and the network transmission delay is reduced, that is, the network collision probability is greatly reduced, thereby improving the real-time performance.
Full duplex switched Ethernet
Replacing the original bus-type CSMA/CD technology with switching technology avoids collisions caused by multiple stations sharing and competing for channels, reducing the waste of channel bandwidth, and also achieving full-duplex communication and improving channel utilization. .
Reduce network load
The industrial control network is different from the commercial control network. The amount of real-time data transmitted by each node is very small, generally several bits or several bytes, and bursty large-scale data transmission rarely occurs, so the network can be restricted. The number of segment sites reduces network traffic and further improves the real-time performance of network transmission.
Application message priority technology
In a smart switch or hub, the real-time nature of the transmission is improved by designing the priority of the message.
(2) Safety
In the industrial production process, many sites inevitably exist flammable, explosive or toxic gases, etc. Corresponding to the intelligent devices and communication equipment used in these industrial sites, certain explosion-proof technical measures must be taken to ensure the safe production of industrial sites. .
Under the current technical conditions, it is more feasible to use the explosion-proof and explosion-proof measures for the Ethernet system, that is, the ignition energy generated by the fault of the field device itself by adopting the explosion-proof measures such as increasing safety, airtightness and sealing on the Ethernet field device. Do not leak, to ensure the safety of the system operation. For non-hazardous situations where strict intrinsic safety requirements are not met, complex explosion protection measures may be disregarded.
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 by various security mechanisms such as authority control and data encryption.
(3) 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. Since the mechanical, climatic, dust and other conditions of the industrial site are very bad, the industrial reliability of the equipment is put forward higher. 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, SynergeTIc Microsystems of the United States and Hirschmann, Jetter AG of Germany specially developed and produced rail-type hubs and switches, which are installed in the standard. On the DIN rail, there is redundant power supply, and the connector uses a solid DB-9 structure.
In addition, in practical applications, the backbone network can be transmitted by optical fiber, and the connection of field devices can be shielded twisted pair. For important network segments, redundant network technology can also be adopted to improve the anti-interference ability and reliability of the network. .
(four) bus power supply problem
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:
Based on the current Ethernet standard, the technical specifications of the physical layer are 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.
The field device is powered by the idle cable in the connecting cable without changing the structure of the current physical layer.Branch Chandelier,Rope Chandelier,Geometric Chandelier,Square Chandelier
GUANGDONG LAVIUS LIGHTING CO., LTD. , https://www.laviuslighting.com