The commercial Ethernet doesn’t meet the requirements of the industrial environment and standard entirely because of it is designed for office automation, and there are 5 obvious differences when use the traditional Ethernet in industrial fields.
1. The uncertainty of communication
The biggest characteristic of industry control network different from common data network is that it must meet the requirements of real-time control , that’s to say, the signal transmission should be fast enough and meet the certainty of signal.And the real-time control often requires accurate and timing data refresh of certain variables.The network uncertainty can not meet the requirement of real-time industrial control when the network load is bigger because of the traditional Ethernet uses CSMA/CD, the traditional Ethernet technology is difficult to meet the real-time performance of control system accurate and timing communication, so it has been regarded as “uncertain” network.
2. The non-real time of communication
The real-time may be defined as the measurability of system response time for a certain event in the industrial control system.That is to say, the system must reflect within a predicted time after an event occurs.However, it is very strict with the data transmission of real-time in the industry, data update is often completed in dozens of ms.And it has to resend the data which can retry at most 16 times when it conflicts because of the Ethernet CSMA/CD mechanism, too. Obviously, this conflict resolution mechanism is at the expense of time.It may cause the stop of production even the safety accidents of device and person once dropped, even if it is just a few seconds.
3. The commercial Ethernet does not have high stability and reliability
The traditional Ethernet is not designed for industrial application at the beginning, it has not considered the bad working condition of industrial field environment, the serious interference between lines and machinery, the bad climate, dust and other conditions. Besides,the Ethernet anti-jamming (EMI) performance is very poor, it doesn’t have intrinsically safe performance when used in dangerous situations. So it put forward higher requirement of industrial equipment reliability.The industrial Ethernet must have good reliability, recoverability , and maintainability in the production environment at the same time. It is a guarantee that it will not lead the collapse of applications,operating system even the network when any component failure occurs in a network system.
4. The security issues
Lots of fields exist inflammable, explosive or toxic gases inevitably in the process of industrial production, and there must have some certain explosion-proof technology for the intelligent devices and communication equipment which can ensure the safety of industrial field.It is much more practical to add explosion-proof and explosion-proof measures in the Ethernet system under the condition of current technology, namely the ignition energy which caused by the devices problem will not leak through increasing explosion-proof measures to the Ethernet field devices, which can ensure the safety of running system.For those dangerous situation where is no strict safety requirements, you can not consider complex explosion-proof measures.
The network safety of industrial system is another security issue must be considered at the industrial Ethernet applications.Industrial Ethernet can make the traditional three layers of the network system, namely, information management layer, process monitoring layer and field equipment layer, an organic whole, which make the faster data transfer, higher real-time and it can integrate with the Internet seamlessly, it realizes data sharing and improves the operational efficiency of the factory. But there is a series of network security problems at the same time, industrial network may under the threat of virus infection, hackers and illegal operation.
5. The bus power supply issues
The bus power supply (or feeder bus) refers to the cable connected to the field devices not only to transmit data signals, but also provide equipment working power supply on-site.The Ethernet hasn’t considered this issue from the design at the beginning, while there are a lot of bus power supply requirements on the industrial site.Because of the above problems, the ordinary commercial Ethernet cannot be applied to the control of industrial field directly.And the industrial Ethernet is produced to solve these problems.