Sensor technology, communication technology, and computer technology are the three foundations of modern information technology. With the rapid development of IT technology and the continuous advancement of industrial automation requirements, industrial control networks are bearing an increasingly heavy workload. Unlike data information networks, the industrial control field demands a high-speed, low-cost network with good real-time performance, openness, stability, and accuracy. Ethernet technology supports almost all network protocols, and is therefore widely used in data information networks, offering advantages such as high transmission speed, low power consumption, ease of installation, good compatibility, high openness, and support for a wide range of devices. In recent years, with the development of network technology and the increasingly demanding network performance requirements in the industrial control field, Ethernet is gradually entering the industrial control field, forming a new type of Ethernet control network technology. The openness of industrial Ethernet gives it unparalleled advantages in the seamless integration of industrial control networks and enterprise information networks.
1. Development of Industrial Control Networks
The development of industrial control networks has accompanied the innovation of control systems. Control systems have gone through six stages: stationary pneumatic instrument control systems, electric unit combined analog instrument control systems, centralized digital control systems, distributed control systems, fieldbus control systems, and the industrial Ethernet control systems that have become popular in recent years. Stationary pneumatic instrument control systems and electric unit combined analog instrument control systems are merely changes in the drive method; both types of control systems can only control a single loop, and the loops cannot exchange information. Each loop is an independent information island and does not belong to the scope of a network.
With the development of computer technology, computers have been introduced into control systems. These systems can not only process data, but more importantly, they can directly derive their output values—the operational variables—based on input values, process variables, and other measured values within the process, using PID or other advanced control algorithms. These output values are then sent to the actuators to complete the control function. This is the control concept behind Computer Centralized Control Systems (CCS). Because of their simple structure and direct focus on the controlled object, centralized control systems have not yet formed network systems. Although introducing computers into control systems has enabled the implementation of some advanced control algorithms, the increasing complexity of production processes necessitates significant software expenditures, and the complex software structure weakens the system's upgrade capabilities. Furthermore, computer operations often require the centralized control of dozens or even hundreds of loops, compromising the system's real-time performance and reliability.
The true meaning of industrial control network systems lies in the second generation of computer control systems that emerged in the 1970s: Distributed Control Systems (DCS). Developed alongside network technology, DCS is characterized by "centralized management and distributed control," fully embodying the concepts of decentralization and hierarchical structure. Currently used DCS systems include ring, bus, and hierarchical types.
However, distributed control systems also have significant drawbacks:
First, the structure is a multi-level master-slave relationship. Communication between field devices must go through the host, which makes the host heavily loaded and has low power. Moreover, if the host fails, the entire system will collapse.
Secondly, it also uses a large number of analog signals. Many field surfaces still use traditional 4-20mA current analog signals, which have poor transmission reliability and are not easy to digitally process.
Third, each system planning manufacturer has its own independent DCS specifications and closed communication protocols, which greatly limits the integration and application of the system and is not conducive to the further development of modern multinational corporations.
To overcome the technical bottlenecks of the DES system and further meet the needs of industrial sites, fieldbus technology emerged. It further decentralizes the system's control functions. In practice, a fieldbus network is a fully digital, fully distributed, interoperable, and open interconnection network. It is specifically designed for interconnecting the lowest-level field devices or field instruments in process automation and manufacturing automation. It integrates field communication networks and control systems, and the emergence of fieldbus has greatly promoted the realization of equipment automation systems.
However, FE also has many bottleneck problems:
First, there are too many existing fieldbus specifications, each with its own advantages and applicable scope, making it a tricky issue for users to choose the right one.
Secondly, if multiple fieldbuses coexist in the control system, the diversity of bus communication protocols can lead to a situation where the industrial control system and data information network are not seamlessly integrated, and the system function configuration becomes relatively complex, hindering true enterprise-level integrated management and control.
Other systems suffer from technical bottlenecks or fail to meet the information requirements of modern enterprises in areas such as substantive security, system reliability, and data transmission speed. In fact, the root cause of the defects in various control systems lies in their poor openness or conditional and incomplete openness. To address this issue, Industrial Ethernet technology based on the TCP/I protocol has emerged.
The following section will provide a detailed introduction to industrial Ethernet technology.
2. Features of Industrial Ethernet Technology
Ethernet boasts advantages such as high transmission speed, low power consumption, ease of installation, and good compatibility. Because it supports virtually all popular network protocols, it is widely used in commercial systems. In recent years, with the development of network technology, Ethernet has entered the control field, forming a new type of Ethernet control network technology. This is mainly because industrial automation systems are developing towards distributed and intelligent control, making open and transparent communication protocols an inevitable requirement.
2.1 Skill Advantages of Industrial Ethernet
(1) Ethernet is a fully open and fully digital network, and devices from different manufacturers can easily interconnect according to network protocols;
(2) Ethernet can achieve seamless connection between industrial control network and enterprise information network, forming a fully open network for enterprise-level integrated management and control, as shown in Figure 2;
(3) Low hardware and software costs. Because Ethernet technology is now very mature, hardware and software that support Ethernet are highly valued and widely supported by manufacturers, and there are a variety of software development environments and hardware devices for users to choose from.
(4) High communication speed. With the expansion of enterprise information system scale and the increase in complexity, the demand for information is also increasing. Sometimes even the transmission of audio and video data is required. At present, the communication speed of Ethernet is 10M and 100M. Fast Ethernet is widely used. Gigabit Ethernet technology is also gradually maturing. 10G Ethernet is also under research. Its speed is much faster than the current fieldbus.
(5) It has great potential for sustainable development in this era of rapid information change. The survival and development of enterprises will largely depend on a fast and efficient communication management network. Information technology and communication technology will develop more rapidly and maturely, thereby ensuring the continuous development of Ethernet technology.
2.2 Some problems with industrial Ethernet
2.2.1 Real-time issues
In industrial control systems, real-time can be defined as the measurability of the system's response time to a certain event. That is, after an event occurs, the system must react within a precisely predictable timeframe. However, industrial applications have extremely stringent real-time requirements for data transmission; data updates are often completed within tens of milliseconds. Similarly, because Ethernet uses the CSMA/CD media access control method, it is essentially non-real-time. Multiple connections on a single bus compete for the bus equally, and when a conflict occurs, data must be retransmitted, potentially up to 16 times. Clearly, this conflict resolution mechanism comes at the cost of time. Furthermore, a single disconnection, even for just a few seconds, can potentially halt entire production or even cause equipment and personal safety accidents. This method struggles to meet the real-time requirements of industrial control; this is the technological bottleneck preventing Ethernet technology from entering the industrial control field. 3.2.2 Adaptability and Reliability:
Ethernet was initially designed for operational environments, not industrial networks. When applied in industrial settings, it faces harsh conditions and severe inter-line interference, which inevitably leads to reduced reliability. In practical industrial production environments, networks must possess high reliability, recoverability, and maintainability. This means ensuring that a failure in any component of a network system does not cause the collapse or paralysis of applications, operating systems, or even the entire network system.
2.2.3 Application Layer Protocols for Industrial Automation Control
The data structures and other characteristics defined by current application layer protocols in information networks are unsuitable for real-time communication between field devices in industrial process control. Therefore, a unified application layer standard is needed.
2.2.4 Substantive security and network security
If industrial Ethernet is used in hazardous work environments with flammable or explosive conditions, it is necessary to consider practical safety issues. Furthermore, because industrial Ethernet uses the TCP/IP protocol, it may be subject to network security threats, including viruses, unauthorized intrusions by hackers, and unauthorized operations.
2.3 Solutions for Ethernet Industrial Applications
With the continuous development of network technology, the problems mentioned above have been completely or partially solved.
2.3.1 AC Ethernet Skills
To improve network congestion under heavy Ethernet load, full-duplex communication is adopted, which can completely avoid the collisions in ESMA/CD and can easily implement priority mechanisms to ensure maximum utilization of network bandwidth and the best real-time performance. It completely avoids the low power consumption that may occur with CSMA/CD, master-slave, tokens, etc.
2.3.2 High-speed interference-resistant Ethernet
We know that the higher the network load, the greater the probability of a conflict. Data shows that when a network load is below 36%, conflicts are virtually nonexistent. At loads below 10%, the probability of a 10M Ethernet conflict is approximately once every five years.
The probability of a 100M Ethernet connection failure is approximately once every 15 years. However, once this rate exceeds 36%, the probability of failure increases exponentially with increasing load. Significantly improving Ethernet communication speed can effectively reduce network load. Fortunately, Ethernet now offers communication speeds up to 100M/s and even 1G/s high-speed Ethernet. Combined with comprehensive planning, control over the number of network nodes and communication traffic, and specialized anti-interference measures implemented by industrial network equipment manufacturers, Ethernet is increasingly suited to industrial needs and can be fully utilized as an industrial network.
2.3.3 Application Layer Protocol Aspects
Users can add or remove TCP/IP protocol stacks as needed, and also need to develop network protocols that better meet industry requirements.
2.3.4 Substantive Security and Cybersecurity
Equipment manufacturers supply components adapted to industrial environments, using well-sealed, robust, and shock-resistant Ethernet devices and connectors to address practical security issues; they employ various security mechanisms such as user passwords, data encryption, and firewalls to strengthen network security management, but solutions for network security issues in industrial automation control still require careful study.
in conclusion
In conclusion, industrial Ethernet control systems offer significant advantages over other control systems and can be applied across various industrial control fields. With the further development of research in integrated circuits, industrial Ethernet, and embedded Internet technologies, the era of Ethernet-based industrial control networks will soon arrive, becoming the most open industrial control network architecture. This new network system, echoing the development of fieldbuses in Ethernet, represents a revolution in traditional industrial control networks and will undoubtedly bring new possibilities to the industrial control field. However, in certain fields, such as automotive control systems and CNC machine tools, industrial Ethernet is unsuitable due to harsh operating conditions and high requirements for real-time performance and reliability. Current trends indicate that industrial Ethernet's entry into the field control level is undeniable. However, at least for now, it is unlikely to completely replace fieldbuses. As a single standard for real-time control communication, existing fieldbuses will continue to exist for a considerable period. The most likely scenario is the development of a hybrid control system where multiple networks coexist.
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