With the implementation of the "Industry 4.0" strategy, the development of computer technology, communication technology, and IT technology has permeated the industrial control field, most notably in industrial fieldbus technology and industrial Ethernet technology. The widespread use of industrial fieldbus technology, especially Ethernet technology, has brought about profound changes in automation technology.
fieldbus
Fieldbus is a digital, bidirectional, multi-branch communication network used in production sites to connect intelligent field devices and automated measurement and control systems.
It is an industrial data bus, which is the underlying data communication network in the field of automation .
Control composition
1. Fieldbus Control System
Its software is a crucial component of the system. Control system software includes configuration software, maintenance software, simulation software, equipment software, and monitoring software. The first step is to select and develop configuration software and a human-machine interface (MMI) for control operation. Through the configuration software, connections between function blocks are established, function block parameters are selected, and network configuration is performed. During network operation, the system collects data in real time, processes and calculates data, and optimizes control and logic control, alarms, monitoring, display, and reporting.
2. Fieldbus Measurement System
Its features include multivariable and high-performance measurement, giving the measuring instrument more functions such as computing capabilities. Due to the use of digital signals, it has the characteristics of high resolution, high accuracy, and strong anti-interference and distortion capabilities. At the same time, it also has the status information of the instrument equipment, which can adjust the processing process.
3. Equipment Management System
It can provide diagnostic information, management information, equipment operating status information (including smart meters), and equipment manufacturing information provided by the manufacturer for the equipment itself and the process.
4. Bus System Computer Service Module
The client/server model is a popular network computer service model. The server represents the data source (provider), while the application client represents the data user, retrieving data from the data source and processing it further. Clients run on PCs or workstations, while servers run on minicomputers or mainframes, utilizing the combined intelligence, resources, and data of both to complete tasks.
5. Database
It can systematically and dynamically store large amounts of relevant data and applications, enabling full data sharing and cross-access, while maintaining a high degree of independence. Industrial equipment operates with continuously changing parameters, generating large amounts of data, and demanding high real-time performance in operation and control. Therefore, a distributed data system with interoperability and real-time capabilities is formed.
6. Hardware and software of network systems
Network system hardware: system management host, server, gateway, protocol converter, hub, user computer and other underlying intelligent instruments.
Network system software: NetWarc, LANMangger, Vines
Server operating software: Lenix, OS/2, Windows NT, application software databases, communication protocols, network management protocols, etc.
Bus Classification
Currently, there are approximately forty types of fieldbuses in the world. These fieldbuses are mostly used in process automation , medical fields, manufacturing, transportation, defense, aerospace, agriculture, and building applications. Current industrial bus networks can be classified into three categories: 485 networks, HART networks, and Fieldbus networks.
1.485 network
RS485/MODBUS is a popular industrial networking method, characterized by its simplicity and ease of implementation, and the abundance of instruments that support RS485. Instrument manufacturers are increasingly switching to RS485/MODBUS for the simple reason that RS485 adapters are not only inexpensive but also come in a wide variety of types. At least in the low-end market, RS485/MODBUS will remain the primary industrial networking method.
2. HART network
HART, proposed by Emerson, is a transitional bus standard. Its main feature is the superposition of digital signals on top of 4-20 mA current signals. However, the protocol is not truly open; access is only available through Emerson's foundation, which incurs a fee. HART technology is primarily monopolized by a few large foreign companies. While some domestic companies have been developing it in recent years, they haven't yet reached the level of their foreign counterparts. Many smart meters now come with HART cards supporting HART communication. However, in China, this functionality isn't widely used for networked device monitoring; at most, it's used for parameter setting via handheld devices. In the long run, due to HART's low communication speed and difficulties in networking, the application of HART meters is expected to decline.
3. FieldBus Network
Fieldbus is one of the hottest technologies in the field of automation today, hailed as the computer local area network of automation. Its emergence marks the beginning of a new era in automation control technology. Fieldbus is a digital, serial, multi-station communication network connecting instruments in the control field with control devices in the control room. Its key feature is its ability to support bidirectional, multi-node, bus-based, fully digital communication. In recent years, fieldbus technology has become a hot topic in international automation and instrumentation development. Its emergence has revolutionized the traditional control system structure, propelling automatic control systems towards "intelligent, digital, information-based, networked, and decentralized" directions, forming a new type of fully distributed network communication control system—the Fieldbus Control System (FCS). However, to date, fieldbus has not yet formed a truly unified standard. Multiple standards such as ProfiBus, CANbus, and CC-Link coexist, each with its own space for survival. When will unification occur? Currently, the types of instruments supporting fieldbus are relatively few, offering limited choices, and their prices are relatively high, resulting in low usage.
Features and advantages and disadvantages
1. Features
Field control devices have communication capabilities, which facilitates the formation of a factory's underlying control network;
The openness and consistency of communication standards enable the system to be open and the devices to be interoperable.
The standardization of functional blocks and structures enables interchangeability between devices with the same function;
By delegating control functions to the field, the control system structure becomes highly decentralized.
2. Advantages
Fieldbus technology has enabled automation equipment and systems to enter the information network industry, opening up a wider range of applications for them.
A large number of control devices can be connected to a single twisted pair cable, which helps save on installation costs;
Save on maintenance costs;
Improved system reliability;
It provides users with more flexible control over system integration.
3. Disadvantages
In network communication, data packet transmission delays, transient errors and data packet loss in communication systems, and inconsistencies in the order of transmission and arrival can all disrupt the determinism inherent in traditional control systems, making the analysis and synthesis of control systems more complex and negatively impacting the performance of control systems.
Industrial Ethernet
Industrial Ethernet refers to a type of industrial communication network that is technically compatible with commercial Ethernet, but whose product design meets the needs of industrial sites in terms of real-time performance, reliability, and environmental adaptability. It is the most recognized and promising type of industrial communication network that has been developed after fieldbus.
The essence of Industrial Ethernet is that Ethernet technology is used to move office automation towards industrial automation.
Comparison of Industrial Ethernet and Traditional Ethernet Networks
Operating requirements
1. The high temperature, humidity, air pollution, and presence of corrosive gases in industrial production environments require industrial-grade products to be adaptable to different climates and to be corrosion-resistant, dustproof, and waterproof.
2. The presence of dust, flammable, explosive, and toxic gases at industrial production sites necessitates the implementation of explosion-proof measures to ensure safe production.
3. Industrial production sites are subject to significant vibration and electromagnetic interference, so industrial control networks must have mechanical environmental adaptability (such as vibration and shock resistance), electromagnetic environmental adaptability, or electromagnetic compatibility (EMC).
4. The power supply for industrial network devices usually adopts the standard low-voltage DC power supply in the cabinet. In most industrial environments, the power supply required in the control cabinet is low-voltage 24V DC.
5. Standard DIN rail mounting is adopted, which is convenient for installation and suitable for industrial environment installation requirements. Industrial network devices should be easy to install in industrial field control cabinets and easy to replace.
Main standards
Industrial Ethernet is developed according to the requirements of industrial control, with appropriate application layer and user layer protocols, so that Ethernet and TCP/IP technologies can be truly applied to the control layer and extended to the field layer. At the information layer, all effective and latest achievements in the IT industry are adopted as much as possible. Therefore, industrial Ethernet and Ethernet application in industry are not the same concept at all.
1. IDA's communication structure and communication protocol
DA is an industrial Ethernet specification built entirely on Ethernet, combining a real-time, web-based distributed automation environment with a centralized security architecture, with the goal of creating a distributed automation solution based on TCP/IP.
2. Ethernet/IP communication structure and protocols
In addition to DeviceNET and ControlNet, ODVA also controls another bus, EtherNet/IP, which bundles the DeviceNet and ControlNet target library CIP (containing all classic PLC operations) at the application and user layers with the Ethernet physical medium.
3. PROFlnet's communication structure and communication protocol
As shown in the figure, its data link layer employs a transmission protocol designed to reduce the time required to process the communication stack, thereby significantly shortening the network refresh time and ensuring a refresh time of 5-10ms. In addition to cyclic transmission, the real-time channel can also perform non-cyclic transmission (event triggering, process data modification, operation command issuance, etc.). It also incorporates network management, web functionality, and direct integration of I/O devices.
4. HSE communication structure and communication protocol
The Fieldbus Foundation (FF) in the United States uses high-speed Ethernet to develop the backbone network of the FCS system communication network above the control level, while the H1 fieldbus is still used below the control level, forming an open architecture for information integration. HSE follows standard Ethernet specifications. FF defines 21 function blocks in its specifications for use in basic and advanced process control. These standard function blocks reside in the field devices connected to the HSE and are linked through configuration. For complex batch processing and hybrid control applications, FF also defines flexible function blocks that support monitoring of data acquisition, subsystem interfaces, event sequencing, multi-channel data acquisition, and can be used as inter-network connectors for communication with PLCs and other protocols. Therefore, we can conclude that HSE Industrial Ethernet provides various solutions for continuous real-time control required by continuous process control industries and discontinuous manufacturing industries. It provides a fairly mature standard protocol for industrial Ethernet for the integration of continuous process control systems, discontinuous manufacturing control systems, batch control systems, and enterprise information management systems such as MES and ERP.
Problems to be solved in industrial control
Industrial Ethernet, while generally technically compatible with commercial Ethernet, is designed to meet the real-time, reliability, and environmental adaptability requirements of industrial environments, making it a typical industrial communication network. Compared to commercial Ethernet, industrial Ethernet has specific requirements in the following aspects:
1. Requires high real-time performance and good time determinism;
2. The transmitted information is mostly in short frames, and information exchange is frequent;
3. Strong fault tolerance, high reliability and security;
4. The control network structure is highly decentralized;
5. The control network protocol is simple, practical, and highly efficient;
6. The intelligence of control equipment and the autonomy of control functions;
7. It has highly efficient communication with information networks and is easy to integrate with them;
8. Equipment reliability and environmental adaptability;
9. Long-distance transmission;
10. Bus power supply;
11. Network security;
12. Interoperability.
Advantages
1. Wide range of applications
Ethernet is currently the most widely used computer network technology, receiving extensive technical support. The most typical Ethernet application is Ethernet + TCP/IP + Web. Almost all programming languages support Ethernet application development.
2. Low cost
Because Ethernet is the most widely used network, it has received high attention and widespread support from hardware developers and manufacturers. There are many hardware products for users to choose from, and because of its wide application, the hardware price is relatively low.
3. High communication speed
Currently, Fast Ethernet with communication speeds of 10M and 100M is being widely used, 1000M Ethernet technology is gradually maturing, and 10G Ethernet is under research, with a communication speed much faster than current fieldbuses.
4. Abundant software and hardware resources
Ethernet has been used for many years, and people have a wealth of experience in its design, application, and other aspects, and are very familiar with its technology. Abundant software resources and design experience can significantly reduce system development and training costs, thereby significantly reducing the overall cost of the system and greatly accelerating system development and deployment.
5. Strong sustainable development capability
Due to the widespread application of Ethernet, its development has received extensive attention and significant technological investment, resulting in global technical support. In today's rapidly changing information age, the survival and development of enterprises will largely depend on a fast and effective communication network management system. The development of information and communication technologies will be more rapid and mature, thus ensuring the continuous advancement of Ethernet technology.
6. Easy to achieve integrated management and control
It facilitates seamless integration of control and information networks, establishes a unified enterprise network, and enables embedded controllers, intelligent field measurement and control instruments, and sensors to be easily connected to the Ethernet network, and even connected to the Internet.
