Fieldbus and Ethernet Combination Solution Realize the Digitization of Industrial Automation System

Industrial automation technology, mainly marked by the application of computers in industrial control and management, has made great progress in the past two decades. Since entering the 1990s, Field Bus (FB) technology, which is a typical representative of industrial control digitalization, intelligence and networking, has developed rapidly and has a huge impact, which has aroused widespread interest and attention in the engineering and technical circles, and is known as industrial automation. A revolutionary new technology in the field.

foreword

Industrial automation technology, mainly marked by the application of computers in industrial control and management, has made great progress in the past two decades. Since entering the 1990s, Field Bus (FB) technology, which is a typical representative of industrial control digitalization, intelligence and networking, has developed rapidly and has a huge impact, which has aroused widespread interest and attention in the engineering and technical circles, and is known as industrial automation. A revolutionary new technology in the field.

1. The concept of field bus

The so-called field bus refers to a computer network that interconnects field devices (such as digital sensors, transmitters, instruments and actuators, etc.) with industrial process control units, field operation stations, etc. And the characteristics of multi-branch, it is the product of the development of industrial control network to the field level. It is not only a basic network, but also an open, new fully distributed control system. This comprehensive technology with intelligent sensing, control, computer, digital communication and other technologies as the main content has attracted worldwide attention and has become a hot spot in the development of automation technology, which will lead to profound changes in the structure and equipment of automation systems. Many powerful and influential companies in the world have successively developed fieldbus technology and products to varying degrees. The working environment of the fieldbus device is at the bottom layer of the process equipment. As a basic communication network at the factory equipment level, it is required to have the characteristics of simple protocol, strong fault tolerance, good security and low cost: it has certain time certainty and high real-time performance. It also has the characteristics of stable network load, mostly short frame transmission and frequent information exchange. Due to the above-mentioned characteristics, the field bus system has the characteristics of different upper-layer high-speed data communication networks from network structure to communication technology.

Fieldbus technology puts special microprocessors into traditional measurement and control instruments, so that they all have digital computing and digital communication capabilities, and according to open and standardized communication protocols, twisted pairs that can be easily connected are used as the bus. , a network system that connects multiple measurement and control instruments, and multiple computerized measurement and control equipment located on site, such as transmitters, sensors, smart instruments, regulating valves, base controllers, recorders, displays, PLCs and Between remote monitoring computers, data transmission and information exchange are realized, and various automatic control systems that meet actual needs are formed. In short, it turns various scattered measurement and control devices into network nodes, and connects them into network systems and control systems that can communicate information with each other and complete automatic control tasks with fieldbus as a link. The changes it brings to the field of automation, just as many scattered computers are connected by the network, make the function and role of the computer change greatly.

2, the characteristics of the field bus

2.1. The openness of the system. Open system means that the communication protocol is open, and the devices of different manufacturers can be interconnected and information exchanged. Fieldbus developers are committed to establishing an open system for a unified factory bottom network. Openness here refers to the consistency and openness of relevant standards, emphasizing consensus and compliance with standards. An open system that can be connected to any other device or system that adheres to the same standard. A fieldbus network system with bus function must be open, and the open system gives the user the right of system integration. Users can assemble products from different suppliers into a system of any size according to their own needs and objects.

2.2. Interoperability and Interoperability. Interoperability here refers to the realization of information transmission and communication between interconnected devices and systems, and can implement point-to-point, point-to-multipoint digital communication. Interoperability means that devices with similar performance from different manufacturers can be interchanged to achieve interoperability.

2.3. Intelligence and functional autonomy of field equipment. It disperses the functions of sensing measurement, compensation calculation, engineering quantity processing and control to the field equipment to complete, only relying on the field equipment to complete the basic functions of automatic control, and can diagnose the operating status of the equipment at any time.

2.4, the high degree of dispersion of the system structure. Since the field device itself can complete the basic functions of automatic control, the field bus has formed a new architecture of a fully distributed control system. It fundamentally changes the existing DCS centralized and decentralized distributed control system system, simplifies the system structure and improves reliability.

2.5. Adaptability to the site environment. Working at the front end of the field equipment, as the field bus at the bottom of the factory network, it is specially designed for working in the field environment. It can support twisted pair, coaxial cable, optical cable, radio frequency, infrared, power line, etc. Interference ability, two-wire system can be used to realize power transmission and communication, and it can meet the requirements of intrinsically safe explosion-proof and so on.

3. Advantages of Fieldbus

Due to the above characteristics of the field bus, especially the simplification of the field bus system structure, the design, installation, commissioning of the control system to the normal production operation and its overhaul and maintenance all reflect the superiority.

3.1. Save hardware quantity and investment. Since the intelligent devices scattered at the front end of the equipment in the fieldbus system can directly perform a variety of sensing, control, alarm and calculation functions, the number of transmitters can be reduced, and a separate controller, calculation unit, etc. The signal conditioning, conversion, isolation technology and other functional units of the DCS system and their complex wiring are needed again, and the industrial control PC can also be used as the operating station, thus saving a large amount of hardware investment. Due to the reduction of control equipment, the control room can also be reduced. of area.

3.2. Save installation cost. The wiring of the field bus system is very simple. Since a pair of twisted pairs or a single cable can usually be connected to multiple devices, the amount of cables, terminals, slot boxes and bridges is greatly reduced, and the workload of connection design and joint proofing is also reduced. decrease very much. When it is necessary to increase the field control equipment, there is no need to add a new cable, and it can be connected to the original cable nearby, which not only saves investment, but also reduces the workload of design and installation. According to the calculation data of the typical test project, the installation cost can be saved by more than 60%.

3.3. Save maintenance costs. Since the on-site control equipment has the ability of self-diagnosis and simple fault handling, and sends the relevant diagnosis and maintenance information to the control room through digital communication, the user can inquire about the operation of all equipment, diagnose and maintain information, so as to analyze the cause of the fault early and eliminate it quickly. The maintenance downtime is shortened, and the maintenance workload is reduced due to the simplified system structure and simple wiring.

3.4. The user has a high degree of initiative in system integration. Users can freely choose equipment provided by different manufacturers to integrate the system. To avoid the selection of a certain brand of products being “framed” the range of equipment selection, and will not be at a loss for incompatible protocols and interfaces in system integration, so that the initiative in the system integration process is completely in the hands of the user.

3.5. Improve the accuracy and reliability of the system. Due to the intelligence and digitization of fieldbus devices, compared with analog signals, it fundamentally improves the accuracy of measurement and control and reduces transmission errors. At the same time, due to the simplification of the structure of the system, the reduction of equipment and connections, the internal functions of the field instrument are strengthened: the round-trip transmission of signals is reduced, and the working reliability of the system is improved. In addition, due to its equipment standardization and functional modularity, it also has the advantages of simple design and easy reconfiguration.

4. Application Cases of Fieldbus

This article introduces an application case of field bus junction and Ethernet to everyone, thus illustrating the application of field bus, which provides convenience for factory management level to access field data. In this case, the bottom layer adopts the PROFIBUS-DP bus protocol, and the field instrument data is collected through the industrial computer. The upper layer adopts the TCP/IP protocol, and uses the interface communication program to allow the industrial computer and the management computer to exchange data in real time.

4.1. System Features

Bus mode: Since the collection point is located in each process workshop of the entire production line, it is relatively scattered.Therefore, by adopting distributed I/O in the form of bus, a lot of cables can be saved, which is convenient for construction, debugging and maintenance.

Centralized management: the system centrally monitors the instantaneous value of each energy collection amount through an industrial computer, calculates the accumulated amount through another application program, and regularly sends each accumulated amount to the superior management computer system

Cross-platform: Windows2000 operating system runs on the industrial computer, which runs Think&Do

The monitoring software performs real-time monitoring of the instantaneous value, and sends the accumulated amount to the upper-level Unix system through the TCP/IP protocol, realizing cross-platform communication and cross-platform data exchange.

4.2. System configuration diagram

Fieldbus and Ethernet Combination Solution Realize the Digitization of Industrial Automation System

4.3. System description

Think&Do Studio 6.5 software is a monitoring software based on Visio2000 developed by American Entivity and running on WinNT or Win2K operating system, with Flowchart control flow design and detailed and rich HMI man-machine interface. The system utilizes the software’s convenient network scanning function, powerful computing function, and easy secondary development under Windows, so it is used as a development platform for monitoring software.

The analog module and the electricity meter with PROFIBUS-DP interface are connected to the PROFIBUS-DP fieldbus as a sub-station, and the gas, water and other flows are converted into standard 4-20mA signals through the measuring instrument, input to the analog module, and In Think&Do, it is calculated by FlowChart and converted into the actual value of the corresponding engineering unit, while the electricity meter can be directly accessed and read from the Think&Do monitoring software. On the one hand, the Think&Do monitoring software displays data in real time through the monitoring screen, and on the other hand, it is shared with the interface application through DDE Server.

Because this system needs to calculate the cumulant, and upload the cumulant to the upper UNIX system regularly, an interface application program for calculation and communication is specially developed for this system with VB. The application program connects to DDE Server through TextBox control, reads real-time data, and performs cumulative calculation in the timing event of TImer control, thereby obtaining the cumulative amount of each team.

The communication between the application and the Unix system adopts the TCP/IP-based telegram mode, and the communication protocol adopts the communication protocol based on the TCPIP-based SOCKET mode.

The energy acquisition system actively sends data packets regularly and is ready to receive the response signal. If there is no response signal after 5 seconds, it will prompt a connection error; if the response signal is unsuccessful, it will resend the data packet (if it fails three times, it will prompt data transmission failure) ; If the response signal is successful, end this transmission. The program flow chart is as follows:

Fieldbus and Ethernet Combination Solution Realize the Digitization of Industrial Automation System

The main bus technology of this system is to realize all the functions required by customers with an industrial computer, which reduces the cost and facilitates maintenance. It is the product of the perfect combination of bus and computer.

5. Conclusion

The emergence of fieldbus technology has substantially improved the level of industrial production automation, which meets the needs of the era of industrial control networking and informatization, so it has a good development prospect. The complete digitization of the industrial automation system and the further adoption of certain standards are the basis for implementing the fieldbus technology, so its initial investment is relatively large. Fieldbus is one of the hotspots of technology development in the field of automation today, and is known as the computer local area network in the field of automation. Its appearance marks the beginning of a new era in the field of industrial control technology, and will have an important impact on the development of this field.

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