The hottest intelligent sensor fieldbus and FCS

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Intelligent sensor, fieldbus and FCS

I. Introduction

the full digital control system based on Fieldbus replaces the existing analog signal cable with a high-capacity fieldbus network, which greatly reduces the cost and workload of field signal cable connection and improves the signal transmission efficiency. In fact, fieldbus control system is a working platform with fieldbus technology as the core, intelligent i/o or intelligent sensors and intelligent instruments based on Fieldbus as the control main body, and computer as the monitoring command center for system programming, configuration, maintenance, monitoring and other functions

second, the performance characteristics of intelligent sensors

general sensors can only be used as sensitive elements, which must be equipped with conversion instruments to detect the changes of physical and chemical quantities. With the development of microelectronics technology, intelligent instruments appear. Intelligent instruments adopt VLSI and use embedded software to coordinate internal operations. On the basis of completing nonlinear compensation of input signals, zero point error, temperature compensation, fault diagnosis, etc., they can also complete the control of industrial processes, further decentralizing the functions of the control system. Intelligent sensor integrates all functions and some control functions of sensor and intelligent instrument. It has high linearity and low temperature drift, which reduces the complexity of the system and simplifies the system structure. The characteristics are as follows:

1. Artificial intelligence to a certain extent is a combination of hardware and software, which can realize the learning function and better reflect the role of instruments in the control system. According to different measurement requirements, the appropriate scheme can be selected, and the information can be comprehensively processed to predict the system state

2. Multi sensitivity function integrates the original scattered and independent single sensor into a sensor with multi sensitivity function, which can simultaneously measure a variety of physical and chemical quantities, and comprehensively reflect the measured comprehensive information

3. High accuracy and wide measurement range. It can detect the influence of the measured changes on the characteristics of the detection element at any time, and complete various operations. Its output signal is more accurate. At the same time, its range ratio can reach 100:1, up to 400:1. An intelligent sensor can be used to cope with a wide measurement range, especially suitable for control occasions requiring a large range ratio

4. The communication function can adopt standardized bus interface for information exchange, which is one of the key signs of intelligent sensors

the emergence of intelligent sensors has changed complex signals from centralized processing to decentralized processing, which can ensure the quality of data processing and improve anti-interference performance. At the same time, it reduces the cost of the system. It makes the sensor develop from single function and single detection to multi-function and multi variable detection, makes the sensor develop from passive signal conversion to active control and active information processing, and makes the sensor develop from isolated components to systematization and networking

III. architecture and characteristics of Fieldbus

according to the definition of iec/isa, fieldbus is a digital, bidirectional transmission, multi branch communication network connecting intelligent field devices and automation systems. It is the interconnection of field equipment and field instruments at the bottom of process automation, and the integration of field communication network and control system. Fieldbus brings the concept of network communication and management into the control field, and represents a direction of the development of automation control architecture in the future

fieldbus is a simplified architecture system based on ISO OSI model. It generally includes physical layer, data link layer, application layer and user layer

the physical layer connects the data link layer upward and the media downward. The physical layer specifies the transmission medium (twisted pair, wireless and optical fiber), transmission rate, transmission distance, signal type, etc. During transmission, the physical layer encodes and modulates the data flow from the data link layer. During reception, it demodulates and decodes the received data information with appropriate control information from the media and sends it to the link layer; The data link layer is responsible for implementing bus communication rules and handling error detection, arbitration, scheduling, etc. The application layer provides a simple interface for end-user applications, which defines how to read, write, interpret and execute a message or command. The user layer is actually some application software for data or information query, which stipulates some application programs such as standard function blocks, object dictionaries and device descriptions, giving users an intuitive and simple user interface

in addition to the advantages of a pair of n structure, interchangeability, interoperability, decentralized control functions, mutual communication, convenient maintenance and so on, fieldbus also has the following characteristics:

1. The network architecture is simple, and its structural model is generally only 4 layers. This simplified architecture has the advantages of flexible design, intuitive implementation, low price, good performance and so on, and also ensures the speed of communication

2. The integrated automation function takes the field intelligent equipment as a network node respectively, and realizes the information transmission and communication between nodes and between nodes and management through the fieldbus, which is easy to realize various complex integrated automation functions

3. Strong fault tolerance. Fieldbus greatly improves the fault tolerance of the system by using fault detection, self calibration, supervision and determination to affect the accuracy of indication, shielding logic and other fault detection methods

4. The anti-interference ability and measurement and control accuracy of the system are improved. The on-site intelligent equipment can process signals nearby and exchange information with the main control system by digital communication. It not only has strong anti-interference ability, but also has greatly improved its accuracy and reliability

These characteristics of

fieldbus not only ensure that it can fully meet the current industrial requirements for digital communication and traditional control, but also make it possible to have different levels of complex control and advanced control, optimal control functions

IV. fieldbus control system (FCS)

with the continuous development of complex process industry, industrial process control has put forward newer and higher requirements for the acquisition, transmission and data conversion of a large number of field signals, as well as the integration of accuracy, reliability and management and control. The existing DCs can no longer meet these requirements; Moreover, the existing DCs has some disadvantages, such as the control can not be completely decentralized, the fault is relatively centralized, the system is not completely open, and the cost is high. Therefore, through the integration of digital communication technology, sensor technology and microprocessor technology, the traditional mixed system of digital signal and analog signal is transformed into an all digital signal system, thus producing a new generation of Control System FCS

1. Intelligent sensors and fieldbus are two important parts of FCS

fcs uses Fieldbus to establish a highly reliable data communication line in the control field, realize the data communication between intelligent sensors and between intelligent sensors and the main control computer, and turn a single scattered intelligent sensor into a network node. The data processing in the intelligent sensor helps to reduce the workload of the main control station, localize a large amount of information processing, reduce the information round-trip between the field instrument and the main control station, and reduce the requirements for network data communication capacity. The data preprocessed by the intelligent sensor is collected on the host through the Fieldbus for higher-level processing (mainly system configuration, optimization, management, diagnosis, fault tolerance, etc.), so that the system can analyze and judge the controlled object from surface to point, and then from point to surface, which improves the reliability and tolerance of the system. In this way, FCS connects all intelligent sensors into a network system and control system that can communicate information with each other and jointly complete control tasks, which can better reflect the function of "centralized information and decentralized control" in DCS, and improve the accuracy, real-time and rapidity of signal transmission

based on fieldbus technology, microprocessor as the core, and digital communication as the transmission mode, fieldbus intelligent sensors need the following functions compared with general intelligent sensors:

share a bus to transmit information, and have a variety of calculation, data processing and control functions, so as to reduce the burden of the host. Replace mA analog signal transmission, realize the digitization of transmission signal, and enhance the anti-interference ability of signal. Adopt a unified networking protocol to become the node of FCS and realize the information exchange between sensors and actuators. The system can verify, configure and test it, so as to improve the reliability of the system. The interface is standardized and has the "plug and play" feature

fieldbus intelligent sensor is the mainstream instrument of the future industrial process control system. It and Fieldbus constitute two important parts of FCS, which will bring revolutionary changes to the traditional control system structure and method. However, the formulation of Fieldbus international standards has made slow progress, and the disunity of fieldbus standards has affected the application of Fieldbus intelligent sensors

from a worldwide perspective, several popular fieldbuses have their own advantages and characteristics, and it is difficult to unify to a certain fieldbus standard for many reasons. The first reason is technology. All kinds of existing fieldbuses have their own protocol specifications and industry standards, and there are many technical problems to be unified. The second is commercial interests. Fieldbus is closely related to the development companies behind it. In order to occupy more market share in the future, all enterprises hope to adopt their own technology in the international standards of fieldbus. Thirdly, for organizational reasons, the standardization of Fieldbus must be completed by a unified international organization. However, for many years, users urgently need a unified international standard for Fieldbus to realize the interoperability and interchangeability of field devices. In this case, FF (Foundation Fieldbus) came into being. The purpose of FF is to develop a unified fieldbus standard and promote the application of fieldbus. At present, FF includes 95% of the instrument and control system manufacturers in the world, has formulated the low-speed H1 standard (31.25kb/s), and the high-speed H2 standard is being formulated. The final formulation of Fieldbus unified standard will promote the application of FCS in an all-round way, and make great changes in the realization of control strategies and system development

2. The impact of FCS on DCS

the traditional DCS system is formed by connecting various workstations through local networks. The operation station and information management station complete the configuration, monitoring and operation management of the system, and the field measurement and control station completes the collection and control of production process information. The main problem of DCS is poor openness and insufficient dispersion, which requires a large number of cables to transmit signals. FCS has broken through a major bottleneck that restricts the large-scale utilization of carbon fiber composites in automobiles by recycling DC composites: unlike metal materials, the defect caused by the closed system of special network to realize communication in S system has changed the closed and special solution into an open and universal standardized solution, and the distributed system structure into a new fully distributed structure, The basic and independent function blocks in the DCS control station are completely decentralized to the field intelligent instruments, so as to form a virtual control station, which better reflects the essence of the DCS idea

in fact, the development of industrial process control can be roughly divided into several stages: pneumatic instrument control - electric instrument control - computer centralized control - DCS. Electric instrument control is mainly based on electric type 2 meter, which is basically a simple closed-loop control. Its biggest feature is that the danger is completely dispersed in each single circuit, and its biggest weakness is that it is difficult to realize recovery

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