With the rapid development of computer networks, the industrial automation control system structure has been continuously changed. The traditional 4~20mA analog signal system will be gradually replaced by the two-way digital communication field bus system, and the analog/digital DCS system will be replaced by new generations. All-digital fieldbus control system.
One, remote intelligent I/O
The application of remote intelligent I/O makes the process signal digitally processed on the spot, which greatly improves the accuracy of the system's monitoring and control. In addition, the anti-jamming ability and reliability as well as the environmental adaptability have also been improved, which has promoted the development of the field bus. Accelerates the process of digitizing and intelligentizing the primary components at the scene. The smart transmitter is the result of penetration and integration of remote intelligent I/O and on-site primary components.
1. The composition and working principle of the remote intelligent I/O The design of the remote intelligent I/O adopts the network communication technology of DCS and the on-site processing control technology of the PLC and the single loop controller in order to disperse the DCS system and realize the process I/O remoteization. And smart. The remote intelligent I/O system is generally composed of: (1) an intelligent front-end located at the site; (2) a communication bus; and (3) a computer adapter. The number of channels in the smart front end is generally 15-20.
The working principle of the remote intelligent I/O is: After the intelligent front-end machine collects the on-site signal and processes it, it transmits the processing result to the computer through the network bus and adapter through digital communication, and performs comprehensive operation processing for display and analysis. Control; The computer processed data is transmitted to the field control front-end machine through the adapter and the network bus. The control front-end machine sends the adjustment signal to the field device in a predetermined manner to realize the data collection and control of the industrial process and equipment. The core technologies of remote intelligent I/O are communication networks and front-end intelligence.
2. Features of Intelligent I/O (1) Anti-jamming capability and high precision of measurement and control The remote intelligent I/O can process signals nearby and transmit information through digital communication. It has strong anti-jamming capability and improves processing accuracy. The measurement accuracy of analog signals can reach 0.1 or more, and the switch resolution can be as high as lms.
(2) Reduced host load facilitates expansion and increases management functions The I/O front-end machine has a high degree of intelligence and data processing capability. All I/O management tasks can be completed by the adapter, greatly liberating the host, and facilitating function expansion. And achieve advanced control and management capabilities.
(3) High reliability The use of an isolated and floating serial network bus structure avoids electromagnetic interference due to ground return caused by multi-point I/O common ground; each front end is electrically isolated from the network. Independent operation, any failures and dangers are limited to local, and reliability is greatly enhanced. .
(4) Openness The remote intelligent I/O can easily change the adapter type to meet various computer and bus systems. In particular, using a remote I/O system with multiple host networks, it is easy to form a variety of control and monitoring systems, integrate management information systems and the entire network scheduling system, making it a real-time MIS system with on-site information, unified scheduling, optimization Management and coordination of control are of great significance.
2. Fieldbus Fieldbus refers to the digital, serial, multi-point communication data bus installed between the field device in the manufacturing or process area and the automatic control device in the control room. Fieldbuses generally use twisted pair cables, coaxial cables, and optical fibers. Twisted pair or shielded twisted pair cables are currently used. .
1. Fieldbus components (1) Field smart meters (mainly referred to as smart transmitters)
(2) Bus communication part (3) Computer interface 2. Types of fieldbus devices Fieldbus devices are of the type link control station and basic field device. The link control station controls the flow of the digital messages on the fieldbus. It allows each field device to dispatch data messages according to the time when the system is configured. The data communication enables the field device to send not only univariate information but also to send. Multivariate information.
3. communication method·
In the communication mode, synchronous transmission can be used, and asynchronous transmission can also be adopted. Duplex and half-duplex modes can be used. However, there are significant differences in the specific communication protocols. For remote intelligent I/O. The network, almost all manufacturers have their own agreements, but not compatible with other products, but because they can deal with on-site analog signals, so the impact on the operation of the entire system is not.
'4. The HART protocol HART protocol is an addressable remote sensor data highway developed by ROSMOUNT in the mid-1980s. It uses frequency shift keying on the basis of BELL202, uses 1.2kHz and 2.2kHz, and simulates at 4~20mA. Digital signal transmission is completed on the signal.
The HART protocol adopts serial, asynchronous and half-duplex communication. The bus allows up to 2 master devices (computers and handheld terminals). The field device allows up to 15 smart transmitters to be connected to the bus. The bus allows single operation. Grounding. By using fieldbus, users can greatly reduce the field wiring: Multi-variable communication can be realized with a single field instrument, and the devices produced by different manufacturers can be completely interoperable; the control function at the field level is increased; the system integration is greatly simplified and maintained It's very simple.
5. Fieldbus standards and development of fieldbus standards refer to the international standardization of communication networks so that all field devices comply with the same protocol. Products of any manufacturer can be connected to the same bus, connected to computers or control systems, and information and Resource Sharing. From the development point of view, the standardization of fieldbus will bring huge benefits to users, such as saving 60% of signal cables and greatly reducing one-time investment. The unified international standard will have stronger and higher performance indicators based on compatibility with the HART protocol and the DE protocol.
6. The significance of using fieldbus (1) Simplified the structure of the control system Using fieldbus, changing the situation of I / O centralized processing, intelligent devices distributed on the scene to handle the processing of I / O signal in-situ processing tasks, and through the scene Bus communication communicates with the function processor, thereby reducing the amount of I/O card used in the computer control system and simplifying the configuration of the entire control system.
(2) Saving the investment of I/O cable Fieldbus is not only the link connecting the on-site intelligent devices, but also the communication between the communication and the computer control system. Due to the emergence of fieldbus, the connection between the computer control system and the site was inextricably linked to a single bus communication, which avoided the long-distance laying of a large number of field signal cables, and caused a drastic reduction in the UO cable usage. It was estimated that Saves 60% of signal cables.
(3) Improve the reliability of I/O signals After field buses are used, the process I/O processing is completed in the nearest field intelligent device, which avoids the long-distance transmission of small signals and greatly improves the fidelity of the signals. The communication between on-site intelligent devices and computer control systems adopts mature digital communication technologies (including calibration, fault tolerance, and error correction technologies) to ensure the reliability of signal transmission.
One, remote intelligent I/O
The application of remote intelligent I/O makes the process signal digitally processed on the spot, which greatly improves the accuracy of the system's monitoring and control. In addition, the anti-jamming ability and reliability as well as the environmental adaptability have also been improved, which has promoted the development of the field bus. Accelerates the process of digitizing and intelligentizing the primary components at the scene. The smart transmitter is the result of penetration and integration of remote intelligent I/O and on-site primary components.
1. The composition and working principle of the remote intelligent I/O The design of the remote intelligent I/O adopts the network communication technology of DCS and the on-site processing control technology of the PLC and the single loop controller in order to disperse the DCS system and realize the process I/O remoteization. And smart. The remote intelligent I/O system is generally composed of: (1) an intelligent front-end located at the site; (2) a communication bus; and (3) a computer adapter. The number of channels in the smart front end is generally 15-20.
The working principle of the remote intelligent I/O is: After the intelligent front-end machine collects the on-site signal and processes it, it transmits the processing result to the computer through the network bus and adapter through digital communication, and performs comprehensive operation processing for display and analysis. Control; The computer processed data is transmitted to the field control front-end machine through the adapter and the network bus. The control front-end machine sends the adjustment signal to the field device in a predetermined manner to realize the data collection and control of the industrial process and equipment. The core technologies of remote intelligent I/O are communication networks and front-end intelligence.
2. Features of Intelligent I/O (1) Anti-jamming capability and high precision of measurement and control The remote intelligent I/O can process signals nearby and transmit information through digital communication. It has strong anti-jamming capability and improves processing accuracy. The measurement accuracy of analog signals can reach 0.1 or more, and the switch resolution can be as high as lms.
(2) Reduced host load facilitates expansion and increases management functions The I/O front-end machine has a high degree of intelligence and data processing capability. All I/O management tasks can be completed by the adapter, greatly liberating the host, and facilitating function expansion. And achieve advanced control and management capabilities.
(3) High reliability The use of an isolated and floating serial network bus structure avoids electromagnetic interference due to ground return caused by multi-point I/O common ground; each front end is electrically isolated from the network. Independent operation, any failures and dangers are limited to local, and reliability is greatly enhanced. .
(4) Openness The remote intelligent I/O can easily change the adapter type to meet various computer and bus systems. In particular, using a remote I/O system with multiple host networks, it is easy to form a variety of control and monitoring systems, integrate management information systems and the entire network scheduling system, making it a real-time MIS system with on-site information, unified scheduling, optimization Management and coordination of control are of great significance.
2. Fieldbus Fieldbus refers to the digital, serial, multi-point communication data bus installed between the field device in the manufacturing or process area and the automatic control device in the control room. Fieldbuses generally use twisted pair cables, coaxial cables, and optical fibers. Twisted pair or shielded twisted pair cables are currently used. .
1. Fieldbus components (1) Field smart meters (mainly referred to as smart transmitters)
(2) Bus communication part (3) Computer interface 2. Types of fieldbus devices Fieldbus devices are of the type link control station and basic field device. The link control station controls the flow of the digital messages on the fieldbus. It allows each field device to dispatch data messages according to the time when the system is configured. The data communication enables the field device to send not only univariate information but also to send. Multivariate information.
3. communication method·
In the communication mode, synchronous transmission can be used, and asynchronous transmission can also be adopted. Duplex and half-duplex modes can be used. However, there are significant differences in the specific communication protocols. For remote intelligent I/O. The network, almost all manufacturers have their own agreements, but not compatible with other products, but because they can deal with on-site analog signals, so the impact on the operation of the entire system is not.
'4. The HART protocol HART protocol is an addressable remote sensor data highway developed by ROSMOUNT in the mid-1980s. It uses frequency shift keying on the basis of BELL202, uses 1.2kHz and 2.2kHz, and simulates at 4~20mA. Digital signal transmission is completed on the signal.
The HART protocol adopts serial, asynchronous and half-duplex communication. The bus allows up to 2 master devices (computers and handheld terminals). The field device allows up to 15 smart transmitters to be connected to the bus. The bus allows single operation. Grounding. By using fieldbus, users can greatly reduce the field wiring: Multi-variable communication can be realized with a single field instrument, and the devices produced by different manufacturers can be completely interoperable; the control function at the field level is increased; the system integration is greatly simplified and maintained It's very simple.
5. Fieldbus standards and development of fieldbus standards refer to the international standardization of communication networks so that all field devices comply with the same protocol. Products of any manufacturer can be connected to the same bus, connected to computers or control systems, and information and Resource Sharing. From the development point of view, the standardization of fieldbus will bring huge benefits to users, such as saving 60% of signal cables and greatly reducing one-time investment. The unified international standard will have stronger and higher performance indicators based on compatibility with the HART protocol and the DE protocol.
6. The significance of using fieldbus (1) Simplified the structure of the control system Using fieldbus, changing the situation of I / O centralized processing, intelligent devices distributed on the scene to handle the processing of I / O signal in-situ processing tasks, and through the scene Bus communication communicates with the function processor, thereby reducing the amount of I/O card used in the computer control system and simplifying the configuration of the entire control system.
(2) Saving the investment of I/O cable Fieldbus is not only the link connecting the on-site intelligent devices, but also the communication between the communication and the computer control system. Due to the emergence of fieldbus, the connection between the computer control system and the site was inextricably linked to a single bus communication, which avoided the long-distance laying of a large number of field signal cables, and caused a drastic reduction in the UO cable usage. It was estimated that Saves 60% of signal cables.
(3) Improve the reliability of I/O signals After field buses are used, the process I/O processing is completed in the nearest field intelligent device, which avoids the long-distance transmission of small signals and greatly improves the fidelity of the signals. The communication between on-site intelligent devices and computer control systems adopts mature digital communication technologies (including calibration, fault tolerance, and error correction technologies) to ensure the reliability of signal transmission.
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