Programmable logic controller PLC is the mainstream control device in the current automation field with its technical advantages such as high reliability, easy configuration programming, and rich functions. In engineering applications, the number of controlled objects is large, the measuring points are scattered and the distributed distance is long. If a PLC is used for control, all I/O devices are concentrated in one place, and the control cables from I/O devices to on-site production equipment are lengthy. Complex, not only difficult to install and maintain, but also susceptible to various electromagnetic interference. Many small and medium-sized programmable controllers (such as Schneider M340, Twido, Siemens s7 series, etc.) have their own or expandable Ethernet ports and COM ports, and support standard MODBUS-RTU and MODBUS-TCP protocols. The PLC system is connected to Nanjing by communication. The 893-DCB distributed intelligent front-end of Disses Automation Technology Co., Ltd., the PLC and each intelligent front-end are connected by one or two redundant communication cables in a bus and other topology to form a PLC distributed control system, which can It can be easily extended to a second-level distributed acquisition and control system ranging from tens of points to thousands of points. In this way, with a low cost and a small workload to realize the collection and control of field data, especially for users who use configuration software for monitoring or need to upload data to a large system, this is a replacement for large and medium-sized PLCs. Cost-effective and highly competitive solution.
The core of the solution is to use PLC's CPU module as the system brain and center (data central processing and server), and 893-DCB series remote I/O network products as the trunk and limbs (transmission network and IO channel), and users do not need complicated programming , That is, the image of all I/O project data can be obtained in the memory of the PLC system. The user's I/O operation (input or output) is transformed into reading or writing to the corresponding mapping unit of the PLC's memory, so that the PLC's CPU is more focused on the solution of the internal control logic and algorithm of its control system. In addition, the 893-DCB series remote intelligent front-end has strong environmental adaptability, and can disperse the measurement and control location accessories installed nearby in the industrial field, which greatly improves the measurement and control accuracy, saves a large number of signal transmission cables, and reduces complicated engineering installation and Maintenance workload.
The key of this scheme is to free the PLC central processing unit from the complicated IO operation processing. There must be efficient means to ensure the high efficiency of the on-site measurement and control network and the PLC system communication, and fully meet the real-time requirements of data measurement and control.
Industrial computer (IPC) and PLC, as two important pillars in the field of industrial automation, have been widely used in modern industrial production. The use of PLC and industrial computer for distributed measurement and control can make the two complementary functions inadequate. The former is convenient and reliable for control, while the latter is very useful in graphics display, data processing, printing reports, network communication, and human-computer interaction. Strong function. The schematic diagram of a distributed control system composed of an industrial computer (IPC), PLC and 893-DCB intelligent front-end is as follows:
Siemens S7-200 is a small programmable controller familiar to industrial control engineers. Adding the cp243-1 Ethernet module can be connected to the industrial Ethernet. When it is connected to the 893-DCB series, it can be easily and quickly expanded from dozens of The second-level acquisition and control system from point to hundreds of points can realize field data acquisition and control work with low cost and little workload. Therefore, the S7-200 CPU module can complete the important task of "small horse-drawn cart", and its fundamental guarantee is the high efficiency and reliability of the high intelligence in the 893-DCB intelligent front end and the hierarchical partition network. This is similar to the principle of decentralized operation of modern high-speed rail systems. In fact, high-speed rail does not rely solely on front-end traction, but uses the so-called "EMU drive technology" to achieve high-speed operation. Multiple 893 intelligent front-ends work in parallel to directly provide the final engineering data; 893-DCB1004 is used to automatically complete the data scanning and collection of multiple front-ends on site. S7-200 only needs to communicate with DCB1004 to quickly obtain the real-time measurement and control data of the 893 network, which realizes forward and decentralized functions. A large amount of engineering data can be obtained with only a small amount of PLC resources, ensuring that the PLC has enough resources for advanced control algorithm processing. In this way, more efficient use of PLC software and hardware to focus on the internal logic of the control subsystem for control operations, so that the entire system has programmable and PID control functions, and can run independently from the upper computer.
Generally speaking, PLC control CPU has strong functions and abundant resources such as control algorithms. However, in terms of input and output I/O, PLC has a high price, expansion modules are not isolated, IO configuration is not flexible, wiring is centralized, and IO channels are collected. Data is highly dependent on the calculation processing of the CPU module and other issues, which greatly limits the ability of its CPU to perform more advanced control calculations. The 893-DCB series is a highly intelligent networked I/O product. It adopts a general networked control system of open standards (Ethernet and fieldbus technology). It can be installed independently on site, flexible and diverse, and easy to debug. The modular structure can facilitate your reasonable distribution around the application project or on-site installation. Various conventional industrial field signals (current, voltage, thermocouple, thermal resistance and switch signal) and various transmitter signals can be directly connected. After a simple front-end channel working mode software setting, the data obtained by the user is The final engineering value, and the intelligent front end also has the analysis and processing function of the measurement and control data, which greatly reduces the user configuration workload, especially the tedious and annoying low-level programming and debugging work that is necessary when the PLC is used to build the system. Realize the distributed and intelligent control of the IO channel.
In the above figure, DCB1004 is a programmable multi-serial data acquisition server (regional control intelligent front-end) in the 893-DCB series, which is used to manage the hierarchical and partitioned field control network to improve the real-time and reliability of network measurement and control. DCB1004 can automatically scan the measurement and control data of various types of intelligent front-ends scattered in the control site without any intervention from the PLC. At the same time, it can also automatically output the data set by the user to the various intelligent front-ends located in the field. The PLC control system only needs to communicate with DCB1004 to efficiently complete and control various data exchanges on site, which greatly guarantees the real-time performance and reliability of the system. In this way, using the rich and reliable control algorithm resources of the PLC's CPU, using 893-DCB to expand a large number of distributed remote intelligent I/O ports, freeing the PLC's CPU module from the complicated IO work and more focused control operations, The combination of the two makes the distributed system more cost-effective and more reliable, which is especially suitable for second-level control system applications in general industrial scenes.
The 893-DCB1004 regional control intelligent front end can complete the vertical hierarchical and horizontal partition control of the control system, realize the physical and logical complete isolation of the field-level control network, and independently complete the real-time data scanning and exchange control of the regional control network. This not only greatly improves the real-time performance of data measurement and control, but also prevents partial failures from affecting the normal operation of the entire system, guarantees the reliability of the entire system, and facilitates flexible expansion and maintenance of the system. In addition, DCB1004 also supports a variety of serial communication protocols, which can quickly integrate multiple types of smart devices and meters into the PLC control system. The PLC control system further improves the function decentralization and intelligent distribution, and embeds multiple types in the distributed system. The brains work together in parallel, with a reasonable division of labor and close cooperation, which improves the reliability and real-time performance of the entire system.
The 893-DCB intelligent front end can be directly installed on the industrial site, the protective shell is fully sealed, and the protection level can reach the IP65 standard, adapting to the harsh electromagnetic environment and indoor and outdoor installation requirements. The on-site installation of 893-DCB can save users a lot of signal transmission cables. Users can detach the PLC and use the universal serial port or Ethernet port of an ordinary computer to perform function inspection and accuracy test on the connected 893DCB series front end, which greatly simplifies the on-site debugging work. It is very suitable for users who use iFix, InTouch, Kingview, Force Control and other configuration software at home and abroad.
893-DCB was successfully applied to the intelligent safety monitoring and inerting protection system of the largest closed cluster honeycomb coal bunker in Asia at Huaneng Changxing Power Plant. The Huaneng Changxing Power Plant's large-scale and small-scale projects adhere to the concept of "green demonstration, innovation and leadership", and many projects have adopted world-leading technologies. It adopts a super-large closed cluster regular hexagonal coal bunker with a length of 208.35 meters, a width of 60.45 meters, and a height of 45 meters. The total coal storage capacity is about 200,000 tons. The bunker body is composed of 48 small coal bunkers in the form of regular hexagonal reinforced concrete honeycomb structure, which is the first in Asia. The coal storage is fully enclosed and stacked, occupying a small area, and there is basically no fly ash. The stacking and reclaiming adopts the top-in and bottom-out method, which truly realizes the first-in, first-out and precise coal blending of coal storage, thereby realizing economic mixed burning.
Periodic static storage of coal in a closed silo will cause temperature rise, flammable gas accumulation, etc., which may cause spontaneous combustion or even explosion. From the perspective of safety, install point-type temperature measurement, coal seam multi-point temperature measurement cable type sensor, lifting integrated monitoring mechanism, flammable gas sensor (carbon monoxide, methane, smoke, oxygen), and safety explosion venting devices at a reasonable location in the silo. The silo safety monitoring system conducts comprehensive, multi-faceted, and in-depth real-time monitoring of the silo operating status from combustible gas, oxygen, temperature, material level, etc., according to the combination analysis of various parameters, the silo is integrated in the host computer system. The operating status is presented in real time to the management personnel in parallel to activate the inerting protection and control system.
The inerting protection control system receives the monitoring data of the safety monitoring system and performs equivalent protection measures based on the real-time monitoring information. The silo safety control system uses a high-purity nitrogen inerting protection process. The nitrogen delivery pipeline is extended into the silo through different elevations of the silo, and nitrogen is injected into the silo to protect the safety of the silo. According to the internal coal temperature or combustible gas concentration state of the silo, according to the precise control logic, different control schemes are configured for different safety levels, and the silo inerting protection is completed regularly and quantitatively. When detecting abnormalities in data analysis, the safety monitoring system first responds and issues early warning commands in a timely manner. The safety control system issues equivalent control commands according to the alarm level, and the inerting protection system automatically activates the second-level air lock, third-level inflation, and fourth-level ventilation processes to dilute the accumulated flammable and explosive gases inside the coal bunker in time concentration. After the four-level protection is turned on, if there is an abnormal working condition, the automatic explosion venting device will automatically open to provide the fifth-level protection to the silo. The entire monitoring inerting protection system can achieve multi-level and multi-point timely protection to ensure the safe operation of the silo and surrounding equipment.
The intelligent safety monitoring and inerting protection system of the coal bunker of Huaneng Changxing Power Plant adopts PLC and industrial computer to realize distributed measurement and control, and the functions of PLC and industrial computer are complementary. Adopt Rockwell Allen-Bradley (AB) PLC as the control core to complete the control of the actuator and the data acquisition of sensor signals. The man-machine interface of the industrial computer adopts iFIX configuration software to complete the work of graphic display, data processing, printing report form and data exchange with the DCS system of the power plant. On the basis of full analysis and demonstration, the 893-DCB series intelligent front end is used as the IO channel of the PLC control system. The 893-DCB intelligent front-end is installed in the top, middle, bottom and other positions of the coal bunker in a distributed manner according to process requirements and geographical location, and is directly connected to the PLC system through a redundant dual communication network. 893-DCB has collected more than 1500 analog measurement points (mainly collecting silo coal seam temperature and various gas concentrations and other analog data) and more than 300 various switching signals. The intelligent, modular and distributed advantages of the 893-DCB front-end have been well reflected.
The 893-DCB intelligent front-end is installed in the top, middle, bottom and other positions of the coal bunker in a distributed manner according to process requirements and geographical location, and is directly connected to the PLC system through a redundant dual communication network. The following picture shows the on-site installation photo of 893-DCB in the large closed cluster honeycomb coal bunker of Huaneng Changxing Power Plant:
The 893-DCB layered and zoned on-site measurement and control network not only guarantees the stability and real-time performance of the intelligent safety monitoring and inerting protection system for the coal bunker of Changxing Power Plant, but also greatly reduces the project cost. 893-DCB has been operating in the coal bunker intelligent safety monitoring and inerting protection system of Huaneng Changxing Power Plant for one year, and the system has been operating at high speed and stability, and has achieved satisfactory results.
The 893-DCB front-end has high intelligence, strong functions, complete varieties, and high measurement and control accuracy, which can meet the needs of a variety of industrial control.
Various types of intelligent front-ends of 893-DCB comprehensively adopt a variety of strict isolation measures to achieve signal safety isolation and high-precision data acquisition, isolation conversion, monitoring and transmission between multiple sensors and hosts. It not only guarantees that the entire system has strong anti-interference ability and extremely high measurement and control accuracy, but also guarantees the safety and reliability of the object to be measured and controlled and the entire system.
The input and output of the front end are programmable and flexible to use, which can reduce the number of spare parts for users and save investment for users.
893-DCB uses open network technology to realize seamless connection from field devices to the information layer. It can be quickly integrated whether it is a small number of devices, a single network, or multiple devices and multiple bus networks. 893-DCB can efficiently and quickly connect with common SCADA/HMI, PLC, DCS, etc., and can quickly integrate smart meters and equipment that integrate multiple communication methods, and has a wide range of applicability. The schematic diagram of PLC control system application is as follows:
Application of 893-DCB in PLC control system
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