Aiming at the low communication rate of the traditional RTU, the inconsistent communication protocol, and the open system, an open, flexible and reliable Webit-GRTU is designed based on the IEC 60870-5-104 communication protocol and combined with embedded Internet technology. Architecture. The design goals are verified through examples, and a way is opened up for the low-cost replacement of traditional RTUs.
Remote Terminal Unit (Remote Terminal Unit, RTU) is a kind of remote measurement and control intelligent device. It can not only collect, monitor, calculate and store on-site equipment signals, but also independently complete predetermined control procedures, execute instructions from the host computer, and return the execution results and field data to the host computer. RTU has better communication and control capabilities than PLC, and is suitable for harsh working environments and the realization of complex special algorithms.
However, with the continuous development of automation, computer, network and other technologies and the widespread implementation of ERP strategies, various applications and services have put forward higher and higher requirements for the real-time, reliability, and scalability of information. At present, it is difficult for the traditional RTU to meet the requirements of the actual field in terms of structure and implementation methods. Mainly manifested in: (1) The communication protocol is not uniform. There are many communication protocols, such as DNP 3.0, Modbus, SCI, CDC, CDT, etc. Major manufacturers follow their own set of communication protocols, and it is difficult to interconnect and upgrade different devices; (2) Communication rate Lower. The traditional RTU communication method is mostly RS-232/422/485 bus. The most basic "four remote" data can only be transmitted in seconds. The communication rate becomes the bottleneck of system performance, which is far from satisfying the real-time production process. Monitoring requirements.
In the late 1990s, Internet/Intranet technology became more and more mature, and the concepts of equipment networking and pervasive computing mode continued to form. Newly invested automation systems and management networks began to widely adopt TCP/IP network technology, new automation control and communication international standards Also introduced continuously. This requires the new RTU to make full use of existing communication resources, improve data throughput, ensure the real-time performance of the system, and at the same time have better openness and compatibility. In order to adapt to this development trend, in accordance with the IEC 60870-5-104 communication standard of the International Electrotechnical Commission, this article designs a set of universal RTU-Webit-GRTU based on embedded Internet technology, which can be used on any Internet/Intranet node. The Webit-GRTU system carries out comprehensive remote access, which opens up a way for the low-cost replacement of traditional RTUs.
1 Embedded Internet technology and WebitEmbedded Internet technology is a device access technology or a heterogeneous network interconnection technology. The main problem it solves is to achieve access to the Internet from different subnets and different physical areas through Web and embedded technology. Equipment and heterogeneous subnets perform operations such as monitoring, diagnosis, management, and maintenance, so that users can remotely monitor, diagnose, and manage various devices connected to the Internet or other types of subnets. Figure 1 is a schematic diagram of Webit, which uses embedded Internet technology, connects to the Internet after being bound with TVs, cameras, UPS, RTU and other equipment. With the help of the Internet, it breaks geographical barriers and realizes global communication and control.
The Internet communication protocol has high requirements for the CPU speed and memory capacity of the computer system. It does not have any difficulties when used in a PC system, but it must be used in an embedded system with limited resources according to the needs and choose a reasonable communication. The realization and processing scheme of the agreement. According to the characteristics of the embedded system, Webit has made various levels of reductions in the TCP/IP protocol suite based on the real-time kernel WebitX 2.0. The structure is compact, low-cost, reliable, and has high-speed, open, and real-time Strong network communication capabilities.
2 IEC 60870-5-104 communication protocol and TCP/IP protocol stackThe IEC 60870-5-104 communication standard is a telecontrol transmission protocol standard for "IEC 60870-5-101 network access using standard transmission file sets".
It is a communication standard formed by combining the application layer of IEC 60870-5-101 with the transmission function provided by TCP/IP (Transmission Control Protocol/Internet Protocol) according to the series of documents of IEC 60870-5.
Through this standard, within the framework of TCP/IP, different network types can be applied according to actual application needs, including X.25, FR (Frame Relay), ATM (Asynchronous Transfer Mode) and ISDN (Integrated Service Data Network). Figure 2 is a schematic diagram of the standard structure formed by the combination of IEC 60870-5-101 and TCP/IP protocol cluster in IEC 60870-5-104: Because the application protocol control information (APCI) is not used in IEC60870-5-101, IEC60870 The application protocol data unit (APDU) in -5-104 is equivalent to the application service data unit (ASDU) in IEC60870-5-101, and IEC60870-5-104 also defines the application protocol control information (APCI), so APDU is a combination of ASDU and APCI. The control domain of APCI defines the control information to prevent message loss and duplication, as well as the monitoring of message start, stop and transmission connection.
3.1 Design ideas
As a remote measurement and control intelligent device, RTU should fully utilize the functions of RTU and Webit after being bound with Webit, realize the transparent interconnection of field equipment and the Internet, and truly integrate the equipment and network. Intelligent, simple, reliable, universal, and open are the basic design ideas of this RTU system: (1) Webit-GRTU strictly follows the IEC 60870-5-101/104 communication protocol in communication implementation, and is compatible with all standard industrial automation workstation software ; Provide technical support such as API, ActiveX, OLE, DDE, OPC, COM, DCOM, ODBC; it can be easily interconnected with various automation control systems to form a powerful SCADA system. (2) Adopt a separate system structure for communication and control. Data acquisition and control adopt internal expansion bus, which can be combined flexibly according to the complexity of the system and complete logic control independently. The RTU communication part uses a separate microcontroller, and downloads different software according to different communication protocols, which is convenient for software upgrades and expansion. (3) Easy to use.
Through the embedded WEB server, the technical staff can set all the parameters through IE or Netscape browser with the help of prompts; and can simulate the on-site situation through the simulation software, which is convenient for debugging and training. (4) It has strong versatility and can be widely used in ordinary civilian facilities with relatively simple control, and can also be used in complex control in harsh environments.
3.2 Webit-GRTU architecture
Webit-GRTU adopts a separate system structure for communication and control. The data acquisition and control output part of Webit-GRTU uses the INTELMCS80C196 chip, which completes the functions of remote signaling, remote measurement, electric energy pulse counting and remote control output, and uses a 16 bit data bus.
The Webit-GRTU communication module is based on Atmel’s AT90S8515 microcontroller, equipped with Realtek RTL8019AS 10M Ethernet interface chip, with RJ-45 interface, 14-bit TTL level bidirectional I/O, UART port and ECP system programmingå£, as shown in Figure 3. The software structure in the figure mainly includes: real-time kernel WebitX 2.0, thin TCP/IP protocol stack and RSC (Remote System Control). Among them, RSC is mainly used for system parameter setting, power monitoring, remote reset and startup of the system; thin TCP/IP protocol stack includes ARP, IP, ICMP, UDP, TCP, HTTP, TFTP, SNMP and other protocols. In addition, SEEPROM memory is set externally to store user data, such as system parameters, HTML web pages, GIF and JPEG images, etc., which are managed by the WebitX 2.0 file system. The system has RS-232 and RS-485 serial communication interfaces. The data transmission rate is between 300 and 57 600. It is communicated according to the IEC 60870-5-101 communication protocol; the Ethernet communication rate is 10 Mbps and supports standard TCP/ IP protocol, communication with IEC 60870-5-104 communication protocol.
The data exchange between the communication module and the data acquisition control module is carried out through the IDT7130 opening up a common memory area. This is a high-speed dual-port static RAM with a bus arbitration circuit on-chip and two independent control and address buses, which is suitable for fast two-way transfer of large amounts of data between CPUs.
The public memory area is mainly used to store four remote information such as RTU remote signaling and remote measurement.
4 typical applicationsFigure 4 is a topological diagram of the network structure of the LF (Laddle Furnace) refining furnace control system of a steel plant. It is a typical application of Webit-GRTU (because the control system is relatively large and complex, this article mainly focuses on the control part of Webit-GRTU) .
4.1 Process
Webit-GRTU controls the wire feeding machine part of the system. It is in the same TCP/IP local area network as the LF furnace body control PLC, the feeding control PLC and the operator station. In the process of molten steel refining, the LF furnace must continuously add metal composite materials through the wire feeder. The amount of metal added varies with the variety and component content of molten steel, and requires continuous adjustment with the passage of refining time. The work site has high temperature, strong arc interference, and harsh environment, which is not suitable for manual field operation.
On the one hand, Webit-GRTU itself can realize the intelligent control and manual control of the wire feeding machine through the built-in software, and adjust the wire feeding speed and time interval of the wire feeding machine. On the other hand, Webit-GRTU needs to maintain communication with the LF furnace body control system. , Continuously accept the variety, composition, refining time and other related parameters and instructions of molten steel to optimize the control process of the wire feeding machine.
4.2 Performance analysis
The main station communication in this system all adopts the TCP/IP network structure, and the distributed I/O adopts the PROFIBUS field bus structure. Webit-GRTU, Intouch monitoring system, Siemens PLC S7-400, etc. can work together and exchange data better without intermediate conversion devices. Among them, Webit-GRTU has exerted independent intelligent control and coordination capabilities, and has withstood the test of the harsh environment of the steel plant.
Compared with the original RTU using Modbus communication, each operating station and server must be equipped with a special Modbus communication module and communication software to receive RTU data, while using Webit-GRTU, it is very convenient to control RTU and PLC through ActiveX, DDE, and OPC. The system is integrated without additional hardware and software investment. Webit-GRTU uses RTL8019AS 10M Ethernet card. After testing, the single-byte transmission rate is generally about 720μs. Compared with the traditional RTU serial transmission method, the speed is increased by about 30-100 times. In actual application, the data scanning period of the operating station screen is reduced from the original 5~10 s to less than 2 s, which fully meets the requirements of process control. At the same time, Webit-GRTU breaks through the limitation of transmission distance, and can transmit information to any corner of the Internet through gateways and routing.
5 ConclusionWebit-GRTU not only complies with the IEC 60870-5-101/104 communication protocol, and better solves the interconnection and upgrade problems between devices, but also increases the RTU communication rate to the microsecond level to ensure the real-time performance of the system. Practice has proved that Webit-GRTU has simple network wiring, good scalability and strong anti-interference ability. It provides a reference for the low-cost upgrading of traditional RTUs. It covers all intelligent devices through a unified Internet/Intranet network, and opens up an effective way to realize the idea of ​​a transparent factory with integrated management and control.
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