Design and Application of Remote Group Control System Based on SCADA System
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1. Control system functions and requirements 1) Reliability and safety. As each well is used as the raw water of a water plant, the safety and stability of its control system directly affect whether the water plant can normally supply water to the urban area. Therefore, we must improve reliability in all aspects of communication systems, instrumentation, control equipment, and program programming in the system.
2) Remote monitoring function. Because the distribution of wells is very scattered, no one is on duty. In order to reduce labor intensity, the operator can perform remote wireless operation control according to the needs of the water supply in the factory dispatch room, and at the same time can monitor the operating parameters of each deep-water well so as to achieve centralized monitoring.
3) Maintainability. The system software, application software and hardware must have powerful alarm and fault self-diagnosis functions so that engineers and technicians can analyze and maintain system faults.
4) Scalability. The system should adopt hardware devices with certain standards and widely applied, mainly considering the expansion of the system and laying a good foundation for future system connection.
5) Mainly based on logical control. For the control of the well group water pump, logic control is generally used. Logic control is the traditional application area of ​​programmable logic controllers. Therefore, this is the reason why PLCs are widely used in water plant control systems.
6) Openness. With the development and application of computer technology and network technology, people increasingly need to exchange information between the process control system and the management information system so as to realize the integration of management and control. Although all control system manufacturers cannot be completely open or common at the field controller module level, the upper computer monitoring system must be required to be open. For example, the monitoring system should be based on Microsoft's Windows NT, 2000, or 9X platform and support various specification protocols. Such as OPC, ODBC, ActiveX, DDC and so on.
7) Rich screen display function. The screens displayed at each operation terminal include a process flow main screen, a process flow sub screen, a high and low voltage power supply monitoring screen, a device operation screen, a trend chart, and an alarm screen. Operators can fully understand the system operation through these screens, and can easily perform remote operation on each well station.
8) Reports and query functions. Must have historical data query function, report printing function. There are complete historical data storage for the well group operating parameters, generally requiring 15 minutes to store the data once for query and related statistical analysis. At the same time, it can print production daily reports and production monthly reports.
9) With fault diagnosis and alarm handling. For special operating conditions in the system, such as: power-on condition, communication status, pump operation status, local/remote status, etc. When these special status bits change, alarm should be given in time. At the same time, it is necessary to record the information when these status bits change. Such as: fault tag name, alarm information, fault alarm time and alarm confirmation time, etc., and manage alarm information.
2. Composition of the control system 2.1 Since there are 46 wells in the well group, the communication network is geographically dispersed and geographically distributed. It is suitable for wireless communication. Shifo Waterworks Well Group Monitoring System uses T2000IIS digital radio station produced by New Zealand's TAIT company. The radio station is sturdy and durable, with high sensitivity, strong anti-jamming capability, and fast data transmission and conversion time. The radio provides standard RS-232. The interface can be directly connected with computers, PLCs and other data terminals to achieve transparent transmission. The system uses a frequency of 224.75MHz and works in a single-frequency half-duplex communication mode. The power is adjustable from 5 to 10W. AB's 1747-KE, DH-485/RS-232 interface module provides a bridge between the DH-485 communication network and RS-232 devices using the Allen-Bradley DFI communication protocol when used with a modem for SLC500 In the framework, SLC500 is used as a remote terminal station. The DFI protocol is a communication protocol widely supported by the PLC system of the AB company. It includes various series of PLC systems and computers equipped with RSLinx communication software and supports the DFI protocol. Its communication speed is configurable from 110bps to 19.2Kbps. This agreement can constitute a PLC-based SCADA system. The Shifo Waterworks SCADA system uses a point-to-point half-duplex master-slave communication mode. The PLC uses the DFI half-duplex master communication as the master station, and the other wells use the SFI as the slave station to use the DFI half-duplex slave communication mode. The station PLC implements data exchange by polling each slave station.
2.2 Control System Hardware The Shifo Water Plant monitoring system uses two communication methods, DH+ network and wireless communication. The DH+ network is used in the control layer communication between each PLC controller and computer operation station in the plant. DH+ network adopts shielded twisted pair for communication. It has the characteristics of convenient connection and long-distance communication. It is an industrial network with a wide range of PLC communication applications. At a communication rate of 57.6K baud, up to 10,000 feet without relays. (3040m), plus relay up to 12Km, DH, + net can be connected to 64 controllers. Now there are four monitoring stations in the factory, including the dispatch room, the pump room, the chlorination room, and the double-valve filter. Each station uses the PLC5/40 controller to complete the functions of production data collection, real-time communication, and fault alarm. The PLC1 controller of the plant dispatch room station serves as the master station of the SCADA system and is also used to control and monitor the operation status of each well station.
Plant tuning adopts wireless communication for remote monitoring of well groups. It adopts the DFI master-slave communication protocol with SCADA function. The PLC1 controller realizes wireless communication through its standard RS232 port and data transmission radio. Its communication rate is 1200 baud. rate. Each well point adopts a small programmable controller SLC5/02, mainly to complete the acquisition of the wells operating data, remote control, real-time communication, fault alarm and other functions.
2.3 Control System Monitoring Configuration Software Configuration and Function The operating system uses the Chinese version of WindowsNTServer4.0. The configuration software used Rockwell Automation's RSView32 configuration software and RSLinx, a communication software for field devices. Using the configuration software, you can easily construct a data acquisition monitoring system that suits your needs, create a system flowchart, data tables, alarm screens, real-time data and historical data trends, control screens, etc. The information is transmitted to the dispatching room in real time, and the control command is sent to the on-site data terminal in real time to ensure that the information is unobstructed in the entire system network. In addition, as a built-in programming language, VBA can maximize the extension and customization of RSView32 projects. The programming software uses VisualBasic6.0 to manage software development. It mainly completes the real-time database configuration and historical database configuration, establishes a database for the collected data and stores it. In order to achieve historical data query, curve display, and can generate a variety of trend maps. And report generation and printing.
3. Installation and maintenance of system equipment The PLC equipment is very reliable in system operation. According to statistics of related materials, 95% of system failures occur outside the PLC and 5% within the PLC within the PLC-controlled system. Of the PLC internal faults, 90% occurred in I/O templates. Therefore, in the installation and maintenance, we should pay attention to the peripheral circuit. Including a meter, power supply, relays and signal cables and other equipment.
1) Power supply. A stable power supply is the basis for reliable operation of the entire system. The impact of power grids and frequency fluctuations will directly affect the accuracy and reliability of real-time control, sometimes causing devastating damage to the system. Therefore, PLC system power supply should use isolation transformer, AC voltage regulator or UPS power supply. At the same time, the input and output power supplies should be equipped with switches and protective devices, respectively.
2) Equipment chassis. Due to the poor working environment of the PLC, the PLC should be installed in a sturdy chassis and should be dustproof and waterproof. The surface of the chassis should be a good and firm layer to prevent rust and corrosion.
3) Lightning protection measures. Set lightning protection equipment in the PLC box, such as AC power input lightning protection device, sensor signal line lightning protection device, sensor power supply lightning protection device, etc. Install a lightning rod for the antenna tower and lay a lightning protection grounding grid. The grounding resistance of the lightning protection grounding grid is <4Ω and the grounding resistance of the equipment is <10Ω.
4) Anti-jamming treatment. The environment on the industrial site is rather harsh, and there are many high- and low-frequency interferences. These interferences are generally introduced into the programmable controller through the cables connected to the field devices. In addition to grounding measures, some anti-jamming measures should be taken in the design choices and installation of cables. Analog signals are small signals and are easily affected by outside interference. Therefore, double-shielded cables should be used. The frequency of the communication cable between the PLCs is relatively high. Generally, the cable provided by the manufacturer should be used. In the case that the requirement is not high, the twisted pair cable with shielding layer can be used.
5) System grounding requirements. PLC system grounding requirements are more stringent, it is best to have a separate dedicated grounding system, but also pay attention to other equipment related to PLC must also be reliably grounded. However, when multiple circuits are connected together with ground, unexpected currents can flow, causing logic errors or circuit damage.
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