Chapter II: SCADA system

　　2.1. summary

　　The master station generally adopts advanced computers with good graphic support. Now PC computers and windows systems are mostly used. In history, many systems used UNIX system and xwindows graphical interface. The number of possible sub stations of a master station ranges from dozens to hundreds or thousands.

　　SCADA master station system mainly consists of computer hardware and computer software.

　　As a SCADA master station system, a large system may have dozens, hundreds of workstations and multiple servers. In order to ensure the reliability of the system, double front-end system, multi server system and two networks are adopted. However, for a simple SCADA master station system, there may be only one computer running a set of software.

　　The software mainly includes the following modules:

　　1 protocol interface module

　　2 real time database software

　　Graphical interface 3

　　4 drawing software

　　5 historical data software

　　6 upper layer application software

　　7 alarm module

　　2.2. System hardware composition

　　The huge master station system generally includes the following hardware contents:

　　The communication front-end system is mainly responsible for analyzing various protocols and completing communication interface data processing, including data forwarding. Including front-end computer, serial port pool or modem pool, rack, lightning protection measures and network interface. Depending on the size of the system, there may be one, two or even more front-end computers. Serial port pool is a collection of multiple serial ports. There are two ways: one is the multi serial port card inserted into the computer, and the other is the multi serial port server with Ethernet interface. Modem pool is a collection of multiple modems. Multiple modems can be used or integrated modems using DSP Technology (one interface can provide 30 modems)

　　MODEM)。

　　Various data gateways parse different protocols, convert them into unified data and store them in real-time database. In a sense, the front-end system is a special gateway device.

　　The real-time database system mainly includes the server running the real-time database.

　　Engineer workstation, responsible for system configuration, picture production and various maintenance of the system.

　　The production dispatching workstation is the main user of the monitoring system, which can display the screen, browse the screen, and realize various alarms.

　　Various monitoring workstations are mainly used in particularly large systems where several people are unable to monitor. At this time, various monitoring workstations will be set up as needed, and each workstation has staff.

　　The historical database server is the server for SCADA system to save historical data.

　　Web server is a popular trend of SCADA master station system. As long as the user is equipped with browser software and gets the corresponding authorization, he can access the corresponding data he cares about.

　　The upper application workstation is mainly used for mining real-time data and historical data. In power system, such as power flow analysis, load forecasting, accident recall, power grid stability analysis, energy management and so on. In the water industry, it includes pressure loss analysis of pipe network, economic analysis of pipe network, leakage analysis of pipe network, etc. In oil production engineering, including indicator diagram display, indicator diagram analysis, pump condition analysis, indicator diagram production calculation and so on.

　　Support hardware:

　　Because the SCADA system requires 365d × For 24h continuous operation, the power supply system is demanding. In addition to double circuit power supply, UPS system and even diesel generator are required to ensure the power supply of the system.

　　The printer system used for system output is a simulation screen system that is convenient for users to understand the working state. This is because sometimes the picture of the whole SCADA system is too complicated, which may be of concern to the dispatcher

　　There is not so much data, and it cannot be fully displayed on the computer screen. In order for the dispatcher to understand the overall situation, an n square meter simulation screen display is required, and some operations can be rehearsed on the simulation screen.

　　The main modes of large projection devices include rear projection, projector, TV wall, etc. the reason is basically similar to the simulation screen, which can reduce the labor intensity of dispatchers. Installing cabinet and wiring air conditioning system requires air conditioning system for reliable operation and comfort of personnel, and such air conditioning system is different from household air conditioning, which may require 24-hour work.

　　2.3. System software composition

　　The system software is huge and complex, and its software division is sometimes similar to the blind man touching an elephant, which makes sense in every way. The purpose of software division is to compile and maintain software. A good software architecture is more than the hard work of a bunch of programmers. The method of software division is generally divided into module method, which divides the software into many modules. The software is coupled through module communication. For simple programs, the module method is generally adopted. As long as the interface between modules is clearly defined, modifying one module will not affect the functions of other modules.

　　Another division method is the hierarchical method, which divides the software into many layers. The software operates according to the hierarchical relationship. For example, the operating system must be analyzed according to the hierarchy. The benefits of the hierarchical method are not satisfied with a certain layer. Only if the relationship between layers is divided reasonably, you can rewrite a layer to replace the original layer without modifying other codes.

　　In fact, for complex software systems, the division method of module level is generally adopted, which not only defines the hierarchical relationship of operation according to the concept of layer, but also divides the module relationship between the same layer according to the module method.

　　The hierarchical structure of the monitoring system is as follows, but in fact, for the convenience of software programming and the efficiency of software, it may not be divided and written completely according to this hierarchical model, because the efficiency of the system after full modularization and hierarchy may be very low, affecting the performance, allowing cross level access, and generally not cross module access.

　　Upper application software Data mining software State analysis software Web publishing

　　Graphical interface Graphic tools call the police historical data Other applications

　　Real time database Database server / GIS Server

　　Protocol interface OPC OLE Other interfaces

　　operating system

　　Hardware driver Graphic interface file system Network system

　　2.3.1. Protocol interface module

　　From the perspective of software division, the protocol interface module directly deals with the control equipment of the whole monitoring software. From the data source of the monitoring system, it is the lowest data provider, and the object it serves is the real-time database. It is the source of system data and the output module of system operation.

　　Generally, modules are divided according to different protocols. Different protocols are implemented by different modules. OPC and ole are implemented by special modules, and different OPC and ole are implemented by different modules.

　　Some of the implementation of the regulations are not hierarchical, and many are hierarchical. The advantage of hierarchical protocol is that the protocol in one communication mode can be easily implemented in other communication modes. The scheduling of the protocol can adopt the way of single thread or multi thread. The single thread implementation is simple and easy to manage, but the efficiency is low. The advantage of multithreading is high efficiency, while the disadvantage is complex writing and management.

　　All protocols can be described by finite state machine model. After drawing the state transition diagram by using state machine, the transition and transition conditions between states can be very clear when writing programs, so as to avoid entering a dead state or starving state.

　　In fact, many protocols have their hierarchical structure, generally including physical layer, link layer and application layer (it is impossible to adopt the seven layer model, which is too complex, inefficient and complex in software writing industry). They are also implemented according to the hierarchy. Protocol layering refers to the relationship between the header and content of the protocol message. The lower layer generally uses the data of the upper layer as a load.

　　The protocol interface module can be implemented by software in the front-end system or by hardware (gateway equipment). All data is written to the real-time database.

　　At present, there are many protocols of SCADA system, and the problems about the protocols are described in other chapters.

　　2.3.2. Real time database

　　Advanced monitoring configuration software has a real-time database as the core of data processing, data organization and management of the whole system. Others call it a data dictionary. There are great differences between real-time database and database based on traditional database technology (such as relational database) in principle, implementation technology, function and system performance. The application scope of configuration software integrating real-time database function is wider, especially in time critical applications.

　　However, real-time database is not a simple combination of database technology and real-time system. It has its own characteristics in concept, theory, technology, method and mechanism. Such as: database structure and organization; Priority control, scheduling and concurrency control protocols and algorithms of data processing; The semantics of data and transaction characteristics and their relationship with consistency and correctness; Data query / transaction processing algorithm and optimization; I / O scheduling, recovery, communication protocols and algorithms, and so on, these problems are highly related to each other.

　　Real time database seamlessly integrates database and timing. It has an extremely wide application prospect in various fields that require both database capability and real-time processing technology. The monitoring configuration software integrating real-time database is more necessary and urgent for a variety of engineering or process and time critical applications, Provide strong and essential support for the modernization of the country, especially the automation construction and the development of the national economy, and play an important role in the construction of information technology, information highway and information industry.

　　Using real-time database, the following applications can be completed:

　　1. Record the historical data of real-time process for process archiving, historical data query, accident analysis, system modeling, etc.

　　2. Connect various types of automatic control equipment (such as DCS, PLC, intelligent module, board card, intelligent instrument, controller, frequency converter, etc.) with monitoring interface to realize automatic monitoring.

　　3. Build a distributed application system through the database network communication function.

　　4. Run in the upper computer of the control system (including DCS large-scale control system or other small and medium-sized control systems), run advanced control software, optimization control software and other user applications on the database, and run various interface monitoring software on the client, so as to quickly and conveniently achieve the goal of scalable advanced control or optimization control.

　　5. Connect a variety of control systems and equipment to realize comprehensive utilization and management of real-time data at workshop level, branch level and general plant level.

　　6. Cooperate with relational database management system to build production command and dispatching system and other integrated management and control systems.

　　7. Through the web function of data, use the Internet / Intranet resources to access the production process data on the browser.

　　8. Fully open function, redeveloped on the platform of real-time database.

　　2.3.3. Graphical interface

　　It refers to the interface provided to the user by displaying the collected data to the user with various computer graphics technologies.

　　It mainly includes graph and animation connection. Graph refers to the graph displayed to users, and animation link refers to making the graph change with the change of data. For example, if there is an indicator light on the graph, which is animated with a discrete variable x in the real-time database, at least the light is green when x = 0 and red when x = 1. Different software has different names for animation connection. The word of animation connection was first seen in configuration software.

　　In order to facilitate users to generate various convenient graphics according to their needs, the general master station software provides users with many types of primitives for users to use. Element general

　　It can be divided into:

　　Basic primitives such as point, line, rectangle, circle, text, etc. the shape, color, filling, text, etc. of these primitives can be changed with the change of variables after animation connection.

　　Complex primitives can be generated by integrating many basic primitives, with more and more complex properties, such as X-Y curve, pie chart and indicating instrument.

　　Object primitives are more complex and more convenient for users. For example, a furnace can be defined as an object primitives, and a pipe can be defined as an object primitives.

　　Combined with GIS system, the data can be displayed at multiple levels and dimensions. In many SCADA systems, it is necessary to understand the relationship between acquisition and control objects and geographical distribution, which requires the support of powerful GIS system. The current master station software does not combine the two very much.

　　2.3.4. Graphic tools

　　Development tools for engineers. Because no matter how powerful a software is and how many primitives it provides, it can not meet the requirements of users. At this time, we need to provide a tool that can develop complex primitives and object primitives. Users can develop elements according to their own needs. Providing such a tool can hand over the work that needs to be done by software providers to users. If there is a good communication and benefit distribution mechanism, users can become developers, which is very beneficial to developing customers and improving the functions of software.

　　2.3.5. call the police

　　The alarm module is mainly used to prompt the operator, mainly including the following types of alarm information Switching value input state change alarm means that the state of switching value input signal changes, such as the position of circuit breaker changes from on to off, and the state of valve changes from on to off.

　　This change of state may directly lead to serious accidents or have a great impact on the operation of the system. Analog quantity over limit alarm refers to that the analog quantity exceeds or is lower than the set limit, such as the pipeline temperature is higher than the set value, which may lead to the decline of product quality or personal safety accidents.

　　Analog alarm generally includes upper limit, upper limit, lower limit, lower limit, etc., sometimes distinguished by color. The alarm module reads data from the real-time database, processes it and generates alarm events. The alarm event is written into the historical alarm record.

　　Accident recall (SOE), sometimes in order to analyze the state of the system when the system fails and find out the cause of the accident, it is necessary to know the data and time of each important point. This requires SOE. The generation of SOE event record is generated and stored in RTU. In essence, it is information with time scale (that is, time label the information). The master station needs to read and display these data and store them in the historical alarm database. SOE system needs the clock synchronization of the whole system, and the synchronization accuracy is very high (1ms), so it requires the whole system very high. In the past, it was difficult to find a way to solve this problem. Now network clock synchronization and GPS can be well solved.

　　2.3.6. historical data

　　Historical data is the wealth of the whole SCADA system. Historical data is to convert the contents of real-time database into historical records according to time or other rules. The record of historical data is huge. The recorded data in a year may be several GB or even dozens of GB. Therefore, the memory, storage and CPU speed of the historical database server are required to be relatively high. Because in data mining, we need to traverse a lot of historical data.

　　2.3.7. Network publishing

　　In order to meet the requirements of information construction and avoid becoming an information island, the mainstream master station software now has network publishing function or module. Web publishing includes many forms. At present, the most popular is web publishing. This is because with the development of the Internet, web browser has become the main software configuration of personal computer, and most of the browser software is free, with quite powerful functions and a large number of users.

　　In this way, there is no need to install software and train customers for publishing through the web, and users are used to obtaining data in this way. Disadvantages: poor security and slow speed. Another form of network publishing requires customers to install client software, which is charged, so this method is not very popular. However, its advantages are also obvious, with high security and fast speed. It doesn't even need the help of network. It can be through telephone line, RS485 and RS232 interface. Another form of network release is through real-time database and historical database. This release is generally not for people to see, but a way of data transmission between application software. Other methods, such as network-based OPC, cobra and so on.

　　2.3.8. Working stage division of master station system

　　According to the working stage, the master station system can be divided into system development stage and system operation stage. System development stage: it is the working environment that the design engineer must rely on for the system generation of application program with the support of master station software in order to implement its control scheme. Through the establishment of a series of user data files, the final graphics target application system is generated for the use of the system running environment. The system development environment consists of several configuration programs, such as graphical interface configuration program, real-time database configuration program, etc. Its main users are development engineers and process engineers.

　　System operation stage: in the system operation environment, the target application program is loaded into the computer memory and put into real-time operation. The system running environment consists of several running programs, such as graphical interface running program, real-time database running program, etc. The master station software supports online configuration technology, that is, it can directly enter the development environment and modify the project content without exiting the system operation environment, so that the modified project can take effect directly. The first contact of the design engineer must be the system development environment. Through the system configuration and debugging of a certain workload, the target application will finally be put into real-time operation in the system operation environment to complete an engineering project.

　　2.4. Upper layer application of SCADA software

　　The upper application of SCADA system is relatively complex, various and diverse, which is the essence of the difference between different SCADA systems. Because 85% of all SCADA system applications are the same, the difference is very small. The difference is mainly in the upper application and sensor. There are too many kinds of applications, which are limited to the author's experience and knowledge, so we can only give some simple examples. The calculation of lighting on time of street lamp monitoring is an important module of outdoor lighting application. It is to calculate the daily lighting on and off time according to the longitude and latitude of the control location, and set it down to RTU equipment for light on and off control. This module does not need historical data, but only the local longitude and latitude.

　　The short-term load forecasting of power system needs to use the historical data of last year, the historical data of the current few days and the weather forecast. According to the data model, the short-term load forecasting can be carried out to guide dispatching and power generation. The indicator diagram analysis and indicator diagram production calculation of oil well monitoring need to analyze the pump condition and pump efficiency according to the indicator diagram data of each well, so as to provide data basis for well workover, well opening and well shutdown. In areas with complex terrain (mountains, hills and plateaus) where the metering room cannot be set, the output can be estimated according to the indicator diagram. Although there are errors, the errors can be tolerated, and even the data with errors are better than those without errors.

　　For the pipe efficiency analysis of heating pipe network, according to the pressure and temperature at the outlet of the pipe network and the data of each pressure and temperature measurement point, take a time section to analyze the efficiency of the pipe network and the economy of heating, and even provide data basis for adding and modifying the direction of the pipe network. For flood warning of hydrological monitoring, a mathematical model is established according to the precipitation information and water level information collected by each RTU, combined with the geomorphic characteristics of the river basin, which can estimate the flow of the main stream and tributaries of the river, estimate the water level, issue flood forecast, find out dangerous sections, etc. This application is related to the production and life of the people and the safety of life and property. The upper application can only be developed separately according to the industry, and it is impossible for one software to meet the requirements of all walks of life.