The basic equipment of a chemical water treatment system of a power plant has good controllability. It is monitored and managed in real time by PLC and industrial control computer. The basic composition of the system is shown in Figure 1.
Three Siemens SIMATIC S5-115U programmable controllers are used to control the primary equipment on site. The program control system is divided into three sets, which are #1 make-up water treatment unit, #2 make-up water treatment unit, and #3 condensate treatment unit. .
The operator station selects two Advantech 586 industrial computers, and the software development platform uses FIX5.5 configuration software from IntelluTIon. FIX5.5 is a complete industrial automation software that can complete data acquisition and control, alarm, graphic data display and other functions. This version runs under WINDOWS or WINDOWSNT environment and adopts graphical user interface. The corresponding internal graphics processing is based on Third generation graphics technology.
The data communication system uses the SINEC L2 network, which connects the SIMATIC series of programmable controllers and industrial computers into a network. SNEC L2 is a token bus network, and the network transmission medium is a twisted pair or optical cable. Each node is connected to the bus network through a bus connector. In this system, data communication is realized between three PLCs and between two industrial computers.
Figure 1 system structure diagram
The configuration of the scheme embodies the advantages of the distributed control system, that is, the control functions are dispersed and the operation management is centralized. The decentralized control function means that the system has fast response in real time and the system is dangerously dispersed, and the operation management is centralized to facilitate centralized management, and the scheme configuration also has redundancy characteristics.
2 PLC and its programming
2.1 SIMATIC S5-115U hardware components and programming overview
The programmable controller SIMATIC S5-115U adopts a standard modular structure. The power supply, CPU, and various I/O modules are all plugged into one motherboard, and the expansion motherboard can be added according to different I/O points. The fine grading of the output module and the memory makes the device have a strong configuration adaptability; the communication between the PLC and the computer can be conveniently realized through the communication processor and the local network.
The programming language of SIMATIC S5-115U is STEP5. There are three expression methods, namely control system flow chart CSF, ladder diagram LAD and statement table STL. The statement table STL is closest to the internal control program of the machine, and the functions are also better than the first two. The method is much richer, so the statement table STL is used in the actual programming application of the system.
The biggest feature of STEP5 is the use of structured programming methods, and provides a large number of standard function blocks such as multiplication function block FB242, communication function block FB244, etc., which greatly simplifies the programming work, and the program is clear and easy to read, modify and test. This advantage is especially evident when programming large and complex programs.
To complete complex tasks, the entire program can be divided into separate blocks. STEP5 has five block types, namely organization block (OB), program block (PB), sequence block (SB), function block (FB) and data. A block (DB), in which an organization block (OB) is used to manage the user program, forms an interface between the operating system and the control program, and all other types of blocks are called for execution here. Function blocks (FBs) are used to implement repeated calls or particularly complex program functions. These function blocks can be provided in the form of standard function blocks or by the user. For example, the standard function block FB242 can realize the 16-bit binary multiplication function, and the FB244 can realize the data transfer between the CPU and the communication processor. When these functions are used, these function blocks can be directly called.
2.2 Design of large-scale SIMATIC S5-115U program
Taking the control program of the system #1 make-up water treatment unit as an example, there are mainly the following statements in the organization block OB1 to complete the unconditional invocation of each function block.
JU FB1 (Defines the data that PLC1 transmits to two industrial PCs)
JU FB2 (Define the data transmitted by two industrial PCs to PLC1)
JU FB231 (Basic setting for communication between PLC1 and two industrial PCs)
JU FB232 (Basic setting for communication between PLC1 and PLC2, PLC3)
JU FB4 (automatic control and bumpless switching)
JU FB3 (pneumatic door and electric door control)
JU FB10 (implementing analog processing function)
JU FB11 (alarm processing)
In FB1 and FB2, the data that needs to be communicated is mainly written into the corresponding bit of a data block such as DB10, so that it can be consistent with the variables in the communication processor. In the FB231, two standard function blocks FB244 (send data) and FB245 (receive data) provided by STEP5 are called, and then the necessary parameters such as interface and job number are filled in according to the communication processor to realize the data communication function. The data to be transmitted between the three PLCs is defined in FB232 according to the data bits allocated by the communication processor. In FB4, according to the production process flow requirements and operating specifications, make full use of the data transmitted by other function blocks and I/O modules to realize the automatic control and non-disturbing switching function of the system; for the similar characteristics of multiple controlled objects, respectively Several representative function blocks FB20, FB30, FB40, for example, call FB20 multiple times in FB4 to solve the problem that a certain step time in the PLC and the display time of the industrial computer screen are consistent, and the multiplication function is called in FB20. Block FB244.FB3 controls the field devices such as pneumatic doors, electric gates and pumps according to the automatic step instructions issued by FB4. FB10 is responsible for the processing of all analog quantities. Here, the FB5.FB11 of the square function block is called to perform alarm processing on the analog quantity according to the data converted by FB10. Here, we must pay attention to the correspondence between the analog quantity and the internal digital quantity of the PLC. Guarantee the accuracy of analog display and alarm.
3 design of industrial computer monitoring and management software
The industrial computer monitoring and management software is completed under the FIX5.5 software platform. FIX5î€5 is a high-precision modular software system, including more than a dozen software modules. Here, we mainly introduce several software modules used in the development of this application software. .
(1) System Configuration Module (SCU): It mainly completes the configuration of network, I/O driver, database name, system startup parameters and initial startup tasks. Intellution and third-party vendors have written more than 300 I/O drivers for PLCs and I/O cards, such as drivers for SIEMENS, OMRON, MODICON, ABB, etc., and I/O driver development kits. For users to develop their own I / O drivers.
(2) Data Scanning, Alarm and Control Module (SAC): It is used to realize on-site data scanning, signal conditioning, data format and data type conversion, alarm condition discrimination and remote control output, and SAC will process the field data. Send to the real-time database, or send the data from the remote control to the I/O driver for remote output.
(3) Real-time database management module (DATABASE BUILDER): It provides the function of interactively establishing real-time database and online display/modification of real-time database, which is the main data source for system operation. Users need to do a lot of work here, the most important thing is to fill in the tag name of the variable, so that the field data is associated with the variable tags in the database one by one, in order to call this data in other modules. When filling in variable tag names, it is necessary to pay attention to both normative and technical. First, you need to follow the grammar requirements of FIX software, and then define tag names according to certain classification standards, so as to improve efficiency in future data query and application.
(4) Drawing Module (DRAW): FIX has an intuitive, object-based graphical user interface (GUI) that simplifies the graphics development process. In order to create a picture, you can use the toolbox (TOOL BOX) provided by DRAW to generate certain objects such as valves, pumps, recording tables, etc., and define their dynamic characteristics, that is, the object changes state, size, color, rotation, and movement based on field data. Etc., such as valve opening or closing, pump rotation or stop, these tasks can be completed in a dialog box, mainly to link the variable tags in the real-time database with the corresponding objects, so that the object state changes with the field data. In order to reduce the development time of graphics, Intellution also provides a graphics library of common device objects, which has a variety of international standard graphics, which can be pasted into the user's screen at any time, and users can save their favorite common graphics to the graphics library. For future use.
(5) Display module (VIEW): Its main function is to dynamically display the picture created by DRAW, which can switch between multiple pictures, change the picture form, input data, realize monitoring, etc. This is the actual operation picture provided to the user. .
4 system functions
The system has a host computer monitoring function and an analog disk monitoring function, and the two are mutually in a hot standby mode. On the upper computer screen, there are three working modes: upper computer manual, upper computer automatic, and upper computer monitoring. The switching between modes is undisturbed.
When the system needs to be monitored by the analog disk, the upper computer screen selects the upper computer to monitor the working mode. At this time, the system state is determined by the state of the analog disk M/A switch, and the M/A is set to manual. The analog disk button can be used to perform one-to-one manual operation on the analog disk. When M/A is set to automatic, the system can automatically control the water treatment by an automatic program.
When the system needs to be monitored by the host computer, the upper machine manual and the upper computer automatic function can be selected on the upper computer screen. When the upper computer is selected manually, the one-to-one operation of the local device can be realized on the upper computer screen. When the upper computer is selected automatically, the automatic start/stop control can be performed on the upper computer screen, and the automatic control program has the same function as the automatic control of the analog disk.
5 Conclusion
In large and medium-sized production systems, the era of using programmable controllers in a single machine has passed. The organic combination with industrial computers and the application of computer networks have greatly improved the automation control level and management level of the production site. This is an inevitable trend.
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