Zhao Yantao Hao Bao Zhang Hao
Abstract: This article describes our understanding of the application of PLC in sewage treatment and understands the application of high-performance PLC in the control of production sewage and domestic sewage. First of all, through the analysis of the status quo of the sewage control system, the selection of system equipment, the use of SIEMENS S7-400 products to achieve control, and sophisticated high-level operations; then explain the instrument control system, give full consideration to the specificity of high concentrations of sewage hydrogen sulfide , Carry out cabinet design and programming with STEP7 programming software and network formation. The main frame and other racks are connected by PROFIBUS-DP bus. The protocol is Siemens' own bus protocol. The communication between the PLC and the host computer is Ethernet, and an open TCP/IP network protocol is used to facilitate the network expansion in the future. The MPI (multi-point interface) on the CPU is used to communicate with the programmer and other CPUs. According to the operating procedures, the configuration of the upper system (IPC) is performed. The upper system adopts the WINCC configuration software, which has powerful functions, complete reports and trend system, and makes the operation safe and convenient. Use the communication protocol of Siemens products for data linking. Through experiments and debugging, a control system that is more flexible than DCS and more reliable than relays and secondary meters is formed.
Keywords: PLC; rack; Ethernet; MPI network; PROFIBUS-DP bus; interlock
Abstract: This paper describes our application of PLC in wastewater treatment and understand high-performance PLC in the production of waste water and sewage control applications. First by the status of the sewage control system analysis system equipment selection, with the SIEMENS company's S7-400 Product to achieve control, and complex high-level operations; and then a description of the instrument control system, give full consideration to the special nature of high concentrations of hydrogen sulfide water conducting plate cabinet design and programming with STEP7 programming software and the network formation , the host aircraft, and other rack with PROFIBUS-DP bus connection, the agreement for the Siemens built-in bus protocol. PLC and PC communication for Ethernet, with TCP / IP open network protocols to facilitate the future network expansion. CPU on the MPI (Multi Point Interface) is used and the programmer as well as other CPU communications. The use of Siemens products, communication protocols, data link. Of a set of debugging more flexible than the DCS than the relays, the second table control more secure and reliable control system.
Keywords: PLC; rack; Ethernet; MPI network; PROFIBUS-DP bus;
1 Introduction
Tianjin Petrochemical's olefins wastewater treatment plant was originally Siemens S5-115U. The wastewater plant was put into production in 1994. The system has been in operation for more than a decade now, and most of the components are in accordance with the product component replacement cycle provided by Siemens. (Ex: I/O cards, communication cards, etc.) have all exceeded the service life, and some components have experienced significant aging. Production accidents caused by PLC faults have been increasing in recent years, sometimes causing certain environmental impacts; Sewage control system has some margin, but over the past few years, with some technical changes, many monitoring and control points have been added, the original surplus point has been basically utilized, and there is no position for new reconstruction or additional monitoring and control points. In this way, it will bring certain difficulties for the development of technological upgrading of the sewage plant in the future. Also because of the elimination of this type of product, spare parts production is less, the price is relatively high and the procurement cycle is long.
Some time ago, the communication card between the operator station and the PLC failed to communicate, and the hard disk of the IPC also malfunctioned. The technicians only had to go to the scene to manually control the working conditions on the site. Therefore, they decided to immediately upgrade the control system. After comprehensive consideration, it is decided that the control system adopts Siemens S7-400, and the monitoring system uses Siemens WINCC monitoring software to make the operation safe and convenient.
2. Control system hardware configuration scheme
Because PLC has the characteristics of strong versatility, ease of use, wide adaptation, high reliability, strong anti-interference ability, and simple programming. It uses a programmable memory to store instructions for performing logical operations, sequence control, timing, counting, and arithmetic operations, and controls various types through digital and analog inputs and outputs. Mechanical or production process. Programmable logic controllers and related equipment should be designed in such a way that they can be easily integrated with industrial control systems and can easily be extended. Using the S7-400 as the core of the control system to make the system more secure, reliable and easy to operate, easy to manage, easy to maintain, can be optimized control and advanced control. In addition, from the consideration of price factors, the PLC control system used in the retrofitting can be used to control the original set of control systems in the sewage plant. It is not necessary to newly purchase the S7-400's hardware equipment, which greatly saves money, and the cost of future maintenance and repairs. Are lower.
After the statistics of the number of control points of the device and the analysis of complex loops and interlocking loops, the system consists of a main rack (CPU rack) and an expansion rack.
The digital input template is 6ES7 421-1BL00-0AA0, DI32*24VDC,
The digital output template is 6ES7 422-1BL00-0AA0,DO32*24VDC/0.5A,
The analog input template is 6ES7 431-1BL00-0AB0, AO8*13Bit;
The analog output template is 6ES7 432-1HF00-0AA0, AO8*13Bit;
The PLC system power supply is provided by a 20A SIEMENS power supply to ensure good system operation.
System hardware configuration structure shown in Figure 1, Figure 2, Figure 3:
System hardware configuration structure as shown in Figure 1
System hardware configuration structure as shown in Figure 2
System hardware configuration structure as shown in Figure 3
3. Control system software configuration scheme
This system uses STEP7 V5.3 for PLC programming and hardware and network configuration on the software; control room upper computer adopts DELL product, system software uses WINDOWS2000, man-machine interface uses WINCC to complete the configuration, hollow can complete open, Parking and control of all operations, the host computer CRT display device stop state, pressure, temperature, level, and other parameters, display alarm status, historical trend charts, control valve switch status, and has a report print function.
4. Control system network structure and network protocol configuration
The system S7400 main frame and other racks ET200M and touch screen are connected by PROFIBUS-DP bus. The communication between the PLC and the host computer adopts the MPI network, and is connected through the network card on the main frame to facilitate the network expansion in the future. The MPI (multi-point interface) on the CPU is used to communicate with the programmer and other CPUs.
The control system S7-400 network configuration is shown as in Fig. 4:
Fig. 4 Network configuration diagram of control system S7-400
5. Difficulties in this transformation
The software needs to convert the S5-115U program to the S7-400 program. At the beginning, it is attempted to convert the S5-115U program to the S7-400 program by software. However, the converted program S7-400 is unrecognizable and unsuccessful. Software programming can only be rewritten by oneself, the address needs to be redefined, and the duration is very tight, giving only a half-month duration, so the workload is heavy.
10. The integrated fault monitoring system is the core production equipment for the whole sewage treatment plant. Its safe operation is very important. Its operating parameters such as pressure, temperature, liquid level, analysis parameters, etc. must be strictly monitored, otherwise it will affect the environment. As a result, it is necessary to set up an integrated fault monitoring system.
It should be pointed out that the above control systems are not isolated and they should be linked to each other to achieve coordinated control of the entire system. In order to make the system safe and reliable, the products of internationally renowned companies such as AB, SIEMENS and HONEYWELL are mainly used as system hardware. All monitoring points and control loops are configured into screens. The composition is more flexible, economical, and faster than DCS. Safer and more reliable control system; with parameter monitoring, history record, adjustment of each control circuit, alarm interlock, interlock cut-off, operating status display: fault analysis prompts, communication with the host computer, self-diagnosis (including line diagnosis) and Various printing functions. PLC control and manual control dual control system, that is, in the case of power failure or normal operation of the PLC, manual control system to operate the main system valves to ensure the safe operation of sewage.
6. System configuration features
Safe and reliable, the 220V AC power supply and 24V DC power supply in the system cabinet are all connected to the UPS power supply. When the external power supply fails, the uninterruptible power supply can be maintained for 40 minutes without affecting the PLC system power supply.
Easy to configure, can be modified online. The engineer station and the operator station can carry on off-line programming configuration and flow chart modification, can also carry on on-line programming configuration, and use the soft connection way to carry on the dynamic display and the simulation operation to the configuration control plan. All components can be plugged in and out online, increase or decrease the I/O card online, modify the configuration and download online and modify the flow chart online and download it online.
Easy to maintain: Configuration of proprietary function blocks allows testing, diagnosis, and maintenance of individual components. Once a card is damaged, the system immediately detects the name of the printer's printing device, the type of failure, and the time of occurrence in the form of audible and visual alarms. . At the same time, the malfunctioning device also has a light-emitting diode (LED) indicator and maintenance personnel can deal with it in time.
7. Conclusion
After the set of control system was debugged, the unit was successfully started in July 2008. The control system of the S7-400 PLC is running well. The man-machine interface is intuitive, the flow chart is elegant, and the starting conditions and interlocking of the running equipment are clear at a glance. It is simple and convenient, and the control system is reasonable and reliable. It has obtained unanimous recognition from the operation and management personnel. The hardware configuration and software configuration of the control system reflect a very high cost performance. It can be seen from the above that today's high-performance PLC can completely complete the sequence control, complex loop control and advanced computing functions, and the method is flexible, safe and reliable. Has a wide range of application prospects.
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