Summary:The AC500 series PLC control system and the three-stage distributed sewage treatment automatic control system based on it are introduced. The composition, function and main characteristics of the system are given, and the application of the system in SBR sewage treatment is also discussed.
Key words:PLC control system sewage treatment
I. Introduction
After ABB acquired Bailey (Bailey), a variety of its control systems were integrated into the 800XA series control system based on industrial IT and targeted at the target technology. In addition to continuing to provide overall solutions for the domestic electric power, metallurgy, petrochemical, papermaking and other industries, it has introduced its small and medium-sized control system AC31 with a history of more than ten years into China as a product. At present, the more advanced AC500 series is launched on this basis, which can provide more choices for domestic system integration and OEM applications. This article will introduce this system and its application in wastewater treatment.
Two AC500 control system introduction
AC500 system consists of CPU, communication module, CPU base plate, I/O module and terminal board, FBP interface module and terminal board, CPU base plate, etc., as shown in Figure 1.
CPU
The CPU has three different grades: PM571, PM581 and PM591. All have: LCD Display, operation keys, an SD card expansion port and two integrated serial communication ports. The CPU can be directly inserted into the CPU backplane, and the backplane can choose to integrate Ethernet or ARCNET network interface. In addition, the reserved communication interface of CS31 takes into account the compatibility with other series PLCs of ABB company such as AC31.
Communication module
In addition to the communication interface integrated on the CPU, each CPU can be extended with up to 4 communication interfaces. These four communication interfaces can be extended to any standard bus protocol. In addition to the two Modbus communication interfaces integrated on the CPU and the optional integrated Ethernet or ARCNET network interface, it can also be expanded through the communication expansion interface: bus interfaces such as ProfibusDP-V1, DeviceNet, CANopen and Ethernet.
I/O modules
There are two types of input/output modules: analog quantity and switch quantity. Each input/output module can be directly inserted into the terminal board, and the sub-station of the CPU local and distributed expansion through FBP can be expanded to a maximum of 7 input/output modules. AC500 can also provide switch modules that can be set as input and output according to the needs of users.
Interface module for FBP
This kind of module integrates a certain number of switch input/output, and realizes the communication with CPU and distributed I/O through it. This distribution module can be extended with a maximum of 7 input/output modules behind it.
AC500 Control Builder Programming
AC500 Control Builder programming is a set of engineering tools for programming all series of AC500 CPUs. This programming software complies with the international standard of IEC61131-3 and supports five different programming languages:
– Function block (FBD)
– Statement List (IL)
– Ladder Diagram (LD)
– Structured Text (ST)
– Sequence Control Chart (SFC)
This set of software can complete all settings of the AC500 system, including all bus interfaces, as well as comprehensive self-diagnosis functions, alarm processing, visual debugging tools and open data interfaces. In addition, it can provide offline simulation, variable tracking function, recipe management and watch list, visual debugging tools, communication interface settings, open data interface, and engineering interface.
Three SBR sewage treatment process introduction
The Sequence Batch Activated Sludge Process is abbreviated as SBR (Sequence Batch Reactor) process, which is an improvement of the early fill-and-discharge reactor. With the improvement of automatic control level, the SBR method has attracted people’s attention again, and more in-depth research and improvement have been carried out on it. Since the first SBR treatment equipment in my country was put into operation in 1985, it has been widely used in industrial sewage. and urban sewage treatment.
The basic operation process of the SBR process consists of five basic processes: water inflow, reaction, precipitation, water effluent and idleness. A cycle is formed from sewage inflow to the end of idleness. In each cycle, the above processes are performed in a It is carried out sequentially in the reactor of the stirring device.
The composition of the SBR process system is simple (as shown in Figure 2), there is no secondary sedimentation tank, the aeration tank has the function of the secondary sedimentation tank, and there is no sludge return equipment. SBR has the advantages of high efficiency, good dehydrogenation and phosphorus removal effect, strong anti-sludge bulking performance, strong shock load resistance and processing capacity.
The concrete realization of four AC500 in SBR control
The automatic control system of SBR sewage treatment plant consists of three-level distributed control system (as shown in Figure 3).
The first level—monitoring and management, is realized by the operation station of the central control room. Select industrial computer, communicate with PLC system through TCP/IP industrial Ethernet, and implement centralized control. Real-time monitoring of changes in process parameters, equipment operation, failures, etc. of the entire plant through industrial control software, and is also responsible for daily report printing, accident printing and data recording.
The second level – process control, is realized by the control system of each sub-system or complete set of equipment on site. Taking the AC500 PLC system as the core of on-site control, the sub-stations are configured according to the field area, and the parameters such as flow, liquid level, pH value and motor are collected and controlled through the CS31 network and the corresponding distributed I/O communication.
The third level – single machine on-site control, realized by the on-site electrical control system. ABB’s AC31 series products are used to form distributed I/O, collect on-site parameters, and execute the control commands of the upper-level PLC master station.
Monitoring configuration design and communication with PLC master station
Because the sewage treatment control objects are many and scattered, and the production process is complicated, if the centralized control method is adopted, a large number of wires need to be used, and it is very easy to be disturbed during the long-distance transmission process. Control separation. The computer uses HP industrial PC, pre-installed with the MCGS 5.5 general version of Beijing Kunlun Tongshi Company. MCGS monitoring configuration design includes monitoring interface design, defining data variables, configuration design, animation and so on. Use the basic drawing tools and component library provided by MCGS to create graphic blocks and carry out configuration design, the process flow configuration screen of sewage treatment system (as shown in Figure 4):
The working status of the blower, water pump, and operating valve can be displayed in real time through animation; the flow direction of sewage, sludge, liquid medicine, air and the data of the flow meter can also be updated at any time according to the situation on site. After logging in and entering the user name and password, the operator can arbitrarily call in each local process diagram, running table, setting table and control table. It is necessary to directly set the corresponding parameters on site (for example, the constant water level of the inverter of the pump station, the alarm water level, the setting of the pump stop water level, the setting of the sludge discharge time, etc.). In addition, the system can also provide functions such as fault alarm query and work report generation. The real-time database in MCGS is the core of the monitoring system, and the data variable is the basic unit that constitutes the real-time database. The graphic objects in the user interface are connected with the data variables in the real-time database, and the running situation of the scene can be displayed on the monitoring interface in real time through animation.
The industrial computer only needs an ordinary network card to receive the data from the PLC master station through the Ethernet LAN. The PLC master station consists of one AC500 series PLC and corresponding peripheral equipment, which is placed in the central control room. The PLC master station receives data from the distributed I/O, performs related processing and control, and transmits it to the industrial computer through the standard industrial Ethernet TCP/IP communication module (TB521-ETH), the transmission rate is 10Mbit/s, and the medium is shielded double Stranded.
Communication between PLC master station and distributed I/O
The block diagram of the communication network between the PLC master station and the distributed I/O is shown in Figure 5.
The PLC master station forms a high-speed communication network through the CS31 communication interface reserved on the CPU (PM581), the CS31 communication bus and the distributed I/O (AC31 remote expansion module) to collect the operating status and fault information of the field equipment at any time, and upload it to the industrial control computer. Form distributed control.
There are 8 distributed I/Os in this system. From an economical point of view, since the AC500 system can be compatible with the remote expansion module of the AC31, 1# ~ 8# distributed I/O select the remote expansion module (ICMK14 N1-24DC) of the AC31 system respectively. The distributed I/O is placed on the sewage control site, and it controls the equipment nearby, forming the ability of distributed control, and collects the operating status and fault information of the field equipment, and connects to the PLC master station through the CS31 bus. CS31 bus is a point-to-multipoint RS485 serial communication. Each communication system consists of a master station and a maximum of 31 slave stations. The communication distance is 500 meters without relay, and the maximum can reach 2000 meters with relay. The communication medium is: shielded twisted pair.
Take 1# distributed I/O remote expansion module as an example, define its address table, as shown in Table 1:
Addresses %MX0.0.0 to %MX0.0.7 are system reserved areas of ICMK14N1-M and cannot be used. Addresses %MX0.1.0 to %MX0.1.7 are used as digital inputs of the remote expansion module, corresponding to the corresponding equipment of the water inlet pump room and the grit chamber respectively. According to the same method, you can continue to define 1# distributed I/O (XI16E1, XC32L, HE10-20, … etc.) switch and analog input/output modules, and then 2# ~ 8# distributed I/O All modules.
After completing the setting of all the I/O address tables, you can write the PLC internal communication program through the AC500’s Control Builder software. Since AC500’s Control Builder software can provide ready-made MODBUS function blocks, programming is very simple. Take the read command of 1# distributed I/O as an example, as shown in Figure 6:
Just set the parameters of the MODBUS function block (COM, SLAVE, FCT, ADDR, NB, etc.), and the PLC master station can smoothly read data from the 1#I/O slave station. The parameters of FCT and NB can be determined according to Table 2 according to the actual situation.
Use the MODBUS function block to complete the reading of 1~8# distributed I/O and the programming of the write instruction in turn, and the communication between the PLC master station and the distributed I/O is established and completed. In the actual debugging, it is found that it is necessary to set the MODBUS parameters: RTS control to “telegram”, Parity to “none”, and Operation Mode to “Master” through the PLC configuration option of the software. So far, the master station of the PLC can collect and control various parameters in the I/O slave station, and Display them on the monitoring interface of the industrial control computer through the Ethernet.
Five Conclusions
The technical scheme based on the research results of this paper is implemented in a domestic sewage treatment plant in Zhejiang. The actual operation results show that the design is reasonable, safe and reliable, and the control precision is high, which meets the actual needs of production and is cost-effective. In addition to its beautiful appearance, reliable performance and moderate price, AC500 PLC system has the following advantages in the specific implementation of the project: the switch module of input/output can be set, which provides convenience for the setting of spare points and can further reduce the cost; Each input channel of the analog quantity can set input signals such as current, voltage or thermal resistance, which is easy to use; the MODBUS function block integrated in the programming software is very practical, easy to operate, and greatly saves programming time; in addition, the CS31 bus The connection can be completed only by ordinary shielded twisted pair cables, which is low in cost and flexible and simple in operation.
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