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Using PLC and InTouch to realize double valve automatic control in waterworks
Abstract: This paper introduces the application of SLC500 and InTouch to realize the full automatic control of the four-company dual-valve filter of Hangzhou Waterworks from the features of double-valve filter, process flow, control system structure, program structure, InTouch and its realization control functions. Program structure 1 Introduction Hangzhou water company four in the four valve filter on the successful experience of transformation based on the use of the United States Rockwell SLC500 products to achieve the 30,000 tons of dual-valve filter (Six-valve filter) automatic control and two sets of filter networking control. Difficulties in this project are twofold: (1) 30,000 tons of filter to achieve centralized control, that is, the four filters are fully automatic centralized control to a PLC, the key lies in the program structure of the layout, reasonable layout of the entire program control to achieve a great impact ; ②Thirty tons of filter on the host computer to achieve 40,000 tons of filter control, the rational use of multiple read and write commands, sampling time to avoid sampling time is too short cause read and write interrupt, crashes, public PLC lost and Thirty tons of filter PLC communication, which can not control the 40,000 tons filter. The characteristics of the 2-valve filter The entire process of each filter is divided into three processes: backwash process, finishing process, the normal filter that is PID regulation. Double valve filter control with the four-valve filter control difference is to achieve the siphon control of water and drainage, how to determine the formation of siphon conditions is to achieve dual-valve filter automatic control of one of the key points, Of the contact stability is poor, should not be used; installation of pressure transmitter feedback negative pressure value to determine the degree of vacuum, but the cost is relatively increased, it should not be used; here is the calculation of the relative changes in liquid level to determine the formation of siphon, from The actual results, it is feasible. 3 control system structure 3.1 hardware structure and network structure The control system is divided into two systems: a set of 40,000 tons filter, a total of six groups of filters, each filter has its own PLC, the use of electric valve control; The other is 30,000 tons of filter, a total of four filters, only one PLC, the use of dual-valve control. Because two sets of filters share a single backflush tower, the two sets share a common PLC, which is used primarily to control backwashing of two sets of filters. Each PLC and the host computer using DH485 industrial LAN (Local Area Network) to communicate, DH485 communication protocol is a token-based communication, the maximum rate of 19.2Kbps, the maximum distance of 1.2 km; 40,000 tons of PC The connection between the PLC and the serial port connection method; Thirty thousand tons of PC and PLC using KTX card to connect. PLC is Rockwell company products SLC500 series. Water level meter using E + H ultrasonic level measuring instrument. 3.2 The principle of the filter tank water level The filter tank water level control can achieve constant speed filtration control mode, the adjustment principle shown in Figure 2. Measured by the water level meter filter and water level set point of the deviation, after the PID operation, the calculated value of the servo function block on the water valve to switch. The servo function block performs the PID control by using the motorized valve as an actuator with two on and off actions. When the deviation value is greater than zero, open the valve; when the deviation is less than zero, turn the electric valve; when the deviation is equal to zero, the electric valve to maintain the original state. 4 The overall structure of the program For the 30,000 tons dual-valve filter control methods and points, taking into account the four filter blocks longer, more repetitive, in order to facilitate the preparation and post-commissioning, using a main program and the various filter subroutine Program structure. The advantages: ①clear structure of the program structure, debugging easy to find the program segment; ② debugging process easy to find problems and solve problems; ③ between the program segment and the impact of subroutine between the small, easy to program. A main program (SLC500 program can only have a main program) The main contents of the initialization command, four automatic filter subroutines, four filter subroutines on-site state, four filter subroutine manual state, row Mud valve manual order (sludge valve manual command state only), as shown in Figure 3. The main contents of the first try command include: analog module first try command; intermediate variables cleared; each time, the initial value of the counter assignment. The four automatic filter subroutines contain sub-main and subroutines for this filter. Sub main program contains recoil state subroutine, filter finishing state subroutine, subroutine normal filtering state. The main contents of the four sub-program of the state of the four filter fields include: ①All commands that have been issued when the filter is transferred from the automatic status to the site must be reset. ② some variables in the automatic state, such as time variables, counter variables, etc. must be reset. ③ For recoil must issue an end in this state recoil command. The four-cell manual status subroutine contains manual operation commands for each valve. The recoil control constraints for the filter: filter working time exceeds the set value, or the water valve open enough and the filter water level for a long time not in place. As long as one of the conditions, to recoil. In addition, you can also use forced kick button or remote manual way to complete the recoil from time to time. For a total of 10 filters in the case of a recoil tower, the system uses a PLC to achieve a ten filter queue, through the public program to read and write commands to collect the entire filter recoil information and specific water level and issue a command . The main contents of public programs are: recoil pump control procedures, public PLC and other PLC information read and write procedures and filter queuing procedures. Thirty tons of filter read and write command program is: Each filter in the public program has a read command, and the use of a write command, the sampling time is 1 second. 5 Software and Features The host computer monitoring part of the system is compiled by Wonderware's InTouch software. At the same time, InTouch uses Dynamic Data Exchange (DDE) protocol to communicate with third-party I / O server RSLinx programs. RSLinx communicates with PLC via DH485 protocol. DDE Communication protocol developed by Microsoft that allows applications in the Windows environment to send / receive data and instructions to each other. It realizes the client-server relationship between two applications running at the same time. Server applications provide data and accept requests from other applications. The requesting application is called a client. Some applications, such as InTouch, can act as both a client and a server. InTouch uses a three-part name to identify the data elements in the RSLinx program for the I / O server. These three sections are the application name, the subject name, and the project name, opening the channel to the server program by specifying these three sections. The application name in the project is RSLinx; the subject name is a predefined name in RSLinx, which mainly includes information such as PLC model and station number; and the project name is a specific address in the PLC. The system consists of a computer management and control, you can clearly grasp the filter filter, waiting, recoil and other operating conditions. On the screen there is a dynamic process display, real-time, historical alarm log and curve record window, as well as a variety of parameters set the pop-up window. Mainly to achieve the following functions: (1) on the computer can dynamically reflect the water tower water level, the water level of each pool and the filter level, at the same time these data have real-time and historical records, technicians can easily on the production operation Analyze. (2) For all kinds of pumps, valves and other equipment operating status with real-time dynamic reflection of the function of real-time alarm of equipment failure to confirm the alarm information for the record and has a history of alarm records to check the operation of the equipment. (3) to achieve the pump, filter and valve control. For the filter valve and recoil pump valve can achieve three kinds of control methods, namely, manual, on-site and automatic mode. Operators have a variety of options to adapt to different production practices. The set working hours back into the normal wash back. Or according to the actual operation of the filter, forced by the operator recoil. (5) process parameters set. Including the control of the filter water level, the highest water level, the lowest water level, set the working time, recoil set time, recoil setting time after completion, recoil valve opening time and PID parameters. (6) The system can set multiple access users and permissions, different permissions corresponding to different operations, play a protective role. 6 Conclusion Practice has proved that under normal circumstances, 30,000 tons of filter water level control in the set water level ± 3cm range, PID regulation in 3 to 5 minutes to enter the normal setting of water level control, and to achieve automatic filtering, and Three thousand tons of four filters and four tons of six filters automatically queue and recoil timed. The system also achieved in 30,000 tons of filter on the host computer to complete the two sets of filters on all valves and recoil pump and vacuum pump manual / automatic centralized control. Overcome the double valve siphon caused by fluctuations in the water level up and down the volatile factors. From the trial operation point of view, the design of the control system to meet the basic production requirements, to achieve the desired results, with the realization of the use of domestic valve dual-valve automatic control valve purposes. [2] Hu Shousong. Automatic control principle [M]. National Defense Industry Press. [3] Intouch software electronic help manual [ (1978-), male, Zhejiang Shengzhou, assistant engineer, bachelor, majoring in computer science, software engineering, Mainly engaged in control system development, design and research work. Set the control method. After a year of reform and development and commissioning to meet the production needs and improve the company's technical level.