Programmable manipulators (PLCs) have always played an important role in industrial field control. With the increase of the state's investment in the water supply profession, the level of automation of water plant operation has been continuously improved, and the use of PLC in the water supply profession has gradually increased. The touch screen and PLC are used together, so that the use of PLC is more sensitive, and together you can set parameters, display data, and depict the automation process with animation, so that the use of PLC can be visualized.
Variable frequency constant pressure water supply has become a main stream of water supply profession, and it is an important means to ensure that the water supply network is at constant pressure. The perfect network communication engineering of modern inverter, the synchronous operation of Wei Motor, long-distance centralized control and online monitoring provide the necessary support. The touch screen connected with the PLC can make the operation more intuitive, and the operation more simple and convenient.
The combination of PLC, touch screen and inverter, the communication method is used to control the inverter to complete the variable frequency constant pressure water supply.
Architecture
Variable frequency constant pressure water supply system, which is mainly composed of PLC, frequency converter, touch screen, pressure transmitter, power and control circuit and pump set. Users can control the operation of the system through the touch screen, and can also understand and control the operation of the system through the indicator lights and buttons on the control cabinet panel, and the transfer switch. Through the pressure transmitter installed on the outlet pipe network, the outlet pressure signal is turned into a standard signal of 4-20mA or 0-10V and sent to the built-in PID conditioner of the PLC, and the operating frequency is output to the inverter after the PID calculation is compared with the given pressure parameters. The control system is controlled by the inverter to control the speed of the pump to regulate the water supply, according to the different water consumption, the PLC frequency outputs the operation frequency of the given inverter, so as to adjust the speed of the pump to reach the constant pressure water supply. The internal program set by the PLC drives the output of the switching quantity of the I/O port to complete the switching of the AC contactor group, so as to coordinate the number of pump motors put into operation, and complete the switching of motor start-stop, frequency conversion and power frequency. After adjusting the number of motors put into operation and controlling the frequency conversion speed of one motor in the motor unit, the operating pressure of the system pipe network has been stable, and then the intention of constant pressure water supply has been reached.
How it works
The system has two operating methods: manual and active. When the manual method is used, the start and stop buttons on the control cabinet control the pump operation, and the start and stop of the 1#-3# pump can be controlled respectively according to the needs, and the method is mainly used for equipment debugging, active faults and maintenance. When it is actively running, the 1# water pump is first operated by frequency conversion, and the output frequency of the inverter rises from 0HZ, and the PID conditioner compares the received signal with the given pressure and sends it to the inverter for control. If the pressure is not enough, the frequency rises to 50HZ, and the output of the I/O port switch is driven by the program set by the PLC to complete the switching of the AC contactor group, so that the 1# pump frequency conversion is quickly switched to the power frequency, and the 2# pump is started by frequency conversion, if the pressure still does not reach the set pressure, the 2# pump is switched from frequency conversion to power frequency, and the 3# pump is started by frequency conversion; If the water consumption is reduced, the PLC controls the pump from the beginning to cut off, and together with the PID conditioning parameters, the system runs smoothly and maintains the pressure of the pipe network all the time.
If there is an instantaneous power failure of the power supply, the system will be shut down, and after the power supply is restored to normal, it will be manually started, and the system will be actively restored to the beginning of the initial condition. The active function of frequency conversion is the most basic function of the system, and the system actively completes the whole operation process of starting, stopping and circulating frequency conversion for multiple pumps.
Setting of device parameters
The communication parameters of the PLC, touch screen and inverter must be set correctly before communication. This system is defined as the Modbus protocol, the baud rate is 9600, the data bit is 8, there is no check, and the abort bit is 1. In addition to setting the communication parameters, the inverter also needs to enable "free parking" to maintain the motor.
PLC communication parameter setting: TWDLCAA24DRF - hardware - port - port setting, port parameter setting in the port setting; Touch screen communication parameter setting: IO Manager - ModbusRTU01 [COM1] - Modbus Equipment, double click "Modbus Equipment" to set communication parameters.
PLC control system
The system uses Schneider's TWDLCAA24DRF, the number of I/O points is 24 points, relay output, PLC programming uses Schneider PLC special programming software Twidosoft, the software provides a complete programming environment, and can be used for offline programming, online connection and debugging. In order to improve the cost performance of the whole system, the system selects the switching input and output of the programmable controller to control the start and stop of the motor, active input, regular switching, frequency conversion of the water supply pump and fault alarm, etc., and through the built-in PID of the PLC, the speed, set pressure, frequency, current, voltage and other simulated signals.
Schneider PLC's easy-to-understand programming instructions and responsive programming are provided by the Step Counter Utility Module (%SCi) that can be assigned to the action. Moving from one step to another depends on external or internal things. By imitating input and output modules TWAMM3HT as well as the built-in PID combinator, the sequential cutting pump is completed.
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