The communication method is selected to control the inverter to complete the system control function, and the user can control the operation of the system through the touch screen. Through the pressure transmitter installed on the outlet pipe network, the outlet pressure signal is turned into a 4-20mA or 0-10V standard signal 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, and then adjusts the speed of the pump to reach the constant pressure water supply.
1. Architecture
The variable frequency constant pressure water supply system is mainly composed of PLC, frequency converter, touch screen, pressure transmitter, power and control circuit and pump set. Users can understand and 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 conversion switch. Through the pressure transmitter installed on the outlet pipe network, the outlet pressure signal is turned into a 4-20mA or 0-10V standard signal 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, and then adjusts 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 harmoniously put the number of pump motors into operation, and complete the switching of the 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 is always stable, so as to achieve the purpose of constant pressure water supply.
2. Operating principle
The system has two operating methods: manual and automatic. When the manual method is used, the pump can be controlled by the touch screen or the start and stop buttons on the control cabinet, and the start and stop of the 1#-3# pump can be controlled separately according to the demand. When it is running automatically, 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 does not work, 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 control starts to cut the pump from the first, and together with the PID conditioning parameters, the system runs smoothly and the pressure of the pipe network is maintained at all times.
If there is an instantaneous power failure, the system will be shut down, and after the power supply is restored to normal, it will be manually started, and the system will automatically return to the initial state and start operation. The automatic function of frequency conversion is the most basic function of the system, and the system automatically completes the whole operation process of starting, stopping and circulating frequency conversion of multiple pumps.
3. Setting of equipment parameters
The communication parameters of the PLC, touch screen and inverter must be set correctly before communication. This system is defined as Modbu
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