With the continuous improvement of people's requirements for water supply quality and drinking water quality, the frequency conversion constant pressure water supply method came into being. It not only solves the problem of secondary pollution of water quality brought by the old-fashioned roof tank water supply method, but also solves the operation mode of the water pump. The adjustment and the outlet valve adjust the water pressure and water pressure of the water supply. A large amount of energy is wasted due to the consumption of the outlet valve. It also plays a good role in protecting the pump and effectively saving the consumption of electric energy. Frequency conversion constant pressure water supply system is now widely used in many fields such as urban water pipe network system, residential fire fighting water system, building central air conditioning cooling circulating water system, industrial equipment flushing system and so on.

The community frequency conversion constant pressure water supply system is composed of PLC, frequency converter, air pressure tank, centrifugal pump and pressure transmitter. The work process is to use the pressure sensor installed in the pipe network to change the water pressure in the pipe network system due to the change in water consumption. The pressure signal is fed back to the PLC in time, and after the PID is compared with the set pressure, the frequency conversion output command is given to change the running speed of the pump so that the water pressure of the pipe network is consistent with the control pressure.

Working principle

When the pneumatic tank cannot meet the water supply requirements, the three water pumps will work with frequency conversion, and the working principle is as follows:

First put the water pump M1 into frequency conversion operation. If the pressure of the pipe network cannot be stabilized, the water pump M1 in the original frequency conversion state is put into power frequency, and M2 is operated by frequency conversion to ensure the stable water supply of the pipe network. The two water pumps are still unable to meet the pressure stability of the pipe network. The standby pump M3 is put into variable frequency operation M1, M2 power frequency operation.

When the water volume decreases, the frequency lower limit signal of the inverter appears, stop the current inverter pump, and change the previous one to inverter operation at the same time. If the above two signals still exist, the PLC repeats the above work.

The system diagram is as follows:

PLC configuration

PLC uses NA200 series CPU201-2002 and DOM201-0802. CPU201-2002 comes with 8 digital inputs, 6 digital outputs, 4 analog inputs, and 2 analog outputs. Two built-in communication ports can communicate with text display and inverter respectively.

The point table is as follows:

PLC address function definition

%I0001 Start the pneumatic tank water supply

%I0002 Manually control water pump M1 frequency conversion work

%I0003 manual control water pump M1 power frequency work

%I0004 Manual control water pump M2 frequency conversion work

%I0005 Manual control of pump M2 power frequency work

%I0006 Manually control water pump M3 frequency conversion work

%Q0001 Open the valve and use the pneumatic tank to supply water

%Q0002 start the inverter

%Q0003 water pump M1 frequency conversion work

%Q0004 pump M1 power frequency work

%Q0005 water pump M2 frequency conversion work

%Q0006 pump M2 power frequency work

%Q0007 water pump M3 frequency conversion work

%Q0008 Start small water pump M4

%MW0001 pipe network pressure

%MW0003 inverter output frequency

Procedure design

NA200Pro software is IEC61131-3 programming, debugging and running software for NA200PLC. NA200Pro includes editors, compilers, debuggers, simulators and graphical user interface tools. It mainly completes hardware configuration, measurement point configuration, software programming, simulation, debugging and downloading.

NA200Pro provides a series of complete functions to achieve higher productivity and better software collaboration capabilities. NA200Pro software can ensure the optimization of customers' software investment, reduce training costs, and provide unmatched potential in development and compatibility from multiple aspects such as reducing development costs and optimizing operations.

Summary

NA200's excellent analog input and output processing capabilities and its own PID function ensure the reliability and stability of the constant pressure water supply system. It also indicates that the domestic PLC has a bright future in the water supply industry.