| In recent years, PLC and frequency converter technology has been widely used in various industries, especially in the industrial and residential water supply. Yan’an refinery living water supply systems operates through two 75KW motors (380V). Operators regularly observe the pressure of living water supply pipe network several times a day, to ensure 0.5MPa water pipes pressure through the method of changing the number of water pump and regulating valve opening. The disadvantage of the method is the small valve opening caused by small water consumption results in inefficiency and waste of great amount of electric power. At the same time, the pressure of the network fluctuates according to the amount of water consumption and sometimes exceeds the normal pressure which usually poses potential hazards.The overall design is to install a pressure sensor at the network export to transfer the pressure to 4-20mA current signal and sends the current signal to the pressure controller. Then the pressure controller will compare the 4-20mA current and set pressures, and sets the run speed for the pump. The frequency converter and the pressure controller send to PLC the frequency and the pressure signal. Subsequently the PLC controls the number of the pump and makes water pressure to achieve user requirements. At the same time, the manual mode is designed in order to secure the safety of water supply and to prevent the failure in automatic mode which affects the normal supply. In the manual mode, the user manually inputs a pump and makes a potentiometer send 0-10V voltage signal to frequency converter to regulate the pressure of the network.This design, if putting into use, will completely solve the issue of pressure of network export fluctuation and the waste of electric energy, and automated unattended constant-pressure water supply will become a reality, which will surely improve the reliability of the system of water supply, reduce the labor intensity, and create impressive economic benefits. |
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