Constant pressure variable frequency water supply system is mainly composed of pressure sensor, liquid level switch, frequency converter governor, PLC controller, water pump unit and low-voltage electrical equipment. The control tasks of the system are: according to the change of water pressure, control the speed regulation of water pump operation, realize the water pressure stability, realize the soft start / soft stop of water pump motor, automatic switching of power frequency / frequency conversion of water pump, cumulative timing and pump countdown of water pump operation, and system fault protection. According to different requirements of water consumption scale, site size, site environment, system reliability requirements and investment scale, the following control schemes are analyzed and compared<br>
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