The CX-B series variable frequency constant pressure water supply automatic control device has the following control functions: (1) It is equipped with a manual/automatic switching circuit. When switching to the automatic position, the system can automatically adjust the speed of the variable frequency pump and start or stop the backup pump according to the change in outlet pressure to maintain a constant outlet pressure. When the variable frequency control circuit malfunctions, it can be switched to the manual position, allowing the water pump to operate directly at power frequency to ensure normal water supply; (2) Able to set 1-9 water supply time periods within 1 day, with different water supply times for each day of the week; (3) Use PLC to control the full cycle soft start of the water pump (including the backup pump), periodically and automatically switch to use, in order to ensure that the service life of the water pump is basically consistent; (4) When the underground water storage tank is short of water, the water intake pump will automatically shut down for protection, and the make-up pump will automatically start to replenish water. After the water is fully stored, the make-up pump will automatically stop, and the water level in the storage tank will be displayed in digital form; (5) Fault display and alarm, with electrical protection functions such as phase loss, short circuit, overheating, overload, overvoltage, undervoltage, leakage, and instantaneous power outage protection