Provided is a liquid level
control system. A closed-loop
system composed of a controller, a
pressure sensor, an A / D converter, a control output, an MM420 frequency converter, and a water pump driven by a direct-current brushless motor is used as the control core of the liquid level
control system. The liquid level
control system further comprises a photoelectric
coupling circuit, an I / V conversion circuit, a
voltage matching circuit, a filter circuit and the like. In order to realize constant-liquid-level
water supply, first,
water pressure information of a water tank is periodically acquired through a
liquid pressure sensor arranged in the water tank, the
water pressure information is converted into a standard
signal within an amplitude range, and the standard
signal is input to a DSP for AD conversion, filtering and scale transform so as to convert the pressure information into a digital pressure Hf. The DSP compares the actual pressure value of the water tank with a set pressure value to form a deviation control quantity, and an output PWM waveform
signal is controlled according to the law of a
PID control algorithm. The output frequency of the MM420 frequency converter is changed by changing the duty ratio of the PWM waveform signal so as to change the speed of the water pump, change the pumping rate of the water tank and maintain the stability of the
water level of the water tank.