First, adjust the manual valve to a constant opening so that the speed of the water is only related to the working condition of the pump and leave it as it is. By adjusting the water discharge switch to a constant opening and connecting the liquid level system and plc system by the method shown in Fig. 2-12 above, a simple liquid level control system that adjusts water intake with a pump is configured. In addition, the liquid level feedback signal of the liquid level measuring device is acquired and controlled as a pid.