Abstract: To improve and stabilize the quality of beer within its shelf life, the key factors are accurately controlling the amount of silica gel added and the reaction time between silica gel and beer. This article describes the composition and principle of an automatic silica gel addition speed control system and introduces a method for controlling the automatic addition of silica gel using a Siemens MM420 frequency converter and PLC. Keywords : frequency converter, speed control system, programmable logic controller In beer production, to improve and stabilize the quality of beer within its shelf life, the key factors are accurately controlling the amount of silica gel added and the reaction time between silica gel and beer. The silica gel addition process is shown in Figure 1. Silica gel is added to the pipeline from the fermentation tank to the filtration tank. The reaction time between silica gel and beer depends on the liquid level in the filtration tank. If operated manually, it is greatly affected by external human factors, and the addition of silica gel cannot maintain a good ratio with the beer flow rate, making it difficult to guarantee product quality. This also increases the labor intensity for workers and easily leads to waste. Therefore, a variable frequency speed control system composed of Siemens MM420 frequency converters is introduced to automatically control the addition of silica gel. 1. Control System Composition The system principle block diagram is shown in Figure 2. The system works as follows: The differential pressure transmitter measures the liquid level in the filtration tank, displays it on the screen, and compares it with the original set value. The resulting deviation is processed by the intelligent PID control in the regulator and then sent to frequency converter #1 (multiple frequency converters can be used in parallel if the control load is large) and frequency converter #2 respectively. These two frequency converters adjust the main pump motor and the addition motor accordingly based on the magnitude of the input signal and their respective adjustment rules. The entire control system uses PLC control: when the differential pressure transmitter detects that the liquid level in the filter tank has reached the set value, the PLC prompts or allows the filter tank to supply wine to the filter; when the amount of wine in the fermentation tank is relatively low and a large amount of foam begins to appear in the wine, the PLC stops the silica gel dosing pump motor based on the liquid level in the filter tank and the operating status of the frequency converter, and allows the main pump motor to run at low speed or stop running. [b][align=center]For details, please click: Application of Siemens Frequency Converters and PLCs in Automatic Silica Gel Dosing Speed ​​Control System[/align][/b]