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How does the fan achieve accurate speed regulation in a laminar flow hood?
How does the fan achieve accurate speed regulation in a laminar flow hood?In the laminar flow hood, the fan achieves accurate speed regulation mainly through the following ways:First, use frequency converter speed regulation Working principle A frequency converter is a device that can change the power frequency of a motor. The speed of the motor is proportional to the frequency of the power supply, and by changing the power supply frequency of the input fan motor, the precise control of the fan speed can be achieved. For example, at the power frequency of 50Hz, the fan runs at the rated speed. When the frequency converter reduces the frequency to 30Hz, the fan speed will be reduced accordingly, thus changing the air volume. Control mode Frequency converters can usually be controlled in a variety of ways. A common way is analog control, that is, through an external analog signal (such as 0-10V or 4-20mA signal) to control the output frequency of the inverter. In the control system of the laminar flow hood, the wind speed signal detected by the wind speed sensor can be converted into an analog signal and input to the inverter. If the detected wind speed is higher than the set value, the analog signal is reduced, so that the inverter reduces the output frequency, thereby reducing the fan speed, and vice versa, the speed is increased. Another way is digital communication control. Through the communication interface such as RS-485, the controller (such as PLC or special control system) of the laminar flow hood is connected to the frequency converter. The controller can accurately adjust the speed of the fan by sending instructions to the inverter through the digital signal according to the pre-set program or according to the real-time monitoring data. In this way, more complex control strategies can be implemented, such as setting different fan speed curves according to different working modes (such as cleaning mode, and working mode). Second, the use of speed regulation motor DC speed regulating motor The DC speed regulating motor adjusts the speed by changing the armature voltage or the excitation current. In a laminar flow hood, the linear change of speed can be realized by adjusting the armature voltage of the DC motor. For example, the thyristor rectifier device is used to control the armature voltage of the DC motor. When it is necessary to reduce the fan speed, the conduction Angle of the thyristor is reduced, the armature voltage is reduced, and the motor speed is reduced. This speed regulation method has high precision and can achieve smooth speed regulation in a wide speed range. Ac speed regulating motor (such as variable frequency speed regulating motor, electromagnetic speed regulating motor) The principle of variable frequency speed regulation motor is similar to the above inverter speed regulation, but the motor itself is specially designed for variable frequency speed regulation, which can better adapt to frequency changes and reduce motor loss and heating. The electromagnetic speed regulating motor adjusts the output speed by changing the excitation current of the electromagnetic clutch. It has a main motor and an electromagnetic clutch, the main motor is running at constant speed, and the output shaft of the electromagnetic clutch is connected with the fan. When the excitation current of the electromagnetic clutch is changed, the slip rate between the magnetic pole of the clutch and the armature changes, to realize the speed regulation of the fan. This speed regulation method is simple and reliable, but the speed regulation range is relatively narrow. Third, a speed regulation strategy based on the intelligent control system Closed-loop control The intelligent control system of the laminar flow hood can adopt a closed-loop control mode to accurately speed regulation. It monitors wind speed in real-time by installing wind speed sensors in the outlet or working area. The sensor feeds the wind speed signal to the controller, and the controller compares the feedback signal with the set wind speed value. If there is a deviation between the two, the controller will calculate the fan speed that needs to be adjusted according to the pre-set control algorithm (such as the PID control algorithm), and then adjust the speed through the frequency converter or speed regulating motor. The proportion (P) item in the PID control algorithm can quickly adjust the speed according to the size of the deviation, the integral (I) item can eliminate the steady-state error of the system, and the differential (D) item can predict the changing trend of the deviation and adjust it in advance so that the fan speed can quickly and accurately reach and stabilize at the set value. Multi-parameter cooperative control In addition to wind speed, the intelligent control system can also consider other parameters for fan speed regulation. For example, in the working process of the laminar flow hood, the fan speed is adjusted comprehensively according to the air cleanliness (detected by the dust particle counter), temperature (detected by the temperature sensor), and humidity (detected by the humidity sensor). If the air cleanliness decreases, it may be necessary to increase the fan speed to speed up air filtration; If the temperature is too high, under the premise of ensuring the laminar flow state, the fan speed is appropriately reduced to reduce heat generation, and other cooling measures are combined to achieve accurate control of the laminar flow hood environment. |
