| 摘要 |
PURPOSE:To prevent the operating point of a fan from being entered into a super low-frequency sound generating area and preclude an environmental noise pollution by a method wherein a sensor detecting amount of information with respect to whirling stall is provided in a casing or a pipeline and the opening degree of a discharging damper as well as the revolving number of the fan are controlled by the output of the sensor. CONSTITUTION:Flow amount in a duct 9 is detected by a flow sensor 7 to input the output thereof into a control unit 8. At the same time, the amount of information or noise, pressure vibration, speed fluctuation and the like with respect to the whirling stall of the fan 1 is detected by the sensor 10 and the output thereof is inputted into the control unit 8. The output of the control unit 8 is inputted into the discharging damper 2 by feedback to control the opening degree of the damper 2. In this case, the discharging damper 2 is closed in such a manner that the amount of airflow is changed along a high-revolution curve H from large to small and when the operating point of the fan has arrived at the operating point A immediately before generating the super low-frequency sound, the revolving number of the fan is reduced so that the operating point of the fan is brought to the point C on a low revolution curve L. By opening the discharging damper 2 in such a manner that the amount of airflow is changed from small to large, the operating point of the fan may be prevented from being entered into the super low-frequency sound generating area D. |
