| 摘要 |
PURPOSE:To detect the number of rotation of a fan with a good accuracy upon not only low-speed running but also high-speed running, by a method wherein the method of measurement of a rotating speed is changed due to whether the rotating speed is a low speed or a high speed. CONSTITUTION:A pulse period measuring means 10 measures the period of a pulse generated in accordance with the predetermined angular rotation of an AC motor 2. A rotating speed operating means 11 compares the period of pulse, measured by the means 10, with a set period. When the measured period of pulse is longer than the set period, the rotating speed operating means 11 operates the number of rotation based on the measured period of pulse. When the measured period of pulse is shorter than the set period, the rotating speed operating means 11 operates the number of rotation based on the sum of the periods of plural set pulses. |
