| 摘要 |
A method and sensor for sensing the rate of rotation of a fan in order to monitor and detect a variation in the rate of air flowing through the fan, such as to indicate a restriction in the air flow path or failure of the fan. A Hall-effect transistor (HET) is placed in the fixed field of a magnet adjacent the path of a preferably ferrous moving element capable of changing the magnetic field coupled to the HET. As the ferrous element passes the magnet and HET, the strength or alignment of the field changes sufficiently to produce an output pulse from the HET. The pulse rate decreases with slowing of the fan such as may occur with a restriction or blockage in the air flow path.
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