| 摘要 |
The inventors have revealed that the actual rotation speed of the rotor in a fan structured as a centrifugal fan exceeds the designated rotation speed if the ventilation opening of the centrifugal fan is occluded. If a larger amount of dust accumulates at the ventilation opening of the centrifugal fan, for example, the actual rotation speed of the rotor in the centrifugal fan exceeds the designated rotation speed by a predetermined deviation. The accumulation of dust at the ventilation opening can in this manner be observed in a facilitated manner. The occlusion of the ventilation opening can thus be detected.
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