| 摘要 |
PROBLEM TO BE SOLVED: To inexpensively and simply detect a failure of a fan by detecting the maximum value of the number of revolutions of a fan and the minimum value of the number of revolutions of the fan in a plurality of fans, detecting that the ratio of these minimum to maximum values becomes a prescribed value or below and outputting a signal showing the detection result. SOLUTION: A number of revolutions detecting part 3 detects the number of revolutions for each fan based on a pulse that a fan outputs and determines the average number of revolutions for a second of the number of revolutions for each fan from a fan 1 to a fan (n) in order. An arithmetic part 6 detects a minimum value and a maximum value of the number of revolutions of a fan based on the average number of revolutions and calculates the ratio. A deciding part 7 decides the size between a failure detection value based on an error of the number of revolutions of the fan which is stored in a storage part 5 and a result that the arithmetic part 6 calculates. As a result, a control part 8 outputs voltage showing the presence of a failure when a ratio that the arithmetic part 6 calculates a signal according to the decision result is smaller than the failure detection value. |
