| 摘要 |
PROBLEM TO BE SOLVED: To solve such a problem that when a pulse width of an output pulse of a monostable multivibrator fluctuates due to a temperature characteristic, reduction of revolution speed is erroneously detected regardless of not reducing of the revolution speed, in a circuit detecting the reduction of the revolution speed of a blower by using one monostable multivibrator. SOLUTION: The two monostable multivibrators 5, 11 for inputting a digital signal 4 of the blower 2 are provided. Respective output signals 10, 16 of the respective monostable multivibrators 5, 11 are inputted to a flip-flop 17 operating as a revolution speed detecting circuit. Though pulse widths of outputs of the multivibrators 5, 11 fluctuate corresponding to an ambient temperature, temperature compensation in the fluctuation of the output pulse widths of the multivibrators 5, 11 can be preformed by using each of the output signals 10, 16 as a clock for detecting revolution speed. |
