| 摘要 |
PURPOSE:To make it possible to neglect all the momentary breakages within a given period of time, by switching from a voltage of a reference voltage terminal to a second reference voltage termial at the time when a given period of time has passed after an input voltage crossed the reference voltage. CONSTITUTION:When an input signal level is normal, an input voltage is higher than a reference voltage, and a voltage comparing circuit 1 charges a capacitor C1 through a diode RC1 and a saturation voltage of an output of a voltage comparing unit 2 is fed back to a reference voltage terminal of the voltage comparing circuit 1. When the input signal level became lower than a given value, the voltage comparing circuit 1 is inverted to charge the capacitor C1 negatively through a diode RC2 and a resistance R4. When a given period of time elapsed, the input voltage of the voltage comparing circuit 2 becomes lower than a given value, and the voltage comparing circuit 2 is inverted to activate an alarm device. By doing so, when the input signal level returned to normal within a given period to time, level drop is neglected and it becomes lower than a given value, and the alarm device is activated only when a given period of time elapsed. |
