| 摘要 |
PURPOSE:To simplify circuitry by detecting the time width of the unit time signal frequency-dividing the frequency of a commercial power source by counting reference oscillation signals and switching the frequency division value of the frequency of the commercial power source by the magnitude of the value of this counter. CONSTITUTION:A counter 28 measures the interval of the two continuous unit time signals from a 1/60 minute frequency dividing circuit 12 or 1/50 minute frequency dividing circuit 14 by counting the number of the reference pulse signals per every 5 m second. For example, the interval of the unit time signals from the circuit 14 is not exactly one second and is 1/60X50=0.83 sec and the count value of the counter 28 is 168 when a switch SW is connected to the 1/50 minute frequency dividing counter 14 side and the commercial power source of 60 Hz is impressed. A 60 Hz/60 Hz control circuit 30, therefore, switches the switch SW to the 1/60 minute frequency dividing circuit 12 side. The need for a 1/200 minute frequency dividing circuit for deciding 50/60 Hz is eliminated in this way. |
