| 摘要 |
PURPOSE:To make it possible to certainly discriminate the frequency of a power source, by measuring the frequency corresponding to two times of pulse inputs given by the double frequency of the frequency of the power source. CONSTITUTION:A period (a)+(b), that is, period (c) or (d) is measured ant it is compared whether said period is received in a 50Hz data range or a 60Hz data range to discriminate power source frequencies (50/60Hz). In this case, the period (c) or (d) becomes constant regardless of the difference between the characteristics of photocouplers 2, 3. Further, when the discrimination results (50/60Hz) continuously coincid N times, for the first, time, it is determined whether the frequency of the power source is 50Hz or 60Hz. Therefore, erroneous discrimination of power source frequency due to external force is prevented. On the basis of said discrimination results, the counting of a base timer is performed by pulse input of 100Hz or 120Hz thereafter and the same control is performed regardless of the difference of power source frequency.
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