| 摘要 |
PROBLEM TO BE SOLVED: To stably and speedily detect the frequency of an AC signal, even when DC components and harmonic components are superposed by creating an AC signal following the phase of the fundamental wave component of the AC signal, and detecting a frequency from the signal. SOLUTION: The voltage of an AC power supply 503 is detected by a voltage detector 501, and the amplitude is adjusted by a gain adjuster 502. An adjusted AC voltage Vi is inputted to a fundamental wave operation means 100 for constituting a frequency detector 500, and a signal Va following the fundamental wave component of the AC signal Vi and a signal Vb whose phase differs by 90 degrees are outputted. A frequency operation means 200 calculates a frequency fb of the AC signal Vi, by using both the AC signals Va and Vb and the frequency detector 500 outputs the frequency fb. Since the frequency fb is calculated from an AC signal which followed the fundamental wave of the input AC signal Vi, the frequency of the fundamental wave can be stably calculated, without being affected by the harmonic and DC components contained in the input AC signal Vi of the frequency detector 500.
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