| 摘要 |
PROBLEM TO BE SOLVED: To correctly measure harmonic waves to a high order at an arbitrary time with a simple circuit configuration by sampling an input signal at a predetermined fixed frequency, obtaining number of sampling for a plurality of cycles by rounding, operating discrete Fourier transforming(DFT) of its data and measuring harmonic wave components. SOLUTION: A frequency of a fundamental wave of a input signal is measured, and sampled by a predetermined fixed frequency. A sampling number N used for its measurement is, for example, four cycles of the input signal. Then, a sampling point near a zero-crossing position of two sampling points sandwiching a zero-crossing position of a fourth cycle is used as an N-th point. Thus, N-th sampling point is decided by a rounding method to minimize an error. Thus, the harmonic wave components can be measured based on the DFT calculation based on N pieces of the obtained sampling data.
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