| 摘要 |
PROBLEM TO BE SOLVED: To provide a method for evaluating the stability in a period of an oscillation waveform which accurately measures a fluctuation in a basis oscillation frequency independent of a selection of a time width of a window, and dealing with the fluctuation as an indicator of the stability in the period of a substantially periodic oscillation. SOLUTION: With respect to a certain time T1, time-series data of the substantially periodic oscillation waveform has the approximative period of 0.7T1-1.4T1. The time-series data belonging to the window between time t-t+T2 undergo a first FFT (Fast Fourier Transform). The time T2 is larger than the time T1. M(t) is the maximum amplitude value in the basic oscillation at a frequency spectrum obtained by the first FFT. The time-series data M(t) is obtained by sequentially shifting the window by T3 smaller than T1 to undergo a second FFT. A frequency spread coefficient DFc/Fc is the indicator as a ratio of a frequency spread width DFc of the basic oscillation at the obtained frequency spectrum to a basic frequency Fc. COPYRIGHT: (C)2008,JPO&INPIT
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