| 摘要 |
PURPOSE:To enable measurement of various input signals of a small level low in the frequency with a higher S/N ratio, by performing a spectral analysis of a correlation function with respect to a sampling data train to subtract a noise intrinsic to a measuring device from the results. CONSTITUTION:A signal magnetic flux applied to a DC skid 1 with an input coil 3 is made to overlap a signal magnetic flex of an AC oscillator 8 to be withdrawn as DC voltage value via an AC amplifier 5, a phase detector 6 and a feedback DC amplifier 7. This DC voltage is sampled with a phase detector 12 according to a frequency of an AC oscillator 14 and inputted into a modulation coil 4 through a feedback amplifier 13 to keep the magnetic flux of the DC skid 1 constant. On the other hand, a signal processor 16 calculates a correlation function about a sampling data train and subsequently, a Fourier analysis of the correlation function thus obtained is performed. A noise component intrinsic to a measuring device is subtracted from a spectral distribution obtained from the Fourier analysis to determine the spectral component of a signal.
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