| 摘要 |
PURPOSE:To measure fundamental frequency at high accuracy even when a signal to be measured containes noise of high order by high speed Fourier transforming the input signal and finding out frequency that makes ampliture maximum by this Fourier coefficient. CONSTITUTION:An A/D converter 10 converts a signal to be measured inputted in a measuring time T into a digital signal and adds to a storage device 11, and a high speed Fourier transformer 12 calculates the Fourier coefficient and adds to a storage device 13. An arithmetic device 14 calculates the sum of square of the Fourier coefficient and adds to a storage device 15. A comparison arithmetic device 16 detects the degree (n) that makes am<2>+bm<2> maximum and adds it to an arithmetic device 17. On the other hand, a correction arithmetic device 18 to which Fourier coefficient of (m), (n) degree is added by the high speed Fourier transformer 12 determines the ratio of Fourier coefficient and finds out an error DELTAn. Then, the arithmetic device 17 adds (n) and DELTAn and displays the fundamental frequency on a display device 19. By this way, correct measurement can be effected without influenced by noise. |
