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Periodicity

Periodicity. Prepare by Ji Kim, Bokman Kim. FFT spectrum. FFT Spectrum Analyzers, such as the SR760, SR770, SR780 and SR785, take a time varying input signal, like you would see on an oscilloscope trace, and compute its frequency spectrum.

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Periodicity

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  1. Periodicity Prepare by Ji Kim, Bokman Kim

  2. FFT spectrum FFT Spectrum Analyzers, such as the SR760, SR770, SR780 and SR785, take a time varying input signal, like you would see on an oscilloscope trace, and compute its frequency spectrum. Fourier's theorem states that any waveform in the time domain can be represented by the weighted sum of sins and cosines. The FFT spectrum analyzer samples the input signal, computes the magnitude of its sine and cosine components, and displays the spectrum of these measured frequency components.

  3. Electronic Test Instrument Function generator Oscilloscope FFT (Fast Fourier Function) Spectrum SPC Gauge

  4. Formula and Data • F=C/λ • F= Frequency • C=Line speed • λ=Wave length • Wave length is given by customer (Defect Spacing) RFS Provided Data March (2009)

  5. Applied Formula • Defect spacing are given by customer. • Line speed=300FPM • Example F=(300/60)/(6.516/12) =9.208HZ T=1/(9.21)=0.108S

  6. Justify of the FFT Analyzer 1 6.14HZ Test with 24.41HZ span

  7. Justify of the FFT Analyzer 2 13.07 HZ Test with 48.82Hz span

  8. Justify of the FFT Analyzer 3 149.81HZ Test with 781.25HZ span

  9. How to Avoid the Frequency band? • V=2pR/T • V=2pRF • V=DF • D=V/F • Change Rolling Mill and Bearing. Rolling Mill Bearing

  10. Conclusion • Line speed and Wave Length to determine the affects on periodicity. • Ready to set up with FFT to Gamma Gauge. • FFT analyzer is functionally correct, Ready to test at Rolling Mill.

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