How to

Calculate Auto RMS Spectrum using ASI Datalab

Auto RMS Spectrum

Auto RMS spectrum is tool to convert time domain data to frequency domain, where amplitude is represented as RMS value of that frequency. It uses Fourier transform and averages of overlapped sections of the input data.

To Calculate RMS Spectrum in ASI datalab following parameters are required as Input:

  • Required Frequency Spacing (Hz)
  • Data Window (Default: Hann)
    • Available Window Options
      •  Parzen
      • Bartlett
      • Hanning
      • Hamming
      • Kaiser
      • Flat Top
      • Blackman-Harris
  • Percentage Overlap (Default: 75%)
    • Available: 0%, 25%, 50% and 75%
  • Analysis Mode
    • Available Modes
      • Spectrum Level
  • Use nearest spacing (Default: No)

Frequency Spacing

The required spacing, Δrequired, between adjacent spectrum output points is in Hz. Often Δrequired is different from the actual spacing, Δactual. This happens because the value of actual spacing depends on the input data spacing, Δinput and the FFT size (N). Δactual is calculated as follows The FFT size, N is always a power of 2. FFT size is selected by finding p such that If “Use Nearest Spacing” is selected to be No, then the module selects FFT size, N = 2p. If it is Yes then either 2p or 2p-1 is selected depending on which of the two values of Δactual are nearest to Δrequired.

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