Hi

I need help let me know how to convert the data Hz nd the Power Spectrum Density to Grms (Graviti root mean square). This data was capture using my spectrum analyzer using a tri-axial accelerometer for my vibration HASS measurement. Hopefully someone can provide me a template in excel how to auto calculate these data to a GRMS one digit number. Thx

 

 

How to do it in Excel (works for non-uniform bin widths)

Assume your sheet looks like the screenshot:

• A: Frequency_Hz

• B: PSD_X (g²/Hz)

• C:_PSD_Y (g²/Hz)

• D:_PSD_Z (g²/Hz)

Add helper columns:

• E (Δf): bin width

  • In E3: =A3-A2 → copy down

• F (area_X): trapezoid area for X

  • In F3: =0.5*(B3+B2)*E3 → copy down

• G (area_Y): trapezoid area for Y

  • In G3: =0.5*(C3+C2)*E3 → copy down

• H (area_Z): trapezoid area for Z

  • In H3: =0.5*(D3+D2)*E3 → copy down

At the bottom (replace LASTROW with your last data row):

• X-axis grms:
  =SQRT(SUM(F3:F_LASTROW))

• Y-axis grms:
  =SQRT(SUM(G3:G_LASTROW))

• Z-axis grms:
  =SQRT(SUM(H3:H_LASTROW))

• Overall tri-axial GRMS: (vector RMS)
  =SQRT( X_grms^2 + Y_grms^2 + Z_grms^2 )

• Round to one decimal place (if you want a single “one-digit” figure):
  =ROUND( Overall_GRMS , 1 )

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Notes 

• Your PSD columns must be linear g²/Hz, not dB. If they’re in dB:
  convert first with PSD_linear = 10^(PSD_dB/10).

• If your analyzer exported ASD (g/√Hz) instead of PSD, square it first to get g²/Hz, then use the same steps.

• Only bins inside your band of interest should be included in the sum.

• GRMS is in g. If you need m/s² RMS, multiply by 9.80665.

That’s it—drop those formulas in and you’ll get GRMS per axis and overall.