Power Spectrum Measurements

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Changing Power Spectrum Amplitude Units

The strength of the frequency component can be displayed in either engineering units or relative magnitude in the form of decibels (dB). The default scale of decibels (dB), assuming the scale has not been changed by adjusting Y-axis scaling as described, is derived from the following equation:


dB = 20 × log10 (32768 × MAG / FS)


where MAG is the magnitude in engineering units of the frequency component and FS is the full scale value of the Y-T waveform from which the transform was derived. For example: if the full scale value was 100 mmHg and the magnitude at a given frequency component is 39.78, the dB value would be 82.30. After the power spectrum is plotted, the strength of the frequency component can be toggled from engineering units to relative magnitude (or vice versa) by:


  In the Transform menu click on Mag Engr Units.


   Choosing Transform Mag Engr Units (ALT, T, M).


This causes the display in the analysis reporting area to change as follows: