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App-19
IM 701210-06E
Appendix
App
Power Spectrum
Power spectrum expresses the power (squared value) of each frequency component
included in the measured signal. It is determined by taking the product of the linear
spectrum and its complex conjugate. It does not contain phase information.
The following spectrums can be determined with this instrument.
Item
Equation
Computation
Magnitude
PS-MAG
(R
2
+I
2
)/2
Log magnitude
PS-LOGMAG
10*log(R
2
+I
2
)/2
Log magnitude reference (0 dB): 1 Vrms
2
Power Spectrum Density
Power spectrum density expresses the power spectrum per unit frequency. It is
determined by dividing the power spectrum by the frequency resolution
∆
f found during
the analysis of the power spectrum. The computation varies depending on the window
function.
Power spectrum density is used to compare power spectrums analyzed at different
frequency bands. However, it is not necessary for signals having a line spectrum such
as sine waves.
The following spectrums can be determined with this instrument.
Item
Equation
Computation
Magnitude
PSD-MAG
PS-MAG/
∆
f (for rectangular window)
PS-MAG/1.5
∆
f (for Hanning window)
Log magnitude
PSD-LOGMAG
10
×
logPS-MAG/
∆
f (for rectangular window)
10
×
logPS-MAG/1.5
∆
f (for Hanning window)
Log magnitude reference (0 dB): 1 Vrms
2
Overall Value
The overall value is the total RMS value determined from the frequency spectrum
included in the signal. The overall value is determined by summing the power spectrum
of all frequencies and then taking the square root.
k
2
×
PS
0
+
Σ
PS
i
(Vrms)
Overall Value =
The k value varies depending on the selected time window as follows:
Time Window Type
k
Rect (Rectangular)
1
Hanning
1.5
Flattop
3.19693
If the channels (Math1 to Math8) on which power spectrum computation (PS or PSD*) is
selected are in the middle of the automated measurement of waveform parameters
(MEASURE: ON) and Rms is ON, the screen shows "Rms = overall value."
However, the overall value is not displayed when the time window is set to Exponential.
Appendix 5 User-Defined Computation