YOKOGAWA ScopeCorder DL850E - Page 242

App-8
IM DL850E-01EN
RMS Spectrum
The RMS spectrum expresses the amplitudes of the linear spectrum with RMS values. It dose not contain phase
information.
The DL850E/DL850EV can determine the following spectra.
Item Expression Computation
Magnitude RS-MAG
(R
2
+I
2
)/2
Log magnitude
RS-LOGMAG 20 × log
(R
2
+I
2
)/2
Log magnitude reference (0 dB): 1 Vrms
Power Spectrum
The 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 DL850E/DL850EV can determine the following spectrums.
Item Expression Computation
Magnitude PS-MAG DC component R
2
+ I
2
AC component (R
2
+ I
2
)/2
Log magnitude PS-LOGMAG DC component 10 × log(R
2
+ I
2
)
AC component 10 × log{(R
2
+ I
2
)/2}
Log magnitude reference (0 dB): 1 Vrms
2
Power Spectrum Density
The power spectrum density expresses the power spectrum per unit frequency. It is determined by dividing
the power spectrum by the frequency resolution Δf 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 DL850E/DL850EV can determine the following spectrums.
Item Expression Computation
Magnitude PSD-MAG PS-MAG/(
Δ
f
×
k)
Log magnitude
PSD-LOGMAG 10 × log PS-MAG/(
Δ
f
×
k)
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 the square root of the summation of the power spectrums of all frequencies.
k
2 × PS0 + Σ PSi
(Vrms)Overall value =
“Rms = overall value” appears on the screen when automated measurement of waveform parameters is being
performed (MEASURE is set to ON) on the channel that has been selected for power spectrum computation (PS
or PSD) and Rms is set to ON.
However, when Window is set to Exponential, overall values are not displayed.
k
k varies as indicated below depending on the selected time window.
Time Window Type k
Rect (rectangular window) 1
Hanning (hanning window) 1.5
FlatTop (flattop window) 3.19693
Hamming (hamming window) 1.3628
Appendix