2-42
IM 701240-01E
FFT is performed on 1000, 2000, 5000, 10000, 20000, 50000, or 100000 points of
measured data. The data is converted to half the specified number of points and
displayed.
T
T
T
T
t
Sine wave
Window
Integral
Power spectrum
Rectangular
window
Hanning window
Rectangular window
Hanning window
Flat top window
: W(t) = u(t) – u(t – T)
U(t): Step function
: W(t) = 0.5 – 0.5 cos(2
π
)
: W(t) =
{
0.54 – 0.46 cos(2
π
)}
T
T
Flat top window
t
T
t
T
sin{2
π
(1
–
2t/T)}
2
π
(1
–
2t/T)
FFT Function
Given that the complex function resulting after the FFT is G = R + jI, the power spectrum
can be expressed as follows:
Power spectrum = 10 log
R: Real Part, I: Imaginary Part
Reference value (0 dB) of the logarithmic magnitude (Log mag): 1 Vrms
2
R
2 +
I
2
2
( )
Phase Shift «For procedures, see section 10.4.»
You can shift the phase of CH1 to CH16 and Math1 to Math7 waveforms and display the
resultant waveforms or perform computation using the phase-shifted data.
Scaling of Computed Waveforms «For procedures, see chapter 10.»
Normally, the SL1400 performs auto scaling when computed waveforms are displayed.
However, you can also select manual scaling. When auto scaling, the upper and lower
limits suitable for displaying the waveform are determined from the first computed
waveform. If you select manual scaling, you can arbitrarily set the upper and lower limits
of the computed waveform display.
2.6 Waveform Computation
