YOKOGAWA WT3002E User Manual page 183

11.1 FFT Function
11-2
FFT Measurement Examples (Conceptual Diagrams)
• Input signal:
• Number of FFT points: 200 k (FFT measurement time: 1 s)
• Left end of the graph: dc, right end: 100 Hz
Rectangular
Sine wave
t
Rectangular window:
Hanning window:
Flattop window:
• Number of FFT Points and Frequency Resolution
The frequency range of the FFT is DC to 100 kHz. FFT is performed on 20000 points
or 200000 points of measured data, and the result is displayed using 10001 data
points or 100001 data points, respectively.
52.2-Hz sine wave
Hanning
Window Integral
Rectangular
T
window
T
T
Hanning window
T
T
Flattop window
T
W(t) = u(t)–u(t–T)
W(t) = 0.5–0.5cos(2π
W(t) = {0.54–0.46 cos(2π
Flattop
Power spectrum
U(t): Step function
t
)
T
t sin{2π(1–2t/T)}
)}
T
2π(1–2t/T)
IM WT3001E-51EN