13-3
IM DL350-01EN
Detail Settings (Detail Setup)
Number of FFT Points (Points)
You can set the number of points from the start of computation on the T-Y waveform to one of the options below.
1k, 2k, 5k, 10k, 20k, 50k, 100k
Window Function (Window)
You can select the window function from the following options.
Rect (Rectangular window)
The rectangular window is suited to transient signals, such as impulse waves, which attenuate completely within
the time window.
Hanning (Hanning window)
The Hanning window encourages continuity of the signal by gradually attenuating the parts of the signal located
near the ends of the time window down to the 0 level. Hence, it is suited to continuous signals. The Hanning
window has a higher frequency resolution than the flattop window.
FlatTop (Flattop window)
The Hanning window encourages continuity of the signal by gradually attenuating the parts of the signal located
near the ends of the time window down to the 0 level. Hence, it is suited to continuous signals. The flattop
window has a higher spectral level accuracy than the flattop window.
Hamming (Hamming window)
In the Hanning window, the values at the ends become 0 and the signal components there do not affect the
spectrum. The Hamming window is a corrected Hanning window. Its characteristics are similar to those of the
Hanning window, but the frequency resolution of its main beam is greater than that of the Hanning window. The
Hamming window is suited for dividing close signals.
T
T
T
T
t
Sine wave
Time windows
Integral
Power spectrum
Rectangular
Hanning
T
T
Hamming
Rectangular
Hanning
Flat top
Hamming
: W(t)
=
u(t)
–
u(t
–
T)
u(t):
Step function
: W(t)
=
0.5
–
0.5cos( 2π )
: W(t)
= {
0.54
–
0.46 cos( 2π )}
: W(t)
=
0.54
–
0.46cos(2π )
T
T
Flat top window
t
T
t
T
t
T
sin{2π(1
–
2t/T)}
2π(1
–
2t/T)
13 FFT
