SPM leonova emerald - Page 137

E
Vibration measurement E:15
1
1
Window
To compensate for the leakage effect introduced
by the FFT process, a window function is usually
applied. The user should choose the appropriate
window(1)functionforthespecificapplication.If
the windowing is not applied correctly, errors may
be introduced in the FFT effecting amplitude,
frequency or even the overall shape of the
spectrum.
- Rectangle.TheRectangle(None,Uniform)
window is the one to choose for transient
signals. The Rectangle window has the best
frequency resolution but poor amplitude
accuracy and high spectral leakage.
- Hanning/Hamming. The Hanning and Hamming
windows are best for random signals. These
windows have good frequency resolution and
also rather fair amplitude accuracy. Since the
Hanning window also has somewhat lower
spectral leakage, this window is usually the one
to prefer.
- Flat-top. The Flat-top window should be
applied on sinusoidal signals. This window
has the best amplitude accuracy, but poor
frequency resolution.
As general advice, use:
- Hanningwindowforfrequencyaccuracy(thisis
themostcommonwindowtouse).
- Rectangle window only on transient signals.
- Flat-top window for amplitude accuracy.