7.13.1. Selecting an FFT Window
The FFT feature provides four windows. Each is a trade-off between frequency resolution and magnitude accuracy.
What you want to measure and your source signal characteristics help determine which window to use. Use the
following guidelines to select the best window.
This is the best type of window for resolving frequencies that
are very close to the same value but worst for accurately
measuring the amplitude of those frequencies. It is the best
type for measuring the frequency spectrum of nonrepetitive
signals and measuring frequency components near DC.
Use rectangle for measuring transients or bursts where the
signal level before and after the event are nearly equal. Also,
use this window for equal-amplitude sine waves with
frequencies that are very close and for broadband random
noise with a relatively slow varying spectrum.
This is a very good window for resolving frequencies that are
very close to the same value with somewhat improved
amplitude accuracy over the rectangle window. It has a slightly
better frequency resolution than the Hanning.
Use Hamming for measuring sine, periodic and narrow band
random noise. This window works on transients or bursts where
the signal levels before and after the event are significantly
different.
This is a very good window for measuring amplitude accuracy
but less so for resolving frequencies.
Use Hanning for measuring sine, periodic and narrow band
random noise. This window works on transients or bursts where
the signal levels before and after the event are significantly
different.
This is the best window for measuring the amplitude of
frequencies but worst at resolving frequencies.
Use Blackman-Harris for measuring predominantly single
frequency waveforms to look for higher order harmonics.
Fig. 54, 55, 56, 57 shows four kinds of window function referring to sine wave of 1 kHz.
Fig 54: Rectangle window
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