Iwatsu DS-8814, Operation Manual

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F-19
5.2 Hanning
A Hanning window differs from a Rectangular window in that the signal can be
analyzed without regard for waveform continuity at the front and rear of the
computation range. Precision of the frequency increases, but amplitude errors may
occur. The Hanning window is suitable for the frequency analysis of a repetitive
waveform.
YT waveform FFT waveform FFT waveform (peak is max)
5.3 Flat Top
A Flat Top window differs from a Rectangular window in that the signal can be
analyzed without regard for waveform continuity at the front and rear of the
computation range. Precision of the amplitude increases, but frequency resolution is
degraded. The Flat Top window is suitable for the amplitude analysis of a repeating
waveform.
YT waveform FFT waveform FFT waveform (peak is max)
6. F Points Selection and Result
When the memory length (Length) is Long, the number of data points (1024 or 4096) can
be selected for the FFT with F Points. Whichever number of data points is selected, the
amplitude precision will not change. However, there are the following characteristics.
1024 : Since the data for computation is small in quantity, processing can be performed at
high speed. The frequency axis range of the FFT waveform will be 1/4 that of the
case when 4096 is selected.
4096 : The processing speed slows, and the frequency axis range of the FFT waveform
becomes 4 times that of the case when 1024 is selected. Selection of 4096 data
points is effective to prevent aliasing.