Hioki MEMORY HiCORDER 8855, Instruction Manual

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APPENDIX 21
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Appendix 3 Reference
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Input waveform
Waveform as calculated
by FFT processing
Setting points
Stored
waveform
ˆ Window processing
Fourier transform is defined as the integration from negative infinity to
positive infinity, but in actual measurement this calculation is not possible.
Therefore only a limited segment of the continuous signal is taken for
processing. This is called window processing.
The FFT algorithm assumes that the data of that limited segment are
repeated and defines the input signal using a periodic function for
determining the frequency spectrum.
Depending on the phase at the start and end of the stored waveform, there
may be a difference between the waveform as calculated by FFT processing
and the actual input waveform.
ˆ Leakage error
When the signal waveform as assumed by the FFT algorithm and the actual
waveform are different, the processing result will contain an error. This error
is called the leakage error.