SV SLA-PA201, Руководство пользователя

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<Table V-2-1> Defined Parameters for FFT
Parameters Definition Equation
s
F
Sampling Frequency User Definition
span
F
Useful Frequency Range
2.56
s
span
F
F
=
N Buffer Size User Definition
L
Display Line 1 or
2.56 2.56
N N
L L
= + =
f
Δ
Frequency Resolution
s
F
f
N
Δ =
t
Δ
Sampling Interval(sec)
1
s
t
F
Δ =
T
Recording Time
or Total Time of Saved Data in Buffer
T N t
= ⋅Δ
Freq Freq
Buffer 1
Buffer 2
Buffer 3
FFT of Buffer 1 FFT of Buffer 2
[Fig. V-2-1] Instantaneous FFT results from each FFT calculation
As previously mentioned, the basic assumption of FFT analysis is that time signal has infinite
periodicity. But buffer size is so finite that energy leakage causes. So we call it “leakage error”. As
shown in [Fig. V-2-2], time signal with infinite periodicity generates just one peak in FFT results.
However, as shown in [Fig. V-2-3], time signal with finite buffer causes finite periodicity. If we
calculated FFT using this buffer, we got the broaden peak of FFT.