41
Freq
[Fig. V-2-2] Ideal FFT
Freq
[Fig. V-2-3] Actual FFT
2. 1 Windowing
We must use windowing function to solve leakage error. The procedure shown in [Fig. V-2-4] is the
windowed time signal which is original time multiplied by windowing function. The figure (b) is
shown the finite periodicity of time signal that is recognized in FFT algorithms, but figure (d)
represents the infinite periodicity of time signal by multiplying original time signal and windowing
function. Therefore, a windowed time signal has not leakage error.
[Fig. V-2-4] Windowing Procedure
Windowing is multiplied time signal and the coefficients of window which has number
N
. Here is
the equation below :
( )
( )
( )
w
x i
w i
x i
=
×
,
0
1
i
N
≤ ≤ −
<Eq.
V-2-2>
Summary of Contents for SLA-PA201
Page 64: ...64 Appendix 1 The Theory for calculating RMS by ISO2631 and ISO8041 ...
Page 67: ...67 Appendix 2 Frequency Response of Filter in the Vibration Level Meter ...
Page 75: ...75 Appendix 3 Theory of WBCombined Filter and Frequency Response ISO6954 Filter ...
Page 79: ...79 Fig 2 Lowpass Filter with 100Hz Cutoff Fig 3 a v transition Frequency Response ...
Page 88: ...88 Fig 12 Error between theoretical value and measured value ...