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2-48
IM 701210-05E
Exponential Window
The exponential window eliminates noise components from the signal. It can be
selected only when the user-defined computation option is installed. It is effective
against frequency response test signals generated through impulse excitation.
For details on each window, see page app-21.
FFT is performed on 1000, 2000, 5000, 10000, 20000, 50000 or 100000 points of measured
data. The data is converted to half the specified number of points and displayed.
T
T
T
T
t
Sine wave
Window
Integral
Power spectrum
Rectangular
window
Hanning window
Rectangular window
Hanning window
Flattop window
: W(t)=u(t)–u(t–T) U(t) : Step function
: W(t)=0.5–0.5cos(2
π )
: W(t)={0.54–0.46 cos(2
π
)}
T
T
Flattop window
t
T
t
T
sin{2
π
(1–2t/T)}
2
π
(1–2t/T)
FFT Function
Given that the complex function resulting after the FFT is G = R + jI, the power spectrum
can be expressed as follows.
Power spectrum=10 log
R: Real Part, I: Imaginary Part
Reference value (0 dB) of the logarithmic magnitude (Log mag): 1 Vrms
2
R
2
+I
2
2
( )
Phase Shift (Phase Mode) <Section 10.4>
You can shift the phase of CH1 to CH16, Math1 to Math7, and DSP1 to DSP6 (optional)
waveforms and display the resultant waveforms or perform computation using the phase-
shifted data.
User-Defined Computation (Optional) <Section 10.5>
You can define computing equations by combining the following operators:
+, -, *, /, SHIFT (phase shift), ABS (absolute value), SQRT (square root), LOG (logarithm),
EXP (exponent), NEG (negation), SIN (sine), COS (cosine), TAN (tangent), ATAN
(arctangent), PH (phase), DIF (differentiation), DDIF (2nd order differentiation), INTG
(integral), IINTG (double integral), BIN (binarization), P2 (square), P3 (cube), F1
(
C1
2
+ C2
2
), F2 (
C1
2
– C2
2
), FV (inverse of the pulse width PHWW), PWHH (pulse width),
PWHL (pulse width), PWLH (pulse width), PWLL (pulse width), PWXX (pulse width),
DUTYH (duty ratio), DUTYL (duty ratio), FILT1 (digital filter), FILT2 (digital filter), HLBT
(hilbert), MEAN (moving average), LS- (linear spectrum), PS- (power spectrum), PSD-
(power spectrum density), CS- (cross spectrum), TF- (transfer function), CH- (coherence
function), variable (T), and constants (K1 to K8). In addition, you can average or compute
the peak value on the computed data. The following four operations are available.
Linear Averaging
The values are summed linearly the number of average counts (the number of
acquisitions, 2 to 128, 2
n
steps) and divided by the average count. The resultant
waveform is displayed. For the equation, see “Acquisition Mode” on page 2-31.
2.6 Waveform Computation