GRAPHTEC WR300 - Page 86

4-6
FFT Mode
(8) Function .................... The analysis function can be specified as Y-T, Linear spectrum, Power spectrum,
P.S.D., Cross spectrum, Transfer function, or Coherence.
TIP
Description of the Function settings
The time-axis data "x(i), where i = 0, 1, ... N-1)" is subjected to a Fast Fourier
Transformation and its result is represented as:
X(i) = XR(i) + jXl(i), Where: i = 0, 1...N-1, j = an imaginary unit
An FFT analysis of time-axis data, which consists of real numbers, results in multiple
elements containing information that indicates the amplitude and phase.
•Y-T
The X axis is fixed to time and the Y axis is fixed to LIN. Just as in Recorder
mode, you can detect changes in the signal input with respect to the time axis.
•Linear (Linear Spectrum)
Based on the result of FFT analysis of time-axis data, either the amplitude or
phase is displayed.
Display
RMS = Off RMS = On
Y axis
Amplitude
LIN.
LOG.
PhasePhase
X
R
(i)
2
+X
I
(i)
2
[V]
10 logX
R
(i)
2
+X
I
(i)
2
[dBV] 10 log
FFT result of measured signals : X(i) = XR(i) + jXI(i)
[V rms ]
X
R
(i)
2
+X
I
(i)
2
2
[dBV rms ]
X
R
(i)
2
+X
I
(i)
2
2
tan
—1
[deg]
X
I
(i)
X
R
(i)
– The amplitude is the voltage of the reference wave height value.
–When the RMS setting is On, the root-mean-square value is displayed instead.
– When the Y (axis) setting is LOG., the display is identical to that for the Power
Spectrum setting shown in the following table.
–When the Y (axis) setting is LOG., the reference value is either 0 dB = 1 V or 0
dBVrms = 1 Vrms.
• Power (Power Spectrum)
Based on the result of FFT analysis of time-axis data, the power spectrum of each
frequency component is displayed.
X
n
(i)
2
+ X
I
(i)
2
[V]
10 logX
R
(i)
2
+X
I
(i)
2
[dBV] 10 log
FFT result of measured signals : X(i) = XR(i) + jX I (i)
[V rms
2
]
X
R
(i)
2
+ X
I
(i)
2
2
[dBV rms ]
X
R
(i)
2
+ X
I
(i)
2
2
tan
—1
[deg]
X
I
(i)
X
R
(i)
Display
RMS = Off RMS = On
Y axis
Amplitude
LIN.
LOG.
PhasePhase
– The amplitude is the voltage of the reference wave height value.
–When the RMS setting is On, the root-mean-square value is displayed instead.
–When the Y (axis) setting is LOG., the display is identical to that for the Linear
Spectrum setting shown in the preceding table.
–When the Y (axis) setting is LOG., the reference value is similarly either 0 dB =
1 V2 or 0 dBVrms = 1Vrms2.
–When the Y (axis) setting is Phase, the Phase display is identical to that for the
Linear Spectrum setting shown in the preceding table.