MR8740、MR8741_user_manual_eng_20191016H.pdf - 第299页

12.8 FFT Analysis Modes 287 11 Chapter 12 FFT Function 12 W aveform Example Auto Correlation Function Shows the correlation of two point s on the input signal at time differential t . Main uses : • T o detect periodicy i…

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12.8 FFT Analysis Modes
286
Waveform Example
Emphasizing only a Specific Portion (Highlighted Display)
A specific portion of a phase spectrum can be emphasized and displayed.
See: "12.3.8 Emphasizing Analysis Results (phase spectra only)" (p.259)
Phase Spectrum
Shows the phase characteristics of the input signal.
Main uses:
• To inspect the phase spectrum of channel 1. Displays the phase of a cosine waveform as a reference (0º).
• To inspect the phase difference between channels 1 and 2.
See: About the Functions"12.8.2 Analysis Mode Functions" (p.293)
1 Ch FFT: Displays the phase of the signal on channel 1. Displays the phase of a cosine waveform as a ref-
erence (0º). Unless the waveform is synchronous, phase values are unstable.
2 Ch FFT: Displays the phase difference between channels 1 and 2. Positive values indicate that the phase
of channel 2 is leading.
Axis Display Type Description
X axis
Linear Frequency is displayed with equal spacing
Log Frequency display of logarithm interval
Y axis Lin-Mag Analysis values are displayed linearly.
1chFFT
X axis: Log
Y axis: Lin-Mag
2chFFT
X axis: Log
Y axis: Lin-Mag
12.8 FFT Analysis Modes
287
11
Chapter 12 FFT Function
12
Waveform Example
Auto Correlation Function
Shows the correlation of two points on the input signal at time differential t.
Main uses:
• To detect periodicy in irregular signals (improving and detecting SNR)
• To inspect periodic components in a noisy waveform.
See: About the Functions"12.8.2 Analysis Mode Functions" (p.293)
Axis Display Type Description
X axis Linear
Time display
The center (
t = 0) is the reference. To the right is lag time (+t), and to the left is
lead time (-t)
Y axis Lin-Mag
+1 to -1 (dimensionless units)
The closest correlation at time differential
t is +1, and the least correlation is 0.
-1 indicates completely reversed polarity.
Because of the characteristics of the function, t = 0 becomes +1.
X axis: Linear
Y axis: Lin-Mag
This instrument provides a circular auto-correlation function. Analysis results are
normalized to the maximum value.
12.8 FFT Analysis Modes
288
Waveform Example
Waveform Example
Cross-Correlation Function
Using two input signals, shows the correlation of two points on the input signal at time differential t.
Output is displayed as a function of differential time t.
Main uses:
• To determine the phase shift of two signals per unit of time
• To determine the speed and distance of time lag between two signals
See: About the Functions"12.8.2 Analysis Mode Functions" (p.293)
Axis Display Type Description
X axis Linear
Time display
The center (t = 0) is the reference. To the right is lag time (+t), and to the left is
lead time (-t)
Y axis Lin-Mag
+1 to -1 is displayed in dimensionless units.
At time differential t, this value is +1 when the correlation of input and output sig-
nals is the closest, and 0 when correlation is the least. -1 indicates completely
reversed polarity.
X axis: Linear
Y axis: Lin-Mag
This instrument provides a circular cross-correlation function.
Analysis results are normalized to the maximum value.
1/1 and 1/3 Octave Analysis
Analyze spectrums such as noise using fixed rate spectrum filters of 1/1 octave band or 1/3 octave band.
Main uses:
To analyze noise frequency
See: About the Functions"12.8.2 Analysis Mode Functions" (p.293), "Octave Filter Characteristics" (p.25)
Axis Display Type Description
X axis Log
Displays the center frequency of each band.
Y axis
Lin-Mag
Octave analysis values are displayed linearly.
Log-Mag
Octave analysis values are displayed as dB values. (0 dB reference value: 1eu)*
* eu: engineering units that are currently set are the standard (e.g., when the unit settings is volts, 0 dB = 1 V)
1/1 Octave
X axis: Log
Y axis: Log-Mag
Filter: Normal