13.3 Setting FFT Analysis Conditions
217
13
Chap
ter
13 FFT
Fun
cti
on
FFT Analysis Modes and Averaging
When averaging time-domain waveform values:
Waveforms are acquired and averaged within the time domain. After averaging, FFT
calculation is performed.
When the trigger mode is
[Auto]
: Data is acquired when the
START
key is pressed,
even if trigger criteria are not met after a certain interval. So if averaging is applied to an
asynchronous signal, the resulting data is meaningless.
Synchronous signals have better SNR (signal-to-noise ratio) and are more suitable for
analysis.
When averaging spectrum values:
Acquired data is first subject to FFT analysis. After analysis, averaging is performed
within the frequency range, and the result is displayed. This differs from time-domain av-
eraging in that averaging can be performed without trigger synchronization. However, if
the characteristics of the input waveform allow triggering, using the trigger for synchro-
nization is recommended.
Spectrum peak hold:
After performing FFT calculations on the acquired waveform, peak values are retained
(held) and displayed within the frequency range.
: Settable,
×
: Cannot be set, O: Partially settable
Analysis Mode
Averaging
Waveform Averaging
Spectrum Averaging
Simple
Exponen-
tial
Simple
Exponential
Peak
Hold
OFF
×
×
×
×
×
Storage Waveform
×
×
×
Histogram
×
×
×
Linear Spectrum
O *2
O *2
O *2
RMS Spectrum
O *2
O *2
O *2
Power Spectrum
Power Spectrum Density *1
LPC analysis(Power Spectrum Density) *1
×
×
×
Transfer Function
O *2
O *2
O *2
Cross Power Spectrum
O *2
O *2
O *2
Impulse Response
Coherence Function
×
×
×
Phase Spectrum
×
×
×
Auto-correlation Function
Cross-correlation Function
1/1 Octave Analysis *1
1/3 Octave Analysis *1
*1. Not available for external sampling
*2. Not available when the y axis is real (linear) or imaginary (linear), or for Nyquist plots
Summary of Contents for 8847
Page 1: ...MEMORY HiCORDER Instruction Manual 8847 December 2010 Revised edition 4 8847A981 04 10 12H ...
Page 2: ......
Page 18: ...Operating Precautions 8 ...
Page 26: ...1 4 Basic Key Operations 16 ...
Page 74: ...4 4 Waveform Observation 64 ...
Page 98: ...5 5 Managing Files 88 ...
Page 110: ...6 6 Miscellaneous Printing Functions 100 ...
Page 126: ...7 8 Seeing Block Waveforms 116 ...
Page 160: ...8 10 Making Detailed Settings for Input Modules 150 ...
Page 198: ...10 6 Numerical Calculation Type and Description 188 ...
Page 296: ...15 7 Controlling the Instrument with Command Communications LAN USB 286 ...
Page 304: ...16 2 External I O 294 ...
Page 362: ...Appendix 5 FFT Definitions A28 ...
Page 368: ...Index Index 6 ...
Page 369: ......
Page 370: ......
Page 371: ......