User Manual

3.1 Overview and Features
37
FFT analysis can only be used with the FFT function.
The FFT (Fast-Fourier Transform) functions provide frequency analysis of input
signal data.
Use these functions for frequency analysis of rotating objects, vibrations, sounds
and etc.
For details, refer to "3.11 FFT Definitions" (⇒ p. 103).
Analysis can be performed on data as it is being measured, on pre-existing ana-
log waveform data previously acquired with the Memory function, and on data
output from waveform calculations.
However, FFT analysis cannot be applied to data acquired with the Model
8958
16-Ch Scanner Unit. Also, FFT analysis cannot be applied to pre-existing wave-
form data acquired from channels that used Timebase 2 for sampling.
When using an input module equipped with an anti-aliasing filter, the cut-off fre-
quency can be automatically set by linking with the frequency range setting.
(Model 8938 FFT Analog Unit, 8947 Chargh Unit, 8957 High Resolution Unit,
8960 Strain Unit)
Major Features
• FFT analysis frequency range: 133 mHz to 8 MHz
• Frequency resolution: 1/400
th
, 1/800
th
, 1/2000
th
or 1/4000
th
of the frequency
range
• FFT Analysis Modes (16 types)
* Not available when using external sampling.
For phase spectra, only the required phase information is highlighted and dis-
played.
See "3.4.7 Emphasizing Analysis Results (phase spectra only)" (⇒ p. 61)
Also, when performing FFT analysis with the instrument connected to a sound
level or vibration meter, scaling by dB can be set from the Channel Settings
screen if you want to read values directly in calibrated units of measurement.
See "Scaling" (⇒ p. 71)
Refer to the Instruction Manual for FFT function specifications.
FFT Function Chapter 3
3.1 Overview and Features
• Storage Waveform • Linear Spectrum
• RMS Spectrum • Power Spectrum
• Power Spectrum Density* • Cross-power Spectrum
• Auto-correlation Function • Histogram
• Transfer Function • Cross-correlation Function
• Impulse Response • Coherence Function
• 1/1 Octave Analysis* • 1/3 Octave Analysis*
• Phase Spectrum • Power Spectrum Density (LPC)*
To suppress the effects of aliasing distortion
We recommend using input modules that are equipped with anti-aliasing filtering
to suppress the effects of aliasing distortion when sampling.
See Aliasing Distortion and Anti-Aliasing Filters
"3.11 FFT Definitions" (
⇒ p. 103)