13.9 FFT Analysis Modes
238
Waveform Example
• If the cursor is displayed, the total harmonic distortion (THD), which sets the
fundamental wave as the cursor position, is displayed. When 2 cursors appear,
the one with the low frequency becomes the fundamental. When results can-
not be obtained, [---%] is displayed.
• When only sine waves are input, the level of this component becomes approx-
imately 1.4 times (3 dB) larger than the overall value. To measure at a refer-
ence the same as the overall value, analyze using RMS spectrum or power
spectrum.
See: RMS Spectrum ( p.238), Power Spectrum ( p.240)
RMS Spectrum
The oscillation component (actual value) is calculated by the frequency axis waveform of the input signal.
RMS and power spectra displays use the same analysis results displayed logarithmically (amplitude in dB).
Main uses:
• To inspect the execution value of the frequency component of the waveform
• To inspect the RMS value at each frequency
See: About the Functions"13.9.2 Analysis Mode Functions" ( p.254)
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.
Log-Mag
Analysis values are displayed as dB values. (0 dB reference value: 1eu)*
Lin-Real
The real-number component of analysis values are displayed.
Lin-Imag
The imaginary component of analysis values are displayed.
* eu: engineering units that are currently set are the standard (e.g., when the unit settings is volts, 0 dB = 1 V)
Normal display
X axis: Log
Y axis: Lin-Mag
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