Math
89
9.2.3 FFT Operation
FFT is used to compute the fast Fourier transform using analog input channels. FFT takes the digitized time record of
the specified source and transforms it to the frequency domain. When the FFT function is selected, the FFT spectrum
is plotted on the oscilloscope display as magnitude in dBV versus frequency. The readout for the horizontal axis changes
from time to frequency (Hertz) and the vertical readout changes from V to dB.
FFT operation can facilitate the following works
:
• Measure harmonic components and distortion in the device under test
• Measure the characteristics of the noise in DC power
• Analyze vibration
To display a FFT waveform
1. Press the
Math
key on the front panel to open the MATH function menu.
2. Press the
Operator
softkey and then turn the
Universal Knob
to select
FFT
. The resulting math waveform is
displayed in white and labeled with “M”.
Figure 9.3
FFT Menu
3. Press the
Source
softkey, and then turn the
Universal Knob
to select the source to do FFT operation. Analog
channels can be used as the source.
4. Press the
Config
softkey to enter CONFIG menu.
Figure 9.4
FFT Config Menu
• Press the
Maximum points
softkey, and then turn the
Universal Knob
to select the Maximum points.
• Press the
Window
softkey, and then turn the
Universal Knob
to select an appropriate window.
Spectral leakage can be considerably decreased when a window function is used. The oscilloscope provides five
windows (Rectangle, Blackman, Hanning, Hamming and Flattop) which have different characteristics and are
applicable to measure different waveforms. Select the window function according to different waveforms and their
characteristics. Refer to table
to make an appropriate option according to the input signal.
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