DPO6000
，
MPO6000 Series Digital Phosphor Oscilloscope Instruction V1.1
- 53 -
transform. FFT is used to transform time domain signals to frequency components
(frequency spectrum). Select FFT function and plotted FFT spectrum shows the
relationship between dB V and frequency.The horizontal reading changes from time to
frequency (Hz) and the vertical reading from V to dB.The FFT operations can be used for
the following purposes:
Measure harmonic components and distortion in the system.
Display the characteristics of the noise in DC power
Analyze vibration
Display FFT spectrum:
1.Press
【
Math
】
on the frontal panel to turn on math function menu.
2.Press the soft key of
【
operator
】
,and rotate the multifunctional knob V0 to select
FFT.The resulting mathematical waveform is displayed on the screen and marked "M".
3. Press the source soft key and rotate the multifunctional knob V0 to select the FFT
operating source.All four analog channels can be used as signal sources.
4.Press the center soft key and rotate the multifunctional knob V0 to adjust the frequency
of the frequency domain waveform corresponding to the horizontal center of the screen.
5. Press the span soft key and rotate the multifunctional knob V0 to adjust the horizontal
scale of the frequency domain waveform.
6. Press the vertical unit soft key to select the vertical axis unit.Units of the vertical axis
can use either a logarithmic scale to show the dB of the vertical amplitude or a linear scale
to show the Vrms of the vertical amplitude.dB Vrms is recommended if you need to display
FFT spectrum over a relatively large dynamic range.
7. Press the scale soft key to select the vertical scale.
8. Press the window soft key to select the appropriate window.
Spectral leakage can be greatly reduced by using window functions.The range provides
six different characteristic FFT window functions for measuring different waveform.You
need to select window functions according to the different waveform and their
characteristics.Please read the table below carefully and make appropriate choices based
on the input signals.
Window
Measurement
Characteristics
Rectangular
Transient or short pulse
waveform
Dedicated window for discrete window
similar to the situation when no
window is multiplied
Hanning
Period waveform
Better frequency resolution
Poorer amplitude resolution
Hamming
Transient or short pulse
waveform
A little bit better frequency resolution
than Hanning
Blackman
Single frequency signal, search
for higher order harmonics
The best amplitude resolution;
the poorest frequency resolution
Bartlett
(Triangle)
Stronger narrow band signal
Better frequency resolution
Flattop
Period waveform
Better amplitude resolution
Poorer frequency resolution
9.Press the alone soft key to select only display FFT result and not display source
channel.
Note
:
1.A signal with a dc component or bias will result in an error or bias in the FFT waveform
component.To reduce the dc component, the "channel coupling" of the source can be set
to "ac" mode.
2.In order to reduce the random noise and aliasing frequency components of repeated or
single pulse events, the "acquisition mode" of oscilloscope can be set to "average" mode.
Use the cursor to measure the FFT waveform.
To make cursor measurements, First press [Cursors] in the front panel of the oscilloscope
to turn on the cursor measurement.
Press the Mode soft mode key to select manual or trace.Use AX and BX cursors to
measure the frequency and difference between two frequencies (BX-AX).Measure
amplitude and amplitude difference using AY and BY cursor (BY-AY).
