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UTD1000L User Manual 75
CH2
Set CH2 as Source 2 of Math operation
FFT
Source
CH1
Set the source to CH1
CH2
Set the source to CH2
Window
Hanning Set to Hanning window
Hamming Set to Hamming window
Blackman Set to Blackman window
Rectangle Set to Rectangle window
Vertical
Unit
Linear To set vertical unit to linear or dBV
dBV
FFT Spectrum Analysis
FFT (Fast Fourier Transform algorithm) mode can convert time domain (YT) into Frequency
domain for signal waveform graph, which helps to easily observe signals of following kinds:
● Harmonic component and distortion in the measurement system.
●Characterize noises in DC source
●Analyze the virbration
FFT Operation Tips
Signals with DC components or bias may cause error or deviation to FFT waveform
components. In order to reduce DC component, you can set coupling to AC mode. And you can
set ACQUIRE type to AVG to lower down random noise or mixed overlapped frequency
component in repetitive or single pulse event.
Select FFT Window
Suppose YT waveforms repeats constantly and the Oscilloscope then performs FFT on limited
length record. When the period numers are integer, YT waveform at the start and finish points
share same amplitude values and will not cause any interruption to the waveform. If it is
non-integral, the start and finish amplitude are different, and high-frequency transient
interruption will happen at joint points, which is called leakage in frequency domain. To avoid
the leakage, FFT mode will multiply original waveform with one window function to force the
start and finish values all go to 0. Refer to following windows for details:
Table 6-21
FFT
Window
Features Best Applications
Hanning Compared with rectangle type, it has
better amplitude accuracy and less so
for frequency resolution.
Used to measure sine, periodic and
narrowband random noises.
Hamming Frequency resolution for Hamming is
a little better than that of Hanning.
Used to measure transient or short
pulse; and for signals whose signal
levels before and after the event are
greatly different.
Blackman Offers best amplitude accuracy and
worst for the frequency resolution.
Mainly for measuring single frequency
signals and looking for higher order
harmonics
Rectangle Offer best frequency resolution, but
worst for the amplitude accuracy. No
big change before and after adding
window function.
Applicable for measuring transient or
short pulse, the signal levels before
and after the event are approximately
equal. And also for measuring
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