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Select the FFT window
•
Assuming the YT waveform is constantly repeating itself, the oscilloscope will carry
out FFT conversion of time record of a limited length. When this cycle is a whole
number, the YT waveform will have the same amplitude at the start and finish.
There is no waveform interruption.
•
If the YT waveform cycle is not a whole number there will be different amplitudes
at the start and finish, resulting in transient interruption of high frequency at the
connection point. In frequency domain this is known as leakage.
•
To avoid leakage multiply the original waveform by one window function to set the
value at 0 for start and finish compulsively. See the following table:
FFT Window
Rectangle
Hanning
Hamming
Blackman
Note: FFT resolution means the quotient of the sampling and math points. When the
math point value is fixed, the sampling rate should be as low as possible relative to the
FFT resolution.
•
Nyquist frequency: To rebuild the original waveform, at least 2f sampling rate
should be used for waveform with a maximum frequency of f.
•
This is known as Nyquist stability criterion, where f is the Nyquist frequency and 2f
is the Nyquist sampling rate.
Digital Filtering Function
Notes
1.
Upper Limit: effective only in low pass filtering - use MULTIPURPOSE control.
2.
Lower Limit: effective only in high pass filtering - use MULTIPURPOSE control.
3.
Y Offset: use MULTIPURPOSE control to move waveform vertically.
4.
X Offset: use MULTIPURPOSE control to adjust vertical gratitude factor.
Feature
The best frequency resolution,
the worst amplitude resolution.
Basically similar to a status
without adding window.
Frequency resolution is better
than the rectangle window but
amplitude resolution is poorer.
Frequency resolution is
marginally better than Hanning
window.
The best amplitude resolution
and the poorest frequency
resolution.
Most suitable measurement item
Temporary or fast pulse. Signal level is
generally the same before and after.
Equal sine wave of very similar frequency.
There is broad-band random noise with
slow moving wave spectrum.
Sine, cyclical and narrow-band random
Temporary or fast pulse. Signal level varies
Mainly for single frequency signals to
search for higher-order harmonic wave.
Functions
Setup
Menu
Type
Filter
CH1
CH2
Source
CH3
CH4
Low Pass
High Pass
Filter Type
Band Pass
9
noise.
greatly before and after.
Notes
Digital filtering
Set CH1 as filter target
Set CH2 as filter target
Set CH3 as filter target
Set CH4 as filter target
Set filter to low pass filtering
Set filter to high pass
filtering
Set filter to band pass
filtering
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