22
UNI-T
®
UT4000 User Manual
Table 2-3 Explanatory notes for the FFT menu
Function Menu
Setup
Explanatory Note
Type
FFT
To carry out FFT algorithm functions.
Signal source
CH1
CH2
Set CH1 as math waveform.
Set CH2 as math waveform.
Window function
Hamming
Blackman
Rectangle
Hanning
Set Hamming window function.
Set Rectangle window function.
Set Blackman window function.
Set Hanning window function.
How to use FFT functions
Signals with DC quantities or DC offset will cause error or offset of FFT waveform
quantities. To reduce DC quantities, select AC coupling. To reduce random noise and
frequency aliasing resulted by repeated or single pulse event, set the acquiring mode of
your oscilloscope to average acquisition.
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. However, 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 to
0 for start and finish compulsively. For application of the window function, please see the
table below :
Table 2-4
FFT Window
Feature
Most Suitable Measurement Item
Rectangle The best frequency
recognition rate, the worst
amplitude recognition rate.
Basically similar to a status
without adding window.
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.
Hanning
Frequency recognition rate is
better than the rectangle
window, but amplitude
recognition rate is poorer.
Sine, cyclical and narrow-band random
noise.
Hamming
Frequency recognition rate is
marginally better than
Hanning window.
Temporary or fast pulse. Signal level
varies greatly before and after.
Blackman The best amplitude
recognition rate and the
poorest frequency recognition
rate.
Mainly for single-frequency signals to
search for higher-order harmonic wave.
Содержание UT4000 Series
Страница 13: ...2 UNI T UT4000 User Manual Figure 1 1 Front panel of UT4000 Oscilloscopes ...
Страница 14: ...3 UNI T UT4000 User Manual Figure 1 2 Schematic diagram for operating the UT4000 front panel ...
Страница 15: ...4 UNI T UT4000 User Manual Figure 1 3 Schematic diagram for the display interface ...
Страница 74: ...63 Figure 3 14 Dual time base function ...
Страница 98: ...87 UNI T UT4000 User Manual This user manual may be revised without prior notice ...