koban KMOS-01 Guía De Usuario página 249

Oscilloscope Section
If adopt FFT (Fast Fourier Transform) mode, take following steps:
1. Set up time domain waveform
•
Press "AUTO" to display proper waveform.
•
If displayed waveform shows unsatisfactory, press
" " and " " for adjustment.
•
Press F4 (FFT), the oscilloscope may adopt the 256
central points of time domain waveform to calculate
FFT frequency spectrum.
•
According to Nyquist criterion, press "
sampling rate up to at least 2 times of input signal
frequency.
2. FFT frequency spectrum display
Press "F4" FFT button, display FFT frequency spectrum, in which a channel waveform
and FFT waveform are shown in the split screen.
FFT windows instructions
As the oscilloscope takes FFT transform for time
records of limited length, FFT calculation mode bases
on repeated YT waveform. In this case, if the cycle is
integer, frequency values of YT waveform are the same
at the beginning and the end, the waveform may not be
interrupted. However, if the YT waveform cycle is not
integer, frequency values shows different at the beginning
and the end, high-frequency transient interrupts occur at
connecting part. That is so-called "leakage" in frequency
domain. Therefore, in order to avoid leakage, multiply
a window function with the original waveform, forcing
the values at the beginning and the end to 0.
3. Position FFT frequency spectrum
•" " button can still be pressed under FFT interface to change sampling rate, to realize
horizontal amplification or minification;
•Adjust " " to realize vertical amplification or minification.
4. Measure FFT frequency spectrum by cursor
•Two kinds of measurement can be taken for FFT spectrum by using cursor: amplitude
(relative value) and frequency (unit: Hz).
•Under FFT interface, press F2 (
cursor, corresponding frequency and relative amplitude can be measured
46
", make
Picture 2-10-1(split screen)
) or F3 ( ) according to prompt bar to move red
Picture2-10-2
.