If adopt FFT (Fast Fourier Transform) mode, take following steps:
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 “
”, make
sampling rate up to at least 2 times of input signal
frequency.
1. Set up time domain waveform
•
•
•
•
.
2. FFT frequency spectrum display
3. Position FFT frequency spectrum
4. Measure FFT frequency spectrum by cursor
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.
•“
” 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.
•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 (
) or F3 (
) according to prompt bar to move red
cursor, corresponding frequency and relative amplitude can be measured
Picture 2-10-1(split screen)
Picture2-10-2
46
Oscilloscope Section
Summary of Contents for ET2704
Page 2: ...True RMS Multimeter...
Page 33: ...True RMS Multimeter...
