Basic Operation
DSO1000B Series HandHeld Oscilloscope User Manual 19
Analyze vibration.
To use the Math FFT mode, perform the following tasks:
Set the source (time-domain) waveform;
Display the FFT spectrum;
Choose a type of FFT window;
Adjust the sample rate to display the fundamental frequency and harmonics without aliasing;
Use zoom controls to magnify the spectrum;
Use cursors to measure the spectrum.
5.3.1.1
Setting Time-domain Waveform
It is necessary to set the time-domain (YT) waveform before using the FFT mode. Follow the steps
below.
1. Push the AUTO button to display a YT waveform.
2. Click the Vertical Position key to vertically move the YT waveform to the center (zero division)
so as to ensure the FFT will display a true DC value.
3. Click the Horizontal Position key to position the part of the YT waveform to be analyzed in the
center eight divisions of the screen. The oscilloscope uses the 2048 center points of the
time-domain waveform to calculate the FFT spectrum.
4. Click the VOLTS Key to ensure the entire waveform remains on the screen. If the entire
waveform is invisible, the oscilloscope may display wrong FFT results by adding
high-frequency components.
5. Click the TIME/DIV key to provide the resolution you need in the FFT spectrum.
6. If possible, set the oscilloscope to display multiple signal cycles.
If you Click the TIME/DIV key to select a faster setting (fewer cycles), the FFT spectrum will
display a larger frequency range and reduce the possibility of FFT aliasing.
To set the FFT display, follow the steps below.
1. Push the M/R button;
2. Set the Operation option to FFT;
3. Select the Math FFT Source channel.
In many situations, the oscilloscope can also generate a useful FFT spectrum despite the YT
waveform not being triggered. This is especially true if the signal is periodic or random (such as
noise).
Note: You should trigger and position transient or burst waveforms as close as possible to
the screen center.
Nyquist Frequency