Tektronix TPS2012B, User Manual

Page: 87 / 184

Math FFT
This chapter contains detailed information on how to use the Math FFT (Fast
Fourier Transform). You can use the FFT Math mode to convert a time-domain
(YT) signal into its frequency components (spectrum). You can use the Math FFT
mode for the following types of analysis:
Analyze harmonics in power lines
Measure harmonic content and distortion in systems
Characterize noise in DC power supplies
Test impulse response of fi lters and systems
Analyze vibration
To use the Math FFT mode, you need to perform the following tasks:
Set up the source (time-domain) waveform
Display the FFT spectrum
Select 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
NOTE.
For viewing the harmonics of power systems, the harmonics feature
available with the optional TPS2PWR1 Power Analysis application is optimized
for power measurements.
Setting Up the Time-Domain Waveform
Before you use FFT mode, you need to set up the time-domain (YT) waveform.
To do so, follow these steps:
1. Push AutoSet to display a YT waveform.
2. Turn the Vertical Position knob to move the YT waveform to the center
vertically (zero divisions).
This ensures that the FFT will show a true DC value.
3. Turn the Horizontal Position knob to position the part of the YT waveform
that you want to analyze in the center eight divisions of the screen.
The oscilloscope calculates the FFT spectrum using the center 2048 points of
the time-domain waveform.
TPS2000B Series Digital Oscilloscope User Manual 61