PeakTech 1145 Bedienungsanleitung Seite 71

6.3. Using FFT (Fast Fourier Transformation)
With Fast Fourier Transform (FFT), you can transform a waveform from a displayed value of its amplitude
against time to one that plots the amplitudes of the several discrete frequencies the waveform has. Use FFT in
the following applications:
Analyzing impulse response of filters and Amplifier
Analyzing noise in DC power source
Measuring harmonic content and distortion in systems
Analyzing harmonics in 50 and 60 Hz power lines
Analyzing vibration frequency
The FFT computes and displays the frequency content of a waveform you acquire as an FFT math waveform. This
frequency domain waveform is based on the following equation:
Where: x(n) is a point in the time domain record data array
X(k) is a point in the frequency domain record data array
n is the index to the time domain data array
k is the index to the frequency domain data array
N is the FFT length
j is the square root of -1
Procedure of using FFT:
1. Push the math menu button
2. Push the menu button of the advanced function to select FFT.
3. Select FFT source channel
4. Select FFT window (Rectangular, Hamming, Hanning)
5. Push the menu button of stop
Rectangular
Best window for resolving frequencies but worst for accurately measuring the amplitude of those frequencies. Best
window for measuring the frequency spectrum of non-repetitive signals and measuring frequency components near
DC.
Hamming
Very good type for resolving frequencies with somewhat improved amplitude accuracy over the rectangular window.
Hanning
Very good for window measuring amplitude accuracy but degraded for resolving frequencies.
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