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Generally, it is hard to analyze the signal's features in time domain. But it is easy to analyze the component of the signal at
each frequency if the signal is in frequency domain. This is beneficial to evaluate the signals in all aspects.
FFT comes from the improvement of DFT. To DFT, the result is proportional to the square of N. If N is large, like 1024,
1048576 operations are required. Therefore, it is impossible to analyze spectrum and process the signal in real time by
using DFT.
The FFT algorithm rapidly computes such transformations by factorizing the DFT matrix into a product of sparse factors
and reduce the complexity of the computing the DFT by using periodicity and symmetry. For example, divide the
N-sequence into two N/2-sequence. (N/2)^2 times' calculations are needed for every N/2 point DFT. Then every two N/2
point DFT can combine into one N point DFT after N times' operations. After this transformation, the total operation times
will be N+2*(N/2)^2=N+N^2/2. Thus, when N=1024, the total operation times are 525312, which save about 50% of the
computation.
SE1022 develops and integrates the function of FFT high accuracy spectrum analysis, which can realize the frequency
domain analysis from 1 kHz to 102 kHz and display the spectrum distribution of the signal in real time. The setting of FFT
is in the menu of [DISPLAY].
1.15
Multi-harmonic Detection
Harmonics represent waves at multiple frequencies. Periodic function can be described as the linear combination of one
constant and many sine or cosine functions with the base frequency and the multiple frequencies. The constant is the DC
component. The base frequency component is the base wave. The multiple frequencies are harmonics.
Now many lock-in amplifiers can only measure one base wave or one component of harmonics at one time. But in most
practical applications, it is necessary to measure and record multiple harmonics simultaneously. In order to solve this
problem, SE1022 realized multi-harmonic detection. Up to 3-channel harmonic components can be measured by one
SE1022 at the same time.
