In this newsletter, we will introduce the Time frequency Analysis Function OS-0527, the optional function of O-Solution. This function can evaluate transient phenomena that were difficult to capture by FFT analysis, and display clearly time change of the frequency component while maintaining its frequency resolution . The OS-0527 is equipped with STFT (Short Time Fourier Transform) and Wavelet transform.
The Short-time Fourier TransformFourier analysis is able to be performed with any points (frame length and interval) set by the user. In other words, the user can set any cutting out time length, so this method is effective for observing spectrum changes over an extremely short time.
The wavelet transform is an analysis method that enables simultaneous analysis of temporal fluctuation and spatial transition of complicated waveforms such as a sudden or unstationary sound or vibration. The analysis time length is changed depending on the frequency in this method. It brings a good balance between time and frequency, so this method is effective for capturing the analysis result as a whole.
Case Study: Analysis of mechanical operating sound
This is an example of analyzing transient noise generated from a machine tool. The time length of abnormal sounds is very short and their frequency components are seen over a wide range. In the FFT analysis, the frame length cannot take long enough to obtain the resolution of low frequency components. While, by using the wavelet transform, it is possible to comprehensively capture time and frequency information. In this example, the components (low frequency components) in the red circles that are not seen in the FFT analysis can be seen in the right figure. In this way, the wavelet transform raises the time resolution for high frequency components with sufficiently high frequency resolution, and raises the frequency resolution for low frequency components with gradual time change. This is an analysis method using a constant ratio filter bank similar to 1/N octave band analysis that is often used for acoustic analysis.
1...Good product Clear sound (no abnormality)
2...Defective product 1 Abnormal noise with a little unclear sound
3...Defective product 2 Abnormal noise with unclear sound
System Configuration
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