Note Technique Tfen
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Technical note TF01-290409
Signal processing applied to vibration signals involves many techniques allowing the investigation of the machine reality trough the signal representation. Among all representations, the time waveform representation and spectral representation are the most popular. Each one of these representations has its own advantages and disadvantages that we list in the following table:
Representation
Time waveform
Spectral
Advantages Respects events time repartition = easy recognition of isolated events Relatively easy recognition of amplitude modulation Frequency component separation = localize easily the frequency range containing vibration energy
Disadvantages Quite Impossible to recognize the events frequencies for signals containing more than one harmonic component Ignores events time repartition
A simple reading of the above table shows that the disadvantages of each technique are compensated by the advantages of other Here comes the utility and the originality of the Time frequency representation, it combines in fact the time waveform and the spectral representations and thus eliminates all the disadvantages.
www.betavib.com
Technical note TF01-290409
Challenge : The challenge is a competition between time waveform, spactral, and Time Frequency representations to recognize a combination of 4 numbers typed on a telephone keypad.
The frequency representation allows us to pinpoint the frequencies containing the energy of the signal - recognize the used keys, while the time waveform representation gives us the time duration of each event (0.2s). The time-frequency spectrogram combines these two informations in the following table:
Event n Duration frequency Used Keys
1 0-0,2 s 690 + 1200 1
2 0,2-0,4 s 850 + 1330 8
3 0,4-0,6 s 770 + 1470 6
4 0,6-0,8 s 690 + 1330 2
The spectrogram in this case is the only technique understanding the reality of the phenomenon, thanks to him we know that the numbers are in order: 1 - 8 - 6 - 2 and that each key was pressed during 0.2 s.
www.betavib.com
Technical note TF01-290409
Vibration case study Original Signal measured on a bearing with an outer ring defect BPFO= 96.4Hz
Wavelet Recursive filters
Source : www.mathworks.com
www.betavib.com
Technical note TF01-290409
Results
www.betavib.com
Signal processing applied to vibration signals involves many techniques allowing the investigation of the machine reality trough the signal representation. Among all representations, the time waveform representation and spectral representation are the most popular. Each one of these representations has its own advantages and disadvantages that we list in the following table:
Representation
Time waveform
Spectral
Advantages Respects events time repartition = easy recognition of isolated events Relatively easy recognition of amplitude modulation Frequency component separation = localize easily the frequency range containing vibration energy
Disadvantages Quite Impossible to recognize the events frequencies for signals containing more than one harmonic component Ignores events time repartition
A simple reading of the above table shows that the disadvantages of each technique are compensated by the advantages of other Here comes the utility and the originality of the Time frequency representation, it combines in fact the time waveform and the spectral representations and thus eliminates all the disadvantages.
www.betavib.com
Technical note TF01-290409
Challenge : The challenge is a competition between time waveform, spactral, and Time Frequency representations to recognize a combination of 4 numbers typed on a telephone keypad.
The frequency representation allows us to pinpoint the frequencies containing the energy of the signal - recognize the used keys, while the time waveform representation gives us the time duration of each event (0.2s). The time-frequency spectrogram combines these two informations in the following table:
Event n Duration frequency Used Keys
1 0-0,2 s 690 + 1200 1
2 0,2-0,4 s 850 + 1330 8
3 0,4-0,6 s 770 + 1470 6
4 0,6-0,8 s 690 + 1330 2
The spectrogram in this case is the only technique understanding the reality of the phenomenon, thanks to him we know that the numbers are in order: 1 - 8 - 6 - 2 and that each key was pressed during 0.2 s.
www.betavib.com
Technical note TF01-290409
Vibration case study Original Signal measured on a bearing with an outer ring defect BPFO= 96.4Hz
Wavelet Recursive filters
Source : www.mathworks.com
www.betavib.com
Technical note TF01-290409
Results
www.betavib.com
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