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Which of the following are the basic differences between vibration signature and noise signature? 1. Vibration signature is essentially in the frequency range zero to 100 cps whereas noise signature is in the range 20 cps to 3000 cps. 2. Vibration signature has well-defined peaks whereas the noise signal is smeared. 3. The intensities of noise signatures arc much less than that of vibration signatures. 4. Detection of vibration signature calls for a microphone whereas that of noise can do with a pickup. Select the correct answer using the code given below.

Which of the following are the basic differences between vibration signature and noise signature? 1. Vibration signature is essentially in the frequency range zero to 100 cps whereas noise signature is in the range 20 cps to 3000 cps. 2. Vibration signature has well-defined peaks whereas the noise signal is smeared. 3. The intensities of noise signatures arc much less than that of vibration signatures. 4. Detection of vibration signature calls for a microphone whereas that of noise can do with a pickup. Select the correct answer using the code given below. Correct Answer 2 and 3

Concept:

Vibration signatures and Noise signatures are obtained from a gear set up using an accelerometer on bearing housing and a sound level meter placed near the gear test setup.

Analysis of the signatures is generally performed by three techniques:

Spectral analysis- Information about the frequency content of the signals

Cepstral analysis - providing information about the modulating frequencies

Wavelet Transform analysis - Giving simultaneously the time and frequency features of the signal

Explanation:

  • The unit of frequency is Hertz. It can also be measured in cps i.e. cycles per second.
  • 1 cps = 1 Hertz
  • Vibration signature range can go beyond 100 cps and may be even more than 20000 cps
  • Vibration signature has well defined peaks because of acceleration pickup.
  • For Noise signals the location of the microphone is important.
  • They are very effective in detecting early faults as well as for continuous monitoring of the fault.
  • However the intensities of the noise signals arc much less than that of vibration signatures.

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