07-04-2010, 03:23 PM
I need the details of the seminar on the topic as mentioned above.[/size][/font]
07-04-2010, 03:23 PM
I need the details of the seminar on the topic as mentioned above.[/size][/font]
11-04-2010, 02:18 PM
Structural behavioral Measurements
This article concentrates on the measurement of the vibration of mechanical structures and machinery. Spectral Analysis: the most convenient way to analyze a vibration signal is to obtain its frequency spectrum because Resonances are also manifested as peaks in a frequency spectrum. also because Excitation forces (especially in rotating equipment), often provide sinusoidal excitation at specific frequencies. The FFT Analyzer: The FFT computes a discretized (sampled) version of the frequency spectrum of a sampled time signal.Present day FFT analyzers can compute a DFT in milliseconds. Rules of Digital Measurement: Time Waveform:The DFT assumes that the sampled time waveform contains N uniformly spaced waveform samples Frequency Waveform: The DFT assumes that the digital frequency spectrum contains N/2 uniformly spaced samples of complex valued data Nyquist Sampling: Shannonâ„¢s Sampling Theorem says that a frequency spectrum can only contain unique frequencies Zoom Measurements: A Zoom transform is essentially a digital filtering operation that takes place after the time waveform has been sampled and it involves re-sampling, frequency shifting, and low pass filtering of the sampled data. Digital Measurement Difficulties: Aliasing Aliasing of a signal occurs when it is sampled at less than twice the highest frequency in the spectrum of the signal.In FFT it is solved by passing the analog signals through anti-aliasing filters before they are sampled. Leakage: If a time signal is not periodic in the transform window, when it is transformed to the frequency domain, a smearing of its spectrum will occur. This is called leakage. for details , refer this pdf: Structural Dynamics Measurements.pdf (Size: 481.33 KB / Downloads: 91) VIBRATION-BASED STRUCTURAL MONITORING.pdf (Size: 496.18 KB / Downloads: 123) |
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