Vibrational analysis frequency components

Collection and analysis of vibration signatures is a complex procedure. By looking at a vibration spectrum, one can identify which components of the pump system are responsible for a particular frequency component. Comparison of vibration signatures at periodic intervals reveals if a particular component is deteriorating. The following example illustrates evaluation of the frequency composition of an electric motor gear pump system. 

From this it can be seen that vibration is the universal manifestation that something is wrong. Therefore, many units are equipped with instruments that continuously monitor vibration. Numerous new instruments for vibration analysis have become available. Frequency can be accurately determined and compared with computations, and by means of oscilloscopes the waveform and its harmonic components can be analyzed. Such equipment is a great help in diagnosing a source of trouble. 

Most of the early vibration analysis was carried out using analog equipment, which necessitated the use of time-domain data. The reason for this is that it was difficult to convert time-domain data to frequency-domain data. Therefore, frequency-domain capability was not available until microprocessor-based analyzers incorporated a straightforward method (i.e.. Fast Fourier Transform, FFT) of transforming the time-domain spectmm into its frequency components. 

Broadband analysis techniques have been used for monitoring the overall mechanical condition of machinery for more than twenty years. The technique is based on the overall vibration or energy from a frequency range of zero to the user-selected maximum frequency, Fmax Broadband data are overall vibration measurements expressed in units such as velocity (PK), acceleration (RMS), etc. This type of data, however, does not provide any indication of the specific frequency components that make up the machine s vibration signature. As a result, specific machine-train problems cannot be isolated and identified. 

All components have one or more natural frequencies that can be excited by an energy source that coincides with, or is in close proximity to, that frequency. The result is a substantial increase in the amplitude of the natural frequency vibration component, which is referred to as resonance. Higher levels of input energy can cause catastrophic, near instantaneous failure of the machine or structure. The base frequency referred to in a vibration analysis that includes vibrations that are harmonics of the primary frequency. 

The second method uses the slip frequency to monitor for loose rotor bars. The passing frequency created by this failure mode energizes modulations associated with slip. This method is preferred since these frequency components are within the normal bandwidth used for vibration analysis. 

Machine components The EIS should provide information on all components (e.g., bearings, gears, gearboxes, electric motors, pumps, etc.) that make up the machine-train. Since these components generate vibration energy and unique frequency components, this information is essential for proper analysis. At a minimum, the information sheet must include detailed bearing information, passing frequencies, and nameplate data. 

Unlike the two trending techniques, signature analysis provides visual representation of each frequency component generated by a machine-train. With training, plant staff can use vibration signatures to determine the specific maintenance required by plant machinery. 

All vibration monitoring systems have finite limits on the resolution, or ability to graphically display the unique frequency components that make up a machine s vibration signature. The upper limit (Fmax) for signature analysis... 

AR is defined as the least difference between similar backscatterers that can be resolved in an EXAFS analysis, and is sufficient for the two frequencies to cause a beat in the EXAFS within the i-range of the data. Thus, the resolution is approximately given by the relation AR = jt/2fc, where k is the extent of the data in k. Thus, to resolve two different Mo-S bond-lengths differing by 0.10 A k would need to extend to 15.7 A. The values of mean-square deviation in average interatomic distance R, and the EXAFS resolution are related. We recall that is composed of vibrational and static components with c7 = + Ostat - Interactions that are not resolved in the EXAFS appear... 

To discuss the recurrences in the real-time spectra described above, the frequency components have first to be calculated by Fourier analysis. In Fig. 3.33, Fourier spectra of the real-time data for Na K (Fig. 3.33 a) and Na K (Fig. 3.33 b) are presented. Again the signal-to-background ratio for the heavier isotope is worse than for Na K, owing to the abundance ratio of and in natural potassium. Besides the frequency components corresponding to neighboring vibrational energy levels at and a 1 ... 

In this third edition, the general plan of the previous editions has been retained in order to provide a book that covers in one volume those aspects of vibrational spectroscopy that a chemical spectroscopist will find useful in the study of chemical structure or composition. This includes introductory theory of vibrational and rotational spectra, basic infrared instrumental components and experimental techniques, quantitative analysis, the use of symmetry in vibrational spectroscopy, and a detailed example of theoretical vibrational analysis. The most extensive part of this book (Chapters 4-13) is an in-depth study of group frequency correlations and how to use them in spectral interpretation. 

The predicted IR and Raman spectra, based on the data printed out from the vibrational analysis in O Fig. 10-6 are shown in O Fig. 10-7. These are direct screen captures from PQSView, which is the job output and visualization component of the PQSMol GUI (PQS 2010). For each spectrum, the frequency range (horizontal axis), the intensity range (vertical axis), and the band half-width (fitted using a Lorentzian band profile) can be varied it is also possible to zoom in on selected regions of the spectrum. 

The real advantage of frequency-domain analysis is the ability to normalize each vibration component so that a complex machine-train spectrum can be divided into discrete components. This ability simplifies isolation and analysis of mechanical degradation within the machine-train. 

In addition, it should be noted that frequency-domain analysis can be used to determine the phase relationships for harmonic vibration components in a typical machine-train spectrum. Frequency-domain normalizes any or all running speeds, where time-domain analysis is limited to true running speed. 

Narrowband trending, like broadband, monitors the total energy for a specific bandwidth of vibration frequencies. Unlike broadband, narrowband analysis utilizes vibration frequencies that represent specific machine components or failure modes. 

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