Vibration measurements

In this work, a microwave interferometric method and apparatus for vibration measurements is described. The principle of operation is based on measurement of the phase of reflected electromagnetic wave changing due to vibration. The most important features of the method are as follows simultaneous measurement of tlie magnitude and frequency of the rotating object high measurement accuracy weak influence of the roll diameter, shape and distance to the object under test. Besides, tlie reflecting surface can be either metallic or non-metallic. Some technical characteristics are given. 

Pump vibration measurements and analysis of the ampHtude—frequency spectmm have led to the deterrnination of possible equipment ailments. Examples of frequency relationships to particular pump vibration problems are available (62). Eor example, a one-time (lx) frequency corresponding to a mnning speed usually indicates the presence of rotor unbalance, a 2 x peak may mean a bent shaft, and a - O.dx may be a symptom of an oil whip at the sleeve bearing. 

Shaft vibration measurement methtxls, 350 Shaking forces reciprocating, 368, 378 rotary, 382... 

As the measuring distance for such equipment can be up to about. 50 m, this technique is advantageous in cases when conventional acoustic or vibro-meter devices are difficult or even impossible to use, such as high-frequency vibration measurements on the walls of high-level air ducts. 

The transducer most commonly used to obtain vibration measurements is an accelerometer. It incorporates piezoelectric (i.e., pressure-sensitive) films to convert mechanical energy into electrical signals. The device generally incorporates a weight suspended between two piezoelectric films. The weight moves in response to vibration and squeezes the piezoelectric films, which sends an electrical signal each time the weight squeezes it. 

The maximum value of the displacement is X, which is also called the amplitude. The period, T, is usually measured in seconds its reciprocal is the frequency of the vibration, /, measured in cycles per second (cps) or Hertz (Hz). 

Figure 43.25 Resultant shaft velocity vector based on radial vibration measurements...

For accuracy of data, a direct mechanical link between the transducer and the machine s casing or bearing cap is necessary. This makes the method used to mount the transducer cmcial to obtaining accurate data. Slight deviations in this link will induce errors in the amplitude of vibration measurement and may create false frequency components that have nothing to do with the machine. 

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. 

A visual inspection of the blower indicated that the discharge is horizontal and opposite the measurement point location. By checking the process parameters recorded concurrent with the vibration measurements, we found that the motor was in a no-load or run-out condition and that the discharge pressure was abnormally low. In addition, the visual inspection showed that the blower sits... 

On the experimental side, one may expect most progress from thermodynamic measurements designed to elucidate the non-configurational aspects of solution. The determination of the change in heat capacity and the change in thermal expansion coefficient, both as a function of temperature, will aid in the distinction between changes in the harmonic and the anharmonic characteristics of the vibrations. Measurement of the variation of heat capacity and of compressibility with pressure of both pure metals and their solutions should give some information on the... 

Raman spectroscopy comprises a family of spectral measurements based on inelastic optical scattering of photons at molecules or crystals. It involves vibrational measurements as well as rotational or electronic studies and nonlinear effects. Following, Raman will be used in the established but slightly inaccurate way as a synonym for the most important and most common technique of the family, linear vibrational Raman scattering. 

These vibration measurements have linked the vibration modes in several working conditions to the bolometer noise. 

For existing equipment a vibration measure survey should be undertaken or examination of piping suspected of being under stress. Critical examination of connection points should be made where the induced piping vibration stress is the greatest. For new designs a stress analysis can be prepared on the pipework by specialized consultants. 

C. Ovren, M. Adoleson, andB. Hok, Fibreopticsystems fortemperatureand vibration measurements in industrial applications, Proc. Int. Conf. Optical Techniques in Process Control, The Hague (1983). 

Vibration Measured frequency (cm ) Ab initio frequency (cm ) Meas./A6 init. Ratio Vj,/Vj5 (ab initio)... 

During the performance test, unfiltered vibration measurements and a Fast Fourier Transform (FFT) spectrum shall be made at each test point except shutoff. The measurements shall be as follows ... 

Bearing housing overall vibration measurements shall be made in root mean square (RMS) velodty and, when U.S. dimensions are specified, in both RMS and True Peak velocity, mm/sec (in./sec). 

Optional arrangement for mounting vibration measuring equipment (see 2.9.2.11 and 2.9.2.12)... 

The units for shaft vibration measurement shall be peak-to-peak displaeement in pm (mils). 

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