Vibration probes

More informative and precision instruments are devices based on the dynamic methods of indentation. The impedance of a vibrating probe perturbing the medium is related to the... 

Auxiliary bearing and shaft vibration probe length (given by manufacturer)... 

Expander-compressor shafts are preferably designed to operate below the first lateral critical speed and torsional resonance. A flame-plated band of aluminum alloy or similarly suitable material is generally applied to the shaft in the area sensed by the vibration probes to preclude erroneous electrical runout readings. This technique has been used on hundreds of expanders, steam turbines, and other turbomachines with complete success. Unless integral with the shaft, expander wheels (disks) are often attached to the shaft on a special tapered profile, with dowel-type keys and keyways. The latter design attempts to avoid the stress concentrations occasionally associated with splines and conventional keyways. It also reduces the cost of manufacture. When used, wheels are sometimes secured to the tapered ends of the shaft by a common center stretch rod which is pre-stressed during assembly. This results in a constant preload on each wheel to ensure proper contact between wheels and shaft at the anticipated extremes of temperature and speed. 

Figure 4-6 is an amplitude-speed eurve showing the loeation of the running speed to the eritieal speed, and the amplitude inerease near the eritieal speed. When the rotor amplifieation faetor, as measured at the vibration probe, is greater than or equal to 2.5, that frequeney is ealled eritieal and the eorresponding shaft rotational frequeney is ealled a eritieal speed. For the purposes of this standard, a eritieally damped system is one in whieh the amplifieation faetor is less than 2.5. 

Although the idea of generating 2D correlation spectra was introduced several decades ago in the field of NMR [1008], extension to other areas of spectroscopy has been slow. This is essentially on account of the time-scale. Characteristic times associated with typical molecular vibrations probed by IR are of the order of picoseconds, which is many orders of magnitude shorter than the relaxation times in NMR. Consequently, the standard approach used successfully in 2D NMR, i.e. multiple-pulse excitations of a system, followed by detection and subsequent double Fourier transformation of a series of free-induction decay signals [1009], is not readily applicable to conventional IR experiments. A very different experimental approach is therefore required. The approach for generation of 2D IR spectra defined by two independent wavenumbers is based on the detection of various relaxation processes, which are much slower than vibrational relaxations but are closely associated with molecular-scale phenomena. These slower relaxation processes can be studied with a conventional... 

WEAVER ETAL. Vibrational Probes of Electrochemical Interfaces 305... 

When noncontacting vibration probes are furnished in aecordance with 3.4.3.1, the rotor shaft sensing areas to be observed by radial vibration probes shall be concentric with the bearing journals. All shaft sensing areas (both radial vibration and axial position) shall be free from stencil and scribe marks or any other surface discontinuity, such as an oil hole or a keyway, for a minimum distance of one probe tip diameter on each side of the probe. These areas shall not be metallized. 

Electrical and mechanical runout of the rotor surfaces to be observed by vibration probes shall be determined and recorded. The runout shall be determined by rolling the rotor supported by V-blocks positioned at the centerhne of the bearing journals while measuring runout with a noncontacting vibration probe and a dial indieator simultane-... 

When noncontacting vibration probes are furnished, accurate records of electrical and mechanical runout for the full 360 degrees at each probe location shall be included in the mechanical test report. 

When specified for equipment with hydrodynamic bearings, provision shall be made for mounting two radial vibration probes in each bearing housing, two axial position probes at the thrust end of each machine, and a one event per revolution probe in each machine. The purchaser will specify whether the vendor is to supply these detectors. The detectors and their mounting and calibration shall be supplied, installed, and tested in accordance with API Standard 670. 

All purchased vibration probes, transducers, and oscillator-demodulators shall be in use during the test. If vibration probes are not fnmished by the vendor or if the purchased probes are not compatible with shop readout facilities, shop probes and readouts that meet the accuracy requirements of API Standard 670 shall be used. The vibration measured with this instrumentation shall be the basis for acceptance or rejection of the pump (see 2.8.3.7 and 2.8.3.8). 

Rotor mechanicai and eiectricai runout for pumps designed to use noncontacting vibration probes. ... 

If non-contacting vibration probes are furnished in accordance with 6.4.2.2, the shaft sensing areas (both radial vibration and axial position) to be observed by radial vibration probes shall ... 

For areas to be observed by radial vibration probes, 25% of the allowed peak-to-peak vibration amplitude or 6 pm (0,25 mil), whichever is g reater. 

If it is specified that equipment shall have provisions for mounting non-contacting vibration probes (6.4.2.2), the shaft shall be prepared in accordance with the requirements of 5.6.10 and API 670. 

Cullander, C., and R.H. Guy. 1992. Visualization of iontophoretic pathways with confocal microscopy and the vibrating probe electrode. Solid State Ionics 53-56 197. 

Johnston, C.T., G. Sposito, and G. Erickson (1992). Vibrational probe studies of water interactions with montmorillonite. Clays Clay Min., 40 722-730. 

Recent advances in the development of non-invasive, in situ spectroscopic scanned-probe and microscopy techniques have been applied successfully to study mineral particles in aqueous suspension (Hawthorne, 1988 Hochella and White, 1990). In situ spectroscopic methods often utilise molecular probes that have diagnostic properties sensitive to changes in short-range molecular environments. At the particle-solution interface, the molecular environment around a probe species is perturbed, and the diagnostic properties of the probe, which can be either optical or magnetic, then report back on surface molecular structure. Examples of in situ probe approaches that have been used fruitfully include electron spin resonance (ESR) and nuclear magnetic resonance (NMR) spin-probe studies perturbed vibrational probe (Raman and Fourier-transform IR) studies and X-ray absorption (Hawthorne, 1988 Hochella and White, 1990 Charletand Manceau, 1993 Johnston et al., 1993). 

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