Proximal Probes

Central to all SPMs (or local probe methods , or local proximal probes as they are sometimes called) is the presence of a tip or sensor, typically of less than 100 mn radius, that is rastered in close proximity to—or in contact with—tire sample s surface. This set-up enables a particular physical property to be measured and imaged over the scaimed area. Crucial to the development of this family of teclmiques were both the ready availability of piezoelements, with which the probe can be rastered with subnanometre precision, and the highly developed computers and stable electronics of the 1980s, without which the operation of SPMs as we know them would not have been possible. 

Staufer U 1995 Surface modification with a scanning proximity probe microscope Scanning Tunnelling Microscopy II ed R Wiesendanger and Fl-J Guntherodt (Beriin Springer) ch 8... 

Two non-eontaeting proximity probes positioned at 90° shall be supplied at eaeh radial bearing. The probes shall be supplied eomplete with proximitors and intereonneeting wires. 

The limits expressed in Table 7-3 (x-axis = operating speed in rpm, y-axis = overall vibration level in mils [peak to peak]) are based on experienee in refineries. The guide refleets the typieal proximity probe installation elose to and supported by the bearing housing and assumes the main vibration eomponent to be of [lx rpm] frequeney. The... 

A funetional alternative to the use of proximity probes for bearing proteetion is bearing temperature, bearing temperature rise (bearing temperature... 

Eddy-current proximity probes are primarily used as displacement transducers. Eddy probes generate an eddy-current field, which is absorbed by a conducting material at a rate proportional to the distance between the probe and the surface. They are often used to sense shaft motion relative to a bearing (by mounting them within the bearing itself) or to measure thrust... 

Jackson, C.J., Alignment Using Water Stands and Eddy-Current Proximity Probes, Proceedings of the 9tli Turbomacliinery Symposium, Texas A M University, pp. 137-146, 1980. 

Axial proximity probes are another means of monitoring rotor position and the integrity of the thrust bearing. A typical installation is shown in Figure 21-11. In this case two positions are being monitored one at the thrust runner, and one at the end of the shaft near the centerline. This method detects thrust-collar runout and also rotor movement. In most cases this ideal positioning of the probes is not possible. Many times the probes are indexed to the rotor or other convenient locations and thus do not truly show the movement of the rotor with respect to the thrust bearing. 

A critical installation should have the metal temperature sensors in the thrust pad. Axial proximity probes may be used as a backup system. If metal temperatures are high and the rate of change of those temperatures begins to alter rapidly, thrust-bearing failure should be anticipated. 

By using the positional information available from a proximity probe, another valuable parameter can be measured. The axial position or axial shift detection can be added to the monitored information. Probes are generally installed at the shaft end in pairs to provide redundancy. Fhe probes, preferably, should be sensing the axial position from two differ ent surfaces. A typical arrangement can be seen in Figure 8-37... 

Figure 8-37. Typical axial proximity probe installation. (Courtesy of Turbocare, A Division of Demag Delaval Turbomachinery Corp. Houston facility...

The alternate method uses the proximity probes and an oscilloscope. A Lissajous figure is established on the oscilloscope. The orbit pattern and the keyphase mark are used to generate a vector. Weights are added or removed and the changes in the orbit are noted. Triangulation is used to anticipate the next move. For more complete information or technique, the reader is referred to a book on the subject by Jackson [ 1 ]. 

Displacement is the actual change in distance or position of an object relative to a reference point and is usually expressed in units of mils, 0.001 inch. For example, displacement is the actual radial or axial movement of the shaft in relation to the normal centerline usually using the machine housing as the stationary reference. Vibration data, such as shaft displacement measurements acquired using a proximity probe or displacement transducer, should always be expressed in terms of mils peak-to-peak. 

Abstract Described are the synthetic routes to precisely defined molecular wires which are of discrete length and constitution. They are fully conjugated systems and are expected to have nearly linear current-voltage response curves. Their ends are functionalized with molecular alligator clips, based on chalconides and isonitriles, for adhesion between proximal probes. Both solution and solid-phase approaches have been used to prepare these molecular wires that are based on oligofthiophene ethynylene)s and oligofphe-nylene ethynylene)s. Molecular device syntheses are also described that would be expected to have nonlinear current-voltage responses. 

In some cases, they have more than two termini. The testing of the wires or two-terminal device packets is described using proximal probes that have been litho-... 

If the vendor can demonstrate that there is electrical or mechanical runout of the rotor surfaees at the proximity probes (see 2.5.9), a maximum of 25 pereent of the measured value or 6 microns (0.25 mils), whichever is greater, may be vectorially subtracted from the vibration signal measured during the shop test. 

Pumps furnished with proximity probes shall meet both bearing housing and shaft vibration limits. 

Note The principal objective of shop verification by response to unbalance is to verify the existence of a critical speed (vibration peak) within tolerance of the calculated value, or if the analysis predicted a highly damped critical speed, the absence of a vibration peak within tolerance of calculated value. Shop verification by this method is feasible only for pumps that have sleeve bearings and are furnished with proximity probe pairs at each journal bearing. 

Molecular Self-Assembly. Reductive techniques, such as those used in the microelectronics industry, can produce structural features smaller than about 200 nm. The use of proximal probes and other nanomanipulative techniques can be considered to be a hybrid of the reductive lithographic techniques and die synthetic strategies of assembling functional nanostructures atom by atom, or molecule by molecule. The organization of nanostructures and devices by the self-assembly of the component atoms and molecules, a ubiquitous phenomenon in biological systems, forms die noncovalent synthetic approach to nanotechnology. 

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