Floating Measurement Techniques

Floating measurements are also used to avoid ground loops where equipment and test cell are grounded at different points leading to noise and interference in the measurements. If the cell is grounded but the equipment is floating then this problem can be avoided. 

It has been known for earth connections to be removed from nonfloating systems to convert them into floating systems. This is a very dangerous practice and is not recommended from the safety point of view since the whole equipment could become hve which could lead to injury or fatalities. 

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The most serious possible problem with this measurement technique is the possible loss of OH prior to detection. The primary diagnostic indicator for the presence of contamination is the temperature of the sample air flow after passage through the detection volume. If boundary-layer air has intruded into the detection volume, the sample air temperature will rise above ambient because the walls of the detection module are always warmer than the ambient air temperature. For example, at float altitude the temperature difference is —15 °C. 

No complete characterizatl071 of an electrode process, combining capacitance, floating junction, and simple kinetic measurements as outlined above, has yet been made on a semiconductor electrode. A number of semi-quantitative studies have been made on germanium electrodes using the floating-junction technique (or variations on it) described above. 

Raman scattering on NdBg has been reported by Pofahl et al. (1986). The Raman measurements were carried out on the (110) face of a NdBg single crystal which was prepared using the arc floating zone technique (Verhoeven et al. 1976). The measurements were performed as a function of temperature between 300 K and 7K, with the sample under vacuum. Several different laser wavelengths (5145 A, 5130 A, 5682 A) were used. 

Various shear stress measurement techniques have been proposed in the literature. Some of the principal measurement techniques are Stanton tube, Preston tube, electrochemical technique, velocity measurements, thermal method, floating element sensors, sublayer fence, oil-film interferometry, and shear stress-sensitive liquid crystal [5]. 

Ultrapure silicon is not only important for transistors, it is also required for solar batteries. Zone refining of silicon using a quartz boat is unable to remove the last traces of boron except when a chemical purification is simultaneously applied. The reactivity of molten silicon creates problems of contamination with oxygen. For higher purity, the floating zone technique has been used to quantify the concentration of boron, an electron acceptor, and phosphorus, an electron donor. The electrical conductivity measured as a function of distance along the rod is found to be proportional to the difference in concentration of boron and phosphorus their concentration after refining is of the order of 10 atoms cm . ... 

Various shear stress measurement techniques have been proposed in the literature. Some of the principal measurement techniques are Stanton tube, Preston tube, electrochemical technique, velocity measurements, thermal method, floating element sensors, sublayer fence, oil-film interferometry and shear stress sensitive liquid crystal. The Stanton tube is a rectangular shaped pitot tube located very close to the boundary wall and the mean velocity measured from this pitot tube pressure difference is directly related to the shear stress. The Preston tube is similar to the concept of the Stanton tube using a pitot static tube close to the surface and the difference between the stagnation pressure at the center of the tube from the static pressure is related to the shear stress. The electrochemical or mass transfer probe is flush mounted with the wall and the concentration at the wall element is maintained constant. The measurement of mass transfer rate between the fluid and the wall element is used for determination of the wall shear stress. One of the limitations of the mass transfer probe is that at very high flow rates, the mass transfer rate becomes large and it may not be possible to maintain the wall concentration constant. A detailed discussion on the above three techniques can be found in Hanratty and Campbell [1]. These shear stress measurement techniques are not ideal MEMS-based techniques. 

A great variety of level measurement techniques are available. These involve point-contact, visual, buoyancy, float, and hydrostatic methods, and radio-frequency, ultrasonic, microwave, nuclear radiation, resistance tape, and thermal level systems [3]. 

Due to numerous benefits of MEMS-based shear stress sensors, the following shear stress measurement techniques having great promise for future MEMS applications have been discussed in the following sections (1) velocity measurements, (2) thermal sensors, (3) floating... 

The common technique used to measure the API gravity of a hquid sample is with a hydrometer graduated in degrees of API gravity. The hydrometer is inserted in the liquid sample and allowed to float freely. When equilibrium is reached, the API gravity may be read from the exposed portion of the hydrometer. 

This discrepancy between the apparent level, in the gauge glass, and the actual level (see Fig. 6.1), in the tower, also occurs in any other type of level-measuring device. This includes external float chambers, kidneys, displacement chambers, and level-trols. The one exception to this is level-measuring devices using radiation techniques. 

There are several instruments which employ highly sensitive weighing techniques. One particular meter is based upon the measurement of the upthrust on a float(45). Any displacement of the float due to a change in the gas density (and consequently buoyancy) is counterbalanced by a magnetic field produced by an electromagnet. The float is thus maintained in the null position by the force generated by the flow of a direct current in the coil of the electromagnet. This current is directly proportional to the density of the gas. A temperature correction is applied to the readout and densities up to 500 kg/m3 at pressures up to 17 MN/m2 can be measured. 

Good descriptions of practical experimental techniques in conventional electrophoresis can be found in Refs. [81,253,259]. For the most part, these techniques are applied to suspensions and emulsions, rather than foams. Even for foams, an indirect way to obtain information about the potential at foam lamella interfaces is by bubble electrophoresis. In bubble microelectrophoresis the dispersed bubbles are viewed under a microscope and their electrophoretic velocity is measured taking the horizontal component of motion, since bubbles rapidly float upwards in the electrophoresis cells [260,261]. A variation on this technique is the spinning cylinder method, in which a bubble is held in a cylindrical cell that is spinning about its long axis (see [262] and p.163 in Ref. [44]). Other electrokinetic techniques, such as the measurement of sedimentation potential [263] have also been used. 

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