Bridge measurements

A common known method to get eddy-current informations about material flaws is the measurement of real- and imaginary part of the complex impedance of a coil in absolute circuit. The measurement, shown in this paper, are done with an impedance analyzer (HP4192A). The device measures the serial inductance L, and the serial resistance Rs of the complex impedance with an auto-balance bridge measurement circuit [5]. 

Protons attached to the C atoms of the 1,2,4-trioxolane moiety of FOZs have chemical shifts at distinctly lower field than alcohols, ethers or esters. For example, the chemical shifts of the ozonide product in equation 100 (Section Vin.C.b.a) are S (CDCI3) 5.7 ppm for the H atoms of the trioxolane partial structure, and 4.1 ppm for the protons at the heads of the other ether bridge . Measurement of the rate of disappearance of these signals can be applied in kinetic studies of modifications in the ozonide structure. The course of ozonization of the methyl esters of the fatty acids of sunflower oil can be followed by observing in H and C NMR spectra the gradual disappearance of the olefinic peaks and the appearance of the 3,5-dialkyl-1,2,4-trioxolane peaks. Formation of a small amount of aldehyde, which at the end of the process turns into carboxylic acid, is also observed . 

Cells for Conductimetry. Reliable and precise measurements of electrolytic conductance require attention to the design of cells, electrodes, and measuring circuitry. Extraction of an ohmic resistance from AC bridge measurements is not a trivial task, particularly in solutions with high resistance (such as organic solvents) or low resistance (molten salts). Expositions of the principles are provided in monographs that emphasize aqueous solution,54,55 and in a review of conductimetry and high-frequency oscillometry that emphasizes analytical applications.56... 

Bridge measurements provide the most direct way to compare an unknown impedance with known standard impedances. The impedance may be a pure resistance, capacitance, or inductance, or may be represented by some series or parallel combination. The DC Wheatstone bridge95 provides a simple and... 

Measurement of solution conductance. Because the measurement of solution conductance (or resistance) is a common procedure that provides useful information to the electrochemist, the principles of a bridge measurement are illustrated by such an application. 

AC bridge measurements provide only an absolute impedance and phase shift, so there is no way to distinguish between either a series or parallel R-C combination by use of a pure sinusoidal waveform. Thus the series R-C combination of the cell may be matched by the series combination shown in Figure 6.24b or the parallel combination of the Wien bridge shown in Figure 6.24c. Either an oscilloscope or phase-angle voltmeter100 are recommended as null indicators because they allow both the phase shift and the imbalance potential to be nulled. 

Figure 4 Dielectric parameters of poly methyl methacrylate obtained from the Reddish-Hyde spectrometer e - scale on left, e" - scale on right. The l.f. and h.f. instruments overlap at 10 — 10 Hz the a.c. results are careful bridge measurements...

The x(Tg) is difficult to measure directly by conventional dielectric bridge measurement, but the x(Tg) value is calculated from o(Tg) through Eq. (15). The x(Tg) values have been reported to be from 12 to 69 s for some DGEBA oligomers (1396experimental error taking into account the accuracy of the measurement of Tg ( 1 °C). 

Problem Draw a diagram, show balanced equations, and write the notation for a voltaic cell that consists of one half-cell with a Cr bar in a Cr(N03)3 solution, another half-cell with an Ag bar in an AgN03 solution, and a KNO3 salt bridge. Measurement indicates that the Cr electrode is negative relative to the Ag electrode. 

Fig. 6.8. A CV curves from a pentacene OFET with a WjL of 1000/20/xm from [117]. The quasi-static CV captures the entire device capacitance, whereas the capacitance bridge measures too quickly to fully charge the channel and reads an incorrect value.

Dielectric measurements have developed Ifom cumbersome Wheatstone-bridge measurements to an efficient, precise, and rapid spectroscopic technique. The new technique dielectric spectroscopy soon found interesting applications within the field of eolloid chemistry. The technique can be applied as a preeision method in a thorough mapping of the static and dynamic properties of colloidal systems. Industrially, dielectric measurements ean be utilized in the online eharaeterization of sueh eomplex systems. 

FIGURE 13. Noise conductivity of collagen (1 g/liter of collagen (1 g/liter in methanol + 5 % water, 10 mol/liter HCl) versus frequency, at 25 °C, after subtracting the noise conductivity of the solvent. Vertical bars correspond to the error measure. The 1-MHz data point was obtained by a bridge measurement. 

ABSTRACT The results of analysis of temperatures based on experimental bridge measurements indicate that the partial factors of temperature components may be reduced to 1,3 for steel and composite steel-concrete bridges. The partial factors of temperatures for concrete bridges are found in a rather big range from 1,1 to 1,6 and should be further analysed. It appears that the application of the unique value of the partial factor for most variable actions should be reassessed during the upcoming period of Eurocodes maintenance. 

The results of analysis of temperatures based on the experimental bridge measurements indicate that the partial factors of the uniform temperature component may be reduced to 1,2 for steel and composite steel-concrete bridges and to 1,4 for concrete bridges. 

The double-layer structure and adsorption of various surface-active substances may be examined by this method, which replaces cumbersome balancing bridge measurements. 

The mathematics and methodology of such measurements are well understood (Hague [1957], Armstrong et al. [1968]). However, considerable use still may be made of passive audio frequency bridge measurements in this age of active circuitry, principally in high-precision applications. Following a brief review of bridge cir-... 

Because of the use of buffer amplifiers, null adjustment does not vary the potential across (or current through) the unknown impedance, as is the case for classical and transformer ratio bridge measurement. 

When pairs of electrodes, such as would be used in an impedance bridge measuring cell, are platinized, the electrodes, after preparation, should be shorted together in a saline solution and left for several days so that the residual potential difference produced by plating can be equalized. 

Now, if the bulk concentrations in the solution are changed by oxidative or reductive titration, E will vary. At zero current, E = 0.44 V from the experimental measurement. Figure 3.2 presents a nearly linear relation, which indicates that for high bulk concentrations the electrolyte can be replaced by a fixed resistor. Had the solution been stirred, a more nearly straight line would have resulted Experimentally, the curve slope is 53 kfl. A 1-kHz impedance bridge measurement of the system yielded 58 kQ. 

The alkylcyanobiphenyls are specially suited for the investigation of the dielectric relaxation because the two main modes of dipole relaxation are well separated. The hindered rotation about the short molecular axis is shifted to relatively low frequencies conveniently accessible in impedance bridge measurements. This relaxation process is coupled to the strength of the nematic potential q, which should be sensitive to a variation of the intermolecular distance. Hence a strong pressure dependence is expected for this relaxation process. 

Figure 3 is the schematic diagram for the bridge measuring circuit. The Coupler Box consists of a heavy rod suspended directly between the and OUT connector. This center conductor along with the shielding box forms the primary line and has a characteristic impedance of approximately 150 ohms. The secondary line Is formed by a small rod mounted... 

The characteristic electrocapUlary curve that one would obtain from a typical electrolyte solution is shown in Fig. 2.9. From such measurements and, more accurately, by AC impedance bridge measurements, the structure of the electrical double layer has been determined. ... 

The discharge properties of these solid-state batteries are characterized by high practical energy densities, low-rate capability, and low rates of self-discharge. From the linear polarization curve (Fig. 15.3) it is apparent that the resistance is essentially ohmic. Bridge measurements of cell resistance at 1 kHz are in agreement with values determined from polarization curves. 

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