Resistivities measurement

If a pressure measuring device were run inside the capillary, an oil gradient would be measured in the oil column. A pressure discontinuity would be apparent across the interface (the difference being the capillary pressure), and a water gradient would be measured below the interface. If the device also measured resistivity, a contact would be determined at this interface, and would be described as the oil-water contact (OWC). Note that if oil and water pressure measurements alone were used to construct a pressure-depth plot, and the gradient intercept technigue was used to determine an interface, it is the free water level which would be determined, not the OWC. 

The resistance due to a circular junction is given by / = /2ak, where a is the radius of the junction and k is specific conductivity of the metal. For the case of two steel plates, the measured resistance is 5 x 10" Q for a load of 50 kg the yield pressure of steel is 60 kg/mm, and the specific resistance is 5x 10 Q/cm. Calculate the number of junctions, assuming that it is their combined resistance that is giving the measured value. 

Figure C3.2.16. Dependence of measured resistance in an STM junction consisting of a bare tip a tip with one Xe atom attached, and a tip with two Xe atoms. Note that the Xe atoms facilitate tunnelling (compared to empty space). From Yazdani A, Eigler D M and Lang N D 1996 Off resonance conduction tlirough atomic wires Science 111 1921-4.

Knoop developed an accepted method of measuring abrasive hardness using a diamond indenter of pyramidal shape and forcing it into the material to be evaluated with a fixed, often 100-g, load. The depth of penetration is then determined from the length and width of the indentation produced. Unlike WoodeU s method, Knoop values are static and primarily measure resistance to plastic flow and surface deformation. Variables such as load, temperature, and environment, which affect determination of hardness by the Knoop procedure, have been examined in detail (9). 

Electrical—Thermal Conductivities. Electrical conductivities of alloys (Table 5) are often expressed as a percentage relative to an International Annealed Copper Standard (lACS), ie, units of % lACS, where the value of 100 % lACS is assigned to pure copper having a measured resistivity value of 0.017241 Q mm /m. The measurement of resistivity and its conversion to % lACS is covered under ASTM B193 (8). 

Measuring cable to pipeline or reference electrode interrupted Measure resistance of cable and electrode... 

Control electrode resistance too high Check connections, measure resistance and potential of electrode, possibly renew... 

The data obtained from the resistance measurements are shown in Fig. 4.10. The assigned values of conductivity are limited in accuracy because the measured resistance was found to be somewhat time dependent. The [100] datum at the lowest strain was particularly so and a definite resistance value cannot be assigned to that point. 

For local deviations from random atomic distribution electrical resistivity is affected just by the diffuse scattering of conduction electrons LRO in addition will contribute to resistivity by superlattice Bragg scattering, thus changing the effective number of conduction electrons. When measuring resistivity at a low and constant temperature no phonon scattering need be considered ar a rather simple formula results ... 

Resistivity. Control of the resistivity of the mud and mud filtrate while drilling may be desirable to permit better evaluation of formation characteristics from electric logs. The determination of resistivity is essentially the measurement of the resistance to electrical current flow through a known sample configuration. Measured resistance is converted to resistivity by use of a cell constant. The cell constant is fixed by the configuration of the sample in the cell and is determined by calibration with standard solutions of known resistivity. The resistivity is expressed in ohm-meters. 

Cathodic-protection instruments may be classified as potential-measuring, current-measuring, resistance/conductance-measuring, multicombination, recording and ancillary. 

Measurement of resistance As previously mentioned, the four-electrode resistivity meters can be used to measure resistances. For this purpose the... 

In many cases it will suffice to include in the circuit a shunt of appropriately low resistance over which 7/ -drop potential measurements can be made for ready calculation of the magnitude of the current flow. This technique permits measurements to be made as required without opening the circuit even momentarily for the introduction of current-measuring devices. It is also possible to arrange instruments in a circuit so that no measuring resistance is introduced in the galvanic current circuit . 

This formula shows the factorial effect of the separator on the electrical resistance the measured resistance of the electrolyte-filled separator is the (T2]P) - fold multiple of the electrolyte resistance without the separator by definition, T2/P > 1. 

Electrical resistance blocks Measures resistance resulting from a gradient between the sensor and the soil higher resistance indicates lower soil moisture Consists of electrodes embedded in a gypsum, nylon, or fiberglass porous material... 

The data in Figure 5 can now be considered in light of the conduction model developed above. As stated previously, conduction in reduced poly-I behaves like an activated process. There are two sources that potentially could be responsible for this behavior. The first is the Boltzmann type concentration dependence of the 1+ and 1- states discussed above. The number of charge carriers is expected to decrease approximately exponentially with T. The second is the activation barrier to self-exchange between 1+ and 0 sites and 0 and 1- sites. For low concentration of charge carriers both processes are expected to contribute to the measured resistance. 

Fig. 3.34 LDA of the microarray signal patterns obtained in practical KAMINA tests to detect gaseous precursors of smoldering fires through overheated cable insulation. Prior to the LDA the measured resistances of the sensor segments were normalized to the median of all sensor segments and the number of variables was reduced by a Principal Component Analysis (PCA) to cutback the noise. Clear distinction is achieved between clean air...

Change of electrical conductance in a reacting system involving ionic species (e.g., the hydrolysis of ethyl acetate) the reaction is carried out in a conductivity cell in an electrical circuit for measuring resistance. 

Dissolution Measurement. Resist solutions 1n mixtures of Isoamyl acetate/cyclohexanone/methyl Isobutyl ketone (90 5 5 by volume) were filtered through 0.45 pm disc filters, then spin-coated onto silicon wafers at about 2000 rpm. The coated wafers were prebaked 1n a convection oven at 90°C for 1 hour, then stored 1n a desiccator. The basicities of the alkaline solutions were titrated by a standard HC1 solution with a Fisher Accument pH meter, Model 805 MP. The film thickness 1s about 2 pm. Resist dissolution was measured by a He-Ne laser Interferometer 1n a thermostated bath at the desired temperatures (12.131-... 

V79 System. The Chinese hamster V79 line was established in 1958 (Ford and Yerganian, 1958). Publication of the use of the line for mutation studies (by measuring resistance to purine analogues due to mutation of the Hgprt locus) occurred 10 years later (Chu and Mailing, 1968). The V79 line was derived from a male Chinese hamster hence, V79 cells possess only a single X chromosome. 

Check out the socket board to verify the statements above indicating which sockets are connected internally. To do this, set the multimeter to measure resistance (set to the 2-KQ range) and touch the contact tips of the test leads to any two sockets on the board. If there is internal contact, the resistance measurement will be zero (no resistance). If there is no internal connection, it is an open circuit and the resistance will be infinite. Record the results for each pair of sockets tested. 

Now measure one of your resistances with the multimeter as follows. Insert the wire ends into two sockets on the socket board so that they are not connected internally, such as in sockets FI and F5. (You will have to bend the end wires at about a 90° angle.) Measure the resistance with your multimeter by setting the selector switch to measure resistance and then contacting the lead tips to sockets that make contact with FI and F5, such as G1 and G5. You may have to adjust the selector switch to the proper range for the resistor being measured. Record the value in your table. Measure all the other resistors in the same way. Determine if the accuracy of each, as indicated by either the gold or silver stripes, is correct based on your data and comment on this. 

Variations of resistance with frequency can also be caused by electrode polarization. A conductance cell can be represented in a simplified way as resistance and capacitance in series, the latter being the double layer capacitance at the electrodes. Only if this capacitance is sufficiently large will the measured resistance be independent of frequency. To accomplish this, electrodes are often covered with platinum black 2>. This is generally unsuitable in nonaqueous solvent studies because of possible catalysis of chemical reactions and because of adsorption problems encountered with dilute solutions required for useful data. The equivalent circuit for a conductance cell is also complicated by impedances due to faradaic processes and the geometric capacity of the cell 2>3( . 

In short, small but definite frequency dependence upon measured resistance is generally observed and the problem becomes one of obtaining the correct ohmic resistance of the solution by an extrapolation procedure. (See discussion of extrapolation procedures below.)... 

Solutions in a conductance cell are often stirred to hasten salt dissolution, to promote solution mixing, or to prevent temperature gradients. Some workers observe an upward drift in measured resistances of unstirred solutions 12-17) while others report a downward drift unless the unstirred solution is mixed by shaking of the cell immediately before the measurement9-18-26>. The magnitude of this change is often 0.1 % or more. The effect has not been observed in other cases 8>10). The source of this problem has been variously attributed to temperature variations, electrode adsorption effects and solvent impurities, although the problem has not been analyzed in detail. In all but one of the above cases 12> the resistance of the stirred solution was taken as the true value. 

The type and magnitude of frequency dependence upon measured resistance depends upon the design of the conductance cell. Generally, measured resistance decreases with increasing frequency, although the opposite effect is observed in some cases with Erlenmeyer-type cells 21>2S>. Mysels et al. 2S> analyze this effect and extrapolate to zero frequency on a plot of resistance vs. f 2. 

Figure 24 illustrates what gives rise to the measured resistance and capacitance of a mixed-conducting film (as determined by impedance) when the reaction is limited by either (a) chemical reduction of O2 to at the gas/film interface or (b) transport of oxygen ions in the bulk of the film (where electronic conduction is facile). 

NOTE Make sure that the spark plug is not resistor type (measure resistance from tip to center electrode, should be less than a few ohms), otherwise the capacitor does not discharge fast enough through the plug. 

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