Electrical Resistivity Inductive Method

A second, non-destructive technique to determine porosities by resistivity measurements uses a coil as sensor. A current flowing through the coil induces an electric field in the unsplit sediment core while it is automatically transported through 

Generally, the coil characteristic is defined by the quality value(Q) 

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The two accepted methods used for heating platens are both electric resistance heating and induction heating. 

A selection of different methods of evaporation is available—including electrical resistance heating, electron beam, induction heating, and sputtering. 

Electric resistance weld pipe is made from strip in coil form. After being uncoiled, flat strip is progressively rounded as it passes through a series of vertical and horizontal forming rolls before welding. Small-diameter pipe is welded by the high frequency induction method and medium-diameter... 

In both cases the electric potential distribution recorded by the receiver electrodes is used to map the spatial resistivity distribution of the rock formation. The main limitation of the resistivity method is that direct current cannot penetrate through resistive formations. Electromagnetic induction methods, based on transient electromagnetic fields, overcome this difficulty because a transient field can easily propagate through resistors like a radiowave propagates in the air. At the same time,... 

Fig. 2.11 Comparison of electrical resistivities (galv.) measured with the small hand-held prohe and determined hy the inductive method (ind.) for the gravity cores PS1635-1 and PS1836-3. (a) Cross plots of hoth data sets. The dashed lines indicate a difference of 15%. (b) Downcore resistivity logs determined hy hoth methods. Modified after Gerland et al. (1993).

Oxidative induction time (OIT) provides an index useful in comparing the relative resistance to oxidation of a variety of hydrocarbon materials. The OIT procedure was first developed in 1975 by Gilroy and coworkers at Bell Laboratory as a test procedure to screen polyethylene insulation used in telephone wire and cable for its oxidation resistance. The method first became available as a Western Electric Specification and later as ASTM Test Method for Copper-Induced Oxidative Induction Time of Polyolefins. Polyolefin manufacturers quickly embraced the procedure and began to apply it to other applications including raw resins, finished pipes, wire and cable insulation, and, most recently, geosynthetic waste pit liners (ASTM D3895 2009). 

For experimental details, high pressure apparatus and techniques, references to original articles can be found in the review by Bloch and Pavlovic (1969). Briefly, the most common methods used in following a magnetic transition are change in the mutual inductance sensed through a set of coils placed around the specimen in a transformer-like set up, magnetic susceptibility, electrical resistivity and in some cases thermal dilation. To a limited extent more sophisticated... 

The development of the transistor— and the electronic revolution that followed—made it possible to measure extremely small electric currents of as little as 10 amperes, as well as corresponding values of voltage, resistance, induction, and other electronic functions. Basically, this made it possible to precisely measure fundamental properties by electronic means rather than physical methods. 

Vin] Inductance bridge method, four-point method Curie temperature, electrical resistivity, coercive field... 

Electricity is normally charged for on the basis of power (kilowatts) and the supply authority must install plant whose rating (and therefore cost) is a function of the voltage of the system and the current which the consumer takes (i.e. kilo-volt-amps). The relationship between the two is kW = kVA x cos (j> where cos (j> is the power factor and is less than 1.0. In the case of loads which have a low power, factor the supply authority is involved in costs for the provision of plant which are not necessarily reflected in the kWh used. A penalty tariff may then be imposed which makes it economically worthwhile for the consumer to take steps to improve his power factor. Low power factors occur when the load is predominantly either inductive or capacitive in nature (as opposed to resistive). In most industrial circumstances where the load includes a preponderance of motors, the load is inductive (and the power factor is therefore lagging). Consequently, if the power factor is to be brought nearer to unity the most obvious method is to add a significant capacitive component to the load. 

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