Direct current applications

It is noteworthy for people busy in the field of electrical power engineering that ohmic-inductive circuits with L/R ratios <1 ms (even in the range L/R = 10 ps or L/R = 100 ps) are considered as inductive circuits in EN 50020. For comparison, in power circuits, contactors and motor starters for direct current application are rated for L/R ratios within a range 1 ms = L/R 15 ms... 

Only the anode foil is anodized in dry electrolytic assemblies intended for direct current applications. Anodized electrodes are of high purity, whereas the nonanodized electrodes utilize foil ribbons of lower purity. Prior to anodizing, the foil is usually (but not always) etched to increase eflective surface area. Containers for dry electrolytic capacitors can be either drawn or impact extruded. 

In contrast to a direct injection of dc or ac currents in the sample to be tested, the induction of eddy currents by an external excitation coil generates a locally limited current distribution. Since no electrical connection to the sample is required, eddy current NDE is easier to use from a practical point of view, however, the choice of the optimum measurement parameters, like e.g. the excitation frequency, is more critical. Furthermore, the calculation of the current flow in the sample from the measured field distribution tends to be more difficult than in case of a direct current injection. A homogenous field distribution produced by e.g. direct current injection or a sheet inducer [1] allows one to estimate more easily the defect geometry. However, for the detection of technically relevant cracks, these methods do not seem to be easily applicable and sensitive enough, especially in the case of deep lying and small cracks. 

Superconductivity The physical state in which all resistance to the flow of direct-current electricity disappears is defined as superconductivity. The Bardeen-Cooper-Schriefer (BCS) theoiy has been reasonably successful in accounting for most of the basic features observed of the superconducting state for low-temperature superconductors (LTS) operating below 23 K. The advent of the ceramic high-temperature superconductors (HTS) by Bednorz and Miller (Z. Phys. B64, 189, 1989) has called for modifications to existing theories which have not been finahzed to date. The massive interest in the new superconductors that can be cooled with liquid nitrogen is just now beginning to make its way into new applications. 

Electrochemical Impedance Spectroscopy (EIS) and AC Impedance Many direct-current test techniques assess the overall corrosion process occurring at a metal surface, but treat the metal/ solution interface as if it were a pure resistor. Problems of accuracy and reproducibility frequently encountered in the application of direct-current methods have led to increasing use of electrochemical impedance spectroscopy (EIS). 

Typical applications for adjustable-voltage, adjustable-speed dc drives include winders, paper machines and auxiliaries, blending systems, feeders, extruders, calendars, machine tools, range and slasher drives, cranes, hoists, shovels and draghnes, and an almost unhmited variety of drives requiring the flexibility and efficiency possible with direct current. 

Location of faults by the direct current method is based on the application of Ohm s Law. It is assumed that, because of the good pipe coating, virtually no current passes into the measured span and that the longitudinal resistance R is known. When the fault-locating current, I, is fed in and takes a direct path via the foreign line to the protected pipeline, the fault distance is determined from the voltage drop AU over the measured span ... 

A further objective is the evaluation in group (c) of the local polarization state by taking account of IR errors due to direct currents. Here Eq. (3-28) and the further explanations in the second half of Section 3.3.1 are relevant. In practical application, the error effect of A /<,ff must be estimated [2]. When foreign fields are present, it is necessary to substitute for the At/ value the average of the measurements made on both sides of the pipeline [2,52]. Figure 3-30 gives an example of... 

Direct current motors are most appropriately used in applications where a dc power supply is available or where a simple method of speed control is desired. The fans used in automobile heating and air conditioning systems are driven by direct-current motors. 

Direct Current (DC). This current is transmitted for industrial uses only in exceptional situations. The most common sources of direct current are storage batteries and industrial devices called rectifiers, in which alternating current is changed (rectified) to direct current, as is used in electrolytic cells for the manufacture of chlorine gas, magnesium, aluminum, and a few other chemicals. The direct current is flowing from the source through the user application and back to the source, in one direction. The motor is primarily used for speed control of selected equipment. 

This is a very good motor for direct connection to certain loads, particularly where constant speed is required. NEMA defines it as a synchronous machine which transforms electrical power from an alternating-current system into mechanical power. It usually has direct-current field excitation by a separately driven direct-current generator or one directly connected to the motor. This motor remains synchronous with the supply frequency and is not affected by the load. Proper application requires consideration of the following ... 

The deliberate raising of the electrical potential of titanium, either by the attachment of discrete particles of a noble metal, such as platinum or palladium, at the surface, or by the application of positive direct current to force the formation of a protective film, is dealt with at a later point. The electrochemical aspect of the corrosion of titanium is comprehensively treated in a number of papers ... 

Direct-current sputtering is not generally applicable for the preparation of thin-film solid electrolytes since these compounds are electronic insulators. The target surface would be charged with the same polarity as that of the ions in the plasma, and the sputtering plasma would rapidly break down. 

The function that plastics serve in most applications is that of a dielectric or insulator that separates two conductors with an electrical field between them. The field can be a steady direct current (DC) field or an alternating current (AC) field and the frequency range may vary such as from 0 to 1010 Hz. 

The resistance of most plastics to the flow of direct current is very high. Both surface and volume electrical resistivities are important properties for applications of plastics insulating materials. The volume resistivity is the electrical resistance of the material measured in ohms as though the material was a conductor. Insulators will not sustain an indefinitely high voltage as the applied voltage is increased, a point is reached where a drastic decrease in resistance takes place accompanied by a physical breakdown of the insulator. This is known as the dielectric strength, which is the electric potential in volts, which would be necessary to cause the failure of a 1/8-in. thick insulator (Chapter 4, ELEC-TRICAL/ELECTR ONICS PRODUCT). 

The scope of this review Is limited to electrothermal atomic absorption spectrometry, with emphasis upon Its clinical applications. This article Is Intended to supplement the recent treatises on the basic technique which have been written by Aggett and Sprott ( ) > Ingle ( ), Klrkbrlght (34), Price (63), and Woodrlff (83). This resume does not consider various related topics, such as (a) atomic fluorescence or emission spectrometry (b) non-flame atomization devices which employ direct current... 

Rahman S, Leong AS. Diagnostic immunohistochemistry current applications and future directions. Malays J. Pathol. 1991 13 17-28. 

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