Alternating and direct currents

Direct current (dc) has a constant positive value above zero and flows in one direction only, unlike ac. A simple example of direct current is that produced by a standard dry battery. 

DC is really ac which has its positive or negative surges rectified to provide the uni-directional flow. In a dc generator the natural ac product is rectified to dc by the conunutator. 

DC will be found in industry in the form of battery supplies for electrically powered works plant, such as fork lift trucks, togetiier with associated battery charging equipment. Otherwise, dc, obtained by rectification of the mains ac supply, will be encountered for specialist applications, e.g. electroplating. Some railway traction supplies also adopt dc. 

Danger from electricity may arise irrespective of whether it is ac or dc. Where dc is derived from ac supply the process of rectification will result in some superimposed ripple from the original ac waveform. Where this exceeds 10%, the electric shock hazard must be considered to be the same 

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Both alternating- and direct-current units are available. While dc pumps (Fig. 10-60) are simpler, their high-current requirement is a definite limitation ac pumps can readily obtain high currents by making use of transformers. Multipole induction ac pumps have been... 

Both alternating and direct current techniques can be used (see also impedance spectroscopy), but the electrode polarization effects should be minimized or taken into account in all cases. For this goal, a four-electrode method where the potential probes are placed between current probes, is often used. 

To determine the effect of alternating and direct current, an RCA CR 212 half-wave rectifier was added to the circuit, plus a resistance... 

E.N. Ervin, R. Kawano, R. White, and H.S. White, "Simultaneous alternating and direct current readout of protein ion channel blocking events using glass nanopore membranes," And. Chem., vol. 60, no. 6, pp. 2069-2076, Jan. 2008. 

In addition to fabrication and use techniques, there is extensive discussion of various problems associated with electrodes. Attention is directed to electrode polarization (both alternating- and direct-current phenomena), electrical noise, and requirements for backup instrumentation such as electronic amplifiers. A brief treatment of signal analysis and filtering techniques is included to complement the chapter dealing with amplifiers and the discussions of noise. 

Finegan, I.C., Tibbetts, G.G. Electrical conductivity of vapor-grown carbon fiber/ thermoplastic composites , J. Mater. Res. 16(6) (2001), 1668-1674 Kilbride, B.E., Coleman, J.N., Fraysse, J., Fournet, R, Cadek, M., Drury, A., Hutzler, S., Roth, S., Blau, W.J. Experimental observation of scaling laws for alternating and direct current conductivity in polymer-carbon nanotube composite thin films , J. Appl. Phys. 92(7) (2002), 4024-4030... 

Overall the Institute was outfitted with more modern and high-performance equipment than most universities at the time. In addition to providing for standard chemical procedures, the laboratory furnishings enabled researchers to pursue a number of specialized lines of research - such as studies of thermodynamic constants in the constant temperature rooms. The apparatus at the Institute conformed to the latest standards in physical chemistry research. For example, the electrical equipment was the best available at the time, offering not only alternating and direct current facilities but also a high-voltage installation in the machine hall. Similarly, the Institute possessed apparatus for research at the extremes of available gas pressures and at the limits of spectroscopic precision. ... 

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