Circular of the Bureau of Standards, Vol. 31

Bücher

Angebote / Angebote:

Excerpt from Circular of the Bureau of Standards, Vol. 31: Copper Wire Tables Copper wire tables are based on certain standard values for the conductivity or resistivity and the temperature coefficient of resistance of copper. When accuracy is important, the electrical engineer does not consult the wire table, but makes actual measurements of the resistivity of samples of the copper used. Frequently the resulting conductivity is expressed in per cent of the standard value assumed for conductivity. Per cent conductivity is meaningless without a knowledge of the standard value assumed, unless the same standard value is in use everywhere. But the standard value was not formerly the same everywhere, as may be seen by inspection of Table I, page 35, and confusion in the expression of per cent conductivity has accordingly resulted. The temperature coefficient of resistance is usually assumed as some fixed standard value, but the standard value was not formerly the same everywhere, and results reduced from one temperature to another have accordingly been uncertain when the temperature coefficient assumed was not stated. These conditions led the Standards Committee of the American Institute of Electrical Engineers to request the Bureau of Standards to make an investigation of the subject. This was done and resulted in the establishment of standard values based on measurements of a large number of representative samples of copper - values which in certain respects are more satisfactory than any preceding standard values. The investigation is described below. This investigation finally led to the adoption of an international copper standard by the International Electrotechnical Commission. Table I gives a number of the most important standard values that have been in use. (See p. 39 for the table and p. 27 for a short explanation of the table.) The resistivity is uniformly given in terms of the resistance in ohms of a uniform wire 1 meter long weighing a gram. This unit of mass resistivity is conveniently designated for brevity as ohms (meter, gram). About the Publisher Forgotten Books publishes hundreds of thousands of rare and classic books. Find more at www.forgottenbooks.com This book is a reproduction of an important historical work. Forgotten Books uses state-of-the-art technology to digitally reconstruct the work, preserving the original format whilst repairing imperfections present in the aged copy. In rare cases, an imperfection in the original, such as a blemish or missing page, may be replicated in our edition. We do, however, repair the vast majority of imperfections successfully, any imperfections that remain are intentionally left to preserve the state of such historical works.