Circular of the Bureau of Standards Volume 60

Circular of the Bureau of Standards Volume 60

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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1916 edition. Excerpt: ...is usually used. The terminals of the standard must have sufficient contact area so that there shall be no undue heating because of contact resistance. The design must be such that the current distribution in the resistance material does not depend upon the mode of connection to the circuit. Care is necessary to see that oil used as a cooling fluid has no constituents which corrode the metal. 11 For the investigations of the Bureau of Standards into voltameter problems, see reference No. 63, Appendix.1. Resistance standards for current measurements are often called "shunts" when used in conjunction with millivoltmeters for current measurement. (They are actually used as a shunt upon the instrument.) For the standards used with a potentiometer in precise measurements the expression "resistance standard" is preferable. (c) Absolute Ampere.--The absolute ampere, or "ampere" defined as one-tenth cgs electromagnetic unit, differs by a negligible amount from the international ampere. Its relation to the international ampere has been determined by a number of methods. An absolute measurement of current involves fundamentally the precise measurement of a force in a medium of unit permeability. This is seen from the dimensional formula of current in the electromagnetic system: -LHM-11_ TV J Since the dimensions of force are given by it follows that In most absolute current measurements of high precision an electrodynamometer has been used, of the form known as a current balance. Probably the most accurate determinations with current balances were made by the National Physical Laboratory n of England and by this Bureau." In both of these investigations, comparisons of the silver voltameter and the current balance...show more

Product details

  • Paperback | 30 pages
  • 189 x 246 x 2mm | 73g
  • Rarebooksclub.com
  • United States
  • English
  • black & white illustrations
  • 1236857119
  • 9781236857118