670 ELECTRICAL MEASUREMENTS 



the generator by means of change gears which permit the speed 

 to be varied so that the frequency may be made 1, 3, 5, 7 . . . 

 times that of the main* current. Also the machine must be so 

 constructed that the phase of the sinusoidal current may be al- 

 tered at will, a scale being provided so that the phase displacements 

 are readily determined. 



The maximum value of the sinusoidal current, A' k , is de- 

 termined from the reading of a current dynamometer. The 

 process of making a measurement is to change the phase of the 

 machine giving the sinusoidal current until the dynamometer 

 stands at zero, then to shift the phase 90 and take the dynamo- 

 meter reading. A contact arrangement and galvanometer which 

 by means of a double-throw switch may be connected to the 

 terminals of non-inductive resistances in either the main circuit or 

 in that of the sine generator, permits the zero points on the waves 

 to be located. The phases of the harmonics may then be de- 

 termined from the readings on a scale of degrees attached to the 

 movable field frame of the sine dynamo. 



The disadvantage of this method is that it requires special 

 apparatus. 



References 



1. "Sur les Courants Alternatifs et la Force Electromotrice de 1'Arc 

 Electrique," J. JOUBERT, Journal de Physique, vol. 9, 1880, p. 297. 



2. "An Apparatus for Recording Alternating-current Wave Forms," 

 F. A. LAWS, Proc. American Academy of Arts and Sciences, vol. 36, 1901, 

 p. 321. "The Slow Registration of Rapid Phenomena by Stroboscopic 

 Methods," E. HOSPITALIER, Journal Institution of Electrical Engineers, vol. 

 33, 1903, p. 80. See also Electrician, vol. 52, 1903-04, p. 298. "Mechan- 

 ical Integration of the Electromotive Force When Even Harmonics are 

 Present," M. MORRISON, Southern Electrician, vol. 43, 1911, p. 60. "The 

 Oscillograph and Its Uses," L. T. ROBINSON, Trans. American Institute 

 Electrical Engineers, vol. 24, 1905, p. 185. 



3. "A New Method of Tracing Alternating-current Curves," F. TOWN- 

 SEND, Trans. American Institute Electrical Engineers, vol. 17, 1900, p. 5. 

 "The Use of the Synchronous Commutator in Alternating-current 

 Measurements," FREDERICK BEDELL, Journal of the Franklin Institute, vol. 

 176, 1913, p. 385. 



4. "An Apparatus for Determining the Form of a Wave of Magnetic 

 Flux," M. G. LLOYD and J. V. S. FISHER, Bulletin Bureau of Standards, vol. 4, 

 1908, p. 467. 



5. "Oscillographes, nouveaux appareils pour l'e*tude des oscillations 

 electrique lentes," A. BLONDEL, Comptes Rendus, vol. 116, 1893, p. 502. 



