A Braun Tube Hysteresigraph 



By J. B. JOHNSON 



In this paper apparatus for observing hysteresis loops of magnetic 

 materials is described. It combines a cathode ray oscillograph with a 

 vacuum tube amplifier and an electrical integrating circuit consisting of 

 condenser and resistance. The device describes the B— H curve for alter- 

 nating magnetization in the frequency range of five to perhaps several 

 thousand periods per second. The specimens may be either long strips or 

 closed rings. Alternating flux as low as one maxwell may be readily 

 observed. 



The operation of the apparatus is analyzed so as to account for the 

 effects of finite time constants of the amplifier and integrator, of conductance 

 in the condensers, of demagnetization by current in the search coil and by 

 the stray fields of coils and specimen, and of eddy currents in the specimen. 



THE use of the cathode ray oscillograph for delineating magnetic 

 hysteresis curves has proved a convenience in a number of 

 studies of magnetic phenomena.^ The essential advantage of the 

 method lies in the speed with which the hysteresis loop is traced. 

 Complete curves are drawn in rapid succession by the oscillograph 

 tube, and any change in these curves resulting from altered mechanical 

 or magnetic conditions of the specimen can immediately be observed 

 and recorded. Furthermore, the area bounded by these curves 

 represents the total energy loss in the specimen corresponding to the 

 particular kind of magnetic cycle that is used, and not the hysteresis 

 loss alone as is the case in the curves derived by the slower point-by- 

 point methods. 



In the present article is described an apparatus combining a cathode 

 ray oscillograph with an electric circuit, for magnetic measurements. 

 A fairly extensive analysis of the operation of the device is presented 

 in order to show how accuracy may be maintained in the measurements 

 and the probable errors estimated. 



The apparatus has been in use since 1924, particularly for observing 



the magnetic properties of various alloys. It is so designed that by 



suitably choosing the circuit constants it can be used for obtaining 



the hysteresis curves of magnetic materials from the saturation value 



down to fields where the amplitude of alternating flux is about one 



maxwell. The purposes for which the apparatus has been employed 



are illustrated by the hysteresis curves reproduced in Plates I and II. 



1 K. Angstrom, Phys. Zeits., 1, p. 121, 1899; Phys. Rev., 10, p. 74, 1900. 

 E. Madelung, Ann. d. Phys., 17, p. 861, 1905; Phys. Zeits., 8, p. 72, 1907. 

 C. W. Waggoner and F. A. Molby, Phys. Rev., 17, p. 427, 1921. 

 Y. Niwa, J. Matura, and J. Sugiura, "Researches of the Electrotechnical Labo- 

 ratory (Ministry of Commerce, Tokyo)," No. 144, May, 1924. 



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