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BELL SYSTEM TECHNICAL JOURNAL 



Fig. 5 illustrates the nature of this distortion. The straight line aa' 

 is the curve for the ideal material and perfect apparatus for which 



^^TTjs" 



Fig. 5 — Distortion produced by integrator and amplifier at low flux densities. 



the maximum amplitude in the B direction may be taken as unity. 

 The ellipse is the curve 



X = cos co/, 



y 



cos a;/ — ^/s sin co/, 



(10) 



which the apparatus traces. The point of tangency of the ellipse with 

 a line parallel to the B axis is at the point a and always remains there. 

 The intersections with the B axis are at ± S/j and th e height exc eeds 

 that of the point a by the usually very small quantity Vl + {^Js)' — 1- 

 In the present system the constants are: Rs — 2 Y. 10^ ohms; 

 C, = 4 X 10-6 farad; r' = 2 X 10« ohms. We may set R = 10^ 

 ohms, C = 20 X 10"^ farad, co = 100, and assume four stages of 

 amplification. For the type of condensers used in the integrator and 

 amplifier, Z = 250. The vertical width of the ellipse is then 3 per 

 cent of the total height, of which .5 per cent is caused by the time 

 constant of the integrator, .5 per cent by the time constant of the 

 four amplifier couplings (including the output circuit), and 2 per cent 

 by the conductance of the condensers in the circuit. The conductance 

 therefore contributes the largest error in the present system, showing 

 that the time constants have been made large enough for practical 

 purposes. 



2. Circuit Corrections for the Case of Large Magnetizing 

 Fields. 

 When the induction in the specimen changes abruptly between 

 negative and positive saturation as the magnetizing field passes 



