290 



BELL SYSTEM TECHNICAL JOURNAL 



The principle of the arrangement whereby the cycUc magnetization 

 curve is recorded on the oscillograph tube, will be made clear by 

 reference to Fig. 1. The specimen of magnetic material M, is mag- 



Fig. 1 — Elementary diagram of the circuit. 



netized by alternating current flowing through the primary winding P. 

 The varying magnetic flux in the specimen induces in the secondary 

 winding or search coil T a voltage which is proportional to the rate 

 of change of flux. This voltage is applied to the integrating circuit 

 consisting of the resistance R and the condenser C. When the 

 resistance is large compared with the impedance of the condenser, 

 the current in this circuit is limited largely by the resistance and it is, 

 therefore, proportional to the voltage applied by the search coil. 

 The charge on the condenser, and therefore the voltage across its 

 terminals, is proportional to the time integral of the current in the 

 circuit. The voltage of the condenser is, therefore, proportional to the 

 magnetic flux in the sample. 



This voltage is amplified by the distortionless amplifier A, the 

 output side of which is connected to one pair of deflector plates of 

 the oscillograph tube. While the deflection of the indicating spot 

 thus follows the flux in one direction, deflection in a line at right 

 angles to this and proportional to the magnetizing field is produced by 

 the magnetic field of the deflector coils H which are connected in 

 series with the magnetizing winding P. The spot then traces out a 

 path on the screen during each cycle of current which is the hysteresis 

 diagram for the sample, and which by suitable calibration yields 

 quantitative results. 



The voltage on the integrating condenser at any time is given by 

 the relation 



where R and C are the resistance and capacity of the integrator, 

 N is the number of turns in the search coil, 5' is the cross-sectional 



