A BRAUN TUBE HYSTERESIGRAPH 



291 



area of the sample and B the flux density. The voltage e is amplified 

 and applied to the deflector plates of the oscillograph. This part of 

 the apparatus is calibrated in terms of a small alternating voltage of 

 known amplitude applied to the amplifier, which produces a deflection 

 of d cm. per volt on the oscillograph tube. An ordinate 6 on a 

 hysteresis curve therefore indicates an induction of 





gauss. 



(2^ 



The calibration for magnetizing field is done by measuring the 

 deflection produced by a known direct current passed through the 

 coils H, and the magnetizing field in the coil P is then calculated 

 from the dimensions of the coil in the usual way in terms of the 

 current indicated by the oscillograph. 



The greatest difference between the actual circuits used and the 

 simple one shown in Fig. 1 is that the amplifier is constructed with 

 the push-pull arrangement in order to reduce distortion. This makes 

 necessary the maintenance of symmetry on the two sides of the 

 circuit so that the apparatus is really two similar circuits in parallel 

 as shown in Fig. 2. 



Fig. 2 — Diagram of the symmetrical circuit. 



The fact that the integrator and amplifier are thus connected makes 

 no difference in the final results of the calculations, if for N is used 

 the total number of turns on the search coil and for the other constants 

 only the values on one side of the system. 



II. Description OF THE Apparatus 



For greater flexibility the apparatus has been made in a number 

 of separate units which will now be described. A photograph of the 

 complete assembly is reproduced in Plate III. 



