FLUX DISTRIBUTION 



133 



calibrated to read air-gap permeance per square centimeter of 

 armature surface, it follows that, for a given value of m.m.f. 

 between pole and armature, the flux density at any point 

 as for instance d will be 



B d = (m.m.f.)d X value of ordinate of Fig. 48 at d, 

 but in order to get the flux into the armature core the reluctance 

 of the teeth must be considered. 



Fia. 48. Permeance curve. 



O P* P a PC P 



Ampere.-Turns Required for Air-Gap, Teeth and Slots 



FIG. 49. Saturation curves for air gap, teeth, and slots. 



For any value of the air-gap density B g (considered as the 

 average density over a slot pitch) there is a corresponding value 

 of the tooth density, B t , which can be calculated by formula 

 (62) or (63), as the case demands; and the ampere-turns required 

 to overcome the reluctance of the tooth can be found, all as 

 explained in Art. 38. This value can be plotted in Fig. 49 



