ARMATURE LAMINATIONS 



13 



from this value will the more often be justified in order to employ 

 thicker sheets, than in order to employ thinner sheets. 1 



There is such a great variation in the quality of sheet iron, 

 even when obtained from the same manufacturer, that it is hope- 

 less to obtain any approach to uniformly satisfactory results unless 

 the material is ordered to comply with a suitable specification, 



FIG. 9. E wing Hysteresis Tester. 



and ultimately ruthlessly rejected if unsatisfactory. Otherwise, 

 cases will frequently arise of machines overheating when on test, 

 due to excessive core loss. The Ewing hysteresis tester is widely 

 employed in England, and is a very convenient instrument with 

 which to control the hysteretic quality of the samples received. 

 Fig. 9 is a photograph of this hysteresis tester. The instru- 



1 According to Brunswick and Aliamet (Construction des Induits a Courant 

 Continu, Partie Mecanique, p. 57), the thickness of sheet iron most generally 

 employed in France for armature discs is 0'4 mm. 



