28 



ARMATURE CONSTRUCTION 



angular circuit, as shown in Fig. 12, and are secured in position 

 by wooden clamps at the four corners. At the butt-joints, they 

 are separated from one another by presspahn of 015 mm. thick- 

 ness. In building together the circuit, care must be taken that 

 the cores fit well with one another: as indications of which, are 

 the deadening of the noise when magnetised, and the obtaining 

 of a minimum deflection on the ammeter in the magnetising 

 circuit. 



-600 



crJ 



FIG. 12. Sectional Drawing of an Epstein Tester. 



The magnetising coils are constructed on presspahn bobbins, 

 with internal dimensions of 38 mm. x 38 mm. and a length of 

 435 mm. Each of the four bobbins contains 150 turns of copper 

 of a cross section of 14 sq. mm. It is suggested in the rules 

 that the winding may conveniently consist of two edge-wound 

 conductors measuring 2 x 3'5 mm. and wound in parallel. 



Originally it was thought preferable to build up these Epstein 

 samples to a weight of 20 kgs., but this weight has ultimately 

 been reduced to 10 kgs., which is now standard. A photograph 

 of a wound sample is shown in Fig. 13. In Fig. 14 is shown 



