fypSlGX Cll.lR.tCTr.RISTtCS OF ELECT ROM AG NET 5; 



223 



in turn may bo taki-ri as a measure of the effective ampere turns. The 

 determination of the leakage lUix invdives reasonable assumptions 

 from experience of tlie armature air-gap in terms of the core diameter. 

 If the electromagnet is to be ofXTated on a definite voltage the 

 assumption of a definite railiating surface to dissipate a certain input 



I — r 



V as eu iM ^ ■ ic 



^ - zc 



Si/r ///tf//£'ST COST 



^ 



\/////\ 



4 - c 



3 



V-/ lOCil /N 



-/■7 SC 



Fig. 11 



wattage will fi.\ the resistance of the coil. Copper windings of electro- 

 magnets in telephone systems are generally wound with wire which 

 varies from Xo. 20 B. & S. to Xo. 39 B. & S. gauge. The resistance 

 generally varies throughout a range of '2 ohm to 2,000 ohms. Various 

 gauges of wire wind with diflferent efficiencies due to variations in 

 the space factor but a number of different gauges may be assumed 

 and the calculations carried out which give the relation between the 

 winding depth and the effective ampere-turns. With a constant 

 radiating surface a variation in the winding depth causes a variation 

 in the length which, of course, is reflected in the leakage flu.x. The 

 results of a number of calculations on various windings are shown in 

 Fig. !). In Fig. 10 is shown the relation between the volume of wire 

 on the spool and the per cent loss in efficiency due to a variation in 

 the depth of winding which, with a constant ' radiating area, causes 



' The radiating area is taken as the surface only of the coil and the ability to 

 dissipate through the ends and otherwise is reflected by the heating constant A',. 



