.WM.YSIS OF I'll. I. AM) MAGXKTIZ ATIOX MKASTHKM KXTS 107 



pcrt'oi'inaiicc ot ihc contif^'uratioii, (liiiKMisioiis and niat(Mials of the clcc- 

 tr()ina,<iii('1 . They are most readily and accui'alely d(>tei'nuiied from coil 

 niau;i let i/.al ion measurements. It is conxcnient louse l-^llwood mmf gauge 

 measurements to determine tlu> core reluctance, hut these may be 

 omitted and the method of Fig. 9 employed, pro\i(led saturation is con- 

 tined to the core. Subject to this same limitation, the design constants 

 ma\' be evaluated from the pull measurements if these are sui)plemented 

 w ith mmf gauge measurements. 



For armature saturation, the magnetic design circint constants can 

 only be evaluated from magnetization measurements, which must in- 

 clude armature search coil as well as coil flux determinations, and be 

 supplemented by mmf gauge measurements. 



Limits of Application 



The \-alidity and usefulness of the procedures described here rest on 

 the agreement of measured ([uantities with the relations used to analyse 

 them. As all the relations used lead to linear plots, the extent of agree- 

 ment in any specific case is apparent from the plot obtained. So far as 

 the presentation of pull results is concerned, this is the only question of 

 \-alidity in\-olved. 



The relations found for the magnetization results are used to estimate 

 the field energy and the pull. To the extent the magnetization results 

 relate to the flux linkages of the coil, the conclusions drawn from rela- 

 tions fitting those results are valid. This follows from the energy balance 

 considerations discussed in Section 2. The supplementary measurements, 

 such as those with the mmf gauge or an armature search coil, are in 

 principle only convenient means for determining the relations to which 

 the coil magnetization conforms. The relations found b}'^ these means 

 are only \alid to the extent of such agreement. 



The conformity of magnetization relations to the expressions used 

 here, corresponding to the magnetic circuit schematics, is closest for 

 electromagnets in wliich the reluctance of the iron parts is small com- 

 pared with that of the joints and air gaps. This condition is satisfied for 

 most ordinary relays and similar electromagnets in the low density 

 r;uige, where the expressions given here most closely apply. The expres- 

 sions used for the high density range do not give as close agreement, but 

 provide a satisfactory basis for engineering analysis, particularly when 

 saturation is confined to the core. The treatment is less satisfactory for 

 structures that deviate from these conditions, such as those with arma- 

 ture saturation, or those with long cores of small cross section, where the 



