100 THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



recognition of inconsistent observations is facilitated by a supplementary 

 plot of F'/F versus JF' (or {Nif) as in Fig. 13. 



Estimation of Pull 



Estimates of pull are made in preliminary de\Tlopment either from 

 estimates of the magnetic circuit constants, computed from the dimen- 

 sions as discussed in the companion article, or from magnetization meas- 

 urements. The low density pull is given by (13), reciuiring only the efiuiv- 

 alent circuit constants A and (Ho for its evaluation, and is represented 

 by the F' lines of slope two in a logarithmic plot of F ^'ersus N^I. Esti- 

 mates of the high density pull may be prepared as linear plots of F'/F 

 versus (NI)". As these conform (for core saturation) to (15) they recjuire 

 estimates of ip', <p", and of 61', as given by (3). 



Estimates of pull may also be reciuired in preparing pull data for 

 engineering use, with respect to the changes in pull associated with di- 

 mensional and other variations in a commercial product. Such estimates 

 may be obtained by estimating the effect of the A'ariations on the mag- 

 netic circuit constants fitting the observ^ed pull, and computing the pull 

 for the changed constants in the manner described in the preceding 

 paragraph. 



Evaluation of Equivalent Magnetic Circuit Constants 



The equivalent magnetic circuit constants, which define the field 

 energy and the pull characteristics through the low density range, 

 largely suffice for the prediction of performance. This is illustrated by 

 the use of these constants in the analysis of capability relations in one 

 companion article and in the dynamic relations presented in another. 



These constants are most readily and accurately evaluated from mag- 

 netization data by the procedure illustrated in Fig. 7 and the associated 

 computations. A check on the values of A and (Ro is provided by analysing 

 pull data by the procedure illustrated in Fig. 12. When only pull data 

 are available, A and (Ro can be determined in this way, but the deter- 

 mination of (Rl rec^uires the measurement of ^e by the Ellwood mmf 

 gauge. With ^e known, the pull results suffice for the determination not 

 only of (Rz, , but of the design circuit constants of Fig. 5 (provided satura- 

 tion is confined to the core). 



Evaluation of the Magnetic Design Circuit Constants 



The magnetic design circuit constants are reciuired only for compari- 

 son with estimated values, in development studies of the effect on the 



i 



