FERRITE CORE INDUCTORS 



287 



gaps, as illustrated in Fig. 11 (c). Here the distance d, travelled by the 

 screw is longer than the effective air gap g, by the amount 



d 



9 



sm 9 



One means of overcoming the nonlinear characteristic of gaps such 

 as these is to introduce compensation in the form of a secondary gap 

 that opens as the main gap closes.'^ Such an arrangement is shown in 

 Fig. 12 (a). When there are two gaps in series their reluctances are 

 additive and their effect on permeabihty is given approximately by 



9i + 92 



Fig. 12 (b) shows the inductance characteristics that would result 



from either of the two gaps alone, and the effect of the two gaps in series. 



From (46) it can be seen that the effective permeability varies ap- 



» 



AIR GAP LENGTH 



(b) 



Fig. 11 — Inductance adjustment by variation of air gap length, (a) Gap formed 

 by parallel plane surfaces, (b) Adjustment characteristic, (c) Cone or wedge 

 shaped gaps. 



