208 



THE BELL SYSTEM TECHNICAL JOURNAL, JANUARY 1954 



The expression for N/R given by these equations gives the following 

 expression for the coil constant N'/R, or Gc : 



Gc = 



et Ti — n 



(21) 



For unit length of coil, values of Gc are shown in Fig. 13, plotted 

 against /■2/ri for various values of e, together with the corresponding rela- 

 tion for Gs , as given by (19). This shows that the slee^•e provides the 

 maximum value of conductance for the space occupied. It also shows 

 that the space used for a given value of sleeve conductance reduces the 

 value of Gc that can be provided. When the full depth of the winding 

 space is used by both coil and sleeve, called a slug in this case, each oc- 

 cupying part of the length, the value of Gc attainable is reduced in pro- 

 portion to the length used by the slug. When the coil is outside the sleeve, 

 the outer radius of the sleeve is the inner radius of the coil, and the value 

 of Gc is reduced in proportion to the value of Gs . For a given value of e 

 (given wdre size and insulation) the value of Gc is fixed by the winding 

 space and the value of Gs ■ 



2 2.5 3 



Fig. 13 — Relation between coil constant and coil dimensions. 



