452 



BELL SYSTEM TECHNICAL JOURNAL 



armature at the other.-'' Non-magnetic stop pins are required on the 

 armature to prevent sticking. This compHcated magnetic circuit has 

 been developed to meet the numerous requirements placed on ringers. 

 Polarization is necessary for an a-c. ringer which is to operate without 



20,000 



5000 

 4000 



3000 

 'in 

 > 2000 



O 1000 

 If) 



>■ 



_l 



OQ 500 

 uj 400 



£ 300 

 a. 



-I 200 



6 8 10 12 14 16 18 



POLARIZING FLUX DENSITY IN GAUSSES 



20 



100 



24 



XIO- 



Fig. 5 — Reversible permeability and relative polarized tractive force 

 for various magnetic alloys. 



interrupter contacts, and it is employed in selective ringing on party 

 lines. A high coil inductance is required to limit the transmission 



''^ K. B. Miller, "Manual Switching and Substation Equipment" (McGraw-Hill, 

 1933 ed.), p. 67. 



