998 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1952 



done -with the ordinary (luick-to-release relays, for slow release relays 

 the armature is allowed to contact the core, finish to finish. When plane 

 flat pole face surfaces are provided, it is e\j)eiisi\e and diflicult to insure 

 in commercial practice that pi-ecise and uniform alignment of the pole 

 face surfaces will ol)tain. A'ariations in the aligmnent of these two sur- 

 faces will cause variations in the closed magnetic circuit reluctance and 

 conseciuently on the release time of the rela3^ 



In Fig. 12 is shown a design where the necessity for holding the align- 

 ment of core and armature so precisely is not so great.* A spherical surface 

 of rather large radius is embossed on the front end of the armature, so 

 that with commercial variations in alignment, the armature always pre- 

 sents a point on the surface of a sphere for contacting the flat surface of 

 the core. Similarly, the legs of the armature where the}^ pi\'ot on the 

 front ends of the hinge bracket are likewise embossed. The results of 

 the effects of these structural differences on the closed circuit re- 

 luctance are shown in Fig. 13 for a design with flat surfaces and one 

 with embossed surfaces. While it is true that with perfect alignment the 

 relay with flat surfaces will give longer release times, it is apparent that 

 as variations in alignment occur from time to time and from relay to 

 relay, it will have larger variations in performance than the relay with 

 the embossed surfaces. This is a feature which has proven of great value 

 in the manufacture of slow release relays of reasonable time precision. 



REFERENCES 



1. C. Schneider, "Cellulose Acetate Filled Coils," Bell Labs. Record, 29, p. 514, 



Nov., 1951. 



2. W. C. Slauson, "Improved U, UA and Y Tvpe Relaj's," Bell Labs. Record, 29, 



p. 466, Oct., 1951. 



3. B. F. Runvon, "Contacts for Crossbar Apparatus," Bell Labs. Record, 18, p. 278, 



Alav, 1940. 



4. P. W.' Swenson, "Contacts," Bell Labs. Record, 27, p. 50, Feb., 1949. 



5. H. M. Knapp, "The UB Relay," Bell Labs. Record, 27, p. 355, Oct., 1949. 



6. L. H. Germer and F. E. Haworth, J. Appl. Phijs., 20, p. 1085, 1949. 



7. L. H. Germer, J. Appl. Phijs., 22, p. 955, 1951. 



8. R. M. Bozorth, Ferromagnetism, D. Van Xostrand Co., Inc., 1951. 



9. F. A. Zupa, "The Y-Type Relay," Bell Labs. Record, 16, p. 310, May, 1938. 



