1058 THE BELL SYSTEM TECHNICAL JOURNAL, NOVEMBER 1952 



-BUFFER SPRING 



Fig. 28 — The buffer spring is used to control the operated spring load, and 

 therefore the release current and release time. 



to make the relay slow to release. ^^ When the current in the winding of 

 such a relay is interrupted, the flux decays slowly due to the circulating 

 currents in the sleeve. Also, the low magnetic reluctance increases the 

 time for the flux decay by permitting relatively high flux values to be 

 maintained by smaller circulating currents. However, to achieve better 

 control of the release times and to maintain stable adjustment diu'ing the 

 life of the relays, the following additional features are used: 



1. The cores are annealed in a hydrogen atmosphere, chiefly to stabi- 

 lize the coerci^'e force of the iron. 



2. The core and armature have a wear-resisting chromium plate finish 

 to maintain the nonmagnetic gap between the embossed surface of the 

 armature and the core. 



3. The use of a spherical embossing reduces variations in reluctance 

 caused by small angular misalignments between the armature and core. 



4. Four sleeves are available including light, medium and heavy cop- 

 per sleeves and a light aluminum sleeve. These sleeves provide various 

 ranges of release time. 



5. A buffer spring is provided on the relay to control the operated 

 load and therefore the release time. As shown in Fig. 28, the buffer 

 spring is normally tensioned against the end of the middle core leg. As 

 the relay operates, however, the card strikes the adjustable tab in front 

 of the middle leg and lifts the spring away from the core so that the 

 spring tension is added to the operated load of the relay. The spring 

 may be adjusted for any desired tension, witliin limits, and the tab can 



" H. N. Wagar, "Slow Acting Relays", Bell Lab. Record, April, 1948, p. 161. 



