1128 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1954 



are planned to study protected contact erosion and susceptibility to 

 open contact failures. 



When contacts of the new high speed relay are operated, initial chatter 

 does not normally exceed 0.1 millisecond. There is no shock chatter 

 caused by spring vibration due to impact of the armature with the core 

 or backstop. There is no chatter caused by hesitation of the armature 

 in its travel at the point where it picks up the contact load. This is due 

 largely to the low mass of 0.020 inch diameter twin wires, the low mass 

 and short travel of the actuating mechanism, the type of card operation, 

 and the rigid mounting of the relay structure. 



Electrical erosion of contact material is reduced in the new relay, 

 because of the reduction in chatter. For this reason, the contact size 

 provided is expected to be adequate for all normal use for the life of the 

 relay, and contact maintenance should be greatly reduced. 



Locked contacts are substantially eliminated in the new relay by the 

 single card release method of operation. Static and dynamic forces 

 associated with the restoring spring and card system are powerful enough 

 to break loose any random pair of locked contacts. 



Contact failures due to dirt or the formation of insulating films on 

 the contacts are difficult to check in laboratory tests. Long-term ac- 

 celerated tests are necessary, with, a large test sample, under carefully 

 controlled dust conditions. Many precautions were taken in the design 

 to minimize failures from this source, as follows: (1) a dust cover. Fig. 

 16, encloses the contacts, but does not enclose the coil; (2) the cover 

 partially segregates the contacts in groups of three pairs of contacts, 

 reducing air movement in the vicinity of the contacts; (3) palladium 

 contact material is used on all relays; (4) twin contacts are coined- — 

 the rounded surface reduces the area in contact, effectively restricts the 

 area w^hich may trap lint or other foreign matter, and increases contact 

 pressure; (5) card release actuation and wire springs with large pre- 

 deflections insure that no appreciable loss of contact force will occur due 

 to age or erosion; and (6) twin contacts are attached to completely 

 independent wires. 



Rebound chatter is another form of false operation which occurs in 

 the form of contact reclosures caused by rebound of the armature after 

 striking the backstop when the relay is released. Fundamental studies 

 were made of rebound behavior in relay structures and various models 

 were constructed and measured. As a result there is no rebound chatter 

 in the new high-speed wire spring relay within the range of normal 

 adjustment. A comprehensive survey was made to determine the prob- 

 ability of reclosures due to rebound, in relays having limiting adjust- 



