1130 THE BELL SYSTEM TECHNICAL JOURXAL, SEPTEMBER 1954 



mated life term of forty years. Life tests show that no readjustment 

 should be necessary during the first 100 million operations. The tests 

 also indicate that not more than a small percentage of relays will re- 

 quire readjustment prior to an estimated maximum life of 200 million 

 operations. In extreme cases, still greater life may be obtained if re- 

 quired, by replacing the molded card. This is an inexpensive part and 

 replacement is easily accomplished. 



Stability 



When the new relays are exposed to extreme temperature and hu- 

 midity cycles, the greatest change in contact separation is, in general, 

 about 0.004 inch, and only a small percentage of relays are likely to be 

 used in this manner. Tests indicate that changes of this magnitude leave 

 adequate margin for 100 million operations before readjustment is 

 necessary. 



For economy, most equipment is shop assembled and wired on a 

 frame basis, and shipped complete, read}^ for installation as equipment 

 units. It is important, therefore, that apparatus units should be capable 

 of withstanding physical shock far in excess of normal usage. Design 

 features in the new relay which provide an adequate margin of safety 

 in this respect are: (1) a rigid mounting bracket; (2) the wire spring 

 pile-up is attached securely to the bracket with two specially heat 

 treated steel screws; (3) the cover is held in place by the bending moment 

 of an embossed section of a spring clip with a force many times greater 

 than the compressive force of a single spring; and (4) guard surfaces 

 molded m the cover prevent twin wires from leaving their respective 

 guide notches in the single wire combs. 



Excessive shocks during shipment have, at times, damaged flat spring 

 relays by bending their brackets. The new relay's have been subjected 

 to shocks of similar magnitude without damage. 



Magnetic Iiiierjerence 



Under certain marginal conditions, a relay may be affected by leak- 

 age flux from adjacent relays entering its magnetic circuit, and changing 

 its operate and release values. Tests show that interaction is negligible 

 between the new relays and also between new and old type relaj's when 

 they are used in adjacent positions. 



CONCLUSIONS 



The new 30-contact rela3^s provide faster operate and release times, 

 longer life, improved contact performance, reduced maintenance, and 



