DESIGN FACTORS INFLUENCING RELIABILITY OF RELAYS 



993 



excellent magnetic properties are needed in difficult applications. They 

 are substantially non-aging. Low silicon-iron alloys are being more widely 

 emploj^cd. They have good magnetic properties and the aging effect is 

 small. Where the intrinsically inferior magnetic properties of low carbon 

 steel alloys, such as SAE 1010, can be tolerated they are used. While 

 initially they have poorer magnetic characteristics than magnetic iron, 

 their aging effect is considerably smaller. 



<r) 



360 

 320 

 280 



240 



5 

 < 



5 200 



z 



^ 160 



< 



S 120 

 80 

 40 







20 40 60 80 100 120 140 160 180 200 220 240 260 

 OPERATE AMPERE TURNS 



Fig. 8 — Improvement in relay performance by hydrogen anneal. 



STRUCTURAL STABILITY 



Response of a relay depends upon the value of the magnetic force 

 of attraction produced between the armature and core when the coil 

 is energized, and upon the magnitude of the mechanical forces acting 

 upon the armature. To keep the response constant during the life of 

 the relay, it is essential that the relationships between these two forces 

 be not changed. The force of attraction varies approximately inversely 

 with the square of the length of the air-gap between the armature and 

 core. Since this distance is usually small, any small change will have a 

 relatively large effect on the pull. The core and armature, together with 

 their associated members, should be of stable design and secured in 

 such fashion that their dimensional relationships remain unchanged 

 when the relay is subjected to shock, \'ibrations, and stresses incident 

 to attaching the relay to its mounting. The design of the structure and 

 the thermal coefficients of expansion of the materials used should be 

 such that deformation does not take place when the temperature is 

 varied throughout the operating range. 



