ESTIMATION' AND CONTKOL OF Ol'KK ATIO TIMK OF HKLAVS 



137 



variably the case, and interest attaches to the conditions under which the 

 motion time may become relatively large. Another important aspect of 

 the release motion is the final velocity attained when the armature 

 strikes the backstop. This impact results in a rebound which may, in 

 the relay case, result in re-actuation of the contacts: rebound chatter. 

 Rebound may be reduced by appropriate mechanical design, as dis- 

 cussed in an article by E. E. Sumner, but its amplitude is always, other 

 things being equal, proportional to the kinetic energj" of the armature in 

 impact on the backstop. 



Fig. 9 shows the force travel relations in release, corresponding to 

 the operate relations of Fig. 4. The soHd line, as in Fig. 4, represents 

 the spring load, which has an operated value Fo at the point marked 2, 

 This corresponds to the similarly marked point in Fig. 7, which shows 

 the corresponding <p versus CF relations. The field decays along the de- 

 magnetization curve for x = to the point 2, where load and pull are 

 in equilibrium. Further decay results in a pull less than the spring load, 

 and hence in a net accelerating force producing armature motion. The 

 flux continues to decrease as indicated in Fig. 7, following the path 

 2-3-4. The pull follows the similarly marked curve in Fig. 9, related to 

 the flux-travel path by equation (5). 



The net accelerating energy is therefore represented by the area 

 marked T, lying between the pull curve and the spring load. Thus only 

 this portion of the energy V stored in the spring load appears as kinetic 

 energy of the armature. The remainder of V is represented by the area 



Fig. 9 



TRAVEL, X — *- X, 



Load and pull relations in release. 



