Estimation and Control of the Operate 

 Time of Relays 



Part I — Theory 



By R. L. PEEK, Jr. 



(Manuscript received August 31, 1953) 



The dynamic equations applying to the operation and release of elect ro- 

 niagnets are derived in a form in which the armature position and the Jinx 

 linkages of the coil are the variables to he determined as functions of time. 

 The effective magnetomotive force and pull are taken as given by the static 

 magnetization relations. This formulation is valid if the dynamic field 

 pattern is substantially that of the static field, and it is shown that this con- 

 dition is satisfied if the effective conductance of the eddy current paths is 

 small compared with that of the coil or other linking circuits. This is usually 

 the case in operation, but is not the case in normal release. 



Approximate solutions are obtained for both fast and slow operation, 

 giving the time as related to the 7nechanical work done, the mass and travel 

 of the moving parts, and the steady state power input to the coil. Expres- 

 sions are derived for optimum coil design and pole face area, and design 

 requirements for fast operation are discussed. 



An approximate expression is derived for the release waiting time, the 

 initial period of field decay prior to armature motion. The effect on this 

 decay of contact protection in the coil circuit is discussed. The sloiu release 

 case is treated in another article in this issue. An analysis is given of the 

 armature motion in release, and the residts of an analog computer solu- 

 tion to this problem reported. These show the effect of design parameters, 

 particularly the armature mass, on the velocity attained in release motion, 

 and- hence on the amplitude of armature rebound. 



INTRODUCTION' 



The operate and release times of most telephone relays lie in the 

 range from 1 to 100 millisecs. (0.001 to 0.100 sees.). To use these relays 

 in telephone switching, involving complex patterns of sequential switch 



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