Estimation and Control of the Operate 

 Time of Relays 



Part II — Design of Optimum Windings 



By M. A. LOGAN 



(Manuscript received September 4, 1953) 



For each relay structure, there exists a best winding, once the circuit 

 'power has been specified. The best winding is that one which operates the 

 relay in the least time. Methods for determining the best umuiing are de- 

 veloped. 



On the basis of the operating time, the relay behavior is classed as mass 

 or load controlled. The design method chosen depends upon this classifica- 

 tion. 



The design of ivindings for series connected relays is based on a method 

 of determining eouivalent single relays, the behavior of each corresponding 

 to one of the series relays. This method is generalized to allow for differejit 

 magnetic structures for the several relays. Each relay winding is then de- 

 signed in turn, using the design data for its own type of structure. 



The best winding design is not given directly by an explicit formula. 

 Rather, methods are developed for determining the operate time for any 

 winding. Then by choosing a range of windings, the best one is selected by 

 interpolation. 



INTRODUCTION 



The selection of a relay for a circuit application, particularly so in 

 common control systems, involves in part a determination of its operat- 

 ing and releasing time. In Part I of this article expressions are derived 

 for the relations between these times, the design parameters of a relay, 

 and the conditions of operation. These expressions are approximate, 

 and have been developed with primary reference to the selection of 

 favorable characteristics in design. The timing estimates they provide 

 are of sufficient accuracy for the comparison of design alternatives. 

 Once a basic design has been selected, the choice of windings and the 

 prediction of the limiting times occurring in specific applications requires 



144 



