Magnetic Design of Relays 



By R. L. PEEK, Jr., and H. N. WAGAR 



(Manuscript received Seplembnr 24, 1953) 



The mechanical work and the speed of opera! ion of telephone relays are 

 determined in a large measure by the characteristics of the relay magnet. 

 The underlying magnetic principles and the resulting design relationships 

 for magnets are discussed in this article, which is in part a review of the 

 hackground material and in part a description of its use in developing 

 methods for magnet design and the analysis of magnet performance. 



Basic energy considerations are shown to determine the relations between 

 the work capacity and the magnetization characteristics, and analytical 

 e.rpressions for the latter are given in terms of the dimensions and materials 

 of the magnet. These expressions are developed for the magnetic circuit ap- 

 proximation to static field theory, which is shown to provide an adequate 

 representation of the field relations controlling performance. Methods are 

 given for representing the magnetic circuit relations by means of a simple 

 equivalent circuit. Expressions are derived for the mechanical output of the 

 relay in parameters of this simple equivalent circuit, and these expressions 

 used to determine optimum conditions for meeting specific design objectives. 



INTRODUCTION 



The complex switching equipment which handles the telephone traffic 

 in automatic central offices is built up of simple component elements, of 

 which the great majority are telephone relays. The large investment in 

 these relays, of which tens of millions are made each year, has led to 

 intensive effort to construct and use them as cheaply as possible, so that 

 they will perform their function at a minimum over-all cost to the tele- 

 phone system and thus to the subscriber. As the costs of use vary with 

 the efficiency and speed, maximum economy requires the solution of 

 technical problems in magnet design as well as the related problems of 

 mechanical design for economy in manufacture. As a result, the tech- 

 nology of magnet design is under constant study at Bell Telephone Labo- 

 ratories, directed to increased understanding of magnet pcM-formance 



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