304 



THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1952 



functions at present employed in Bell System standard switching equip- 

 ment. The previous dial pulse counter used in the latest crossbar system 

 required a total of ten relays. Thus the present design represents a 

 considerable saving in cost and space. To a certain extent this result can 

 be ascribed to the use of switching algebra during the circuit develop- 

 ment. 



Relay circuits designed on the basis of utilizing a large proportion of 

 the possible combinations permitted by the component relays usuallj'" 

 require heavy spring pile-ups. Since general purpose relays are limited 

 in the number of springs which they can carry, this type of circuit usually 



(A) 



T^i'^ 



(<3) 



(b) 



(B) 



TJ^I.hL 



J7 



X"^ 



(A) 



B A 



'b. 



jx-l ^ 



- B A 



— X— »— X — 



'b_ 



(B) -^ 



(d) t 



Fig. 8 



entails considerable design effort to make most effective use of the avail- 

 able springs. Application of switching algebra to this aspect of the design 

 problem can often provide crucial assistance. 



It is recognized that switching algebra, in its present state of develop- 

 ment, does not permit complete mathematical statement and manipula- 

 tion of multi-terminal networks as represented by the counting and 

 translating circuits. It does provide, however, facilities in manipulating 

 two-terminal networks into a variety of forms from which can be selected 

 those that combine most readily. This can result not only in a saving of 

 time, but also in improved circuits which might not be realized by other 

 design techniques. Unfortunately the algebra in its present state does 

 not indicate when the optimum circuit has been attained. To some extent 

 this is caused by apparatus or circuit considerations to which, since it is 



