292 THE BELL SYSTEM TECHNICAL JOURNAL, MARCH 1952 



By noting that A + B -\- C is the negative of A'B'C, this can be 

 reduced to 



f{D) = (.4 + 5 + C + E')(D + A'B'C) (3b, 12a) 



Howevev, this transformation introduces a hazard caused by the 

 transit time of .4 relaj^ contacts in passing from relay combination 9 to 

 10. Therefore the original expression will be used for relay D. The control 

 path is sho^^Tl in Fig. 3c. 



For the E relay which operates and locks only once in the cycle 



giE) = (A' + B' + C' + D) 



h(E) = E 

 and 



f(E) = (A' -\- B' -\- C -\- D)(E + E) 



(A' -{- B' + C + D)E (4a) 



This control path is shown in Fig. 3d. 



Apart from the problem of developing the rec}uired contact network, 

 the practical problem of what operating power must be given to the 

 relays in order to meet speed requirements must be dealt with. Since 

 the use of low resistance windings in series with protective external 

 resistors is called for to obtain the speed required, it appears that the 

 use of two windings per relay might prove advantageous. By operating 

 on the low resistance winding while locking on the high resistance wind- 

 ing, the current drain may be reduced (thereby saving a fuse) and 

 furthermore some code reduction may be made possible as showni later. 

 If double windings are used, two of the external series resistors may be 

 eliminated by combining the control network so as to make certain that 

 only one of the low resistance windings on the C, D, or E relays is 

 energized at any one time. This W'ould permit the use of one common 

 external resistance with the aforementioned relays instead of three. 



Keeping these practical considerations in mind, further savings may 

 be made by combining the control circuits as shown in Fig. 3e. Although 

 there is in this circuit a possibility of contact stagger on the A relay 

 contacts causing the C and D low resistance windings to be energized at 

 the same time, this will not be harmful since, when the stagger occurs, 

 both relays are firmh^ locked operated by their high resistance holding 

 windings. 



TRANSLATING CIRCUIT 



The translating circuit is particularly adaptable to switcliing algebra 

 manipulation. Table I show^s the combinations which prevail at the end 



