TRANSLATORS AND IDENTIFIERS IN SWITCHING SYSTEMS 615 



bar and card types by the fact that there is no bus-bar system, each output 

 lead having only one connection on the translator. Each electrical bus-bar 

 is replaced respectively by a coil, a code bar channel or a light tunnel. 



In systems using bus-bar output multiples the coding elements solve the 

 coding and back-up problems in four general ways, as shown in Fig. 10, 

 assuming that the output consists of four code groups: 



(1) By having an individual lead through the code-point selector and 

 cross-connection field for each code group as shown in Fig. 10(a). 

 Each lead is directly connected to the required bus. All are open in 

 the selector except those involved in any individual translation, thus 

 avoiding back-up. No apparatus other than the wiring is involved in 

 the coding element. This saves apparatus, but the cost of the cross 

 connections and the wiring apparatus in the coding element selector 

 are higher than for the other cases because of the larger number of 

 wires. 



(2) Figure 10(b) shows a one-wire arrangement with back-up prevented 

 by a unilateral or non-Unear element in each lead to the bus-bars. 



(3) Figure 10(c) shows a one- wire arrangement which is connected to each 

 of the four required output buses through a terminating and coding 

 resistance network which reduces back-up through the unilateral ef- 

 fect provided. 



(4) Figure 10(d), again one- wire through the selection and cross-connect 

 field uses a relay to effect coding, back-up of course being prevented 

 by the fact that the leads to all code buses are open at the relay 

 contacts except those involved in a particular translation. Figure 8 

 operates on similar principles for avoiding back-up. 



Schemes (b), (c) and (d) reduce the wiring and the selector costs as com- 

 pared to (a) through the use of only one wire but this is done at the ex- 

 pense of the additional apparatus in the coding element. 



Figure 6 shows a compromise between (a) and (c) of Fig. 10. 



Different conditions for one-way translators may warrant a careful choice 

 between one of the four general methods of coding shown in Fig. 10 and the 

 methods involving no bus-bars mentioned above. 



In the case of the arrangements of Fig. 10 some cost changes can be ef- 

 fected by juggling, in the design, with the coding elements and the bus-bar 

 grouping. 



For instance, if the number base of the output were changed from deci- 

 mal to binary, the number of output bus-bars would be reduced from 40 

 to 14, but the increased number of places in each output would require 14 

 leads from each coding element instead of the present four. This complica- 

 tion of the coding elements would probably prove-out this change. 



