MAGNETIC DRUM TRANSLATOR FOR TOLL SWITCHING OFFICES 723 



the B slot which immediately follows. The parallel (simultaneous) pres- 

 entation of the entire input code to the translation selecting unit permits 

 that unit to indicate, by a pulse, that the translation item is the one de- 

 sired and to gate-out the output code in the same slot while it is still 

 passing under the heads. Having thus identified the first slot of a trans- 

 lation item, it is a simple matter to pro\'ide the facilit}^ for gating-out 

 the remaining information recorded in the next succeeding slot. 



It will be seen, from the circuit arrangement shown, that the transla- 

 tion selecting unit also receives a portion of the output code recorded in 

 the second slot of each pair. It is therefore necessary to distinguish be- 

 tween the A and b slots of a pair. This is most conveniently done by the 

 Timing Unit, which is provided with two outputs, the pulses defining 

 the slots appearing alternately at these outputs. One output lead is cho- 

 sen to define all the a slots and it is routed to the translation selecting 

 unit to provide a portion of the pulse-pattern required for complete and 

 proper identification of an input code. 



The action of the magnetic drum translator in making a translation 



may now be traced by following the block diagram of Fig. 4. The decoder, 



of course, gives the same preliminary signals as for the card translator, 



but these are ignored by the drum translator, because it is continuously 



presenting all 1024 translations at the rate of 30,000 per second and need 



not take any preparatory steps, provided its relays have returned to 



normal after the last translation. The normal state of the relays 



is checked by means of a circuit through their contacts; if this circuit is 



complete, the decoder receives the signal to apply the input code as soon 



as it seizes the translator. A more elaborate checking arrangement could 



} have made this signal conditional upon other tests, such as a "standard 



1 translation," to determine that the electronic circuitry (in bulk) was 



functioning properly, but it was not considered worthwhile to do so in 



I the system described here. 



1 The decoder, then, furnishes the input code of the desired translation 

 1 item, causing certain of the relays labeled code check relays in Fig. 4 

 ! to operate. Contacts on these relays are interwired to provide the same 

 checking network as in the card translator, and a check on the authen- 

 ticity of the input code will be evidenced by operation of the relay labeled 

 CBK. This event is signaled to the decoder so that it may start its "no- 

 I card" timer action. When cbk closes, it also operates a chatter-free mer- 

 cury-contact relay, cbkm, in the translation selecting unit, permitting 

 that unit to produce an output at the appropriate time. Each code-check 

 relay which operates applies a positive voltage to one of the input ter- 

 minals of a "match" unit in the translation selecting unit. For each of 



