TELETYPKWRITKR EXCHANGE SYSTEM 



519 



operator answers by plugging the answering plug of a cord circuit into 

 the jack. This action by the operator connects the station line to the 

 cord circuit, and in addition energizes another winding of the relay 

 previously energized when the subscriber called. This relay, being 

 differentially wound, is then released and the answering lamps are 

 extinguished. 



In addition to calling the central ofihce the subscriber must be able 

 to recall the operator in case new services are required during the 

 progress of the communication. This is accomplished by the sub- 

 scriber simply turning the power switch off and then on again, which 

 causes certain relays in the cord circuit to operate and the cord lamp 

 to flash intermittently, indicating to the operator that her services 



SUBSCRIBER 



110 



VOLTS 



AC 



I MOTOR 



CENTRAL OFFICE 



SUBSCRIBERS 

 MULTIPLE 



1^ V 



SENDING K^iArMFT 

 CONTACTS MAGNET 



Fig. 10 — Fundamental teletypewriter circuit. 



are required. The subscriber must also be able to indicate to the 

 operator when a disconnection has been made. This is accomplished 

 by the subscriber turning off the power switch, causing the motor of 

 the teletypewriter to stop and a lamp in the cord circuit to light. 



The operator must also be able to signal the subscriber that a call 

 is being completed to him. To provide this signal the station is 

 equipped with a standard telephone type ringer which is energized, 

 when the station is in the idle condition, by 20-cycle alternating current 

 which flows over one side of the loop when the operator depresses a 

 ringing key in the cord. 



The teletypewriter lends itself admirably to the function of leaving 

 messages on the subscriber's machine when no one is in attendance. 

 When such service, known as unattended service, is desired, the station 



