Patent GB-228593-A (GB)
Title: Improvements in telephone exchange systems
IPC: H04M9/00
Filed: 1923-10-08
Abstract: 228,593. Western Electric Co., Ltd., (Capek, A., and Broeck, F. van clen). Oct. 8, 1923. Manual exchange systems; metering.-A cord circuit is provided with a sleeve relay 31 which keeps the cord open if an operator attempts to answer a call that has already been answered by another operator. A relay 47 exercises an analagous function at the calling end of the cord. When either plug is put in a busy jack a flash signal is given. A position counter 120 operates when the called party replies and is thereafter disconnected. A lamp signal is given if the subscriber's meter 123 or the counter 120 fails. Ring- ing is interrupted by the abandonment of the call or if the operator throws her listening key and during ringing the called supervisory lamp glows dimly. The operator cannot normally listen-in when both receivers are down. but if the calling party operates his hook switch during conversation an automatic flash signal is started up and the operator is enabled to connect herself to the cord by means of her listening key. General operation. The insertion of the answering plug P energizes cut-off relay 12 in series with relay 31 which shunts its high-resistance winding 32 by a low resistance 38 so that if another operator attempts to answer the call, her relay 31 will be unable to energize and the energization of her relay 49 will connect her interrupter 52 to her lamp 51. Relay 31 energizes supervisory relay 36 and listening relay 41. The insertion of the calling plug P<1>, if the wanted line is idle, energizes relay 47, which shunts its highresistance winding by the low-resistance middle winding of relay 86 and energizes relay 44. Relay 44 releases listening relav 41 and energizes ringing relay 91. The energization of ringing- trip relay 89 when the called party answers removes a short-circuit from the right-hand winding of relay 88 which pulls up in series with relay 91 and locks itself to ground at the re-ring key 111, thereby short-circuiting ringing relay 91 which completes the talking circuit. During ringing the supervisory lamp 116<1> receives enough current over resistances 113, 114 to glow clearly. If the call is abandoned during ringing, the relapse of relay 36 energizes relay 80 which locks over its left-hand winding and that of relay 88. Relay 88 pulls up and short-circuits the ringing relay 91. Relay 91 can also be released by throwing listening key 42. Secrecy feature. During conversation, listening relay 41 cannot normally be operated since its left-hand winding is disconnected by relay 44 and its right-hand winding by the supervisory relays 36, 90. If, however, the calling party depresses his switch hook, the momentary relapse of relay 36 energizes relay 80 which locks up, connects interrupter 131 to lamp 132, and energizes relay 82. The throwing of the listening key 42 now energizes relay 41 over 134, 41, 40, and unlocks relay 80 so that relay 82 holds up only while the listening key is thrown. Metering. The energization of the supervisory relay 90 when the called party responds energizes relay 39 in series with relays 85, 87 whereupon relay 84 pulls up over 86. 33, 122 and energizes the magnet 83 of the position counter 126 which short-circuits the left-hand winding of relay 84 to allow the operation of the magnet 122 of the subscriber's meter 123 over its 1400 ohm. winding. Magnet 122 shunts its high-resistance winding by a low-resistance winding and relay 86 now operates, locks itself over its right-hand winding and cuts off relay 39. Failure of relay 86 to operate is indicated by the energization of relay 85 and the consequent lighting of lamp 129. Non-charge lines are given a special sleeve potential so that relay 86 pulls up over its middle winding as soon as the plug is inserted, and cuts off relay 39. In case a wrong connection is made, a second operation of the meters is prevented bv a momentary operation of the re-ring key 111 after the plug has been inserted in the proper line. This shunts the called cut-off relay by the resistance 113 so that relay 86 operates over its middle winding and locks up. The Specification gives the resistances of most of the relays used.