Patent GB-268150-A (GB)
Title: Improvements in private automatic branch telephone exchanges
IPC: H04Q3/00
Filed: 1926-04-20
Abstract: 268,150. Relay Automatic Telephone Co., Ltd., and Johnson, B. B. April 20, 1926. Automatic exchange systems.-Private branch exchange subscribers on dialling a particular digit are connected for outgoing calls automatically to the first idle main office trunk. Incoming calls arriving over the same trunks are answered by an attendant who informs the subscriber of the number of the trunk that wants him. The subscriber then dials that number to connect himself to the calling trunk. The invention is described with reference to a relay system in which local calls are set up as described in Specification 205,861. The outgoing trunks. however, are provided between the subscriber and the A and B feed with relays SW connecting them over links LC to service lines SL associated with main office trunks J. Incoming main office calls. Ringing current coming on over the trunk J1 energizes relay IR1 in service line SL1 to light the calling lamp CL1 and at night to operate an audible signal 93 (the keys SR1 &c. being normally in position 1). The attendant then throws the key to 2 extinguishing the lamp, unlocking the relay IR1 and putting his telephone set in communication with the trunk. On learning the wanted number he throws the key to 3, connecting relay HR1 to the trunk to hold the main office and associating his telephone set over 91 with a line circuit like a subscriber's line circuit, calls up the wanted subscriber in known manner and then hangs up. Relay HR1 re-lights the calling lamp and connects battery to one end of circuit 606. The subscriber then dials the single digit number of the calling trunk, whereupon the register marker connects ground to the other end of circuit 606 energizing relay MR1 which, assuming the outgoing trunk OT1 was used in picking up the marker, completes circuit 71 to the marker, ener. gizing relays CR1, SW1, and energizes relay SR1 which completes holding circuit 86. Relay SV1 pulls up over the main office battery and energizes relay HO1 which holds up relay SR1. When the trunk is switched over, relay HR1 puts out the calling lamp, whereupon the attendant should restore the key to position 1. If he fails to do so, the release of the connection re-connects relay HR1 to the trunk, giving a permanent call at the main office. An alarm may be connected where indicated by a cross 95 to indicate this condition. Had the call come in over J2, the subscriber would have dialled a different number and the marker completed circuit 807. Outgoing main office calls. The subscriber dials a different number such as O and the marker closes circuit 94 energizing the relay MR of the first idle trunk (say MR2). Relay MR2 energizes relays CR4, SW2 (assuming trunk OT2 is being used) in a circuit 72 terminating in the marker and relays SR2, SV2, H02 pull up as before, relay MR2, however, holding up in circuit 87 until the marker is released to delay the extension of the marking circuit to a third service line. Modified registermarker. The register-marker shown is identical with that described in Specification 205,861 in which 100 subscribers are divided into 20 groups of 5. To adapt it for systems using decimal grouping the tens marking wire 601 is led direct to contacts of the relays TH and the units marking wire 602 goes over changeover contacts of the relay U6c to either of two crains of contacts such as that shown on the left of the relays U.