Patent GB-141703-A (GB)
Title: Automatic and semi-automatic telephone systems
IPC: H04Q3/00
Filed: 1920-04-12
Abstract: 141,703. Western Electric Co., (Assignees of Deakin, G.). April 11, 1919, [Convention date]. Automatic and semi-automatic exchange systems.-A connector selects the first idle line of a group of lines leading to a private branch exchange, but means are provided for varying (especially at night) the test circuits of certain lines of the group, so that these lines, which have separate numbers in the directory, can then be called individually in the same way as ordinary subscribers' lines. During the day, incoming calls to the private branch exchange are extended to the wanted party by an operator at a manual switchboard, and outgoing calls are set up by the operator's impulse sender, but when the operator leaves her position at night she plugs the individually-selectable exchange lines into the jacks of those parties who require night service, and these parties can then receive calls direct from the main exchange, or can set up calls by means of their own impulse senders. The invention also includes the following features. (1) Ringing-current from the main exchange operates self-looking signal circuits at the P.B.X. operator's position, and is then immediately cut off, as a result of current sent back over the exchange line. (2) The P.B.X. accumulator is kept charged by the main exchange battery over idle lines of the P.B.X. group. Test circuit arrangements. The connector B, Fig. 1, has access to ordinary subscribers' lines and also to groups of P.B.X. lines, such as the two groups shown in the dotted rectangles 20, 21. Ordinary lines, and also the final lines of P.B.X. groups, have a resistance 43 bridging the cut-off relay 44 in the test circuit, as described in Specification 132,546, so that in the 6th position of the connector sequence switch 100, a relay 35 is energized if the connector has been set on an ordinary line, whether that line is idle or busy, and energizes relay 40 to drive switch 100 to its 10th position. As the switch runs through its 8th position, relay 57 is connected to the test circuit to test the idle or busy condition of the line, energizing if the line is idle, and locking up in series with relay 40 to drive the switch to its 12th or ringing position, but failing to energize if the line is busy, so that the open-circuiting of relay 35 at contact 48 is followed by the relapse of relay 40, stopping the switch in its 10th position to send a busy signal to the calling line. On the other hand, if the connector has been set to the first line of a P.B.X. group, the absence of a bridge resistance 43 in the test circuit ensures that relay 35 is only energized if this line is idle, but if it is busy, relays 35, 40 remain unenergized and a circuit is closed for the power magnet 36, which advances the connector to test the other lines of the group. The hunting movement of the connector is stopped by the energization of relays 35, 40 as soon as an idle line is found, or as soon as the connector reaches the last line of the group, whether that line is idle or busy. To enable certain lines of a P.B.X. group to be selected individually, these lines (such as 33, 34) are provided with resistances 210, 211 which can be bridged across the cut-off relays to render their test circuits identical with those of ordinary lines. These resistances may be brought into circuit either by a sequence switch (such as 200, for the group 20) or by a relay (such as 225, for the group 21) controlled either by an attendant at the main exchange or by the P.B.X. operator. For example, by operating a key 206 to energize relay 208, the switch 200 can be driven to its 18th position, closing resistance circuits at 201, 202, and remains in this position until key 206 is opened, when relay 208 relapses and drives the switch to normal. Call from main exchange to P.B.X. operator. Ringing-current is supplied, in the 12th position of switch 100, over the circuit 58, 59, 68, 69 and energizes a relay 65, which energizes a lamp 77 and alarm relay 76 and locks itself in series with relay 70, which switches the ringing-current to a relay 73. Relay 73, by grounding the tip side of the exchange line, energizes relay 69, which drives the switch 100 at once to its 15th or speak ing position. The operator answers the call by throwing the key 72, which unlocks relays 65, 70, energizes relays 82 to light the supervisory lamp 84, and connects her speaking-set to line. She then extends the call to the wanted party by means of the plug 78, relay 82 being mantained energized over the plug sleeve circuit. When leaving her position at night, the operator opens the keys 85, 95, to prevent the cord circuit from being opened by relay 70 in response to ringing- current. Charging the P.B.X. accumulator from the main exchange. As long as any P.B.X. line is idle, the accumulator 325 is connected to the main exchange battery through a resistance 329; the tip side of the line, and the left-hand winding of the line relay 327.