Patent GB-191413523-A (GB)
Title: Improvements in Telephone Exchange Systems.
Filed: 1914-06-03
Granted: 1915-03-18
Abstract: 13,523. Western Electric Co., [Woodward, F. T., (acting for Western Electric Co.)]. June 3. Automcatic and semi - automatic exchange systems.-Outgoing connexions from a manual 'or other main exchange to a satellite or suboffice are made over trunks which terminate at both ends in switches having terminals individual to the lines at the sub-office. When connexion is made at the main exchange to the terminals of a particular subscriber on the suboffice, the switch at the main-exchange end of an idle trunk is set in action to find these terminals, and the switch at the sub-office end of the same trunk operates in unison with the switch at the main-exchange to connect the trunk to the wanted line. The invention enables outgoing calls to be dealt with in just the same way as if the sub-office subscribers were connected directly to the main exchange. Incoming connexions from the sub-office to the main exchange may be made over a separate set of trunks in the same way, a call being delivered at the main exchange on a jack individual to the calling subscriber at the suboffice. Alternatively, however, the switches at the main-exchange ends of the incoming trunks may be dispensed with, incoming calls being delivered at the main exchange on jacks which are common to all the subscribers at the suboffice. The trunk circuits for an outgoing connexion are shown in Fig. 5, a subscriber's line at the sub-office being indicated at 43<3>, 44<3>, and two of the main-exchange calling-jacks individual to this line being shown at 63, 63'. The inter-exchange trunk is represented by the broken lines 45<1>, 46'. The circuits for incoming calls are of a generally similar nature and will not be described. Construction of switches. The switches are of a simple rotary ratchet-driven type, as shown in Fig. 1. The stepping-magnet is shown at 10, and the release magnet at 12. These magnets each control a group of contact springs, and a third group of springs forming an off-normal switch is controlled by a pin 41. Selection of an idle trunk capable of quickest connexion to a calling line. Supposing there are 100 subscribers on the sub-office and 10 trunks from the main exchange, the lines at the sub-office and the corresponding jacks at the main exchange are divided into 10 sub-groups, which are differently connected in the terminal banks of the switches of the different trunks. Thus, the 10 lines of the first sub-group are connected to the first 10 places in the first switch, and to the second 10 places in the second switch, and so on, while the 10 lines of the second sub-group are connected to the first 10 places in the second switch and to the second 10 places in the third switch, and so on. When a call occurs in a given sub-group of lines, the switch in which the first 10 places are allotted to that sub-group is set in action, provided that the corresponding trunk is idle. If this trunk is already engaged, the next switch in rotational order is selected, namely that in which the eleventh to the twentieth places are allotted to the sub-group of lines in which the call occurs, and if this switch is already engaged, the next is selected, and so on. By this arrangement, all the trunks are made available to all the lines, while at the same time it is ensured that the particular trunk taken into use shall be the one which can be most speedily connected with the calling line. The circuits for effecting this are shown in Fig. 7. When a call occurs in the first sub-group of 10 lines, a starting-wire 90' belonging to that sub-group is grounded to effect a preliminary energization of the stepping-magnet 91' of the first switch, and this switch, if idle, moves from its normal position and connects itself to the calling line. At the first step, the starting-circuit 90<1> is disconnected from the magnet 91' at the normal contact 93', and when the switch completes its movement, a relay 92' de-energizes and connects the starting-circuit 90' to the starting-circuit 90<2> of the second sub-group of lines. If a second call should then occur in the first subgroup of lines, the second switch would be set in action to find it. If the first nine switches should all be engaged, the starting-wires of all the sub-groups would be connected to the starting-wire 90<10> of the tenth switch, and this switch would be set in action in response to a call in any of the sub-groups. It will be seen that the tenth switch is related to the first switch in exactly the same way as the first switch to the second switch, so that a complete rotary order of precedence is established. Operation of the trunk-line switches. When a main-exchange operator inserts the plug 57', Fig. 6, of a cord circuit into a calling-jack 63 or 63', Fig. 5, of a wanted subscriber 42', a relay 61 is energized and grounds the starting- wire 52<2> of the first available trunk. This energizes the stepping-magnet 10<2>, which moves the call-finder of the selected trunk to its first set of terminals. The original circuit of the stepping-magnet 10<2> is then opened at the normal contact 36<2>; but until the switch arrives at the terminals of the calling jack, a circuit for the magnet 10<2> is maintained over the test-wiper 4<2>, to which it is connected by a slow-release relay 19<2>, which is energized as long as the switch is in motion. Another slow-release relay 18<2> is energized at the same time and serves to keep the wipers 1<2>, 2<2> disconnected while the switch is moving. When the wiper 4<2> comes to the ungrounded terminal of the calling-jack, the circuit of the magnet 10<2> is opened and the relavs 18<2>, 19<2> de-energize. The de-energization of the relay 18<2> completes the trunk circuit and extends the starting-circuit 52<2> to the circuit 52<3> of the next trunk. The de-energization of the relay 19<2> prepares a release circuit, connects ground to the wiper 4<2> to render the jack non- selectable to other switches, and completes a circuit through the wiper 3<2> for a relay 62, which disconnects the starting-circuit from ground. In the meantime, the switch at the sub-office end of the trunk has been stepped in unison with the main-exchange switch to complete the connexion with the wanted line, an impulse being sent over the trunk wire 45<1> to energize the magnet 10<3> at each energization of the magnet 10<2>. The first impulse passes through the normal contact'37', while the succeeding impulses pass through front contacts of the relays 67, 18<3>, which are energized by the magnet 10<3>. The relay 20<3>, which is energized in parallel with the relay 67 over the trunk wire 46', holds open the circuit of the release magnet 12<3>. When the switch has completed its movement, the relays 67, 18<3> are de-energized. Busy test and signal. If the wanted line is already engaged in either an incoming or outgoing call, there will be a ground connexion to the test terminal 84<3>, and upon the deenergization of the relay 18<3>, a circuit is completed for the magnet 12<3>, which releases the switch. Upon the closure of the normal contact 37<3>; the stepping-magnet 10<3> is energized once more and moves the switch to its first set of terminals, which are connected to a busy-signal circuit. The operator, hearing the busy signal, releases the connexion by withdrawing the plug 57<1>. Supply of ringing-current. If the wanted line is idle, the operator intermittently presses the ringing-key 64 to connect the ringing- generator to the trunk wire 45'. The ringing- current passes through a condenser to the relay 67, which closes a bridge between the upper windings of the trunk repeater 68<3> to complete a conductive circuit for the ringing-current. In the first non-ringing interval after the wanted subscriber has answered the call, the relay 56<3> is energized and connects together the trunk wires 45', 46' through the release relay 20<3> and the left-hand windings of the repeater 68<3>. The supervisory relays 58', 59<1>, Fig. 6, are energized in this circuit, and the lamp 60' is extinguished. Supervisory signals; release. When the subscriber 42<3> hangs up his receiver, the relay 56<3> becomes de-energized and open-circuits the trunk wire 45<1>, while the trunk wire 46' is connected to ground through the release relay 20<3> and resistance 56<5>. The supervisory relay 58<1>, Fig. 6, is thus de-energized, while the relay 59<1> remains energized, and the lamp 60<1> therefore lights up. When the operator withdraws the plug 57<1>, the main-exchange and sub-office switches are released successively, as follows. The de-energization of the relay 61 connects ground to the wiper 5<2>, completing the circuit of the release magnet 12<2>, which locks itself up and energizes the relay 18<2>. The energization of the relay 18<2> serves to disconnect the wipers 1<2>, 2<2> and provides a holding-circuit for the release relay 20<3>. When the main-exchange switch regains its normal position, the magnet 12<2> and the relays 18<2>, 20<3> are de-energized, and a circuit is completed for the release magnet 12<3> of the sub-office switch. Releasing switches accidentally started from normal. At the end of its travel, the wiper 5<2> comes to a grounded terminal 89<6>, and the switches are released as described above.