Patent GB-550210-A (GB)
Title: Improvements in or relating to switching systems particularly for automatic telephones
IPC: H04Q3/00
Filed: 1942-03-13
Abstract: 550,210. Automatic exchange systems. WESTERN ELECTRIC CO., Inc. March 13, 1942, No. 3336. Convention date, Feb. 8, 1941. [Class 40 (iv)] In a cross-bar switching system comprising a number of 10-line primary switches 107 .. 109, 110 .. 112 &c. arranged in a co-ordinate field and connected to links so that a connection is possible from any primary switch to any of a number of secondary switches 116 .. 118, neon tubes are used for controlling the selecting operations. When a call is made, a line tube breaks down and causes discharges in two tubes corresponding respectively to the horizontal and vertical rows in which the primary switch of the calling line is situated. An idle link between this switch and a secondary switch having an outlet is then selected by applying impulses simultaneously and in synchronism to the tubes of a set representing the secondary switches and to those of another set representing the links. Impulses are only effective on the tubes of idle links and on those of switches with two or more outlets (or, on a second test, one outlet). A link-selecting operation is performed when tubes in both sets are operated simultaneously. Further groups of tubes are then brought into play for the selection of an outgoing trunk and of the calling subscriber. In general, simultaneous operation of two tubes in a set is prevented by making the respective tubes operable in turn and causing a discharge in one tube to cause a disabling potential to be applied to the others. The condition of a number of elements (e.g. outgoing lines) is signalled between different parts of the control circuit over a single circuit by using synchronous impulse generators at the two parts of the circuit and giving the elements characteristic positions in a time cycle measured by the impulse generators. Identification of calling primary switch. When a call is made, current flows over the loop in an individual resistance 229 and the resulting voltage drops causes ionization of the subscriber's individual tube 208. The main anodes of the tubes of a primary sub-group receive impulses from a generator 227 in turn and when a tube is ionized, the impulses are passed on over a start wire 213 common to the sub-group to one of the starting anodes of a tube such as 306 common to a horizontal row of primary switches. The tube ionizes at once and then discharges during the make period of an interrupter 337 via a relay 332 which renders the testing circuits operative for a limited period. The discharge causes a potential to be applied from pick-up electrodes such as 341 to the upper starting electrode of the corresponding one of a further set of tubes individually associated with the tubes such as 306. The other starting electrode receives impulses from a generator 349 and in due course ionization occurs and a discharge takes place through a relay such as 320 , characteristic of the horizontal row of the calling switch. At,the same time, the potential of the grids, of the other tubes is. so modified by the effect of a resistance 317 that they are rendered incapable of discharging. The starting lead is extended by 320 over one of the wires 324 .. 327 to the lower starting electrode of the appropriate one of a group of tubes 406 .. 407, each of which corresponds to a vertical row of switches, .and the tube ionizes and permits a discharge through the corresponding relay such as 419. Ionization of more than one tube is prevented by a common resistance 416 in the ionizing circuit and the occurrence of a discharge renders the other tubes incapable of discharging with the aid of a resistance 424. Relay 320 also energizes the select magnets such as 221 in the secondary switches corresponding to the calling horizontal row of primary switches, and energizes 330 to prepare for subsequent tests. Selection of link circuit.- Each group of secondary trunks is represented by a group of relays 725 .. 727 &c. and resistances 704 .. 706 &c. the relays being energized and the resistances disconnected when the corresponding trunks are busy. If there are two or more idle trunks in a group, the potential of the corresponding wire such as 707 determined by the relative values of resistance such as 708 and of the group of resistances such as 704 .. 706 is sufficient to cause the ionization of an associated tube 716, 721 &c. Impulses from a generator 735 are fed to the main electrodes of these tubes and the resulting impulses in those that are ionized are passed on to the upper starting electrode of a pair of tubes 602, 603 by a transformer 604. At the same time, impulses are applied to the lower starting electrodes from a set of tubes 431, 432, of which one corresponds to each link, those corresponding to idle links being ionized on the operation of 320 which connects battery to their starting electrodes and those corresponding to busy lines being prevented from ionization by connections over wires such as 218 to the corresponding cwire. The same set of tubes is used for the links from other horizontal rows, different starting electrodes coming into play when a different horizontal row relay, e.g. 321, is operated. When the tubes 602, 603 receive simultaneous impulses from both sides, ionization occurs and a momentary discharge across one of the main gaps, which are fed by an impulse generator 631, produces an impulse in wire 614 to cause the ionization of a corresponding one of a group of tubes 500, the lower starting electrodes of which receive impulses synchronous with those given to the main electrodes of tubes 602, 603. Two tubes are used taking odd and even pulses respectively to ensure deionization between pulses. The resulting main discharge in the tube of group 500 energizes a relay such as 514 characteristic of the secondary switch to be used and this energizes the appropriate select magnet such as 222 in the primary switch. If no secondary switch has two outlets, a circuit is made, after a time interval measured from the operation of 330 by the charging of a condenser 528, by the discharge of a tube 520 for a relay 503 which modifies the potential of the electrodes of tubes 720 to enable them to ionize when only one resistance 704, 705 &c. is connected up. Selection of idle trunk in the selected group.-Impulses are fed over the back contacts of such of the relays 725, 726 &c. as correspond to idle trunks to transformers such as 712 and are passed on over wires such as 741 and contacts of the operated relay such as 514 characterizing the group to be used to the upper starting electrodes of a group of tubes 615, the lower starting electrodes of which receive synchronous impulses in turn from a generator 632. Ionization occurs therefore in a tube corresponding to an idle outlet and the resulting main discharge energizes a corresponding relay such as 624 which operates the secondary switch hold magnet corresponding to the selected trunk. Selection of calling line release of control circuit.-The starting wire carrying impulses from machine 227 is extended by the relays such as 320, 420 to the lower starting electrodes of a group of tubes 800, the upper starting electrodes of which receive synchronous impulses from a machine 803. Ionization therefore occurs in the tube that corresponds to the position of the calling line in its line switch and the resulting main discharge ionizes the corresponding one of a number of auxiliary tubes 820. Relay 220 which operates over the extended starting wire in series with 819 connects the main electrodes of these tubes to the respective hold magnets in the calling primary switch and the appropriate one row operates to complete the connection. To ensure the previous operation of the select magnet in the primary switch, the main discharge of the tubes 800 is delayed until the charging of a condenser 822, permitted by the operation of 819, causes the breakdown of a tube 825 and consequent energization of 826 to complete the main circuits of the tubes 800. Relay 834, which pulls up in series with the primary switch hold magnet, energizes a relay 838. When ground is returned over the c-wire to hold the hold-magnet, the discharge in the tube of group 820 ceases owing to the effect of alternating current from a transformer 833 in series with the battery 832 and 834 falls followed shortly afterwards by 838. An impulse is thus given over wires 840, 841 to operate momentarily a relay 333 which releases all the operated elements.in the control circuit. The circuit is released if it fails to be released normally and in consequence 843 charges sufficiently after the operation of 826 to break down a tube 844 and allow operation of a relay 845 by a circuit over a front contact of 834.