Patent GB-615312-A (GB)
Title: Automatic telephone system
IPC: H01H67/26
Filed: 1945-05-25
Abstract: 615,312. Automatic exchange switches. LEICH ELECTRIC CO. May 25, 1945, No. 13189. Convention date, March 19. [Class 40 (iv)] The invention relates to a cross-bar switch of the type described in Specifications 544,954 and 601,965 in which 300 conductor bars being the speaking and test conductors of 100 circuits extend laterally through 10 trunk units and a cross-section of 30 x 10, each vertical column of 30 belonging to a particular '' tens " group and the vertical height of a set of three conductors determining " units " designation. Connection is established between a set of conductor bars and a trunk associated with a particular trunk unit by means of 30 intermediate trunk elements in each trunk unit, each element consisting of a metal strip extending horizontally perpendicular to the conductors and having 11 spring fingers 10 for connection with the conductor bars and the eleventh for connection to the trunk. One of 10 " tens actuators " move the springy fingers in a selected column into contact with their adjacent conductor bars, and one of 10 " units actuators " moves the eleventh spring finger of a selected intermediate trunk element into contact with members permanently connected with the trunk. The mechanism differs from that described in Specification 601,965 in that whereas, in the latter, a common "selection control unit " was provided having " tens " and " units " solenoids which controlled the selection of " tens " and " units " actuators of all the trunk units, the present invention provides each trunk unit with its own'solenoids for selecting its actuators. As in the above-mentioned Specification, the selected actuators are moved into the operated position and maintained there after de-energization of the " tens " and " units " solenoids by a trunk or gating magnet individual to the trunk unit. Arrangements facilitating the rapid dismantling of a trunk unit include (1) forming the fixed contacts for connection with the eleventh fingers of the intermediate trunk elements as projections from vertical metal strips readily removable from the trunk unit; (2) removably mounting the " tens " solenoids assemblies, " units " solenoids assembly and the trunk magnet assembly; (3) wiring each of these assemblies to separate jack strips which co-operate with different portions of a single plug strip to which all incoming wiring is brought. In a circuit, Figs. 14, 15, for using the switch as a line-finder, connections are established under the control of "pilot" relays 329, 330 ... individual to each tens group and 382, 392 ... associated with each units digit. Operation of line relay 307 of subscriber No. 11 puts negative potential on the test conductor 30 of the switch and operates the pilot relay 329 (associated with the tens digit 1), which locks, disconnects the operating circuits for the other tens pilot relays, and operates the tens solenoids 125 associated with tens digit 1 in all the trunk units. Relay 329 also operates tens solenoids 315 and the gating magnet 266 of the test unit (a unit similar to a trunk unit but having no units actuators or solenoids, and effecting connections with the test conductors only), thereby operating the actuator 276 and extending the negative potential on the test bar 30 to operate the pilot relay 382 (associated with units digit 1) which locks, prevents operation of the other units pilot relays, energizes the units solenoids 173 corresponding to digit 1 in all the trunk units, and operates start relay 350. A test is made for the first free trunk (marked by negative battery on the test wires 372, 373 ...) for which a trunk distributer relay (e.g. 331, 332 ...) is operated. If relay 331 is operated and the associated trunk free, trunk test relay 341 operates, locks and disconnects subsequent trunk test relays 342 ... and operates the gating magnet 205 of trunk unit No. 1 so that the tens and units actuators 95, 168 connect the conductors 28 ... 30 through to the trunk 370 ... 372, whereupon wire 372 is earthed to operate the subscriber's cut-off relay 306, which holds the gating magnet 205 which alone maintains the connection. The trunk distributing relays 331, 332 ... release in turn as connections are set up on their associated trunk units until all are released when a circuit is closed for relay 351 which resets them all.