Patent GB-530087-A (GB)
Title: Improvements in or relating to automatic telephone systems
IPC: H04Q3/00
Filed: 1939-06-16
Abstract: 530,087. Automatic exchange systems. ELECTRICAL RESEARCH PRODUCTS, Inc. June 16, 1939, No. 17619. Convention date, June 17, 1938. [Class 40 (iv)] In a system in which calls are extended over a number of link circuits in tandem under the control of markers, the markers are arranged to test the sleeve wire of each link for abnormal conditions, to test whether the connecting switches have closed properly and finally to test the continuity of the sleeve circuit over the operated switch contacts and to test whether the proper metering conditions have been set up. The invention is described in relation to a cross-bar system of the kind described in Specification 466,986 in which a marker seized by a register-controller selects an idle junction 200 in the appropriate direction in response to the exchange digits and controls the extension of the calling line thereto at district and office switch frames each comprising primary and secondary switches 105, 106, 202, 201. Relay 400 which is individual to the selected junction closes circuits for the holding magnets 107, 205 over wires 119, 212 in series respectively with upper windings of differential relays 300, 304, both of which operate provided (1) the sleeve of the junction is ungrounded, (2) the junction has not been sized by two markers, (3) the marker is properly associated with the switch frames indicated by the operation of 406, 416, (4) there is no ground on the magnet windings. Relays 300, 304 open the locking circuits of 305, 306, which connect 417 to the metering wire and connect ground on wire 117 to operate the holding magnets 109, 204, the latter circuit being opened if 417 fails to pull up. Ground on wire 117 is extended through the district and office links 108, 203 to ensure the operation of the magnets 107, 205 and to shunt down 300, 304, and is then further extended over wire 126 over contacts of relays 328-334 (see later) to operate 303 and over wire 216 to operate 412. Differential relay 421 energizes provided (1) 303, 412 both operate and (2) there is no ground on the windings of magnets 109, 204, and effects the release of 406, 416. Relay 412 transfers the sleeve circuit, which was previously grounded by the operation of 420, to relay 423 which energizes provided the ground is properly applied at 225 and initiates the release of the marker. Any abnormal condition results in the transmission of a trouble signal to the registercontroller. Relays 328-334 are concerned with checking the operation of relays in the district trunk circuit 103 on various classes of call. If the call is from the tip party on a two-party line, 333 operates and connects up a relay in the trunk circuit which in turn connects up 334, while for all other calling parties 332 operates. The circuit for 303 therefore depends on either 332 or both 333 and 334 being up. Relays 328-331 are dependent on the metering condition set up in the trunk circuit, 330 operating for normal metering, 331 on a free call and 328 when zone metering apparatus is taken into use. If the latter apparatus is not available, 329 operates and brings about the normal metering condition in the trunk circuit and 330 is connected up.