GB1290822A - - Google Patents

Abstract

1290822 Two-wire switching networks INTERNATIONAL BUSINESS MACHINES CORP 14 Jan 1971 [28 Jan 1970] 1788/71 Heading H4K A two-wire switching path is set up by connecting winding WA1 of transformer TA to winding WB1<SP>1</SP> of transformer TB by way of a single wire and by connecting winding WAl<SP>1</SP> of TA to winding WB1 of TB by way of a second single wire path, the single wire paths being switched with cross-points comprising unidirectionally conductive elements CR poled in one sense in one wire and in the other sense in the other wire. The cross-points are controlled semi-conductor rectifiers in matrices of a fourstage network. Transformers such as TA serve extension lines while transformers such as TB serve main exchange lines. Path selection is effected by cross-point marking wires G1 to G4, each of which marks the pairs of cross-points common to a row of a switching matrix, and by means of junctor circuits J provided on the links between the second and third stages. With markings on leads G1 and G a pulse is applied to transistor FP in junctor J and cross-points CR1, CR2 break down and conduct. Markings on G1 G2 are withdrawn and markings on G3, G4 applied with a pulse applied to transistor FQ in the junctor so that CR3<SP>1</SP> and CR4<SP>1</SP> conduct, Markings G3, G4 are withdrawn and markings G1 G2 are reinstated so that crosspoints CR1<SP>1</SP>, CR2<SP>1</SP> and line switch CRA conduct, CRA being primed to conduct by conduction in the other line as detected by transistor TRA. Markings G1 and G2 are withdrawn and markings G3, G4 are reinstated so that cross-points CR3, CR4 and line switch CRB conduct, CRB being primed by conduction in the other line as detected by transistor TRB. With conduction established from end-to-end of each wire the junctor J can stand idle with transistors FP and FQ switched off. Current in each wire of the path is detected by leads SA, SB, in order to test that the path holds up following junction feed standing down. Release is effected by switching on transistors DP, DQ in the junctor so that the earth side cross-points are starved of current and switch to open circuit.