GB1290064A - - Google Patents

Abstract

1290064 Automatic exchange systems SIEMENS AG 17 Dec 1970 [19 Dec 1969] 59846/70 Heading H4K . A switching matrix comprising a relay in series with a diode at each cross-point is provided with a first voltage supply for normally reverse biasing the diodes and a second voltage supply of opposite polarity and lower absolute value than the first for forward biasing a single diode and thus bringing up a unique relay when it is applied to a relevant row and column. The first potential is applied to each column and row supply wire over the break-side of a changeover contact, e.g. xm, yn while the second potential is applied over the make side of these contacts. The breakside contact is shunted by a resistor, e.g. Rxm, Ryn to ensure continuity of the current paths during the selection operation. Since the reverse bias potential ŒU directly applied to a row or column wire not having its change-over contact operated is always greater than the forward bias potential Œu applied to a row or column wire having its change-over contact operated, then, even if a diode such as G43 has broken down so as to draw operating current for its associated relay R43, no other cross-point relays will be inadvertently operated. Thus the potential on X4 is -U irrespective of whether G43 is faulty or not so that if say Y2 is marked with -u during a selection operation, diode G42 will still be reverse biased and so R42 will not operate. Similar considerations apply to the row wires. The system is a development of that in Specification 1,015,451. The switch is monitored for faults so that a faulty cross-point can be marked permanently busy in a path finder's memory map. The arrangement also confines the fault to a single switch of a stage having common supply wires for each of the switches therein, an example being provided by Specification 1,171,075.