Patent GB-817547-A (GB)
Title: Improvements in or relating to electronic selectors for telecommunications installations
IPC: H04Q3/00
Filed: 1957-07-15
Abstract: 817,547. Automatic exchange systems. SIEMENS & HALSKE A.G. July 15, 1957 [Ju]y 16, 1956], No. 22386/57. Class 40 (4). An electronic selecting arrangement comprises a number of inlets, each connected via an electronic switching device to an associated outlet, an input on an inlet operating the associated electronic device if the associated outlet is marked free, the inlet also being connected via rectifiers to succeeding switching devices which are operated if the outlet associated with the inlet is marked busy. As described, the inlets are connected to code points associated with exchange codes and the outlets are associated with various routes which can be taken by a call to the exchange in question, the routes being arranged in order of priority. The invention is applicable to a national network system having terminal exchanges, junction centres, main centres and sectional centres, each centre being fed by a plurality of the immediately preceding centres or exchanges and each sectional centre being linked by a direct route with each other sectional centre so that in the last resort a connection may be established by passing through one of each of the above exchanges or centres to a sectional centre, thence to another sectional centre and thence through a similar sequence down to the wanted exchange. Such a path is hereinafter referred to as a " code number path ". In addition, however, numerous tie lines are also provided between physically adjacent exchanges or centres so that a shorter path may often be found. As shown, Fig. 1, incoming lines L1 have access over selectors RW to outlets KA1 leading to a junction centre, outlets HA1, HA2 to two different main centres, outlets ZA to a sectional centre and outlets KZ to the code number path. An incoming call takes into use a register Sp8, say, in which the exchange code is stored on a device DW. When these are stored a translator U is taken into use and the digits are transferred thereto to cause the marking of a code number point in the selecting device W. The latter receives earth potential over wires x1 ... x4 if any of the associated groups of outlets contains a free outlet. The selecting device W then selects the highest priority group of outlets having a free outlet and passes its identity to a route relay in the store E in the register Sp8 which thereupon marks the shid group for selection by selector RW of an idle outlet therein and determines the code translation to be used for routing the call. As shown, Fig. 2, earth potential on a code point KP1 causes the transistor Ta1 to conduct, thereby lowering the base potential of transistor Tb1 to cause the latter to conduct, provided a free outlet is indicated by earth potential on the emitter. The result of the selection is indicated by the operation of route relay EK1 in the collector circuit. If no outlets in this direction are free transistor Tb1 fails to conduct, but the drop of potential is transferred via rectifier Gl1 to the base of transistor Tb2 which causes route relay EH1 to operate to indicate that a second choice route is to be used, and so on. In the event of there being no busy relays whose contacts can be used for energizing the bases of the Tb transistors, the test-wires can be coupled via rectifiers to the base of a third transistor, so that if an outlet is free the third transistor can be made to conduct and so bring the emitter of the Tb transistor to earth potential, Fig. 3 (not shown). In a modification, Fig. 4, the transistor Tc1 is rendered conductive or non- conductive according to the indication on wire x1, to pass or not to pass positive potential from the collector of the conducting transistor Ta1 to cause Tb1 to conduct in the former case. To prevent double marking in the event of two relays pulling up in quick succession due to changes in the busy conditions in the various groups whilst the selecting device is still connected, the circuit of Fig. 5 may be used. The points B1 ... Bn are connected to corresponding points in Fig. 2. When point B1 is earthed (due to Tb1 conducting), transistors T1, T2 remain non-conductive but condenser Co1 is changed so that if Bn is now connected to earth potential the base potential of transistor T1 is now sufficiently high to cause T1 and hence T2 to conduct. Positive feed-back over Wi1and Wi3 maintains this state after Co1 has discharged. Transistor T2 energizes U which directly marks the code number path and cancels the other markings.