Patent GB-857236-A (GB)
Title: Improvements relating to automatic telephone exchange systems
Inventor: WARMAN BLOOMFIELD JAMES
IPC: H04Q3/00
Filed: 1958-08-13
Abstract: 857,236. Automatic-exchange systems. SIEMENS EDISON SWAN Ltd. July 30, 1959 [Aug. 13, 1958], No. 26046/58. Class 40 (4). In a system employing line-finders served by a plurality of control circuits each of which may cause a free line-finder to search for and set to a calling line, there is provided at least one start circuit having an initiating element operable in response to the calling condition of a line to render effective in that start circuit an electronic one-only selector device which selects at random a free control circuit and initiates its operation. In the arrangement described the incoming lines are in 200-line groups, each served by a group of 25 linefinders. Of the four 50-line sub-groups into which each line-group is divided, two (the A and B sub-groups) are connected in the 200- outlet motor-driven uniselectors which constitute the line-finders, to arcs for which the associated wipers are connected up when a wiper-switching relay in an individual circuit for the line-finder is unoperated, and the other two (C and D) to arcs for which the wipers are connected up when the wiper-switching relay is operated. Each control circuit serves four line-finder groups, to each of the 100 linefinders of which a number of connections are established by way of respective, corresponding, outlets in a like number of arcs of a coupling switch included in the control circuit, which switch is also a motor driven uniselector. These connections are also multipled to the coupling switches of other control circuits serving the same four line-finder groups. A start circuit is provided individually for each 50-line subgroup, each of the sixteen start circuits of four line-groups having access to all the control circuits serving the four line-finder groups concerned. Initiation of a call by a line in the A subgroup.-Looping of the line wires L1A, L2A (Fig. 1), of a subscriber in the A sub-group renders the junction of resistors Rs2, Rs3 sufficiently negative for transistors Tr1 (Fig. 1), and TrA (Fig. 2), to conduct, whereupon the test lead L3A (Fig. 1), is marked with a negative potential and relay SA in the start circut (Fig. 2) operates. SA applies negative potential over the start circuit identification lead ILA to all the line-finders (Fig. 3) of the relevant line-finder group, this marking being extended in the case of free line-finders over back contacts of the busy relay GR to the relevant outlets of arc CA1 (Fig. 4) of the coupling switches of the control circuits concerned. SA also completes a discharge circuit for the multi-cathode selector tube SSA (Fig. 2), whereupon a discharge randomly irvests a cathode connected to a free control circuit; a starting signal, provided by the potential rise of that cathode, being extended over the corresponding starting lead SLA, say, to the control circuit concerned. The potential rise on lead SLA busies the control circuit to A sub-groups of other line groups by raising the potential of the corresponding cathodes in the selector tubes of their start circuits. In the control circuit (Fig. 4) the potential on SLA cuts off transistor Tr5 wherepon Tr6 conducts and the control relay STA operates, thus disabling the operating circuits for STB, STC and STD. STA also energizes the latch magnet LMC of the coupling switch and connects the transistor Tr7 to wiper CA1. The coupling switch hunts for a free line-finder in the required group. For each free line-finder encountered " free " potential is extended over a back contact of busy relay GR (Fig. 3) and the relevant contact of arc CA5 to the base of Tr8 (Fig. 4), which transistor conducts. However Tr7 does not conduct until the start circuit identification signal on lead ILA is extended over arc CA1 to its base. When Tr7 and Tr8 conduct simultaneously, signifying that a free line-finder in the required group has been found, both of the rectifiers Rf3 and Rf4 are backed off and transistor Tr9 is cut off. Transistor Tr10 thereupon conducts and operates the high speed test relay TF to stop the coupling switch. A temporary busying of the line-finder is effected by making the value of Rs22 such that in combination with the similar resistor of another control circuit which may test the line-finder it prevents the transistor Tr8 of the other control circuit from conducting. In order to prevent another control circuit taken into use by a start circuit of an A sub-group of a different line group from taking into use a second free line-finder in the first group by reason of the start signal on ICA, the value of Rs21 is chosen to prevent the transistor Tr7 of the second control circuit from conducting in such circumstances. The operation of TF removes the short circuit from the priming relay TC, which then operates in series with latch magnet LMC (which is not energized). TC energizes the slow-operating switching relay SF and attempts to operate the wiper-switching relay SW of the line-finder under control over arc CA7. On a call initiated by a line in an A or B sub-group neither of the relays STC and STD is operated and no circuit for SW is completed. However, for a call from a C or D sub-group line STC or STD will be operated and SW comes up. The operation of SF opens the operating circuit for SW (SW if operated holding over its own " x " contact), completes a circuit over arc CA6 for the latch magnet LMF of the line-finder; and completes a testing circuit over arc CA8. When the calling line is found the negative potential on the emitter of Tr1 (Fig. 1) is extended to the base of Tr11 (Fig. 4), whereupon Tr11 conducts and test relay T pulls up to stop the line-finder. The busy relay GC then operates in series with LMF (which does not reoperate) and applies ground to the P- wiper (Fig. 3), to back off Rf1 (Fig. 1), thereby terminating the calling signal to start circuit SCA (Fig. 2). TrA (Fig. 2) becomes non- conductive thus releasing SA. The tube SSA reverts to normal and the start identification signal is removed from ILA. GC also brings up the second busy relay GR, and the two busy relays disconnect the leads ILA to ILD from the arcs CA1 to CA4 of the coupling switch, and connect to these arcs leads from the line-finder. The operation of test relay T brings up TL (Fig. 4), which connects the linefinder over arcs CA7, CA6 and CA8 to leads LE1, LE2 and LE3 extending to register circuits (not shown) by which the subsequent setting-up of the call are controlled, holds GC, and brings up TR (Fig. 4) which busies the control circuit by disconnecting the start leads SLA to SLD. Fault operation.-If a calling condition is terminated after a control circuit and a linefinder have been taken into use but before the calling line has been found, the line-finder is stopped on its penultimate outlet by operation of test relay T consequent upon Tr11 being rendered conductive by the negative potential connected via Rs31 (Fig. 3) to the test arc penultimate contacts. Completion of connection.-When the dialled digits have been received the register brings up FA (Fig. 4) which operates relay H in the linefinder, thus extending leads LE1, LE2 and LE3 from the register via arcs CA7, CA6 and CA8 to leads SL1, SL2 and SL3 (Fig. 3), leading to the selector stages. When the final selector has been set to the wanted line and this line is free, the register brings up BSA (Fig. 4) which brings up HA (Fig. 3) over arc CA1, thus extending the line circuit of the calling line to transformer TX, whereupon A operates to the calling loop, and connecting up ringing tone from the source Rt. Relay HA also connects up ringing current (over contacts not shown) to the called line, the operation of ring-trip relay F on the reply of the called party disconnecting the ringing-tone source Rt and the ringing current source (not shown). Called line busy.-In this event the register brings up BSA and BSB (Fig. 4) so that HA comes up as before and in addition HB (Fig. 3) is operated over arc CA2. Busy tone is thus connected up from source Bt, instead of ringing tone from source Rt.