Patent GB-811244-A (GB)
Title: Improvements in or relating to automatic telecommunication exchanges
Inventor: BRAY FREDERICK HARRY
IPC: A45D8/38
Filed: 1956-12-21
Abstract: 811,244. Automatic exchange systems. STANDARD TELEPHONES & CABLES Ltd. Dec. 21, 1956, No. 39000/56. Class 40 (4). In an automatic exchange of the type described in Specification 794,812 the 10,000 lines are divided into first sets each consisting of a block of 200 sequentially numbered lines, each block being sub-divided into sub-blocks of 10 lines and the corresponding sub-blocks in all first sets forming second sets; a first detector detects the second set which includes a calling line and marks the line circuits of all lines in that second set; there being also second detectors, each individual to a first set, one of which responds to a calling line which is marked by the first detector and marks the line circuits of the lines in each sub-block of its first set having the position in the sub-block corresponding to that in which the marked calling line is detected, so that the only line circuit marked by both the first and a second detector is that of the calling line, which responds to cause that line to be extended over a switch for handling outgoing calls. Seizure of free first link.-In the idle condition of the line circuit (Fig. 1) point a is at approximately - 40 volts, but rises to - 5 volts when the line is looped. The leads A of line circuits of all lines in the same second set are multipled and each of the twenty multipled sets of leads is connected to one of twenty thyratrons such as V1 in the first detector (Fig. 2). Negative pulses PN are applied sequentially to the cathodes of these thyratrons and the first thyratron corresponding to a second set including a calling line (- 5 volts on lead A) fires to the cathode pulse, thus causing the common tube V3 to conduct. The fall in voltage at the tap of the anode bleeder of V3 is applied to the second grids of all the thyratrons and prevents any other thyratron from firing. The cathode output from the fired V1 (+ 160 volts) is also applied via lead F<SP>1</SP>x to the F<SP>1</SP> leads (Fig. 1) of all lines in the corresponding second set, and to the control grid of a further thyratron V2 (individual to V1) which fires and applies earth potential to the C leads of all lines in the second set. The calling line (among others) now has its leads Fl and C marked but only in the case of the calling line (a at - 5 volts) is the lead B raised to - 5 volts. A second detector (Fig. 3) is provided for each first set and includes ten thyratrons such as V4. The leads B (Fig. 1) of the corresponding lines in the sub-blocks within the first set are multipled and each of the ten sets of multipled leads is connected to the relevant one of the ten thyratrons V4. The V4 cathodes are sequentially pulsed in the same way as were those of the tubes VI. The tube V4 having its grid marked at - 5 volts over a lead B fires, V5 functioning in the same manner as did V2. The cathode output of the fired tube V4 is applied via lead F<SP>11</SP>x to the leads F<SP>11</SP>of those line circuits in the first set whose position in their sub-blocks corresponds to that of the fired tube. Hence one calling line has both its leads F<SP>1</SP> and F<SP>11</SP>marked and in its line circuit point b rises to + 75 volts. Calls outgoing from and incoming to subscribers are set up via terminal connector multi-switches each having outlets to first links (for outgoing calls) and to final links (for incoming calls). At each inlet/outlet crosspoint there is a double anode/single cathode tube such as SGT (Fig. 1), which is of the type described in Specification 734,345, [Group XL (a)], and which in a circuit such as that of Fig. 1 provides a bi-directional speech path between its anodes when discharges exist between the cathode and both anodes. The point b is connected to the left-hand anodes of as many tubes such as SGT as there are first and final links accessible from the terminal connector. The cathodes of the tubes'such as SGT for all free first links are pulsed sequentially by negative pulses, a tube having its left-hand anode at - 75 volts firing across its left-hand anode-to cathode gap. The right-hand gap then fires automatically and the cathode current marks the first link busy. The cathode current of the fired tube SGT is about 20 ma., about 10 ma. of which flows through each anode/cathode gap. The voltage drop across the anode/cathode gap and the cathode resistor is such that the lefthand anode potential of SGT, and hence the potential at point b, falls to about - 20 volts. MR1 and MR6 conduct and the potential at a falls to about - 20 volts. A current of about 8 ma. flows in R2 via MR1 and one of about 2 ma, in R1 via MR6. After the testing of first links has been completed the marking condition is removed from leads F<SP>1</SP> and F<SP>11</SP>. The operation may be modified so that the second detectors operate first and the first detector responds to a calling line marked by a second detector. Extension of connection.-The caller dials in the usual manner, and on each break impulse the potential of a falls from about - 20 volts to about - 40 volts. MR1 is thus rendered non- conductive and the 8 ma, current flow in R2, MR1 ceases; the potential at b remaining substantially constant and the current flow in R1 rising to about 5 ma. As the total cathode current flowing in SGT remains substantially constant, the current in the right-hand gap rises to about 15 ma, which change is detected by MD, thus repeating the impulse. Connecting to called subscriber.-The wanted number is received by a register which transfers it to a called line marker. The latter marks the leads D<SP>1</SP> (Fig. 1) of all lines having the same tens/units digit combination as the wanted line, and the leads D<SP>11</SP>of all lines having the same hundreds/thousands digit combination as the wanted line. In the called line circuit, therefore, both D<SP>1</SP> and D<SP>11</SP>are marked and point b  rises to + 75 volts. The cathodes of the tubes such as SGT giving access to final links are then pulsed sequentially, but at different times from those of tubes giving access to first links, the arrangements whereby collision of calls and conflict between co-existing calls is avoided being fully described in Specification 794,812. A tube SGT giving access to a free final link is fired exactly as was that giving access to the first link. An audio ringing signal would, in general, be supplied from the first link or, if preferred, from the final link. The reply of the called party would be detected in the same manner as was dialling by the calling party, and would trip the ringing. Called line busy.-In the case of a line circuit connected to a first link or to a final link point b is at about - 20 volts and the markings from the called line marker are ineffective. Busy tone is reverted at a fixed time if no response to those markings has occurred. The detectors are able to distinguish between the - 20 volts at a of a. busy line and the - 5 volts of a calling line, so that multiple seizure of a line which is busy is avoided and busy lines cannot simulate calling lines. Release.-Calling party release is provided the first link detecting the clear condition.