Patent GB-832727-A (GB)
Title: Remote line concentrator
IPC: H04Q3/52
Filed: 1957-10-07
Abstract: 832,727. Automatic exchange systems; controlled non-linear inductors. LUCAS, P. Oct. 7, 1957 [Oct. 5, 1956], No. 31369/57. Classes 40 (4) and 40 (9). In an automatic satellite (non-exchange) each subscriber's circuit includes a gate to which are applied pulses in a time position characteristic of the subscriber and a continuous alternating current signal of a fixed frequency, the gate being capable of assuming four different conditions in dependence upon the condition (looped or open) of the subscriber's line, and whether or not the subscriber's line is extended to an exchange line leading to the main exchange. In the first condition, that of an idle line (unlooped-unconnected), the gate passes the pulses at a predetermined amplitude; in the second, that of a calling line (loopedunconnected), it passes the pulses at a higher amplitude; in the third, that of a dialling or clearing line (unlooped-connected), it passes the continuous signal; and in the fourth, that of a line engaged in a call (looped-connected), it passes neither the pulses nor the continuous signal. Such a gate, as shown at 3 (Fig. 2), consists of the two saturable-core transformers 5 and 6 associated with the line transformer 4, the pulses being applied over lead 19 to first windings of transformers 6 and 5 in series, and the continuous signal of frequency f over transformer 25 to a second winding of transformer 5. Current flowing in the subscriber's loop traverses a third winding of 5, and that flowing in a fired cold cathode tube, such as 13, connecting the subscriber to a trunk, such as 15, traverses a fourth winding of 5 and the second winding of 6 in series. The condition of the cores of transformers 5 and 6 is illustrated in Fig. 7, the black spot in each case indicating the operating point and the thick line the cycle described during the application of a pulse. It will be seen that in the idle line condition, Fig. 7 (a), the cycle for transformer 5 lies wholly in the saturated region and gives rise to no signal, whereas transformer 6 describes a hysteresis loop and supplies a positive.low-amplitude pulse 106 to the output lead 11 (Fig. 2). For a calling line, Fig. 7 (b), the current flow in transformer 5 moves the operating point to the right and both transformers 5 and 6 describe hysteresis loops giving rise to a pulse 107 of about twice the amplitude of 106. When a tube 13 fires (looped line connected to exchange line) the current flow therethrough moves the operating point of both transformers to the right into the saturation region, Fig. 7 (d), and the input pulse produces no output. Opening of the loop (dialling or hanging up) causes the operating point of transformer 5 to move to the left to the vicinity of the saturation knee of the hysteresis curve, Fig. 7 (c), so that the input pulse is practically without action. The frequency f, however, causes transformer 5 to describe a small loop as indicated by the arrows and this signal consequently appears on the output lead 11. General arrangement and allocation of time positions to subscribers.-In the system described the main exchange is assumed to serve one hundred satellites, each having fifty subscribers and each connected to the main exchange by ten exchange lines. A cycle one hundred milli-seconds long is divided into five thousand-time positions each of 20 Ásecs. In each satellite each of the fifty subscribers is allocated a block of one hundred-time positions as indicated in line a of Fig. 1, whereas in the exchange each subscriber is allocated one time position only, which characterizes both the satellite to which his line is connected and the number in the satellite. Thus all subscribers numbered 02 in their satellites are allocated in the satellite the third block of 100 time positions, but in the exchange, subscriber No. 02 of, say, the fifth satellite is allocated the fifth time position of that one hundred. Satellite subscriber initiates a call.-When the subscriber 1 (Fig. 2), who is assumed to be subscriber No. 02 of the fifth satellite, lifts his handset his gate 3 delivers high-amplitude pulses 107 (Fig. 7) in response to the application by the generator 18 of subscriber identifying pulses 102 (Fig. 1) in the block of time positions characteristic of the subscriber's number in his satellite, which pulses are applied to the cold cathode tubes 13. If an exchange line is busy the potential drop across its resistor 16 prevents firing of any further tube 13 connected to that exchange line, but the tubes leading to free exchange lines may be fired by a pulse 107. However, these tubes have a common load resistor 17 so that only one of these tubes 13 remains conductive, thus extending the calling line to one of the free exchange lines, such as 15. The resulting sharp increase in potential across resistor 16 is differentiated by condenser 47 and is transmitted over the trunk as a connection-control pulse 103 (Fig. 1). At the exchange this pulse passes from tap 31 (Fig. 3) to the pulse detector 49 and triggers the trigger circuit 50. The phase displacement between the cycle at the exchange and that at a satellite is such that, taking into account the propagation time over the exchange line and the mean firing time of the tubes 13, the triggering of circuit 50 occurs slightly before the time position of the satellite subscriber concerned but after the time position of the preceding subscriber of the same satellite, thus allowing a margin of slightly less than two milliseconds in the relative timing of the cycles. In the next time position allocated to the satellite concerned (viz. that of the calling subscriber) the generator 88 supplies a pulse 104 to the wire 53 which passes through the gates 51 and 52 opened by circuit 50. This pulse triggers the circuit 57 which opens the gate 59, thus allowing dial tone FN to be reverted to the caller, passes via wire 81 to the decoder 54 which records the number of the exchange line concerned, and restores the circuit 50, thus closing gates 51 and 52. When the caller dials the wanted number each break of his dial causes the transmission of the " loop " frequency f over the exchange line, this frequency being detected by detector 55 to produce direct current impulses on lead 56. The first impulse restores the trigger circuit 57 to stop the reversion of dial tone via gate 59. With trigger circuit 58 in the normal condition the gate 70 is open and the impulses pass to the device 74. Extension of call to the wanted subscriber.- The exchange, having received the identity of the wanted subscriber, transmits by means of the pulse generator 39 (Fig. 3) a negative lowamplitude pulse in the block of time positions corresponding to the number of the subscriber in his satellite over free exchange lines leading to that satellite. This pulse operates the trigger circuit 42 (Fig. 3) which opens the gate 64, and passes via condensers such as 47 (Fig. 2) to the resistors 16 at the satellite end of the exchange lines. At this instant the gate 3 of the wanted substation passes a positive lowamplitude pulse 106 (Fig. 7) to the lead 11 (Fig. 2) so that all tubes 13 capable of connecting the wanted subscriber to free exchange lines receive a potential which is the sum of the two pulses and exceeds the firing potential. One of these tubes 13 fires to connect the subscriber to a free exchange line, the resulting connection-control pulse triggering the trigger circuit 50 as in the case of the calling subscriber. The chosen exchange line is identified and the exchange proceeds to connect the incoming exchange line to a junction 43 (Fig. 3) via stages 34 and the outgoing exchange line to the same junctor via similar stages 34. However, the wanted subscriber's loop being open the frequency f is sent over the exchange line, is detected by detector 55 of the outgoing exchange line circuit and prevents trigger circuit 57 from being triggered by the pulse from gate 51. This pulse passes instead via gate 64 (opened by trigger circuit 42) to operate trigger circuit 58. It also restores trigger circuit 42, thus closing gate 64. Trigger circuit 58 opens the gate 60 to the passage of the ringing frequency F and the super-audio supervisory frequency F<1> from generator 62. The exchange line circuit associated with the calling party detects the frequency F<1> by means of detector 65 (Fig. 3) and with its trigger circuit 58 at rest this passes via gate 67 to the device 68. On the reply of the called party the transmission of frequency # by his gate 3 ceases, whereupon the device 63 in his exchange line circuit produces a pulse which resets trigger circuit 58, thus closing the gate 60 and stopping the transmission of F and F<1>. In the exchange line circuit of the caller the cessation of frequency F<1> causes the device 68 to transmit a pulse on lead 69 to control metering of the call. To prevent metering by the called line exchange line circuit also, it is arranged that upon the resetting of trigger circuit 58 a delay is introduced before gate 67 is opened. Release.-When a subscriber hangs up his gate 3 passes frequency f to the exchange, producing a direct current potential on lead 90 as during dialling. A delay device (not shown) operates when this potential persists for more than 200 milliseconds and initiates release. This is effected by pulse generator 33 (Fig. 3) transmitting a positive disconnection pulse over the exchange line concerned to effect extinction of the fired tube 13 (Fig. 2) connected thereto, and of the fired tubes in the stages 34 connecting that exchange line to the junctor 43. Current supply.-Current is supplied over the phantom of pairs 20 and 22 (Fig. 2) from the exchange.