Patent GB-597688-A (GB)
Title: Telephone systems
IPC: H04M15/08
Filed: 1944-05-09
Abstract: 597,688. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (International Standard Electric Corporation). May 9, 1944, No. 8783. [Class 40 (iv)] A demand for identification causes the seizure of a control circuit 1CC, Fig. 1, and the application of a tone current to the c-wire of the established connection. The switch 1CF of the control circuit hunts for the first finder 1LF to which the tone has been applied over the switches ahead, thus identifying the calling hundreds (or two hundred) group, and then sets up a connection to a normal final selector serving this group over an individual 2nd group selector and a normal 3rd group selector. This final selector is then controlled to hunt for the tone and so identify the line. In the system described, the numerical switches hunt for a tone current, the phase of which agrees with that of a tone current selected in the control circuit as described in Specifications 555,530 and 563,666. Selection of identification control-circuit and identification of calling group. Ground is applied from the circuit needing the identification to terminal A, Fig. 4, of an allotting circuit in which relay 1B pulls up and a switch 1M hunts for a control circuit under control of relays CT, CD. Relays UH, IL then operate and 1B falls back. Relay 1SR in the control circuit energizes CTR and starts the finder 1CF. Tone current from a transformer T1 is applied via terminal B in the allotter circuit to the c-wire of the established connection from which it reaches via terminal C, an isolating resistance and a transformer TA, the appropriate a-terminals of the identification finders 1CF. When switch 1CF finds this terminal, a cold-cathode tube CT1 fires and relay TT stops the switch and energizes KC, whereupon CTR begins to release. To ensure that the firing of CT1 by transient conditions is not effective, KC also starts a switch 1S which delivers impulses to 1P to produce an intermittent interruption of the tube circuit. If the tube re-fires each time its circuit is remade, KC remains up and in due coarse CTR falls back. Meanwhile, a direct current test is made over the b-wiper to guard against double connections. If no other switch is in a corresponding position, DC pulls up and holds over a low-resistance winding in series with DZ to exclude other switches. With DZ up and CTR back, a circuit is made for OK which locks. If either test fails, the switch is driven on. OK grounds the a-terminal to remove the marking tone from other switches and prevent the re-firing of CT1 when next it is put out. Relays CT, CD, UH in the allotter and 1S, KC, DC, DZ in the control circuit then fall back and GG, GH are operated. Group selectors select a final selector in the calling group. GH energizes TO, SS and DT pulls up over the c-wire to the permanently associated 2nd selector shown in Fig. 2 and is followed by SA, VR. At the same time, the selector A relay pulls up over the b-wire in series with T and removes the idle potential from the c-wire, whereupon DT, VR, SA fall back, the sequence switch SM is given a step, releasing TO, and the selector power magnet is energized over the a-wire. The selector is stopped by the firing of a tube CT2 and energization of VT when its d-wiper encounters a tone current of the same frequency and phase as that on the c-wiper of switch 1CF. VT also energizes FT to release CH and extinguish the tube. FT locks in series with FH which pulls up when a short-circuit is removed by the relapse of VT and re-operates CH. If the firing of the tube was not due to a transient condition, it now fires again and VT operates TO. If the tube fails to fire, K1 comes up, VR operates momentarily to release FT, FH and the power magnet is re-operated. On the operation of TO, T is connected over the b-wire in series with switching relay B in the 2nd selector and the idle potential in the selected 3rd selector. T pulls up and shunts itself by the low resistance of DT, whereupon B switches through and A pulls up in the 3rd selector. If T is unable to operate, GB comes up instead, disconnects T, connects the b-wire to a coldcathode tube CT4 and re-makes the circuit over the a-wire for the power magnet. The switch is stopped by the operation of FS, VR when the tube is fired by the test potential of an idle outlet. FH, FT, TO, GB, CH, VT then fall back, the tube is extinguished and control is taken by CT2 in accordance with the A.C. conditions now encountered by the selector d-wipers. In the case of the successful seizure of a 3rd selector, the operation of relay A therein releases DT, the momentary operation of which drives the sequence switch into its next position in which the 3rd selector is controlled in a similar manner. Control of final selector. In position 3 of sequence switch SM, SS is released and LS, FO are operated. The final selector now has a driving circuit over the a-wire and the b-wire is coupled via transformers 1T2, IT to tube CT1. Consequently, when the final selector encounters the identification marking, CT1 fires and TT stops the selector. As in the case of switch 1CF, the A.C. test is repeated and if TT continues to re-operate until CTR has fallen back, BT comes up releasing KC and'sequence switch SM moves to position 4 in which FO is released. As the final selector passes each tens terminal it sends an impulse of characteristic phase over the c-wire to fire CT2 in conjunction with a reference current of the same phase connected up in successive positions of the tens register TM which receives an impulse for each operation of VT by the firing of CT2. Transmission of identified number. In position 4 of SM, DS is operated and energizes 1C which is followed by 1D, IF and starts the impulse-generating switch IS. The first impulse from the latter energizes F1 which locks at the end of the impulse in series with FL which connects the sending tone source T2 to the b-wire of the identification switch train from the final selector of which the tone passes over the ordinary switch train to the registering circuit. Relay 1X responds to each impulse from switch 1S after the operation of FL and steps a counting switch CM until the latter finds with its b-wiper current of the same phase as that connected to transformer HC2 by the b-wiper of the sequence switch from the wire 16. VT then energizes ED which locks and releases 1C, F1, FL, 1D, 1F, the latter falling sluggishly to time a pause period. The relapse of 1F releases ED, resulting in a temporary operation of VR to release CH and extinguish tube CT2 and of SA to cause the sequence switch to move on as before. The relapse of FL terminates the preliminary impulse and causes 1X to interact with CM until the latter reaches normal. CH re-operates on the relapse of VR and when CM reaches home, 1C pulls up and then 1D, IF, F1, FL as before. In this case, however, each relapse of IX interrupts the sending tone circuit and the digit is terminated in accordance with the phase of the current connected to wire 17 which represents the exchange digit. The thousands and hundreds digits are sent similarly in accordance with the phases found by the c- and d-wipers of the identification finder 1CF and the tens digit in accordance with the phase on the c-wiper of the tens register TM. The units digit is determined by the phase of current fed back from the final selector over the c-wire which is connected to the sequence switch b-wiper in position 9. When position 10 is reached, RL operates, the switches go home and all relays are released. During sending, the ground connection to the point D is removed by relay S1 to enable other lines in the group to be identified.