Patent GB-744291-A (GB)
Title: Improvements in or relating to electrical communication systems
IPC: H04Q3/42
Filed: 1950-01-16
Abstract: 744,291. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (Hertog, M. D.). Jan. 12, 1951 [Jan. 16, 1950], No. 1094/50. Class 40 (4). [Also in Group XXXVIII] In a system employing register-controllers, translating apparatus is provided in common to a group of register-controllers which may all, at the same time, send the exchange prefixes received from calling substations to the translator and receive therefrom a translated routing number. A system of pulse-controlled gates in reverse tree formation extends from the register-controllers to the translator and is such that one time position in a recurring cycle is allocated to each register-controller. During that time position the prefix is sent to the translator and is by means of a jumper field converted into a routing number by the grounding of the relevant routing number terminal. These terminals are connected via a second system of gates controlled by another series of pulses to a common impulse repeating valve whose output is applied to a third system of gates operating similarly to the first one mentioned above so as to enable a path to each of the register-controllers in its allocated time position, over which path the routing number is received. In the embodiment disclosed the translator is capable of translating one hundred two-digit prefixes into thirty-three routing numbers indicative of local exchange, manual main exchange, tandem exchange, twenty automatic exchanges, and ten spare indications, respectively. The selection of the wanted direction of the twenty-three or more is made by a single selection using a 2-step selection stage such as is described in Specifications 653,524 and 698,802. In general the following cases occur: Local call. The class of line indication received from the local junction in the manner disclosed in Specification 737,866 causes the register-controller to proceed with the thousands selection as described in Specifications 737,865 and 737,866. Call to distant exchange over direct junction. The class of line indication from the outgoing junction causes the register-controller to function for distant operation and the routing number causes it to transfer the four numerical digits of the called number to a terminating register at the distant exchange. Call to distant exchange via tandem exchange. As in the last case, but the routing number, being indicative of the tandem exchange, causes the register-controller to transfer the exchange prefix only to the tandem register. This prefix is translated at the tandem exchange into a routing number, a free junction is selected, the tandem register is disconnected and the connection is switched through at tandem. The numerical digits are then sent from the originating register-controller to that at the terminating exchange by through V.F. signalling. Detailed operation of translation (Fig. 1). One translator is provided for 100 registercontrollers and is capable of translating any one of 100 two-digit prefixes for each registercontroller into any one of 33 routing numbers. The dialled digits may be registered in any code; for example, in Fig. 1 four relays R are equipped for each digit in the prefix and the digital values are registered in the 1-2-4-6 code. With two-digit prefixes each register comprises two sets of four relays of which a single one R has been shown. Each set locks up in series with front contacts r2 and the winding of a relay L (one per set), the operation of which grounds the four front contacts r1 For each of the eight R relays one wire is taken from each register-controller individually to a resistance of 100,000 ohms and the one hundred sets of eight wires are connected in eight groups i.e. " A " digit " 1 " wires, " A " digit " 2 " wires, and so on. Each group of 100 wires is connected to an electronic scanning circuit such as is described in Specification 716,782. These circuits, one of which is shown in Fig. 1, are controlled by pulse sources Pa 1-5, Pb 1-5 and Pc 1-4; the wave forms of which are shown in Fig. 3. The paths from the 100 wires to the grid of tube DT1 are thus enabled in turn cyclically. The time position allocated to each register-controller may conveniently be that corresponding to its number. The grid of each triode DT1 is normally relatively negative but when ground is applied over contact L1 a pulse is transmitted in the time unit of the relevant register-controller to the grid of DT1 thus making it relatively positive. The eight output leads from the triodes DT1 (A1 +, A2 +, A4 +, and A6 + for the A digit and B1 +, B2 +, B4 +, and B6 + for the B digit) are normally negative but each goes positive when the corresponding triode receives an impulse. The grids and output leads of triodes DT2 have potentials of the opposite polarity. Assuming the prefix " 25 " to be received on registercontroller No. 1, then during time unit No. 1 wires A2 +, B1 + and B4 + will go positive and wires A2 -, B1 - and B4 - will go negative, the potentials on the other wires remaining unchanged. Fig. 2 shows how the two groups of eight wires are interconnected with leads A0 ... 9 and B0 ... 9 to convert the digits into decimal code as explained below. In the translator a 30,000-ohm resistance with one end grounded is provided for each two-digit prefix. The other end of each resistance is connected via a series rectifier to one of the terminals C00 . . . 99, and to two branch rectifiers which are strapped in groups of ten for the prefixes having equal first digits and equal second digits respectively. The twenty common points thus obtained are connected to leads A0 ... 9 and B0 ... 9 respectively. As long as no signals are received from the register-controllers the negative potential from the cathodes of triodes DT1 is connected to all leads AO ... 9 and BO ... 9 and the terminals COO ... 99 remain negative. When the prefix " 25 " is sent by register-controller No. 1 leads A2 and B5 go positive since they are connected to a positive potential through all four rectifiers (Fig. 2) connecting them to the cathode leads of tubes DT. The lead to terminal C25 thus goes positive (ground potential) in time unit No. 1 indicative of prefix " 25 " from register-controller No. 1. Each terminal C is jumpered to one of the terminals D1 ... 33 indicative of the 33 directions into which the prefixes are to be translated. These terminals are connected by another scanning circuit controlled by pulse sources Pd1 ... 11 and Pe 1 ... 3 (Fig. 3) such that the 33 paths from the terminals D to the grid of tube AT are enabled cyclically. When a terminal C becomes positive in the time position characteristic of the register-controller concerned the associated terminal D also becomes positive and will apply positive potential to the grid of AT when the register-controller time unit in the first cycle of 100 time units coincides with the terminal D time unit in the second cycle of 33 time units, i.e. in a time unit in a cycle of 3300 time units characteristic of the register-controller and of the routing number. Valve AT repeats the impulse to a wire multipled to the 100 register-controllers and terminating in each on a 100,000 ohm resistance connected to a set of three rectifier gates controlled by the three pulse sources Pa, Pb, Pc allocated to that register-controller in the first time cycle. A pulse from AT is thus received only by that register-controller which sent the corresponding prefix, whereupon the grid of its tube BT goes positive. The pulse is repeated to two sets of cold cathode tubes Td 1 ... 11 and Te 1 ... 3 controlled by sources Rd 1 ... 11 and Re 1 ... 3 (Fig. 5) in the manner disclosed in Specification 701,686, [Group XXXVIII], so that one tube in each set is ionized to register the time position of the pulse and hence the routing number concerned. The operation of tubes Td, Te also disconnects the ground over l1. The translator is capable of translating for register-controllers requiring translations at the same time, each receiving only the routing number corresponding to the prefix sent after a maximum time of one 3300 unit cycle, e.g. 660 m.s. Modifications. Prefixes of three or more digits may be translated by providing 4 extra scanning circuits for each additional digit, extra wires C0 . . . 9 &c., and corresponding branch rectifiers. For single digit prefixes, e.g. " 0 ", the connections to wires B0 ... 9 are omitted. In all cases the corresponding terminal C00-99 becomes positive when, and only when, all the prefix digits have been received. In the modification of Fig. 7 (not shown) ten scanning circuits per digit are provided and the contacts of relays R are arranged to ground the one corresponding to the value of the digit. Ten single triodes repeat the resulting impulses to leads AO ... 9 and B0 ... 9 directly. This arrangement has the advantage that signalling is positive for all digital values and does not depend upon the absence of a pulse to show the non-operated condition of a relay R as does that of Fig. 1. Alternative arrangements also possessing this advantage are described employing eight and seven scanning circuits per digit respectively (Figs. 8 and 9, not shown).