Patent GB-598188-A (GB)
Title: Improvements in or relating to telecommunication systems
IPC: H04Q1/38
Filed: 1945-03-30
Abstract: 598,188. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. March 30, 1945, No. 8129. Convention date, May 1, 1944. [Class 40 (iv)] The exchange selectors are controlled by the multipotential marking method under control of the calling party's apparatus, keys of which insert resistors into the line loop to produce at a valve in a register-controller predetermined potentials characteristic of the keyed digits, which are detected by the register - controller and recorded on relay registers. A register-controller is used in the setting up of every connection and storage of digits in the relay registers, normally three in number, allows very rapid keying of the first three digits making the system particularly suitable for highspeed 3-digit PABX operation. If the line numbers comprise more than 3 digits, some or all of the relay registers are used again, except in the case of register-controllers reserved for the use of operators which are provided with a register for each digit so that numbers may be disposed of as fast as they can be keyed. The register-controller normally compares the test potentials on the banks of the selectors with a marking potential selected by the register, but it May be used to control outgoing calls to Strowgertype exchanges, arrangements being made for numerical impulses to be transmitted over the junction depending upon the marking potential selected. Keying of digits at a faster rate than the selections can be made is prevented by locking a depressed key until a register is free to accept the next digit. Subscriber's equipment (Figs. 3, 6, 9). Besides the normal telephone set, a subscriber has a ten-button key set. On depression of any key, contact 25 open-circuits the receiver and contact 24 short-circuits the transmitter, while the upper of two locking plates 16 (Fig. 6), prevents the depression of a second key until the first key is fully restored. The lower locking plate 18 (Figs. 6, 9) opens contact 38, removing a short-circuit from the keys, and releases a latch spring 35 (Fig. 6), causing momentary opening of the line circuit by contact 37, and, when the key is fully depressed, operation of the release magnet RM (Fig. 6). Keys 1 and 6 connect resistor R1 in the line circuit (Fig. 3) ; 2 and 7, R2 ; 3 and 8, R3 ; and 4 and 9, R4, while keys 5 and 0 do not connect up resistors. Resistor RC is adjustable to produce a standard line loop resistance. When any one of the keys 6 to 0 is depressed, a second upper locking plate 17 (Fig. 6) reverses at contacts 26 the connections of a rectifier S, which normally prevents current flow through RM. The locking of keys in the operative position is prevented unless the hand-set is first removed. Signalling circuit (Fig. 2). A source of potential, e.g. a normal exchange battery at the central office, has a potentiometer connected across it and four potentials P1-P4 obtained therefrom are applied in rotation to the grid of V1 by the counting relays CR1-3 (Fig. 11). Corresponding potentials applied to the grid of V2 are obtained from the same battery by the insertion into the line loop by the keys of resistors R1-4, the connection of the rectifier S being such that RM is not energized. The resistors R1-4 are chosen to produce a series of potentials on the grid of V2 which differ by approximately 3 volts from each other. Operation of register-controller (Figs. 1, 11, 11a). Closure of the line loop by the removal of the calling party's hand-set operates the line relay, an R-link seizes a line-finder/group selector link and then a register-controller ; the line-finder then seizes the calling line and RAR (Fig. 11) falls away while RBR pulls up, as in Specification 628,174. The release of RAR connects a valve circuit including the counting relays CR1-4 to the calling line, while RBR energizes AR, BR and FR. Dialling tone is transmitted and relay AR1 operates over the loop and holds AR. On depression of a key, the momentary opening of the line circuit by contact 37 (Fig. 3) releases AR1 and AR, connecting NR to the a wire and grounding the b wire. For keys 1-5 the connection of the rectifier S prevents current flow through RM and the current through NR is insufficient to operate it ; but for keys 6-0, the reversal of the connections of S causes momentary operation of NR, to introduce its high resistance winding and stop its further operation, and to bring up CR which reverses the line connections to prevent operation of RM and prepares additional circuits under the control of relays CR1-4 for the storage relays XR1-4. This effectively halves the number of potentials necessary for the operation of the valve circuit. The release of AR disconnects FR which after its slow period energizes DR, disconnects NR from the a wire, connecting the grid of V2 in parallel with resistor RN in its place. DR brings up DTR to cut off dialling tone. If the keyed digit is 1, R1 produces a potential P1 on the grid of V2 and since the grid of V1 is normally connected to the same potential over the back contact of CR1, gas valve GV fires, energizing GVR which disconnects CR1 before it can operate. If the digit keyed were 2, CR1 would operate and connect potential P2 to VI, whereupon GV would fire, and so on for digits 3 and 4. Operation of GVR brings up TR1 (Fig. 11a), CR6 and GSR, TR1 energizing XR1 to place a marking potential PN1 on terminal 1 of bank C of the switch PO, while GSR energizes RM in the calling party's key-set to release the depressed key and extinguishes GV; GVR releases followed by GSR which restores the line circuit ready for reception of the next digit, and prepares for its storage by operation of CR5 in series with CR6 to connect up TR2 in place of TR1. XR1 stays up in series with XHR1 which grounds terminal 1 of bank B of PO, operating the AR relay of the selector under control which starts hunting. When the t wiper which is connected over the b wire to the grid of V3 (Fig. 11a) encounters the potential PN1 which is already applied to V4 (Fig. 11a) by the c wiper of PO, GV1 (not shown) fires and brings up GSR1 to energize PO and place battery on terminal 1 of bank X to release XR1 and XHR1 and thus free the first group of XR relays. If digit 5 is now keyed, since no potential is applied to the grid of V2 (Fig. 11), GV will not fire and CR1, CR2, CR3 and CR4 all operate in turn followed by TR2 and XR1, XR3 to mark the C bank terminals with PN5. Control of the selector takes place as before, GSR in this case being connected up by CR4. When keys 6-0 are depressed, operation of CR brings up extra XR relays, when the TR relay operates, in order to mark the C bank with the potentials PN6-10 instead of PN1-5. If digits are keyed at a quicker rate than the selections are carried out so that all three XR groups are in use, the simultaneous operation of XHR1, XHR2 and XHR3 brings up ER which opens the line circuit, releases DR and energizes GSR, thus preventing release of the depressed key until one of the XHR relays releases, whereupon ER falls away followed by GSR, causing AR1 to pull up and release the key. Out-going calls. The PN potentials selected by the registers are placed on a bank of a switch such as PT in Specification 628,174, which delivers impulses to the junction. The method of release is the same as that in Specification 628,174, but if the calling party hangs up before the selection is completed, AR1 falls away and initiates the release of the connection. In a modification (Figs. 2a, 2b, not shown), V<2> is eliminated and the potentials set up by the calling party are applied to the cathode of V1 while the comparison potentials are applied by CR1-4 to its grid, GV firing when grid and cathode potentials are equal. Specifications 598,224 and 598,225 also are referred to.