Patent GB-688413-A (GB)
Title: Improvements in or relating to telephone switching systems
IPC: H04Q3/00
Filed: 1950-09-08
Abstract: 688,413. Automatic exchange systems. WESTERN ELECTRIC CO., Inc. Sept. 8, 1950 [Sept. 10, 1949; Sept. 16, 1949; Sept. 16, 1949; Sept. 16, 1949], No. 22190/50. Class 40 (iv). In a relay system in which a plurality of routes may be taken from an inlet to an outlet, discharge tubes are associated with each cross-point and the application of a marking potential causes these tubes to fire to mark all free paths between the inlet and the outlet. As described, this method is applied to trace the free paths between a calling subscriber's line circuit and a plurality of junctors and between a further plurality of junctors and an out-trunk thereby doubly marking one or more free junctors suitable for completing the whole path, where. upon one of these junctors operates, to the exclusion of the others, to complete the talking path by operating the cross-point relays. General description, Fig. 2. The subscriber's number sending equipment is arranged to repeat the wanted number continuously under control of the exchange until the latter has set up the connection. Each digit is represented by the interval between a " start " and " stop " pulse, a digit n being represented by n+7 fundamental increments of time. A calling line circuit 212 seizes an originating actuator 214, which supplies power to the subscriber's number signalling device, and an originating receiver and register 215. The latter registers only that part of the wanted number identifying the wanted exchange and seizes, via the connector 216, the trunk number group or marking circuit 218 which marks all idle out-trunks 256, 258 connected to in-trunks such as 257 of the local exchange. Markings are extended back through trunk frames 227, 246, each comprising primary and secondary switches to some or all of the junctors J1 ... J8, the discharge tubes associ. ated with cross-points in the primary and secondary switches being fired to indicate all free paths to the junctors. Likewise markings applied via the line circuit 212 are applied to the line frame 219 to fire discharge tubes indicating free paths from the line circuit to some of the junctors. Some junctors will thus be marked from both sides and in one of these a discharge tube fires in a circuit 242 which prevents other similarly marked junctor tubes from firing. The thus-seized junctor then changes conditions on the marking leads to operate relays at the cross-points whereby the subscriber's line is switched through to the out-trunk (say 256) and releases the originating actuator 214 and the originating receiver and register 215. The out-trunk, 256 meanwhile seizes an outward actuator 244 which keeps the subscriber's sender supplied with power and the in-trunk 257 seizes an incoming receiver and register 266. The latter registers only the digits designating the wanted subscriber within the exchange (i.e. rejects the exchange code) and seizes a subscribers' number group or marker 268. The latter then marks the wanted subscriber's line in the primary switch 272. The in-trunk 257 is also marked in the primary switch 228 and free paths to some of the junctors J1 ... J8 are marked from both sides and a connection established through one of them from the in-trunk to the subscriber's line in a similar manner to that described above. Polarity of battery feed from the out-trunk 256 to the calling subscriber is then reversed to disconnect the calling subscriber's numbersending equipment and connect up his telephone set. If the call is to a neighbouring exchange an out-trunk such as 255 is seized which is connected to an in-trunk of the neighbouring exchange and the call proceeds as described above. Connections are set up on a one-at-a-time basis, gas-tubes being provided for associating calling equipment with common equipment, these tubes being arranged normally to transfer an initial discharge in one gap via one or more intermediate gaps to a main gap which effects the association. If, however, two or more tubes attempt the transfer simultaneously all but one is blocked. In the following description the drawings should be arranged as shown in Fig. 4. In general the first one or two figures of each reference indicate the figure on which it is to be found. Subscriber's equipment. This comprises eleven pulse-producing transformers 40, 50 ... 59, Fig. 41, the first for producing the start pulse and the rest for producing the stop pulses designating the respective digits. Each has two primary or upper coils which are provided with currents having 90 degree phase difference from the 45# current fed over the phantom from the exchange when the handset is lifted. The turns ratio of the two coils in the various transformers is varied so that the flux passes through zero at different instants in the cycle for the different transformers. The magnitude of the flux induced is arranged to saturate the cores except for the brief instant when the flux passes through zero, whereupon a sharp 'pulse is produced in the secondaries of the transformers. The respective secondaries of transformers 50 ... 59 are connected in series with the secondary of 40 to the leads 0 ... 9 which may be connected to leads 11 ... 18 by manual means described below. These leads are connected to right-hand contacts of relays 101 ... 108 of the counting chain 101 ... 114, which comprises relays of the type whose contacts are closed when current in one direction only (as indicated by the arrows) is applied to their operating winding, and remain closed until a reverse current is applied. All the relays also possess a common coil 38 energized by a discharge current from condenser 31 when the handset is lifted to prepare the relay chain by operating one relay and releasing any of the others which may be operated. The 45# current is fed via the leads 48, 49 to the relay chain in such a way that at each half-cycle the relay succeeding the presently operated one is operated, thereby releasing the latter. The relays 101 ... 108 successively connect the leads 11 ... 18 to the line, over whose loop impulses representing the digits of the wanted number are thus transmitted. Only 6 of these digits are used for the setting up of the connection as subsequently described. The next four relays 109 ... 112 are used to transmit pulses indicative of the calling subscriber's line should these be required for ticketing purposes. Again, however, no exchange equipment for dealing with these is described. Relays 113, 114 short-circuit the line to provide a " blank interval " by which the exchange equipment recognises that a complete digit sequence is about to commence. When the subscriber wishes to call he first sets the finger-pull dials, Figs. 45, 46, by pulling them down to the stop 139 where they are held against the return spring 46 by the pawl 36. This moves the attached brush 26 (corresponding to contacts 11 ... 18, Fig. 41) into contact with fixed bars 61 ... 70 (corresponding to bars 0 ... 9, Fig. 41). The whole may be restored to normal if desired by operating lever 133 to move arm 138 to release the pawl 36. When the handset is raised springs 24, Fig. 41 (but not 23, which are held by the latch magnet 27) are operated thereby connecting power from the line phantom to the transformers 40, 50 ... 59 and to the distributer relays 101 ... 114 and the output from the latter is connected to the line loop. When the exchange has effected the connection it reverses the polarity of battery applied to the line loop to operate the latch magnet 27 which disconnects the number-sending equipment and connects up the telephone subset. Connection of line circuit to incoming receive and register circuit and reception of digits. The subscriber sets up the complete wanted number on his set and then lifts his handset, whereupon only contact springs 24 operate and a loop is extended from the polarized latch magnet 27 to the exchange to bring up relay 812 in the subscriber's line circuit, whereby the start gap of tube 814 is fired. If this tube is not locked out by the firing of a similar tube in another line circuit desiring or having access to the originating actuator, the discharge in tube 814 transfers to its main gap to bring up relays 819, 811 and 911 in the actuator, which thereupon feeds 45# current over the phantom to the subscriber's equipment. Relay 917 monitors the outgoing 45# current so that if the subscriber hangs up at this stage the reduction in this current causes it to release, whereupon 819 falls off to restore the subscriber's line circuit to normal. Relay 811 releases relay 812. Relay 819 also brings up 510 and 512 and releases 511, 515, 516 to prepare the signalling receiver, Fig. 5. The number signals arriving over the subscriber's line are fed via transformer 513, band-pass filter 517 and limiter 518 to the digit detector 521 and the code detector 520. The latter feeds a blank interval timer 522 which recognises the blank interval which precedes the transmission of the first digit of the wanted number. When this is received the code start circuit 523 enables the digit detector 521 which responds to the "start" pulse for the first digit and is thereupon disabled by circuit 541 for a period of 7 increments to allow transients to die down. Reception of the " start " pulse also operates a square wave generator 524 which starts a timing multivibrator 525 feeding a minimum interval timer 529 which counts off seven pulses and then permits the rest to be fed to the digit steering circuit 527. This circuit has meanwhile been conditioned by the square wave generator 524 to pass received pulses to the A-digit register 531 where they are received on an electronic binary counter. On receipt of the " stop " pulse the square wave generator is restored and prevents the circuit 529 from transmitting further pulses to the A-digit register. The digit detector is again disabled for 7 increments of time as before. The square wave generator is operated by s