Patent GB-742307-A (GB)
Title: A telephone system
IPC: H04Q3/52
Filed: 1952-02-13
Abstract: 742,307. Automatic exchange systems. AUTOMATIC ELECTRIC LABORATORIES, Inc. Feb. 13, 1952 [April 27, 1951], No. 3837/52. Class 40 (4). In an automatic exchange connections between subscribers' lines and a common transmission circuit are set up over a switch comprising a co-ordinate array of impedance networks, each network including asymmetrical conductors and being individually associated with one of the lines to form a switching element between that line and the transmission circuit; provision being made of a first co-ordinate and a second co-ordinate group of control connections for controlling the networks, and means for selectively impressing control voltages simultaneously on a set of first and second control connections, the network at their intersection being thus rendered conductive for connecting the line with the transmission circuit. Other features of the embodiment described are claimed in Specification 742,358. Seizure of allotter and setting of line finder. Initiation of a call by the subscriber at substation 12 (Fig. 3) causes current flow in resistors 148, 13 thus driving start lead S11 negative, so that the normally conducting tube 15 (Fig. 1) is cut off. Anode relay 20 restores, and relay 30 operates over the allotter units and tens switch off-normal contacts A.U.O.N. and A.T.O.N. Wiper 52 of the distributer switch 50 (Fig. 1) is normally connected to the grid of tube 57 and to negative battery through the lower winding of relay 60 of the idle finderconnector link 17 (Fig. 2) to which it gives access ; but, on the operation of relay 30, wiper 52 is grounded and the control grid of tube 57 is transferred to the wiper 59 of the allotter tens switch 58 (Fig. 1). If this wiper is not connected to the calling line, tube 57 conducts, and anode relay 40 operates thus grounding wiper 53 of the distributer. Relay 60 (Fig. 2) pulls up and locks over its upper winding and the finder units and tens switch off-normal contacts F.U.O.N. and F.T.O.N. The ground on wiper 53 is thus extended over break contacts 105, 104 of the finder switch drive magnets to wiper 54 and thence to the allotter tens switch magnet 106 (Fig. 1). Magnet 106 operates energizing the finder tens switch magnet 103 over wiper 56 so that 106 and 103 step the two tens switches successively as long as wiper 53 is grounded. When wiper 59 encounters the tens lead T1 to T0 of the calling line, tube 57 is cut off and relay 40 restores thus removing the ground from 53 and bringing up relay 110 (Fig. 1) over operated A.T.O.N. (magnet 106 stays down in series with 110). Common start lead SC is grounded, resistance battery is connected to wiper 59, and the grid of tube 57 is transferred to wiper 121 of the allotter units switch. Tube 57 conducts, and relay 40 reoperates connecting ground to wiper 53 and thence to the allotter units switch magnet 122. Operation of 122 energizes the finder units switch magnet 102 (Fig. 2) over wiper 55, and the two units switches step successively until wiper 121 encounters the units lead U1 to U0 of the calling line. Tube 57 is then cut off and 40 again. restores. Slow-to-release relay 70 thereupon pulls up (122 remains down), transfers the grid of 57 to wiper 52, and grounds wiper 51. The allotter is released as described below and tube 15 again conducts bringing up relay 20. Relay 30 restores followed by 110 and 70 and the allotter tens and units switches go home. As ground from the finder over wiper 52 causes tube 57 to conduct and relay 40 reoperates before 70 restores, the distributer magnet 125 (Fig. 1) drives to an idle line finder, battery from the lower winding of relay 60 of which cuts off tube 57. Relay 40 restores and 30 re-operates, whereupon the allotter may deal with another call. Dealing with simultaneous calls. The allotter tens switch, drives to the first tens lead corresponding to a calling line and the ground placed on SC by the operation of 110 shunts all the tens leads to ground except that to which battery is connected over wiper 59. All the individual start leads S11 to S00 are thus shunted except those in the marked tens group, and hence units leads may be marked by lines in that tens group only. Thus selection of tens lead 2 and units lead 3 when lines 25 and 33 are calling is prevented. Establishing connection over rectifier matrix. As soon as relay 60 (Fig. 2) operates, pulse generator leads P1A, P1B are connected to transformers 133, 134 respectively. Each source delivers a rectangular negative pulse for 1/(2N-1) of a cycle, where N is the number of finders in a group, such that the PA pulses occur successively in all finders in the first half of the cycle and are followed by the successive PB pulses in the second half of the cycle. Rectifiers 135<1>-138<1> are normally non-conductive but when P1A delivers a pulse they conduct and the grid of tube 139 and one terminal of condenser 139<1> are effectively connected to rectifiers 140 and 141. The rectifiers of matrix 142 (Fig. 3) are connected to positive and negative potential sources so that they are all normally non-conductive. When the finder has been set to calling line 11, wipers 153, 154 of finder tens switch 149 are connected to bus wires 10A, 10B respectively and wipers 151, 152 of finder units switch 150 to bus wires 1A, IB respectively. Thus when P1A pulses, rectifiers 145, 145<1> conduct and line 11 is extended to the grid of tube 139 and to condenser 1391. Condenser 209 (Fig. 2) is brought to the potential then appearing across condensers 156 and 157 of the line circuit and retains this charge during the non-pulsing intervals. The voltage drop in resistor 148 due to line current is thus transferred to tube 139 bringing up relay 160 when wiper 51 (Fig. 1) is grounded by the allotter. Slow-to-release relay 90 follows, and grounds wiper 52 to step the allotter on to another link. The previous operation of relay 60 (Fig. 2) brought up 170 so that the impulsing circuit to the connector tens magnet 178 is completed. Condenser 139<1> is connected to hold tone lead 175 fed with 7000 c.p.s. A.C. which thus appears across condenser 157 (Fig. 3) and hence in the primary winding of line transformer 147. There it is rectified by 176 and cancels out the voltage across resistor 13, thus removing the start potential from lead S11. Tube 15 (Fig. 1) therepuon conducts to initiate release of the allotter. Setting of connector. Each break impulse from the caller's dial drives the grid of tube 139 negative, thus releasing relay 160 which repeats the impulses to the connector tens magnet 178. At the end of the digit, 170 falls back whereupon 180 comes up over C.U.O.N. and C.T.O.N., and reoperates 170 so that the second digit is repeated to the connector units magnet 203. Relay 170 then restores. The connector thus extends a circuit from the grid of tube 207 to the called line similar to that from 139 to the calling line. Called line busy. The grid of 207 will go positive due to voltage drop across the resistor (148) of the line circuit and relay 210 operates, thus preventing release of 180 which would otherwise follow that of 170, connecting busy tone to the calling line, and disconnecting the hold tone. Called line idle. Relay 180 restores, bringing up 220 which transfers condenser 139<1> from the hold tone lead to the ring back tone lead, and connects ringing tone to the called line via condenser 235. Ringing tone triggers apparatus such as a cold cathode tube at the called station to connect up a local ringing source thereat, and charges a condenser such as 177 in the called line circuit to prevent marking of the start lead when the called party answers. On the reply of the called party, tube 207 conducts and relay 210 is operated, thus bringing up 230 which releases 220 and switches through by connecting the anode of tube 207 via condenser 236 to the junction of rectifiers 135<1>, 1361, and the anode of tube 139 via condenser 242 to the junction of 238, 239. Speech paths are provided alternately in the two directions when the two pulse generators of the finder are pulsing. Release. Last party release is provided. When the calling party hangs up relay 160 releases and when the called party does so relay 210 releases. With both these relays down, relay 90 restores, whereupon relays 60 and 230 release and the connector and finder switches go home in succession.