Patent GB-816131-A (GB)
Title: Improvements relating to automatic telephone systems
Inventor: FLOOD JOHN EDWARD
IPC: H04Q11/04
Filed: 1954-06-18
Abstract: 816,131. Automatic exchange systems. SIEMENS EDISON SWAN Ltd. Sept. 16, 1955 [June 18, 1954], No. 35278/53. Class 40 (4). In a 5000-line exchange, line finders LF and final selectors FS consisting of high speed latch magnet selectors are linked by electronic switches IS, OS and pulse highways. Pulse groups XYZ, MNO, PQR of a cycle are allotted to the highways so that adjacent pulses of the cycle are allotted to different links. The latch magnet selector control circuits include master selectors and are similar to those described in Specification 759,599. The electronic switches and the highways are substantially the same as those described in Specification 814,882. Each selector has 200 outlets, 100 outlets on each of two banks. Each line SL is multipled to 30 line finders LF and 250 line finders LF are connected through incoming relay sets IRS to each electronic switch IS. The lines are similarly connected through final selectors FS and outgoing relay sets ORS to the switches OS. A line finder is allotted in response to a calling line. When the line is found, the incoming switch IS receives a forward hold signal from relay set IRS. A register switch RS is connected to the incoming switch IS in a free pulse channel, a register R is selected and a pulse of the channel is stored in a delay line in the register. The register returns dialling tone to the calling line. The digits are dialled into the register by pulsing the forward hold. The exchange marker MK is seized and the called line is marked. A back marking is extended over all free paths to the incoming switch IS. Each outgoing switch OS selects only one of the trunks over which the back marking is received and transmits pulses in all free channels on all the link pulse highways available thereto. The incoming switch IS, to which the calling line is connected, selects one of the pulse channels over which it receives the back-marking and stores a pulse of that channel in a delay line and signals the marker over lead EMI. Pulses in the same channel are transmitted from IS to OS as a forward hold. A pulse in this forward hold channel is stored in delay lines identifying the selected trunk in the switch OS and the marker is signalled over lead EM2. The pulses of the free channels are replaced by pulses in the selected channel, serving as a backward hold. The forward hold is extended to the outgoing relay set ORS which transmits a brief setting signal to the final selector. The final selector proceeds to connect the called line and the signal marker is signalled over lead 17. The marker releases on receipt of signals over leads EM1, EM2 and 17. The register, at this stage, is connected to the incoming and outgoing trunks using different pulses but communication between the switches IS, OS is inhibited. Ringing and metering are controlled from the outgoing relay set ORS. In response to ringing tone, the register releases, drops the pulses used in its original connection to the calling trunk and establishes a path between the switches IS, OS. Line circuit and line finder LF, Figs. 4, 4a.- When line SL is looped, the potential drop across resistor RA1 enables point A to be clamped to - 20 v. In a common starting circuit the upper winding of polarized relay PP is energized. If there are more calling lines than busy starting circuits (busy circuits being marked by contacts rl1) relay PP completes a circuit for relay PB which feeds pulses from a discharge tube relaxation oscillator PG to a discharge tube distributer D. A trigger T operates in the first free start circuit and relay RL follows in the allotter, PP falls back and latch magnet LMA operates to drive the switch until test relay TA operates when wiper A6 finds a negative marking on lead c of an idle line finder, relay B in the relay set IRS, Fig. 5, being normally up. Relay HA pulls up in series with the latch magnet which relapses and stops the switch. Latch magnet LMB operates over contact ha4 to drive the finder switch which stops when either of relays TB, TC pulls up in response to a potential detector PD1 or PD2 with wiper M engaging the marked contact of the calling line. If TB pulls up, relay WS connects the speech wires and the P-wire to the wiper set shown. Relay HB follows TB (or TC) in series with magnet LMB, the switch stops and relay H extends the line to the incoming relay set IRS. The trigger T is reset when ground is returned on the P-wire from relay set IRS later. If there are more busy starting circuits than calling lines, as there will be if the caller clears before his line is seized, relay PA pulls up. The last contacts of the finder banks engaged by wipers M and P are marked as calling (-20 v.), the finder runs to that position and the trigger T is reset as before. The meter SM is operated over the P-wire. A class of service tone may be transmitted to the P-wire from CS. If a caller fails to clear when the called party clears or if he fails to dial, ground is disconnected from the P-wire in the relay set IRS and a - 50 v. pulse over resistor RA8 strikes tube N1. The potential at point A is raised sufficiently to inhibit back-marking through gate F14, Fig. 10a, without giving a starting signal. Relay set IRS, Fig. 5.-The set includes a hybrid linking the speech wires to a 4-wire circuit. The potential drop across RA11 provides a forward hold on lead FH. Backward hold from the register on lead BH cuts-off valve V1, normally operated relay B falls back and the c and p wires are grounded to release the common starting circuit. Class of service tone on the P-wire is transmitted to the " go " speech wires via rectifier MRA7 until the P-wire is grounded at b2. Impulses are transmitted over lead FH as pulses of ground potential on a negative base. Meter tone (4.2 Kc/s) on the " return " speech wires is extracted by a tuned circuit T2, CA2. Series resonant circuit LA1, CA3 and an attenuator pad RP prevent false operation of the meter by speech frequencies. Tube CT1 strikes and transmits meter tone during positive half-cycles of a 50 c/s supply superimposed on the H.T. The rectified current transmitted to the P-wire is smoothed by condenser CA4 and rectifier MRA8. The electronic switches IS, OS and the link pulse highways are substantially the same as those described in Specification 814,882. Final selector, Figs. 10, 10a.-The components of the control circuits are substantially the same as corresponding parts of similar circuits described in Specifications 759,599 and 811,107. Two master selectors are shown comprising respectively storage circuits FS1, FD1 and FS2, FD2, the circuitry of FS1, FD1 being imcomplete. When a called line is marked on lead BM, multiplex MX1 generates the pulses corresponding to the line. Pulse lengthener FPL1 applies a back marking over lead 4 to leads BM in all free trunks, the markings being inhibited by gates FI2 in busy trunks. All such markings will be inhibited at gate FI1 if there is no free master-selector. In response to the brief setting signal on lead s derived from the forward hold to the outgoing relay selector ORS, Fig. 9, a master selector is seized by allotter FA and the final selector to be used is recorded in store FS2. Over lead 9 store FS2 operates latch magnet FLA, and over lead 6 it marks the appropriate trunk on arc FA6 of the allotter. Store FD2, signalled by FS2 over lead 7, records a pulse from MX1 identifying the outlet to which the selector is to be set and over lead 13 marks the line on the arc of wiper M. It also causes differentiating element B to transmit a fleeting signal to the marker over lead 17. Relay FTA pulls up when wiper FA6 finds the marked contact, relay FHA follows and the switch stops. Switching relay FWS pulls up, if necessary, latch magnet FLB is energized and the selector is driven in search of the called line. Each master selector uses a characteristic marking potential to which only its own detector PD responds. When the line is found, relay FTB pulls up, FHB follows in series with the latch magnet FLB, the switch stops and relay FH pulls up to complete the connection over the speech wires. Multiplex MX2 transmits busy markings from line circuits, Fig. 4, to inhibit back markings applied to busy lines. Outgoing relay set ORS, Fig. 9.-Valve V2 is cut off by a forward hold signal on lead FH. A positive pulse is transmitted over lead s and normally operated relay BF falls back after a delay. The P-wire is grounded in the forward direction. A negative backward hold condition is applied to lead BH. Ringing current from generator RGG is connected through transformer FT2 to the called line. The bell circuit across the line unbalances transformer FT2 and the ringing current gives rise to an interrupted potential across resistor R802 which enables gate MR801 to transmit pulses of ringing tone from a continuous generator FRT through valve V3 to the calling line. Slow relay HF does not respond to the intermittent unbalance but pulls up on reply and trips the ringing. Relays JF, FF combine to transmit a pulse of metering tone from generator MT and valve V3 to the calling line-circuit. Acceptor circuit L2, C30 provides a low impedance shunt across the line at the meter tone frequency and filter T7, C31 prevents speech imitation of meter tone. If the calling party clears first, the forward hold signal is removed, relay BH pulls up, relays HF, FF fall back and the circuit returns to normal. If the calling party clears first, relay HF falls back and slow relay RF pulls up to connect the backward hold lead BH to ground. In the relay set IRS, Fig. 5, this disconnects the P-wire from ground as described.