Patent GB-357153-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1930-06-16
Abstract: 357,153. Automatic exchange systems. AUTOMATIC TELEPHONE MANUFACTURING CO., Ltd., Strowger Works, and TAYLOR, R., 30, Oulton Road, Wavertree, both in Liverpool. June 16, 1930, No. 18433. [Class 40 (iv).] In a private branch exchange system the operator is signalled and the switches released if a subscriber endeavours to get a call to which he is not entitled or if a party in a local call delays in replacing his receiver, the connections to the operator being controlled by the removal of holding potential from the test lead. Local call. When a call is initiated L operates marking the line as calling and energizing S which completes a circuit over 10, 11, 6 for FDM to step the finder in search of the calling line. When this is reached K energizes in series with L and CO, and locks, breaking the circuit of FDM and earthing wire 21 to enable CO to pull up. L holds in series with CO and S releases. KO operates and DDM steps the distributer to the next idle link. K switches the subscriber's line through to the connector, A pulls up, B operates (before S has released) and C energizes. The tone motor is started up over b5. Dial tone is returned to the calling subscriber from 36. Relay A repeats the first impulse train, which is less than nine impulses, to VM and C in parallel and the wipers move to the required level. When the train ceases C releases, E energizes, changing over to the rotary magnet RM, and C re-operates. The second train is repeated to RM and C in parallel and when this train terminates C releases and opens the circuit E. During the slow period of E, H is connected to the test terminal of the wanted line and if this is free, H pulls up switching the circuit through. When E releases ringing is fed over F to the called line, ring back tone being returned over 37. When the called party replies F energizes, switching through, and D pulls up. Speaking current is supplied through D and A. Release ; signalling operator on delayed release. If the calling party releases first, A and B fall back and K, H and F de-energize. H completes a circuit for the release magnet Z to release the link, it being guarded by Z1 until the switch is fully restored, and removes earth from the test wire of the called party, releasing the called L and CO relays. L releases at once and during the slow period of CO, MB is energized and locks, on the release of CO, to the called loop. The called subscribers' manual board lamp, such as 15, is lit until the circuit is cleared. Ring back tone is supplied over 14. Should the called party clear first D releases and SP pulls up. SP prepares a circuit for ZP and completes one, at sp1, for driving the delay set motor. When the fixed time delay pulse is received ZP pulls up and opens the circuit of K. A de-energizes and releases the link as before and K breaks the circuit of L and CO. During the delay period of CO, MB is energized and the manual board is signalled as before. Called party busy. If the called line had been busy, H would not have operated over the test wiper and when E had de-energized, G would have pulled up to return busy tone from 40. Operator call. To call the operator the digit O is dialled which raises the switch to the tenth level. On the release of C, ZP is energized, over 67, releasing K and A. The link is released and the operator signalled as described above. Out service calls. To call the main exchange the digit 9 is dialled, the switch is raised to the ninth level, and JS operates over 17. JS opens the tone-motor circuit and when C re-operates after E has pulled up, F pulls up and a circuit is completed for G and RM to interact to step the connector in search of a free outgoing line. When this is reached G does not re-operate, RM remains energized. C releases and H switches through. Further impulse trains are repeated by al to the distant exchange, relay C energizing during impulsing to remove D, which is placed across the speech conductors by JS, from the impulsing circuit. If all trunks on the out-service level are busy the wipers are rotated past the tenth bank contacts and as G does not re-operate C de-energizes. When C falls away H does not pull up and when E releases G re-energizes to connect up busytone, the tone motor being started by cam springs S2. Barred subscriber. Barred subscribers have their contacts in bank 7 connected by a strap 5 to front contacts of CO and should one of these attempt to get an exchange call, when JS energizes a circuit is completed for ZP which releases the link and signals the operator as before described. Fault and trouble arrangements. If a finder switch fails to find a calling line, SP energizes over 14,27 and after a period ZP pulls up. KO energizes, S releases and DDM steps the distributer in search of another idle link. If dialling is delayed for longer than the period of SP, ZP; ZP is energized releasing the link and routing the call to the manual board as described above. The blowing of a fuse operates ZP over the alarm lead and k6. ZP locks over zp2 and marks the link busy by earth on conductor 25 until the trouble is removed.