Patent GB-389867-A (GB)
Title: Improvements in or relating to telephone systems
IPC: H04Q3/62
Filed: 1931-09-25
Abstract: 389,867. Automatic exchange systems. AUTOMATIC ELECTRIC CO., Ltd., Strowger Works, Liverpool, BAKER, G. T Blackbrook, Caerphilly, Glamorgan, and TAYLOR, R., 30, Oulton Road, Wavertree, Liverpool. Sept. 25, 1931, No. 26837. [Class 40 (iv).] In a small P.B.X. in which a subscriber, Fig. 1, is connected over a finder TFS, Fig. 5, to a main-exchange junction 26, 27, the operation of a substation key NLP causes the junction to be held whilst the local line is connected to a transfer circuit, Fig. 6, from which by normal operation of the dial a temporary local connection to a third party may be made over a local connecting circuit, Figs. 2 and 3, provision being made for breaking-in on an existing conversation if necessary. At the end of the local connection, a further operation of key NLP causes the original connection to be restored. Alternatively, if the original party hangs up, the main-exchange call is automatically transferred to the other local line. The transfer circuit is common to all the mainexchange junctions. Outgoing main-exchange calls are made by dialling the digit 9 into a local connecting-circuit thereby causing this to be released and the finder TFS of an idle junction to hunt for the calling line. Incoming mainexchange calls may be answered by any one of a number of subscribers, no special operator being provided. In the system shown, subscriber's numbers consist of a single digit only. The subscribers have graded facilities according as they can make and/or answer mainexchange calls.. Local call. When the subscriber, Fig. 1, removes his receiver,' two-step line-and-cut-off relay LK operates partially to mark lead 10 and to energize relay 1ST on the first local connecting circuit over lead 11 or 12. Relay 1ST connects relay FH in series with the righthand winding of relay K, and relay FH operates and energizes the finder stepping magnet LFM. When the calling line is found, relay FH is shunted and switching relay K energizes in series with relay LK which operates fully. Relays A, B operate and impulses are repeated to magnet CNM, relays C, E, IR, energizing at the first impulse. The wanted line is tested between the release of relays C, E, and ringing and busy-signalling take place in the usual manner. On release, magnet CNM interacts with relay IR to restore CNS to normal. Call to main exchange. A subscriber privileged to initiate calls to the main exchange has his contact in bank 6a of finder LFS connected to lead 22 so that when the digit 9 is dialled by such a subscriber relay H operates over wipers 3b, 6a, and lead 22 in series with relay 3ST of the first idle exchange line EXL1, shown in detail in Fig. 5. (If all the exchange lines are busy, lead 22 is earthed, relay H does not operate, and a busy signal is given.) Relay 3ST connects relay IT in series with the lefthand winding of relay 1K, and the finder TFS hunts in a similar manner to LFS for the calling line which is marked in bank 3c over conductors 24, 23, and wipers 5a, 5b. When this is found relay 1K operates in series with relay S which releases the local connection, and relay 1H operates in series with relay LK. Relay 1A operating over the loop energizes relay 3B. Interim conversation with or transfer of call to a.third party.. Operation of key NLP earths both wires short-circuiting relay 1D to complete a circuit for relay P. If the transfer circuit, Fig. 6, is free, relay P operates bridging conductors 26, 27, to hold the junction and extending the local connection to relay L. When key NLP is restored, L operates to start up a local connecting circuit LCL1 and to mark the transfer circuit in the bank of wiper 3a. When this circuit is reached, relays CO, K operate, and the subscriber's line is extended to relay A of the local connecting circuit and may set up a local call as before. If the wanted third party is busy, relay G operates, and relay TR completes a break-in circuit. If it is desired to return to the main-exchange call, key NLP is again operated when the release of 1D energizes relays R, RR, and during their subsequent release, relays CO, P are released. If, however, it is desired to transfer the mainexchange call to a third party, the calling local subscriber hangs up, releasing relays 1A, 1D, 3B, 1H, A. Relay 1T is now energized over the left-hand winding of relay 1K to advance switch TFS in search of the third party whose line is marked over wipers 4c, 4b. When this is found relay S operates, releasing the local connecting circuit. Incoming main-exchange calls. Subscribers privileged to answer incoming calls have connections made to lead 11 instead of to lead 12. A call incoming over junction 26, 27 energizes relays 1F, 1C to operate calling signals over circuit 36. When a privileged subscriber removes his receiver, the 'earthing of lead 11 energizes relay 3ST causing the finder TFS to hunt for the subscriber's line which is marked in bank 5c. A third party may be called and the call, if necessary, transferred in the manner already described. Ringing, busy-tone, and dialling-tone equipment. When a subscriber's relay LK operates fully, earth is connected over lead 13 to start up the common equipment, Fig. 1. Relay BR by intermittently short-circuiting a resistance 18 generates busy-tone in lead 14. A relay VR rendered slow-to-release by a short-circuited winding intermittently opens its own circuit and also connects the earthed lead 13 alternately to the two primary windings of coil XFR, thus producing ringing current in lead 15. The current variations in the primary windings of coil XFR produce dialling-tone in lead 17 through condenser 16.