Patent GB-694726-A (GB)
Title: Improvements relating to telephone systems
IPC: H04Q3/00
Filed: 1950-05-26
Abstract: 694,726. Automatic exchange systems. SIEMENS BROS. & CO., Ltd., and YATES, K. R. May 25, 1951 [May 26, 1950], No. 13303/50. Class 40 (iv). When a caller connected to an automatic exchange sets up a call over a two-way line to a manual exchange the voice frequency signals for effecting supervision and release of the connection after an operator has become connected to the line are transmitted in the same directions over the line and are identical to the signals appertaining to a call from the manual to the automatic exchange. The line may be seized by transit selectors at the manual exchange in which case the outgoing relay set responds only to clearing signals. Outgoing call from manual exchange, Figs. 3, 4, 5. When the operator plugs into the calling jack CJ, relay H brings up SP, GS and CB which busies the line to the incoming transit selector multiple. GS connects up TN and a sluggish relay GT, a brief X-pulse being sent forward before GT releases TN and operates MA. The dialling plug is inserted in a jack DJ whereupon relay 5 operates TN, HB, followed by Z. The digits are repeated as X-pulses by MA. The removal of the dialling plug releases S followed by TN, SP, the latter connecting the cord circuit to the line. The answer signal, a Y-pulse, brings about the operation of G, ZR and breaks the circuit of Z. Relays Z, ZR release slowly in turn to energize MT which releases GS and operates MM. At the end of the answer signal, Z operates and G falls back. During the release period of MT, relays SP, TN send an acknowledgement Y- pulse terminated by the operation of GS. The relapse of MT removes the shunt on MN which controls the supervisory lamp. When the called party hangs up a Y-pulse is sent back which is received and acknowledged at the manual end in a similar manner to the answer signal excepting that operation of MT energizes an opposed winding of MM which falls back and the subsequent release of MT is followed by that of the supervisory relay MN. The operator removes the calling plug whereupon relays H, GS fall back to cause SP, TN to send a release signal. This is a twosecond Y-pulse timed by a switch M which is stepped to its fourth position by earth pulses over lead EP and then self-steps to its ninth position whereon SP, TN are disconnected. Before the earth pulses step the switch to its eleventh position a backward release signal consisting of a Y-pulse should be received in which case G, ZR, operate to release Z and GT follows to return the circuit to normal. Otherwise the switch M steps on so that the release signal is repeated and if this produces no result the switch releases GT. Outgoing call from transit selectors associated with the manual exchange. A circuit is made over the incoming p-wire from the selector multiple to operate relay TR. Relay TT changes the line connections from the manual board to the selector multiple and GS connects up SP, TN which send the calling X-pulse. Relay GT releases SP, TN and operates MA, CB which lights the engaged lamps ESL at the manual board. Since GT is up and HB back, further signals have no effect on the circuit. When the long clear forward signal passes through earth is removed from the p-wire so releasing TR. Relays TT, GS follow and HB, SP pull up and since the switch M moved to its ninth position as a result of the operation of GT the circuit is prepared to receive the clear back signal. Incoming call to automatic exchange, Figs. 1, 2. Relay AB pulls up in response to the seizing X-pulse to shunt the high resistance winding of L and so to prepare a repeater. The pulse is followed by the operation of relays AA, AX, BR, BS, AZ, AGT. Relay AA repeats the digits to the repeater over a lowimpedance loop closed by the dialling relay C which also releases AX to prevent surges resulting from the D.C. impulses reaching the line. The current reversal when the called party answers operates the polarized relay L which is followed by AD, ASP, whereupon ATN responds to earth pulses from lead AEP to revert the Y-pulse or pulses of the answer signal. The acknowledging Y-pulse operates AG, AZR. AZ, AZR release in turn and a circuit is completed for AM to disconnect the pad AP. At the end of the pulse AN, AZ pull up and AG, ASP relapse. When the called party hangs up, L, AD release in turn and ASP operates so that Y-pulses are sent back by ATN under the control of the earth pulses from lead AEP. The acknowledging Y-pulse acts as before excepting that the pad switching relay AM is released by energization of an opposed winding so that AN follows at the end of the pulse. The forward releasing Y-pulse holds AG operated and AZ, AZR released for a period sufficient to release AB which removes the shunt on the high resistance winding of L to signal the release to the repeater. AB also initiates release of AA, AX, BR, BS, AZ. Relay C pulls up releasing AG which disconnects AGT and for the release period of AGT, ATN, ASP revert a releasing Y-pulse. The incoming circuit is thereafter returned to normal. Outgoing call from automatic exchange, Figs. 1, 2. When the line is seized by an incoming selector current reversal at the repeater operates L, followed by AGS which brings up AH, AS. Relays ATN, ASP send a calling X-pulse during the energizing period of AGT which connects up C to end the pulse. When the operator plugs in a backward calling X- pulse is sent which operates AB. At the end of the pulse AA releases C, relays AX, BR, BS, AD, AZ, ASP operate, AGS, AGT, AH release, and the outgoing circuit is in the same condition as when the called subscriber answered an incoming call. Subsequent operations and signals are as described above for an incoming call. If the caller flashes by means of his switchhook successive answering and clearing signals are sent forward thus flashing the supervisory lamp. Incoming call to manual exchange. Figs. 3, 4, 5. The calling X-pulse operates B, followed by HB, SP, CB and the calling and line engaged lamps CSL, ESL are lit. At the end of the pulse, relay Z releases SP. The operator plugs into the answer jack AJ, whereupon D brings up GS, followed by SP, TN which revert the backward X-pulse. After a short delay GT, energized by GS, releases SP, TN to terminate the pulse and B to extinguish the calling lamps at the other operators' positions. The subsequent operations are similar to those described for an outgoing call. If the caller clears before the operator answers a Y-pulse is sent forward and all circuits are released. Busying the line. By applying Y-frequency to one end of the line CB (manual) or AG (automatic) at the other end busies the line. Signalling class of calling subscriber. When the operator at the manual exchange plugs into a call originating at a call-box associated with the automatic exchange she receives a tone pulse. She verifies this signal by removing her plug from the answer jack AJ whereupon R, S pull up and MA releases. When she replaces the plug, R releases disconnecting S and temporarily operating SP, TN to send back an X- pulse terminated by the release of S. At the automatic end, the X-pulse operates XR which results in the temporary operation of AS to remove and afterwards to replace the shunt on the high resistance winding of L, so signalling the repeater to repeat the tone pulse.