Patent GB-405741-A (GB)
Title: Improvements relating to telephone systems
IPC: H04M5/10
Filed: 1932-09-14
Abstract: 405,741. Exchange systems. SIEMENS BROS. & CO., Ltd., Caxton House, Tothill Street, and DURKIN, E. W., 13, Eltham Park Gardens, Eltham, both in London. Sept. 14, 1932, No. 25515. [Class 40 (iv).] In a system in which a supervisory lamp is included in a sleeve circuit, means are provided for effecting a control in an associated line circuit by changing the current in the sleeve circuit without changing the current through the lamp. The invention is described with reference to the cord-circuits at a tandem office. Answering incoming call.-Ringing current on the junction, Fig. 2, energizes L which is shunted by a rectifier. LL pulls up, locks itself and lights the line lamp. On the insertion of the answering plug, the supervisory lamp AS lights momentarily in series with S but SS pulls up immediately and cuts a winding of the high resistance differential relay DR into the sleeve circuit and the lamp goes out. This winding is intermittently short-circuited by LF to flash the lamp until the key SP is thrown to operate SK and associate the cord with the common circuits. SL then cuts relay TA into the sleeve circuit and removes a shunt from lamp AS. As the result of these changes the current through the lamp is not altered but the reduction in the total sleeve current unbalances DR which releases LL to stop the flashing signal. SL also short-circuits the high resistance winding of SK to make it slow to release and to prevent the operation of SK in another cord if its key SP is thrown by mistake. As a further safeguard, the low resistance winding of SK is shunted. SL also energizes MN to disconnect the monitoring transformer T2 and TA completes the talking circuit to the operator's set. Extending call over outgoing junction.-The junctions, Fig. 3, are tested in the usual way, the operator hearing the " busy " clicks through transformer T3. When the plug CALL is inserted, the calling supervisory lamp CS glows but is at once extinguished by S, in the junction circuit. TC is operated also and completes the talking circuit to the operator's set from the calling end of the cord. Dialling key DCK energizes DC which cuts a resistance YH into the calling end sleeve circuit and energizes DD which transfers the outgoing talking wires from the operator's set to the dial in series with an impedance I from which connections are made to the operator's set to enable her to hear the dialling tone. This impedance is short-circuited by DK when the dial is off-normal. On the completion of the dialling bridge, RR in the junction circuit energizes DT which locks and cuts out the transmission bridge. On the restoration of the dialling key and when the dial has reached normal DC short-circuits the resistance YH to energize LR which unlocks DT to replace the transmission bridge and bridges the junction through IL and the supervisory relay D. IL shunts the high resistance winding of S to light the lamp CS. The line is rung automatically or by operating key RC before restoring the dialling key to connect battery to the upper junction wire. Supervisory signals.-Lamp CS continues to glow whether or not the key SP is restored until the subscriber replies, whereupon D removes the short-circuit on the high resistance winding of S to extinguish it. When he clears, the short-circuit is replaced. The calling operator clears by applying ringing current to the junction whereupon L energizes LL and LF flashes the lamp AS. Additional keys.-(1) Ringing on the answering side is effected by key RA which energizes RR to apply ringing current to the junction. (2) Dialling on the answering side is effected with the aid of key DAK. (3) Trunk calls are effected with the aid of key TOK which applies battery to the tip of the calling plug and disconnects the answering side of the cord from the operator's set. (4) Splitting keys SPC, SPA are provided to enable either party to be spoken to to the exclusion of the other. (5) Monitoring is effected with the aid of key MON which connects the cord to the primary of a special monitoring transformer T2 and energizes M which connects the operator's receiver to the secondary. Supervision of operator.-The operator herself can be monitored over the circuit LC.