Patent GB-383713-A (GB)
Title: Improvements in or relating to circuit arrangements for combined telegraph and telephone installations
IPC: H04M11/06
Filed: 1931-10-09
Abstract: 383,713. Automatic exchange systems. LORENZ AKT.-GES., C., 1, Lorenzweg, Tempelhof, Berlin. Oct. 9, 1931, No. 28136. Convention date, Nov. 15, 1930. [Class 40 (iv).] In a system serving both for telegraphy and for telephony, D.C. impulses are sent and received by subscribers but are converted into A.C. impulses during their passage through the exchange. A group of impulse converters for converting D.C. into A.C. impulses and vice versa is provided at the exchange and a free one of these converters is selected by means of a hunting switch by any subscriber requiring a telegraphic as distinct from a telephonic connection. Preparation of amplifier. The amplifiers are made available by closure of switch ET, which energizes an indicator magnet A1 and a relay G ; the latter switches on the filament circuit of the amplifier AR at g2. The anode current energizes relay E. Contact e3 brings into circuit relay S (which prepares the input circuit at s3) and winding K1/2 (which breaks the relay chain at k4). When the amplifier is engaged or out of order, contact k4 closes again and the next amplifier of the chain is inserted in known manner. Making a telephonic connection. A subscriber is called by his alarm W, energized over wire a and earth. When the subscriber lifts his switch hook Hu he closes a loop circuit from earth at h1, through line b, his own telephone set TS, line a and relay RV to battery negative. Relay RV starts the preselector VW which sets itself to a free group- or line-selector, whereupon relay TV responds and marks the line busy, and contacts tv1, tv2 provide access to the group- or line-selector. The above loop circuit passes through winding H 2/1, and relay H, being energized, removes short-circuit h1 from its winding H 3/2. During dialling, however, the line-interruptions cause the short-circuit to be temporarily restored, to prevent impulse-distortion. Change from telephony to telegraphy. When connection has been established, each subscriber closes his telegraph-starting key AnT, so that his relay An cuts in motor Mo at an1 and substitutes the telegraph for the telephone by reversal of contact an2. Relay An is held operated by a locking spring adapted to be released on receipt of a code signal which comprises five spaces and so can be produced by opening a simple key. At the exchange, on the increase of current in X 4/5 the differential relay X operates and acts through relays Y, R to cut in at r1 the rotary magnet DJS, which steps the converter-finding selector JS to seek for a free impulse-converter. When this has been found, its testing-relay P cuts off the rotary magnet at p3 and marks itself busy by short-circuiting at p5 its high-resistance winding P 1/2. Its circuit extends through offnormal contact k2 and relay C 4/5, whose contact c3 inserts the high-resistance winding C 1/2 into the testing circuit. Double selection is prevented since if two relays P test in parallel, relays C pull up first and prevent relays P from acting. Relay P acts through relay U 1/5 to connect wire b to the d.c. side of the converter at u3 and to connect the exchange pair through u1, u5 to the a.c. side of the converter. Relay C acts through contact c6 and relay Ma to start the common alternator Su. Contact c5 causes the successive operation of the relays shown at the right of the drawing, leaving relays V, Z, K energized, while relays F, A hold on through their windings F 4/5 and A 1/2. Transmission of telegraphic impulses. The subscriber sends d.c. impulses by means of the transmitter contact Sk. Relay S responds and at s3 connects the a.c. source Su through z5 to the transformer Tr which feeds the exchange pair. via u1, u5. It thus converts the d.c. impulses into a.c. impulses which pass through the exchange like voice currents. Outgoing a.c. impulses receivable by the subscriber shown pass from the exchange via u1, u5, the transformer Tr and the amplifier and rectifier AR to the normally energized relay E, so that contact e3 repeats the signals as d.c. impulses to the receiving subscriber's line relay EM. On the in side, relay N responds to the signals under control of armature a3, while slow-release relay V holds on ; on the out side, however, relay N is held on by winding N 4/5 when armature e3 sends on an interruption impulse. Making a telegraphic connection. Instead of first effecting a telephonic connection, a subscriber can dial an alternative call-number which gives him a telegraphic connection at once. In this event, the line selector LW reaches the called subscriber's line. through conductor cf, so that relay M responds and at m5 cuts in relay O which at o5 makes a circuit for An and R 1/5. Relay An prepares the called subscriber's telegraph while relay R brings about the selection of a free impulse-' converter as described above, so that relays P, U pull up. Winding O 1/2 holds on temporarily through m5, r5, but when R 1/5 is cut cut off at u3, relay O also falls off retarded. A reply signal is sent back to the calling subscriber on excitation of relay I 1/2 through contacts p5, o3. The reply signal comprises a code call such as " F " effected by interrupter FBs which, when i1 is closed, actuates relay B so that contact b3 intermittently connects the a.c. source Su. The code signal is received by the calling subscriber either as a buzz in his telephone. receiver or as a printed letter. At the first impulse of the message proper the reply signal ceases, since the holding coil I 1/2 of relay I is cut off at n1 on relay N 1/2 being operated by a3. Release by subscriber. To change from telegraphy to telephony with hook-switch Hu up or to ring-off with hook-switch down, a subscriber opens the stopping-key SchT. Relay S on his side of the exchange is therefore out off and sends on a long break impulse which breaks circuit on the outgoing side at the contact corresponding to e3. Relays A, S on both sides fall off and effect release of all the telegraphic connections at the exchange. At the subscriber's station the prolonged falling off of receiving-magnet EM releases the locking- spring of relay An. If the hook-switch is down the exchange connection is released, as soon as relay U releases, owing to interruption of the line at an2. In systems where release of the line selector takes place on the called sub-- scriber's hanging up, relay M breaks line b at m1 while t1 is open and so effects release of the telegraphic connections. If a subscriber rings a wrong number and then hangs up, release is effected by the time-switch described below. Release by time switch when subscriber makes a false call and hangs up without sending a message. When relay I pulls up on the establishment of a telegraphic connection, as described above, winding II 2/1 is connected through i5 to a contact stud 20 of the rotating switch RS. When, in the absence of message signals, the wiper 21 reaches stud 20, winding II 1/2 pulls up via i5 and winding II 4/5 holds on. At the next revolution the opposing winding I 4/5 is cut in via stud 19 and contacts ii5 and i4 so that relay I releases while II holds on. At the third revolution winding F 2/3 is cut in via contact stud 18 and opposes winding F 4/5, so that relay F releases, energizing N 1/2 at f5 and breaking the line b at f1 to initiate release of the connections. If, however, the calling subscriber begins signalling before release has been effected, relay N responds to the signals and at n1 breaks the holding circuits for relays I and II. Thereafter winding II 1/2 is cut off at i5 and winding F 2/3 at ii6, so that the time-switch no longer effects release.