US2170903A - Telephone system - Google Patents

Description

Aug. 29, 1939. U.KES1"EN 2,179,903

TELEPHONE SYSTEM Filed May 29, 1956 IN VENTOR. ULRICH I K E5 TEN ATTORNE Patented Aug. 29, 1939 UNITED STATES 2,170,903. TELEPHONE SYSTEM Ulrich Kesten, Staaken, Germany, assignor to Siemens & Halske Aktiengesellschaft, Berlin,

Germany Application May 29, 1936, SerialNo. 82,390

In Germany June 1, 1935 10 Claims.

The present invention relates to a circuit arrangement for subscribers lines in telephone systems provided with freely hunting switches and more particularly preselectors. It aims at rendering false calling conditions at the subscribers lines inoperative as regards their effect on the hunting switches in such systems.

False calling conditions can be produced on .account of y the completion of loops of subscribers lines or connecting lines. They can also occur during the establishment of a connection or during the releasing operations. In the first case the calling condition produced when setting up a call may be recognized as false if a subscriber after initiating a call delays for a definite period before completing the call. The second case occurs when in systems in which the release of a connection is dependent upon the calling subscriber, the final selector becomes released before the called subscriber has replaced his receiver.

For the purpose of rendering inoperative the false calling conditions occurring in all these cases the arrangement according to the invention produces a circuit arrangement which does not involve any further expenditure of switching means at the subscribers lines .and without using special constructional means.

This is achieved in that a two-stage relay brought under the influence of the subscribers line through the operation of a releasing impulse transmitted when a false calling condition is set be applied to freely hunting switches of various constructions for example preselectors or group selectors especially since in the case of group seto outgoing lines over the preselector VW. One of these outgoing lines is represented by Lal,

Lb! and Lcl. The preselector possesses four wipers which are indicated by so, sb, so and sd. The wiper sd serves to return the preselector to the rest position. To contact I l in the contact bank of the testing wiper so a relay G is con-'- nected which is common to several preselectors and which controls a time switch which transitorily opens contact 970. It is not necessary to point out the object of this operation as it forms no part of the invention. I A two-stage line relay R having windings I, II andIII, is associated 5 with the subscriber Tn at his connectingline. Cut-off relay T having windings I and II is connected to the subscribers line and serves as a testing relay. ,When energized in its first stage (winding I) relay R, operates only the contact 81*. When fully energized i. e. over winding III the relay operates contacts 51', 61" and Tr. Winding II of relay R serves as a locking winding and maintains the relay energized in the second stage. a

.When the subscriber at the station Tn initiates a call the following circuit is established on the removal of the receiver: earth, battery, resistance Wi, contact It, lead La, loop at the subscribers station Tn. lead Lb, contact 2t, winding I of relay R, contact 51', and earth. In this circuit relay R energizes in the first stage. It accordingly operates contact 81' so that the following stepping circuit is established for the preselector: earth, battery, wiper sd, position 0 of wiper sd, contacts 81", 3t, 17', rotary magnet DVW, interrupter RU and earth. The rotary magnet DVW is energized impulsivel-yin this circuit. When the preselector findsa free line for example the line Lal, Lbl, Lc l, shown, the following testing circuit is set up: earth, battery, wiper sd, contact 81', windings II and I of relay T, winding III of relay R, contact 61", wiper so, lead Lcl, contact Hit?" of a thermal relay TR, switching means (not shown) in the subsequently arranged switching devices,vrelay TR, and earth. In this circuit relayT energizes while the current flowing through relay TR heats the thermostatic element associated therewith, to cause the operation of contact n after a predetermined time. By switchingover'contact it the testing circuit is maintained. Bythe switching over of contact 3t the stepping circuit is broken and thus the preselector is brought to rest. In the circuit just mentioned relay R becomes fully energized over its winding IIIJ It then operates contacts 51', 61' and 11'. This, however, does not produce any particular switching operation.

It may be mentioned that .a meter can be arranged in parallel with winding I of relay T.

If the subscriber now operates his calling device to operate the switching mechanism connected to line conductors Lal, Lb I, Lcl, the initial movement of the switch closes contacts. onl, which remain closed as long asthe switch is offnormal, to short circuit relay TR and to thereby prevent the opening of contacts llltr.

If the subscriber does not continue the further establishment of the connection within a given period, for example, by delaying the dialling operation, the contact Illtr is momentarily opened. This has the effect of breaking the circuit passing over wiper so and winding I of relay T. Relay T releases and returns its contact to the normal position. The switching over of contact 315 does not, however, establish the stepping circuit for the preselector since contact 11' is still open. On the return of contacts It and 272 to the rest position the following circuit is established: earth, battery, resistance Wi, contact It, lead La, loop at the subscribers station Tn, lead Lb, contact 213, windings I and II of relay R and earth. In this circuit relay R remains fully energized. Contacts 5T, 61' and Ir are accordingly in the working position. The line originally seized is again accessible to general trafiic since the seizing circuit is broken at contacts 4t and 61.

The subscriber can now be given a signal in any known manner indicating that he has become disconnected. When he replaces his receiver relay R returns to normal and contact 11" reestablishes the stepping circuit, whereupon the preselector is advanced until its wipers have reached the rest position, i. e., when wiper sd reaches contact 0. Testing during the return to the rest position is: prevented by the fact of contact 81 having been opened on the release of relay R.

It will be assumed that on initiating a call on the part of subscriber Tn all the outgoing lines are engaged. In this case the preselector is advanced to position I I. In this position the following circuit is established: earth, battery, wiper sd, contact 8r, windings II and I of relay T, winding III of relay R, contact 6r, wiper 80, position H of wiper so, the common relay G, contact 9k and earth. In this circuit relay T energizes and switches over its contacts. In addition relay R is energized completely. Relay G connects up a device which causes contact 9k to be transitorily opened. This causes relay T to release so that relay R is brought under the influence of the calling station by way of its windings I and II. Relay R is maintained energized completely over the subscribers loop so that the testing circuit is broken at contact 61' and the stepping circuit is broken at contact Ir. The preselector accordingly remains in position I I until the calling subscriber replaces his receiver and thus releases relay R. Guarding of contact ll does not take place during the disconnecting condition on account of the opening of the testing circuit at contacts 4t and Br. When the subscriber replaces his receiver the preselector returns to the normal position in the manner already described.

The arrangement illustrated can also be used in systems in which the release of a connection is effected by the calling subscriber in such a way that thefinal selector also is returned to normal. Assuming that subscriber Tn is called a circuit is established over the incoming testing line Lcn which passes over resistance Wil wiper so in its rest position, contact 61*, winding III of relay R, windings I and II of relay T, wiper sd, battery and earth. In this circuit relays T and R are energized. Relay T energizes before relay B, so that no stepping circuit is established over contacts 81" and 3t. If the release is effected by the calling subscriber the earth connected to the lead Lon is disconnected in any known manner. Relay T accordingly deenergizes. Relay R which is constructed as a slow to release relay does not yet release, but remains energized over the subscribers loop of the called subscriber Tn. No stepping of the selector takes place since the stepping circuit which is prepared by contact 81' remains broken at contact 11'. When the subscriber replaces his receiver relay R is deenergized and contacts 8r, H, 61' and 51' return to normal.

What is claimed is:

1. In an automatic telephone system, an automatic switch having access to a plurality of trunk lines, a cut-off relay and a two-step line relay in said switch, means responsive to the initiation of a call for operating said line relay in its first step, means controlled by said line relay in its first step to operate said switch to find an idle trunk line, means for operating said line relay in its second step and also said cut-off relay when an idle line is found, and means for automatically deenergizing said cut-oil relay while holding said line relay fully operated in the event that dialling over the seized trunk line is delayed.

2. In an automatic telephone system an. automatic switch having access to trunk lines, a two-step line relay in said switch, means responsive to the initiation of a call for operating said line relay in its first step, means controlled by the operation of said line relay in its first step for controlling the operation of said switch to hunt for an idle trunk line, means for operating said line relay in its second step when an idle trunk line is found, a cut-off relay in said switch, said cut-01f relay operated responsive to the selection of a trunk line to extend the calling line thereto, means in said trunk line automatically operated in case the subscriber delays dialling for releasing said cut-off relay and for maintaining said line relay operated, and circuit connections controlled by the restored cut-off relay and operated line relay for rendering said trunk line accessible to other switches and locking said calling line out of service.

3. In an automatic telephone system, a subscribers line circuit including a line relay and a cut-off relay individual thereto, an automatic switch operable responsive to the operation of the line relay when a call is initiated over the line for extending said line, a timing device associated with said switch effective in the event the calling subscriber delays dialling, said line relay arranged to operate part way only pursuant to the initiation of a call, means for operating said line relay fully when the cut-off relay operates in response to the extention of the line, and means responsive to the operation of said timing device and depending upon said line relay having been operated fully when the line is extended to lock the subscriber's line out of service.

4. In an automatic telephone system, a subscribers line circuit including an automatic switch individual thereto having a cut-off relay and a two-step line relay, means responsive to the initiation of a call for operating said line relay in its first step to control the operation of said switch to find an idle trunk line and extend the call, means for operating said cut-off relay and for operating said line relay in its second step when the switch finds an idle trunk, means in said selected trunk line efiective in case the subscriber fails to dial over the trunk line for deenergizing said cut-ofi relay, and means for maintaining said line relay fully operated over said line circuit and to release said trunk line for service and lock out said line circuit from service.

5. In an automatic telephone system as ill iii

claimed in claim 4 in which the operating circuit for the switch is controlled jointly by the cut-oif relay and the line relay and the circuit is prevented from being efiective when the line is locked out of service by the restoration of the cut-off relay and the operation of the line relay, said line relay arranged to be slow acting and held operated over the subscribers line after the cut-off relay restores.

6. In an automatic telephone system as claimed in claim 4 in which the testing circuit for the switch in its operation of hunting an idle trunk line is controlled jointly by the cutoff relay and the line relay in its first step, said testing circuit rendered ineifective responsive to the deenergization of said cut-off relay and the full operation of the line relay over the line circuit at a time when the line circuit is locked out.

7. In an automatic telephone system as claimed in claim 4 in which the line circuit is also accessible to incoming calls, means for energizing said line relay initially in its second step and said cut-oil relay responsive to an incoming call, means responsive to the release of. the incoming call for deenergizing said cut-off relay, and means for maintaining said line relay fully operated over said line circuit after said cut-off relay deenergizes, said line relay arranged to be slow acting so as to remain operated during the interval in which the cut-off relay restores and connects the line relay to the line circuit.

8. In an automatic telephone system as claimed in claim 4 in which the line relay is arranged to be slow acting and is provided with a plurality of windings, one of. said windings serving to energize the relay in its first step when a call is initiated, and another Winding serving to energize the relay in its second step when the call is extended.

9. In an automatic telephone system, a subscribers line circuit including an automatic switch individual thereto having a cut-off relay and a two-stage line relay, means responsive to the initiation of a call for operating said line relay in its first stage, means controlled thereby for operating said switch to find an idle trunk line to extend the call, means responsive to the switch encountering an idle trunk line for operating said cut-oil relay and for operating said line relay in its second stage, means for operating said switch to a particular position in case all trunks are busy, and means connected to the said particular position on which the switch stops for deenergizing said cut-off relay, said line relay remaining fully operated over the line circuit to lock out the line from service.

10. In an automatic telephone system as claimed in claim 9 in which the line relay in its second stage controls the circuit of the switch for testing-the condition of the trunk lines and also the operating circuit of the switch, means responsive to the full operation of said line relay when the particular position of the switch is reached and all trunk lines are busy for disconnecting the testing and operating circuits of the switch, and means for deenergizing said line relay responsive to the disconnection of the calling subscriber and for restoring said switch to normal position.

ULRICH KESTEN.

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