US1547456A - Trunk circuits for automatic telephone systems - Google Patents

Description

July 28, 1925.

A. B. SMITH TRUNK CIRCUITS FOR AUTOMATIC TELEPHONE SYSTEMS Filed Sept. 18, 1919 Fm &

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entree ARTHUR BESSEY SMITH, OF EVANSTGN, ILLINOIS, ASSIGNOR 'IO AUTOMATIC E LEO- TRIC COMPANY, O'F CHICAGO, ILLINOIS, A CORPORATION OF IIlLIlfl'QIS.

TRUNK CIRCUITS FOR AUTOMATIC TELEPHONE SYSTEMS.

Application filed September To all whom it may concern Be it known that l, ARTHUR. Bnssnx SMITH, a citizen of the United States of America, and a resident of Evanston, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in Trunk Circuits for Automatic Telephone Systems, of which the following is a specification.

My invention relates in general to auto matic trunk circuits, but more particularly to trunk circuits connecting more or less isolated or separated automatic exchanges, and has for its primary object the provision of means for handling a special case having-to do with the collection of tolls on incoming calls, although certain broad features may be found to be of utility for other purposes.

Fig. 1 is a layout of the relative position of a group of exchanges in which my invention may be best illustrated.

Fig. 2 is a diagram of the selective switching mechanism which is used to illustrate the features of my invention.

Referring to Fig. 1 of the drawings, the reference characters A, B, and C represent three exchanges which may be located in three difierent towns. Vi e will assume that the towns in which exchanges B and C are located are relatively close together, or these exchanges may be in the same town or city. At any rate, they are so situated that a fiat rate for calling is in force for inter-exchange as well as local calls. Exchange A however, is somewhatmore distant and while calls from exchange A to exchange B may carry no extra charge, there will be a toll charge for calls from exchange A to exchange C. lnter exchange as. wellas local calls are established automatically by the subscribers except that an operator may complete those calls which carry an extra toll charge. The trunking may be described briefly as follows: At exchange A selector switches are provided as usual which are common to the subscribers and which are used during a preliminary stage in all connections, local or inter-exchange. Thus the selector S has access to local trunks and also to trunks extending to exchange B, one of which is shown in the drawing. This-trunk line terminates at exchange B in a selector S which may be termed a trunk selector to distinguish it from the local selector S which is similar to selector S at eXchange A. Se

18, 1919. Serial No. 324,284.

lectors S and S have access in common to local trunks in exchange B and to interexchange trunks extending to exchange C. It will be seen now that subscribers in both exchanges haveaccess to trunk lines extending to exchange G. Since there is no extra charge for calls between exchanges B and C such calls are preferably established auto-v. matically, and to this end each trunk line is provided with a branch at exchange Cwhich terminates in an automatic switch. But there is a charge for calls from exchange A to exchange 0 which makes it necessary to route such calls thru an operator who can make appropriate record thereof. In order to take care of this latter class of calls a sec ond branch is provided for each trunk line which extends to an operators position. Heferring again to the drawing'it will be seen that the trunk extending from exchange B to exchange C terminates at the latter point in a switching device X which is adapted to connect. the trunk line to the branch extending to jack J, or to the branch extending to the switch S The object of my invention is, specifically, the provision of automatic means at exchange C which is able to differentiate between calls from exchange A and calls from exchange B, and which is effective to dire-ct calls from exchange A to an operator and calls from exchan e B to automatic switches thru the medium of which the subscribers complete the desired'connections The precise manner in which this is accomplished and the preferred embodiment of the invention. will be described more in detail hereinafter, reference being had to the accompanying drawing.

In the drawing (Fig. 2), the reference,

characters and 31 indicate the two line conductors of one of the trunk lines connecting exchanges B and C. This trunk line terminates at exchange 13 in the repeating coil It thru the medium of which the trunk conductors are inductively connected to con-' ductors 8 and 9. These latter conductors terminate in multiple contact sets in the banks of local selectors such asselectors S Fig. 1, and also extendto multiple contact sets in the banks of trunk selector 'such as the. selector S, Fig. 1. In the drawing here is shown one contact set, comprisingcontacts 2, 3, and 4, which is located in the bank of a local selector; and another contact set comprising contacts 5, 6, and 7 which is located in the bank of a trunk selector. It is understood that while the line contacts are multipled between the local and trunk selectors, the private or test contacts are not so multipled. Thus the test contact 3 is multipled to other local selectors but not to trunk selectors while similarly test contact 6 is multipled only to other trunk selectors.

At exchange C the repeating coil R is provided thru the medium of which the trunk conductors 30 and 31 are inductively connected to conductors 32 and 33, which are normally connected to branch conductors 44 and 45 extending to jack J. The other branch comprises conductors 42 and 43 which extend to a selector switch which may be the selector S Fig. 1. This latter branch is normally disconnected but may be substituted for the other branch by the operation of relay 37.

It is thought that the operation and functions of the various relays can best be explained by describing the operations incident to the establishment of several representative connections over the trunk circuit. Accordingly it will be assumed first that a calling subscriber in exchange B has estab' lished connection thru the medium of the selector S with the bank contacts 2, 3, and 4 for the purpose of connecting via the trunk circuit with a subscriber in exchange C. Upon the completion. of the connection to the bank contacts 2, 3, and 4, the line relay 13 is energizedin the usual manner over the calling subscribers loop and upon attracting its armature 15 closes an energizing circuit for the slow acting relay 14. This latter relay pulls up and closes the well known holding circuit back to the selector S which extends from ground G by way of armature 16 and its working contact, winding of relay 20, and conductor 10 to bank contact 3, whence it continues by way of the test wiper of the switch thru a relay whose function it is to maintain the switch in operated position, and thence to the ungrounded pole of the battery. Current flow in the holding circuit serves to energize relay 20, which upon energizing, completes a control circuit over the trunk line to exchange C as follows; ground at G thru the battery 13, working contact of armature 22 and the said armature, armature 18 and its working contact, working contact of armature 17 and the said armature, conductor 19, right hand windings of repeating coil R in parallel, trunk conductors 30 and 31 in parallel, left hand windings of repeating coil R in parallel, conductor 51, and windings of polarizedrelays 46 and 47 in series to ground G Upon the completion of the above circuit the direction of lay 47 is able to operate its armature, but polarized relay 46 remains inoperative. Relay 47 upon operating, com" pletesa circuit for the relay 36 which in turn closes acircuit for the slow acting relay 37. This relay, upon energizing, dis

connects the conductors 32 and 33 from branch conductors 44 and 45 at armatures 40 and 41, respectively, and connects them instead tothe branch conductors 42 and 43 which extend to a selector switch, assumed to be the selector S Fig. 1. Relay 36 has already closed at its armature 39 a normally open contact in conductor 42 and it Will be seen that relays 36 and 37 have now completed a loop circuit including the right hand windings of repeating coil R :and which extends to the line relay of the selector. V

Controlling impulses for operating the selector switch and subsequent switches, in exchange C are transmitted over the trunk line in the following manner: Then the subscriber at exchange; Boperates his calling device a series of interruptions are produced in the line circuit, thereby causing a corresponding series. of deenergizations of line relay 13. At each deenergization relay 13 breaks the control circuit extending to current flow is such that polarized re- 1 exchange "C, thereby causing the polarized relay 47 t0 deenergize a like number of times. Since relay 47 controls the circuit of relay 36, this relay also deenergizes a plurality of times and thereby produces a series of interruptions in the circuit which extends over the branch conductors 42 and 43 to the selector switch. Subsequent op-' erations of the calling device by the subscriber at exchange B will result in the operation of an additional switch or switches in exchange G whereby the connection will be completed to the desired line, all in the well known manner.

Having described. briefly the establishment of aconnection between a subscriber in. exchange B and one in exchange G, I will now describe the operation when a subscriber in exchange A is calling. It will be assumed that the calling subscriber desires to obtain connection with a subscriber in exchange C and that he has extended his line through the medium of selectors S and S to the trunk line terminal comprising bank contacts 5, 6, and 7. Upon the completion of the connection, line relay 13 is energized, followed by the energization of relay 14, which relay closes the holding circuit back to the selector S the same as was described in the case of selector S except that now the relay 21 is included instead of relay 2() Upon energizing, relay 21 connects the battery B in the control circuit extending over the two conductors of the trunk in parallel to exchange C, where it includes the polarized relays 46 and 47. Batteries B and B have'different poles adapted for connection to the control circuit, or inother words, they have opposite v and will thereafter proceed as is usual in such cases, making proper record of the call, and then completing it to the called line in any suitable manner.

The foregoing explanation is believed to be sufficient to enable the invention to be readily understood. It will be seen that I have devised a trunk circuit connectingtwo exchanges and accessible at one end to two different classes of subscribers, and having means at the other end whereby calls from ill one class of subscribers are automatically routed to an operator, and whereby calls from the other class of subscribers are automatically routed via automatic switches.

lVhat I claim as my invention is:

1. In a telephone system, a trunk line, two classes of subscribers having access to said trunk line when calling, two outgoing branches of said trunk line, automatic selective means for routing calls from said trunk line via either of said branches, a pair of relays constituting said selective means, a. controlling circuit for said relays, a pair of batteries each adapted to operate a particular one of said relays, and means controlled according to the class of a calling subscriber for connecting one or the other of said batteries in said circuit.

2. In a telephone system, an exchange comprising an operators position and a plurality of automatic switches, subscribers lines grouped at two outside points, means whereby subscribers in both groups can call said exchange automatically, and automatic means controlled by currents of different character for selectively switching such calls independent of control by the subscribers, whereby calls from one group of subscribers are directed to the operator and calls from the other group are directed to automatic switches.

3. In a telephone system, a trunk line having two branches at one end thereof, subscribers lines grouped at two points, means whereby subscribers in both groups can connect with said trunk at the end opposite said branches and extend calls thereover, and automatic means controlled over two sides of said trunk line in parallel for selectively switching such calls independent of control by the subscribers, whereby calls from onev group of subscribers are extended over one branch of said trunk line and calls from the other group'are extended over the otherbranch.

4. In a telephone system, a trunk line, branches of said trunk line at one end there of, one branch extending to,- an operators position and the other branch terminating in an automatic switch, two selector switches having access to said trunk at the opposite end thereof, and means for always signalling the operator'via one of said branches when the trunk is seized by a particular. one of said selectors and for always operating said automatic switch when the trunk is seized by the other ofsaid selectors, said means controlled by currents of different character.

I 5. In a telephone system, a trunk line having two branches at one end thereof and a simplex circuit superimposed thereon, one branch being normally connected and extending to an operators position and the other branch being normally disconnected and terminating in an automatic switch, two selector switches having access to said trunk at the undivided end thereof, and automatic means controlled over said superimposed circuit for completing the connection to the operator via the said connected branch whenever the trunk is seized by a particular one of said selectors, and for connecting the said normally disconnected branch and for disconnecting the other branch whenever the trunk line is seized by the other of said selectors.

6. I n a telephone system, a trunk line having two branches at one end thereof, two selector switches having access to said trunk at the other end, a circuit superimposed on the conductors of said trunk line and including at the divided end of the trunk two relays for controlling extensions of said trunk over its two branches, respectively, two separate batteries at the o her end of said trunk for separately operating said relays, and means whereby each of said selectors when it seizes the trunk line includes a particular one of said batteries in the said circuit.

7. In a telephone system, a trunk line having two branches at one end thereof, two selector switches having access to said trunk at the other end, a ground return circuit superimposed on the conductors of said trunk line, two polarized relays included in said circuit at the divided end of said trunk for controlling the connection of said trunk .vith its two branches, respectively, two batteries at the other end of said trunk having opposite poles grounded, and means whereby each of said selectors when it seizes the a particular one of said relays.

e .8. In a telephone system, an exchange comprising an operators position and a plurality of automatic switches, second and third exchanges each having subscribers" lines terminating therein, a trunk line accessible to subscribers lines in the second exchange and extending to said third exchange, another trunk line accessible to calls coming over said first trunk and also to subscribers in said third exchange, the said second trunk constituting means whereby subscribers in either the said second or third exchanges can call the said first exchange,

and automatic means for selectively switching such calls independent of control by the subscribers whereby calls from the second exchangerare directed to an operator and whereby calls from the third exchange are directed to automatic switches.

9. In a telephone system, two classes of lines, a trunk, means for connecting any line with said trunk at the incoming end thereof, two branches of said trunk at the outgoing end, discriminating mechanism at, the incoming end of said trunk sensitive to the class to which a connected line belongs, and switching mechanism at the distant end controlled over a talking conductor of said trunk by said discriminating mechanism for routing all calls from lines of one class via one of said branches and all calls from lines of the otherclass via the other of said branches.

10. In a telephone system, a trunk line having two branches at the incoming end, an automatic selector switch having access to the first branch only, a second automatic selcctor'switch having access to the second branch only, two branches at the outgoing end of said trunk line, means including said selectors for extending calls over said trunk line, and cooperating means atopposite ends of said trunk line for insuring that all calls reaching the trunk line by way of one selector will be routed away from said trunk line via a particular branch at the distant end and that all calls arriving by way of the other selector will be routed via the other branch at the distant end. a e

11. In a telephone system, a trunk line having two branches at one end thereof, automatic switching inechanismfor connecting a calling line with said trunk line at the other end, a circuit including the two talking conductors of said trunk line in parallel, and switching means at the junction of said branches controlled automatically over said circuit responsive to the establishment of said connection for routing the call over a particular one of said branches. i

12. In a telephone system, a trunk line having two branches at the incoming end and two corresponding branches at the outgoing end, automatic switches torextending calls over said trunk line, a circuit including the two talking conductors ofsaid trunk line in parallel, and mechanism at the outgoing end of said trunk line controlled over said circuit from the incomingend for automatically and selectively switching said calls, said mechanism including means for routing eachcall away from the trunltover the outgoing branch corresponding to the incoming branch inuse.

Signed at Chicago, Cook County, Illinois, this 13th day of September, 1919.

ARTHUR BESSEY SMITH.

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