US1334755A - Telephone-exchange system - Google Patents

Description

G. S HOFFMAN.

TELEPHONE EXCHANGE SYSTEM.

APPLICATION FlLED MAY3I,1917- Patented Mai. 23, 1920.

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GORDON S. HOFFMAN, 01? BUIZlTING-VILLE, CALIFORNIA.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters li'atent.

Patented Ma1a23, 1920.

Application filed May 31,1917. Serial No. 171,961.

To all whom it may concern:

Be it known that I, GORDON S. ITOFFMAN, a citizen of thellnited States, residing at Buntingville, in the county of Lassen and State of California, have invented certain new and useful Improvements in Telephone Exchange Systems, of which the following is a specification, reference being had therein. to the accompanying drawing.

My invention relates to telephone ex change systems and especially to branch toll line systems.

Tn cases where telephone companies 0pcrate toll lines extending through districts which have become somewhat populated but which are remote from the central oilice and not sufficiently settled to warrant the building of a separate line, and it is desirable to hold the territory in case of future develop ment, it becomes necessary to connect branch. or branches to stations along the line. This, however, is subject to the disadvantage that such branch stations become a hindrance to the use of the main line as a long distance toll line, and an annoyance to the central o'lliice operator through electrical disturbances in the branch lines which make them noisy, and by their users listening in and ringing in on a busy line.

lit is the object ofmy invention to over come the objection above mentioned by the provision of a control system consisting of a combination and arrangement of circuits and apparatus whereby the connection of such branch stations with the main line may be controlled by the operator at the central oflice, which system shall be simple, ec0- nomical and effective in operation and may be readily installed at low expense compared to that of making an additional line.

The invention consists geiieraliy in the provision of clectromagnetically operated switching means associated with each branch line operable to control the connection between the branch and the main line, and itself controlled preferably from the central station or from both ends of the main line and one or more of the branch stations, the control being el'lected over a grounded circuit phantomed on the main line throughone winding of repeating coils, through which the talking circuits are connected to the main line.

The invention further consists in the various combinations and arrangements of apparatus and circuits as described and illus trated in the accompanying specification and drawings and particularly pointed out in the appended claims.

My invention is illustrated in the accompanying drawings in which- Figure 1 is a diagrammatic view of a preferred form of my invention. I

Fig. 2 is a similar view showing a method of controlling the branch line connections from a branch station.

Fig. 3 shows an arrangement for efiecting; the central oflice control through contacts in the terminal jacks of the main line.

Fig. t shows an arrangement for controlling a branch line connection individually.

Referring; to the drawings in detail, the circuits and apparatus indicated to the left of the vertical dotted line in Fig. 1 consti tute the Central o'llice line terminal ar angement of my invention. This portion. of the system consists of a repeating coil 1 having its primary winding 2 bridged across the terminals of the main trunk line conductors 3-4, and its secondary coil 5 bridged across the terminals of a line jack 6, which jack may have multiple connections, not shown, leading to other jacks in a manner well understood by those skilled in the art. The repeating coil 1 has a central. tap 7 which connects through a suitable conductor 8 and an operators control key 9 to a grounded battery 10. The main toll line 3i leads out of the central oflice station to one or more distant exchanges, not shown, as is the usual practice in the use of such lines. At one or more points intermediate the central office and the distant exchanges, usually, in practice, points more or less remote from the central oflice, a branch or branch lines are connected with the main line, as indicated in the dotted rectangles 1]. and 12. This connection is made through a repeating; coil 13,

the primary winding 14- of which is bridged across the main line and is provided with. a central tap as at 15 connected through a conductor 16 and the windings of a relay 17 to round. The secondary winding 18 of the repeating coil 13 has its terminals connected to the branch line 1920 through conductors 2122 and norm ally closed contacts 23-24 of the relay 17. The primary windings 2 at the central oflice and 1d at the branch line connections are, of course unidirectional coils so that by tapping at the center as at 7 or 15, it forms a differential, winding offering impedance to the flow of alternating current across the trunk conductors and forming a non-inductive resistance for direct current passing in opposite directions through this winding. It will thus be seen that the relay 17 is included with the battery 10 in a grounded phantom circuit which may be traced as follows: battery 10, key 9, conductor 8, 7 primary winding 2 in opposite directions to trunk conductors 34, primary Winding let in opposite directions to tap 15, conductor 16, winding of relay 17 to ground and back to battery 10.

In the drawings, for the sake of clearness, I have omitted various details and accessories such as signaling, listening, calling and testing-apparatus which, it is to be understood, could be readily added by those skilled in the art.

In the use and operation of my invention as illustrated in Fig. 1, the apparatus and circuit connections are normally in condition as indicated in the diagram, with the operators control key 9 open and the relay or relays 17, associated with the branch lines, deenergized. This leaves the branch lines normally connected with the main line through their respective repeating coils 13 so that they may signal over the main line when it is to be found in idle condition and also receive signals and talk thereover through suitable substation apparatus connected with the branch conductors 1920, but not shown. hen it is desired to use the main line for trunking a long distance call from the central station, the central station operator makes the talking connection with the main line through the jack 6 in the usual manner and closes the key 9 which clears the main line of the branch circuit connections by energizing the relay or relays 17 over the phantom circuit previously described. This energization of the relay 1? causes it to attract'its armature, opening the contacts 23 and 24 which disconnects the branch line 1920 from'the leads 2122, thus severing operative connection between the branch line and the main line. The relay 17 is held energized from the central station during the use of the main line as a long distance trunk. The station or stations on the branch line have no means for controlling this connection and so cannot interfere with the use of the trunk by ringing or listening in; At the end of this use of the trunk, the operator at the central ofiice may release the relay 17 by opening the key'9 which relay upon deenergization permits its armature to retract and again.

close the connection from the branch line to the main line through the contacts 23'24. In practice I use a 500 ohm double contact relay for the relay17, and adjust the battery 10 according to the resistance of the line. It is obvious that in cases where the line 3-4 is to be used as a two-way trunk, controlling means such as that shown at the central station in Fig. 1 may be duplicated at the remote exchange.

In some cases where it is desired to give the branch stations control of their connection with the main line, I provide the arrangement as shown in Fig. 2 in which a relay 25 having normally open contacts included in the connection between the branch line and the main line is substituted for the relay 17 of Fig. 1. This relay 25 is arranged to be controlled from the branch station by a key 26 situated at the branch station and included in the circuit of a local battery 27 connected across the terminals of the relay. With this arrangement the branch line 19-20 is normally disconnected from the main line 8-4- so that any electrical disturbances on the branch line will not affect the use of the main line by the central oilice or other branch stations connected therewith. A party at the branch station, however, can

connect with the main line by closing the key 26 which connects the terminals of the local battery across the terminals of the relay 25 which upon 'encrgization operates to close the normally open contacts 2829 connecting the branch line 19-20 across the terminals of the secondary winding 18 of the repeating coil 13 and consequently placing the branch in operative connection with the main line through the secondary coil 14. When the operator at the central station desires to connect the branch station with the line for the purpose of calling the same, she may do so by energizing the relay 25 over a circuit such as that previously described for Fig. 1.

In order to make the control of the branch line relay or relays 25 automatic upon the insertion of a plug in the line jack at the central station, I provide the arrangement as shown in Fig. 3 which is in all respects similar to the line terminal arrangement of Fig. 1 except that the conductor 8 connects with the battery 10 through normally open contact springs 30 arranged to be closed upon the insertion of a plug in the jack 6.

In order to enable a subscriber at a branch station having the circuit arrangement of Fig. 2 to energize his control relay 25 without energizing those of any other branch. stations that might be connected to the same main line, I connect the relay 25 as shown in Fig. 4c, the circuit arrangement remaining the same as that of Fig. 2 except that the energization of the relay .25 of the branch station is controlled by a make-and-break contact key 31 arranged to keep the relay 25 normally connected with the conductor 16 through the normally closed contact 32 and upon operation to disconnect the relay from the conductor 16 and connect it to the free side of the grounded battery 27 through the normally open contact It will be seen that with this arrangement the relay 25 is normally connected for energization from the central otlice over the phantom circuit and upon actuation of the key 31 will be energized by current from the battery ii? in a local circuit entirely disconnected from the main line. Thus the central otlice operator is given control of the relays of all the branch stations while each branch station has control only of its individual relay so that the main line when connected with it will be free of all other branch connections. With several branch stations on the main line having relays 25 connected as shown in Fig. t, a branch station could not :all the other branch stations but could call the central station from which the relays 25 the other branch stations could be Operated to complete a connection between such stations, thus permitting connection between branch stations, but under supervision of the central station.

My invention may be applied to the control over a two-wire talking trunk, or the connection of a central othce with a toll line for talking thereover to either end of the toll line to the exclusion of the other.

While I have herein shown and described certain preferred forms of my invention, it is to be understood that various other modifications may be made thereof without departing from the spirit of the invention and that all such modifications are contemplated by me. For example, it will be obvious to those skilled in the art that the circuit conductors connected to the central. Oll'lCG 210k and control key may be connected instead to the contacts of automatic switching mecha nism tor use in automatic exchange systems. Again it will be obvious that where the branch line control arrangement of Fig. 41: is

sed and installed near the telephone set at the branch station, the battery 27 may be done away with and the branch line connection controlled manually at the central otlice in any well known manner. However, it is usual and preferable to install the apparatus, associated with the branch line, at or near the junction with the main line.

llavin g thus described my invention what I claim and desire to secure by Letters Pat- 1. In a telephone exchange system, a toll line, a branch line, a repeating coil connecting said lines intermediate the terminal stations 011 the toll line, and an electrically operated switching means in said branch circuit energized in a simplex circuit phantomed on the toll line through a winding of the repeating coil, and controlling means at the central oflice for said simple): circuit.

2. In a telephone exchange system, a toll line, a branch line, a repeating coil having one winding bridged across the toll line intermediate the terminal stations on the toll line, and the other winding connected to a branch line, an electrically operated switching means having contacts included in the branch line and itself connected between a central point of the said bridged winding and ground, a repeating coil at the central station having one winding bridged across the toll line, and means at the central station for connecting a source of current between a central point of the said the central station and ground.

8. In a telephone exchange system, a toll line, a branch line, a repeating coil connecting said lines intermediate the terminal stations on the toll line, electrically operated switching means in said branch line, a simplex energizing circuit for said switching means including a source of current and phantomed 011 the toll line through one winding of said repeating coil, and controlling means for said energizing circuit.

t. In a telephone exchange system, a toll line, a branch line, a repeating coil connecting said lines intermediate the terminal stations on the toll line, electrically operated switching means in said branch line, means at the central station for controlling said switching means, and other means associated with said branch circuit for controlling said switching means.

5. In a telephone exchange system, a toll line, a plurality of branch stations intermediate the terminal stations on the toll line, electromagnetic switching means at each branch station for connecting its associated station with said toll line, said electromagnetic means being connected in multiple in a simplex circuit phantomed on the toll line, a local source of energy at each of said terminal and. branch stations, and means at each said station for connecting its local soiu-ce oi energy across said simplex circuit in multiple with said electromagnetic means.

In testimony whereof I aflix my signature.

GORDON S. HOFFMAN.

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