US 536920 A
Description (OCR text may contain errors)
NlTED STATES ATENT Eric.
' FRANK R. coLvm, on NEW YORK, N. Y.
SPECIFICATION forming part of Letters Patent No. 536,920, dated April 2, 1895. Application filed December 20, 1894. Serial No. 532,388- (No model-l To aZZ whom it may concern- Be it known that I, FRANK R. COLVIN, a CllllZBIl of the United States, residing in the city, county, and State of New York, have invented certain new and useful Improvements n Telephone Systems, of which the following 1s a specification.
This invention relates to telephone systems,
the object being to provide a simple and effective exchange system for interconnecting a plurality of subscribers whose instruments are located in dilferent circuits, and for operating the system by batteries or electric generators located only at the central station.
In carrying out my invention I provide a number of independent circuits, preferably metallic circuits, containing the several subscribers instruments and extending from the outlying stations to the central office, the several subscribers having a call-receiving apparatus normally included in their circuits, the central office being provided with a calling generator adapted to be out into the circuits.
At the central station is located a normally completed ground containing an electric generator and an indicator or annunciator for each circuit, a normally open ground with a circuit-closer beingprovided at the several subscribers stations so that upon operation of the circuit-closer the indicator or annunciator at the central station will be actuated. Each circuit terminates at the central station in a contact device by which a conducting cord provided with suitable plugs may be used to connect in series relation two subscribers desiring inter-communication. Interposed between the plugs is a battery or other direct current generator by which, when a connection between two circuits is established, current is thrown over the line to render operative the talking instruments of the inter-communicating subscribers. At central station is also provided a listening or talking circuit having normally completed contacts with a plug by which communication may be established with anyoutlying subscriber. A switch is also provided by which the listening circuit may be out out and a magneto or other calling generator thrown into circuit with the plug so that any desired subscriber may be called up.
The several features of novelty of the inven tion will be more particularly hereinafter described, and will be definitely indicated in the claims appended to this specification.
In the accompanying drawing whichillustrates my invention is shown diagrammatically asystem embodying my improvements. 1, 2 and 3 represent a plurality of circuits connecting a number ofoutlying stations with a common station located preferably at some central point. Each of these circuits may contain one or a plurality of instruments as may be desired. In the circuit 1 a single subscribers station is interpolated, which is therefore a private line. In the circuit 2 two subscribers stations are interpolated, the circuit thus being shared by two stations. Each of the circuits terminates at the central station in a switch 4, 4 4. comprising preferably two contacts normally held in engagement by a spring but adapted to be forced apart by a plug 5 carrying two contact plates or surfaces of metal which engage the two contacts.
A convenient organization comprises for the switch 4 a metallic post and a spring normally bearing against the same, the plug 5 comprising a central metallic socket adapted to be forced over the pin and form contact with the same and an insulated outer tube adapted to engage the spring. Thus, when the plug is inserted over the pin, the two concentric metallic surfaces engage the two contact points of the switch. The two parts of the plug connect with flexible conductors which lead to another similarly constructed plug 5, a continuous current generator 6 beingincluded in one of the conductors.
In a normally closed ground 7 at the central station is contained a signaling battery or other suitable generator 8, annunciators or other indicators 9, 9, 9 connecting in multiple with this ground and with the several subscribers circuits. At each subscribers station is provided a normally open ground 10, 10*, 10*, 10 containing a circuit-closing key 11, &c., by which a ground circuit may be completed through the respective annunciators or indicators at the central station and thus give an indication that communication is desired with some other subscriber.
Since a common generator 8 is provided for the several indicators 9, 9 9 and the latter therefore grouped in multiple-arc relation to the generator, the generator 6 is connected in that branch of the double conducting cord which will be disconnected from the indicator branches when the plug is inserted in the switch. For example, the indicatorbranches are shown in the diagram as connected with the spring contact of the respective switches and the battery 6 is in circuit with the socket which forms a connection with the other contact. It is evident therefore that when two circuits are connected a short circuit will not be afforded through the indicators 9, 9, and the latter may be made of low resistance.
At each subscribers station is provided a call-receiving instrument 12, 12, &c., which may be of any suitable character, but is preferably a magneto bell. This call-receiving instrumentis normallyincludedin circuit but is adapted to be cut outof circuit by shifting the telephone hook 13, the circuit then being completed by a normally open contact leading through the subscribers talking outfit as indicated. This hook is preferably of the character described in a former patent issued to me, No. 517,263, dated March 27, 1894, and is adapted when in its normal position to sup port a telephone, but when thrown by a positive action of the subscriber to the talking contact to be tilted to such a position that the telephone will not be supported by the hook. At the central ofiice is also provided a listening circuit 14 provided with a battery and having a normally completed connection with a plug 15, similar to the plugs 5 5, hereinbefore described. Thus, when the plug 15 is applied to the jack switch corresponding to any subscriber, the central station operator will be placed in a position to talk with any subscriber.
In normally open relation to the switch contacts 16 16, connecting with'the plug 15 is an electric generator 17, preferably a magneto generator, so that when the double key or switch 18 is actuated the listening circuit 14 will be disconnected and the generator 17 connected with the terminals of the plug 15. Thus by inserting the plug 15 in any subscribers switch and then shifting the switch 18 an operation of the magneto generator 17 will send suitable currents over the subscribers circuit to actuate his bell 12 and call him up.
I preferably use as a talking instrument a battery transmitterof the character described in a patent issued to me, No. 513,305, dated January 23, 1894, in which a source of direct current exists on the talking circuit continuously during conversation, the conversation being maintained by a variation of resistance by the action of the transmitter. Thus both transmitters and both receivers of the two communicating subscribers are in series relation during conversation. It is evident, therefore, that a single battery, such as 6, for each pair of connecting cords may be used at the central station and that no battery whatever need be employed at the subscribers stations. A subscriber, however, is able to send in a call over a grounded circuit, one end of which is normally closed at the central station through a battery and indicator, and the other end of which is open at his station. Moreover, all subscribers are furnished with talking currents by central station batteries. It is evident, therefore, that since no battery is employed at the outlying stations the listening circuit 14 of the central station operator should also be provided with a battery as indicated. It is evident also that since the subscribers bells are not in the grounded circuit a call sent to central office by one of two or more subscribers on the same circuit will not operate any subscribers bell, which can only be actuated by the central office operator. A
The subscribers bells should be of low inductance when more than one is employed in series on the same circuit, since in such cases one or more will be in the talking circuit.
The several subscribers circuits are preferably metallic circuits though some features of the invention are applicable also to cases in which grounded talking circuits might be employed.
Some features of the invention will also prove of value in magneto telephone systems where no batteries, so far as the talking circuit is concerned, are employed; such a feature, for example, as the normally open ground at the outlying station and the co-opcrating call-receiving apparatus at the central station. Where two or more subscribers are located on the same circuit, as, for instance, on circuit 2, they are preferably connected in series relation to the circuit. The bells being of low inductance will not materially interfere with successful telephonic transmission.
Having thus described my invention, what I claim as new, and desire to secure by Letters Patent, is
1. A telephone system comprising a plurality of outlying subscribers stations, at plurality of metallic circuits containing the telephone receivers and direct current transmitters of the several subscribers leading to a central station, connectors at the central station including a source of continuous current for connecting any two metallic circuits and charging the transmitters, a calling generator at the central station, call-receiving instruments at the several stations, a normally completed ground including indicators for the several circuits and a source of continuous current at the central station, and normally open grounds including a circuit-closer at the several stations.
2. A telephone system comprising a plurality of outlying subscribers stations, a plurality of metallic circuits containing the telephone receivers and direct current transmitters of the several subscribers leading to a central station, a normally completed ground at central station for the several circuits including an indicator and battery, a normally transmitter and telephone receiver adapted I 5 to be cut in at each subscribers station, connectors at the common station for coupling two subscribers circuits in series relation to each other, and a source of continuous current between said connectors for charging the transmitters.
In testimony whereof I have hereunto subscribed my name this 18th day of December,
FRANK R. OOLVIN. Witnesses:
RoBT. H. READ, G. W. GRAHAM.