US2114253A - Telegraph exchange system - Google Patents

Description

April 12, 1938. w. v. K. LARGE ET AL I TELEGRAPH EXCHANGE SYSTEM 5 Sheets-Sheet 1 Filed Oct. 29, 1936 IN VE N TORS W M K. LARGE By GALOCKE JWJM ATTORNEY A ril 12, 1938. w. v. K. LA RGE ET AL 2,114,253

TELEGRAPH EXCHANGE SYSTEM Filed Oct. 29, 1936 5 Sheets-Sheet 2 QQOM FM zmiRomKwEk llvmvmns: W GE G.A.LOCKE 3 Wit/QM I ATTORNEY W. V. K. LARGE ET AL TELEGRAPH EXCHANGE SYSTEM:

April 12, 1938.

5 Sheets-Sheet s Filed 001:. 29, 1936 QQOU ENE? QQQU had? 1 QQQU INVENTORS ATTORNEY.

A gil 12, 1938. w. v. K. LARGE. ET AL 2,114,253

' TELEGRAPH EXCHANGE SYSTEM Filed Oct. 29, 1956 5 Sheets-Sheets INVENTORS 1 W L K.

G.A.LOCKE A TTORNE V Patented Apr. 12, 1938 UNITED STATES TELEGRAPH EXCHANGE SYSTEM Wayne V. K. Large, Hollis, and George A. Locke,

Glenwood Landing,

Telephone Laboratories,

assignors to Bell Incorporated, New

York, N. Y., a corporation of New York Application October 29, 1936 Serial No. 108,154

7 Claims.

This invention relates to switching and exchange circuits for telegraphy.

An object of the invention is to improve and simplify manual exchange circuits; to improve the operation thereof and to make the cord circuit and supervisory equipment interchangeably operable with a variety of types of lines under a variety of conditions.

A feature consists of relays in a cord circuit which are connected with battery instead of ground at the artificial line to provide a markingholding effect through their bias windings when a spacing signal is transmitted into the apex connection. This eliminates the need for an antikick-off network at the central ofiice end of the local loops and lengths of loops will therefore have the same switchboard termination except for the value of whatever current regulating resistance may be necessary.

A further feature is that a single cord circuit is universally utilizable for interconnecting short subscribers lines, toll lines to other exchanges and long subscribers lines including long line equipment. In combination with this feature is the feature that the supervisory equipment is incorporated in the cord circuit rather than in the line circuits. The selectors required for toll line supervision and the differential relays needed for local supervision are in the cord circuit. Although this increases the amount of equipment in the cord circuit, it reduces the amount of equipment required in the subscribers line circuit, the toll line circuits and the toll subscriber line circuits.

A further feature is that the toll line circuit is so designed as to be slow to operate on calling signals, which eliminates false toll line call signals due to short impulses.

A further feature is that a permanent open trouble condition upon the toll line causes a signal indication at the exchange.

A further feature is that of automaticfiashing recall signals in connection with local subscribers lines as well as with toll subscribers line and toll trunk lines.

A further feature is that certain well-known unattended as well as attended subscriber equipments may be utilized on subscribers lines as well as subscriber and toll lines.

As in the case of certain previous telegraph switching arrangements, regenerative repeaters may be utilized in the cord circuit by a simple substitutionfor the non-regenerative repeaters more usually employed.

The switchboard is designed on a non-multiple basis, that is, it is more particularly intended for use in small ofiices where the number of oper ators does not ordinarily exceed three and where the ultimate number of lines terminating at the ofiice is not to be in excess of about eightyto one hundred. I The desirable feature of home and team operation is provided whereby a call may be answered and supervised by more than one operator f The physical appearance and location of the various elements of the switchboard, including jacks, key-shelf arrangement, etc., may bevaried to fit circumstances. One switchboardshowing the physical arrangement which may be conveniently employed is disclosed in the patentQof Burgess and Knowlton, No. 2,037,193, granted April 14, 1936. The equipment at the central ofiice is concentrated in or associated with the cord circuit; The cord circuit includes various keys. The general functions of the various keys associated with the cord circuit (Figs. 4 and 5) may be outlined as follows: H Typing key TK is a locking key and when oper ated in one position connects the operators circuit to the cord with which it is normally associated; when operated to the other position it connects the cord circuit to an operators circuit to the right or the left.

Key RC (Fig. 5) when operated to the left transmits a ten-second open signal to a circuitconnected to the plug 6 and supplies a holding circuit for a circuit connected to the plug l; when operated to the right with a calling cord plug 6, connected to a subscriber ringing current is transmitted to the subscriber's line connected tothe' plug 6 and holding battery is connected to acir -l cuit connected to the plug 4; when the cord plug 6 is connected to the toll line and the key RC is operated to the right for a couple of seconds a toll call signal is transmitted and the circuit con nected to the answering plug 4 is held closed;j'and when the calling plug 6 is connected to atoll line and key RC is held operated to the right for seven secondsv until the cord lamps flash a recall signal is transmitted over the toll line and any circuit connected to the answering plug 4 is held closed.

The splitting key SK may be operated either to with a typing key operated supplies-ringing current to the circuit connected to the plug 4 and holds the circuit connected to the plug 6 closed; When the answering plug 4 is connected to a toll line with a typing key operated and the ringing key is operated to the right for twoseconds a break signal effective as a toll call on a toll line is transmitted; when operated to the right under similar conditions for seven seconds until the cord lamps flash a recall signal is sent to the toll line and the circuit connected to plug 6 is'held closed.

When no operator is using a position the key K may be operated to disconnect ground from both of its contacts which prevents unnecessary current flow and power consumption during idle periods.

The remaining elements of the system will be sufiiciently understood by reference to the following outline of operations in which the methods of making, establishing, and terminating calls between various types of lines will be described in detail.

Conventional features which would be well understood by those skilled in the art, such as fuses, test jacks, current limiting resistances, power supply connections, night alarm circuits, etc., are either omitted from the description in order to simplify the disclosure of the more fundamental features or disclosed only fragmentarily and incidentally.

In the accompanying drawings:

Fig. 1 indicates how the circuits of the various sheets fit together for convenient description;

Fig. 2 shows a simple form of subscribers line and station circuit;

Fig. 3 illustrates diagrammatically one terminus of a toll line; I

Figs. 4 and 5 together diagrammatically illustrate the equipment of one cord circuit and the equipment of one operators position together with various interconnecting keys;

Fig. 6 illustrates the line termination equipment and repeater of a subscribers line provided with long line equipment commonly referred to as a toll subscribers line circuit for differential duplex operation;

Fig. '7 illustrates a subscribers station to be connected to Fig. 6;

Fig. 8 illustrates a modified arrangement of Fig. 6 adapted for two-path polar operation; and

Fig. 9 illustrates a subscribers station to be connected to Fig. 8.

Connection of one local station to another local station In the idle condition the subscribers circuit includes ringer l in series with a condenser in the tip side of the subscribers line Fig. 2. The tip of the line is grounded at the subscribers station. Consequently, no current flows in the line when it is idle. In order to make a call the subscriber operates the power switch 3 which closes the loop and shunts the ringer. The current flowing through the loop causes the relay A to operate and light the line lamp LL.

To answer the call the operator places the plug 4 in the jack of the subscribers line which opens the circuit of the relay A and extinguishes the lamp LL. The sleeve of the cord is connected through a resistance 5 to ground. The relay SA is operated over the sleeve circuit but the marginal relay MA is not operated. The operation of relay SA causes relay C to operate which closes battery supply to the contacts of the repeater relays RA and RC. The subscribers line now extends from the tip of the plug 4 through the make contact of relay SA, back contact of relay H, back contact of relay T, through the upper Winding of relay RA to the armature of repeater relay RC and thence to negative battery When the armature thereof is operated to the left. The ring side of the subscribers line extends over the back contact of relay MA, make contact of relay SA, to battery on the left armature of relay C. The differential relay DA is included in both sides of the line and does not operate. The typing key TK is now operated to home which extends the subscribers circuit through the polarized relay PR and sending contacts of the operators machine which enables the operator and the subscriber to intercommunicate. Upon receiving the information that a connection to a local subscriber is Wanted. the operator connects the calling plug 6 of the cord circuit to the jack of a subscribers line similar to that of Fig. 2. The sleeve circuit causes the relay SC to operate but the relay MC is a marginal relay and does not operate because of the resistance 5 in the ground connection of the sleeve. Because the line of the called station is open at the subscribers station the differential relay DC operates and causes the cord lamp CL to light and operates relay FC to hold the calling subscribers line closed. The operator rings the called subscriber by moving the key RC to a position corresponding to the right on the drawing. The key has a contact to maintain the communication circuit towards the subscriber making the call. Moreover after the release of the key and inasmuch as the relay R operates and locks operated under control of the relay DC, and. causes the relay FR to operate, the line of the subscriber making the call is closed from the left lower normally made contact of key RC to battery on the right-hand make contact of relay C through the inner upper contacts of relay FR. The line of the calling subscriber is also closed and 20-cycle ringing current is supplied from a source of ringing current I over a make contact of relay FR to the tip of the called line which causes the ringer l to be actuated.

The called subscriber answers by actuating the key 3 thereby applying power to his teletypewriter motor (through contacts and mechanism not shown) and closing the line. When the line closes the differential relay DC is deenergized and the lamp CL goes out. All supervisory lamps are now extinguished and the differential relays in each side of the cord circuit do not operate as the subscribers communicate. The operator may monitor and then retire from the circuit by restoring the key TK to the normal position.

Recall or disconnect signals from a local subscriber In order to signal the operator a subscriber may momentarily open and reclose the power switch 3. For obvious reasons this causes the differential relay DA or DC associated with the line to operate which lights the associated cord lamp AL or CL and also causes the relay FA or F0 to operate. The operated one of these relays locks up. Assuming the relay FC to operate, for example, the locking circuit extends from battery over back contact of relay FR, winding of relay FC, the make contact thereof through the back contact of relays H and T and thence to ground on the upper inner make contact of relay SC. When the line circuit is closed again the particular relay DA or DC which has been operated. releases and removes the ground connection from the lighted lamp AL or CL. However, the locked up relay FC supplies a periodically interrupted ground to the lamp which causes it to flash until the operator operates a typing key, such as key 'I'K, to the left to connect her machine to the recalling line which causes the operation of the relay H or the relay T to release the relay FC and extinguish the lamp CL.

For a disconnect signal the subscriber opens the power switch permanently which operates the differential relay DA or DC nearest his line which causes the associated lamp AL or CL to light and remain lighted. Although the relayFC operates and supplies interrupted ground to the lighted lamp it does not flash because a steady ground connection is also supplied from a lower make contact of whichever relay DA or DC happens to be operated.

Connection of a local line to a toll line The operator receives a call from a local subscriber as previously described and connects the calling plug 6 to the toll line jack 8, such as shown in Fig. 3. The sleeve of the toll line jack is grounded with no series resistance and this causes both the relays SC and MC to operate. The relay MC short-circuits the upper winding of the relay DC and connects the ring side of the plug 6 through the winding of the relay ST to negative battery. The relay MC also disconnects the lamp CL from its path to the winding of relay FC and connects it over a path through the back contact of the relay ST to the left brush arm of the supervisory selector SEL. The relay SC closes the tip of the transmission path from the toll line 9 through the make contact of the relay MC and a make contact of the relay SC, which is now operated, over contacts of the key RC to the repeater Ra, R in the cordcircuit. The operator calls the distant office by operating the key RC to a position corresponding to the right in the drawing for about two seconds. This opens the toll line but holds the communication circuit closed towards the answering side of the cord.

At the distant exchange the line is terminated in a toll line circuit similar to that of Fig. 3 or its equivalent. The line relay L releases and the relay TA which normally stands with its armature on its left-hand contact is operated to its righthand contact after the current in the upper winding has charged the condenser l 0 surficiently so that the current in the lower winding takes control of the armature. The object of this condenser and winding arrangement on the relay TA is to delay the operation of the relay TA so that short line interruptions of less than about one second will not cause a false call upon the line. Operation of relay TA to its right-hand contact puts ground upon the lead II extending to the toll line lamp TL thereby causing that lamp to light. The distant operator connects an answering plug 4 into the jack of the toll line thereby opening the circuit of the lamp TL and extinguishing the lamp and extending the communication circuit into the cord of the distant office from a toll line connection. Inasmuch as relays MA and SA at the distant station will both operate, the communication circuit will proceed from the tip of the plug and jack through a contact of relay MA shunting the differential relay DA over the upper make contact of relay SA, a back contact of relay H, a back contact of relay T and through the winding of repeater relay Ra to the armature of repeater relay Rc. As will be understood from the previous description the distant operator may operate a typing key TK and connect the cord circuit teletypewriter for communication and will thereafter proceed to extend the call through the station as may be desired.

Transmission and reception of recall and disconnect signals over a toll Zine Returning now to the central office originating the call and assuming that the operator wishes to recall the operator at the distant central office, this will be accomplished by operating the key RC to a position corresponding to the right on the drawing until the cord lamp CL flashes. This will occur in about five or seven seconds after which the key should be released. The operation at the station originating the recall signal is that the relay L (Fig. 3) releases and one second later the relay TA operates to the right. This supplies ground to the ring of the plug and jack, thereby causing the relay ST to operate and connect the stepping magnet ROT on the selector SEL over a contact of relay ST to a source of interrupted ground operating at about sixty interruptions per minute. The selector steps up and when the right-hand brush arm thereof reaches contact No. 6 the relay RD operates and short-circuits the contacts of the key RC which were opening up the line, thereby reclosing the line, reoperating the relay L and releasing the relay ST. The selector remains on the sixth contact and the lamp CL continues to flash because it is con-' nected in a circuit extending from battery through the lamp CL, a make contact of relay MC, a back contact of relay ST, left-hand brush arm of selector SEL to interrupted ground. The lamp continues to flash until the operator connects her teletypewriter instrument to the circuit by means of a typing key TK. Operation of the typing key closes the circuit through the relay RR which upon operating closes the circuit which extends from battery on the release magnet RLS of the selector over the make contact of the relay RR to ground, thereby causing the selector to return to normal. The same ground which operates the release magnet RLS also operates the relay RR which again opens the ground connection to the release magnet and thus makes it possible for an operator to receive a recall or disconnect signal from a toll line even though the typing key is already operated.

The transmission of a disconnect over a toll line is accomplished by operating the key RC to a position corresponding to the left in the drawing until the cord lamp CL lights steadily. Since the relays SC and MC are operated the operation of the key terminates the cord circuit of the repeater and opens the circuit towards the toll line. The release of relay L, operation of relay TA to the right and operation of relay ST causes the selector to step and inasmuch as the circuit of the relay RD is not completed on the sixth contact of the selector the selector continues to step until it reaches the tenth contact at which time relay RD operates. The cord lamp CL becomes continuously lighted over a circuit extending through the left-hand brush arm of the selector to ground upon the tenth contact and continuously lighted until it is extinguished by removal of the plug cords from the associated jacks, whereby the upper of the two off-normal contacts of the selector closes a circuit through the release magnet RLS to a back contact of the relay C which is released when the cord is idle.

The reception of recall and disconnect signals over a toll lineeis as follows: Inasmuch as the line is opened the relay TA is operated to the right Sending a recall signal from the answering end of the cord circuit When the plug 4 is connected to a toll line a recall signal may be transmitted to a distant central oflice by operating the recall key RK to the right with the operators teletypewriter circuit connected to the cord by the throwing of the key TK, and holding the key RK in the operated position until the cord supervisory lamps flash. Battery on the right-hand contact of the key RK maintains the circuit toward the plug 6 closed and the left-hand side of the key interrupts the communication circuit toward the plug 4. When the selector reaches the sixth contact the righthand brush arm thereof causes the relay RD to operate and shunt the left-hand contact of key RK which is opening the line, thereby closing up the line and reoperating the relay L in a toll line circuit. The relay operation is otherwise generally the same as previously described in connection with sending a recall signal over the toll line by means of key RC except that the operations take place with respect to the other end of the cord.

Ringing subscriber an answering side of cord Provision is made for ringing on a subscriber line from the answering side of the cord, that is, the side connected to the plug 4. This is accomplished by connecting the operators machine to the circuit by means of the typing key TK and then operating the key RK to the left. This causes ringing current to proceed from the ringing generator I over the tip side of the subscriber line and at the same time the battery on the operated contact of key RK maintains the communication circuit closed toward the plug 6. Under this condition upon first connecting the plug 4 to the subscribers line the relay DA operated and caused the relay FA to operate. Likewise, a typing key TK was operated which opens the locking path for the relay FA so that when the subscriber answers the relay FA will release.

In all cases where a cord is connected to an idle subscriber line it is necessary to hold the cord repeater closed on that side until the subscriber answers in order that the subscribers machine on the other side of the cord will not run open. The upper contacts of relay DA provide this holding path with the typing key either operated or nonoperated and open the ath as soon as the subscriber answers. In addition, when a subscriber, connected to a toll line, disconnects, provision must be made to insure that the open condition is not transmitted through the cord to the toll line. The upper contact of relay DA also performs this function.

Connection of a toll line to a local line The toll line call is acknowledged by connecting the plug 4 to the jack of the calling line which arranges the side of the cord next to the plug 4 for a toll line connection. The calling cord is connected to the subscriber line jack by means of the plug 5 and the sideof the cord adjacent the plug 6 is then arranged for a local connection. A ringing signal is sent to the subscriber in the same manner as previously described in connection with a local to local connection and when the subscriber answers the cord lamp is extinguished. Supervisory signals are sent from and received in the cord circuit in the same manner as previously described.

Toll line to toll line connection When a through connection is to be established the marginal sleeve relays MA and MC at both ends of the cord operate and thereby arrange the cord for toll line connection on the answering and calling sides. Any incoming supervisory signals, such as recall and disconnect, operate both supervisory lamps and are repeated through the cord repeater. These signals are extinguished by momentary operation of the teletypewriter key TK.

Toll, line subscriber connections-Geneml In furnishing service to subscribers it occasionally happens that certain subscribers are too far from the exchange oflice to be furnished service over a simple loop. For example, with certain types of cable the maximum physical mileage of cable which may be included with satisfactory operation is of the order of forty miles. In such cases service may be furnished to such subscribers over line circuits operating on an upset duplex, two-path polar, or differential duplex basis. A terminating circuit suitable for use with such a toll line is required at the central oilice in addition to the toll telegraph repeater. There is described herein and illustrated in Fig. 7 the equipment for cooperating with such a toll line subscribers circuit as shown in Fig. 6. This arrangement is adapted for diiferential duplex operation. With a slight modification, namely, the utilization of .a single additional armature and contact on a relay as will hereinafter be described, the transmission may be accomplished by a two-path polar circuit as shown in Figs. 8 and 9.

Toll subscriber line equipment for differential duplex operation Consider now the operation of a cord circuit such as shown in Figs. 4 and 5, a subscribers line termination such as shown in Fig. 6, and a subscribers station equipment such as shown in Fig. 7 connected to the line termination equipment by means of the line l3.

To make an incoming call the subscriber closes switch II. This supplies power to the station equipment and causes relay I2 to be operated. This connects marking battery to the line 13. In this case marking battery is arbitrarily chosen as positive battery. In Fig. 6 the polar relay E is aperated by positive potential upon the line it and the ordinary relay D is also operated. Relay E operates relay F which operates relay C6. Relay C6 closes a circuit to ground to operate the relay J and to cause lamp TLB to light under the control of .a contact on the line jack l6. Relay J replaces the positive battery on windings of relays D and E with negative battery over a circuit extending from negative battery over the upper make contact of relay J to winding of relay E. Relay C6 also connects line lead l3 to the repeater R over conductor 14 which closes the loop and applies marking battery to the line relays of the repeater. A circuit is then closed through the upper winding .of relay B over the back contact of relay A6, thusoperating relay B to close contact l to maintain the operating circuit for relay F which is a slow release relay.

When the operator answers she places the plug 4 into the jack IS with the same effect in the cord circuit as in answering a subscriber line call. This also prepares a path for the relay A6 over the jack terminals. The termination circuit from the repeater R is now closed to the tip of the plug and cord and the lamp TLS is extinguished. Communication may take place between the subscriber station and the operator or another subscriber. Relay B follows the teletypewriter signals but relay F is slow to release and relays C6, D and J remain operated.

Relay B follows the signals and supplies ground and open-circuit alternately to the ring of the jack to balance the relay DA or DC in the cord circuit. In this manner signal transmission is prevented from causing operation of relay DA or DC.

Consider now a break signal from the subscriber at the station of Fig. '7. This opens the path through the relay B which causes the relay B to open the contact I5 for a time sufficient to allow relay F to release. This releases relay C6. This connects the line I3 over a contact of relay J to ground by way of a back contact of relay G6, a front contact on the lower armature of relay J, through the high resistance I611. The charge stored in the capacity of the line passes through the high resistance lfia before the slow release relay J releases. Upon release of the relay J the operating path for the relays D and E is transferred back to the line circuit 13 but inasmuch as negative or spacing potential is now applied to the line circuit the relay D is held operated but relay E remains released during the continuance of the break signal. Upon completion of the break signal marking potential is again applied to the line [3 which holds relay D operated, causes relay E to operate, which causes relay F to operate, which reoperates relays CB and J to restore the transmission circuit, after which the relay F is held operated by the relay B. Relay B is reoperated to close contact l5.

Consider now a break signal originating in or beyond the cord circuit of Figs. 4 and 5. Relay B opens contact l5, which releases relay F, which releases relays C6 and J. Relay J connects the operating path for relays D and E to the line l3 but inasmuch as marking potential is applied from the line 13 during the break period the relay E is operated, which in turn reoperates relays F, C6 and J. Upon reoperation, relay J causes relay E to release by virtue of negative battery supplied locally from the source I! over a back contact of relay C8 and front contact of relay J. If the break signal is continued beyond this time, this cyclic operation and reoperation may continue as relay F again releases upon the release of relay E because relay B maintains contact [5 open and, therefore, the break signal condition is continued until the loop circuit is reclosed to operate relay B which reoperates relays F, C6 and J.

Consider now a disconnect signal transmitted into the cord circuit of Figs. 4 and 5 from the station of Fig. 7. The attendant at the station of Fig. 7 opens the switch II which sends an open signal through the repeater R to the cord circuit, thereby releasing relays B and F, which thereupon releases relay CB. Upon release of relay C6 and during the holding time of relay J the charge on the line will be discharged to ground through the high resistance 16a. Upon release of relay J the relay D will release and cause the operation of relay A6 over a circuit from battery through the winding of relay A6, a contact upon jack E6 to ground upon the back contact of relay D. When relay A6 operates it connects ground to the ring of jack to operate the differential relay DA or DC in the cord circuit because at this time the tip lead through the differential relay is open. Relay A6 also closes the loop circuit to the repeater from a source of plus 130 volts over an upper make contact of relay A6 through the upper winding of relay B and conductor Ha to the repeater. The lighting of the disconnect lamp in the cord circuit in the manner previously described will call the attention of the operator to the disconnect signal and appropriate action will be taken as previously described.

If the subscriber station attendant disconnects during the time a break signal is being transmitted from the cord circuit, relay B will already have been released and the release of relay D will cause the operation of relay A6. Since relay A6 upon being operated maintains ground on the ring lead to the jack and plug of the cord circuit, a disconnect signal will be produced.

Consider now the transmission of a recall signal from the station of Fig. 7. The line circuit is temporarily opened as in the transmission of a disconnect signal which causes the release of relay B to open contact I5, and the release of relays F, C6 and J so that relay D is connected to the line l3 and is released, which connects ground over the jack to operate the relay A6, which connects ground to the ring of the plug and jack of the cord circuit. When the recall key I8 is released, relays D and E reoperate and relay E reoperates the relay F, which in turn operates relay C6 to close the line circuit and also reoperates relay J and the repeater R acts over the conductor to reoperate relay B. When the line circuit is reclosed the relay B holds the relay F reoperated. Inasmuch as relay D is operated relay AB is released which removes the ground connection from the ring lead to the cord. The momentary connection from ground to the ring lead of the cord with the tip of the cord open causes the differential relay DA or DC of the cord circuit to operate. Upon release of the differential relay when the cord circuit is again closed the cord circuit supervisory lamp AL or CL will flash in the manner previously described.

The recall signal from the station of Fig. '7 may be transmitted and indicated correctly even though a break signal is being transmitted from the cord circuit or from a station beyond the cord circuit.

Consider now the operation in calling the subscribers station. The plug 6 of the cord circuit Will be inserted in the jack I6. Relay A6 will be operated by virtue of ground at the back contact of relay D. Relay A6 connects ground to the ring of the jack and plug to operate the differential relay in the cord circuit and hold the cord supervisory lamp lighted. The operator transmits ringing current in the manner previously described from the cord circuit over the tip of the plug and jack through contacts of relays A6 and C6 to operate the relay H6 in series with a condenser to ground. In operating, relay H6 operates relay J and connects the ringing current generator I over the contact of relay H6 and contact of relay J and back contact of relay C6 to the line I3 which causes the ringer l at the subscribers station of Fig. '7 to operate. Upon cessation of the ringing current relay H6 releases and during the time required to allow slow release relay J to release the resistance Ilia discharges the line and prevents momentary operation of relays D or E when they are reconnected to the line.

When the subscriber answers the relays D and E operate, relay E operates relay F, which operates relay C6, which closes the line up to the repeater R and operates relay J, which closes a holding path for relay D over the back contact of relay A6, which was released when relay D operated upon the closure of the line circuit. Upon the release of relay A6 it closes the tip of the plug and jack through the upper winding of relay B to the repeater R and. opens the ground connection from the ring of the plug and jack to extinguish the supervisory lamp AL in the cord circuit.

Two-path polar toll subscriber line For two-path polar operation the subscribers station will be in accordance with Fig. 9 and the line circuit in accordance with Fig. 8. Operation of relay H2 in Fig. 9 connects the subscribers set for operation over a two-wire line comprising a receiving leg l3 and a sending leg BA. The ringer I, the sending relay 20, the receiving relay 2!, the sending contacts 22, the recall key it, the power supply switch II and other equipment will be generally the same in Fig. 9 as in Fig. '7.

Consider now Fig. 6 in comparison with Fig. 8. It will be seen that Fig. 8 includes two additional leads connected to one armature and one contact respectively of relay C6. These leads are included in the transmission conductor 13A. A resistance 24 is connected from the inner lower make contact of relay C6 to the outer lower armature thereof. Except for these differences, Fig. 8 is the same as Fig. 6. When relay C6 is operated its armature closes the transmission conductor [3A and when relay C6 is released the conductor I 3A is opened. The repeater R of Fig. 8 is generally similar in function and mode of operation to repeater R of Fig. 6 except that it is designed for two-path polar operation. It will be seen that the transmission conductor I8 is extended to the repeater R in Fig. 8 through the transmission conductor I4 in Fig. 8 in the same manner as in Fig. 6 and that it extends through the windings of relays E and D in Fig. 8 over the back contact of relay C6 and back contact of relay J in the same manner as in Fig. 6. Consequently, a subscribers line equipment may be furnished so that by leaving the extra armature and contact of relay C6 idle it may be employed for differential duplex transmission as in Fig. 6 or by connecting up the armature and contact to the line of conductor I3A it may be used for two-path polar operation as in Fig. 8.

When relay C8 is released under the condition of two-path polar operation the line receiving relay of the repeater R is held to its spacing contact by negative battery supp-lied from the source I! through resistances 23 and 24 over the back contact of relay C6.

The operation of the recall key [8 at the subscribers station connects the line l3 to the line 18A at the subscribers station and isolates them from the transmission circuit at the subscribers station. Under this condition when resistance [8a of Fig. 6 discharges the line as hereinbefore described it discharges both conductors l3 and MA and thus prevents false operation of relay E in the case of transmission of recall signals or ringing signals.

One other condition remains to be discussed; this is the case known as upset duplex transmission. Marking battery on line 13 is negative at the subscribers station of Fig. 8. Now refer to Fig. 6. To make the circuit operate under this condition it is necessary that the polar relay E be connected reversely and that provision be made to supply positive current rather than negative to the relay E under the break signal condition. To do this the upper end of resistance 23 may be disconnected from the negative terminal of battery I! and connected to the positive terminal of a grounded battery or source (not shown).

It will thus be seen that essentially the same circuit with slightly different wiring will serve to terminate subscribers toll (repeatered) lines working on the differential duplex, upset duplex, or two-path polar basis.

In addition to attended stations a subscriber may be provided with unattended service which enables him to receive messages when no one is present at the station by utilizing a subscribers line and station, such as shown in Fig. 3 of the application of Singer, Serial No. 89,828, filed July 9, 1936 to which specific reference is made as a part of the present disclosure.

To utilize a regenerative repeater in the cord circuit as hereinbefore mentioned may be done; the relay Ra and its contacts are removed from the circuit and its two leads on the left of its winding transferred to a regenerative repeater such as shown in Fig. 2 of Vernam Patent 1,619,897, March 8, 1927; relay Re and its contacts are removed and its two leads on the right of its winding are also transferred to the regenerative repeater; the inner left armature of relay C may control the motor start circuit of the regenerative repeater. The four transmission leads and the motor start lead. are so shown in the Vernam patent, although of course, in the present arrangement the regenerative repeater will start on open line and repeat open and close signals rather than polar signals.

What is claimed is:

1. In a telegraph exchange system, a link circuit for manual lines, a differential relay in each end of said link circuit having opposing windings for the flow of signaling currents, a single conductor transmission line towhich an end of said link circuit may be connected, a relay in and controlled by signal current traversing said transmission line, a path controlled by said relay extending to said differential relay over a terminal of said link circuit whereby current is supplied to said difierential relay in one winding to balance the signal current in another winding and prevent the operation of said differential re- 1ay by signal current.

2. In a telegraph manual exchange system, a link circuit, an operators circuit connectable at will to any one of a plurality of link circuits, a ringing key individual to a link circuit and a ringing key individual to an operators circuit.

3. In a telegraph manual exchange system, a cord circuit including a cord lamp, two types of line circuits to which said cord circuit is connectable, a selector in said cord circuit, a relay selectively responsive dependent upon the type of line to which said cord circuit is connected for connecting said lamp to an energizing circuit directly or under the control of said selector.

4. In a communication circuit, a selector, a key under the control of an operator, means whereby recall conditions established at a remote point 75 actuate said selector, a recall signal produced by actuation of said selector to a given point, a release winding for said selector, said winding being energized by actuation of said key to a given position, and means whereby if said key is already operated to said given position prior to the actuation of said selector to said given position said release winding is not energized.

5. A system according to claim 4, including means whereby if said key is already operated when said selector is actuated, release and reoperation of said key energizes said release winding.

6. In a supervisory circuit arrangement for a telegraphic line, a relay (A6) included in a path closed at a jack when a cord circuit is connected to said jack, another relay normally opening said path when said line is closed for intercommunication, a relay chain for actuating said relay to maintain said path open upon change of polarity of break signal length upon said line at a distant point, means whereby said path is closed upon an opening of said line of break signal duration at a distant point, and asupervisory signal established by actuation of said first named relay by closure of said path.

'7. In a telegraphic exchange system, a cord circuit, a selector therein, means for connecting said cord circuit to single conductor or two-conductor lines interchangeably, and means whereby said selectors control the sending of supervisory signals over said single conductor lines.

WAYNE V. K. LARGE. GEORGE A. LOCKE.

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