US2073468A - Communication system - Google Patents

Description

March 9, 1937. K. E. FITCH 2, 7 COMMUNICATION SYSTEM I Filed April 25, 1936 3Shet-Sheet 1 DlFI-E'IENTIAL March 9,1937. K. E. FITCH 2,073,468'

' pommumcnron SYSTEM Filed April 25, 1936 3 Sheets-Sheet 2 FIG. 2

POUR/Z50 IN VE N TOR /r; 5. FITCH QWM - POLAR/ZED ATTORNEY K. .E. FITCH COMMUNICATION SYSTEM Filed April 25,-1936 March 9, I 193 7.

FIG. 3

. :5 sheets sheet '3 POLAR/ZED INVENTOR K. E. FITCH WJM A TTORNEY Patented Mar. 9, 1937 UNlTED STTES PATENT OFF ICE Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application April 25, 1936, Serial No. 7.6.335

10 Claims.

This invention relates to communication systems and particularly to telegraph exchange systems in which operators serve to establish connections between subscribers lines. 5 The objects of this invention are to facilitate the work of the operators in answering and completing calls; to safeguard against the transmission of false communications; and otherwise to secure improvements in systems of this character.

A feature of the invention is a system in which the subscribers lines appear in multiple answering jacks at a plurality of operators positions and which is so arranged that the first cord in- 15 serted by an answering operator in the jack of a calling line causes the completion of a transmission circuit between the line and the operators position transmitter and typewriter, Whereas, if, a second cord is subsequently inserted by a sec- OO nd operator in another jack of the same line, the transmission circuit between the line and the second operators position is held ineffec- .tive, and the act of inserting the second cord automatically disables the transmission circuit to the first position to prevent any further communication with the subscriber, and a signal lamp is lighted at :the position of the second operator to advise her that another operator has previously answered and that she should with- 30 draw.

Another feature of the invention is a circuit arrangement such that the prolonged release of the signal receiving relays at both the first and second operators positions, caused by the disabled transmission circuits resulting from the insertion of the second cord, does not cause the typewriters at these positions to run in an idling or open movement. And the operation of the. keyboard of the teletypewriter in this condition 40 will not cause printing to take place. To prevent such idle operation of the typewriters, the circuits are arranged to maintain the receiving magnets in an energized condition the same as when the positions are normal. The virtually 45 locked condition of the first operators typewriter informs her that another operator has subsequently answered the same line and that she should postpone her communication with the subscriber until the second operator withdraws.

50 When the second operator to answer a line observes her busy signal lamp and finds her typewriter locked against operation, she recognizes that another operator has preceded her, and she removes her cord circuit from the line. This re- 55 stores the transmission circuit between the line and the first operators position and unlocks the first operators typewriter so that she may proceed to communicate with the subscriber.

These and other features of the invention will be described more fully in detail in the following specification and will also be set forth in the appended claims.

The specification should be considered in connection with the accompanying drawings, in which: 10

Fig. l discloses a telegraph subscriber's line, illustrating the equipment at the subscribers station and also the line circuit at the central ofiice;

Fig. .2 illustrates an operators position at the central office, showing in the upper portion thereof .one of the operators cord circuits and in the lower portion "thereof the common posi tion equipment; and

Fig. 3 shows a second operators position in the central office, illustrating one of the cord circuits .and the common position equipment.

Each of the telegraph subscribers stations, such as the .one disclosed in Fig. l, is equipped with a keyboard transmitter for transmitting requests to the central ofiice operators and for sending messages to other subscribers. Also the substation is provided with a teletypewriter for printing communications received over the line from central oflice .operators and from other telegraph subscriber-s. Since these devices are well known in :the art, they are :not .disclosed in detail herein, it being sufiicient to illustrate them in diagrammatic manner. The subscribers substation is further equipped with :a :driving motor, :a source of power, controlling relays, a start :key, and aringer.

At the central oflice the subscribers lines appear in jacks at the :operatordpositions. These lines may .be multipled to jacks in 'a plurality of 40 operated positions for use both in answering and completing .calls, .or they appear in multiple jacks at answering operators positions and also in multiple jacks at other operators positions where calls to the :lines are completed. The subscribers line disclosed-in thedrawings'is illustrated as appearing in the imultiple answering jacks at the two operators positions shown in Figs. 2 and .3. This line mayhave further appearances in the answering jacks at other operators positions .50 andmay also appear in the multiple jacks at positions where calls to this line are completed.

The operators cord circuits are provided with answering and calling plugs, with telegraph 're-' peaters for repeating the telegraph signals, and

with necessary relays and other equipment for controlling the various operations involved in the establishment of connections and in giving the necessary supervision. The cord circuits illustrated in the drawings disclose only as much of this equipment as is necessary to an understanding of the present invention, all parts not particularly essential in such an understanding being omitted for the sake of brevity. For example, the supervisory lamps and circuits, the operators ring keys, and some of the equipment associated with the calling end of the cord circuits have been omitted. Each of the operators positions is equipped with a telegraph keyboard transmitter and a teletypewriter in order that the operator may communicate with the subscribers and with other operators in the system. The operators position is also equipped with signal devices to enable her to determine the condition of subscribers lines.

While only one subscribers line has been illustrated, it will be understood that the central office operators may complete connections with their cord circuits between local subscribers lines, or they may extend a calling subscribers line over a trunk or toll line to a distant ofilce, or they may complete calls incoming over trunks or toll lines from distant ofifices to local called subscribers.

For a better understanding of a telegraph exchange system in which the operators in the central oflices complete both local and interoffice telegraph connections reference is made to the copending application of Locke and Kinkead, Serial No. 459,684, filed June 7, 1930, which discloses operators positions of the type to which the present invention is particularly applicable, and which contains a detailed disclosure and description of the different operations involved in the establishment of telegraph connections.

Since the subscribers lines in the present system appear in a plurality of operators positions, it is possible that two or more operators, seeing the line lamps burning, will attempt to answer the calling line at about the same time. And the cord circuits and position circuits are so arranged that any operator, who first answers a subscribers line, will succeed in establishing a transmission circuit from the line through to her position equipment, which will enable her to communicate with the subscriber. Should, however, another operator, attempting to answer the same line, subsequently plug one of her cord circuits into a jack of the line, this act on the part of the second operator disables the transmission circuit previously established between the subscriber and the first operator, prevents the establishment of a, similar transmission circuit between the subscribers line and the second operator, and causes a busy signal lamp to light at the position of the second operator, notifying her that another operator has already answered the call and that she should withdraw from the line. Moreover, the act of the second operator in attempting to answer the subscribers line causes the energization of the magnets of the typewriters at both positions to prevent these machines from operating. The disabling of the typewriter at the first operators position acts as a signal to her that another operator has entered the connection and that she should wait until the second operator withdraws. The signal lamp at the second operators position is a signal to her that another operator has already answered the call and she should withdraw her cord circuit from the jack of the subscribers line. As soon as she does remove her cord circuit, the transmission circuit between the first operator and the subscribers line is again rendered eifective, and the operators printer is unlocked, and communication between the operator and the subscriber may now proceed.

A better understanding of the invention may be had from a detailed description of the operation of the system. For this purpose assume that the subscriber at the substation shown in Fig. 1 wishes to make a call. To initiate a call, he closes the start key I06. Key I06 completes a circuit from the source of current I63 for operating the relay I05. Relay I looks through its right-hand contact independently of the key I03. Relay Hi5 closes an obvious circuit for starting the motor I02 and also closes a circuit for the relay HM. Relay I M at its back contact disconnects ground from the line and at its front con tact closes the line loop. A circuit may now be traced from the positive pole of telegraph battery I69, resistance I IE3, left normal contact of relay iii, left winding of line relay H2, resistance H3, conductor H4, front contact of relay I64, contacts of the subscribers keyboard transmitter I03, key I I5, signal receiving relay I ill, conductor BIS, inner right back contact of relay III to ground through the contacts of relay Ill. The battery N39 is a 48-volt battery. This is called the telegraph battery and is illustrated throughout the drawings by the convention using four units. This four-unit convention is employed to distinguish from the signaling battery which is a 24-volt battery and which is illustrated in the drawings as having two units. The line relay H2 operates in the circuit above traced and closes an obvious circuit for the slow-release relay II8. Relay II2 also closes a circuit from its grounded contact, over conductor I I 9, outer right back contact of relay III through the winding of relay ill to the negative pole of the telegraph battery. Relay i I8 operates but without elTect at this time. Relay ill in operating closes a circuit from the signaling battery, through the inner left contact of said relay, through the windings of relay Ill in series to ground. The windings of relay III are difierential, and current flowing through them in the circuit traced does not cause the relay to operate. Relay Ill also closes a circuit from the signaling battery through the outer left contact of said relay, conductor I23 and thence in multiple through the lamps 2&2, 263, etc., associated with the multiple answering jacks at the several operators positions. These lamps light as a calling signal to the operators. Relay ii! at its inner right contacts removes ground from the line conductor IIS and substitutes therefor the negative pole of telegraph battery. The line circuit may now be traced from the positive pole of the telegraph battery we, resistance IIEl, normal contacts of relay III, through the left-hand winding of line relay H2, thence over the subscribers loop and returning over conductor H6 through the inner right back contact of relay l I I, right front contact of relay II'I, resistance I 2i to the negative pole of the telegraph battery. This increases the current flowing over the subscribers line.

Assume that the operator at position 293, being idle at the time, observes lamp 282 burning and answers the call with her cord circuit To do this, she inserts the answering plug 2% in the multiple jack 295 of the calling line. A circuit is now closed from the negative pole of signaling battery, potentiometer resistance 206, winding of relay 201, right winding of polarized relay 208, through the sleeve of the plug and the multiple jack, through the right winding of relay III to ground. The current flowing in the polarized relay 208 is in the proper direction to operate this relay. Relay 201 also operates in this circuit. Relay 208 closes obvious operating circuits for relays 209 and 2I0. Relay 209 closes a circuit from signaling battery through the winding of relay 2 I I, resistance 2I2, contact of relay 209, left winding of relay 208, thence as traced through the right winding of relay III to ground. The combined resistance of the series-parallel circuit through the right winding of relay I I I is such that sufficient current flows through this winding to cause the relay to operate. The resistance of the circuit through the relay 2I I, resistance 2I2, and the left-hand winding of the polarized relay 208, being comparatively low, causes an increase in the potential on the sleeves of the multiple jacks 205, 2I3, etc., these sleeves being multipled together by the conductor I22. Since the sleeves are now negative with respect to ground the current in the right-hand winding of relay 208 reverses, but the current in the left-hand winding is greater and is in the direction necessary to hold relay 208 operated. Relay I I I in operating opens the circuit of relay II1, which releases and extinguishes the lighted lamps 202, 203, etc. Relay I I1 also opens the left-hand winding of relay I I I, and the latter relay now remains energized over the circuit closed from battery in the cord. Relay II I opens the previously traced circuit for supplying telegraph battery to the subscribers loop and replaced'this circuit with a new one, which extends to telegraph battery in the operators cord. The

new circuit may be traced from negative pole ofv telegraph battery I23 in the line circuit, resistance I2I, back contact of relay I24, right winding of line relay II2, inner right front contact of relay I i i, thence over line conductor I I6, through the substation loop and returning over conductor I I4, resistance II3, left Winding of relay II2, left front contact of relay II I, conductor I25, over the ring contacts ofthe jack 205 and the plug 204 through the lower front contact of relay 209, outer right contact of relay 2M, resistance 2I5, lower winding of the polarized repeating relay 2 I6, marking contact of repeating relay 2 I1, resistance 2 I8 to the positive pole of telegraph battery 2 I 9. Since current flows through both windings of the line relay I I2, this relay releases because of its diiferential character. lfielay I I2 in releasing causes the release of relay Before proceeding further with the extension of the transmission circuit to the operators position, an explanation will be given of the operation of the cord circuit repeater, including the polarized repeating relays 2 I 6 and 2 I I. The upper windings of these relays are biasing windings, and, when current flows through these biasing windings in a given direction, the relays tend to operate their armatures to the front or space contacts. The lower windings are the line windings, and, when current flows through these windings in a given direction, the eiiect of the biasing windings is overcome, and the relays maintain their armatures on the lower or marking contacts. When the line winding is opened or rendered currentless by opposing batteries, the relay operates its armature to the space contact, unless at the same time the current through the biasing winding is reversed to maintain the armature on the marking contact. When the transmission is coming from the calling line and is proceeding toward the operator or toward a distant called line, the repeating relay 2I1 maintains its armature constantly on its marking contact, and the relay 2I6 follows the signals and operates its armature from the marking to the spacing contacts to open the transmission line toward the outgoing line.

At the, time the relay 2I0 operated a circuit was closed from the positive pole of telegraph battery 2I9 through resistance 2I8, marking contact of relay 2 I1, biasing winding of relay 2 I6 through the artificial line 22I to ground at the contact of relay ,2 I 0. Similarly a circuit is closed from positive pole of battery 2E9, resistance 22!), marking contact of relay 2I6,biasing winding of relay 2I1 and the artificial line 22I to ground. The current flowing in these biasing windings is in the direction which tends to cause the armatures to move to the spacing contacts. time also has a circuit traceable from positive telegraph battery, resistance 22!), marking contact of relay 2I6, lower or line winding of relay 2I1, normal contact of relay 222, inner upper contact of relay 209, resistance 223, to the negative pole of telegraph battery. The current flowing through this circuit is in the proper direction to cause the line winding of relay 2I1 to oppose the biasing winding, thereby holding the armature on the marking contact. circuit previously traced is in the direction to cause the line winding of relay 2 I 6 to overcome its biasing winding, thereby maintaining the armature on the marking contact.

The operator, having inserted her cord circuit in the answering jack of the calling line, now operates the typing key 225 individual to the cord to prepare her position equipment for communication with the calling subscriber. The closure of key 225 completes a circuit from positive telea graph battery through the winding of relay 226, normal contacts of relay 2I4, key 225, through the right winding of polarized signal receiving relay 221 to ground. The current flowing in this circuit is in the direction such that relay 221 tends to move its armature from the marking contact to the spacing contact. Relay 226 operates 'in the circuit traced and extends the grounded conductor leading from the right winding of relay 221 to the contacts of key 225 through the r outer right contacts of relay 226 and the winding of relay 2 I4 to positive telegraph battery. Relay 2 I4 operates and closes a holding circuit for relay 226 at the same time opening the original operating circut of relay 226. Relay 2I4 also closes an obvious circuit for the energization of relay 239. The operation of relays 2I4 and 226 results in the extension of the telegraph transmission circuit into the operators position. This circuit may now be traced from the negative pole of the telegraph battery I23 in the line circuit, thence over the subscribers line loop and returning as above explained over the ring conductor I I4, thence to the ring of the jack and plug, through the closed contacts of relay 209, outer left close-d contacts of relay 226, conductor 228, through the operators transmitter 229, key 230, through the left winding of polarized receiving relay 221, conductor 23I, inner left front contact of relay 225, through the line winding of relay 2I6, marking contact of relay 2I1, resistance 2I8 to the positive pole telegraph battery. The current flowing in this circuit through the line winding of relay 2i6 is in the same direction as before, with the result that the relay maintains its armature on Relay 2I1 at this the marking contact. The current flowing in this circuit through the line winding of relay 221 is also in the proper direction to oppose the effect of the biasing winding, maintaining the armature on its marking contact.

Considering the operators position for the moment, while the armature of the signal relay 221 is on its marking contact, a circuit may be traced from positive telegraph battery through said armature and its marking contact, resistance 232, through the printer magnet 233, resistance 234 through the contacts of the closed key 235 to the negative pole of telegraph battery. The purpose of this closed circuit is to maintain the magnet 233 energized to prevent the operators typewriter from running in an open or idling condition while no signals are being received by the relay 221. Furthermore the relay 236 at the operators position remains in an energized condition so long as the armature of the relay 221 does not rest on its space contact for any appreciable length of time. The energizing circuit of relay 236 extends from the positive pole of telegraph battery through the winding of said relay, resistance 23? through the contacts of key 235 to the negative pole of battery. Each time the armature of relay 22'! moves to its space contact while signals are being received a circuit is closed from the positive pole of telegraph battery through said space contact, conductor 238 to the upper terminal of relay 236. This path constitutes a direct short circuit on the winding of relay 236. The relay, however, maintains its armature energized during the brief periods that the signal receiving relay 22! holds its armature on its space contact in the normal course of signaling. However, as will be explained later, should the relay 227 move its armature to the space contact for an extended interval, the relay 236 then releases its armature. With the relays 226 and 239 operated, a circuit is also closed for operating the relay 240 in the operators position. This circuit may be traced from battery through the winding of relay 240, conductor 24l, inner right contact of relay 228, left contact of relay 239 to ground at the bottom contact of relay 2H]. Relay 22!) operates but does not perform any function at this time.

The operator having answered the subscribers call, by inserting the plug of her cord circuit in the subscribers line and operating her typing key 225, and the relays 209, 2M and 226 having been energized as above explained, and the transmission circuit having been completed from the subscribers line through the cord circuit to the operators keyboard transmitter and signal receiving relay, the equipment is now in condition for communication between the operator and the subscriber. The operator challenges the subscriber by manipulating the keyboard transmitter 229 to send telegraph code impulses over the transmission circuit to operate the polarized signal receiving relay I61, which in turn operates the printing magnet ml at the substation. Each time the transmitting contacts are opened at the operators position, the line windings of polarized relays 22'! and 2H1 are deenergized and these relays shift their armatures to the space contacts. The magnet 233 follows the operation of the armature of relay 22?, and the characters set up by the operator on her keyboard are printed on her typewriter. The magnet ll'il follows the operations of relay Hill, and these characters are also printed on the typewriter at the subscribers station. On each opening of the transmission circuit through the line winding of relay 216 the armature of relay 2| G'moves to its spacing contact, opening the circuit tlnough the line winding of relay 2H. When the armature of relay 2 I 6 reaches the spacing contact, a circuit is closed from negative pole of telegraph battery 242, resistance 243, spacing contact of relay 2 l6, through the biasing winding of relay 2 I! to ground. Current in this circuit flows through the biasing winding of relay 2|! in the direction to maintain the armature of the relay on the marking contact. The repeated operation of relay H6 in response to the code signals is without effect.

After the operator has challenged the subscriber, the subscriber manipulates his keyboard transmitter I00 and sends his order to the central office operator where it is printed on her typewriter. In response to the subscribers order the operator inserts the calling plug 244 of the cord circuit 20] in the jack 245 of the outgoing circuit. The outgoing circuit may be another subscribers line or a trunk or toll line. Before inserting the plug 244 in the jack 245 the operator tests the jack by touching the tip of the plug to the sleeve of the jack to determine whether the circuit is busy or idle. If the circuit is busy a negative potential exists thereon. In case the outgoing circuit is a subscribers line, the negative potential is supplied through the contacts of a relay such as relay i I! and the left winding of a relay such as relay HI if the subscriber of the line has just initiated a call and the operator has not yet answered it. In case the line is one that is made busy by reason of a cord circuit having been inserted in the jack 245, the negative potential on the sleeve of the jack is then maintained by reason of a circuit from the negative pole of battery in the cord circuit through the winding of a relay 2! l resistance 2 l2, thence as previously traced to the sleeve of the jack. Because of the busy negative potential on the sleeve of the jack 2 15 a current will flow through the tip of the plug 224, when the operator touches the jack to test it,

middle upper back contact of relay 222, through the winding of relay 246 to ground. Current flowing in this circuit is in the proper direction to operate the polarized relay 246. Relay 246 closes a circuit for the busy signal lamp 241. The lamp lights to notify the operator that the circuit tested is busy. If, however, the outgoing circuit is idle, the operator inserts the plug 244 into the jack 245 thereof and applies ringing current to the called line to signal the called subscriber or the called operator. The insertion of the plug in the jack causes the operation of the sleeve relay 248. This relay closes an obvious circuit for relay 222. Relay 222 extends the transmission circuit through the line winding of the repeating relay 2|! over the ring of the plug 244 thence to the ring of the called line. After obtaining the called party, the operator releases the cord circuit fro-m her position by opening the typing key 225. The opening of this key releases relay 214 which restores the transmission circuit previously traced from the calling line through the resistance 215 to the line winding of relay 2 i6. Relay 2M releases relay 226 and relay 239. Relay 226 disconnects the operators position from the transmission circuit and jacks, allowing all associated equipment to restore to its normal condition.

Assume next that the operators at both positions 206 and 300 observe the calling condition of 5 the subscribers line and that both attempt to answer the call. Assume also that the operator at position 200 is the first of the two operators to insert the answering plug of one of her cord circuits in the jack 235 of the subscribers line. As has already been described in detail, the insertion of the plug 204 of the cord 201 in the jack of the calling line causes the operation of relays 208, 201, 209 and 250 in the cord circuit 201. Also the act of inserting the plug 204 in the jack 205 causes an increase in the potential on the sleeve of jacks 205 and 213 and on other multiple jacks associated with this line. When, therefore, an instant later, the operator at position 300 inserts the plug 249 of her cord circuit 301 in the jack 213, the 0 increased potential on the sleeve of jack 213 is sufficient to cause current to flow from the jack over the sleeve conductor 250 of the cord, through the right-hand winding of relay 308, winding of relay 301, through the potentiometer resist- 5 ance 360 to ground. It will be noted that the current flowing through the right-hand winding of relay 308 is in a direction opposite to the flow of current through the right winding of relay 208 when the first cord was inserted. This direction is such that the polarized relay 308 of the second cord does not attract its armature. Consequently relays 309 and 310 do not operate, and the low resistance relay 311 is not connected in series with the left winding of relay 308. Relay 301, however, operates and, in so doing, closes a circuit from ground through the back contact'of relay 300, left contact of relay 361, winding of relay 361 to battery. Relay 351 in operating closes a path from positive telegraph 0 battery 319 in the cord 301, through the plug 249 and jack 213 to the transmission circuit of the subscribers line. This path, which acts as a shunt on the transmission circuit in the first operators cord 201, may be traced from the positive pole of telegraph battery 319, resistance 320, conductor 362, contact of relay 361, conductor 363, thence through the ring of the plug 249 and jack 213, conductor 125, left front contact of relay 11 1, which was operated when the first cord 0 was inserted, thence through the left winding of relay 112, over the line circuit and returning to the negative pole of telegraph battery 123, as hereinbefore traced. The resistance 320 in this path is sufiiciently low to reduce the current flow- 5 ing through the line winding of the signal relay 221 of the first operators position to the point where this relay moves its armature to the space contact under the influence of the biasing winding. After the armature of relay 221 has 0 rested on the space contact for an interval, the slow relay 236 releases, being short-circuited by the armature of relay 221, and closes its contacts. A circuit is now completed from the positive pole of telegraph battery 251, contacts of relay 236, 5 closed contacts of the energized relay 246, resistance 232, magnet 233, resistance 234, through the contacts of ke 235 to the negative pole of telegraph battery. This circuit maintains the magnet 233 energized while the armature of relay 0 221 is resting on its space contact. Thus the transmission circuit extending to the first operators position is disabled, and the manipulation of the operators keyboard transmitter is ineffective to transmit telegraph signals to the sub- 5 scribers sub-station because of the low resistance shunt that is being maintained through the. resistance 320 in the second cord circuit 301. Similarly, the manipulation of the transmitter at the subscribers station is without effect to cause the operation of the signal receiving relay 221. Furthermore, the magnet 233 is held energized in the'circuit above traced, and the typewriter at the first operators position is prevented from running in an idle or open condition. The operator at position 200, noting that her typewriter does not follow the manipulation of her keyboard, realizes that another operator has inserted a cord in a jack of the same line and that she should wait until such otheroperator has withdrawn.

The operator at position 300 having inserted her answering cord as above described closes her typing key 325, and relays 326, 314 and 339 operate as explained in connection with the first cord circuit, and a circuit is closed through the righthand winding of the signal relay 321. Since, however, the relay 303 of the second cord does not operate, the transmission circuit from the ring conductor 125 of the subscribers line is not extended into the operators position and through the left-hand winding of the. signal receiving relay 321, nor is the transmission circuit completed to the repeating relays 316 and 311 in cord 301. Accordingly, the relay 321 is controlled by its biasing winding and moves its armature over to the space contact, and the operators keyboard transmitter 329 is ineffective to send code impulses. Also it will be noted that the relay 340 in the second operators position is not energized for the reason that its circuit is not closed at the lower contact of relay 310. After the armature of relay 321 has rested on its space contact for an interval, the normally-energized slow-release relay 336, being short-circuited by the armature of relay 321, releases and closes its contacts. The

release of relay 336 at this time is without effect.

As soon as the armature of relay 321 leaves its marking contact, the normally-closed holding circuit for the magnet 333 is opened, but this magnet is now held in a circuit from the positive pole of telegraph battery, through the Winding of relay 352, normal contacts of relay 340, resistance 332, magnet 333, resistance 334, key 335 to the negative pole of telegraph battery. Thus the magnet 333 is held energized to prevent the operators typewriter from running in an idle or open condition. Relay 352 operates in the circuit traced and closes an obvious circuit for the busy signal lamp 341. The operator at position 300, noting the lamp 341 burning, realizes that another operator has preceded her in answering the calling subscriber. The second operator thereupon withdraws her plug 249 from the jack of the calling line, permitting the equipment in the cord circuit 301 and at the position 366 to restore to normal.

As soon as the second cord 301 is removed from,

the jack of the subscribers line, the shunt on the transmission circuit is opened, and full telegraph current now flows over the transmission circuit between the subscribers line and the equipment of the operator at position 200. Thereupon the relay 221 moves its armature back to the marking contact, and relay 236 again operates. Relay 236 opens the locking circuit of the magnet 233. This magnet is now held under the control of the marking contact of the relay 221-. The operator at position 200 now proceeds to communicate with the calling subscriber, and the connection is established as previously described.

Whenever a subscribers line is out of order,

a special plug (not shown) is inserted in one of the jacks 205 for the purpose of placing a positive battery potential on the sleeve of the jack. If, while the line is in this condition, an operator tests a sleeve of one of the multiple jacks, a circuit is closed, and current flows from the positive source of potential over the tip conductor of the plug 204, contacts of relays 299 and 201, thence through the winding of relay 253 to ground. Relay 253 is polarized in such a direction that current flowing in this circuit causes the relay to attract its armature. Relay 253 in operating closes an obvious path from ground through the winding of relay 254 and the signal lamp 241 to battery. The lamp lights, telling the operator that the line is busy, and the relay 24'! closes a circuit to the buzzer 255 to inform the operator as to the reason why the line is not available.

What is claimed is:

l. The combination in a communication system having operators positions, of a subscribers line appearing in multiple jacks at said positions, cord circuits at said positions, operators sets, one at each position for communication between the operator and the subscriber, means responsive to the insertion of a cord by any particular one of said operators in a jack of said line for completing a communication circuit between said line and the operators set, and means responsive to the insertion of a second cord by another operator in a jack of said line for closing a shunt around the first-mentioned operators set to render it ineffective for communication.

2. The combination in a communication system having operators positions, of a subscribers line appearing in multiple jacks at said positions, cord circuits at said positions, operators sets, one at each position for communication between the operator and the subscriber, means responsive to the insertion of a cord by any one of the operators in a jack of said line for completing a communication circuit between said line and the operators set, means responsive to the subsequent insertion of another cord by a second operator for disabling the communication circuit to said firstmentioned operators set, and means for notifying the second operator that another operator has already answered the line.

3. The combination in a communication system having two operators positions, of a subscribers line appearing in terminals at both positions, cord circuits at said positions, operators sets for communication between the operators and the subscriber, means responsive to the insertion of a cord circuit by one of said operators in a terminal of said line for completing a communication circuit to the operators set, means responsive to the subsequent insertion of a cord by the second operator for closing a shunt around the first operators set to render said communication circuit ineffective, and means responsive to the closing of said shunt for looking the first operators set against operation.

4. The combination in a communication system having two operators positions, of a subscribers line appearing in jacks at both positions, each of said positions having a cord circuit thereat for making connections with said line, operators sets for communicating with the subscriber, means in each of said cord circuits effective when the cord is the first one to be inserted in a jack of the subscribers line for establishing a communication circuit between the line and the corresponding operators set, means in each of said cord circuits efiective when the cord is a subsequent one to be inserted in a jack of the subscribers line for disabling the communication circuit between the line and the set of the operator first to insert her cord, and means for signaling the operator who makes connection with the line subsequent to the other operator.

5. The combination in a communication system having two operators positions and a. line appearing in both positions, of operators cord circuits at said positions for making connections with said line, operators sets for communication with said line, means in each of said cord circuits effective when the cord is the first one to be connected to the line for establishing a communicationcircuit between the line and the corresponding operators set, and means in each of said cords efiective when the operator connects the cord to said line subsequent to the connection of a first cord by the other operator for closing a low resistance path from the subsequent cord to said line to shunt the set of the operator who previously made connection to the line with said first cord.

6. In a communication system having operators positions, a line appearing in jacks in all of said positions, cord circuits at said positions for making connections with said line, operators sets for communication with said line, signal lamps, one at each of said positions for use by the operators in testing said line to determine whether it is busy or idle, means responsive to the insertion of a cord by any particular one of said operators in a jack of said line for completing a communication circuit between said line and the operators set, means responsive to the subsequent insertion of another cord by a second operator for disabling the communication circuit to said first-mentioned operators set, and means effective in response to the subsequent insertion of a cord circuit by one of said operators for lighting the signal lamp at her position to apprise her that another operator has preceded her in answering the call.

7. A communication system having two operators positions and a subscribers line appearing in both positions, cord circuits at said positions for making connections with the line, means at each of said positions for sending communications to the line, typewriters, one at each of said positions for receiving communications from said line, means responsive to the insertion of a cord at either of said positions in the subscribers line for establishing a. communication circuit between such position and the line, and means effective when one of the operators inserts a cord circuit in the line subsequent to the other operator for causing the typewriter of the first operator to make connection with the line to be locked against operation.

8. In a communication system having operators positions and a subscribers line appearing in all of said positions, cord circuits at said positions for making connections with said line, typewriters, one at each of said positions for receiving communications from said line, means for operating said typewriters, means responsive to the insertion of a cord circuit at any one of said positions in said line for establishing a communication circuit between the line and such position, and means effective in response to the subsequent insertion of a cord circuit in the line at a second position for locking the typewriters at both the first and second positions.

9. The combination in a communication system having operators positions and a line anpearing in jacks at all of said positions of cord circuits at said positions for making connections with said line, communication sets, one for each of said positions for communication with said line, busy signal lamps, one at each of said positions, means responsive to the insertion of a cord circuit at any particular one of said positions in a jack of said line for establishing a communication circuit between the line and such position, and means responsive to the subsequent insertion of a cord at a second operators position in a jack of said line for disabling the communication circuit between the line and the first-mentioned operators position and for lighting the busy signal lamp at said second operators position.

10. The combination in a telegraph system having operators positions, of a subscriber's line appearing in jacks at said positions, transmitting and receiving mechanisms at said positions for communication between the subscriber and an answering operator, cord circuits at said positions, each having means therein for closing a transmission circuit from said line to the corresponding operators position when the cord is the first one to be inserted in a jack of said line and for detecting the presence of a previously inserted cord to withhold the closure of said transmission circuit, means responsive to the subsequent insertion by a second operator of one of her cords for disabling the transmission circuit closed to a first operators position by the insertion thereat of a previous cord, and further means responsive to subsequent insertion of the cord at said second position for locking the receiving mechanisms at both said positions and for notifying the second operator to withdraw.

KARL E. FITCH.

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