US2149386A - Intercommunicating and broadcasting switchboard - Google Patents

Description

March 7, 1939. i A. s. BENJAMIN 2,149,386

TNTERCOMMUNICATING AND BROADCASTT NG SWT'I'CHBOARD Filed April 2, 1936 N INVENTOR ABRAHAM 5. BENJAMIN ATTOR Y Patented Mar. 7, 1939 PATENT OFFICE IN TERCOllflVIUNICATIN G AND BROAD CAST- ING SWITGHBOARD Abraham S. Benjamin, Chicago, Ill., assignor to Teletype Corporation, Chicago, 111., a corporation of Delaware Application April 2, 1936, Serial No. 72,272

13 Claims.

" I This invention pertains to switching systems for interconnecting radiating telegraph lines in an automatic printing telegraph system for telegraphic communication.

The principal object of the invention resides in the incorporation, in a switching system comprising instrumentalities for either interconnecting stations for individual'communication or for connecting all stations with the central office for communication of the central office simultaneously with all stations, and instrumentalities for preventing omission of any station when such simultaneous communication is proposed.

, The object of the present invention is attained by providing at the central office, switches for interconnecting any two lines through a central ofiice relay repeater and further switches for connecting any of the several lines of the system to a central office telegraph set for monitoring purposes or for intercommunicating purposes, and by providing a system of broadcasting relays capable of repeating telegraphic signals into all lines under control of one of the central ofiice telegraph sets, together with switches for connecting one of the telegraph sets into communication with the broadcasting repeating relays. To prevent omission of any station from any broadcasting operation, a system of interlocking supervisory relays controlled by a code signalresponsive selector in connection with the driving motors which condition the central office sets for operation is provided, the arrangement thereof being such that it is necessary to dissolve all established connections and condition all substations into operative condition for reception of broadcasting code signals before a central office telegraph set will be conditioned to transmit a broadcasting message to all stations. I

The system to which the invention is applied has a plurality of substations grouped upon each line radiating from the central ofiice, which have functions of automatic intercommunication between and among the substations upon the line to which they are connected without requiring the cooperation of the central ofiice operator, and of automatic intercommunication between all substations of any two radiating lines while connected together byconnective means at thecentral ofiice. 1

A better understanding of the invention may be had from the following detailed description,

oifice equipment having provision for several lines of which line 3, line B, and line N are illustrated, line 3 being indicated as equipped with three identical substations of which one is shown in detail. The system of the lines and the apparatus and operating methods of the substations are disclosed fully and claimed in application Serial No. 232,073, filed November 9, 1927 which matured into Patent No. 2,083,552 on June 15, 1937. The

structure and operation of the substation apparatus disclosed is as follows: Line 3 is connected to a substation through a transmitting dial 4 of so-called telephone type, a permutation code transmitter l, and signal receiving relay 5 which may be neutral or polarized. The relay controls two step-by-step selectors 6 and l which may be of any of well-known constructions, such, for example, as that shown in the patent to Gill 906,523, December 15, 1908, which operates in response to a predetermined code to close its contacts asfully and completely described in the foregoing application. A selector of any other desired type may be used. Selectors 6 at the several stations operate in response to variant individual predetermined code combinations of impulses, different from any printing telegraph permutation code combination, to close the contacts of their members 8. Selectors l at all stations operate uniformly in response to. a common code combination of impulses, different from any printing telegraph permutation code combination, to close the contacts, of their members 9 and also respond uniformly at all stations and to different common code combination, of impulses for operating their contact members I0, inde: pendently of members 9. Each selector 6 controls an energizing circuit for relay i atthe contact of its member 8 and each selector 1 controls energizing circuits for relays II and H at its upper and lower. contact members respectively. The relays. l0 and II in turn control an energizing circuit for relay l3 at their respective armatures l4 and I5. Relay I2 controls locking circuits for relays l0 and II at armature l9 and its back contact, and control a second circuit for relay l3 at armature l9 and its front contact. Relay l3 opens and closes the circuit for motor 20 at armature 2| and its back contact. Motor 20, when rotating, supplies the mechanical motive power for a printer whose magnet is shown at 2. Each printer, while its motor is operating, is selectively controlled by its magnet 2 in response to code combinations of impulses in line 3 over a line circuit which will be traced in detail in connection with the description of the central office apparatus, energy being supplied from a source of current at the central oflice. In the drawing, a positive sign or plus sign indicates a grounded battery or equivalent source of current. Operation of the substation apparatus is as follows: Normally, a line circuit is closed at each station through contacts of transmitter I, transmitter a break signal key 22, and a line signal receiving relay 5, all of the substations 25, 26, and 21 being in series in the line. With all apparatus at rest, an energizing circuit is completed over the line 3 for relay 5 which thus remains continuously energized and holds its contact closed, in turn closing local circuits for printer magnet 2 and for selector magnets 6 and 1. A further local circuit is closed at the station to energize relay I3,

the circuit being traced from ground through winding of relay l3, closed contact and armature it, closed contact and armature I5, closed contact and armature l9, and resistance to battery. The motor-control relay l3 thus is continuously energized while the substation is not operating and holds the operating circuit of motor 20 open at the back contact of armature 2|. The printer controlled by motor 25, whose magnets are illustrated at 2, therefore is idle or at rest, and is inefiective to record a message even though the magnet 2 may operate its armature.

In order to facilitate the description of operation it will be assumed that an operator at substation 21 desires to communicate with an operator at the detailed substation 25, both stations being connected to the line 3. To transmit and make record of permutation code signals, it is first necessary to start the motors of the receiving printers at both stations preparatory to transmitting by the motor-driven mechanical transmitter l at one station, and receiving and recording by the motor-driven mechanical printer controlled by magnet 2 at the other station. This the operator at station 21 accomplishes by rotating the spring-driven dial of the transmitter t at his station so as to transmit the predetermined calling code combination of signals allotted to station 25. These code impulses transmitted over the signaling line 3 operate the relay 5 at station 25 which in turn controls the energizing circuit for the selectors 6 and 1 as well as printer magnet 2, both local circuits being obvious from inspection of the drawing.

The selector 6 at station 25 responds effectively to this code combination of impulses in the manner explained in the Gill patent cited and well known in telegraphic art, to close the contact of its member 8, and a circuit is thereupon completed from battery through member 8 and its contact and through winding of relay it to ground. All other selectors on the line 3 respond, but ineffectively. Upon energization of relay H], a holding circuit is provided therefor through the front contact and armature [4, back contact and armature l5, back contact and armature l9, and resistance to battery.

The result of the energization of relay I is to open the energizing circuit for relay l3 at the back contact of armature I4, so that relay I3 becomes de-energized and releases its armature 2 l, closing a circuit for motor 28 from battery through motor 20, back contact now closed, and armaure 'Zl to ground. Motor 20 starts the mechanism of receiving printer and transmitter I at station 25, thus preparing the station for the receipt of permutation code combinations of im' pulses from the transmitting station. Line relay 5! also responds to the signaling impulses described and all other signaling impulses over the line 3, a description of the manner of response being reserved at this time to be embodied in a description of operation of central ofifice apparatus.

The operator at the calling station 21 now dials the calling code combination of impulses assigned to such station thereby operating selector 6 effectively to close its armature circuit to energize relay l0 and de-energize relay [3 to close contact 2| and start motor at his own station 21, all other selectors on the line operating also, but ineffectively.

Transmitter at the remote station 21 is now operated to transmit permutation code signals over line 3 to signal receiving relay 5 at station 25 to which relay 5 is responsive and to which printer magnet 2 and the print-er mechanism governed thereby is responsive to record the message. At station 26 Whose call code has not been dialed and whose motor therefore has not been started, relay 5 and magnet 2 are operated but the printer of which magnet 2 forms a part does not respond eifectively to'record the message because its associated motor 2!) is not providing mechanical power. A reply of the message mat be made by station 25 by operation of permutation code transmitter l at station 25 to which relay 5 and magnet 2 at station 21 will be responsive and magnet 2 will cause its printer to record the message since it is being provided with mechanical power by its operating motor 20 at station 21.

When the stations have completed inter-communication, the operator at either station, presumably the originating station, will transmit a disconnect code to operate selector 1 at both stations concurrently, whereupon both selectors 1 will close their contacts l6 and complete release circuits at each station from battery over contact l 5 and winding of relay E2 to ground. The energization of relay l2 operates armature l9 to open the holding circuit of relay l0 previously described through back contact of relay l2. At the front contact of relay l2 a circuit is completed for relay it from battery through operated armature and front contact of relay l2 and winding of relay l3 to ground, thus energizing relay l3 and attracting its armature 2! which opens the power circuit of the motor 20. De-energization of relay Ill by attracted armature l9 releases its armature l4 and prepares the originally described circuit for relay it. The substation equipment will remain in this condition until the transmission of any subsequent signal over line circuit 3 which will cause selector 1 to open its contact [6, which will de-energize relay 12, which in turn will open the instant circuit of relay l3 and by closing armature E9 to its back contactwill form again the energizing circuit for relay l3 originally described for the non-operating station. The station thus is returned to its original condition of idleness.

If it be desired to connect all of the substations for receiving code combinations of broadcasted messages simultaneously on the signaling line, the code of impulses transmitted over the line will be such as to operate the selectors 1 at all stations to close all upper contacts 9. As a result of closing contacts 9, circuits are completed at all stations from battery through closed contact 9 and Winding of relay H to ground. All relays I l are energized and complete locking circuits from battery through armatures l9 and back contact, armatures l5 and front contact,

and winding of relays II to ground. The energization of all relays I I will result in opening the energizing circuits for all relays I3 at the back point of all armatures I5. The de-energization of all relays I3 closes the energizing circuits for all motors 29 at all stations connected to line 3, and the receiving printers of all stations are thereby conditioned for receiving and recording permutation code combinations of impulses. After broadcasting, the stations are stopped by the same signal and in the same manner described for the communication between stations 25and 21. Broadcasting signals for starting all stations and subsequent signals for stopping all stations after broadcasting may be impressed upon line 3 by mechanism at the central ofiice, as will be described in connection with description' of operation of the central ofiice.

At the central office are provided interconnecting keys 28, monitor keys 29, line relay sets 3|,

broadcasting relays 32 and 33, repeating sets 34,

35, audible signal device 36, supervisory relays 31, 38, 39, telegraphic recording monitor sets 49, 4|, broadcasting key 42, and a system of broadcasting supervisory apparatus comprising a broadcast supervisory selector 43, a broadcast supervisory lamp 44, and five interconnected broadcast supervisory relays 45 to 49 inclusive.

Keys 28, 29, and 42 are manually operable switchboard keys of double-locking type in each of which the plunger 59 in key 42, may be operated upwardly to change the contactual relations of the upper contact members of the key or alternatively may be operated downwardly to change the contactual relations of the lower contact members of the key. A key when operated into either upper or lower position locks mechanically and remains in its operated position until manually restored.

' One line relay set 3| is provided for each line, each set comprising a quick-acting line relay 5|, a choked relay or slow-to-release relay 52 whose characteristic feature is indicated by, its choke block 53, a slow-to-operate relay 54 whose characteristic feature of slowness is indicated by the connected resistance 55 and condenser 56. Associated with the relay set 3| are a calling lamp 51, and a busy-signal lamp 59. A line equipment includes also a broadcasting relay 32 and a ballast or line-adjusting resistance 59, one of the keys 28 and'one of the keys 29.

Repeating set 34 comprises relays II4, II1, and resistors II2, I22, I21, I29, while repeating set 35 comprises similar relays and resistors, similarly connected but unnumbered. The repeating sets are of the type disclosed in Patent 1,895,015 issued January 24, 1933 to Vernam et al., Fig. 1, but may be of any desired type with neutral or polar relays or may be of motor driven regenerative type.

' Thetelegraphic monitor sets 49 and 4| comprise each a spring operated transmitting device or telephone dial 69, not requiring power from an external motor, a receiving recorder of printing telegraph type whose signal receiving magnet is illustrated at El a permutation code transmitter of direct keyboard or tape type whose transmitting contacts or contact is illustrated at 62, a motor 63, a motor control relay 64, and a battery or other source of power supply.

1 Circuits at the central ofiice are provided as follows. V

A line circuit extends from battery through resistance 59, armature 65 and front contact of normally energized relay 32, key contacts 66 to 13 inclusive, conductor 14,-and winding of line relay 5| to line wire 3, and as hereinbefore described, through substations 25, 26, 21, to ground. When relay 5| becomes deenergized, its armature 18 engages its contact 19 and two circuits are formed, choked relay circuit from battery through resistance 11, armature 18, contact 19, and winding of choked relay 52 to ground, and slow relay circuit from battery through resistance 11, armature 18, contact 19, winding of slow-to-operate relay 54, and key contacts 89 and 8I to ground.

Busy-signal lamp circuit extends from battery through resistance 82, lamp 58, contact and armature of energized relay 52, conductor 83, and contact'84 of relay 41 to ground. A branching circuit extends from lamp 58 through open key contacts 89 or alternatively 8| and to ground when the keys are operated. Holding circuit for slow-acting line relay 54 extends from battery through resistance 11, thence directly through armature .and its front contact, winding of relay 54, and key contacts 89 and 8| to ground. A calling line lamp circuit extends from battery through resistance 86, lamp 51, front contact and armature 81, wire 83, contact 84 and armature of relay 41 to ground. A circuit for the audible signal device 36 extends from battery through resistance 88, winding and contact of audible signal device 36, conductor 89, and contact and armature 99 to ground.

An operators monitor loop circuit for monitor set 49, extends from key contacts 9| in upper half of monitor key 29, contacts 923, 9IB, and similar contacts in all similar keys, conductor 93, contacts 93, 94, conductor 94 to monitor set 49, through spring-dial transmitter 69, printer magnet 6| and permutation code transmitter 62, thence over conductor 95, contacts 96' in key 42 and over conductor 96 in branching multiple to homologous contacts 91 in upper halves of all monitor keys 29. A branching conductor extends from conductor 94 to contact 98 in key 42. An alternative monitor loop circuit may be traced from homologous contacts in the lower halves of the same keys 29 and through the alternative monitor set 4|, from key contacts I93 over conductors I94 and I95 through monitor set 4| and over conductors I96 and I91 to key contacts I98.

The repeater set 34 comprises two circuits, one of which connects to leftward contacts of interconnecting keys 28 and the other of which connects'to rightward contacts of those keys. The circuit which connects to leftward contacts of the keys may be traced from battery through resistance II 2, winding of relay II4, contact H5 and armature H6 of relay II1 when energized, and over conductor II8 to contact II9 of upper half of key 28 and through closed contacts I29 and |2I of upper half of key 28, thence in similar manner to and through homologous contacts in other keys to contact II9N in key 28N which is the last key of the series. The circuit which connects to rightward contacts of keys may be traced from battery through resistance I22, winding of relay -I I1, contacts II3 and armature I23 of relay I I4 when energized, and over conductor I24 to contact I25 in key 28 and in branching multiple to homologous contacts in other keys of the series, excepting key 28N which is the last key of the series. When idle, one of the relays I I 4, H1 is energized through contacts of the other relay, which remains deenergized, aswill be explained in description of operation Alternative paths for terminating the repeater circuits are from contact II to contact I28, while relay H1 is de-energized and through compensating resistance I21 to ground, and from contact M3 to contact I28 while relay H4 is deenergized and through compensating resistance I29 to ground. Repeater circuits when switched are extended over line circuits to substations as will be described in the description of operation of the switchboard.

Additional and identical repeater circuits duplicating the circuits traced above may be traced through the lower halves of keys 28 to 28N in connection with repeater set 35.

Additional keys 28 with repeater sets 34, 35 and additional keys 29 with monitor sets 40, 4| may be added as the traflic of the switchboard requires, the several line circuits being looped through similarly locgtted keys of the several added sets of equipment.

Supervisory circuits and motor control circuits for the motors of monitor sets 40 and 4! are as follows:

Upper supervisory circuit extends from battery through resistance H30, winding relay 38 and closed chain contacts I3I in series in upper halves of all keys 29 to ground.

Lower supervisory circuit extends from battery through resistance I32, winding of relay 31, and closed chain contacts I33 in series in lower halves of all keys 29 to ground. A repeater supervisory circuit extends from battery through resistance I34, winding of relay 39, armature and contact I35 of relay 31, armature and contact I38 of relay 38, conductor I31 and closed chain contacts I38 and I39 in series in upper and lower halves of all repeater keys 28. A first motor control circuit extends from battery through resistance I40, armature I45, and contacts I42 of relay 41, conductors I43 and I44, winding of relay-84, conductor I45, contact I48 and armature of relay 38 to ground. A second motor control circuit extends from battery through resistance I41, armature i48, contact I49, conductors I50 and I5I, motor control relay I52 of monitor set 4I, conductor I45, contact I53 and armature of relay 31 to ground.

A broadcast control circuit extends from battery through resistance E54, armature I55 and contact of relay 89, conductor I58, key contacts i5'i', I51, E58, and conductor I59 through winding of supervisory broadcasting relay 33 and of all line broadcasting relays 32 to ground.

For control of motors in sets 40 and M during broadcasting operations, branching conductors I58, SI, and I43 connect armature MI and contact 42 to key contacts I62 to by-pass the relay contact while the key contact is closed, and branching conductors I83, I64 and I58 connect armature I48 and contact I49 to key contacts I85 to by-pass the relay contacts while the key contacts are closed.

Circuits in the broadcast supervisory system comprising relay 33, selector 43, lamp 44, and relays 45 to 49 inclusive are as follows: A supervisory selector circuit extends from battery through resistance I88, armature I61, winding of magnet of selector 43, conductor I88 and contact I59 and armature to ground. A supervisory lamp circuit extends from battery through resistance M8, armature I4I when operated, contact I10, conductor I1I, lamp 44 and resistance I12 to ground. A selector relay circuit extends from battery through resistance I13, selector contact I14, contact member I15 when in operated position, and winding of non-locking selector relay 45 to ground. A circuit for locking selector relay 46 extends from battery through resistance I16. right-hand winding of relay 46, conductor I11, conductor I99 contact I18 and armature I19 to ground. A holding circuit for the locking selector relay 48 extends from battery through resistance I16, left-hand winding of relay 46, contact I80 and armature I8I, common holding conductor I82, armature I83, contact I84, conductor I85 and contact I88 and armature to ground. An energizing circuit for broadcast enabling relay 41 extends from battery through resistance I81, winding of relay 41, conductor I88, contact I89, and contact member I90 of selector 43 when operated, armature i9! and contact I92, contact I18 and armature I19 to ground. A holding circuit for enabling relay 41 extends from battery through resistance I81, winding of relay 41, contact and armature I94 thence over common holding conductor I82 to ground. An energizing circuit for release relay 48 extends from battery through resistance I95, winding of release relay 48, armature I91 and contact, conductor I99, contact I18 and armature I19 to ground. A holding circuit for release relay 48 extends from battery through resistance I95, winding of relay 48, contact and armature 20I, and thence over conductor I82 to ground.

An energizing circuit for unlocking relay 49 extends from battery through resistance 282, winding of unlocking relay 49, armature 203 and contact of relay 48, conductor 205, contact I18, and armature I19 to ground.

Operation of the central oflice equipment in cooperation with the substations is as follows:

The line circuit conveys current continuously when line 3 is not being operated, thus holding line relay 5I at the central ofiice and signal receiving relays 5 at all substations continuously energized. Circuits for local relays 52 and 54 and for the lamps are open when the line circuit is not in use. Relay 52 responds to relay 5! quickly and relay 54 responds after a slight delay so that when relay 5I is operating in vibratory manner in response to a code transmitter I at any substation as 25 or at the central office, each engagement between 18 and 18 is so brief that relay 54 does not respond, but relay 52 does respond so that relay 52 closes the circuit for busy-signal lamp 58 and no action occurs in relay 54 nor in any of its controlled circuits. The result is that when stations 25 and 21 or any other pair of stations are intercommunicating, the busy-signal lamp 58 giows to warn central office operators that the line is busy so that intercommunication between substations shall not be interrupted inadvertently.

Should an operator at a substation as 25 desire the attention of a central office operator, he will operate his break signal key 22 which will produce a comparatively long period of deenergization of relay 5| which will supply a continuous current at first to charge condenser 56 and thereafter to flow through the winding of the slowacting relay 54 to energize the relay to operate its armatures in response to the longer closure. Slow relay 54 when operated closes its holding circuit the calling lamp circuit and the audible signal circuit resulting in continuously operated visual and audible signals to call the central oifice attendant.

The central office attendant, desiring to use central oflice set 40 for response, operates the plunger of key 29 to change the co'ntaotual relations of upperhalf of the key contacts,'thereby connecting central oifice telegraph set 40 in series with line 3 over a monitor circuit which may be traced from battery over the line circuit to the operated key contacts 9| through the monitor loop circuit,

through monitor set 40 to key contact 91, thence from operated key contact H over the line circuit through substations 25, 26, 21 to ground, and communication may be had between the calling station and monitor set 40. Operation of the upper half of key 29 has opened the upper supervisory circuit at switch contacts I3I, and has closed the branching circuit to energize busy lamp 58 which renders the continuance of illumination of busy lamp 58 independent of relay 52 and dependent only upon key 29 so that after conclusion of communication between the central oflice and the substation and after cessation of operation of relay and therefore after release of relay 52, the busy lamp 58 will continue to glow until key 29 is restored to normal position by the central ofiice operator. Starting of motor 63 was efiected-by the opening of the upper supervisory circuit, de-energizing relay 38 which by its contact I46 opened the first motor control circuit,

de-energizing relay 64, which by closing its contactrcontrols the motor 63 to operate by power over an obvious circuit. Upon conclusion of communication and restoration of switch 29 to normal, the line circuit is restored, contacts 8| open the lamp circuit and contacts I 3I reclose the supervisory circuit and re-energize relay 38 which operates and recloses the motor control circuit which re-energizes relay 64 and causes motor 63 to come to rest. Had the calling signal been received upon another line, the central ofiice attendant desiring to use set 40 in responding, would have operated the upper half of monitor key 29B in response to a call upon line B or the upper half of monitor key 29N in response to a call upon line N.

Had the operator at station 25 desired communication with a station upon another line, for example line B, he would have recorded the request upon the recording printer SI and the central ofiice attendant then would have operated keys 28 and 28B to change the contactual relations of the upper'half of the keys substations 25, 26, 21 to ground. The associated repeating circuit rightward from keys extends from battery through resistance I22, winding of relay 1, contact II3, operated armature I23, conductor I24, key contact I25, and operated key contact I2I, key contact H93 and thence through operated key contact 61B, and over the line circuit for line B, over line B and through the substations of line B to ground. The attendant at calling substation 25 now may dial the number of the station on line B with which it is desired to communicate, the dialing signals being repeated by the repeating assembly 34, a

motor at a selected station on line B being thus started, after which communication code signals may be transmitted by transmitter I of station 25 and recorded by therecording printer under control of magnet 2 at the selected station on line B, after which reply may be made before disconnection or the operator at station 25 may stop the motors at both stations by sending the disconnectingcode signal. Should the central office operator leave the set 48 connected in this communication by leaving key 29 in its operated position as described, the communication between the connected stations will be recorded by the monitor printer of the set 48, but the monitor operator at the central oflice may restore key 29 at any time, thus leaving the two stations in communication without central office record. Both busy-signal lamps of the two connected lines will glow during transmission of signals and the monitor operator at any time may reoperate key 29 to include set 40 in the communication circuit or upon noting an absence of illumination of the busy-signal lamps, may restore the keys 28 and 283. Should either station at close of communication desire immediate attention of the monitor operator, the key 29 having been restored, an operation of the break signal key 22 as described will operate relay 54 and again cause display of an illuminated line lamp 51.

Broadcasting to all substations or broadcasting to all lines may be effected only by the central oflice operator by operation of the broadcasting control circuit which by relays 32 repeats into all lines any signals originated in the monitor sets 48 or M, supervisory equipment being provided which, by interdependent circuits, automatically disables both of the sets 40 and M for broadcasting purposes until the operator has performed in an invariable order three acts; (1) has restored to normal all keys 28 and 29 thus disconnecting every line from every other line, (2)- has broadcasted to all lines an 01f or substation. restoring code signal, thu's stopping the motors at all stations, and (3) has broadcasted to all lines an on or motor starting code signal thus starting the motors at all substations. Thereupon the central ofiice motor in set 40 or 4| will start according as one or the other monitor set is connected to the broadcasting control circuit and all signals generated by the connected monitor set will be broadcasted upon all lines and to all stations. 7 Following the completion of a broadcasted message, an off signal again is broadcasted to release the central office apparatus and this broadcasted signal also stops all motors at all substations, completing the cycle of broadcasting operation.

For operation in broadcasting, the central ofiice attendant sets all keys 29 into normal position, thus closing upper and lower supervisory circuits and energizing relays 31 and 38, also sets all keys 28 into normal position, thus closing the repeater supervisory circuit and energizing relay 39. Desiring to use monitor set 40, the attendant then operates key 42 and plunger 50 to reverse the contactual relations of the upper half of key 42, thereby connecting set 4!] into the broadcast control and forming an operating circuit extending from battery through resistance I54, armature I55 and its contact, conductor I56, key contacts I 51, 98, conductor 94, to monitor set 48, dial transmitter 69, recorder magnet 6|, permutation transmitter 62, conductor 95, key contacts 95' and I59, wire I59, through winding of relay 33 and windings of all relays 32 to ground. Transmission cannot begin from permutation transmitter 62 because motor 93 has not been started. To start motor 63, the operator dials an 01f code signal, stopping all substation motors if any are running for the purpose of intercommunication between stations on any line, and

also operating relay 33 to control the-selector 43 to closeits off contact I15 which closes a circuit to energize and operate relay 45which closes a circuit to energizeand operate relay 46 which looks over its holding circuit, and the operator then dials an on code signal, starting all substation motors for the purpose of recording the proposedbroadcast message and also operating relay 33 to control the selector 43 to open its off contact and to close its on contact I90, which closes the circuit to energize and operate relay 4'5 which looks by its holding circuit and which by its armature -I4I opens the first motor control circuit and deenergizes relay 64, thereby starting the motor 63 at monitor set 40 and conditioning the ,monitor set 40 to transmit the broadcast message to all lines and to all stations, also opening lamp circuits at contact 84, so that no line can call the central office during the .broadcasting operation. When opening the circuit to start motor 63, relay 41 also opened contact I49 in the second motor control circuit but this contact was shunted by branching conductors and key contacts I65 so that the circuit was 'held closed and the motor of monitor set M was held inert. After completion of the broadcasting message, the operator again dials the off code signal, stopping all station motors and also operating relay 33 to control the selector 43 to close its off contact I15, which now closes the circuit energizing and operating relay 48 which looks over its holding circuit. The operator now dials 2 or any other signal, thereby causing the. selector to open its contact I15, de-energizing relay 45 which closes a circuit to energize and operate relay 49 which opens its contact I84 and thereby opens all holding circuits which de-energizes all locked relays, including relay 48 whose de-energization de-energizes relay 49. The operator now may restore key 42, bringing the central office apparatus into its original condition.

A subcombination is disclosed in that were there but one station on each line, the off code signal is not required as a preliminary to broadcasting, wire 285 may be connected directly and permanently to ground, and relay 46 may be omitted.

It is obvious that many variations may be embodied in structures according to this invention Without departing from the spirit of the appended claims.

What is claimed is:

1. In a telegraph exchange system, a central station, a plurality of telegraph lines radiating from said central station, a plurality of telegraph sets on each of said lines, means associated with each set responsive to signals for connecting selectively any of the sets of their lines for intercommunication independently of said central station, means at said central station for connecting said lines for intercommunication between selected sets of said interconnected lines, a broadcasting set at said central station, means at the central station for rendering each telegraph set on each line and said broadcasting set efiective, and means for preventing any set of any of said lines from signaling the central station during broadcasting operation.

2. In a telegraph exchange system, a central station, a plurality of telegraph lines radiating from said central station, a plurality of telegraph sets on each of said lines, signal responsive switching means associated with each set for connecting selectively any of the sets of their lines for intercommunication independently of said central station, manually operated means at said central station for connecting said lines for intercommunication between selected sets of said interconnected lines, a broadcasting set at said central station, means at the central station for rendering through said switching means each telegraph set on each line and said broadcasting set effective, and means for preventing any set of any of said lines from signaling the central station during broadcasting operation.

3. In a telegraph exchange system, a central station, a plurality of telegraph lines radiating from said central station, a plurality of telegraph sets on each of said lines, signal responsive switching means associated with each set for connecting selectively any of the sets of their lines for intercommunication independently of said central station, means at said central station for connecting said line for intercommunication between selected sets of said interconnected lines, a broadcasting set at said central. station, switching means at the central station for rendering each telegraph set on each line and said broadcasting set effective, and means for preventing any set of any of said lines from signaling the central station during broadcasting operation.

4. In a telegraph exchange system, a central station, a plurality of telegraph lines radiating from said central station, a plurality of telegraph sets on each of said lines, signal responsive switching means associated with each set for connecting selectively any of the sets of their lines for intercommunication independently of said central station, means at said central station for connecting said lines for intercommunication between selected sets of said interconnected lines, a broadcasting set at the central station, stepby-step switching means at the central station for rendering each telegraph set on each line and said broadcasting set effective, and means for preventing any set of any of said lines from signaling the central station during broadcasting operation.

5. In a switching system, a central station, a plurality of telegraph lines radiating from said station, manual means for interconnecting said lines, a telegraph set on each of said lines, means at the central station for broadcasting signals simultaneously to each set of the system, and relay means at the central station requiring manual operation of said manual means to disconnect each of said lines from every other line to enable the operation of said broadcasting means.

6. In a switching system, a central station, a plurality of telegraph lines radiating from said station, manual means for interconnecting said lines, a telegraph set on each of said lines, means at the central station for broadcasting signals simultaneously to each set of the system, and contacts in said manual means interfering with operation of said broadcasting means except when said manual means are conditioned to disconnect each of said lines from every other line to enable the operation of said broadcasting means.

'7. In a switching system, radiating telegraph lines, a monitoring and broadcasting telegraph set, a system of apparatus and circuits adapted to interconnect any one of said lines to said set for intercommunication, line relays for each of said lines, visual calling signaling devices controlled by said line relays, a system of apparatus and circuits adapted to broadcast from said set to all of said lines simultaneously, and a system of relays, manual keys, relay circuits and manual key circuits connecting said broadcasting set and said visual calling signaling devices and preventing signaling operation of said visual calling signaling devices and said broadcasting set concurrently.

8. In a telegraph exchange system, a central station, a plurality of telegraph lines radiating from said station, a plurality of telegraph sets on said lines, manual keysfor establishing connections between said lines for intercommunication between sets on said lines, a telegraph set for broadcasting to the sets of all of said lines simultaneously, and contacts in said manual keys connected to said telegraph broadcasting set and acting to interrupt said broadcasting set in the event of establishing intercommunication between stations of a line during operation of said broadcasting set to all radiating lines and all sets on said lines.

9. In a telegraph exchange system, a plurality of radiating telegraph lines, a plurality of telegraph sets on each line, switching means responsive to signaling impulses for connecting the sets of a single line for intercommunication, a broadcasting telegraph set, and means for conditioning said broadcasting set to broadcast to all sets on all lines, said last mentioned means including means for interrupting all said intercommunication connections.

10. In a telegraph exchange system, a central station, a plurality of telegraph lines radiating from said central station, a plurality of telegraph sets on each of said lines, switching means associated with each set responsive to signals for connecting selectively any of the sets of their lines for communication independently of said central station, switching keys at said central station one for each line for interconnecting said lines for intercommmunication, a broadcasting set at said central station, and means at the central station for rendering said telegraph set on each line and said broadcasting set effective, said last mentioned means including means for preventing any set of any of said lines from signaling the central station during broadcasting operation.

11. In a telegraph exchange system, a'pluraiity of radiating telegraph lines, a plurality of telegraph sets on each line, switching means responsive to signaling impulses for connecting the sets on each line for intercommunication, means for interconnecting the lines whereby sets on such lines may intercommunicate, a transmitting relay individual to each line, abroadcasting set, means common to said radiating lines for connecting said broadcasting set to each of said transmitting relays, and means responsive thereafter to cause the operation of said transmitting relay for the transmision of corresponding signaling impulses simultaneously and invariably to each of said telegraph lines.

12. In a telegraph exchange system, a plus rality of radiating telegraph lines, a central station common to said lines, a plurality of telegraph sets on each of said lines, switching means at said central station for interconnecting said lines for intercommunication by the sets on the interconnected lines, a broadcasting set at said central station, means at the central station for connecting said broadcasting set invariable to each of said lines, a motor control at said broadcasting set, and means responsive to said switching means at said central station in non-interconnecting condition for conditioning said motor control means for operation to render said broadcasting set operative.

13. In a telegraph exchange system, a central station, a plurality of telegraph lines radiating from said central station, a plurality of telegraph sets on each line, switching means responsive to signaling impulses for connecting the sets on each line for intercommunication, means for interconnecting the lines whereby sets on such lines may intercommunicate, a broadcasting set at said central station, a step-by-step switching device at said central station, a motor control relay for said broadcasting set, a plurality of relays operated from said step-by-step switching device, and means controlled by one of said relays for conditioning an operating circuit for said motor control relay to render the broadcasting set efiective for communication simultaneously to all of the sets on all of said lines.

ABRAHAM s. BENJAMIN.

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