US2419729A - Printing telegraph system having serially connected step-by-step selective stations - Google Patents

Description

Apnl 29, 1947. POT-rs 2,419,729

PRINTING TELEGRAPH SYSTEM HAVING SERIALLY CONNECTED, STEP-BY-STEP SELECTIVE STATIONS Filed Jan. 29, 1944 2 Sheets-Sheet l I n *4 my j l... l

FIG. I

ATTORNEY April 29, 1947. M PQTTs 2,419,729

PRINTING TELEGRAPH SYTEM HAVING SERIALLY CONNECTED,

STEP-BY-STEP SELECTIVE STATIONS Filed Jan. 29, 1944 2 Sheets-Sheet, 2

'IBI

ATTORNEY IINVQENTOR gj LOUIS M. POTTS,

l aten tecl Apr. 29, i947 UNITED STATES PATENT OFFICE PRINTING TELEGRAPH SYSTEM HAVING SERIALLY CONNECTED STEP-BY-STEP SELECTIVE STATIONS Louis M. Potts, Evanston, Ill., assignor to Teletype Corporation, Chicago, 111., a corporation of Delaware Application January 29, 1944, Serial No. 520,158

the several electrical components at such station and which is rendered efiective in response to a condition established at the central station.

A further object of the invention is to provide a station calling system which embraces a single series of counting relays with a single unit of the counting relays located at each remote substa tion. 7

A feature of the invention resides in the provision of a triode vacuum tube at each remote station for supplying the electrical energy required for the relays associated therewith which has its grid circuit under the control of a condition established at the central station where the station selection impulses are generated.

The invention, according to one of its embodiments, contemplates a central station with a plurality of remote stations interconnected with the central station by a single grounded line conductor. There may be a pluralityof such line conductors radiating from the central station to other various remotely situated stations, each of the line conductors With the stations thereon constituting a separate system. Each of the stations including the central station is equipped with printing telegraph apparatus including a receiv-.

ing printer and a signal transmitter. The receiving printer and the signal transmitter are normally ineffective andrto render such equipment- Each of the remote stations is equipped, in addition to the printing telegraph equipment including the receiving printer and the signal transmitter, with a plurality of relays which together function in the nature of a. counting chain in response,

to impulses generated at the central station in response to the 'operation-oi acalling dial for estab 27 Claims. (01. 178--2) lishing a condition to start the driving motor of the printing telegraph equipment at such station and for connecting such equipment in circuit with the line conductor whereby the transmission and reception of messages over the line conductor can be efiected. Such a condition will prevail until a condition is established at the central station to restore the system to its normal condition preparatory to the establishment of another communication circuit.

Each of the remote stations is equipped with mechanism manually operated for establishing conditions at the central station to apprise the operator thereat of the desire to communicate with such station.

The required battery supply for the relays at the remote stations is provided by a triode vacur um tube which will respond to the application of a source of power to the line conductor at the cen'- tral station to discontinue the battery supply for the several relays individual thereto and thus effect the de-energization of such relays. Suchrelays are de-energized and will be in such a condition preparatory to the reception of a subsequent call from the central station.

The invention according to another embodiment contemplates a central station and a plurality of remotely situated stations connected with the central station by a pair of line conductors constituting a metallic circuit as distinguished from the grounded circuit referred to in connection with the other embodiment of the invention. Selection of any of the several stations and establishment of communication conditions are similar to those outlined in connection with the first embodiment.

The invention Will be more fully understood from a consideration of the following description taken in conjunction with the accompanying drawings, in which Fig. 1 discloses one embodiment of the invention; that is, the embodiment involving a single grounded line conductor and wherein Fig. 2 illustrates another embodiment of the invention involving a pair of line conductors with the central and remote stations connected thereto.

Referring now to the drawings and first to Fig. 1, there is disclosed a line conductor '5 extending from a central station 6 to a plurality of'remotely situated stations 1, 8, 9, and I0. While Fig. 1 shows a single line conductor 5 extending from the central station to the several remote stations it is manifest that other similar line conductors may extend or radiate'from the central station 6 to which there are connected a plurality of stations equipped with apparatus similar to that illustrated in connection with stations I and Ill. The radiating lines may be to other stations and equipped with entirely separate central station equipment. Stations I and II) have been shown complete whereas stations '8 and 9 have been shown diagrammatically, but it is understood that stations 8 and 9 are equipped with apparatus s1milar to the apparatus disclosed for stations I and I 0.

The line conductor has battery connected thereto at the central station and terminates at the last station to ground, establishing what is referred to as a grounded line conductor. The central station is equipped with a multi-contact key I3 which has three positions identifiable, as shown, as a call, a print, and an idle position. This key I3 operates in conjunction with a standard form of telephone calling dial I5 to establish the several operative conditions with line conductor 5; that is, with the key I3 in the position shown in Fig. 1, namely, the call position, the calling dial I5 may be operated to generate stepby-step impulses sufficient in number to establish a connection with the desired remote station. Such operation also controls the energization of relays I6, I1, I8, and I9, which function in conjunction with the other apparatus at the central station to establish the desired communication condition.

There is also located at the central station printing telegraph equipment 20 including a receiving printer 2| and a signal transmitter 22 which are shown diagrammatically but which may be of any one of several commercially available types.

Each of the remote stations 1, '8, 9, and II] is also provided with printing telegraph equipment such as 25 and 26, similar generally to that constituting a part of the central station equipment. The printing telegraph equipments 25 and 26 are under the control of relays 2'! and 28 at stations I and I0, respectively. Each of these relays is of the slow-to-operate type which function in response to their energization to establish with the line conductor 5 a communication path to the printing telegraph equipments 25 and 2-6, respectively, and the completion of the power supply with the motor 30 of equipment 25 and motor 3| of equipment 26. Also located at each of the stations I, 8, 9, and III are relays 32 and 33 and relays 34 and 35 at stations I and I0, respectively. These relays 32, 33, 34, and 35 at the respective stations I and II) function in response to conditions established through the operation of apparatus at the central station 6 to establish the desired communication path with the printing telegraph equipment at such desired station.

Each of the relays 21, 32, and 33 at station I is arranged upon their energization and contingent upon other conditions to remain energized by the establishment of locking circuits to which power is supplied from the output circuit of a triode vacuum tube 31 which has its grid circuit connected to line conductor 5 and which, accordingly, is under the control of conditions established on lineconductor 5. l

At each of the other stations 8, 9, and I0 there is a triode vacuum tube such as 31 shown at station I for supplying holding current for each of the relays 21, 32, and 33. The triode vacuum tube for station I0 is designated by the reference numeral 38.

A remote station may, of course, desire to signal the central station when it elects to communicate with that station. To achieve this result each of the stations I, 8, and 9 is equipped with a key 40, the corresponding key at station I0 is identified by the reference numeral 46, which controls the energization of a relay M which, when energized, is maintained energized from current supplied from an alternating current source and which functions through its armatures and contacts to open the line circuit 5 to stations beyond and establish alocking circuit for relay 33. When relay'4l energizes, it establishes a condition resulting in the de-energization of relay 44 at the central station, assuming, of course, that the key I3 is in its idle position. When in such position relay 44 will be energized, provided relay 4| is not energized. Accordingly, when relay 44 is de-energized a circuit will be established for energizing lamp 45 which serves as a signal to the operator that a station desires to communicate telegraphically.

The operator in observing lamp 45 illuminated will operate the calling dial I 5 to establish conditions necessary to select or connect the station where key 40 has been operated.

Station ID is equipped with a key 46 and a relay 41 which correspond in construction and operation to key 40 and relay 4I described for station I.

A more complete understanding of the invention may be obtained from a description of the operation of the system. Assume for this purpose that the apparatus at the several stations is in the position shown in Fig. 1 wherein the line conductor 5 is capable of being extended from the central station 6 through the several stations I, 8, 9, and I0 in seriesto ground at the last station, which in the arrangement shown in Fig. 1

is station I 0, and also that connection between the central station and station I is desired. Assume that the operator at the central office operates key 55 to restore all of the relays in the system to normal and then operates key I3 to the position shown in Fig. 1, namely, the call position, whereupon a circuit is completed from grounded battery through normally closed contact 49 operated by the calling dial I5, conductor 50, contact 5| of key I3, conductor 52, now closed contact 53 of relay H (which was de-energized when key 55 was operated to open contact 54 in the locking circuit), Winding of relay I8 and winding of relay IT to ground. Relays I6 and I1 will be energized over the described circuit. Relay I1, through its right-hand front contact and armature establishes a locking circuit extending from grounded battery through contact 54 of key 55, conductor '56, right-hand armature and front contact of relay I'I, to ground.

Assume also that the operator at the central station will operate calling dial I5 to the position identified with station I with the result that normally closed contact (off-normal contact) 49 under the control of the'calling dial I5 will be opened, removing battery 64 from conductor 50 which extends through contact 5I of key I3, conductor 52, and front contact and armature of relay I'I. Opening of contact 49 results in the de-energization of relay I6 whereupon its contact 58 is closed to establish an energizing circuit for relays I8 and I9. When pulsing contact is closed upon return movement of dial I5, a circuit will be established, upon generation of the first stepping pulse, extending from grounded battery 64, contact 65, conductor 50, contact 5!, conduc toi- 52, front contact andleft-hand armature of s relay [1, contact 58 of relay I6, make-beforebreak contact 55 of relay l8, and the windings of relays l8 and it in series to ground. Relays l8 and IE will be energized and relay it will be locked up over the circuit established through its right-hand armature and front contact and through contact 54 of key 55 to battery. Upon the opening of contact 65 relay l9 will be deenergized and will close its contact 67 to extend conductors 55 and 52 through contact 58 of relay l6, contact 6'? of relay l9, and contact 59 of key [3 to contact 5| of key 55 and thence to line conductor 5. Conductor 5 extends as shown in Fig. 1 through make-before-break contact 62 of relay 21 at the first remote station, make-before-break contact 53 of relay 32, and windings of relays 33, 32, and 27 to ground at relay 21.

Upon the release of calling dial l5 the pulsing contact 55 under the control thereof will be closed and opened to generate a number of impulses determined by the degree of rotation of the calling dial 15. The first stepping impulse generated by dial l5 through the operation of contact 55 conditions relays l8 and i9 (relays l5 and 51 having been conditioned as an incident of the positioning of key E3 to the call position). Since in the embodiment disclosed, the station labeled 7 is the first remote station in the counting chain,

. only one stepping impulse will be generated by dial 55. Then, upon reclosure of ofi-normal contact 49, the current passes from grounded battery 64 through contact 49, contact 5| of key l3, conductor 52, left-hand front contact and armature of relay 11, contact 58 of relay l6, left-hand front contact and armature of relay I8, contact 67, contact 59 of key it, contact 60 of key [3, contact 6| of key 55, over line conductor 5 to station 1, contact 52 of relay 2?, contact 63 (now closed) of relay 32, and thence through the windings of relays 33, 32, and 27 to ground. Relays 32 and 33 operate immediately in response to the current impressed on the conductor 5 pursuant to the closure of cit-normal contact 49, and relay 2! which is slow to operate is not energized at this time. The current impressed on the conductor 5 by battery 65 is not strong enough to pull up armatures 69 and ill of relay 35. Armatures 69 and 10 will be pulled up, as will presently appear, when battery 12 is substituted for battery 54 when key it is actuated to its idle position. When relay 32 operates, it extends the circuit originating at battery 64 through closed contact 62, left-hand armature of relay 32, conductor 52, closed contact-s i3 and 51 of relay 33, and through the windings of relays 33, 32, and 2'! to ground. Relay 33 is energized immediately to attract armatures 5! and 68. As previously mentioned, the current from the battery applied through contact 65 of the calling dial [5 is insufiicient to energize relay 33 to the extent necessary to attract its armatures 69 and it; that is, relay 33 operates on current from battery 65 to attract armatures El and 58 but under such conditions armatures 59 and 10 thereof will not be attracted. However, with the application of the higher potential at battery 12, all of such armatures will be attracted.

The stepping impulses from the battery 65 applied through contact 55 at the central station cause the energization of slow-to-release relay 32 and relay 33 but do not, for the period applied, cause the energization of relay 21 which requires a considerably longer period of time to attract its armatures than is required for the energize.- tion of relays 32 and 33 and the attraction of their armatures. However, in the present in stance, only one stepping impulse is generated to select station I. Two impulses would be generated to select station 8, and three to select station 9, etc. Irrespective of which station is selected, it is the closing of the off-normal contact 45 that extends the connection to the selected station, and not the last stepping impulse. In other words, the last stepping impulse selects the penultimate station, and the off-normal contact causes the selection of the ultimate or selected station (desired station). Since in the present instance, the closure of oil-normal contact 49 causes a prolonged pulse to be impressed on conductor 5, the relays 32 and 33 will be energized as previously described, and due to the prolongation of this impulse, relay 33 will not be de-energized (as it would in response to the short stepping pulses) thus contact 78 of relay 33 will be held opened, and front contact and armature 57 thereof will be closed, thereby directing the current through said armature 61 and through the windings of relays 33, 32, and 21 to ground. This final pulse through off-normal contact 49 will be long enough to cause the energization of relay 2?. Relays 21 and 32 will have their looking circuits established at this time through the output circuit of triode 31. The selection of station 7 is thus completed, and relay 2! upon energizing is locked up through its right-hand front contact and armature. As long as current is supplied in the output circuit of vacuum tube 31, relay 32 remains energized. Relay 2'! in energizing completes several separate and distinct circuits. At the extreme right-hand armature and contact of relay 2? the circuit of relay 4| is opened, assuring that for the period of energization of relay 21 relay 4| cannot be energized even though key 4!] has its contacts closed. At the innermost right-hand armature of relay 2! a locking circuit therefor is completed from the output circuit of the vacuum tube 37. At the extreme left-hand armature and front contact of relay 2'! a circuit is completed for the driving motor 35 of the printing telegraph equipment 25. Motor 35 thereupon starts and functions to supply power to the printing telegraph equipment 25. At the innermost left-hand armature and front contact of relay 21 the receiving printer and the signal transmitter constituting the printing telegraph equipment 25 are connected to the line conductor 5. Such operation causes contact 62 to be opened with the result that the line conductor 5 is not extended beyond the station 1 so that none of the other stations can establish a condition which might interrupt the intercommunication between the central station 6 and the remote station E.

The operator at the central station 6 now operates key is to the print position or the position wher contacts 5! and 59 are opened and contacts fi l and 15 are closed. Through contact 14, the printing telegraph equipment 20 including the signal transmitter 22 and the receiving printer 2! are connected to the line conductor 5. Through contact 15 power is applied to the driving motor 16 which furnishes the driving power for the receiving printer 2| and the signal transmitter 22. Upon the establishment of the conditions just described communication can take place between central station 6 and the remote station I.

When the intercommunication between stations 6 and i has been completed the operator at central station 6 operates key 55 to apply battery to line conductor 5 through contact 11,

Current from the battery applied through contact 11 of key 55 results in the application, of negative battery to the grid circuit of vacuum tube 31 to render said tube nonconductive, with the result that current no longer flows in its output circuit. Removal of current from the output circuit of the vacuum tube 31 results in the deenergization of relays 21 and 32 and the restoration of the relays at station 1 to the condition shown in Fig. 1.

The operation of key 55 at central station 6 also removes battery from contact 54 and consequently the winding of relay I1 and that of relay I8. Relays l1 and I8 are thus de-energized.

As set forth more clearly, the different conditions of the circuit are developed in the following three paragraphs. The call condition is that in which the circuit is conditioned so that the central station may call any one of the outlying stations. In Fig. 1, the circuit is shown in condition for placing a call. However, key |3 may be in the same position when the circuit is not conditioned for making the call but if key 55 is operated the line will be in such condition since all of the relays at the various stations will be released by making the grid electrodes of the several triode vacuum tubes negative. When key 55 is released, positive battery is again applied to the line conductor, and relays l6 and I1 will be operated, as shown in the drawing, in the manner previously described.

Assume that the operator at the central station 6 desires to communicate with station I rather than station 1. Under such circumstances calling dial would be operated correspondingly with the result that in response to the first stepping impulse relays l8 and I9 would be energized, and relay l8 would be locked up. In response to the second stepping impulse relay 32 at station 1 would be energized and locked up. However, since relay 33 was not maintained energized but rather is to be energized only for the duration of the stepping impulses, the line conductor 5 would be extended through normally closed contact 62 of relay 21, front contact and left-hand armature of relay 32, conductor 12, contacts 13 and 18 of relay 33 in series, conductor 19, through the contacts of the correspondingly numbered relays of stations 8 and 9, normally closed contact 82 of relay 28, normally closed contact 83 of relay 34, conductor 85, and thence through the left-hand windings of each of relays 35, 34, and 28 in series to ground. Relay 35 will operate immediately. Subsequently, relay 34 will be energized to establish a condition similar to that described for relay 32 at station I. With a cessation of impulses from the central station 5 through pulsing contact 65 or the maintenance of current on the line through normally closed contact 49 of the calling dial 5, relay 28 will be energized to establish through its armatures the several circuit connections previously described for the energization of relay 2'1. With relay 2B energized, telegraphic communication between central station 6 and remote station I0 may be effected. Relays 21 and 28 and other corresponding relays are operated, if its particular station is selected, by the closure of the off-normal contacts at the calling dial which will occur after all dialing impulses have been transmitted. These relays will not respond to the dialing or stepping impulses.

Following the completion of communication between central station 6 and remote station l0, key 55 will be operated clockwise to establish conditions similar to those described in connection with the restoration of the apparatus at station I to a condition preparatory to the reception of another call. Corresponding operations will be produced at station I0 upon the operation of key 55 to open contacts 54 and 5| and close contact 11. Under some conditions it is necessary for the central station operator to operate key 55 to release the relays at all of the substations since the line conductor maybe opened at some point due to a previously made connection. After key 55 is released, key I3 is returned to its central position.

When key i3 is rotated in a clockwise direction about its pivot to the idle position the contact 31 is closed, connecting the winding of relay 44 with its grounded battery to line conductor 5, through contact 6| of key 55. Relay 44 will be energized over a circuit extending from grounded battery 12 at relay 44, through the winding of relay 44, contact 3! of key l3, contact 6| of key 55, line conductor 5, through contact 52 of relay 21, through contact 63 of relay 32, then through the windings of relays 33, 32, and 2! to ground. Relay 21, being slow to operate will not be operated at this time. Relay 32 will be operated to pull up its right-hand and left-hand armatures. Relay 33, due to the stronger current impressed on the conductor 5 by battery 72 will now energize to pull up all of its armatures 61, 68, 69, and 10. It is recalled that relay 33, when energized by current from battery 64, only pulled up its armatures 51 and 68. Now, when relay 33 is so energized, its armature 10 will pull up to establish a locking circuit for relay 33 through the output circuit of triode 31. Also, armature 53 will pull up to establish, over conductor and through contact 9|, a by-pass for the line conductor 5 so that now the line circuit will be completed from battery 12, through the winding of relay 44, through contacts 81 and 6|, over conductor 5, through contact 62 of relay 21, through front contact and left-hand armature of relay 32, over conductor 72, through contact 13, through front contact and armature 63 of relay 33, over conductor 90, through contact 9| of relay 4|, thence over conductor 19 and 5 to succeeding stations, where the same results will be effected in step-by-step fashion to station H], where the circuit will terminate at ground 88. Relay 44 in energizing opens the circuit of station call lamp 45. Current applied to line conductor 5 from the battery at relay 44, which causes the energization of such relay, also causes the energization of relays 32 and 33 at station I, relays 34 and 35 at station l3 and the relays corresponding to such enumerated relays at stations 8 and 9. With regard to relays 33 and 35 it is significant to note that the battery under the condition described applied to line conductor 5 is sufficient to energize and attract all of the armatures of relays 33 and 35. When the lamp 45 is illuminated, as will hereinafter appear, the operator is apprised of the fact that a station desires to have a telegraphic communication circuit established.

While the system is thus in the idle condition, and any one of the stations I, 8, 9, and I0 desires to call the central station 6, the key at the calling station corresponding to key 40 at station 1 is closed, with the result that relay 4| is energized and is locked up through its right-hand armature and front contact and is maintained energized regardless of the opening of key 40. Also, with the energization of relay 4|, the extreme lefthand armature of relay 4| is attracted to open con-tact 9| with the result that the line conductor 5, which in the idle condition extended through armature 69, conductor 90, and contact 9| is opened, with the further result that ground is removed from line conductor to effect the deenergization of relay 44. Relay 44 in de-energizing, closes at its back contact the circuit for energizing lamp 45. The operator, in observing the illumination of lamp 45, appreciates that one of the several remote stations desires to have a telegraphic channel established. Relay 4|, upon energization, also establishes a circuit for relay 89 from A. C. source, through lamp 89, then through front contact and right-hand armature of relay 4| back to A. C. source.

The operator now operates key I3 to the call position, opening the circuit of relay 44 and connecting the contacts of calling dial I5 with line conductor 5. The removal of the battery at contact 81 of key I3, however, does not result in the de-energization of the relays 33 and 35 at stations 1 and I0, respectively, nor of the relay corresponding to relay 33 at the station where the relay corresponding to relay 4| is energized and locked up inasmuch as relay 4| in energizing prepared -a second or auxiliary locking circuit for its associated relay 33. Consequently, when relay 33 was energized, its locking circuits were established through its armatures 68 and and one of its locking circuits extended through armature 92 of its companion relay 4 I.

The operator at the central station 6 now operates the calling dial I5 to hunt for the calling station at which relay 4| is locked up. At the first substation the relay corresponding to relay 33 will be energized as previously described through the closure of pulsing contact 65. The pulses from the operation of pulsing contact vI55 will stop at the station Where relay 4| is energized and upon the energization of relay 21 thereat, inasmuch as the line circuit beyond that station is at that instant opened at the extreme left-hand back contact 9| and armature of relay 4|. This is so because relay 33 of the calling station is locked up through contact 92 of that station, and hence armature 69, controlling the by-pass 90--9I of conductor 5 around relay 33 is held attracted. Under such conditions relay 21 at station 1, assuming that station to be the station desiring to establish the intercommunicating circuit, will be energized upon a prolonged closure of contact 49 at calling dial I5 (the dial is now in its rest position) with the result that the printing telegraph equipment 25 will be connected to the line conductor 5. The operator at central station 5 will then operate key I3 to the print position, in which position the printing telegraph equipment 20 will be connected through the previously described contacts of key I3 to the line conductor 5 and thus to the printing telegraph equipment 25 at station 1.

Modification The circuit arrangement disclosed in Fig. 2 represents a modification of the system disclosed in and described in connection with Fig, l and differs generally from such system in the interconnection of the central station with the several remotely situated stations by a metallic circuit; that is, two line conductors instead of a single grounded conductor. Of course, as was described in connection with Fig. 1, the circuit arrangement disclosed in Fig. 2 is adaptable to radial operation; namely, operation wherein several metallic circuits extend radially from the central station to the several remotely situated 10- stations grouped on the respective metallic circuits.

Referring now specifically to Fig. 2, there is disclosed a central station I05 and a plurality of remotely situated stations I06, I01, I08, and I09 which are connected with the central station by means of line conductors I I2 and I I3. These line conductors H2 and. H3 extend from the central station I05 through the several remotely situated stations and through a'resistanoe II 4 located at the last station, as disclosed in connection with station I09. While Fig. 2 shows the stations I06 and I09 complete, it is, of course, understood that equipment similar to that illustrated for such stations is also embodied in stations I01 and I08 which, for the purpose of clarity, are represented merely by broken lines.

Central station I05 embodies printing telegraph equipment IIB including, as described for Fig. 1, a receiving printer I I1 and a signal transmitter II 8 which may be of any commercially available type. The equipment H6 is intended to be connected with corresponding equipment H9 and I20 at any one of the stations I06 and. I09, respectively, pursuant to the operation of a calling dial I22 similar to the type employed in automatic telephone systems which includes the usual off-normal contact I23 and a pulsing contact I24. These contacts function as will be subsequently described to control the selection of the desired station through the. operation of the calling dial I22.

Also at the central station I05 is a multi-position key I26 which has a disconnect, a call, and a print position in which its contacts will be operated for the several identified functions.

Assume, for example, that station I05 desires municate telegraphically with that station through the operation of the printing telegraph equipments H6 and I20 at the respective stations. The operator, preparatory to initiating such a connection, operates key I26 from the position shown in the drawings counterclockwise, thereby opening certain of its right-hand contacts and closing the other of such contacts. Through the closure of contact I28, battery I29 of negative polarity is applied to conductor I30 which is connected to line conductor II3. Current is applied from such battery to line conductor II3 with the result that negative current passing through the several stations and resistance H4 is applied to the grid electrode of vacuum tube I3I at each of the stations I06, I01, and I08, which is noted I68 at'station I09. These vacuum tubes, when operative, provide through their output circuits current for locking the several relays at each of the stations individual thereto. However, th application of negative battery to the grid electrode of each of the vacuum tubes renders such tubes nonconducting, with the result that current no longer flows in the output circuit of each of such tubes. Consequently, any of the relays locked up at stations I06, I01, I08, and I09 will be de-energized. Through the operation of key I26 as described, ground is removed from contacts I33 and I34, thereby releasing relays I35 and I36 which, with the key I26 in its idle position, as shown in Fig. 2, will be energized and locked up through their locking circuits provided these relays were previously energized.

Key I26 is now restored to the position shown in the drawing, whereupon contacts I33, I34, and I31 will again be closed. Upon the closure of such a .11 contacts relays I36 and I38 are energized over a circuit extending from ground at battery I38 at the printing'telegraph equipment II6, conductor I40, normally closed (off-normal) contact I23 of the calling dial mechanism, contact I4I, righthand back contact and armature of relay I42, conductor I43, contact I44 of key I26, right-hand winding of relay I45, conductor I46, closed contact I41 of relay I36, winding of relay I38, lefthand winding of relay I36, conductor I48, contact I31 of key I26, conductor I30, left-hand winding of relay I45, resistance I49, conductor I50, and contact I34 of key I26 to ground. Relays I38 and I36 are energized over the circuit just traced. Relay I36, upon being energized, establishes through its right-hand contact and armature a locking circuit, extending from battery I5I, right-hand winding, contact, and armature of relay I36, and contact I33 of key I26 to ground. Also, with the operation of relays I36 and I38 at central station I05, relay I55 and relay I56 at station I06 and I09, respectively, and the relay corresponding thereto at each of the other stations such as I01 and I08, will be energized over a circuit including conductor II3, left-hand winding of each of relays I51, I55, and I58 at station I06, contact I53 of relay I58, then closed contact I60 of relay I55, and normally closed contact I6I of relay I51 to line conductor II2. Circuits similar to that traced for station I06 will be established at each of the other stations I01, I08, and I09, with the result-that the relay thereat corresponding to relay I55 at station I06 and relay I56 at station I09 will be energized. However, relays I 51 and I58 at station I06 and relays I62 and I63 at station 'I 09 as well-as the relays corresponding thereto at stations I01 and I08 will not be energized.

Consequently, the armatures of such relays will, for the described operation, remain in the position showninFig. 2.

The operator at station I05 now operates calling dial I22 pursuant to the assigned number of station I00. Off-normal contact. I23 will be opened, opening the energizing circuit of relay I38. De-energization of relay I38 and the closure of its contact I65 extends the circuit under the control of calling dial I22 to relays I35 and I66. When the circuit is again closed through the closure of pulsing contact I24, relays I 35 and I66 will be energized. Relay I35 will be locked up over a circuit extending from grounded battery I5I to ground at contact I33 of key I26. Upon the opening of such circuit through the openin of contact I24, relay I66 is de-energized to extend the pulsing circuit over the line conductors II 2 and I I3 to the counting relays I55 and I58 at station I08 and the corresponding counting relays at each of stations I01 and I08 and the counting relays I56, I63, at station I09. At station I06 and in response to the succeeding stepping impulses thecircuit is extended to the corresponding relay at station I01 and the stepping impulses are in a similar manner extended to succeeding stations in response to each succeeding stepping impulse until the final stepping impulse advances the circuit through the relays at station I09 or the final station. When the stepping impulses are all transmitted, the calling. dial I22 returns to its normal position closing contact I23 with the result that a continuous current now flows through relay I62 which is thereupon operated. Through the operation of contact I24 of the calling dial I 22 and the generation of pulsing impulses, relays I56 and I63'will be energized. Following a closure of contact I23 at call- 12 ing dial 122, slow-to-operate relay I62 will be energized. Each of the relays I56 and I62 will be locked up and maintained energized by locking potential supplied through their right-hand armature contact and winding from the output circuit of a triode vacuum tube I68. Relay I62'in energizing operates its left-hand contacts to connect the printing telegraph equipment 20 through its armature I69 to line conductor H2 and thence through the several intermediate stations to the central station I05 and finally to the telegraphic apparatus II6 thereat. Through another armature of relay I62 the source of power for the motor for driving the rotary elements of the printing telegraph equipment I20 is completed.

The operator at station I 05, following a lapse of time sufiicient to permit the connection of the desired station to the metallic circuits H2 and H3, operates key I26 in a clockwise direction to open contact I44 and close contact I10. With the closure of contact I10 the printing telegraph equipment H6 at the central station I 05 is con-- nected for telegraphic communication with the printing telegraph equipment I20 at station I09 over line conductors IE2 and II3. The printing telegraph equipments H6 and I20 are now connected through the line conductors H2 and H3 in series and telegraphic communication may be conducted between such stations.

Following the completion of the telegraphic communication between the designated stations the operator at central station I05 operates key I26 counterclockwise, and thus applies negative battery to the line conductor and also to the grid electrodes of all of the vacuum tubes such as I3I and I68.

All relays at the several substations are thu released, The key I26 is now returned to its middle position, the position shown in Fig. 2, and is again in position for the operator to call another station, if desired, or if no calls are to be made, key I1! is depressed and held depressed for a period sufficient for vibrating relay I42 to generatea number of stepping impulses greater than the total number of substations on the line conductors. if no stations have registered a number through the operation of a key corresponding to I15, the line conductors will be extended, as previously described, but will now pass through resistance I I4 and not through the winding of any of the relays at the substations. The circuit just described, however, extends through the winding of relay I45 at the central station. The system is now in its idle condition preparatory to the reception of a call. When any of the stations such as I06 desires to communicate with the central station I35 the operator at station I06 operates key I15 to close contacts I16, I11, and ,I18. Uponthe closure or" contacts I16 current flows through the two windings of relay I45 to produce opposite magnetic effect with the result that relay I45 remains deenergized. There is a winding of such relay in each of conductors II2 andiI3 to effect the energization of relay I45. Relay I45 closes through its armature and front contact an energizing circuit for relay I which is locked up over a circuit extending to ground under the control of armature I8I of relay I42. Relay iiill, in energizing, also completes an operating circuit for signal lamp I82 which, when illuminated, serves to apprise the operator atsta-tion I05 that one of the remote stations on the circuit including the conductors I I2 and I I3 desires to communicate telegraphical- 1y. .Through the closure of contact I11 at key I15 ground is applied to the right-hand armature of relay I58 at station I85 so that when relay IE8 is energized it will be maintained energized over a locking circuit extending from the output circuit of vacuum tube 53!, right-hand winding, front contact and armature of relay its, and contact I1? of key 515 to ground. The operator at central station I435 now depresses key iii to transmit through the operation of relay #52 a series of impulses. ihe counting relays at the several stations will be energized pursuant to the impulses generated and until the station at which the armature corresponding to relay I58 is rounded is reached. When such condition is established, relay I55 is energized and locked up through the circuit previously described. The energization oi relay its opens at its contact I59 the circuit extending to the other stations. When the impulses generated through the operation of relay I42 cease, and off-normal contact I23 is closed, relay i? is energized to connect the printing telegraph equipment III? to the line conductors H2 and IE3. Ehe operator at station )5 now moves key I25 in a clockwise direction to connect, as previously described, the printing telegraph equipment Ilfi at station N35 to line conductors H2 and IE3. Stations It? and its may now communicate with each other telegraphically. The receiving printer at each of the stations I56, H17, H38, and IE9 is equipped with a, mechanism indicated generally by the bar I85 and bar lat at stations H36 and I09, respectively, which, in response to a particular code signal, will be operated to restore the key H5 to the position shown in Fig. 2. When such an operation occurs, contacts Fit and II? are opened, with the result that relays I5? and IE3 are de-energized and the printing telegraph equipment such as III! is disconnected from the line conductors I I2 and I I3 and is also rendered inelfective inasmuch as the operating circuit of its driving motor is discontinued at the armature and front contact of relay I51.

It is significant to note that key H5 at station I06 or the key corresponding thereto at each of the other stations such as I57, I98, and I99, may be operated during the time communication is being conducted between central station 35 and any of the other remotely situated stations Without interfering with the communication. Such operation, of course, will result in the energizetion of relay I45 and consequently the energization of relay I86 and the lighting of lamp I 82 which serves to appris the operator of the desire of one of the other stations on the circuit a to communicate with the central station. Consequently, upon the completion of the communication then in process, the operator will, with the restoration of key i255 to the position shown in Fig. 2, operate key ill to establish a connection similar to that previously described in connection with station I06.

While only four stations are indicated, a maximum of ten stations may be connected to a single circuit and a regular telephone dial used in the usual manner for calling the stations. However, through the addition of a key such as i ll Fig. 2, which may also be applied to the. disclosure of Fig. 1, any number of stations may be connected in the line and selectively connected through the operation of the calling dial. With signaling stations requiring more than ten impulses, key I5! is depressed to open the line circuit and is held in such position until the dialing is completed. If station numbered I 2 is desired, 10 may be dialed and after the dial has come to rest, 2 may be dialed and after completing the dialing of 2 the key MI is released so that station numbered I2 is connected to the line conductor. Similar operation may be achieved in connection with the arrangement disclosed in Fig. 1.

While the invention has been disclosed and described as applied to particular circuits and apparatus, it is manifest that modifications are possible without departing from the spirit and scope of the invention.

What is claimed is:

1. In a telegraph system, a central station, a line conductor extending from said station to a plurality of remote stations and serially connecting said central and remote stations, printing telegraph apparatus at each of said stations, means at said central station for generating station selooting impulses, means at each of said remote stations responsive to said station selecting impulses for connecting the printing telegraph apparatus at such selected station to said line conductor, electronic means individual to each of said remote stations for supplying holding current to said station selecting means for maintaining the connection with said line conductor, and means at said central station for establishing a condition on said line whereby said electronic means is rendered inefiective as a holding current supply means and the printing telegraph apparatus individual thereto is disconnected from said line conductor.

2. In a telegraph system, a central station, a line conductor extendin from said station to a plurality of remote stations and serially connecting said central and remote stations, printing telegraph apparatus at each of said stations, means at said central station for generating station selecting impulses, means at each of said remote stations responsive to said station selecting impulses for connecting the printing telegraph apparatus at such selected station to said line conductor, a vacuum tube rectifier individual to each of said remote stations and having its grid electrode connected to said line conductor for supplying holding current to said station selecting means to maintain the connection with said line conductor, and means at said central station for changing the polarity of the grid electrode of said vacuum tube rectifier whereby said vacuum tube rectifier is rendered ineffective and the printing telegraph apparatus individual thereto is disconnected from said line conductor.

3. In a telegraph system, a central station, a plurality of remote stations, a line conductor connecting said remote stations serially with said central station, printing telegraph apparatus at each of said stations, means at said central station for generating predetermined station selecting impulses, counting relay means individual to each of said remote stations responsive progressively in accordance with the operation of said station selecting impulse generating means at the central station for controlling the connection of the printin telegraph apparatus individual thereto to said line conductor, and means thereafter operative at said central station for connecting the printing telegraph apparatus at said station with said line conductor whereby telegraphic communication may take place between said central station and the selected remote station.

4. In a telegraph system. a central station, a plurality of remote stations, a line conductor extending from said central station to each of said remote stations and interconnecting said stations serially, printing telegraph apparatus at each of said stations, means at said central station for generating station selecting impulses, counting relay means at each of said remote stations responsive to predetermined station selecting impulses generated at said central station, and means associated with said counting relay means and responsive after a predetermined cessation of the station selectin impulses for connectin the printing telegraph apparatus associated therewith to said line conductor.

5. In a telegraph system, a central station, a plurality of remote stations, a line conductor extending from said central station to each of said remote stations and interconnecting said stations serially, printing telegraph apparatus at each of said stations, means at said central station for generating station selecting impulses, counting relay means at each of said remote stations responsive to predetermined station selecting impulses generated at said central means, and a slow-to-operate relay energized after a predetermined cessation of said station selecting impulses for connecting through its armature and contact the printing telegraph apparatus at said remote station with said line conductor.

6. In a telegraph system, a central station, a plurality of remote stations, a line conductor extending from said central station to each of said remote stations and interconnecting said stations serially, printing telegraph apparatus at each of said stations, means at said central station for generating station selecting impulses, counting relay means at each of said remote stations responsive to predetermined station selecting impulses generated at said central means, a slowto-operate relay energized after the return of the means at the central station returns to its normal condition for connecting through its armature and contact the printing telegraph apparatus at said remote station with said line conductor, and means controlled by said sloW-to-operate relay for opening the line circuit extending to said other remote stations.

'7. In a telegraph system, a central station, a plurality of remote stations, a line conductor extending from said central station and connecting said remote stations serially with said central station, printing telegraph apparatus at each of said stations, a calling dial at said central station for generating station selecting impulses, a pair of counting relays at each of said remote stations responsive to the operation of said calling dial, and means at each remote station and included in circuit with said counting relays and operated upon the return of the calling dial to its normal position for rendering the printing telegraph equipment thereat effective to permutation code impulses to said line conductor.

8. In a telegraph system, a central station, a plurality of remote stations, at line conductor extending from said central station and connecting said remote stations serially with said central station, printing telegraph apparatus at each of said stations, a calling dial at said central station for generating station selecting impulses having an oil-normal contact, a pair of counting relays at each of said remote stations responsive to the operation of said calling dial, means at each remote station operated upon the closure of said oil-normal contact for rendering the printing telegraph equipment thereat effective to permutation code impulses to said line conductor, and means at said central station operative thereafter 16 for connecting the printing telegraph equipment at the central station with said line conductor.

9. In a telegraph system, a central station, a plurality of remote stations, a line conductor extending from said central station and connecting said remote stations serially to said central station, printing telegraph apparatus at each of said stations, means at said central station for generating station selecting impulses, counting relay means at each of said remote stations responsive to the operation of said means at the central station for connecting the printing telegraph apparatus thereat with said line conductor, a signaling device at said central station, means at each of said remote stations for establishing a condition for the operation of the signaling device at said central station, and means at each of said remote stations controlled by said counting relay means thereat responsive following the operation of said counting relay means at the signaling remote station under the control of the operation of said signaling means at the central station for connecting the printing telegraph apparatus at the signaling remote station with said line conductor.

10. In a telegraph system, a central station, a plurality of remote stations, a line conductor extending from said central station and connecting the remote stations serially with said central station, printing telegraph apparatus at each of the stations, means at the central station for generating station selecting impulses, a pair of counting relays at each of the remote stations responsive progressively to the impulses generated by said impulse generating means at the central station for controlling the connection of their printing telegraph apparatus with said line conductor, and means for establishing upon the energization of one of said relays a locking circuit therefor whereby upon predetermined conditions being established at the central station the printing telegraph apparatus at said remote station will be connected to said line conductor.

11. In a telegraph system, a central station, a plurality of remote stations, a line conductor extending from said central station and connecting the remote stations serially with said central station, printing telegraph apparatus at each of the stations, means at the central station for generating station selecting impulses, a pair of counting relays at each of the remote stations responsive progressively to and in accordance with the impulses generated by said impulse enerating means at the central station, and means responsive following a predetermined operation of said impulse generating means for establishing a condition whereby said printing telegraph apparatus is connected to said line conductor for communication with said central station.

12. In a telegraph system, a central station, a line conductor extending from said station to a plurality of remote stations, printing telegraph apparatus at each of said stations, means at said central station for generating station selecting impulses, counting relay means at each of said remote stations responsive to said station selecting impulses for connecting the printing telegraph apparatus at such selected station to said line conductor, electronic means individual to each of said remote stations for supplying holding current to said station selecting means for maintaining the connection with said line conductor, and means at said central station for establishing a condition on said line whereby said electronic means is rendered ineifective as a holding current supply means and the printing tele- 17 graph apparatus individual thereto is disconnected from said line conductor.

13. In a telegraph system, a central station, a line conductor extending from said station to a plurality of remote stations, a pair of line conductors extending from said central station to the remote stations and serially connecting said stations, printing telegraph apparatus at each of said stations, means at said central station for generating station selecting impulses, means at each or said remote stations responsive to said station selecting impulses for connecting the printing telegraph apparatus at such selected station to said pair of line conductors, a vacuum tube rectifier individual to each of said remote stations and having its grid electrode connected to one of said line conductors for supplying holding current to said station selecting means for maintaining the connection with said line conductors, and means at said central station for changing the polarity of the grid electrode of said vacuum tube rectifier whereby said vacuum tube rectifier is rendered ineffective and the printing telegraph apparatus individual thereto is disconnected from said line conductors.

14. In a telegraph system, a central station, a plurality of remote stations, a line conductor connecting said remote stations serially with said central station, printing telegraph apparatus at each of said stations, means at said central station for generating predetermined station selecting impulses, a pair of counting relays individual to each of said remote stations responsive progressively in accordance with the operation of said signal generating means at the central station, means for maintaining one of said relays energized with the operation of said impulse generating means, means operated following a predetermined cessation of the station selecting impulses for controlling the connection of the printing telegraph apparatus individual thereto to said line conductor, means thereafter operative at said central station for connecting the printing telegraph apparatus at said station with said line conductor whereby telegraphic communication may take place between said central station and the selected remote station, and means subsequently effective for restoring said relays and said means at the remote station to their normal condition.

15. In a telegraph system, a central station, a plurality of remote stations, a line conductor extending from said central station to each of said remote stations and interconnecting said stations serially, printing telegraph apparatus at each of said stations, means at said central station for generating station selecting impulses, counting relay means at each of said remote stations responsive to predetermined station selecting impulses generated at said central station, means associated with said counting relay means and responsive after a predetermined cessation of the station selecting impulses for connecting the printing telegraph apparatus associated therewith to said line conductor, and means at said central station effective following the completion of the communication for transmitting impulses sufiicient to restore the counting relays at each station to their normal condition.

16. In a telegraph system, a central station, a plurality of remote stations, a line conductor extending from said central station to each of said remote stations and interconnecting said stations, printing telegraph apparatus at each of said stations, means at said central station for generating station selecting current impulses, counting relay means at each of said remote stations responsive to predetermined station selecting impulses generated at said central means, and a slow-to-operate relay energized after a predetermined cessation of said station selecting impulses and upon the application of normal line current for connecting the printing telegraph apparatus at said remote station with said line conductor.

17. In a telegraph system, a central station, a plurality of remote stations, a line conductor extending from said central station to each of said remote stations and interconnecting said stations serially, means at said central station for generating station selecting current impulses, counting relays at each of said remote stations responsive to predetermined station selecting impulses generated at said central means, a slowto-operate relay energized afterv a predetermined cessation of said station selecting impulses for connecting through its armature and contact the printing telegraph apparatus at said remote station with said line conductor and for opening at its contacts the line circuit extending to said other remote stations, means at said remote stations for maintaining, when operated, said counting relays and said slow-to-operate relay energized, and means at the central station for establishing a condition on said line conductor whereby said relays are restored to their normal condition.

18. In a telegraph system, a central station, a plurality of remote stations, a line conductor extending from said central station and connecting said remote stations to said central station, printing telegraph apparatus at each of said stations, means at said central station for generating station selecting impulses, counting relay means at each of said remote stations responsive to the operation of said means at the central station for connecting the printing telegraph apparatus thereat with said line conductor, a signaling device at said central station, means at each of said remote stations for establishing a condition for the operation of the signaling device at said central station, means at each of said remote stations controlled by said counting relay means thereat responsive following the operation of said counting relay means at the signaling remote station under the control of the operation of said signaling means at the central station for connecting the printing telegraph apparatus at the signaling remote station with said line conductor, and means at the remote station and operated through the operation of the printing telegraph apparatus thereat for restoring the means at the remote station to normal station selecting condition.

19. In a telegraph system, a central station, a plurality of remote stations, a line conductor extending from said central station and connecting the remote stations with said central station, printing telegraph apparatus at each of the stations, means at the central station for generating station selecting impulses, a pair of counting relays at each of the remote stations responsive progressively to the impulses generated by said impulse generating means at the central station for controlling the connection of their printing telegraph apparatus with said line conductor, means for establishing upon the energization of one of said relays a locking circuit therefor whereby upon predetermined conditions being established at the central station the printing telegraph apparatus at said remote station will be connected to said line conductor, and means at the remote station responsive through the operation of the printing telegraph apparatus thereat for opening said locking circuit and restoring said remote station to normal station selecting condition.

20. In a telegraph system, a central station, a plurality of remote stations, a line conductor extending from said central station and connecting said remote stations to said central station, printing telegraph apparatus at each of said stations, means at said central station for generating station selecting impulses, counting relay means at each of said remote stations responsive to the operation of said means at the central station for connecting the printing telegraph apparatus thereat with said line conductor, a signaling device at said central station, a switch at each of the remote stations operated manually for establishing a condition for the operation of said signaling device, means at each of the remote stations controlled by said counting relay means thereat responsive following the operation of the switch at the signaling remote station and def;

pendent upon its operation for connecting the printing telegraph apparatus thereat with said line conductor upon the transmission from said central station of station selecting impulses, and

means included in and operated by the printing telegraph apparatus at said station for operating said switch to its normal position.

21. In a telegraph system, a central station, a plurality of remote substations, a line conductor extending from said central station and connecting said substations in series therewith, means at said central station to transmit over the line conductor'stepping impulses for establishing telegraphic conditions selectively with any of said substations and for terminating the line conductor at theselected substation, means at said substations responsive to the stepping impulses and operative to conditions generated at the central station for extending the line conductor step-by-step from substation to substation until the called substation is selected, and means to complete the line conductor through all of the several substations by transmitting a number of impulses in excess of the number of stations included in the line conductor.

22. In a telegraph system, a central station, a plurality of remote substations, a line conductor extending from said central station and connecting said substations in series therewith, means at the central station to transmit over the line conductor stepping impulses, means at each of the substations responsive to the stepping impulses, and means to complete the line conductor through all of the several substations by transmitting a number of impulses in excess of the number of stations included in the line conductor.

23. In a telegraph system, a central station, a plurality of remote substations, a line conductor extending from said central station and connecting said substations in series, telegraphic apparatus at each of the substations and at the central station, counting relay means having an element thereof located at each substation to connectin response to impulses transmitted from the central station in the line conductor the telegraphic apparatus at one of the substations pursuant to the number of impulses transmitted from the central station, and means to disconnect the telegraph apparatus at the substation in response to a telegraphic signal.

24. In a telegraph system, a central station, a plurality of remote substations, a line conductor extending from said central station and connecting said substations in series therewith, telegraph apparatus at the central station, telegraph apparatus at each of the substations, a single series of counting relays with a single unit of said counting relays located at each remote substation, means at the central station to transmit a variable number of stepping impulses over the line conductor to operate the relay units at the different substations in succession, and means to connect the printing telegraph apparatus at the substation with the line conductor determined by the number of stepping impulses transmitted from the central station.

25. In a telegraph system, a central station, a. plurality of remote stations, a line conductor extending from said central station and connecting said substations in series therewith, switching relays at each of the substations, a three-electrode vacuum tube having a control grid and a plate at each of the substations, a locking circuit for each of the relays connected to the plate electrode of the associated vacuum tube, said grid electrode being connected to the line conductor, and means to alter the potential of the line conductor to change the potential on said grid electrodes whereby the plate circuit of each of'said vacuum tubes is rendered nonconducting.

26. In a telegraph system, a central station, a plurality of remote substations, a line conductor extending from said central station and connecting said substations in series therewith, means at the central station to transmit a different number of impulses according to the substation desired for communication, a single stepby-s'tep device, an element of said device located at each of the substations, and means to operate the element at each substation by one of the transmitted impulses in the same location in the group of impulses as the substation is in the sequence of the substations.

27; In a telegraph system, a central station, a plurality of remotestations, a line conductor extending from said central station and connecting said substations in series, a set of switching' relays at each substation, means at the central station for applying an increased potential to said line conductor whereby saidswitching relays are energized to establish the line' conductor through their contacts and independently of their windings, a call indicating relay at the central station, and means at each of the substations for establishing a condition with the line conductor so extended for controlling said call indicating relay.

LOUIS M. POTTS.

REFERENCES CITED The following references are of record in the file of this patent;

UNITED STATES PATENTS

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