US2400124A

US2400124A - Telegraph exchange system

Info

Publication number: US2400124A
Application number: US480264A
Authority: US
Inventors: George G Light
Original assignee: Western Union Telegraph Co
Current assignee: Western Union Telegraph Co
Priority date: 1941-07-31
Filing date: 1943-03-24
Publication date: 1946-05-14
Anticipated expiration: 1963-05-14

Description

May 14, 1946. l G, U HT 2,400,124

I TELEGRAPH EXCHANGE SYSTEM Original Filed July 51 1941 5 Sheets-Sheet l F :uu: Hnnr! T v r a g *Hll l m l 1 E INVENTOR L l T :Q) 1' s. c. LIGHT i I o D N man aY w ATTORNEY -TO FIG. 4

3 1946- e. s. LIGHT 2,400,124

TELEGRAPH EXCHANGE SYSTEM Original Filed July 31 1941 5 Sheets-Sheet 2 ATTORNEY May 14, 194-6. UGHT 2,400,124

' TELEGRAPH EXCHANGEVSYSTEM Original Filed July 51 1941 5 Sheets-Sheet 3 FIG. 3

Eii

INVENTOR e. c. LIGHT {ll U l H: ATTQRNEY May 14, 1946. LIGHT TELEGRAPH EXCHANGE SYSTEM Original Filed July 51 1941 5 Sheets-Sheet 4 BY ATTORNEY m (PM i N vu.

TO FIG.5

Patented May 14, 1946 2,400,124 TELEGRAPH EXCHANGE SYSTEM George G. Light, Kew Gardens, N. Y., assignor to The Western Union Telegraph Company, New York, N. Y., a corporation of New York Original application July 31, 1941, Serial No.

404,765. Divided and this application March 24, 1943, Serial No. 480,264

. 12 Claims. Cl. 178-2) This invention relates to telegraph systems and more particularly to multi-station printing telegraph systems embodying a plurality of stations or oifices and arrangements for selectively interthe transmission of code signals to the line through the switchboard.

Another object of the invention is to provide a system as outlined above which is capable of connecting the transmitting and receiving ap- 5, operating in conjunction with a multistation or paratus or printers of the system. The present way-station circuit in such a manner that the invention involves an improvement in or modifi central ofilce'may select any one of the stations cation of the telegraph systems shown in the. on the way-station and lock out the unselected patent to Wheeler, Hoover and Dirkes, No. stations.

2,193,810, granted March 19, 1940, and in the V In accordance with the above, another object pending application of G. G. Light and W. B. of the invention is to provide means whereby the Blanton, Serial No. 350,402, filed August 3, 1940, selection of a station on a way-station circuit is and is a division of the application of G. G. Light automatically effected from the central station by Serial No. 404,765, filed July 31, 1941, now Patent a plugging operation into one or-the other of a No. 2,351,621, granted June 20, 1944. plurality of jacks, each individual to one of the In general terms, the object of this invention stations on t e way-station circuit. is to simplify the selecting and control apparatus A still further object of the invention is to proin systems of the above-mentioned character, and vide a system of the above type embodying the guard against faulty operation, as for example above enumerated features operating in consending to a station where the receiving appara- 0 junction with a central ofiice wherein the receivtus is not conditioned for operation or has been ing equipment thereat is in a concentrator ardisconnected. Heretofore code transmittersand rangement. code-responsive equipment have been commonly Qther objects and advantages of the invention employed for selecting stations, operating signals will appear from the followin description of the and motor controls, and eifecting other functions preferred embodiment thereof shown in the acin a multi-station system. The control equipment companying drawings, wherein: in some instances is quite complex, and the sys Fi s. 1, 2 and 3 taken together constitute a tern istfutlgher ctomlplicateld ts it neccsigry to wiring diagram of a single-station line circuit and sepala e e 0011 r0 Sigma 5 Tom 6 prm the terminal equipment at the main station or nals which are ordinarily sent over the same line switching t circuitsm Pystems, the character of the Figs. 4 and 5 form a wiring diagram of a multitelegraph 11116? llmlts the character of the station or way-station circuit, also terminating in tronmg code S1gna1s that P usedone the equipment at the main station shown in Figs. ture of the present invention 18 anovel arrangeor 2 and 3; ment fill effecting station selecttion, for selzting m) 6 is a timing chart illustrating the and re eaS1 ng prmtntg or tepea appam ferred timing adjustments of the various timing and operating supervisory signals or other funcunits. and tions over the line circuit without employing V g. 7 illustrates the manne1 in which Figs. 1 ell/hi1 code transmitters or code-responsive equlpto 5 are arranged to form th omplete circuit i other obect of the invention is to nterlocl: diagram the sending and receiving apparatus in a tele- In t t l an eyf'change system. is Shown graph exchange system, wherein the transmitting m i g smile q q Y m: statlqn apparatus at a main station or switching center I, a fi t clrcu S a a 2 may be temporarily connected with an outgoing S 3 Ion SW1 0 mg f er SW1 0 line, in order that line circuit interruptionsmay mi for ntterconneitltlg P11311118 clrcults' the be transmitted for signaling and control purposes remote stations, a cal 1s imtiated by actuating a calling key and terminated by restoring said key. from a remote station to the switching center and vice versa, irrespective of connections made to a r The opFratlPn of caumg W calls? a line at the switchboad in the Switching centen determined interruption of the line circuit to the w this feature f the invention, t, becomes main station which is effective to pick up an idle possible to transmit control circuit-interruptions storage and trans i g l AS soon as an idle of predetermined length in both directions over mill; is eized, a 11118 c1rc u1t interruptionof a D the'line circuit without the possibility of the dura- I determined length is produced at the main station tion of the signals being altered or distorted by which is efiective to operate a go-ahead signal at the remote station. If the line circuit becomes opened or the storage equipment accidentally disconnected, the go-ahead signal at the remote station is extinguished or restored to indicate at said station that transmission should be stopped. At the end of the message, the release and restoration of equipment are also accomplished by the transmission of line circuit interruptions of 'predetermined length, and certain guard features are incorporated, as will be pointed out hereinafter.

In the case of a multi-station or way-station line circuit, the initiation of a call from one of the remote stations to the main station locks out the other station and also initiates a call to the main station in substantially the same manher as in the case of the single station circuit. In making an outgoing connection to the waystation circuit at the switchboard, the desired station is selected by the transmission of a, line circuit interruption, of different length for each station on said circuit. The selecting interruption signal is automatically produced upon plugging into one or the other of a plurality of jacks, each individual to one of the stations in the Way station circuit. At the end of the call, the circuit is released and the control equipment automatically restored to normal, a "clear-out circuit interruption signal being transmitted to the remote stations from the main office as in the case of a call to or from a station on the single-station line circuit.

Single-station Zine circuit Referring to Figs. 1, 2 and 3 of the drawings, the printer PI at station A, Fig. 1, is connected through the line LI to the main olfice where messages received from station A may be recorded or stored and retransmitted over outgoing lines or channels terminating at said office at the switchboard represented by the jacks J IJ 4, Fig. 3. Messages received from station A at the main office and from the other stations over lines terminating at said ofiice are stored in the form of perforated tape in the receiving reperforators such as that shown at RR, Fig. 2, and repeated by the associated tape transmitter TT after the tape transmitter has been plugged into the jack representing the selected outgoing line circuit or channel substantially as described in the abovementioned copending application of Light and Blanton. The tape transmitter may be similar to that shown in the patent to Angel, No. 2,172,269, dated September 5, 1939. The reperforator may be a printer perforator similar to that shown in the patent to Dirkes and Wentworth, No. 2,143,- 828, dated January 10, 1939. When one of the remote stations, such as the station A, initiates a call to the main office, a finder switch SI or S2 is operated to connect an idle receiving reperforator RR to the calling line in a manner to be described below. This general arrangement including a series of finder switches for connecting an idle receiving unit or a reperforator to a calling line is shown in a number of patents in the prior art including the above-mentioned patent to Wheeler et al. The arrangement shown herein is conventional except for certain features to be described, and therefore certain details of construction are omitted for the sake of simplicity.

The line LI may be any suitable telegraph channel but for purposes of illustration it is shown as terminating at the respective ofiices or stations in terminal duplex sets II and I2 of a conventional character. The keyboard of the printer PI is connected to the sending leg of the terminal duplex set I l and the printer magnet is connected to the receiving leg thereof in series with a normally operated relay I3. The sending leg of the terminal duplex set I2 at the main office is connected through the back contacts of relay I4 to the switchboard, while the receiving leg is connected through the conductor I5 and contacts of relay 26 to the winding of relay 25. The energization of relay 26 when the finder switch SI has connected to the calling line disconnects relay 25 from the receiving leg which is then connected through conductor I5 and the finder switch to the selector magnet of the reperforator RR.

When it is desired to initiate a call from station A to the main ofiice or to one of the lines or channels terminating at the switchboard in the main office, the key I8 is actuated, thus closing a circuit from positive battery through the outer left hand contacts of the key I8, condenser I9 and shunt resistor 20 to the right hand winding of relay 2!. The charging current of the condenser I9 causes relay 2I to attract its armatures momentarily, thus opening the line circuit extending from ground through the inner armature and back contact of said relay, the left hand armature and back contact of relay 49 in shunt relation to the keyboard contacts of the printer PI, and the winding of the transmitting relay 22. The operation of the transmitting relay 22 momentarily opens the rest or marking contacts of the differential relay of the terminal duplex set I2 at the main oflice, thereby opening the circuit of the normally operated relay 25, and said relay becomes deenergized. Upon the deenergization of relay 25, a circuit is closed through the left hand armature and back contact of said relay and the left hand armature and back contact of relay 26 in shunt relation to the winding of relay 25, thereby short-circuiting relay 25 to prevent the attraction of the armatures of said relay when the line circuit is reclosed. The deenergization of relay 25 closes a circuit through its right hand armature and back contact for initiating the operation of the first idle finder switch SI, S2, and so forth, to connect the associated idle reperforator to the line extending to the calling station A. AS pointed out above, this general arrangement is well known in the art and various arrangements for distributing successive calls to idle receiving units or reperforators may be employed. As shown, the grounding of the initiate conductor 28 by relay 25 closes a circuit through the inner left hand armature and back contact of relay 29 and the right hand winding of relay 32 to battery, assuming that the receiving reperforator RR is idle. If the reperforator RR is in use, relay 29 will be operated to transfer the initiate circuit to the next finder switch S2, as shown.

The energization of relay 32 closes a circuit to the stepping magnet 33 of switch SI, which circuit may be traced through the right hand armature and front contact of relay 32, the left hand outer armature and back contact of relay 29 and the upper wiper of the switch SI to the grounded bank contacts representing idle lines or lines which are already connected to a receiving reperforator and are thus grounded through the wipers of other finder switches. When the stepping magnet 33 of the switch SI, which is provided with self-interrupting contacts, as shown, has actuated the wipers of the switch into engagement with the bank contacts representingthe calling line, in this instance the first bank contacts, the stepping of the switchstops, since the bank contact associated with the upper wiper is no longer grounded through the conductor 34 and the front contact associated with the right hand armature of relay individual to calling station A. Thereupon the short circuit around

relays

29 and 32 is opened, and relay 29 becomes energized through a circuit from battery through the stepping magnet 33, the left hand armature and front contact and left hand winding of relay 32, the left hand Winding of relay 2 9, and the armatures and back contacts of relays 36and 31 to ground. Relay 32 is locked up in series with the left hand winding of relay 29. Since the stepping magnet 33 is of low resistance compared to the windings of

relay

29 and 32, the current through the stepping magnet is insufiicient to actuate the switch wipers at this time.

The energization of relay 29 as described connects ground potential through the outer left hand armature and front contact thereof to the bank contact associated with the upper switch wiper of the switch SI to prevent another of the finder switches from connecting to bank contacts multipled to the first contacts of switch Si. The energization of relay 29 transfers the initiate circuit through its left hand inner armature and front contact to the control relays associated with the second witch S2 so that the next succeeding call will be picked up by the second storage unit until the first storage unit has been released. The energization of relay 29 also closes a circuit through its second right hand armature and front contact, the middle wiper of the switch SI, conductor 39, the winding of relay 26 and the right handarmature and front contact of normally energized relay 21 for energizing relay 26. The energization of relay 2B closes the circuits of relays 25 and at, the right hand inner and middle contacts of said relay, and relays 25 and 30 become energized. The energization of relay 26 also opens at its outer right hand armature and back contact the circuit of slow release relay 21, and after a short interval the latter relay releases its armatures. The energization of relay 30, as described, removes ground potential from the conductor extending to the jacks J l and J2 of the switchboard individual to the line Ll As indicated, the conductor 40 forms a part of the clutch magnet circuit of any distributor (corresponding to the circuit of the clutch magnet 63 of the distributor shown in Fig. 2) when the associated transmitter is plugged into the jack J I or J2. Thus, the energization of relay 30, indi-; vidual to the line Ll, stops transmission from the main office over said line to permit control signals or line interruptions, to be transmitted to station A. Similar relays are associated with the switchboard circuits of each full duplex line to stop transmission from the main office momentarily while an incoming call is being set up or disconnected over the same line. The slow-release relay 21 is adjusted so that it does not release its armatures until the lapse of sufficient time to insure that the cam shaft of the distributorcontrolled by relay 30 has come to rest. I In order to indicate to the operator or attendant at station A that a comiection to the receivingreperforator has been established and transmission may be commenced, the rest or marking line condition is interrupted for a predetermined period at the main oflica' ,This is accomplished as follows: Upon the deenejrgization of relay 21 as described, the short circuit around the right hand winding of relay 4| is opened, and said relay becomes energized in series with relay 26. Thereupon a circuitis closed from ground through the left hand outer armature and back contact of relay 42, the left hand outer armature and front contact of relay 4| and the winding of relay I4 to positive battery, whereupon relay 14 becomes energized to open the sending leg of the terminal duplex set l2, which operates the receiving differential relay of the terminal duplex set II at station A, causing relay l3 to become deenergized. At the same instant the energization of relay 4| opens the connection from negative battery to the grid .of a Vacuum tube 43 having the plate circuit thereof connected to the winding of relay 42. The vacuum tube 43 constitutes a timing device for operating relay 42 after a predetermined lapse of time, and for this purpose, the grid circuit of the tube 43 is provided with a shunt condenser 44 and grid leak 45 so that the potential of the grid of said tube gradually drifts toward the ground or open-:circuit potential whenever the negative cut-off potential has been removed from the grid by the operation of relay 4 I. Thus,

after a predetermined time delay which may be only a fraction of a second, relay 42 becomes energized and opens at its outer armature and back contact the above-described circuit of relay M. The deenergization of relay l4 recloses the line circuit so that the line interruption is accurately timed by the characteristics of the grid circuit of the vacuum tube 43. The operation of relay 42 also opens the circuit of relay 30, and said relay recloses the clutch magnet circuit 43, thus permitting transmission over the line Ll through the switchboard to be resumed.

At station A, the deenergization of relay l3 as described removes negative cut-off potential from the grid of the slow-to-operate or timing vacuum tube 48 and, after a predetermined period of time slightly less than the length of the line interruption caused by the timing tube 43, current flows through the vacuum tube 48 to energize the associated relay 49 and light the supervisory lamp 50 to indicate to the attendant at station A that the connection to the idle reperforator has been completed and transmission may be commenced. The

vacuum tubes

48, 5! and 52 at station A and tube 53 at the main office are all arranged like the tube 43 to impart a delayedoperating characteristic to the relay in the plate circuit thereof by control of the grid potential as described above, but the timing of the vacuum tubes is fixed at different periods for the purposes to be pointed out below. By Way of exam-- ple, suitable timing adjustments for the respective timing control units are shown in Fig. 6.

Upon the energization of relay 49 as described, a locking circuit for said relay is closed through its right hand inner armature and front contact and the inner armature and back contact of relay 56. A circuit is also closed through the right hand middle armature and front contact of relay 49, the armature and back contact of relay 55, the left hand winding of relay 2i and the right hand inner contacts of the key l8 whereupon relay 2| becomes energized and removes ground potential at the inner armature and back contact thereof from the keyboard of placed in operating condition, the line circuit through the keyboard contacts being connected through the left hand armature and front contact of relay 49 to ground at the left hand inner contacts of the key H3. The operation of the keyboard of the printer Pl transmits alternate rest or marking and spacing permutation code signals over the line Ll, the signals being transmitted through the conductor l5 and the contacts of the receiving relay of the terminal duplex set I2 at the main oflice and the contacts of the lower wiper of the switch S| to the magnet of the receiving reperforator RR, which records the received message in the form of perforated tape adapted to operate an associated tape transmitter TT to repeat the signals through the selected outgoing line circuit of channel.

After transmission has been completed the operator or attendant at station A releases the connected storage and transmitting equipment by restoring the key I8. If the operator fails to restore the key |8 at the end of the message or if, for any reason, no message signals are transmitted for, say thirty seconds, the timing vacuum tube 64 becomes conducting at the end of the selected period and relay 36 in the plate circuit of said tube is energized. The energization of relay 3B releases relays 29 and 32 to release the switch SI and transmit a disconnect signal to station A in a manner described below in connection with the normal disconnect operation. This feature of the invention prevents the operator at a calling station from tying up a reperforator indefinitely, but it will be noted that release of the switch in this manner will not be effected if the line circuit goes open, as in that case the series line relay 3| remains deenergized and maintains a negative cut-off potential on the grid of vacuum tube 64. Upon the restoration of the key l8 at the end of a message, the line circuit including the winding of the transmitting relay 22 and the left hand inner contacts of the key I8 is opened and at the same moment, the negative cut-off bias potential is removed from the grid of the vacuum tube 5|. After a predetermined time interval, current flows through vacuum tube 5| and the relay 55 in the plate circuit thereof becomes energized. The energization of relay 55 opens the circuit of the left hand locking winding of relay 2| and said relay becomes deenergized, thereby reclosing the line circuit including relay 22.

The timing of the line interruption as described is adjusted by employing suitable characteristics for the condenser and leak in the grid circuit of the vacuum tube 5| so that its duration is equal in length to transmission of one character from the keyboard of the printer Pl. Therefore, the receiving reperforator RR at the main ofiice responds as though a "blank or all-spacing code combination had been transmitted, and the blank-reading contacts 59 on the reperforator will momentarily close. The construction of a reperforator having contacts closed upon the reception of a particular code combination, for example, a blank, is disclosed in the above-mentioned Dirkes and Wentworth patent. The contacts could be applied to the stop member for the blank selection if the sixth pulse cutout was omitted. The closure of contacts 59 effects release of the finder switch SI in a manner to be described. Upon the operation of relay 55 as described above, the circuit of the left hand or looking Winding of relay 2| is opened and the latter relay becomes deenergized. Negative cutoff potential is connected through the outer armature and back contact of relay 2| to the bridge circuit of the vacuum tube 5| whereupon relay 55 becomes deenergized. All relays except relay 49 at station A are now restored to normal but the supervisory lamp 5%] remains lighted through a contact of relay 49 until finder switch S| at the main oifice has been restored to normal. The purpose of this arrangement will be described hereinafter.

The closure of the blank-reading contacts 59 of the reperforator at the main oiiice closes the circuit of relay 30 and at the end of the blank the line relay 3| which responds to line ignals is reenergized to close a circuit through its armature and front contact and the left hand armature and front contact of relay 60 for operating disconnect relay 31. The energization of relay 3'! interrupts the circuit through the left hand windings of

relays

29 and 32 and said relays become deenergized, thus restoring the selector switch SI to normal in readiness for the next call. Upon the deenergization of rela 29, the circuit of rela 26 is opened at the second. right hand armature and front contact of relay 29. The deenergization of relay 26 operates relay 30 to stop transmission over the line Ll from the main office While transmitting the break signal of such duration as to extinguish the supervisory lamp 5|] at the remote station A. The circuit of relay 30 may be traced through the middle right hand armature and back contact of relay 25 and the inner armature and front contact of relay 42. The energization of relay 30 opens the circuit of the clutch magnet of the transmitting distributor of any transmitter which may be connected through the switchboard to the line L! as described above, The deenergization of relay 26 further opens at its outer right hand armature and front contact the circuit of slow relay 2? and, after a short interval sufficient to permit the cam shaft of the sending distributor to come to rest, relay 2'! releasesits armatures. Upon the deenergization of relay 21, the circuit of relay 3-5 is interrupted at the left hand armature and front contact of the firstmentioned relay, and relay 35 becomes deenergized. Upon the deenergization of relay 35, a circuit is closed through the inner armature and back contact of said relay, the outer armature and front contact of relay 42 and the outer left hand armature and front contact of relay 4| for operating relay M to interrupt the line circuit at station A at the same instant that negative cut-off potential is removed from the grid of vacuum tube 53 at the outer armature and front contact of relay 35. After a predetermined time interval fixed by the characteristics of the grid circuit of the vacuum tube 53, current flows through the winding of relay 54 in the plate circuit thereof and said relay becomes energized. Upon the energization of relay 54 the circuit of the left hand locking winding of relay 4| is interrupted, whereupon said relay becomes deenergized and opens the above-described circuit of relay |4. The deenergization of relay I4 recloses the line circuit. Upon the deenergization of relay 4|, negative cut-off potential is applied through the right hand armature and back contact of said relay to the grid of the vacuum tube 43 whereupon relay 42 becomes deenergized and opens the circuit of relay 30. Upon the deenergization of relay 3!], the sending distributor of the transmitter plugged into the line Ll is again rendered operative for transmission. 1

At station A, the line relay I3 in the receiving leg of the terminal duplex set I I becomes deenergized in response tothe opening of the line circuit by the operation of relay M, as described above, thereby removing negative cut-ofi potential from the grids of

vacuum tubes

48 and 52. After a predetermined time interval long enough to permit both

tubes

48 and 52 to become conductive but slightly shorter than the timing of vacuum tube 53 at the main ofiice, current flow is established through the tubes 58 and 52, and their associated relays 49 and 56 respectively. Since relay 49 was previously locked up through its inner right hand armature and front contact, it remains energized until relay 56 becomes energized. Upon the energization of relay 56 the circuit of relay 49 is interrupted and said relay becomes deenergized to thereby extinguish the lamp 50. At the end of the line circuit interruption, relay l3 again becomes energized and connects negative cut-off potential through its armatures and front contacts to the grids of

tubes

48 and 52, thereby deenergizing relay 56 and maintaining relay 49 deenergized.

It will be noted that an important feature of the invention is the operation of the supervisory lamp 5!) solely' under the control of the finder switches at the main ofiice, the lamp being lighted as soon as one of the switches has seized an idle reperforator and being extinguished, not by the disconnect key l8, but when the finder switch has been released. Thus, if a false or accidental blank signal is received at the main office owing to line or apparatus trouble, which would cause the switch to release the connected reperforator, the supervisory lamp 50 will become extinguished to indicate that the receiving unit at the main office has been disconnected. Similarly, if the receiving reperforator is disconnected either by the operation of the relay 36 as described above or in any other manner by an attendant at the main oflice, for-example, the supervisorylamp 50 would serve as a positive indication to the operator or attendant at station A tostop sending until the line has been connected to another receiving unit.

As shown, the printer Pl at station A does not respond to its own keyboard to make a home copy of the messages transmitted from the station but is always in readiness to respond to transmission from the main oifice. However, on lines which are not arranged for full duplex op eration, the printer magnet may be connected in series with the keyboard as usual, Since the keyboard contacts are short-circuited by relay 49 when the receiving reperforator at the main office becomes disconnected, the failure of the printer to function provides an immediate signal to the operator that the circuit is not in readiness for-transmission;

Way station circuit The operation of a way station circuit where a plurality of stations are connected through a single series line circuit to the main station includes additional features not embodied in the single station circuit described above. Stations B and 0, Figs. 4 and 5, are shown connected to a line circuit L2, which terminates at the main station in the finder switches SI? and S2, as inthe case of the line Ll. For the purposes of illustration, the line L2 is arranged for half duplex operation, providing for transmission from either of the stationsB and C to the main office or switching center or for transmission from the switching center to either of said stations, but not for transmission in both directions at the same time. This illustrates the flexibility of the control system provided by the invention which will operate over either a half duplex, a full duplex (single-station operation), or any normally closed circuit adapted to transmit telegraph signaling impulses.

The operation of the Way station circuit is generally similar to that of the single station circuit described aboveexcept that provisions are made for operating a busy signal and looking out one of the remote stations when a call is initiated to the main station from the other remote station, and means is provided at the main office or switching center for selectively calling either of the remote stationsand locking out the other station. In the idle line condition, the printers P2 and P3 at stations B and C, respectively, are non-responsive to line signals, since the printer magnet is connected to holding ground. In view of the fore going detailed description of Figs. 1 to 3, the description of the operation of the way station circuit will be directed to these additional features. Assuming that the line circuit is idle and that the operator or attendant at station B desires to initiate a call to the main office or transmit a message through the main office switchboard to an outgoing line or channel, upon the operation of the calling key 10, relay H becomes energized to interrupt the line circuit at the left hand armature and back contact of said relay to initiate the operation of one of the finder switches SI or S2, as described above in connection with Figs. 1, 2 and3. In this instance, however, instead of a line interruption of indeterminate length, the duration of the line interruption is timed in order to lock out the printer-P3 and operate a busy signal at'station C.

The circuit of relay ll may be traced through the left hand armature and back contact of relay 12 the right hand inner armature and back contact offrelay 13,the third left hand armature and back contact of relay 14, the right hand make contacts of the-key 10, the outer armature and back contact of relay 15, the winding of relay H, and the middle left hand armature and back contact of relay 1E. Relay H locks up through its right hand inner armature and front contacts to ground at'the right hand armature and back contact of relay 12. The opening of th line circuit by relay H closes the back or spacing contacts oi the line relay 11, thus closing a circuit through said contacts, the winding of relay 13 and the right hand winding of the normally operated relay 19 for operating relay 18. The energization of relay .18 removes negative cut-off potential from the grid of the timing tube to cause the operation of the associated relay 16 after a predetermined time interval fixed by the characteristics of the grid circuit of said tube. Thetiming units or tubes 80, 8|, 82, 83, as well as the other vacuum tubes shown at the main office and station C, are similar in arrangement and operation to those described above in connection with Figs. 1 and 2, and the timingcharacteristics of the tubes are shown in Fig. 6. The grid circuit of the vacuum tube 80, however, further includes a tapped leak resistor which is operative to change the timing of the associated tube depending upon whichtap on the resistor is connectedto ground, as obviously the less resistance that is connected in shunt to the grid condenser, the more rapidly the charge on the condenser will be equalized'to permit the associated tube to become conducting. During the sending of the calling signal, the taps on the resistor 85 are ungrounded; thus delaying the operation of the tube 80 and relay IE to the maxi mum extent. When the tube 80 becomes conducting, relay I6 in the plate circuit thereof becomes energized, locks up, and at its left hand middle armature opens the circuit of relay II, whereupon the line circuit is reclosed. Relay I6 also opens the circuit of relay I9, thus removing holding ground from printer P2. The reenergization of the line relay 11 causes the deenergization of relay I8 and the tubes 8|, 82 and 83 are rendered ineffective.

The line interruption initiated as described above and transmitted through the duplex sets 81 and 88 operates the armature of the differential relay of the duplex set 88 to spacing, thus opening the circuit of the line relay 90, and said relay becomes deenergized. A circuit is closed from ground through the armature and back contact of relay 9!], the winding of relay 9|, and the inner left hand armature and back contact of relay 92 to battery, whereupon relay 9| becomes energized and locks up through its right hand inner armature and front contact to a circuit that is independent of the contacts of relay 90.

The energization of relay 9| closes a circuit through its left hand armature and front contact for energizing relay 93 to open the seize circuit of the switchboard control equipment to prevent a transmitter plugged into the line L2 from seizing the circuit until the call that has been initiated from station E has been completed and the circuit released. At the end of the line interruption resulting from the operation of calling key I0, as described above, the line relay 90 is reoperated and closes a circuit through its armature and front contact and the right hand outer armature and front contact of relay 9| for operating relay 96. The energization of relay 96 applies ground potential to the initiate circuit 91 to start one of the finder switches hunting for the calling line in the same manner as described above in connection with Figs. 1 and 2. It will be noted that the initiate circuit is not closed until the end of the circuit interruption in order to prevent the receiving reperforator RR being connected to the line while the line is still open.

The transmission of the calling line interruption from station B to the main oflice also releases the line relay H0 at station C for a predetermined interval to cause the operation of the busy lamp III at said station and to lock out the station until the line circuit is released by station E. Upon the release of the line relay III! at the beginning of the calling line interruption, a circuit is closed through the spacing contacts thereof and the windings of relays I I5 and H6 for operating relay I I5, relay I I6 being normally operated through a circuit including its left hand winding, the left hand outer armature and back contact of relay II I and the second left hand armature and back contact of relay IIB. Upon the energization of relay II5, negative cut-off potential is removed from the grid of vacuum tubes I20, I22 and I23, and after a predetermined time interval, somewhat less than the interval for which the timing unit 80 at station E is. adjusted, tube I22 becomes conducting to operate relay I24 in the plate circuit thereof. Relay I24 locks up through its right hand inner armature and front contact and the inner left hand armatures and back contacts of relays Ill and II 8 so that, if

a longer line interruption is received, the operation of either relay II! or H8 by the associated tubes I29 and I2I will cause the release of relay I24. In the present instance, however, the reclosure of the line circuit deenergizes the relay H5 and tube I2!) is maintained non-conducting, whereas the tube I2I has been held non-conducting by the cut-off potential applied to the grid thereof through the contacts of relay II I. The energization of relay I24 closes a circuit through its outer right hand armature and front contact for lighting the busy lamp III, and opens at its middle right hand armature and back contact the circuit of relay I25 so that said relay cannot be operated to open the line circuit or initiate a call in response to the operation of the calling key I26. Thus, the apparatus at station C is locked out while the line circuit is in use by station B, and the busy signal I I I remains lighted to indicate to the attendant or operator at station C the busy condition of the line.

Referring again to Figs. 2, 3 and 4, the connection of an idle reperforator through the instrumentality of one of the finder switches SI and S2 to the calling line applies battery potential through the second right hand armature and front contact of relay 29, the middle switch wiper of the finder switch and the conductor I30 to the windings of

relay

98 and 92 to disconnect the line relay 9!] from the line circuit and to initiate the transmission of the go-ahead signal to station B, as described above in connection with the transmission of a signal to station A when an idle reperforator has been connected to the line. The operation of relay 98 also establishes circuits for opening the line and timing the opening through the control of tube I02 in response to the subsequent disconnect signal. The energization of relay 92 closes a circuit through its right hand outer armature and front contact for operating relay 95 to open the sending leg of the terminal duplex set 88 at the same instant that negative cut-off potential is removed from the grid of the vacuum tube I9I employed to time the line interruption for operating the go-ahead signal at station B (or station C, in case of a call initiated from that station). When current is established through the relay 99 by the vacuum tube In I, the circuit of relay 95 is broken at the left hand armature and back contact of relay 99 to reclose the line circuit.

At station B, the deenergization of the line relay 11 operates relay I8, as described above, to remove negative cut-off potential from the grids of the

vacuum tubes

80, 8I, 82 and 83. Just before the end of the line circuit interruption, the tube BI become conducting and relay I4 in the plate circuit thereof is energized. Relay I4 becomes locked up and opens the locking circuit of relay I6 at its inner left hand armature. The energization of relay I4 lights the go-ahead supervisory lamp 86 to indicate that transmission may be commenced, and at its outer left hand armature and back contact removes the short circuit around the keyboard contacts of the printer P2. After transmission has been cornpleted, the circuit is released and the equipment restored to normal by restoring the key I0. At this time a line interruption is again produced under the control of the timing unit 8!], but now the upper tap connection on the resistor 85 in the grid circuit of the tube is grounded through the second left hand armature and front contact of relay I4, thus decreasing the time required for the grid of the vacuum tube 80 to return to a potential which will permit current fiow through the tube. The shorter line interruption indicated by the diagram of Fig. 6. The length of the line interruption corresponds to the transmission of a blank and the receiving repertorator closes its blank-reading contacts, as described above, to release the associated finder switch. When the control relays'associated with the finder switch are restored to normal, battery potential is removed from the conductor I30 to cause the release of relay 98 and the transmission of a line interruption for the purpose of clearing out the apparatus at the calling station B and extinguishing the busy lamp and restoring the equipment at station 0.

In view of the foregoing description, it will be evident that the release of relay 98 operates and then releases relay 96 after atime interval deter mined by the adjustment of vacuum tube' I 02 and its associated relay I03. The release of the line relay 1! at station B for this period of time causes the energization of relay 18, as. described above, to operate first to remove cut-01f potential from the tubes 80, 8|, 82 and 83. The tubes 80 and 8! become conducting, but a moment later the

tubes

82 and 83 also become conducting and the clearout relay I2 and relay I3 are operated. As soon as the line circuit is reclosed and relay I8 deenergized, relays I2 and I3 become deenergized and the equipment at station B is restored to normal.

Similarly, at station 0, the reception of the lon circuit interruption causes the energization of the clear-out timing unit I 23 and the associated relay I21 to unlock the relay I24, extinguish the busy lamp II I and restore the equipment at station C to normal. 7

In the case of a call initiated from station C'by the actuation of the calling key I26, an idle reperforator at the main oflice'is seized and the printer at station E locked out in substantially the same manner as described above in connection with the placing of a call from station B. However, as indicated in the diagram of Fig. 6, the calling signal sent from station is of longer duration than that sent from station B, and the timing unit 82 of station B which responds to the busy signal (call from station 0) is adjusted to require a longer circuit interruption than the timing unit I22 controlling the busy signal at station C. Upon the operation of relay "I3 in response to the initiation ofa call from station C, the busy lamp 89 at station E is lighted and the circuit to relay II is opened to prevent its operation if key Ill should be actuated at this time. Station C receives a go-ahead signal from the main station, sends a disconnect signal and responds to a clear-out signal from the main station, generally in the same manner as described above in connection with a call from station 13.

When a message is received at the main station for one of the stations B or C onthe multistation circuit, the operator plugs the call into line L2 at the switchboard and the transmission of the message is preceded by an automatic selection signal which renders the printer of the called station operative and looks out the printer of the other station. Thus, for example, assuming that the reperforator RR, Fig. 2, has recorded a message for the station B on the line L2, the associated tape transmitter TT is plugged into the jack J3 individual to said line. Likewise, calls for station C are plugged into jack J4 individual to the line L2. Assuming that the line circuit is not in use when the plug is inserted in the jack J3, a circuit is closed from ground at the Winding of relay 62 in the cord circuit through saidwindin-g to the lower contacts of the plug and jack' J3, the winding of relay I3I, circuit 94 extending through the armature and back contact of relay 93, and the left hand armature and back contact of relay I34 to positive battery whereupon the relay I3I becomes energized. The control relays and circuits associated with the cord circuit and switchboard are not shown in detail, since they are shown in the copending application of; Light and Blanton referred to above and are unnecessary for the understanding of the present invention. Since this circuit for seizing the line L2 includes contacts of relay 93, it will be apparent that relay I3I will not be energized until after any call which is in progress from 7 one of the remote stations B and C has been completed.

The energization of relay I3I closes a circuit from ground through the third armature and front contact thereof, the left hand winding of relay I35, and the inner armature and back contact of relay I36 for operating relay I35. At its second armature and make-before-break contacts relay I3I transfers the line circuit through the contacts of relay I35, conductor I38 and the contacts of relay 95 to the sending relay so that the tape transmitter T'I will be operative to send over the line circuit L2 when the clutch-magnet circuit is closed at the end of the selection signals. The operation of relay I35 interrupts the sending circuit for a predetermined interval efiective to render the printerP2 at station E operative and to operate the busy signal at station C. The operation of relay I35 is timed by the vacuum tube I40, since negative cut-01f potential is removed from the grid of said tube at the left hand armature and back contact of relay I35, and the tube I40 after a predetermined interval energizes relay I36 to break the circuit of relay I35 and thereby reclosethe line circuit. The grid leak resistor I43 associated with the vacuum tube I40 has a, tapped connection to the outer armature and front contact of relay I3I so that the timing of the tube I40 is comparatively short in the case of a transmitter plugged into the jack J3' (see timing chart, Fig.6). In the case of a transmitter plugged into the jack J4, relays I32 and I35 are operated in a similar manner to that described above, but the tapped connection to the resistor I43 isnot grounded so that the timin unit I40 causes a longer line interruption, operative to cut in station C and operate the busy lamp at station E. i

In the case of the shorter line interruption, the deenergization of line relay II at station E energizes relays. I8 and I9, as described above, and after a predetermined. time interval the timing unit causes relay 16 to become energized and locked up. The energization of relay I6 interrupts the left hand locking circuit of relay I9, and relay 18 becomes deenergized when the line circuit is reclosed. The deenergization of relay 19 removes ground potential from the printer magnet of the printer P2 and said printer will respond to the printer signals received over the line L2. At station C, however, the same line interruption operates the line relay IIII, control relays H5 and H6, the timing unit I22, and the associated busy. relay I24, thereby lighting the busy lamp III. .Relay I I3 remains locked up to contacts of relays I I I and I I8 so that the printer magnet of: printer P3, which is grounded at the contacts of relay I I6, does not respond to the line signals. The operation of relay I24 also looks the equipment, so that the operation of the calling key I25 will not be effective to render the printer operative or initiate a call.

In the case of the longer circuit interruption to select station C, the timing unit I20 operates after timing unit I22 and causes the energization of relay II! to render the printer P3 operative,

and the busy lamp I I I is extinguished when relay I I is restored. At station B, however, the longer circuit interruption operates relay I3 through the instrumentality of the timing unit 82 to light the busy lamp 89, and the printer magnet of the printer P2 is locked against operation by the energization of the relay I9.

When the connection to the line L2 is electrically broken in response to the end-of-messagc signal, as described in the above-mentioned copending application of Light and Blanton, relay I3I becomes deenergized and opens at its third armature and front contact the locking circuit of relay I36, whereupon said relay becomes deenergized. The decnergization of relay I36 open the circuit through the left hand operating winding of relay I31, but said relay is locked up through. the left hand armature and front contact of said relay and the winding of relay I34 to ground, whereby relay I31 remains energized and relay I34 becomes energized as soon as relay I36 becomes deenergized. The energization of relay I34 removes negative cut-off potential at its right hand armature and back contact from the grid of timing unit IllI at the same instant that the line circuit is opened by the energization of relay I35 through a circuit including the left hand armature and front contact of relay I34. After a predetermined time interval fixed by the grid circuit of the tube I4I, the flow of current through said tube and the right hand winding of relay I31 in opposition to the left hand winding of said relay causes said relay to become deenergized. Thus, the timing unit Ill times the circuit interruption employed to clear out the called station and restore the busy lamp at the other station in the same manner as described above. The deenergization of relay I31 open the circuit of relay I35, which in turn opens the circuitof relay I35. The deenergization of relay I35 recloses the line circuit in readiness for the next call either from or to one of the remote stations B and C. It will be noted that the seize circuit 94 is held open at the left hand back contact of relay I34 until the end of the clear-out signal to prevent another transmitter which might be plugged into the line from Obtaining a connection until the equipment is restored to normal. In the case of a call through the jack J 4, the same clear-out signal is transmitted under the control of timing unit I4I upon the deenergization of relay I32 when the cord circuit is disconnected.

It is contemplated that various types of control and switching equipment may be employed, since the invention is not limited to that shown and described herein but includes modifications falling within the terms of the appended claims.

What is claimed is:

1. In a multi-station telegraph system, a main office or switching center and a plurality of other branch stations, telegraph lines or channels connectin said other stations to said main ofiice, switching means at said main oflice for interconnecting said lines or channels, printer at said stations for efiecting communication over said lines or channels, certain of said lines or channels having more than one branch station serially associated therewith, means at the main ofiice for continuously interrupting the normal condition of such multi-station line or channels for different periods and means responsive thereto and dependent upon the length thereof for selecting one of said branch stations and locking out the other of said stations.

2. In a multi-station telegraph system, a main office Or switching center and a plurality of other stations, telegraph lines or channels connecting said other stations to said main ofiice, switching means at said main ofilce for interconnecting said lines or channels, printers at said stations for efiecting communication over said lines or channels, one of said lines having more than one branch station seriall associated therewith, means at each station on said last-mentioned line to interrupt and close the circuit a single time to thereby initiate and complete a call, and means operative upon the initiation of a call from one of the plurality of stations on a single line by a single line interruption for looking out and maintaining locked out the other of said stations thereon.

3. In a multi-station telegraph system, a main office or switching center and a plurality of other stations, telegraph lines or channels connecting said other stations to said main oflice, switching means at said main office for interconnecting said lines or channels, means at said stations for eiTecting communication over said lines or channels, one of said lines or channels having a p1urality of stations in series thereon, said last-mentioned line or channel terminating in a plurality of jacks at said main ofiice equal in number to the number of branch stations thereon, means dependent upon the connection to one or the other of said jacks for interrupting the line circuit for respective different lengths of time and means responsive to such interruptions to effect selection of a desired station on said line or channel.

4. In a multi-station telegraph system, a main cfiice or switching center and a plurality of other stations, telegraph lines or channels connecting said other stations to said main office, certain ones of said lines or channels serially connecting more than one of said other stations with said main ofiice, terminals at said main ofiice for each of said multi-station lines or channels equal in number to stations connected thereto, telegraph signal storage repeating means at said main ofilce, means for connecting said storage repeatin means to said terminals and means operative 0n the connection of said repeating means to a terminal of a multi-station line or channel to select the station individual thereto and lock out the other station on said line or channel.

5. In a multi-station telegraph system, a main ofiice or switching center and a plurality of other stations, telegraph lines or channels connecting said other stations to said main office, certain ones of said lines or channels connecting more than one of said other stations with said main ofiice, terminals at said main ofiice for each of said multi-station lines or channels equal in number to stations connected thereto, telegraph signal repeating means at said main ofiice, means for connecting said repeating means to said terminals' and means operative on the connection of a repeating means to a terminal of a multistation line or channel to select the station individual thereto and lock out the other station on said line or channel and to prevent the operative connection of other repeating means at said main ofiice to'other terminals of said line or channel. i

6. In atelegraph system, a main station or switching office, a-plurality of branch stations,-a

telegraph line or channel connecting said branch stations in series with said main station, a plurality offjacks one for each of said branch stations at said main station associated with said line or channel, permutation signal transmitting means at said main station, said means terminating in a plug insertable in said jacks to sheet transmission of permutation signals over said line or channel, a line interrupting means at said main station, means operative on the insertion of said plug in any one of said jacks to control said line interrupting means to interrupt said line or channel prior to the transmission of permutation signals thereover, and means dependent upon the jack into which said plug is inserted to determine the length of time said line interrupting means interrupts said line or channel.

7. In a telegraph system, a main station or switching oflice, a plurality of branch stations, a telegraph line or channel connecting said branch stations in series with said main station, a plurality of jacks one for each of said branch stations at said main station associated with said line or channel, permutation signal transmitting means at said main station, said means terminating in a plug insertable in said jacks to effect transmission of permutation signals over said line or channel, a line interrupting means at said main station, means operative on the insertion of said plug in any one of said jacks to control said line interrupting means to interrupt said line or channel prior to the transmission of permutation signals thereover, means dependent upon the jack into which said plug is inserted to determine the length of time said line interrupting means interrupts said line or channel, means responsive to line interruptions at said branch stations and means controlled by said last-mentioned means to select the branch station on said line or channel represented by the jack into which said plug is inserted at said main omce.

3. In a telegraph system, a main station or switching ofiice, a plurality of branch stations, a telegraph line or channel connecting said branch stations in series with said main station, a plurality of jacks one for each of said branch stations at said main station associated With said line or channel, message signal transmitting means at said main station, said means terminating in a plug insertable in said jacks to effect transmission of message signals over said line or channel, a line interrupting means at said main station, means operative on the insertion of said plug in any one of said jacks to control said line interrupting means to interrupt said line or channel prior to the transmission of permutation signals thereover, means dependent upon the jack into which said plug is inserted to determine the length of time said line interrupting means interrupts said line or channel, station selecting and looking out means at each of said branch stations and means controlled by the line interruptions transmitted from said main station to select the branch station represented by jack into which said plug is inserted and to lock out the other of said branch stations.

9. In a multi-station telegraph system, a main ofiice r switching center, a plurality of branch stations, telegraph lines or channels each'connecting a plurality of said branch stations to said main ofilce, switching means at: saidmain ofiice for interconnecting said lines or channels, message signal' transmitting and receiving means at said branch stations for. effecting communication over said'lines. or channels, message signal receiving and storing devices .at' said main office for receiving and storing message signals from said branch stations, means to automatically and temporarily connect a message signal receiving and storing device to a line or channel in response to a call consisting of a single line interruption from a branch station on said line or channel, and means to lock out the others of said branch stations while said message signal receiving and storing device is connected to said line or channel in response to the call from the calling branch station.

10. In a multi-station telegraph system, a main oifice or switching center, a plurality of branch stations, telegraph lines or channels each connecting a plurality of said branch stations to said main ofiice, switching means at said main oifice for interconnecting said lines or channels, permutation signal transmitting and receiving means at said branch stations for efiecting communication over said lines or channels, permutation signal receiving and storing devices at said main office for receiving and storing permutation message signals from said branch stations, means to automatically and temporarily connect a permutation'signal receiving and storing device to a line or channel in response to a call consisting of a single line interruption from a branch station on said line or channel, and means to indicate at the others of said branch stations on said line or channel when a permutation signal receiving and storing device at said main ofiice is connected to said line or channel in response to a call from the calling branch station.

11. In a multi-station telegraph system, a main office or switching center, a plurality of branch stations, telegraph lines or channels each connecting a plurality of said branch stations to said main office, switching means at said main oflice for interconnecting said lines or channels, permutation signal transmitting and receiving means at said branch stations for effecting communication over said lines or channels, permutation signal receiving and storing devices at said main office for receiving and storing permutation message signals from said branch stations, means to automatically and temporarily connect a permutation signal receiving and storing device to a line or channel in response to a call consisting of a single line interruption from a branch station on said line or channel, means to lock out the others of said branch stations while said permutation signal receiving and storing device is connected to said line or channel in response to the call from the calling branch station, and means t indicate at the calling station when the connected permutation receivingand storing device has been disconnected from said line or channel.

12. In a multi-station telegraph system, a main office or switching center, a plurality of branch stations, telegraph lines or channels each connecting a plurality of said branch stations to said main oflice, switching means at said main oiiice for interconnecting said lines or channels, permutation signal transmitting and receiving means at said branch stations for eiiecting communication over said lines or channels, permutation signal receiving and storing devices at said main ofiice for receiving and storing permutation message Signals from said branch stations, mean responsive to a calling branch station'for connecting an idle permutation signalv receiving and storing device to the associated lineor channel and locking out the other of said branch stations on saidhne or channel, means at the calling branch station to 5 initiate'disconnection of the connected permutation signal receiving and storing device from the