US2351621A

US2351621A - Printing telegraph exchange system

Info

Publication number: US2351621A
Application number: US404765A
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: 1941-07-31
Publication date: 1944-06-20
Anticipated expiration: 1961-06-20

Description

PRINTING TELEGRAPH EXCHANGE -S'I S'JHFIM a. LIGHT June 20, 1944.

Filed July 31, 1941 5 Sheets-Sheet 1 ATTORNEY June 20, 19,44. a. e. LIGHT 2,351,621

PRINTING TELEGRAPH EXCHANGE SYSTEM INVENTOR G. G. LIGHT BYZQ ATTORNEY June 20, 1944.

G. G. LIGHT PRINTING TELEGRAPH EXCHANGE SYSTEM Filed July 31, 1941 5 Sheets-Sheet 3 m wE INVENTOR GJG. LIGHT BY 2 (2 2% ATTORNEY TO Plaz- June 20, 1944, a. G., LIGHT PRINTING TELEGRAPH EXCHANGE SYSTEM Filed Jilly 31, 1941 5 Sheets-Sheet 4 K n: ,L o q- "I h- 4n .-o- 8 ATTORNEY June 20, 1944. G. e. LIGHT PRINTING TELEGRAPH EXCHANGE SYSTEM Filed July 31,1941 5 Sheets-Sheet 5 'TO FlG.4,----- 69 Um-O 59 .PDO K UJU Z .50 an! ATTORNEY Patented June 20, 1944 SYSTEM PRIN'riNG TELEGRAPH EXCHANGE "George G. Light Kew Gardens, N. Y., assignorto The Western Union Telegraph Company, New

i York, N. Y., acorporation of New York W V j 1 r, V Application Julyflsi, 1941, Serial No. 404,765

. l H 15Claims. Th sflinvention relates o l graph systems .and more-particularly to multi-station printing telegraph systems embodying a; plurality of stations or officesan d arrangements for selectively interconnectingpthe transmitting and receivin apparatus-or printers of the system. The in- ,yention-involves an improvement in or modification of the systems shown in the patent to -Whee1er, -Hoover and Dirkes Noq 2,193,810,

granted March 19, 1940,;and in the copending application of G.-, I. -igh t and W. B Blanton, .Serial No. 35Q,fl0Z, filed .August 3, 1940. .Ingeneralierms, theobject of this invention is]. to simplify the selecting Z and control apparatus inf systems off-the above -mentionedcharacter, and .guardagainstiaulty operation, as for example sending to a station where the receiving apparatus is not conditioned for operation or ha peendisconnected; .Heretofore code transmitters. and code-responsive equipment have;

been. commonly. employed for selecting stations,

. operating signals and motor controls, and effecting other functions in a multi-station system.

. The control equipment in some instances is quite complex, and the system is. further complicated hythe-necessity for separating the control sig-' nal'sf-irom theprinter signals which are ordinarily' sent overl the same line circuits. In many systemsthe. character of the telegraph lines lim- .it the character ofthe controlling code signals that .jcar' b i'nfg orjrjepeatingapparatus, and operating super- .visory. signals .orfother. functions over the line 'cirouitwithout employing either, code transmit-' ters "or -Tcode-resporisive equipment.

Another object of the 'nvention is to interlock the sending and receiving apparatus'in a telegraph' exchange system, 'wherein the-transmittingl'apparatus, at a main station or switching .center mayjbe temporarily connected with an outgoing line, inorder that line circuit interruptions maybe transmitted. for signaling and trol Y jcircuit-interruptions lengthinboth.directions over the line circuit Without the possibility. of the duration of the signals being alteredor fdistorted by the transmission of code signals to] the line throughthe .switchlpoardu- I :used... One feature of the present jinventionis; a. novel arrangement for effecting l st atio'n selection; iorsei zing andreleasing printpredetermined at the main station which is effective tooperate a go-ahead? signal at the remote station. If

- shown in Figs. 2 and 3.;

of the preferred embodiment; thereof shown in the accompanying drawings; wherein: a v

Figs. 1, 2pand 3 taken together constitute a wiring diagram o f ca singleestatio'n line circuit and'the terminal equipment. at the; mainsta- -tion or switching center;

Figs. 4 and .5 "form a wiring disease a multi-station or Way station-circuit, alsolterminating in the equipment at the main station 'Fig. 6 is a timing chart illustratingjthe preferred timingadjustments of the various timingunit syand i Fig. '7 illustrates the mannerinwhich Figs. 1 tot are arranged toiform the completeycircuit diagram 1 In accordance with they invention, an exchange system is l provided] injwhich both single station and way station line circuits terminate at. a main station or switchingcenter containing a switchboard forlinterconnecting the line circuits. At thefremote stations, aucall is initiated by actuating a calling key. and terminatedby restoring said key. Theoperation of the calling key causes a predetermined interruption of the line circuit to the main station which is effective to pick up an idle storage and transmitting'funit.

.As soon as, an idle unit is seized, a line 'circuit interruption of apredetermined lengthis produced the line circuit becoms'openedior the storage equipment accidentally disconnected, ;'the goguished or restored t 'indica'te atsaidstatiQn ahead signal at the remotestation' i's' extinthat transmission should 'be"'stopped. At' the "endof the message; tnefreiease and restoration of'equipment are also' accomplished by the transj mission of line circuitinterruptions'of predeterined length, and certain guard features are incorporated; as :willbe pointed out hereinafter."

. In thecase of a inulti-station or way station :line circuit, the initiation of a calllfrom one of 50v the remote stations to the main station-locks out t the otherstation n also initiates a call to the main station in sub tantially thesanlemanner as in the case of the single station circuit In making an outgoing L connection to the way station 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,

I each individual to one of the stations in the way Single-station Zine circuit.

Referring to Figs. 1, 2 and s of the drawings,

the printer Pl at station A, Fig. 1, is connected through the line Ll to the main office where" messages received from station A may be recorded or stored and retransmitted over outgoing lines or channels terminating at said oflice at the switchboard represented by the jacks J-l--J4, Fig. 3. -Messages received from station A at the main office and from the'other stations over lines terminating 'at said office 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' TI after the-tape transmitter has been plugged into the jack representing the selected outgoing line circuit or channel substantially as described in the above-mentioned 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. 2,143,328, 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 S1 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 forcertain features to be described,fand therefore certain details of construction are omitted for the sake of simplicity.

The line Ll 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 H and I2 of a conventional character. The-keyboardof the printer Plis-connected to the sending-leg of the terminal du'plexset- I l and the printer magnet is connected to the receiving leg thereof in series with a normally operated relay I3. I The sending leg of theterminal duplex setlZ. at the main oflice is connected-through-the back contacts of relay 14 to the-switchboard, while the receiving leg is connected through the conductor [5 and contacts of relay-26 to the winding of relay 25. The energization of relay 25 when-the finder switchqsl has connected to the calling line disconnectsrelay 25, from the receiving leg whichis then connected. through con ductor l5 and the finder switch to theselector magnet of the reperforator RR.

When it is desired to initiate a calllfrom 5a-.

tion A to the main ofiice or to one of thelines 'the receiving reperforator RR is idle. rep'erforator RR is in use, relay 29 will be operrelay, 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 l2 at the main office, 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 an 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 If the ated 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 representing the calling line, in this instance the first bank contacts, the stepping of the switch stops, 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 25 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 29, and the arma- V tures and back contacts of relays 36 and 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 insuflicient to actuate the switch wipers at this time.

The energization of relay 29 .asdescribed 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 preventanother of the finder switches from connecting to bank contacts multipled to the first contacts of switch SL] The energization of relay 29 transfers the initiate circuit through its left hand inner armature and frontcontact to the control relays associated with the second switch 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 acircuit through its second right hand armature and front contact, the middie wiper'of the switch SI, conductor 39, the

winding of relay 26 and the right hand armature and front contact of normally energized relay 2! for energizing relay 26. The energization of relay 26 closes the circuits of relays and 30 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 and J2 of the switchboard individual to the line Ll. As indicatedthe conductor 40 forms a part of the clutch magnet circuit of any distributor (corresponding to thecircuit of the clutch magnet 63 of the distributor shown in Fig. 2) when the associated transmitter is plugged into the jack J or J2. Thus, the energization of relay 3|], individual to the line Ll, stops transmission from the main office over said line to the connection from negative battery to the grid of avacuurn tube 43=havingthe 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 forthis purpose, the gridcircuit 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 'operationof 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. 4 'recloses theline circuit so that the line interruption'is' accurately timed by thecharacteristics of the grid circuit of the vacuum tube 43. The operation of relay 42 also opens the circuit of. relay 3|l, and said relay recloses the clutch magnet circuit 40, thus permitting transmission over theline LI through the switchboardto be resumed.

At station *A, the deenergiz'atiomof relay |3 as described removes-negative out-off potential from the grid of theslow-to-operate or timing vacuum tube and, after a predetermined period of time slightly: less:than the length of the line interruption'=*caused by the timingtube 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 maybe 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 delayed-operatingcharacteristic to the relay in' theplate circuit thereof by control of the grid potential as. described'above,

7 but the timing of the vacuum-tubes is fixed at 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 2! is adjusted so that it does not release its armatures until the lapse of suflicient time to insure that the cam shaft of the distributor controlled by relay 3|] has come to rest.

In order to indicate to the operator or attendant at station A that a connection to the receiving reperforator has been established and transmission maybe commenced, the rest or marking line condition is interrupted for apredetermined period at thernain office. This is accomplished as follows: Upon the deenergization of relay 2'! as described, theshort circuit around the right hand winding of relay 4| is opened, and said relay becomes energized in series with relay 26. Thereupon a circuit is 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 M to positive battery, whereupon relay 4 becomes energized to o en the sending leg of the terminal duplex set l2, which operates the receiving differential relay of the terminal duplex set N at station A,

causing relay |3to"becorne deenergized. At the same'instantthe energization of relay 4| opens PI. at its left. hand armature and back contact a different periods for the purposes to'be pointed out below. By way'of example; 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 the right hand inner armature and front contact thereof that is independent of vacuum tube 48. A circuit is also closed through the right hand middle armature and: front contact ofsaid relay, the armature andbackcontact of relay 55, the lefthand winding of relay 2| and'the right hand inner contacts'mof the key 18 whereupon relay 2| becomes energized and removes ground potential at the inner armature and back contact thereof from the keyboard of the printer The energization of relay 49 also opens short circuit around the contacts of the keyboard of the printer PI so that the printer is placed in'op'erating' condition, the line circuit through the keyboard contacts being connected through theleft hand armature and-front contact of relay 49 to ground at the left hand inner contacts of the key 18.- The operation of the keyboard of the printer 1-Pl transmits alternate rest or marking "andksp'acing permutation code signals over the line -L|,:the"signals being transmitted through (the conductor |5and the contacts of the receiving relay of the terminal duplex set I2 at the main ofiicexandbthe contacts of the lower wiper of the switch SI to. the. magnet of the receiving reperforatorRR. which records the receivedmessage in the form :of perforated tape adapted to Operate an associated tape transmitter IT .to repeat the signals through the selected outgoing line circuit or channel." 1

After transmission has been completed the op erator or attendant at station A releases the connected storage and transmitting equipment by restoring the key Hi. If the operator fails to restore the key l8 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 36 releases relays 29 and 32 to release the switch SI and transmit a disconnect signalto 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 inde fi' nitely, 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 vac uum 'tube 64. Upon the restoration of the key I 8 at the end of amessage, 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-ofi bias potential is removed from the grid of the vacuum tube 51. After a predetermined time interval, current flows through vacuum tube and the relay'55in 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 PI. 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 abovementioned Dirkes and Wentworth patent. The

contacts could be applied to the stop member for i 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 cut-off 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 50 remains lighted through a contact of relay 49 until finder switch SI at the main office 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 oflice closes the the line relay 3| which responds to. line signals is reenergized. to close a circuit throughits arma ture 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 be-' come deenergized, thus restoring the selector switch SI to normal in readiness for the next call. Upon the deenergization of relay 29, the circuit of relay 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 oflice while transmitting the break-signal of such duration as to extinguish the supervisory lamp 55 at the remote station A. Thecircuit of relay 30 may be traced through the middle right hand armature and back contact of relay and the inner armature and front contact of relay 32. The energization of relay opens the circuit of the clutch magnet of the transmitting distributor circuit of relay 60 and at the endof the blank scribed above.

of. any transmitter which may be connected through the switchboard to the line L! as de- The deenergization' of relay 25 further opens at its outerright hand armature and front contact the circuit of slow relay 21 and, after a short interval sufiicient to permit the cam shaft of the sending distributor to come to rest, relay 2'! releases its armatures. Upon the deenergization of relay 21, the circuit of relay 35 isinterrupted at the left hand armature and front contact of the first-mentioned 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 I 5 to interrupt the line circuit at station A at the same instant that negative cut-01f 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 M. The deenergization of relay l4 recloses the line circuit. Upon the deenergization of relay 4!, negative cutoff 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 39. Upon the deenergization of relay 3!), the sending distributor of the transmitter plugged into the line Li is again rendered operative for transmission.

At station A, the line relay IS in the receiving leg of the terminal duplex set ll becomes deenergized in response to the opening of the line .circuit by the operationof relay M, as described its inner righthand 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 ruption, relay l3 again becomes energized and connects negative cut-ofi potential through its armatures and front contacts to the grids of tubes 4B 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 50 solely under the control of the finder switches at themain office, the lamp being lighted 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 oifice owing .lamp 50. At the end of the line circuit inter- .15 as soon as one of the switches has seized an idle 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 'oifice 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 office, for example, the supervisory lamp 50 would serve as a positive indication to theoperuntil 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 oflice. However, on lines which are not arranged for full duplex operation, the printer magnet may be connected in 'ator or attendant at station A to stop sending stationcircuit-will be directed to these additional features. Assuming that the line circuit is idle and that the operator or attendant at sta- 'tion 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 "Ill, relay ll 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 and 3. 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 H may be'traced through theleft hand armature and back contact of relay "E2, the right hand inner armature and back contact of relay 13, the third left hand armature and back contact of relay 14, the right hand make contacts of the key l0,the outer armature and back contact of relay 15, thewinding of relay H, and the middle left hand armature and back contact of relay 16. Relay H locks up through its right hand innerarmature and front contacts to ground at the right hand armature and back contact of relay [2. The opening of the line cirseries with the keyboardas 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 C, 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 in the case of the line Ll. For the purposes of I illustration, th line L2 is arranged for half duplex operation, providing for transmission from either of the stations B and C to the I 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 cause the operation of the associated relay l6 after a predetermined time interval fixed by the flexibility of the controlsystem 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 above except that provisions are made for operating a busy signal and looking out one of the remote stations when a call is initiated cuit by relay 'H closes the'back or spacing con tacts of the line relay '11, thus closing a circuit through said contacts, the'winding of relay l8 and the right hand winding of the normally operated relay l9 for operating relay 18. The energization of relay l8 removes negative cut-off potential from the grid of the-timing tube to characteristics of the "grid circuit of said tube.

The timing units or tubes 80, a l, 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 timing characteristics 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 dependingupon which tap on the resistor is connected toground, as obviously the less resist- 60 ance that is connectedin 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 signaLthe taps on the resistor 85 are ungrounded, thus delaying the operation of the tube 80 and relay 16 to the maximum extent. Whenthe tube 80 becomesconducting, relay I6 inthe plate circuit thereof becomes energized, locks up, andat its left hand middle armature opens the circuit of relay 1|, whereupon the line 7 circuit is reclosed. Relay 16 also opens the circuit of relay 19, thus removing holding ground from printerPZ. The reenergization of the line relay "l1 causesthe deenergization of relay 18 and the

tube

81,82, and 8 3 are rendered ineffective.

The line interruption initiated as described above'and transmittedthroiigh the duplex sets {81 and 8-8 operates the armature of the diflferential relay of the duplex set '88 to spacing, thus opening the circuit of the line relay 9:0 and said relay 'becomfes deenergized. A circuit is closed from ground through'the armature and back contact of relay "90 the winding of relay PI, 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 cirsuit that is independent of the contacts of relay9Il. j p 4 I 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 seizingthe circuit until the call that has been initiated from station B has been completed and the circuit released. At the end of the line interruption resulting from the operation of calling key III; as described above, the'line relay 99 is reoperated and closes a circuit through its armature and front contact and the right hand outer armature and front contact of relay 9I for operating relay 96. The energization of relay 96 applies ground potential to the initiate circuit 51 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. V

The transmission of the calling line interruption from station B to the main office also releases the line relay I II] at station for a predetermined interval to cause the operation of the busy lamp I I I at said station and to lock out the station until the line circuit is released by station B. Upon the release of the line relay H0 at the beginning of the calling line interruption, a circuit isclosed through the spacing contacts thereof and the windings ,of relays H5 and HB 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-contaotof relay H! and the second left hand armature and back contact of relay II8 Upon the energization of relay H5, negative cut-off potential is removed from the grid of vacuum tubes 129, I22 and I23 and, after a predetermined time interval somewhat less than the interval for; which the'timing unit 80 at station B is adjusted, tube I22 becomes conducting held non-conducting by' the cut-ofi potential applied to the grid thereof through the contacts of relay H1. The energizatioh of relay I24 closes a circuit through its outer right hand armature and front contact for lighting 'the fbusy" lamp? III, and opens at its middle right hand Mme-" ture 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 HI 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 relays '98 and 92 to disconnect the line relay from the line circuit andto 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 controlof tube m2 in response to the subsequent disconnect signal. The energiz'ation of relay 92 closes a circuit through its right hand outer armature and front contact for operating relay S5 to open the sending leg of the terminal duplex set 88 at the same instant that negative cut-oil potential is removed from the grid of the vacuum tube IQI employed to time the line interruption for operating the go-ahead signal at station E (or station C, in case of a call initiated from that station); When current is established through the relay 99 by the vacuum tube IUI, 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 I7 operates relay 18, as described above, to remove negative cut-oil potential from the grids of the

vacuum tubes

88, 8I, 82 and 83. Just before the end of the line circuit interruption, the tube 8| becomes conducting and relay I4 in the plate circuit thereof is energized. Relay 14 becomes locked up and opens the locking circuit of relay 16 at its inner left hand armature. The energization of relay I4 lights the go-ahead supervisory lamp 6 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. Aftertransmissionjhas been completed, the circuit is released and the equipment restored tonormal by restoring the key 70. At this time a line interruption is again produced under the control of the timing unit 80, but now the upper tap connection on the resistor 85 in the grid circuit of the tube '89 is grounded through the second left han'd'armature and front contact of relay 14, thus decreasing the time required for the grid of the vacuumtube 80 to return to a potential which will permit current flow through thetube. The shorter line interruption is indicatedby the diagram of Fig. 6. The length of the'line interruption corresponds to the transmission of a biank and the receiving reperforator 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 frointhe conductor I 30 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 C.

In the foregoing description, it will be evident that the release of relay 98 operates and then releases relay 95 after a time interval determined by the adjustment of vacuum tube I02 and its associated relay "I03. The release of the line .relay TI at station E for this period ofytime causes the energization of relay 13, as'described above, to operate first to remove cut-off potential from. the tubes 80, BI, 82,and 83. The tubes 80 and BI become conducting, but a moment later the tubes 82 and 83'also become conductingjand the clear-out relay I2and relay I3 are operated. As soon as the line circuit is reclosed and relay l8 deenergized, lrelays I2 and I3 become deenergized and the equipment at station B is restoredto normaL- I Similarly, at station C the reception of the long circuit interruption causes the energization of the clear-out timing unit I23 and the associated relay ,IZl to unlock the relay I24, extinguish the busy lamp III and restore the equipmentat station G to normal.

In the case of a call initiated from station C by the actuation of the calling key I26, an idle reperforator at the maingofiice is seized and the printer at station B 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 C is of longer duration than that sent from station B andlthe timing unit 82 of station B which. responds to the busy signal (call from station C) 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 of a call I from stationC, the busy lamp 89 at station B is lighted andthe circuitto relay II is opened to prevent its operation if key I should be actuated at this time. Station C receives a .go-

for one of the stative and looks out the printer of the other station. Thus, for examplegassumingthat the reperforator RR, 2, has recorded a message for the station B 'on the line L2, the associated tape transmitter TT is plugged into the jack J {individual to said line. station C are the line L2.

Likewise, calls for plugged into jack J4 individual to Assuming that the line circuit is not in use when thefplug is inserted in the jack J3, a circuit is closed from ground at the Winding of relay 6'2 inthe cord circuit through said winding tothe lowercontacts of the plug and jack J 3, t he winding of relay I3I,. circuit '94 extending through the. armature and back contact of relay 33, and the lefthand armature and back contact of relay I34 to positive battery where- I upon the relay v control relays and vcircuits associated with the cord circuit andswitchboard are not shown in detail, since they are shown I3I becomes energized. The

in the copending jthe circuit of relay'l35 and thereby 'reclose the line circuit. The grid leak resistor I43 associated with the vacuum tube I40 has a tapped connection to the outer armature and front contact 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, relayv 03, it will be apparent that relay I3I will not be energized until after any call which is in progress from one of the remote-stations Band C has been complated.

i I 'Ilie'energization of relayrI3I closes a'circuit 10.

from ground through the third armature and front contact thereof, ithe left" hand winding of relay I35, andthe 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 tothesending relay'so that 'the tape transmitter T'I" will be operative to send over the line' circuit L2 when the clutchmagnet circuit is closed at the end of .the selectionsignals. The operation'of relay I35 interrupts the sending circuit for a predetermined interval effective to render the printer P2 at station B] 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-off potential is removed from the grid of said tube at the left hand armature and backcontact of relay I35, andthe tube I40 after a predetermined interval energizes relay I36 to break of relay I3I'sothat 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 is not grounded so that the timing unit I40 causes a longer line interruptionfoperative to cut in station C and operate the busy .lampat station B. a s

In the case of the shorter line interruption, the

deener ization of line relay 'I'I at station B energizes relays "I8 and 1 9,. as describedabove, and after a predetermined time interval the timing unit 80 causes relay 16 to become energizedand locked up. .Theenergization of relay 'Ifiinterrupts theleft hand locking circuit of relay 19, and relay [8 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 respondto the printer signals received ovjer the line L2: At-stationrC however, the same, line interruption operates the line. relay IIO,,control relays II5 and=I I6, the timingunit I 22, and the associated busy relay 124, therebylighting-the busy lamp III. Relay H6 remains lockedup -to contacts of relays LIT andIIB so' that the printer magnet of printer-Ptwhich is grounded at the1contacts-of relay H6 does not respond to the line signals. Theoperation of relay I24 I also looks thegequipmentso that theoperation .ofthe calling key I26 will not beeffe ctivefto render theprinter operativeor initiate a call.

In the case of the longer circuit interruption to select. station 0, the timing unit I20 operates after timing unit:I;22 and causes the energization of relayIIL to render the printer P3 operativeand the busy lamp ..I. .I.vis extinguished -Whenrelay I I5. is: restored.;:- .At station l3, hgwever, the longer circuit-interruption operates relay 113 through the instrumentality of the timing unit 82 to light the busy lamp. B9, and the printer magnet of the printer P2 is locked against operation by the energization of relay I9.

When the connection to the line L2 is electrically broken in response to the end-of-message signal, as described in the above-mentionedcopending 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 deenergization of relay I36 opens the circuit through the left hand operating winding of relay, I31, but said rela is locked up through the left hand armature and front contact of said relay and the winding of relay I 34 to ground, whereby relay I31 remains energized and relay I 34 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 I M at the same instant that the line circuit is opened by the energization of relay I through a circuit including the left hand armature and front contact of relay" I34. After a predetermined tim interval fixed by the grid circuit of the tube I4I, the flow of current through said'tube'andthe right hand winding of relay I3'I in opposition to the left hand winding of said relay causes said relay' to become deenergized. Thus, the timing unit I4I times the circuit interruption employed to clear out the called station and restore the busy lamp at theother station in the same manner. The deenergization of relay as described above. I31 opens the circuit of relay I34 which in. turn opens the circuit of 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 backcon'tact of relay I34 until the end of the =c1ear-outsi'gnal 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 J4, the same clear-out signal'is transmitted 'underthe 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 inventionis not limited to that shown and described herein but includes modifications falling within the terms of the appended claims- I claim: v V 1. In a multi-station telegraph system, telegraph lines or channels,- a plurality of stations at which said lines or channels terminate, printers' at said stations for effecting communication 'betweenstations over said lines or channels, each of said printers including means responsive to alternate restor marking and spacing signalconditions in permutation code in said lines or channels for controlling'the printer, means at one station for interrupting-the rest condition of the line or channel to anotherv station for two different periods of predetermined duration, timing means at said other station for detecting said two line interruptions, means including said tim-1 ing means for rendering saidother station responsive to the call uponreceipt of one of said line interruptions and for restoringthe equipment thereat to normal upon receipt of the other line terrupt the rest condition of said line or channel for a third period of predetermined duration and timing means at said one station for detecting said third line interruption.

2. In a multi-station telegraph system, telegraph lines or channels, a plurality of stations at which said lines or channels terminate, printers at said stations for effecting communication between stations over said lines or channels, each of said printers including means responsive to alternate rest or marking and spacing signal conditions in permutation code in said lines or channels for controlling the printer, means at one station for interrupting the rest condition of I the .line or channel to a main or switching station for two difierent periods of predetermined duration, means at said main station responsive to one of said two line interruptions for rendering the main station responsive to the call from said one station and to the other line interruption for clearing out the call, means at said main station for interrupting the rest condition of said line or channel for a third period of predetermined duration as a clear-cut signal and means at said one station for restoring the equipment thereat to normal upon receipt of said clear-out line circuit interruption.

3. In a multi-station telegraph system, a main oflice or switching center and a plurality of other stations, telegraph lines or channels connecting said other stations to said main office, switching means at said main oifice for interconnecting said lines or channels, printers at said stations for efiecting communication over said lines or channels, receiving devices including tape reperforators at said main office for storing mes sage signals from the other stations, means to connect a tape reperforator temporarily to a line or channel when a call is initiated from thestation on said line or channel and means at the calling station to indicate that the connected reperiorator has been disconnected.

4. In a multi-station telegraph system, a main ofiice or switching center and a plurality of other stations, telegraph lines or channels connecting saidother stations to said main office, switching means at said main ofiice for interconnecting said lines or channels, printers at said stations for efiecting communication over said lines or channels, receiving devices including tape reperforators at said main ofiice for storing message signals from the other stations,

means to connect a tape reperforator tem- "porarily to a line or channel when a call is initiated from the station on said line or channel and means at the calling station automatically controlled from the main ofiice to render the local printer inefiective if the connected reperforator becomes accidentally disconnected.

5. In a multi-station telegraph system, a main ofiice or switching center and a plurality of other stations telegraph lines or channels connecting interruption, means at said other station to in-r perforator if the calling station operator fails to disconnect.

6. In a multi-station telegraph system, a main oflice or switching center and a plurality of other stations, telegraph lines. or channels connecting said other stations to said main office, switchingmeans at said main office for interconnectin said lines or channels, printers at said stations for effecting communication over: said linesor channels, receiving devices including, tape reperforators at said main ofiice for storing message signals from the other stations, means to connect a tape reperforator temporarily to a line or channel when a call is initiated from the station on said line or channel, means for interrupting the line circuit to the calling station for a predetermined period in case the reperforator is disconnected from the line and means at the calling station responsive to said line interruption for indicating that the connected reperforator has been disconnected.

'I. 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 oflice, switching means at said main office for interconnecting said lines or channels, printers at said stations for effecting communication over said lines or channels, receiving devices including tape reperforators at said main ofiice for storing message signals from the other stations, means to connect a tape reperforator temporarily toa line or channel when a call is initiated from the station on said line or channel, means responsive to a prolonged open line circuit for releasing the reperforator and means responsive thereto for opening the line circuit after the same has been reclosed to signal the calling station.

8. In a multi-station telegraph system, a main oflice and a plurality of branch stations, telegraph lines or channels from each of said branch stations to said main office, printers at said branch stations for effecting communication over said lines or channels, receiving apparatus at said main oflice, control equipment at each branch station including means for initiating the connection of said receiving apparatus at the main office to a calling branch station which desires to transmit a message, said control equipment including means at each branch station for opening the line circuit for a predetermined time at the end of the message or when disconnection is desired, means at the main oflice to disconnect the receiving apparatus in response to said opening of the line circuit, means for opening the line circuit for a different time at the main office upon such disconnection as a clear-out signal and means for restoring the equipment at the branch ofiice to normal in response to said clear-out signal.

9. In a multi-station telegraph system, a main oflice and a plurality of branch stations, telegraph lines or channels from each of said branch stations to said main office, switching means at the main office for interconnecting said lines or channels, printers operatively associated with said lines or channels, signal storage units at the main office for printer signals from the branch stations, manually operable means at each branch station for initiating a call to the main oflice, means responsive thereto for connecting an idle signal storage unit to the calling branch ofiice and means effective when no signals are received from the calling branch ofiice for a predetermined period of time for automatically releasing the connected signal storage unit.

10. In a multi-station telegraph system, a main oflice and a plurality of branch stations, telegraph lines orchannels from each of the branch stations to the main ofiice, receiving means including tape reperforatorsat the main oflice means for connecting an idle reperforator to the line or channel from a calling branch station, manually operable means at said calling branch station for initiating disconnection at the end of transmission, means at the main oflice for thereupon transmitting a clear-cut signal to said branch station and means at said lastmentioned station for restoring the equipment thereat to normal or idle condition in response to said clear-out signal.

11. In a multi-station telegraph system, telegraph lines or channels, a plurality of stations at which said lines or channels terminate, printers at said stations for efiecting communication between stations over said lines or channels, each of said printers including means responsive to alternate rest or marking and spacing signals in permutation code in said lines or channels for controlling the printer, signal storage and repeating devices at one station also including means responsive to permutation code marking and spacing signals, means at said one station responsive to a momentary interruption of the rest condition of a line terminating thereat for seizing an idle signal storage device and connecting it to the calling line, means effective upon such connection to interrupt the rest condition of the calling line for a predetermined period of time at said one station and signaling means at the calling station responsive to said lastmentioned line interruption.

12. In a multi-station telegraph system, a main oifice or switching center and a plurality of other stations, telegraph lines or channels arranged for the transmission of signals thereover in one direction at a time connecting said other stations to said main oflice and having separate sending and receiving terminals in the main office, switching means at said main office for interconnecting said lines or channels, printers at said stations for efiecting communication over said lines or channels, means at said main ofiice for extending the receiving terminal of a first line to the sending terminal of a second line to permit transmission of signals from the branch station of said first line to the branch station of said second line and to prevent the transmission of message signals through the sending terminal of said first line, and means at the calling branch station to control said last-mentioned means.

13. In a multi-station telegraph system, a main station, a plurality of other stations, a first and a second line connecting a first one and a second one of said other stations with said main station, means for transmitting signals in either direction, one direction at a time over said first line, means for transmitting signals in either direction simultaneously over said second line, electronic timing means at said main cfiice for generating selective control signals comprising timed line circuit interruptions of different lengths and means for transmitting said control signals over either of said lines.

14. In a multi-station telegraph system, a main ofiice or switching center and a plurality of branch stations, telegraph lines or channels connecting said branch stations to said main bflice, switching means at said .m'ain ofiice for interconnecting said'lin'es or channels, printers at said station's for effecting communication over said lines or channels, means at :said main ofiice for transmitting a' control signal consisting of a circuit interruption of predetermined duration over said lines or channels "and automatically operative-means for temporarily 'stopping message transmission over said lines or channels while said control signal is "being transmitted.

15. In-combination; a'main station-or switching offi'ce, a branch telegraph-station, a line or channel arranged for duplex operation between said main oflice and said branch station, means for transmitting printing telegraph signals from each station to the other station, means for transmitting a :control signal consisting of a circuit interruption of predetermined duration from the main oifice to the branch station and automatically operative means for interrupting 'normaltran-smission of message signals from the 10 main ofiicet'o said branch station upon the ini-