US1677859A - Automatic reversing system for multiplex circuits - Google Patents

Description

July 17, 1928. 1,617.8.59

w. A. DUDLEY AUTOMATIC nzvsasme SYSTEI we; mum-Inn cmcurrs Filed Iarch 2.4, 1925 Shuts-Sheet 1 STATION 2 Dudley STAT/(Ml .2

July 17, 1928.

w. A. DUDLE Y AUTOMATIC REVERSING SYSTEI FOR IULTIYLBX CIRCUITS 2 Shouts- Sheet 2 i 'L J v gyvvento c W A. Dudley m 6.1mm,

Patented July 17, 1 928.

UNITED! STATES PATENTOFFICE.

WILLIAM A. DUDLEY, or BROOKLYN, new YORK, ASSIGNOR To THE wrzsrnnn union TELEGRAPH oomrnNY, or NEW YORK, n. Y., A CORPORATION or new YORK.

AUTOMATIC nnvnnsme SYSTEM FOB. uULrn-Liix cmounis;

Application filed March 24, 1925. Serial No. 17,986.

My invention relates generally to automatic telegraph systems, and particularly to an automatic reversing switch for automatic telegraph circuits, more especially circuits of multiplex printing telegraph systems of the Baudot and similar types. It comprises meanswhereby the direction of operation of an automatic telegraph circuit may be automatically reversed with a minimum of lost time and in a manner which will insure correct continuity of a message regardless of when the switching may occur.

The patent issued to WMA. Houghtaling, No.1,27 5,559 dated Aug. 13,1918, illustrates and describes a multiplex printing telegraph system of the type with which the invention is intended to be used, as may be seen in the accompanying description and drawings, but my invention is by no'means restricted to use with that particular type of system. I t I The multiplex system of automatic telegraphy, as usually applied, provides for 'rection at a time it becomes desirable to re-- from one to four separate transmissions in one direction or in both directions simultaneously over a single line wire. The latter practice calls for a 'duplexed line and must, therefore, employ an artificial line at each terminal for balancing purposes. Occasionally, however, line conditions are encountered which are so unstable that the use duplex principle becomes impractical. In such cases a greater circuit output can be obtained by operating in only one direction at a time, using as many channels of transmis, sion as desired. 1

When operating a circuit in only one diverse the direction of transmission periodically and at ,frequentintervals, in order to give eachterminal an equal opportunity to discharge its business with a minimum of delay. The device described below is designed to automatically reverse the direction of op eration of the circuit at predetermined intervals, to make possible adjustment of the length of the transmission period for either station in order to take care of varying traflicrequirements, to accomplish the [switching without causing falser o peration of the receiving and correction-apparatus or mutilation of the message being transmltted of an artificial line and consequently the at the moment when switchingoccurs, and to insure correct sequence and-least possible delay in the operations necessary to effect the switching. The construction of the de-' vice is, moreover, of such a nature, that when more than one channel of a multiplex system is provided with the automatic reversing switch of my invention, the additional apparatus required is a minimum According to my invention, I control the direction of operation of the circuit through that portion'of the system which is known in the art as the auto control. The auto control is described in detail on pages 9 and 10 of the patent to Houghtaling, already mentioned, and comprises, auxiliary transmitting means ada ted to communicate automatically to the distant station requests for reruns, repunches, and other signals inciof contacts in the tongue circuits of: the recelver and corrector relays respectively; the

third cam transfers connection of the line from the receiver and corrector relays to a ring of the transmitting distributer, and the fourth operates contacts in the circuit oi a relay which in turn controls operation of the cam-driving means. Inone embodiment ofmy invention the automatic switching operations are initiated by energization of a relay at thestation then transmitting and sis subsequent operation of cam driving motors at both stations. The energizing circuit of this relay is established at predetermined intervals bya pair of clock controlled contacts. In the second embodiment, the clock and motor are dispensed with, and the synchronous distributors act as synchronized timing devices tocontrol, through their local segments, a magnet which actuates a ratchet and pawl device, this in turn causing rotation of the system of cams.

. Fig. 1 shows thatembodiment of my invention which utilizes a clock control and a 'cam driving motor.

Fig. 2 shows a second embodiment of the invention which utilizes the synchronous distributers to control initiation of the switching operations, and a pawl and ratchet device for rotating the cams.

In the following detailed description, the same letter is used to designate corresponding elements at the two stations, the subscripts indicating the particular station at which the element is found.

Fig. 1 shows two terminals joined by a line L with contacts in the proper positions for station 1 to transmit to station 2. The usual transmitter, of the type disclosed in the patent to G. R. Benjamin, No. 1,298,440 dated Mar. 25, 1919, is schematically indicated at T, as comprising five separate sets of contacts, each f the sets of contacts be ing arranged to produce current reversals. The sets of contacts are connected to segments of a synchronous distributer in the well known manner, and to the auxiliary signaling apparatus A6,, in the manner disclosed in the patent to Houghtaling. The eleven terminals indicated at the'bottom of the dotted line rectangle AC, corresponds to terminals a, b, c Z in Fig. 1" of that patent. 1

PR, represents the usual printer relay as sociated with the usual printer P through the usual receiving distributer segments. GR, is a corrector relay forming part of the usual phase correcting mechanism, which may be of the type disclosed in the patent to Rothermel 1,253,889, dated Jan. 15, 1918.

T ACQPR P, and CR represent corresponding apparatus at station 2.

In accordance with my invention additional switching apparatus is rovided at station 1 in the form of a plura ity of cams A,, 3,, 0,, and D, anda motorM,, which is connected through reduction gears V, to a shaft carrying the cams. Cam A,, through a pair of contacts 41,, controls the circuit of the usual transmitter magnet TM, so that when a, is closed TM, is permitted to operate. The energizing circuit of TM, also passes through the contacts of an automatic stop device Le, controlled by the tension of the transmitter tape.

Cam B, simultaneously opens, or closes, two pairs of contacts I), in circuits which lead to the tongues of the printer relay PR, and corrector relay CR,. When these contacts are opened the printer and corrector relays are rendered inoperative, and by this means thevpinter and corrector mechanisms are safeguarded from false operation.

Cam C, by its contacts a, and d, is adapted to connect line conductor L to a conductor leading to the printer and corrector re.- lays, or to a conductor connected to the transmitting distributer ring. It is obvious that when 0, is open, d, is closed, and vice versa.

' Cam D, through its contact 6,, controls a circuit of relay LR,, which, in turn, through forward movement of its armature contact P,, closes the circuit of motor M,. Relay LR, may be energized during either the transmission period or the reception period, this being dependentupon which station, is at the time initiating the reversing operations. For this purpose it is provided with three circuits, the third being a locking or holding circuit closed through its armaturecontact 0,. The clock H, can be set to stop or prevent operation of the transmitter at any desired time. 'This clock through its contact K, controls the energization of a magnet S,. Magnet S,'causes the auto control AC, to send a one bell signal to the distant station, and also to close a contact W, in a circuit leading to LR,. When, however, station 1 is the receiving station to which the one bell signal is sent, relay LR, is energized through a circuit controlled by relay R,. Relay R, tacts J, in printer P. Upon receipt of a one bell signal, however, contacts J, are opened with consequent energization of relay R,, and, through it, of relay LR,. In either case, sults in the establishment of a locking circuit, which, as indicated above, is opened by cam D, after the lapse of a predetermined short interval of time.

Station 2 is equipped with switching apparatus like that at station 1.

From the preceding discussion of the functions of the various parts of the automatic switching apparatus, the manner of operation of the system of Fig. 1 will be aparent in the following description:

The signals set up by transmitter T, pass through the sending rings of the distributer at station 1 and contacts d, to line L, then through contacts a, at station 2, printer relay PR and corrector relay CR to ground. As

the contacts at 6,, are closed, the circuit from the tongue of the printer relay PR, through contacts I), and the receiving ringsof the distributer at station 2 to printer P is complete, and the signals are received at station 2 by the printer.

The circuit from the tongue of the cori'ector relay CR, through contacts I), to the correcting rings is also complete, allowing the correcting mechanism at station 2 to function and maintain the. synchronism of the circuits. Asis usual, the distributer at station 2 runs slightly faster than the distributer at station 1, and the corrector at station 2 steps the brushes backward.

At the receivingterminal, the transmitter T is prevented from operating because of the open contacts a, in the auto stop cir is normally shortcircuited by conthe energization of relay LR, re-

cuit, i. e. the circuit through transmitter magnet TM and the contacts of rod L6,.

When this circuit is open the tape feed is i stopped andthe transmitter tongues are held against their spacing contacts, in'the manner disclosed in the patent to Benjamin.

It will be noted .that during transmission from station 1 the tongue circuits of printer relay PR and correctorrelay CR are open at?) so that neither the printer P nor the correcting mechanism at station 1 can be affected by these idle relaysrwhile the station is sending.

In order to reverse the direction of the 'cir chit it is-necessary to stop the transmission from station 1, open the printer and corrector relay circuits at station 2, switch the line from sending to receiving at stationlf and from receiving to sending at station 2,

then close the printer and corrector relay tongue circuits at \station 1 and start the transmitter at station 2. These operations a minimum of lost time' 7 The intervals between reversals of operations are controlled by clocks H at the terminals but each switching is initiated and controlled by the transmitting'station.

After the circuit has been operating in the direction shown for a predetermined length of time, a contact K in the clock I-I closes, completing a circuit from battery through must occur in the proper sequence and with contacts K and magnet S to-ground. The magnet S being energized, attracts its armature'which draws forward with it the; ffinger wheel of the auto-control AC a distance sufiicient to transmit one bell signal. In accordance with the well known manner of operation-of the auto-control, as the finger wheel starts to move, forward a contact arm within theauto control (as in the patent to Houghtaling) opens the auto stop circuit, thus stopping the transmitter in such a wayf't at the last character set up in the transmitter is completed without regard to I "the instant when the contacts open. This feature of the auto control is described in detail -in lines 84 to 126; page 12 of the patent to Houghtaling.

At this point it' may be noted that though it is old to prevent mutilation of a trans:

mitted signal by automatically delaying the opening of a transmitter circuit until the-last to battery. When therelay LR is energized the contacts ,0 are closed to establish a locking circuit' forLR in which the locking current flows from ground through the apparatus at'station 2 is idle."

closed contacts 0 resistance HR contacts 0 and relay LR to battery.

Energizing relay LR also closes contacts I P and permits current to flow from the bat tery through'contacts P and motor'M to ground, and the shaft carrying-cams A B C and D is thereby caused to rotate.

- As the cams start to rotate inthe direction shown by the arrows, contacts K in (3100!:

H opens, deenergizing magnet S and permitting the finger wheel of auto control AC to start its return motion step by step as con trolled by a local segment of the distributer.

This step by step operation of the'finger.

wheel is described on page 10 of the patent to Hough-taling. As the finger wheel moves backward, contacts W are opened but the energization of relay LR is maintained by the said locking circuit.

As the backward motion of the finger wheel continues, the characters figures, bell, and letters are transmitted to the line, after which the auto stop 5 contacts inside the auto control are closed and would permit the transmitter to again function normally were it nofifor the fact that contacts 1, also in the auto stop circuithad in the mean time been opened by the action of v cam A,. With the auto stop circuit open at a; the transmitter T remains inoperative wlth 1ts tongues against the1r spaclng contacts, and as a consequence successive spacing impulses are transmitted following the letters character.

When the bell signal is received at station 2, contacts J 2 in the printer P are opened, causing current to flow from battery through relay. R to ground. Relay R being energized attracts its armature closing contacts N and permits a current to flow from battery through relay LR and contacts N to ground. Relay LR locks up and closes' the circuit of motor M in the same manner as described for station 1.

' With both cam shafts in motion the next action which takes place" is at'b which opens the tongue circuits of printer'relay PR and corrector relay CR This action is delayed. 1

until after the printer P has received the letters. signal transmitted fromgauto con-- trol AC and occurs while the succeeding spacing impulses are being received. As spacing impulses do npt affect the printer, the printer relay tongue circuit may be opened at any time during the selection without introducing false characters andthe printer will bestopped in position toreceive the next character, which transmitter T will transmit after the circuit is restored to its original condition, i. e., sending from station 1 to station 2. Openingthe tonguecircuit' of-the Corrector relay prevents false operation of the corrector while the receiving As soon as contacts 5 are opened, the line i at station 1 is switched froinsending' to the receiving position by opening contacts cl and closing contacts 0, and the line at station 2 is switched from receiving to sending by opening contacts 0 and closing contacts d,. This reverses the previous condition, i. e., station 2 now sends spacing impulses from its transmitter T through contacts d, to the line and thence through contacts 0,, relay PR and CR, to ground. These spacing impulses are insured by the open contacts 00 in the auto stop circuit of the transmitter T These impulses cannot yet reach the printer P, however, as the tongue circuit of printer'relay PR is open at 1),. While these spacing impulses are still being received at station 1, the tongue circuits of the printer and corrector relays PB, and CR are closed at 6 This action can in no way throw false characters into the printer P as the spacing impulses have no effect upon it. Closing the tongue circuit of the corrector relay permits the correcting mechanism at station 1 to operate and maintain the synchronism of the circuit. As previously stated, the distributer at station 1 is revolving slightly more slowly than the distributer at station 2, therefore the corrector at station 1 must be arranged to step the brushes ahead rather than backward as is the customary practice. It is obvious that the speeds of the two distributers must be matched closely enough so that they will remain phased within the margin of the corrector during the brief interval when neither corrector is operative.

Now station; is in position to receive any signals which may be transmitted from station 2 and the movement of the cams at this station is stopped by cam D which opens contacts e thus deenergizing relay LE This allows contacts 0 and P to open, thus removing the operating current from the motor M and opening the locking circuit of relay LR, at a second point 0,. The momentum of the motor M is sufficient to carry the protrusion on cam D far enough to again close contacts 0 thus leaving station.

1 in the receiving position with the cams moved to the positions shown on the drawing for station 2.

With station 1 sary to start the regular transmission from station 2 in order to completely reverse the condition original] assumed. This is"accomplished by the c osing'of contacts a in the auto stop circuit of the transmitter T when normal operation of this transmitter is resumed. This action completes the switching, and the motion of the camsv at station 21s stopped by opening contacts e which de: energizes relay LR, and-stops the motor M in the manner described for M receiving impulses trans-- mltted from station 2, it isnow only neces- Transmission will continue in this direction, i. e. from station 2 to station 1, for a predetermined length of time, when contacts K controlled by the clock H at station 2 will close to again start the switching proc ess in the reverse direction. i

It is apparent that when additional channels are used, it is only necessary to employ one additional contact for each added channel. These added contacts are used tocon trol the auto stop circuits of the transmitters and serve to start and stop their operation as described for the ones shown on the drawing. One channel is all that is necessary to' control the switching of the circuit.

Use of the clocks rather than motors to determine the sequence of switching operations is not practical, as any departure from perfect synchronism would introduce that amount of lost time in the switching process. Used as they are, any discrepancy between the clocks will serve only to give one station slightly more transmitting time than the I other, which is in no sense a loss.

The clock contacts can be arranged so that by simple manual adjustments the periods of transmission can be lengthened or shortened for eithenstation to take care of varyng traffic requirements. 1

While the foregoing is given with specific reference to the multiplex system, its application is in no sense limited to that sysadditional two controlling contacts, one in the circuit of a magnet N operating the finger wheel of the 'auto control and the other in the energizing circuit of the magnetv M, which circuit extends from battery through the local distributer rings, armature contacts of relay LR and the windin of magnet M to ground, contacts we being eld closed ,by the locking circuit of relay LR. This energizing circuit is supplied withcurrent twice per revolution of the distributer and,'through gears G, causes motor M to rotate the cam system step by-step by means of a pawl and ratchet device. Unlike the first method described, this method provides that the cams at the transmitting station shall be in motion during the entire transmitting period. 7

The cams continue in motion iwithout change inthe positions of the contacts for the entire transmittingperiod. At the end of this time (which must be predetermined) contacts h are closed, thus energizing magnet N, which pulls the finger wheel of the D, E and F, in each system of cams, the 1.0.

transmitter T froni operating and causing spacing impulses to be transmitted after the finger wheel has returned to its back stop.

The bell signal from 'auto control AC, when receivedby the printer P momentarily opens the bell contacts J permitting a current to flow. through relay R to ground. The energization of relay-R closes contacts K permitting current to flow through K and relay LR thus energizing relay LE which closes contacts Z and m and causes relay LR, to lock closed through contacts Z Contacts m being closed, magnet M isoperated through the local rings of the distributer and motion of the cams at stations 2commences.

At station 2, after the figures, bell andfletters signals have been received by the printer P, and while the spacing impulses are being received, contacts 7, are opened, thus opening the tongue circuits ofthe printer and corrector relays PR and CR preventing further reception or correcand closing contacts at, and c tion at that station.

Following this, the line is switched from sending to receiving at station 1 and from receiving to sendingat station 2. This is accomplished by opening contacts (Z and e, As the auto stopcircuit of transmitter T is open at g station 2 now sends spacing impulses to station 1, and while these spacing impulses are, being received at station 1 contacts. f are closed, completing the receiving circuits for station 1 Station 1 is now in position to receive,

and the motion of the cams at-this station is stopped by cam A which closescontacts 5 a momentary! charging v current through relay UR into the condenser V contacts a and a The momentary energization of UR, opens contacts at, in the locking circuit of LE long enough to deenergize relay LR and allow. contacts Z and m, toiopen. Thus the circuit through magnet M is broken and motion of the cams at station 1 ceases.

The cams at station 2 will continue 'in motion and contacts g, are closed, restoring the auto stop circuit of transmitter T and completing the sequence of switching operations. Motion of they cams atistation' 2 continues for the full period 01 transmission,

after which the sequence is repeated in the reversedirection. It will be noted tha't before theconden'sers V and V are charged, they are completely discharged by closing Switches S and S may-be opened man- -ual1y to double the period oftransmissio'n,

for with these switches open, magnets M and 0 are used to insure that the actual switching operations take-place at thehigh rate of speed (i. e., with a minimum of lost time) regardless of the position of the switches S and S I v This method, like the first, is not limited in its/application to the multiplex system.

What I claim as my invention is: 1 1. A printing. telegraph system adapted for alternate operation in both directions, comprising a plurality of stations, an'automatic transmitter and a receiving. printer at each station, means at each station to automatically and periodically reverse the connection of the line-from the transmitter to the receiver, and additional means at each station operative through the printer at the distant station to reverse the connection of the line at the distant station from receiver to transmitter.

2. A printing telegraph system adapted:

for alternate operation in both directions,

comprising a line extending between an au tomatictransmitter and a receiving printer,

prising a line, a receiving printer connected thereto, a plurality of switching elements arranged-to perform a plurality of switch; ing operations in a given order, a system:

106 =of cams adapted to operate the switching elements in the required order, a magnet and means for periodically energizing it to operate the cam driving mechanism, a control relay for said magnet under control of the receiving printer, a locking circuit for said control relay and means for momentarily breaking the locking circuit 'to 'deenergize said magnet. I

4. A printing telegraph system compris-- ing a line conductor, automatic transmitting means therefor, a receiving printer and auxiliary signal receiving means, auxiliary signal transmltting means arranged to operate the auxiliary receiving means through the receiving printer, a reversing switch, a I

magnet adapted to actuate said'switch, and

means controlled by operation'of the'auxil- Y.

iary transmitting and receiving means .to preparea circuit for said magnet.

5. A printing telegraph system comprising a line conductor, automatic transmitting means therefor,- a receiving printer and au xiliary slgnal receivingmeans, auxil ary -s1gnal transmitting means arranged to operate the auxiliary receiving means through "the;

receiving printer, a reversing switch, a. magnot adapted to actuate said s'witch, means '10 ciated with the controlled by operation of the auxiliary transmitting and receiving means toprepare a circuit for said magnet, and means to peri odically energize said magnet by completing the prepared circuit.

6. A printing telegraph circuit comprising a line conductor extending between an automatic transmitter and a receiving printer, auxiliary transmitting means assoautomatic transmitter, means controlled by the rinter and responsive upon operation of c -he auxiliary transmitting meansv to disconnect the printer from the line.

7. A printing telegraph circuit comprising a line conductor adapted for operation in both directions, a plurality of stations,

an automatic transmitter and a receiving printer at each station, auxiliary signal transmitting means associated with the automatic transmitter, and means controlled by the printer and responsive upon operation of the auxiliary transmitting means to disconnect the printer from the line and connect the automatic transmitter thereto at the station distant from the auxiliary transmitting means.

8. A printing telegraph system comprising a line conductor, an automatic transmitter therefor, auxiliary transmitting means at the same station, a magnet controlling said auxiliary means, and means for periodically and automatically energizing said magnet to operate said auxiliary transmitting means.

- 9. A telegraph circuit adapted for alternate transmission in both directions comprising a line conductor, a system of cams at each station arranged to reversethe di- 40 rection oftransmission over said line, means for rotating said c ams, amagnet controlling said rotating means, and means to close an energizing circuit for said magnet from either station.

nate operation in both directions, comprising a line conductor a system of cams at each station arranged to reverse the connection of the line from the transmitter to receiver and vice versa, means for rotating said cams, a magnet controlling said rotating means a circuit for said magnet including the armature contact of a control relay, means to close the circuit of said control reday from either station, a holding circuit for said control magnet and an additional cam member adapted to break'the holding circuit upon completion of the reversing operation. 1

11. A printing telegraph system comprising a line conductor extending between .two stations, an automatic transmitter at each station, means at each station to maintain one transmitter inoperative while the other .05 is operative, an auxiliary automatic trans 10. A telegraph circuit adapted for altertwo stations,

mitter and controlled means periodically actuating said auxiliary means to render operative the inoperative transmitter.

12. A printing telegraph system comprising a line conductor extending between two stations, an automatic transmitter and a receiving printer at each station, means at each station to maintain one transmitter inoperative while the other is operating, an auxiliary automatic signal transmitter, controlled means periodically actuating said auxiliary means to control said printer, and

means controlled by said printer to renderoperative the inoperative transmitter.

13. In a printing telegraph system, a line conductor, a plurality of stations therefor, an automatic transmitter and a receiver at one station adapted to permit operation of the conductor in either direction, auxiliary signal transmitting means associated with the automatic transmitter, and means including said auxiliary transmitting means .for automatically reversing the direction of operation at will.

14. An automatic telegraph system com-- prising a line conductor extending betweentwo stations,

an automatic transmitter and a receiving printer at each station, switching means to open the operating circuit of the transmitter at the first station, switching means to open the circuit of theprinter at the distant station, switching means to reverse connection of the line from transmitter to printer at the first station and from printer to transmitter at the second station, switching means to gclosethe circuit of the printer at the first station, switching means to close the transmitter circuit at the second station, a plurality of cams arranged to operate the switching means in the order given, a motor at each station arranged to rotate said plurality of cams, and means at the station transmitting for causing energization of the motors at both stations.

15. An automatic telegraph system comprising a line conductor, a plurality of stations therefor, an automatic transmitter and a printer at each station, switchi'ngcontacts adapted to reverse the directionof operation of the system, a system of cam members at each station arranged to operate the switching contacts,

.motors at each station for rotating the systerms of cams, an auxiliary transmitting meansQat one station adapted to cause ener: ization of both motors, an automatic starting circuit for said auxiliary means, and clock controlled contacts in said starting circuit adapted to be operated to initiate the reversal automatically and intermittently.

16. An automatic telegraph system comprising a' line conductor extending between an automatic transmitter and a receiving printer at each station, a plurality of switching contacts adapted to reverse the a plurality of j direction of operation of the system, a system of cam members at each station arranged to operate the switching contacts, a ratchet and pawl device at each station adapted to'cause rotation of the system of cams, a magnet controlling actuation of the ratchet and pawl device, an energizing circuit for said magnet, and additional switchingcontacts and an actuating cam therefor arranged to cause a break in the energizing circuit of the magnet when tho l'eversal of operation has been completed.

17. An automatic telegraph system coinprising a line conductor extending betweentwo stations, an automatic transmitter and a receiving printer at each station, a plurality of switching contacts adapted to reverse the direction of operation of the system, a system of cam members at each star" tion arranged to operate the switching contacts, a ratchetand pawl device at each station adapted to cause rotation of the system of cams, a magnet controlling actuation of 'the ratchet and pawl device, a distributer at each station and an energizing circuit for said magnet extending through the local ring of the distributer at the station.

18. An automatic telegraph system comprising a line conductor extending between two stations, an automatic transmitter and a receiving printer at each station connected to line through a distributor, a plurality. of switching contacts adapted to reverse the direction of operation of the system, a system of cam members at each station arranged to operate the switching contacts, a ratchet and pawl device adapted to cause rotation.

of the system of cams, a magnet controlling actuation of the ratchet and pawl device, an energizing circuit for said magnet extending through the local ring of the distributer, a. pair of normally open contacts in said energizing circuit and means to control closing energizing circuit for said magnet extending through the distributor comprising a pair of normally open contacts, an auxiliary transmitter at one of said stations and means operative through the auxiliary means and the receiving printer at "the distant station to cause closing of said normally open contacts.

20. A printing telegraph system adapted for alternate operation in both directions,

comprising a line conductor extending between two stations, an automatic transmitter, a receiving printer and a synchronously operating distributor at each station, means for locking the transmitter at the first sta 'tion upon its spacing side thereby causing the distributor to send spacing impulses over the line conductor, means for disconnecting the printer at the second station while said spacing impulses are being transmitted, means for thereafter reversing the connections of the transmitters and printers at bothstations and simultaneously locking the transmitter at the second station upon-its spacing side and means for thereafter unlocking the transmitter at the second station.

In testimony whereof I affix my signature.

.WILLIAM A. DUDLEY.

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