US2368826A - Centralized traffic controlling system for railroads - Google Patents

Description

Feb. 6, 1945. w. D. HAlLEs ET Al.

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed May 11, 1942 8 Sheets-Sheet 1 FWBrixner,

Feb. 6, 1945. l

F'IG

A Termimng Impedance CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS W. D. HAILES ET AL.

Filed May' 11, 1942 8 Sheets-sheet 2 INVENToRs W.D.Hai\es und FM/.Brixnen THEIR ATTORNEY Feb; 6, 1945. w. D. HAlLEs ET AL 2,368,826

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Feb. 6, 1945. w. D. HAILEs Ef A1. 2,368,826

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed May l1, 1942 8 Sheets-Sher#l 4 Fl G. 3.A. Control Of'cg 75 1TK 76 c-) 125 q15ML.

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Feb. 6, 1945.

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS See 8 Sheets-Shee'kI 7 BY W THEIR ATrEY W. D. HAILES ET AL Filed May l1, 1942 Feb. 6, 1945.

CENTRALIZED TRAFFIC CONTRLLING SYSTEM FOR RAILROADS Fl e. 4 B.

INVENToRs W.D.Ha|es and EWBrixner` Feb. 6, 1945. w. D. HAlLEs ErAL CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed May l1, 1942 8 Sheets-Sheet 8 To NTQL.

Stau +2..: 205 92.55 wzwmmnnw Paiented Feb. 6, 1945 UNITED STATES PATENT OFFICE CENTRALIZED TRAFFIC GNTROLLING SYSTEM FOR RAILROADS.

William, D..v Hales, Brighton, and: Frederick Brxner,A (States,` N. XLI assgnors to General Rail- -way Signal Company, Rochester, N`. Y.

Application May 11,1942, serial No. 442,508

17y Claims.

This invention relates. to; the communication;-

part. of acentralized traiflc controlling System used for governi-rre` tramo on railroads1 and `more.- particularly pertains to a communication system of the carrier currentV codedty-pe.

In, acentralized traffic Qontrol system forrail-` roads, often conveniently termed 'l'. sys,-

tem the switches. andsignals at Various.; points along the railroad are: placed undery the control of an operator in a central oice so that, hemay change the position of the switches., subject to automatic approach and detector locking circuits. which prevent unsafe operation of any switch,

and may hold at stop any of. the signals or allow.

them to clear dependent upon the` position oi their associated switches; and in. accordance with traiiic conditions- A1so such a system provides, means whereby indications arel displayed in, the control ofceto informk thev operator of the4 loca-1 tion of trains on the various track sections throughout the territory under his supervision, and tov indicate the position and; condition of the various switchesand signals.

Those switches and signals Whichv are, located adjacent each other comprise what is` con veniently termed afield. Station,l and a cornnriuni-t.

cation system is then provided to interconnect the central control,A office with the several field stations for the transmission of controls to the. iield stations, and for the reception of indications from the field stations.

In accordance with the present inventiom'it.

selected' frequencies on the line circuit at. the,

control oiiice'for the selection of any desired field, station and the transmission of controls to that eldlstation. Although, the system of the present invention accomplishes this `by the manner in which the apparatus at the control oce and eld stations is inductively coupled to the line, circuit and also byreason of the use of 'the proper frequencies which-'may `be superimposed upon thev line circuit vWithout interferingrv with the transmissionA ofthe other services already employed oratore.

on the, line circuit, it is to be understood thatthe invention may justas-Well be used in connection With a line circuit` free from all' other? types of services. f'

TheA field stationsV must, off course, `bel able toV transmit indications to the control olice and in accordance vvi-th the present invention these eld stations are also provided with'v frequency gen-` Each station is vthen provided with: means for superimposing a distinctive series of4 codel impulses of' alternatingl current on the lineA circuit for its own selection and alsov for its registrati'oninv the control oce as Well as for the'` transmission of' its indications afterit has been selected and registered.- For'the` purpose of the i present disclosure, the. frequency kgenerators at the eldi stations are-assumed to `produce the same frequencies as the frequency generators at` the control oiiice, and the: description is based on this. organization. Buthk it is to bewunderstood that` diierent frequencies might be. employed at` the, field stations (assuming, of' course,proper receiving apparatus is employed at. thev cont-rolfV office.) and still come. within the scope of the present: invention.

When afstation is. ready to transmit indications to theA control ottico., it appliesv an initiating.

0r startinerimnulse of alternating current of a particularr frequency to the line circuit which initiating: impulse prevents all other stations not ready t0 begin at that instant trom. thereafter interfering withthe. Series 0f; mllLllSeS that Station is about to tianSinit--` Althouent start impulse. from the field is or relatively short duration, the control ofce apparatus immediately respondsby placing conditioning impulse 'Y current, of the same frequency on the line circuit, which.A currentv is maintained by the. ofe.

for' the, time, required to` condition `the o'ice, and al1 field stationsfor an indication cycle of operatim After the conditioning period. that, station which. is ready to transmit indications.: to` diamine trol' cnice, r,Dplies to thedine circuit av series,` of

.code impulses of alternating current, each im:

pulse beine. of.. a Selected frontierscy,4 and, which series'of impulses forms a code characteristic of that station and includes impulses characteristi-icv i of the indications for that station.` When ylie eld station appliesA an impulse of anyseries to the line circuit,A s uch impulse is receivedat the control cnice/andan iin-pulse, of thesame, characteristic frequency` is' contemporaneousl'y applied tothe line' circuit atthe `controll binge, Afterv a very short interval7 of time,l the field station impulse ceases, but thecontrol office applied persists or continues for a certain additional time during which it is effectively received at all eld stations and forms what may be conveniently termed a test period. This is done on each succeeding impulse belonging to the station selection impulses until that station has been selected.'

When a plurality of field stations are ready to transmit indications at the same time, each stadtion applies impulses to the line circuit during the station selecting portion of the cycle in ac cordance with its station code until it no longer has a chance of being selected. At the control oflce, means is provided in accordance with 'the present invention whereby one frequency has superiority or preference over the other, so that those stations which apply an impulse of this superior frequency to the line circuit have an impulse of this superior frequency returned to them by the control office vwhile the others do not'have their inferior frequency returned to them. Thus, those stations applying or calling for the superior frequency on any given impulse have their station selecting means conditioned, while those stations which apply or call for the inferior frequency drop out and cease transmission until some subsequent cycle of operation. This automatic selection by giving one of the frequencies a relative superiority continues throughout those impulses of the series required for station selection and registration until only one station remains on the line circuit which station then proceeds to transmit impulses characteristic of its indications. In brief, the station selection for the transmission of indications is accomplished on a code superiority basis with the relative superiority between the diierent code elements being selectively determined at the control office. This principle of selection is employed so as to increase the integrity or reliability of such a system, and

particularly for the purpose of solving certain problems inherent in a system employing different frequencies superimposed on a line circuit. For example,-if the system were of the type where it is necessary that an inferior field station receive the superior frequency as transmitted from the superior field station, -it is entirely possible that the inferior eld station might fail to detect the presence of the superior frequency because of phase cancellation due to conflict between the transmitters of two superior field stations. Under such conditions, the inferior station which failed to receive the superior frequency would not be cancelled or drop out; and would continue to transmit although its code might be inferior to the codes transmitted from the other two stations and which would thus cause erroneous indications to be registered in the control office. I'his particular problem is solved by the present invention inasmuch as the field stationsA can always hear the control office, so to speak, although they may not always be able to hear each other.

. In other words, the retransmission of each impulse from the control office in response to a, corresponding impulse received from the eld stations, makes it possible to organize a system in which the problem of phase cancellation is avoided by providing a short interval of time near .the close of each impulse of the code during which the control oce transmitter is the only trans-` mitter onV the line circuit, together with a eld station selecting equipment which requires that the retransmitted impulse must be received by the field station during this short interval of time at the close of such impulse (conveniently termed test period) in order for that station to be selected.

Another object of the present invention is to provide a coded type system which will minimize the effects of the cross-fire between the different frequencies on the line responsive relay In a carrier current type of communication system, lters and amplifiers must be provided to respond to certain frequency bands, but, with these frequencies reasonably close together, the application of onevfrequency may cause a transient condition vwhich simulates the other frequency thereby interfering with the line responsive relay means for such other frequency. The present invention minimizes this possibility by providing suitable selectingr vcircuits which need function only during test periods when the control office transmitter is the only transmitter on the line and transients have subsided.

In a system of this character, it is necessary to have the transmitters and receivers at the eld stations vset with the proper gains to insure that each field station will transmit at an energy level suiciently high to be received at the control ofce and to insure thatthe impulses transmitted by the control ofce will be properly received at the eld stations. For example, this means that a distant iield station receiver must be set at a high gain in order to properly receive the impulses transmitted from the control office at the otherl end of the line, and it also means that the output energy level of the transmitter at such distant field station must be high in order to be received by the control` oice. This combination of a receiver of high gain at the same or an adjoining location with a transmitter of a high output level increases the tendency of one frequency to cross-fire into the other'frequency at that receiver. This source of potential difficulty due to cross-fire between frequencies, is overcome by the "feature of the present invention employing retransmission of each impulse by the control olce, the latter part of whichfforms a test period during which the control oiiice transmitter is the only transmitter on the line circuit, because it is obvious that with but a single frequency on the line circuit, there is no possibility of cross-rei conditions. l

Another advantage of a system organized in accordance with this invention is the manner in which the output levels of eld transmitters may be adjusted in accordance with their geographic relationship to the control office so that code impulses received from the various field stations are received with substantially the same intensity or energy level at the control office. 'I'his is particularly advantageous when it is remembered that the control ofiice receiver must be adjusted with sufficient amplifying gain to properly re. ceive impulses transmitted from the most distant ofthe frequency characteristic of any impulse ascaaae cations', and is: arranged. so that. if there is ,al n

since the. control office receivermust be set at such again as to most profltably receive the most distant transmitter on the line. circuit. However, by employing the feature of retransmission in a system organized in accordance -with the present invention, this diculty from cross-fire at the control oice is eliminated Without additional cost and` complication.

Another object of the present invention is to provide a system in which a field station is retired (or fails to be selected) when it'has a defective synchr'onizing or locking-in type so that if two field stations start transmission at the same time v these generators will operate in phase for each of theV impulses transmitted from such stations. Each ofthese arrangements of generators provides distinctive problems and characteristics in connection with the line circuits, but the object of the present invention is to provide localv con.. trol circuits for the control cnice and the iield stations which will be operative Witheitherr ar-v rangement.

Another object of this-invention is to provide a simplex type of communication system, that is, a system in which only controls or indications can be transmitted on'any particularcycle of operation even though the control oflice and eld stations have separate sources of energy and can initiatexa cycle of operation at any-timewhile the system is at rest.' This feature is accomplished by arranging that the initiating or conditioning impulse applied at the control oflice, as above mentioned, is of one frequency if acontrol'oilce start occurs to initiate a cycle ofoperation' for the transmission of controls, but such initiating or conditioning impulse is of a different vfrequency if a field station initiates a cycle-of oper ation for the transmission of indications. At` the end of a cycle of operation,the control ofce applies a permission impulse on the line which is of the same frequency `as applied for a field station start impulse, and this permission impulse places the eld station incondition to initiate an indication cycle of operation,`but when the control oiiice has new `controls to transmit to a eld station, this permission impulseis not applied to the line bythe control oflice, so that the following cycle `of operation is for the transmission of controls. The field stations, although ready to transmit, cannot elect a eld station start until the control office has completed the transmission of the new controls and places the temporary permission impulse on 'the line.

Another object of the linvention is to provide a system in which the indication cycles will be distributed between the different eld stations having'indications to transmitso that if `any particular station has a large number of indications to transmity because of frequent changesy in' indication conditions at that station it cannot dominate the system. In other words, the*V system provides what isl `conveniently termed group of viield stations ready to transmit attire same timeyeach of these stations has. an oppor-` tunity to transmit only one cycle of operationun'- til all of the stations in that group have transmitted. Atthe .end ofthe transmission of the successive cycles of operation by this' group ofV stations, a prolonged period of rest occurs during which all stations then having indications ready to transmit form another group, so as` to speak, and indications are then transmitted on successive cycles of operation from such another group of stations. l Other objects, purposes, and characteristic features of the present invention will be in .part obvious from the accompanying drawings andin part pointed out as the description of thehinvention progresses.

In describing the invention in detail, 'reference will bemade to the accompanying drawings, in which those parts having similanfeatures and functions are designated throughout the several figures by like letter reference characters which are generallymade distinctive either by reason of preceding numerals representative of their location or by reason of succeeding numerals or, exponents representative of the order of their operation, and in whichf Y Fig. 1: illustrates in a diagrammatic manner the relationship oftthe C. T. C. system of the present invention to the various other services which may be associated .with aline circuit upon which the` system` of the present invention may be superimposed;

Figs. 2A and 2B when placed end to endillusz trate diagrammatically the line circuitarrange: ment of the present invention whenv applied to a line circuit having no other services thereon as well as showing the interconnections betweenthe line circuit and the control apparatus in the control ofiice and at a typical one of the lieldstations;

Figs. 3A and 3B when placed side byside il.. lustrate `the apparatus and circuit arrangementv employed at the control cnice;

Figs. 4A and 4B when placed side by sideillus.- trate the apparatus and circuitsemployed at a typical eld station `arranged and controlled in accordance with the present invention;` and.,

parts and circuits constituting the embodiment-l or theY invention have been shown diagrammatically and certain conventional illustrations have been employed; the drawings have been `made more with the purposel of facilitating the disclosure` as' to the` principles and mode of operation than With the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts are illustrated in a conventional mannenand symbols are used to indicate the connections to Ythe terminals obatteries' or other` vsources ofV electric current lnsteadof' bring"-` ingall of the wiring connections to those termina1s Y The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries or other sources of di. rect current; and the circuits withv which these symbols are used. always have current owing in the same direction. The symbols' (B+) and (B) indicate connections to the opposite terminalsof a suitable battery or other direct current source which has a central tap or intermediate tap designated (CN) and the circuits with which these symbols are used may have current owing in one direction or the other depending upon the particular terminal used in combination with the intermediate tap (CN). Whenalternating current is used in place of direct current, the particular symbols employed should be considered to represent the relative instantaneous vpolarities.

GENERAL ORGANIZATION C. T. C. SYSTEM SUrimIMPosEDk oN LINE CIRcUIr HAVING OTHER SERVICES `With reference to Fig. 1 of the accompanying drawings, a line circuit having line wires l0 and II is shown extending between two repeat coils I6 and I1. Connected across Athe line wires of this line circuit is a dispatchers telephone equipment graph line circuit. Similarly, one purpose of the repeat coil I1 is to terminate the telegraph line circuit and still permit the telephone frequencies and the frequencies of the centralized traiic controlling communication system to be repeated in the usual way. If the centralized traflc control is to be terminated at this point, it is to be un-` derstood that suitable termination impedances must be associated with or incorporated into the coil Il. The features of proper line termination,v

of course, have nothing to do with the present invention and should be accomplished in the usuali well known manner.

The control'omce selective ringing equipment effects the transmission of impulses over the line` circuit at the rate of about 3'1/2 cycles per second in a manner to form different number codes.V Thev telephone selector for each station is responsive to only the code assigned to its telephone station.

When a telephone station is selected, its bell is caused .to ring until a stop ringing pulse is transmitted by the selective telephone ringing equipment. The operator at the telephone called will then communicate with the dispatcher by voice'. It may be noted Athat the dispatcher is always listening and will hear any telepho-ne without bel ing called 4by ringing. If someone at one tele-v phone station desires to communicate with someone at another telephone station, he merely asks the dispatcher to call such another telephone station.

It is, of course, understood that the telephone voicefrequencies may have a very wide range, but for allpracticalvoice conversations a range of frequencies between 200 and 2500 cycles is all that is required. The Vcontrol oice equipment and -the eld station equipment for .the centralized traic controlling (C. T. C.) system are connected in multiple across the line circuit through suitable coupling units and lters which, are designed to pass only the frequencies desired for the operation of the C. T.C. system, whereas the low-pass lters for the telephone equipment are arranged to pass only the frequencies required for voice transmission, namely 200 to 2500 cycles. For the purpose of the present disclosure, the frequencies selected for the C. T.V C. system are 3300 In systems of this character where various fre` quencies are to be imposed upon the line circuit,l it isdesirable to properly terminatethe line cir.-

cuits so as to prevent the reflection of the, alternating currents when theyfreach the end of the line. For example, assuming that the line circuits are improperly terminated, the application of an alternatingV current potential at one end of the line circuit results in the rotation of the vector or phase relationship in Aone direction as this potential is taken from the line circuit at successive points away from the control oi-ce, and with the line circuit improperly terminated, such alternating current potential is reected bythe improper condition at'the end of the line so as to produce potentials which in eiect originate at such end of the line and which flow toward the originalend of the line with the phase relationship rotating in an opposite direction. This produces nodes and anti-nodes at various points along the line circuit. Thus, if a C. T. C. field station equipment were located at a point along the line circuit at which a node occurs in this improperly terminated line circuit, such eld sta-r tion would not receive signalling current. .Howeven such undesired end of line reflections. would noto-cour if the line circui-t were of an infinite length or were properly terminated by the placing of impedances Aacross the ends of the line equal to the natural surge impedance of such line circuit; l Thus, it is desirable that suitable terminal impedlances be placed at the ends of the line circuit used for the C. T. C. system. With` be properly terminated with respect to the C. T. C. f

portion ofthe line circuit.

, C. T. C. SYSTEM ALONE oN LrNE CIRcUrr In Figs. 2A and 2B, a une circuit having uve wires I2 and I3 is shown for a C. T. C. system provided in accordance with the present invention kin `which there are no other services on the line circuit.` These line wires I2 and I3 provide a line circuit which, Yof course, must have similar characteristics asA the one disclosed in connection with Fig. vf1, that is, itv must 'beproperly terminated so as to prevent reflection from Y the ends of the line.. Tjhus, terminatingimpede.y ances- I andV` I 9 are provided; at theV opposite ends of the line to properly terminate the line circuits `each having an impedance equal to the natural surge impedance of an innnitely long line havthis connection, it shouldbe noted that the present invention can also be applied to a commerl cial power distribution system .providingalternating current of the usual 60 cycle type. Such an application of the present invention is particularly advantageous in view of the usual organization of signallingv systems for..railroads in which the field locations are provided with storage batteries having a 60 cycle alternating cur.- rent trickle charge apparatus vassociatedtl'ierewith. Thus, the system ofthe present invention could be applied to such a railroad signal- .ling system without the installation vo1 added line wires. When the system. issuperimposed on a power network or line circuit, it is necessary to provide blocking impedances at power: connections to such line circuit in order to prevent .the escape o-r attenuation of the carrier frequencies. Also, the ends of such power line .circuit would, of course, necessarily have tor be provided with terminating impedances in the usual way.

In Figs, 2A and 2B, the line circuit is shown as having a control office at one end and several field stations spaced at intervals along the line circuit toward the other end, but it is to be understood that the system might be arranged to have the control cnice at some intermediate point with respect to the eld stations.

Each field station equipment as well as the control office equipment is connected to the line wires l2 and I3 through condensers 20 and `2l which `have a suitable insulation strength to protect the C. T. C. 4equipment from high voltages.

Each field station and the `control oiiice` includes code transmitting and receiving apparatus. This transmitting` apparatus for the control ofce or any field station comprises selector apparatus, frequency generatingr apparatus and the filters required to impress the potential on the line circuit; while the receiving apparatus comprises lters and amplifiers for receiving impulses over the line circuit and directing the impulses of the different frequencies to the proper line relay responsive means which in turn act upon the selector apparatus.

The transmitting apparatus for the control office and any eld station has two frequency generators designated respectively f1-Gen. and f2-Gen. which are controlled by the selector apparatus in the control ofceor at the field station as the case may be to impressy alternating ner and .filter units are arrangedk to provide such relay means F1 and F2 with energy to pick up their contacts only when their respective frequencies 3300 and 3500 are impressed upon the line circuit. .It is, ofcourse, understood that these amplifier and filter units will pass ia. certain band of frequencies at 3300A and 3500 respectively and also thatthese particularfrequencies have been chosen as examples of frequenciesv which do not interfere with the telephone equipment illustrated in Fig. 1 and also which dor not interfere with radio receiving sets adjacent the line circuit of either Fig. 1 or Figs. 2A and 2B. Detail consideration will not be given in this application to the amplifier and filter arrangement for'the receiving units., as they'may. be ofv any suitable type known in the art. Similarly, the coupling units may be -of yany suitable type operable with the particular types of generators and receivers used,

Withl reference 'to Figs. 2A and 2B, itv will be seen that the frequency generators, amplifier and filter units, and coupling `units receiving the tWo different frequencies havebeen shown diagrammatically for the control omce and for field station No.1 and the connections tothese units eX- tend to dotted rectangles. The selector apparatus for the control office is shown in Figs. 3A and 8B while the selector apparatus for field station No. l is shown in detail in Figs. 4A and 4B as designated in the drawings. It will be noted that field stations No. 2 and No. 3 have current impulses on the line circuit through a tion and control office are provided `with two lineresponsive relay means designated F1 and 1"2 which are respectively .connected to their re'- spective amplier and lter units to vthe line Wires I2 and I3 through ia coupling unit and condensers 20 and 2l. VTheir lrespective amplimerely been designatedv by rectangles bearing .thelegend receiving and transmitting'appal as the description progresses.

CONTROL OFFICE APPARATUS v With reference to-Figs. 3A and 3B placed side to side, it will be seen that the line responsive peat each of the impulses impressedy on the line circuit as repeated `by the line relays. F1 and F2 except in the case ofthe permission pulse.- The usual cycle demarking relays SA, SB and SC, all of the slow-acting type, are associatediwith the line repeating relay FA. Two line condition relays L and R areprovided to bevresponsive to the permission impulse at the endof a cycle of operation which permission vimpulse occurs only if the control cnice has no morevcontrols to `transmit and the line circuit may be employed on a successive cycle Aof a field station for transmitting indications. Inuthis connection; two starting relays C-jand CF are provided. TherelayC y is responsive to manual actuation of start buttons for starting a cycle of operation for the transmission of controls and the relay CF is responsive to a start 'pulse automatically applied at a field station for` starting a cycle of operation for the transmission ofindications.

The above mentioned relays together with an impulsing relay E and its repeater EP cause the operation'of the stepping relay bank including` stepping relays V and a half-step relayVP. i

The control panel has mounted thereon the various control levers, start buttons, indicator lamps and the like, as well as the usual miniature track diagram. Each eld station has its group of control levers and a start button B. But for the sake of .simplicity only the switch control lever I SML for the switch machine ISM at the field station No. 1, has been shown with an associated start button IB;

A cancel button CNB is located on the panel and is rendered effective when actuated, to cancel the transmission of any new controls that have been set up by the operator.

When a start button B'is manually actuated, it causes the .picking up of its corresponding change relay CI-I which in turn acts upon its associated code determining relay LC if the system is then in condition for transmitting control code.

xThis `relay LC acts throughv an associated LCS relay to energize the control starting relay C.

The control starting relay then causes the trans-` mitter relays T1 and 'I'2 to be rendered effective to transmit 'the station code and controls to the desired station. Relay T1 when energized causes frequency generator f1-Gen. to be effective to impress 3300 cycle current on the line circuit, while relay T2 when energized causes frequency ,generator f2-Gen. to be effective to impress 3500 cycle current on the line circuit.

A slow-acting relay OC is provided to cause the system to go into a period of rest if for some stations.

The li'ne responsive relay means. includes the line relays IFl'and IF2. The line repeating relay IFA is associated with these line relaysfor repeating each of the impulses of a series of impulses which are impressed upon the Vline circuit. However, relay vIFA does not respond to the permission pulse. Cycle demarking relays SA and SB are also provided.

The line condition relays IL and IR are provided at the eld ystation and are conditioned to render the eld station elective to transmit only if a permission impulse is placed upon the line circuit following any series of impulses which permission impulses advises each of the field stations and the control office that the system, a1- though at rest, may be initiated into operation for the transmission of indications as well as the transmission of controls. It is through the functioning of these relays and their associated circuits that the control oce is made superior or dominant over the field stations so that an operator may transmit controls on successive control cycles to any number of eld stations irrespective of the fact that indications may bel standing ready at various field stations awaiting transmission. The line repeating relay IFA causes the operation of a stepping relay 4bank reason the system should fail to properly operate and cause an indenitely prolonged impulse to be placed upon the line circuit.

Through the line repeating relay FA and suitable circuit connections tWo relays TON and LON are provided to time the length of the on or impulse intervals during `the transmission of indications so as to .properly control the indication receiving relays, such as ITKR, in accordance with the length of the impulses as well as in accordance with the distinctive frequencies of such impulses.

'Ihe station registration relays RF are controlled in accordance with the station selecting code so as to cause the energization of the station relay ST for the particular station then selected to render the indication relays for that station responsive to the character of the impulses received over the line circuit for the remaining impulses of that indication cycle of operation. The relay ITKR is an indication relay of the twoposition magnetic-stick type and is associated in this disclosure with the condition of track occupancy at station No. l. When its contact 22 -is positioned to the left, it energizes lamp ITK to indicate that a train is on the associated track section at station No. l.v It might be noted in thisconnection that theregistration relays RF are provided, one for each impulse of the station;

selecting and registration portionvof a code, while there is a relay ST provided for each of the field stations. `It is, of course, understood that these relays are controlled through suitable selections which are made in accordance with the regular well-known Baudot code as shown in thev prior Patent No. 2,259,561, dated October 21,1941, granted to Hailes and Brixner.

FIELD STATION APPARATUS including steppingrelays V and a laststep relay ILV as well as a half-step relay IVP.

The operation of thesystem during* the trans-,

mission of a control code effects the selection of the station through the proper control of the station selecting relay ISO and its repeating relay ISOS, 'but during the transmission 'of the impulses for an indication cycle of operation the station vis selected for transmitting indication impulses by the proper control of the relay SI and at the same time i's registered in the control office on the registering relays RF. and station lrelay ST.

The transmission of a control to the field station after its selection actuates a suitable relay means to a proper position for controlling any desired traic controlling device which has been typically illustrated in the control of the relay ISMR whichin turn controls the switch machineof proper frequencies to ,select that field station Y and register its indications in the control oiiice. An impulsing relay IE is provided to cause the proper timing of the relays. Associated with this apparatus is a transmitting timer relay ITC and its repeating relay ITCP. Relay ILON is provided to time the long impulses impressed by the line circuit by the field station. It isf of course, understood that the transmitting relay IT1 and I'I2 control the frequency generators at the eld station in accordance with the code to be transmitted as indicated in Fig. 2B.

It is, of course, understood that various other auxiliary devices and circuits therefor will be employed in a C. T. C. system embodying the OPERATION The communication system provided by the present invention is normally at rest. When the system is applied to the line circuit arrangement of Fig. 1, it is normally deenergized so far as the C. T. C. communication system is concerned, but it is to be understood Athat the other vservices may be employing the line circuit. In Figs. 2A

and 2B where the C. T. C. communication system is the only service on the 'line circuit, it is, of course, obvious that the line circuit is de'energized unless the C. T. C communication system is in operation.

Any iield station or the control office can initiate the system into operation to transmit new indications or controls respectively. If several field stations are ready for transmission atthe same time, they are transmitted from such`fle1d stations to the control office one cycle =for each field station until each of those stations have ob- NORMAL CONDITIONS While the system is at rest most of the relays and circuits are deenergized, and are `thus organized to save energy while the system `is not in operation. However, the line condition relays L and R. at the contol oflice and at the field stations lare normally energized.

With reference to Fig. 3B, it will be seen that the relays R and L are energized in series from (-1-), through a circuit including back `contact 3.0 of relay SB, winding of relay L, front contact 3I, winding of relay R, to This stick circuit can, of course, be broken only by the picking up of contact 3U of relay SB, in which case the relays R and L both drop away.

When these relays are dropped away and the back contact 30 of relay SB is again closed, the relay R can only be picked up by an energizing circuit closed from (-I-) and including vback contact 30 of relay SB, back contact 32` of relay L, front contact 33 of relay F2, winding of relay R, to It will be noted that the picking up of the relay R closes its front contact 3I, but the relay L canot pick up to open its back contact 32 so long as the iront contact 33 of relayF2 is closed thereby providing a shunt circuit across both terminals oi the relay L. However, when the front contact 33 of relay F2 isopen, at the end of a permission pulse as will be hereinafter described, the relay L then picks up inseries with v the relay R and is vmaintained energizedthrough the stick circuit above traced.

With reference to Fig. l4A, 'a similar energizing stick, circuit is normally closed for the relays IR and IL from through a circuit including back contact 34 of relay ISB, wind-ings of relay IL, front Contact 31 of relay IR., windings of relay IR, to When relay ISB is picked up, both relays IR and IL are released, but may be again picked up when relay ISB is again released. The pick-up circuit for the relay IR is provided from (-I-l through a circuit including back contact 34 of relay ISB, back contact 35of relay IL, front contact 36 of relay IF2, windings of reiay IR, to IL is, of course, the same as the stick circuit above traced, but with the. pick-up circuit for the relay IR open at front'contactv 36 of relay 'I'he change relay ICH (see Fig. 4B) is also normally energized from (-1-) through a circuit `including front contact 21 ofrelay IT, front contact 38 of relay` IM, front contact 39 of relay ICH, lower winding of relay ICI-I, to It is, of course, understood that the track relay IT ,is normally energized by a track circuit` not shown in detail, and the signals at stop relay IM is also normally `energized by circuits not shown. Al-

though .these relays IT and IM are shown normally energized with the system at rest. it is to be understood'that either or both may be deenergized and the `system still remain at rest, the indications associated therewith having been transmitted on some operating cycle and caused the restoration of the Vchange relay ICH to a picked-up position in which itis also maintained energized through its stick circuit through either front or back contacts 21 or front or back conf tacts 38 until anotherfchange in condition occurs.

MANUAL START At any time that the operator desires to transmit controls to a particular station, he first `positions the control'levers forthat station and then actuates momentarily the start button B associated therewith.

The arrangementof the circuits for thelcontrol of the associated relays CHI, ILC, and LCSis vsuch as to provide that only one eld stationmay Vhave controls i transmitted thereto at .any one time, but these relays and associated circuits are also eiective to store a manual start for any one or several `'leld stations until the system is available for the transmission of controls to those stations. 'I'his is necessary even though the system is arranged to make the control ofce superior to the iield stations, because at the time the operator actuates a start button B the systemv may be transmitting indicationsfirom some iield station or may be transmitting `controls to `some other field station. The predetermined order in which the controls are transmitted tothe 'different field stations when the operator actuates several start buttons B'in quick succession is determined by the interlock between the various CH y and LC relays of the interlocked bank as shown 'of cancel button CNB, to

and described in our above-*mentioned Patent No.. 2,259,561.

Let us assume that the operator desires tok transmit controls to eld station No. 1 and properly positions the control levers for that station lto the desired positions, such as lever ISML, for

It will, of course; be apparent that the start buttonvIB need be actuated only momentarily by the operator, because the relay CHI is maintained energized by its stick circuit as soon as its front contact Mis closed.

If the system is at rest, the picking up of the relay CHI closes lan energizing circuit for the The pick-up circuitr for the Vrelay of relay SB, back contact 45 of relay LCS, back contact 4'! of relay CF, wire 48, back contact 49. of relay CH2, front contact 50 of relay CHI, upper winding of relay ILC, bus wire 5I, front contact Y 42 of cancel button CNB 'to It will, of course, be noted that if the system is in operation, the relay SB will be energized and the back contact 45 will be opened so that the relay ILC could not be picked up. Also, the system may have been just initiated' by some other start button-B or by some change in conditions at the eld station causing the pick up of either the relay LCS or the relay CF opening either contact 46 or 41 respectively as will be presently pointed out. However, assuming that the system is at rest, the relay ILC picks up closing a stick circuit from through a circuit including back'contact 52 of relay SB, winding of relay LCS, wire 53, front contact 54, lower winding of relay ILC, bus' wire 5I, front contact 42 of cancel button It will be noted that the relay LCS is in series with this stick circuit for the relay LC and as soon as it picks up, it opens its back contact 4B and prevents all other ,LC relays from being picked up. Also, energy (-1-) is applied to the right hand terminal of relay LCS by back contacts SI and |50 of relays C and V4 respectively in'multiple with back contact 52 of relay SB for reasons 4later pointed out. i

Both the bus wires 4I and 5I are connected t negative potential through normally closed front contact 42 of cancel button CNB, so that if at any time a start button B is actuatedprematurely or inadvisedly theA operator can immediately cancel such storage of a start condition by the actuation of the cancel button CNB opening front contact 42 and thereby deenergizing any relay CH or LC then picked up.

As so-on as the relay ILC picks up and is energized through its stickv circuit also energizing the relay LCS to initiate the system into operation, the back contact 43 of relayILC is opened to deenergize the relay CHI so that it drops away.

It will be seen that the pick-up circuit for the relay ILC includes back contact 49 of relay CH2 so that if both the buttons IB and 2B were actuated simultaneously, the relay 2LC would pick up in preference to the relay ILC, but the relay CHI would remain stuck up so that after an operating cycle had occurred .for the'transmission of controls to the field station No. 2 corresponding to the relay 2LC, 'the relay CHI would then be effective to pick up its associated relay ILC, because at such time the relay 2CH would be dropped away. Under the circumstances, assumed above, where the -button IB has been actuated and the relay ILC picked up, then the actuation of the start button 2B merely causes the energization of relay H which is stored until the transmission of controls has been eiected for the station No. 1.

The picking up oi the relay LCS closes a p ickup circuit for the control office starting relay C from (-|r-) ,throughacircuit including back contact 55 of relay SB, back contact 56 of relay F2, front contact 5'! of relay LCS, back contact 58 of relay CF, windings of relay C, to As soon as the relay C picksup,itsstickcircuit is c1'osedfrom(-{-)1, through a circuit including front contact 59 of relay LCS, front contact 60 of relay C, windings of relay C, to Another stick circuit is also closed for the relay C from (-|-),.through a circuit including back contact 6I of relay SC, front contact 62 of relay C, windingsof relay C, to The picking up of the control ofce start relay `C opens its back contact 62 included in the stick circuit of the field start relay CF. This gives the control oce start relay C the priority .in the event both the relays C and CF are energized LV, back contact 61 of relay V4, back contactV -68 of relay V3, backl conta-ct 89 of relay V2, back Contact I0 of relay V1, to the bus Wire 'I5 which extends to the relay T1, windings of relay T1, to l The picking up of the contacts of the transmitter relay T1 closes its front contact 'I1 (see Fig. 2A) for completing an obvious energizing circuit for the frequency Vgenerator f1-Gen. which in turn impresses the frequency f1 on the line circuit to condition and initiate the apparatus at the control office and each of the eld stations for a control cycle of operation. This conditioning impulse is indicated as the iirst impulse of a cycle in the chart of Fig. 5A showing a typical control cycle.

As heretofore mentioned, this frequency f1 is always impressed on the line circuit for the conditioning impulse of a control cycle and the length of this conditioning impulse is determined by the sequence of certain relays immediately following the picking up of the relay C.

More specifically, the picking up of the relay C also closes a pick-up circuit for the relay OC from through a circuit including back contact 80 vof relay SC, front contact 8l of relay C, f

back contact 82 of relay CF, windings of relay OC, to The relay OC is, of course, slow acting but it picks up after a short time to close its front contact 83 in readiness to complete ay stick circuit and also to supply energy to the impulsing circuits for the transmitter relays T1 and T2 during the operating cycle being initiated.

At the control ofce, the line responsive relay F1 responds to the frequency `f1 of the conditioning impulse and closes its front contacts. 'Ihis completes an energizing 'circuit for the line repeating relay FA .from through a circuit including front, contact 84 of relay F1, windings of relay FA, t0

The picking up of the relay FA closes its front contact 85 to complete an obvious energizing circuit for the relay SA; the relay SA in turn closes it's front conta-ct 86 to-complete an obvious energizing circuit for the relayv SB; and the relay SB in vturn closes its front contact 8l to/ complete an obvious energizing circuit for the relay SC. Thus, it' will be seen that the relays FA, SA, SB and SC' pick up in sequence.

The picking up of the relay SC opens the pickup circuit for the relay OC at back contact 8l), but prepares a stick circiut for the relay OC at front contact 83 which is closed at the termination of the conditioning impulse and during each succeeding impulse. This stick circuit for thev relay OC is closed from through a, circuit including front contact 83 of the relay OC, front contact 88 of the relay SC, back contact 89 of the relay F1, back conta-ct 90 of the relay F2, windings of the relay OC, to It is noted, howaccesso ever, that this sticklcircuit is `nosed only during Also, if lthe conditioning impulse should be maintained for an unusual `length of time, the stick circuit would be open at vback contacts 89 and 90 and the relay C would be dropped away.

At the time the relay .C picks up, an energizing circiut is closed for the relay E from through a .circuit including-atront contact 9| of the relayC, wire 92, .back contact .93 .of relaylLV, back ,contact 94 `of relay V4, .back `contact195 of relay back contact Shot-relay'V?, .backcoutact 295| of .relay V1, Aback .contact .198 Aof relay Wire. 9:9., windings of relay E, .to

'l'.fl'ie picking-.up of therelay Eicloses yits .front contact |^01| .so that upon 'the picking lupof'the relay ySB .and prior to thepick-ing up of the relay. SC opening back .contact 88 -an .energizing circuit is closed .for the transmitting relay T1, from through a circuit including front contact 83 .of relay IOC, front contact 0.2 fof relay SB, `front contact .|0| of relay E, lfrontcontact 64 of relay C, wire y65', back contact`r 66 of relay LV, llaack'contact B1 of relay V4, back contact 68 `ci relayV3, back .contact .59 lof relay V2; back-contact 10 of relay V11, .tothe bus wire .15; and thence .through OPER-Arron or" STEPPING RELAY BANK AT' THE CONTROL OFFICE l The .stepping relay` bank-at the` .control office comprises a series ofY stepping 4relays V, la' last stepping relay LV and a. half-step relay These stepping relays are successively picked up on each off period of Vany series of impulses, while the half-step relay VP assumes anv opposite position foreach on period of the Asame series. T-he first operation of the stepping .relay bank thatoccurs subsequent to the YactuationI of a start button for the transmission of controlsis the picking up -o the half-step -relay VP during the conditioning impulse following the picking up of theslow acting relay SC. These sequential operations of the relays V and VP are indicated inthe chart of Fig. 5A where the arrows pointing up and down respectivelyindicate the'pcking. up or 'dropping away vof are associated. y v

The pick-up `circuit .for the relay VP is closed. from through a circuit including front contact y45 `of relaygSB. front contact 03 of relay SC,`fro-nt Contact |04 of relay FA, fwire |05, backv contact IDS -of relayLV; back Contact .I 01 of vrelay V4, back contact +08 of relay'Vf, back contact |09 the relaysfwith which they4 of relay V2, back contact 'H0 Y*of relay V1, windings of' relay VP, to As'soon `as "the relay VP picks up, the stick circuit is completed therefor from "(+9 through a circuitl including front contact I|5of relay/SB, front contact |03 of relay SC, wirel I, front contact ||2 of relay VP, back contact |06 of relay LV, back contact |01y of relay V4, back contact |08 vof relay V3, back contact |09 'of relay V2, back contact H0 of relay V1, windings of relay VP, to This stick rcircuit is maintained closed until the iirst stepping relay of the bank is vpicked yup which voccurs during the first oil period of the `series vofimpulsesto `be transmittedfromthe control cnice. 'l

Upon the ,picking up of the vrelay 'VP,'ba'ck Contact 98 is open so Athat the relay -E 'is deenergized Awhich opens lfront contact |'0"| included in front contact 84 which inturn deenergizes `they relay FA. 'In other. Words, the relay. FAMrepeats the line responsive relay nieansregardlesstof whetherlit Thus, it

is the relay F1 orthe relay F2 which is actuated in response to' the corresponding frequencies placed'upon the line circuit. The reason for 'this` is `because the'relaySB picks up and closes front contact I3 so'that front contact .||4.of relay F2 can .control the Lrelay JFA the same as frontcontact '814 Tof .relay FI. fIt is noted inthis connection that the picking up of relay` SBopens backcoutact 3i) 'and deenergizes the line .condition .relays R and L, opening front contact ||5 of krelay .'L,

the significance of which willbe discussed here- 1 inafter. l p y Y Assuming that 4the rst foff;perio.d is repeated by the relay FA, the closure of -back contact .|04A completes a stick circuit foi-'the relay VVPLfrom j througha circuit' including front contact 45 of relay SB, front contact..|.0.3 of .relay..SC,

back contact |04 ofrelay EA, Wire .|'|'6 iront. Contact' l of relay VP, windings of relay to,

( Thus, the relay VPis maintained energized duringthe ofPperiods even 'though 'its pick-up circuitis opened at 'frontcontact ||0 by the picking up.of the flrs't step relay V1, .for

example. .i

The yiirst step `rela'y V1 is'caused to vbe picked up upon the release of the'relay 'FA by reason of a circuit closed from ,and including front contact '6| .of relay SC,"back-.contact `|V|8 of .relay FA, wire H9, front contact-|20 of relay VP, back contact |2| of relay V4, back .Contact |22 of .relay V2, windings of relay V1, to (a). `As soon as the relay V1 is picked up, its stick circuit is closed from through a circuit including front conrelay V3; front contact"|25 ofrelay V1, windings of relay V1, to

an' energizing 'circuit for relay E incll'lding front Contact 91 of relay V1 and front contact. 98 .of re- |01 for energizing eitherrelay T1 or relay VVT2 in accordance with the character of impulse re-. quired for the rst `element of the code for ther station being selected. i

Disregarding for the moment the particular The picking up of the stepping relay closes4 character of the next impulse, it is impressed on the line circuit by the picking up of either the transmitting relay T1 or the transmitting relay T2, and such impulse is repeated by the corresponding line responsive relay means F1 or F2 which in turn is repeated by picking up of the relay FA.

The opening of back Contact |04 of relay FA opens the stick circuit for the relay VP including the front contact I I1 of relay VP, the other stick circuit forthe relay VP including its front contact I I2 already having been opened at back contact I I by thepicking up of the relay V1. Thus, the relay VP drops away .in response to the second picking up of the relay FA.

This dropping away of the relay VP opens the energizing circuit for the relay E at front contact 98 of relay VP, which causes relay E to terminate that impulse by deenergizing the particular transmitting relay T then energized at open front contact 0I. i

The second dropping away of the relay FA a the end of the second impulse of the series closes the pick-up circuit for the stepping relay V2 fromk (-l-)fthrough a circuit including front contact 6I of the relay SC, back contact I I8 of relay FA, wire I I9, back contact of relay VP, back confa tact I of relay LV, back Contact |26 of relay V3, front contact |21 of relay. V1, windings of relay V2, to As soon as the relay V2 picks up, its stick circuit is closed by the closure of its front contact |28 completing a stick circuit through back contact |29 of the relay V4 to the bus wire |23, which bus wire is energized throughout the cycle of operation. The picking up of the stepping relay V2 prepares the relays T for en,- ergization and causes the relay E to be energized by closure of front contact 90. v

During the next on period of the series of impulses, the relay FA is picked up, and causes an; other pick-up circuit to be closed for the relay VP by reason of the closure of front contact |04 of relay FA andthe closure of front contact |69 of the relay V2. c This picking up of the relay VP causes the relay E to be again deenergized to terminate that impulse. v During the following oi period of the series of impulses as repeated by the relay FA, the closure of back contact I8 completes a pick-up circuit for the relay V3 from (-1-) ,through a circuit including front contact 6I of relay SC, back contact II8 of relay FA, wire II9, front contact |20 of relay VP, back contact I 2| vof relay V4, front contact |22 of relay V2, windings of relay vV3, to v As soon as the relay V3 `picks up, it closes front contact |30 to complete a stick circuit through contact I3I of relay LV to the bus |23. The picking up of relay W opens back contact |24 included in the stick circuit of the relay V1 so that such relay V1 drops away, its function i'or this particular cycle of operation having been completed.` From the above description of the operation of the stepping bank up to the point of the picking` up of the relay V3, it will be seen that the half-` step relay VP assumesopposite positions on alternate impulse periods while the successivel stepping relays V pick up on the successive o periodsY of the series of/impulses. This stepping operation continues until the last stepping relay LV is `picked up to end the cycle of operation as will later be described. It is of course understood that the number of stepping relays is commensurate with the number of controls andindications necessary to be transmitted in actual practice.

It will be noted that the last stepping relay LV and the next to the last is maintained energized until. relay SB drops at the end of the control cycle.

It will also be noted that each of the other stepping relays is dropped away upon picking up of the second succeeding stepping relay in the steppingvrelay bank.` This serves the purpose that the stepping relays are not using energy for a longer period than necessary and also reduces the amount of current that needs to be broken at any one time upon the dropping away of a stepping relay which wouldbe of a substantial value if/all of the stepping relays were maintained until the end of the operating cycle.

FREQUENCY SELECTION FOR CONTROL Cones When controls are to be transmitted from the control oice, the iield stations are selected one at a time in accordance with the combination of thedifferent frequencies used for the impulses applied to the line circuit for a portion of the complete code, while the remaining impulses have frequencies selected in accordance with the controls to be transmitted to the selected station. In brief, a complete control code comprises a station selecting code and the controls for theselected station.'

' As above mentioned, each impulse applied to the line circuit causes the stepping means at the control oice and the field stations to take one stepl irrespective of 'the particular frequency of such impulse.l f

In accordance with the present invention, each impulse may be either of two frequencies, and the number of diierent combinations of impulses for the station selecting portion of the vcontrol code depends upon the number of impulses used. The dilerent frequencies are arranged in combina.-k tions in accordance with lthat code principle which provides that when two diierent frequencies are employed two diierent Vcombinations of code calls are obtained for one step; four different f combinationsy of impulses for two steps; eight combinations for four different steps; sixteen combinations for four steps; thirty-two dilierent combinations 'for ve steps; and so on, each additional step orimpulse doubling the number of possible code calls. In the present disclosure, only three steps have been shown, and although any number of steps may be employed, it is believed that this number is sucient for an understanding of the present invention, and a typical code rtable is given below.v

Typical code table Number of station code call' Step 1 Step 2 Step 3 1 f1 f1 f1 fl fl f2 l 2 l .il ff', f2 a i f i t il t f2 fz f1 Y fr fa fz With a code call assigned .to each field station selections are made between half of the total number of stations on the rst station selecting step in accordance with the frequency of the im.- pulse for that step; and similarly on the second station selectingstep, selection is made between half of the stations remaining after the rst selection, the particular half depending upon the frequency of the second impulse. This selection field stations.

.fZ-iz feontinues .until :the fend of thelestatinn: selecting '.steps when:` only fone stationimans the-f selectedastation.

In: accordance with this principle of` `codeise- -,lection, the. eodeijumpersfinntheontrol oiiceI can bearrangedto assignanyneode eallxto anyield station as mayzbe desired. Butgior-tbe sakee'of fsimplicitygm assigning kthe codes, 'it fis; probably desirablezto assign .the 'codeszirrttherorderfofithe flhshas been "done forzthe .pur- .poses :of "the presentadisclosure ntoirprov'ide that lwhich .requires Athree impulsesl of ffrequeneyiyl (see fcodeztablefabove). :Thisiisfzeieeted :by the l ooderjumpers |35, l-eand H131; -whilei the'station ,codefcall TNO. i 2 for istation\;No.:2t ist provided .of .the frequencies "f1, f1, f2. .1However,:itrist0;be understood that any ofthe possible codesmightibe .assigned to'thesel stationsby :merelyishifting'sthe positions of these code jumpers. Also,r-tbis assign :ment of..codes.is ifor station seleetionizforz'control .position-off theilewerLSMLi toaenereizeieithenthe relay 'IiP-:or :thefrllelay YInother Words, the aii'npulsesofthezfourthstep isof a:f1;or f2;frequency r,depen-dingupen:whethena;normalerreyerseeon- `trol 4is :desired -fior '.the1swtch'-machine @at ythe .niieldflocation ,:Inra simila-ixmanner.I the difienentrfrequencies to be transmitt'edfcan beselected.ontanyl number of station selectingsteps in accordancewith the number of stations in thesystem; and any 1- number of :controlfgsteps can '.be-used; depending @upon the Agnurnbersof switches fand-.signals ,tombe :controlled :at the fstation.

1Eim'or" CONTROLJCYCLE: AT THE 'CONTROL OFFICE AThei,application,-oftlfxelast impulse of a control eycleto the line circuitis yterminated by the .dro-pping away of :the y.relay E rwhieh realises the 1steppingzrelay LV to V,pickup ibut in; so :doingy no ..energysisapliedto the `line circuitlbecausefthere A-cycles -of operation Lwhich is indepe-ndentfoffthe -c-ode` assignment for 'station .-selection for :indi-- "cation cycles -of -operationfasy Will be explained more =in zdetail ihereinafter.

'IMBULSING OPERATION. A'LKCCJBHIROLt ,OFEIGE lAt the ybeginningioflthe `eontrolrzyele ofvoperation the initiatingfor.' eenditioningfimpulse` is provided loyatheenergization 'of'the transmitting frelay T1 to provide that the` pulses fofithe ffrequency f1. .'As -above .pointed out,AA this -energy'rfor the relay T1 is supplied through back Aczontaetftl `of` the relay SCat the same timevthatfthe relay E is -pioke'd:up'bynitsenergizing circuit-(above pointed out. fButlWhenthefVP relayfrespon'dsfias 'is the case asy soon as the'relayfSC picks-up) ,fthe rrE lrelayiisr dropped so that upon the 'pickin-g `up 'of "the 4.relay SC the *continued energization 'of er the `relay "T1 'for Athe initiating impulse Yis'lcontinued through-'front contaotfll of the1relay/E lwhich very shortly 'thereafter' drops away. `jThe dropping of the relay E, of course, -causes :the -rst1steppingrelay 'V1--to piek up. l

(As soon as `the-relayVlpicks unibe-circuit :forthe relays'T1 or T2-is5preparedfso*that-oneor 4the other `can' beenergizedin raccordancewith the eharacteref the code elementrequiredffor the rst step Whenithe relay El-piek-supv andcloses vits Yiront Contact m to cause-"energy` to,` be aprelayf LV. 4:Thiscessation of `the .applcationfoi `impulses'lizoftlie line circuit fis, of f'coursee repeated by the relay 1 FA which ,L in turn deenergizes y the 4ArelaysirSA,@SlnandeSCsuccessively i .'Iheedrop- 'zp'ngrfofrthe relay SC'gdeenergfizesy the 'relayzgGC :atiitsfrontontaet88,-sozthat no more energyzoan be dapplied to :thefrelays T1.,or TZLthroughithe Wire @Seinem-*fronticontact 83 offrelayfC,

:andzthevrelaygLC'are: droppedv vbut when itl-le-step-l ping relay `V4:'isgipioked: upibfecauserthe Nback con- -ftact 9 I -foffthe -relay'C is,v of eourse.: alreadympen sanditheveontactzzof the relay SB isalsofopen, y-`making thercontaetr-txof relay V4theflastncon- .ILC and' LGS. Asnsoonzasithe :relay :LCS :drops -away,` the front -eontact 159' is :opened conditioningithezrelay "C for :deener-gization upon vtl'lezi'release of the relay SA subsequentvto'ithef-termination ofthe last..impulsaoi.` the control,l cycle. This rs'tiek :circuituof `:the"frelay'ft'l is opened Ably-""fnoiit `contact/Hier relay 'SA' bllts :again closed by'back ',conta'eti l ofz'relayf SC.

when the last cyclefdemarking relay "SC-"becomes 'deenergiz-ed; a pernssion'impulse is place'duponvthe line `eireuit'for restoring the line v"tact |5| of relay SC, backy contact"|52 of relay -ingfeitherthe relay`Tl or'therelay i VFor example, tlfielrelayt I LC `is picked'up for; the

station No. l so 'that' the `stepping` relayV1 Ycloses its 'front Contact 1Utoconnectenergyto the bus Wire ldd. which supplies `energytlfrrouglfi--ront` which through uPfront contaoti M9 'effrrelay flLC' R.="b-ack'contactf |53'of vrelayC,r-to"tlf1elous Wire 4"16,:'vyiriciirifzs of relay'TZ; to

*The resulting Aapplication of animplulse Voffrequency f2 causes the line responsive relay `means fF2- toibe Eenergized fat VVthe 'control 'Iofce and*v at -ea'ch of 'the' eld stations. ""I'hiskenergizationwof relay F2 at i th control Voffice f does,l not energize Vthe yrelayF-A,.loeoause front contact?! |"3 of Arelay ASB is yopen fas Well as the 'fronteontact ||15.of

the line eonditionrelay L, However,y the closure 4scribed.ibut the relay/"L ldoes not ypickup until this permission impulse is fterrinated. "The length fof this permission nulseis fdeterrnin'edby the jpickup period, vof, the relay flRcin 'the cont-rol "oice 'which is made slow-acting lfonthevv purpose of timingjthis'impulse. i

2Att-er atimetherelay R picksgupfte'openi back dropping' "the `relay "T2 which', off course. is repeated by the line responsive relay means Fzin the foontrol oflice and 7fforrevspondiner relays at each-fof'theoeld stations. "If'he'opening'offfront contact 33 of relay F2 then allows the relay L to pick up so as to close front contact II to .permit the relay FA to be responsive to any initiating impulse originating at a leld location. This will be appreciated by again noting that the initiating pulses from the iield locations are of the frequency f2 While the initiating impulse from the control office is of the frequency f1.

OPERATION AT FIELD STATIONS The reception of a conditioning impulse of frequency f1 at each of the iield stations causes the line responsive relay means to repeat such impulse and effect certain conditioning operations at each of the eld stations which can be typically considered in connection with the eld station No. 1 disclosed in Figs. 4A and 4B.

More specifically, the picking up of the relay IFl closes front Contact I5@ for energizing the line repeating relay IFA through an obvious circuit. front contact I55 to energize the relay ISA, which in turn closes its contact |56 to energize the relay ISB. As soon as the relay ISB picks up, it opens back contact 34, deenergizing the line conditioning relays IR and IL to prevent any initiation of an indication cycle from the eld station as will be described in detail hereinafter. As soon as the relay ISA picks up it closes front contact |58 while the picking up of relay ISB closes contact |59. Both of these contacts |58 and |59 are in multiple for completing the pickup circuit for the relay IFA as controlled by contact |60 of relay IF2. This is necessary to maintain relay IFA controllable by relay IF2 inasmuch as the dropping away of the relay IL opens contact I6I which is not again closed until the end of a permission impulse, as will be described inconnection with the end of the control cycle at the field station.

The reception of the conditioning impulse at the field locations also closes 'a pick-up circuit for the station selecting relay SO at each 'and every station so that any station is available for its selection in accordance with the particular code received. For example, the pick-up circuit for the relays 'ISO and ISOS is closed from (-1-) through a circuit including back contact |62 of relay ISB, front contact |63 of relay IFl, back contact |64 of relay IFZ, Wire I65, back Contact |66 of relay IV4, back contact ISB of relay IV3, back contact |69 vof relay IV2, back contact |10 of relay IV2, winding of relay I SOS, Winding of relay ISO, to

It is noted that this pick-up circuit for the relays ISO and ISOS is closed uponfthe reception of the -conditioning impulseonly until the yrelay ISB is picked up at which time an immediate shift-over is made to hold the relay ISO through stick circuits. More specifically, the relay ISOS is provided with a stick circuit from through circuit including front contact I1I of relay ISB, front contact I12 of relay IFA, wire |13, front contact |14 of relay ISOS, lower winding of relay ISOS, to

With the relay ISOS thus maintained energized, a holding stick circuit is also closed for the relay ISO from (-1-), through a circuit including front contact I1I of relay ISB, wire |15.

front contact I 16 of relay ISOS, front contact- |11 of relay ISO, lofwer winding of relay ISO, to ).Y

As soon as the relay ISB picks upA during the vconditioning period, -a pick-up circuit 'is closed The line repeating relay lIlA closes its '5b ILV, back contact |61 of relay 300 `which completes a shunt circuit for the contact 293 of relay IFA until the stepping relay IV1 is picked up at Iwhich time the 'front contact 30| 'of relay IVP completes a stick cir-cuit including back contact 293 of relay IFA which will be understood by analogy to the circuits described for the relay VP in the control olice.

With the relay IVP picked up during the conditioning period, together lwith the picked-up condition of the station selecting relay ISO, the stepping bank is prepared to pick up the stepping relay IV1 upon the first 01T period following the conditioning period.

More specically, as soon as the relay IFA is released, a pick-up circuit is closed for relay IVI from through `a circuit including front contact 34 of relay ISB, back contact 302 of relay IFA, wire 303, front contact 304l of relay ISO. front contact 305 of relay IVP, ba-ck contact 306 of relay IV4, back contact 301 of relay IV2, windings offrelay IVl, to As soon as the relay I V1 picks up a stick circuit is closed from (-I), through a circuit including front contact 308 of relay ISB, wire 309, back contact 3| 0 of relay IV3, front contact 3II of relay IV1, winding ofrelay |V1, to

It is believed to be unnecessary to'point out in detail the operation of the stepping bank at the field station, inasmuch as the operation of such stepping bank can be readily understood by analogy to the detail operation given with respect to the stepping bank in the 'control cnice. However, it should be noted that the circuit 'for the stepping relays IVat the field station include front contact 304 of the relay ISO, so that if such relay drops away at any point in a control cycle of operation, vthe stepping operation is immediately stopped. A similar functioning of the system occurs during an indication cycle of operation because at such time the front Contact 3|2 of relay ISI is lincluded in the stepping circuit, and such relay ISI drops out Whenever the station fails t-o be selected for transmitting indications. When the stepping relays V at any station fail to follow the impulses on the line circuit because of the dropping of the corresponding relay SO or SI, the relay VP also ceases its operation.

The stepping operation at the eld station may be briey summarized by stating that the halfstep relay IVP is causedto assume an opposite position on alternate impulse periods; while a stepping relay IV is picked up during each succeeding off period so long as a station continues to be selected.

STATION SELEcTroN pulses fo-rming a part of the station selection code, the station selecting relay SO for each station is selectively maintained energized or is deenergized dependent upon whether the character of the impulse for such impulse period corre-

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