US2126209A - Centralized traffic controlling system for railroads - Google Patents

Description

Aug. 9,1938. N. D. PRESTON 2,126,209

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Original Filed Nov. 26, 1952 5 Sheets-Sheet 1 a m C a j .2 o- I111: E a can i 'l Eli Fla. 1.

ConTrol 5 Sheets-Sheet 2 N. D. PRESTON Original Filed Nov; 26, 1932 CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Aug. 9, 19: 8.

Aug. 9, 1938. N. o. PRESTON CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Original Filed Nov; 26, 1932 5 Sheets-Sheet 3 A 2 R L I A R R O F M E T S Y S G N I L L O R T N O C C I F A R T D E Z I L A R T N E G Aug. 9, 1938.

N. D. PRESTO N Original Filed Nov. 26, 1932 5 Sheets-Sheet 4 mON Patented Aug. 9, l 1938 PATENT OFFICE 2,126,209 CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS I Neil D. Preston, Rochester, N. Y., assignor to General Railway Signal Company,

' N. Y. Application 18 Claims.

This invention relates to centralized trafiic controlling systems for use in dispatchingqtrains on railway systems and more particularly to the communication part of such systems; and an improvement over the invention disclosed in my earlier filed applications Ser. No. 589,186 filed January 27, 1932, and Ser. No. 596,516 filed March 3, 1932, and no claim is made herein to any invention disclosed in either of said earlier filed applications.

In railroad trafiic controlling systems the trafiic iscontrolled from a central control office and also the location of trains and the, condition of the trafilc controlling devices at remote 1ocations are indicated to the attendant at the con- 'trol office. This invention is particularly useful in such a system which is called upon to carry out,

a large number ofcontrol and indication func-,

tions during a very short time. A single dispatcher can handle the traffic over a large section of track, so it is apparent that the controls and indications should be capable of transmission at such a high rate of speed that the accumulation of stored controls and indications. is avoided.

Such a traffic controlling system I is supplemented by the well known automatic block .sig nalsystem and other local means ordinarily provided to guard against unsafe train movements, improper operation of track switches or the like. The switches and signals are distributed through out the territory but those located relatively near or adjacent each other together with the apparatus provided to govern these switches and signals, are conveniently referred to as. comprising a field station. The communication system is provided to interconnect the control office with the several field stations and is so organized that complete supervision is obtainedby the operator of the various switch and signal devices at'the remote stations.

In accordance with the present invention, the

' together. at the last field station of the series in order to provide a return circuit for the S line. In accordance with the present invention, it is proposed touse the three line wires for transmitting to and from the field stations for selecting and registering field stations and for actuating con- 55; trolling devices at the field stations and indica- Rochester,

November 26, 1932, Serial No. 644,481

Renewed March 6, 1936 tiondevices at the control office. Combinations of impulses of distinctive character are applied to the S line, using the A and Btlines inmultiple for the return circuit, to select a desired field station, after which a relay or control device for 5 each switch or signal at the selected station may be actuated or conditioned, by means of these characteristic impulses-for controlling the respective devices and therebygoverning the trafiic at the selected station. Such selection and con- 1n trol is referred to as transmission of controls.

The communication system is also used totransmit to the control office indications of the positions of the switches and signals and for indicating the presence or absence of trains in particular track sections, as well as any other indications which may be useful in directing and supervising train movements. These indications are precededby the registration in the control office of the particular field station that is transmitting. This function is automatically effected when a new indication is ready to be transmitted to the control office and is conveniently referred to as transmission of indications.

The system is of the coded duplex type and is operated through cycles, during each of which transmission of controls and transmission of indications can occur separately or simultaneously to and from the same station or to and from different stations.

When controls are transmitted, a station selecting code is first applied to the line for selecting the particular station desired, after which the controls are transmitted to the selected station by means of code impulses. When indications are transmitted, the field station transmitting such indications first sends a station registering code for registering that station in the control ofiice; Thereafter, the particular indications are transmitted tothe control ofiice by means of an additional code and are displayed on indicator devices, such as lamps or the like associated with the station sending.

For the transmission of controls, a predetermined number of impulses of selected polarities is placed on the line circuit for operating the apparatus at the control office and at the field sta tions through a cycle of operations, irrespective of the character of the impulses, While the distinctive character of such impulses determines the particular station to be selected and the controls to be transmitted to the selected station.

For the transmission of indications, means are provided to condition the A and B lines during a portion ofthe energized periods of the S line for creating two code characters, either one of which may be selected for conditioning an indication receiving device in the control ofl'ice. During another portion of the energized periods of the S line, the A and B line wires are again conditioned to provide a choice of three code characters, any one of whichmay be selected for conditioning an indication receiving device in the office.

gized periods of the S line circuit. The energized periods of the S line circuit will be referred to as the on periods, while the deenergized periods of this line circuit will be referred to as the off periods.

One feature of the present invention relates to the manner in which indications are preconditioned during the off periods for obtaining a choice of two code characters and the manner in which indications are conditioned during the onperiods for obtaining an additional choice of three code characters, with the chosen indications executed during a portion of the on period and a portion of the next succeeding off period. For example, insystems of this type, one energizationof the stepping line or on period and one deenergi zation or ofi period has. usually been designated as comprising a single step, with the field station circuits so arranged that indications are transmitted by distinctively changing or varying the conditioning of the line circuit once for each step. In the present embodiment, with the S line energized at the start of an on period, the A or 13 line may be energized resulting in two distinctive conditions. With the S- line energized later during the same on period, the return circuit may be by way ofthe' A line alone, the B line alone or the A and B lines in multiple,

- thus giving three more distinctive conditions resulting in five distinctive conditions or code combinations for each step for the transmission of indications. 7

Obviously, the provision of five distinctive code characters for each step results in obtaining twenty-five distinctive codes where each complete code comprises two steps. Similarly, one

hundred and twenty-five distinctive complete codes may be obtained where each complete code comprises three steps. In other words, the number of code combinations obtained is equal to five raised to the power of the number of steps. Therefore, one purpose of the present invention is to provide a code type selector system which builds up rapidly as the number of steps in creases and to accomplish this over a minimum number of line Wires.

Other objects and advantages of the present invention will behereinafter set forth in the specification and claims and shown in the drawings, the characteristic features will be explained more in detail in the following description of one embodiment of the invention, while vari-' which illustrate in a diagrammatic manner the apparatus and circuits employed. Those parts having similar features and functions are designated in the different figures-by like letter reference characters, generally made distinctive either'by the use of distinctive exponents-repre- Therefore, a choice of five code char. acters for each step is obtained during the enercircuits employed at the control oflice;

Fig. 4 illustrates the apparatus and circuits employed at one of the fieldstations;

Fig. illustrates an operation chart which will be conveniently referred to during the following description for obtaining a concentrated picture of the sequence of operations of the system during control and indication cycles.

In tracing the detailed circuits, Fig. 4 is placed "tothe right of Fig. 2 and Fig. 3 is placed below Fig. 2.

General description The three Wire line circuit which connects the control ofiice with the field stations, extends from the right hand portion of Fig. 2 to the left hand portion of Fig. 4, the S line being in the upper part of these drawings with the A and B lines located near the center. The dotted rectangle in the upper right hand portion of Fig. 4 indicates that the S line extends through other field stations and includes other line relays such as F and that the A and B lines extend through other field stations and include back contacts of the respective impulsing relays located at these other field stations, such as PLA and PLB This is also clearly indicated in Fig. 1.

It will be understood that these additional stations have apparatus and circuit arrangements practically the same as that shown in Fig. 2. As will be more specifically pointed out in the following description, the points of difference in the circuit connections at different field stations are the distinctive connections of the code jumpers for conditioning the circuits, so that. a particular field station will be fully responsive only to the: particular code assigned to. that station.

For the purpose of simplifying the drawings and facilitating the explanation, various parts and circuits have been diagrammatically shown and certain. conventional illustrations have been employed. The drawings have been. made more with the. purpose of making it easy to understand the principles and mode of operation, than with the idea of illustrating the specific construction and arrangement of parts and circuits that would be. employed in practice. Thus, the various relays and their contacts are illustrated in a. conventional manner, the use of symbols being employed. to indicate the connections to the terminals of batteries, or other sources of current,. instead of showing all of the wire. connections to these terminals.

The symbols. and indicate the positive and negative terminals, respectively, of suitable batteries or other sources of current and the circuits with which these symbols are used always have current flowing in. the same direction. The symbols (3+) and (B) are employed to indicate the positive and negative terminals, respectively, of a suitable battery, or other source of current, having an intermediate tap (CN) and the circuits with which these symbols. are used may have current flowing in one direction or the other, depending upon whether the terminal (B:-|-) or (B)' is used in combination with the intermediate tap (CN).

No attempt has been made to. show all of the apparatus employed, such as the total'number of manual controls at the control office, the. total amount of the equipment or its exact arrangement at the field stations, since this apparatus, and equipment may vary to suit local conditions. The character of that apparatus illustrated in the typical control ofiice andthe typical field station will now be, considered. r H

. Control ofiice equipment-As typical of, .the equipment located in the control ofiice-illustrated in Fig. 2, a control machine having axgroup of control levers for each field station is provided. A miniature track switch, indicated by reference character ts, corresponds to a particular track switch in the v-field and is considered to be representative of the actual track layout in the field. Various indicating lamps, or equivalent devices, together with apparatus and circuits to accomplish the desired operation of the system are likewise provided. The portion of the control ofiice apparatus illustrated in Fig. 2 shows more particularly that part of the control machine which is typical of the apparatus associated with a single field station having a track switch, a crossover orthe like, together with the common transmitting apparatus employed for controlling the circuit operation for all such stations.

7 This equipment for one track switch comprises a switch machine lever SML, a self-restoring starting button SB, the miniature track switch is and the indication lamps RI, NI, UI, OS'and M. Similarly, one or more signal control levers (not shown) would be associated with the single field station, but in order to simplify the drawings and description, these devices have been omitted. It is obvious that the selection of the field station illustrated in Fig. l, by means of starting button SE of Fig. 2 and thereafter the control of a track switch TS by means of .a lever SML may be considered as typical of the selection ofother field stations and the control of other traffic controlling devices. 7 i g l Theactuation of the lever SML to one extreme position or the other, followed by the actuation of the starting button SB, results in the normal or reverse operation of the track switch corresponding to lever SML at that field station which is associated with starting button SB. The momentary actuation of the starting button SB is preferably stored by a storing relay (not shown), which in turn picksup the corresponding code determiningrelay CD of the associated station. The starting button SB is shown connected to the code determining relay CD by means of a dotted line in order to simplify the present disclosure.

The storing relays for each starting button and their corresponding code determining relays CD are so interconnected that only one relay CD for one particular station may be picked up during one cycle of operations, irrespective of the number of storing relays which are simultaneously energized or energized in rapid succession. This interlocking circuit connection is so, arranged that if several storing relays are up at the same time, their corresponding CD relays will be picked up one at a time during successive operating cycles, in an order predetermined by their relative locations in the bank of relays, all of'which has been completely disclosed in the prior ap plication of N. D'..Preston et al., Ser. No. 455,304, filed May 24, 1 930, corresponding to Australian Patent No. 1501 of 193 1.

The control ofiizce includes a line relay F, and a i ii f di Iglay wil O Whichaw. nor:

mally down or deenergized during the normal period of rest of the system and also during the period of blank between, successive operating cycles.

Slow acting line repeating relays SA and SAP are picked up at the beginning of each cycle and dropped during the change to normal period at the end of each cycle. The releasing or dropaway time of relay SA is sufiiciently long so that its contacts remain in their actuated positions during all.off periods between successive impulses of a cycle, except the last off period which is comparatively long for the purpose of returning the system to the normal period of rest or period of blank.

Associated with the line relay F and its repeating relays is a bank of stepping relays, including stepping relays IV, 2V and 3V together with a half step or steering relay VP, which are provided to mark ofi the successive steps of each cycle. Steering relay VP serves the purpose of steering the impulses from relay FP to the proper stepping relay and for steering the executing circuits to the proper selecting contacts of the stepping relays, all at'the proper time. An impulsing relay E is jointlycontrolled by the stepping relays and the steering relay. The pick-up and drop-away operations of relay E are repeated by relay EP which governs the opening and closing of the S line conductor.

Relay in addition to controlling the line pulsing relay EP, jointly controls, with relay FP, the stick circuit of relay MX. Relay E'- also controls the stick circuit of relays MAP and MBP, all of which will be specifically pointed out in the detailed description. Relay E also controls the circuits over which the indications are executed.

Relay MA is controlled over the A line conductor, relay MB is controlled over the 3 line conductor and their repeating relays MAP and MCBP provide a choice of five indication code combinations during the on period of each step. Relay MX is jointly controlled by relays MAP and MBP to record the choice of two indication code combinations during the firstpart of the on period with the station code and the controls to be transmitted for that particular cycle.

A starting relay STR. is picked up to initiate a cycle of operations both when controls are to be transmitted, due to the manual initiation of the cycle in the control office, and when indications are to be transmitted, due to the automatic initiation of a cycle by a field station. Field start relay FC is picked up when the cycle of opera tions is initiated by a field station and office start relay 0 is picked up when a cycle of operations is initiated by the control oifice.

For the purpose of illustrating station registration, a typical pilot relay arrangement is shown in Fig. 3. Pilot relays lPT, ZPT and 3PT are connected to the indication buses so that they may be positioned on the first step of the cycle when indications are transmitted. Relay IPT is connected to No. 1 off bus so that this relay ispositioned to the right or left as predetermined during the first ofi period. Relay 2PT is connectedtocNohlAton bus and it. is positioned to the right or left as predetermined by the condition of the A line conductor during the first on period. Relay 3PT is connected to No. IE on bus and is positioned to the right or left as predetermined by the condition of the B line conductor during the first on period. Similarly, additional pilot relays (not shown) may be provided for additional steps up to the point where a sufficient number of codes for station registration are obtained.

A station relay ST is provided 'for registering,

in the control ofiice, the station transmitting indications. Relay ST is merely typical of a number of such relays which would ordinarily be provided to register individual stations, other relays similar to relay ST being connected to the conductors leading to bracket STN. The conductor indicated phantom, leading to bracket STN, is not used in this embodiment for connection to a station relay similar to ST. This is because when controls alone are being transmitted, the system inherently transmits back to the control ofiice a code combination which is not sent by a field station.

A choice of five code characters for each step results in selectively positioning the three pilot relays as illustrated in Fig. 3 and although six combinations are obtained, as indicated by the six conductors connected to contacts of relay 3PT, only five of these combinations are used since the sixth is associated with the phantom code.

The control machine also includes suitable indication storing relays 1R 1R IR and IR for storing the various indications transmitted from the field stations, after a field station has been registered in the control oflice by the selection of a relay similar to ST. The indication storing relay IE is controlled in accordance with the occupied or unoccupied condition of the detector track section, associated with the outlying track switch illustrated in Fig. 4, as repeated by a track relay T so that an indicating lamp OS is controlled by the passage of a train.

Indication storing relays IR and IR store the indications of whether the associated track switch is locked normal, locked reverse, or unlocked in mid-stroke as repeated by the switch repeating relay WP at the station, so that indicator lamps NI, RI, and UI'are displayed to indicate the normal locked, reverse locked, and the unlocked positions respectively of the track switch. Indication storing relay 1R stores any other required condition of a device at the field station such as relay M and controls indicating lamp M of Fig. 2 todisplay the condition of the device which causes relay M to be up or down.

The fundamentalcoding arrangement for indications disclosed in the present invention is. ofparticular advantage, since the preselection of two indications during each on period may be used to indicate the two conditions of a track circuit, that is, occupied or unoccupied. Similarly, there are three conditions of a switch to be indicated, namely, locked normal, locked reverse, or unlocked in mid stroke so that the selection of three additional indications during each on period may be advantageously used for registering these switch conditions. a

Field station equipment.-The field station illustrated in Fig. 4 includes, besides the apparatus above mentioned, a quick acting line relay F and a quick acting line repeating relay FP which repeat the .energizations and deener gizationsof the S line circuit. Relay FP repeats the impulses in' the S line circuit irrespective of their polarities, while relay F is conditioned to the right by a positive impulse and to the left by a negative impulse.

A slow acting relay SA of the neutral type repeats the energized condition of the FP relay. Relay SA defines the bounds of each cycle of operations, being energized at the beginning of each'cycl'e and remaining energized or actuated until the change to normal period at the end of the cycle.

The field station likewise includes a bank of stepping relays IV 2V and 3V together with the associated steering or half step relay VP operating in a similar manner and in synchronism with the stepping relay bank in the control ofiice. Steering relay VP steers the impulses from relay FP to'the proper stepping relay and it also steers the line impulsing relays PLA and PLB to the proper indication buses, all at the proper time.

Line impulsing relays FLA and lPLB are provided to open the A and B lines respectively, to provide code combinations during the transmission of indications, these two relays being conditioned in accordance with the condition of the indication buses shown in the lower right hand portion of Fig. 4. Relay VPC controls the steering relay VP in such a way that relay VP can not shift until the line impulsing relays PLA and PLB are in their normal or deenergized positions.

A change repeating relay CHP is provided to register a change in the traffi'c controlling devices at the station, so that the system will be initiated for the transmission of new indications as required. A lock-out relay L0 is provided at each field station to determine when a particular field station is to transmit new indications. Relay L0 is picked up during the initiating period of a cycle when indications are transmitted and is stuck up until the change to normal period at the end of the cycle. The lock-out relaysupplies potential to the A and B line pulsing relays PLA and PLB so that these relays receive current only at the station transmitting indications.

A station selecting relay S0 is picked up at all stations during the conditioning period of a cycle, when controls are being transmitted. These relays are dropped out at various stations during the code transmitting periods, so that only the one associated with the desired station remains actuated after the transmission of the station selecting code. Relays S0 and L0 control the circuits to the stepping relays so that stepping is not efiective at those stations not in connection with the communication circuit.

Resistance units R and R illustrated within the dotted rectangle in the upper right hand portion of Fig; 2, are of such value that a sufiicient drop in potential isprovided for picking up a lock-out relay similar to L0 during the initiating period of an indication cycle.

A track switch T3 is operated by a switch machine SM of any suitable type, such for example, as disclosed in the patent to W. K. Howe, 1,466,903, dated September 4, 1923. This switch machin'em'ay, if desired, be provided with a dual control selector as disclosed for example, in the pending application of W. K. Howe, Ser. No. 354,- 039, filed April 10, 1929, the purpose of such a selector beingto permit the local manual operation-orthe track switch. The position, locked and unlocked conditions of the track switch is repeated by the usual switch repeating relay WP of the polar neutral type. This relay is controlled by a suitable circuit (not shown) so that it is energized with one polarity or the other, depending upon the normal or reverse positions of the track switch. In this disclosure, it will be assumed that the polar contact of relay WP is positioned to the right when the track switch is in its normal locked position, to the left when the track switch is in its reverse locked position and its neutral contact is dropped when the track switch is in mid-stroke.

The track switch has associated with it the usual detector track section having a track battery and a track relay T also suitable approach locking and detector locking means are provided (not shown) togovern the safe operation of the track switch in accordance with traffic conditions. It is understood that a change in the position of the track switch TS is repeated by the relay WP and a change in the condition of the detector track section is repeated by relay T The field station also includes suitable bus wires, circuit connections, code jumpers and other devices which are necessary in operating the system, but which have not been completely illustrated in this disclosure for the sake of simeach cycle of operations.

plicity.

It is believed that the nature of the invention, its advantages and characteristic features, may be best understood with further description being set forth in the manner of operation.

General operation The system of the present invention is shown in Figs. 2, 3 and 4 in the normal or condition of rest, from which it may be initiated into a cycle of operations, either by a manual operation, at the control office or an automatic operation at any of the field stations, whenever there are new controls or new indications, respectively, to be transmitted. In the event that there are several different controls ready for transmission to field stations at substantially the same time, they are transmitted on separate cycles, one station for Likewise, if several field stations have indications to be transmitted at substantially the same time, they are transmitted to the control ofiice, one station at a time, on separate operating cycles.

It may happen that there are new controls and new indications ready for transmission at a given time, and in this event controls are transmitted simultaneously with the indications. On, such occasions, indications may be transmitted from the same field station to which controls are transmitted, or they may be transmitted from some other field station, during the same cycle of operations.

Irrespective of whether the cycle is for the transmission of controls and/or the transmission of indications, a predetermined number of impulses is applied to the line circuit to accomplish the synchronous operation of the stepping relays at the control office and at the field stations. These impulses are of comparatively short duration, the deenergized or off periods of the stepping line circuit being comparatively shorter than the energized or on periods.

When'a cycle of operations is initiated for the transmission of controls, the character of the impulses applied to the stepping line is determined by the particular station to be selected i and the particular contr l t be transmitted t the selected station, in accordance with the code jumper connectionsand the positions of the control levers, respectively, for that station.

When a cycle of operations is initiated for the transmission of indications alone, the character of the impulses applied to the stepping line is the same for all impulses and this particular combination does not effect the selection of any field station, since the initiating impulse applied tothe stepping line is of such a character, for example that none of the station relays similar to S0 of Fig. 4 are picked up. When such a cycle of operations is initiated from a field station, the line circuit is energized with a series of impulses. Since such a cycle starts out with no station relay (similar to S0 up, the impulses which follow are not efiective to select a station or a control device at a station.

The A and B line conductors are normally energized, the stepping line conductor S is normally deenergized, and when controls or indications are initiated, start relay S'I'R in the control office is picked up, resulting in switching the battery connection so that temporarily the S line is energized, the return circuit being by way of both the A and B lines for transmission of controls and by way of the B line alone for transmission of indications. This period during which the battery is switched from the A and B line conductors to include the S line is conveniently referred to as the conditioning period at the start of a control cycle and the initiating period at the start of an indication cycle. Immediately following the conditioning or initiating period is the look-out period, which is efiective to so condition the circuits that only one station may transmit indications to the control office at the. same time.

After the conditioning and lock-out periods, the system continues through a complete cycle of operations consisting of a number of o and on periods, this number being determined by the number of steps required and the number of steps in turn being governed by the size of the system. After the last on period, a comparatively long off or deenergized period is effective to condition the relays for changing to normal or the period of blank. After this change to normal period, the A and B line conductors are again energized by current from battery B, which restores the system to the normal period.

For convenience in describing the operation of the present invention, an operation chart is shown in Fig. 5. In the upper portion of this chart the important functions of the system during a control cycle are illustrated, while the lower portion illustrates the important functions of an indication cycle. Referring to the chart illustrating a control cycle, the normal period is shown at the extreme left and during this period line S is deenergized or open, as indicated by reference character 0. Line A is energized with potential and line B with potential as illustrated. It is during this period that the system is manually started by an operation in the control office. This normal period is an off period since line S is deenergized.

During the next or conditioning on period, line S is energized with potential, the return circuit being by way of lines A and B as indicated by the reference characters. It is during this on period that all relays similar to S0 are picked up.

From the beginning of the conditioning period, up to and including the end of the cycle is conveniently referred t oas'the operatin'glcycl'e'; The beginning of the first off period and the' end of the third "on period is bounded by what may be conveniently referred to as the'transmitting period. 'f

The transmitting period 'is'divided into off and on periods and since the present disclosure shows only three steps, the first, second and third off and on-"periods are indicated in this'chart. It will be understood that additional steps, when provided, are inserted between'the third on period and the change to normal period.'- o a c The indication cycle chart shown in the lower portion of Fig. 5 comprises a normal period followed by an operating cycle divided into initiating, lock-out, conditioning, transmitting and change to normal periods. The transmitting period is divided into off and on periods, with these off and on periods subdivided as indi cated. For want of space, the third ofi" and on periods of the indication cycle have not been included but it will be understood that they are similar to preceding periods.

'An'analysis of a duplex cycle has not been provided since such a cycle is merely a combination of control and indication cycles. During duplex transmission, impulses of distinctive character are placed on line S for operating the apparatus at the control office and at the field stations, the character of these impulses determining the selection of the station and thereafter the control device at the station, The A and. B lines are conditioned foi the return circuit in accordance with the indication code combinations to be transmitted from 'the field station to the control oflice in the same manner as when indications alone are transmitted.

- Detailed operation Normalper'iod.-With the communication part of the centralized traflic controlling system, with which this inventionis'concerned at normal, most of' the "relays in the control ofiice and at the field stations are in their normal or 'deener'gized positions. The exceptions are relays MA, MB, MAP and MBP in the control oflice and relay VPC at the field station. Relays MA and MB are energized by current flowing from battery B over the A and. B lines in series and, as" indicated in the operation chart under normal period, potential is applied to the A line and potential to the B line. 'Referring to Fig. 2, this circuit may be traced from the terminal of battery B, back contact ID of relay STR, winding of relay MA, A line II, back contact I50 of relay PLA of Fig. 4, over the A line conductor I5I extending through all of the field stations in series, including back contacts of other A line impulsing relays such as PLA resistance coils R and R in series, located at the last station, back contacts of the B line impulsing relays such as PLB B line conductor I52, back contact I53 of relay PLB B line I2, winding of relay MB and back contact I3of relay STR to the side of battery B. The circuit for energizing relay MAP extends from front contact I28 of relay MA and lower winding of relay MAP,'to The energizing circuit 'for relay MBP extends from front contact I29 of relay MB and lower windingyof relay MBP, to

The circuit for energizing relay VPC extends through back contacts I90 and I95 of relays PLA and PLB respectively.

At the field station, the change repeating relay CHP is" "normally picked 'up over circuits (not shown), track relay T is normally picked up by a"circuit (not shown) energized by the track battery and'relay WP is normally energized, with its polar contacts to the right, by means of a circuit (not shown) which is controlled by the switch machine. Although these circuits for controlling relays CHP T and WP have not been included in the drawing of Fig 4, it will be readily under stood by 'those skilled in the art how they are conditioned by'the' difierent devices at the field station.

Manual starting.With the system in its normal condition, it will be assumed that the operator in the control office desires to transmit controls to a particular field station, such as the one illustrated in Fig. 4. When the starting button SB is actuated, a suitable storing relay is positioned and the CD relay associated with the desired station is picked up. The actuation of the CD relay closes a circuit for picking up relay C, extending from back contact I4 of relay SA, back contact I5 of relay NC, front contact I8 of relay CD and winding of relay C, to Relay C closes a stick circuit for itself extending fror'n' back contact 6 of relay SAP, front contact 68 and winding of relay C, to

The operation of relay C opens the pick-up circuit of relay FC at back contact H, which prevents the picking up of relay FC after the cycle is initiated by a manual start in the control office. This gives the control ofiice' priority, since relay C can be picked up with relay SA down, while relay FC can not be picked up until relay SAP is down. Thus, a time interval is introduced between the dropping of relay SA and the dropping of relay'SAP, when the system advances through the change to normal period during which the control oihce may take control of the system.

If a field station attempts to start the cycle by picking up relay FC at the same time the control oflice starts the cycle, the actuation of relay C prevents the picking up of relay FC so that the control oflice gets first choice of the system. If the field station start occurs slightly in advance of the control office start, relay FC is picked up, which energizes relay NC so that relay C can not thereafter be picked up during this same cycle, because the pick-up circuit of relay C is opened at back contact I5.

The actuation of relay C closes a circuit for picking up relay STR, extending from front contact I8 of relay C and winding of relay S'I'R, to Relay C also closes a circuit for picking up relay PC, extending from back contacts I9, 20 and 2I in series of relays 3V, 2V and IV, front contact 22 of relay C, bus 23, back contact 24 of relay FC' and winding of relay PC, to

This is the conditioning period. The energization of'relay PC causes the S line to be energized with potential, while the A and B lines are energized as indicated in the conditioning period of the operation chart. The circuit for energizing the line conductors extends from the terminal of battery B, front contact I of relay STR, front contact 25 of relay PC, back contact 26 of relay NC, winding of relay F, back contact 21 of relay EP, Sline conductor 28, winding of relay F of Fig; 2, windings of other line relays similar to F at other field stations, resistance coils R and R, at the last field station, back contacts of'relays such as PLA and PLB at other field stations, A and B line conductors II and I52, backcontacts I50 and. I53 of relays PLA and PLB respectively, A and B lines II and I2, windings of relays MA and MB and thence from the Winding of relay MB through back contact I of relay NC and front contact 8 of relay PC to the terminal of battery B. The A line conductor circuit extends from the winding of relay MA through front contact I3 of relay STR, back contact I of relay NC and front contact 8 of relay PC to the terminal of battery B.

The stepping line conductor S being energized causes relay F in the control office and relay F at the field stations to be positioned to the right. Relay F closes a circuit for actuating relay FP extending from contact 29 of relay F in its right hand dotted position and winding of relay F'P, to Relay F closes a circuit for picking up relay FP extending from contact I54 of relay F in its right hand dotted position and winding of relay FP to The actuation of relay FP in the control office closes a circuit for picking up relay SA, extending from front contact 30 of relay FP and winding of relay SA, to The operation of relay SA closes a circuit for picking up relay SAP, extending from front contact 3| of relay SA and Winding of relay SAP, to

Referring to the field station, the actuation of relay FP opens its back contact I55 which disables the pick-up circuit of relay PLA extending through back contact I56 of relay SA and back contact I5'I of relay CHP to the lower Winding of relay PLA which pick-up circuit is effective to start a cycle of operations from a field station. It Will thus be seen that as. soon as relay FF is picked up and its contact I55 opened, no field station can obtain access to the line for transmission of indications.

The picking up of relay FP also closes a circuit for picking up relay S0 extending from back contact I58 of relay SA front contact I59 of relay FP contact I66 of relay F in its right hand dotted position, back contacts I6I, I62 and I63 in series of relays 3V 2V and IV control bus I64 and lower winding of relay S0 to At this time, relays similar to S0 at all other stations are picked up by means of similar circuits, but as will be specifically pointed out during the detailed description, these relays are dropped out at the other stations, while the one illustrated inFig. 2 is maintained energized.

The actuation of relay FP also closes a circuit for.picking up relay SA extending from front contact I55 of relay FP and winding of relay SA to The operation of relay SA interrupts the above described pick-up circuitof relay S0 but it is not released since a substitute circuit is closed for holding relay S0 which extends from make-before-break front contact I58 of relay SA front contact I 65 of relay S0 contact I60 of relay F in its deenergized position and the remainder of the circuit above described, to the lower winding of relay S0 Referring back to the control office, the actuation of relay SAP closes a circuit for picking up relay EP which extends from front contact 32 of relay SAP, back contact 33 of relay E and lower winding of relay EP, to It will be mentioned here that the purpose of front contact 9 of relay EP is to short circuit the upper winding of this relay when it is actuated which has the effectof rendering this relay quick to pick up and slow to release for obtaining the desired timing of the stepping operation. The actuation of relay EP opensthe stepping line circuit, at back contact 21, which advances the cycle into the first off period.

Polarity selection of impulses-As above pointed out, the first impulse in line S is when a cycle of operations is started from the control ofiice. This is indicated in the chart under the conditioning period and is due to the fact that control relay PC is picked up at the start of a control cycle.

When line S is deenergized, by relay EP opening its contact 21 to advance the system into the first off period, relay F is released and by opening its contact 29, causes the release of relay FP. As will be specifically pointed out later on in the description, stepping relay IV is picked up during the first off period. This is effective to condition the No, 1 control, by selecting the polarity to be appliedto line S during the first on period. This conditioning circuit holds relay PC in its actuated position and extends from back I contacts 35 and 36 of relays 3V and 2V,front contact 31 of relay IV, No. 1 code bus M, front contact 38 of relay CD, code jumper connection 39, bus 23, back contact 24 of relay FC and winding of relay PC, to This connection of code jumper 39 to the bus selectively conditions the first control impulse If code jumper 39 were connected to the bus 47, then relay NC would be picked up instead of relay PC, thus providing a impulse-for the No. 1 controls The control of the PC and NC relays is effected during other off periods by means of other code jumpers such as jumper 40. Thus, in the second off period, relays 2V and VP will be up and the selection of the or bus, by means of jumper it, is extended by way of front contact 4| of relay CD, No. 2 code bus 45, front contact 36 of relay 2V and back contact 35 of relay 3V to so that relay PC will be again picked up if code jumper 46' connects to the bus. However, in the present embodiment it is assumed that the No. 2 code jumper 46 connects to the bus, so that relay NC is picked up terminal of battery B through back contact ll of relay PC and front contact 26 of relay'NC to the S line. The terminal of battery B is con nected to the A and B line conductors over circuits extending through front contact I!) of relay STR, back contact 25 of relay PC, front contact I of relay NC to the B line and through front contact I 3 of relay STR to the A line.

During the third off period, it will be assumed that relay 3V is up as indicated in the operation chart. The No. 3 control is conditioned during this period by dropping relay NC and picking up relay PC, since the polarity of the third on period is assumed to be in the S line. Relay NC is dropped when the No. 2 code bus 45 is opened at back contact 35 of relay 3V and relay PC is picked up when the No. 3 code bus 46 is closed from front contact 35 of relay 3V, No. 3 code bus 46, front contact 42 of relay CD, contact 43 of switch machine lever SML, assumed to be in its right hand position, bus 23, back contact 24 of relay FC and winding of relay PC,-to The actuation of relay PC selects a potential to be applied to line S during the third on period.

It willbe apparent that a impulse would be conditioned during the third off period and applied to the S line during the third on period if lever SML should be in its left hand dotted position, because this would extend the above traced circuit to relay NC instead of relay PC. From the above it will be observed that different code combinations may be chosen for selecting different stations, by arranging the jumper conncctions 39 and 40 in different positions, but with these jumpers arranged as shown in Fig. 2, the two impulses applied to the line for selecting the station are for the first impulse and for the second impulse. It will also be obvious that while only two steps are indicated for making station selection, additional steps and associated code jumpers may be provided in systems requiring a larger number of code combinations. It will also be understood that more than one step may be provided for selecting additional control devices, similar to lever SML, but it is believed that the typical arrangement disclosed is sufiicient to illustrate the complete functioning of the system.

From the above it will be seen that the impulses applied to the line circuit during a control cycle always begin with a and a combination of and impulses follow. These following impulses are dependent upon the code jumper connections and the control lever positions, made effective by the particular code determining relay CD which is picked up during the control cycle. Also, the character or polarity of the impulses in the stepping line circuit is selected by polarity determining relays, PC for a impulse and NC for a impulse and these polarity determining relays are positioned during the off periods, in readiness for the application of the preselected polarity during the following on periods.

Line pulsing and operation of stepping relays. It has been mentioned that the impulses which follow the conditioning period Vary in polarity and with the code jumpers and switch machine lever conditioned as shown in Fig. 2, the impulses in the S line energize this line during the three on periods with and polarities. Irrespective of the particular polarities with which line S is energized, relay F? in the control office and relay FP at the field station repeat the operations of relays F and F Relay IV in the control oflice is picked up during the first off period by means of a circuit extending from front contact I4 of relay SA, back contact 48 of relay FP, back contact 49 of relay VP, back contact 50 of relay 2V and winding of relay IV, to The operation of relay IV closes a stick circuit for itself extending from front contact I4 of relay SA, stick conductor 64 and front contact 5I of relay IV to the winding of relay IV. When relay IV is picked up, a circuit is completed for picking up relay E, extending from back contact I9 of relay 3V, back contact 20 of relay 2V, front contact 2I of relay IV, back contact 34 of relay VP and Winding of relay E, to Relay E opens its back contact 33 which allows relay EP to drop and.

" again energize line S.

This is the first on period. Relays F and FF are now picked up in turn and relay FP closes a circuit for actuating relay VP extending from front contact 32 of relay SAP, front contact 52 of relay FP, front contact 53 of relay MBP, front contact 54 of relay MAP, back contact 55 of relay 3V, back contact 55 of relay 2V, front contact 51 of relay IV and. winding of relay VP, to Relay VP establishes a stick circuit for itself extending from front contact 32 of relay SAP, front contact 58 of relay VP and over the remainder of the above described actuating circuit, to the winding of relay VP. This stick circuit for relay VP is effective until stepping relay 2V is picked up and opens contact 56, which occurs during the second off period. For maintaining relay VP in its actuated condition during the second off period, an additional stick circuit is established extending from front contact 32 of relay SAP, back contact 59 of relay MBP or back contact 60 of relay MAP or back contact 52 of relay FF and front contact SI of relay VP, to the winding of relay VP.

Relay VP, in picking up, opens the circuit of relay E at back contact 34, so that relay E drops after a short time interval and closes the circuit for picking up relay EP, which has been described. This advances the system from the first on period into the second off period, since the actuationof relay EP opens its contact 21 and deenergizes the S line as well as the A and B lines.

This is the second off period. Relays F and FP are dropped and a circuit is established for picking up relay 2V extending from front contact I4 of relay SA, back contact 48 of relay FP, front contact 49 of relay VP, back contact 62 of relay 3V, front contact 63 of relay IV and winding of relay 2V, to Relay 2V closes its own stick circuit to stick conductor 64 by way of its front contact 65. A circuit is now closed for picking up relay E, extending from back contact I9 of relay 3V, front contact 20 of relay 2V, front contact 34 of relay VP and Winding of relay E, to Relay E opens its back contact 33 which allows relay EP to drop and energize the S line at its back contact 21. This advances the system out of the second off period.

This is the second on period. Relays F and FF are again energized and relay VP is dropped during this period, since its pick-up circuit is open at back contact 56 of relay 2V and its stick circuit is open at back contacts 52 of relay FP, 59 of relay IVIBP and 60 of relay MAP. The circuit of relay E is now interrupted at front contact 34 of relay VP, allowing relay E to drop and establish the pick-up circuit for relay EP which has been previously described. Relay EP picks up and deenergizes the S line and the A and B lines, which advances the system out of the second on period.

This is the third off period. Relays F and PP are again dropped and a circuit established for picking up relay 3V, which extends from front contact I4 of relay SA, back contact 48 of relay FP, back contact 49 of relay VP, front contact 50 of relay 2V and winding of relay 3V, to Relay 3V closes a stick circuit for itself to stick conductor 64 by way of its front contact 66. A circuit is now established for picking up relay E, extending from front contact I9 of relay 3V, back contact 34 of relay VP and winding of relay E, to Relay E opens its back contact 33 which allows relay EP to drop and close the energizing circuit for the line conductors to advance the system out of the third off period.

This is the third on period. Relays F and FP are again picked up and a circuit is established for picking up relay VP which extends from front contact 32 of relay SAP, front contact 52 of relay FP, front contact 53 of relay MBP, front contact 54 of relay MAP, front contact 55 of relay 3V and winding of relay VP, to Relay VP again closes a stick circuit for itself which is effective untilthe system advances through the change to normal period and which extends from front contact 32 of relay SAP, front contact 58 of relay VP and front contact 55 of relay 3V, to the winding of relay VP. The circuit of relay E is now open at back contact 3 5 of relay VP, which allows relay E to drop after a short time interval and establish the pick-up circuit for relay EP. Relay EP is actuated and opens the S line circuit at its contact 2i, which deenergizes the line conductors and advances the system out of the third on period.

This is the change to normal period. Relays F and PP are dropped and since there are no more stepping relays to be picked up during this off period, relay E can not be picked up and relay EP can not be dropped, in the manner described for the previous off periods. This results'in relays F and PP remaining down for a sufiicient time to allow relay SA to drop, which opens its front contact i i and allows all the stepping relays to be restored to normal. Relay SA opens its front contact 3i which deenergizes relay SAP which releases and by opening its front contact 32, causes the release of relay VP. Relay SAP, in opening its front contact 32, also opens the circuit of relay EP allowing this relay to drop.

Relay SA, in releasing, opens its front contact (all which deenergizes the stick circuit of relay C allowing this relay to be released and by opening its front contact it the circuit of relay STR is interrupted and relay STR restores to normal. The S line conductor is deenergized shortly after the dropping of relay SA and before the release of relay SAP causes relay EP to release and close its contact 2?. The A and B line conductors are again energized with potential on the A line and potential on the B line, as indicated in the second part of the change to normal period. Relays MA, MB and their repeating relays MAP and MBP are now picked up and the system is advanced into its normal period with the A line conductor still energized. (-1-) and the B line conductor energized It is to be understood that these circuit connections may be extended for as many steps as desired, with the pick-up and stick circuits of the stepping relays and the steering relay extended inan obvious manner. It has already been mentioned that the stepping relays and the steering relays at the field stations operate in a substantially identical manner and for this reason it is not believed necessary to describe the operating and pick-up circuits of these relays in detail. Relays iV 2V and 3V of Fig. 4 are picked up in synchronism with relays lV, 2V and 3V of Fig. 2. The pick-up circuits of the stepping relays shown in Fig. 4 extend from front contact itt of relay SA back contact lfil of relay FP (which operates in synchronism with relay FP in the control office) and front contact W8 of relay S during the transmission of control impulses. The extension of this circuit to the stepping relay windings is through back and front contacts liiil of relay VP which circuits are simi" lar to those of Fig. 2.

As will be later explained, some of the relays similar to S0 at other stations are dropped out, which is effective to open. their contacts similar to ltil and at these stations the stepping circuits are interrupted, so that stepping does not continue throughout the cycle at such stations. During the transmission of indications when no relay similar to S0 is picked up, front contact iii] of relay L0 is effective to complete the pick-up circuits of the stepping relays.

From the above description and by referring to the operation chart, it will be observed that the stepping relays are picked up in rotation during successive off periods and the steering relays are shifted during the on periods. The steering or half step relays VP and VP pick up during the odd on periods and release during the even on periods.

Contacts 59 and All of relays MBP and MAP of Pig. 2, connected in multiple with back contact 52 of relay PP, are for the purpose of preventing the release of relay VP during the even on periods, until relays MBP and MAP are picked up. The purpose of contacts 53 and d of relays MBP and MAP, in series with front contact 52 of relay PP, is to insure that relays MBP and MAP are picked up at the beginning of the odd ,on periods before relay VP can be picked up. These four contacts on relays MBP and MAP therefore serve the purpose of holding back the shifting of relay VP until the relays, which are to be conditioned over the line conductors, are properly positioned.

During the change to normal period, the stepping relays and the steering relay of Fig. 4 are released in a manner similar to those in the control office, when relay SA drops and opens its front contacts M56 and ill.

The purpose of relay VPS is to prevent the shifting of relay VP until the relays in the line even on"- period until-relay VPC picks up and opens its back contact H3. Relay VPC can not pick up until both the A and B line impulsing relays PLA and PLB- are down. Therefore, relay VP can not drop until both the A and B line conductors are conditioned by relaysPLA and PLB during the even on periods. Similarly, relay VP can not be picked up during the odd on periods until relay VPC picks up and closes its front contact H4 and relay VPC as above mentioned, can not pick up until both relays PLA and PLB are down. This insures that the relays at the field station in the A and B line conductors will be in their proper positions, as well as the relay in the S line conductor, before relay VP can be shifted.

Transmission of controls-It will now be assumed that the stepping relays in the control office and at the field station illustrated in Fig. 4, together with the respective steering relays, operate as above described and an explanation will be given of the circuits which are effective during this operation to transmit controls.

As above explained, line S is conditioned with a impulse for picking up relays. similar to S0 at all field stations and during this conditioning period, relays SA and SAP in the'control office and relays similar to SA at the field stations are actuated.

It is assumed that the impulse applied to line S during the first on period is determined all others are to be dropped out. At those stations having a jumper similar to I15, relays similar to S0 will be maintained energized during the first on period by means of a circuit similar to that extending from front contact I58 of relay SA front contact I65 of relay S0 contact I60 of relay F in its right hand dotted position, back contact I6I of relay 3V back contact I62 of relay 2V front contact I63 of relay IV code jumper I15, bus I64 and lower winding of relay S0 to At those stations not 'having a code jumper similar to I15 connected to bus I64, the relays similar to S0 are dropped.

When the system advances into the second off period, those relays similar to S0 which are up will be stuck up over a circuit similar to that extending from front contact I58 of relay SA front contact I65 of relay S0 contact I60 of relay F in its deenergized position, front contact I11 of relay SO and upper winding of relay S0 to It is of course obvious that the stick circuits of those relays similarto S0 which are dropped during the first on period, are not completed during the second off period, since their contacts similar to I11 are open.

The system now advances into the second on period by means of a impulse applied to line S, which was conditioned during the second off period in a manner which has already been explained. Relay 2V is up and relay VP is down during this period and a circuit is completed for holding relay S0 in its operated position, which extends from front contact I58 of relay SA front contact I65 of relay S0 contact I60 of relay F in its left hand dotted position, back contact I19 of relay 3V front contact I of relay 2V code jumper I8I, bus I64 and lower winding of relay S0 to It will be understood that, in the embodiment disclosed herewith, only the relay SO illustrated in Fig. 4 will be maintained energized during this period, since it is assumed that only two stepping relays are used for station selection. With two steps for station selection, four stations may be selectively chosen by dropping out one half of the stations on the first step, which leaves two relays similar to S0 picked up. On the second step, one half of the remaining relays similar to S0 will be dropped, leaving only one (which is assumed to be that one illustrated in Fig. 4) in its actuated position.

During the third off period, relay 3V is picked up and relay S0 is stuck up over the above described circuit, including its front contact I11 and make-before-break contact I60 of relay F in its deenergized position. As soon as relay 3V is picked up, potential isconnected through its front contact I82 to the stick circuit of relay S0 so that this relay is maintained energized during the remainder of the stepping impulses. With relay S0 stuck up after station selection, additional impulses are effective to operate only those stepping relays at the station illustrated in Fig. l, since the-circuit for these relays is by way of front contact I68 of relay S0 at the one station illustrated.

During the third on period, which occurs after station selection, the No. 3 control is executed by actuating relay F of Fig. 4 to the right. A circuit is now closed for actuating switch machine relay SMR to the right, which extends from front contact I5 8 of relay SA front contact I65 of relay S0 contact I60 of relay F in its right hand dotted position, front contact I6I of relay 3V and upper winding of relay SMR to With relay SMR positioned to the right,

a circuit is closed from contact I84 of relay SMR in its right hand position and normal operating winding of switch machine SM to (ON) This results in operating the switch machine in such a direction that switch TS is advanced to its normal locked position.

It will be noted that in the event of a impulse during the third on period, relay F would be positioned to the left and the above described circuit for operating relay SMR would be extended by way of contact I60 of relay F in its left hand dotted position, front contact I19 of relay 3V and lower winding of relay SMR to This would result in positioning relay SMR to the left and by closing its contact H36 in its left hand dotted position, would energize the switch machine in the opposite manner for moving the track switch TS to the reverse locked position.

In brief, the positioning of control lever SML determines the polarity applied to the switch machine control relay SMR which in turn governs the operation of the switch machine. Obviously, if the control lever is moved to a position out of correspondence with the track switch TS this track switch will be operated, but if the control lever is in a position which corresponds with the position of the track switch, the track switch will remain in its former position.

Although no signal relays or other control devices, other than relay SMR have been shown, it will be understood that the step-by-step operation of the stepping relays may occur in sequence and in synchronism for as many steps as required to transmit controls to such other signal relays or other devices as desired.

This transmission'of controls continues until the predetermined number of steps have been taken, which by way of example, has been specifically illustrated as including three steps, two of which have been employed for station selection, followed by one which is employed for transmission of controls after station selection.

End of control cycZe.It has been explained that relays F, FP, SA, SAP and all stepping relays in the control ofiice are released during the change to normal period which follows the third on period. It will be recalled that the change to normal period is long compared with other 01f periods, resulting in relays F and FP in the control ofiice and relays F and FP at the fieldstation being down for a time interval sufiicient to allow relays SA and SAP in the control oflice and relay SA at the field station to be released. The stepping relays and the associated steering or half step relay at the field station release when relay SA drops and opens its contacts I66 and I 1 I. The stick circuit of relay S0 including its front contact I11, is interrupted when relay 3V drops and opens its front contact I82 and since relays FP and SA are down at this time, there is no circuit for holding relay S0 and it is dropped.

Simultaneously with the dropping away of the stepping relays in the control oflice, the particular code determining relay CD which was picked up during the cycle, is deenergized so that the next code determining relay in order may be effective at the begining of the next cycle, if its corresponding starting button has been actuated and this condition stored by a storing relay (not shown).

The release of relay SA in the control ofiice breaks the energized stick circuit of relay C which extends through its front contact 68 so that relay C drops and b'y'op'en ing its front contact l8, causes the release of relay STR.

Automatic start by a field station.-'Whenever the system is in the normal period or period of f blank, it may be initiated from a field station,

from a normal position to a reverse position in response to a control transmitted by lever SML, in a manner previously explained. When the track switch responds to such a control signal, it causes relay WP to deenergize during the transition period, when the switch is shifting from normal to reverse, after which relay WP is energized with opposite polarity. The deenergization of relay WP as well as its reenergization,

momentarily interrupts the stick circuit of a change relay in a manner which is not shown in Fig. 4 but which is well known in the art, and is shown, for instance, in the patent to De Long and Plank No. 1,852,402, dated April 5, 1932. Relay CI-IP is dropped as a result of such a change at the field station.

Relay CHP may also be released upon a change in traffic conditions, such for example, as the deenergizationof track relay T when a train passes over the associated detector track circuit, in accordance with the usual practices. In brief, the stick circuit for the change relay is carried through front and back contacts of the WP relay, the T relay and may be similarly carried through like contacts of other trafiic controlling devices associated with the field station.

Irrespective of the particular change which occurs, it results in dropping the change repeating relay CHP which closes a circuit for picking up relay PLA extending from back contact I55 of relay FP back contact I56 of relay SA back contact Iil'l of relay CHP and lower winding of relay PLA to Relay PLA closes a stick and MBPin the control ofiice.

Referring to the indication cycle portion of Fig. 5, the system is now in the first part of the initiating period with all three line conductors deenergized as indicated by reference character (open) associated with all three lines. The

release of relay MAP closes a circuit for pickingup relay FC extending from back contact ii! of relay MAP, back contact 69 of relay SAP, field start conductor 'lI, back contact ill of relayC, back contact E2 of relay STR and winding of relay FC, to Relay FC, which is operated only during a cycle which is initiated at a field station, prevents the picking up of relay PC during such a cycle, by opening the circuit of relay PC at back contact 24. 'Relay FC closes a stick circuit for itself extending from back contac 6 of relay SAP, front contact 19 and winding of relayFC, to A circuit is now completed 7 for picking up start relay STR, extending from front contact 13 of relay FC and winding of relay STR, to A circuit is also closedfor picking up relay NC, which extends from back contact 14 of relay C, front contact I of relay FC and winding of relay NC, to

Since this is a cycle for the transmission of indications alone, all of the impulses applied to the S line are because relay NC is held in its picked up position throughout the cycle. Relay NC opens its back contact I5, which is effective to prevent the control office breaking in on the connection after the communication system has been initiated from a field station. The operation of relay STR closes a circuit for energizing the S line conductor with potential, which extends from the terminal of battery B, back contact 8 of relay PC, front contact '26 of relay NC, winding of relay F and back contact 2? of relay EP to line 28.

This is the second portion of the initiating period with line S energized the A line open (O) and the B line energized as indicated in the operation chart. The potential, applied to the 8 line conductor 28, extends from the control ofiice through relay F at the field station shown in Fig. 4, through relays F at other field stations, resistance coils R and R at the last field station, back contacts of relays such as PLB at other field stations, conductor I52, back contact I53 of relay PLB B line conductor I2, winding of relay MB, front contact I of relay NC, back contact of relay PC and front contact I I) of relay STR to the terminal of battery B. The circuitv branches from resistance coil R and leads through back contacts such as PLA at other stations, conductor I5I, front contact I of relay PLA ,-lower winding of lockout relay L0 back contact ISI of relay SA to the B line conductor I2 and thence by way of theremainder of the circuit just traced to the terminal of battery B.

It will be noted from the above traced circuit that the A line conductor II is open toward the control oifice, at back contact I56 of relay PLA at the station initiating the call. The A line conductor I5I extending toward stations farther away from the control oiiice, is connected to the B line conductor at the station initiating the call through the lower winding of relay L0 The resistance coils R and R provide a sufficient drop, in the A. and B line conductors, extending from the station shown in Fig. 4 to the end of the line, so that the lower winding of relay L0 is not short circuited, but receives sufficient potential across the terminals of its winding to cause it to be energized.

With the system in the second part of the initiating period and with line S energized line A extending to the control office deenergized and line B energized relays F, MB and MB? in the control ofiice are picked up and relay Fl at the field station is positioned to the left. Relay FP in the control office and relay FP at the field station are picked up over circuits closed by contacts 29 and I54 of relays F and F respectively. Relay L0 is picked up by means of current flowing in line conductor I5I, as above described.

The system is now in the lock-out period. Relay SA in the control office is picked up over its previously described pick-up circuit and a circuit is closed for sticking relay MBP, extending from front contact M of relay SA, stick conductor 64, back contact ll of relay E, front contact E8 of relay MBP and upper winding of relay MBP, to An additional stick circuit is 75 closed, for relay FC extending from front contact 61 of relay SA, front contact 19 of relay FC and winding of relay FC, to

Relay SA at the field station is picked up by a 5 circuit completed at front contact E55 of relay G FP With relays FP or SA up, no other relay similar to FLA can be picked up because the pick-up circuit is open at back contacts similar to 155 or I56. Relay SA closes a stick circuit g for relay LO extending from front contact I93 of relay SA front contact 194 of relay L and upper winding of relay L0 to The picking up of relay SA opens the pick-up circuit of relay PLA at back contact I56 and the stick circuit of relay PLA at back contact I88 so that relay PLA is dropped.

The system is now advanced into the conditioning period. The A line conductor is now energized, due to the current in conductor l5i,

gg through back contact I50 of relay PLA A line conductor 1 l, winding of relay MA, front contact l3 of relay STR, front contact I of relay NC, back contact of relay PC and front contact H] of relay STR to the terminal of battery 5 B. As shown in the operation chart, during the conditioning period line S is energized and lines A and B Relays MA and MAP in Fig. 2 pick up when the A line is energized during this period and gg relay MAP establishes a stick circuit for itself, ex-

"tending from on stick conductor 64, back contact H of relay E, front contact 80 of relay MAP and upper winding of relay MAP, to Relay SAP is picked up when relay SA closes its 5 front contact 31. Relay VPC of Fig. 4 is again picked up when relay PLA releases by means of a circuit extending from back contact I99 of relay PLA back contact I95 of relay PLB and Winding of relay VPC to Relay EP 4? of Fig. 2 is picked up during the conditioning period, over a circuit extending from front contact 32 of relay SAP, back contact 33 of relay Eand winding of relay EP, to Relay EP opens the S-line conductor at its back contact 21, which deenergizes the three line conductors '28, II and I2.

The system is now advanced into the first off period. The stepping relays and their associated steering relays in the control office and at the 5 field stations are operate-d during an indication cycle, in the same manner as previously described in connection with a control cycle, so that the detailed description of this operation will not be repeated. The line conductor S is impulsed by relay EP in the same manner as previously de- 'scribed so that this operation will not be again explained. The relays similar to S0 at the field stations are not picked up during an indication cycle, because the conditioning impulse is 60 which actuates relay F to the left so that their pick-up circuits are not effective. Relay L0 however, is picked up as above described and completes a circuit for the stepping relays by way of its front contact I10.

65w Registration of a field station-4t will now be 'assumed that the system is advanced through the transmitting period and the change to normal period, the transmitting period including first, second and third off periods and first, second 70 and third on periods.

One of the features of the present invention resides in means for obtaining an increase in the number of indications which may be transmitted during an operating cycle. It is believed that 7 this feature may be best understood by assuming that the field station shown in Fig. 4 is assigned indication code combination as indicated in the station registration period at the lower part of the indication cycle of Fig. 5. The above assumption means that the No. 1 off indication is executed because relay MX is down, connecting (B) to the No. 1 off indication bus. The No. 1 on indications are exeouted and because relay MAP is down, connecting (B) to the No. 1A on indication bus and relay MZBP is up connecting (13+) to the No. IE on indication bus.

It will be noted that this station registering code is obtained with only one step of the stepping relay bank. The choice during the off period is or and the choice during the on period is or or a total of five choices. This does not mean that the line circuits are energized and but is simply a convenient manner of indicating the different combinations obtained. The choice of or off refers to relay MX up and down respectively. The on choices refer to relays MAP down and MBP up, relays MAP up and MBP down and relays MAP and IVEBP up, respectively, all as determined by the combinations of the A and B lines for the return circuit for line S.

It has been explained how the system is advanced into the first off period during an indication cycle. The stepping line S and the return lines A and B are all deenergized during the first off period, resulting in the picking up of relays IV and l V in the manner previously described. Relays F and FF are dropped during the first off period and relays MAP and MBP are stuck up by means of a circuit extending from front contact 54 of relay SA, stick conductor 64, back contact ill of relay E and front contacts and T8 of relays MAP and MBP respectively, to the windings of these relays.

Relay E is picked up during the second part of the first off period, which opens the above described stick circuit of relays MAP and MBP and these two relays are released. Relay MX is not picked up during this period because the pick-up circuit through its lower winding is open at back contact lei! of relay MBP, when these relays are up and at front contact 8! of relay MAP when they are down.

When relay W of Fig. 4 picks up during the first off period, a circuit is completed for pick ing up relay PLA which extends from back contact I55 of relay FP front contact I56 of relay SA off indication bus I91, code jumper l fi, No. 1A ofi indication bus 200, front contact 2% of relay IV back contact 201 of relay 2V back contact 268 of relay 3V back contact 269 of relay 'v'P upper winding of relay PLA and front contact 5% of relay L0 to Relay PLB is down during this off period because the No. 113 on? indication bus Zlll is not energized.

The system is next advanced into the first on period by the dropping of relay EP in the control office and the energization of line S. The return circuit is by way of line B alone because relay PLA is up, which opens line A at its back contact I 5|]. With the return circuit extending over line B, relays F, FP, MB and MBP are picked up in the control ofiice. With relay MAP down and relay MBP up, there is no circuit for picking up relay MX so that the No. 1 off indication is conditioned by relay MX remaining down and connecting (B-) to the No. 1 off indication bus 89, to be executed as will be later described.

With relay PLA up, the circuit of relay VPC is open at back contact I90 so that relay VPC is dropped. During the first-part of the first on period, relays F and FP at the field station are picked up, which results in disconnecting potential from the off indication bus ill! at back contact I55 of relay FP Relay PLA- is therefore released during the second part of the first on period, which results in energizing the A line and picking up relays MA and MAP in the control ofiice. Relay MX can not be operated under this condition because it requires relay MAP up and relay MBP down to energize the pick-up winding of relay MX. Both relays MAP and MBP are now up.

When relay PLA drops at the field station, the circuit of relay VPC is again completed and this relay is picked up. With relays FP, MAP AND MBP up in the control office, the circuit is completed for picking up relay VP which has previously been described. With relay VPC up at the field station, the circuit is complete-d for picking up relay VP which extends from front contact ill of relay SA front contact I86 of relay FP front contact I'M of relay VPC back contact 58'! of relay 3V back contact 222 of relay 2V front contact 223 of relay IV and winding of relay VP to It will thus be evident that the combinatio indicated in the operation chart for the second part of the first on period, that is, line S and lines A and B is used to control the picking up of relay VP in the control office and relay VP at the field station in synchronism. This feature is provided as a means for synchronizing the steering or half step relay operation at the control ofiice and at the field station.

With the VP and VP relays up, the system is advanced into the third part of the first on period by picking up relay PLA over a circuit extending from code jumper I98, No. 1A on indication bus 2%, front contact Zlil of relay IV back contact 2H of relay 2V back contact 212 of relay 3V front contact ace of relay VP upper winding of relay PLA and front contact I99 of relay L0 to Relay PLA is picked up because code jumper 198 is connected for energizing the No. 1A on indication bus. Relay PLB remains down at this time because the No. 1B"on and I98 being connected as shown in Fig. 4.

indication bus 295 is deenergized.

With relay PLA up and relay PLLB down, the A line is deenergized and the return circuit for. line S is by way of line B alone, which results in dropping relays MA and MAP and holding relays MB and MBP in their operated positions. As indicated in the third part of the first on period, this is the point in the cycle when the No. 1 on indication is conditioned and in the present example the B line conductor is energized and the A line conductor is deenergized. With relay MAP down, (B) is connected to conductor 82 and with relay MBP up, (3+) is connected to conductor 83 for later executing the first on indication.

The picking up of relay VP during the second part of the first on period opens the circuit of relay E, as has already been described and after a time interval measured off by the slow acting characteristics of relay E, it releases its armature and closes the executing circuits for the No. l indications which have been conditioned as described.

It will be recalled that relay MX is down, re-

sulting in (13-) being connected to conductor 84, so that this circuit from (B') is extended through back contact 85 of relay E, conductor l6 (Fig. 3),front contact 8% of relay VP, back contact 37! of relay 3V, front contact 88 of relay IV, No. 1 off indication bus St and winding of relay lPT, to (CN). This results in actuating relay iPT to its left hand position as shown.

Recalling that relay MAP is down, a circuit for executing the No. 1A on indication is now com-, pleted, extending from (B-) back contact 90 of relay MAP, conductor 82, back contact ill of relay E, conductor Q36, front contact 92 of relay VP,

back contact 93 of relay 3V, front contact lli l of relay lV, No. 1A on indication bus i (35 and winding of relay EPT, to (CN). This results in actuating the contacts of relay ZPT to the left hand position as shown in Fig. 3.

Recalling that relay MBP is up, a circuit for executing the No. IE on indication is now, completed, extending from (B+) front contact fit of relay MBP, conductor 83, back contact 95 of relay E, conductor 13!, front contact 96 of relay VP, back contact 91 of relay 3V, front contact 98 of relay W, No. 13 on indication bus W9 and winding of relay 3PT, to (ON). in this circuit is in such a direction that relay 3PT will be positioned to the right as shown.

The system is next advanced into the second off period and as indicated in the operation chart and as will be evident from an examination of the circuits above traced, the No. 1 execution circuits remain effective during the first part of the second off period. These execution circuits are broken at contacts 85, 9! and 95 of .relay E when it is picked up to mark the beginning of the second part of the second off period.

Relay 2V is picked up in the first partof the second off period, closing a circuit for operat ing relay ST of Fig. 3, extending from front H contact l2!) of relay 2V, contact 112! of relay IPT in its left hand position, contact E22 of relay ZPT in its left hand position, contact l23 of relay SPT in its right hand position and winding of relay s'r, to

The above explanation sets forth in detail the manner in which the station shown in Fig. 4, having code combination registers itself in the control office by selecting and operating relay ST of Fig. 3. The code combination of this station is determined by code jumpers 955 The selection of one of two combinations during the off period is obtained by selectively connecting code jumper 1% toindication buses 26%) and 2! as explained. With jumper I96 connected as shown, relay PLA is picked up, opening line conductor A so that the return circuit is by way of line conductor B, for picking up relays MB and MBP in the oilice. k MAP down, relay MX remains down to execute a code as explained. The alternate connection of jumper I96 to indication bus 28! would result in picking up relay PLB thus establishing the return circuit by way of the A line conductor so that relay MAP would be up and relay MBP down, which would complete a circuit for picking up relay MX. With relay NX up, the code combination executed is This is the choice of two code combinations for the off period.

With jumper 98 connected as shown in Fig. 4, relay PLA is picked up, which opens the A line conductor and establishes the return circuit by way of the B line conductor, so that relay MBP in the control ofiice picks up and relay MAP stays The current flow With relay MBP up and relay W60 down. As has been explained, relay MAP down results in positioning relay ZP'I to the left and relay MBP up establishes a circuit for positioning relay 3PT to the right.

If jumper I98 were connected to indication bus .205, then relay PLB would be picked up and relay PLA would remain down, which would open the B line conductor and establish the return circuit by way of the A line conductor. This would pick up relays MA andMAP and leave relays MB and MBP down. With relay MAP up the No. 1A on indication bus of Fig. 3 would be energized for positioning relay ZPT to the right. With relay MBP down, the No. IE on indication bus would be energized for positioning relay 3PT to the left.

If jumper I98 is not connected to either bus 204 or 205, then both relays PLA and PLB would be down and the return circuit would be by way of both the A and B line conductors and relays MAP and MBP would both be picked up. This would result in a potential being applied to both the No. 1A on and the No. IE on indication buses for positioning relays ZPT and 3PT to the right. This is the method of obtaining a choice of three combinations during the on period.

It will be understood that there is no combination for positioning relays 2PT and 3PT both to the left during an on period, because this would require both the MA and MB relays being down which is not possible during an on period, because one or the other or both the A and B line conductors must be energized for the return circuit for line S.

The conductor indicated phantom is not used for connection to 'a relay similar to ST, because when controls alone are being transmitted, the -off and on combinations provided by the A and B line conductors inherently result in positioning relay lPT to the left, relay ZPT to the right and relay 3PT to the right. This is due to the fact that both the A and B line conductors are energized in multiple during all of the. conditioning periods, which results in relay MX being down to energize the No. 1 off indication bus relay MAP being up to energize the No. 1A on" indication bus and relay MBP being up to energize the No. IE on indication bus Transmission 07 indications- Relays 2V and 2V are picked up during the first part of the second off period. The No. 2 off indication is conditioned, after the picking up of these two stepping relays, during the second part of the second off period and the first part of the second on period. With relay 2V up and relay VP up at the field station, a circuit is closed for picking up relay PLB which extends from back contact I of relay FP front contact I56 of relay SA off indication bus I91, front contact 2I3 of relay T No. 2B off indication bus 203, front contact 2M of relay2V back contact 2L5 of relay 3V front contact 2H3 of relay VP winding of relay PLB and front contact I99 of relay L0 to Relay PLA is not picked up during the second off period because the No. 2A off indication bus 202 is deenergized.

When relay E of Fig, 2 is picked up, after the picking up of relay 2V, in a manner which has been previously described, relay M'BP is dropped because relay E opens its stick circuit at back contact 11. Relay MAP is already down and the system therefore goes through the second busIH'I at its back contact PLA and PLB down, the pick-up circuit of part of the second off period with relays MAP, MBP and MX down. When relay EP drops and closes the line to advance the system into the first part of the second on period, the line S is energized and the return circuit is by way of the A line, because relay PLA is down closing the A line at its back contact I59 and relay PLB is up opening the B line at its back contact I53.

Relays F, FP, MA and MAP of Fig. 2 now pick up and. with relay MAP up and relay MBP down, a circuit is closed for picking up relay MX, which extends from back contact I9 of relay 3V, front contact 20 of relay 2V, front contact 34 of relay VP, back contact 99 of relay EP, back contact I00 of relay MBP, front contact 8| of relay MAP and lower winding of relay MX, to Relay MX closes a stick circuit for itself extending from front contact IBI of relay FP, front contact B2 of relay MK and upper winding of relay MX, to Relay MAP is up, relay MBP is down and relay MX is up at this time.

The system is now advanced into the second part of the second on period by the picking up of relay FP at the field station. The circuit above traced, which picked up relay PLB is now interrupted at back contact I55 of relay FP so that relay PLB is dropped. This results in energizing both the A and B line conductors with potential and as a result, relays MB-and MBP are picked up. With relay MAP up and relay MBP up, the pick-up circuit of relay MX is broken but relay MX remains stuck up to potential at front contact I [II of relay FP.

With the MAP, MBP and PP relays all picked up, the stick circuit of relay VP is interrupted at back contacts 60, 59 and 52 of these respective relays. Relay PLB is dropped, when relay FP disconnects potential from 01? indication I55. With relays relay VPC is again established and this relay is actuated, opens its back contact I13 and interrupts the stick circuit of relay VP Relay VP drops and establishes the conditioning circuit for the second on indication. This results in picking up relay PLA over a circuit extending from front contact 2F of relay WP contact 2I8 of relay WP in its right hand position, No. 2A on indication bus 2I9, front contact 201 of relay 2V back contact 268 of relay 3V back contact 209 of relay VP upper winding of .relay PLA and front contact I99 of relay L0 to Relay PLB remains down because the No. 2B on indication bus 220 is open at contact 2I8 of relay WP Relay VPC is now dropped because its circuit is open at contact I90 of relay PLA The picking up of relay PLA opens the A line conductor return circuit so that relays MA and MAP in the control office are dropped. Relay MAP is now down, relay MBP is up and relay MX is stuck up. The release of relay VP during the second part of the second on period opens the circuit of relay E and this latter relay is dropped, after a short time interval. The exeouting circuits are now closed for the No. 2 indications.

Since relay MX is up, a circuit is extended from (3+) front contact I03 of relay MX, conductor 84, back contact 85 of relay E, conductor 16, (Fig. 3) back contact 36 of relay VP, front contact I06 of relay 2V, No. 2 off indication bus I01, front contact I08 of relay ST and winding of relay 1R to (ON). This results in actuating relay IE to the right as shown in Fig. 3.

Since relay MAP is down, the circuit for executing the No. 2A on indication is now complete, extending from (B), back contact 95 of relay MAP, conductor 82, back contact-9i of relay E, conductor I38, back contact 92 of relay VP, front contact III! of relay 2V, No. 2A on indication bus 'I I I, front contact I I2 of relay ST and winding of relay 1R to (CN). This results in actuating the contacts of relay IE to the left hand position as shown in Fig. 3.

With relay MBP up, the circuit for executing the No. 2B on indication is now complete, which extends from (13+), front contact 94 of relay MBP, conductor 83, back contact 95 of relay E, conductor I3I back contact 96 of relay VP, front contact I it of relay 2V, No. 2B on bus I4, front contact I if: of relay ST and winding of relay 1R to (CN). The current flow in this circuit is in such a direction that relay IE is positioned to the right as shown. I

It will be noted that the stick circuit for relay MBP is effective when relay E releases and closes its back contact I7, so that relay MBP will not be released during the first part of the next off period, with the circuit through its lower Winding incomplete. The system is next advanced into the thir off period and as will be evident from an examination of the circuits above traced, the No. 2 execution circuits remain effective during the first part of the third off period. These execution circuits are broken at contacts 85, 9| and 95 of relay E when it is picked up to mark the beginning of the second part of the third off period. Relays 3V and 3V are picked up during the first part of the third off period and the No. 3 off indication is conditioned, after the picking up of these stepping relays, during the second part of the third off period and the first part of the third on period. With relay 3V up and relay VP down at the field station, a circuit is closed for picking up relay PLA which extends from back contact I55 of relay FP front contact I56 of relay SA- off indication bus IS'l, back contact 224 of'relay M N0. 3A off indication bus 225, front contact 208 of relay 3V back contact 209 of relay VP upper Winding of relay PLA and front contact I98 of relay L to Relay PLB is not picked up during this off period because the No. 313 off indication bus ZZS'is open at front contact 224 of relay M When relay E of Fig. 2 is picked up after the picking up of relay 3V, in a manner which has been previously described, relay MBP is dropped because relay E opens its stick circuit at back contact TI. Relay MAP is already down and the system therefore goes through the second part of the third off period with relays MAP, MBP and MX down. When relay EP drops and closes the line to advance the system into the first part of the third on period, the line S is energized and the return circuit is by way of the B line because relay PLB is down closing the B line at its back contact I53. Relays F, FP, MB and MBP now pick up and since relay MAP is down and relay MBP is up, relay MX remains down.

The system is now advanced into the second part of the third on period with relays MAP down, MBP up and MX down. When relay FP at the field station picks up to advance the system into the second part of the third on period, it interrupts the circuit of relay PLA at contact I55 so that relay PLA drops and energizes the A line.

This results in picking up relays MA and MAP so that relays MAP and MBP are both up and relay MX is down at this time.

With relays FP, MAP and MBP all up, the pickup circuit of relay VP is completed, extending from front contact 32 of relay SAP, front contact 52 of relay FP, front contact 53 of relay MBP, front contact 54 of relay MAP, front contact 55 of relay 3V and winding of relay VP, to At the field station, a circuit is completed for picking up relay VIPC when relay PLA drops and with relay VPC up, the previously described circuit is completed for picking up relay VP except that it now extends through front contact 5 81 of relay 3V instead of contact 223 of relay IV With relay VP up, the No. 3 on conditioning circuits are established, resulting in dropping both relays PLA and PLB becausethe No. 3A on bus 221 and the No. 313 on bus 228 are both shown incomplete in Fig. a. This results in the MA, MAP, MB and MBP relays picking up in the control ofiice and when relay E is released during the fourth part of the third on period, the No. 3 indication circuits are executed.

With relay MX down, the No. 3 off indication is executed by means of a circuit extending from (B), back contact I93 of relay MX, conductor a l, back contact 85 of relay E, conductor I6, front contact 86 of relay VP, front contact 81 of relay 3V, No. 3 off indication bus I I6, front contact ll! of relay ST and winding of relay 1R to (CN). This results in actuating relay IR to its left hand position as shown in Fig. 3. If relay IE is actuated to the right, lamp M is lighted by way of conductor I21 as an indication that relay M of Fig. 4 is up.

The circuits of the No. 3 on indication buses of Fig. 4 are not completed, since it is believed that the examples specifically described above are sufficient to indicate how the selection of five indication choices is obtained during each step. Likewise, the No. 3 on buses I I8 and I I9 of Fig. 3 are not completed, since they may be connected, in an obvious manner, to other relays similar to the IR relays indicated I With the indication storing relays 1R IE and IE positioned as shown, the circuits to the indication lamps are selectively conditioned. Since relay 1R has its contacts actuated to the right, the circuit to lamp OS is not completed, as an indication that the detector track section is unoccupied as repeated by relay T of Fig. 4 being up. Relays IE and IE complete a circuit for lighting lamp NI which extends from contact I24 of relay 1B in its right hand position and contact I25 of relay 1R in its left hand position to lamp NI. Lighting lamp NI is an indication that the switch TS of Figx is in its normal locked position as repeated by relay WP The alternate connection of the contacts of relay WP to indication bus 220 would result in opening the B line conductor by picking up relay PLB ,,so that the return circuit would be by way of the A line conductor alone. This would result in relay MAP being up and relay MBP being down, so that the No. 2A on indication bus III of Fig. 3 would be energizedf-k), to position relay IR to the right and the No. 213 on indication bus II -i would be energized to position relay IE to the left. Likewise, the No. 2 off selection is made by positioning relay MX, in the manner above described, for selectively actuating relay 1R of Fig. 3. Relay 1B

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