US2082333A

US2082333A - Centralized traffic controlling system for railroads

Info

Publication number: US2082333A
Application number: US750295A
Authority: US
Inventors: William D Hailes
Original assignee: General Railway Signal Co
Current assignee: SPX Corp
Priority date: 1934-10-27
Filing date: 1934-10-27
Publication date: 1937-06-01
Anticipated expiration: 1954-06-01

Description

4 Sheets-Sheet 1 w. D. HAIILES co +d+m 32 vacuum Filed Oct. 27, 1934 CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS 52m 221 Em G22 53mm 33 gn June 1, 1937.

W. D. HAILES June 1, 1937.

CENTRALIZED TRAFFIC CONTROLLING SYSTEM'FOR RAILROADS Filed ot. 27, 19:54

4. Sheets-Sheet 2 INVENT R w. AZ. Wm, BY m MORNEY mLoqE v owou i 395 UZ UQ. Q.

June 1, 1937.

w. D. HAILES CEN'I RALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS 4 Sheets-Sheet 3 Filed Oct. 2'7, 1934 June I, 1937.

w. D. HAILES CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS 4 Sheets-Shee t 4 Filed Oct. 27, 1934 35 2053 5 +ndm ATTORNE Y $2.0m 0:5 tcou Patented June 1, 1937 UNITED STATES CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS William D. Hailes, Brighton, N. Y., assignor to General Railway Signal Company, Rochester,

Application October 2'7, 1934, Serial No. 750,295

14 Claims.

This invention relates to centralized trafiic controlling systems for railroads and it more particularly pertains to the communication part of such systems.

The present invention contemplates a centralized traffic controlling system in which communication is established between a central control oflice and a number of outlying field stations distributed along the railway system. This communication is effected by means of a system of the station selective coded duplex type. In

a system of this type a series of impulses forming a particular code combination are transmitted over a control line circuit interconnecting the control ofiice with the various outlying field stations for the selection and control of a particular station.

Similarly a series of impulses forming a particular code combination are transmitted over an indication line circuit interconnecting the control ofiice with the several outlying field stations for the registration of a particular station in the control ofiice and the transmission of indications from the registered station. The control line circuit and the indication line circuit are so interrelated in the selector type apparatus employed that controls and/or indications may be transmitted during any particular cycle of operations.

In such a system where there are a plurality of field stations it is apparent that more than one of these field stations may have new indications ready to transmit at the same time. The system of the present invention provides a lockout means at each field station so that only one station may transmit its code call and its indications during any one particular operating cycle. Suitable means are provided to restore the transmitting station to its normal condition as soon as it has completed its transmitting operation.

In a railway system there are usually certain locations that have more traffic than others, such as division headquarters or a city located at an intermediate point along a particular division of the system. In applying a centralized traffic controlling system to such a layout it becomes expedient to locate the control ofiice at that point from which the most trafiic is to be handled. The present invention particularly provides for such a situation by employing a system so arranged that the control and indication line circuits extend in a plurality of directions from the control ofiice, with the proper functioning of the system accomplished in the same manner as if the field stations were all located in one direcvember 3, 1932, as well as providing certain additional features in such a system as will be described in detail hereinafter.

It has been the practice to provide the field stations in such an order as to be connected in series relationship insofar as the line circuits are concerned when a lookout system in connection with the indication line circuit is employed. However, the present invention provides a direction selecting means in the control oilice which is efiective to select the direction for the transmission of controls and indications. Similarly, a lockout means is provided in the control oflice between the indication line circuits extending in the opposite directions which is effective to determine which direction of the indication line circuit is to have control of a particular indication cycle. This is accomplished during the initiating period of the system and immediately following this period the particular field station (located on the selected section of the line) having indications to transmit is selected in accordance with the usual lockout means, after which the code call and indications are transmitted from that station.

In the present embodiment, as a typical arrangement it is assumed that certain of the field stations are associated with a section of railway track located to the west of the control office, while certain other field stations are associated with the section of railway track located to the east of the control ofiice. The control line circuit is divided into two branches in the control ofiice, one branch including all of the west field stations in series and the other branch including all of the east field stations in series. These branches are selected at the beginning of an operating cycle in accordance with the direction of location of the station which is to be selected during that cycle.

Similarly the indication line circuit extends in a west direction and includes all of the field stations to the West of the control office which are connected in series to the indication line circuit. The branch of the indication line circuit which extends east from the control ofiice connects all of the east field stations in series to this branch of the indication line circuit.

Other features of the present invention reside in the various circuit arrangements particularly adapted to systems of this type.

These characteristic features thus briefly stated will be explained more in detail in the following description of one embodiment of the invention and various other features, functions and advantages of a system embodying this invention will be in part pointed out and in part apparent as the description progresses.

In describing the invention in detail, reference will be made to the accompanying drawings in which those parts having similar features and functions are designated throughout the several views by like letter reference characters which are generally made distinctive, either by reason of distinctive exponents representative of their location in the system or by reason of preceding numerals representative of the order of their operation and in which:--

Fig. 1 is an abbreviated showing of the control and indication line circuits connecting to a first and a second field station located to the west of the control oifice.

Figs. 2A and 2B illustrate the apparatus and circuits employed in a typical control office for accomplishing the functions of the system.

Fig. 3 illustrates in abbreviated form a third field station and in more detail a fourth field station connected to the control and indication line circuits extending to the east of the control office.

For convenience in understanding the operation of the present system and for making it easy to trace the circuits, Fig. 1 should be placed to the left of Fig. 2A, Fig. 3 should be placed to the right of Fig. 2A and Fig. 2B should be placed below Fig. 2A, with correspondingly numbered lines in alinement. In order to reduce the v number of lines crossing the center figure of the drawings, indication line conductors l4 and I6 are terminated in the lower right hand portion of Fig. 1 and indication line conductors l5 and I6 are terminated in the lower left hand portion of Fig. 3. These conductors connect to corresponding conductors located in the left central and the right central portions respectively of Fig. 2B.

Similarly, in order to simplify the drawings and description, various parts and circuits constituting the embodiment of the invention have been shown diagrammatically 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 that would be employed in practice. Thus the various relays and their contacts are illustrated in a conventional manner and symbols are used to indicate connections to the terminals of batteries or other sources of electric current instead of showing all of the wiring connections to these terminals.

The symbols and are employed to indicate the positive and negative terminals respectively of suitable batteries or other sources of direct current and the circuits with which these symbols are used always have current flowing in the same direction. The symbols (3+) and (B) indicate connections to the opposite terminals of a suitable battery or other direct current source which has a central or intermediate tap (CN) and the circuits with which these circuits are used may have current flowing in one direction or the other depending upon the particular terminal used in combination with the intermediate tap (CN) Although the present invention may be considered applicable to any selective type of communication system, it is deemed expedient to explain and disclose in a general manner the application of the present invention to a typical selective type communication system such as shown, for example, in the pending application of T. 'J. Judge, et al., Ser. No. 640,062, filed October 28, 1932, corresponding to British Patent No.

419,399, to which the present invention has been more particularly adapted. Thus in considering the structure and mode of operation of the present invention it is necessary to explain some of the features of the communication system which are material to an understanding of the present invention, reference being made to said prior application for other details of the structure and operation not directly related to the features of the present invention.

Communication system.-The general plan of organization of a centralized traffic controlling system embodying the present invention provides a control office located in a central or intermediate location with regard to the plurality of outlying field stations. As represented in the drawings, the field stations extend to the west and to the east of the control oflice, being connected thereto by separate control and indication line circuits.

The west control line circuit includes control line conductor II and return line conductor 12, while the east control line circuit includes control line conductor l0 and return line conductor i2. The west control line circuit includes a three position biased-to-neutral line relay F (with suitable exponent) at each of the west field stations. The east control line circuit includes a three position biased-to-neutral line relay F (with suitable exponent) at each of the east field stations. These two line circuits (west and east) are selected in the control office but irrespective of which one is selected a neutral line relay F is included in the line circuit at the control office.

In the control office, positive and negative code sending relays PC and NC are provided to determine the polarity of the energy supplied to the selected control line circuit from control line battery CB for the impulses applied to the selected line circuit for each cycle. An impulsing relay E is provided for interrupting the energizing circuits of the code sending relays for periodically opening the line circuit to determine the time spaces between the successive impulses of each cycle of operation of the system. The west control line conductor is connected to the control line return conductor at the west end field station and the east control line conductor is connected to the control line return conductor at the east end field station in order to provide a closed circuit for energizing the respective control line circuits from the central oflice control battery CB.

The west indication line circuit includes indication line conductor l4 and return line conductor IS. The east indication line circuit includes indication line conductor 15 and return line conductor [6. The west and east indication line conductors l4 and I5 are serially extended from station to station by conductors l3, 2H], [1, and [8. At each end of the system the indication line circuits are left open so that they are normally deenergized. Whenever a field station initiates the system into a cycle of operations, the indication line circuit is completed up to the initiating station and is supplied with energy from an indication battery IB located in the control oflice.

The west indication line conductor l4 normally includes in series therewith a message receiving relay MF at the control office. This conductor includes a back contact of a lookout relay LO (with suitable exponent) at each field station to determine whether the West indication line wire is to be extended to the next field station or to be connected to the west return line conductor I6.

Similarly, the east indication line conductor I5 normally includes in series therewith a winding of message receiving relay MB. At each field station to the east of the control ofiice, a back contact of a lockout relay, LO (with suitable exponent) of its associated field station is included in the indication line conductor to determine whether the east indication line should be extended to the next field station or be connected to the east return line conductor l6.

Each field station except the end station of each division of the line includes suitable resistances, such as resistance R (with suitable exponent) for compensating for the difierence in distance between the several stations and the control office, to maintain the current fiow from the indication battery 13 within a predetermined range irrespective of which particular field station is; transmitting.

Although the present disclosure makes use of four line conductors leading each way from the ofiice, it will be understood that a single return conductor can be used for the control and indication lines, thus providing a three-wire line circuit. For example, the control line return conductor I2 leading both ways from the office can be connected to the negative terminal of indication line battery 13 and the indication line return conductor eliminated by connecting the circuits of the lower windings of the lockout relays to conductor R2 at the various stations.

Control oflice equipment-The control ofiice equipment includes, besides the above mentioned apparatus, a quick acting line repeating relay IFP together with its associated repeater relay 2FP. These relays repeat each energized and each de-energized condition of line relay F.

A slow acting line repeating relay SA is provided to mark off the cycles of o eration by being picked up at the beginning of a series of impulses and by being released at the end of such series. Relay SA is provided with such slow acting characteristics that it is slow in picking up thereby requiring a slightly longer impulse at the beginning of a series. Relay SA is provided withrelatively slow acting characteristics in releasing so that its contacts are maintained in picked up positions during the time spaces between the successive impulses of the series until the end of the cycle when relay SA is deenergized for a comparatively long interval of time. Associated with relay SA is a repeating relay SB having an associated repeating relay SC each of which is provided with slow acting characteristics similar to relay SA.

The impulses placed on the control line circuit for a cycle of operations are repeated by relay 2F? which causes the step-by-step operation of a stepping relay bank illustrated as including stepping relays IV and 2V together with a halfstep relay VP. This stepping relay bank is arranged to take one step for each deenergized condition of the control line circuit between the successive impulses of a cycle following the application of the first impulse of the cycle. Impulse relay E is associated with the stepping relay bank in order to time space the impulses on the control line circuit.

As previously mentioned, a message receiving relay MB is associated with the indication line circuit for receiving the indication messages over the back branch of the indication line circuit, whi1e a message receiving relay MP is provided for receiving the indication line messages over'the front branch of the indication line circuit. This provides for the double capacity transmission of indications by selecting the MB and MF relays through back and front branches respectively of the line repeating relay 2FP. These message receiving relays are selectively associated with the particular division (west or east) which is transmitting by selecting relay The control office includes, besides the selector typeapparatus, a suitable control machine having a group of control levers for each of the outlying field Stations, a miniature track diagram corresponding to the actual track layout in the field and-various indicating lamps or equivalent devices for indicating the condition of the operating devices and the position of trains along the trackway. In other words, the present invention is contemplated as being applied to a complete centralized traffic controlling system, but for convenience thecontrol machine including the control levers, miniature track diagram and indication devices has been omitted since this portion of the system may be of any approved type such, for example, as disclosed in the above mentioned prior application Ser. No. 640,062.

I The present disclosure omits the illustration of the usual code determining relay bank for determining which group of control levers is to be Selected for the transmission of controls to their associated field station, all of which has been disclosed in the above mentioned prior application Ser. No. 640,062. However, it is assumed that the actuation of a suitable starting button, or other means, causes the energization of conductor WCD (located in the lower portion of Fig. 2B) when a starting button or other means is actuated for selecting a west station. Similarly, conductor ECD is energized when a starting button or other device is actuated for selecting an east station. The conductor connecting to the left hand terminal of code determining stick relay CDS of Fig. 5 of the above mentioned application indicates how energy is applied to corresponding conductors, such as ECD for an east station or WCD for a west station.

Control ofi'ice starting and cycle controlling relay C is provided for initiating the system into operation. Relay C is energized by the operation of west code determining stick relay WCDS or east code determining stick relay ECDS, which code determining stick relays are energized and picked up by the operation of the respective starting means above mentioned.

The initial energization of one of the code sending relays is effective to apply the first impulse to the control line circuit when cycle controlling relay 0C is picked up in response to the operation of office starting and cycle controlling relay C. This first impulse is cut ofi from the control line circuit after a predetermined time measured off by the picking up of relays F, lFP, ZFP, SA, SB, SC, E and the dropping of the selected code sending relay.

- During the first impulse period, relay VP is picked up. During the first deenergized period of the control line circuit the first stepping relay is picked up which renders the next code jumper or control lever contact effective to position the code sending relays PC and NC for determining the particular character of the next impulse. Various other functions accomplished during a control operation of the system will be explained during the detailed description which follows later.

A field starting and cycle controlling relay CF is picked up in response to the occurrence of a change in condition at one or more field stations and its energization, when there are no controls to be transmitted, causes the initiation of a cycle of operations for the transmission of indications. Throughout such a cycle the impulses on the control line circuit are all of one character. This is accomplished by allowing relay CF to directly control negative code sending relay NC.

The energization of relay NC by relay CF causes the initial 'energization of the control line circuit which is repeated by the line and line repeater relays as above mentioned resulting in the operation of the stepping relay bank and the impulsing of the control line circuit, but since relay NC is always operated throughout a cycle of this class the impulses are all of negative character. As will be pointed out in detail, relay SR is picked up to select the west control line for receiving this series of impulses in response to the initiation of the system by a west'station. Relay SR remains down to select the east control line for receiving this series of impulses when the east station initiates the cycle.

Field station equipment.With reference to Figs. 1 and 3 it will be noted that three field stations have been indicated while a fourth field station has been shown somewhat in detail. This fourth station may be considered as a typical station and includes only those devices more particularly required to make plain an understanding of the present invention.

With reference to the fourth field station shown in Fig. 3, a turnout track is illustrated as connected to a main track by a track switch TS which is operated by a switch machine 8M It is contemplated that this switch machine is governed in accordance with a suitable switch machine control lever (not shown) in the control oflice through the medium of the communication system as disclosed in the above mentioned application, Ser. No. 640,062. It is also contemplated that suitable signals are associated with this track switch for governing traffic thereover and that such signals are also controlled from the control ofiice.

Associated with the track switch is a detector track section having the usual track relay T and a track battery forming a closed circuit type of track circuit. A signals-at-stop relay M is normally energized when all of the signals governing traffic over track switch T are at stop and this relay is deenergized when any signal is cleared.

It is assume-d that any number of traffic controlling devices may be located at the field stations and may have indications to transmit the same as the track relay T and the signals-atstop relay M but for convenience in describing the present invention such additional traffic controlling devices have been omitted. Associated with the traflic controlling devices at the station is a suitable change relay CH which is normally energized but which is deenergized upon a change in the condition of any of the trafiic devices, being restored during a cycle of operation during which its station has been successful in transmitting the new indications, all of which has been shown and described in detail in Patent No. 1,852,402, dated-April 5, 1932 and issued to D. F. DeLong et al.

The communication part of the system at the typical station includes, besides the apparatus already mentioned, a quick acting line repeating relay FP which repeats each energized and each deenergized condition of line relay F in a manner similar to the operation of corresponding relays in the control office. A slow acting relay SA is employed to mark oii the cycles by being picked up at the beginning of a cycle and released at the end of such cycle a predetermined time after the removal of the last impulse of that cycle, in a similar manner as explained for relay SA in the control office. Associated with relay SA is a quick acting repeating relay SB provided to properly time the system for providing positive operation by relieving relay SA of an excessive number of contacts.

The field station includes a bank of stepping relays including relays 1V and 2V together with a half-step relay VP which are controlled as described in the above mentioned application Ser. No. 640,062 and need not be explained in detail for an understanding of the present invention. These stepping relays and the half-step relay operate in synchronism with corresponding relays in the control office.

A lockout relay L0 is provided to register when station No. 4 is selected for the transmission of its indications from among other stations having indications ready to transmit.

For the purpose of governing the front and back branches of the indication line circuit when this field station is rendered effective by its lockout relay L0 impulse relays PF and PB are provided to operate in accordance with code jumpers 51 and 58 and the indication contacts of the station.

It is to be understood that the field station includes various other adjuncts and apparatus necessary for a complete system, a description of which is unnecessary for an understanding of the present invention. It will also be understood that stations I, 2, and 3, as well as any other stations which may be included in the system, have similar and corresponding equipment for operating in a manner similar to that described in connection with-station No. 4.

It is believed that the nature of the invention, its advantages and characteristic features can best be understood by setting forth further description from .the standpoint of operation.

Operation The primary object of the present invention is to enable the use of one control ofiice stepper for two duplex systems extending, for example, in opposite directions from a control ofiice, thus doubling the capacity of the system served by one ofiice stepper. In the past this has been handled by the use of a control ofiice stepper for each end of the system. A system operating in accordance with the present invention can be used to control either of two duplex systems one at a time and will give the full single end capacity for each of the two ends by the use of a single control office stepper.

The operation while connected to either one of the two ends is the same as if it were a single end installation. The operation will be duplex for each end thus enabling controls to be sent to any station and indications received from the same or any other station during the same cycle, provided the stations are on the same end of the installation. Indications cannot be brought in from one end of the installation during the same cycle that the system is in use for transmitting controls to the other end of the installation.

Controls are given preference over indications so that the control office can always over-rule the field station, in case controls are to be sent to one end while indications are in condition for transmission from the other end. Indications which are thus prevented from being transmitted are stored until the system is not in use for control purposes or until the system sends controls to the same end having stored indications, in which case the operation will be duplex.

No'rmal conditions.The line circuits of the present system are arranged to be normally deenergized and similarly the remaining circuits are arranged to be normally deenergized with a few exceptions. For example, the detector track circuit associated with track switch TS of Fig. 3 is preferably of the closed circuit type which effects the normal energization of track relay T Of course other track relays associated with other track switches located at other stations are similarly operated.

The change relays are normally energized. For example, relay CH of Fig. 3 is normally energized in a manner which has been pointed out and disclosed in the previously mentioned Patent No. 1,852,402. Likewise, the change relay at other stations of the system are normally energized and in response to the deenergization of a change relay at a particular station, this station is eifective to initiate the system into a cycle of operations for the transmission of indications.

When a cycle of operations is initiated for the transmission of controls alone, the characters of the impulses placed upon the control line circuit are determined in accordance with the code call of the station to be selected and in accordance with the controls to be transmitted to the selected station, as set up by the code jumper connections and the control lever positions for that station. Similar determination of the characters of the impulses on the control line circuit occurs during a duplex cycle and, as above mentioned, selecting relay SR determines which end of the system is to be used for the transmission of controls and/or indications.

During a cycle of operations initiated for the transmission of indications alone, the characters of the impulses placed upon the control line circuit are such as to fail to select any station, these impulses being employed to merely cause the step-by-step operation of the stepping relay banks at the control office and at the particular field station which is transmitting indications.

In other words, when a cycle of operations is initiated from a field station for the transmission of indications the control line circuit to which that station is connected is impulsed either for the transmission of controls or with a nonselecting code call during which the indication line circuit is impulsed for the transmission of indications. On each step taken by the step-by-step mechanism at the station which is transmitting, the indication line circuit associated with that particular end of the system is either opened or closed in accordance with the indication contacts for that step, that is, one indication contact is effective during the energized condition of the control line circuit while another indication contact is effective during the deenergized condition of the control line circuit for that step.

This conditioning of the front and back branches of the indication line circuit at the field station is transmitted to the control ofiice and rendered effective to position the message receiving relays MF and MB .of the corresponding branches in the control oflice. These mes sage receiving relays then store such conditions in suitable indication storing relays or pilot relays (not shown) in the period immediately following their positioning over the indication line circuit. Relays MF and MB are positioned alternately on the successive energized and deenergized periods of the control line circuit so that for each period an indication storing relay or pilot relay is being positioned in accordance with the code call or indication transmitted.

In the present description it will be pointed out how these front and back branches are conditioned and received on the MF and MB relays and how these relays in turn execute these conditions to selected channel circuits. The connections of these channel circuits to pilot and indication storing relays have been omitted, since for an understanding of the features of the present invention it is unnecessary to complicate the drawings and description by including this portion of the system. For an understanding of the manner in which the indication channel circuits are connected to pilot relays and indication storing relays reference is made to the above mentioned application, Ser. No. 640,062.

Manual start.With the system in a condition of rest it may be manually initiated into a cycle of operations for the transmission of controls to any desired station. Whenever such a cycle of operations is desired the operator first positions the control levers associated with the desired station and then actuates the corresponding starting button. This operation eifects the energization of a code determining relay which, by means of code jumpers connected in a particular combination, determines the particular code call which is applied to the communication system. The code determining relay also selects the control levers associated with that particular station for determining the code call applied to the communication system for operating the desired devices at the selected station.

As clearly pointed out in the above mentioned prior application Ser. No. 640,062, no code deterk mining (CD) relay can be picked up as long as the system is in any other but its normal condition. This is accomplished by opening a control conductor, such as conductor LC indicated in the left hand portion of Fig. 2A of the present drawings, which conductor in this embodiment is deenergized as long as the system is in active operation. This is due to the fact that conductor LC is deenergized at back contacts 35 and 36 of relays MB and ME as soon as a station initiates the system for an indication cycle, because one .or the other of these relays will be picked up as a result of such initiation. Since relay SA has its back contact 31 open during a cycle, conductor LC is maintained deenergized. The picking up of back contacts 33 and 34, in response to the initiation of a control cycle by the picking up of relay WCDS or ECDS, likewise maintains conductor LC deenergized.

Assuming that the system is in its normal condition a circuit is completed from back contact 31 of relay SA, back contact 34 of relay ECDS, back contact 33 of relay WCD'S back contact 36 of relay MF and back contact 35 of relay MB, to conductor LC. This supplies energy to the code determining relays so that the selected one of these relays may be energized in response to the operation of the starting button.

If a code determining relay corresponding to a station associated with the west end of the system is energized, the stick circuit for this relay is completed through a code determining stick relay CDS as shown in Fig. 5 of the above mentioned prior application, Ser. No. 640,062. However, in this embodiment two code determining stick relays are provided, one (WCDS) for the stick circuit of the code determining relays associated with the stations on the west end of the i system and another (ECDS) for the code determining relays associated with the stations on the east end of the system.

It will now be assumed that the operator desires to transmit controls to field station No. I on the west end of the system (Fig. 1). To do this he first positions the control levers associated with this station and then actuates the associated starting button. The actuation of the starting button effects the energization of the code determining relay associated with the desired station. This code determining relay is then stuck up over a circuit extending to conductor WCD of Fig. 2B of the present embodiment, which conductor is connected to (-I) through back contact I9 of relay LV and winding of relay WCDS.

In the event that the operator desires to transmit controls to field station No. 4 (Fig. 3) for example, he first positions the control levers associated with this station and then actuates the corresponding starting button. The results in the energization of the associated CD relay which is then stuck up by the energy which is applied to conductor ECD of Fig. 2B over a circuit extending to at back contact I9 of relay LV and winding of relay ECDS.

Assuming that controls are to be transmitted to a station on the west end of the system, the energization of the stick circuit for the CD relay associated with this station effects the picking up of the relay WCDS. As above mentioned the opening of back contact 33 of relay WCDS removes energy from conductor LC so that the pick up circuit of all CD relays is rendered ineffective. The picking up of relay WCDS also opens the east indication line l5 at back contact 20 so that a condition requiring the transmission of indications from an east station is ineffective to pick up relay MB which, as will be later pointed out, is the station start relay for the east end of the system.

In the event that relay ECDS is energized because controls are to be transmitted to an east station, the picking up of back contact 34 removes energy from conductor LC and the picking up of back contact 2| disconnects west indication line M from relay MF which, as will be later pointed out, is the station start relay for stations on the west end of the system.

Assuming that relay WCDS is picked up to initiate the system for transmitting controls to a west station, a circuit is closed for picking up relay SR extending from front contact 22 of relay WCDS, back contact 23 of relay SC, back contact 26 of relay ECDS and winding of relay SR, to Relay SR opens the east indication line circuit at back contact 24 to prevent energy which may be applied to this line circuit during the present cycle from being extended to the indication conditioning circuit which includes conductor 25.

In the event that relay ECDS is picked up to initiate a call to an east station, the picking up of back contact 26 of this relay opens the pick up and stick circuits of relay SR and when relay SC picks up its back contact 23 (to be later described), the pick up circuit of relay SR is further opened so that this relay cannot be energized when a call is initiated for a station on the east end of the system. This gives east stations the preference because both the pick up and stick circuits of relay SR, which when picked up selec'ts west stations, is opened by the picking up of relay ECDS which initiates calls to east stations.

From the above description it will be noted that relay SR is picked up when calls are to be transmitted to stations on the west end of the system and remains down when calls are to be transmitted to the east end of the system. With relay SR down the indication line conductor l4 extending to the west is open at front contact 24 and when relay SC picks up its back contact 3! this indication line conductor is completely isolated from the circuits in the control ofiice.

The picking up of relay SR closes a circuit for picking up relay C which extends from back contact 40 of relay SC, front contact 4| of relay WCDS, front contact 42 of relay SR, back contact 43 of relay ECDS and winding of relay C to In the event that the call is for an east station, the picking up of relay ECDS closes a pick up circuit for relay C extending from back contact 40 of relay SC, back contact 4| of relay WCDS, back contact 44 of relay SR, front contact 43 of relay ECDS and winding of relay C to Relay C closes a pick up circuit for relay OC extending from front contact 49 of relay C, back contact 53 of relay SB and winding of relay OC to The picking up of relay OC closes a circuit for picking up the selected code sending relay PC or NC extending from front contact 54 of relay 00, back contact 55 of relay E, front contact 56 of relay C, back contact 59 of relay 2V, back contact 69 of relay IV to channel IC and thence through the code jumper connection to the PC or NC relay as selected by this jumper. This picks up the PC or NC relay for energizing the west control line (with relay SR up) or for energizing the east control line (with relay SR down).

The selection of the PC bus for energizing the PC relay to apply a impulse to the selected control line circuit and the selection of the NC bus for energizing relay NC to apply a impulse to the selected control line circuit is not shown but may be accomplished in the manner disclosed in the above mentioned prior application, Ser. No. 640,062.

Polarity selection of impul'sea-When the system is initiated from the control office, resulting in the energization of relays C and OC and the energization of a code determining relay (such as one of the CD relays of the above mentioned prior application Ser. No. 640,062) the impulses placed upon the line circuit for the succeeding cycle are of polarities in accordance with the positions of the code jumpers and the control levers rendered effective by the picking up of the particular code determining relay.

As soon as the code determining relay is picked up, one or the other of the code sending relays PC and NC is energized depending on the position of the first code jumper. For example, if the first code jumper is in a first position, relay PC is energized but if it is in a second position relay NC is energized. Assuming that the code jumper is in a first position, relay PC is energized over a circuit extending from at front contact 54 of relay 00, which circuit was previously described.

The energization of relay PC results in the application of a. impulse to the west control line circuit (relay SR picked up) over a circuit extending from the terminal of battery CB, front contact 64 of relay PC, back contact of relay NC, winding of relay F, front contact 66 of relay SR, West control line conductor I I to the second field station, through the winding of relay F over control line conductor I I to the first field station, through the winding of relay F to the return line conductor I2 and thence to the control ofi'ice and the terminal of battery CB through back contact 61 of relay NC and front contact 68 of relay PC.

It will be apparent that a similar circuit may be traced for energizing line relays F and F of the third and fourth stations associated with the east end of the system in series with line relay F in the control ofiice when relay SR is deenergized and its back contact 66 closed.

It will be apparent that the energization of relay NC instead of relay PC, reverses the direction of current fiow in the control line circuit due to the reversed positions of

contacts

64, 65, 61, and 68. The energization of either the West or the east control line circuit with a impulse positions the contacts of line relays F (with suitable exponent) to the right, while the energization of either of these control line circuits with a impulse positions the contacts of these line relays to the left.

When the first impulse is placed upon the control line circuit the energization of relay F in the control ofiice closes a circuit for picking up relay IFP extending from front contact ID of relay F and winding of relay IFP to Relay 2F'P is now picked up over a circuit extending from front contact 'II of relay IFP and winding of relay 2FP to Relay SA is: picked up over a circuit extending from front contact I2 of relay F and winding of relay SA to The picking up of back contact 31 of relay SA removes energy from conductor LC so that no other code determining relay can be picked up until the system is restored to normal. When relay SA picks up, a stick circuit is closed for relay C extending from front contact 31 of relay SA, front contact 9 and winding of relay C, to

Relay SA closes a circuit for picking up relay SB extending from front contact I3 of relay SA and winding of relay SB to Relay SB closes a circuit for picking up relay SC extending from front contact 15 of relay SB and winding of relay SC to The picking up of back contact 11 of relay SC opens the circult of field control relay CF so that this relay is rendered ineffective during this cycle. When relay SB picks up, a stick circuit is closed for relay SR extending from front contact 19 of relay SB, back contact 26 of relay ECDS, front contact BI] and winding of relay SR, to

The application of the first impulse to the control line circuit is repeated by relay 2F? which causes relay VP to be picked up. The circuits for controlling the VP relays and the stepping relays are not shown but may be identical with the circuits for controlling these relays which are disclosed in the above mentioned prior application 640,062. In this connection it need only be pointed out that relay VP is picked up during the first energization of the line circuit dropped during the second energization of the line circult, picked up during the third energization of the line circuit, dropped during the fourth energization of the line circuit, etc. The stepping relays IV, 2V and LV are picked up during the time spaces between successive impulse periods, that is, relay IV is picked up during the time space following the first impulse, relay 2V is picked up during the time space following the second impulse, and relay LV is picked up during the time space following the third impulse.

It will be noted that the operation of the stepping relays shift the energizing circuits of the PC and NC relays from one code bus or control lever contact to another by the selection of

channel circuits

2C and 30 when relays W and 2V are picked up. This is accomplished during the time that the control line is deenergized because the stepping relays are picked up during the deenergized periods of the line circuit, so that the change in position of relays PC and NC is immaterial insofar as the then. existing condition of the line circuit is concerned. 1

Impulsing the control line circuit.--The initial application of the first impulse to the control line circuit results in the successive energization of relays F, IFP, ZFP, SA, SB, SC and VP as above pointed out. The energization of relay VP closes a circuit for picking up relay E which extends from front contact I8 of relay SC, through the stepping relay bank (as disclosed in the above mentioned prior application 640,062) and winding of relay E to The picking up of relay E deenergizes the PC or NC relay, whichever is picked up, by opening back contact 55. With both relays PC and NC dropped, the control line circuit is deenergized to mark the end of the first impulse period. This drops relays F, IFP and HP but since relay SA is sufficiently slow acting it maintains its contacts in picked up positions until the succeeding application of energy to the control line circuit.

When relay SB picks up its back contact 53 the energizingcircuit of relay 0C is interrupted, but

since this relay is slow acting it is not released during the interval of time before relay E is picked up to close a stick circuit for relay OC which extends from front contact II6 of relay E, front contact ill of relay 0C, front contact 53 of relay SB and winding of relay OC, to Relay 0C is sufficiently slow acting to remain in its picked up position during the intervals when relay E drops its front contact I I5.

The dropping of relay ZFP effects the picking up of relay IV which in turn deenergizes the circ'uit of relay E for again closing, at its back contact 55, the energizing circuit for the selected code sending relay PC or NC. The picking up of the selected code sending relay energizes the control line circuit to mark the beginning of the second impulse period.

Relays F, IFP and ZFP are picked up in se-- quence and relay VP is dropped. The dropping of relay VP effects the picking up of relay E which deenergizes, at its back contact 55, the selected PC or NC relay and the dropping of this particular code sending relay deenergizes the control line circuit to mark the end of the second imcuit for the selected code sending relay which.

picks up to again energize the control line circuit to mark the beginning of the third impulse period.

Relays F, IFP and ZFP are now picked up, after which relay VP picks up to cause the picking up of relay E which deenergizes, at its back contact 55, the circuit leading to the selected code sending relay. The code sending relay is now dropped to deenergize the line circuit which marks the end of the third impulse period.

Relays F, IFP and ZFP are now dropped and relay LV is picked up. Relay LV, however, does not control the release of relay E so that it remains picked up, which results in both code sending relays remaining down to deenergize the control line circuit for a comparatively long interval of time which results in dropping relays SA, SB and SC in sequence.

The picking up of back contact I9 of relay LV deenergizes the circuits of relays WCDS and ECDS, which circuits are the stick circuits for the code determining relays. This eifects the release of the particular code determining relay which was picked up to initiate this cycle and likewise releases relay WCDS or ECDS. The closure of

back contacts

31, 34 and 33 again applies energy to conductor LC so that another code determining relay can be picked up to initiate another cycle. The dropping of front contact 31 of relay SA deenergizes the stick circuit of relay C which results in the release of this relay.

The dropping of relay SB deenergizes the stick circuits of the stepping relay bank so that these relays are deenergized. The dropping of front contact 19 of relay SB, before the closure of back contact of relay SC, deenergizes the stick circuit of relay SR which allows this relay to release. Since front contact 49 of relay C is open, the dropping of contact 53 of relay SB deenergizes the circuit 'of relay OC which allows this relay to release. The dropping of front contact 18 of relay SC removes energy from the circuit extending to relay E.

Station selection for controls-The impulsing operation of the control line circuit and the stepby-step operation of the stepping relay bank in the control office may continue for as many steps as may be required for the chosen capacity of the system.

Similar step-by-step operation of the stepping relay bank at the field stations takes place in response to the impulsing of the control line circuit. Of course, the stepping relay banks at the stations on the west end of the system only are operated when controls are transmitted to this portion of the system and similarly the stepping relay banks at the stations connected to the east end of the system are only operated when controls are transmitted to this portion of the system. The stepping relay banks at the field stations preferably respond only when they have the possi- I bility of being selected for the reception of controls or when they are transmitting indications. In other words, operation of the stepping relay bank at a particular field station is made dependent upon station selection either for the reception of controls or for the transmission of indications.

Such optional features are immaterial to an understanding of the present invention and may be understood by reference to the abovementioned prior application Ser. No. 640,062. It is considered sufficient to know that the stepping relay bank at a field station operates as long as the station relay (relay SO disclosed in Ser. No. 640,062) remains picked upor the lockout relay LO (with suitable exponent) remains energized following the lockout period.

The manner in which a predetermined number of impulses of selected polarities are applied to the control line circuit to comprise a cycle of pulses are repeated by the line relay F (with suitable exponent) at each station, but for convenience in describing the operation at the field stations reference will be more particularly made to Fig. 3 which illustrates a typical station and which for convenience is considered to be the fourth station of the system.

The application of the first impulse to the east control line circuit causes the line and line repeating relays to be picked up, with the line relay actuating its polar contacts to either right or left-hand positions dependent upon the positive or negative character respectively of the impulse. If the first impulse of the code call placed upon the control line circuit is of one character, then part of the field stations will have their selecting relays (relay SO as disclosed in Ser. No. 640,062) picked up during the application of this impulse. If the first impulse of the code call placed upon the control line circuit is of the other character, the remaining field stations will have their selecting relays picked up during the application of this impulse. In other words, depending upon the code call transmitted only one or the other part of the field stations will have their station selecting relays energized at the beginning of a cycle of operations.

It will be understood that the present invention is also applicable to a system in which the station selecting relays at the stations are not operated on an indication cycle by using the con ditioning impulse to distinguish between an indication cycle and a control or duplex cycle. In such a system (disclosed in Judge application Ser. No. 613,353) the first or conditioning impulse ofeach control or duplex cycle is of a particular character for conditioning all stations for station selecting relay operation, while the conditioning impulse of each indication cycle is of another character which prevents the station selecting relay operation at all stations.

At those stations where the station selecting relays are picked up, the FP relays (with suitable exponents) follow the impulsing of the control line circuit until the station selecting relays drop out. Thus at only one station of the system will the FP relay (with suitable exponent) operate throughout the control cycle, since those station selecting relays which are picked up at the beginning of a cycle are selectively dropped out until only one remains, all of which is explained in detail in the above mentioned prior application.

It will be understood that the stepping relays at the field station operate in synchronism with those in the control ofiiceand that the polar impulses position line relay F for example, to the right or the left in response to or impulses respectively for making a selection through contacts of the stepping relays to jumper connections, which effect the operation of the station selecting relays in such a way that the desired station is selected. After the station is selected then the polar impulses are efiective to condition switch control, signal control or other circuits which are selected by the stepping relay bank at the station.

It is believed that sufilcient general information has been given with regard to the operation of the system in connection with the transmission of controls so that the specific operation with regard to the transmission of indications and the interlock between the opposite directions to prevent more than one field station from transmitting indications at the same time can be considered. In considering such detailed operation the functioning of the system with regard to the transmission of indications from a single field station will be given with more particular reference to the fourth field station illustrated in Fig. 3. Following such description the interlock between field stations which allows only one station for any one extension of the indication line circuit to transmit at the same time will be considered, after which the interlock between the opposite extensions of the indication line circuit will be explained.

Transmission of indicatioms.-The selection of field stations for outgoing controls and the transmission of controls to a selected station is accomplished, as briefly mentioned above, over the control line circuit, while the transmission of indications is accomplished over the indication line circuit following the proper registration of a particular field station in the control office.

It will be assumed that the system is in a condition of rest, from which it is automatically initiated when a train enters the detector track section associated with track switch TS This causes the deenergization of track relay T which in turn causes the release of change relay CH It will be understood that similar initiation of the system occurs when a train passes off the detector track section by picking up relay T since change relay CH is also released under this condition. It will also be understood that a large number of traffic governing devices may cause the release of change relay CH but for convenience the specific control of the change relay has been omitted.

The deenergization of relay CH closes a pickup circuit for lockout relay L extending from back contact 38 of relay FP back contact 29 of relay 83*, back contact 28 of relay SM,

upper winding of relay L0 and back contact 21 of relay CH to The response of relay L0 connects the. indication return line to the east indication line at front contact 32 which energizes the east indication line conductor and picks up relay MB in the control ofllce over a circuit extending from the terminal of indication battery 1B, lower winding of relay MB, back contact 28 of relay WCDS, back contact 8! of relay SC, conductor l5, back contact 38 of relay L0 conductor ll, front contact 32 of relay L0 back contact 39 of relay SE lower winding of relay L0 and conductor [6 to the terminal of battery IB.

In this connection it should be noted that relay MB functions as a station start relay for stations connected to the east end of the system. Relay MF functions as a station start relay for stations connected to the west end of the system, since the dropping of a change relay at a station connected to the west portion of the system (for example, the second field station) operates the associated lockout relay which closes a circuit for picking up relay MF extending from the terminal of battery IB, lower winding of relay MF, back contact 2! of relayECDS, back contact 3| of relay SC, conductor l4, front contact T4 of relay L0 back contact 15 of relay SE lower winding of relay L0 resistance R and conductor to the terminal of battery 13.

The picking up of either relay MB or relay MF opens the LC conductor at either contact 35 or contact 36 respectively so that no code determining relay can be picked up for initiating controls after this point of the cycle is reached. Since the LC conductor is open no energy can be connected to conductors ECD or WCD for picking up relay ECDS or WCDS during this cycle.

The response of relay MB in the control oifice closes a pick-up circuit for the field starting and cycle controlling relay CF which extends from (+),.front contact 82 of relay MB (or front contact 83 of relay MF if the cycle is initiated from the west end) back contact ll of relay SC and winding of relay CF to The picking up of relay CF prepares its stick circuit at front contact 84 and also closes an energizing circuit for relay 00 at front contact 85. Relay 0C closes a circuit for picking uprelay NC which extends from front contact 54 of relay OC, back contact 55 of relay E, back contact 56 of relay C, front contact 86 of relay CF, back contact 81 of relay ECDS, back contact 88 of relay WCDS and winding of relay NC to The energization of relay NC actuates its contacts 65 and 61 to thereby energize the east control line circuit with a negative impulse. The east control line circuit is energized because relay SR is not energized when relay MB is picked upso that back contact 65 is closed.

This circuit extends from the positive terminal of batteryCB, back contact 64 of relay PC, front contact 61 of relay NC, conductor I2, to the far end of the east line and thence back through the winding of relay F winding of relay F conductor I0 leading to the control office, back contact 56 of relay SR, winding of relay F, front contact 65 of relay NC and back contact 68 of relay PC to the terminal of battery CB. This energization of the east control line circuit causes the polar contacts of the line relays associated with east stations to be actuated to left-hand positions.

The energization of the line relays is repeated by their respective line repeating relays F? (with suitable exponent) which marks the end of the initiating period, after which no lockout relay LO (with suitable exponent) can be picked up since their pick-up circuits are open at back contacts of the line repeating relays similar to back contact 30 of relay FP".

However, during the lockout period, that is during the time subsequent to the picking up of the FP relays and prior to the response of the slow acting line repeating relays, the particular lockout relay nearest the control oflice on its respective extension of the indication line circuit is maintained energized over this line circuit as previously described. For example, subsequent to the picking up of relay FF and prior to the response of relay 8A lockout relay L0 is maintained energized over the indication line circuit including front contact 32 of relay L0 and back contact 39 of relay SB After relay 3A is picked up a stick circuit is closed for relay L0 from through front contacts 45 and 28 of relays L0 and SA respectively.

The'picking up of relay SA closes a circuit for picking up relay SE extending from front contact d6 of relay SA and winding of relay SE to With relay LO picked up a stick circuit is closed for relay SB extending through front contacts 4'! and 48 of relays L0 and SB respectively.

The picking up of relay SE connects the east indication line conductor l1 through front contact 32 of relay L0 and front contact 39 of relay SB to control contact 50 of relay FP from which point the indication line circuit is connected to the indication line return at front contacts 5| and 52 of relays PF and PB", but since relay PF is deenergized at this time the indication line circuit is open. Relay BB is energized but the circuit through its front contact 52 is open at this time at back contact 50 of relay FTP.

In the control office, the energizing circuit for relay MB is maintained through back contact 8| of relay SC until after the'response of relay SB at the field station so that relay MB is maintained energized over the indication line circuit by relays L0 and SB until after the response of relay SA in the control office. This insures that relay CF is maintained energized by reason of the closure of its stick circuit at its front contact 84 and front contact 37 of relay SA before its pick-up circuit is opened at back contact 71 of relay SC.

Following the response of relay SB to the first impulse on the control line circuit, relay VP is picked up in the manner explained in connection with a control cycle which causes relay E to be picked up. The picking up of relay E drops relay NC by opening back contact 55 as previously described in connection with a control cycle, which marks the end of the first impulse period. The de-energization of the control line circuit by the dropping of relay NC is repeated at the control office and at the east field stations by the FP relays (with suitable exponent) dropping.

The remaining impulses of the cycle are placed on the east control line circuit at time spaced intervals as previously described, it being understood that during an indication cycle alone the field starting and cycle controlling relay CF is picked up so that all of the control impulses of the cycle are negative in character.

It will be understood that in the event a station connected to the west end of the system initiates a call the apparatus at this station functions in a similar manner for energizing relay MF as previously described. The closure of front contact 89 of relay MF closes a pick-up circuit for relay SR which extends through back contacts I30, i3l and 23 of relays SA, MB and SC respectively. Relay SR is stuck up over a circuit extending from front contact 19 of relay SB, front contact 90 of relay SR, back contact 26 of relay ECDS and winding of relay SR. to This stick circuit is effective after relay SB picks up and a similar stick circuit is effective before the picking up of relay SB, extending from at back contact 80 of relay SC. This arrangement provides for de-energizing relay SE at the end of the cyclewhen relay SB opens its front contact 19 before relay SC closes its back contact 80.

During the first energized period of the control line circuit, relay SA is picked up to close a stick circuit for relay CF extending through front contacts 3'? and 8 of relays SA and CF respectively. If the system is initiated from the east end of the system by the picking up of relay MB, then when relay SB is picked up during the first energized period a stick circuit is closed for relay MB extending from front contact 9| of relay SB, front contact 92 of relay ZFP, front contact 93 and upper winding of relay MB, to

As will be later explained relay MB is conditioned during the first off period for registering indications over the back branch of the indication selecting circuit and in order to remove the control of MB from this stick circuit before this first conditioning period is effective, the dropping of relay 2FP opens the above described stick circuit at front contact 92 and since relay E is picked up during the deenergized period the stick circuit including back contact 94 of relay E is open. Relay MB is then made dependent upon the indication line circuit extending to the cast for the registration of indications.

In the event that the system is initiated from the west end of the system by the picking up of relay MF, this relay is deenergized during the first impulse period by the SB relay of the initiating station being picked up. For example, in the case above assumed, the pick-up circuit for relay MF extends through back contact 15 of relay SB When relay SB is picked up during the first impulse period the energizing circuit of relay MF is opened and since its stick circuit is open at back contact 92 of relay ZFP (this relay being picked up) and at front contact 94 of relay E (this relay being down) the MF relay is dropped. Since the pick up of relay E is delayed during the first impulse period until relay SC is picked up, this causes relay MF to be deenergized when relay SE at the initiating station is picked up because this latter relay will be picked up before relay SC in the control oflice.

Consideration will now be given to the manner in which impulsing relays PB and PF are positioned at the transmitting field station for governing the indication line circuit. In this connection it will be understood that similar PB and PF relays at other stations on the east end of the system function in a similar manner.

. Also if the system is initiated from the west end,

then the PB and PF relays associated with the initiating station on this end of the system operate in a similar manner, except in this case the West indication line M is impulsed instead of the east indication line 95. This is due to the fact that relay SR. has its back contact 24 closed when the east station is transmitting and its front contact 24 is closed when a West station is transmitting.

During the first energized period of the control line circuit, impulsing relay PB is positioned in accordance with the code juniper 51 at the field station. If code jumper 57 is in a contacting position relay PR is energized but if code jumper 5'! is in an open position the circuit extending to through this juniper is open so that relay BB is left deenergized. For example, with code jumper 5i in a closed position a circuit is completed for picking up relay PB which extends from jumper 5?, back contact 95 of relay 1V back contact 83 of relay 2V front contact 65 of relay FP Winding of relay PB and front contact iii of relay L0 to With relay PB picked up by reason of the above described circuit, it is maintained energized during the following deenergized period of the control line circuit by reason of a stick circuit which extends from (-1-), front contact 62 of relay PB back contact 60 of relay F1 winding of relay PB and front contact 6| of relay L0 to In the event that relay PB is left deenergized during the first energized period of the control line circuit, it remains deenergized during the following deenergized period of the control line circuit because its stick circuit is not complete. It is to be noted that the control of relay PB is shifted from its pick-up circuit to its stick circuit without interruption because of make-before-break contact 60.

In a similar manner relay PB is positioned on each energized period of the control line circuit in accordance with its respective code jumper or indication contact for that period as selected by the stepping relays, with each condition thus established during the energized period being m-aintained for the deenergized period immediately following.

For example, during the first deenergized period of the control line circuit the first stepping relay IV is picked up so that during the second energized period of the control line circuit relay PB is positioned in accordance with the energized or deenergized position of track relay T. If re1ay T is energized then relay P13 is left deenergized but if relay T is deenergized relay PB is energized over a circuit extending from back contact 63 of relay T 7 front contact of relay IV, back contact 96 of relay 2V front contact 6% of relay FP winding of relay P13 and front contact 6| of relay L0 to If relay PB is not picked up it remains deenergized during the following deenergized period (second) of the line circuit but if it is picked up during the second energized period then it is maintained energized during the following deenergized period (second) of the line circuit by reason of its stick circuit.

Similar control is provided for relay PF with the exception that it is positioned during the deenergized periods of the control line circuit and the positions thus established are maintained during their immediately following energized periods of the control line circuit.

For example, during the first deenergized period of the control line circuit following the first energized period (during which relay VP is picked up), re1ay FF is positioned in accordance with the open or closed position of jumper 53. If jumper '58 is in an open position, then relay FF is deenergized, but if jumper 58 is in a closed position, relay PF is energized over a circuit extending from jumper 58, back contact I25 of relay 2V front contact !22 of relay VP back contact I23 of relay F1 winding of relay PF and front contact 6! of relay L0 to If relay PF is not picked up it remains deenergized during the following energized period of the line circuit, but if it is picked. up then it is maintained energized during the following energized period of the line circuit by reason of its stick circuit extending from front contact I24 of relay PF front contact I23 of relay FP, winding of relay PF and front contact 6! of relay L0 to As pointed out above, impulsing relays PB and PF are ineffective to govern the indication line circuit during the first energized period of the control line circuit. This is because relay FP is picked up routing the indication line circuit through contact 5! of relay PF but this contact cannot be closed nor is relay PF positioned in accordance with any code jumper until the first deenergized period.

Thus relay MF in the control ofiice is not positioned during the first energized period of the control line circuit for the reception of indica tions. It will be recalled that this relay acts as a station start relay for the west end of the system and although it may be picked up during the first energized period of the control line circuit it is .not effective to executeindications during this period. However, relay P33 is being positioned during the first energized pe'iod so as to be effective to govern the indication line circuit during the first deenergized condition of the control line circuit and thereby position message receiving relay MB.

For example, if relay PB is deenergized relay MB remains deenergized but if relay BB is picked up by reason of the closed position of code jumper 51, then. relay MB is energized over a circuit extending from the terminal of battery IB, lower winding of relay MB, back contact 9'! of relay PC, back contact 98 of relay NC, back contact 99 of relay IFP, back contact lei! of relay 25?, front contact in! of relay SC, front contact 102 of relay SA, back contact 2 3 of relay SR, conductor 15, back contact 38 of relay L0 conductor ll, front contact 32 of relay L0 front contact 39 of relay 8B back contact eliof relay FP front contact 52 of relay PB and conductor iii to the terminal of battery 113.

If r-elay MB is not picked up during the first deenergized period of the control line. circuit (after relay ZFP opens its front contact 92 in the event that relay lVIB was picked up to start the system from an east station) then it remains deenergized during the following energized period (second) of the control line circuit. 'If r..- lay MB is picked up on the first deenergized period of the control line circuit (after the above described stick circuit through front contact 92 of relay 2F? is opened) then it is maintained energized during the second energized period of the control line circuit by reason of a stick circuit extending from front contact 9i of relay SB, back contact 94 of relay E, front contact 93 and upper winding of relay MB, to This stick circuit is closed prior to the picking up of the code sending relay PC or NC and the resulting opening of the governing circuit for relay MB at back contact 97 or back contact 98.

Upon the energization of relay ZFP a multiple stick circuit is closed from front contact SI of relay SB, front contact 92 of reiay ZFP, front contact 93 and upper winding of relay MB, to In other words, a stick circuit for relay MB is initially closed by back contact 3 of relay E and is finally opened by front contact 92 of relay 2FP. This insures that relay MB is held energized during the proper time periods. It will be apparent that re1ay MB may be positioned on each deenergized period of the control line circuit and will be maintained in such position through the following energized period of the control line circuit.

During each energize-d period of the control line circuit (beginning with the second) the p0 sition of relay MB, as determined by the indication message received, is executed or stored by reason of the closure of front contact H13 of relay IFP. During this second energized period channel MF extends from (18+) at front mm of the control line circuit the position of relay tact I01 of relay MB. This gives a selection of MB is executed to a suitable pilot relay (not two indications of the front branch and as above shown) it being assumed that this is accompointed out two indications are made up on the plished in the usual way. After a prescribed back branch. number of registration steps have been taken a It is not believed necessary to point out in station registering relay is picked up, after which detail the conditioning circuits for the PB and the various indications are executed. PF relays during other periods of the cycle, since For example, if track relay T is energized, then these circuits are immaterial to an understandrelay PB will be left deenergized on the second ing of the present invention and since they may energized period and the second deenergized pebe exactly the same as disclosed in the above riod of the control line circuit so that relay lvfl3 mentioned prior application Ser. No. 640,062. The is left deenergized on the second deenergized pepick-up circuit for relay MP is completed only riod and the third energized period. Then durwhen one or the other of the relays PC and NC ing the third energized period, potential is is picked up. For example, if relay NC is down applied to the indication storing relay over a cirits front contact H2 is open and if relay PC is cuit extending from (B), back contact I04 of down its front contact H3 is open which interrelay MB, front contact I03 of relay I FP, front rupts the circuit extending to the lower winding contact I05 of relay CF, front contact I06 of of relay MF. If both these relays are picked up, relay 2V and indication channel M3 which then back contacts II 2 and H3 are open which leads through a front contact of the station relikewise interrupts the circuit leading to the lay to the proper indication storing relay. It will pick-up winding of relay MF. With relay NC be apparent that if track relay T is deenergized down and relay PC up, then the circuit is comthen relays PB and MB will be picked up durpleted through back contact H2 and front coning their respective periods so that the above tact II 3. With relay PC down and relay NC up, 5 traced circuit to channel M3 is completed from the circuit is completed through back contact (B+) at front contact I04 of relay lVl'B. H3 and front contact H2. This conditioning It will be understood that relay MP is similarly circuit for relay MF extends through front conpositioned during each energized period of the tacts I00 and H4 of relays HP and IFP respeccontrol line circuit, beginning with the second, tively because the MFrelay is conditioned during in accordance with the position of relay PF and the energized periods when these contacts are that such positions will be maintained through closed. The conditioning circuit for relay MB the immediately following deenergized period, at extends through back contacts I00 and 99 of which time the messages then stored will be exrelays ZFP and IFP respectively since relay MB ecuted tothe indication storing relays or pilot is conditioned during the deenergized periods of relays as the case may be. the control line circuit.

Further operation of the system for the trans- Interlock between field stations.It will be obmission of indications may be understood by vious that when the third and fourth field staanalogy to the description already given or the tions have indications ready to transmit at the disclosure in the above mentioned prior applicasame time, relays L0 and LO will be picked up tion Serial No. 640,062. at the same time. However, the east indication After the last impulse has been applied to the line conductor I5 is routed through the lower control line circuit and then removed, the slow winding o e ay 0 by front contact 38 in such acting relays drop away as previously explained a case, which prevents the energization of relay for the end of a cycle of operations. The stick L0 over the indication line conductor Il during circuit for relay L0 is opened by reason of the the lookout period after its pick-up circuit is opening of front contact 28 of relay SA. The opened by back contact 30 of relay FP In dropping of relay LO opens, at front contact 41, other words, during the lookout periods preferthe stick circuit of relay SE and the field staence is given to that station nearest the control tion is returned to its normal condition. During ofiice having its lockout relay LO (with suitable the cycle of operations (after relay L0 is seexponent) picked up. The same is true in conlected) change relay CH is returned to its nornection with stations associated with the west mal energized condition through suitable means end of the Systemnot hown in the above men staTt from west ends-It is Considered tioned application unnecessary to describe the detailed operation of In the control omce the relays are returned to the system when initiated for the transmission of indications from a west field station, but it normal condltlons as prevlously mentioned re is believed sufficient to merely point out the dif- P CF bemg deenerglzed by reason of the Open ference in the operation in the control oifice for mg of from] Fontact of relay accomplishing such initiation before considering The condltlon of relay W for the first the condition where a field station on both ends cation registered on this relay is executed during of a System endeavor to transmit at the same the deenergized period of the control line circuit time.

following the second ene ed p i d- For example, the energization of a lookout relay ample, if relay MB is down during this period, LO (with suitable exponent) on the west end due to the fact that relay PF was deenergized establishes a closed indication line circuit similar during the second energized period of the control to that explained for the picking up of lockout line circuit, then a circuit is completed to the relay L0 with the exception that the closure of channel conductor MF which extends from the west indication line circuit picks up relay ME (B), back contact I01 of relay MF, back conwhich energizes the direction selecting relay SR. tact I08 of relay IFP, front contact I09 of relay The picking up of relay SR switches the con- CF, back contact H0 of relay VP and front control and indication line circuits of the west end tact III of relay IV to channel conductor MB. of the system on to the circuits extending to the In the event that relay MF is picked up during control and indication batteries in the control the above mentioned periods then the circuit to office. The picking up of relay MIF' effects the energization of the field starting relay CF in a manner previously pointed out.

It will be noted that the response of relay SR in shifting contact 24, disconnects the east indication line conductor l5 and connects the west indication line conductor M to the control ofilce circuits. It will also be noted that the pick-up circuit for relay SR is disconnected from the circuit leading to contact Bil of relay MF upon the response of relay SC by reason of the open back contact 23. Also the energizing circuit for relay MB is maintained open until relay SC is picked up to close its front contact IEH by reason of open back contact 2d of relay SR.

It is believed that further operation will be readily apparent since the indication impulses are transmitted over the west indication line conductor It in a similar manner to that explained for the east indication line conductor l5.

Interlock between east and west ends-It will now be assumed that lockout relays L and L0 are picked up at the same time. Under such conditions the pick-up circuit for relay MB is closed over the east indication line conductor it as above pointed out. This circuit includes back contact 8! of relay SC while at the same time the pick-up circuit for relay MP is closed over the west indication line conductor Hi including back contact 31 of relay SC.

The closure of front contact 39 of relay MF causes relay SE to be picked up and upon the response of relay SR its previously described stick circuit is closed. Now when relay SC is picked up a little later in the cycle, the pick-up circuit of relay MB is opened at back contact 8! and since back contact 2 3- of relay SR is now open, conductor I5 is disconnected from all circuits in the office.

Relay lVl'B remains stuck up however until the first de-energized period over a circuit extending from front contact 95 of relay SB, front contact 92 of relay ZFP, iront contact 93 and upper winding of relay MB, to When relay ZFP is dropped during the first ole-energized period, this stick circuit is interrupted at open front contact 8'2 and relay MB is released. Relay MF is stuck up after relay SE is picked up over a circuit extending from front contact 9! of relay SE, back contact 92 of relay EFF, front contact H5 and upper winding of relay ME, to

After relay 2F? is picked up, relay MF remains up until the SE relay at the initiating station on the west end of the system is picked up as previously pointed out. Relay MB is then dropped but since relay SR is picked up and stuck up by this time the system is controlled by the station on the west end of the system to the exclusion of the station on the east end of the system. In other words, preference is given to a west station when simultaneous calls are initiated on both ends of the system for the transmission of indications.

Since relay CF is picked up when the station is initiated from either end of the system it will be apparent that the operations above pointed out will now take place in the control oilice and at the second field station. If two or more lockout relays are picked up at the same time, only the lockout relay nearest the control ofiice on that particular extension which has been given preference will be maintained during the lookout period as has been previously described. In other words, that particularly indication line which is connected to the control ofice by reason of its preference receives energy to select a lockout relay during the lockout period. All other lockout relays are dropped out.

Summary A system has been thus shown and described which is of the coded duplex type provided with a control line circuit extending in a plurality of directions from the control office which may be selected in accordance with the direction from the control ofiice in which a station is located for the transmission of controls. An indication line circuit has been disclosed which employs the lookout method of providing superiority between stations for the transmission of indications and a direction selecting arrangement which provides superiority between the different divisions of the system connected to the control office. The present invention provides a system of this character in which the control office may be located at an intermediate point in the system without in any way preventing the usual functioning of the lockout operation between stations.

The control office may be located at any intermediate point since it is immaterial insofar as.

the preference between the two extensions of the two systems is concerned, such preference being determined before the preference between the stations is established. The indication line circuit employs compensating resistors at the field stations to fix the proper degree of line current in the indication line circuit in accordance with the distance that these stations are located from the control oflice.

This method of locating a control office in the center of a geographic lookout on the line circuit may be adapted to any type of system and still be within the scope of the present invention, it being understood that it is disclosed as applied to the type of system shown in the above-rnentioned prior application Ser. No. 640,062 only for the purpose of explanation and it should be understood that this in no way limits the use of the present invention toa duplex type of system or to a system providing the double capacity transmission of indications.

It should be noted in connection with the registration of stations in the control ofiice that a number of station codes are employed equal to-half the total number of field stations of the system. This is because the stations connected to the west end of the system can have their code calls duplicated by the stations connected to the east end of the system because these two ends are selected in accordance with the station desired. In other words, each field station on the west end of the system is given a distinctive code call and each field station on the east end of the system is given a distinctive code call, with no consideration being given to the duplication on one end of the system of the code calls of the other end. The specific code calls which may be assigned and the particular manner in which they are arranged has not been disclosed in detail in the present disclosure, it being understood that code systems are well known to those skilled in the art and have been explained and disclosed in various other prior applications.

It might be well to point out that a control start for a station on the east line rules out a simultaneous indication start from a station on the west line and a control start for a station on the west line rules out a simultaneous indication start from a station on the east line. In the first case, the picking up of relay ECDS opens (at back contact 2|) the circuit for west start relay MF and in the second case, the picking up of relay WCDS opens (at back contact 20) the circuit for east start relay MB.

It will be understood that a simultaneous start condition for sending controls to a station on the same end of the system having indications to transmit, effect the duplex operation of the system in a manner fully described in Ser. No. 640,062.

Having thus shown and described a centralized trafiic controlling system as one specific embodiment of the present invention, it is desired to be understood that this form is selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume and it is further to be understood that various modifications, adaptations and alterations may be applied to the specific form shown to meet the requirements of practice without in any manner departing from the spirit or scope of the present invention except as limited by the appended claims.

What I claim is:

1. In a remote control system, a control ofiice, a plurality of field stations divided into groups, a first control line circuit connecting said oflice with a first group, a second control line circuit connecting said oilice with a second group, a first indication line circuit connecting said ofiice with said first group, a second indication line circuit connecting said office with said second group, a single transmitter in said oflice, means operable to cause said transmitter to selectively apply series of impulses to a particular one of said control line circuits in response to the energization of the corresponding one of said indication line circuits, control line circuit repeating relays at the ofiice and at each station marking the end of an initiating period upon repeating the first impulse of a series, slow acting control line circuit repeating relays at the office and at each station marking the end of the lockout period upon repeating the first impulse of a series, means in said ofiice efiective during said initiating period to determine which indication line circuit is to be employed, means at each of said field stations efiective during said lockout period to select a particular field station on a particular indication line circuit which is selected during said initiating period, and means at each station governed by impulses on the control line circuit when that station is selected to transmit indications during said series of impulses on said control line circuit over its said indication line circuit.

2. In a remote control system, a control ofiice, a plurality of field stations divided into groups, a first control line circuit connecting said office with a first group, a second control line circuit connecting said ofiice with a second group, a first indication line circuit connecting said ofiice with said first group, a second indication line circuit connecting said office with said second group, a single transmitter in said oflice, means operable to cause said transmitter to selectively apply series of impulses to a particular one of said control line circuits in response to the energization of the corresponding one of said indication line circuits, a control line circuit repeating relay at the office and at each station marking the end of an initiating period upon repeating the first impulse of a series, a slow acting control line circuit repeating relay at the omce and at each station marking the end of the lockout period upon repeating the first impulse of a series, means in said control ofiice effective during said initiating period to automatically determine which indication line circuit is to be selected, means at each field station efiective when that particular station has indications to transmit for energizing its indication line circuit to the end of said lockout period, means at each field station effective during said lockout period to select a particular field station on a particular indication line circuit which is selected during said initiating period, and means at each field station governed by impulses on its control line circuit and rendered efiectlve when that particular station is selected for transmitting indications over its indication line circuit whereby only one station is in communication with said ofiice over an indication line circuit during any one series of impulses on the corresponding one of said control line circuits.

3. In a remote control system, a control office, a plurality of field stations divided into groups, a' first control line circuit connecting said oflice with a first group, a second control line circuit connecting said office with a second group, a first indication line circuit connecting said office with said first group, a second indication line circuit connecting said oflice with said second group, a single transmitter in said ofiice, means operable to cause said transmitter to selectively apply series of impulses to a particular one of said control line circuits in response to the energization of the corresponding one of said indication line circuits, a control line circuit repeating relay at the ofiice and at each station marking the end of an initiating period upon repeating the first impulse of a series, a slow acting control line circuit repeating relay at the ofiice and at each station marking the end of the lookout period upon repeating the first impulse of a series, indication registering means in said control ofiice, means in said control oilice responsive to the initial energization of each of said indication line circuits for connecting that particular indication line circuit to said indication registering means, said means being efiective to give priority to a particular one of said line circuits in the event of simultaneous initial energization of said indication line circuits, means at each field station eifective during said lockout period to select a particular field station on a particular line circuit which is selected during said initiating period, and means at each station rendered eifective only at the selected station to transmit indications over its said indication line circuit and governed by said series of impulses on its corresponding said control line circuit.

4. In a remote control system, a control oflice, a field station connected to said ofiice by a stepping line circuit and an indication line circuit, another field station connected to said oilice by another stepping line circuit and another indication line circuit, impulsing means in said ofiice for impressing a series of time spaced impulses on either of said stepping line circuits, line selecting means in said office for selectively associating said impulsing means with said stepping and said indication circuits or said another stepping and said another indication line circuits, .a line repeating relay at each field station for repeating impulses on its stepping line circuit, step-by-step means at each field station operated by said line repeating relay at that station, two code transmitting relays at each field station selectively conditioned in accordance with indications to be transmitted on each step of its said step-by-step means, means at each field station controlled by said line repeating relay at that station for causing one of said code transmitting relays to selectively energize its said indication line circuit during an impulse period on its stepping circuit and to cause the other of said code transmitting relays to selectively energize its said indication line circuit during time space on its said stepping circuit, and means controlled over said indication line circuits for causing said line selecting means to select the stepping and indication line circuits for the first field station having indications ready to transmit.

5. In a remote control system, a control olfice, a field station connected to said ofiice by a stepping line circuit and an indication line circuit, another field station connected to said ofiice by another stepping line circuit and another indication line circuit, impulsing means in said ofilce for impressing a series of time spaced impulses on either of said stepping line circuits, means in said ofiice for selectively determining the character of each of the impulses impressed by said impulsing means when manually conditioned, line selecting means in said ofifice for selectively associating said impulsing means withsaid stepping and said indication circuits or said another stepping and said another indication line circuits, a line repeating relay at each field station for repeating impulses on its stepping line circuit, step-by-step means at each field station operated by said line repeating relay at that station, two code transmitting relays at each field station selectively conditioned in accordance with indications to be transmitted on each step of its said step-b-y-step means, means at each field station controlled by said line repeating relay at that station for causing one of said code transmitting relays to selectively energize its said indication line circuit during an impulse period on its stepping circuit and to cause the other of said code transmitting relays to selectively energize its said indication line circuit during a time space on its said stepping circuit, means at each of said field stations selectively controlled on each step of its said step-bystep means in accordance with the character of the impulses impressed on its said stepping circuit. means at the control office selectively responsive to the condition on each step of its said stepby-step means of that particular one of said indication line circuits associated with said control office by said line selecting means, and means causing said line selecting means to select those stepping and indication line circuits for the field station having indications ready to transmit or for the field station having controls manually conditioned in the central office.

6. In a remote control system, a control office, a first field station connected to said control oflice by a first stepping line circuit and a first indication line circuit, a second field station connected to said control office by a second line circu t and a second indication line circuit, a normally at rest impulsing means in said control ofiice for impressing a series of positive and/or negative impulses on said first and second stepping line circuits only one at a time. step-by-step means at said control ofiice caused to take one step for each impulse of any series, manually governahle means at said control ofiice for" selectively determining the positive or negative character of each impulse of every series when said impulsing means is initiated from said control ofiice, step-by-step means at each of said field stations caused to take one step for each impulse on its respective stepping line circuit, means at each field station effective on each step of said step-by-step means at that station to distinctively condition its respective indication line circuit in accordance with indications to be transmitted when a change in such indication conditions occurs, indication receiving means in said control ofiice governed on each step of said step-by-step in said control office when connected to a particular one of said indication line circuits, line selecting means in said oflice for selectively connecting said impulsing means and said indication receiving means to said first stepping line circuit and said first indication line circuit respectively when a change in indication conditions occurs: or connecting said impulsing means and said indication receiving means to said second stepping line circuit and said second indication line circuit respectively when a change occurs at said second station, and manually operab-le means for causing said line selecting means to selectively connect said impulsing means to said first stepping line circuit and said indication receiving means to said first indication line circuit or connecting said impulsing means to said second stepping line circuit and said indication receiving means to said second indication line circuit irrespective of a change in the indication,

conditions at either the first or the second field I stations,

7. In a remote control system; two line circuits, each connecting a separate field station with a control oflice; a single code transmitter normally at rest; and means for initiating and connecting said transmitter with one or the other of said two line circuits comprising, a selector relay which connects said transmitter to one line circuit when deenergized and connects said transmitter to the other line circuit when energized, two neutral relays each respectively associated with one of said two line circuits and at times picked up automatically to initiate said transmitter into operation, a pick up circuit for said selector relay including a front contact of one of said two neutral relays and a back contact of the other, said pick up circuit being capable of being closed only when said transmitter is at rest, manually operable means for energizing said pick up circuit and initiating said transmitter into operation, and manually operable means for opening said pick up circuit and initiating said transmitter into operation.

8. In a remote control system; two line circuits,

each connecting a separate field station with a control office; a single code transmitter normally at rest; and means for initiating and connecting said transmitter with one or the other of said two line circuits comprising, a selector relay which connects said transmitter to one line circuit when deenergized and connects said transmitter to the other line circuit when energized, two neutral relays each respectively associated with one of said two line circuits and picked up automatically to initiate said transmitter into operation, a pick up circuit for said selector relay including a front contact of one of said two neutral relays and a back contact of the other, said pick up circuit being capable of being closed only when said transmitter is at rest, manually operable means for energizing said pick up circuit and initiating said transmitter into operation, a stick circuit for said selector relay including contact means closed whenever said transmitter is at rest or is in operation but momentarily opened at the end of each operation, and manually operable means for opening said pick up and stick circuits and initiating said transmitter into operation.

9. In a remote control system; a control ofi'ice; two groups of stations; a first control line circuit and a second control line circuit connecting corresponding groups of stations to said office; stepby-step code transmitting means in said ofiice for impressing series of distinctive control impulses on said control line circuits; manually controllable means in said ofiice for selectively determining the character of the impulses of each series transmitted by said transmitting means; means at each field station responsive to the distinctive control impulses on its respective control line circuit; a first indication line circuit conmeeting said ofiice with said first group of said v stations; a second indication line circuit connecting said omce with said second group of stations; step-by-step code transmitting means at each of said stations for transmitting distinctive irnpulses over said indication line circuit connecting that station with said central ofiice and rendered effective by the impulses transmitted over said control line circuit for its group of stations, whereby the code transmitting means at the OffiC and at any particular station in a, group are maintained in synchronism; code receiving means in said ofiice responsive to said distinctive indication impulses received over said indication line circuits; a group selecting device for selectively associating said ofiice code transmitting means and code receiving means with said first control and indication line circuits or said second control and indication line circuits; means responsive to said manually controllable means for selectively operating said group selecting device and initiating transmission of a series of distinctive control impulses over the selected control line circuit, and means automatically controlled over each of said indication line circuits for selectively operating said group selecting device and initiating transmission of a series of distinctive control impulses over the selected control line circuit correspond ing to that indication line circuit over which the automatic control was received.

10. In a remote control system; a control oflice; two groups of stations; a first control line circuit and a second control line circuit connecting corresponding groups of stations to said office; stepby-step code transmitting means in said ofiice for impressing series of distinctive control impulses on said control line circuits; manually controllable means in said office for selectively determining the character of the impulses of each series transmitted by said transmitting means; means at each field station responsive to the distinctive control impulses on its respective control line circuit; a first indication line circuit connecting said oflice with said first group of said stations; a second indication line circuit connecting said office with said second group of stations; step-by-step code transmitting means at each of said stations for transmitting distinctive impulses over said indication line circuit connecting that station with said central ofiice and rendered efiective by the impulses transmitted over said control line circuit for its group of stations, whereby the code transmitting means at the ofiice and at any particular station in a group are maintained in synchronism; code receiving means in said oihce responsive to said distinctive indication impulses received over said indication line circuits; a group selecting device for selectively associating said ofiice code transmitting means and code receiving means with said first control and indication line circuits or said second control and indication line circuits; means responsive to said manually controllable means for selectively operating said group selecting device and initiating transmission of a series of distinctive control impulses over the selected control line circuit, said means giving a predetermined priority between said two groups of stations; and means automatically controlled over said indication line circuits for selectively operating said group selecting device and initiating the transmission of a series of distinctive control impulses over the selected control line circuit corresponding to that indication line circuit over which the automatic control was received, said means giving a predetermined priority between said two groups of stations.

11. In a remote control system; a control oflice; two groups of stations; a first control line circuit and a second control line circuit connecting corresponding groups of stations to said oifice; step-by-step code transmitting means in said ofiice for impressing series of distinctive control impulses on said control line circuits; manually controllable means in said ofiice for selectively determining the character. of the impulses of each series transmitted by said transmitting means; means at each field station responsive to the distinctive control impulses on its respective control line circuit; a first indication line circuit connecting said office with said first group of said stations; a second indication line circuit connecting said ofi'ice with said second group of stations; step-by-step code transmitting means at each of said stations for transmitting distinctive impulses over said indication line circuit connecting that station with said central ofiice and rendered effective by the impulses transmitted over said control line circuit for its group of stations, whereby the code transmitting means at the ofiice and at any particular station in a group are maintained in synchronism; code receiving means in said ofiice responsive to said distinctive indication impulses received over said indication line circuits; a group selecting device for selectively associating said office with said first control and indication line circuits, or said second control and indication line circuits comprising, a selector relay which connects said office code transmitter to said first control line circuit when deenergized and to said second control line circuit when energized, and which connects said office code receiving means to said first indication line circuit when deenergized and to said second indication line circuit when energized, two neutral control relays each respectively associated with one of said two control line circuits and at times manually picked up to initiate said ofiice code transmitter into operation, two neutral indication relays each respectively associated with one of said two indication line circuits and at times automatically picked up over said indication line circuits to automatically initiate said oflice code transmitter into operation, a pick up circuit for said selector relay including a front contact of one of said two neutral indication relays, a back contact of the other of said two neutral indication relays, and a back contact of one of said two neutral control relays,, said pick up circuit being capable of being closed only when said code transmitter is at rest, and a pick up circuit for said selector relay including