US2090912A

US2090912A - Centralized traffic controlling system for railroads

Info

Publication number: US2090912A
Application number: US11090A
Authority: US
Inventors: William D Hailes; Robert M Phinney
Original assignee: General Railway Signal Co
Current assignee: SPX Corp
Priority date: 1935-03-14
Filing date: 1935-03-14
Publication date: 1937-08-24
Anticipated expiration: 1954-08-24

Description

Aug. 24, 1937. w. D. HAILES 'ET AL 2,090,912

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS I Filed March 14, 1955 4 Sheets-Sheet 1 INVENTORS WDHaHes and PMPhinney BY KM THEIPATTORNEY i 5 U2 3 e.

Aug. 24, 1937. w, D, HAILES ET AL 2,090,912

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed March 14, 1935 4 Sheets-Sheet 2 Circuifs H 9 LL i 14 F INVENTORS WDHailes and RM'Phinney' t BY 7 THEIR ATTORNEY 1937- w. D. HAILES ET AL 2,090,912

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS 4 Sheets-Sheet 5" Filed March 14, 1935 INVENTORS WDHailes and RMPhinne MM THEIR ATTOR NEY Au .'24,1937. w. D. HAILES ETAL 2,090,912

CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Filed March 14, 1955 4 Sheets-Sheet 4 INVENTORS v WDHailes and QMPhinney THEIR ATTORNEY Patented Aug. 24, I937 UNlTE@ STATES PATENT OFFIE CENTRALIZED TRAFFIC CONTROLLING SYSTEM FOR RAILROADS Appiication March 14, 1935, Serial No. 11,090

. 16 Claims.

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

The present invention contemplates a centralized trafiic controlling system in which communication is established between a central control ofiice 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 office 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 office and the transmission of indications from the registered station. The control line circuit and the indication line circuit are so in terrelated 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, lockout means are provided at each station so that only one station may transmit its code call and its indications during any one particular cycle of operations. Suitable means are provided to restore apparatus inthe control office and at the field stations to normal conditions as soon as a cycle of operations has been completed.

For the transmission of controls the impulses placed upon the control line circuit are of selected polarities. The apparatus at the control oihce and at each field station is operated through a cycle of operations (with exceptions hereinafter described) for each series irrespective of the character of the impulses of the series, while the character of the impulses of each series determines the particular station selected for that cycle and the controls transmitted to the selected station.

For the transmission of indications the impulses applied to the indication line circuit set up distinctive conditions by reason of their presence or absence on the steps of each cycle, which steps are marked off by the impulses placed upon the control line circuit. Since the operation of the present embodiment with respect to the transmission of indications is immaterial for an understanding of the present invention this portion of the communication system is omitted in order that the drawings and descrip- 5 tion may be made as simple as possible. A portion of the indication line circuit is shown in the drawingsin order to provide a means for indicating how the system is initiated from the field station when new'indications are ready for 10 transmission and when the system is to be initiated for the purpose of rechecking indications. The recheck feature forms an important part of the presentinvention, which feature will be explained in detail. 15

Another feature of the present invention relates to the provision of a special maintainers calling signal which may be a visual signal, an audible signal or the like, so controlled'that it responds to a deliberate over-step of the step by-step mechanism at the field station, which 20 over-step is governed from the control office by the operation of a maintainers call button.

The recheck feature above mentioned is provided by means of an under-step of the step-bystep mechanism at the field station initiating an 25 indication cycle in response to the actuation of a recheck button in the control office.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings and 30 in part pointed out as-the description of the invention 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 or by reason of preceding numerals representative of the order of their operation and in which:'

Figs. 1A and 1B illustrate the apparatus and circuit arrangement provided for the control office constructed and arranged in accordance with the present invention.

Figs. 2A and 2B illustrate the apparatus employed at a typical field station arranged in accordance with the present invention.

In tracing the detailed circuits of the present disclosure Fig. 1A should be placed above Fig. 1B, Fig. 2A should be placed above Fig. 2B and Fig. 2A should be placed to the right of Fig. 1A, with correspondingly numbered lines in alignment. 55

flO

For the purpose of simplifying the illustrations and facilitating in the explanation the 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. For example, the various relays and their contacts are illustrated in a conventional manner and symbols are used to indicate connections to the terminals of batteries 7 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 fiowing from to While the features of the present invention are applicable to and usable with many types of communication system for centralized traffic control, the specific embodiment of the invention illustrated has been shown in a form adapted for use with a selective communication system of the coded duplex type such as shown and described in the pending application of T. J. Judge, et al., Ser. No. 640,062, filed October 28, 1932. Before considering the structure and mode of operation of the parts constituting this invention a general explanation will be given of some of the features of a centralized traflic controlling system of this particular coded duplex type insofar as is material to an understanding of the present invention, it being understood that various other details of the structure and operation of the complete system not directly related to the features of this invention may be as shown and described in the above mentioned pending application, Ser. No. 640,062.

A centralized trafiic controlling system applied to a railway system as contemplated by the present invention comprises a control ofiice and a plurality of field stations located throughout the territory under the control of an operator in the control ofiice. Each field station is provided with transmitting and receiving equipment which is connected by suitable line circuits to receiving and transmitting equipment located in the control ofiice.

A portion of such control office has been illustrated in Figs. 1A and 113 as being typical of that part of the control ofiice associated with the communication system. A control wire I!) extends from the control ofiice to the first field station, at which point line relay F is connected in series therewith. The control line wire then extends to the second field station and so on to the end of the system Where it is connected to the control line return conductor [2, which conductor extends from the control oilice through each of the field stations.

Similarly an indication line wire [4 extends from the control office to the first field station, from the first field station to the second field station and so on to the end of the system where it is left open. Associated with the indication line wire it is an indication return line conductor l6 exten from the control office through the several field stations and to which the indication line is connected at that particular field station selected for the transmission of indications during a cycle of operations.

The control line circuit includes a three position biased-to-neutral polar line relay (such as relay F at each field station. This line circuit includes a quick acting neutral type relay F in the control office. Energy for the control line circuit is supplied from a control battery CB in the control oflice, with the particular polarity of energization of the control line selected by pole changing contacts located on positive code sending relay PC and negative code sending relay NC.

When relay PC is energized a positive impulse is applied to the control line circuit and when relay NC is energized a negative impulse is applied to the control line circuit. In the event that both relays PC and NC become energized, or when both remain de-energized the control line circuit is maintained (lo-energized. When energy is applied to the control line circuit by the code sending relays, such energization is broken up into time spaced impulses by the periodic operation of relay E which energizes and de-energizes the selected code sending relay PC or NC.

Control Office equipmcnt.The control ofiice (see Figs. 1A and 13) includes, in addition to the above mentioned apparatm, a control machine having a group or" control levers for each field station, a miniature track layout corresponding in every way to the actual track layout in the field and various indicating lamps or equivalent devices, together with apparatus and circuits arranged to accomplish the desired functioning of system. Since an understanding of the present invention may be had without referring to these various devices they have been omitted from the present disclosure, it being understood that the code sending relays PC and NC are selected during various steps of the cycle in accordance with the positions of code jumpers and control levers in a manner which has been disclosed in the above mentioned application, Ser. No. 640,062. It will be understood that the conductors leading to the bracket associated with the upper row of contacts of the stepping relay bank selectively connect to the PC and NC buses through the code jumpers and control lever contacts as indicated by the reference to this connection in the upper portion of Fig. 1A.

Associated with each group of control levers is a change storing relay and a code determining relay (not shown but which are indicated by reference characters CH and CD respectively in the above mentioned application Ser. No. 640,062) The actuation of a starting button causes the energization of its corresponding change storing relay, which in turn energizes the corresponding code determining relay for transmitting a code for the selection of the associated field station. In the event that several starting buttons are simultaneously actuated or actuated in rapid succession the change relays and the code determining relays, together with a stick relay LCS (see Fig. 1A), are so interlocked that only one code determining relay may be picked up for any one particular cycle of operations, with the interlock so arranged that the code determining relays are picked up in a predetermined sequence dependent upon their location in the bank of relays.

Line relay F has associated therewith a neutral quick acting line repeating relay FP which repeats each energization and each de-energization of line relay F irrespective of the polarity with which relay F is energized. For purposes later to be explained relay FF is provided with a neu- '5 relay has such characteristics that its pick up time is relatively slow compared to the pick-up time of neutral relay FP for example, although its pick-up time is relatively fast in comparison with its drop away time. Relay SA is thus sumciently slow acting to maintain its contacts in their picked up positions between successive impulses applied to the control line circuit during a cycle of operations. Associated with relay SA is a neutral slow acting repeating relay SB which has associated therewith a neutral slow acting repeating relay SC, for purposes hereinafter pointed out.

Associated with the line and line repeating relays is a bank of stepping relays including half step relay VP and stepping relays IV, 2V, 3V

and LV. This bank of stepping relays marks OK the steps of each cycle of operations. Impulsing relay E is jointly controlled by the stepping and half-step relays and by controlling the operation of code sending relays PC and NC governs the impulses and the time spacing of the impulses applied to the control line circuit. As above mentioned the polarity of these impulses is determined by code sending relays PC and NC.

For the purpose of illustrating the manner in which a cycle of operations is initiated from a field station the two neutral message receiving relays MB and MF disclosed in the above mentioned application Ser. No. 640,062 are shown in Fig. 13. It will be understood that these relays are provided to repeat the condition of the indication line circuit for each step, with such conditions stored in suitable pilot relays and indication storing relays for registering the station which is transmitting indications and the indications transmitted therefrom. Since this portion of the system is immaterial for an understanding of the present invention it has been omitted from the disclosure.

For the purpose of initiating the system and determining whether such operation occurs at a field station or at the control oflice, relays LCS, C, CF and 0C are provided. The functions of these relays will be more readily apparent from the description which follows, it being suflicient lCD at back contact H of relay SA opens the energizing circuits of the CD relays to prevent any one of these relays being picked up after the cycle is initiated, all of which is explained and shown in detail in the above mentioned application Ser. No. 640,062. Relay 0C is picked up for both control and indication cycles and its detailed operation will be explained later in the description.

A maintainers call button MCB is provided in m the control ofi'ice to enable the operator to use the communication system for actuating a maintainers cell signal at a selected station. A recheck button RCB is provided in the control ofiice for the purpose of enabling the operator to cause 7;: any desired field station to initiate the system into a cycle for the transmission of indications. This is accomplished by the operator selecting the desired station with button RCB actuated.

Field station equipment-I'he field station i1- lustrated in Figs. 2A and. 2B is typical of all stations of the system and may be adapted for use at the first, second or any other location by merely altering thee code jumper connections to arrange for its response to the proper code. For convenience in describing the present invention it is assumed that this field station is at the first location along the line extending from the control oflice and is so designated by reason of the distinctive exponents employed in connection with the reference characters.

A turnout track is illustrated as being connected to a main track by a track switch TS. This track switch is operated from one extreme locked position to the other by a suitable switch machine SM, which in turn is governed bya switch machine control relay SMR. of the two position polar magnetic stick type. Relay SMR is governed from the control ofiice through the medium of the communication system herein described. Relay SMR controls the operation of the switch machine to its normal locked position by energizing its normal operating wire by way of contact 260 in its right hand position. This relay controls the operation of the switch machine to its reverse locked position by energizing its reverse operating wire by way of contact 200 in its left hand dotted position. This control preferably includes suitable approach and detector locking (not shown) in order to prevent the unsafe operation of track switch TS.

Suitable signals are associated with the track switch for governing traffic thereover and they are provided With automatic block signalling means, with selections made in accordance with the position of the track switch and the condition of the detector track section and such other sections of track and trafiic controlling devices as may be associated therewith, all in accordance with approved practice in connection with such control. The signal controlling circuits are not shown since they form no part of the present invention and their arrangement is immaterial for an understanding of the present invention. It will be understood that these signals are go'verned from the control office by means of the communication system over which suitable control relays are positioned in a similar manner as relay SMR.

A detector track section having a normally closed track circuit is provided with a track relay T and a suitable track battery for indicating the passage of trains over the section.

The communication part of the system includes the three position biased-to-neutral polar line relay F above mentioned, together with its quick acting line repeating relay F1 Slow acting line repeating relays SA and SE correspond to similar relays in the control office and are used to define the bounds of a cycle of operations of a field station by being picked up at the beginning of each cycle and dropped at the end of each cycle.

The field station has a bank of stepping relays including half-step relay VP and stepping relays IV 2V and 3V Relay EX is an executing relay used for controlling certain executing circuits as will be later described in detail.

For the selection of the station for the reception of controls a station selecting relay S0 together with a station selecting stick relay SOS are provided to determine when the code call placed upon the control line circuit corresponds to the code call assigned to this field station.

The selection of a station for the transmission of indications is effected at the station by the continued energization of lockout relay L When the lookout relay is picked up for a cycle of operations, pulsing relays; (not shown) are effective to transmit the code call of a station, followed by the transmission of the indications. Similarly, when the lookout relay is picked up the indication line circuit extending from this station to the control office is energized to initiate the system into a cycle of operations.

A change relay CH is provided to register a change in any of the traffic controlling devices at the station and it functions to initiate the system for the transmission of indications by picking up the lockout relay at the associated station.

At any one or more of the stations a maintainers call signal MC, which may be a vibrating bell or any other suitable audible or visual signal device, is provided and arranged to operate-in response to an actuation of the maintainers call button MCB in the control office for the purpose of calling a member of a train crew or a signal maintainer, or for any other purpose desired.

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

Operation The system of the present invention is normally in a condition of rest from which it may be initiated into a cycle of operations either from the control ofiice or from any field station whenever there are new controls or new indications respectively ready to be transmitted. If new controls for several different field stations are ready for transmission at substantially the same time these controls for the several stations are transmitted on separate cycles of operation. Similarly, if several field stations have transmissions ready at the same time these indications are transmitted from such field stations to the control ofiice, one station at a time on separate operating cycles.

It may happen that there are new controls and new indications ready for transmission at the same time and in such instances controls are transmitted to a selected field station during the same cycle with the transmission of indications from the same or some other field station. This feature of the present invention is conveniently referred to as duplex transmission but it is convenient to first consider the transmission of controls, after which the initiation of an indication cycle will be explained.

Normal at rest conditions.-The line circuits of the system are arranged to be normally deenergized and similarly the remaining circuits of the systems are arranged to be normally de-energized with a few exceptions. For example, the detector track circuit associated with the track switch TS of Fig. 2A is of the closed circuit type for normally energizing track relay T. Change relay CH is normally energized by means of its stick circuit extending from back contacts. 28! and 202 of relays SB and SO in multiple, lower winding and front contact 203 of relay CH and front contact 204 of relay T to 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 desiredstation. Whenever such a cycle is desired the operator first positions the control levers associated with the desired station and then actuates the corresponding starting button. This operation effects the energization of a change relay and a code determining relay. By means of code jumpers connected in a particular combination associated with the actuated code determining relay a particular code call is applied to the control line circuit. The actuated code determining relay also selects the control levers associated with that particular station for determining the code combination applied to the communication system for operating the desired control devices at the selected station.

As clearly pointed out in the above mentioned prior application Ser. No. 640,602, no code determining 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 I CD, shown in the left hand portion of Fig. 1B, which conductor in this embodiment is de-energized as long as the system is in active operation at back contact [0| of relay SA. This conductor is likewise de-energized the instant the system is initiated from a field station due torelay MB opening its back contact I92. The conductor is similarly de-energized at back contact I03 of relay MF so that the energization of either one of these message receiving relays prevents the picking up of any code determining relay.

With the system in its normal condition a circuit is completed from back contact II of relay LV, winding of relay LCS to conductor lCI-I. This supplies energy to the bank of code determining relays so that the relay of this bank which is selected by the actuated starting button may be energized. Since relay LCS is included in this energizing circuit it is picked up in response to the actuation of the starting button.

The energization of relay LCS closes a circuit for-picking up relay C which extends from back contact l3 of relay SC, front contact I5 of relay LCS and winding of relay C, to A circuit-is now closed for picking up relay OC which extends from front contact ll of relay C, back contact 18 of relay SB and winding of relay OC to The picking up of relay OC closes a circuit for picking up the first selected code sending relay PC or NC extending from front contact [9 of relay 00, back contact 20 of relay E, front contact 2| of relay C, back contacts 22, 23 and 24 of relays 3V, 2V and IV respectively, channel conductor 25,and through the code jumper connection (not shown) to the PCor NC relay as selected by this jumper. It will be assumed that the first code jumper associated with the station desired connects to the PC bus in which case the above described circuit is completed through the winding of relay PC to This picks up relay PC for energizing the control line circuit with a impulse. It will be obvious that the'NC bus will be energized for picking up relay NC in the event that the code jumper is connected to this bus instead of the PC bus previously assumed.

Polarity selection of impulses.When the system is initiated from the control office, resulting in the energization of relays C and 0C 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 during the succeeding cycle are of polarities determined in accordance with the positions of the code jumpers and the control levers rendered effective by the picking up of this 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 upon 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 as above described.-

The energization of relay PC results in the application of a impulse to the control line over a circuit extending from the terminal of battery CB, front contact 25 of relay PC, back contact 21 of relay NC, winding of relay F, control line conductor I ll to the first field station, through the Winding of relay F and thence over the control line conductor through such other field stations as are provided to the return line conductor 2 at the end field station, back contact 38 of relay NC and front contact 29 of relay PC to the terminal of battery CB.

When the first impulse is placed upon the control line circuit relay F in the control oflice is energized and a circuit is closed for energizing relay FP at front contact 30. Relay F also closes a circuit at its front contact 3| for energizing relay SA and relay FP closes a circuit at its front contact 32 for energizing relay ZFP. Relay SA closes a circuit at its front contact 33 for energizing relay SB and relay SB closes a circuit at its front contact 3 3 for energizing relaySC The picking up of relay SA completes a stick circuit for relay C extending from front contact 35 of relay SA, front contact 35 and winding of relay C to The picking up of relay SB opens the energizing circuit of relay at back contact I8, but due to its slow acting characteristics relay 00 does not drop before relay E picks up to complete a stick circuit for relay OC as will be presently described.

This application of the first impulse to the control line circuit causes relay VP to be energized over a circuit extending from front contact 31 of relay SB, front contact 33 of relay 2FP,.back contact 39 of relay IV andwinding of relay VP to Relay VP closes a first stick circuit for itself extending from front contact 3? of relay SB, front contact if of relay VP, back contact 39 of relay iV and winding of relay VP to A circuit is now closed for picking up relay E which extends from front contact 93 of relay SC, back contacts 4|, 4-2, 43 and 44 of relays LV, 3V, 2V and IV respectively, front contact 4-5 of relay VP and winding of relay E to The picking up of relay E .opens back contact 26 which de-energizes the control line circuit by dropping relay PC.

As will be presently described the stepping relays are successively picked up during the following de-energized periods of the control line circuit and the VP relay is shifted during each energized period of the control line circuit. That is, relay VP, which is picked up during thefirst energized period, is dropped during the second energized period, picked up during the third energized period and dropped during the fourth energized period.

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

55, 65 and I5 when relays IV, 2V and 3V respectively pick up. This selection is accomplished during the time that the control line circuit is de-energized because the stepping relays are picked up during the deenergized periods, so that the change in position of the PC and NC relays is immaterial in so far as the condition of the line circuit is concerned, because the line circuit is de-energized during these periods and by the time the circuits are ready to energize the line circuit during the following periods the PC and NC relays have taken their proper setting.

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, FP, 2FP, SA, SB, SC and VP as above pointed out. The energization of relay VP picks up relay E over the above described circuit, which tie-energizes the particular PC or NO relay which is picked up by opening back contact 26. With both relays PC and NC de-energized the control line circuit is de-energized to mark the end of the first impulse period. This drops relays F,

FP and ZFP 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.

The picking up of relay E closes the stick circuit for relay 00 which extends from front contact 46 of relay E, conductor 86, front contact 41 of relay 0C, front contact l8 of relay SB and Winding of relay 0C, to This stick circuit is closed each time relay E picks up during the cycle and is opened each time relay E drops during the cyc1e, ,but relay OC remains in its picked up condition throughout the cycle due to its slow acting characteristics and the intermittent energization of this stick circuit.

The dropping of relay 2FP effects the picking up of relay IV over a circuit extending from front contact 31 of relay SB, back contact 51 of relay 2FP, front contact 58 of relay VP, back contact 59 of relay 2V and winding of relay IV, to

extends from front contact 31 of relay SB, back contact 38-01 relay ZFP, front contact i8 and winding of relay VP, to The picking ,up of relay IV closes a stick circuit for itself 1' which extends from front contact 3! of relay SB, front contact 49 and Winding of relay IV, to

The picking up of relay IV opens the above traced energizing circuit of relay E at back contact 44 which allows relay E to drop and at its .;back contact 20 a circuit is completed for picking up. the selected PC or NC relay (assumed to be relay PC), which circuit has been previously described and extends through front contact 24 to and relay VP is dropped because its second stick circuit is open at back contact 38 of relay ZFP and because its first stick circuit is open at back contact 39 of relayIV. Relay E now picks up over theipreviously described circuit extending from at front contact I3 of relay SC, but

which now includes front contact 44 of relay IV and back contact. 45 of relay VP. The picking up. of relay E opens the circuit of relay PC at back contact 20, allowing this relay to release and The dropping of relay ZFP also closes a second stick circuit for relay VP which tie-energize the control line to mark. the end of the second impulse period.

Relays F, PP and HP are dropped and relay 2V is picked up over a circuit which extends from front contact 3'1 of relay SB, back contact 5? of relay ZFP, back contact 58 of relay VP, back contact 55 of relay 3V, front contact 66 of relay iv and winding of relay 2V, to Relay 2V completes an obvious stick circuit for itself at its front contact 5?. The picking up of relay 2V cifects the dropping of relay E by de-energizing its'circuit at back contact 43. Relay E closes the circuit for energizing the selected code sending relay (PC or NC) at back contact 29 and the picking up of this selected code sending relay energizes the control line circuit with or potential as determined by the particular code sending relay which is picked up.

This marks the beginning of the third impulse period and relays F, F? and ZFP are again picked up in sequence and the above described circuit is closed for again picking up relay VP, but which now extends through back contact 68 of relay 3V, and front contact 55 of relay 2V. Relay VP again completes its first stick circuit which obviously extends to front contact 31 of relay SB by way of front contact 43 of relay VP.

Relay E is now energized over the above described circuit which now includes front contact 45 of relay VP and front contact 43 of relay 2V. The picking up of relay E de-energizes the code sending relay at back contact 2|! which de-energizes the control line circuit to mark the end of the third impulse period.

Relays F, PP and ZFP are again dropped in sequence and relay 3V is picked up over the above described stepping relay pick up circuit including back contact 5'! of relay ZFP, front contact 58 of relay VP, front contact 59 of relay 2V and winding of relay 3V, to Relay 2F? again closes the second stick circuit for relay VP as above described and relay 3V closes an obvious stick circuit for itself at its front contact 11. Relay E is now de-energized by the opening of its circuit at back contact 42 of relay 3V. This again completes the selective pick up circuit for the PC and NC relays by way of back contact 20 of relay E and front contact 22 of relay 3V to channel conductor 15. This channel conductor is completed in this instance because contact 18 of button RCB is closed. The energization of the selected code sending relay energizes the control line circuit with the fourth impulse, which is or as determined by the particular code sending relay which is picked up.

Relays F, FF and ZFP are now energized and relay VP is de-energized because both of its stick circuits are de-energized as previously mentioned. Relay E is now picked up overthe previously described circuit which now includes back contact 45 of relay VP and front contact 42 of relay 3V. The picking up of relay E opens the code sending relay circuit at back contact 20, allowing this relay to drop and de-energize the control line circuit to mark the end of the fourth impulse period.

Relays F, PP and ZFP are now dropped and relay LV is picked up over the previously described stepping relay circuit which now extends through back contact 58 of relay VP, front contact 56 of relay 3V and winding of relay LV, to Relay LV completes an obvious stick circuit for itself at its front contact 16.

Relay LV, unlike the other stepping relays, does 75 not effect the dropping of relay E, therefore the control line circuit is maintained in its de-energized condition for a substantially long period of time which results in the dropping of relays SA, SB and SC. The dropping of relay SA deenergizes relay C by opening front contact 35 and the opening of front contact 37 of relay SB de-energizes the stepping relays. The opening of front contact l8 of relay SB de-energizes relay OC which is dropped after a predetermined period of time is measured off. Relay E is deenergi-zed both by the opening of front contact I3 of relay SC and by the restoration of the contactsof the stepping relays which select this relay.

The picking up of relay LV removes potential from the circuit extending to the change and code determining relay bank (conductor ICH), which circuit includes the winding of relay LCS. Relay LCS will therefore be de-energized and the operation of the change and code determining relay bank previously mentioned will be properly effected.

Station selection for controZs.-The impulsing operation of the control line circuit and the stepby-step operation of the stepping relay bank in the control office has been described and it will be understood that additional steps may be provided, the number of which is determined by the capacity of the system.

Similar step-by-step operation of the stepping banks at the field stations takes place in response to the impulsing of the control line circuit. The stepping relay banks at the field stations in the present embodiment respond only when they have the possibility of being selected for the reception of controls or when they are transmitting indications. In other words, the 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.

It will be apparent that the impulses are received at all stations and are then repeated by the line relay, such as relay F of Fig. 2A, at each station. However, for convenience in describing the operation at the field stations reference will be more particularly made to Figs. 2A and 2B, which illustrate a typical station and which for convenience is considered the first station of the system and which is responsive only to impulses applied to the control line circuit on the first two steps of the cycle.

The application of the first impulse to the control line circuit causes the line and line repeating relays to be picked up, with the line relays actuating their polar contacts to the right in response to a positive impulse and to the left in response to a negative impulse. Since it is assumed that the first impulse of the code call placed upon the control line circuit is positive, then a portion of the field stations will have their selecting relays SO and SOS picked up during the application of this impulse. If the first impulse of the code call placed upon the control line circuit is negative, then the remaining field stations will have their selecting relays picked up during the application of this impulse. In other words, depending upon the polarity of the first impulse transmitted only one or the other part of the field stations will have their station selecting relays energized at the beginning of a cycle.

More specifically, the first impulse actuates the contacts of relay F to the right which closes a circuit for picking up relay FP extending from contact 295 of relay F in its right hand dotted position, back contact 208 of relay SB and winding of relay FP to Relay FP closes a circuit for picking up relay SA extending from front contact 209 of relay FF, and winding of relay SA to During the intermittent operation of relay FP in response to the succeeding impulses, relay SA is maintained picked up over the circuit including front contact 299 of relay FP Relay SA closes an obvious circuit for energizing relay SE at contact 2"].

Prior to the picking up of relay SB a circuit is completed for picking up relays S0 and S08 which extends from back contact 2 of relay SE contact 7H2 of relay F in its right hand dotted position, back contacts 2l3, 2M and 2l5 of relays 3V 2V and [V respectively, code jumper 216 and lower windings of relays S0 and SOS in series, to The picking up of relay S0 applies potential by way of its front contact 2!? to the above described circuit, so that this circuit will remain energized after the opening of back contact 2 of relay S13 A stick circuit is completed for relay $08 which extends from front contact 2| 8 of relay SB front contact MS of relay F1 front contact 220 and upper winding of relay SO8 to It will be apparent that the F, FP, SA and SB relays at all of the field stations respond to the first impulse. The F'P relays at the several field stations are all insured of being picked up by reason of a circuit including a back contact of their corresponding SB relays (similar to contact 208 of relay SE However, the FP relays are maintained energized throughout the remainder of the first impulse following the picking up of the SB relays and are maintained operated throughout the remainder of the cycle only at those stations still having possibilities of selection by reason of the picked up condition of the SO relays at such stations. This is because after the SB relays open the back contact similar to contact 208 the associated FP relays cannot thereafter be energized unless an associated lockout relay has its front contact 286 closed or an associated SO relay has its front contact 207 closed. At those stations Where the SO relays are picked up the FP relays follow the impulsing of the control line circuit until their associated SO relays drop out. Therefore at only one station of the system will the FP relay operate throughout the control cycle, since the SO relays which are picked up at the beginning of a cycle are selectively dropped out until only one remains.

For example, with relay S0 of Fig. 2A picked up because jumper 2H3 is in the position shown, the next impulse of the series is assured of being received at this station. Upon the following deenergized condition of the control line circuit relays F and FP are de-ener'gized and the upper winding of relay S08 is de-energized because of open front contact N9 of relay FT Thus relay SOS is maintained energized by way of its stick circuit until after the de-energization of relay F'P While relay S08 is still picked up, relay S0 is maintained energized by a stick circuit which extends from front contact 2l8 of relay SE front contact 22! of relay SO8 front contact 222 and upper winding of relay S0 to Then upon the dropping away of relay SOS this stick circuit is opened at front contact 22!, but prior to its dropping away the contacts of relay FP assume de-energized positions thereby closing another stick circuit for relay S0 by way of back contact 2 IQ of relay F'P and front contact 222 of relay S0 Upon the next energization of the control line circuit a part of those SO relays which are still picked up are energized through their lower windings, depending upon the correspondence between the polarity of the impulse and the position of their respective code jumpers.

For example, assuming that relay S0 is still picked up by reason of a positive impulse having been applied during the first energized period, the relays S0 and S08 will be energized in series if the second impulse is positive by means of a circuit extending from front contact 2!? of relay S0 contact 2l2 of relay F in its right hand dotted position, back contacts 2| 3 and 21s of relays 3V and 2V respectively, front contact 2l5 of relay [V code jumper 223 and lower Windings of relays S0 and SOS to At those stations where code jumper 223 is connected in an upper position for a negative impulse the SO relays will not be energized through theirlower windings. Therefore the picking up of their corresponding FP relays, which opens the stick circuits through the upper windings of these SO relays, they will be de-energized and thereby eliminate the associated stations from the possibility of selection during the cycle in progress.

This dropping out of an S0 relay in response to an impulse which does not correspond to the character assigned its code jumper for that step may be best understood by considering the dropping out of relay S0 of Fig. 2A when the second impulse is negative. This negative impulse applies potential by way of contact N2 of relay F in its left hand dotted position,

back contacts

224 and 225 of relays 3V and 2V respectively, front contact 226 of relay IV to the terminal directly above jumper 223. Since jumper 223 is in its lower position this circuit remains incomplete at the upper position of this jumper so that relays S0 and S08 are not energized Then upon the through their lower windings. picking up of back contact 2E9 of relay FP the stick circuit for relay S0 is opened. Upon the second de-energized period of the line circuit the stick circuits for relay S0 cannot be closed. In other words, those SO relays which are deenergized when the impulse on the control line circuit does not correspond to the position of their code jumpers drop away when such impulse is repeated by their associated FP relays.

In the present embodiment only two impulses are used for selecting the station for controls. Therefore the single SO relay which is maintained in its picked up position during the second impulse period is continued in this position throughout the remainder of a cycle by means of a stick circuit which extends from front contact 2I8 of relay SB jumper 221, front contact 228 of relay 2V back contact 229 of relay EX front contact 222 and upper winding of relay S0 to It will be understood that this jumper connection 22'! may be associated with any stepping relay of a bank as determined by the number of steps required for station selection.

It will be evident that the selection of the station selecting relays, such as relay S0 may continue for as many steps as necessary until the stations have been selectively dropped out until only one SO relay will remain energized at the end of the station code call. It is believed that the above example is sufiicient to indicate how stations are selected for controls by the various combinations of jumpers 2I6 and 223. This station selection operation is explained more in detail in the above mentioned prior application Ser. No. 640,062.

Stepping operation at the field station.--The manner in which the FP relays pick up at the various field stations independent of the SO relays, by reason of the back contacts of their respective SB relays, has been pointed out. With reference to Fig. 2A it will be apparent that as soon as relay S13 has been picked up and its back contact 288 opened, relayFP is dependent for its energizing circuit upon front contact 201 of relay S0 in order to repeat relay E. This of course is assuming that relay L0 is not picked up during the cycle in question. It will be understood that it is necessary for relay FP to operate in order to cause the step-by-step operation at the associated field station.

At the beginning of a cycle of operations the response of relays FF and S0 closes a pick up circuit for relay VP which extends from (-1-), front contact 230 of relay SE front contact 23f of relay S0 front contact 232 of relay FP back contact 233 of relay IV and winding of relay VP to The response of relay VP closes its first stick circuit which extends from (-1-), front contact 239 of relay SB' front contact 234 of relay VP back contact 233 of relay iv and winding of relay VP to During the following de-energized period of the line circuit the second stick circuit for relay VP is completed from back contact 235 of relay FP front contact 236 of relay SB front contact 231 and winding of relay VP to It will be understod that these pick up and stick circuits for relay VP are effective during the steps of the cycle in a similar manner as described in detail for relay VP in the control office. Therefore the detailed description of the VP relay operation at the field station will not be given.

Upon the next de-energized period of the control line circuit, relay IV is energized over a circuit extending from (-1-), front contact 230 of relay SB front contact 2M of relay S0 back contact 232 of relay FP front contact 238 of relay VP back contact 239 of relay 2V and winding of relay IV to Relay 1V closes an obvious stick circuit for itself at its front contact 246 which extends to at front contact 2 25 of relay 8B It is believed unnecessary to explain the further operation of the field station stepping relay bank, since it is apparent that the operation of relay FP is dependent for its repeating the operation of relay F upon the closed condition of front contact 291 of relay S0 so that upon the dropping away of relay S0 during any impulse period, the circuit to relay FP is immediately opened. The dropping away of relay FP at the beginning of an impulse by reason of the dropping of relay S0 (because of the lack of correspondence between the polarity of that impulse and the position of its code jumper) does not result in the picking up of the next stepping relay since this pick up circuit is opened at front contact 23!.

Since relay SO can only be picked up at the beginning of a cycle it is obvious that when it is once dropped out the stepping operation is discontinued and relay F2 is prevented from repeating relay F However those stepping relays that have been picked up prior to the dropping out of relay S0 are maintained energized until the end of the cycle.

Further operation of the stepping relay bank at the field station is similar to that explained in connection with the control office stepping relay bank. It will be understood that the stepping relays at other field stations of the system are operated in a similar manner.

Transmission of controls-Assuming that the field station illustrated in Figs. 2A and 2B is selected by having its relay S0 maintained energized, then upon the application of the third impulse to the control line circuit (the second stepping relay 2V having been picked up on the preceding de-energized period) the two position polarized relay SMR is energized in one direction or the other depending upon the character of this third impulse.

For example, if the third impulse is positive the lower winding of relay SMR will be energized over a circuit extending from (-1-), front contact 2|! of relay S0 contact 2l2 of relay F in its right hand dotted position, back contact 213 of relay 3V front contact 2E4 of relay 2V and lower winding of relay SMR, to

If the third impulse applied to the control line circuit is negative then the upper winding of relay SMR is energized over a circuit extending from front contact 2H of relay S0 contact 2l2 of relay F in its left hand dotted position, back contact 224 of relay 3V front contact 225 of relay 2V and the upper winding of relay SMR, to

With the lower winding of relay SMR energized by a impulse, polar contact 20!] is actuated to a right hand position for closing the normal operating circuit of the switch machine. With the upper winding of relay SMR energized in response to a negative impulse, polar contact 260 is actuated to its left hand dotted position for closing the reverse operating circuit of the switch machine.

In a similar manner any number of additional control relays similar to relay SMR, may be suitably positioned for governing additional trafiic controlling devices by the use of additional channel circuits selected at additional steps of the stepping relay bank.

Transmission of indicatio-ns. -The selection of field stations and the transmission of controls to a selected station is accomplished over the control line circuit as above described. The transmission of indications is accomplished over the indication line circuit, following the registration of a particular field station in the control oflice.

It is not believed necessary to describe the detailed arrangement for transmitting indications in the present embodiment, since this arrangement forms no part of the present invention and is immaterial to an understanding thereof. It will be pointed out how a change in conditions at a field station initiates the system into a cycle of operations in order that an explanation may be given of the operation of the system for accomplishing the recheck feature which forms an important part of the present invention.

A change in conditions at a field station may include a change in the condition of the detector track section, a change in the condition of the track switch, a change in the condition of the signals or any one of several other changes may occur, but as illustrative of such conditions only the change in the condition of the detector track section has been shown as being effective to initiate the system into an indication cycle.

For example, the movement of track relay contact 204 from a front point to a back point, or vice versa, momentarily opens the stick circuit of relay CH so that its contacts assume dropped away positions prior to the reclosure of its stick circuit insofar as contact 20 3 is concerned. This will be readily understood, since it is well known in the art that a quick acting relay such as relay CH will accomplish this result when employed with relatively slow switching contacts such as contact 204 of relay T.

With the system in a normal at rest condition the de-energization of relay CH closes a pick up circuit for lockout relay L which extends from back contact 242 of relay SE back contact 243 of relay SA back contact 244 of relay FP upper winding of relay L0 and back contact 245 of relay CH to As soon as the contacts of relay LO have responded, a holding circuit is closed for this relay which is not shown in the present disclosure but which is clearly disclosed in the above mentioned prior application Ser. No. 640,062.

The closure of front contact 24b of relay LO energizes the indication line over a circuit which extends from this particular station to the control office. This circuit which may be traced from the terminal of indication battery IB, lower winding of relay MB, back contact E03 of relay SC, indication line conductor i4, front contact 246 of relay L0 back contact 241 of relay SB lower winding of relay L0 resistance IE and indication line return conductor [6, to the terminal battery IB.

The lockout feature, which is for the purpose of allowing only one field station to actively associate itself with the communication system at any one time, is not shown in detail in the present embodiment, since this feature is immaterial to an understanding of the present invention. It may be accomplished in the manner disclosed in the above mentioned prior application Ser. No. 640,062.

The energization of the indication line circuit, including the lower winding of message receiving relay MB, results in the initiation of the system. The picking up of relay MB opens the circuit of conductor lCD at back contact H02, which prevents the operation of any code determining relay in response to an attempt to initiate the system for the transmission of controls from the control mice. Since relay SA will be picked up and its back contact I 0i opened before back contact I02 is again closed, this circuit is maintained open throughout the cycle. However, it will be explained in connection with a duplex cycle how a CD relay (controlled over conductor I CD) may be in its picked up position at the start of a cycle during which the look-out relay at a transmitting field station may also be in its picked up position.

The picking up of relay MB closes a pick up circuit for relay CF which extends from front contact 34 of relay MB, back contact 105 of relay SC and winding of relay CF, to A circuit is now closed for picking up relay 00 which extends from front contact 19 of relay CF, back contact l8 of relay SB and winding of relay OC, to

Since this is a cycle for the transmission of indications alone and since no code determining relay will be picked upto select the PC and NC buses, it is necessary that a circuit be provided for energizing one of the code sending relays throughout this cycle at the various steps. This circuit extends from. front contact IQ of relay 00, back contact 20 of relay E, back con- I tact 2| of relay C, back contact of relay LCS,

front contact 50 of relay CF and winding of relay NC, to This circuit causes the intermittent energization of relay NC for applying, a series of impulses to the control line during an indication cycle.

The application of the first negative impulse to the control line circuit is repeated by the F and FF relays at the control office and at each of the field stations. The repeating of this impulse by the FP relays at each field station opens the pick up: circuits of all of the lookout relays so that no other lockout relay may thereafter be picked up, but the lookout relay which is already picked up will remain energized by reason of the circuit including its lower winding, which is connected to the indication line circuit.

The application of the first negative impulse to the control line circuit continues until the system is initiated as described in connection with a control cycle. In other words, this impulse remains on the control line circuit until the F, FP, SA, SB, SC, VP and E relays are all picked up, after which the line is de-energized to mark the beginning of the first de-energized period in the manner previously described. Each impulse applied to the control line circuit is negative in character since relay CF remains energized throughout the cycle by reason of a stick circuit which is closed by the picking up of relay SA and which extends from. front contact ll of relay SA, front contact I06 and winding of relay CF, to

The series of negative impulses thus impressed upon the control line circuit do not result in the selection of any field station for the reception of controls because the station code call is assigned to the phantom station as shown. and described in the above mentioned prior application Ser. No. 640,062.

The closure of front contact 241 of relay SB together with the closure of front contact 246 of relay LO places the control of the indication line circuit in the pulsing relays, which are connected to thefront contact 241 of relay SB and from.

this point the circuit leads through contacts of relay FP for the purpose of preconditioning the front and back branches of the indication line circuit for the transmission of the station code call and the indications from this station, all of which is not shown. in the present embodiment but which may be arranged as in the above mentioned prior application Ser. No. 640,062.

After the last impulse has been applied to the control line circuit the slow acting relays drop away as previously explained in connection with a control cycle. The stick circuit of relay L0 is then interrupted and the fieldstation is restored to its normal condition. During the cycle of operations (after relay L0 is selected), change relay CI-I is restored to its normal energized condition through suitable means not shown in the present embodiment but which are disclosed in the above mentioned application. In the control ofiice the relays are restored to normal conditions as previously mentioned, with relay CF being de-energized by the de-energization of its stick circuit when relay SA opens its front contact llJl.

Duplex operation.1't is apparent from the above description that the step-by-step operation at each field station is dependent upon the station selection for outgoing controls and upon the selection of a. field station .during the lookout period for incoming indications. Considering that a control cycle is in progress, the stepping relay banks will operate at all of those stations necessary to accomplish the selection of a station. Then if some other station (at which the stepping operation is not effected by reason of its non-selection for controls by the SO relay),

is transmitting indications, the stepping operation at such a station is effected by reason of the energization of the associated lockout relay. Therefore regardless of whether a. cycle of operations is initiated for the transmission of controls alone, indications alone or both controls and indications, the stepping relays will operate at all of the necessary field stations.

From the above description and an examination of the circuits it will be apparent that relay LO at the field station may be picked up (and stuck up throughout the following cycle) at the same time that a code determining relay in the office is picked up. In this event the closure of front contact 248 of relay LO permits the conditioning of the indication line (by means of circuits selectedthrough front contact 241 of relay SB for transmitting indications. Since relay C is energized by the picking up of relay LCS, the control line is impulsed in accordance with a code selected through front contact 23 of relay C.

The above condition may be brought about for example by controls and indications awaiting transmission when a previous cycle is terminated. In this event, relay LO will be picked up when relay SE at the station closes its back contact 242, and stuck up over the indication line duririg the lock-out period when relay SC in the office closes its back contact W3. During the interval between the picking up of relay L0 in response to the closure of back. contact 242 and the opening of back contact I82 by relay MB picking up in series with the stick circuit of re- 40 lay L0 a code determining relay can pick up and effect the picking up of relay LCS. Then when relay SC drops to pick up relay 1\[B by way of back contact I93, relay C is picked up by way of back contact 1%. Relay FC will also pick up but the closure of front contact 2! of relay C marks the cycle as one for the transmission of controls. Relay L0 being up also marks the cycle as one for the transmission of indications.

The only diiference between a duplex cycle and 50 a cycle for the transmission of indications alone is that the stepping relay operation at the field station which is transmitting during a duplex cycle is accomplished by a code call which is characteristic of a particular station being called instead of by the code call of a phantom station which is employed when there is no station being called for the reception. of controls during an indication cycle. This is because relay C in the control ofiice is made superior to relay CF by reason of front contact 2| of relay C (closed at the beginning of a cycle of operations) allowing the character of the succeeding impulses on the control line circuit to be determined in accordance with the code jumper and code lever contacts rendered effective, regardless of the fact that relay CF may be picked up to close its front contact 58, since the circuit leading from front contact 59 is open at back contact 2| of relay C.

Indication recheck-It will now be assumed that the operator in the control oflice desires to be informed of the conditions of the control devices at a particular field station. This result is accomplished by momentarily opening the stick circuit of the change relay such as relay CH at the station in question.

The starting button for the station to be rechecked is pressed and recheck button RCB is actuated and held actuated until buzzer BZ sounds. The operation of the starting button selects the station with which it is associated. Since button RCB is actuated a cycle of operations is effected with one less than the normal number of impulses.

Assuming for example that the station illustrated in Figs. 2A and 2B is to be selected, the starting button associated with this station will effect its selection during the first part of the control cycle previously described. With button RCB actuated contact i8 is open. The open condition of contact 18 prevents the energization of either the PC or the NC relay after the third step has been taken (picking up of relay 3V). This is because the circuit for energizing the selected code sending relay extending through front contact 22 of relay 3V is open at contact '18 of button RCB. Therefore the fourth impulse described in connection with the previous control cycle is not sent over the control line circuit. This means that relays F, F FP, FP ZFP and the slow acting relays at the station and control ofiice will all be de-energized during this de-energized condition of the control line circuit without the transmission of the fourth impulse.

Since the fourth impulse is not transmitted, relay LV at the office is not picked up and relay EX at the station is not picked up. Relay S0 at the selected station will be in its picked up condition with its back contact 202 open. Relay SA will be dropped and its front contact 243 will be opened before back contact 2M of relay SB is closed and since relay EX is not picked up, its front contact 249 will not be closed. Therefore the stick circuit including the lower winding of relay CH is momentarily interrupted when front contact 248 of relay SA drops.

This de-energizes relay CH which initiates a cycle for the transmission of indications from this station so that the operator is advised of the conditions of the various control devices such as track relay T and the like.

The reason that the stick circuit of relay CH is not opened when button RCB is not actuated (as in the operation of the control cycle previously described), is because relay EX is picked up in synchronism with relay LV in the control office following the fourth impulse. is therefore applied to the stick circuit of relay CH at front contact 249 and since the stick circuit for relay EX is controlled by relay SE contact 249 remains closed until after back contact 20! of relay SB is closed. This prevents the interruption of the stick circuit of relay CH Referring to the control office, the buzzer is energized when relay SA is de-energized to close its back contact 52 before front contact 53 of relay SB is opened. The energizing circuit for buzzer BZ extends through these two contacts to at back contact 54 of relay LV. Since relay LV is picked up during a control cycle when button RCB is not actuated, the energizing circuit for buzzer BZ will not be completed during such a cycle because relay LV is not de-energized to close its back contact 54 until after relay SB opens its contact 53. With button RCB actuated relay LV is not picked up, therefore the closure of back contact 52 of relay SA before front contact 53 of relay SB is opened momentarily completes the energizing circuit for buzzer BZ.

Contact 60 applies potentialto the circuit including the winding of relay LCS for the following purposer-The operator is instructed to actuate the recheck button and hold it actuated until the buzzer sounds. If some other field station happens to actively associate itself with the communication system for the transmission of indications at the start of this cycle (which is possible because of the duplex feature of the system), relay CF would be picked up and the closure of its front contact 6| would allow the full number of steps to be taken, since this front contact bridges contact 18 of button RCB; Therefore the buzzer would not be energized and Without contact 60 on button RCB the operator would need to restore the recheck button and start all over again. With contact 60 provided, 20 potential is continuously maintained on conductor ICH (through the winding of relay LCS) which leads to the change and code determining relay bank so that a control cycle will be initiated again and again as long as the button is held until a cycle is effective with one less step than normal to accomplish the energization of buzzer BZ as described.

Front contact 6| on relay CF is for the purpose of nullifying the recheck feature if the recheck 0 is attemped at the time indications are coming in. This is accomplished by shunting contact 78 of button RCB so that the full number of steps will be taken both in the oflice and at the selected station. This is to prevent the loss of an indication which might otherwise occur.

M aintazners caZZ.Thermaintainers call signal, such as bell MC at the station, is energized by causing the system to take one more step than normally provided. This is accomplished by the operator actuating the starting button for the station desired, actuating the maintainers call button MCB and holding it actuated during the cycle and as long thereafter as it is' desired to ring the bell. This action causes the control office stepper to control line circuit and maintain this impulse on the control line circuit until the maintainers call button is released. I

Assuming button MCB in the office to be actuated and the starting button associated with the station illustrated in Figs. 2A and 2B to be actuated, this station will be selected as previously described with relay S0 remaining picked up until the end of the cycle.

Assume that button MCB in the control ofiice is actuated and the system in the period when the control line circuit is de-energized following the fourth impulse period: Relay LV will be picked up and stuck up as before but relay E Will be de-energized under this condition upon the picking up of relay LV because of open back contact M of relay LV. The reason relay E was not de-energized during the previously described control cycle at this point was because back contact 4! of relay LV was shunted by normally closed contact 62 of button MCB. Under the present assumed condition however, front contact 62 is open to permit the dropping of relay E and back contact 62 is closed to maintain relay QC energized after relay E drops its front contact 46.

The dropping of relay E closes its back contact 20 to pick up the last selected code sending relay for again energizing the line circuit (for the fifth.

--time during the cycle) and this energization of apply one extra impulse to the 1 circuit would be energized when the line circuit is maintained as long as button MCB is held actuated. Contact 63 of button MCB applies energy to the change and code determining relay bank for maintaining the selected relay energized which corresponds to the selected station.

At the selected station, relay S0 is de-energized because of open back contact 229- of relay EX which relay was picked up by the de-energized condition of the control line circuit following the fourth impulse. It will be recalled that the circuit for maintaining relay S0 energized after static-n selection (during the energized condition of the control line circuit) extends from at front contact 2 l 8 of relay SB jumper 221, front contact 228 of relay 2V back contact 229 of relay EX front contact of relay S0 to Since back contact 229 is o-penthis energizing circuit for relay S0 is interrupted and the relay drops. Since the line is energized, relay F is picked up to close a circuit through back contacts 206 and 20'! of relays L0 and SO Relay FP is de-energized because of open front contacts 206 and 201 and open back contact 208 of relays L0 S0 and SB respectively. It will be noted that the closure of back contact 2l9 takes place after relay S0 is de-energized so that its stick circuit is not energized at this time because of open front contact 222 of relay S0 Since relay SA is energized, relay SB remains energized by reason of closed front contact 2H]. The because of the energized stick circuit extending to through front contact 2M of relay SB The maintainers call signal is operated over a circuit extending from back contact 250 of relay S0 front contact 25! of relay SE front contact 252 of relay EX and maintainers call signal device MC, to

When button MCB is restored to normal, relay E is energized over a circuit extending from front contact [3 of relay SC, front contact 62 of button MCB, front contact 42 of relay 3V, back contact 45 of relay VP and winding of relay E, to The picking up of relay E opens the circuit of the code sending relay at back contact 20, which de-energizes the control line circuit for restoring the system to its normal condition as previously described. 7

Front contact 260 of relay S0 of Fig. 2A is for the purpose of preventing the maintainers call signal at a station not selected for controls 222 and upper winding.

for maintaining relay SA energized.

stepping relays remain energized being operated when the associated station is transmitting indications. If it were not for contact 250 preventing relay EX picking up and closing its front contact 252 (as will be obvious from the drawings) the maintainers call signal not desired. By thus preventing the closure of front contact 252 by preventing the energization of relay EX on an indication cycle (because relay S0 is not picked up on such a cycle) bell MO is not energized even though back contact 250 of relay S0 and front contact 25! of relay SE are closed at the same time.

The operation of the maintainers call signal at the selected station may be used for calling a maintainer, an engineer or conductor of a train to a telephone located at the station. or it may be used. for such other purposes in connection with a centralized traiiic controlling system as may be desired. 7

Having thus shown and described a centralized traffic 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 we claim is:-

1. In a remote control system, a control ofiice and a field station connected by a control line circuit, step-by-step mechanisms at said office and at said station, means in said office for impressing series of impulses on said control line circuit, means controlled by a first series of impulses for operating said mechanisms in synchronism through a cycle comprising a first number of steps, means controlled by a second series of impulses for operating said mechanisms in synchronism through a cycle comprising a second number of steps, and means controlled by the response of the mechanism at said station to said second number of steps for causing said office to impress another series of impulses on said control line circuit.

2. In a remote control system, a control office and a field station connected by a control line circuit, step-by-step mechanisms at said office and at said station, means in said ofiice for applying series of impulses to said control line circuit, a special calling button in said ofiice and a special calling signal at said station, means controlled by a series of impulses for operating said mechanisms in synchronism through a cycle comprising a first number of steps, means responsive to the actuation of said button for causing said series of impulses to operate said mechanisms in synchronism through a cycle comprising a second number of steps, and means responsive to the operation of said mechanism at said station through a cycle comprising said second number of steps for operating said special calling signal.

3. In a remote control system, a control ofiice and a field station connected by a control line circuit, step-by-step mechanisms at said office and at said station, means in said oifice for applying series of impulses to said control line circuit, a special calling button in said office and a special calling signal at said station, means controlled by a series of impulses for operating said mechanisms in synchronism through a cycle comprising a first number of steps, means responsive to the actuation of said button for causing said series of impulses to operate said mechanisms in synchronism through a cycle comprising a second number of steps, and means responsive to the operation of said mechanism at said station through a cycle comprising said second number of steps for operating said special calling signal as long as said button is maintained actuated.

4. In a remote control system, a control ofiice and a field station connected by a control line circuit, step-by-step mechanisms at said office and at said station having normal positions, means in said office for applying series of impulses to said control line circuit, a special calling button in said office and a special calling signal at said station, means controlled by a series of impulses for operating said mechanisms in synchronism through a cycle comprising a first number of steps, means responsive to the actuation of said button for causing said series of impulses to operate said mechanisms in synchronism through a cycle comprising a second number of steps, means responsive to the operation of said mechanism at said station through a cycle comprising said second number of steps for operating said special calling signal as long as said button is maintained actuated, and means for preventing the return of said mechanisms to their normal positions as long as said button is maintained actuated.

5. In a remote control system; a control ofiice and a field station connected by a stepping line circuit; means for impressing a plurality of series of control codes on said stepping line circuit, each code comprising the same number of impulses of current; step-by-step mechanisms in said office and at said station operable in synchronism through a separate cycle of operationsin response to each of said series of impulses; means controlled by each control code for transmitting control messages to said station; means for impressing a checking code on said stepping line circuit comprising a number of impulses difierent from said control codes; a first initiating means for initiating said mechanisms into cycles of operations for the transmission of said control codes; a manually operable checking device cooperating with said first initiating means for initiating said mechanisms into a cycle of operations for the transmission of said checking code; and means responsive to said checking code for initiating said mechanisms into cycles of operations.

6. In a remote control system; a control office and a field station connected by a stepping line circuit and an indication line circuit; means for impressing a plurality of series of control codes on said stepping line circuit, each code comprising the same number of impulses of current; step-by-step mechanisms in said ofiice and at said station operable in synchronism through a separate cycle of operations in response to each of said series of impulses; means for impressing a plurality of series of indication codes on said indication line circuit; means controlled by each control code for transmitting control messages to said station; means for impressing a checking code on said stepping line circuit comprising a number of impulses different from said control codes; a first initiating means for initiating said mechanisms into cycles of operations for the transmission of said control codes; a manually operable checking device cooperating with said first initiating means for initiating said mechanisms into a cycle of operations for the transmission of said checking code; and means responsive to said checking code for initiating said mechanisms into cycles of operations for the transmission of indication codes.

'7. In a remote control system; a control office and a field station connected by a stepping line circuit and an indication line circuit; means for impressing a plurality of series of control codes on said stepping line circuit, each code comprising the same number of impulses of current; step-by-step mechanisms in said office and at said station operable in synchronism through a separate cycle of operations in response to each of said series of impulses; means for impressing a plurality of series of indication codes on said indication line circuit in synchronism with said control codes; means controlled by each control code-for transmitting control messages to said station; means for impressing a checking code on said stepping line circuit comprising a number of impulses difierent from said control codes; a first initiating means for initiating said mechanisms into cycles of operations for the transmission of said control codes; a manually operable checking device cooperating with said first initiating means for initiating said mechanisms into a cycle of operations for the transmission of said checking code; and means responsive to said checking code for initiating said mechanisms into cycles of operations for the transmission of indication codes.

8. In a remote control system; a plurality of locations comprising a control oflice and a field station connected by a control line circuit and an indication line circuit; means for impressing a plurality of series of control codes on said stepping line circuit, each code comprising the same number of impulses of current; means controlled by said control codes for transmitting messages between said locations; means for impressing a checking code on said control line circuit comprising a number of impulses difierent from said control codes; an initiating means for initiating said system into operation for the transmission of a control code; a manually actuated checking device having active and inactive positions; means responsive to the operation of said initiating means and the actuation of said checking device to its active position for initiating said system into operation for the transmission of said checking code; means for impressing a series of indication codes on said indication line circuit; means controlled by said indication codes for transmitting indication messages between said locations; and means responsive to said checking code for initiating said system into operation for the transmission of an indication code.

9. In a remote control system; a plurality of locations comprising a control ofiice and a field station connected by a control line circuit and an indication line circuit; means for impressing a plurality of series of control codes on said stepping line circuit, each code comprising the same number of impulses of current; means controlled by said control codes for transmitting messages between said locations; means for impressing a checking code on said control line circuit comprising a number of impulses. different from said control codes; an initiating means for initiating said system into operation for the transmission of a control code; a manually actuated checking device having active and inactive positions; means responsive to the operation of said initiating means and the actuation of said checking device to its active position for initiating said system into operation for the transmission of said checking code; means for impressing a series of indication codes on said indication line circuit; means controlled by said indication codes for transmitting indication messages between said locations; means responsive to said checking code for initiating said system into operation for the transmission of an indication code; and a signal operable to indicate when said device is to be restored to its inactive position.

10. In a remote control system; a control office and a plurality of stations connected by a control line circuit and an indication line circuit; means for impressing a plurality of series of control codes on said stepping line circuit, each code comprising the same number of impulses of current of distinctive character; means controlled by the character of the impulses of said control codes for selecting said stations and transmitting controls thereto; means for impressing a checking code on said control line circuit comprising a number of impulses different from said control codes; an initiating means for initiating said system into operation for the transmission of a control code; a checking device having active and inactive positions; means responsive to the operation of said initiating means and the actuation of said checking device to its active position for eifecting the impression of said checking code on said control line circuit; means for registering said checking code; and means responsive to the registration of said checking code for conditioning said indication line circuit for the transmission of an indication code.

11. In a remote control system; and a plurality of stations connected by a control line circuit and an indication line circuit; means for impressing a plurality of series of control codes on said stepping line circuit, each code comprising the same number of impulses of current of distinctive character; means controlled by the character of the impulses of said control codes for selecting said stations and transmitting controls thereto; means for impressing a checking code on said control line circuit comprising a number of impulses diiierent from said control codes; an initiating means for initiating said system into operation for the transmission of a control code; a checking device having active and inactive positions; means responsive to the operation of said initiating means and the actuation of said checking device to its aca control ofl'lce tive position for effecting the impression of said vice, said last mentioned means being independent of the polarities of the impulses.

13. In a centralized traific controlling system for railroads, an indication line circuit, a control line circuit, an impulse transmitter, control initiating means for causing said transmitter number of checking impulses to said control line circuit differing in number from said fixed number, and indication transmitting means responsive to said checking impulses for applying a combination of indication impulses to said indication line circuit.

14. In a centralized trafiic controlling system for railroads, an indication line circuit, a control line circuit, an impulse transmitter, control initiating means for causing said transmitter to apply a fixed number of coded control impulses to said control line circuit, a railway track section including a traific controlling device, means controlled by said fixed number of control impulses for operating said device to a plurality of different positions, a manually operable key, means governed by the conjoint control of said control initiating means and said key for causing said transmitter to apply a number of checking impulses to said control line circuit differing in number from said fixed number, and indication transmitting means responsive to said checking impulses for applying a combination of indication impulses to said indication line circuit.

15. In a centralized trafiic controlling system for railroads, an indication line circuit, a control line circuit, an impulse transmitter, control initiating means for causing said transmitter to apply a fixed number of coded control impulses to said control line circuit, a railway track section including a traflic controlling device, means controlled by said fixed number of control impulses for operating said device to a plurality of difierent positions, a manually operable key, means governed by the conjoint control of said control initiating means and said key for caus- 16. In a centralized traffic controlling system for railroads; a control line circuit adapted to have a plurality of combinations of coded impulses applied thereto, each combination comprising the same fixed number of impulses; a

railway track switch; means controlled by thevarious code combinations of said control impulses for operating said track switch to different positions; means including a manually operable key for applying a special call combination of impulses to said line circuit comprising a numh ber of impulses differing from said fixed number; and means responsive to said special call combination of impulses for operating a special call signal as long as said key is operated.

WILLIAM D. HAILES. ROBERT M. PI-IINNEY.