US2318545A - Railway traffic controlling apparatus - Google Patents

Description

May 4, 1943. J, J, vAN HORN RAILWA TRAFFIC CONTROLLING APPARATUS Filed Nov. 29, 1941 2 Sheets-Sheet l mw Il- NGUNU mA W .NQ 4 TM NNQQNN. nu@ @EN iw -Fue r. .Q MSE@ QS www wm. gw NNNS J SQQEN w m b m E E m Lm) SEN wm gm @S kw w www Mw L'HLI. I-l Jl bw. S@

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J. J. VAN HORN Filed Nov. 29, 19

RAILWAY TRAFFIC CONTROLLING APPARATUS May 4, 1943.

Patented May 4, 1943 James J. Van Horn, Pittsburgh, Pa., assigner to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application November 29, 1941, Serial No. 426,923

19 claims.

My invention relates to railway trac controlling apparatus and is particularly directed to the control of tramo in a single track, two-direction system of signaling, this control being preferably exercised from a remotely located control oce over a C. T. C. line circuit, although other manual control may be employed, if desired. The system employs non-coded track circuits and a polarized coded line circuit for providing selection of the traiiic direction.

One object of my invention is to provide a relatively simple form of line Wire circuit for selectively governing the traffic direction. Another object of my invention is to establish traic in a given direction and maintain that direction during occupancy or during such time as the entrance signal for the given direction is cleared, merely by operation of the proper signal lever at the control oiiice. A further object of my invention is to provide a simple form of block indication for informing the operator at the control oice of the occupied or unoccupied condition of the single track stretch. Other objects, purposes, and characteristic features of my invention will become apparent from the description which follows.

I accomplish the foregoing objects by normally transmitting a master code of normal relative polarity over the line circuit for establishing trac in the normal direction over the stretch. When the traino direction is reversed, Ina-ster code of reverse relative polarity is transmitted over the line circuit and feed-back code is eiiective during oi intervals in the master code for restoring the apparatus to its normal condition following the exit of the train. I check the traiiic direction by means of a polarized line relay and employ the proceed code detecting relays at the two ends of the stretch for controlling the block indication at the control office.

I shall describe one form of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

Figs. la and lb of the accompanying drawings when placed end to end With Fig. lo at the left are a diagrammatic View showing one form of apparatus embodying invention as applied tc a stretch of single track having one intermediate signal location and two cut section locations Within the stretch.

Referring to the drawings, the stretch oi track between the passing sidings PSE and PS2 is divided by the usual insulated rail joints at locations D, E, F, G, and I-I into a number of track circuit sections ZRT, 3T, 'I, and LT. Locations E and G are out section locations and F is an intermediate signal location.

The basic operation is as follows. Thesystem is so arranged that normally, master code of positive polarity is effective inthe line circuit and causes tra-nic to be established in the eastbound direction. Under normal conditions, therefore, in order to permit an eastbound train to enter the stretch, all that the operator is required to do is to clear one of the eastbound headblock signals ERA or 2R13. To reverse the established traiilc direction, the operator must iirst detect the master code of positive polarity at the West end of the stretch, reverse the polarity of the master code, check the stop position of the eastbound headblock signals ZRA and 2R13, and apply feed-back code to the line circuit at the west end to provide control for the westbound headblcck signals BLA and (5LB.

Normally, the approach locking repeater relay GLI/IMP at the east end is maintained energized over a circuit Which includes the front contact 4I of relay LKM and front Contact |2501 the track relay 5TH, for the approach section 5T. Relay 6LKM is the usual approach locking relay controlled by signals ELA and @LB in well-known manner so that its front'contact il is closed when both of these signals are at stop. With relay BLKMP energized, the code transmitting relay CTM will operate at either the '75 or the 180 code rate according as the home relay RAHR for signal SRA is energized or deenergized' The 180 code circuit for relay CTM includes the coding contact I3 of the 180 code transmitter IllCT, the iront point of contact Il of relay SRAHR, and the front point of contact I5 of relay LKMP. The code circuit for relay CTM includes the coding contact i5 of the 75 code' transmitter 75CT, the back point of contact It of relay SRAHR, and the front point of Contact I5` of relay SLKMP. When relay ESLKMP is deenergized, as it'will be for a Westbound move, a 75 code circuit will be effective for relay CTM over coding contact I6 and the back point'of contact I ii of relay ELKMP.

When relay GLKMP is energized so that the front points of contacts Il and I8 are closed, relay CTM will apply code current impulses of positive relative polarity to the line circuit over the front point of its contact I9; This code is transmitted over the front contacts 20 and V2|, and 22 and 23 of the intervening track relays ELI'R and llTR, respectively, and the back point of contact 24 of the code following relay 4Z, to the location F where it maintains the polarized well as the corresponding relays ZRCR and.

ELCR at locations D and Gi, respectively.,) will operate only if the polarity of the line circuit code corresponds with the position assumed -by the yassociated polarized relay.

The code operation of relay 15CR will energize one or both of the code detecting relays IHR and 4DR, respectively, according vas .the code which is supplied to the vdecoding transformer DT is `75 or 180. The manner in which this decoding apparatus operates is well known `so that al detailed description is unnecessary. Relay lil-IR will be energized when the code is either '75 or 180, vand relay 4DR will be energized only when the code is 180. It will be noted that relay 4HR is controlled over the polar contact 28 of relay TRA in its normal position so that it will not .become venergized when the code in the line circuit is-of negative relative polarity.

Relay SCTM is operated either at 1,30 or 75 code, according as relay lll-IR is energized or deenergized, respectively, as will be apparent from the drawing. Operation of the coding contact 29 of relay SCTM will apply code of positive relative polarity to the line circuit extending between locations D and F, and to polarized relay IRTRA as follows: :Starting .at the ypositive terminal B, the circuit includes the winding of the approach relay AAR, wires 3B, -3I, and 32, front point of contact 33 of relay AHR, back ,point of contact 34 of the directional stickrelay BSR, front point of contact 29 of jrelay SCTM, front contacts V35 and 35 of fthe intervening track relays STR and ERTR, back point of contact 31 of relay 2RZ, winding of -rela-y ZRTRA, front contacts 38 and 39 of relays "ZRTR and STR, Vback point of contact 49 of 4relay `SSR, and the front point of contact il of -relay Yll-IR, to the negative terminal C of the source.

As in the case of relay 4TRA, `the polarized relay 2RTRA will be `energized in the normal direction so that its `polar contacts 42 Yand .43 occupy the normal or left-'hand position. Since these polar contacts now agree Yin position with the polarity of energization of the line circuit, relay 2RCR will be energized iover an obvious circuit and will follow the line circuit code impulses. If the code is '75, relay 2RI-'IR will be energized from the `decoding transformer DT.

Y If the code is 180, then Vboth relays ZRHR and ZRDR will be energized. It will be rnoted that relay ZRHR is energized over the ypolar contact '44 of relay ZRTRA ywhich is .closed to nthe left.

Accordingly, relay ZRHR Ywill not become :energized when the polarity of the line circuit code .is negative, .as it will be when the :entrance sig- Veach time that the back point of .contact 4,5

closes. The manner in which this impulse operation of relay 2RZ is obtained is well known, and is described, for example, in the United States Reissue Patent No. 21,783 granted to Herman G. Blosser on April 29, 1941.

Each time that relay 2RZ closes the iront point of its contact 3l, an impulse of feedback code will be supplied to the line circuit during the off period of the master code being received by relay ZRCR. The circuit -for supplying the feed-back code includes the front contacts t and 4l of relays ITR and ZRKM, and the back points of contacts 48 and 49 of relay `ZLAHR. rfhis feed-back code is polarized, being of negative polarity when relay ZLAHR is deenergized, as shown, and of positive polarity when this relay is energized. That is to say, the feed-back code is either positive or negative according as signal ELA is cleared or not.

Relay STRA will be energized by the feed-back code during the time `that the back point of coding contact 29 of relay @CTM is closed so that relay BCR will be caused `to follow the feed- 'back code, provided that relay SI'TRA `has properlyresponded to the polarity of this code so that .the code is positive.

its polar contacts 50 and 5I occupy a position in agreement with the code polarity, whereby the polarized relay SCR is permitted to respond, as previously explained.

Code operation of rela-y SCR on feed-back code will cause the energization of Yrelay 3HR over the polar contact 52 inits right-hand position when the ,polarity of the code is negative, and will cause the energization of relay ,3DR over polar contact 52 in its left-hand posit-i011, when Relay SHR thus provides the approach aspect and relay 3DR provides the clear aspect of the intermediate signal 3, in the .usual manner. V

It willbe apparent from the foregoing that Athe master code in the section D-E provides a channel for the return of feed-back code to location vFisc that block control of ,the intermediatesignal 3 may b-eprovided. A `reversa-l of the polarity of the master code will cause jrelay HR at the intermediate signal to release due to opening of polar contact 28 of relay 4TRA, thus insuring that the eastbound intermediate signal 4 will remain at stop under the westbound traffic condition. The opening of the front point of Contact 69 of relay JlHR will prevent pick-up of the eastbound directional stick relay llSl. under the westbound trac condition. The eastbound di- .rectional stick relay SSR will be picked up in the usual manner over the front point of contact 6l of relay SHR and the back contact 62 of relay STR at the moment when the train enters *section 2RT. Relay SSR will `subsequently .remain energized over Vits stick `circuit until feed-back code to pick up relay EHR is yrestored Vin section D-F.

'Ihe operation of the line circuit between signals 3 and 6L on feed-back code is videntical-with that just described yfor the block between signals 2R and 3 except for 4the inclusion Yof a back contact 53 of the opposing directional stick relay ASR, and the inclusion of the additional front contact 5t of thedirectional stick relay v3SR when relay 3ER is deenergized, in 'order to provide control for following moves. rilhe -feed-back code which is applied at location F is detected at the east end H by relays tLHR and ELDR in the same manner as described for relays GHR and 3DR `at location F so that no further ldescription of vthis operation is required.

When an eastbound move is to be made and signal 2RA is cleared for such a move, the approach locking relay ZRKM governed by signal 2RA will be deenergized and so will open the feed-back circuit described above for the control of signal 3, at its front contact 41. Relay 3CR will accordingly be deenergized causing relay 3HR to release, and as relay 3SR will also be deenergized, both front contacts 55 and 56 of relays 3HR and 3SR, respectively, will be open so that no feed-back code will be applied to the line circuit between locations F and H. Accordingly, relays 6LHR and 6LDR will both be deenergized so that signal 6L must remain in the stop position. Master code alone will thus be applied for the eastbound trafc condition.

As the eastbound train proceeds through the stretch and passes signal 4, the eastboundirectional stick relay 4SR will be energized in the usual manner. Since relay 4HR is now deenergized because the train is between the signals 4 and 6R, relay 3CTM will operate at the 75 code rate so that master code of positive polarity will be applied to the line circuit between signals 2R and 4 over the front point of contact 5'.' of relay 4SR and the back points of contacts '4l and 4U of relays 4HR and 3SR, respectively.

Since the line circuit code is 75 and is of positive polarity, relay 2RHR at location D will be energized in the manner previously described, Vto

provide an approach aspect on signal 2RA, in A preparation for a following move into the single track stretch. If signal 2RA is maintained at stop, then the coded feed-back circuit will be operative to provide an approach aspect on the westbound signal 3.

If a westbound move is to be made with the stretch unoccupied, the clearing operation for signal 6LA or SLB will open the control circuit for relay SLKMP at front contact I I, thus releasing relay GLKMP, whereupon relay CTM will v operate on 75 code. The deenergization of relay SLKMP reverses the polarity of the master code supplied to the line circuit between signals 4 and 6R over its contacts l1 and I8 so that relay 4TRA will now close its polar contacts to the reverse or right-hand position. With relays 4HR and 4SR both deenergized, the polarity of the line circuit between signals 2R and 4 will also be reversed to negative, whereupon relay ZRTRA will likewise reverse its polar contacts, thus preventi ing the display of a proceed aspect by signal 2RA or 2RB.

It is apparent from the foregoing that the presence of negative polarity master code prevents the clearing of an eastbound signal and provides a path for the coded feed-back circuit which is effective in establishing westbound signal control.

In order to provide a block indication at the control oiiice, any of the usual and well-known indication arrangements may be employed. One suitable arrangement for-a. stretch having but one intermediate signal location is to control the block indication light on the C. T. C. panel over a front contact 63 or 64 of the usual eastbound or westbound block indication relay EBK or WBK, in multiple, as shown in the drawings. With this arrangement, the block light will indicate occupancy of the stretch independently of the position of the entrance signals. Other wellknown block indication arrangements may be used where the stretch includes more than one intermediate signal location. l

If it is desired to approach light the intermediate signals, a series relay such as 4AR may be used. This relay is connected into the master code circuit and will be deenergized only when the block between signals 2R and 4 is occupied. When relay 4AR is deenergized, a circuitwill be 'completed for lighting the lamp of vthe eastbound signal 4 in the usual manner.

The approach lighting of the westbound signal 3 can be limited to the time during which the block between signals 3 and 6R is occupied. This is accomplished by means of the relay 15P at location F. This relay will be energized only when the associated line circuit is transmitting master code of negative polarity. The illumination of signal 3 will then be controlled over the back contacts 58 and 59 of relays 4HR and 15P respectively. If relay 15P is not used and the illumination of signal 3 is controlled over the back contact 58 of relay 4HR alone, then signal 3 will be illuminated under the same conditionsk which cause illumination of signal 4. Relay 2RHS is the usual home stick relay for the eastbound signal 2R and becomes picked up when signal lever 2 at the control oflice is moved to the R position, thereby transmitting a C. T. C. code to the eld station unit at the west end for energizing the terminal 92 which'causesfpick-up of relay 2RHS. Once relay 2RHS picks up, it closes a'stick circuit vfor itself over the front contact 65 land the'ront contact 66 of relay ITR, to theenergized terminalY 94. The details ofthe communication systemfby means of which the operator at the' control oice may selectively operate the apparatus at the eld station locations over the C. T. C. line and receive indications from these field stations, do not enter actively into my present invention. One`form of communication system suitable for use in my system is thatl shown iny Letters Patent of the United States No. 2,229,249 granted to Lloyd V. Lewis on January 21, 1941, for Remote control system, and the numbering of the terminal wires which are used to perform analogous functions corresponds with that used in this patent.

When the eastbound train enters section ZRT, relay ZRTRwill be shunted so that relay ZRCR will release due to opening of the line circuit at front contacts 36 and 38 of relay ZRTR. iDeenergization of relay ZRC'R will discontinue'the code output from transformer DT so that'relay ZRDRwill release, closing its back contact 69 ,to energizeterminal 81,of'the eld station unit. Energization of this terminal causes a C. T; C. indication code to be transmitted inwell-known manner to the controloilice for-energizing'the eastboundfblock indication relay EBK which now closes its front contact 63 .to energize the block light for providing a block occupied indication. Referring again to the pick-up of relay 2RHS over the C.A T. C. code equipment, when this relay picks up, its back contact 10 will open the normally closed circuit for the locking relay 2RKM for signal 2R, releasing this relay so as to prevent the supplyof feed-back code at the west end and thus prevent the establishment of westbound traic at such time as relay 2RHS is energized for clearing the eastbound signal 2R. The stick circuit for relay 2RKM also includesthe iront contact 1| of relay ZRRGPR (whichis energized only when signal 2R is Vat stop), and the front point of its own front contact 12. The pick-up circuit for relay ZRKM alsovincludes front contact 13 of the approach relay ZRAR and the front contact 14 of relay lNWPwhich repeats the normal position ofthe track switch l for the passing siding PSI. Front contacts'13 and 14 of relays ZRAR and INWP can be shunted inthe usual manner over either one of two parallel paths, the first of which includes the back contact l5 of track relay ITR and the second of which includes .the checking contact 'i6 of the usual time element release 2RTER and the front contact 'l1 of the time element -stick relay ZTESR. All of these circuits -for relay ZRKM are Well known in C. T. C. signaling and are shown merely to make the disclosure more complete.

At vthe east end of the single track stretch, relay SLI-IS will be similarly controlled by a movement of signal lever 6 at the control oiice to the L position and when picked up for clearing the Westbound signal 6L, Will cause the locking relay GLKM to release. so as to lock out the eastbound traiiic direction. v

From the foregoing ldescription it Will be apparent that I have provided a simple form of coded line circuit control for traflic 'moving in either direction over a stretch of single track. By employing master and feed-back codes and by polarizing `these codes, I obtain selective control of the traffic direction as Well as control of the signal indications over the stretch.

Although I have herein shown and described only one form of railway trailic controlling apparatus embodying my invention, .it is understood that various changes and vmodifications may be made therein Within the scope of the aippended claims `Without departing from `the spirit and-scope of my invention.

1 Having thus described my invention, what I claim is:

1. In combinationwith astretch of track over which traiiic may move in either direction, a line circuit extending from one to the other end of said stretch; means for normally transmitting line current impulses of a master code from one to the other end of said line circuit to establish tralric in the normal direction over said stretch, an entrance signal for each tramo direction over said stretch, means effective when the entrance signal for said normal direction is at stop for transmitting line current impulses of a feed-back code during 01T intervals in said master code from said` other end to said one end of the line circuit, means responsive to the receipt of said feed-back 'code at said one end for controlling the entrance signalfor the reverse traic direction, and means effective when the entrance signal for said lnormal direction is cleared for discontinuing said feed-back code to thereby prevent clearing of the entrance signal for said reverse direction.

2.A In combination with a stretch of track over Which traic may move in either direction, a line circuit for controlling traiiic over said stretch, a first entrance signal for the normal direction of traliic and a second entrance signal for the reverse direction of tramo, means for lnormally transmitting line current impulses of a master 'c'ode from one to the other end of said line circuit to provide control for said rst signal, means effective when said rst signal is at stop for transmitting line current impulses of a feed-back code during off intervals in said master code from said other to said one end of the line circuit, said feed-back code impulses being of positive or of negative polarity in accordance with the condition of traic moving in said reverse direction beyond said stretch, a polarized relay responsive tothe receipt of said feed-back code at said one end for selectively governing the indication of said second entrance signal according as said feed-back code is positivem" negative, and means effective when said rst entrance signal is cleared for discontinuing said feed-back code to thereby prevent clearing of said second entrance signal.

3. Incombination with a stretch of track over which traine may move in either direction, a line circuit extending from one to the other end of said stretch for controlling traiiic over the stretch, an eastbound and a westbound entrance signal for said stretch, means for transmitting line current impulses of a master code of positive or negative relative polarity from said one to said other end in accordance With the direction ol traiiic being established over said stretch, a polarized line relay ladjacent said other end assuming a normal or a reverse position according as said master code impulses are of positive or negative polarity, means effective when said polarized relay is in its normal position for clearing said eastbound signal, other means eiectiv-e when said polarized relay is in its normal position and said eastbound signal is at stop for transmitting line current impulses of a feed-back cote from said other to said one end, means responsive to the receipt of said feed-back code at said one end for clearing said westbound signal, and means eiiectlve when said eastbound signal is cleared for discontinuing said feed-back code to thereby prevent `clearing of said westbound signal.

4. In combination with a stretch of track over which trame may move in either direction, a line circuit extending from one to the other end of said stretch for controlling tramc over the stretch, a normal direction entrance signal and a reverse direction entrance signal located at said other and said one end respectively of said stretch., means effective when and only when said reverse entrance signal is at stop for transmitting line current impulses of a master code from said one to said other end of the stretch, means responsive to the receipt of said master code at said other end for clearing said normal entrance signal, means controlled by said master code effective When and only When said normal entrance signal is at stop for transmitting line current impulses of a feed-back code during off intervals in said master code from said other end to said one end, and means responsive to the receipt of said feed-back code at said one end `for clearing said reverse entrance signal.

5. In combination with a stretch of track over which traiiic may move in either direction,v a line circuit for controlling traino over said stretch, means for transmitting line current impulses of a master code of positive relative polarity in a given direction over said line circuit to thereby permit traflicmoving in the normal direction to enter said stretch, means for reversing the polarity of said line current impulses to thereby prevent normal direction traflic from entering said stretch, and means effective when the polarity of said line current impulses is reversedv for transmitting line current impulses of va feed-bacl code during off intervals in said master code in the reverse direction over said line circuit to thereby permit traic moving in the reverse direction to enter said stretch.

6.In combination with a stretch of track over 'which traiiic may move in either direction. a

line circuit for controlling tralc over said stretch, a normally energized traino direction control relay, means eiective`when said relay is energized for transmitting line current impulses of a master code of given polarity over said line circuit to thereby permit traic moving in the normal direction to enter said stretch', means for deenergizing said relay to reverse the traiiic direction over said stretch, means eiTective When said relay is deenergized for reversing the polarity of the master code transmittedover said line circuit, means responsive to said reverse polarity master code for preventing normal direction traffic from entering said stretch, and means operating when said reverse polarity master code is eiective for transmitting line current impulses of a feed-back code during off intervals in said master code over said line circuit to thereby permit traic moving in the reverse direction to enter said stretch.

. '7. In combination with a stretch of track over Whichtrac may move in either direction, a line circuit for controlling traic over said stretch, a normally energized trairlc direction control relay, means effective when said relay is energized for transmitting line current impulses of a master code of given polarity over saidline circuit to thereby permit traiiic moving in the normal direction to enter said stretch, manually controlled means for deenergizing said relay to reverse the traiiic direction over said stretch, means eiective when said relay is deenergized for reversing the polarity of the master code transmitted over said line circuit, means responsive to said reverse polarity master code for preventing normal direction-trahie from entering said stretch, and means operating when said reverse polarity master code is eiective for transmitting line current impulses of a feed-back code during off intervals -in said master code over said line circuit to thereby permit traiiic moving in `the reverse direction to enter said stretch.

8. Apparatus for controlling trado moving in one or the other direction over a stretch of track by means of a line circuit comprising, in combination, means for transmitting currenty impulsesvof a master code of given polarity over the line circuit, means responsive to said current impulses for establishing traffic in the normal direction over the stretch, means for reversing the polarity of said master code impulses, means responsive to master code impulses of said reverse polarity for preventing entry of normal direction traic into the stretch, means for transmitting current impulses of a feed-back code during oft intervals in said master code over the line circuit, and means responsive to said feed-back code impulses for permitting traiic'moving -in the reverse direction to enter said stretch. Y

9. Apparatus for controlling traic moving in one or the other direction over a stretch of track by means of a line circuit comprising, in combination, means for transmitting current impulses of a master code of given polarity over the line circuit, means responsive to said current irnpulses'for permitting initiation of traiiicin Vthe normal direction over said stretch, means for transmitting current impulses of a feed-back code during oi intervals in said master code over the line circuit, means responsive to said feed back code impulses for permitting initiation of traino in the reverse direction over said stretch,

means for discontinuing said feed-back code to prevent completion of traffic in said reverse direction and permit completion of traic'in said normal direction, and means for reversing the polarity of said master codeto prevent completion of traflic in said normal direction and permit completion of traffic in said reverse direction.

10. In combination with a stretch of track over which trailicV may move in either direction, a line `75 circuit for controlling traic over said stretch, a normally energized traffic direction control relay, means eiective when said relay is energized for transmitting line current impulses of a master code of given polarity over said line circuit to permit initiation of the normal trafiicv direction over said stretch, meansl for transmitting line current impulses of a feed-back code during oir intervals in said master code over said line circuit to permit initiation of the-reverse traine direction over said stretch, means for discontinuing said feed-back code during the time that .relay is operated toits rstrposition fortransmitting line current impulses of a mastercode of given polarity over said liney circuit to permit initiation of the normal traine direction over said stretch, means for transmitting line rcurrent impulses of a feed-back code during oi intervals in said master code over said line circuit to permit initiation ofthe reverse traino direction over Vsaid stretch, meansY for discontinuing said feed-back code dring the time that said master code is effective for completing said nortion and for completing the reverse traiicdirec-- tion. v

l2. In combination4 with aV stretch of track over which traffic may move in either direction,

a line circuit for controlling Atraiic yovermsaid stretch, a i'lrsft and a second normally energized checking relay adjacent the respectiveV ends of thevstretch for checking the stop position-of the entrance signal associatedtherewith, meanseiecf tive Whensaid nrst checking relay is energized A for transmitting line current impulses of amaster code oiAgiven polarity over said linecircuit ,to-

permit initiation of the normal trac direction oversaid stretch,rmeans eiective when said second checking relay is energized for transmitting line current impulses of a feed-back code duringv oir intervals in said master code over said line; circuit to permit initiation of the reverse trainc.

direction over said stretch, means for selectively deenergizing saidV rst or vsaid second checking relay, means effective when s aid second checking relayvis deenergized for discontinuing said feedback code to prevent initiation of said reverse` traiiic direction, and means eiective when said first checking relay is deenergized fortreversing the polarity of said master code to prevent intiation of said normal trailcdirection.

13. In combinationwith a stretch of track over which trafc may move in either direction, aline circuit for controlling traiiic over said stretch, a

first and a second entrance signal at therespece.

tive Jends of said stretch for controlling the .entry of normal and reverse traiiicv respectively intov said stretch, a rst and a second manuallyopers,

able lever for governing said first and said second entrance signal respectively, means effective When said rst sig-nal is at stop for transmitting line current impulses of a master code of given polarity over said line circuit to permit clearing of said second signal by said second lever, means effective when said second signal is at stop for transmittingv line current impulses of a feed-back code during oi intervals in said master code over said line circuit to permit clearing of said-first signal by said rst lever, means effective when said second signal is cleared for discontinuing said feed-back code toprevent clearing of said first signal, and means effective when said rst signal is cleared for reversing the polarity of said master code to prevent clearing ofsaid second signal.

14. In combination Witha stretch of track over which traffic may move in either direction, a line circuit for controlling traffic over said stretch, means for transmitting line current impulses of a master code of given polarity over saidline circuit, rst decoding means selectively responsive to said mastercode of given polarity and eective for controlling the. entryofv normal direction traffic into said stretch, means for transmitting line current impulses of a feed-back code during off intervals in said master code over said line circuit, second decoding means selectively responsive to said feed-back code and-effective for controlling the entry of reverse direction traffic into said stretch, meanseiective for establishingnormal traine conditions-by` discontinuing said feedback code to render said second decoding means ineffective, and means eiective for establishing reverse traffic conditions-by reversing the polarity of said mastercode te thereby rendersaid first decoding means ineffective.

15. In combination with a stretch of track over which traffic may move in either-direction, a lineA circuit forcontrolling traino over saidstretch, means for transmitting line current impulses of a master code of given polarity oversaid line circuit, rst decoding means selectively responsive to said master code ofgiven polarity and effective for controlling the entry of normaldirection trai-ric into said stretch, means for transmitting line current impulses ofa-feed-back code-during off intervals i-n-saidmaster-code-over` said line circuit, second decoding means selectivelyresponsive-tosaid-feed-backcode-and-effective for controlling the entry ofreverse directiontraffic into said stretch, manually controlled means efiective` for establishing normal -traiie conditions byl discontinuing saidfeed-bacio code to render said seconddecoding means-ineffective,- and manually controlled means effect-ivefor establishing reversetraiiic conditions-by reversingthe polarityofsaidmaster codeto thereby rendersaid first decoding means ineffective.

16. InY combination With a stretchcftrack over which trailc Amay ymove ineither-direction, a line. circuit for controllingtrafcover-saidstretch, means-for transmitting line current imy pulses of a master; code ofv given polarity over saidy line circuit, first` decoding means selectivelyresponsive to said master code of given-l polarityand effective for controllingj the entry ofnormal direction traic into saidstretch, means for transmitting lineA current impulses of a feedback code. during off intervals insaid mastercode over saidv line circuit, second decoding means selectively responsive to said feed-backcode and effective for controllingV the entry'- ci reversek direction traine into said stretch,- manually operable means. at a control office effective for establishing normal traflic conditions by causing said feed-back code to be disconnected to thereby render said second decoding means ineffective, manually operable means at. saidA control oiiice effective for establishing reversetrafc conditions by causing the polarity of said master code to be reversed tothereby render said first decoding means4 ineffective, .anda

block indicator at said control oilce for providing an,l indication when either said irst or said.

second decoding means is effective.

17. In combination with a stretch of track..

over which traffic may move in eitherdirection,

said stretch including a first and a secondY ad-vr joining track section, an. intermediate; signal adjacentv the junction of said; tvvov sections,. a. line circuit from said rst to said second section for permitting traffic moving in the normal direc.-

tion to enter: said second section, means; forreversing the polarity of. said master code to thereby prevent,I IQIIIlalV directiontrafc fromentering said stretch, means effective when the. polarity of said master code is reversed for transmitting line current-l impulses o-, a feed-back code.. during ofi intervals in said master code.- over; the

line circuit from Said second section tol said-first, section to thereby permit, traic, moving; in; the

reverse direction to enter. saidrst section-,and

meansA adjacent said junction and: responsive; to Y prior tothe establishment of traiiic inthe normal direction for transmitting line current impulses ofa feed-back code during off intervals in said master code over said line circuit from said second to saidflrst section, to thereby permit traffic moving in the reverse direction,4 to enter said rst section, means effective during occupancy of saidrst section` by-,saidv reverse direction traiiic for transmitting line current impulses of a master-code of reverse polarity over the line circuitof said second section-to. thereby provide a channel for ythe return of feed-back c ode to the intermediate signal location, means stretchincluding aliirst and a second adjoining track section, an intermediate Ysignal adjacent the junction of said. two sections; a linecircuit for controlling traffic over said stretchymeansfor transmitting; linecurrent impulses of; ai master code of` normal polarity over saidl line; circuit from`said first to. said second section for-'perline current impulses of a master code of reverse polarity to the line circuit of said second section to thereby provide a channel for the return of feed-back code to the intermediate signal location, means effective when said master code is present in the line circuit for said second section for supplying feed-back code thereto, and means eiective when said feed-back code is received at the intermediate signal location for clearing said 10 intermediate signal.

JAMES J. VAN HORN.

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