US2341261A - Remote control system - Google Patents

Description

sheets-sheet 1 G. W. BAUGHMAN REMOTE CONTRLSYSTEM Feb. 8,1944.

Original Filed March 28, 1940 mcm@ @QN Gi W. BAUGHMAN REMOTE CONTROL SYSTEM Drignal Filed March 28, 1940 Feb` I8, 1944.'

2 Sheets-Shet 2 NTA aww

ne mj bow@ Patented Feb. 8, 1944 REMOTE CONTROL SYSTEM George W. Baughman, Swissvale, andNorman F. Agnew, Penn Township, Allegheny County, Pa., assignors to The Union Switch & Signal Company, .Swissvala Pa., a corporationof Pennsyl- Vania 4Original application 'March '28, 1'940, Serial No.

326,440, now Patent No. 2,303,875, .datedDecem- .ber 1, 1942.

Divided and this application August 2'1, .1942, Serial No. 455,578 y 10 Claims. (Cl. 17T-353) yOur invention relates to remote control systems, :and ymore particularly, to the communication or .line circuits for centralized traffic control systems for railroads, in which a train-dispatchers `office or other .suitable point o'f control is connected with Va plurality of eld stations by line-Wires, over which impulse codes of -signals are transmitted .at times for controlling selected `devices at the stations, and at other times Vfor indicating the condition of station devices at the olce.

Our invention is ian improvement*uponv the system disclosed Letters lfatent of the United ASta-tes No. 2,229,249, granted 'January A21, 1941., to L. V. Lewis,:for Remote control systems. The present :application is va Adivision of our copending application, `Serial No. 326,440, filed March 28, V1940 for Remote control systems, issued :as Letters Patent ofthe United States No. 2,303,875, on December 1, 1942.

Since Va .dispatchers telephone or telegraph line .is generally required in connection with systems `of :this character, it `is almost always the case that line wires are :available throughv out the length of any stretch of territory lwhich is to be controlled by a centralizedtraic control ;system, which are suitable `for use for communication by code between the ofce and :sta-- tions of that system, butwhich are already in use for other communication purposes.

One object `of our invention xis to provide 'an improved centralized trafc vcontrol system of the code type 4which is adapted to employ existing line @Wires for the transmission of -codesignals, Without interference with the `joint use'of these wires for telephone and telegraph communication or for -other purposes.

It is often convenient to employv the .dispatchers telephone line .-for C. T. C. communication. This Jgenerally comprises two line wires across which way station telephones and call selectors are bridged, and which, in addition, is simplexed to Aprovide a continuous metallic circuit over the two ,line wires in multiple which may be included in :a through duplex telegraph circuit. Furthermore, :a message line which is similarly arranged generally parallels the dispatchers line, `in which case a long distance or phantom telephone :circuit is usually superimposed upon the two telegraph branches, butas is Well-known, this requires that a reasonably accurate balance be maintained between the two side circuits. On this account it is preferable to maintain the continuity of the line wires intact .from end to end. This is accomplished Vthe stations to. thev oiiice.

in the .system of ourinvention by so arranging `the-C.v T. C.apparatus that it may be connected to the line wires by means of simple bridged connections, and in our system there is no C. 5'I'. C. apparatus Whatever in series with the ilinewires,l an arrangementwhich is also of advantage -in ,testing ythe lline circuits and in arranging @for the independent maintenance of the different services as usually provided.

The system of our invention as herein disclosed employs two-non-interfering sources of current of different characters normally connected to the opposite ends ofthe line, the one -atithe oilice end .being employed for the transmission ofcontrol codesto the several stations, -zand-thefone'at the remote end being employed forthe transmission of indication codes from In respect to this vfeature, the present invention is an Iimprovement-uponfthat disclosed in the Letters Patent of .the yUnited States No. 2,224,374, granted December 10, 1940, to George W. Baughman, for Remotefcontrol systems. Y

Heretoforefbridged line circuit lsystems have nusually'recmired sources of line current at each eld station, and consequently the series C. T. C.

v:circuit `as illustrated, for example, inPatent No.

2,229,249 above mentioned, has generally been preferred lbecause it can be energized more conveniently and `economically when the source of vcurrent iiscentrallylocated vat a central ofce where it may .be readily maintained by the usual supervisory forces in charge of the Wire plant. These advantages lare attained in the system herein disclosed even though two sources of line current are used, inasmuch as one of these may be located :at the C. T. C. ofce as heretofore, vwhile the second `may be located at another `point Where supervision is available, a suitable point being lthe :main oiflce at which the remote end .oi the line is terminated, `even though this may be situated yat a considerable distance beyond the last C. T. C. station.

Another ,object of our invention resides in the provision of apparatus for signaling to a central office from' a plurality of spaced points located along va .line circuit by merely connecting the line wires together, preferably through an impedance :suitably `:arranged so as to permit the joint use tof :the Iline wires for other purposes Without interference. Our invention also includes in a system of this character provision for `signaling from the transmitting stations in the field not only in one direction to the control oilice but also in the oppositie direction to lock out the apparatus at any higher degree of attenuation of the line currents"` to be tolerated and permits simple one way repeaters of well-known forms to be interposed in the line as required, and is .thereforewell usual manner by the provision of a choke coil 'l and resistors 8 and 9 bridged across the line wires Y and Z at each end, to the mid point of which a connection ismade toawireXl or X2, to provide a'. duplex telegraph .circuit extending from ground at each end through standard terminal i apparatus such as that shown connected to wire Xl, comprising the line batteries Bl and NI, the contacts of the pole changer PCI, and thence adapted to long distance transmissionpurposes.

Other objects, purposes and features of our invention will be pointed out as the descriptionv proceeds.

Two modications of our invention will now be described, and the novel features thereof will'l then be pointed out in claims.

Referring to the accompanying drawings, Fig.

1 illustrates in diagrammatic form one form of centralized traffic control apparatus embodying our invention employing a source of direct current atthe office and a sourc'eof alternating current at the remote end of theline for two-way code communication between a control oce and a plurality of stations connected by line wires which are continuous from end to end. VFig. 2 illustrates the second form of our invention, in which alternating currents of different frequencies are used for code transmission in the two directions. l

Similar reference characters refer to similar parts in each lof` the several views.

Referring to Fig.Y 1, the reference characters Y and Z designate the two line wires which providena circuit for code communication between thefofcve and stations of our centralized traic control system, and it has been assumed that the4 liney wires' are arranged to provide other communication facilities in a manner whichis more or less typical'of actual conditions'in this eld, but ,with which'we'are not concerned further than to point out the'variety of facilities that may be provided and to make clear that these vfacilities and our C. T. C. systemare mutually noninterfering. These facilities will first be briefly'explained.

Primarily, the line wires Y and Z provide a telephone circuit arranged for train dispatching purposes, and are connected at one end through condensers 2. and the telephone transformer 3 to telephone apparatus 5 located at the dispatchers oflice, and at the other end through a similar connection to similar telephone apparatus 5 located at another'main ofce. VThe dispatchers oiilce is also providedA with a telephone call selector system which is assumed to be of the type shown in the Field Patent No. 1,343,256, granted lJune 15, 1920, comprising a plurality lof lcode wheels .189 by which the dispatcher may transmit impulse codes to selectively call various way stations to establish telephone communication therewith. Since these stations are all alike, but one is shown, as indicated by the legend Selector station on the drawings, and each comprises a :selector 'lz'bridged across the line wires Y and Z through'avr condenser 14, for selectively operating a callzbell 16. The station operator, when called, establishes a connection with the dispatchers office by connecting his telephone acrossthe line'by means of jack'l'l. In order to -facilitate anunderstanding of this apparatus, the; reference .characters designating the elements of theselector system shown herein are the `same as those of the Field patent. j'l'he dispatchers line is simplexed in the -other contacts are identied'by number.

differentiallythrough the windings of the line relay RI to' wire XI or X2, or through an arti- The dispatchers line is also phantomed in a well-known manner, the two line wires Y and vZ inr multiple constituting one side of a telephone circuit extendingfrom a telephone jack 6 at each end over wire'Ul or U2 to a connection to the line wires Y and Z effected at the mid point of condensers 2. It is to be understood that the other side of the phantom circuit, not shown, is similarly arranged and comprises another pair of line wires, similar tof-Y 'and Z. It will be seen that each side'of the phantom circuit, one of whichl comprises Vthellinewires Y and Z in'multiple, is employed jointly for telephone and telegraph purposes in-accordance with a well-known composite arrangement,vv by reason of the condensers 2 in series with wires Ul=-and U2, and of the choke Icoils 'I0 in series with wires XI and X2,and condensers H connected between these wires and ground. l

The central omce equipment ofthe C. T. C. system of our invention: is assumed t'o be located at the dspatchers oice, this being identified by the legend Ofcein Fig. 1, and the C. T. C.

v`eld stations are assumed to'be located at various pointsrv along the line indicated by branch connections to line'wire's VY and-Z. 'Since all the C. T; C.l stations are similarly arranged, for simplicity but one is shown, this being indicated by the legend-0. T. C.'station on the drawings.

ThefC. T lC. 'apparatus'which is employed in the system "of our invention for generating and receiving the lcodes'may be of any suitable type, but' inthe speciflcembodiment `of our invention disclosed he'reinthis` is to be'understood to b'e of the well-knownl time code'typeasdisclosd in the Lewis Patent No; v2,229,249 hereinbefore 'referred'tm but modified incertainrespects in accordance with the'requirements'ofvour invention as` will hereinafter be'lpointed out. In the drawingsof this patent, the lrelay contacts are identified by lower case letters, and to facilitate an understanding of our invention, we have desig- "nated those relay contacts shown in the accompanying drawings whichfcorrespond to contacts of correspondingly designated'relays inthe sys'- tem of this Lewis vrpatent by the same reference characters as are employed in the patent, while Furthermore, relays located at the oflce are distinguished by the prefix O, where similar 'relays are used'at the oiice andv stations, as in 'the patent, and it is to'be understood that all of the C. T. C. apparatus theoperation of which is not rspecifically describedwhereinl functions in the manner' described in the patent. `The circuits by which the slow acting relays Llare controlled by the line relays as shown herein and likewise the circuits for the master relays OM and M are similar to the corresponding circuits of the patent and are reproduced herein merely for convenience.

Our invention relates particularly to the provision of improved line circuits and-'those disclosed herein differ `very materially from that of the Lewis patent, where the' oflice line relay OR and the station line relays R Aare all normally energized in series overv line wires-Y and `Z by a central oce battery 8U. As disclosed herein in Fig. 1, the ofce battery Si] is employed as a source of code impulses for both the C. T. C. system and the selector system, in. transmitting codes from the office, and the twov systems are so arranged that but one can obtain control of the line at a time in a manner somewhat similar to that disclosed in Letters Patent of the United States No. 8,248,935, granted July 15, 1'94-1, to George W. Baughman, for lRemote control systems. In Fig. 1 the line wires 'Y'y and Z are nor.- mally energized by current from battery sover a connection which may be traced from line Y, through the upper coils of a low pass filter network I2 similar to that of the Field patent, back contact I3 of the connecting relay 8.6 of the selector system, back contact I4 of relay PC, back contact b of the C. T. C. transmitter relay OT, battery 8f3, back contacts I5 and II of relays PC and 8B, the lower coils of the lter I2 to wire Z. Relay PC is an additional relay, not shown in the Lewis patent, the purpose of which ywill be explained hereinafter.

The station line relays R employed herein are of the high resistance biased polar type. In Fig. 1 each relay R is connected across the line wires Y and Z through a low pass filter I2, over back contacts 29 and 3i) of the station master relay M, and is normally energized by current from the office battery 8D to maintain its left-hand or lfront contact 158 closed, as shown. Each relay R as employed herein therefore functions to control the station coding unit precisely like the normally energized relay YR of the Lewis patent, -in response to the control codes delivered to the -line circuit as the result of the periodic opening of contact b of the office transmitter relay OT as rdescribed in that patent. For convenience, the normal direction of current -in the winding of each biased polar line relay is indicated by an arrow.

The ofiice line relay OR is also of the biased polar type like the relays R, but itis normally energized from a different source, namely, by amplified and rectied currents supplied over line wires Y and Z from a source of alternating current indicated by the supply terminals BXI and CXI, which source is connected through `a transformer 'l5 across the vline wires at a point ladjacent to or at the right 4of the last station connection, as shown.

In view of the fact that the line wires are ar.- ranged Ain Fig. vl for joint communication pur poses, a relatively high `frequency of alternating current is employed to avoid telephone interference, but it will be `understood that under other circumstances sixty cycle current or the like may be used. As shown, therefore, the terminals BXI and CXI represent a source of alternatingcurrent of a frequency I above the voice frequency range which continuously supplies current to the line wires VY and Z through transformer '15 and a coil 'I8 and condensers CI tuned -to the free quency f1. This apparatus maybe located at the main oice at which the line wires Y `and Z terminate, for convenience in maintenance, even though this may be at a considerable distance beyond the last C. T. C. station, as already mentioned. The alternating current received lat the -C. T. iC. otlce over line wires Y and Z energizes a circuit tuned Ato the frequency fl comprising 1 the Lcoil 8l and ,condensers CI bridge across line Wires Y and Z, the resonant potential across coil 8l being amplied in a conventional manner by the amplifier A if required. The output of ampl-ier A of frequency fI, passes through trans former 83 and is converted to direct current by rectiier 84 to energize the office line relay OR.

The starting circuit at the ofce by which relay .OM is energized to initiate control codes is arranged as heretofore, to include a front contact c of a start relay identified by the legend Start on the drawings, and back contacts b .of relays OLI and CL2. Since the two last named relays are both released only when relay OR remains steadily energized, it will be apparent that control codes .can be initiated as heretofore only when the system is in its normal at rest condition.

However, this diierence is to be noted: Since the ,oiice line relay OR as shown herein is energized vby a source at the distant end of the line, it follows that a control code, being dependent upon the operation of relay OR, cannot be delivered to an open line, nor can it be de.- livered to a short circuited line as when a series line circuit is used as in the system of the patent, but only to a line that is free and available throughout its entire length, and that either a cross or an open circuit i-n the line at `any point is immediately made manifest at the oilice by the release o f the line relay OR, so that the proper action may be promptly taken.

When relay OT operates its contact ib to deliver a control code, relay VOR is operated in unison with the station relays R by the contact 85 of relay OT just as if relay OR were in series with the battery line as in the system of the patent. Thus each time relay OT picks up to open the line circuit at its contact bi, relay OR is deenergized by the opening of its local Circuit at contact 85 of relay OT, causing relay OR to operate its Contact 24 t0 the left to connect terminal B to wire I8, which corresponds with the wire leading .to the back contact of the normally energized oillce line relay OR of `the Lewis patent. Likewise, each `time relay OT releases to .close the line circuit, the local circuit -jfor relay OR is completed at contact 85 to restore relay .OR to its normal position as shown, thereby to .connect terminal B over its righthand contact v2.41 to wire Il, which .corresponds `with the wire leading to the front contact of re- .;lay yOR of the patent. It will be clear that during the trans-mission vof control codes, relay OR, as disclosed herein lfunctions to control the oice ,coding unit in the s ame manner, and consequently these codes will be transmitted precisely as .described inthe patent.

The wires Ila and IzBa. leading to contact 58 of each station line relay R correspond to the con- .trol wires of the coding units which lead to the -f-ront and :back contacts, respectively, of the station vline relays R .of the patent, and consequently the stations will receive the control codes as described in the patent. No further description of vthe transmission or reception of control codes is .deemed necessary.

A -feature .of .our invention is the transmission l.of indication codes 'by shunting the line, that is, by connecting the line wires together periodi- .cally over a Contact .of the station transmitter relay T to thereby divert the current supplied .constantly to the line wires from the source at the distant end away from relay OR, so that relay .OR will be released periodically to repro.-

duce the code' thus delivered to the line wires by relay OT. In Fig. 1 ahigh frequency bridge across the line, which presents a minimum impedance toi-the frequency fl delivered by the alternating current source having the terminals BXI and CXI, extends at each station from line wire Z, through one of the condensers CI and a coil 'F8 tuned to the frequency fl and over contacts 90 and 9| of relays E and T and the other condenser Cl to line wire Y. A low frequency, or direct current bridge, which is closed at the same time, extends from line wire Z through the low pass lter I2 and over contacts b of relays E and T to line wire Y.

It will be seen that in response to the code operation of the station transmitter relay T, the eiect of closing contact 9| is to shunt the cur rent of frequency fl from the office line relay OR, and the effect of closing contact b of relay T is to shunt the current from battery 80 from the station line vrelay R, since this shunt is applied across the terminals of relay R, so that these relays release each time relay T picks up the same as when they are included in a series circuit including a back contact of relay T as in the patent. In addition, a second high frequency bridge is closed at the beginning of an indication code for the purpose of initiating the code, extending over front contact 92 of relay M and back contact 93 of relay LBP, and a second low frequency bridge is closed at the same time over front contact 30 of relay M and back contact 3| of relay LBP.

The transmission of an indication code by a C. T. C. field station will now be explained. It is to be understood that a change in condition of a station device having indications to transmit picks upa start relay ST, which in turn, provided the station line relay R is steadily energized, picks up the master relay M to prepare circuitsfor governing transmitter relay T, and that relay T picks up in response to the closing of Contact e of relay M, in the usual manner. Relay T, when picked up, shunts line wires Y and Z by closing its contacts b at 9| as already explained. Relay M by the operation of its pole changer contacts 29 and 30 reverses the connections of relay R and at the same time completes the shunts including the front contacts 92 and 30. It will be seen, therefore, that at the be'- ginning of the code, the shunt is applied by relay M slightly before relay T picks up, and that relay R is released at about the same time that relay T picks up. The current'in the portion of the line circuit extending to stations more ref mote fom the ofce is reduced to release the line relays at these stations, while at the same time, the alternating current in the line portion extending to the oice is reduced to release relay OR, as a result of connecting the line wires together at the transmitting station by relay M, but since the shunts are selective as to frequency the use of the line wires for the transmission of other frequencies, such as for voice frequency communication, is not interfered with.

Furthermore, when the line is shunted the current flow from battery 8l! will be limited principally by the impedance of the intervening line wires, and the battery voltage as measured across line wires Y and Z will decrease in proportion to the distance from the office to the transmitting station to a value which is suiciently low to reliably release the relay R at that station as Well as those at most remote stations. It may be that this voltage is only slightly less than that 'of battery 80 at points near the ofce, if the shunt is applied at a far distant point. Consequently the shunt cannot be relied upon for the release of the relays R at stations between the office and the transmitting station, when long distances are involved. Our invention includes provisions for releasing these relays positively, this being effected in Fig. 1 by a reversal of the line polarity, as Will now be explained. When the oice line relay releases in response to the closing of front contact 92 of relay M, it disconnects terminal B from wire l1 and connects it to wire I8, so that the timing relays OL pick up sequentially, as described in the Lewis patent. Relay OR also completes a circuit from terminal B over wire I8, back contact d of relay LBP and back conta-ct 59 of relay OM through relay PC to terminal C. Relay PC therefore picks up and its contacts I4 and l5 reverse the polarity of the current delivered by battery to the line wires Y and Z. Whenv relay OLBP picks up, a stick circuit for relay PC is completed from terminal B, contact 35 of relay OLBP, back contact 36 of relay OlB. front contact 37 and winding of relay PC to terminal C. Relay PC remains energized until its stick circuit is opened either by the energization of relay Ol at the end of a completed code,or in other cases, 'such for example as when relay OR is accidentally reversed as a result of a line failure, by the release of relay OLBP.

The reversal of the line polarity by relay PC, which occurs at about the same time as the station relay T picks up, releases the line relays R at the remaining stations, or more particularly, at each station relatively so close to the office in comparison'to the location of the transmitting station that the low frequency shunt across line wires Y vand Z is not suflicient to elect the release of the corresponding line relay. At all stations,-therefore, the line relays R will release at nearly the same time, due either to the shunt initially applied by relay-M at the transmitting station or to the resulting reversalin the polarity of the line current, and each will disconnect terminal B from wire Ha and connect it to wire IBa to eiect the sequential energization of the associated timing relays L. It will be seen thatY each relay R which is supplied with current ofreverse polarity during the transmission of the code, that is, the relay R at each station that does not have its relay M picked up, will yremain in its reversed position for the duration of the code to hold relay L2 energized over wire I8a, so that its starting circuit will be held open at contact b of relay L2. The twoshunts across the line wires Y and Z which are due to relay-M are opened at contacts 3| and 93, respectively, as soon as relay LBP picks up and are held open by relay LBP for the duration of the code, When relay LBP picks up, it causes relay T to release to complete the first step of the code, as explained in the Lewis patent, whereupon the two shunts across the line Wires Y and Z which Aare due to relay T are opened at contacts b and 9i, allowing relay R at the trans-4 mitting station and the oiiice line relay OR to .pick up. Relay T then continues to operate its contacts repeatedly in the usual manner to transmit the code, relay R atthe transmitting station and relay OR at the oce picking up each time relay T releases, and releasing each time relay T picks up, to govern the operation of relay T and of the station coding unit precisely as heretofore, so that relay OR operates inunison with relay R and controls the oflice coding unit in the, usual manner to receive the code.

As explained in the Lewis patent, each indication code has sixteen steps, the last step comprising the return yof the line circuit to its normal condition, a relay I6 at the transmitting station and a similar relay OIG at the oliice being picked up momentarily on this step. It will be evident that Whereas in the system of the patent all line relays assume their Vnormal position at the beginning of this step, in the present case that is true of the oflice line relay OR and relay R at the transmitting station only, the remaining .line relays having been held reversed due to the reverse polarity of the line current.

At the oflice, relay Oil-6 opens its contact 36 at the beginning of .the final step, thereby opening the stick circuit for relay PC, which .therefore releases to restore the line polarity to normal. At this time relay OR is energized and so remains picked up.

At the transmitting station, relay I6 at its contact 40 disconnects Wire I 8a from the righthand contact 58 of relay R and connects wire lla to that contact, and at its contact c opens the stick circuit for relay M thereby releasing relay M to restore the connections of relay R to normal at contacts 2.9 and ,3U and .to complete the restoration ofthe station coding apparatus to normal. It will be seen that relay R at the transmitting station will be reversed momentarily on the last step unless relays PC and M happen to release .at precisely the same time, but that this is without eiect because the temporary connection over front contact l0 of .relay |16 maintains the coding unit in the same condition as if relay R remained steadily in its normal position.

The restoration of the line polarity to normal by relay PC causes the line relays R at the remaining stations to assume their normal positions, the resulting operations .of restoring all the apparatus to normal then ,being effected in a well-known manner as explained fully in the patent.

` It will'be apparent that the .mode of initiation of an indication code asabove described is positive in its action to .prevent interference in the event the oflice and a station initiate codes at the same time. More particularly, when rlayT releases to 'beginthesecond step o'f an indication code, the associated relay "R is"held released on the first step unless Ycurrent 'of reverse polarity is received from 'the 'o'ce If 'the oce'initiates a control code at this time, the line will'beheld open 'by relay-OT for a relatively long interval to release relay LI to thereby complete the'usual pick-up circuit forrelay-E;Whichcircuit as shown includes back contact g of `relay `-Ll,'fron1, contact c `of the counting'relay `I, contact 41 of relay LBP andthe reverse-contactSB of the 'line relay R. Relay E -upon picking up opens @its back contacts 'b` and f90 in the `shunts including contacts b andl, respectively, of relay T, and also opens the icircuitfor relay M at its `contact d .to release .relay M to stop `furthertransmission :from the station. .Relay M upon lreleasing conditions thestation coding unit=to receive the control code, .by rendering 'relay NR again responsive .to .line current .of .normal polarity.

It may happen, however, that Itwo lor more stations initiate indication ,codes .iat the same time. In this instance Y.they may Acontinue .Operation las long as the code elements :are alike,

but when a dinerence occurs one @1r-another is locked out by .means of an additional pick-up cir-- cuit provided for the station relay E. Y

It is to be vunderstood iin this connection that as described in the Lewis patent, the code selec.-V tion .of the several stations and of the corre- Sponding. .office panels is effected by the .combination of three long and fou-r short Vvsteps in a group comprising Steps 2 to 8, inclusive, of each. code. The code .calls are identified by .the 'long steps which they contain, for example, when the second, third and fourth stepsof a c ode are long and steps tive to eight are short, the station employing the code is designated 2,34 and a` selector relay 234s at the olice and a vcorresponding re-v lay S at station 234 will be picked up.

It will be evident from Fig. .l that when relay T picks up to begin an odd-fnumberedpstep of the code, the .associ-ated relay .R -will release, and that if relay T remains picked up to produce a long step, the shunt .produced by contact ib of relay T at .the transmitting station will remain effective at any station more remote Vfrom the oiicefor acorresponding length of time. At any such :station having a .code call in Which the corresponding step is short, relays R and Twill both 'fbe ldeenergized `for ka .time equal to the ldifference between 1a .short and ,a long step, during which time a lookout circuit will -be closed from terminal B, right-hand contact 58 of V*relay R, front contacts 4I and 42 of relays LBP and .M, back .contcat 43 .of relay T, relay E to terminal C, so that relay E twill'pick up to establishea stick circuit at :its .contact a and ,to open its ,Contact d to release relay M .and to also open its .contactsb andll .to prevent the transmission .of any additional code elements from that station.

On :the other hand, whenever relay T releases to begin an .even-'numbered :step of a code, itis necessary .that ,relay R becomeenergized immediately to open the lockout circuit ,for .relay `lil just traced before vrelay E picks up, as ordinarily `oo cursbeoause relay R is :relatively quick acting in comparison with relay E. If, however, relay T remain released to produce ajlong even-numbered step, .a .shunt applied by another station .nearer the-ollcehavinga callin `which the corresponding :even step isshort :will release relay Rat the more :remote station to :pick up relay tE vover ,its lockout circuit. It will Joe ,seen therefore that a 'long odd-numbered step ltakes precedenceover a A.short one, but that a short even-numbered step takes precedence lover along one. Tolinsure that the shunts Vproduced by relays Tlare `fully eiective, it is desirable to assign .the code calls :to the several stationsln a geographical order, that is, lso that the `call -for each station is superior to those Tfor all more remote stations .and 1inferior to those :for all stations nearer the goiice. The emost superior vcodecall is 351, conseguently, as vindicated in Fig. .1, this is assigned to lthe stationY nearest the oice, the nextin theorder of vcode superiority .is the lcode call 358 'which `:is assigned to the'gsecondgstation; next come .1356, :318, V36.1, :368 yand '345, in 4that order, and itall the zcodes are used, :the most remote station will havethemost inferior code call 24B.

'Itwill Ybe .apparent from the :foregoing that when indication codes .are Ainitiated by two v or more stations at the same time, the stationfnearest the oice :retains sole control of the v line, vand that several -codes 4initiated simultaneously will be stransmitted one A ata time in a ;-predetermine d orderasvheretofzore. y V

The `:relation fof the fdispatcherfs telephone call selector apparatus to the C. T. C'. system will now be explanied. This apparatus, as explained in the Field patent, comprises a plurality of code wheels 89, one for each selector, of which but one is shown herein, each of which when wound up and released makes one revolution during which a connecting relay 86 is energized to connect a source of direct current to the line over the contacts 44 and 45 of a pole-changer relay 81. As the code wheel rotates, relay 81 is intermittently energized over a circuit including the code wheel contacts 96 and 91 in accordance with the arrangement of the code wheel teeth to deliver a code of impulses of alternately opposite polarity to the line wires Y and Z to operate the selectors 12.

As disclosed herein, the selector apparatus is arranged so that the operation f a code wheel is ineffective unless it is released when the C. T. C. apparatus is in its normal at rest condition as manifested by the deenergized condition of relay OLBP at the oce. When relay OLBP is, in its released position, the release of a code wheel completes a circuit from terminalv B at the code wheel contact 96 over code Wheel 89, back contact 46 of relay OLBP, relay 86 to terminal C. Relay 86 picks up to disconnect the C. T. C. line battery 80 from lineV wires Y and Z and to connectV the line wires over its front contacts I3 and I1 to the pole changer contacts 44 and 45 of relay 81. l

Since the selectors require a considerably higher voltage for their operation than the usual C. T. C. line relay, it is customary to provide a separate source of line current, which in practice usually comprises rectied alternating current obtained by means of a vacuum tube rectier 41 and transformer 48 having its primary connected to the local alternating current lighting circuit as indicated by the legend a. c. in Fig. 1, with a tank condenser 49 connected across the transformer secondary in series with the tube, as shown.

When relay 86 picks up it completes a stick circuit at its contact 50 which remains closed until the code wheel returns to normal, and at contact 5I completes a circuit for energizing the lament of the rectifier tube 41. Tube 41 is to be understood to be of a type requiring its filament circuit to be closed for at least one-half second before suflicient electron emission is developed to deliver appreciable current to the line. Since relay 86 disconnects battery 80 from the line at the beginning of this period, each -selector code begins with a long line-open period, similar to that of the rst step of a C. T. C. control code, and which is likewise effective to lock out any eld station that happens vto initiate Va code at that time. Relay 86 when energized opens the circuit for relay OR at contact 88, thereby holding relay OR reversed for the duration of the selector code, with the result that relay OL2 is energized to hold the pick-up `circuit for relay OM open to prevent the initiation of a C. T. C. control code until the selector code is completed. When relay 8B releases at the end of the selector code, the closing of its back contacts completes the circuit for relay OR Iand reconnects battery 80 to the line to thereby restore the C. T. C. apparatus to its normal condition. The selector codes and C. T. C. battery codes are mutually non-interfering in respect toV the operation of the code receiving apparatus because of the difference in the relative proportion of long and short code elements as explained more fully in Patent No. 2,259,573, granted October 21, 1941, to L. V. Lewis, for Remote control systems, and since the' transmitters do not interfereone with another, for the reasons that have just been pointed out, and since the usual selectors have far'too high a reactance to respond to the alternating current 'codes or to appre-V ciably shunt. the voice frequency currents.' it will be clearthat both systems may'employ the same line channel without interfering with each other'o'r with the joint use'of the line wires as hereinbefore described.

A characteristic of the novel mode of transmitting indications from the eld stations by connecting the line wires together as disclosed herein, is that the indication codes are transmitted in' two directions at the same time in response to the operation of the contacts of the station transmitter relay T, for two different purposes. When relay T is operated to transmit an indication code, its contact 9| is effective to transmit an alternating current code in the direction from right to left, to which the oice line relay OR responds, while at the same time, its contact b transmits a battery code in the opposite direction which as heretofore not only operates relay R at the transmitting station to govern the transmission but is also effective to lock out any station more remote from the oce which initiates an indication code at` the same time.

It is also to be noted that the disagreement between the positions of the relays T at two stations which locks out the station more remote from the oiice does not interfere with the alternating current code element then being vtransmitted to the oice by the nearer station.

In this connection, it has already been exn plained that in respect to the odd-numbered code steps, a long step takes precedence over a short step.A -Thus ifr relay T at the transmitting station nearer the office remains picked up to maintain its shunt for a relatively long period, relay OR will be released for a corresponding long period irrespective of the release of relays T and M to remove the shunt at the more remote station. Furthermore, in respect to the even-numbered code steps, a short step takes precedence over a long step. Therefore if a relay T picks up to shunt the line after a relatively short interval, relay OR will release irrespective of whether or not the line is shunted at the same time by relay T at any station more remote from the office.

The apparatus of our invention may also be arranged to'employ alternating current transmission in both directions. One manner in which this may be vaccomplished is shown in Fig. 2 which illustrates a modification of our invention which differs from Fig. 1 principally in that the oice pole changer relay PC has been replaced by a frequency changer relay FC, and in place of battery 80, two sources of alternating current of frequencies f2 and f3, respectively, are provided at the oice, of which only the terminals are shown, these being designated BX2 and CXZ for the source of frequency f2, and BX3 and CX3 for the source of frequency f3. Current of frequency fI is supplied to the remote end of the line from a source having the terminals BXI and CXI .in the same manner as in Fig. l, and each station line relay R in` Fig. 2 is' arranged to respond normally toY current ofy frequency f2. only, in the line wires, but 'responds to current ofA frequency'fa only, in` the event' thezassociated relay M- is picked'up. In2 other: words', alternatingcurrent of frequencies fZand f3.in the line circuit of Fig. 2 takes the place of direct current of normal and reverse polarity, respectively, in the line circuit of Fig. 1. y

Referring to Fig. 2, a local circuit isnormally closed at the oiceextending from one terminal BX2 of the source of: frequency' f2i over' back: contacts' b andStl' of relays OT and FC', con-` denser C2, the primary winding of a hybridI transformer. Illll, backcontact 951of relay FCto the other terminal CX2 of 'said source'.' .Thevout-*v put of the hybridtransformer. isr delivere'dfby.- its'secondary windings in one direction through ahigh .pass lterindicatedyby-the condensers 98 to the line wires Y1 and Z, and` in the other directiontoa balancingnetwork99.'

Current receivedlat'thepice .from -the'fsourcef of frequency fi, which is. connected .across lin'e' WiresY and Z at the remote .-endof the line .asf alreadyy explained. in connection with Fig; 1,I passes through condensers .98a and the .upper-'sec'- ondary windings of transformer Ill' 'and thence through parallel resonant circuit elementsy desig# nated f2 and f3 (to indicate! that they'are forv blocking the passage of ycurrents-of vthe corresponding frequencies) and thence-as in Fig. 1, through a coil 8l and condenser Cl tuned'to thefrequency fi, ampliflerA', transformer 83 and! rectifier 85 over backcontact Sllof relay OTtof relay'OR.v Since the system of Fie. -2 does not use battery current in the line, no provisions other than selective tuning are needed to rprevent, interference 'with the telephone call selector system and' theA latter'therefore doesrnot' need to be inter-l lccked with'the C. T. C. system as in' Fig. 1 and accordingly is not shown'in Fig. 2.`

At each/field station in Fig.. 2vtheA line relay is associated with the line by means of circuitsv which are` generally similar to thosey provided` for relay OR', but which-differ by including acoil 8i and condenser C2 tunedtoseries re'so-I nance Ato Vrender relay R`normally responsive-tol current of frequency f2only, and'lby-including parallel resonant elements c omprising'acoil andcondenser designated -fl 'torender relay lR` nonresponsive tocurrent offrequency-H as shown.

rent supplied fromY the'so'urce of 'frequency' f2' at the office, while the 'oflice line' relay OR is normally energized by rectified alternatingcurrent supplied from the source of frequency fl at the remote endfofthe line. l

In the system of Fig. 2, relay'YOT-'is arranged to interrupt the current of frequency f2 `at its contact b to controlithe-relays R, and to interrupt the local circuit for relay ORat its vcontact 85, to thereby effect thetransmission of lcont-rol codes to the stations in an obvious manner, lrelays OR and R'operating in' unison' as` in rthe other vform of our invention.- v

With the apparatus of Fig. 2 in its normal condition, as shown; if relay'fM at a station'pi'cks up to initiate an indication code, the currents of both frequencies lin' line wires -Y andZ are shunted, first` over contacts -30' and 3l of relays M and LBP', and then over contacts' b ofrelays E and T, as in the `first'form of our invention already described',"thereby releasing relay Brat thetransmitting station and at each station'more" remote'from the 'oiliceyand alsol releasing'the oi'ce line-relay ORL.`r Relay-'M at'thetransmit-i ting station| furthermore at its contact Illl connects; a' condenser C3' in parallel with condenser C2 to change the tuning' of `the series resonant circuit governing' relay Rf, so'that upon removal of the shunt bythe opening of contact 3| when relay LBP picks up', relay R will be responsive only to current of frequency f3. Relay OR upon releasing effects the energization of relay FC, over a circuit extending from terminal B, lefthand'contact 24`of relay OR, wire' I8, contact d of relay OLBP, Contact 59 of relay OM, relay FC to terminal C, and relay FC picks up, completing its stick circuit at Contact E03, and at its .front contacts 94 and-95 relay FC connects terminals 'BX3 and 0X3 of the source of frequency f3 to the' primary of transformer lill), disconnecting the terminals BXZ and CK2, and at the same time closes contact H12 to connect a condenser C3 in parallel with condenser C2' at theofilce to change the tuning of the primary of the transformer |60 to render it responsive to frequency f3.4 The change in frequency of the current delivered to `the line at the oiice effects the release of each line relay R which is energized when relay'FC picks up, and all `the relays Rr will remain released for theduration of the code except the one at the transmitting station, as heretofore.

It will be seen, therefore, that in Fig. 2 the shunting of the line wires byV relay T is effective to transmit an indication code of periodically interrupted alternating current of frequency j I from right to left to govern relay OR at the office, and to transmit a similar code of frequency f3 from left to right for governing relay R at the transmitting station and for locking outl any station more remote from the office which may happen to initiate an indication code at the same time, while the absence of current of frequency f2 in the line insures that no station at the left of the transmitting station which is relatively so near the ofce that the shunting of the line at they transmitting station is in ineffective, will initiate a code. It follows therefore that the coding units -when controlled by the apparatus of Fig. 2 will function in the same manner as when controlled by that of Fig. l, and it is believed therefore, thatthe operation of the system of Fig. 2 will be readily understood without further description.

Since in both Figs. 1 and 2 the currents ernployed for transmission in the two directions are of dissimilar character, the transmission distance maybe extended by the use of ordinary one-way repeaters, and it follows therefore that not only may a wide variety of existing line facilities be made use vof to provide the necessary transmission channels between the control ofee and the C. T. C. eld stations, but the office may be located at any required distance without impairing the quality of the code transmission.

This may be readily shown by considering the initiation of indication codes as hereinbefore described. In the system of Patent No. 2,229,249 as l the 'effect ofshunting the current of frequency fl at the transmitting station is propagated along the line through the repeaters to the office, to operate relays OR or FC successively, and then an impulse of current of frequency f3 is propagated from the office back to the station to render current of that frequency available to pick up relay R upon the release of relay T. Obviously the length of the rst step is not aiected unless it is less than the time required for these impulses to travel twice the length of the line as described, which time, under any condition likely to be encountered in practice, is less than 0.2 second. Furthermore, the latter value, being arbitrary, may readily be increased to match the line conditions if required. Since except for theflrst step o an indication code as pointed out above, the system employs one way transmission with the source of the line signals back of the transmitter, the propagation time of the impulses due to long line conditions is of no practical consequence.

It is also to be noted that the C. T. C. apparatus of Fig. 2, since it is connected to the line wires through condensers of relatively small capacity, may employ line circuits which are quite dilTerent from those of Fig. 1, such for example, as an alternating current power transmission line. Y

Such a transmission line is almost always available throughout the length of territory comprising a C. T. C. installation. Usually the track switches, signals and other apparatus involved are energized locally by storage batteries maintained energized by the trickle-charge method, by energy supplied from an alternating current source over a transmission line comprising a pair of added line wires on the pole line carrying the communication circuits, the voltage in the power line being limited by practical considerations to the maximum value permissible in such circuits, that is, to less than 500 volts.

The system of Fig. 2 may be superimposed on such a line, as is self evident, but the system of Fig. l may also be used by the provision of suitable arrangements for preventing interference, such, for example, as those shown in Figs. 6, and 7 of our prior application, Serial No. 326,440.

Although we have herein shown and described but two forms of our invention, it will be understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of our invention.

Having thus described our invention, what we claim is:

l. In a remote control system, an ofce and a plurality of stations connected by two line wires, a line relay included in a branch circuit bridged across the line wires at each station, a normally closed code signaling channel including a first source of current and a transmitting contact lcated at the office, said channel also including said line Wires and said line relays, means at the oli-ice for periodically operating said transmitting contact to control said line relays in accordance with different codes, a second normally closed code signaling channel including a line relay at the oice, said line wires and a second source of current of different character from said iirst source connected across said line wires at a distant point, a code transmitter at each station effective when operated to connect said line wires together periodically in accordance with a code to shunt said rst source to therebycotnrol the line relay at such station and the line relays at stations more remote from the office, each'such operation being also elective to shunt said second source to control said cnice line relay, a code receiver controlled byrsaid cnice line relay, and means controlled by each station line relay for governing the operation of the associated code transmitter.

. 2.' In a remote control system, two line wires extending from a control oiiice through a plurality of .stations to a distant point, a source of direct current'connected across said line wires at said ofiice,a source of alternating current connected across said line wires at said distant point, a direct current line relay connected across said line wires at each station, a normally energized line relay at the office responsive to alternating current only in said line wires, a code transmitter at the office effective to periodically disconnect said direct current source from the line wiresto operate the station line relays in acordance with dilerent codes, a code transmitter at each station effective to periodically connect the line wires together to shunt said alternating current to operate said oflice line relay in accordance with a code, and code responsive means controlled by each said line relay.

3. Ina remote control system, two line wires extending from a control oilice through a plurality of stations to a distant point, a source of direct current connected across said line wires at said office, a source of alternating current connected across said line Wires at said distant point, a direct current line relay connected across said line wires at each station, a normally energized line relay at the office responsive to alternating current only in said line wires, a code transmitter at the oilice eiective to periodically disconnect said direct current source and said office line relay simultaneously from the line wires to operate the oice and station. line relays in accordance with different codes, means controlled by the oflice line relay and dependent upon its energization at least intermittently by the alternating -current supplied from the source at said distant point 'for maintaining said code transmitter in operation to complete the transmission of said code, and means controlled by the station line relays selectively responsive to said codes.

Y 4. In a remote control system, a line circuit extending from a -control office through a plurality of stations to a distant point comprising twov line Wires, two non-interfering current sources connected across said line wires, one at the oce and the other at said distant point, a line relay responsive to current from theofflce source only connected across said line wires at each stationa line relay responsive to current from the source at the distant point only connected across said line Wires at the oilice, a code transmitter at the ofce effective to periodically disconnect the oice source from the line wires to operate the station line relays in accordance with diierent codes, and a code transmitter at each station effective to periodically connect the line wires together to shunt the current from the source at the distant point to operate the olce line relay in accordance with a code.

5. In a remote control system, two line wires extending from a control oiice to a distant point, a source of alternating current of one frequency connected across said line wires at said distant point, a source -of alternating current of another frequency connected across said line Wires at said oflice, a line relay at each station controlled over a .branch circuit bridged across said line wires,

and responsive to alternatin'gfcurrent of said another frequency only, acode transmitter at said ofoe effective to periodically disconnect -said oicue source from the line wires to operate the station line relays in accordance with diiierent codes, a normally energized line relay at the cnice responsive only to current of the frequency of the source at said distant point, code transmitting means at eachrstationeiective when initiated to change the`connections of the associated line relay to render such relay responsive only to a third frequency, and to momentarily connect the line Wires together to release the ofice line relay, means controlled by the olce line relay when so released for supplying alternating current of said third frequency only to said line wires, and means controlled by the station line relay responding to said third frequency for continuing the operation of the associated transmitter to transmit a code to which the oilice line relay responds.

6. In a remote control system, a line circuit extending from a control oflice through a plurality of stations to a distant point comprising two line wires which are continuous from end to end to form a portion of a transmission circuit connecting said oiice and distant point, two noninterfering current sources for supplying current to which said transmission circuit is non-respon sive connected to said line wires, one being 1ocated at the ofce and the other at said distant point, a line relay selectively responsive to current from the oiiice source connected to said line wires at each station, a line relay at the ofce selectively responsive to the current from the source at said distant point and adapted to be controlled over said line wires, a code transmitter at each station effective when initiated to connect the line wires together periodically in accordance with a code to selectively shunt the line current supplied from the oice to operate the line relay at such station, each such operation being also effective to selectively shunt the current supplied from said distant point to operate the oiiice line relay but without varying the condition of said transmission circuit, and means controlled by each line relay for governing the operation of the associated code transmitter.

'7. In a remote control system, line wires eX- tending from a control office through a plurality of stationsto a distant point, two sources of line current of different character located respectively at the ofce and the distant point, the one at the distant point being normally connected across said line wires, a line relay at the office selectively responsive to current from the source at said distant point, a line relay at each station selectively responsive to current from the source at the ofce, a code transmitter at each station effective when initiated to connect the line Wires together periodically to produce a multiple impulse code of line current variations therein, means controlled by the cnice line relay for con,- necting the ofce source to the line Wires for the duration of such code, means controlled by each station line relay for preventing the initiation oi the associated transmitter when current from the office source is being supplied to said line wires, and means eiective to stop the operation of any code transmitter which has started to deliver its code if such code is changed in character as manifested by the operation of the associated line relay, due to the operation of another code transmitter.

8. In a remote control system, a line circuit eii't'ending from' a' control omce through a 'plu'- ral'it'yV ofstations to a distant point, a1A line relay at'tlie office' and at'each station bridged'across saidc line wires, a normally closed signaling' channel' including said oce line'rela'y and said line wires," said"cliannel having al. source' of current t'dvvhich'V the' station line' relays are' nonresponsive connected to the lin'ewires'at saidv distant point; a transmitter relay and a master relay at eachstation; meanscontrolled by' each master relay when operated to initiate the operation of the associated transmitter relay, means controlled by each transmitter relay when operated for connecting the line wires together periodically to deliver a multiple impulse code to said line wires to control the office line relay, means controlled by the oce line relay in response to the first impulse of such code for supplying to the line Wires current of a diierent character to which the office line relay is non-responsive, for the duration of each such code, means controlled by each master relay when operated for conditioning the associated line relay to respond to said current of diierent character, means controlled by each station line relay for preventing the operation of the associated master relay to initiate a code during the time said ourrent of different character is being supplied to the line circuit, and means controlled by the line relay at each station dependent upon its operation in accordance with a code identifying that station for continuing the operation of the associated transmitter relay to complete such code.

9. In a remote control system, a line circuit extending from a control oce through a plurality of stations to a distant point, a line relay at the oice and at each station bridged across said line wires, a normally closed signaling channel including said oflce line relay and said line wires, said channel having a source of current to Which the station line relays are non-responsive connected to the line wires at said distant point, a second normally closed signaling channel including said station line relays and said line wires, said second channel having a source of current to which the ofce line relay is nonresponsive connected to the line wires at the oiiice, a transmitter relay and a master relay at each station, means for operating each master relay to initiate the operation of the associated transmitter relay efective only when the associated line relay is steadily energized over said second channel, means controlled by each transmitter relay when operated for connecting the line wires together periodically to deliver a multiple impulse code to said line Wires to control the ofnce line relay, means controlled by the oice line relay in response to the first impulse of such code for opening said second channel and for supplying current of a diierent character to the line wires to which none of the line relays are normally responsive, for the duration of such code, means controlled by each master relay when operated for conditioning the associated line relay to respond to said current of different character, and vmeans controlled by the line relay at each station dependent upon its operation in accordance with a code identifying that station for continuing the operation of the associated transmitter relay to complete such code.

10. In a remote control system, an oice and a plurality of stations connected by line wires extending from the oilice to a distant point, a line relay responsive only to direct current bridged across the line wires at each station, a line relay the'fline wires together periodically through a 1U low pass lter to control the associated line relay and through a high pass filter to control the o'ice line relay in accordance with a code, a code receiver at the oiice governed by the oice line relay, and means controlled by each station line relay for governing the operation of the associated code transmitter.

GEORGE W. BAUGHMAN. NORMAN F. AGNEW. n

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