US2289789A - Remote control system - Google Patents

Description

L. v. LEWIS REMOTE CONTROL SYSTEM July 14,1942.

Filed March 25, 1939 Z Sheets-Sheei 1 H15 ATTORNEY July 14, 1942. L. v. LEWIS 2,289,789

- REMOTE common SYSTEM Filed March 25. 1939 2 Sheets-Sheet 2 R. Y O. I E T N ww ENB W 3 figm m .NQWQQNMBXW TIM. 1U. m ..A P I. N m Q Ari..- MN m U M U WNNN & W n F F w Tr r n m Wy N v Q w DJ DJ QN b s fi LL EE EM LE L\ a -JFEF gati- Patented July 14, 1942 REMOTE CONTROL SYSTEM Lloyd V. Lewis, Pittsburgh, Pa., assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of Pennsylvania Application March 25, 1939, Serial No. 264,182

10 Claims.

My invention relates generally to remote control systems, and more particularly to the communication or line circuits for such systems.

My invention is particularly adapted for, though in no manner limited to, centralized traffic controlling systems for railroads in which a train dispatchers office or other suitable point of controlis connected with a plurality of field stations by line wires, over which code'signals are transmitted at times for controlling-selected devices at the stations, and at other times for indicating the condition of station devices at the office.

My invention is an improvement upon the line circuit portions of centralized trafiic control systems disclosed in my pending United States applications, Serial No. 600,786, filed March 23, 1932, for Remote control systems, which corresponds with British Patent No. 415,787, issued September 3, 1934', and Serial No. 261,241, filed March 11, 1939, for Remote control systems.

One object of my invention is to provide additional communication channels over theline wires of the centralized traffic control system in order that the number of field stations and the extent of territory to be controlled may be increased, without increasing the number of line wires.

A further object of my invention is to decrease the number of line wires required by the systems of my prior applications when one or more of 4 the field stations are located on a branch line.

Other objects, purposes and features of .my in vention will be pointed out as the description proceeds.

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

Referring to the accompanying drawings, Fig. 1 illustrates the line circuit for a centralized tramc control system such as the one disclosed in the patent hereinbefore referred to, which has been modified in accordance with one form of my invention so as to permit its use independently by two sets of centralized traffic control apparatus such as is disclosed in the patent, whereby the number of stations may be doubled and two codes may be transmitted at the same time without interference, one system employing impulses of one polarity only and the other system employing impulses of the opposite polarity only. Fig. 2 illustrates another form of line circuit arranged to secure a similar result, but in this form one set of apparatus employs a normally closed D. C. line circuit as in the patent hereinbefore referred to while the other employs a superimposed A. C. communication channel with In its specific embodiment, my invention is illustrated as arranged for use with the system of my prior patent, but it is to be understood that the improved line circuit arrangements comprising myinvention are not limited to use by that particular system but may be used withany suitable coding system in which impulse codes are transmitted from different spaced points over a single line channel without interference. For an understanding of my invention, a knowledge of the details of the coding apparatus is not required, and for that reason only those parts of the system of my patent are shown herein which are associated directly with the line circuit. These parts include first, a line relay R, at theoffice and at each station, for governing the associated coding apparatus, not shown, in accordance with the condition of the line, to selectively receive codes and to prevent transmission except at times when the line is free; second, a master relay M'v'vhich is energized for the duration of each code transmitted by the associated coding apparatus; third, a transmitter relay T by means of which the coding apparatus delivers its codes to the line, each relay T being operated repeatedly in accordance with a code when the associated relay M is energized; fourth, a relay E at each field station which picks up when the first impulse of a received code is long as is the case when the code is transmitted from the control ofiice, but which is not picked up in response to a code having a short first impulse, as is the case when the code is transmitted from another field station, and finally, a starting relay ST (Fig. 3) at the office and at each station. Each relay ST may be operated at any time to store a code for transmission, and initiates the transmission when the line is free, by energizing the associated master relay M.

The designations for the various relays disclosed herein are the same as those of my British patent, except that the relays for the two different sets of C. T.'C. apparatus which employ the same line Wires are distinguished by the suifixes A and B, respectively, where necessary.

Relays P, PO and V are additional relays not shown in the patent.

The purposes and detailed mode of operation of those relays which are not fully described herein, and of the coding units which they control. may be ascertained from the patent. The line circuits as arranged in accordance with the present invention differ, however, in a number of respects from those of the patent, and these differences will now be explained.

Referring to Fig. 1, the main source of current for energizing the line circuits comprises a transformer 4, the primary winding of which is normally energized by a connection to a commercial alternating current source as indicated conventionally by the references BX and CK identifying its terminals. A direct current relay PO is normally energized by a connection to rectifiers 3 which are connected across the secondary of transformer 4. In the event of failure of the main sourceof current, relay PO releases to connect one terminal B of a suitable local source of direct current through the back contact and winding of a vibrator relay V to the other terminal C of the same source. Relay V is of a well-known vibrating type arranged to pick up intermittently at a rate approximately the same as the frequency of the A. C. supply source. The front and back contacts of relay V connect terminal B of a suitable local source of direct current alternately to the two end terminals of the primary of a step-up transformer I2, the midpoint of which is connected to the other terminal C of the same source, transformer I2 being thereby energized so as to deliver alternating current from its secondary. As will be clear from the drawings, transformer 4 normally supplies alternating current to the line wires Y, Z through the office code signaling apparatus comprising the windings of the line relays ORA and ORB and the back contacts of the corresponding transmitter relays OTA and OTB, but in the event of the failure of the A. C. source, the release of relay PO will render available an emergency source of A. C. current for energizing the line wires comprising transformer I2. Relay ORA and the upper back contact of relay OTA are connected in series between line Y and the righthand secondary terminal of transformer 4 or l2 through a rectifier I, while the return connection from line Z through the lower back contact of relya OTA to the opposite transformer terminal includes an oppositely connected rectifier 2, so that pulsating unidirectional current comprising the positive half waves only, of the A. C. supply, are delivered to line Y through relay ORA and are controlled b the back contacts of the transmitter relay OTA. Relay ORB and the contacts of relay OTB are similarly arranged but connected oppositely, so that pulsating unidirectional current comprising the negative half waves only, of the A. C. supply, are delivered to line Y and return from line Z to the source through relay ORB under the control of transmitter relay OTB.

It-is to be understood that whereas in the system of my prior patent the relays R are ordinary neutral relays, relays ORA and ORB are of the biased polar type as indicated conventionally on the drawings, and respond only to current of the proper polarity. The rectifiers I and 2 in the circuits for these relays prevent current of the opposite polarity from flowing through these relays in amount sufficient to interfere with their operation. A snubbing rectifier 5 bridged across each relay ORA and ORB has the same efiect,

but in addition each rectifier 5 provides a discharge path for the inductively stored energy of the relay to maintain it picked up without chat-- tering during the intervals between successivehalf waves of a series which constitute an element of a code signal. The line relays are of relatively low inductance and discharge quicklyso that rectifiers 5 do not delay their release enough to materially distort the code signals.

The line relay R at each of the stations A is similarly arranged and is connected in series with line wire Y to operate in unison with relay ORA, the positive impulses in wire Y for energizing these relays returning via line wire Z, while the line relay R at each station B is connected in series with line wire Z to operate in unison with relay ORB when positive impulses are impressed on wire Z and the current in wire Y is negative.

The circuit for the line relays A may be traced from the source of positive pulsating current comprising transformer 4 or I2 and the upper rectifiers I and 2, back contacts of relay OTA and relay ORA at the office to line wires Y, Z thence through rectifiers I and 2, relay R and back contacts of relay M at station IA, to the line circuit portion comprising the wires YI, ZI leading to the next station, and so on to the end of the line, the line wires Y34, Z34 leading to the station 35A most remote from the ofiice being connected together through relay R and back contacts of relay M at that station to complete the circuit. The circuit for the line relays B may be traced from the source of negative pulsating current comprising transformer 4 or I2 and the lower rectifiers I and 2, back contacts of relay OTB, through relay ORB at the office to line wires Z, Ythence through the by-pass rectifiers I and 8 at station IA to the line wires ZI, YI leading to the next station and so on through each station A in turn to wires Z33, Y33 leading to station 34A. In the layout chosen for illustration, each of the stations B is on a line branching at this point from the main line extending to station 35A. Beyond this point the circuits for the relays A and B are entirely separate, therefore, a single pair of rectifiers 9 and II] in series with the line wires Z36, Y36 leading to station IB is sufiicient to block the now of positive pulsating current through line B relays, and similarly, the single pair of rectifiers II, I2 blocks the flow of negative pulsating current through the remaining A relays. The remaining portion of the B circuit extends from wires Z36, Y36, through rela R and back contacts of relay M at station IE to wires Z31, Y3! and so on through each station in turn, wires Z39 and Y69 being connected together through relay R and back contact of relay M at station 35B to complete the circuit.

It is clear that the circuit arrangements are such that the B stations may be relocated if desired and that they may all be placed on the main line at the left of station 34A. In this case each station B would be arranged like station IA except that the connections to the line wires would be reversed, the branches of the line circuit including rectifiers 2 and I at each intermediate station B being included in line Y and the branches including relay R and rectifier 8 being in series with line Z. The positive pulsating current delivered to the line over the back contacts of relay OTA will thus pass through the relays R at stations A only, while the negativepulsating current delivered over the .back contactsof relay ,O'I'B .will pass through'relays R at stations B only. It follows thatsrelay OTA may be operated,:likerelayIOT'in the patent, to transmit a code whichin this casecomprises interrupted .positive pulsating current, to operate relay ORA andrelay .R .at each of the stations A, while at thesame time relay OTB may be operated to transmit a code comprising interrupted negative pulsatingcurrent to operate relay'ORB and the relay R at each of the stations B, withoutinterference.

Furthermore, as explained in the patent, indication codes indicatingthecondition of station devices are transmitted from each stationto the control oflice. Such codes areinitiated by picking up relay M at the transmitting station, which at itsback contacts opensthe line circuit portion extending to stations more remotefrom the ofiice to prevent interference with the codeby such stations, and: shunts. the remaining. portion throughthe contacts of a transmitter relay T which is then operated" to deliver a code to which relays R andOR respond. It will be seen that similar operations are .provided for in Fig. 1. Relay M at station IA, for example, opens the lineextending to stations beyond only as far as the transmission of'positive pulsatin current is concerned, and relay 'Tatstation IA interrupts only the .positivexpulsating current to control relay ORA. The negative pulsations find free passage through rectifiers 1. and .8 and are not interfered with by the operation of relays M and T. Theenergization of relay M'at a station B in a corresponding main line location would similarly block the flow of the negative pulsating current only, and the relay T at that station would interrupt only the negative pulsating current and would therefore control'relay ORB'and not relay ORA. It is clear that a control or indication code of interrupted positive current may be transmitted at the: same time that a control or indication code of interrupted negative current is being transmitted, without interference.

Referringfurther to station IA, it will be seen that normallywhen" line Y is positive a relatively low-potential is" impressed upon rectifiers 8 and 1 comprising only the drop through the apparatus at station IA which is usually but a-small fraction of the total line voltage from line wire Y to wire Z, and when line Y is negative the potential impressed upon rectifiers 2. and I at station IA is only the drop through rectifiers'l and .8 in their low-resistance direction. On the other hand, when M is energized therre'ctifiers at station I'A are required to block the full line voltage when line Z is positive, consequently an additional rectifier 6 is included in series with 2 and I to avoid overloading of these units.

As'fully explained in the patent, each line-relay R'or OR so controls its associated transmitter that codes can be initiated only when the line circuit has been steadily closed for at least a brief interval somewhat longer than any line-closed impulse in a code, and means are provided to prevent interference in theevent two or more transmitters are initiated simultaneously, in which case the several codes are transmitted one at a time in a predetermined order. Each of the two systems A and B of Fig. 1 operate in this manner so that there is no interference between codes within either system, and both systems may operate simultaneously without interference due to the use of line currents of different character with elements: included inthe circuits for confining the currents of' ieaclysystem to the proper channels. .Since the line circuit system of Fig. 1 permits double thenumberxof codes to be transmitted per unit of time, it is of advantage in minimizing delays in transmission even though thenumber of stations iswithin the capacity of the system asillustrated in the patent. Furthermore, the line circuit of the patent when used with a branched line layout requires three line wires for one of the branches, whereas but two are required in the systemas disclosed herein.

Referring now to Fig.2, in this view the stations A are controlled as in the patent over a normally closed series linecircuit extending from the line battery through relay ORA and back contacts of relay OTA at the ofiice to line wires Y, Z, thence over back contacts of relay M at station IE to line wires Yl, Zl, thence through relay Rand back contact of relay M at station IA, andsimilarly through each station B or A in turn. The circuit differs from that of the patent in that it is modified to provide an A. C. communication channel over the same line wires by including a low pass filter l4 in circuit between each transmitting contact, and by including a high-pass filter l5 in the line circuit at each intermediate station A which bridges the normally closed back contacts of relay M and maintains the continuity of the A. C. channel through the station while such relay M is energized. Furthermore, the relays R'at stations B are not included in the circuit and are non-responsive to the D. C. codes. A filter I3 in the line circuit at each intermediate station B bridges the back contacts of relay M at such station and maintains the continuity of the D. C. line circuit while blocking the flow of A. C. signaling current while relay M at a station B is energized.

The C. T. C. system for controlling the apparatus at stations B and for indicating the condition of such apparatus at the office comprises the system of my British patent modified as disclosed and claimed in my copending application, Serial No. 261,241 hereinbefore referred to in order to employ a normally open bridged line circuit, this system being further modified so as to employ alternating current generated locally at each transmitting station for the line signals.

As explained in my patent, a control code is initiated by energizing relay OM at the office, and in the system of Fig. 2 when this occurs a circuit is completed from terminal B of the local D. C. source over the back contact and winding of a vibrator relay V to the other termintl C of the source. Since this circuit includes a back contact of relay V, thatrelay is energized intermittently like the relay v already described in connection with Fig. 1 and similarly energizes the primary of a transformer [2 to cause the latterto deliver alternating current from its secondary, the rate of vibration of the contacts of relay V being controlled in a well-known manner by a tuned reed armature .or the like so as to maintain the frequency of the A. C. current delivered by transformer constant at .a suitable value, which, in the system of Fig. 2, is preferably in the voice frequency range.

Relay OM upon becoming energized also causes the transmitter relay OT to be energized intermittently its front contacts connecting the.secondary of transformer [2 across the line wires .Y, Z through condensers Hi to impress an A. C. voltage across the line. The line relay ORB at the ofiice and likewise relay R- at each station B is rendered responsive to the A. C. codes by the provision of a tuned circuit element or resonant shunt comprising a coil l1 and condensers l8 connected across the line, this circuit Being selectively responsive to the frequency of the A. C. current. Relay ORB and the similar relay R at each station B are rendered responsive to the A. C. signals by connecting them through a rectifier l9 across a portion of the winding of coil l'l, as shown. Condensers I6 and I8 prevent the diversion of battery current from system A to the apparatus of system B, and the low pass filters M prevent the diversion of A. C. current from system B through the apparatus of system A, so that the two systems may operate simultaneously without interference.

Since the A. C. line circuit is normally open, the codes of system B are reversed with respect to those of system A, that is, the line-open condition in system B corresponds to the line-closed condition in system A, and vice versa, and the connections to the contacts of the line relays in system B are correspondingly reversed so that the coding units of that system function in the same manner as if a normally closed line were used. Furthermore, it is to be understood that in this system as well as in the series line system of the patent each transmitter is controlled by the associated line relay in such a manner that codes can be initiated only when the line is free. In the bridged line circuit system, this means that each line relay 1 must remain released for a period somewhat longer than a, line-open interval of a code in order to permit a code to be initiated by the associated transmitter, and conversely, each transmitter may be prevented from starting by impressing a steady A. C. potential across the line wires of the character which is impressed thereon when another station initiates a code. The circuit arrangements which in the series line circuit system prevent a station from attempting to send a code to an open line thus in the bridged line circuit system prevent it from attempting to send a code to an energized line.

Considering now the intermediate station of the bridged line circuit system designated as station IB in Fig. 2, it is to be understood that indication codes for registering at the office indications of changes in th'e condition of the devices at the station are initiated by energizing the station master relay M, and that in order to insure proper operation in the event that two or more codes are initiated at the same time, each control code is arranged to begin with a relatively long impulse and each indication code with a relatively short impulse, the apparatus at each station including a relay E which is selectively responsive to a long first impulse of a code and which is required to be energzed in order to condition the station apparatus to respond selectively to a control code.

When relay M picks up, it energizes relay V to cause the associated transformer l2 to deliver A. C. line voltage as in the case of relay OM already described, but in this case the upper front contacts of relay M impress this voltage upon line wires Yl, Zl leading to the stations more remote from the oifice. The contacts of the line relays R at each more remote station B are thus operated to the left, just as if the office apparatus had initiated a code. The current th'us supplied to the more remote section of the line serves as a source of A. C. signaling current for the transmitting station IB, being delivered over the contacts of relay T to line Wires Y, Z to operate relay ORB each time relay T becomes energized. At each more remote station, relay E becomes energized,

which as explained in my patent releases the relay M at any station which attempts to transmit a code at the same time.

It will be seen that as long as a station is transmitting a code to the ofiice, the transmitters at the more remote stations will be held locked out by th'e A. C. voltage maintained on the line wires extending to these stations by relay M at the transmitting station. Furthermore, the apparatus at each intermediate station between the transmitting station and office will not respond to the code because the relays E at such stations are nonresponsive to the short first impulse of the code, the transmitters at these stations being also looked out by the code impulses.

It may happen also that the oflice and one or more stations initiate codes at the same time. In this case, when relay T at the transmitting station releases to terminate the first impulse, relay R will be held energized by current delivered to the line by relay OTB to pick up relay E at the transmitting station. The front contacts of relay E bridge the filter l3 in the line so that the current delivered to wires Yl, ZI by relay M will also be supplied to wires Y, Z after relay T has released, maintaining the oflice line relay ORB energized even though relay OTB releases. Relay E will release relay M as already explained, but it will be seen that the ofiice transmitter is held on the first step until this occurs. When relay M releases, the receivers at the office and at all stations B will have completed the first step of a control code and are ready to advance to the second step under the control of relay OTB which is then free to complete the code.

It will be apparent from the foregoing that the operation of the system B is analogous in all respects to that of the system employing the series line circuit as described in my patent, and that the provisions described are adequate to insure that the several codes will be transmitted one at a time in predetermined order without interference.

In the layout chosen for illustration in Fig. 2 certain of the stations B are located on a branch of the main line extending to station 35A, as in the layout of Fig. 1. Likewise in Fig. 2 the circuit conditions on the branches differ from those on the main line, thus the single filter l4 con.- nected to line wires Y34, Z34 serves for all stations A to the right of that point, while no series filter is required at any station B on the branch line when, as shown, all the branch line stations control the same office line relay ORB.

It will be evident from a consideration of Fig. 2 that this arrangement may be still further expanded by adding another transmitter OTC and line relay ORC, not shown, which are similar to OTB and ORB but employ a difierent frequency of A. C. line current, so that a third group of stations may be controlled. For this reason the filter I3 at station IB as shown is arranged to block only the frequency employed by the station with which it is associated. The filters l3 and I5 may take various forms depending upon specific requirements. Filter [5 may, for example, be a simple condenser arranged as shown in the Baughman application Serial No. 256,976 filed February 17, 1939, for Remote control systems, now Patent No. 2,208,446, granted July 16, 1940.

The A. C. system of Fig. 2 is furthermore not limited to those frequencies which can be efficiently generated by vibrating devices such as the relays V but may employ higher frequencies in order to render the such casesa'vacuum tube oscillator of circuit for the vacuum ther modificationofthe systemis in this -case .cient utilization .of

wandmodifications may .closed channel extending l from the office and to then repeatedly interrupt shunting or interrupting said normally open line wires available for telephone communication-or other: purposes. In a suitable type such'as isshown in-Fig. 3 maybe used.

It will be seen that in-Fig. 3 the'vibrator relay V'and transformer l2 are retained, but in this case theyierve to provide the --relatively high voltage reg red for theenergization oftheplate tube oscillator. A iurdesirable due to the fact that a certain time elapses after the filament circuit'is closed before it is heatedto a point where the tube-delivers its normal output, and further, to insure-proper operation it is desirable -to-avoid energizing relay M, which-as shown in Fig.r2 disconnects the: more .remotestations from the office, except under--the condition that its=operation results in, the energgization oi the line prevent the. operation: of their transmitters.

Accordingly as shownin Fig. 3 a tuned-circuit comprising a-coil l leading to such :stations to 1' and condenser l8 similar to ,that associated with each line relay R is connected .across the output terminals of the source of-the ;A.:-C.-linesignals and is usecl -to control a relay P-which inturn controls relayM while the startingcircuitcontrolledlby relay ST which 1 in the system: of my patent controls relay- M-directly isused: to control the energization, of relay V and of the vacuum tube oscillator. By this-arlVL and the energization of: relay T to I beginthe code delayed following theoperation of relay ST iuntil line voltage of the properuvoltage .and frequency is available as indicated by themergization of relay P.

It will be apparent from the foregoing that the system .oi Eig...2 not only provides the facili- .ties.of .Fig. 1 in an. analogous manner butmay beeven.furthersextended to efiectavmore eflithe line wires. .jAlthoughLI. have herein shownv and described .but two forms of myinvention and one modification thereof, 'it is understood that various changes bemade within the scope of ';the appended claims without departing from thejspirit. and scope of my invention.

Having thus described my invention, what I claim is:

1. In .a. remote control system, an. ofiicetand a pluralitylof. stations connected by two line-wires, .a normally closed signaling channel including saidjline wires, va source line relays at.the-.office. and atone or moreof said of direct current, and

stations," all in series,.a normallynopen signaling channel including said line wiresvand aplurality of other line relays arrangedto respond to-alterhating current each of which .is connected through .a condenser .acrosssaid line, wires, one of said other .line relays being located at the oflice and one at each remainingstation, code transmitting, apparatusncontrolled by theline relays, at each of said one or more stations efiective atltimes to open the portion of said normally the remaining ;-portion to operate theofiice line relay in ,said normally closed channel without the continuity -,of said normallyopen channel, and other code transmitting apparatus controlled by the line relay at'each remaining station effective at times to impress a steady alternating potential upon the portion of hannel extending to stations-more remote from to stations more remote the oiiice andto then im-- rangement the sectionalizing of the line by; relay 2 presslarcode oi ,alternatingcurrent impulsesupon the?1:emaining j portion to ,operate theofiice line :rclay ijsin 'x,the normally open channel without .rnormal-ly-i closed channel.

; 2.;Inza remotecontrol system, an oflice and a pluralityxofistations connected by two line wires, va:normallyclosed,cojde signaling channel includ- ;ing;said line wires ag-source ;of direct current and .linerr'elays1; at;.the ,oflicefand-at one or moresta- :tions, .a11,..in:scric a n rma ly p n signaling phannel includingsaid line wires, and a plurality :of resonant circuit elements each comprising, in ,j s'eries, ;;agcondenser; anda; coil controlling a line zreley -eachlsuchresonant circuit element being ibrldgcd across;th.e ;line wires one atthe ofiice and :onegpat, each remaininggstation, a source of alter- :nating.currentateaoh:such remainingstation for ,zchannel, code: transmitting means, controlled by theyjline, relay at'each;remain ing station for repeatedly connecting the -;alternating current sourceito said normally; open channel to operate uthe'rofiice: line relaypzinl said :op n chann l, and zmeanss; at ca h..-intcrm flia sta ion ff c ive as ;l.ongr-. zsuch=stat on is ransmiting a cod for :controllin h c esp nding channel t pr vent -:a station; more remote :irom ,the ofiice" from initiating ga ;co.de ior transmission over the same channe1 --3 -:.Inarom t contr l-s tem. anj fl c nd a :plurality of stat onsa rnormal y .d cncrei d masrelayat;;each station;-a;norrnal1y open line cir- @163 m nding: f m-.th offi 't ouehw s id; sta- TtiQI'lSyflD-d; including back-- contacts of 1 the master lay: at each station; local sourcesof line current at ach station,;rneanseffective when the master layaat an intermediate stationyis energized to deliveruninterrupted current from the source at 17.311911 station to'th line circuit portion extending 1 to :more: remote: stationa; a code transmitter aseach. master 'relayrendered efiective-when .suoh -master relay isenergized for supplying-lineqcurrent from the local source, repeateiedly interruptedin. accordance with-a ode, to ,the linewcircuit portion extending to the office, ;and meansiior energizing each master relay ef- ;fective onlyingthe eventline current is available :at; :the, corresponding station.

4. m a remotecontrol system comprising a .single ;line circuitzoonnecting, a; plurality of stations; and hav n nateach station, a line relay rei sponsive to :current supplied "to said line circuit at any station, a normally inactive source of line current,: a transmitter relay having contacts opwerable-at times to deliver to saidline circuit a -1=multiple step code of impulses of current to zwhich-said line relaysareresponsive, and a mas- .tergrelayefiective .when energized to connect the local sourceof .currentctolthe contacts of the as.- -ysociated transmitter -re1ay;and to cause such 1 transmitter relay toideliver its code; the combination'ofa-repeatingrelay ateach station con- -.-nected across the line terminals of the local --source,;with a startingrelay operable only when -:the;line relay-at-such-station is steadily deener- -.;gizedand-effective when operatedto render the z-local source active to; energize such repeating rei lay, and; circuit; means: controlled by each :repeat- ,ing-relaywhenenergized for-energizing the :associated-master relay.

; shunting or interrupting the ,continuity of said 5. In a remote control system comprising;a

single line circuit connecting a plurality of stations with a plurality of tuned circuit elements responsive to current of the same frequency bridged across the line circuit, one at each station, and having a line relay at each station responsive to the current in the associatedttuned circuit element, the combination of a normally inactive local source of alternating current of the frequency to which said tuned circuit elements respond, at each station, a transmitter relay having contacts operable at times to connect said source intermittently to said line circuit to deliver a multiple impulse code thereto to which said line relays are responsive, with a starting relay operable only when the line relay at such station is steadily deenergized to render the associated source active to supply current of said frequency to the contacts of the transmitter relay at such station, a master relay at each station effective when energized to cause the associated transmitter relay to deliver its code, and circuit means for energizing said master relay dependent upon the conditioning of the local source to supply current of said frequency to the contacts of said transmitter relay.

6. In a remote control system, a single line circuit extending from a control oflice through two groups of stations, and arranged to provide two non-interfering communication channels, one for each group of stations, a line relay at each station of one group responsive to current of one kind in one channel, a line relay at eachstation of the other group responsive to current of an-- other kind in the other channel, a code transmit-l ter at each station controlled by the associated line relay and adapted to deliver a code of impulses of current of the kind to which that line relay is responsive to the corresponding channel; sectionalizing means in one channel and bypass means in the other channel at each intermediate station of one group, sectionalizing means in the other channel and b -pass means in said one channel at each intermediate station of the other group, the sectionalizing means at each intermediate station of each group being effective to shunt the channel employed by such station as long as such station is transmitting so as to establish a circuit for transmission to the oflice while holding the portion of such channel extending to more remote stations in condition to prevent any more remote station of the same group from transmitting until the nearer station has completed its code, the by-pass means at each intermediate station being efiective to maintain the continuity through such station of the line channel employed by the stations of the other group.

7. In a remote control system, a single line circuit extending from a control office through two.

groups of stations, and arranged to provide two non-interfering communication channels, one for each group of stations, a line relay at each station of one group responsive to current of one kind in one channel, a line relay at each station of the other group responsive to current of another kind in the other channel, a code transmitter at each station controlled by the associated line relay and adapted to deliver a code of impulses of current of the kind to which that line relay is responsive to the corresponding channel; sectionalizing means in one. channel and by-pass means in the other channel at each intermediate station of one group, sectionalizing means in the other channel and by-pass means in saidone channel at each 1 intermediate station of the other group, the sectionalizing and by-pass means at each intermediate station of each group being eifective as long as such station is transmitting a code to so govern the continuity of the corresponding channel as to render only that portion thereof extending to stations more remote from the oflice unavailable for transmission without'interrupting the continuity through such station of the channel employed for transmission by the stations of the other group.

8. In a remote control system, a single line circuit comprising two line wires extending from a control ofilce through a plurality of remote stations and arranged to provide two non-interfering line channels including the same line wires for simultaneous communication between the ofiice and different ones of said stations, code transmitters at certain of said stations for transmitting multiple impulse codes to said ofiice over one of said channels, by-pass means at each of said certain stations for maintaining the continuity of the other channel through such station as long as it is transmitting its code, code transmitters at other stations for transmitting multiple impulse codes to said ofiice over the other channel, bypass means at each of said other stations for maintaining the continuity of said one channel through such station as long as it is transmitting its code, and sectionalizing means at each intermediate station of said plurality efiective as long as it is transmitting a code to interrupt the corresponding channel to disconnect from the control ofiice only those more remote stations employing the same channel for the duration of such code.

9. In a remote control system, a single line circuit extending from a control ofiice through two groups of stations, said line circuit having parallel branches at the ofiice and at each stationincluding oppositely connected rectifiers and providing two non-interfering communication channels, one for each group of stations, a line relay at each station of one group included in one branch circuit and thereby rendered responsive to current of one polarity only in one channel, a line relay at each station of the other group included in the other branch circuit and thereby rendered responsive to current of the other p0- larity only in the other channel, a source of current of periodically alternating polarity connected to said line circuit for supplying current to both channels, a code transmitter at each station controlled by the associated line relay and effective when operated to repeatedly interruptthe branch circuit over which such line relay is controlled to deliver a code of impulses of current of one polarity to the corresponding channel, sec tionalizing means at each intermediate station effective to shunt the branch circuit which the associated transmitter controls as long as such transmitter is in operation, so as to establish a. circuit comprising that portion of the corresponding channel extending to the office while holding the portion of such channel extending to more remote stations open to prevent any more remote station of the same group from transmitting until the nearer station has completed its code, the other branch circuit at each intermediate station being eifective to maintain the continuity of the line channel employed by the stations of the other group.

10. In a remote control system, a control oflice and a plurality of stations, a single line circuit ternating polarity at the oiiice and extending through said stations, 'said line circuit providing two non-interfering line channels including the same line wires for the transmission of currents of different polarities between the oifice and different ones of said stations, code transmitters at certain of said stations for controlling one line channel to transmit codes of current impulses of one polarity to said office, by-pass means at each of said certain stations for passing current of the other polarity only to maintain the continuity of the other channel through such station as long as the code transmitter thereat is in operation, code transmitters at other stations for controlling the LLOYD V. LEWIS.

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