US2398572A - Remote-control system - Google Patents

Description

G. w. BAUGHMAN 2,398,572

REMOTE CONTROL SYSTEM April .16, 1946.

Filed Dec. 18, 1945 2 sheets-sheet 1 m N o ag c H m. V R m A m w. l IIIII. Z ,Qhm QTQNN v. E4 W mvfi 1 w mm a s5 u wvmwmmwxmwm Fw. Kw... g min ,Awi ;1 m y a Q My 1 4 Kw Q L s m5 r w Lm I -s LN Q H m m 1 $3 Ema Mmw AW L $5? w EEK mwv 5% T1 1 Vll\ flZS ATTORNEY Patented Apr. 16, 1946 UNITED STATES AT NT orricgfc REMOTE-CONTROL SYSTEM 'George W. Baughman, Swissvale, P assignor to The Union Switch & Signal Company, Swissvale, Pa., a corporation of- Pennsylvania Application December is, 1943, Serial Pia-514,812

6 Claims.

My invention relates to remote control systems, and more particularly to centralized traffic control systems for railroads for the control of rail.- way signals or othertraffic controlling devices from a central point of control, such as a train dispatchers office, and for the indication at the control ofiice of the condition of such devices or of train movements.

One object of my invention is the provision of a system of remote control suitable for the direct control of unattended manual block signals in the absence of the usual continuous track circuits.

a result of the .joint use of the same line wires.

by other communication facilities, and also possessing immunity from interference by the foreign currents occasionally encountered in long distance line circuits. These carrier currents are transmitted over different communication channels all employing the same line wires but each including circuit-elements renderingthe channel selectively responsive to a particular frequency or related band of frequencies.

' A feature of my invention resides in'arrangements wherebythe transmission of current, from the ofiice over a particular control channel to select a signal for clearing results in the transmission of current from the selected station over a related indication channel to control apparatus at the oflice to render the signal responsive to the operation of its control lever. controls and indications are thus made dependent upon the continuous transmission of current over two channels, thereby increasing the reliability of operation of the system.

Another feature of my invention resides. in the provision of means for interlocking the circuits for controlling signals at different locations-so as to prevent the simultaneous clearing of'two' opposing signals governing traffic movements into the same block and alsoof two successive signals governing traffic movements in the same direction. w 1

Other objects, features and purposes of my:

The signal moms through control ofthe signals. 3 t

invention will be pointed out as the description proceeds. t i

My invention is an improvement upon those disclosed in Letters Patent of the United States No; 2,332,963, granted to me on October 26, 1943, for Remote control systems, and in my copending application for Letters .Patent of the United States, Serial No. 484,397, filed April 24, 1943, for Remote control systems, and also upon that dis:- closed in the copending application for Letters Patent. of theUnited States, Serial No. 514,642, filed December 1'7, 1943, by Willard P. Place, for Remote control systems. i

. Certain features of my invention, disclosedbut not claimed herein, are claimed in my divisional application for Letters Patent of theJUnited States, Serial No.565,450, filed November 128, 1944, for Signaling systemfor railways. i I shall describe one form of apparatus embodying my invention, and shall then point'out the novel features thereof in claims. Referring to the accompanying drawings, Fig.1 illustrates a .portion of the operator's control board located in a traindispatchers ofiice or other suitable .point of control showing the circuitszand apparatus of the control panel for the signals at one fieldstationin its entirety, together with portions of the adjoining panels, including circuits by means of which the signals at one stationareelectrically interlocked with those at the next station in either direction.

Fig. 2 shows the apparatusat a typicalfielu station arranged for communication with the apparatus of Fig. 1 over a pair of line wires Y and Z, which it is to be understood, extend from they control office ofiFig. 1 through a plurality of stations, such as the one shown in Fig. 2, located at spaced points along a stretch of single track railway. j

Similar reference characters refer to similar parts in each of the views.

In its specific embodiment as shown, the apparatus of my invention is arranged for the control of a pair of manual block signals, LH andRI-I at each station,-as shown inFig. 2, and it may be assumed that the stretch is notprovidedwith 'trackfcircuits except for a short detector section "'I' at each station having a track relay TR ,for

the control of the signals and forindicating the movement of trains past the'station, trainmovethe stretch being governed primarily' by-train orders, supplemented by manual 1 The signals as shown are to be understood to be of the usual colorli ht type arranged togive active. 2 button such as the push button 2PB for setting the control apparatus into operation, and a pair of signal control levers such as the levers ZI-IL and ZDL which may then be moved to their lefthand or right-hand positions to cause the, corrsponding signal LH or RH to display its permissive or proceed indication, respectively. Each panel also includes a group of indication-lamps E, arranged to indicate the positions assumed by the signal control relays in responseto their manual control and to also report automatically when a train governed by signal LH or RH passes the station and thereby releases the track relay TR. In prior manual block systems, employing local operators at the stations to operate the signals and to report their condition and the passage of trains to the central oifice operator, additional protection is afforded by requiring the local operators to observe the usual rear end markers before reporting the train, to insure that the block will not be reported clear unless the departing train is complete and intact. My system attains this end by the provision of apparatus at each station similar to that disclosed in my prior application for Letters Patent of the United States, Serial No. 396,745, filed June 5, 1941, now Patent No. 2,342,315, issued February 22, 1944, for Train detecting and reporting apparatus. This apparatus includes portable markers in the form of permanent magnets M, one of which-is mounted at the rear end of each train V, asindicated in the drawings, in such a position as to cooperate with an inductor J in each detector section T-and to induce a voltage impulse therein to pick up a stick relay S, the energization of which indicates that the passing train is complete and intact. Each relay S is of the biased polar type and has associated therewith a slow release stick relay K for governing the transmission of indications of its operation, as hereinafter described.

My system employs alternating current codes of the continuous type for communication between the office and stations over the line wires Y and Z, characterized by the sustained modulation or periodic interruption of alternating carrier' currents of selected frequencies. Each signal is controlled by modulated carrier current of a distinctive carrier frequency, a pair of related frequencies designated fill and fll being used to control signals RH and LH, respectively, at the station shown in Fig. 2. Each station employs a distinctive carrier frequency in another band of frequencies, designated as I for the station shown, for'the transmission of indications from thestation, this carrier frequency being variably modulated in accordance with conditions at the station and serving to selectively control a group of indication lamps E associated with the signal levers. It is to be understood that the carrier currents are generated by oscillators 080 of the electron tube type, of which one is provided for each pair of control frequencies, and one for each indication frequency. It is'to be underst d t a each oscillator is normally energized over connections to terminals BX and CK of a local source of current, as indicated on the drawings. In Fig. 1, for simplicity, but one such oscillator is shown, designated 0802 and adapted to generate either of the two frequencies flu or fl! by the provision of an adjustable tuned circuit comprisingacoil 26 and a condenser Cl. .A similar oscil-.

. quency 'code,'by the periodic operation of contacts a of coding relays RCTM, LCTM and ICTM.

*A second contact b' of relays RC'IM and LCTM serves to select the frequency j! I] or fl I generated by oscillator OSC2 by completing the tuned circuit mentioned. The. continuous frequency codes delivered by these coding relays CTM comprise periodic interruptions of the carrier current at difierent rates, such as 75, 120, 180 or 240 times per minute, whichcodes are generated by continuously operating code transmitters, each of which is identified on the drawings by the reference CT, prefixed by a number indicating its rate of operation. Three such-code transmitters are provided at the oifice, as shown in Fig. l, and a set of four is providedat each station, as shown in Fig. 2, all of which may be .of the type shown in Letters Patent of the United States No. 1,858,876, issued May 17, 1932, to Paul N. Bossart, for Coding apparatus. At the oifice the code transmitters CT supplycoded currents to bus wires designated 75, and 180, respectively, which afiord connections for energizing the coding relays CTM of each panel.

The transmission of the carrier currents of different frequencies over the same line Wires Y and Z without interference one with another, or with the use of the line wires for other communication purposes, is effected in a Well-known manner, by interposing an electrical filter comprising a suitable arrangement of resonant circuit elements in each channel at each end of the line, designated LF, RF and IF, respectively, and it is to be under stood that each such filter presents a low imof the signals at a station, since but one of these can be cleared at a time. It follows that the number of signalswhich may be controlled over the same line wires is limited only by the number of available channels. The carrier frequencies used are preferably of the order of from 4 to 17 kilocycles for one direction and from 17 to 30 kilocycles for the other direction. Since the modulation frequencies'used are relatively low, the different channels may be closely spaced.

At the receiving end of the line, each selective frequency channel includes a suitable amplifier designated AMP connected to the line through a filter as mentioned, which amplifier delivers the modulated current of the correspondin carrier frequency to a demodulator or detector DET to convert it to a form suitable for operating a code when one of the coding relays CTM is set into periodic operation at a rate determined by one of the code transmitters CT this periodic operation is repeated by the corresponding "code following relay CF at the distant end of the line. Contact a of the operated relay CF then completes circuits from one terminal B of a suitable local source of direct current alternately in opposite di- 'rections through the primary of a decoding transformer 27 to the other terminal C of the same source, so that voltage impulses of alternately opposite polarity are generated therein and impressed by its upper secondary winding upon a plurality of resonant decoding units DU, each of which controls a slow release relay, such as the signal relays HR and DR in Fig, 2, or the indication relays ZSK, ZNK and ZYK in Fig. l. The designation of each decoding unit DU includes a numerical prefix indicating the frequency in impulses per minute to which it is selectively responsive, these units being of a well-known type such as is shown in Letters Patent of the United States No. 1,773,472, issued August 19, 1930, to Paul N. Bossart, for Railway trafiic controlling apparatus. The periodic operation of a code following relay CF as above described also induces alternating current of the corresponding code frequency in the lower secondar winding of the as* sociated decoding transformer 21, which current is rectified by the periodic operation of contactb of the code following relay CF to energize a slow release code detector relay, such as RCD, LCD

or 2CD, the circuits for relays RCD and LCD being interlocked over their back contacts a so that but one of these relays can be energized at a time. a It will be seen therefore that relayRCD responds selectively to a control code of the frequency fill and relay LCD to one of frequency fl l, and that these relays serve to select signal RH or LH, respectively, for clearing. The lamps R of signals LH and RH are both lighted to cause the signals to indicate stop'when the track relay TR is released or when the code detector relays RCD or LCD are released as shown,

the signals also remaining at stop when a 75 code of the carrier frequency no is received, this code serving to pick up relay RCD without energizing relay HR or DR as will readily be understood.

In order to enable my invention to be more readily understood, the operations involved in clearing a signal and in indicating its condition at the oiiice will now be briefly described, before tracing any of the circuits in detail.

Normally, the signals stand at stop as shown,

with the control apparatus inactive and the os- .cillators OSC disconnected from the line wires and all of the relays released except relays TR and K at the station, which relays ar held normally energized over their respective stick circults. The system is set into operation by depressingv a push button such as ZPB, as already Imentioned. If the associated signal levers ZHL and 2DL are in their normal positions as shown, the operation of the push button 2PB completes a circuit for relay RCTM which is interrupted at the 75 code rate, thereby effecting the transmission of 75 code current of frequency fIU over the line wires Y and Z, to which relay RCF at the selected station responds so that relay RCD becomes energized. Assuming that the track relay TR is picked up, relay RCD completes arcircuit for relay ICTM which is interrupted at either the 240 or'f 180 code rate, dependent upon whether relay K is pickedup or released, resulting in the -K is released upon clearing either signal and is picked up when relay S of the train reporting device is operated by a magnet M following the release of the track relay TR, consequently the lighting of lamp WE indicates the passage of a complete train through section R.

When the red lamp RE becomes lighted, signal LH or RH may be caused to display its permissive indication by moving lever 2HL to the left or right, respectively, while holding button 2PB depressed. This result in picking up a, stick relay ZLP associated with the lever, thereby completing a, circuit for relay LCTM or RCTM whereby a control code is transmitted having a carrier frequency ill or fill, depending upon whether the lever ZHL is in its left-hand or right-hand posi tion, which frequency is modulated at the code rate so as to energize relay HR along with relay LCD or RCD, thereby causing the yellow lamp Y of the selected signal to become lighted. The energization of relay HR changes the rate of modulation of the indication current of frequency I20 to the 120 code rate, thereby energizing relay ZYK along with relay 2CD, in place of relay ZSK or ZNK, to light the yellow indication lamp LYE or RYE which repeats the permissive indication of the'selected signal.

The push button 2PB may now be released and relay 2LP will be held energized over its stick circuit by relay 2CD as long as the transmission of the control code of frequency fill or ill and of the resulting indication code of frequency 120 continues. relay to maintain the signal control relay HR energized, subject to track circuit and lever control, as long as the indication code continues to be received; 1 i i 7 When lamp LYE or RYE becomes lighted, the selected signal may be caused to display its proceed indication under certain conditions as hereinafter pointed out, by moving lever 2DL to its left-hand or right-hand position corresponding to the operated position of lever ZHL. This results in a change in the rate of operation of relay LCTM or RCTM, to the code rate, to energize relay DR in place of relay HR, along with relay LCD or RCD, theneby causing the green lamp G of the selected signal to become lighted, and relay DR then changes the rate of modulation of the indication current of frequency f2!) to the 75 code rate, releasing relay ZYK but maintaining relay 2CD energized to lightthe green lamp LGE or RGE which repeats the proceed indication of the selected signal.

I shall now describe the operation of the system of my invention under different assumed conditions by tracing the various circuits in detail starting with the apparatus in its normal inac-' tive condition as shown, and assuming that the operator desires to clear signal LH to permit a train moving from right to left to enter the block including section T and the non-track circuited stretch to the left of section T, it being understood that this block is unoccupied at the time.

Normally, the track relay TR is energized over Relay ZLP thus serves as aslotting ing of relay K to the other terminal C of the local source. The code transmitters CT are energized and operate their contacts periodically as alreadymentioned, and each of the remaining relays shown in Figs. 1 and 2 are deenergized.

The operator will first press the push button 2PB completing a circuit from terminal B at the periodically operated contact a of the code trans mitter CT,'Fig. 1 A, over the normal contact (1 of levers 2DL and ZHL, contact 0 of push button ZPB, back contact 0 of relay ZLP, through relay RCTM in terminal C. Relay RCTM therefore operates to deliver 75 code current of frequency fl 0 to the line to operate relay RCF, Fig. 2, at the 75 code rate, as already described, thereby ener- 'gizing relay RCD to complete a circuit from terminal B at contact a of the code transmitter 240CT at the station over front contact f of relay TR, front contact b of relay K, front contact 0 of relay RCD, and contacts at of relays HR, DR and TR through relay ICTM to terminal C. Relay ICTM therefore operates to deliver 240 code current of frequency to the line to operate relay ICF, Fig. l, at the 240 code rate thereby energizing relays 2CD and ZSK. Relay ZSK completes a circuit from terminal B at its front contact a through the white lamp WE to terminal C, a branch of which extendsover back contact a of relay ZNKthrough the red lamp RE to terminal C, consequently lamps WE and RE become lighted.

It is to be understood that the block for which signal LI-I constitutes the entering signal extends to another station similar to the one shown and which has an opposing entering signal RH controlled by another signal lever IHL of which only the contacts e, f and g are shown in Fig. 1. It will be assumed that this opposing signal RH is at stop, in which case lever IHL will be in its normal or left-hand position or if it has been inadvertently moved to its right-hand position, the associated stick relay ILP will be in its released position.

As soon as the red indication lamp RE associated With lever ZHL becomes lighted, the operator moves that lever to its left-hand position while continuing to hold th button ZPB pressed, thereby completing a circuit from terminal B at contact a of button ZPB over, front contact 0 of relay 28K, contacts 1 of relay IL? and lever IHL, left-hand contact e of lever ZHL through relay ZLP to terminal C.

Relay 2LP therefore picks up, completing a stick circuit extending from terminal B at its front contact a over front contact 0 of relay 2CD, contacts J of relay ILP and lever IHL, left-hand contact e of lever ZHL, through relay 2LP to terminal C. Relay lLP is provided with circuits similar to those for relay 2LP including the righthand contact e of lever lHL and contacts g of relay ZLP and lever ZHL, and since these contacts g are now open, relay ILP cannot be picked up to clear the signal RH controlled by lever IHL nor can the clearing of the signal LH controlled by lever ZI-IL be interfered with by the manipulation of lever IHL.

When relay 2LP picks up, the energizing circuit for relay RC'I'M is opened and one for relay LCTM completed, extending from terminal B at the periodically operated contact a of the code transmitter IZOCT, Fig. 1, over contacts b of levers ZDL and ZI-IL and of relay ZLP through relay LCTM to terminal C. Relay LCTM therefore operates to deliver code current of frequency fl i to the line to operate relay CLF, Fig. 2, at the 120 code rate, thereby releasing relay RCD and energizing relay LCD and also energizing the signal control relay HR.

The opening of back contact 1 of relay HR opens the normally closed stick circuit for the indicating relay K, which extends from terminal B at the back contact b of relay S over back contacts I of relays HR and DR, front contact a of relay K, front contact e of relay TR through relay K to terminal C, thereby releasing relay K and cancelling the indication of the report clear device which otherwise would be displayed by lamp WE if lever ZHL were to be restored to its normal position prior to the movement of a train into section T. The closing of front contacts b of relays LCD and HR completes an obvious circuit for lighting the yellow lamp Y of signal LH, the red lamp R of this signal becoming dark. The closing of front contact d of relay HR completes a circuit from terminal B at contact a of the code transmitter IZUCT, Fig. 2, over contacts (1 of relays I-IR, DR and TR through relay ICTM to terminal C. Relay ICTM therefore operates to deliver 120 code current of frequency I20 to the line to operate relay IFC at the 120 code rate, thereby releasing relay 28K and energizing relay ZYK, relays 2CD and ZLP remaining picked up. Lamp LYE now becomes energized over the circuit extending from terminal B at the back contact a of relay ZSK, back contact b of relay ZNK, front contact a of relay TYK through lamp LYE to terminal C over the left-hand contact a of lever ZHL, lamp WE and RE becoming dark. The push button ZPB may now be released, relay ZLP being held energized over its stick circuit under the control of relay 2CD.

It will be noted that the system of circuits by which relay 2CD is supplied with coded current to hold relay 2LP energized includes front contacts d of relays TR and HR, Fig. 2, relay HR being supplied with coded current over a system of circuits including the left-hand contacts b and e of lever 2HL and front contact I; of relay 2LP. Consequently the signal LH may be returned manually to stop by restoring lever ZHL to normal, or automatically in response to the release of the track relay TR by a train entering the detector track section T.

When the yellow indication lamp LYE becomes lighted indicating that signal LH is displaying its permissive indication, the operator may move lever 2DL to the left-hand position, whereupon contact b of lever 2DL shifts the circuit for the coding relay LCTM to a branch extending over back contact e of relay ILP associated with the next signal-in advance, and thence to contact a of the code transmitter 1851GT, thereby energizing the signal relay DR over front contact a of relay HR, relay DR completing a stick circuit at it own front contact a. Relay LCD remains picked up, and relay HR releases, causing signal LH to display its proceed indication. Contact (Z of the signal control relay DR shifts the circuit of the coding relay ICTM from contact a of the code transmitter IZIJCT of Fig. 2 to that of the code transmitter T, resulting in the release of the indication relay 2YK. Relay 2CD remains In a manual block signaling system of the type being described, it is considered desirable to re strict the simultaneous clearing of successive signals governing traffic movements in the same direction to the display of their permissive indications asis accomplished by the circuits for relay LCTM just traced. It will be seen that if relay ILP is picked up to clear the signal LH controlled by"levers IHL and IDL, contact 6 of relay ILP shifts the circuit for relay L CTM above traced from contact a of the code transmitter 1800? to contact a of the code transmitter IZUCT, thereby changing the aspect of the signal LH controlled by lever ZHL and 2DL from proceed to permissive. When relay 2LP is picked 'up, its contact 6 similarly controls the circuits govern: ing the operation of the next signal LH at the right, controlled by the levers 3HL and 3DL. It will be clear that the arrangement is such that two successive signals cannot display their proceed indications at the same time.

One purpose of this arrangement is to enforce closer attention to train movements by the operator by requiring him to delay operating any signal to proceed'until the train has passed the next signal in the rear and has entered the block in approach to the signal. i i

I shall next assume that the train moving from right to left passes signal LH while displaying its permissive or proceed indication.

When the train enters section T, the trackrelay TR releases; the opening of its front contact a disconnects the track battery 2-8 from the track rails, the dropping of its contact I) restores signal LE to stop, and the opening of its front contact d stops the code operation? of the relay lCTlVLthe branches of the circuit for that relay which include back contact d of relay 'IRbeing open at back contact 0 of relay LCD, which relay is still energized. The code operation of relay ICEconsequ'ently ceases, releasing relay 2CD and also" relay- 2YK if energized, extinguishing lamp LGE or LYE, the opening of contact 0 of relay 2CD releasing relay 2LP. This stops the code operation of relays LCTM and LCF, releasing relay LCD and also relayI-IR or. DR.

The release of-relay LCD completes a circuit from contact a .of the code transmitter IBDCT, Fig. 2, over back contact b of relay K,'back'contacts c of relays RODand LCD and back contact (1 of relay TRthrough relay ICTM, which relay then operates to deliver 180 code current of frequency: I to the line to operate relay ICF at the;180 .code'irate, thereby energizing relays 2CD andZNK, and lightingthe red lamp RE.

When the: rear. of the "train passe through section T; .the magnetM' of itsreport clear device coacts with the inductor J to induce a. voltage impulse first-in one direction and then inthe opposite; direction inthe circuit for relay S. This relay is of a sensitivezbiased polar type and operates its contacts toihtheleft in response to one oftthese impulsesandisthenheld energized over astick circuit including battery 28, the left-hand contact a and winding of relay S,- and back contact; q g1}; relayf-I'R. -Rel ay K now picks up over the circuit including the left-hand contact b of relay S and back contact e of relay TR. Since contact J of relay TR is now open, the opening of back contact b of relay K terminates the code operation of relays ICTM and ICF, thereby releasing relays 2CD and ZNK'and extinguishing the red lamp RE. This indicates-to the operator that substantially the entire train has passed through section ,T, or more particularly, that the rear end of the train has passed the inductor J and has conditioned the repo ting device to function to report the passage: of a complete train.

After lam'p RE becomes dark, the operator returns levers 2HL and 2DL to normal and then presses the push button 2PB, completing a circuit .at its contact'c to operate relay RCTM to deliver 75 code current of. frequency flfl to the line as previously described, thereby energizing relay RCD; If the operator should happen to press button ZPB while section T is still occupied, relay TR of course remains released and the only effect of the'energization' of relay ROD is to'terininate the transmission of the indication code and to extinguish lamp RE, this lamp becoming lighted again when the button is released.

Normally button ZPBwill be pressed after the train has vacated section T, inwhich case the closing of front contact d of relay RCD connects battery 28 across the rails ofv section T over back contacts e relays DR and HR to reenergize the track relay TR, whereupon front contact a of relay TR closes to complete its stick circuit to hold it energized. When relay TR picks up, relay S releases due to the opening of back contact a of relay TR. Relay K is sufiiciently slow to release to remain picked up until relay S releases to close the stick circuit for relay K extending from terminal B at the right-hand contact I) of relay S over back contacts 1 of relays HR. and DR, front contact a of relay K, front contacts of relay TR through relay K to terminal C, and therefore relay K is maintained energized and relay ICTM is set into operation atthe 240 code rate over the circuit including front-contacts f and b of relays TR and K, and front contact c of relay RCD as already traced, thereby energizing relays ZSK and 2NK tulight lampsRE and WE as hereinbefore described. It will be clear thatthe lighting of thewhite lamp WE indicates that relay K has been reenergized by the operation of relay S, and consequently indicates the passage of a complete train through section T.

If push button ZPBis now released with lever ZHLin its normal position, the code transmission iscterminated, the indication lamps become dark and'the apparatus assumes its normal inactive condition as shown. V

In the foregoing, the operations involved in clearing the signal LH have been traced in detail. These include the holding of push button ZPB in its depressed position, with levers 2H1 and 2DL normal, to obtain a stop indication from the selected stationythe successivereversal of lever; and the release of the push button ZPB following the receipt of the stop indication; the reversal cf lever ZDL following the receipt of an indication of'the lightingof thepermissive signal lampY inlresponsetothereversal of lever zm, nd finally, the lightingof the prcceedsignal lamp (G I in response tov the reversal of lever ZDLQ and thedisplay of the correspondingproceed indication. Since the circuits for the two directions are symmetrical, it will be clear that signal RH may be cleared for a train V moving from left to right, as shown on the drawings, by operations similar to those described, levers ZHL button for picking up the stick relay, code transmitting means at the station rendered effective when said control relay and said detector relay are both energized to transmit coded indication currents over said line wires, means at the ofiice responsive to said coded indication currents for indicating the energized condition of said control relay and for maintaining said stick relay energized, and locally controlled means at the station for releasing said detector relay to stop the transmission Of said coded indication current, thereby releasing said stick relay to stop the transmission of said coded control current.

5. Ina remote control system, an ofiice and a station connected by line wires; a control lever, a push button and a stick relay at the ofllce; a controlrelay at the station; code transmitting means at the ofiice rendered effective when the control lever is reversed and the stick relay is picked up to transmit coded control current over said line wires to which the control relay is responsive, a circuit including said push button for picking up the stick relay, code transmitting means at the station rendered effective when said control relay is energized to transmit coded indication current over said line wires, a detector relay at the office responsive to said coded indication current, and a stick circuit for maintaining said stick relay energized controlled by a front contact of said detector relay.

6. In a, remote control system, an ofiice and a station connected by a line circuit, an ofiice coding relay controlling an oscillator for supplying coded current of a predetermined frequency to said line circuit, a control lever at the ofiice operable to a normal and to a reverse position, a stick relay at the office, a circuit including a reverse contact of said lever and a front contact of said stick relay for periodically energizing said office coding relay at a selected rate, a code following relay at the station selectively responsive to the current of said predetermined frequency in said line circuit, a decoding relay at the station controlled by said code following relay and arranged to be steadily energized provided the operation thereof is at said selected rate, a signal controlled by said decoding relay, a station coding relay controlling an oscillator for supplying coded current of a second predetermined frequency to said line circuit, a circuit including a front contact of said decoding relay for periodically energizing said station coding'relay at a second selected rate, a code following relay at the ofiice selectively responsive to the current of said second predetermined frequency in said line circuit, a detector relay, means for steadily energizing said detector relay in response to the periodic operation of the code following relay at the office, a pick-up circuit for said stick relay including a reverse contact of said control lever and a manually operable normally open contact, and a stick circuit for said stick relay including a front contact of said detector relay and a reverse contact of said control lever.

GEORGE W. BAUGHMAN.

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