US2437326A - Remote control system - Google Patents

Description

Patented Mar. 9, 1948 Nr OFFICE nEMoTE CONTROL srs'rEM Lloyd V. Lewis, Pittsburgh, Pa., assignor to The Union Switch 8a Sign al Company, Swissvale,

Pa., aV corporation of Pennsylvania Application November 1o, 194.4, sena: No. 562.85

My invention relates to remote control systems,

and more especially to .apparatus suitable for use in centralized trailic Vcontrol systems for railroads. Y

In systems of this character, as Villustrated by y9 claims. (ci. 177-353) Letters Patent of theUnited States Nos. 2,303,875 and 2,350,668, for example, it is .customary to provide a code type communication systemfor controlling track switches and railwaysignals over an extensive stretchA of territory by means of codes of direct current impulses transmitted l from the dispatchers olilce,'andv to provide a dispatchers telephone line usually using the same line wires by means'of which the crews'of trains at various Way stations may` Vcommunicate with the dispatcher. A selectivecalling system is also f n needed in order to enable v'the dispatcher to establish telephone communication with the field stations, and since the selector systems commonly used employ codes of low frequency impulses which are of such archaracter as to interfere with the operation of the centralized traic controlling system it has beennecessary to providemeans for suspending the operation vof the latterwliile the line is in use -for selective'calling. `Furthermore, the selectors present an additional load 4on i the line circuit for Ythe centralized traiiic control system; and forthese. reasons the selector system decreases the capacity'lof4 the centralized traliic control systemy to 'some extent even though the two' systems arefnon interfering.

OneV object of my invention is the provision of aV code system of remote lcontrolsuitable rfor selective calling or the like which 'employs 'codes of alternatingv current impulsesfof different frephone line without interfering with the transmission of low frequencygcode impulses over the same line. Y Y l f Another4 object of my invention isV the provision of a. remote control system particularly suitable for. use for the control and'indication of outlying traiic' governing devices, such as velectric switch locks. for handthrow switches. thefcontrol of which heretofore has required the installation of line'wires ofteneirtending several miles from the switch locationrto the nearest eld stationof the centralized traic control system.

My invention, `is an, improvement upon that disclosed in application forLetters Patent of the United States Serial No..514,641, filed December 17, 1943, now U. Letters Patent y2,396,134 granted March 5, 1946, by A. J. Sorensen, for Remote control systems. Y Y

A feature of my inventionis the provision of V quencies suitable fortransmission over a'tele-l-Y 2 Y code receivers responsive to a plurality of frequencies and connected to aline through different tuned` circuits, vone circuit atV a time, so as to present a high impedance to the line.

Another feature of my invention is the provision of code receivers of the electronic type which areY normally deenergized and employ local sources of' direct Vcurrent as their sole source of energy vso that they may be efficiently employed at isolated locations, with infrequent mainte- Il shall describe one form ofapparatus embodying ymyinvention.l and shall then point out the novel features thereof in claims.

vReferring tothe accompanying drawing, the reference characters Y and Z designate a pair of line wires which provide a communication channel for my remote control system extending from a control oiiice equipped with transmitting apparatus as shown inthe lower portion of the drawing, through arplurality of stations located at spaced points valonga stretch of railway at each rof which areceiver similar to the one shown in the'upper portion of thedravving is located. Each receiver is adaptedrto control an electro-responsive devicesuch/as a bell orbuzzer BZ, or the magnet WL of an electric switch lock, or the like.

The system of my invention employs alternating currentvcodes each` comprising a series of steps marked byV periodic changes in the frequency of the line current, without interposed pauses, each -frequency combination comprising astation code call.l In its specific embodiment as shown herein,;ithe system is arranged to use ve frequencies', designated ,fl to f5, and three code steps.:,- Thefiirst code'step may have any ,.oneof'vefrequencies. Any one of the four not used for the first step are available for the sec- VondV sten-and any one of the four not used for thegsecond stepY may be usedfor the third step,

' providing 5X4 4=80 dierent code calls for the selection ofthe corresponding number Vof stations. The frequencies may be in or above the yvoice frequency .band depending upon the circuit requirements. In the form shown herein, the

line currents are generated by an oscillator tube `Vicorltrlled bya'tuned circuit comprising a coll`L3 having an adjustable number of effective turns and a condenser C3'so las to deliver any one of the iive frequenciesv fl-f. The tube V3 controls anampli'er tubeV V4 by'which the alter- 'nating current yoftheselected frequency is delivered through a coupling transformer L4 to the line'wiresY and Z. The transmitting apparatus includes aserlesof push buttons or keys PI-P80.

to respond selectively fl,- f2, f3; as-indicated by sponsive are indicated by the references jacent the transformer connectionson t ings, and-as shown, the front contacta of key 1 P2 is connected-toamire" marked fl, ,indicating that coil L3 and. condenser C3 are. tuned tothat assiste Each station receiver includes lve relays-Rij and S2, two electron tubes VI land: V2-

R2, L, Sl

of the cold cathode, controlled ionization type,

and V4. Tubes V3 and Vit shown. Theplate; c

so that tubes:

. 1 Thafreguency of 4 rent of frequency fl and to supply it through tube V4 to the line.

When relay TI picks up, the energizing circuit for relay T2 is opened. Relay T2 releases after a suitable interval and shifts the connection of the positive terminal of battery B3 from contactd of key-P2 toy tliebranch .circuit including Vfront` Contact b` of -r'elay T3, backcontact c fQi key PI and front contact c of key P2, tuning the circuit L3-'C3 to the frequency f2..

the line current thus shifts to another upon the release romA one frequency ---of--relay-T2j, the-second frequency being deter- Y d by;the-cornection to contact c of the "operated key,

this being lfrequency f2 in the case 5 1 beine. :described-:15.

and a transformer LI having an adjustable pri-wL mary tuned by condenser C2 connected across the line andan adustable secondary turned by condenser-CI; by means of' `which-the--r'ec'eiver-at eachstation --is rendered selectively responsive to a distinctive sequence -offrequencies-supplied to the line by the operation of the corresponding Each station-is provided-With the usual local lbattery having-the terminals-B and C for energizing the-relays L,"'S|'-and S2, andthe buzzer arid---f-or supplying an answer back signal to the line in response to the operation-'of *the electr-icswitch-lock conltrolleol by magnet-WL--and-has a second battery BI for energizing-the electron-tubes--VI and V2 The station-apparatus 'as-shown is connected to--the code combination the connections to contacts b and c Lof relays S 'and-therelays Rl and R2 connected in series l and VSL-the` oiiice key JWhichisi-similarly 4fconriec-tefsl and- Which therefore controls-the station shown-being the key. P2.

- I-t-is believed that my-invention may be most --readily understood--fromwawdescription .of rits mode of operation,and-accordinglyfI--shall now assume that the op'eratorI-presses-the key P2 to operate -acalling-device illustrated as a buzzer BZ- at thestation-shovvn il c The closing Aof -contact a--ofkey P2 completes a-circuit-from:terminal-B-ofthe local source ofwcurrent-over back contact-a ofrelay TI through -relay- TZ--to terminal- C. Relay-'T2 --picksup 'and byclosi-ngits contact-a en-ergizes relay iT?.

y which turn closes-itscontacta to-energize relay Tl. Y y Relay .picked up-aslong as the `Vtery B3 .through the primary of transformer L4 T-I. completes astick circuit at its con- '-tact a so that itis-held key-P2 is pressed; and closes-:a circuit `from the `positive terrninalv of battery: B3. contacts bof relays.l Tlof keyPl and iront contact d.. of vkeyPZthroughs;4 the primary-:of transformer- L3 tube V3.

to the plate of tube V4, and the closingl of contacts c and d of relay Tlconnects the :secondary of transformers-L4,-throughf the condensers C4 across the line .wires-:Y and Z.- `Thefrequency to which the adjustable tuned circuitsrarerethe draw- P2, therefore, tube V3 is caused to generate cur- When relay T2 releases, it opens the energisirgciroult for relay T3, and the second frequency is supplied only untill. relay T3 releases, after which thevfrequency-lis-.'again. shifted, the frequency-,lof the -third nimpulse `being ,determined --by the connection-,to ,contacth of-the operated key, this being frequency f3 when key P215 operated, or wfrequency .fl .Whenkey Pl .is operated, as! will be Aseenfromthe. drawingthe third impulse-.being terminated., by the ,release of relay Tl lfollowing. the releasecf the operated key.

Each code thus-comprises a sequence ofthree ,impulsesv Without interpos ed;pauses, the last of which, comprisingthe operating .or deliver'y` impulse -ofthe; code, may be .prolonged as long as desired'byholding. the operated- `keyl depressed.

- Considering -noyvY -ifl'i-e.- station apparatus, it is fto beeunderstood that-thesprimaryof ltransfer-'mer .Ll is tuned by condenser G2 and presents a rela- -tively highy impedance;- 13o-,the line,v and that due `to line losses, thetuningis somewhat broadso -thatifrthis Wieregthe onlytunedY circuit provided, :the receiverwould respond, `more or less to a iband `of, frequencies; .asi required` for certain application-S, Ias ,illustrated-,- for-example, by Letters f 4Patentfof the-.United Statesbld 2,272,786, granted February10,--,19l;2, toNornjranA. Agn-ew. `In accordance with :the requirements `of i the present fi-nventiom asharper selectivityds required, and -vthis-is accomplishedgby-.the provisionof a second tuned circuit, comprising-a loosely coupled low resistance secondaryiortransformer Ll which is-,tuned-/byacondenser Gl., y -f Normally-, :transformer-Lt is tuned ,by circuits `completedover back-.contacts b vand c-V of there- .laysf-S I1. and 152,1 and-at;` the station shown these aretuned tothefrequency` fl, so thataresonant n.voltage -.,is`V developer-l-` across. .the terminals of `condenser Cl1whn current of that frequency is supplied-.tothe 1ine'.;fc- Y, f Relay `R tais Vconnected-.1in kseries ywith the' 4plate circuit of tube Vl across battery BI, the voltage vof which is, insuiiicien't to start ionization 4of the wtube VI, consequentlyrelay RLis normally deenergized adjustable posltivepotential derived fromcbatteryv-Bl .issupplied-to the grid of --tubeVl inseries Withthe alternatingpotential across-,condenser C:I,-,due-.t`o.y the line current, by zmeans Vofwhich.ionization-is caused to star-tin response tolline current-of the proper value and frequency, so astocause theplate circuit. of tube lVl tobecorne:conducting-,and relayRl to become energized. L'Ihecvol'tage appliedV to the plate circuitby batteryBLalthough,insufficient to start ionizatioma-,is .c'apable'fmaintaining the tube in thecOnducting- 'condition-.so as; to .hold relay R I energized after the tube.is, .once fired by the application fof.- thelproper. positive :potential to the grid circuit, even though this potential is applied butiinomentarily.' .and it is necessary to deionize thev tube before itcan` again serve as a detector. `This is accomplished by including a back contact of relay Rlin the plate circuit so that as soon as relay RI becomes energized the source of current BI becomes disconnected, tube VI becomes deionized andrelayRl releases.

Relay Rl therefore 'responds but once to a single positive impulse applied to its grid circuitl and operates repeatedly only in the event a sustained resonant A. C. voltage of a predetermined value is present across condenser Cl.. As used in practice the constants of its circuit are such that relay RI vibrates at the rate of about twenty times per second.

In order to differentiatev between-the random operation of relay RI, due to. impulse or shock excitation or the like, and periodic operation in response to sustained oscillations, a second tube V2 is provided. Each time relay Rl is energized, the potential of battery Bl is applied across a f resistor r4 ,of relatively low, value and v in series therewith, a condenser C4 anda resistor r2 having ahigh resistance, in parallel. The potentiall acrosscondenser C4 is applied through relay R2 to theplate of tube V2 and a positive potential derived therefrom is applied overan adjustable connection to resistor r2 to the grid of tube V2. When relay Rl is energized, condenser C4 charges at a rate determined by the product of thevalues ofr4 and C4, and when relay Rl is released, condenser C4 discharges slowly through resistor r2. The potentials thus applied to the grid and plate circuits of tube V2 increases step by step in response Vto the vibration of relay RI until they reach valuessufl'icient to cause tube V2 to fire Vwhereupon relay R2 bec'omes energized. The energy stored in condenser C4 causes current to continue to flowthrough relay R2 duringthe intervals when, due to its vibration, the

front contact a of relay Rl is open, so that relay R2 is held picked up as long as relay R l continues to vibrate. When relay Ri ceases to operate, condenser C4 discharges and tube V2 is deionized so that relay R2 releases following a relatively short pause in the operation of relay RI Y kAt each stationresponsive to a 4first code step of frequency fl therefore, relay Rl vibrates and energizes relay` R2, whichin turn energizes a slow release relay L over its front contact a. When the frequency Vof the line current is shifted to the second frequency f2, the energized relays RI cease tovibrate and the associated relays R2 release, for the kreason that the impulse of frequency fl to which the circuits for these relays are adjusted.V to respond has been terminated. Each such relay R2 then closes a pickup -circuit for a rst stepping relay Sl which extends from terminal Bat contact a of relay L oyer back contact b of relay R2, `back contact e Vof relay S2` through relay Sl to terminal C, so that relay Sl becomes energized. v

Assuming that there are eighty stations, arranged in flve groups with respect to the frequency towhich they respond on the rst step, the receivers at sixteen stations will operate as described, and of these, a group of four will have the tuning circuit which include front contacts vb and c of relay SI connected so as to respond to'frequency f2. At each station of this group, when relay SI picks up the tuning adjustment at that station is shifted from frequency fl -tothe frequency f2 ,which is being supplied to the line at the time and consequentlyrelays Ri and R2 become reenersized. t hold the slow release relay 6; L picked up, while. at the others relays RI and R2 remain released 'so that their relays L 'and SI release.V Each energized. relay R2 completesra stick circuit for relay SIv extending from terminal B at contact a of relay L over front contact b of relay R2 and the front contact a and winding ,of relay SI to terminal C, and vcompletes a pick-up circuit for the second stepping relay S2 extending from terminal B at contact a of relay L over front contact c of relay R2, front 'contact d of relay Sl and the winding of relay S2 to terminal C so that relay SI is held energized and relay S2 picks up on the second step. e When the frequency ofv line current is shifted to the third frequency f3, the termination of the impulse of frequency f2 causes the relays RI and'RZ to release at each of the four stations at which relaysSI and S2 are energized, and each such relay SI releases, due to the opening of its stick circuit at contactb of relay R2. Each energized relay S2 is held picked up by relay L over a stick circuit-,including its front contact a.

It will be understood that at each station of the selected group, thetuning circuits which include the back contacts b andc of relay SI1 and the front contacts band c of relay S2 are differently connected, those at only one station of the group being arranged as shown in the drawing to respondto frequency f3. At this one station,

Vtherefore, the release of relay SI vdue to the termination ofthe irnpulsefof frequency f2 shifts the tuning adjustment from frequency Vf2 to the frequency f3 whichat this timeis being supplied to the line, and at that station, relays RI and R2 are'reenergized to hold relay L energized, while at the others relays RI and R2 remain released so that their relays L and S2 release.

At the selected station, the response of relay R2 to the third Vstep completes a delivery circuit extending from terminal B at contact a of relay L, front contact c .of relay R2, back contact d of relay SI, front contact d of relay S2 throughv buzzer BZ to terminal C. The buzzer" B Zvv at only one station is thus sounded selectively in response to the operation of the corresponding rkey P2, and continues to sound until the key P2 is released.

It will be understood that the apparatus at those stations arranged to respond to arst frequency f2 or f3 will respondto the second or third frequency of the code described but at none of these will the delivery circuit be closed, and at the end of the code theapparatus at these sta-v tionswill be restored to normal after responding to only oneor two of the code steps,

It will be seen thatthe number of tuned cir? cuits which are resonantA to the line current at any given time is relatively small in comparison with the number of stations, consequently the impedance presented by the apparatus to the line may be made. suiciently high to adapt the system readily for use on electrically long lines.

Considering now ther application of the system of my invention to thecontrolrof anelecf tric switch lock; the'diagram at the upper right in the drawing indicates a portion of railway track Vwhich includes ahand throw switch W, the unauthorized operation of which is prevented by the provision of an electric switch lock. This device, as shown, isV to beunderstood to be of the type shown in Letters Patent of the United States No. 1,126,834, issued VFebruary 2, 1915, to Neubert etal., comprising `a rotatable shaft car-j rying a Vsegment 25 and two contacts 46 and 48, whichshaft in the ,nesltignhvwn Altkethe;er:

segment 25 theoper -vguishalole from the'freguency ,V3, assuming the latterhtolb nthe -audio erating nleverv 8 zof. the swltchtsinl. risposi-tions to maintain the trackziswitch- W..?l'ock.edf. normal', While the shaft-.in turnlslocked inthe position shown .by .a padlookzhavingraibail. 50.:`

To unlock `the svvitcli` the- .padlockmust.flrst be removed .by the train. crew,.. aftenbbtaining .permission .by telephone. from. the operator at .the dispatchers oice,il.thuspeimitting .-ithez-segment to`- bemoved a short-.ldistance-taipositiornto engage the locking dog '21u-andato close. contacts 46441". Then if traffic '.conditimsA .are .proper -as indicated by the energizat'ion .of airelafy-TR, a magnet WL may be energizedbverga oircuitinf cluding contacts l 464-411 tollifti-the i.lock-ingdog 214, permitting 'segment 25.to: be-'movedgto .itsl full reverse position inwhicn-the-sWitcndever 8. is `free to be operated.-

Itis .desirable toinsurethat the'operations described are carriedl out.only-=withlthe knowledge and 'cooperation' or the central oilice1 operator; and this rnayv readily be.: acco-'mplishedby con.- trolling magnet WL overthe-delivery circuit; of my receiver` as shown.4

In accordance Withthe preferredmod'eof operation, a member of the traine crew advises the operator by telephone-When he isi'eady to reverse i atop then presses .key P2Y to selectively energize the delivery circuit' and cause buzzer BZ-tfsound l at the location ots-witch Wg?. thereby informing 'the train crewA that the switch is electricallyhunlocked, and `energizing magnet WL When 'contactsilB-I-izarel closed by the'l train crew.v When theAbuZzer-signallisheard, therefore, theV segment-may.- be movedto full reverse, whereupon the closingof contacts 48-49 connects terminals B and C offV the "local source of current across the Kline lWires through resistors r5'and condensers C5',` the connection'coin-prising a 'branch 0f the delivery' ciruit--wmninciudes in addition, a iront'cot'act Y1;"o-i relay-RI. Y.A variablepotential thus' appliedto the Iline dueto'the vibration of-` relay Rlxvhleriproduces an audible ansvver bac Vsig'aAl` iny Vtldewo'perators loudspeaker ILSlvvhich readily distinrange.

The loperator therefore* holds the key V'PZi pressedfuntll the answer Abaclffsigival is'received, indicating that thfunlocling operations have been completed.WT "N Itis to be noted that the answer backv impulses impressed uponthe l'i're by thefhclosingqof'front contact b of relayR'l-"are incapable -ofcontrolling the tube VI so as tofcontinue 'rl'z'i'y7R11-,vibra-v tion 'after key' l2fis'V` releasil,` correspon ingV to the mode of operation"dscibedin-fthe Agnew patent hereinbefore referred' to, for ftloereason that 'the impulses are applied tofut'he line over front contacts 'bof relay Blot-,1ay time `v'vhn tube VI' isV d eenergized by the opening fbik contact aof relayfn|.

Although I have herein shown and vdescribed only one form of remote contr d`lsystern"enibodyQ ingwrny invention; itis uhd/Mstoodthat various changes and modificationsniay be made therein within the scop'eoftne appndeddiaiips 'without departing from the spirit and?,scc'ipiffnl'y invention. A f,

Having thus described invention, what; clai'mg, l

l.' Ina remote control system having aV pair of line` Wires to which differentcodes-are"sup1olie :it each 'Comprising ia? entre?? tif-.alternates sur# rent impulses "of- 'successively l"difieren-tf frequencles, a. receiver .including .a plurality. off ftuned circuitszeach. tuned 4to a ,diierent frequency and each ...coupled to a sharply tuned. localwcircuit tuned Vto .the same frequency for determining the frequenciesof the line current towhichsuch receiver is responsive;` and stepping `means controlled by said receiver in response to the code impulses forconnecting said-tuned circuits across theline wires only one .atta time andforsim-ultaneouslyfconnecting the local circuits-tuned to the corresponding. frequencies to said receiver vonly one at a time to renderA vthe receiver-responsive to a distinctive sequence ofA impulses constituting a code call.

2. In a remote control system having-a pair'of line-Wires to-Whichdifferent codes are supplied each --compr-ising a sequence of -alternating V curren-timpulsesof' successively *different` frequencies, a receiver including ani-adjustable tuned circuit connected to the line Wires iorgoverning its operation,A said tuned circuit-being 4normally adjustedl to vrender the n receiver selectively responsive"-toline current having a selected one ofY said frequencies, stepping means controlled "by said receiver and Yacting in response to the terminationvof'an impulse oi a particular frequency to change the adjustment oi said tuned circuitrto renderV the receiver -selectively-responsive to the next impulsewof a distinctive sequence of impulses constituting a code, and a delivery4 circuit prepared by said steppingmeans-and closed by said receiver in response to the last impulse of said code.

. 3. Inl a remote control system, a receiver responsive toa sequence of alternating current impulses of' successivelydiierent frequencies', cornprisingfa receiving relay, an electron tube having an inputcircuit supplied with said impulses over one of a'plurality of tuned circuits each tuned to a different-,one ci said frequencies, and anoutput circuit for controlling said receiving'relay, a series of stepping relays, a slovv release relay., means controlled'by said receiving relay for intermittently 4energizing said slovv release relay to maintain it picked up as long as the receiving relay continues rto respond to said impulses, meansicontrolled jointly by saidl receiving' relay and byv said-slow release relay for energizingsaid stepping rrelays one'at a time to count' the impulses; means controlled by said steppingrelays for connectingV theV` grid circuit of Vsaid tube to different' ones of'sa-id-tuned vcircuits kone at a time torender--said receiver' responsive to a distinctive sequence of impulses constituting a station code callgand a delivery circuitjprepared by said stepping relays and closed"bysaidreceivinggrelayf,in

response to Vthe lastjimpulse Vof said' distinctive sequence.

4. Ina -rernotej,control systen1,)a receiver respon;4 ive to-a ysequence of4 alternating currentl impulses of successively different frequencies supplied to ,a liney circuit, comprising a line-relay `controlled` by said impulses and a series of stepping relays operable one at a time in vorder in response tofdiierentoperations oftheline relay to2-countl 'the impulses as received,l 'means comprising aplurality' ofadiustable tuned cirfcuits for rendering the line relay responsive only to'linecurrent of a particular one ofsaid'frequencies, means controlled by i said stepping f. relays iorfshi-ftling `the connections ofv saidl tuned circuits to condition vthe 'line relay to respond to successiveimpul'ses of ld'iferent frequencies,V and a VdeliveryP circuit 'closed-by thelinerelay and by thelast' stepping relay of the vser-ies A'-v'vhen-v said lineV relay has responded 'to a predeterminedli number of impulses. l

5. yIn a remote control system, a receiverresponsive Ato a code of alternating current iinpulses of successively different frequencies, comprising any electrontube having a plate circuit connected to a local sourceof current and a grid circuit to Which said impulses are supplied, a

receiving relay controlled bythe current in said plate circuit,a plurality orf-tuned circuits yeach selectively responsive to a diiferent one ofsaid frequencies one of which circuits is normally interposed in said grid circuit to render said tube effective to operate the relay in response to the first impulse of a code only when suchimpulse is of the corresponding frequency, adjustable connections controlled by said relay for interposing different ones of said tuned circuits in said grid circuit successively as the impulses are received, said connections being arranged in a distinctive code pattern corresponding to a code of impulses identifying said receiver and serving to render the tube effective to operate the relay in response to the succeeding impulses of said code only when they have said distinctive code pattern, and a delivery circuit closed by said relay only when it responds to the last impulse of said code.

6. In a remote control system, a receiver responsive to a code of alternating current impulses of successively different frequencies, cornprising an electron tube having a plate circuit connected to a local source of current and a grid circuit to which said impulses are supplied, a receiving relay controlled by the current in said plate circuit, a series of stepping relays controlled by said receiving relay, a `plurality of tuned circuits each selectively responsive to a different one of said frequencies one of which cirl cuits is interposed in said gridy circuit to render the tube effective to operate the relay in response to the first impulse of a code only when such impulse is of the corresponding frequency, acljustable connections selected by the operation of said stepping relays for interposing different ones of said tuned circuits in said grid circuit one for each operation of said receiving relay said connections being arranged in a distinctive code pattern corresponding to a code of impulses identifying said receiver, and serving to render the tube effective to operate said receiving relay only so long as the received impulses conform to said code pattern, and a delivery circuit prepared by said stepping relays and closed by said receiving relay when it has responded to each of the impulses of a code.

7. In a remote control system, a receiver responsive to a code of alternating current impulses of successively different frequencies, comprising an electron tube having a plate circuit connected to a local source of current and a grid circuit to which said impulses are supplied, a receiving relay controlled by the current in said plate circuit in response to said impulses, a series of stepping relays, circuits controlled by said receiving relay for operating the stepping relays one at a time in order to count the impulses as received, adjustable connections controlled by said stepping relays for interposing differently tuned circuits in said grid circuit, one for each impulse, to render the tube effective to operate the receiving relay in response to the successive impulses of a code only when their frequencies have a particular pattern constituting a distinctive code call, and a delivery circuit prepared by circuit supplied with codes each comprising a sequence of alternating current impulses of suc.-

cessivelyl'fdifferent frequencies, a receiver comprising an electron-tube having a plate circuit and a grid circuit, a receiving relay controlled` by current supplied to saidV plate circuit, a plurality cfprimary tuned circuits each responsive to Va different frequency, stepping means controlled by said receiving relay, means controlled by the stepping means for connecting said primary tuned circuits to the line circuit one at a time in order, a plurality of secondary tuned circuits each responsive to a different frequency and each coupled loosely to that one of said primary circuits which is tuned tothe same frequency, means controlled by the stepping means for connecting each secondary tuned circuit to the grid circuit of the tube when the corresponding primary circuit is connected to the line circuit to render the tube effective to operate said receiving relay; and means controlled by said receiving relay When it releases upon the termination of a code impulse of a particular frequency for operating said stepping means to change the connection of said tuned circuits to render the tube responsive to a succeeding impulse of another particular frequency.

9. In a remote control system, a code receiver responsive to a sequence of alternating current impulses of different frequencies, comprising a first electron tube of the controlled ionization type having a plate circuit normally connected to a source of direct current, a receiving relay responsive to the current which flows in said plate circuit when the tube is ionized, a grid circuit including tuned circuit elements for causing the tube to become ionized to effect the energization of said relay when alternating current of a particular frequency only is supplied thereto, means for deionizing said tube comprising a back contact of said relay in said plate circuit for interrupting the ilow of current when said relay becomes energized causing said relay to vibrate as long as alternating current is supplied to said grid circuit, a second electron-tube of the controlled ionization type having a plate circuit connected to a source of current over a front contact of said receiving relay, a second relay responsive to the current which flows in its plate circuit when said second tube is ionized, said second tube having a grid circuit connected to a condenser which is charged through a resistor by the repeated operation of said receiving relay for causing said second tube to become ionized to energize said second relay only in response to the sustained vibration of said receiving relay, a series of stepping relays, circuits controlled by said second relay for operating said stepping relays one at a time to count each alternating current impulse as received, means controlled by said stepping relays for changing the connections of said tuned circuit elements as each impulse is received to render said first tube responsive only to current having the frequency of the next impulse of a particular code, and a delivery circuit prepared by said stepping relays and closed When said second relay has responded to each of the impulses of said code.

LLOYD V. LEWIS.

(References on following page) 2,131,164 Chauveau .,S ept. 27, 1.93.8: 5

The following references are of record'inthg @157539,542 Bemam sept 19, 1939

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