US2259573A - Remote control system - Google Patents

Description

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0; HIS ATTORNEY L. V. LEWIS REMOTE CONTROL sYsTEM Filed March 11, 1939 g w m mmlmmwmw.

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Oct. 21, 1941. 1., v. LEWIS REMOTE CONTROL SYSTEM Filed March 11, 1939 5 Sheets-Sheet 3 INVENT OR Llagdld 961/65.

H15 A'i'ToRNEY Patented Oct. 21 1941 UNETEQ azsasn ear Y orr 2,259,573 REMGTE CGNTRQL SYSTEM Lioyd V. Lewis, Pittsburgh, Pa., assignortof'lhc Union Switch & Signal Company, Swrssvala. Pa, a corporation of Pennsylvania Application March ll, 1939, Serial No.126L241 (iJl. 177--353) 9 @laims.

My invention relates 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 trafno control systems for railroads in which a train dispatchers office or other suitable point of control is 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 ofiice.

My inventionis an improvement upon the centralized trafiic control system disclosed in my pending United States application, Serial No. 600,786, filed March 23, 1932, for remote control systems, which corresponds with the United States Letters Patent No. 2,229,249, issued J anu any 21, 1941.

One object. of my invention is to provide additional communication channels over the line wires of the centralized traflic control system, the additional channels being suitable, for example, either for telephone communication, or for code signaling, or for both purposes. A specific object of my invention is to so arrange the systern of my prior application that it may be used in connection with a normally open, or bridged line circuit.

A further object of my invention is the provision of an arrangement of apparatus which will permit, the line circuit of the centralized traffic control system to be used by other codesystems employing difierent nodes, without interference, even though two or more codes are initiated simultaneously.

In the specific embodiment herein illustrated, the code system of my prior patent hereinbefore referred to is so modified that the line circuit is rende ed available for voice frequency communication and also for code signaling by means of selector systems of the code wheel type, such systems being well known, as shown, for exempie, in the Field Patent No. 1,3 l3,256 or in the Gill Patent No. 1,070,301.

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

I shall describe one form 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 traffic control system and associated apparatus :IR

arranged in accordance with one form of my invention, while Fig; 2 illustrates an alternative form of apparatus suitable for-use at anintermediate fieldst'ation in the system of Fig. 1. Figs. 3 and 4 show the local circuits at the ofiice and station, respectively, for the system ofrny invention, these circuits being'generally similar to those of my Patent No. 2,229,249, hereinbefore referred to, except that as here shown they have been arranged in a more condensed form and have been modified to conform with Fig. l.

Similar reference characters refer to similar partsin each of the two views.

Referring to Fig. 1, the reference characters Y, Z designate the line wires of the system which extend from the point'ol control, usually a train dispatchers cilic'e, as indicated by the legend Oflice on the drawing, through each of a plurality. of field stations of the centralized trailic control system, in turn. Since the field stations are generally similar, but one is shown in order to simplify the drawings, this being identified on the drawing by the legend CTCStation.

(The line circuitsare'arranged as shown in the Field patent hereinbefore referred to in that the telephone and code signaling apparatus are bridged across the line wir'es' Y, Z. As shown, a Voice frequency communication channel extends from the telephone apparatus 19 at the office through a high pass filter illustrated as the condensers 25 to line wires Y, Z thence through slinilarcondensers 2c and telephone apparatus It at the distant end of the line, as shown on the drawing, or through a jack 24 to telephone apparatus, not shown, at an intermediate point such as at one of the field stations. The selector apparatus is also arranged as shown in the Field patent, and this comprises a plurality of code wheels d9, 93 at the ofiice, each of which when manually wound up and released makes one revolution during which a code sending relay St is energized over a circuit including the code wheel 89 or- 90 and contact 96 to connect a line battery through the contacts of a pole changer relay 8?, a low pass filter l8 and choke coils l1, to the line wires Y, Z. As the code wheel rotates, relay 8'! is intermittentlyenergized over a circuit including contacts 95, Q1 in accordance with the arrangement of the code wheel teeth to deliver a code of direct current impulses of alternately reversed polarity to the line wires Y, Z. These impulses selectively control the codewheel selectors 72 which are located as required at different points along the line. Since all the selectors are similarly arranged, but one is shown in order to simplify the drawings, this being lo cated at a point designated Selector station on the drawing.

Each selector [2 is connected across the line in the usual manner through a condenser 14 and a choke coil l1, and may be used to operate a call bell 16, a stick relay F, or for other purposes. The relay F, for example, may be used to govern railway traflic apparatus as shown for the similar relay F in the Wallace Patent No, 1,650,575.

The remaining relays of Fig. l are a part of my centralized traffic control system, as shown in detail in Figs. 2 and 3 and with the exception of the added relay V these relays bear the same designation as the corresponding relays of my patent hereinbefore referred to and the purposes and detailed mode of operation of these relays and of the coding units which they control may be ascertained from the patent.

The circuits of the system 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.

The relays OR and R are the line relays of the system which control coding units for selectively receiving code signals from the line and for also governing the operation of the relays OT and T, which are the transmitting relays for delivering code signals to the line. In the patent, a normally closed line circuit is used which includes the windings of the line relays OR and R and back contacts of the transmitter relay OT and of the master relay M at each station, all in series. This arrangement has been changed in accordance with the present invention and in Fig. 1 and likewise in Figs. 2 and 3 the line relays OR and R, which are to be understood as being high resistance biased polar relays, are bridged across the line through choke coils H for preventing the diversion of voice frequency currents through the relays, and the transmitter contacts are the normally open front contacts of the relays OT and T which are bridged across the terminals of the line relays, and therefore across the line, through low-pass filters l8 which limit the rate of change of the code signaling currents to values below the voice frequency band. As in the patent,

each line relay R controls two slow release relays r LI and L2 which in turn control a third slow release relay LB. For an understanding of the present invention it is believed to sufiice to point out that all these relays are normally deenergized, but that as long as the line relay R is intermittently operated by code signals one or the other of the relays Ll or L2 will remain picked up, that relay LB remains picked up for the duration of the code, and that the ofiice relays OLI, L2 and OLB are similarly governed by relay OR. Furthermore, relays OLI and LI are the last to release at the end of a code, and serve to interpose a pause to properly space two successive codes. Since the line circuit is normally open, the codes are reversed with respect to those of the patent, that is, in the present instance the line open condition corresponds to the line closed condition in the codes of the patent, and vice versa, and it will be seen by comparison with the patent that the connections of the line relay contacts to the relays of the coding unit are correspondingly reversed.

Each code delivered to the line wires Y, Z by a transmitter relay OT or T consists of a series of either '7 or 8 impulses, each of which may be relatively short or long, the intervening line open intervals also being relatively short or long to characterize the code.

One feature of the present invention relates to the means for preventing interference between different codes, and the manner in which this is accomplished will now be pointed out.

As explained in the patent, a control code for governing the railway traffic control apparatus at a selected field station of the CTC system, in accordance with the positions of the corresponding control levers at the office, is initiated by picking up a start relay identifying the code to be transmitted, such as relay 234ST, Fig. 3, to complete a circuit for the office master relay OM, which circuit may be traced in Fig. 1 from one terminal B of a suitable source of current over a front contact of the start relay, back contacts of relays OLI and 0L2 through relay OM to the other terminal C of the same source. In the form of the apparatus disclosed herein, relay OM upon be coming energized connects the line battery to the contacts of the office transmitting relay OT. Relay OM completes circuits, as shown in Fig. 3, for intermittently energizing relay OT to deliver the desired code to the line wires Y, Z to operate the line relays OR and R. The apparatus at the ofiice and at one station only responds selectively to such code by closing various circuits shown in Figs. 3 and 4 to pick up a selector relay such as 234s at the office and a similar relay S at the selected station and then other relays controlled by relay S are controlled in accordance with the condition of control levers associated with relay 234s. The first impulse delivered to the line by relay OT by energizing relay OR effects the successive energization of relays OLl, 0L2 and OLB, the latter relay completing a stick circuit extending to terminal B, for holding relay OM energized for the duration of the code. The stick circuit for relay OM has been modified as shown herein by including a back contact of the code sending relay 86 of the selector system.

The circuits for relay 86 in Fig. 1 differ somewhat from those of the corresponding relay of the Field patent. Thus in Fig. l, relay 86 has a pick-up circuit extending from terminal B, back contacts of relays OLI, 0L2 and 85, code wheel 89 or 90, contact 9G, relay 85 to terminal C, which is closed upon the release of the code wheel only if no code is then being delivered to line relay OR so that relays OLI and 0L2 are both deenergized. Relay 86 upon becoming energized completes a stick circuit extending to terminal B over its own front contact which is independent of relays OLI and 0L2 and which is opened at contact 96 upon the return of the code wheel to normal at the end of the code delivered by the pole changer Bl.

It will be apparent from the foregoing that neither the release of a code wheel nor the operation of a start relay at the office is effective to initiate a code unless relay OR has been deenergized for a time sufficient to effect the release of relay OLI, indicating that the line is free, while if both systems are initiated at the same time, the selector system takes precedence, relay OM of the CTC system being released upon the energization of relay 8B of the selector system.

Considering now the apparatus at the CTC station of Fig. 1, it is to be understood that an indication code, that is, a code indicating a change in the condition of the railway traffic governing devices at the station, is initiated by energizing a station start relay such as therelay'S-T of Fig. 4

to complete a piclnup circuit for the master relay M.

Relay M, upon becoming energized, at its upper front contact completes a circuit for a vibrator relay V, Fig. 1, and since this circuit includes also a back contact of relay V, that relay is caused to vibrate to close its front and back contacts alternately as long as relay M remains energized, that is, for the duration of the code. The upper contacts of relay V connect terminal B of the local direct current source alternately to the two end terminals of the primary Winding of the step-up transformer i2 which-has its midpoint connected to the other terminal C of the direct current source, causing current impulses of alternately opposite polarity tobe impressed upon the primary so that a relatively high 'alternating current voltage of a frequency the same as the rate of vibration of relay V is developed across the secondary terminals of transformer l2. This voltage is rectified by the operation of the lower contacts of relay V, andthe resulting rectifiedcurrent isdelivered to the terminals BH and CH and thence over contacts of relay M to ,v the code transmitting contacts of relay T. Relay V and transformer 12 thus provide a relatively inexpensive and convenient, local source of line current which is generated only when needed, avoiding the necessity for providing a high volte line battery such as -85 at each field station. Relay M, upon becoming energized, completes circuitsas shown in Fig. 4. for intermittently energizing relay T to deliver an indication code to line .wires Y, Z through the low-pass filter l8 and choke coils ll, this code operating the line relays OR and R, but as explained in the patent, only the coding units at the oiiice and at the transmitting station respond selectively. At the ofiice, a selector relay such as 23% becomes energized, and likewise relay S at the transmitting station, these relays controlling the operation of indication devices at the ,ofiice in accordance with conditions at the station.

Relay R at the transmittingstation governs the transmission of the code by relay T at that station, while relay R at each station effects the energization of the associated relays Li, L2 and LB. Relay LB at the transmitting station upon becoming energized completes a stick circuit for holding relay M energized, which circuit as shown in my patent extends over front contacts of relays M and LB, and also over a back contact of relay iii which opens to release relay M at the end of the code. This circuit as shown in Fig. a differs frointhe corresponding circuit of my patent in that the connection to terminal B is not made at the contact of relay i i but the circuit includes B over a front contact of relay T and the other extending to terminal B over a back contact of relay T and the right-hancl contact of the line relay R. Since relay T controls R, these contacts operate approximately in unison to maintain the stick circuit for reiay M closed substantially continuously soas to maintain relay M picked up as long as the code to which relay R responds is the same as. that delivered to the line by relay '1.

In order to distinguish. between controls and indications, 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 energized in order to condition the station appatwo branches, one extending to terminal a long impulse to transmit, will take ratus to respond selectively to the code. It follows that a code delivered to the linecircuit by any station, since it begins with a short impulse, will operate the receiving apparatus at the office but not that at any other station. Furthermore, in the event the ofiice and one or more stations initiate codes at the same time, current will be maintained on the line by relay OT after relays T have released and consequently. the

event of simulaneous initiation of'codes from the office and one or more stations, and that control codes take precedence over indication codes when both are initiated simultaneously. 7 v It may also happen thata calling key is opera-ted to initiate a selector code-at the same time that oneor more stations initiate indication codes. I 7

By reference to Fig. "1 or to the Field patent, it will be seen that the code wheels 89, -90 are arranged to apply current tothe line circuit by the energization of relay 8%, prior to the transmission-of code impulses by relay 8?, for an interval similar to a long step of the code. By reference to Fig. 1 it will be seen that the connections to battery have been arranged so that the initial impulse of a selector code is of the same polarity as the first impulse of a 'CTC code. This impulse is arranged to be long enough to lock out the station transmitters, so that selector codes take precedence over indication code when both are initiated simultaneously.

Another-condition to be considered is the mode of operation when two or more stations initiate indication codes at the same time. When this occurs, the transmitter relays T are held in synchronism by their respective line relays R as long as the code elements of the dilferent codes are alike, but since the codes diiier in at least one eleinent,.-a step will be reached which is long in the code delivered byone transmitter and short in the-code delivered by another. If this occurs on a line-cl0sed, or odd-numbered step, the resu t will be the same as when it occurs on the first step as above described, and the station having precedence, the master relay M at the other station releasing to discontinue the operation of the transmitter at that station. If it occurs on a line-open, or even-numbered step, relay T at the station having a long interval to transmit will remain released after the contact of relay R at that station is operated to the left by the next impulse following the short interval of release of relay T at another station, to release relay M. It follows that a station having a short line-open interval to transmit takes precedence over one having a long interval to transmit. In any case, it is evident that but one station transmitter will continue in operation to the end of the code and that but one code will be delivered to the ofiice at a time, the several codes being delivered to the line circuit one at a time in a predetermined order of code superiority, without interference.

A similar arrangement for lockingout the stations of a system employinga normally closed series line circuit is disclosed in the Snavely,

Miller and Jackel application, Serial No. 31,592, filed July 16, 1935, for Remote control systems, now Patent No. 2,183,155, issued December 12, 1939.

There remains to be considered the effect of the different codes upon the receiving apparatus of the CTC system and upon the selectors. In my CTC system, the selection of a station or of an office panel is effected by a combination of three long and four short steps directly following the first step, and each of the remaining five or seven steps may be either short or long.

The selector code includes only two long steps out of a total of 32 or less. In the Field patent, the total number chosen for illustration is 15 but a total of 17 or 2'7 steps is used in practice. The selectors are immune to ordinary Morse signals because the latter contain more than two long steps in any 17 successive steps, and for the same reason they are non-responsive to the CTC codes. Likewise the CTC receivers are non-responsive to the selector codes because the latter do not contain three long steps in any group of eight, as required to effect a selection in the CTC system. It follows, therefore, that the total number of codes provided by both systems may be used, without interference,

Another arrangement for preventing interference in the event that the transmitters at two or more stations are initiated at the same time may be used in the system of Fig. 1, this comprising an arrangement for sectionalizing the line as in the system of my patent.

This alternative arrangement is illustrated in Fig. 2, and referring to this view, it will be seen that the line wires Y, Z, which extend to the control office are carried through each intermediate station over back contacts of the station master relay M to the line wire sections Yl, Zl which, it is to be understood, extend to the next station to the right, while at the station most remote from the ofilce they extend to the telephone apparatus l9 at that end of the line, as in Fig. 1. In order to maintain the voice frequency communication channel while relay M is energized, the back contacts are bridged by highpass filters or condensers 2|, in the manner disclosed in the Baughman application, Serial No. 256,976, filed February 17, 1939, for Remote control systems, now Patent No. 2,208,446, issued July 16, 1940.

When relay M picks up to initiate transmission from the station shown in Fig. 2, relay V is intermittently energized to generate direct current as already described, but in Fig. 2 as long as relay M remains energized, this current is supplied from terminals BH and CH over the front contacts of relay M to the line wires Yl, Zl extending to the stations more remote from the office.

The contacts of the line relays at such stations are operated to the left, just as if the office apparatus had initiated a code. Since terminals BH and CH remain connected to the more remote section of the line for the duration of the code, this section serves as a source of code signaling current for the transmitting station, current from terminals BH and CH being delivered through the filter l8 and the contacts of relay T to relay R, and also through the choke coils I! to line wires Y, Z and thence to the office, each time relay T becomes energized. It will be seen that as long as a station is transmitting a code to the Office, the transmitters at the more remote station are held locked out by the current delivered to line Wires extending to these stations by relay M at the transmitting station.

In the event the office and a station initiate codes simultaneously in the system of Fig. 2, relay E at the first station will become selectively energized due to the long first impulse delivered from the ofiice as already explained, and relay E at each more remote station will become energized due to the similar impulse delivered to line wires Yl, Zl. When relay E at the first station picks up, its front contacts bridge condensers 2! in the line circuit, and the current delivered to line wires Yl, Zl will then be supplied also to line wires Y, Z after relay T has released, thereby maintaining the office line relay OR reversed even though the office transmitter relay OT releases, until relay M releases. The office transmitter is thus held on the first step of the code until relay M releases to disconnect the station source of current from the line circuit. It will be evident from Fig. 1 that relay M will be released by relay E, the circuits for relay M in Fig, 2 being the same as in my patent, these circuits having been already explained in connection with Fig. 1. It will be seen, therefore, that when relay M releases, the receivers at the ofiice and at all stations will have completed the first step of a control code and are ready to advance to the second step under the control of the office transmitter relay OT, which is than free to complete the code.

In view of the foregoing description it is believed that it will be apparent that the apparatus will also function properly in the event the office and two or more stations initiate codes simultaneously, and that the several codes will be transmitted one at a time in a predetermined order without interference.

Selectors of the types hereinbeiore referred to are used quite extensively by the railroads, and there are many train dispatchers telephone lines in use over which selectors are controlled. In accordance with the present invention such circuits are rendered available also for the control of centralized traflic control apparatus, rendering installations of the latter commercialy feasible, in many cases, under conditions which otherwise would not be justified on account of the relatively large cost of the line wires if a separate line circuit were required.

In many instances the office equipment of the CTC system will not be directly under the control of the train dispatcher or operator who manipulates the selector calling keys, but will be in charge of a different operator. In such cases it is desirable to indicate by suitable means adjacent the calling keys when the line is free so that a calling key will not be operated when the line is in use. To this end I provide a normally energized indicator lamp IE adjacent the selector calling keys which is controlled over back contacts of relays CL! and 0L2 as shown in Fig, 1. This lamp will be extinguished when ever a code is being delivered to the line circuit either by the CTC apparatus or by a calling key. In order to definitely inform the operator of the delivery of a selector code to the line circuit, I provide a second lamp 2E which is controlled by relay 86 so as to be lighted only while a selector code is being transmitted.

Although I have herein shown and described but one form of my invention and one modification thereof, it is understood that various changes and modifications may be made within the scope spasms of the appended claims without departing from the spirit and scope of my invention. 7 Having thus described my invention, what I claim is: 1 I

1. In a'remote control system, an office and a plurality of stations, a normally deenergized master relay at each station, a normally open line circuit extending from the oflice through said stations and including back contacts of the master relay at each station, local sources of line current at each station, means effective when the master relay at an intermediate station is energized to supply steady current from the source at said station to the line circuit portion extending to more remote stations and to also supply current from said source interrupted in accordance with a code to the line circuit por tion extending to the office, and means for energizing said master relay for the duration or such,

code effective only when the line circuit at such station is deenergized.

2. Remote controlling apparatus comprising a single line circuit connecting a plurality of stations, a line relay at each station connectedtacross said line circuit, a normally open code transmitting contact and a local source of' line current at each station, means at each station effective only if the line relay at such station is deenergized for at times connecting said local source across said line circuit through said code trans mitting contact and for disconnecting the portion of said line circuit extending beyond said station, and means for steadily energizing said portion as long as it remains disconnected.

3. Remote controlling apparatus comprising a single line circuit normally'ccnneoting an office and a plurality of stations, a line relay connected across said line circuit at each station, a local source of line current and a code transmitting contact at each station, means at each station eiiective only if the line relay at such 7 station is not energized for connecting the local source across the line circuit through the associated transmitting contact and for disconnecting the portion of the line circuit extending to stations more remote from the office, means for subsequently operating said transmitting contact to deliver a code to the remaining portion of said line circuit, means for steadily energizing said disconnected portion of the line circuit while said code is being delivered, and means for operating upon the completion of said code to restore the normal line circuit.

4. In a remote control system, a normally open line circuit extending from an oiiice to a plurality of stations, a normally deenergized line relay bridged across said line circuit at each station, a local source of current and a code transmitting contact adapted to be connected in series across said line circuit at each station, a master relay at each station, a pick-up circuit for each master relay closed only when the associated line relay is deenergized, a stick circuit for each master relay, means effective when each master relay is energized for connecting said local source across the portion of the line circuit extending to stations more remote from the office and for interposing means blocking the flow of current from said source between said portion and the remainder of said line circuit, and means for operating the associated transmitter contact when such master relay is energized to deliver a code to said oflice.

5. In combination, an office and a station connected by a single line circuit, a remote conline circuit during mitte'rs including one at said oifice'an'd one" at said station each operableonly if'initiated-W-hen the'lin'e is free, to deliverimpulse codes to said line circuit, starting means for each transmitter free to be actuated at any time tocondition that transmitterto deliver its code, indication means at the oilice effective for indicating when theline is free, a plurality of manually releasable code Wheels at said office, an additional code transmitter'atsaid oiiice operable immediately in response tothe manual release of a code Wheel but only if the code wheel isreleased when the line circuit is'freeg-to deliver other controlled over said linecircuit in response to the first impulse of a code and eiiective to disconnect said station transmitter from said line circuit during the transmission of a code initiated '5 simultaneously and jointly by said station transmitter'and by the omcetransmitter of said remote control system or by said additional transmitter, means for disconnecting the oiiice transmitter of said remote control system from said the transmission of a code initiated simultaneously and jointly by said ofiice transmitter and said additional transmitter, and storing means associated with each remote control system transmitter for initiating its operation as soon as the line is free if the starting means for such transmitter is actuated-when the line is in use or if such transmitter has been disconnectedfrom the line circuit by'the operation of another transmitter.

6.- In combination, an oiiice and a station connected by a single line circuit, a remote control systemhaving a plurality of code transmitters including one at said oflice and one at said station each operable when initiated, to deliver impulse codes to said line circuit, a plurality of manually releasable code Wheels at said office, an additional code transmitter at said oflice operable immediately in response to the manual release of a code wheel, to deliver other impulse codes to said line circuit, line relays at said office and at said station, means for initiating each code transmitter to deliver its code effective only when the line is free as manifested by the condition of the associated line relay, means for interrupting the transmission of a code by the transmitter at said station when the response of the associated line relay is not in accordance with the character of the first element of such code, means for interrupting the transmission of a code by the ofiioe transmitter of said remote control system when said additional transmitter is initiated at the same time, and storing means associated with the transmitters of said remote control system for storing each such interrupted code for subsequent transmission when the line is again free.

7. In combination, an oifice and a station connected by a normally open line circuit, a remote control system having a control code transmitter at said oiiice operable when initiated to deliver impulse codes to said line circuit in each of which the first impulse is relatively long, and also having an indication code transmitter at said station operable when initiated to deliver impulse codes to said line circuit in each of which the first impulse is relatively short, a plurality of manually releasable code Wheels at said office, an additional transmitter at said ofiice adapted to be initiated in response to the manual release of a code wheel to deliver an initial relatively long impulse to said line circuit followed trol system having a plurality of code trans V impulse codes to said line circuit, interference preventing means t3 aesasve by a code characteristic of the operated code wheel, line relays at said ofilce and station responsive to the code impulses in said line circuit, means for initiating each code transmitter effective only when the line is free as manifested by the steadily deenergized condition of the associated line relay, means for interrupting the transmission of a code by the transmitter at said station in the event the station line relay fails to release in response to the operation of that transmitter for terminating the first impulse of such code, means for interrupting the transmission of a code by the oflice transmitter of said remote control system when said additional transmitter is initiated at the same time, and means associated with the transmitters of said remote control system for storing each such interrupted code for subsequent transmission when the line is again free.

8. In combination, an office and a station connected by a single line circuit, a remote control system having a plurality of code transmitters including one at said office and one at said station each operable when the line is free, to deliver impulse codes to said line circuit, a plurality of manually releasable code wheels each operable it manually released when the line is free, to immediately deliver other impulse codes to said line circuit, interference preventing means effective when a code is initiated by the station transmitter and by the ofiice transmitter of said remote control system or by a code wheel at the same time for interrupting the operation of said station transmitter, other interference preventing means efiective when a code is initiated by a code Wheel and by the office transmitter of said remote control system at the same time for interrupting the operation of said o-fi'lce transmitter, and storing means associated with the transmitters of said remote control system for storing each such interrupted code for subsequent transmission when the line is again free.

9. In a communication system having an oflice and at least two stations connected by a line circuit, the combination with a remote control system having a plurality of cod-e transmitters including one at said oflice and one at each station each operable when initiated to deliver an impulse code to said line circuit, and having starting means for each transmitter free to be operated at any time to condition such transmitter to transmit its code but effective to initiate its operation only when the line circuit is free, and also having storing means efiective to maintain each actuated starting means in its actuated condition until the corresponding code has been fully transmitted, said remote control system also including interference preventing means effective when two or more transmitters are initiated simultaneously and they jointly deliver the first impulse of a code to the line circuit, to prevent further operation of all but one during such code, of an additional transmitter for delivering other impulse codes to said line circuit, together with manually operable means free to be operated at any time but effective only if operated when the line if free, to initiate the operation of said additional transmitter, and interference preventing means effective when said additional transmitter and one or more transmitters of said remote control system are initiated simultaneously and they jointly deliver the first impulse of a code to said line circuit, to prevent further operation of any remote control system transmitter during such code.

LLOYD V. LEWIS.

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