US2965882A

US2965882A - Remote control system

Info

Publication number: US2965882A
Application number: US711393A
Authority: US
Inventors: Arthur P Jackel
Original assignee: Westinghouse Air Brake Co
Current assignee: Westinghouse Air Brake Co
Priority date: 1958-01-27
Filing date: 1958-01-27
Publication date: 1960-12-20
Anticipated expiration: 1977-12-20

Description

Dec. 20, 1960 A. P. JAcKl-:L

REMOTE CONTROL SYSTEM Filed Jan. 27, 1958 TIES-;

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H15 A TTRNE'Y United States Patent Olitice 2,965,882 Patented Dec. 20, 1960 'REMOTE CONTROL SYSTEM Arthur P. Jackel, Penn Township, AlleghenyCounty, Pa., assignor to Westinghouse Air Brake Company, Wilmerding, Pa., a corporation of Pennsylvania Filed Jan. 27, 1958, Ser. No. 711,393

4 claims. (cl. 340-163) My invention relates to remote control systems. More particularly, my invention relates to a remote control system which incorporates compensation means for transmission channel delays to enable the checking of code transmission to be properly accomplished.

In many remote control system installations, particularly those relating to the control ofoil pipe lines and similar apparatus, a check of the correct transmission of the control and/or indication functions has been found necessary. One method of making such a transmission check, for time code type control systems, is shown, for example, in the copending application for Letters Patent of the United States Serial No. 570,366, filed March 8, 1956 by Paul K. Eckhardt and Arthur P. Iackel for Remote Control Systems, now Patent No. 2,942,238, issued June 2.1, 1960. It is relatively well-known, of course, that all communication channels and particularly those including carrier-current circuits cause delays in the transmission and reception of codes or other type signals. This transmission channel delay is `a particular disadvantage where the answer-back type of check signal is used. The transmission loop time delays the reception of the answer-back signal for a measureable period after the transmission of the corresponding signal from the originating location. Such delays prevent proper operation of the check system, particularly of the type shown in the above-mentioned prior patent where the check depends upon the simultaneous transmission and answer-back of corresponding signals.

In the system of the aforementioned patent, the answerback or feed-back detector relay means may on occasion be provided with a sufficient slow release period to bridge the transmission loop delay time. This permits satisfactory operation for nominal loop times. The slow release period provided, however, must not exceed the time length of the shortest code stepl in the remote control system in use. If this slow release period exceeds such code step length, the detector relay will fail to detect the absence of an answer-back signal for a short code step. This failure results from the holding circuit arrangement shifting to its opposite condition prior to the end of the slow release period so that the Acircuit falsely indicates that a proper answer-back has been received. Thus some other means must be provided for introducing the necessary compensating delay period to overcome the transmission time.

Accordingly, it is an object of my invention to provide, in remote control systems, an improved means of compensation for transmission channel delay time.

It is also an object of my invention to provide an irnproved and novel timing means which lcompensates for the-transmission channel delays in a remote control system. Afurtherobject of my invention is to provide means in a control system which compensates for the transmission channel loop delay between the time of transmission of selected vsignals and the reception of corresponding answer-backchecking signals. Y

Another object of my invention is to provide, in remote control systems, an improved means for establishing a delay period equal to the transmission channel loop delay encountered -between the transmission and reception of corresponding signals.

Still another object of my invention is to provide, in a remote control system, a novel delay period prior to the response vof answer-'back detection means to compensate for doop delays in the reception of .these answer-back signals.

A still further object of my invention is to provide, in a remote control system of the time code type incorporating an answer-back checking signal, an improved means of providing -a delay prior to the operation of the answerback detection means to compensate for the transmission loop delay between the transmission of a selected code step and the reception at the same location of the corresponding answer-back code step.

Other objects, features, and advantages of my invention -will become apparent from the following specication when taken in connection with the Iaccompanying drawing.

The single drawing is a diagrammatic representation of one form of circuit arrangement embodying my invention when employed with a time code remote control system.

In practicing my invention, the added delay compensation includes a timing means comprising front and back Contact slow release repeater relays for the oiiice transmitter relay. In the specic example shown in the drawing, these repeaters are actually controlled by the carrier transmitter relay which in turn follows directly the ofce transmitter relay. The slow release period of each repeater relay is established at slightly less than the minimum length of a short code step. A third repeater relay is used to repeat the exact operation of the oicetransmitter relay or its follower, the carrier transmitter relay. This third relay is of the magnetic stick type and is energized to operate alternatelybetween its two positions at the expiration of the slow release period of one or the other of the other repeater relays. In other words, the transmitter repeater stick relay operates to its opposite position to repeat the operation of the carrier transmitter relay only when the corresponding deenergized slow release repeater relay finally releases to close its back contact. The operation of this transmitter repeater stick relay between its two positions is thus the equivalent of the operation of the carrier transmitter relay but each movement occurs at the end of the established delay period. Since each of the slow release repeater relays has a retardation period slightly less than the minimum time of "a short code step, their release is assured during any code step so that the circuits willbe established to operate' the direct repeater stick relay. vAnswer-back detection then depends upon the position'of the repeater stick relay and the reception of an equivalent answerback code step from the remote station. With the slow release repeaters properly adjusted, the operation of the repeater stick relay to an opposite position occurs at substantially the same time as the operation (pick-up or release) of the carrier receiver rel-ay at the office, as controlled by the answer-back signal from thev station. The usual comparison of the transmitted code and thereceived answer-back is thus made and used to control the continued transmission of the' code from the oce loca.

tion.

I shall now describe the apparatus and circuits embody ing one form of my invention as shown in the drawing. Following this, I shall describe the operation of 'the appa'-l ratus in lconnection with the operation of the lgeneral control system. Certain modications alsopartl'ofmjy invention will be discussed although `not 'sp'.{ciiically'v shown -intheY drawing.

The general remote control system used in the single station installation illustrated in the drawing, and to which the circuits of my invention are applied, is of the time code type employing codes of long and short elements which are transmitted in each direction over the communication channel. More specifically, the remote control system may be of the type disclosed in Letters Patent of the United States Serial No. 2,442,603, issued to me on June l, 1948 for a Remote Control System. Reference may be had to this prior patent for details of the general system which are illustrated only conventionally in the present drawing. The system as shown has added an answer-back code check similar to that disclosed in the aforementioned Patent 2,942,238.

In the drawing, certain conventional symbols are used in order to simplify the showing and the circuit arrangement. The double winding transmitter repeater relay TPP is of the magnetic stick type. The movable portion of its contacts are shown in the vertical plane and a current direction arrow is shown within each winding symbol. The operation of magnetic stick relays is such that when current ows in either or both windings in the direction of the current arrow, the relay armature is operated to its left-hand position, as shown in the drawing, closing normal contacts. When the ow of current through either relay winding is in the direction opposite to the arrow, the relay armature operates to its righthand position closing reverse contacts. When the relay windings are deenergized, the contacts remain in the position to which they were last operated. In addition, the contacts of relays which have slow release characteristics are conventionally designated by a downward pointing vertical arrow drawn through the movable portion of such contacts. The apparatus shown in the drawing is provided with a local source of direct current energy which may be a battery of proper size and capacity. However, the direct current source as such is not shown, only its positive and negative terminals being designated by the reference characters B and N, respectively.

At the ler't of the drawing, the oce coding unit is shown conventionally by a dot-dash rectangle designated OCU. Only such details of the circuit arrangement within the coding unit as are necessary for an understanding of my invention are actually shown, the complete circuits being shown and described in the previously mentioned Patent 2,442,603. The coding unit may also be similar to that shown in the instruction pamphlet Manual No. 510 entitled, Time Code Control Systems, published by the Union Switch and Signal Division of Westinghouse Air Brake Company in November, 1944. The coding unit OCU includes a master relay OM which is energized during a control code in the manner shown in the two above publications. It is suiicient here to understand that relay OM is energized and picks up to initiate a control code. This relay is then held energized during the entire control code, releasing during the inal code step. During indication codes, relay OM is not energized and remains in its released position. The otice location is also supplied with a master repeater relay MP, external to the coding unit, which is energized by the circuit from terminal B over front contact a of relay OM and the winding of relay MP to terminal N. It is obvious that relay MP is also energized at the beginning of a control code and holds up during the entire control code, repeating the operation of relay OM.

Unit OCU also includes transmitter relay OIT. This relay produces the code being transmitted from the office to the station. Relay 01T is controlled by the timing and counting chains of unit OCU and also in accordance with the control functions that it is desired to transmit. The control and operation of relay 01T is completely described in the aforementioned system publications and reference is made to them for a complete description of its operation. It is sufficient to understand that, during a. control code, relay 01T is periodically energized So that its front contact a alternately closes and opens. The oflice is provided with a repeater of the transmitter relay, the carrier transmitter relay TC. The energizing circuit for relay TC extends from terminal B over front contact a of relay OT, front contact b of relay OM, front contact b of feed-back detector relay FBD, and the winding of relay TC to terminal N. During control codes, with relay OM energized and assuming relay FBD to remain energized, relay TC obviously follows the operation of relay 01T and thus picks up and releases its armature in accordance with the control code being transmitted.

As shown in the drawing, the oice and station are connected by a carrier communication channel. This carrier channel may be of any well-known type and is shown as being of a duplex nature having two unidirectional carrier circuits. The rst carrier circuit extends from the oice to the station, that is, from left to right, while the second circuit extends from the station to the office, that is, from right to left. The first carrier circuit utilizes a carrier current having a frequency F1 which is produced by carrier transmitter F1 at the oce and received by the carrier receiver F1 at the station. Similarly, the second circuit utilizes a carrier current having a frequency F2 which is produced by the F2 carrier transmitter at the station and received by the F2 carrier receiver at the oice. Both can-ier currents are normally on during the at-rest condition of the system. These carrier circuits may be superimposed on a physical line circuit between the cflice and station which is normally used for other types of communication and which thus additionally provides a duplex carrier channel for the control system. These carrier circuits may also be superimposed upon a multichannel VHF carrier system or may be carried by microwave or radio channels. Details of the carrier transmitters and receivers and the channels used are herein shown conventionally as they are not part of my invention. Such apparatus is Well-known in the art and any one of several different types may be used with the system. It is to be further understood that a physical line circuit with a direct current power source may be used. Such an arrangement is shown as one form of the answer-back checking system disclosed in the aforementioned Patent 2,942,238.

It is suflicient to understand that each carrier receiver when supplied with carrier current holds the carrier receiver relay connected thereto energized. Thus oflice carrier receiver relay OC is normally energized by carrier receiver F2 which receives carrier current from the station during the at-rest condition of the system. Similarly, carrier receiver F1 at the station holds eld carrier receiver relay FC normally energized since carrier current of frequency F1 is normally received at this station. The circuit for relay FC is completed through the station coding unit, such circuits being conventionally shown by a dotted line in the upper right corner of the drawing. Relay FC is further controlled, to transmit indication codes, by these circuits within the station coding unit which are not involved in my invention and are thus not shown in detail. Again reference is made to the system publications aforementioned for complete understanding of such operation. Suppression of the carrier current in either circuit causes the deenergization of the corresponding carrier receiver relay. It is particularly noted that each time relay FC releases, the closing of its back contact a suppresses carrier transmitter F2, removing carrier current o f that frequency from the channel and causing the deenergization and release of relay OC at the oice.

When the oce equipment is not transmitting a control code, relay OC controls ofce line relay OR. This circuit may be traced from terminal B over front contact a of relay OC, back contact a of relay MP, which is closed under these conditions, front contact c of relay FBD, and the winding of relay OR to terminal N. Relay OR is thus normally energized to close its front contacts. The release of relay OC to open its front contact a deenergizes relay OR which releases to close its back contacts. Periodic operation of relay OC to alternately open and close its front contact a causes relay OR to operate its contacts in a similar manner, alternately closing its back and front contacts a and b. This operation of relay OR drives the timing and counting chains of unit OCU to lreceive whatever code isvtransrnitted over the .second carrier circuit from the station to the oice. Such reception and registry of an indication code is completely described in the aforementioned system publications.

- Relayv OR is also provided with a second control circuit which is brought into use during the transmission of control codes. This circuit extends from terminal B over back contact a of relay TC, front contact a of relay MP, front contact c of relay FBD, and the winding of relay OR to terminal N. In some installations, contact a of relay TC may be replaced by a contact of relay 01T itself. The periodic operation of relay TC, following the operation of relay 01T within unit OCU, results in similar operation of relay OR. Under these conditions, the operation of relay OR drives the relay chains of unit OCU to advance the coding action through successive steps of the code. This action in turn produces proper operation of relay 01T to produce the desired code. Again reference is made to the previously referenced system publications which fully describe the action of coding unit OCU during the transmission of control codes.

One of the timing chain relays of unit OCU is the bridging repeater stick relay LBPS shown in the lower part of the conventional dot-dash rectangle. The oice is further supplied with a repeater relay LBPSP which is energized by an obvious circuit including front contact a of relay LBPS. Relay LBPS and likewise its repeater are held energized during any coding raction so that front contacts are closed.

As part of my invention, the oice is provided with a timing arrangement including a front and a back contact repeater of relay TC. Each of lthese timing relays is provided with slow release characteristics and is further snubbed by a resistor-rectifier combination in multiple with the relay winding. The circuit for front contact repeater relay TCFP includes front contact b of relay TC so that the repeater relay is energized each time relay TC is energized and picks up. A circuit for back contact repeater relay TCBP extends from terminal B over back contact b of relay TC and the winding of relay TCBP to terminal N. This second repeater relay is thus energized during coding action when relay TC releases to close its back contact b. Relay TCBP is continuously energized during the lat-rest condition of the system when relay TC is released. It is to be noted at this time that the retardation period of these two repeater relays, established by their own slow release characteristics and by l the resistor-rectifier snub, is adjusted to the desired length but does not exceed a time length slightly less than the minimum time length of a s hort code step in the system employed.

Another repeater relay to follow the code operation of relay TC is also provided at the oice. This transmitter repeater relay TPP, as previously mentioned, is of the magnetic stick type and has two windings. A circuit for the upper winding of relay TPP extends from terminal B over front contact a of -relay LBPSP, back contact a of relay TCFP, back contact c of relay TC, and the upper winding of relay TPP in the direction of the arrow to terminal N. It is to be noted that the flow of current in ,this circuit through the upper winding of relay TPP is in Athe direction to cause therelay to close its left-hand or normal contacts. A circuit for the lower winding extends from terminal B at front Contact a of relay LBPSP over -back contact a of relay'TCBP, front contact d of relay TC, and the @lower winding of relay TPP in the direction oppositethearrow to terminal N. The llowof'curre'nt in thiscircuit when completed is in a direction opposite to the arrow so that yrelay TPP operates to close its revers contact.

When relay TC periodically operates to follow the code produced by relay 01T, the alternate closing of front contact d and back contact c of relay TC causes relay TPP to also follow the coding action, alternately closing its reverse and normal Contact a as relay TC picks up and releases, respectively. It will be appreciated, however, that the circuit for the lower winding of relay TPP is not completed until relay TCBP releases at the end of its retardation period to close its back contacta. This occurs, of course, a selected time period after relay TC picks up. Likewise, when relay TC releases closing its back contact c, the upper winding of relay TPP is not energized until back contact a of relay TCFP closes, which occurs at the end of the slow release period of relay TCFP which was deenergized by the release of relay TC. Since relay TPP is of the magnetic stick type, its contact a remains in the position to which it was last operated during the period that both windings of the relay are deenergized during the coding action. Contact a is operated to its opposite position only upon the enf ergization of the other winding of relay TPP.

The nal relay shown at the oce location provides answer-back detection for the system. This is the feedback detector relay FBD, which is energized during the at-rest condition of the system and during indication codes over back contact b of relay MP. A stick circuit network is provided to hold relay FBD energized during control codes if the answer-back pulses are correctly received at the oice to indicate the correct reception of the code at ythe station location. The rst stick circuit path, as shown, includes front contact b of relay OC, normal contact a of relay TPP, and front contact a and the winding of relay FBD. A second path includes back Contact b of relay OC, reverse contact a of relay TPP, and front contact a and the winding of relay FBD. The first and second paths of the stick network operate alternately during successive steps of the code. During the odd numbered steps, when relay TC picks up, relay TPP is energized in a manner to close its reverse contact a, as previously described, and relay OC, in response to an answer-back step, is deenergized and releases to close its back contact b. During the even numbered code steps, relay TPP is energized, as result of the release of relay TC, in a manner to close its normal contact a while relay OC is reenergized, since carrier current is received at the office, and picks up to close its front contact b. This action will be more fully described hereinafter durlng the operational description. It will also be noted that relay FBD is supplied with a resistor shunt in parallel with the relay winding to provide a slight degree of retardation when the relay is deenergized.

I shall now describe the operation of the system of my invention, particularly in connection with the operation of the feed-back checking system and the transmission delay compensation which is necessary to provide proper operation. It is to be understood that the general control system upon which my invention is based is capable of transmitting both control and indication codes. The answer-black checking system and the associated transmission delay compensation may be used with either control or indication codes, as may be desired. However, in the specific system shown in the drawing, the indication codes are not involved in my invention and will be mentioned only briefly in order to provide a complete picture of the operation.

Y As previously mentioned, relay FC at the station is controlled by the station coding unit in order to transmit indication codes from that location. This control of relay FC by the station coding unit is described fully in the previously mentioned references. Briefly, relay FC is controlled sothat it releases during each` odd numbered step of the code and is reenergized and picks upduring each even numbered step of an indication codel .Carrier current of frequency F1 is continuously received at the station during the period that an indication code is being transmitted, and the control of relay FC is accomplished in that portion of its loop circuit shown conventionally by dotted lines in the drawing. The alternate release and pick-up of relay FC to close and open its back contact a causes carrier transmitter F2 to be periodically shunted so that carrier current of frequency F2 is removed from the communication channel. This results in a coded carrier current of frequency F2 being received by carrier receiver F2 at the office, and in turn relay OC periodically follows the indication code transmitted from the station. Relay OC, through the coded operation of its contact a, as previously described, drives ofce line relay OR. The resulting coded operation of contacts a and b of relay OR drives the relay chains of office coding unit OCU, and the indication code is received and registered in the coding unit. It will be remembered that relay OM and 01T remain released during an indication code. Upon the completion of an indication code, the circuit for relay FC remains closed so that relay FC is again energized by receiver F1. Carrier current of frequency F2 is then steadily transmitted from the station and the system returns to its normal at-rest condition.

Control codes, of course, are originated and transmitted from the oflice location to the station. Relay OM is energized and picks up to initiate the coding action followed by the energization and pick-up of its repeater relay MP. Relay 01T is driven by the coding unit to produce the desired code and in turn, over the previously traced circuit, drives relay TC in a similar code pattern. With relay MP picked up closing its front contact a, periodic operation of back contact a of relay TC drives line relay OR which in turn drives the coding unit to advance the coding action throughout the desired code. As mentioned heretofore, the complete details of such operation are described in Patent 2,442,603 and in Manual 510. The periodic closing of front contact e of relay TC to shunt carrier transmitter F1 causes coded carrier current of frequency F1 to be transmitted from the oice to the station. This results in a similar operation of relay FC to follow the received coded carrier current. As described in the above prior publications, this operation of relay FC drives the station coding unit to receive and register the desired control functions.

At the same time, in a manner similar to the transmission of an indication code, the periodic closing of back contact a of relay FC shunts carrier transmitter F2 and results in the transmission of an answer-back code from the station to the office. Each code step received over the first carrier circuit by relay FC is simultaneously retransmitted over the second carrier circuit back to the oce. Each odd numbered code step, which because of the shunt of transmitter F1 by front contact e of relay TC is a period of no carrier current of frequency F1, results in a similar period of no carrier current of frequency F2 due to the shunt completed by back contact a of relay FC. Periods during which pulses of carrier current of frequency F1 are transmitted result in similar periods of transmission of carrier current of frequency F2. The answer-back pulses are received by relay OC at the ofiice. However, due to the open back contact a of relay MP, the periodic operation of contact a of relay OC has no effect upon the coding unit, but the operation of contact b of relay OC in the stick circuit network for relay FBD is involved in the checking arrangement which will be described shortly.

The actual reception of each answer-back pulse is delayed beyond the transmission of the corresponding control code pulse by a time period which is equal to the loop transmission time of the communication channel in use. That is, a delay period occurs which is equal to the total time required to transmit a pulse of carrier current from transmitter F1 to receiver F1 and return a similar pulse from transmitter F2 back to receiver F2.

This time period varies according to the type of channel that is in use and particularly, as previously mentioned, to the necessary equipment which may be inserted in the channel such as carrier repeaters and filters for long circuits. When this transmission delay time approaches or exceeds the minimum time length of a short code step in the system in use, the circuit arrangement shown in Patent 2,942,238 cannot provide an accurate answer-back check since sufficient retardation cannot be applied to feed-back detector relay FBD without making the relay insensitive to the detection of short code steps. In these cases, the circuit arrangement of my invention is necessary to provide proper operation.

The periodic operation of relay TC to follow the coding action of relay 01T during the control code results iu the alternate energization of relays TCFP and TCBP over the circuits previously described. To review, relay TCFP is energized during each odd numbered code step and releases a selected time interval after the beginning of each even numbered code step when relay TC releases, Relay TCBP is energized during each even numbered code step and is deenergized and releases a selected time interval, equal to the release time of relay TCFP, after the beginning of each odd numbered code step. A previously mentioned, it is to be remembered that relay TCBP is energized at the beginning of a code and releases during the first code step. The release time of these back and front contact repeaters is adjusted as near as possible to equal the transmission delay time of the communication channel loop, but in no event is it more than the minimum time length of a short code step in the system being used. Thus each of these relays positively releases when deenergized before relay TC operates again to the position to reenergize the repeater relay. This action is assured unless a fault occurs within coding unit OCU which will eventually result in the interruption of the control code.

The coded operation of relay TC is also repeated by relay TPP, each corresponding operation of relay TPP occurring at the end of the delay period established by the release times of relays TCFP and TCBP. During the code, relay TPP closes its reverse contacts in response to each energization of relay TC, that is, during each odd numbered code step. Relay TPP operates to close its normal contacts during each even numbered code step which compares with the deenergization and release of relay TC. It will be noted that, during the final code step, which is an even-numbered step, the energizing circuit for the upper winding including back contact c of relay TC, back contact a of relay TCFP, iand front contact a of relay LBPSP is effective to operate the relay to its normal position, Irelay LBPSP remaining energized until the coding unit has reset which follows the release of relay TCFP. Relay TPP remains in this normal position until the next control code. In review, during control code operation, each time relay TC is energized and picks up, relay TPP is energized in a manner to operate its contacts to close in their reverse position, this action occurring at the end of a delay period established by the release time of relay TCBP. Likewise, each time relay TC is deenergized and releases, relay TPP repeats the operation by moving its contacts to close in the normal position at the end of a delay period established by the release time of relay TCFP.

At the beginning of a control code, the energizing circuit for feed-back detector relay FBD is opened 'at back contact b of relayMP. However, relay FBD is held energized over the first path in the stick circuit network which includes front contact b of relay OC and normal contact a of relay TPP. At some time after the beginning of the first code step, as established by the predetermined release time of relay TCBP, relay TPP operates to close its reverse contact a. However, at the same time, relay OC is deenergized as a result of the answerback code step from the field station and releases, Closing its back contact b. This establishes the second 9. path of the stick circuit network including back contact b of relay OC and reverse contact a of relay TPP. Relay FBD is thus retained energized at this time. During the second step of the code, relay OC is eventually reenergzed in response to the second answerdback code step from the station which is a pulse of carrier current. Back contact b of relay OC is open and front contact b closed. However, at about the same time, the upper winding of relay TPP is energized by the closing of back contact a of relay TCFP, back contact cof relay TC having previously closed. As previously described, this causes relay TPP to close normal contact a completing the rst path of the stick circuit network and retaining relay FBD energized. Any short interruption in the energization of relay FBD is overcome by the slight retardation provided this relay due to the resistor snub across the relay winding.

As long as the code is properly received at the station and the answer-back pulses received by relay OC, relays TPP and OC operate alternately to opposite positions simultaneously, or nearly so, to retain relay FBD energized. This cooperation between relays OC and TPP is, of course, dependent upon the proper adjustment of the slow release periods of relays TCFP and TCBP to approximately equal the transmission loop delay time. It will be obvious that if any answer-back pulse is not received by relay OC due to some fault in the communication channel or in the manner in which the code is received at the station, the stick circuit network for relay FBD will be interrupted upon the operation of relay TPP to its proper position following the operation of relay TC. Relay FBD, thus deenergized, will release, interrupting the circuits controlling relays TC and OR and halting the coding action, causing the system to reset to its at-rest condit-ion. The control code then must be reinitiated for a second attempt at transmission.

It is to be seen that, if contacts of relay TC are used in the stick -circuitnetwork for relay FBD instead of contact a of relay TPP, the slow release time of relay FBD must equal the transmission loop delay-period. Since this time period may exceed the time of a short code step, relay FBD will fail to detect the absence of a short answer-back code step because it holds, although deenergized, for a longer period. -The next code step, that is, the next operation of relay TC, occurs prior tothe expiration of this slow release period. The new position of relay TC matches the position of relay OC, relay FBD is reenergized, and the coding action continues.

For similar reasons, if the transmission loop delay time is longer than the time of a short code step, the slow release period of relays TCFP and T CBP can not exceed the maximum time length already described. The extra time required prior to the operation of relay TPP is then obtained by cascading another set of timing relays into the system operation. In that event, the relay TPP shown in the drawing drives a second set of front and back contact repeater relays similar to relays TCFP and TCBP. These relays in turn, in conjunction with relay TC, control a second repeater relay such as relay TPP. Contacts of this second relay TPP are then inserted into the stick circuit network for relay FBD and act in conjunction with contact b of relay OC to retain the stick circuit network complete and hold relay FBD energized in the proper manner. 4It is believed that this operation can be understood by those familiar with such systems in view of the preceding discussion and a complete showing and description is not herein provided.

Although I have herein shown and described but one form of circuit arrangement embodying my invention, it is to be understood that various modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

l. In a remote control system in which codes comprising a series of consecutive code steps are transmitted from a iirst location to a second location, said second location retransmitting each code step simultaneously with its reception to provide an answer-back check of the correct reception of the code, continued transmission of a code from said iirst location being dependent upon the reception of anidentical answer-back code, a circuit network 4at said rst location for compensating for transmission vdelay prior to receiving said- -ansWer-back code steps, said network including-a timing means responsive tothe transmission of each code stepfor establishing a predetermined delay period substantially equal to said transmission delay, a code repeater relay jointly responsive to the transmission of a code step and to the operation of said timing means to repeat each transmitted code step at the end of said delay period, and answer-back detection means jointly responsive to each operation of said repeater relay and the reception of each answer-back code step for effecting the continued transmissionv of said code when the transmitted and answer-back code steps are identical.

2. In a remote control system in which codes comprising a series of consecutive code steps are transmitted from a flirst location to a second location, each received code step being retransmitted simultaneously with its reception from said second location to said rst location to provide an answer-back check of the correct reception of the transmitted code, continued transmission of a code from said iirst location being dependent upon the reception of an identical answer-back code, said iirst location being provided with a detector relay effective when energized to permit the continued transmission of a code, apparatus at said rst location to compensate for transmission delay in the reception of said answer-back code, said apparatus including a timing means responsive to the transmission of each code step for repeatedly establishing a predetermined delay period substantially equal to said transmission delay, a repeater relay controlled by said code transmission to repeat each code step being transmitted, said timing means having connections eiective to delay each response of said repeater relay until the end of said predetermined delay period, a code comparison circuit network connected to retain said detector relay energized, said circuit network including contacts of said repeater relay and other contacts responsive to the reception of said answer-back code, for establishing a completed circuit path only when said repeater relay con- -tacts Iand said code-responsive contacts simultaneously occupy corresponding positions.

3. In a remote control system in which master codes comprising consecutive code steps are transmitted over a communication channel from a rst location to a second location and identical answer-back codes are transmitted from said second location to said iirst location, each answer-back code step being transmitted simultaneously with the reception at said second location of the corresponding master code step, the combination at said iirst location comprising, a normally energized answerback detector relay effective when deenergized to halt the transmission of a code, a stick circuit network for sa1d detector relay including a contact operable between a irst and a second position in response to the receptlon of alternate answer-back code steps and Ianother contact operable between a rst and a second position in response to alternate master code steps, said stick circuit network being effective to retain said detector relay energized during the transmission of a code only when both contacts occupy corresponding positions, a timing relay means responsive to the transmission of each master code step for repeatedly establishing a predetermined delay period substantially equal to the transmission loop delay period of said communication channel, and a circuit means responsive to the operation of said timing means and effective for delaying the response of said other contact to the code transmission until the end of said loop delay period.

4. In a remote control System including a control oice and at least one station connected by a duplex communication channel, said oflice being provided with a coding unit including a transmitter relay means which at times operates between a first and a second position to transmit a control code comprising a consecutive series of code steps to said station, said station being adapted to receive such code steps and to simultaneously retransmit each code step upon reception to said office to indicate proper reception of the control code, the combination comprising, a first position and a second position slow release repeater relay of said transmitter relay means, each repeater relay having an established release period equal to a predetermined time inlerval `and less than the time length of any single code step, another transmitter repeater relay of the magnetic stick type and an energizing circuit network therefor including released position contacts of said slow release repeater relays and rst and second position contacts of said transmitter relay means, said circuit network being elective to operate said repeater stick relay to a position corresponding to the existing position of said transmitter relay means after a time interval equal to the release period of said slow release repeater relays, a normally energized feed-back detector relay eiective only when energized to permit the continued transmission of a control code, and a stick circuit network for said feedback detector relay comprising a first path including a rst position contact of said repeater stick relay and a contact closed in response to the reception of an answer-back code step corresponding to the lirst position of said transmitter relay means and a second path including a second position contact of said repeater stick relay and a contact closed in response to the reception of an answer-back code step corresponding to the second position of said transmitter relay means, said stick circuit network being effective to hold said feed-back relay energized when the reception of each answer-back code step is delayed said predetermined time interval after transmission ofthe corresponding control code step'.

References Cited in the tile of this patent UNITED STATES PATENTS 1,923,724 Griith Aug. 22, 1933 2,121,163 Robinson June 21, 1938 2,242,196 Thompson et al May 13, 1941 2,354,534 Mason July 25, 1944 2,816,218 Rees et al Dec. 10, 1957