US2574805A - Indication transmitting apparatus for remote-control systems of the code type - Google Patents

Description

E. B. WALKUP 2,574,805 NSMITTING APPARATUS FOR REMOTE Filed Oct. 31, 1946- S S w -S a WI E n ma m n 5 .w fim .wsfim 1,0,. v

Nov. 13, 1951 INDICATION TRA CONTROL SYSTEMS OF THE CODE TYPE Patented Nov. 13, I951 INDICATION TRANSMITTING APPARATUS FOR REMOTE-CONTROL SYSTEMS OF THE CODE TYPE Edgar B. Walkup, Swissvale, Pa., assignor to Westinghouse Air Brake Company, a corporation of Pennsylvania Application October 31, 1946, Serial No. 706,865

5 Claims. 1

My invention relates to remote control systems, and more particularly to centralized traffic control systems of the code type and to indication transmitting apparatus for use in such systems.

In its specific form, as herein shown and described, the apparatus of my invention forms a part of a remote control system having a code transmitter for transmitting indications at times to a distant point over two intermittently available communication circuits, to indicate the condition of different movable devices. The remote control system includes a repeating relay for controlling the character of the indications transmitted over the two circuits in accordance with the condition of certain movable devices, and also includes two indication relays for modifying their character in accordance with the condition of other movable devices. In addi-. tion, these relays cooperate with certain register relays, which locally register the character of the transmitted indications, to control circuits by which a starting relay may be actuated to initiate the transmission of indications.

My invention is of particular utility for indicating the condition of two railway signals which govern traffic movements over conflicting routes, Where each signal has an approach looking relay which is released by the indication relay for the signal when the signal is cleared, and which remains released when such signal is put manually to stop, for a predetermined time looking interval, to delay the clearing of the other signal. As shown herein, each signal has an indication circuit controllable individually by its indication relay to indicate its clear or stop condition, and in addition, the approach locking relays govern the repeating relay referred to, so as to indicate when this time looking is in effect, by the energization of both indication circuits.

The primary object of my invention is the provision of a novel arrangement of code starting circuits controlled by the relays which govern the transmission of the indications, so as to insure the transmission of correct indications in response to any change in the condition of these relays even though successive changes occur during the transmission of the indications. To this end, I provide an additional relay which cooperates with the register relays, and at times, with the repeating relay, to provide additional circuits for the starting relay. This additional relay is a neutral relay which is normally energized over pole-changer contacts of the indication relays, and which releases momentarily, due to the reversal of polarity, when either indication relay picks up or releases, its circuits being arranged so that it cannot be restored to its energized position during the transmission of indications. My invention also includes an additional circuit for the repeating relay mentioned above, to prevent a change in its condition during the transmission of indications, under certain conditions.

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

Referring to the accompanying drawing, the track diagram shown illustrates a stretch of single track railroad including a switch section IT over which traific movements are governed in opposite directions by the opposing head block signals 2R and ZL, together with two approach sections 3T and ST over which trailic approaching section IT is governed by the distant signals 4R and GL, respectively. Each track section is provided with a track battery BI, B3, etc., at one end, and a normally energized track relay ITR, 3TB, etc., at the other end, for governing the signals in accordance with traffic conditions in the stretch. Each signal is governed by a polarized signal relay such as relay ZRHR. or ZLHR. which relays are electrically interlocked, and are controlled in accordance with traffic conditions, and is arranged to indicate stop when its relay is released and to indicate proceed or caution when its relay is energized in a normal or reverse direction, respectively. To simplify the drawings, only the terminals of the local sources of current for energizing the various relays are shown, these being identified by the reference characters B and C, designating the positive or supply terminal and the negative or common return terminal, respectively.

The relays 2RHR and ZLHR for the head block signals 2R. and 2L are also manually controllable from a central ofiice by the operation of signal control relays 2RHS and 2LHS, governed by a suitable remote control system, which in part is shown in the lower portion of the drawing, and corresponds to that shown in Letters Patent of the United States No. 2,229,249, issued January 21, 1941, to L. V. Lewis, except as modified in accordance with my invention. The general mode of operation of this remote control system is well known and a detailed explanation thereof is not needed for an understanding of my invention, further than to point out that it employs a plurality of groups of relays or coding units, including one at a control oflice and one at each of a plurality of field stations, connected by a pair of line wires, not shown herein, over which control codes are transmitted at times from the ofiice to a selected station and at other times indication codes are transmitted over the same line wires from the different stations without interference.

Each code comprises a series of steps transmitted one at a time by the. operation. of a chain of counting relays, the steps including a first group of code elements constituting a code call by which a selector relay at the ofiice and a similar relay at the station identified by the code call are selectively operated, and a second group of elements for controlling or indicating the condition of selected devices.

My invention involves the use of only two control code elements and two indication code e1ements and requires consideration of only one field station, and in order to simplify the. disclosure, only the portions of the. remote control system relating directly to my invention. are illustrated herein, these being shown in a simplified diagrammatic form.

The remote control system includes a starting relay for each different code call, the energization of which initiates the transmission of the corresponding code at once if the system is in its normal at-rest' condition and otherwise as soon as the system assumes that condition. The starting relays at the office, not shown, are operated by push buttons, such as. the button STB, associated with the lever or levers which govern the control elements of the corresponding code. At the end of each. control code a delivery relay D, selected by the code call, operates the control relays at the selected station in accordance with the positions of these levers as refiected by the control elements of the code.

The code control of relay D by button STB is illustrated diagrammatically herein by an equivalent direct wire connection.

To effect the energization of the signal control relay 2RHS or 2LHS. for example, the central ofiice operator moves the signal lever 28G to its right-hand or. left-hand reverse position and then presses the starting button STB, thereby initiating a control code, as explained in the patent, whereby the delivery relay D is momentarily energized, and the signal controlrelays ZRHS and 2LHS are actuated in accordance with the character of signal control elements in the code which reflect the position of the signal lever 25G. For simplicity, these code elements are indicated by the equivalent direct wire connections in. the drawing, and the wires 12 and I04 correspond to those similarly designated which extend to the contacts of the signal lever HK in Fig. 5 of the patent and govern the transmission of these code elements.

The track layout shown, including the signals 2H. and 2L, corresponds generally to that shownin Fig. 9 of the patent above referred to, and each signal relay is provided with a normally energized indication relay 'ZRGP or 2-LGP which relays govern the transmission of indications to the office reflecting the condition. of the signals and also control approach locking relays ERAS and ZLAS, corresponding to the relays- LMR and RMR. of the patent by which the signals are interlocked, the locking relays being governed by a time element relay TE in a manner generally similar to that described in the patent so as to delay the clearing of a signal following the manual return of an opposing signal to its stop position in front of an approaching train.

By reference to the drawing, it will be seen that when signal 2R is cleared, relay ZRAS releases, due to the opening of its stick circuit by the. release of relay ZRGP, and that the release of the track relay ITR, by a passing train restores signal 2R to stop and completes a pickup circuit for relay ZRAS, provided relay 4RHR is reversed or released, indicating that signal 4R. is at caution or stop, in which case relay ZRAS picks up at once.

When signal 2R is put manually to stop, by the release of the signal control relay ZRHS, if the approach zone including section ST is unoccupied, an approach relay 2RAR is energized and provides a pick-up circuit for relay ZRAS. If the approach zone is occupied, or if as shown by the circuits associated with the opposing signal 2L, an approach relay is not provided, relay TE becomes energized over a back contact of relay Z-RAS or -ZLAS following the manual return of the signal to stop.

When relay TE is energized, its checkin contact shown in the circuits for relays ZRHR and ZLHR opens at once, but its normally open contacts in the circuits for relays ZRAS and ZLAS do not close until the end of a measured time interval constituting a time locking period during which relay ZRAS or ZLAS is held deenergized, one purpose of which is to insure the release of relay ITR before relay 2LAS or ZRAS picks up, in the event a signal is put to stop in front of an approaching train which is unable to stop without over-running the signal.

It is to be understood that an indication code reflecting wayside conditions is initiated by the energization of a starting relay ST at the transmitting station as explained in the patent, relay ST being released by the opening of its stick circuit by the operation of a relay VC which as shown in Fig. 7 of the patent, picks up momentarily in the last step of an indication code, that is, when the code is fully transmitted. Relay ST is energized by the delivery relay D each time relay D is operated, so that an indication code follows each control code, and is also energized automatically in response to a change of the position of any of the relays such as relay 2RGP- which governs the transmission of indications.

Each indication code includes sixteenv steps requiring for transmission about 3.5 seconds, the steps including a first group of selecting elements followed, by a second group of seven elements controllable as required to indicate the condition of different devices. Whereas in the patent, three steps are used for indicating the condition of the relays LG? and RGP, the circuits as shown herein are re-arranged so that but two are used, namely, the twelfth and fourteenth, corresponding to wires 92-42 and 94-44 in Figs. 7 and 8 of the patent, by means of which the signal indication relays ZLI-IK and ZRHK at the ofiice, corresponding to relays |2K and MK in Fig. 5 of the patent, are energized over Wires H2 and H4. The fact that these circuits are closed at different times is shown by the contacts 1 of the remote control system counting relays 4 and. 6 in the circuits, and it will be understood that such relays are energized only one at a time, to designate the two code steps referred to. The circuits as shown are I also arranged to distinctively indicate the condition of the approach locking relays 2RAS and ZLAS over the same code steps, by the provision of a repeating relay ASP which picks up whenever relay ZRAS or ZLAS is released, following the clearing of the signal.

When the indication transmitting apparatus at the station is in the condition shown in the drawing, the energization of relay ASP results in the energization of the starting relay ST over a circuit which may be traced from terminal B at front contact I) of relay ASP, the front or back contacts 11 of relays 2LGP and 2RGP, in parallel, wires 92 and 94, and back contacts at and j of a transmitter control relay MSP in parallel, thence over back contact I) of a valve relay I2-I4V through relay ST to terminal C.

The circuits of those relays of the remote control system which have a bearing upon the present invention and which operate as a direct result of the energization of relay ST are indicated diagrammatically herein by dotted lines extending from terminal C through their windings over contact c of relay ST to terminal B at a back contact of a relay VC. These relays include a control relay MSP shown in Fig. 7 of the patent, the counting relays 4 and 6 shown in Fig. 6 of the patent, and the office delivery relay OD which corresponds to relay 234D shown in Fig. 5 of the patent. When relay MSP picks up, it opens the pick-up circuit for relay ST, but relay ST is held energized over a stick circuit including back contact e of relay V0. The closing of front contacts (1 and j of relay MSP connects terminal B at front con tact b of relay ASP over wires 92 and 94 and contacts ,1 of relays 4 and 6 to the two indication circuits which, as shown diagrammatically herein, include wires 42 and 44 at the station and wires H2 and H4 at the office, so that when relay OD is operated, the indication relays ZLHK and ZRHK are operated in accordance with the positions of contacts d of relays ZLGP and ZRGP and contact In of relay ASP.

Concurrently, the transmitted indications are registered locally by two register relays l2 and I4 as indicated diagrammatically by dotted line connections from their windings to wires 42 and 44, these relays corresponding to those of the group of relays 9 to I3 shown in Fig. 7 of the patent. To terminate the code transmission and restore the apparatus to its inactive condition, a valve relay W) is picked up over contact h of relay MSP. Contact e of relay VC opens the stick circuit for relay ST, and contact c of relay VC connects a valve relay I2-l 4V, similar to relay HIV in Fig. 7 of the patent, to contacts b of relays l2 and I4 so that relay lZ-MV picks up if either or both relays I2 and 14 are energized, and is released by the transmission of a code in which these relays are not energized. In the first case, the opening of the back contact b of relay I 2I4V interrupts the pick-up circuit for relay ST which includes front contact 71. of relay ASP, and in the second case, the opening of front contact I) of relay I2-I4V opens the pick-up circuit for relay ST which includes the back contact I) of relay ASP.

It is believed that my invention may be readily understood by considering the mode of operation of the system under different assumed conditions. When the signals 2L and 2B, stand at stop as shown, signals 4B. and BL indicate caution, and relays ZLGP, ZLAS, 2RGP and 6'7 ZRAS are energized and relay ASPVis released, so that wires 92 and 94 are deenergized.

Under this condition relays ZLHK and '2RI-lK assume their released position in response to an indication code and their back contacts d complete a circuit to light the red lamp ZNE, mounted above the signal lever 2SG.

Assume now that the operator moves lever ZSG to the rightand presses the starting button S'I'B'to initiate the transmission of a control code to energize relay ZRHS, under the proper traflic conditions relay ZRHR will become energized to cause signal 2R to indicate caution or proceed, and to reverse the polarity of the current supplied to relay 4RHR, to cause signal 4R to indicate proceed, releasing relays ZRGP and 2RAS and energizing relay ASP. Wire 94 will be supplied with current from terminal B at front contact b of relay ASP'over back contact d of relay ZRGP or front contact 01 of relay 2LGP, but wire 92 remains deenergized. Relay ST was energized by relay D in response to the control code, consequently an indication code will be transmitted to energize relay ZRHK, relay ZLHK remaining released,-

and a circuit is completed over back contact at of relay ZLI-IK and front contact d of relay 2RHK for lighting the green lamp ZRE to indicate the clearing of signal 2R. Similarly, if

relay ZLHS is energized to clear signal 2L, wire 92 will be energized and wire 94 deenergized, and the indication code will energize relay ZLHK, relay ZRHK remaining released and in this case a circuit is completed over front contact d of relay ZLHK and back contact e of relay ZRHK to light lamp ZLE. The valve relay l2-!4V will also be energized when relay VC picks up at the end of the code which energizes relay ZRHK or ZLHK, and the opening of back contact I) of relay I2-|4V interrupts the circuit for relay ST which extends to terminal B at front contact b of relay ASP which otherwise would be closed upon the release of relay MSP at the end of the code. In addition, relay VC opens the stick circuit for relay ST, consequently relay ST releases when relay l2-l4V picks up. Relay VC then releases and completes a stick circuit for relay l2|4V so that relay l2I4V remains energized, and relay ST remains released, following the transmission of this indication code. 4

Assuming next that signal 2R has been cleared and is returned manually to stop and that the approach relay ZRAR. hasbeen released by an approaching train to render the time looking effective. Signal 2R is put manually to stop by the transmission of a control code which releases relay ZRHS. Relay ZRHR. releases, reenergizing relay ZRGP and operating relay 4RHR to reverse as shown, thereby completing a circuit from terminal B at the reverse polar contact of relay 4RHR to energize the time element relay TE, which is thus set into operation to reenergize relay ZRAS after a predetermined time interval.

Relay ASP therefore remains energized over the back contact of relay 2RAS for the measured time looking period imposed by relay TE, and at thebeginning of this period a first indication code, initiated by the control code delivery relay D, is transmitted. Since the front contacts (1 of relays ZRGP and ZLGP are both closed, terminal B is connected to both of the wires 42 and 44 so that relays ZLHK and ZRI-IK are both energized by the code, .completing .a circuit for the: red lamp ZNE over their' front contacts which is energized periodically over a contact of a flasher relay CT, so as to cause lamp 'ZNE to flash to display a distinctive indication of the approach locked condition. The station register relays. l2 and 14 are. both energized and the valve relay l2-l4V which was picked up by the. preceding code: which indicated the clearing of: signal 2B, is maintained energized. when relay 2RAS is reenergized. at the end of thetime lockingperiod, relay ASP releases and completes a circuit from terminal 3 at its back contact. 11 over front contacts b of an auxiliary starting relay andof relay I2I4V, to. pick up relay- ST to initiate. the transmission of a second indicationv code. Since terminal. B is. no longer connected to wires 92 and 94, energy is not supplied to-wires 42 and 44 during the transmission of the second: indication code and relays l2- and M remain released- When relay OD operates, relays ZRHK and ZLHK assume their released. positions, and when. relay VC operates, it releases relay l2--l4V, which by opening its front contactv b releases relay ST. Relays ZLI-IK and ZRHK. are now released to cause lamp 2NE to belighted steadily to indicate not only that the signals 2L and. 2R are. at stop but also that their approach. locking relays are. energized.

When signal 2R, for example, is put manually to stop by the transmission of a control codeas above described, the indication code is initiated; immediately due to the. energization of the starting relay'ST by the control code delivery relay D, andit maybe that relay ZRHR, which is generally of the slow release type, is so slow in releasing, that relay ZRGP will not be reenergized soon enough to enable the change in its position. to be indicated by the code initiated as a. result of the operation of. relay D. In this case, relay ASP remains picked. up because the time locking is in effect; relay i4 is energized by the code so that relay I2-I4V remains picked up, consequently relay ST' will be released by relay VC at the. end of the code. Relays ZRHK and ZLHK remain in their last operated positions so. that the signal clear condition continues to be indicated after the re.-'

ception of this code. To initiate a second indication code under this. condition, the auxiliary starting relay AST is provided, controlled over pole changer contacts e and f of relays 2RGP and ZLGP and having a pick-up circuit which isopened at back contact of the code system relay MSP for the duration of the energization of that relay in each indication code. It will be seen that each time relay ZLGP or ZRGP either picks upor releases, relay AST releases, due to the reversal of thepolarity of the current supplied to its winding and completes a circuit: at its back contact 11 to pick up relay ST toinitiate an indication code, provided relay l2--I4V' is picked up. If relay AST releases when the indication transmitting apparatus is in its normal inactive condition, for example, if. it releases shortly after the first indication codev referred to is transmitted, it will. pick. up again as soon as current of the opposite: polarity supplied over contact of relay MSP builds up in its winding, remaining, however, in. its released position long enough to. energize. relay ST over its back contact b and: front contact 11 of relay l'2-I4V, to initiate the. transmission of an indication code reflecting the. change in the condition of relay ZRGP or 2LGP which. caused the release of relay AST. If relay AS'I releases.

whenrelay MSP- is picked up, as, for example; during the transmission of the first indication code referred. to, it may be that this code. will not correctly reflect the condition which caused relay AST to release. If this occurs, relay ST is. not released when relay VC operates at the end of the first code but relay AST is held released until relay MSP releases and so holds relay ST energized over its back contact 12' and front contact b of. relay I2-I4V, for a short time. following the release of relays MSP and V0, with the result that a second indication code is initiated by relay ST. As already explained, relay l'2--MV is picked up by an indication code which energizes either or both of the relays ZLHK and. ZRHK. and is released by a code which releases these relays.

It will be clear therefore that if signal 2R or 2L is put manually to stop and the time looking becomes effective, a code will be initiated upon the reenergization of relay 2RGP or ZLGP to indicate that condition in the event this condition is not correctly indicated by the code initiated by the delivery relay D.

Assuming next that signal 2B. is put manually tostop as above described, but that the approach relay ZRAR is energized to complete a circuit for relay ZRAS which closes as soon as relay ERGP is reenergized and relay ARI-IR, assumes the reverse position as" shown. If relay ZRAS picks up in time to release relay ASP, in which case relay ASP assumes its released position before the transmission of the twelfth step of the first indication code, this code will release relay ZRHK, relay 2LI-IK remaining released, and lamp ZRE will be extinguished and. lamp ENE will be steadily lighted to indicate the return of signal 2R to stop and to also indicate that the time looking is not in effect. It may be, however, that relay 2RAS will be reenergizedduring the thirteenth step of the code, in which case, if relay ASP is permitted to assume its released. position during that step, relay ZLI-IK would be energized on the twelfth step and relay 2RHK would be released on the fourteenth step, to falsely light lamp ZLE. To avoid.

this; relay ASP is provided with a stick circuit extending to terminal B at front contact K of relay MSP, over: which relay ASP is held energ-izedinthe event. relay ZRAS or ZLAS becomes reenergized after relay MSP picks up during the transmission of" the indication code. Consequently, relay ASP will be held energized until. the end of this code and it will correctly indicate the approach locked condition. Relay i2.MV picks up and relay ASP releases at the end of this code and relay ST is reenergized, therefore the code is followed by a second code, due to the release. of relay ASP, to indicate the termination of. the. approach locked condition.

The ararngement of. starting circuits as above described is also of utility when a control code has been. issued for clearing a signal and due to. trackway conditions the response of the signal is delayed. In this case, the indication code initiated by relay D will indicate the stop condition, relays 2LHK, ZRHK and l2-l4V remaining released, and when the signal clears, relay ASP is energized by the release of the approach locking relay and relay ST is energized over the circuit including front contact I) of relay ASP, back contact at or ,f of relay MSP and back contact b of relay I2-I4V; It will be seen that contacts 5. of relays ASP and l2-l4V provide a starting circuit. for initiating. a code in response to changes in the condition of the approach locking relay ZLAS or ZRAS, while relay AST provides one for initiating acode in response to a change in the condition, of the signal indication relays ZRGP and 'ZLGP, thereby provid-:

ing means for correctly indicating successive changes in the condition of these relays.

Although I have herein shown and described only one form of apparatus embodying my invention, it is understood that various changes and 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:

1. In a remote control system for railroads for the control from a central office of two railway signals for governing trafiic movements over conflicting routes, each signal having a normally energized approach locking relay controlled thereby which becomes deenergized when such signal is cleared and which remains deenergized, when such signal is put manually to stop, for a predetermined time interval to delay the clearing of the other signal, said remote control system including a normally inactive code transmitter at the location of said signals for transmitting indication codes to said ofiice over two intermittently available communication circuits which are controllable individually to indicate the clear or stop condition of each signal and jointly to indicate the condition of said approach locking relays; a repeating relay for controlling the energization of said two circuits in each transmitted code in accordance with the condition of said approach locking relays, a signal indication relay controlled by each signal for modifying such control in accordance with the condition of the corresponding signal, a starting relay efiective when actuated to initiate the transmission of indications by said code transmitter, register means controlled by said code transmitter for locally registering the character of said indications when transmitted, circuits controlled jointly by said repeating relay and said register means for actuating said starting relay in response to a change in the condition of said repeating relay, an additional relay responsive to a change in the condition of either signal indication relay, and means controlled jointly by said additional relay and by said register means for actuating said starting relay.

2. In a remote control system for railroads for the control from a central office of two railway signals for governing traflic movements over conflicting routes and having a normally energized approach locking relay controlled by each signal which becomes deenergized when such signal is cleared and which remains deenergized, when such signal is put manually to stop, for a predetermined time interval to delay the clearing of the other signal, said remote control system including a normally inactive code transmitter at the location of said signals for transmitting indications to said ofiice over two intermittently available communication circuits which are controllable individually to indicate the clear or stop condition of each signal and jointly to indicate the condition of said approach locking relays; a repeating relay for controlling the energization of said two circuits in accordance with the condition of said approach locking relays, a signal indication relay controlled by each signal for modifying such control in accordance with the condition of the corresponding signal, a starting relay effective when actuated to initiate the transmission of indications by said code transmitter, means responsive to a change in the condition of said repeating relay or of either signal indication relay for actuating said starting relay, and means effective to prevent a change in the condition of said repeating relay during the transmission of indications by said code transmitter in the event either approach locking relay becomes energized during such transmission.

3. In a remote control system having a code transmitter for transmitting indications at times to a distant point over two intermittently available communication circuits to indicate the condition of different movable devices, a repeating relay for controlling the character of the indications transmitted over said two circuits in accordance with the condition of a first movable device, two indication relays for modifying the character of said indications individually in accordance with the condition of other movable devices when said repeating relay is in a particular condition, a starting relay efiective when actuated to initiate the transmission of said indications by said code transmitter, register means controlled by said code transmitter for locally registering the character of said two indications when transmitted, circuits controlled jointly by said repeating relay and said register means for actuating said starting relay in response to a change in the condition of said repeating relay, an additional relay, means for momentarily actuating said additional relay in response to a change in the condition of either indication relay, and a circuit closed in response to the momentary actuation of said additional relay for actuating said starting relay.

4. In a remote control system having a code transmitter for transmitting indications at times to a distant point over a plurality of intermittently available communication circuits to indicate the condition of different movable devices, a plurality of indication relays including one for each of a plurality of said circuits for controlling the character of the indications transmitted over the corresponding circuit, a neutral relay having a normally energized circuit including in series, pole-changer contacts of each of said indication relays, whereby said neutral relay is released momentarily in response to a change in the condition of any of said indication relays, a starting relay effective when energized to initiate the transmission of indications over said plurality of circuits by said code transmitter, a pick-up circuit for said starting relay closed over a back contact of said neutral relay, a stick circuit for said starting relay, and means for opening said stick circuit in response to the transmission of indications by said code transmitter.

5. In a remote control system having a code transmitter for transmitting indications at times to a distant point over a plurality of intermittently available communication circuits to indicate the condition of difierent movable devices, a plurality of indication relays including one for each of a plurality of said circuits for controlling the character of the indications transmitted over the corresponding circuit, a neutral stick relay having a pick-up circuit including a contact which is opened by said code transmitter when said indications are being transmitted and having a stick circuit including its own front contact, polechanging contacts controlled by the indication relays for reversing the polarity of the current supplied to said pick-up and stick circuits to efiect the release of said stick relay in response to a REFERENCES CITED change in the condition of any of said indication The following references are of record in the relays, a starting relay effective when actuated file of this patent:

to initiate the transmission of said indications by said code transmitter, and a circuit for actuating 5 UNITED STATES PATENTS said starting relay including a contact which is Number Name Date closed in response to the release of said neutral 2,404,303 Law July 16, 1946 stick relay.

EDGAR B. WALKUP.

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