US2305213A - Transmitting system - Google Patents

Description

Dec. 15, 1942. J. WICKS 2,305,213

TRANSMITTING SYSTEM Original Filed May 29, 1956 15 Sheets-Sheet 1 QQW Q5 T 4 HEB INVENTOR JOHN w/cKs ATTORNEY A H 8 z m: T. 4 P R 93 NQ Q E m m: m: Q ii 5 4 a Q 5, w v

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TRANSMITTING SYSTEM Original Filed May 29, 1936 15 Sheets-Sheet 10 m a wm w tot Em QGE INVENTOR JOHN WICKS ATTORNEY J. WICKS TRANSMITTING SYSTEM Dec 15, 1942.

original Filed May 29, 1936 15 Sheets-Sheet ll I TRACK/NTERLOC/f REL/4Y5.

TRACK SIGNAL RELAYS INVENTOR JOHN WICKS ATTORNEY Patented Dec. 15, 1942 TRANSMITTING SYSTEM John Wicks, Oak Park, Iii, assignor to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Original application May 29, 1936, Serial No.

82,508, now Patent No. 2,235,346, dated March 18, 1941. Divided and this application July 5,

1940', Serial No. 344,050

12 Claims. (Cl. 177-380) This invention relates to centralized traffic controlling systems for railroads, and more particularly to a system for remotely controlling track switches and signals at a plurality of field stations from a centralized dispatchers station having a track layout panel with symbols which are set in accordance with the actual track and signal conditions in the field.

In the provision of centralized traffic controlling apparatus, not only is it necessary to remotely control distant track switches and signals, but it is essential to indicate in the dispatchers office train progress along the railway track, and, further, it is also essential to indicate to the dispatcher the actual positions or conditions of the track switches and signals when such switches and signals are operated under his control.

In accordance with the present invention, the centralized traflic controlling system comprises a plurality of field stations along the railroad track and a centralized dispatchers station. Coding apparatus is provided at the dispatchers station and at each field station for transmitting and receiving codes over a two-conductor line conance with the operations of the track signals and switches and in accordance with train travel over the track sections. The codes transmitted to the dispatchers station from the field stations cause corresponding indications to be displayed on the dispatchers panel.

Each field station corresponds to a plurality of track sections and their associated track switches and signals. The dispatchers station is provided with a panel having a miniature track layout thereon corresponding to the railway track asso- 4 switches and signals of each field station. The

panel is also provided with a key for each distant track switch or signal to enable the dispatcher to control the associated panel control relays in accordance with the position such key is actuated to.

The panel control relays control the operation of the dispatchers coding apparatus to transmit a code corresponding to the actuated key. These panel control relays are also operated in accordance with the codes received from the field stations to operate the panel symbols or lamps.

The dispatchers coding unit is common to all of the unit panels and transmits outgoing codes, comprising three digits, in accordance with the particular panel unit connected with and in accordance with the particular key and panel control relay which is operated. The dispatchers coding unit also receives incoming codes from the various field stations and operates a step-by-step switch in accordance therewith to operate the proper train-progress lamps and the proper track or signal symbols on the panel.

Each field station is provided with'the usual and well-known track interlock relays for controlling the track signals in accordance with the train traffic over the corresponding track sections. Ihese interlock relays and circuits are not part of this invention, and are shown and described briefly to enable the invention to be fully understood. Associated with the interlock relays at each field station are position control relays which operate the track switches and signals through the interlock relays in response to the certain codes received from the dispatchers station. These position control relays are provided for each track switch or signal, and control the field station coding apparatus to transmit codes to the dispatchers station in accordance with and in response to the operation of such track switches and signals.

A pair of track-signal relays are associated with each track section and are operated in accordance with track occupancy to control the field station coding apparatus to transmit codes in accordance with such occupancy.

Each field station coding unit transmits outgoing codes comprising three digits, the first two in accordance with the field station which is transmitting and the third in accordance with the particular position-control or track-signal relay which is operated. The field station coding unit also receives incoming codes to operate the proper position control relays in accordance with the codes transmit-ted from the dispatchers station. All the field station coding units respond to incoming codes from the di-spatchers station but only one group of position-control relays at a particular field station is selected for operation due to cross-connections of the code marking relays which are operated by the first two digits.

The first impulse of the first digit in the codes transmitted from the dispatchers station is a prolonged impulse to give the dispatcher preference over transmission from the field stations and to condition the field station coding units to receive the transmitted codes. The field station coding units respond to incoming codes only in case the first impulse is a prolonged pulse and, therefore, since the field stations do not transmit this prolonged pulse other field stations do not respond when a field station is transmitting to the dispatchers station. Each field station is prevented from transmitting a code to the dispatchers station when another field station is transmitting or the dispatchers station is transmitting.

This application is a division of the Wicks Patent 2,235,346, issued March 18, 1941, wherein the subject matter directed to railway signalling is being claimed, while in this division the subject matter being claimed is directed to code transmitting systems.

The main object of the invention is the privision of new and novel circuit arrangements in a centralized traific controlling system of the above described type which are efficient and reliable in operation.

Another object of the invention is the provision of an improved coding arrangement which is quicker in operation than those now in use by reducng the code-transmission time for a large system of this type.

'Other objects and features of the invention relate to the new and novel circuit arrangements which will be apparent from the following detailed description of the drawings.

Referring now to the drawings comprising Figs. 1 to 18, inclusive:

Figs 1 and 2 show the dispatchers panel-control relays, keys, and signals corresponding to the field station signals shown in Figs. 11, 12, 13, and 14.

Fig. 3, in the upper portion, shows the dispatchers track indicating relays and in the lower portion shows the start and distributor relays for the dispatchers coding apparatus.

Fig. 4, in its upper portion, diagrammatically illustrates a vertical and rotary step-by-step switch and associated controlling relays and magnets; while in the lower portion one of the sets of dispatchers code-marking relays are shown.

Figs. 5 and 6 show the common dispatchers coding-unit relays.

Figs. '7 and 8 show one of the field station coding units.

Fig. 9 shows the code-marking relays for this particular field station.

Fig. 10 shows the start and distributor relays at this field station.

Figs. 11, 12. 13, and 14 show the track layout and the well known train interlock relays, the position control relays, and the track-signal relays associated with this field station.

Fig. 15 illustrates a portion of the dispatcher panel corresponding to the field station shown in Figs. 11, 12, 13, and 14.

Fig. 16 shows a detail of the combined key and signal 8SL.

Fig. 17 shows a cross section of the mechanical construction of the combined key and signal BSL.

Fig. 18 shows the manner in which the different figures of the drawings should be placed in alignment.

Throughout the drawings similar reference characters indicate similar apparatus or equipment. Also throughout the drawings the negative and positive battery symbols have been used to simplify the drawings, and it will be understood that where these symbols are used in the dispatchers station all such symbols are connected to a common battery. The negative and positive battery symbols are also used in the circuits disclosed in the field station to simplify the drawings; It will be understood that a separate battery is used for the track-interlock relays in accordance with the usual practice and another battery is connected to the position-control relays, the track-signal relays, the coding-unit relays, the code-marking relays, and the start and distributor relays.

Referring now to that portion of the dispatch ers panel illustrated in Fig. 15, it will be seen that the illustrated track sections are each of a different color, that is, the section corresponding to track section 9 of Fig. 11 is blue, the section corresponding to section 8 is red, and the sections corresponding to sections 6 and I are yellow. Each such illustrated section has a round track symbol, such as 9TPL, BTPL, ITPL, and BTPL. These symbols are round glass transparent caps suitably mounted on the panel and are known as the track-pilot symbols for indicating to the dispatcher the location of trains. Similar round transparent symbols 9MSL, 9SSL, ISL, and 6SL are also suitably mounted on the panel. These symbols correspond, respectively, to the track signals BMS, SSS, IS, and SS in the corresponding field station and are positioned on the panel in accordance with the location of the distant track signals. A lever, or key9, is associated with the symbols 9MSL and SSSL on the panel and is operable by the dispatcher to control the operation of the distant track signals 9MS and SSS. A similar lever, or key-4, is associated with the symbol ISL for controlling the distant track signal 1S. In a like manner the key-6 is associated with symbol BSL ,for controlling its corresponding distant track signal BSL. The stick key-9S is a turn key which is operated by the dispatcher when the dispatcher wants only one train to pass over section 9.

The key-8 is a combined key and signal for both controlling the operation of the corresponding track switch TS in the field station (Fig, 12) and for indicating to the dispatcher the operated position of the same. The mechanical construction of this combined key and symbol is more fully disclosed in Figs. 16 and 1'7. The upper portion of this key-symbol, as seen in Fig. 17, comprises a raised rectangular transparent glass portion indicated as 8SL. This raised portion is provided to enable the dispatcher to turn the same and is made transparent so that different colored lights may be visible through it. A single lamp is mounted directly behind each symbol BTPL, STPL, ITPL, and STPL, in any suitable manner. These lamps are shown in Fig. 3 and have corresponding reference characters.

A red and a green lamp are suitably mounted behind the symbol QMSL on the panel for visibly indicating to the dispatcher a red or a green indication. These lamps are shown in Fig. l and are correspondingly labeled SMSL. In a similar manner the red and yellow lamps marked BSSL, Fig. 1, are mounted behind the symbol QSSL on the panel, the red and yellow lamps marked ISL, Fig. 2, are mounted behind the symbol ISL on the panel, and the red and green lamps marked ESL, Fig. 2, are mounted behind the symbol BSL on the panel. The red and green lamps marked BSL, Fig. 1, are mounted behind the symbol ESL on the panel as shown in Fig. 17. Each key on the panel controls a pair of springs as indicated at keys 9, 9S,1, and B in Figs. 1 and 2.

Th conductors of cable 50 extend from the fifth level of the vertical and rotary step-by-step switch in the dispatchers station to the panelcontrol relays for controlling the operation and the release of the relays prefixed with the letter C. The conductors of cable 1B extend from the panel-control relays to contacts of one of the code-marking relays which operatively connect these conductors to the conductors of cable 80 extending to contacts of the digit-counting relays in the dispatchers coding unit.

The cable 60 includes the conductors for operating and releasing the track indicating relays shown in Fig. 3 and these conductors terminate in the sixth level of the vertical and rotary stepselect the proper group of code-marking relays in accordance with the particular start relay operated.

Certain of the code-marking relays are crossconnected by conductors such as Band 419, in

accordance with the particular numerical designations of the corresponding group of panel-control relays. A separate group of code-marking relays similar to that disclosed in Fig. 4 will be provided for each panel unit. The vertical and rotary step-by-step switch disclosed in the upper 2- portion of Fig. 4 has one-hundred bank contacts accessible to wiper 482. The one-hundred bank contacts of this switch are divided into ten levels of ten bank contacts each. This type of switch is of the well-known type of Strowger switch used 1 in automatic telephone systems. The switch-controlling relays and magnets, and the code-marking relays are connected to the dispatchers coding unit shown in Figs. 5 and 6.

A pulse generating relay 552 is shown in Fig. 5

having a weighted vibratory armature for controlling the generation of impulses which are counted on the digit-counting relays and the space-counting relays shown in 6. The conductors 5d! and. 503 extend from the dispatchers station through all of the field stations in series. The dispatchers coding unit has a line relay 503 which responds to both incoming and outgoing pulses over lin conductors 591 and 588. Each field station is provided with a similar line relay which also responds to both incoming and outgoing pulses over these two line conductors. Each field counting relays. The field station code-marking relays shown in Fig. 9 operatively connect the field station coding unit to its associated position-control or track-signal relays over the conductors shown in the operate cable 00, there nal relays. The associated distributor relays in Fig. 10 cause the operation of the proper codemarking relays so that the track-signal relays or the position-control relays are connected to the field station coding unit. In case this particular field station has a number of traffic governing devices in excess of five to control, then a separate start relay and a separate code-marking relay group are provided for each five trafiic governing devices. Such a field station is then divided into units of five traffic governing devices each, and each such unit has separate start and code-marking relays. As an illustration, in the lower right-hand corner of Fig. 10 is shown a rectangle, labeled field station unit 2, which is similar to the field station units shown in Figs. 11, 12, 13, and 14.

Figs. 11, 12, 13, and 14 show a plurality of track sections numbered 9, 8, 1, and 6. The takesiding signal SSS and the main track signal 9M8 are for routing trains from left to right over the track switch TS to section 1 or over the track switch TS to section 6. Signal TS is for controlling train travel over the track switch TS from the siding, while signal BS is for controlling train travel from right to left over the main line section and the track-switch TS. The track switch TS is operated in the well known manner by the motor SM which in turn is controlled by the polar relay 8WR. The switch contacts !2'|6 and 12?! are contacts which are operated by the track switch TS and which are only operated to circuit-closing positions when the track switch is in either one of its operated positions. The track-interlock relays and associated circuits are not part of this invention and are disclosed to enable the invention to be more fully understood. The position-control relays and the track-signal relays are grouped in accordance with theircorresponding signals and sections of tracks. These latter relays are connected by conductors in- I cluded in the operate cable 0C, the release cable RC, and the track-indicating cable TIC, to the code-marking relays.

Fig. 15 shows one panel unit of the dispatchers panel which corresponds to the field station shown in Figs. 11, 12, 13, and 14, and the different symbols of this panel are controlled in the manner shown in the circuit drawings in Figs. 1, 2, and 3. The combined key and signal BSL is mounted on the panel by means of machine screws 29 extending through a flanged sleeve 32, Fig. 17. Semi-circular clamps are clamped around the sleeve 32 and have extensions (not station coding unit is similar to the dispatchers coding unit and has a pulse generating relay and manner.

mounted within the sleeve 32. The sleeve 33 is shown) extending down to the brackets 31 upon which the springs I11, the springs 25, 21, and 28, and the spring 23 of the detent 24 is mounted. The red and green lamps are mounted in the lamp springs 26, 21, and 28 in the well known An elongated sleeve 33 is rotatably The lower part of the glass piece 313 is glazed The raised portion black as shown in Fig. 15. 8SL is rotated by the dispatcher, in the direction indicated by the arrow, to cause the sleeves 3i and 33 to rotate the sleeve 34 and fiber disc 20 so as to close springs ll! by the cam portion 2! of the disc 20. In this movement the detent 25 disengages from the curved portion 22 and rests in a similar curved portion 25 of the fiber disc 20 Whenthe combined key and signal BSL is operated to a position corresponding to the takesiding position. The raised transparent portion iSSL of glass 30 permits this symbol to be used both as a key and as a signal for indicating the operated or non-operated condition of the track switch by illumination of either the red lamp R or the green lamp G.

In Fig. relay 593 is normally energized over a circuit including battery B, winding of relay 593, conductor 506, contacts 51I, and conductors 509 and 501 over a bridged loop including all of the field stations in series. Slow-to-release relay 550 is normally energized by way of contacts 555. The pulse generating relay 552 is normally energized from positive battery, over 55I, 544 and 559, through the winding of relay 552 to negative battery.

In each of the field stations the line relays such as line relay 103, Fig. 7, are energized over a loop circuit including conductors 501 and 508 extending to the dispatchers station. This loop circuit includes contacts 18!, conductor 105, normally closed springs controlled by contact I, and conductor 191 at each field station. At the last connected field station conductor 101 is connected to conductor 501, thereby completing the loop circuit. Start-in relay 119 is normally energized from positive battery, back contact 104, resistance 101, conductor 146, winding of relay 119 to negative battery. Pulse-generating relay 190 is normally energized from positive battery,

contact 154, conductor 195, resistance 194, to negative battery.

In accordance with the usual practice the track relays 9T, 9T, 1T, and ST are normally energized over their respective track sections. Polar-neutral relay I9HD is energized from negative battery, back contacts H59, H99, i453, I354, I249, I I88, H55, H95, to the common battery point C of the battery associated with the interlock relays. Relay 9HD is normally energized over the following circuit: from negative battery, back contact I465, I499, I49I, over intervening contacts (not shown), and through the winding of relay 9I-ID to the common point of battery C. Relay 9NP is normally energized from positive battery, front contact II5I, polar contact H59, I560, H59 and 5 63, through the winding of relay 9NP, to negative battery. Relay 98 is maintained energized over the following locking circuit: positive battery, contacts I 38, I113, and conductor I 94.

Relay 3T5 in Fig. 12 is maintained energized over the following circuit: from positive battery to the dual control Dual C. 0., contacts I281, I295, 521i, and through the winding of relay 8T8 to negative battery. Polar relay 8WR is normally energized over the following circuit: from positive battery, contacts I212 of relay STS, contacts I219 of the time element relay BTER, I36I, I455, H16, H19, I115, back contact I202, I292, relay BWR, I290, back contact II to negative battery.

Relay 51HP, Fig. .13, is normally energized over the following circuit: from positive battery by way of contacts H53, IIS and 10S associated with a distant field station, conductor I193, and through the winding of relay 6-'IHP to common point of battery. Relay BS in Fig. 14 is maintained in operated position by way of contacts I451 and I555. Relay 6N1? is normally energized over a circuit extending from a distant field station by way of positive battery, back contacts I463 of relay 2I-ID, conductor I310 and intervening contacts (not shown), I350, I369, I459, I41l, and through the winding of relay BNP to the negative battery. The normal condition of the track signals in the field are all set at stop position in which position their respective red lamps are illuminated in the well-known manner.

The signals on the dispatchers panel are set in corresponding positions with the red lamps illuminated. For example, the signal 9MSL of Fig. 1, corresponding to the track signal 9M8 of Fig 11, has its red lamp illuminated over the following circuit; from positive battery, back contact I05, I55, back contact I, I5I, back contact I64, and through the filament of the red lamp R to negative battery. The take-siding signal SSSL, corresponding to the signal 93S of Fig. 11, has its red lamp illuminated over the following circuit: from positive battery, back contact I04, I49, back contact I53, and through the filament of the red lamp R to negative battery. The green lamp of the combined key and track switch signal BSL is normally illuminated over contacts I82 and I92 to indicate that the track switch TS in Fig. 12 is set in position to route trains over the main track section. The red lamp of signal ISL, corresponding to the signal 1S of Fig. 13, is normally illuminated over a circuit from positive battery, back contact i0I, I09, back contact 22I, 23I, and through the filament of the red lamp to negative battery. The red lamp of signal ESL, corresponding to the signal (is of Fig. 13, is illuminated over the following circuit: from positive battery, back contact I02, I I9, back contact 26I, 21I, and through the filament of the red lamp to negative battery.

Operation of key9 It will now be assumed that the dispatcher desires to set the track signal QMS, Fig. 11, to proceed position to permit a train traveling from left to right to pass over track sections 9, 8 and 6. In order to set track signal 9M8 to proceed.

position the dispatcher will operate the key9 on the panel. In response to the operation of key9, relay B9 is energized over the following circuit: from positive battery, contacts I 31 of key 9, I51, 203, 205, 243, I58, normally closed springs controlled by contact III, I 91, and

1 through the winding of relay B9 to negative battery. At contact I3I relay B9 completes an obvious circuit by way of conductor I56 for energizing relay A9, at contact I32 prepares a point in the locking circuit for itself in case the stick relay S9 is operated, at contacts I35 marks the stop conductor 1 of cable 19 and prepares a circuit for operating relay D9; and at front contacts I36 connects positive battery by way of back contact I41 to conductor 299, thereby completing an energizing circuit for start relay 340. At contacts I2I relay A9, upon energizing, opens a point in the circuit to relay B1 thereby render ing the operation of key 1 ineifective at this time. At contacts I22 the circuit extending to relay B6 is likewise opened to prevent its operation in case key 6 should be operated at this time. In a similar manner, relay A9 at contacts I23 opens the circuit to relay B3 to prevent its energization at this time.

Start relay 34%], upon energizing, at contacts 35!, completes a circuit for energizing the fast relay 310 by way of 345, 352, 362, 998, 359, and 395. Start relay 349 in addition at contacts 342 connects the positive pole of battery to stop conductor 343 to maintain relay 310 in operated position when the proper selecting relay is operated. Relay 319 operates very quickly when its circuit is completed and also when its circuit is opened, and at contacts 31! prepares a circuit for relay 459. At contact 312 relay 31!] opens its original energizing circuit, but this relay is now held in operated position in series with the upper winding of selecting relay 389 as follows: from positive battery through the upper winding of relay 389, back contacts 332 and 392, 356, 353, front contact 312, conductors 349 and 395 to relay 319 and negative battery. Relay 319 is maintained energized over this circuit while the relay 389, due to the high resistance winding of relay 319, operates only its X contacts 383 to complete a circuit for its lower winding. This circuit may be traced from positive battery, contact 34!, 395, 345, normally closed springs controlled by contact 35!, 341, 394, 383, and through the lower winding of selecting relay 399 to negative battery. Relay 359 completely energizes over the abovetraced circuit to operate its remaining contacts and at contact 380 prepares a further point in the circuit to relay 459. At back contacts 382 relay 335 opens the holding circuit of fast relay 319 whereupon the relay 319 very quickly deenergizes to open its holding circuit at contact 312 before relay 399 can operate when a circuit is prepared for this relay at front contact 392. At contacts 382 relay 399 completes a circuit for relay 319 from positive battery connected to stop conductor 343 at contact 342. Relay 319 at this time is either energized over its original energizing circuit, previously traced, or over the cir-,- cuit extending from positive battery,'contact 342,

conductor contact 392, conductors 354 and 395. Selecting relay 399 is not operated at this time in response to the operation of fast relay 319 because the upper winding of selecting relay 399 is short circuited as follows: from positive battery, contact 342 over the circuit traced for relay 319 and thence by way of conductor .349, contacts 312, 353, conductor 355, back contacts 392, front contacts 332, and through the upper winding of relay 339 to positive battery. In re-' sponse to the operation of start relay 349 the selecting relay is operated to complete a circuit for relay 459 as follows: positive battery, contacts 31!, 355, 33!, 395, and through the winding of relay 959 to negative battery. From the foregoing it will be seen that start relay 349 associated with the first panel unit at contact 342 has marked the stop conductor 343 so that only the first selecting relay 399 is operated to select the proper group of code-marking relays.

At this time it may be advisable to explain how other groups of code-marking relays associated with other p'anel units are selected. For example, it will be assumed that the dispatcher has operated some key the second panel unit and has 4 therefore caused the operation of start relay 349' of selecting relay 399, front contact 382 back contact 392, conductor 356, contact 353, front contact 312, conductors 349 and 396 and through the winding of relay 319 to negative battery. Selecting relay 399 operates to close only its X contacts 393 over the above traced circuit. When X contacts 393 are closed the following circuit for fully operating the second selecting relay 399 is completed: from positive battery over the previously traced circuit including 34!, 345, 336, 35!, 36!, 341, X393, and through the lower winding of relay 399 to negative battery. At contact 39R, selecting relay 390 prepares a point in the circuit to the relay in the second code-marking panel unit similar to relay 459, at back contact 392 the circuit of fast relay 319 to cause its deenergization, at front contact 392 prepares a point in the circuit to the third selectrelay (not shown), at contact 394 opens the circuit of the first selecting relay to cause its deenerglzation, and at contact 395 connects the stop conductor 344 to the winding of relay 319 to cause the energization of this relay ,and to place a short circuit across the upperwinding of the third selecting relay (not shown). The reenergization of relay 319 then completes the circuit by way of contacts 31 I and 39! over conductor 395' for operating the relay in the code- 'marking relays associated with the second panel ing relay 459 energizes as a result of the energization of the first selecting relay 389, it will be seen that relay 459, upon energizing, at contacts 45! closes a bridge across conductors 454 and 455, at contacts 452 connects the first digit stop relay 459 to the stop conductor 418, at contacts 453 prepares a point in the circuit to relay M9, and at 462 completes a circuit for energizing relay 560 from positive battery, contact 462, 458, 522, 529, 545, through the winding 'of relay 559 to negative battery. Relay 569 is the outgoing start relay in the dispatchers coding unit which prepares the circuits to cause the dispatchers coding unit to transmit outgoing impulses to the field stations. Outgoing start relay 569, upon energizing, at armature 56! connects positive battery to the contacts of the digitcounting relays in order to successively connect positive battery to the conductors 48! to 499, inclusive, of cable 89 in order to complete a circuit for energizing the first digit-stop relay in the connected code-marking relaysn At 562 relay 569 opens a point in the pulsing circuit to the vertical and rotary switch relays to prevent the operation of this switch during the transmission of outgoing codes. At 593 relay 569 completes a locking circuit for itself over conductor BIG and contacts 519 to positive pole of battery, At 564 relay 539 prepares a pointin the circuit to relay 599, at 595 opens the circuit to slow-to-release relay 559, and at 556 completes a circuit for energizing the pulsing relay 519 as follows: from positive battery by way of 566, 528, 592, 526, 611, 455, 416, 46!, 45!, 454, and through the winding of pulsing relay 519 to negative battery.

Pulsing relay 519 upon energizing, at contacts 51! opens the loop circuit extending through all of the distant field stations to transmit the first

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