US2422519A - Code communication system for railroads - Google Patents

Description

June17, 1947. 2,422,519

CODE COMMUNICATION SYSTEM :FOR' RAIAELROADS Filed July 21, 1944 2 Sheets-Sheet 1 FIGIZ.

3nt entot I Gttorneg B; mm 1 June 17, 1947'. w. M. BARKER 2,422,519

CODE COMMUNICATION SYSTEM FOR RAILROADS Filed July 21, 1944 2 Sheets-Sheet 2 FIG.1B.

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Shift to Selector 0N ypical Selector Code J 0- Start 5e|ector Code Brwentor Gttorneg Patented June 17, 1947 CODE COMMUNICATION SYSTEM FOR RAILROADS William M. Barker, Greece, N. Y., assignor to General Railway Signal Company, Rochester, N. Y.

Application July 21, 1944, Serial No. 545,973

7 Claims.

This invention relates to communication systems for railroads, and more particularly to a code communication system of the so-called shunt type for centralized traffic control systems combined on the same pair of line wires with a telephone system using electro-mechanical selectors at way stations to effect selective calling of way stations.

In one type of code communication system for centralized traflic control on railroads, commonly known as the shunt type system and disclosed, for example, in the prior application of Hailes, et al. No. 484,728, filed April 27, 1943, now U. S. Letters Patent 2,399,734 granted May 7, 1946, the code elements for controls and indications are transmitted over a pair of line wires without changing their continuity and in such a way that these same line wires may be employed for telephone communication and the like.

In a code communication system of this character, conveniently termed a C. T. C. system, the field start to initiate operation of the system is accomplished by shunting the line wires at a field station where achange in the occupancy of a track section or the like calls for the transmission of new indications. A field station equipment is operable to shunt the line wires for such a field start only when the associated line relay is energized with a certain polarity.

Assuming such a type of code C. T. C. system, it is often desirable to employ the same line wires for telephone communication and selective ringing by electro-mechanical selectors bridged across the line. One type of selector system, commonly used, and known as the Western Electric train dispatching telephone system, uses an electromechanical selector of the type which is operated by pulses of alternate polarity, and which is sometimes called an A. C. selector.

When such a selector system is combined with a code C. T. C. system of the shunt type above mentioned, it may happen that some of the selector code pulses will be of sufficient intensity and duration to energize the line relays of the v C. T. C. field equipment with the polarity permitting a field start, thereby allowing a C. T. C. field station where some change in track circuit occupany or the like has occurred, to apply a shunt across the line wires during transmission of the selector code and thereby mutilate that code, or otherwise interfere with the desired operation of the combined system.

In view of these considerations, the primary object of the present invention is to provide an improved organization and arrangement of parts and circuits for a centralized traflic control system and a mechanical selector system combined on the same pair of line wires, in such a way that the line relays of the C. T- C. system are not operated by the pulses in the selector code, or at least are not energized sufliciently to permit a field start.

Generally speaking, and without attempting to define the nature and scope of the invention, it is proposed to combine the batteries or like sources of current for the code C. T. C. system and the mechanical selector system in such a way that the desired changes in line circuit energization required for satisfactory operation of the electro-mechanical selectors are produced without creating a difference of potential between the line wires of the proper polarity and intensity to operate the biased polar line relays of the C. .T. C. system and permit any field start to shunt the line circuit during a selector code. Specifically, it is proposed, when sending selector codes, to connect the C. T. C. line battery in series with the line battery of the selector system with the polarity sense that will permit reversing the selector battery, in order to produce the alternating current components required to operate the selectors, without permitting the voltage between the line wires to reach the operating value of the biased polar line relays of the C. T, C. system.

Other objects, characteristic features, and attributes of the invention will be in part apparent, and in part pointed out, as the description progresses.

The accompanying drawings illustrate in a simplified and diagrammatic manner one specific embodiment of the invention applied to a shunt type C. T. C. code communication system, such as disclosed in the afore-mentioned Hailes et a1. Patent 2,399,734. These drawings illustrate certain relays and contacts of the complete system disclosed in this Hailes et a1. application, insofar as appears to be necessary for an explanation and understanding of the present invention; and for convenience these relays and contacts are given the same reference characters as in the Hailes et a1. application.

In the accompanying drawings:

Figs, 1A and 1B show the equipment at the control oftlce and at one typical field location respectively;

Fig. 2is 'a diagram of a simplified equivalent circuit to' illustrate the way in which the batteries are combined during transmission of a selector code; and

Fig. 3 is an explanatory chart or diagram illustrating the character ofenergization of the line wires for a typical selector code.

Considering first the C. T. C. code communication system, it is not necessary to describe the structure and operation for the complete system, but merely point out the features or operating characters of the system material to an understanding of the present invention. This refers more particularly to the conditions under which the field stations act to shunt the line wires for an automatic field start.

Under the normal or at-rest condition shown, the line wires LI and L2 are steadily energized with one polarity, conveniently termed a normal polarity, from the control ofiice battery CB, or equivalent source of current, by a. circuit which may be traced from the line wire Ll, through back contact 5 of a shift or transfer relay SI-I, through coils 2T, 26 of the filter, back contact 25 of relay CF, front contact 24 of relay OR, back contact 23 of relay C, ballast lamp BAL to one terminal of the battery CB, assumed to be through primary 29 of the impulse transformer 30, back contacts 3-! and 32 of relays C and CF, coils 33, 34of the filter, and back contact B of relay SH to the other line Wire L2.

Referring to Fig. 13, this energization of the line circuit with the normal polarity causes current to flow through the line relay-2F at the typical field station illustrated, and similar line relays at all the other field stations, over a circuit path which may be traced from the line Wire Ll through coils 3E, 36 of a filter, back contact 3'! of relay 2L0, upper winding of relay 2F, resistance 38,1ower winding of relay 2F, back contact it of relay 2L0 and coils M, -42 of the filter to the other line wire L2. This normal polarity energizes line relay 21? to cause its polar contact 213 to assume the right-hand positionshown in opposition to its spring bias and close a pick-up circuit for a change repeater relay -2CI-IP which may be traced from (+),'through polar contact 214 of line relay 2F, front contact-332 of relay ZFR, backcontact 833 of relay ZLOT, back 'con- 5 l tact 3-34 of relay 2CD, front contact 335 of relay zF Ryrelay ZC-HP, and through back contact'3'36 of' ch-a nge relay 2Cl-I to The change relay ZCHisnormallymaintained energized 'by a stick circuit including-contacts operated to momentarily break such stick circuit'upon operation of a track relay,,signal, switch position "indicating relay, or like device having its position indicated in the control office. The contacts f45 and 46 shown as operated by trackrelays ATR and TR are typical of such contacts included in the stick circuit for the relay ZCI-I readily traced from through saidcontacts 4'5, '46, front contact '4? of relay 20H, winding ofthis relay, to

Thus, under the normal or at-re'st condition shown, if the track relay TR, for example, should pickup or drop due to a change in the occupancy of its associated ,track section, the stick circuit for the change relay ZCH is momentarily broken to release this relay and close its backcontact 336, thereby permitting ,energization of the change repeater relay 2CHP by the pick-up circuit above pointed out. The energizationof the relay 2CHP and closure of its front contact 3 42 closes a pick-up circuit to restore the'change' relay :ZCH and render it eifective to respond to any subsequent changes in the condition of'the devices to be indicated, for the purposef'and in the manner more fully explained in the I-Ia'ileset al.

4 application above mentioned. The energization of the relay ZCHP and closure of its front contacts 337 and G2! provides stick circuits for maintaining this relay energized until the field station in question has operated to transmit its indications, one of these stick circuits being readily traced from through said front contact 421, back contact $26 of a step'relay V5 in multiple with a back contact of relay 2L0, front contact 335 of relay ZFR, winding of relay ZCI-IP, and its front contact 331 to Another stick circuit includes back contacts of relay 2L0 and a front contact of relay ZLOT.

Also,- the energization of the change repeater relay 2CI-IP in the manner just described and closure of its front contact 340 provides a circuit for energizing the relay 2E0 to close its front contact 35d, this circuit being traced from through front contact 338 of relay ZFR, back contact 339 of timing relay ZLE-T, front contact 3% of relay ECHR back contact 236 of relay winding of relay 2E0 to The-energization of relay EEG and closure of its front contact'352 completes an energizing circuit for the relay {2L0 including various other contacts indicated by crosses and readily traced on the drawing.

This energization of the relays zEQ an-d 2L0 at a field station directly connects the line Wire L1 to line wire L2 through the filter by a circuit connection through front contact Ml of relay 210, front contact 1354 'of relay EEG, and back contact355 of relay ZEE.

If the line relay at a field stationgsuchas relay 2F in Fig. 1B, is'ueenerg-ized, or isenergized with a reverse polarity. its contact 2-14 is in'the left-hand dotted linepositi'on, and'the pick-up circuit for the change repeater relay ZCH-P is open jand regardless of any deenergizati-on of the change relay "20H, the field station cannot-operate to shunt the line circuit for a field start, so long as such condition ofthe line-relay 1F exists. Similarly, if there are's-tored field starts, i."e., a CH? relay ispicked up at any field locationsysb long as the C. T.--C. line relays such as relay "2F are deenerg ized, or energized with a'reverse'polar-ity, no C. field location can pick up its E0 and LOrelays tosh-unt the linecircu'it.

In short, in the type 'of codeC. T. C. system under consideration, an automatic field start from one or more'field stations'to apply a shunt to -,the line circuit cannot occur unless the line relays-at these field stations are energizewwith thenormal or at-rest-polarity;,and this invention is concerned m'ore particularly with the problem of preventing errergization of the line relays of the field stations with such normal at-restpolarity during the transmission of a selector "code involving impulses of alternate polarity, I

Considering now the selector "system, a shift or transfer relay Sl-I, w hi'chi'sarran'ged 'tobe en'- ergized upon manual actuation by the operator of, a suitable key orswitch 'S, subject-to such interlock as desired and indicated generally by the back contact 9 of relay C, acts to'disconne'ct the control office line unit and stepper .from the line Wires L1 and. L2, and 'to connect the'se'lin'e Wire's through the front contacts 5 and "6 of the relay 'SI-Ito the apparatus case o'fthe selector system. In short, manual 'energizati'on of the relay'jSH shiftsfthe line-wire connections from the 'C.'T.TC. system to the selector system. V

It is assumedthat'the, selector system is the well-known WesternEl'ectric train dispatching telephone system employing selector 'and calling key structures such as disclosed'for example, in

the patent to J. C. Field, No. 1,343,256, June 15, 1920. The control ofiice equipment for this selector system comprises a pulsing relay PL operating spring biased contact fingers 10, H for pole-changing the connections between a selector battery SB, or equivalent source of uni-directional current, with respect to the input terminals of a typical filter l 2. A connector relay CR operates biased contact fingers l4, [5 to connect the output of this filter [Z to the Wires ll, l8 which are connected to the line wires LI and L2 through the front contacts 5 and B of the relay SH when that relay is energized.

The connector relay CR is energized at the beginning of each selector code and is maintained energized throughout transmission of such code, while the pulsing relay PL is intermittently energized at time spaced intervals in accordance with the particular selected code being sent by the operation of an individual calling key or equivalent selector key structure. The code wheel CW for one such individual calling key is shown diagrammatically in the drawing as typical of such control devices; and after the calling key has been wound up and released in the regular way, the code wheel CW is turned in the counter-clockwise direction indicated by the arrow by a return spring at a regulated rate to apply to the line circuit a fixed total number of pulses, e. g. 17, divided into three groups of varying number, such as 3l0-4, l-9 l, etc.

The selector for this system under consideration, shown diagrammatically in Fig. 113, has an operating winding i9 connected across the line wires LI and L2 in series with a condenser 20 of suitable capacity. This operating winding l9, when energized with current pulses of opposite polarity, operates a polarized armature 2| back and forth from and through a middle biased position. Each movement of this armature 2| from its middle position, or a movem nt quickly from one extreme position to the other, operates a pawl and ratchet structure to advance a stepping wheel and contact arm one step; but when the armature pauses in the middle position, as distinguished from a quick movement through that position, the stepping wheel is returned by a spring to its initial position unless a pin is provided to hold said wheel in that position. The location of these pins determines the code call for the selector. Various other operating characteristics of this type of selector are shown and described in detail in the J. C. Field patent above mentioned.

Considering a typical operation, assume that the operator desires to send a selector code and operates the switch to energize the shift relay SH at a time when the C. T. C. system is not in operation, and it is otherwise proper to pick up this relay SH and transfer from the C. T. C. system to the selector system. This deenergizes the line wires Ll, L2 and all line relays such as 2F at all of the field stations, thereby rendering all of these stations ineifective to shunt the line for a field start. The operator then actuates the individual calling key for the particular selector station desired, or performs a similar function by manipulation of other selector key structures.

Assuming the code wheel CW shown is thus operated, the initial movement of this code wheel closes a circuit to energize the connector relay CR, which may be traced from contact finger 50, code wheel CW, slip ring connection 5|, and wire 52 through relay CR to This energization of the connector relay CR acts to connect the C. T. C. battery CB'and the selector battery SB in series to the line wires LI and L2 with the reverse polarity by a circuit connection which may be traced from line wire Li, front contact 5 of relay SI-I, wire ll, contact 14 of relay CR, telephone filter l2, wire 55, battery CB, upper or terminal of battery CB, wire 56, contact iii of relay PL, through battery SB, contact II of relay PL, filter l2, contact l5 of relay CR, Wire l8, and front contact 6 of relay SH to the other line wire L2.

It will be noted that the batteries CB and SB are connected to act accumulatively, as indicated in Fig. 2, so that the potential across the line wires LI and L2 is the sum of the voltages of these two batteries. Generally speaking, the impedances and number of the connections for C. T. C. field stations and selectors are much alike, so that ordinarily the voltages of the two batteries CB and SB for operating the C. T. C. field stations and the selectors respectively are much the same; and for purposes of explanation, it is assumed that these batteries are the same and each is a volts.

It should also be noted that when the connector relay CR for the selector system is energized to provide the first energization of theline circuit, the polarity of this energization is opposite to the normal at-rest polarity, so that contact fingers of all of the line relays, such as the contact finger 214 of line relay 2F, remain in the reverse or dotted line position, which they assumed when relay SH picked up and deenergized line Wires LI and L2, thereby maintaining open the circuit for providing a field start. Considering this reversal of polarity more in detail, upon referring to Fig. 1A, it will be noted that the line wire Ll is connected to the terminal of the battery CB under the conditions shown with the relay SH deenergized; but if this relay SH is energized, then the same line wire Ll is connected through front contact 5 of relay SH, wire ll, contact M of relay CR, filter l2, and wire 55 to the terminal of the battery CB.

The initial energization of the line circuit at the beginning of a selector code as just described, sends current through the operating winding 19 of all of the selectors during the charging time of the associated condenser 20, so that the armature of each selector is moved to one extreme position and then, after the condenser 20 becomes fully charged, assumes its middle position. This serves to restore to the initial position the stepping Wheel for any selector that may happen to be in an intermediate position.

Referring to the explanatory diagram in Fig. 3, this clear-out pulse, which is caused by the energization of the line circuit by the two batteries CB and SB acting cumulatively represents a line circuit energization of 200 volts on the assumption previously mentioned that each of these batteries is 100 volts.

After this preliminary movement of the code wheel CW, the first tooth of this wheel lifts the arm 50 into engagement with a stationary contact 58 to close a circuit readily traced on the drawing for energization of the pulsing relay PL, thereby operating its contacts H], I l to poleohange the connections and in eifect connect the batteries CB and SB in opposition. Assuming these batteries to be equal, the impressed potential across the line wires LI and L2 drops to zero, as indicated in Fig. 3, for the first counting pulse designated I, 'When the first tooth passes from arsenic under the contact arm 50 and the relay'PL is deenergiz'ed, the line wires LI, L2 are again energized for count 2 with a potential of 200; and the next time the contact arm 50' is raised by the code wheel CW for count 3 of the selector code, the potential across the line wires LI and L2 again falls to zero.

In the case of the code 3-10-4' assumed, the line circuit condition after the third counting pulse is maintained until the condenser 29 assumes a stable condition and no more current flows through the operating winding ['9' of the selector, whereupon its armature assumesthe middle position, In accordance with the wellknown plan of operation for this type of selector system, the stepping wheels of those selectors having a code call beginning with a count of 3 are held by a pin while their armatures are in the middle position, but all of the other selectors having a different code are restored to the initial position. This same operation is repeated for two more groups of pulses to make up a predetermined code count of 17 in the particular arrangement assumed; and that at the end of the transmission of these 17 pulses in three groups of a certain number in each group, such as 3-l0--4, there is only one selector having this particular code call which has had its stepping wheel advanced the full number of steps to its final position; and hence the last pulse is effective at this one selector to close a circuit for ringing the hell or perform any other desired function. After the last or bell ringing impulse, the code wheel is shaped to cause energization of the connector relay CR for a time while the pulsing relay PL-is deenergized. This restores the selector in questionto its initial condition; and when the code wheel assumes its initial position shown, the relay CR. is released.

From the standpoint of the operation of the selector, which is connected across the line wires LI and L2 through a condenser 20 of the proper capacity, these changes in line circuit energization between zero and 200 indicated in Fig. 3,. are in effect alternating components. It may be said that each time the line circuit is energized, the condenser 20 is charged and the operating magnet !9 of the selector is energized with current of 7 one polarity; and each time the line circuit is deenergized, the discharge of the condenser 29 causes a flow of current through the operating windingof the selector in the opposite direction. The net result is that the selector operates the same as if 100 volt impulses of alternate polarity were impressed across the line wires LI and. L2.

Stated another Way, in accordance with the Well-known transposition theorem, the inclusion of the C. T; C. battery GB in the circuit for energizing the line wires. Li and L2 for selector code transmission does not alter the current conditions produced by the selector battery SB" alone, except with respect to the impedance that the C. T, C. battery CB may add to the circuit.

Referring particularly to a-diagram of: Fig. 3, it can be seen that during the transmission of this typicalselector code, the voltage of the line wire Ll with respect to L2 varies-from 200 to zero, but the line Wire Ll never becomes positive with respect to the line wire L2. Consequently, current through the line relays ofthe C. T. C. field stations, such as the relay ZF in Fig. 1B varies from a reverse polarity to zero. The armature of the line relay: 2F is biased by a spring, as indicated conventionally, to assume the same left-handp'osition when deenergized as it assumes when ener'gized withthe reverse polarity. In short, during selector cod-e transmission the armature of the line relay 2F remains inthe left-hand position, being held there by the biasing spring alone, or by the biasing spring plus electr'o-magnetic attraction.

In this way, the line relays of the C. T. C. field stations are prevented from assuminga condition, even momentarily, for a field start; and

' hence no stored start or change in track circuit occupancy or the like tending to create a field start can become efiective while the system is set for transmission of selector codes, thereby obviating any mutilation of the selector codes by a shunting of the line circuit for a field start during the transmission of such selector codes.

In this connection,- it should be appreciated: that it is not necessary that the C; T. C. battery CB and selector battery SB should exactly equal each other and provide a zero" potential for the line circuit. This condition has been assumed to simplify an explanation and understanding of the nature of the invention,'but i-t can be seen that any relation hip of battery voltages may be employed, so long as there is not enough 'difierence of potential between the line wires of the normal at-rest polarity to provide pick-up energy for the C. T. C. line relays. Such pick-up energy is ordinarily in the order of 50 volts, and the voltage for the selector battery SB may exceed that of the C. T. C. battery CB and cause a POSie tive energization of the line wire Ll with respect to L2, provided such positive energization is not of the C. T. C. battery CB, but if desired, the,

wires 55, 56 may be connected so as to use the appropriate portion of this battery; or to include extra cells if the selector battery should happen to be substantially greater than the: C. T. C.

battery. V r

The particular construction and arrangement of parts shown and described merely represents one typical specific embodiment of the invention; and I desire to have'it understood that various modifications; adaptations and additions may be.

made in this particular construction and arrangernent of parts without departing fromth invention.

What I claim is: 1. In a system of centralized trafiic control combinedon the same line wires with a selector system, a plurality of selectors. bridged. across said line wires with coupling condensers, a plurality of field station equipments each including a polar line relay connected across said. line wires and operable only when said line relay is energized with a particular polarity to permit that field station equipment to shunt the line wires for creating an automatic field start, calling means in a control oflice including a pole-changed selector battery for changing the energization of said line wires to" operate saidzselectors, and manually operable means for rendering said calling 7 means effective and for also connecting another" source of current to-the-line circuit in series'with said selector battery a'id another source of -c1ir= rent and said pole-change selector battery acting cumulatively and in opposition alternately to provide pulses on said line wires of a polarity opposite said one particular polarity and at an energy level suitable for operating said selectors.

2. In a system of the character described for combining a centralized traffic control code system and a selector code system on the same line wires, code transmitting means at a plurality of field stations each including a polar line relay and operable only if said line relay is eifectively energized with a particular polarity to shunt said line wires for an automatic field start, code transmitting means in the control oflice including a source of direct current for normally energizing said line Wires with said particular polarity and operable in response to said automatic field start to energize said line wires with the other polarity, mechanical selectors connecting across said line wires with coupling condensers, a selector battery in a control ofiice, calling meansin said control ofiice for intermittently pole-changing the connections between said selector battery and said line wires in accordance with a selector code, and manually operabl means for rendering said calling means effective and for also connecting said source of direct current in series with said selector battery to provide intermittent energization of said line wires with a polarity different from said particular polarity during the po1e-changing of the selector battery for transmission of a selector code.

3. A combined centralized trafiic control and mechanical selector system comprising, a pair of line wires connecting a control ofiice and a plurality of field locations, code transmitting means at certain of said field locations each including a polar line relay normally energized with one polarity, mechanical selectors at the other field locations connected across said line wires by coupling condensers, calling means in the control ofiice including a selector battery and a pulsing relay for pole-changing the connection between said selector battery and said line wires in accordance with a desired selector code, code transmitting and receiving means at the control office including a separate battery normally energizing said line wires with said one polarity, and manually controllable means for rendering said calling means effective and for connecting said separate battery across the line Wires with its polarity reversed in series with said selector battery and independently of said code transmitting and receiving means, whereby a potential between said line wires is maintained independently of the pole-changing of the selector battery to prevent effective energization of said line relays with said one polarity during transmission of a selector code.

4. In a centralized traffic control and selector system combined on the same pair of line wires, a plurality of field station equipments each including a polar line relay connected across said line wires, each of said field station equipments being operable only if its polar line relay is energized with a particular polarity to create a field start condition by shunting said line wires, code transmitting and receiving means in a control ofiice including a coding source of current for transmitting control codes to selected field station equipments and for initiating transmission of indication codes from a selected field station equipment in response to a field start condition, selectors connected across said line wires at field locations, calling means in the control office including a selector battery and a pulsing relay for pole-changing the connections between said battery and the line wires in accordance with a selector code, and manually controllable means in the control olfice forrendering said calling means effective and said code transmitting and receivingmeans ineffective and for also connecting said coding source of current with its'polarity reversed with respect to the line wires in series with said selector battery, whereby during thetransmission of a selector code the line wires do not assume such difference of potential required for the effective energization of said line relays with said particular polarity'to permit a field start.

5. In a code communication system for railroads, a pair of line wires connecting a control ofiice and a plurality of field stations, code transmitting means at each field station including a polar line relay and operable only when said line relay is energized with a particular polarity to govern the energization of said line wires for transmission of a field start condition to the control ofiice, a mechanical selector bridged across said line wires with a coupling condenser and responsive to the number of changes in the energization of said line wires during a selector code, said selector requiring for its operation changes in the level of energization of said line wiresequivalent to pulses of a certain voltage and alternate polarities, coding equipment at the central office normally energizing said line wires with a predetermined voltage of said particular polarity to maintain said line relays energized to permit an, automatic field start, and manually operable means in the control ofiice including a selector calling key for intermittently energizing said line wires with pulses of the same polarity opposite to said particular polarity in accordance with a selector code, said intermittent energization of said line wires being at a voltage higher than said predetermined voltage and substantially doubl said certain voltage required for selector operation by alternate polarities, said higher voltage acting by charging and discharging said coupling condenser at a high energy level to cause operation of said selector substantially the same as in response to pulses of said certain voltage and of alternate polarity.

6. In a code communication system of the character described for railroads, a pair of line wires connecting a control office and a number of field stations, a plurality of mechanical selectors bridged across said lino wires with coupling condensers and responsive to the nergization of said line wires, coding equipment at each field station connected to said line wires and including a polar relay governing the operation of said equipment, said coding equipment including means efiective only if said line relay is energized with one particular polarity to apply a shunt to said line wires for a field start, transmitting means at the control office including a source of direct current for energizing said line wires with said one particular polarity for the normal at-rest condition of the system, an additional source of direct current in the control office, and manually operable means in the control ofiice including selector calling keys for intermittently energizing said line wires from both of said sources of current acting cumulatively and in opposition alternately to form pulses effective for operating said mechanical selectors and all having the same polarity opposite to said one particular polarity, whereby the condenser coupling the mechanical selector to the line wires is charged and discharged at an energy level by the combined sources of current to cause 11 e eiraibion .ef the .selechor'snbstantially the .same as inresponse to pulses of ai'ternatve pplarity irpm saidwadditienail .source alone.

'7; In a communicafion system 9f the chamoier described, a. pair of iinawiresiconnecitfrri a .6011:- tizol omce and a, plurality mf' field stations; pads transmittin means atzeaich-iield station includ a, palm iine relay governingin oneieneit ized' positn'en only the autamaztic field smart gontxoi: from $hait'fie1d; station, a-pluxality ntmeshariicai seleetors' bridged across said line wires with muplin condensers and m rated by cm-mass firin wire energization, sodmg means in the 5011111191 office including a iselecmr mum: of ciurxem and code generating devices for pplg changixlg. the electrical iepnnections betwaen mid, 5.81%?292. mums of aurrent'andsaid line-wims-in accswrdam the .desinedselecter vcsxele fer @elmiflue epemtienm saidseieemrs', .andrmearis .ferirem'ler sng .S L -fi Imimeans efiecnive and for aonnest ng; answer scmmeni 0111mm; 410 said mewiresdn :sexi'eswith said se1et r .spm'cg 10.5 sunrent' to pm -eilt. gnexgi ation 9i said line wipes with a polarity to energize said line relays ito rsiaikd one engr zesl position, the navel of ener izaiion of aid .liane wires by combinin isaid sou ces Qf current bein chan ed. by -p.o1e-chan ng said sel c or battery to cause operation of ,said sa ector;

WILLIAM BARKER.

CITED The following referen es are f record in the file 79f this patent:

UNITED STATES PATENTS

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