US2135295A

US2135295A - Supervisory control system

Info

Publication number: US2135295A
Application number: US121450A
Authority: US
Inventors: Clyde E Stewart; Leo D White
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1937-01-21
Filing date: 1937-01-21
Publication date: 1938-11-01
Anticipated expiration: 1955-11-01

Description

Nov. 1, 1938.

c. E. STEWART ET AL 2,135,295

SUPERVISORY CONTROL SYSTEM File'd Jan. 21', 1937 2 Sheets-Sheet l Inventors:

Clyde E. Stewart, Leo DWhite,

b filmy d A y Their Attornex Fig.1.

NOV. 1, 1938. c W T ET AL 2,135,295

SUPERVISORY CONTROL SYS TEM Filed Jan. 21, 1937 2 Sheets-Sheet 2 Inventors: 2 1 Cl d E. Stewart,

' Leo DWhite,

by Hum 5 Their Attorney.

fill

Patented Nov. 1, 1938 UNITED STATES PATENT OFFICE SUPERVISORY CONTROL SYSTEM Clyde E. Stewart, Upper Darby, and Leo D. White, Lansdowne, Pa., assignors to General Electric Company, a corporation of New York Application January 21, 1937, Serial No. 121.450

9 Claims.

interconnecting the two station equipments of the system. In such a supervisory control systom, the whole equipment is rendered inoperative if for any reason the individual conductors interconnecting the two station equipments of the system become short-circuited or open-circuited.

One object of our invention is to provide an arrangement whereby a dispatcher at the dispatchers office can effect the transfer of the two station equipments of a supervisory control systerm from its normal set of conductors to a spare set of conductors whenever he so desires.

Another object of our invention is to provide an arrangement whereby a dispatcher can effect the transfer of the two station equipments of any one of a plurality of supervisory control systems from its respective set of conductors to a spare set of conductors which is common to all of the station equipments.

Another object of our invention is to provide an arrangement whereby a dispatcher can effect the selective transfer of the remote station equipment of any one of a plurality of supervisory control systems from its respective set ofconductors to a spare set of conductors which is common to all of the station equipments.

Gur invention will be better understood from the following description when takenin connection with the two accompanying drawings comprising Figs. 1 and 2 which, when joined to ether. diagrammatically illustrate a selective control system embodying our invention, and its scope will be pointed out. in the appended claims.

In the accompanying drawings. we have shown our invention in connection with two supervisory control systems. each of which includes equipment at a dispatchers ofli'ce. equipment at a remote station and an individual set of conductors interconnecting the two equipments of the: system. These supervisory control equipments may be of any suitable type, examplesof which are well-known in the art. They may, for example, be of. the type shown in copending application, Serial No. 689,087,.filed September 12, 1933; by James H. Oliver, and assigned to the same assignee as this application.

Since the circuit details of these supervisory control systems form no part of' our present invention, we have represented the dispatchers office equipment of one of these systems by a rectangle A which is connected by the two line conductors E to a remote station equipment represented by a rectangle B. Similarly, the dispatchers ofiice equipment of the other system is represented by a rectangle A which is connected by two line conductors E to its associated remote station equipment represented by a rectangle B.

For the purpose of this description, it will be assumed that the dispatchers office equipments A and A are located at the same office, but that the remote station equipments B and B are located at different points. Interconnecting this single dispatchers office and the two remote stations is acommon setof conductors consisting of the two conductors LI and L2. Associated with these two conductors L! and L2 at the dispatchers oflice is suitable control means diagrammatically shown indetail in Fig. 1 whereby the dispatcher may transfer the dispatchers office equipment of either supervisory control system to the spare set of conductors LI and L2 and may cause the proper select code and an operating impulse tobe transmitted over the line conductors LI and L2 to eliect the transfer of a desired remote station equipment of either of the two supervisory control systems to the spare set of conductors.- Associated with the spare set of conductors L! and L2 at each of the remote stations is suitable control means which is selectively controlled by the select codes transmitted over the spare conductors from. the dispatchers officeso that only the desired remote station equipment is transferred to the spare set of conductors in response to the transmission of theoperating impulse from the dispatchers office. Since the control apparatus is the same in each of the remote stations, except for certain connections hereinafter described. only the control apparatus associated with the remote station equipment B is-shown in detailin Fig. 2.

At the dispatchers ofiice we provide for each remote station equipment to be connected to the spare set of conductors LI and L2 9. select key which is operated when the dispatcher desires to effect the transfer of the corresponding remote station equipment. Also for each remote station equipment, we provide anindicating lamp which is lighted when the corresponding equip-- ment has been selected for transfer to the spare set of conductors. Although we have shown in the drawings only two supervisory systems having remote station equipments arranged to be connected to the line conductors LI and L2, the disinclusive, which are respectively associated with the select keys SKI to SK8, inclusive. Each of these code relays is energized when the associated selectkey is operated and sets up a select code which is individual thereto. Also associated with the select keys SKI to SK8, inclusive, is a sender S, comprising a group of six relays SI to S6, inclusive, that are sequentially energized, when any one of the select keys is operated, to efiectthe' transmission of. the select code which has been set up by the energized code relay associated with the operated select key. When each of the relays S|,'S3, and S5 is energized, a circuit is com: pleted for either a relay P or a relay N, depending upon the code set up by the energized code relay. The relay P, when energized, is arranged to cause a positive impulse to,be transmitted'over the conductors LI and L2, and the relay N, when energized, is arranged to cause a negative impulse to v select keys eifects the transmission over the conductorsfLl andLZ of a select code comprising a be transmitted over the conductors LI and L2. In this manner, the operation of any one of the series of three positive and negative impulses,

' permutated individual to the operated select key to effect the selection of the desired remote station equipment to be connected to the conductors At each of the remote stations, each impulse. of

. a transmitted. select code energizes a polarized relay L'- so that it eifectsthe energization of an associated relay L'P, if the impulse is a positive one andthe energization of an associated relay LN if'the impulse is a negative one. The sequence in which the relaysLP. and UN! are op-" erated by the threeimpulsesof a select code determines which remote station equipment is selected for'transfer to the spare-set of conductors ,Ll and LZ. Associated with 'each pair of relays L'P andLN' is a group of six relays R! to RB.

inclusive, which are so connected that all six'of the relays" of a group are energized only in response to the predetermined select code which is individual thereto. In the particular arrangement shown in Fig. 2, the only select code which will effect the energization of all the relays R! to R16, inclusive, is the codein which the first impulse is a negative impulse, the second impulse is a negative impulse and the last impulse is a iii) positive impulse. Each of the other seven select 'codes of three positive and negative impulses which are arranged to be transmitted by the sender S, shownin Fig. '1, in response to the operation of the select keys SKI to SK8, inclusive, cannotefiect the energization of more than four of the relays R'l to RB as they are shown connected in Fig. 2. Similarly, in each of the other remote stations the corresponding relays Rl to RB are connected in such a manner that they will all be energized only'in response to a particular select code which does not effect the energization of all of the corresponding relays in any other station. For example, in one of the other stations all of the relays R! to R'B, inclusive, may be connected so that they are all energized only in response to a select code'in which each-of the three impulses is a positive impulse, while in another of the stations all of the relays R! to R6, inclusive, may be connected in such a manner that they are all energized only in response to a select code in which each of the impulses is a negative impulse, while in another station the relays R! to R'B, inclusive, may be connected in such a manner that they are all energized only in response to a select code in which the first two impulses, are

ip'ositive impulses and the last impulse is a negative impulse, etc.

At the termination of the last impulse of a transmitted select code, a sender S, which consists of a group of six relays S'l toS'6, inclusive. operates in the remote station which has been selected to effect thetransmission over the conductors LI and L2 of a check code which is individual to the selected remote station equipment.

Preferably, each sender S is arranged to transmit a check code which is the same as the corre-- sponding select code.

At the dispatchers oifice the check code selec-- tively energizes a group of nine relays, Rl to R9,

inclusive. If the check code received at the dispatchers oflice agrees with the select code which was sent out from the dispatchers office, the relays'Rl to R9 are energized in the proper com 'bination to complete an energizing circuitfor a time relay CI; The energization of this relay Cl completes an energizing circuit for the lamp associated with the operated select key, thereby informing the dispatcher that theproper remote station equipment has been selected for transfer to the spare set of. conductors LI and L2 The energization of the time relay Cl also prepares the necessary circuits at the dispatchers ofilce so that when the dispatcher subsequently operates a common operate key OK a positive operating impulse is transmitted over the conductors Li and L2 to. effect the transfer .of the selected remote station equipment from its normal set of conductors to the spare conductors LI and L2. At the selected'station, the positive operating 7 impulse effects the energization of the relay L'P',

which in turn effects the energization of an associated transfer relay CR to transfer the selected remote station equipment from its normal set of conductors to the spare set of conductors LI and L2. The dispatcher then operates adisconnecting switch LDSW associated with the line conductors LI ofiice' so as to disconnect these conductors from the control apparatus shown in Fig. l and then operates a switch LTSW associated with the dis 'patchersofiice equipment corresponding to the transferred remote stationfequipment so that this;dispatchers office equipment is disconnected from its normal set of conductors and-is connected to the spare set of conductors Ll, L2. The dispatcher then resets to normal in a manner and L2 at the dispatchers well-knownin the art the supervisory equipment 7 now connected .to the spare set of conductors so that itis ready for usewiththe spare conductors. The amber lamp associated withthe transferred equipment remainslighted to indicate to the dispatcher that the spare set of conductors are in use with that particular equipment.

When it is desired to reconnect the two equip:

ments that are connected to the spare set of con ductors LI and L2 to their normal set of conductors, the switch LTSW associated with the dis patchers oflice equipment is restored to'its'non mal position, the switch LDSW'is closed, and 7 then the operated select key is restored to its normal position. A release key RK at the dispatchers office is then depressed for several seconds. The operation of this release key causes a relatively high negative potential to be applied across the conductors LI and L2. This high potential at each of the remote stations effects the operation of a glow tube GP', which in turn effects the energization of an associated reset relay D2, which, when energized, causes the associated remote station control apparatus to be reset to normal.

A detailed description of the'operation of the embodiment of our invention shown in the two accompanying drawings will now be given.

Normally, when the spare conductors LI and L2 are not in use, the switch LDSW at the dispatchers office is in the position shown so that a circuit is completed from the line conductor LI through the upper contacts of the switch LDSW, conductor I00, contacts I) of operate key OK, conductor IOI, winding of polarized relay L, conductor II0, contacts d of relay 9, conductor I02, contacts (1 of relay R, conductor I03, contacts I) of relay P, conductor I04, contacts I) of relay N, conductor I05, lower contacts of switch LDSW to the line conductor L2. At each of the remote stations, except the most remote-station there is connected across the conductors LI and L2 a circuit including in series the contacts b of relay R6, conductor 200, contacts h of relay D'I, conductor 20I, winding of polarized relay L'T', conductor 202, and resistor RE. At the most'remote station, which we will assume is the station where the substation equipment B is located, the neutral of the station battery BAT' is connected to the conductor L2 through contacts d of relay R'L, conductor 203, contacts 1 of relay D I, conductor 204, contacts I) of relay RLX', conductor-202, winding of relay L'T', conductors 20I, contacts h of relay D'I, conductor 200, and contacts b of relay RB. The positive terminal ofthe station battery B'A'T' at the most remote station is'connected to the conductor LI through winding of a relay X'I, contactsj of relay RL', conductor 205, and contacts I) of relay D'I. Therefore, the polarized line relays LT' in all of the remote stations except the most remote station are normally connected in parallel with each other and with the polarized relay L at the dispatchers oflice and these parallel connected relays are connected-in series with the relay X' I and the polarized relay LT in the most remote station. The current in this normal check circuit is not of sufiicient'magnitude to operate the relay X'I.- However. the current is insuch a direction that each of the parallel connected line relays LP' closes its contacts a,-the relayL closes its contacts a and the series connected line relay L'T'- in the most remote station closes its contacts b. At the most remote station, anenergizing circuit is normally completed a for the associated relay -LN through contacts b of the relay UT and the contacts b of the relay LP. The contacts a of relay L'N-' complete an energizing circuit-for its associated relay R'O from the positive terminal of the associated station battery BA T, contacts a of re lay L'N', conductor 215,- contacts b of relay R'L', conductor 201, winding of relay RO, conductor 208, contacts 7' of relay DI to the negative terminal of battery B'AT. W a

At the other remote stations, the relay L'T' completes at its contactsia an energizing circuit for the associated-relay L'P' through contacts I) of the associated relay LN. In each of these other remote stations=,- the energizing circuit of relay RO includes the contacts a of relay LP instead ofthe. contacts a of relay L'N' so that all of the relays RO are normally energized.

Also at each of the remote stations, an energizing circuit is completed for the relay D4 thereat from the positive terminal of the station battery B'AT, winding of relay D4, conductor 209, contacts I) of relay Rl, to the neutral of the station battery B'AT".

At the dispatchers office, the contacts a of the relay L completes an energizing circuit for the relay R0 from the positive terminal of the battery BAT, contacts a of relay L, conductor I40, contacts b of relay CI, conductor I0'I, contacts b of relay RL, conductor I08, winding of relay R0, conductor I09, contacts I) of relayDI to the negative terminal of battery BAT. The contacts 6 of the energized relay R0 completes a circuit for the start lamp ST from the positive terminal of battery BAT'through contacts e of relay R0, conductor I [0, contacts d of relay RL, conductor I I I, start'lamp ST to the negative terminal of battery BAT. The lighted lamp .ST informs the dispatcher that the spare conductors LI and L2 are innormal condition and are not being used.

When it is desiredto transfer a remote station equipment to the spare conductors LI and L2, the dispatcher operates the corresponding select key- Therefore; when he desires to effect the transfer of the remote station equipment B shown in Fig. 2, he operates the select key SK3, which is the select key individual ,to this equipment. The closing of the contacts a ,of the select key SK3 completes a circuit for the associated code relay 3 from the negative terminal of the battery BAT through the winding of relay 3, conductor II2, contacts a of select key- SK3, conductor, II 3, contacts 1 of relay R9, conductor I I4, contacts (1 of relay CI to the'neutral of battery BAT. The, closing of the contactsa of relay 3, completes an energizing circuit .for relay 9 from the positive terminal of battery BAT through contacts a of relay 3, conductor I I5, contacts a ofrelay R0, conductor H6, winding of. relay 9, to, the negative terminal of battery BAT. A circuit is,.also completed for relay P from conductor H6 through contacts b of relay TI, conductor I80, contact (1 of operate key OK; conductor I21, winding of relay P to the negativeterminal of battery BAT. The opening of the contacts d of therelay 9 when it becomes energizedinterrupts the heretoforedescribed normal circuit through the polarized relay L in the dispatchers .ofiice so that this relay opens its contacts a. The opening of these:contacts removesthe short-circuit from around the winding of relay RL so that this relay is energized in series with the relay R0 through the conductor H1 and the contacts 0 of relay R0.

, The c os ng of contacts 0 of relay P connects the p sitive terminal of the main battery BAT to conductor LI and the closing of contacts e of relav P connects the negative terminal of an aux liary ba tery BATI ,to conductor L2 through contacts d of relay TI. ,Since the positive terminal of battery BATI. is connected to the negative terminal of the mainjbattery BAT, a higher positive voltage is appliedacross the conductors LI and L2 at the dispatchers oflice than is applied across them by the battery B'A'T in the most remote station. Therefore, the current through the polarized line. relay LT' in the remote station so that it opens its contacts I) and he. de-energization or" the associated relay LN. and thereby removes a short-circuit from aroundthe associated relay R'L, which LI and L2.

Since at theintermediate stations the line relays L'T are connected across the conductors- Li and L2, the boosted positive'potential across becomes energized in series with the associated relay RO' ina circuit which includes the con-'1 tacts a of relay R'O and the conductor 2"). The

relay RL', by opening its contacts 11 and 1, also disconnects the conductors LI and .L2 from-its normal source of potential B'ATC The contacts e of the relay R'L complete through conductor 2| I an energizing circuit for the associated relay RLX, which, by opening its contacts I and.

closing its contacts 0, transfers the connection of the winding or the associated polarized relay LT' from a series connection with the conductor L2 to a shunt connection across the conductors these conductors does not eifect any change in the position thereof. 7 1

At the dispatchers office, the contact a of the relay 9 completes through conductor I I 8 'an'ener gizing: circuit. for the slow-to-operate relay TI.

The opening of contacts b of relay TI interrupts the heretofore described circuit for relay P so'as g to remove the boosted positive impulse from the conductors LI and L2 and thereby effect the energization of the relay RL and P'LX in each of the intermediate stations. 7

By closing its contacts a, relay TI completes an energizing circuit for the sloW-to-operate'relay T2 from the negative terminal of battery BAT through the winding of relay T2, conductor] I9, contacts d of relay N, conductor I20, contacts'tl of relay P, conductor I2I, 'conta'ctsapf relay TI to the neutral of battery BAT. The closing'of the contacts a of relay T2 completes an energizing circuit for the relay SI of the code sender S 7 from the positive terminal of battery BAT through contacts a of relay T2, conductor I22 contacts at of relay S2, conductor I23, winding of relay SI, conductor I24, contacts d of relay DI to the nega'' tive terminal of batteryBAT. By closing its contacts a, relay SI completes an energizing circuit the conductors LI and L2 closes its contactsd; the heretofore'd-escribed for relay N from the positive'terminaloi battery BAT through oontacts b of relay S2,' conduct or I25, contacts a of relay SI, conductor I26, con

tacts e of relay 3,'conductor I33, winding of relay for relay T2 so that this relay becomesde-ener gized and by opening its contacts a removes. a'

short circuit from the'winding of relay S2, which is now energized in series with relay SI through the conductor I28 and contacts 0 of relay'SI.

By'opening its contacts I), relay S2 interrupts the heretoforedescribed circuit for relay N, thus removing the first impulse of the select code, from energizing circuit for relay T2 is again completed anda circuitisnow completed'for the vrelay S3 70 of the 'code senders from the positive terminal of battery BAT through contacts a Of'relay-TZ,

conductor I22, contacts'a of relay S2, conductor I29, contacts d ofrclay S4, conductor I30, Winding of relay S3, conductor I24, contacts d of relay DI .to the negative terminalof battery BAT.

When the .relay N By closing its contacts a, relayS3 completesan' energizing circuit for relay N from. the positive terminal of battery BAT through contacts b of relay S4, conductor I3I, contacts a of relay S3, conductor I32, contacts '9 of relay3, conductor I33, winding of relay N to the negative terminal of batteryBAT. The closing of contacts a of relay N connects the conductor LI to the'negative terminal of battery BAT. and the closing of 7 contacts 0 of relay N connects the conductor L2 to the neutral of battery BAT through contacts c of relay TI so that a negative'impulse is transmitted over the spare set of'conductors LI and L2 to' each of the line relays LT in the remote stations. The opening of the contacts 41 of relay N interrupts the heretofore described cir-i cult for relayTZ, which in turn opens its conttacts a and removes the short-circuit from around the winding of relay S4, which is now energized in series with the winding of relay S3 through conductor I34and contacts 0 of relay S3;

By'opening its contacts I), relay'S4 interrupts the heretofore described circuit forrelay N, thus 7 removing the second impulse of the select code from the conductors LI and L2. When the re lay N closes its contacts d, the heretofore described circuit for relay T2 is again completed, and this relay T2- in turn'completes an energizing circuit for the relay S5 of the sender S fromthe positive terminalof battery BAT through contacts a of relay T2, conductor I22, contacts a of relay S4 conductor I35, contacts d of relay'SB,

conductor I36, winding of relay S5, conductor I 24, contacts d of relay DI,"to the negative terminal of battery BAT. By closing its contacts a, relay S5 completes an energizingcircuit forqrelay-P' from the positive terminal of battery BAT,

through the contacts b of relay S6, conductor I31, contacts a of relayS5, conductor I38, con tacts d of relay 3, conductor I21, winding of relay P tothe negative terminal of battery BAT. The closing of the contacts 0 and e of relay? causes a' positive impulse to, be transmitted over the spare conductors LI and L2. The opening of the contacts d of relay R efiectsthede-ener 1:

gization'of the relay T2, which in turn, by opening its contacts a, removes a short-circuit fromaround the winding of relay S6 so that'this relay becomes energized in series with the Winding of relay S5 through a circuit which includes the contacts 0 of relay S5 and conductor I39. -By opening" its .contacts'b, relay S6 interrupts the heretofore described circuit of relay P, thus removing the'third impulse of the'select code from the conductors'LI and'LZ. ,By closing its contacts a, relay S6 completes a shunt circuit around the contacts :1 of relay 9 *sothat the" operating Winding of polarized relay L is Ie-y connected across the line conductors 'LI. and L2. 6D

In the remote station where the equipmentB is located, the firstimpulse of the select'code',

LT to close its contacts I) and therebycomplete the energizing circuit for relay L'N'. This relay L'P'fby closingits'cont-act's a, completes an energizing circuit for the relayRnl from the'posie through contacts a of relay L'N', conductor 2l5, contacts e of j relay RFL'X, conductor 2I2, contacts b 101 relay tive terminal of battery B'AT R'Z, conductor 2I3, winding of relay RI, co. n-

"ductor 208, contacts jofrelay'D'I, to the'negative terminal of battery BA/Ts Upon' the removal of the first impulse, of the select code, the relay LT effects the deenergization of the relay LN', which in turn, by opening its con- 'Which is a negative impulse, causes the relay the shunt circuit tacts a, removes a short-circuit from around the winding of relay R2 so that a circuit is completed for this winding in series with the winding of relay R/i through contacts a of relay R! and conductor H4.

The second impulse of the transmitted select code, which is a negative impulse, causes the relay LT' to close its cont-acts b so that the energizing circuit for the relay LN' is completed. By closing its contacts a, relay LN completes an energizing circuit for the relay R'3 from the positive terminal of the battery B'AT' through contacts a of relay LN, conductor 2l5, contacts a of relay RZ, conductor 216, contacts of relay '4, conductor 2H, winding of relay R3, conductor 288, contacts 7' of relay Dl tothe negative terminal of battery B'AT. Upon the removal of the second impulse of the select code from the conductors LI and L2, the relay L'T effects the deenergization of relay LN,- which in turn, by opening its contacts a, removes a shortcircuit from around the winding of the relay R4 so that an energizing circuit is completed for this winding in series with the winding of relay R'3 through the contacts a of relay R13 and conductor H8. ,7

The third impulse of the transmitted select code, which is a positive impulse, causes the relays LT' and LP to become energized so that an energizing circuit is completed for the relay R5 from the positive terminal of battery BA'T' through contacts a of relay L'P', conductor 206, contacts aof relay R4, conductor 2l9, contacts 1 of relay R6, conductor 22!), winding of relay R'S, conductor 268, contacts 7' of relay Dl, to the negative terminal of battery B'AT. Upon the removal of the last impulse of the select code from the conductors Li and L2, the relays LT and L'P become de-energized and the opening of the contacts a of relay LP' removes a short-circuit from around the winding of relay R6 so that an energizing circuit for this winding in series with the winding of relay R'5 is completed through the conductor 22l and the contacts a of relay R5.

Therefore, in the remote station where the equipment B is located, all of the relays R'l to R16 are energized by the select code, which is transmitted in response to the operation of the select key 6K3, but in each of the other remote stations this select code does not efiect energization of all of the corresponding relays R! to R'B, inclusive.

By opening its contacts b, relay R6 opens of the relay LT' across the and L2 so that this relay does not respond to the check code which is transmitted over the conductors Li and L2 as a result of the energization of the relay R'6. The closing of the cont-acts c of the relay R6 connects the neutral terminal of battery BAT' to the conductor L2 through the contacts I) of relay S6, conductor 222, contacts 0 of relay R6, conductor 223, and contacts 1 of relay CR. The closing of the contacts e of relay R16 completes an energizing circuit for a slow-to-operate relay T'l from the positive terminal of battery B'A'T through winding of relay Tl, contacts b of relay Sl, conductor 225, contacts I) of relay 8'3, conductor 226, contacts U of relay S'ii, conductor 221, contacts 6 of relay R6, to the neutral of battery B'AT. By closing its contacts a, relay Tl completes an energizing circuit for the slow-to-operate relay T'2, which in turn, by closing its contacts. a, completes an conductors Ll conductor 224,-

energizing circuit for the relay 8'! of the sender S from the positive terminal of battery B'A'T through contacts a of relay T2, conductor 228, contacts 12 of relay S2, conductor 229, winding oi relay SI, conductor 208, contacts 7' of relay D'i, to the negative terminal of battery B'AT. By closing its contacts 0, relay S. l connects the negative terminal of battery BAT to the conductor Li through conductor 229, contacts (1 of relay S2, conductor 23!), contacts h of relay CR, conductor 23l, and contacts at of relay D l. Therefore, a negative impulse is transmitted over the conductors LI and L2.

The opening of thecontacts b of relay 8! interrupts the heretofore described circuit for relay Tl, which in turn, by opening its contacts (1, effects the de-energization of the relay T2, so that it opens its contacts a and removes a short-circuit from around the winding of relay S2 to cause this winding to be energized in series with the winding of relay S'l, in a circuit which includes the contacts a of relay Sl and conductor 232. The opening of the contacts d of relay S2 disconnects the negative terminal of battery BAT from the conductor LI so as to terminate the first impulse of the check'code.

The closing of the contacts 0 of relay S2 completes an energizing circuit for the slow-to-operate relay T! from the positive terminal of battery B'AT through the winding of relay Tl, conductor 224, contacts 0 of relay S2, conductor 225, contacts b of relay S3, conductor 226, contacts b' of relay S'5, conductor 221, contacts 6 of relay RB to the neutral of battery B'AT. The energization of relay Tl effects in turn the energization of slow-to-operate relay T'2, which in turn, by closing its contacts a, completes an energizing circuit for relay S'3 from the positive terminal of battery B'A'T through contacts a of relay T2, conductor 228, contacts a of relay S'2, conductor 233, contacts b of relay S4, conductor 234, winding of relay S3, conductor 268, contacts a of relay D'l to the negative terminal of-battery B'AT. v

The closing of the contacts 0 of relay S3 connects the negative terminal of battery BA'T to the conductor Ll through conductor 235, contacts d of relay S4, conductor 230, contacts h of relay C'R, conductor 23!, and contacts at of relay D'l. The energization of relay S3 therefore causes a negative impulse to-be transmitted over the conductors LI and L2. The opening of the contacts 0 of relay S3 interrupts the heretofore described circuit for the relay Tl, which in turn, by opening its contacts a, de-energizes the relay T2; The opening of the contacts a of relay T2 removes a short-circ 't from around the winding of relay S4 so that this win-ding is energized in series with the winding of relay S'3 in a circuit which includes the contacts a of relay S'3 and conductor 236.

The opening of the contacts d of relay S4 disconnects the negative terminal of battery B'AT from conductor Ll so as to terminate the second impulse of the check code. The closing of the contacts 0 of relay S'4 completes an energizing circuit for the slow-to-operate relay T! from the positive terminal of battery BAT through winding of relay Tl, conductor 224, contacts 0 of relay S2, conductor 225, contacts 0 of relay S54, conductor 226, contacts b of relay S'5, conductor 221, contacts e of relay R'6, to the neutral of battery B'AT. Relay Tl effects in turn the energization of relay T'2, which, by closing its to the negative terminal of battery B A'T. of relay S'5 con- 7 The closing of the'contacts c meets the positive terminal of battery BA'T' to the-conductor LI through conductor 239, contacts d of relay S6, conductor-230, contacts h of relay CR, conductor 23I, and contacts (1 of relay D'I. Therefore, the energization of relay S5 eifects the transmission of a positive impulse over the line conductors LI and L2.

described circuit for relay TI, which inturn, by opening its contacts a, effects the de-energization of the relay T'2. The openingof contacts a of relay T'2 removes a short-circuit from around the Winding of relay 8'6 '50 that this Winding is energized in series with the winding of relay S'5 in a circuit which includes the contacts a'of relay 8'5 and conductor 240. I The opening of the con"- tacts d of relay SB disconnects the positive terminal of battery B'A'T' V 7 so as to terminate the last impulse of the check code.

At the dispatchers office each impulse of the check code effects the operation'of the polarized relay'L sothat it closes either its contacts a, or contacts b, depending impulse.

upon the polarity of the Since the first impulse of the check code is a negative impulse, the relay L closes its contacts b and completes a circuit for relay RI from the positive terminal of battery BAT through contacts 'b of relay L, conductor I06,

7 contacts b of relay R3, conductor I4I, contacts 0 'lay RI and conductor 'of relay R9, conductor 7 conductor I09, contacts b of relay DI to the" ofrelay RL, conductor I 42, winding of relay RI, conductor I09, contacts b of relay DI to the negative terminal .of 'batteryBAT. I When this first impulse of the check code is removed from the conductors LI and L2, relay L opens its contacts 17, which thereby removes a short-circuit from' around the winding of relay R3, which is now energized in series with the winding of relay RI in a circuit which includes the contactsa of re- The second impulse of the check code, which is a negative impulse, causes the relay L to close its contacts b and complete an energizing circuit for the relay R5 fro the positive terminal of battery BAT through contacts b of relay L, conductor I06, contacts 0 of relay R3, conductor I43, contacts b of relay R6, conductor I44, winding of relay R5, conductor I 09,, contacts b of relay DI to the negative terminal of battery BAT. When the second impulse of the check code is removed from the line conductors LI and L2, relay L opens its contacts'b and removes a short-circuit from around the winding of relay R6, which is then energized in series with the winding of relay R5 in a circuit which includes the contacts a of relay R5, and conductor I45.

The third impulse of the check code, which is a a positive impulse, causes the relay L to close its contacts and complete an'energizing circuit for the relay R! from the positive terminal of battery BAT through contacts a of relay L, conductor I40, contacts 0 of relay R6, conductor I 46, contacts 12 I41,-winding of relay R7,

negative terminal'of battery BAT. When this last impulse of the check code is removed from the conductors LI and The opening of the (contacts b of relay S5interrupts theheretofore tery BAT through winding of relay 3,

from the conductor LI contacts d of the relay DI 0f the energized relays SI L2, relay L opens its contacts a and removes, a short-circuit from around the winding of relay R9, which is now energized in series with the winding of relay R! in a circuit which includes contacts a'of relay R1 and conductor I48.

, When the relay R9 is energized, the opening of its contacts I interrupts the heretofore described circuit of relay 3, which was completed through the contacts a of the operated selectkey 8K3. However, if the select codeagrees with the select code sent out from thedisp'atchers oflice, the

relays RI to R8 are energized inthe proper combination to complete anothercircuit for the relay 3 before the relay R9 operates so that relay 3 does not become de-energized when the relay R9 opens its contacts f. This auxiliary circuitfor is from thenegative terminal of bat- H2, contacts 0 of relay 3, conductor I49, contacts e of relay R1, conductor I50, contacts 0 of relay R5, conductor I5I, contacts 0 of relayRI, con ductor II4, contacts of battery BAT. H

The closing of the contacts a of relay R9 completes an energizing circuit for a slow-to-operate relay CI from the positive terminal of battery BAT through winding of relay CI, conductor I53, contacts 0 of relay 9, conductor I54, contacts a of relay R9 to the neutral of battery BAT. The

, closing of the contacts 9 of relay CI completes another holding circuit for relay 3 from the ative terminal of battery BAT through the ing of relay 3, conductor II 2, contacts 0 of relay 3, conductor I49, contacts 0 of select keyVSK3, conductor I55, to the neunegcontacts 2' of relay lamp LA3 from the positive terminal of battery BAT through contacts 2' of relay CI, conductor I56, contacts k of relay 3, conductor I51, lamp L2 by operating the operate key OK.

relay P from the positive terminal of battery BAT through contacts e of relay CI,

the circuits of the energized relays R0, RL, RI, R3, R5, R6,'R1, R9 and the opening of the interrupts the circuits to S6, inclusive, of the sender S so that all of the relays of the dispatch ers ofiice equipment except relays 3, C I and DI Wind- 7 dof relay CI to theneutralare de-energized. The closing of thecontacts a .of the relay DI completes a locking circuit "for itself from the positive terminal of battery BAT through the winding of relay DI, conductor H59, contacts a of relay DI, conductor IBI, to the neutral of battery BAT through contacts is of relay Rl, contacts e of relay R5, contacts 'e of relay RI, and contacts e of relay 9 in parallel so that the relay DI remains energized until all of these relays have been restored to their respective normal positions.

The closing of the contacts 9 ofrelay P completes a locking circuit for relay CI from the positive terminal of battery BAT, winding of relay CI, conductor I53, contacts a of relay Cl, conductor 562, contacts b of relay R, conductor 163, contacts 9 of relay P, to the neutral of battery BAT. As soon as the relay R0 is de-energized in response to the energization of the reset relay Dl, the contacts b of relay R0 completes a circuit around the contacts g of relay P so that the relay CI remains energized after the'relay P is deenergized by the dispatchers releasing the operate key OK to remove the operating impulse from the conductors LI and L2.

At the selected remote station, the positive operating impulse causes the relay L'T' to close its contacts a and effect the energization of relay UP. The closing of the contacts a of relay L'P completes an energizing circuit for relay C'RX' from the positive terminal of battery BA'T' through contacts a of relay L'P', conductor 205, contacts a of relay S'6, conductor 24!, winding of relay CR'X' to the negative terminal of the battery BA'T. When the operating impulse is removed from the conductors LI and L2 an energizing circuit is completed for the relay CR from the positive terminal BAT' through contacts (1 of relay D3, conductor 242, Winding of relay CR, conductor 243, contacts a of relay C'RX', conductor 24 I, winding of relay CRX, to thenegative terminal of battery BA'T. By opening its contacts b and d and closing its contacts a and c, relay CR transfers the remote station equipment B from its normal set of conductors E to the spare set of conductors LI and L2. By closing its contacts .6, relay C'R' completes an energizing circuit for reset relay D'I from the positive terminal of battery B'AT through winding of relay DI, conductor 243, contacts 6 of relay CR to the neutral of battery B'A'T,.

The opening of the contacts 7' of relayDI interrupts the circuits of the energized relays R/O,

elusive, so that all of these relays are restored to their respective normal positions. The closing of the contacts a of relay Dl extends the conductor L2 to the further remote stations so that they may be reset by the dispatcher in a manner hereinafter described. The closing of the contacts e of relay D'I completes a locking circuit for the relay D! from the'positive terminal of the battery BAT through winding of relay D'I, conductor 243, contacts a of relay Di, conductor 244, contacts f of relay D3, to the neutral of battery BA'T.

After having released the operate key OK, the dispatcher opens the switch LDSW at the dispatchers office and operates the switch LTSW so as to transfer the dispatcher'fs oflice equipment A from its normal set of conductorsE to the spare set of conductors LI and L2. The dispatcher can then control the remote station 75 equipment B over the spare set of conductors LI and L2 by operating the dispatchers office equipment A.

When it is desired to restore the equipments A and B to their normal set of conductors E, the dispatcher first operates the switch LTSW so as to transfer the dispatchers office equipment A from the conductors LI and L2 to the conductors E. Then the dispatcher opens the switch LDSW and restores the select key SK3 to its normal position, thereby effecting the de-energization of 1* the relay 3. The dispatcher next operates the release key RK for several seconds and then releases it. The operation of the release key RK completes an energizing circuit for the release relay R from the positive terminal of battery BAT- through contacts a of key RK, conductor its, winding of relay R to the negative terminal of battery BAT. The closing of the contacts 0 of relay R. connects the positive terminal of battery BAT to the conductor L2 and the closing of the contacts e of relay R connects the negative terminal of the battery BAT-I t6 the conductor LI so that the batteries BAT and BATI are connected in series across the conductors Li and L2 to transmit a boosted negative impulse.

The opening of the contacts 11 of relay R interrupts the heretofore described locking circuit for relay CI so that it is restored to its normal position. The closing of the contacts a of relay B completes an energizing circuit for the reset relay Di to insure that all of the relays of the dis patchers oflice equipment are restored to their normal positions.

At each of the remote stations, the high negative potential impressed across the conductors Li and L2 effects the operation of a glow tube G'T, the grid circuit of which is operatively connected in a well-known manner across the conductors LI and L2 by the contacts 0 of the energized reset relay D'I so that the relay D'2, which is connected in series with the output circuit of the glow tube G'T', is energized. The closing of the contacts 0 of the relay D'2 completes another energizing circuit for the relay D'I so as to insure that this relay remains energized as long as the relay U2 is energized. The closing of the contacts av of relay D'2 completes through conductor 246 an energizing circuit for the relay D3. By opening its contacts I), relay D3 interrupts the circuit of the relay DZ, but the relay D3 is not de-energized by the opening of the contacts a of the relay D'Z because a locking circuit is completed for the relay D'3 from the positive terminal of battery BAT through contacts b of relay RO, conductor 247, contacts 'a q of relay D3, conductor 246, winding of relay D'3 to the neutral of battery BA'T. The opening of the contacts at of relay D3 at the selected remote station effects the de-energization of the relays C'R and C'RX so that the remote station equipment is reconnected to its normal set of conductors E. The opening of the contacts e of relay D3 in each of the intermediate s ations opens the locking circuit of the associated relay D'I so that this relay is restored to its normal position when all of the other relays controlled thereby have been restored to their normal position. In the end station, the relay D'I is not deenergized until the reset impulse is removed from the line conductors. This result is accomplished by having the relay D2 thereat complete through its contacts e an energizing circuit for a relay X2 across the conductors Li and L2. Relay by closing its contacts a, completes a locking circuit for itself and by closing its contacts 0 coml pletes a circuit for relay D! l as long as the-reset impulse continues to flow.

When the relays D! in all of the remote stations have been restored to their normal positions, the heretofore described check circuit is completed so that the relay RO' in each of the remote stations is energized to open its contacts b and restore its'associated relay D3 to its normal position. At the dispatchers office, this check circuit efiects the lighting of the start lamp ST to inform the dispatcher that the equipment is in its normal condition. 7 In each of the. remote stations, the first energization of the relay LP' or L'N' thereat during the transmission of a 'select code completes an energizing circuit for the associated relay R! from the positive terminal of the'battery B'AT' throughthe winding of relay R'l, conductor 249, contacts a of relay R'L', conductor 250, to the neutral of battery: BAT' througheither contact-s'e of relay LP' or contacts eof relay LN'. By closing its contacts a., relay R' 'I completes a locking circuit for itself through conductor 26!] and contacts 1 of relay'D L; By opening its contacts b, relay R"! opens the circuit of the slow-todrop-out'relay D'4, but each time the relay L'P' is energized; its contacts'ccompletes an energizing circuit. for relay D'4. and each time the relay a. of relay R6 to the neutral of battery BAT';

'L'N is energized'its contacts 0 completes through thecontacts d of relay R'G' an energizing circuit forrelay D'l. Normally, the, duration elapsing between select code'impulses is sufficiently short to prevent the relay D4 from closing its contactsb." When the last impulse of the select code is removed from'the conductors'Ll and L2 and relay R'6 becomes energizedin the selected station, a circuit is completed 'for the relay D'4 from the positive'terminal of battery B'A'T' through the winding of relay D'4, conductor 209,

contacts d of relay LNf, conductor contacts In each of the other remote stations, however,

the select code has not effected the energization of the relay R'6 thereat; Therefore, in each of these other remote stations the relay D'4 be comes deenergized' after the last select code im- "pulse has been removed from the conductors LI and L2. By closing its contacts b, relay Dl in these other remote stations completes through conductor 243. an energizing circuit for the associated reset relay D'l, which in turn resets' all of the energized receivin'g'relays R! to R'4, inclusive, in the manner heretofore described. Each relay D'l completes the heretofore de-'- scribed locking circuit for itself through the contacts e of the associated relay D3 so that each relay Dl remains energized until its associated relay D3 is energized by the release impulse transmitted from the dispatchers office.

The selection of each of the other remote stations common to the conductors LI' and L2 in response to'the transmission of the select code individual thereto is effected by having the relays R'l, R'3,.and R'5 connected in a difierent manher in eachof these other stations from that shown in Fig. 2 so. that they, are successively energized by the three impulses of the individual select code. For example, if the select code or a remote station is one negative followed by two positive impulses, the relays Rl and R'5 in that stationare connected in the same manner as in Fig. 2, but the relay R'3 isconnected so that its energizing circuit includes the contacts a of relay LP instead of contacts a of relay LN'. Also in that remote station, the contacts 0 of'relay S'3 of the sender S are arranged to connect the positive terminal instead ofthe negative terminal/of battery B AT to the conductor LI in order to produce a check code of three positive; impulses. If theselect code of a remote station is three negative impulses, the relays Rlrand R'3 are connected in the same manner as in Fig.

2, but the relay R'5 is connected-so that its en.- ergizing circuit includes the contacts a of relay L'N' instead of the contacts a of relay LP'.

Also in thisremote station,the contacts 0 of'relay S'5 of the senders! are arranged to connect the negative terminal instead of the positive terminal of battery B'AT' to the conductor LI in order to produce a check code of a positive impulse followed by two negative impulses.

7 If for any reason the normal check circuit 7 through the conductors LI and L2 becomes interrupted or a short-circuit is completedacross V the conductors, relay L in the dispatchers oflice becomes de-energized and by opening its contacts b effects, in a manner the energization of the relay RL in series with the relay R0. The opening of the contacts d of relay RL interrupts the circuit of the start patcher that the spare set of conductors is'not in an operative condition. a

After the short-circuit across the conductors LI and L2 through'these conductors has been repaired, the dispatcher operates the reset key RK to elfect the energization of the reset relay R. The opening of the contacts 11 of the relay R'interrupts' the circuit through the contacts Ll an-d'L2 and heretofore described,

' lamp ST. The closing of the contacts aof the has been removed or the open circuit the closing of the contacts 0' and e of relay R causes the relatively high voltage negative reset impulse to be transmitted, over the conductors 7 LI and L2. Also, the closing of the contactsa of the relay R completes through conductor I59 an energizing circuit for the relay DI which effects, in the manner heretofore described, the deenergization of the relays R0 and RL.

At each of theremote stations which is not in its normal position, either therelay RL' orthe relay D! is energized so thatthe associated'glow tube G'T'is operatively connected across the conductors LI and L2 by either the contacts, 0 V

or the contacts c of relay D'l;

of the relay R'L Therefore, in each of these remote stations'the negative reset impulse efiectsthe energization of the associated relay DZ which, in a manner' heretofore described, causes the apparatus at the station to be reset to its normal position.'

In case the equipment at the end station is in its normal reset position so that the battery,

BAT is connected to the conductors LI and L2 when the negative reset impulse this reset impulse does not effect is transmitted,

of the short-circuit eiTect of the battery B'A'Tf However, the current through therelayX'l" is now suflicient to cause this relay to close its contacts a and complete an energizing circuit for relay D' l. The opening of contacts'b and d of relay. D'l removes the battery BA'T' from across the conductors LI and L2 so that the voltage across these conductors increases to a V the immediate operation of the glow tube G'T' thereat because value suflicient to effect the operation of the tube GT' and the associated relay D2. The en ergization of relay D2 then effects, in the manner heretofore described, the energization of relay X'2 and the resetting of the apparatus at the end station to its normal reset position when the reset impulse is removed from the conductors LI and L2.

While we have, in accordance with the patent statutes, shown and described our invention as I applied to a particular system and as embodying various devices diagrammatically indicated, changes and modifications will be obvious to those skilled in the art, and we therefore aim in the appended claims to cover all such changes and modifications as fall within the true spirit and scope of our invention.

What we claim as new and desire to secure by Letters Patent of the United States is:

1.. In combination, a plurality of supervisory control systems, each system including equip ment at a controlling station, equipment at a remote station and an individual set of conductors interconnecting the station equipments of the system, a spare set of conductors common to all of said station equipments, means for transmitting over said spare set of conductors an impulse code individual to each remote station equipment, means including means associated with each remote station equipment responsive to said impulse codes for selectively connecting to said spare set of conductors the remote station equipment individual to a transmitted impulse code, and means for connecting to said spare set of conductors the controlling station equipment corresponding to the selected remote station equipment connected thereto.

2. In combination, a plurality of supervisory control systems, each system including equipment at'a controlling station, equipment at a remote station and an individual set of conductors interconnecting the station equipments of the system, a spare set of conductors common to all of said station equipments, means for transmitting over said spare set of conductors an impulse code individual to each remote station equipment, means including means associated with each remote staton equipment responsive to said impulse codes for selectively connecting to said spare set of conductors the remote station equipment individual to a transmitted impulse code and for disconnecting the selected remote station equipment from its individual set of conductors, and means for connecting to said spare set of conductors the controlling station equipment corresponding to the selected remote station equipment connected thereto.

3. In combination, a dispatchers oilice, a plurality of remote stations, a separate supervisory control system interconnecting said dispatchers office and each remote station, each system including equipment at the dispatchers ofiice, equipment at the remote station and an'individual set of conductors interconnecting the two equipments of the system, a spare set of conductors common to the equipments of all of said s yEems, means at the dispatchers oiiice for transmitting over said spare set of conductors an impulse code individual to each remote station equipment, means including means associated with each remote station equipment responsive to said impulse codes for selectively connecting to said spare set of conductors the remote station equipment individual to a trans" mitted impulse code, and switching means at the dispatchers ofiice for connecting the dispatchers oilice equipment of each system to said spare set of conductors.

4. In combination, a dispatchers office, a plurality of remote stations, a separate supervisory control system interconnecting said dispatchers office and each remote station, each system including equipment at the dispatchers oilice, equi ment at the remote station and an indi vidual set of conductors interconnecting the two equipments i the system, a spare set of conductors common to the ments of all of said systems, means at the dispatchers office for transmitting over said spare set of conductors an impulse code individual to each remote station equipment, means including means associated with each r mote station'equipment responsive to said impulse codes for selectively connecting to said spare set or" conductors the remote station equipment individual to a transmitted impulse code and for disconnecting the selected remote station equipment from its individual set of conductors, and manually controlled switching means at the dispatchers office for disconnecting the dispatchers onice equipment of each of said systems from its individual set of conductors and for connecting it to said spare set of conductors.

5. In combination, a dispatchers office, a pinrality of remote stations, a separate supervisory control system interconnecting said dispatchers oilice and each remote station, each system including equipment at the dispatchers office, equipment at the remote station and an individual set of conductors interconnecting the two equipments of the system, a spare set of conductors common to the equipments of all of said systems, means at the dispatchers office for transmitting over said spare set of conductors an impulse code individual to each remote station equipment and a subsequent control impulse, switching means associated with each remote station equipment for connecting it to said set of spare conductors, means associated with each remote station equipment responsive to said impulse codes for selecting the switching means associated with the remote station equipment individual to the transmitted impulse code, means responsive to the control impulse for efiecting the operation of the selected switching means, and switching means at the dispatchers oifice for connecting the dispatchers office equipment of each system to said spare set of conductors.

6. In combination, a plurality of stations, a pair of conductors interconnecting said stations, selective means at each of said stations having a control relay normally connected between said conductors, a source of relatively low potential normally connected in series with the control relay in one of said stations, means for applying a relatively high potential across said conductors in opposition to said source whereby the current through said source and the associated control relay is reversed, means responsive to said current reversal for effecting the connection of said last-mentioned control relay across said conductors independently of said source, and means for transmitting over said conductors to said control relays impulse codes individual to each station to efi'ect the operation of the associated selective means.

'7. In combination, a plurality of stations, a pair of conductors interconnecting said stations, supervisory control equipment at each of said stations, selective means at each of said stations having a control relay normally connected between said conductorsa source of relatively low potential of a predetermined polarity connected I in series with-r-the controlrelay in one o'f'said stations, means for applying a 'relatively high potential o'f said predetermined polarity across said conductors. whereby the current through said source and associated relay is reversed, means responsive to said current reversal for effecting the connection of I said lastmentioned control relay across said pair 'of'conductors independ-V ently of said source; means for transmitting over said pair of conductors to said control relays an impulse code individual to each station, and means including said selective means for selectively connecting to'said pair'of conductors in responseto the transmission of an impulse code I only the supervisory'control equipment at the station individual to the transmitted coder 8; In combination, a plurality of stations, a

pair'of conductors interconnecting said stations,

supervisory controlequipment at'each of said stations, selective means at each of saidstations having a control relay normally connected between said conductors, a source of relatively low -potential'of a predetermined polarity connected in series with the control relay in one of said 7 stations, means for applying a relatively high 7 potential of said predetermined polarity across said conductors whereby the current through said source and associated relay is reversed, means responsive to said current reversal for effecting v the connection of said last-mentioned control relay across said pair of conductors independ- 7 ently of said source, means for transmitting over' said pair of conductors to said control relays an impulse code individual to each station, means including said selective means for selectively connecting 'to said pair of conductors'in response to s the transmission of an impulse code only the supervisorycontrol equipment at thestation' in dividual to the transmitted code, for

transmitting'over said pair of conductors arelease impulse of a predetermined character, and means responsive to said'release impulse at the 7 station in which .the associated supervisory con-' trol equipment is' connected to said pair of conductors for effecting the disconnection of that equipment therefrom.

9. In combination, a plurality of stations, a

pair of conductors interconnecting said stations, supervisory control equipment at each of said having a control relay normally connected bestationsgselective means at e'ach of said stations I tween said conductors, a source of relatively low potential of a predetermined polarityconnected in series with the control relay in one of said stations, means for applying a relatively high potential of said predetermined polarity across said conductors whereby the current through said source and associated relay is reversed, means responsive to said current reversal for effecting the connection of said last-mentioned control. r'elay across said pair of conductors independe" ently of said source, means for transmitting over said pair of conductors to said control relays an impulse code'individual to each station, means including said selective means for, selectively connecting to said pair of conductors in response to the transmission of an impulse code only the sponsive to said release impulse forhdis'connect ing from said conductors any supervisory control equipment that maybe connected thereto and for restoring the normal connection of said control relays to said conductors.

CLYDE E; STEWART; LEO D. .Wrn'rn;