US2111352A - Train dispatching system - Google Patents

Train dispatching system Download PDF


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US2111352A US559671A US55967131A US2111352A US 2111352 A US2111352 A US 2111352A US 559671 A US559671 A US 559671A US 55967131 A US55967131 A US 55967131A US 2111352 A US2111352 A US 2111352A
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Arthur H Adams
Elsie A Blake
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    • B61L7/00Remote control of local operating means for points, signals, or trackmounted scotch-blocks
    • B61L7/06Remote control of local operating means for points, signals, or trackmounted scotch-blocks using electrical transmission
    • B61L7/08Circuitry
    • B61L7/085Common line wire control using synchronous distributors
    • B61L27/00Central railway traffic control systems; Trackside control; Communication systems specially adapted therefor
    • B61L27/20Trackside control of safe travel of vehicle or vehicle train, e.g. braking curve calculation


@web l 193% @L J. BLAKE Err AL 2 TRAIN DISPATCHING SYSTEM Filed Aug. 27, 19:51
fIN-mf/ .95 fag WEST "193 ATTORN EY March M, 193g.V
6 Sheets-Sheet 2 ATTORNEY Much 159 3.933- E. J. BLAKE Erm. '2,111,352
TRAIN DISPTCHING SYSTEM Filed Aug. 27, 1931 6 Sheets-Sheet 5 ch 15 1938. E. J. BLAKE Er AL,
TRAIN DISPATCHING SYSTEM Filed Aug. l27, 1931 6 Sheets-Sheet 4 I l I l March 15, 1938, EI J, BLAKE ET AL '2,111,352
TRAIN DI SPATCH ING SYSTEM Filed Aug. 27, 1931 6 Sheets-Sheet 5 Ira-:zr 13.
INVEN OR my @jah BY a MF- Marc-vg ATTORNEY Malh 15, 1938. E, 1 BLAKE E1- AL Y 2,111,352
TRAIN DISPATCHINQ SYSTEM Filed Aug. 27, 1931 6 Sheets-Sheet 6 Patented Mar. 15, 1938 UNITED STATES 2,111,352 TRAIN DISPATCHING SYSTEM'.
Eli J. Blake, Haddonfield, N. J., and Arthur H.
Adams, Yonkers, N. Y.; Elsie A. Blake executrix of said Eli J. Blake, deceased; said Adams assigner to Elsie A. Blake, East r- 'ange, N. J.
Application August 27, 1931, Serial No. 559,671
11 Claims.
This invention relates to improvements in train dispatching systems, and more particularly to an improved communication arrangement between the control station and the substations connected therewith.
In the train dispatching system to which the present invention is applied, a control station is connected through a single circuit with a plurality of substations in such a manner that by means of suitable units, train signaling, track switching, and other traiiic regulating operations and the like, may be performed at any one of the substations in accordance with instructions transmitted from the control station. The control station is also apprised of the track and roadside signal conditions by means of so-called OS indications, i. e., by means of impulses 'generated at the control station and affecting indicators thereat but modied by the condition of the traffic regulating devices at the substations. The communication is by coded impulses directing a substation to perform certain operations or, at the will of the control station operator, informing the latter whether instructions have been carried out at a particular substation. Thus, the control station automatically and periodically tests traino regulating conditions at all the substations, i. e., obtains information on the positions of track switches, semaphores, track relays, etc.
If it is desired to effect changes at a substation, the operator at the control station adjusts an impulse transmitter to send code symbols typical for the desired substation and the operations to be performed thereat. A receiver is provided at each substation but only the receiver of the desired substation shall respond and .actuate the associated control units in accordance with the code symbols. For the sake of economy and rapidity of communication, the stations are interconnected by a single circuit over which time channels are established through which various stages of the communicating are performed. A definition of this term is given at the end of this specication. In accordance with one embodiment of the invention, the time channels are used in overlapping groups, i. e., the same time channel may serve in two different codes directed to two different results.
The time channels are used also for the purpose of conveying report signals to the control station. The traflic governing devices at the substations are associated with the control circuit over certain channels to actuate receivers at the control station in accordance with code impulses that have originated at the control station. During the same channel both control and report symbols may be sent. The faithful cooperation of the control station and substation equipments is insured by synchronously establishing the channels through which the communication takes pace and making eiiective only those substation channels through which communication should take place.
It will be obvious to those skilled in the art that the present invention may be modified in many respects without exceeding the scope of the appended claims. The dial and distributing switches may be provided with contacts that coopcrate with each other in response to other than rotary motions. In fact, any electromechanical circuit switching arrangement may answer the purpose. The expressions dial switches,v distributor switches, and the like, were arbitrarily chosen and are intended to apply to any circuit switching device suitable for the purpose. larly, the connections to the brushes and stationary contacts of the switches and distributors may be reversed, the lamps, polarized relays and the like replaced by other suitable devices, etc. In the systems herein described, direct current is used for certain, and alternating current for other, phases of the communicating and control operations. This alsc may be modified and varied to suit particular operating requirements. The synchronizing arrangements may be replaced by other arrangements which will insure the timely cooperation between the control station and the substations. The rail switches, track relays and semaphores, which are dened as trai-hc governing devices, may be altered or supplemented by other traffic governing or testing devices, etc.
These and other departures from the speciiic exempliicaticn of the invention will be apparent to those who may wish to employ the characteristic features of the invention. Most of these features are applicable to train dispatching systems of widely varying character and need not be employed in totality.
These and other features are diagrammatically illustrated in the accompanying drawings, only those parts of a train dispatching system being shown which are necessary for explaining to one skilled in the art one manner in which the invention may be practiced.
Fig. 1 shows the relation of the central control station, the line, the substations, and the operating units controlled thereby;
Fig. 2 shows in an elementary form means by which communicating time channels may be established between the central station and each operating unit in turn;
Fig. 3 and Fig. 4:, respectively, show arrangements for utilizing these channels to control track switch and to control a group of roadside signals;
Fig. 5 shows an arrangement for transmitting over one channel a report indicating the position of an operated unit;
Fig. 6 shows sending and receiving devices at the central station involving further refinements,
Simit whereby a greater number of control or report symbols may be transmitted in a given time;
Fig. 7 shows a detail modification of Fig. 6;
Fig. 8 shows means for maintaining synchronism of the substation apparatus with the central station;
Figs. 9 and 10 show arrangements provided at a substation for receiving control symbols and for characteristically affecting report symbols sent from the central station.
Fig. 11 shows a modified system in which direct current impulses are sent for control, and alternating current impulses for report symbols;
Fig. 11a is a detail of Fig. 11;
Fig. 12 is a modification of Fig. 11;
Figs. 13 and i4 illustrate the system in which the time channels are arranged in overlapping groups, and
Fig. 15 is a combination of Figs. 11 and 12.
The same reference numerals occurring in various gures designate identical or similarly functioning apparatus.
Referring to the drawings, Fig. l is a single line diagram indicating the major units involved in the system. I is a central control station from which all other units are controlled and to which their positions are automatically reported. 2, 3, and 4 are substations scattered along the railway route to interpret symbols transmitted from the central station and control adjoining groups of controlled or operating units, and to transmit to the control station reports indicating the actual positions of controlled units. 9 is a control channel which, in the present example, is constituted by a line circuit connecting the central station to all substations. It is grounded at its far end. I0 is a grounded battery at the central station which originates the energy for control and report symbols.
The central station comprises three sections or substation control panels, I2, I3, and I4, on which are localized the control and indicating units for substations 2, 3, and 4, respectively.
At each substation there is a track relay I6, to indicate whether an adjoining track section is clear or occupied. At the top of each central station section there is an indicating lampy 49 to indicate the position of the corresponding track relay. The indicating lamps are located in sections of a track diagram to show visually the relation of the section indicated to the actual tracks.
At substations 3 and 4 are shown semaphores I'I, adapted to operate in three positions, viz: vertical, as at substation 3; inclined, as at substation 4; or horizontal. In the corresponding sections of the central station are control handles 53 having three operating positions corresponding to the three positions of the semaphores or roadside signals; and immediately above are three indicating lamps, one of which is lit to indicate the position actually occupied by the semaphore. Instead of a single semaphore as drawn at each substation, there may be a group of such adapted to be set up in three combined positions Such as "clear for eastbound movement, clear for westbound movement, and stop.
At substations 3 and 4 there are also power operating machines I 8-I8 for operating track switches, and at the central station are corresponding operating handles 55, 55, each operable to two positions normal and reversed; but associated with each operating handle are three indicating lamps, as in the case oi signal control handles. The leftand right-hand lamps, respectively, indicate that the track switch is closed and locked in its normal or reversed position. The middle lamp indicates that the track switch is open or unlocked, which may mean that it is in the process of throwing over or that it has failed to complete its stroke and lock up ready for the passage of a train.
Each operated or reported unit I6, I1, or I8 is shown connected to its substation by a single wire; but it is understood that any number oi wires necessary for the desired control and reports may be employed. These connections are local and short. In addition to the units I6, I7, and I8, there may be also other traic regulating or indicating devices associated with the substations. The single control wire 9 with ground return as shown (or with metallic return), is suflicient for transmitting all necessary control and report symbols between the central station and the substations.
At each substation is shown a local battery I9 to furnish power for operating the track switches, railway signals and reporting mechanisms, subject to control symbols transmitted over the line circuit 9.
One section of the central station is thus actively adapted to control a typical group of railway traffic regulating or indicating units comprising one track switch (or group of switches working simultaneously), and one roadside signal or group of signals, and also adapted for receiving reports which indicate one of three conditions for each. In addition, it is adapted to receive reports indicating the position of one track relay. Part of these units may be omitted, as in section I2, or
other units up to the equivalent of the units associated with the typical section may be included.
Fig. 2 shows an elementary form of means by which a number of communication channels may be established successively between the central station and substations. 6 is a motor at the central station receiving power from battery I and driving a shaft 20 continuously. 8 designates a governor mounted on the shaft comprising centrifugal brake shoes 5 revolving within a stationary ring I I. At a predetermined speed the brake shoes are thrown into frictional engagement with the ring II by centrifugal force and further increase of speed is thereby precluded.
Mounted upon the shaft 20 and insulated therefrom are six movable contacts or brush arms 2 2 constituting, with the associated groups of stationary contacts, six dial switches 2l, 22, 23, 24, 25, and 26. A cam 2T also mounted upon the shaft 20 controls a follower 28 spring-biased to- Ward the cam. The follower controls a pawl 29 r which actuates a six-tooth ratchet 37 in such a manner that the latter advances one step at the end of each revolution of the shaft 20, and completes one revolution or cycle in six steps. The dial switches 2I-26 perform one complete revolution upon each revolution of shaft 20, er six revolutions per cycle of ratchet 31.
30 -designates a shaft driven by the ratchet 31, and 3l designates a six-point distributor dial switch having its movable contact or brush arm mounted upon the shaft 30 and insulated therefrom. The last mentioned brush arm is connected to a conductor 9, which is the control line 9 of Fig. 1. The stationary contacts or segments I, II, III, etc., of distributor 3I, as the brush arm revolves, connect the line 9 successively to the brush arms of dial switches 2|, 22, 23, 24, 25, and 26, each of which in turn, during the time it is connected to the line, connects successively with its own group of segments a, b, c,
etc. The brush arms of switches 2l, 22, 23, 24, 25, and 26 are aligned to contact simultaneously with their corresponding group of segments. Thus, at the instant illustrated, each brush arm contacts with its segment a. During six revolutions of the shaft 20 the control line 9 will be connected successively to each segment of switch 2l, then to each segment of switches 22, 23, 2li, 25, and 26 in turn.
66, 6l, 6l), and 68, respectively, are a motor, a battery, a shaft, and a governor, similar to the parts 6, l, 20, and 8 already described, but located at a substation along the railway. 63 designates a sleeve mounted upon the shaft iiil and driven thereby through friction. Upon this sleeve are mounted the insulated movable contact or brush larm of a distributor switch 6i and a single tooth ratchet 62. The latter may be engaged by a detent (i5, biased toward the ratchet by a compression spring 85, or the detent may be disengaged by the energizing of a magnet winding E9. A second sleeve 8| friction driven from the shaft 60, carries a single tooth ratchet 82 and a cam 64. The latter actuates a follower l2, a pawl 13,
. and the pawl in turn a ratchet i4, similar to the parts 28, 29, and 3l already described. The ratchet 'i4 drives a shaft 8@ and, by the intervention of friction, a sleeve il) mounted thereon. Upon the latter are mounted the insulated movable contact or brush arm of a six-point distributor switch 1l, and a single tooth ratchet i5. After making one revolution the ratchet (with the sleeve l and the brush arm of 1l is stopped by a spring-biased detent 'i6 until released by current in the magnet coil 11. A second detent S3 is coupled to detent i6 by a link 84 and can engage the ratchet 82 only when detent 'i5 drops into notch of l5, i. e., after six revolutions of ratchet 82 and one ci ratchet l5. When engaged, detent 83 restrains the cam 64 against further movement until released by the coil Tl. Current for the coil 'Il is supplied by a battery li and controlled by a polar relay 'i9 in series with the line 9, so arranged as to close its contact only when current flows through the line from the negative pole of a battery.
Each of the switches 2| to 25 is shown for illustration with ve equally spaced stationary contact segments and one large space from the fth segment to the rst. The distributor switch 6l is shown with 've stationary contact segments all symmetrically spaced in a group. In practice, all of these dial switches may have a larger number of stationary contact groups such as eleven. The governors 8 and 6% are so adjusted that the brush arms they control will advance from the rst segment a to the fifth segment in approximately equal time, but owing to the increased space from the fifth segment to the starting point on switches 2i to 26, they willV be somewhat later in returning to the starting point than distributor 6I or at least in no case, even with the maximum deviations from normal speed, will the latter arrive at the starting point later than the f former.
All parts are shown at an instant when the dial switches 2l to 2d have just reached their starting point on segment a. The cam 21 acting through the follower, pawl, and ratchet 23 and and 3l has just advanced the distributor 3i to the stationary contact segment I, and the line 9 is thereby connected through segment a of distributor 2l to the negative pole of battery 54, which is grounded at its midpoint. Before this instant, distributors 6| and H at the substation have advanced to segments a. and I, respectively, establishing a circuit from grounded battery 54 at the central station through distributors 2i and 3i, line 9, the coil of relay 19, distributors 'll and 6I, and through the winding of starting magnet 69 and the next section of line 9 to the succeeding substations, and ultimately to ground at the end of the line, as shown in Fig. l. Since the battery connection, as stated, was at the negative pole, current through polar relay 'i9 is of negative polarity and the relay Contact is closed, energizing magnet 'il by current from battery 'i8 to release the detents le and 83 which just previously held the distributor ll and the cam Ed at theirstarting positions. This occurs at all substations. At the same time, the line current passing through magnet SS has withdrawn the detent 65 which just previously held distributor 6i. This occurs only at one substation at a time: in the illustration it is about to occur at the one shown. Thus at the illustrated substation and instant two independently releasable elements are started rotating together and in step with central. These are: first, shaft di with stop ratchet 82 and cam Sii, which always revolves six times per cycle, giving six steps or one revolution to distributor l i; second, distributor 6l, which makes one revolution in one-sixth of the cycle and is still during iive-sixtns. Because it is contact I of distributor 1I that is connected to distributor 6i in the substation shown, the latter makes its revolution in the rst sixth of the complete cycle. At the ve other substations distributors 6l would be connected, respectively, to contacts II, III- VL of their respective distributors li. Distributors Gi in the six substations thus make single revolu tions each in a different sixth of the full cycle, and in step with one of the six revolutions of dials 2i-2i. In this revolution line 9 rst connects segment a. of ti and a of the corresponding central office dial 2i (as shown), or 22, or etc.; then b and bi, etc. Thus in each cycle five instants of electrical continuity (over line S) exist between ve central oice and iive substation conductors in a xed onetoone correspondence. This is frequently called dividing line time into channels. Time channels of this kind may be spoken cf and treated like separate wires, with the one limitation that no two coexist in time. Of each ive channels one (a) being used for the selhprotective purpose of starting substation dials in synchronism (more properly, in phase) with central office dials, there remain four to each substation for use, i. e., twenty-four pay load channels per cycle. Fig. 2 shows simple novel means for creating and protecting a number of individual usable channels between one central and each of several subsidiary stations, but without regard to how they may be used.
Summarifzing more concretely, dial switches 22 to 2t in turn will be connected to the control line f8 during the five revolutions in which distributor Si is iocked. During each of these revolutions a different distributor at a different substation may be connected to the line and may function and there being set up with each substation as many communication time channels, successively established, with the central station over line circuit 9, as there are stationary segments on each of dial switches 2|, 22 to 26, on each distributor 6|.
It should be observed that the negative pole of battery 54 is connected to the starting segment a only at distributor 2|, while the corresponding segments of distributors 22 to 26 are connected to the positive pole of battery. Since the relay 19 and the corresponding relays at other substations respond only to negative current, it follows that all revolution counting distributors 1| will be started in step simultaneously only during the first revolution of each cycle. Hence, even if. the entire system be thrown out of step (so long as the motors 66 continue to run), all substation distributors will run up to the starting position and stop at some time during the iirst six revolutions of the shaft 20. At the beginning of the next succeeding cycle all will start again in unison.
Fig. 3 shows connections which may be made over two channels to control a track switch in two positions. Current passes from ground, through central battery 54, to one of two points of selector switch 55, at central station, thence (at the instant when they are connected to the line), over one of two segments at central switch 2| to the control line 9, then by one of two segments in substation distributor 6|, through a local control circuit, to a relay operating coil 86 or 69, and so to ground. As shown, 86 was the coil last energized and its Contact linger 88 is closed to the front contact where it is held by current passing from ground through substation battery I9, through the front contact of nger 88 to a holding coil 81, thence through a back contact of nger 92 oi relay 89 to the normal operating wire 94 of the track switch machine, and so to ground. It is understood that a relay or other contact at the track switch machine must remain continuously closed while the track switch is in its normal position to maintain current through the holding coil 81.
If the selector switch 55 be now reversed and suflicient time elapse for the switch 2| and distributor 6| to revolve to the corresponding position, current will pass through the second local control circuit to the operating coil 89, closing contact 9| and opening contact 92 which interrupts the holding circuit through coil 81 and allows back contact at 88 to close. Thus a holding circuit is established from battery |9 through fingers 88 and 9| and the holding coil 90 to the reverse operating wire 93; and in general, when either operating coil 86 or operating coil 89 is energized momentarily, it interrupts the holding circuit of the other relay and establishes a holding circuit for its own relay; so that a momentary impulse through the one coil or the other serves to establish one or the other of the operating circuits, and the circuit established is maintained until superseded by energizing the other operating coil.
Obviously, instead of two track switch or roadside signal operations, switch 2| and distributor 6| may jointly control three or more operations. Fig. 4, for instance, shows roadside signal operating circuits controlled over three channels or control wires of selectors 2| and 6|, in accordance with the position of three-way selector switch 53. The diagram shows connections as they exist at the instant when the control circuit is closed through the upper contact of the selector switch and the corresponding segments of switch 2| and distributor 6|, to relay operating coil 95. The back Contact at 91 being open, interrupts the holding circuits for relays 98 and |02, which are therefore deenergized at the same time, and a holding circuit is established through the front contact of 91, coil 96, and back contacts at and |06, to eastbound operating wire |09. Operating wire |09 passes through any necessary relays (not shown) for establishing a roadside signal set up for eastbound train movements, and finally to ground.
If operating coil 98 is energized, the holding circuits for 95 and |02 are interrupted at back contacts of |0| and |00, respectively, and a holding circuit for 98 is established through front contact |00, coil 99, and back contacts 91 and |05, to the stop operating wire |08 which passes through the necessary relays to ground, setting all roadside signals at stop. It is understood that the local roadside signal control circuits are arranged in accordance with customary railway signal practice to indicate stop" automatically by failure of current or by any unsafe local condition. The energized circuit here described serves only for setting the roadside signals to stop by the initiative of the central control operator at a time when local conditions would permit them to indicate proceed.
If operating coil 02 is energized, it causes the holding circuits associated with 95 and 98, respectively, to be interrupted at back contacts |06 and |05. At the same time, it establishes its own holding circuit through front contact |04 and back contacts 91 and |00, through holding coil |03 and operating wire |01 (which includes the necessary relays to establish the roadside signal set up for westbound train movements), to ground.
Thus any one of the operating coils 95, 98, or |02, when energized momentarily, interrupts the holding circuit which may previously have existed for one of the other relays and establishes its own holding circuit, which holds its contact closed thereafter until released by energy in another operating coil.
Fig. 5 shows a distributor channel connected for transmitting one of two report symbols from a substation to the central station, by the use of central station energy. |09 is a contact inserted in the control line 9 when the latter passes through one segment of the distributor 6|. For example, |09 may be a contact of track relay |6 in Fig. 1, whose position it is desired to report at the central station. At the same instant dial switch 2| at the central station connects the line through the coil of polar relay |08 (which is of negligible resistance), to the positive pole of 25volt battery |01, which is grounded at its negative pole. A branch circuit connects the line through 100G-ohm resistance 2 to the positive pole of 50-volt battery 54, the negative pole of which is grounded.
When the contact |09 is open, as shown, there is a single closed circuit extending from ground through battery 54, resistor 2 and distributor 2| to the coil of relay 08, and thence through battery |01, to ground. The two batteries being opposed in this circuit, the net voltage acting in the circuit is the difference of their potentials, viz.' 25 volts. Resistance of all parts of the circuit other than resistor ||2 is relatively negligible. Hence the current flowing is 25+1000=0-025 ampere, passing upward through the coil of relay |08. The latter is so connected that current in this direction will throw its moving contact to the left or open position, and the relay is designed to have a substantial bias toward either operated position, so that it will remain open or closed as the case may be, until reversed by opposite current through the operating coil. Hence either position established during one momentary closure of the circuit at distributor 2| persists until reversed by opposite current during some subsequent closure of the distributor contact.
If the contact |09 is closed at the instant when the channel illustrated is established, the voltage of the battery |01, viz: 25 volts, will be applied to the line at dial switch 2| without appreciable intervening resistance. For illustration, the total line resistance is assumed to be 500 ohms. The current through the line will be 25+500=0.05 ampere.V The battery |01 is holding the switch 2| at a potential 25 volts above the ground, irrespective of current flowing. The battery 54 is maintaining its positive pole 50 volts above the ground, or 25 volts above the distributor. Hence there will be a current of 25+1000=0-025 ampere owing into the line through resistor H2. The remainder of the line current, viz: 0.025 ampere, must flow downward from battery |01 through the coil of relay |08. Hence the moving contact of relay |08 will move to its right-hand or closed position and remain there until reversed by current. A circuit will thus be established through battery and indicating lamp H will burn so long as each succeeding revolution of distributor 6| and switch 2| finds the contact |09 closed.
As previously stated, reports and indications are desired for three positions of each track switch and each group of roadside signals. In these cases two channels, two contacts like |09, and two relays like IJB may be employed, each relay following the position of one contact |09. There are thus four possible combinations of open and closed positions at the two contacts |09, and consequently four combinations of positions at the two relays |08. By the use of well-known connections of the relay contacts three of these four combinations may be used to produce the desired three indications at the indicating lamps.
Referring now to Fig. 6 which shows typical parts of a central control station, including refinements providing for more controlled and reporting units within a given time cycle, 20 is a shaft driven at accurately constant speed (for example, one revolution per 0.2 second), 2|, 22, 23, 24, 25, and 26 are six dial switches mounted on (and insulated from) the shaft 20, each consisting of a revolving brush arm e and a group of nine contact segments or spaces lettered a to z'. The brush arms z are so positioned that all make contact simultaneously with similarly lettered segments (or blank spaces) for example, at the instant illustrated by Fig. 6, each brush arm is in contact with its segment g. No means for driving the shaft 20 are shown. It may be geared, for example, to a motor provided with a centrifugal brake to limit it to a definite speed.
30 is a second shaft advancing one step for each revolution of the shaft 20, three steps constituting a complete revolution of the shaft 30. No means for driving the shaft 30 are sho-wn, but many well known mechanisms are available for the purpose, such as a three-tooth ratchet, a pawl and a cam on the shaft 20 adapted to move the pawl at the end oi each revolution of 20, advancing the ratchet by one tooth; or a source of continuous torque applied to the shaft 3U, a three-tooth escape wheel on the shaft, and an escapement actuated by the shaft 22 to permit one tooth advance for every revolution of the latter shaft. Mounted on the shaft 30 and insulated therefrom are three brush arms z associated with distributor dials 3|, 32 and 33.
9 is the control wire extending throughout the controlled territory and grounded at the far end. A double throw manually operated switch 40 connects the line at will to the brush arm of dial 23 (as shown) or directly to the segment w, f of the same dial, and thence to the brush arm of dial 33. At the instant illustrated, and the position illustrated for switch 40, the line is connected through segment g, i of dial 23 through neutral relay coil 4| and polar relay coil 42, to the positive pole of battery 44. The battery is also connected through a coil 43 opposed to the coil 42, and throughan artificial line or resistor 45 to ground. At the instant illustrated (and as described hereafter), the line 9 traverses a loop circuit associated with one controlled un' (at a substation) this loop having three con itions, each indicating one state of a controlled unit (e. g., a semaphore) at this substation, viz: closed through low resistance, closed through high resistance, and open circuit. In the case illustrated, assume the loop circuit connected into line 2 is in the rst condition; current passing from battery 44 through relay coils 42 and 4| to the line is a maximum. The resistor 45 is so adjusted that the magnetizing force exerted by the coil 42 under this condition exceeds that exerted by the constant current passing through coil 43 to the resistor; and the upper contact of the polar relay is closed. The upper, or energized, contact of the neutral relay 4| is also closed.
The high resistance in the second condition of the loop circuit is so chosen that it will reduce the magnetizing force, due to line current through the coil 42, to a value less than that in coil 43, with the result that the lower contact of the polar relay will close, but the neutral relay 4| will still be closed at its upper contact. However, if the line circuit is broken at the substation loop, both relays will be closed at their lower contacts.
The upper points of relays 4| and 42 are connected to the positive pole of battery 52 and the lower points to the negative pole, the midpoint of the battery being grounded, so that the moving contacts are positive when up, negative when down. At the instant illustrated the moving contact of the polar relay is connected through brush arm e and segment g` of dial switch 2|, through coil of polar relay 45 and through segment I and brush arm .e of distributor dial 3i, to ground. The polar relay 46 is designed to have a substantial bias toward its last operated position, so that either contact when closed remains closed until reversed by reversal of current in the operating coil. So long as the circuit just described is maintained, the relay 46 is closed to its left-hand contact when the upper contact of 42 is closed, and tothe right-hand contact when the lower contact of 42 is closed. If the operating circuit through 46 is then interrupted, its contact remains closed at the last operated position until the operating circuit is reestablished with the contact of relay 42 in the opposite position.
In like manner, the moving contact of relay 4I is connected through the brush arm and the segment g of dial switch 22, through the coil of polar relay 4l and through segment I and brush arm e of distributor 32 to ground. At the instant illustrated, when the dials 2| and 22 are closed through segments g-g and the distributor dials 3| and 32 are closed through segments I, I, the polar relays 46 and 41 thus assume positions which repeat the positions (at that instant) of relays 42 and 4|. When the distributor and dial switch arms vhave moved on to other segments, the relays 46 and 41 maintain their operated positions until the next occasion when their operating circuits are closed through segments g-g and I-I.
The moving contact of relay 41 is connected to the positive pole of battery 48, the negative pole 'being grounded. The right-hand stationary conn tact is connected through an indicating lamp 49 to ground. The left-hand contact is connected to the moving contact of the relay 46 and thence, according to the position of the latter, either through the right-hand contact and indicating lamp to ground, or through the left-hand contact and indicating lamp 5| to ground. Since the relays 46 and 41'repeat the positions of relays 42 and 4|, and since the latter are dependent on the resistance of the loop circuit which is connected at that instant in the line, the indicating lamps 49, 50, and 5| indicate the connection (or absence of connection) through the loop circuit at the instant when connections are established as described; if the loop circuit is open, neutral relay 4| will be down and indicating lampi 49 will light; if the loop circuit is closed through high resistance, relay 4| will be up and relay 42 down, under which condition indicating lamp 50 will light; if the loop circuit is closed through low resistance, relays 4| and 42 will be up and indicating lamp 5| will light. Furthermore, after the operating circuit through the coils of relays 46 and 41 has been interrupted at the distributor dials 2|, 22, the lighted lamp will continue to burn until the operating circuit is reestablished, at which time the resistance of the substation loop circuit will again determine which of the three indicating lamps shall light.
As described, the indicating lamps 49, 50, and 5| are controlled by operating circuits extending from the segments I--I of distributor dials 3| and 32 to segments g-g of dial switches 2|, 22. Similar circuits may extend from the segments I-I to each of the pairs of segments g--g to z'-z', controlling three groups of lamps successively as the brush arms z-z of dials 2, 22 revolve. At the end of one revolution of the brush arms of dial switches 2| and 22, the brush arms a of distributors 3| and 32 will advance to segments II-II. From these segments three other pairs of operating circuits, controlling three other groups of indicating lamps, may extend to the segments Q--g to ii of distributor dials 2| and 22. Three other groups of indicating lamps may be controlled by circuits terminating on the segments III, III of distributor dials 3| and 32, so that we may have in all three times three or nine groups of indicating lamps controlled by the line circuit 9 successively as the distributor brush arms revolve. If nine substation loop circuits are successively connected in the line, each group of the nine groups of indicating lamps will indicate the condition of the corresponding substation loop circuit when last connected, thereby indicating the position of the corresponding operating unit which controls that loop circuit. In the case of operating units having only two positions, such as track relays, the high resistance connection at the loop circuit may be omitted, together with relay 46 and indicating lamps 50 and 5|. 'I'he two required indications will then be produced by open and closed conditions of relay 41, resulting in dark and light indications at the lamp 49.
Instead of receiving reports to indicate the position of operating units at the substations,
it may be desired to transmit control signals or symbols to change the position of one or more controllable operating units. The manual switches 34, 35, 40, and 56 will then be thrown to the right. Switches 34 and 35 will open the control circuits for all indicating lamps. Switch will be instrumental in transmitting a symbol to render the desired substations receptive to control symbols as described hereafter, and switch 4|? will connect the line 9 through segment af of distributor dial 23 to the brush arm a of distributor 33. At the instant illustrated, line 9 will be connected through segment of the dial 23 and segment I of dial 33 to the brush arm of distributor dial 24 and thence over segment g to the upper blade of three-position control switch 53. When the brush arm of distributor dial 24 advances to segment h, the circuit will be transferred to the lower blade of control switch 53. Thus in the two successive time channels in which the brush arm of dial 24 makes contact at g and h, respectively, the control line is connected first to the upper and then to the lower blade of the manual switch 53. According to the position of the latter, it is connected to the positive or negative pole of battery 54 or to neither in the following order:
Upper position: Neither-negative; Middle position: Negative-positive; Lower position: Positivepositive As described hereafter, receiving elements at a substation are arranged to respond selectively to these three combinations of current during two time channels, establishing a distinctive roadside signal or semaphore indication in response to each combination.
. Similarly, segment i of dial 24 may be connected through manual switch 55 to the positive or negative pole of battery 54, and transmits a positive or negative current impulse over the control line to select one of two possible operations of another controlled unit at a substation. Similar branch circuits, including other control switches, may extend from segments g, 71 and i of dials 25 and 26. During three successive revolutions, as the dials 24, 25, and 26 are connected successively to the line through dial 33, nine control channels will be established. One twoposition operating unit, such as a track switch, may be controlled over any one of these channels; any three-position unit, such as a group of roadside signals, requires to be controlled over two such channels.
All of the connections thus far described have involved only segments g, h, and i of dials 2| to 26. During the passage of the brush arms over these segments, the line may be connected, according to the position of manual switch 40, to the relays 4| and 42 for receiving report symbols, or through dials 24, 25, and 26 to the control (such as 53, 55) switches for transmitting control symbols. During the contact periods at segments a to f, the line is connected to dial 33 irrespective of the position of manual switch 40, vand through one of dials 33 to dial 24, 25, or 26.
The iirst segments a are preferably separated from the last segments z' by an angle slightly greater than that between other segments. Segments a. of dials 24, 25, and 26 are permanently connected to positive battery and serves to start all substation distributor dials simultaneously for each revolution as described hereafter.
At each of the dials 24 to 26, two of the three segments b, c, and d are connected to positive or negative battery. The combination of positive, negative and dead segments at each dial is peculiar to that dial only and constitutes a calling code for one substation which is arranged to respond only to signals transmittedl by that particular dial. While I have shown only three dials, 24, 25, and 26, each arranged to call one substation, it vshould be noted that additional dials, with corresponding segments on the dials 3| to 33, may be provided for any required number of substations. The three segments b, c, and d assigned for calling codes will suffice for twelve distinct codes, viz: codes involving three choices of one dead channel and four combinations of polarity on the remaining two segments. To utilize fully these vtwelve .possible codes (since three-contact distributor 33 can divide line time between only three code sending dials like 24, 25, 26), a twelve-contact distributor must replace 33 and nine more dials like 24, 25, 26 must be added, but each having its b, c, d contacts differently connected. Distributors 3l and 32 also need twelve contacts each, to provide for enough sets of indicating lamps for twelve substations. If the three calling code segments b, c, d are increased to four, there will be six choices of two dead segments, or twenty-four distinct codes in all. If the number of control and report segments on dials 24, 25, etc., be increased from three (viz: g, h, i) to nine, each calling code may establish communication with a group of three substations instead of one. Thus, by increasing the total segments on each dial 24, 25, etc., from nine to sixteen, and by adding the necessary dials and terminal equipment at the central station, the system is adapted to control seventy-two substations instead of three.
If it is desired to transmit one or more control symbols immediately, without awaiting the moment in the automatic cycle when the controlled unit in question would be connected to its manual control switch at the control station, the shaft 3D carrying the distributor dials 3l to 33 may be advanced manually to the position corresponding to the unit to be controlled and held there during one revolution of the shaft 20. The dial selected by the master dial 33 will transmit the calling code for the desired substation and establish the necessary local channels for exchanging report or control symbols.
The segments f of dials 24-26 are connected through manual selector switch 5S either to the negative pole of the battery 54, as shown, or to the positive pole. The former connection constitutes a symbol to establish reporting loop circuits at the substations called, and thereby to control indicating lamps-such as 49, 5t, and 5l at the central station. The latter connection, always accompanied by the right-hand position of manual switch lli), (since tu and 56 are rnechanically interlocked) establishes connections at the central station and the called substations for transmitting and receiving control symbols to operate the controlled units. The segments e are permanently connected to an alternator H3. Their function is to bring all distributors in the substations into step with switches 2l to 26 at central, irrespective of their previous position,
as described hereafter. They also correct any small variation from synchronism which may have occurred since the previous correction by segment a. This latter function is unnecessary with nine segments per distributor as drawn for the sake of clearness, but desirable if a large number of segments is used.
It will be observed that the resistor 45 connected to the polar relay coil 43 corresponds in part with the articial line or balancing network'employed in certain duplex telegraph systems, but differs in that it is not required to balance the line characteristics but merely to produce an effect less than that of the normal line impedance and greater than the line impedance when the latter has been increased to several times its normal value. For this reason a plain resistance as shown, traversed by a constant current, will ordinarily suffice. However, in cases where exceptional line constants make it desirable, the resistor may be replaced by any well--known type of artificial line, as indicated at it in Fig. '7. The battery current may then be cut off after each step and reapplied simultaneously during each channel, y, It, z', both to the physical line 9 and the articial line 45, by a dial switch l5 revolving in step with dials 2l and 22 of Fig. 6. This means for simultaneous application of battery to both lines provides for quick balance (high speed and short channels) even in cases where the line constants of inductance and/or capacitance are unusually high.
Fig. 8 shows means provided to insure that a substation distributor t! will get in step with the switches 2i to 24 of Fig. 6, even if thrown out of step. Sil is the shaft which carries a single tooth ratchet b2 and the brush arm of distributor 6I. It is driven at approximately constant speed; for example, by a motor and governor similar to 66 and 68 in Fig. 2, but through a friction coupling (not shown, but see Fig. 2), which permits the shaft t@ to be stopped by the ratchet 62 without stoppage of the motor. The speed is so adjusted that the brush arm traverses the segments a to e and f to i, substantially in step with dial 2| vto 24 (Fig. 6). The spaces e to f and i to a are shorter than the corresponding spaces on dial switch 24. Thus distributor o! will always make contact at segments f and u.` somewhat before the corresponding contacts are closed at switch 24. A spring i;
biased pawl lt is located to stop the ratchet t2 at the instant when. distributor 6l connects the line to segment e. A magnet ll is provided to release the pawl 'i6 and is connected through a condenser lll to the secondary of transformer 55 l ifi, the circuit being tuned to respond selectively to the frequency of the alternator l i3 (Fig. 6). A moment after distributor 6l has stopped with its brush arm connecting the control line to segment e, dial switch 2d at the central station will connect alternator H3 through its segment e to the line. Alternating current passing over the line and through segment e of distributor 6I will traverse the primary winding of transformer H4 and thence flow over the continuation of control line 9 to the next substation, and ultimately to ground at the end of the line. Current thereby induced in the secondary of transformer I I4 will cause the magnet 'il to release the pawl 16, permitting ratchet 62 and distributor 6| i to start in step with switches 2| to 26.
Even if distributor 5l is entirely out of step, as for example, when the system is first started in operation with the distributors in random positions, it will revolve to segment e at some time within its rst revolution. There it will be held by the pawl 16 until it is released by current to which the magnet 11 is responsive. This can occur only when switch 26 connects the line over segment e to the alternator |I3, since current of the required character is supplied at no other segment. Hence, even under the condition assumed, distributor 6| will start its second revolution in step with switches 2| to 26.
When the distributor 6I has advanced until its brush arm makes contact at segment a, it will be stopped again by engagement of the ratchet 62 with the pawl 65, adapted to be released by current through the magnet 69. A moment later dial switch 24 at central will connect the line through its segment a to positive battery. Current will then flow over the control line and through segment a of distributor 6 I, through coils I I5 and I |6 and magnet 69 to the continuation of control line 9, and so through succeeding substations to ground at the end of the line. The magnet 69 being thereby energized will release the pawl 65 and permit the distributor 6I to start again in step with distributors 2| to 26. The coils ||5 and I|6 are for a purpose described hereafter.
The second starting pawl 65 just described serves to correct any variation from synchronism which may have occurred during approximately one-half revolution, but is not capable of bringing the commutator into step from a random position as may be done by the pawl 16, for the reason that it is responsive to direct current received through segment a of distributor 6|, whether the current originated at segment a of switch 24 or at any other segment.
As previously described, the segments b, c and d of switches 24-26 (Fig. 6), are used to transinit over the line during each revolution a distinctive symbol calling only such substations as are required to respond during that revolution of switches 2| to 26, the symbol consisting of positive or negative current on two of the three channels b, c, and d; and the segment f, together with manual switch 56, serves to transmit positive current over the line when control symbols are to be transmitted from the central station and negative current when report symbols are to be transmitted from the substation.
Fig. 9 shows the means provided at the substation for giving effect to these calling and selecting symbols.
At 6I is shown a portion of the distributor 6| of Fig. 8. At the starting segment a` positive current supplied by the central station passes through the line 9, through coils I I5 and I I 6, andthe starting coil 69 (see Fig. 8 also) through the outgoing portion of line 9 to substations beyond and ultimately to ground at the end of the line. The coils I5 and I I6 are operating coils of two polar relays biased to maintain their last operated position and are connected in each case to move the contact to its open position so that the relays are opened at the start of each revolution of the distributor. I8 and ||9 are additional operating coils on the same relays, connected, respectively, (in the case shown) to segments b and c of the distributor and to the-outgoing section of control line 9. It will be recalled that channels b, c, and d are reserved for the (twelve possible) calling codes of the system shown. Incidentally, the code or symbol necessary to call the one substation shown in Fig. 9 is not one of thosesent by dials 24, 25, 26, as shown in Fig. 6. Since the relays are opened at thestart of` each revolution, i. e., during channel a, they can both be closed only when the channels b and c have been energized during a given revolution by current of the particular polarities required to close the contacts |20 and I2I; in other words, both contacts will be closed only during that particular revolution when the calling symbol which includes these two channels and this polarity combination is transmitted from the central station.
When closed, during one particular revolution, as described, the contacts I 20 and |2| establish and maintain during that revolution only a local circuit from grounded battery I9, to a polar relay contact |23 controlled by a coil 22 which is connected in series with the control line 9 during the channel established by the segments f of dial switches 24 and 6|. If positive current is received during this channel, contact finger |23 will swing to the left as shown, completing the local circuit through neutral relay |24 to ground, to set up circuits for receiving control symbols during the remainder of the revolution. If negative current is received, finger |23 will swing to the right and complete the local circuit through neutral relay coil |25, which sets up loop circuits for characteristically affecting report symbols during the next few channels.
Fig. 10 shows segments g to i of distributor 6| and loop circuits placed in series with the control line 9 through these segments during successive operating stages of the distributor, either to receive control symbols or characteristically to affeet report symbols, viz: from segment i through polar relay coil |26 or through report switch |32 to the outgoing portion of control line 9; from segment h through polar relay coil |28 or report switch |33 to the same point; and from segment y through polar relay coil or report switch |35 to the same point. The relay coils |26, |28, and |30 are bridged by back contacts of relay |24, which is shown energized in Fig. 9. The back contacts are therefore open and current through the loop circuits must traverse the coils. Report switches |32, |33, and |35 are bridged by back contacts of relay |25 which is shown deenergized in Fig. 9. The report switches are therefore shown short-circuited and ineffective.
Line current through the channels g, h, and i respectively, traverses the relay coils |30, |28, and |26 and determines the positions which their respective contact fingers I3I, |29, and |21 will assume, and which (by virtue of inherent bias toward their operated positions) they will maintain until reversed by opposite current in their operating coils. Thus the position of the contact lingers |3I, |29, and |21 is determined by the polarity of line current through the corresponding channels g, h, i in that revolution of dial 6I after relay |24 has been energized as described by the calling symbol for this substation. The coils |26, |28, and |30 are connected to close their respective contact fingers downward when the current through them is positive, upward when negative. As shown, the finger |21 has last been actuated by positive current and is down, connecting the local battery I9 to the reverse operating circuit |38 for the track switch. Had negative current been received in channel i, finger |21 would have been up energizing the normal track switch operating circuit |31.
Operating coil |28, as shown, has last received negative current over the lower blade of control switch 53 (Fig. 6) and channel h, and its contact nger |29 is therefore up, energizing local control wire I 39to set up roadside signals for east- Civ bound traic. This occurs irrespective of the position of iinger iti; but when finger |29 is closed downward by positive current in its operating coil, it interrupts the circuit to the eastbound wire and connects the battery i9 to contact iinger E35. The up or down position of the latter, according as positive or negative current owed through coil im during channel g determines whether battery will now gc on local wire lil that sets the roadside signals for westbound trafiic, or on local wire Mil that sets them to Stopn Response to control symbols over channels g, h, and i, as just described, was dependent upon the previous receipt of positive current through manual switch G (Fig. 6) and channel f, causing contact finger |23 (Fig. 9) to close at the left and energize relay EM. When the manual switch 5t is closed to the left, as shown in Fig. 6, negative current will flow in channel f, and contact finger |23 will close at the right and energize relay |125. The relay coils |26, E28, and i3d will then be short-circuited by contacts of the deenergized relay |26! and therefore rendered ineffective; but the contacts of relay l25 will be open and the impulses sent during channels g, h and i, respectively, wili be characteristically affecte-d by the positions of report switches |32, E33, and |35. Report switch |32 may be, for example, a contact of a track relay used to indicate whether a track circuit is clear or occupied. When open, as shown, it will cause an indicating lamp such as 4S) in Fig. 6 (but controlled over channel i) to light. When closed, it will cause the lamp to be extinguished.
Report switch i3d may be actuated by the mechanism of a track switch operating machine, and when closed through the line resistance only, as shown, it may indicate that the track switch is closed and locked in its reverse position. An indicating lamp similar to 5i (Fig. 6) will then be caused to light. When closed through high resistance G3i-i it may indicate that the track switch is unlocked. An indicating lamp similar to 50 will light. When open it may indicate that the track switch is closed and locked in its normal position and may cause the indicating lamp corresponding to d@ to light.
In like manner the report switch |35 may be actuated by a roadside signal mechanism, or equivalent circuits may be closed through relays associated with the roadside signals, and the three resulting conditions in the loop circuit, viz: open, closed through high resistance, and closed through normal line resistance may control the set of indicating lamps associated with channel g at the central station. The three indicating lamps associated with channel g and report switch |35 may indicate, respectively, that the signals are set up for eastbound traiiic, set up ior westbound traffic and set at stop.
In resum, i. e., of the Figs. 6 to l0 disclosure, using dial switches of only nine positions, as shown in. Figs. 6 to l0, there could be handled twelve substations (three shown), central being able at each to control one track switch (or group of such) to two positions and one roadside signal (or group of such) to three positions; central also receiving continuously from each in succession (except when sending control symbols or codes), automatic reports about one track switch. (or group) having three connections, about one y roadside signal (or group) having three conditions, and about one track relay having two conditions.
Nine time channels to each substation, set up by the synchronous operation at central and at substations of nine-position revolving dial switches, are shown utilized as follows:
Positive on channel a starts off all substation dials in step with central. (Fig. 8, magnet E9 and detent 65). substation dials gain slightly on central, so will be already stopped, and will start each cycle exactly with central. This impulse on a also restores to normal or open contact condition (wiping out the influence of past codes), the two code receiving polar relays at all substations, (|29 and |2|, Fig. 9). It is by the twelve possible combinations of polarities in each of these two relays with their connections to the three time channels b, c, d, that each substation is differentiated from the others and is adapted to answer just one of the twelve symbols or codes.
Positive and/or negative impulses on channels o, c, d, constitute the substation selecting symbols or codes. Each one of these (twelve possible) is determined by the positive or negative battery connections on two out of the a., b, c, segments of dials 24, 25, etc.
Alternating current on channel e puts all substations in synchronism with central, even if badly displaced. f-
Positive or negative goes out on channel f, according to the right or left position of manual switch 56', and this choice determines whether the impulses to be sent on channels g, h, z', shall cause movement of roadside signals, track switches, or the like, or shall light indicating lamps at central to report conditions of the track switch, track relay, semaphore or the like.
Channels g, h, when manual switch 56 is in the right-hand or control position, carry the codes that actually determine motion of roadside signals at the selected substation. As illustrated, only three codes are sent on g, h, (eight are possible, using either of two polarities on either or both of two channels). More are not needed to control roadside signal conditions and would complicate substation receiving arrangements.
Channel i, with manual switch 55 in righthand control position, carries a two-unit code (positive or negative) to set the track switch to normal or reverse.
Channels g, h, i, when manual switch 5S is in left-hand or report position, carry no codes but are used as mere individual channels for connecting a battery at central to individual substation loops, each associated with a track switch, a roadside signal, or a track relay, during which connections these three loop impedances are compared, individually, to an artiiicial line at central and their conditions individually recorded at central on lamps.
Fig. 11 shows a modied system in which positive and negative direct current impulses during three time channels transmit the necessary symbols to control the operating units at one substation, and in which alternating currents superposed on the direct current during the same time channels transmit the necessary report symbols to indicate at the central station the existing positions of the operating units. As in Figs. 6 to 10, the central station automatically transmits a program of several cycles, each of which includes a, calling signal for one or more substations, followed by the necessary channels for control and report symbols at the called substations; and provision is made for manually advancing the program to any particular cycle if immediate communication with the corresponding substations is desired. The calling code in each cycle consists in current flow during three among seven channels assigned for this purpose; and completion of the appropriate calling code automatically starts the receiver at the called substations in step with the central station transmitter,
In some applications of this invention, the control line will extend for many miles and have a resistance of a thousand ohms or more. Certain magnet windings at all substations are required to function simultaneously. If all of these windings were connected to the line in multiple, the required resistance of each winding for ecient operation would be much higher than is readily attainable. Therefore, all substation windings are shown connected serially in the line, under which condition the most eicient resistance values are easily attainable. On the other hand, contact devices are required in certain substation circuits Which function one at a time to transmit report symbols. I'hese circuits are shown as branches from the line to ground in order to keep the line clear of the large number of contacts in series which it would otherwise include.
We have chosen to illustrate a substation receiver and transmitter which is coupled to the line only by the branch circuits for report symbols already mentioned and by two magnets which serve to translate line impulses into mechanical movements. All necessary functions of interpretation and selection are accomplished mechanically by these movements. However, it will be readily understood that the same functions could be accomplished by a dial switch and a group of relays similar to those shown in Figs. 8 to 10.
2|, 22, and 23 in Fig. 1l are three dial switches at the central station, driven at uniform speed by a common shaft 20. 3| is a three-point dial switch arranged to connect the brush arms of dials 2| 22 and 23 successively to the control line 9. It is advanced one step automatically at the end of each revolution of dials 2| to 23 by cam 21, follower 28 and pawl 29 acting on ratchet wheel 31, as shown in Fig. 11a; but a slip coupling F in its driving connection permits of manual setting by knob K to connect either dial to the line when desired. Each of the dials 2| to 23 has eighteen segments lettered from a to T. The segments shown as White circles are always energized with either positive or negative potential, whereas the black circles represent segments which .are always dead. On each dial, nine segments a, to i, transmit a calling signal for the substations associated with that dial. Segments a and i are dead on all dials, and serve to mark the start and nish of the calling signal. Of the seven intervening segments, a distinctive combination of three segments is connected to positive battery and constitutes the selective calling symbol for the associated substations. 'I'hree dials are shown, distinguished by three call combinations, viz: bod, bcc, and bcf; but thirty-five combinations of three segments among seven are available, so that the seven calling segments will sufiice for any number of dials up to thirty-five.
Each of the segments :i to r is energized through a transmitting and receiving channel as described hereafter, but the connections are indicated only for segment r of dial 2|.
As the brush arms of dials 2| to 23 connect control line 9 to each live segment in turn, direct current ows from battery 54 over the control line to condenser |51 at the first substation. Since it is blocked by the condenser it takes a shunt path around it through the coils of polar magnet |63 and neutral magnet 69. In the same manner it traverses the magnet coils of each substation in turn and finally goes to ground through a network |58|59 at the end of the line and returns through the earth and through alternators |42 and |43 to the center of battery 54. During certain time channels polar magnet |63 selects local operating circuits in response to control symbols received over the line. Neutral magnet 69 and associated parts respond selectively to calling codes transmitted during channels a to z' by the central station dial switches, and start sending and receiving elements for report and control signals only during those cycles which include the distinctive calling code for this substation. Magnet 69 releases with a slight time lag sufficient to bridge the interval between two successive live channels, even when they are of opposite polarity, but must release positively when current is interrupted for the duration of one time channel. If necessary mechanical and electromagnetic inertia do not produce the required time lag, the electromagnetic inertia may be increased by well-known means such as a short-circuited path surrounding a por tion of the pole face.
|56 is a shaft driven by local energy at slightly more than two revolutions per revolution of central station dials 2| to 23, and hence completing one revolution in slightly less than nine time channels. |60, I6 and |62 are a group of Wheels rigidly coupled one to another and frictionally coupled to shaft |56, upon which they are mounted. |64, |65, |66, and |61 are four pawls attached to a common rock shaft |68 and jointly actuated by neutral magnet 69. When the latter is energized, pawl |64 engages the single tooth of wheel |60; when it is deenergized, pawl |65 engages the three intermittently spaced teeth of wheel |6|. During nine successive channels y' to r in each cycle transmitted from the central station, magnet 69 will be energized. Irrespective of its previous position, wheel |60 will be stopped by its pawl at some time during this period, and will be released at the first dead channel, a. Thereafter its progress will depend upon wheel |6I. If live channels occur coincidently with the points of engagement for the three teeth of this wheel, the three wheels |60, |6|, and |62 will advance without interruption until Stopped again by pawl |64 at live channel 9'. For teeth as drawn, this condition will obtain during the cycle transmitted by dial 2 in which b, c, and d are live channels. In this case the projection on wheel 62 will lift follower |69 during channel i and thereby release pawl |10 to which it is coupled by rock shaft |1|. If any other calling code than bcd is received, wheel |6| will be delayed at one or more of its three teeth, and cam wheel |62 will release pawl |10 during one of the live channels y' to 1".
|1| is a sleeve mounted upon shaft |56 and frictionally driven thereby. Upon it are rigidly mounted three toothed wheels |12, |13 and |14, a brush arm of dial switch 6|, and a cam |15. Wheels |12 and |13, respectively, are engaged by pawls |66 and |61, actuated by magnet 69. Wheel |14 is engaged by pawl |10. After any group of nine live channels 7 to 1' these wheels will occupy the position shown with wheels |12 and |111 engaged by their respective pawls, and can be released only when both pawls are released simultaneously. Pawl |66 is released only during dead channels, and pawl |1|l .at a time dependent upon the progress of wheels |66, |6|, and |62. As already stated, this time is time channel z' during cycles in which the distinctive calling code for this substation is received, and one of the live channels y' to r during all other cycles. In the former case, pawls |66 and |10 will be released simultaneously and sleeve |1| will be allowed to start. In the latter case, the sleeve will remain locked by pawl |66 at the time it is released by pawl |18. In other words, the sleeve will start if the distinctive call for this station has been received, and not otherwise. At other suhstations having other tooth arrangements on the wheel |6|, sleeve |1| will start responsively to other calling codes.
As in the cycle transmitted by dial 2|, the dead channel may be preceded by other dead channels. In this case pawl |66 will have been previously released when pawl |16 is released by the appropriate calling code. The starting time for sleeve lli will depend solely upon wheel |62, and ultimately upon the speed of shaft |56, after the release of wheel |60 eight time channels earlier. In order to correct the slight gain of shaft |56 during this time with respect to the time channels of line impulses, pawl |61 is arranged to engage wheel |13 and stop it at a position corresponding to time channel y' and release it accuretely in step with that time channel.
For clearness of diagrammatic representation, we have shown wheels |60, |6l, and |62 and wheels i12, |13, and |16 with progressively increasing diameter; but in practice we prefer to make all these wheels of equal diameter.
When released as described, sleeve |1| advances for one revolution in substantial synchronism with the time channels of line current. During this revolution dial switch 6| establishes three local channels p, q and r, for report symbols; and cam acting through follower |16 and rock shaft 11 releases pawl |18 and thereby establishes one mechanical channel, viz: channel 1', for receiving a control symbol. 1
@t6 is a second sleeve loosely mounted upon ait |66. Attached to this sleeve there are three wheels |18. |88, and iSi, and a triple contact brush |89. This assemblage is driven by a spring lli? attached to a hub |82 which is frictionally driven by the shaft, so that the spring always wound and ready to advance sleeve |86 nidly whenever the latter is not restrained. W eel l8| is normally held at one of six positions hv the pawl llt until the latter is released, as already described, at channel T. If the current received by polar magnet |63 during this time channei is positive, pawls |83 and |84 will retain ions in which they are shown, with the till locking wheel |19. No movement of 986 will occur, and th-e triple brush |89 continue to contact with its upper segment, maintain a circuit from battery I9 to local wire |61, which may be the normal operating wire for a track switch or some other operating unit. On the other hand, if current through the polar magnet |63 is negative during time channel r, the position of pawls |83 and |84 ill reverse. Sleeve |86 will advance 60 and me to rest with pawl |84 engaging wheel |80, ai the battery connected through brush |89 to the lower contact segment, supplying current to wire ist. This Wire may operate the track switch to its reverse position. In either case pawl |18 will again engage wheel |8i before the succeeding time channel, and will thereby maintain the status quo until the next recurrence of channel r in a cycle which includes the calling code for this substation. Other units similar to sleeve |86 and the associated parts may be provided Jfor other channels such as ,o and q, and may be jointly controlled by the one magnet |63.
It will be readily recognized that the contact brush |66 with its controlling elements is functionally equivalent to a polarized relay and a dial switch segment, since it selects and holds one oi two contacts in accordance with the polarity of line current during a particular time channel. The mechanical contacts described have certain advantages in that several contacts may be controlled during successive time channels by the same magnet, and in that contact movement and pressure are derived from local energy and are not limited by the energy which can be transmitted over the control line. Hence, we prefer to design the contacts with suicient capacity to control the local operating circuits directly without intervention of secondary relays or contactors.
The upper portion of Fig. il shows the local circuits at the central station over which current is supplied to one signaling channel T. It will be understood that similar circuits extend from each oi segments :i to r on each oi the dials 2| to 23 to the positive and negative terminals of battery 66; but the battery and two alternators |42 and |63 are common to all of the channels. Each signaling segment is connected to the middle fixed Contact of a corresponding control switch 55. The right and left xed contacts, respectively, are connected to the negative and positive poles of battery' E4, while the centre of the battery is connected through alternators |66 and |42 to ground.
For each segment and its associated control switch there is a network as shown connected between the blades of the control switch. When the latter is thrown to the left, direct current flows from positive battery to the left switch blade, and thence from left to right through the network to the right-hand switch blade, whence it flows over the dial switch segment to the line 6. This may be regarded as the positive direction of current in the line, constituting one of the two irect current symbols which may be transmitted over the line. The other symbol, viz: negative current flow is transmitted when the control switch SE is thrown to the right. Current then hows outward from the centre of the battery through alternators M3 and 42 to ground, and the return current reaching the central station over the control line ii passes through a dial switch segment (which, for the channel illustrated will be segment r) to the left-hand blade of control switch 55, and thence from left to right through the network to the right-hand switch blade and the negative pole oi battery 5d. It should be observed that reversal of control switch reverses the direction of current flow in the control line 6, but does not change the direction of fiow through the network which is from left to right in either case. Thus the control switch determines the polarity of current in control line Q during time channel r and thereby determines the local control circuit |31 or |38 which will be selected by contact device |89 at a certain substation; but it does not ailect the network, which comprises the receiving Ielements for report symbols over channel r.
The network includes three branch paths from left to right, joined at their midpoints by a tie conductor |56. The first path includes coils |44 and |41 and reactors |45 and |46; the second path, condensers |50 and |5|; and the third path, coils |52 and |55 and rectifers |53 and |54. Of these paths only the rst is conductive for battery current, the second being blocked by condensers and the third by rectiers opposed to battery current flowing from left to right. |48 is a polar relay Contact responsive jointly to the coils |44 and |52, and |49 a polar relay contact responsive jointly to the coils |41 and |55. These contacts may control indicating lamp circuits similar to those shown in Fig. 6 for the relays 46 and 41. When actuated by battery current flowing through the upper coils only as described, both contacts move to the left as shown.
Superposed upon the battery potential are 500 and 750 cycle alternating potentials induced by the alternators |42 and |43, respectively. The resulting alternating components of current in the line are dependent upon the impedance of the line and connected branches. As already mentioned, the magnet coils at each substation are bridged by a condenser |51 offering little impedance to alternating current of either frequency, so that the line impedance at any given substation is kept as small as possible. The ground connection for direct current at the end of the line is made through a network consisting of two meshes |58 and |59. These two meshes are tuned substantially to prevent the passage of 500 and 750 cycle currents, respectively. Hence the alternating current in the line is substantially limited to that which can ow through a branch circuit at some substation. During time channel r, such a branch may be established at one substation through dial switch 6| and report switch |33. The latter may be actuated by the track switch which is controlled during the same time channel by control wires |31 and |38. The centre position (as shown) of the report switch may indicate that the track switch is unlocked, and may open the branch circuit. In this case no appreciable alternating current will flow into th-e line during time channel r. If the track switch is locked in its normal position, the report switch may establish a branch path to ground through a circuit ISI', tuned to offer little impedance to 500-cycle current, but high impedance to 750- cycle current. A substantial 500-cycle component of current will then flow into the line during time channel 1'. When the track switch is locked at its reverse position, report switch |33 may establish a path |62', tuned to pass a substantial 750- cycle component, but no material 500-cycle current. Thus, according as the track switch is normal, reversed or unlocked, there will flow into the line during time channel r a substantial 500- cycle current component, a substantial '750-cycle component, or neither. It should be noted that the branch circuits IBI and |62 are blocked for direct current by condensers included in both circuits.
The mesh |56, |50, |44, of the receiving network is tuned to offer very high impedance to 500-cycle current, but low impedance to 750- cycle current. Accordingly, a substantial 500- cycle current ilowing intoy the line will cause a large drop oi potential in this mesh, which will be impressed upon the branch path comprising tie |56, rectifier |53 and coil |52. The coil |52, the voltage induced by 500-cycle alternator |42, and the circuit constants are so chosen that,
under this condition, coil |52 will overbalance coil |44 and cause the contact |48 to reverse. In like manner, the mesh |56, |5|, |41, and |46 is tuned to oppose the ovv of '750-cycle current and thereby cause the coil to reverse the contact |49 when a substantial current of this frequency ilows into the line. Thus, either one of the contacts |48 and |49, or neither, may reverse during the contact period at segment 1', according as substantial current of 500 cycles or 750 cycles or neither flows into the line; and hence, according as the track switch is normal, reversed or unlocked.
As described, a single channel 7' is capable of transmitting simultaneously the necessary control symbol to govern the operation of a track switch and the necessary report symbol to indicate its actual position. In like manner, two channels may govern a group of signals operating in three positions; and one of these channels may indicate at the central station the actual attainment of either position. Ihe other channel may indicate the position of a track relay. Thus, three time channels, p, q, and r, surrice for transmitting all necessary control and report signals for one typical substation as shown in Fig. l. In the same manner, channels y', 7c, and l, and channels m, n, and o, of cycle 2|, may be used for communication with two other substations; or control and report symbols may be exchanged with three substations in all during one revolution of either dial at the central station. If the dials are adjusted to complete one revolution in 0.4 second, control symbols may be sent and report symbols received from any given substation within this interval by manually setting dial switch 3| to the desired cycle. Since the control and report symbols are simultaneous, the latter will indicate the initial position of the operated units, not the position they may assume in response to the control symbols. Completion of the desired operation will be reported during the rst recurrence of the same cycle after the actual completion of the operation. If desired, dial switch 3| may be held stationary, causing repetitions of the same cycle until completion of the operation has been reported. In this case, the report will be received within fourtenths second after actual completion of the operation. If the automatic programas det/ermined by dial 3| is not interrupted, communication both ways will be established at intervals, depending upon the number of cycles included in the program. For example, thirty-live cycles would provide for 105 substations. At a speed of one cycle per 0.4 second, the positions of operating units at each substation would be reported every 14 seconds. Control symbols, as determined by the positions of control switches such as 55, would be reaiirmed at like intervals, but would change the local control circuits at the substation only when the positions of control switches had been changed. In effect, the operating units will be continuously responsive to the position of the control switches with a possible time lag of 14 seconds, and will continuously report to the central station With a like time lag.
In Fig. l1 We have shown a duplex system in which control signals and report signals are transmitted simultaneously over the same channels, but the same type of cycle, comprising a substation call followed by control or report signals, is equally adaptable tc other signal arrangements. For example, as in Fig. 6, and as described hereafter in connection with Fig. 13, the automatic program may consist of report symbols only, or
of control symbols only, and provision may be made for manual interruption of the one class of signals and substitution of the other class. Furthermore, the particular choice of symbols we have described is largely arbitrary. We have described for substation calls a code of positive and dead channels; for control symbols, positive and negative direct current channels; and for report symbols, 50G-cycle and 'Z50-cycle alternating current or neither. But the same current symbols could equally Well be distributed in other ways among the same functions. For example, if the polar magnet |63 and the neutral magnet 69 are interchanged, and the former biased to take its positive position when deenergized, calling signals may be given by negative and zero or negative and positive currents, and control signals may be given by positive and zero currents. Or with suitable modifications of the pawls and of the symbols transmitted by the central station, polar magnet |93 may be replaced by a neutral magnet shunted by a rectier to render it unresponsive to current of one polarity and magnet 69 may be shunted by a rectiier to render it unresponsive to current of the opposite polarity. The only essential limitation on the assignment of symbols for calling, control signals and report signals, is that wheels |69 and |12 shall engage their pawls throughout the group of time channels assigned for control and report symbols, and wheels and lli-l shall engage their pawls at certain other times as required for response to calling signals. In the code described, zero current is a symbol reserved exclusively for calling signals, but any other one symbol may be reserved for the same purpose.
The specific cycle described in which nine channels are assigned for call signals and nine for control and report signals, is advantageous in that it permits control of a large number of substations without involving synchronism over a longer period than nine time channels from any given start; but many other assignments 'of channels are obviously possible, for example, eight time channels for calls and twelve, or `three substation groups, for control. This combination permits distinctive calls for twenty groups of four substations, eighty substations in all. The num- -er of calling channels may be less than the number of control channels, but should not be more, because the receiving device for calls must reach its starting point from any position within the period assigned to control signals.
Fig. lf2 shows a modification of Fig. l1 in which polar magnet winding |63 is replaced by two opposed windings |53 and |635, and neutral magnet winding |59 is replaced by two windings 69 and $92. The windings |63 and 59 are energized by pulsating current derived from transformer winding |921 and controlled by an electric discharge relay or valve |92. Windings |53.a and 69a are energized by transformer winding |93, subject to control by a discharge relay or valve |9fi. |95 is a primary Winding inducing potential in both secondary windings |9| and |93. |99 is a source of alternating current, and may be, for example, a pair of slip rings connected to the armature of a high speed direct current motor connected through reduction gearing to drive receiver shaft |55 (Fig. 11).
The valves |92 and 196i are of a relay type such as the socalled Thyratron. They are characterized by the fact that current starts in the plate circuit only when the grid potential, with respect Y to the lament, is above a certain critical value,
but that plate current once started will persist irrespective of grid potential until the succeeding Zero point of the plate current Wave. Alternating potential as described is applied to the plate circuit in order that such zero points may occur at frequent intervals; and in order that the times of current start and interruption may approximately coincide with the make and break times at the central station dial switches, the frequency impressed on the plate circuits should be relatively high, insuring several positive half waves during each time channel. A bias battery |9l is included in the grid connection of each valve and adjusted to prevent the flow of plate current during dead channels with the line at ground potential. Each valve is further provided with a lament battery |98.
The filament of valve |92 is grounded and its grid is connected to control line 9. When the potential of the latter is positive, current will iiow through the plate circuit and through magnet coils |63 and |59, producing the same effects as positive line current through the corresponding coils in Fig. ll.
The grid circuit of valve |9l| is grounded, and the filament is connected to the control line. When the line is negative with respect to ground the grid becomes relatively positive. Current Hows through the plate circuit and through coils Milla and 69a, producing the same effects as negative line current in the corresponding coils of Fig. 11.
In order that positive or negative peaks in the alternating components of line potential may not cause current to flow through the plate circuits of the valves, the potentials of central station battery 54, bias batteries |91, and alternators |42 and |43 must be so coordinated that the grid potential of one valve or the other will be below the critical value required to start plate current throughout the pulsations of the resultant line potential.
It is to be observed that the iilament to grid circuits of the valves |92 and |94 constitute branch circuits from the line to ground, and that two such branches are always connected to the line at each substation. It was previously stated that the high resistance of the line and the limited resistance for which coils can conveniently be wound made this type of multiple circuit undesirable for coils connected directly to the line. Gwing to the exceedingly high resistance of the grid circuits in the valves, the same objection does not obtain in Fig. 12. Since the grid circuits are controlled by line potential rather than line current, the ground connection through network Mii-|59 at the end of the line is unnecessary in the present case.
in Fig. 13, we show another modification in which all control signals required for one substation are embraced within a group of seven time channels, each individual signal comprising two live channels and ive dead channels, The codes are soI arranged that they may overlap without conflict; for example, if channels to 'l are assigned to substation 2, channels 2 to 8 may be assigned to substation 3, and channels 3 to 9 to substation 4; but no substation will respond to signals transmitted for any other of the substations which have certain channels in common. A cycle of N time channels provides codes for N substations; but the last code overlaps the beginning of the cycle by six channels. Any control symbol may be initiated at any time and will be completed whenever the necessary time channels become available thereafter. If initiated coincidentally with the first of the required time channels, the signal will be completed within a space of seven time channels. If initiated at the most unfavorable point in the cycle it will be completed Within a space of N plus 6 time channels.
Control signals are transmitted exclusively by negative current impulses. At all times when such signals are not being transmitted, a program of positive impulses is automatically transmitted, and report signals are thereby received from each operating unit of every substation in rotation. The report program occupies three time channels per substation, and when the line is not in use for control signals, reports are received from all operating units within a period of 3N time channels, or the equivalent of three control signal cycles.
In Fig. 13, parts 29 to 52 are receiving elements at the central station for report signals. They are identical with the corresponding parts in Fig. 6, save only that in Fig. 13 the dials 2| and 22 have segments for each time cycle of the whole program and select directly the relays 46 and 41 for retaining report indications, whereas in Fig. 6 the corresponding selection was eifected jointly by dials 2| and 22 and dials 3| and 32. As drawn, each of the dials 2| and 22 has forty-eight segments, suficient for sixteen groups of three segments per substation. It is to be understood that relays 46 and 4`| of Fig. 13 may control indicating lamps as shown in Fig. 6. Thus, in the absence of manual intervention, dials 2| and 22 will maintain a continuous program of 48 time channels, and during each time channel one group of indicating lamps may be controlled, showing the position of one operating unit at a substation. The indications of each group of lamps will be brought up-to-date at intervals of 48 time channels, or about one second if the dials are operated at a speed of fty channels per second.
In Fig. 6, switches 34, 35, 49, and 56 were provided to select receiving circuits for report signals or sending circuits for control signals. In Fig. 13 the same function is effected by a drum controller 293 mounted upon the shaft 29 and frictionally vdriven thereby. A two-point ratchet |99 and a pawl 299 normally hold the controller at one of two normal positions in which the control line 9 is connected to the receiving circuits and relay coils 46 and 41 are connected to ground. By depressing a push button shown on pawl 299 the latter may be released. Ratchet |99 and controller 293 will then advance one-half revolution with shaft 29. During this time the line 9 is connected for a period of 22 time channels or more to the sending circuits instead of the receiving circuits and the ground connection from relays 46 and 41 is broken to prevent any change at the indicating lamps during the time that their control over line 9 is interrupted.
While the controller 293 is travelling between one normal or receiving position and the next,
each connected substation. This brush arm is geared to shaft 29 and makes three revolutions for each revolution of the latter, so that contacts are made simultaneously at dial 24 and at dials 2| and 22; but contact is made at each segment of dial 24 during three different time channels as established by dials 2| and 22.
From the segments of dial 24 five connections lead to each substation panel, such as |3 or I4 in Fig. 1, terminating on the control switches for signals and track switch machines. These connections are indicated only for control switches 53 and 55 of substation panel I3 and control switches 53fL and 55a of substation panel |4. The complete circuits would include five connections from each segment of the dial switch.
29| and 292 are two dial switches mounted upon a common shaft and manually operated. Both brush arms are connected to the negative pole of battery 54, the positive pole being grounded. Each segment of dial 29| is connected to the blade of the control switch 53, 53a, etc., on one substation control panel, and the corresponding segment on dial 292 is connected to the blade of control switch 55, 55a, etc., on the same panel. Thus, at a given time, the battery may be connected at will to the control switches of one substation control panel and only one. Connections from the segments of dial 24 to all other substation control panels are then dead-ended as can be seen, for example, by tracing connections from the dial through control switches 53u and 55a on panel |4. Thus the panel selected by dials 29| and 292 has exclusive control of battery connections to dial 24. If preferred, it will be readily understood that an equivalent group of relays may be substituted for dial switches 29| and 292, and that battery connections to any panel may then be established by pressing a button on the panel.
When battery connections have been established to a given substation panel, control switches 55 and 53 on that control panel will complete paths, respectively, to one segment selected among an assigned group of two on dial switch 24, and to one segment selected among another group of three. As described hereafter, the receiving relays at the corresponding substations are so connected that they respond only when one negative impulse is received during each of the corresponding groups of two and three time channels, respectively. If channels of the respective groups are indicated by capitals and small letters, the groups for one substation may be assigned according to one of the following two arrangements: ABceg, or ADefg. In either case, each choice of one capital and one small letter is peculiar to a single substation and cannot be duplicated in any overlapping group similarly assigned. Connections shown in Fig. 13 are according to the first arrangement. The complete list of channel assignments for sixteen substatio-ns, involving sixteen channels lettered from a to p, is as follows:
Substation 1 2 3 4 5 6 7 8 l0 l1 12 13 14 15 16 Channel A B C D E F G H I .T K L M N O P B C D E F G H I J K L M N O l A c d c f g h i j l: l m n o 7) a b e f g h i j k L m 'n a p a b c d g h i j k l m n o p a h c d e f control line 9 is connected to the brush arm of dial 24, which has sixteen points, one point for Among the capital letters it will be noted that substation includes A in common with substa-
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Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2444078A (en) * 1942-06-10 1948-06-29 Bell Telephone Labor Inc Trouble alarm system
US2446037A (en) * 1946-03-01 1948-07-27 American Airlines Inc Selective signaling system
US2483718A (en) * 1946-02-28 1949-10-04 Schlumberger Well Surv Corp Phase selective signal transmission system
US2512652A (en) * 1943-09-20 1950-06-27 Int Standard Electric Corp Selective remote signaling system
US2559390A (en) * 1947-07-03 1951-07-03 Gen Railway Signal Co Centralized traffic control system
US2574774A (en) * 1949-04-30 1951-11-13 Westinghouse Air Brake Co Remote-control system
US2581056A (en) * 1948-05-31 1952-01-01 British Telecomm Res Ltd Signal transmission system
US2583088A (en) * 1950-09-13 1952-01-22 Bell Telephone Labor Inc Alarm signaling system
US2901728A (en) * 1951-04-10 1959-08-25 North Electric Co Supervisory control system
US2908894A (en) * 1952-07-01 1959-10-13 Kienast Alfred Meter reading system with pulse train transmitters

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2444078A (en) * 1942-06-10 1948-06-29 Bell Telephone Labor Inc Trouble alarm system
US2512652A (en) * 1943-09-20 1950-06-27 Int Standard Electric Corp Selective remote signaling system
US2483718A (en) * 1946-02-28 1949-10-04 Schlumberger Well Surv Corp Phase selective signal transmission system
US2446037A (en) * 1946-03-01 1948-07-27 American Airlines Inc Selective signaling system
US2559390A (en) * 1947-07-03 1951-07-03 Gen Railway Signal Co Centralized traffic control system
US2581056A (en) * 1948-05-31 1952-01-01 British Telecomm Res Ltd Signal transmission system
US2574774A (en) * 1949-04-30 1951-11-13 Westinghouse Air Brake Co Remote-control system
US2583088A (en) * 1950-09-13 1952-01-22 Bell Telephone Labor Inc Alarm signaling system
US2901728A (en) * 1951-04-10 1959-08-25 North Electric Co Supervisory control system
US2908894A (en) * 1952-07-01 1959-10-13 Kienast Alfred Meter reading system with pulse train transmitters

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