US2055979A - Railway traffic controlling system - Google Patents

Description

Sept. 29, 1936.

s. N. WI GHT RAILWAY TRAFFIC CONTROLLING SYSTEM Filed July 15, 1932 Patented Sept. 29, 1936 PATENT OFFICE RAILWAY TRAFFIo CONTROLLING SYSTEM Sedgwick N. Wight, Rochester, N. Y., assignor to General Railway Signal Company, Rochester, N

Application July 15, 1932, Serial No. 622,645

21 Claims.

The present invention relates to railway traflic controlling systems, and more particularly to a communicating means in such a system whereby a single circuit extending to a remote point may be used for the transmission of a plurality of messages.

In controlling a distant railway traffic controlling device from acentral point, it is expedient to employ a minimum number of line wires extending from the control point to the various distant locations, both because of the cost of the line wire as well as the increased cost of maintenance of a larger number of wires over the considerable distances necessary to extend the line circuits. It is found convenient in such systems to not only provide means for controlling distant devices, such as switches and signals, but to receive indications at the control point of the operated position of such devices, and also of the presence of a train on certain sections of track, which consequently enables considerable saving to be made by multiplying the use of each circuit both for the transmission of controls and indications.

In view of the above and other considerations, it is proposed in accordance with the present invention to provide a communicating means in a railway traffic controlling system whereby a distant traffic controlling device may be controlled by selectively applying continuous current energy to a single line circuit, and whereby one or more indications of the condition of the same or different devices may be transmitted to the control point over the same line circuit by changing the continuity of the control energization. It is also contemplated that a portion of the present scheme may be employed for various other railway signalling purposes in which a very simple and reliable oscillating contact means is required, in as much as it is proposed to operate the present contact oscillating means with a single magnetic structure and a single armature.

Other objects, purposes and characteristic features of the present invention will become apparent as the description thereof progresses, during which, references will be made to the accompanying drawing, in which:-

Fig. 1 diagrammatically shows a typical arrangement of the present invention for controlling a distant signal, and for indicating at the control point the condition of such signal and the presence of the train in an associated track section, and

Fig. 2 is a modified form of the present invention arranged to control a distant signal and to receive indications of the condition of the signal at the control point.

Fig. 3 diagrammatically shows a modified use of a portion of the invention shown in Fig. 2.

A portion of a control panel is diagrammatically shown in the accompanying drawing, which has a straight section of miniature track MT corresponding to a distant section of actual track T, which track T has a signal S governing trailic movements thereover and an associated indicating light SK is shown on the control panel for displaying an indication when the signal S is clear. A means for setting up the controls for signal S is shown on the control panel by a rotary control button SGL, which is shown in its signal at stop position 3 and is operable clockwise to a position e which sets up a control to clear the east bound signal S.

The various relays at both the control point and the distant signal location are shown conventionally on the accompanying drawing, and the relays having heavy base lines, such as relays K, KK and SLP, have slow acting characteristics, or they are so constructed that the time consumed in releasing their armatures is considerably longer than the time consumed in picking up. An impulsing relay P is shown'on the drawing as a neutral relay having its energizing circuit carried through its own toggle contact, and it is to be understood that this arrangement is shown merely as a simple way of indicating a means for periodically oscillating a 'contactto alternately open and close a circuit for substantially equal periods of time, and that in practice a more practical means will probably be employed. The relay P as shown is arranged to open its back contact I when energized but shortly thereafter the energization is interrupted by the-operation of the toggle contact and the back contact I is again made followed by the dropping 40 of the toggle contact, or in other words; oscillation of the contact I is eifected by the lag in the operation of the toggle'contact which controls the energization of the relay. The relay shown in O. S. Field Patent No. 1,969,065 issued August 7, 1934 may be substituted for this relay P in a manner which will be obvious from a study of the patent.

A source of energy for the line circuit is shown as battery B, and it is understood that the wire L is the line wire for the particular distant signal shown herein whichmay be located a consider l able distance from the control point and also that the wire C may be a common line wire for the control or indicating circuits of other traffic C011.

trolling devices. A local source of energy is required at each location, which is not shown herein but the symbols and are used to indicate the opposite terminals of such a source.

Considering now that it is desired to clear the east bound signal S to allow a traflic movement onto the track section T, the signal control button SGLis rotated clockwise to a position e which energizes the line circuit from the battery B as follows:from the terminal of battery B, wire 5, contact 6 of the rotary signal control button SGL in its signal clear position e, wire I, through the windings of relay GP, line wire L, front contact 8 of relay TR, wire 9, back contact I of relay P, wire I0, throughthe winding of relay SLP, wires II and I2, and returning -to the terminal of battery B by the common line wire C and wire I3. The completion of this -circuit allows a continuous current to flow through the line circuit thereby picking up relay SLP which is efiective'to clear signal S by means which is merely indicated herein by contact I4 of relay SLP. The circuit effective to clear signal S is of course dependent in the usual manner upon local blocksignalling circuits, which have herein been omitted to simplify the disclosure, but it is to be understood that the closing of front contact I4 completes a circuit which is efiective to conditionsignal S for displaying a clear signal indication whenever the way is clear ahead. The line being thus energized also picks up the relay GP at the control point which completes a circuit at its front contact l8 to pick up the slow acting relay KK.

When the signal S has thus displayed a clear indication,-an energizing circuit is closed to operate the impulsing relay P, which circuit has diagrammatically been shown as completed through a contact I5 operated in accordance with the position of the semaphore blade of signal S, but it is to be understood that any circuit closing means maybe substituted for this contact I5 which is closed whenever the signal S displays a clear indication. This energizing circuit for the impulsing relay P may be traced from contact I5 in its dotted or signal clear position, wire I6, through its own toggle contact, through its operating winding to and is effective in the manner previously described to alternatelyopen and close its-back contact I at substantially equal periods of time.

The back contact I of relay P being in series with the energizing circuit for the control line previously traced is now effective to change the continuous line energization, to impulses which are separated by corresponding periods of de-energization, which obviously causes the relay GP at'the .control point to operate its armature in synchronism with theoperation of,relay P, in as much as this relay GP is constructed with quick acting characteristics. This oscillating motion of the armature of the relay GP is obviously effective to hold up the slow'releasing relay KK during the energized period of the line over the circuit:previously mentioned, and during the de-energized period, which is shorter than the releasing time of :the relay KK, a circuit is completed to energize relay K from back contact I8 of relay GP, wire I9, front contact 20 of relay KK, wire 2'I, through the windings of relay K to The relay'K having similar characteristics to the relay K is picked up during the de-energized period of the line and is not released during the energized period and consequently both relays K and KK remain picked up as long as the impulsing of the line circuit continues.

An energizing circuit for the indicating light SK is now completed from front contact 23 of relay KK, wire 24, front contact 25 of relay K, wire 26, through a lamp filament of the indicating light SK to In this manner a signal control relay is energized over a line circuit to clear its signal, and when such signal has operated to a clear position, an indication of such operation is returned to the control point over the same line circuit.

Considering now that an approaching train accepts the clear signal S and enters the section of the track-in front of the signal S, a track relay TR arranged in the conventional manner is dropped thereby interrupting the impulsing energization of the line circuit at contact 8 which drops relay GP at the control point. The dropping of relay TR also completes a circuit for holding up the signal control relay SLP from through stick contact 23 of relay SLP, wire lI, through the winding of SLP, wire IIL'back contact I of relay P, wire 9, back contact 8 of relay TR to The dropping of relay GP is efiective at the control point to de-energize relays KK and K thereby energizing the indicating light OSI with the signal control button SGL in the clear position over a circuit from back contact 29 of relay GP, wire 30, back contact SI of relay K, wire 32, contact 33 of the signal control button SGL in its signal clear position, wire 34 through a lamp filament of the indicating light 051 to In this manner, the presence of a train on a track section is indicated at the control point by the de-energization of the same line circuit used for the transmission of signal controls and indications, and it may be seen that this de-energization is only effective to indicate such track section occupancy whilethe signal control lever SGL is in a position to effect the clearing of the signal S.

The modified form of the present invention shown in Fig. 2 is illustrated in the same arrangement as Fig. 1, except that a transformer TF is employed at the control point and a differentially wound relay F is used at the signal location, which relay F has two windings, A and B, arranged to produce equal and. opposite flux thereby releasing the armature when both are energized. It will also be noted that the indication of the track circuit has been omitted in Fig. 2, or this arrangement may be considered as a modified means for changing the character of the control energization of the line circuit for the transmission of indications.

The control of the signal S in Fig. 2 is accomplished in the same general manner as in Fig. 1, or the moving of the signal control button SGL to position 6 causes the line circuit to pick up relay 'SLP from the side of battery B, over wire 36, contact 3'? of signal control button SGL inposition e, wire 38, through the primary winding 39 of transformer TF, line wire L, wire 40, through winding B of relay F, wire 4I, through theoperating winding of relay SLP wires 42 and 43, and returning to the side of battery 13 by the common wire C and wire 14. This eifects the clearing of the signal S in the same general manner as described in connection with Fig. 1,

and when signal S is operated to its clear position, the contact I5 closes a circuit which energizes winding A of relay F in parallel with the winding of relay SLP which parallel circuit/may be traced over the previously traced line energizing circuit to line wire L, and from there over wire 45, front contact 46 of relay F, wire 41, through winding A, wire 48, contact IS in its dotted or signal clear position, wire 49 to the opposite side of relay SLP and again joining the previously traced line energizing circuit.

When this parallel circuit around relay SLP is closed it is obvious that an increased amount of current flows through the line circuit at the control point, but as previously described, when the winding A and the winding B of relay F are both energized, the flux acting to hold front contact 46 closed is neutralized thus causing the parallel circuit through winding A to be opened at front contact 46, and the current in the line circuit is again reduced to its normal lower value at the control point. It may be seen that 'the relay F will again pick up shortly after winding A has been de-energized and continues to operate in this oscillating manner to periodically open and close its contact 46 as long as the signal contact I 5 is in the horizontal position, which oscillation of the contact 45 creates a pulsing current in the line circuit at the control point.

This pulsing current in the line circuit is effective at the control point to induce an alternating current voltage in the secondary winding 50 of the transformer TF, which voltage picks up the sensitive relay K connected thereacross as shown. The picking up of relay K closes an energizing circuit for the signal indicating light SK from front contact 5| of relay K wire 52, through a lamp filament of the indicating light SK to This modified indicating system may then be said to comprise a means for changing the steady control energization to a pulsing energization which effects a means at the control point which is not responsive to the steady energization, such as a. transformer and relay arrangement.

Another use for the relay F has been shown in Fig. 3, and has for example been illustrated as alternately energizing two lights H and H which may be the signal lights of a highway crossing signal system, or it is obvious that various other devices may be alternately controlled in a similar manner. The operation of relay F in Fig. 3 is much the same as described inconnection with Fig. 2, or as may be seen, the closing of back contact 55, which may be any controlling means such as a track relay, energizes the winding B but during the time consumed by the picking up of relay F, which time in most cases will be made comparatively long, the light H is energized through back contact and back contact 56 of relay F. However, when the relay F picks up the circuit is changed to energize lightH instead of light H at front contact 56, and the winding A is also energized at front contactv 56 to neutralize the flux of winding B and again drop the relay armature.

A control and indication communicating means for a railway traffic controlling system has thus been provided which permits the control of a distant trafiic controlling device over a single line circuit by selectively applying continuous current energy to the line circuit, and also permits .an indication to be returned to the control point, such as a particular condition of a traffic controlling device, by alternately opening and closing this circuit at the distant location to change the continuous current to impulsing current. In other words,-a continuous energization of the line circuit is ineffective to a certain arrangement of relays at the control point, but when an oscillating contact at the distant location changesthiscontinuous'energization to energy impulses separated bycorresponding periods of de-energization, the relay arrangement at the control point is effective to. set up .a condition forregistering the condition of the indicated device.

This relay arrangement at the control point is made responsive to pulsing current only by a relay arranged to pick up on the energized period and a second relay arranged to pick up on the deenergized period,.with both of these relays so constructed that their releasing time is substantially longer than their pick-up time, so that when picked up during one of the aforesaid impulsing periods they will not release on the following opposite periods. A second indication may also be transmitted either during the continuous or the impulsing energization of the line circuit by continuously interrupting this 'energization or deenergizing'theline circuit at the distant location which is eifective at the control point to register this second indication providing the control button is in a position ordinarily effecting the energization of the line circuit.

A modified form of this scheme has also been disclosed which differs in that the continuous control current is changed from the transmission of an indication to pulsing current by applying alternate periods of an increased amount of current by means at the distant location, instead of interrupting the current in this period. The indication registering apparatus at the control point in the modified arrangement is made responsive to the pulsing current only by a transformer having its primary winding in series with the line circuit and obviously the continuous control current does not induce current in the secondary winding thereof but the pulsing indicating current induces suliicient alternating current in this secondary to pick up a sensitive alternating current relay connected across the secondary winding. The oscillating relay which is employed at the distant location to periodically increase the line current may be used for various other purposes as has been shown and described in Fig. 3. This simple arrangement employs only a single magnetic structure of the conventional design and a single front and back contact may be employed to effect oscillation of the relay armature as Well as to control various external circuits.

The above rather specific description of one form of the present invention is given solely by the way of example, and is not intended in any manner whatsoever in a limiting sense. It is also to be understood that various modifications, adaptations and alterations may be applied to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention, except as limited by the appended claims.

Having thus described my invention, what I claim is:--

1. In a railway trafiic controlling system, a control point, a distant traffic controlling device tending to assume a predetermined condition, a line circuit extending from said control point to the location of said distant traflic controlling device, means at the control point for selectively applying continuous current energy to said line circuit, responsive means at the location of the traflic controlling device effective to control said traihc controlling device to a different condition in response to the energization of the line circuit and only so long as such energy is applied, means at the distant location for "impulslng the continuous energization of the line circuit during the existence of said difierent condition of the traflic controlling device, (and means at the control point responsive to the impulsing energization of said line circuit to indicate said diiierent condition of the distant traflic controlling device.

2. In a railway traffic controlling system, a control point, a normally deenergized distant trafiic controlling device, a line circuit extending from said control point to the location of said distant traflic controlling device, means at the control point for selectively applying continuous current energy to said line circuit, responsive means at the location of the traific controlling device effective to energize said trafiic controlling device when said iline circuit is energized, means at the distant location for impulsing the continuous energization of the line circuit during the energized condition of said traffic controlling device, and means at the control point responsive to the impulsing energization to indicate said energized condition of said distant traflic controlling device.

3. In a railway traific controlling system, a control point, a distant location, a line circuit connecting said control point and said distant location, means for controlling a tra'flic controlling device at the distant location by selectively applying continuous current energy to the line circuit at the control point, means at the distant location for periodically opening and periodically closing said line circuit in response to the existence of a first static condition of the trafiic controlling device, means at the control point responsive only to the line circuit impulses created by said openings and said closings of said line circuit to indicate said first static condition of the traffic controlling device, means for steadily opening said line circuit in response to the existence of a second static condition at the distant location, andmeans responsive to said steady opening of the line circuit to indicate said second static condition at the control point.

4. In a railway trafiic controlling system, a control point, a distant location, a line circuit connecting said control point and said distant location, a signal, control means for said signal rendered effective by selectively applying continuous current energy to the line circuit at the control point, means at the distant location for periodically opening and periodically closing said line circuit in response to the existence of a first static condition of said signal, means at the control point responsive only to the impulses created by said openings and said closings of said line circuit to indicate said first static condition of said signal, means for steadily opening said line circuit in response to the-existence of a second static condition at the distant location, and means responsive to said steady opening of the line circuit to indicate said second static condition at the control point, when said control means is operated to a position for applying energy to said line circuit.

5. In a railway trafiic controlling system, a control point, a distant traflic controlling device, a line circuit connecting the control point and the distant traffic controlling device, means for controlling the traffic controlling device by selectively applying direct current energy tosaid line circuit at the control point, means at the distant traffic controlling device for pulsing the energization of the line circuit during a certain condition of the controlling device -by intermittentlyLincreasing the direct current energiza- 'tion of the linegand means at the control point responsive to said pulsing line circuit energization to visually indicate said certain condition of the itraffic controlling device.

6. A railway traffic controlling system, comprising, a control point, a distant location, a line circuit connecting the control point and the distant location, a control switch arranged to selectively energize the line circuit at the control point, a signal control relay at said distant location in'series with said line circuit, an oscillating means arranged to periodically open and close said line circuit when a clear indication is displayed by the signal controlled by said control relay, two slow releasing relays at the control point, one of said slow releasing relays picking up during the open circuit line period and the other during the :closed line circuit period, and signal indicating means at the control point energized when'both of said slow releasing relays are picked up.

7. -A railway traflic controlling system, comprising acontrol point, a distant location, a line circuit connecting the control point and the-distant location, 'a control switch arranged to selectively energize the line circuit at the control point, a signal control relay at said distant location in series with said line circuit, an oscillat ing means arranged to periodically open and close said line circuit when a clear indication is displayed by the signal controlled by said control relay, -two slow releasing relays at the control poin't,one of said slow releasing relays picking up during the open line circuit period and the other during the closed line circuit period, signal indicating means at the control point energized when both of said slow releasing relays are picked up, a track relay at said distant location arranged to open said line circuit and to stick up said signal control relay when a train occupies a particular track section, and track circuit indicating means at the control point energized when said control switch is in its line energizing position and the line circuit is de-energized.

8. In combination, a local control oflice, a distant control point, a trafiic controlling device at said control point normally tending to assume a predetermined condition, a control circuit connecting said ofiice and point and for causing said device to assume another condition if and only when said control circuit is energized either continuously or intermittently, means for continuously energizing said control circuit from said local office, means 'for intermittentlybreaking said control circuit when said device assumes said another condition, and an indicator at said local office rendered active when said control circuit is intermittently energized.

9. In combination, a local control ofiice, a distant control point, a traflic controlling device at said control point normally tending to assume a predetermined condition, a control circuit connecting said ofiice and point and for causing said device to assume another condition if and only when said control circuit is energized either continuously or intermittently, means for continuously energizing said control circuit from said local office, means for intermittently breaking said control-circuit when said device assumes said another condition, an indicator at said local ofiice rendered active when said control circuit is intermittently energized, a second indicator rendered active when said control circuit is open at said control point for an appreciable time, and other means at said control point for opening said control circuit for such appreciable time.

10. In combination, a local control ofiice, a distant control point, a trafiic controlling device at said control point normally tending to assume a predetermined condition, a control circuit connecting said oflice and point and for causing said device to assume another condition if and only when said control circuit is energized either continuously or intermittently, means for continuously energizing said control circuit from said local ofiice, means for intermittently breaking said control circuit when said. device assumes said another condition, an indicator at said local office rendered active when energized, two slow acting relays one relay of which is energized when said control circuit is energized and the other of which is energized when said one relay assumes its energized condition and said control circuit is deenergized, and an energizing circuit for said indicator including in series front contacts of said two relays.

11. In combination, a local control office, a distant control point, a tralilc controlling device at said. control point normally tending to assume a predetermined condition, a control circuit connecting said ofiice and point and for causing said device to assume another condition if and only when said control circuit is energized by either a continuous or an undulating current, means for energizing said control circuit from said 10- cal oflice by continuous current, means for intermittently changing the resistance of said control circuit at said control point to change said continuous current to an undulating current when said device assumes said another condition, and an indicator at said local office rendered active in response to undulating current in said control circuit.

12. In combination, a local control oflice, a distant control point, a traflic controlling device at said control point normally tending to assume a predetermined condition, a control circuit connecting said ofiice and point and for causing said device to assume another condition if and only when said control circuit is energized by either a continuous or an undulating current, means for energizing said control circuit from said local oifice by continuous current, an auxiliary relay at said control point having a main winding and a bucking winding with its main winding included in said control circuit, a. circuit branch for said bucking winding to neutralize the effect of said main winding including a front contact of said auxiliary relay and a contact closed when said device assumes said another condition, whereby said front contact is intermittently opened and the resistance of said control circuit is intermittently changed when said device assumes said another condition, and an indicator at said local oifice responsive to the undulation of current in said control circuit.

13. In a railway trailic controlling system, a control point, a distant traffic controlling device tending to assume a predetermined condition, a line circuit extending from said control point to the location of said distant trafiic controlling device, means at the control point for selectively applying continuous current energy to said line circuit, responsive means at the location of the traflic controlling device eifective to control said trafiic controlling device to a difierent condition in response to the energization of the line circuit and. only so long as such energy is applied, means at the distant location for changing the character of the continuous energizationof the line circuit during the existence of said different condition of the traflic controlling device, and means at the control point responsive to the changed character of energization of said line circuit to indicate said different condition of'the distant traflic controlling device. f

14. In a railway trafiic controlling system, a control point, a distant traflic controlling device tending to assume a predetermined condition, a line circuit extending from said control point to the location of said distant trafiic controlling device, means at the control point for selectively applying continuous current energy to said line circuit, responsive means at the location of the trafiic controlling device efiectiveto control said trafiic controlling device to a different condition response to the energization of the line circuit and only so long as such energy is applied, means at the distant location for changing the degree of the continuous energization of the line circuit during the existence of said different, condition of the traffic controlling device, and means at the control point responsive to the changed de-' gree' of energization of said line circuit to indicate said difierent condition of the distant traific controlling device.

15. In a railway traflic controlling system; a line circuit extending between a control office and an outlying field station; means at the control ofiice for at times energizing said circuit; a neutral relay at the field station which is picked up whenever said line circuit is energized; a traflic controlling device operated toa particular static condition whenever and only when" said neutral relay is picked up; meansat the field' sta tion for impressing a series of impulses-onsaid line circuit without-dropping said neutral'relay, said means being effective only when said traffic controlling device is operated to said particular static condition; and means at the control office responsive to the impulses on said circuit to indicate said particular static condition of said traffic controlling device.

16. In a railway trafiic controlling system; a line circuit extending between a control office and an outlying field station; manually controllable means for selectively energizing said line circuit; a trafilc controlling device at the field station: transmitting means at the field station for impressing a series of impulses on said line circuit only when said trafiic controlling device is in a particular static condition; a relay at the field station responsive to the energization of said line circuit either when steadily energized or when impulsed by said transmitting means to continuously actuate said traflic controlling device to said particular static condition; and an indicator in said control ofiice responsive only to the impulsing of said line circuit to thereby indicate said particular static condition of said trailic controlling device.

17. In a railway trafiic controlling system, a traffic controlling device at a field station, a line circuit connecting the field station with a central oflice, control means at the central oflice for selectively energizing said line circuit to thereby control said trafiic controlling device, means at the field station for continuously impulsing said line circuit when said trafiic controlling device is in a particular condition for a prolonged and indeterminate period of time, impulse responsive means at the central ofiice responsive only to impulses on said line circuit, and an indicator controlled by said impulse responsive means and steadily illuminatedwhile there are impulses on said line circuit.

18. In a railway traflicw controlling system, a traflic controlling device. at a field station, a line circuit connecting the field station with a central oflice, control means at the central oifice for selectively energizing said line circuit, means at the field station responsive to the selective energization of said line circuit for controlling said traffic controlling device, transmitting means at the field station for causing recurring variations in the degree of energization of said line circuit while said traflic. controlling device is in a particular static condition, and means at the central oflice responsive to the energization of said line circuit only when its degree is recurringly varied by said transmitting means.

19. In a railway traffic. controlling system, a trafiic. controlling device at.a field station, a line circuit connecting the field station with a central ofii'ee, manually. operable control means at the central oifice for at times continuously energizing said line circuit, means at the field station responsive to the continuous energization of said line circuitifor. actuating said traffic controlling device, transmitting. means at the fieldv station for causing recurring variations in the degreevof said continuous energization of said line circuit while said traflic controlling device is inv av particular static condition,.an electro-responsive means capable of assuming. av normally biased position or. an actuated. position,. and means at. the central oflice responsive to the energization of said line. circuit. only when its degree is recurringly varied by. said transmitting. means to cause said electro-responsive means. to assume an actuated position.

20. In a. railway traflic controlling system, a

line circuit. connecting afield station with a central oflice, manually operable means at the central office for energizing or deenergizing said line circuit, means at the field station for impulsing said line circuit for an indeterminate period of time when said line circuit is energized by said manually operable means, means at the field station steadily maintained actuated in response to the energization of said line circuit irrespective of whether such energization is steady or is impulsed, an indication relay in the control office, and circuit means for energizing said relay only when said line circuit is impulsed, said indication relay remaining picked up throughout such impulsing period, an indicator lamp, and an energizing circuit for said indicator lamp including a front contact of said indication relay, whereby said indicator lamp is steadily illuminated While there are impulses on said line circuit.

21. In a railway traflic controlling system, a normally deenergized line circuit extending from a control point to a distant traflic controlling device, a neutral relay included in series in said line circuit at. the remote point for governing the operation of the traflic controlling device, a manually operable contact at the control point for connecting a source of energy in series in said line circuit whereby said line circuit is continuously energized or deenergized dependent upon the open or closed position of said contact, means at the remote point for at times causing recurring variations in the continuous current flow in said line circuit while said manually operable contact is closed, and electroresponsive means at the control. point steadily actuated in response to said recurring variations in the current in said line circuit.

SEDGWICK N. WIGHT.

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