US2266904A

US2266904A - Railway traffic controlling apparatus

Info

Publication number: US2266904A
Application number: US369929A
Authority: US
Inventors: Willard P Place
Original assignee: Union Switch and Signal Inc
Current assignee: Hitachi Rail STS USA Inc
Priority date: 1940-12-13
Filing date: 1940-12-13
Publication date: 1941-12-23
Anticipated expiration: 1958-12-23

Description

Dec. 23, 1941. w. P. PLACE RAILWAY TRAFFIC CONTROLLING APPARATUS Filed Dec. 13, 1940 INVENTOR ZZ/L'l RPZaoe. BY

Patented Dec. 23, 1941 RMLWAY TRAFFIC CONTROLLING APPARATUS Willard: P... Place, Wiikinsburgf la assignor to.

The Union: Switch & Signal Company, Swissvale, Pa.,. a-corporation of Pennsylvania Application December 13, 1940, Serial No. 369,929

9 Glaima My invention relates to railway traiii'c controlling apparatus, and more particularly to train carried train control apparatus responsive to coded energy.

Railway traffic controlling apparatus using track circuits provided with code impulses of direct current has been proposed. Such impulses of direct current are supplied to a track circuit at different code rates according to different traffic conditions; and the code rates of 1'80, 120 and 7 5 impulses per minute to reflect clear, approachmedium and approach trafiic conditions, respectively, may be employed. Each impulse. of direct current is preferably of relatively high peak voltage and. of short duration. The high peak voltage serves as an aid to the shunting sensitivity of the track circuit and the short duration serves to limit the energy output. of the current source, which is ordinarily a battery, to a low energy level. The duration of such acurrent impulse is short as compared with the duration between successive impulses. In other words, the on period of the impulse during which current flows is small as comparedwith the off period during which no current flows. For example, under the 180' code rate acode cycle is of theo-rder of .33 second and of the .33 second the duration of the impulse (on period) is preferably of the order of .05 second and the duration between successive impulses (ofi period) is of the order of .28

second. 7

Train carried train control apparatus is governed by such coded direct current through the medium of train carried inductors and an amplifier. The inductors are mounted on the train in inductive relation to the track rails to receive an electromotive force in response toeach such current impulse, and are connected to the input terminals of the amplifier and the electromotive force thus received by the inductors is amplified to operate a code following relay connected to the: output terminals of the amplifier, the relay being operated at a rate corresponding to the code: rate of the track: circuit. current. impulses. Two ormore stages of amplification may be employed- The; code following relay governs cab signalsand. brake control equipment through decoding means selectively responsive to the different code rates at which the code fol-lowing relay is operated and. indirectly selectively responsive to the. different code rates of. the track circuit current impulses. Most satisfactory operation ofsuch decoding means is effected when th code following. relay is operated. at substantially equal on and off periods and when code distortion is avoided. Am.-

plifiers for such. train control apparatus preferably include electron tubes of the type that'will' restore themselves to an inactive condition once the controlling current ceases. In other words the amplifier tubes are preferably such that positive action on the part of some restoring device is not required. in order for the amplifier to be restored to its inactive condition.

In View of the above conditions a feature of my invention is the provision in railway traffic controlling apparatus of a novel and improved amplifier of coded direct current.

Another feature of my invention is the pro?- vision of railway traffic controlling apparatus-incorporating. a novel and improved amplifier using high vacuum electron tubes. which are continuously under the control of a grid potential and which automatically become inactive when the control current ceases.

.Again a feature of my invention is the provision of train carried train control apparatus incorporating a novel and improved electron tube amplifier having an equalizing circuit which effects substantially equal on and oif periods in the operationof a control relay and in turn 011 a code following relay in response to energy picked up from a. track circuit supplied with codeimpulses ofdirect current when the duration of,

each such current impulse is short as compared to the duration between successive. impulses. I

Still another feature of. my invention is the provision of an amplifier for railway traffic con-.

trolling apparatus incorporation novel means for:

automatically adjusting the grid bias voltage and code distortion caused by current and voltagevariations of the source of supply and of the control energy received is avoided.

The above features, as well as other advantages of my invention, which will become apparent as the specification progresses, are, attained according to my invention by providing a mul tiplestage amplifier each of which stages includes a high vacuum type of electron tube. The grid circuit for the final stage tube includes a condenser which is coupled to the next preceding stage tube and in turn is coupled to the track circuit to charge the condenser in response to; each code impulse of direct current of the track circuit. This charge on the condenser renders the grid of the final stage tube negative in potential with respect to the cathode. This grid circuit is provided with a grid leak resistorthrough which the condenser'discharges between successive impulses of the. coded current. A neu:

tral relay is interposed in the plate circuit of the equalizing circuit controlled by these contacts of the neutral relay is interposed in the grid circuit of the final stage tube to regulate the grid voltage of that tube. This equalizing circuit comprises two parallel circuit paths each of which preferably includes a resistor and a source of direct voltage, and a first one of these paths is-connected into the grid circuit over the front overlapping contact of the neutral relay and the second pathis connected to the grid circuit over the back overlapping contact of the neutral relay. The sources of direct voltage for these circuit paths are arranged so that the first path is effective to apply to the grid circuit a negative voltage and the second path a positive voltage. When both overlapping contacts areclosed and both circuit paths are closed the resulting grid voltage effected for the final stage tube is such as to create the above-mentioned predetermined normal value of plate circuit current and the neutral relay is held at its mid position. When the plate ciruit current is increased so that the energization of the neutral relay is increased a predetermined amount, the contact member of the neutral relay is picked up to open the associated back contact but leaving the front contact closed and the second one of the two parallel circuit paths is opened and a more negative grid voltage is applied. to the tube through the first circuit path tending to reduce the plate circuit current back to its normal value. When the plate circuit current is reduced below such normal value so that the energization of the neutral relay is reduced a predetermined amount the contact member of the neutral relay is released to open the associated front contact but leaving the back contact closed and the first one of the two circuit paths is opened and a more positive grid voltage is applied to the tube through the second one of the circuit paths tending to increase the plate circult current back to its normal value. A filter including a resistor and at least one condenser is interposed in the connection between the contact member of the neutral relay and the grid of the final stage tube to smooth out the abrupt voltage changes when the overlapping front and back contacts are opened and closed. The grid voltage effected through the equalizing circuit and the overlapping contacts of a neutral relay modifies the control efiected through the condenser and tends to cause the neutral relay to remain about equal periods in its picked up and released positions, notwithstanding the code impulses of direct current of the track circuit which cause operation of theneutral relay are short in duration as compared with the duration between successive impulses. Furthermore, the equalizing circuit is efiective to cause substantially equal on and off operation periods of the neutral relay notwithstanding variations of the charge on the condenser due to variations in the magnitude of the code impulses of direct current, variations of voltages of the current supply for the amplifier, variations of code rates of the current impulses and variations of temperature,

with the net result that code distortion is largely avoided.

The neutral relay is provided with a second contact member having front and back contacts which are closed only when the neutral relay is picked up and released, respectively. A master code following relay is controlled over the second contact member of the neutral relay and hence such code following relay is operated in step with the operation of the neutral relay. This master code following relay is used to govern a decoding means which in turn governs a signal or other train controlling device according to the rate at which the code following relay is operated.

I shall describe one form of apparatus embodying my invention, and shall then point out the novel features thereof in claims.

The accompanying drawing is a diagrammatic view showing one form of apparatus embodying my invention.

Referring to the drawing, the reference characters la and lb designate the track rails of a stretch of railway over which traffic normally moves in the direction indicated by an arrow and which rails are formed by the usual insulated rail joints into a track section DE which section may be one section of a series of consecutive sections of a signal system. The track section DE is provided with a track circuit which comprises a source of coded direct current connected across the rails at the exit end of the section and a code following track relay connected across the rails at the entrance end of the section. The means for supplying coded direct current to the track circuit of section DE may take different forms and may be that covered in my Letters Patent of the United States No. 2,197,414, granted April 16, 1940 for Signal systems, the specific form of track circuit being that shown in Fig. 10 of the above-mentioned patent. It is sufficient for this application to point out that the source of code impulses of direct current for the track section DE comprises a battery 2, a track transformer TI and a code transmitter GT2. The

code transmitter CTZ is of the relay type, the

operating Winding 3 of which is connected to a suitable source of current, not shown, and is effectively energized to operate three code contact members 15, I20 and I80, the arrangement being such that contact member 15 is operated to close contact 1515a at the rate of times per minute, contact member I20 is operated to close contact l20-l20a at the rate of times per minute, and contact member I80 is operated to close contact -180a at the rate of 180 times per minute.

Three relays indicated by the reference characters WA, WR and WL are controlled by traffic conditions in advance of section DE. The apparatus by which these relays are governed by traffic conditions in advance is not shown since it forms no part of my invention, and may, for example, be that shown and described in my aforementioned Patent No. 2,197,414. It is sufficient for the instant application to point out that at such time as relay WA is picked up closing front contact 4 in response to the first traffic condition in advance, or when relay WA is released closing back contact 5 and relay WR is picked up closing front contact 6, in response to a second traflic condition in advance, the battery 2 is connected across winding 1 of transformer Tl over contact l8ll-l80a of code transmitter CT2 and current flows in winding 1 causing magnetic energy to be stored the magnetic core 8 of transformer Ti, and when contact Him-4180a; is opened the flow of current in. winding 1' is interrupted and. the magnetic energy stored in the core of transformer Tl decays. At least a portion of winding 1 is connected across the track. rails: to and lb and the parts are so proportioned that when contact I'M-480a is: closed the current builds: up in winding 1: relatively slow and. little or no electromotive force is applied to the track rails, at. least the electromotive force applied to the rails at this time is so small it can be neglected. When contact Mll -IBM is opened the current is: interrupted and. an electromotive force is applied to the track rails which causes an efiective current. impulse of a prescribed polarity to fiow in the track circuit. Hence under the traific conditions which cause relay WA to be picked up or relay WA to be released and relay WR to be picked up, code. impulses of direct current of the code rate of I80 impulses per minute are-supplied to the track circuit. When relays WA. and WE are released closin back contacts 5- and 9, respectively, and relay" WL is picked up closing front contact It in response to a third trafiic condition in advance, the battery 2' is connected to winding 1 of transformer Tl over contact l20l20a of code transmitter CTZ and current impulses of the code rate of I20 impulses per minute are supplied to the track circuit. Again, whenrelays' WA, WR and WL are released closing back contacts 5, 9 and H respectively, in response to a fourth traffic condition in advance, the battery 2 is connected to winding '1 over contact IE-15a of code transmitter GT2 and current impulses of the code rate of 75 impulses per minute are supplied to the track circuit. The parts are further so proportioned that each such code impulse of current isof relatively high peak voltage and short duration, at least the duration of the impulse is short as compared with the interval between successive impulses. It is to be understood of course that my invention is not limited to the code rates of I80, 120 and '75 impulses per minute, but such are used for illustration since they are the code rates commonly employed in cab signal systems for railways.

A code followingtrack relay XTRI is connected across the rails of section DE at the entrance end E of the section, and when the sectionis unoccupied, that is, when the train shown conventionally at TC does not occupy section D-E, code following relay X'IRl is operated at a rate corresponding to the code rate of the current impulse supplied to the track circuit. Relay XTR'l would be used to control the apparatus for the section next in the rear of section DE, and which apparatus would include relays corresponding to the relays WA, WR and WL controlled by the section next'in advance of section D-E. Such apparatus controlled by relay XTRI is not shown since, as stated hereinbefore, such apparatus forms no part of my present invention and is not required for a fullunderstanding of my present invention.

The train shown conventionally at T0 is provided with train carried apparatus embodying my invention, and which apparatus comprises inductors l2 and. l3, a three stage amplifier, a neutral relay NR, a master code following relay MR, a decoding unit DU and a train control means shown in: the formof a cab signal CS. An; equalizing. circuit and. voltage regulator, to be later referred to, for the amplifier together with a suitable source. oi current are. also. provided for the carried apparatus.

The inductors it and liare: mounted on the train in Inductive: relation torails Id and lb, respectively, for" inductively receiving electrometive forces in response toeach code impulse of direct current supplied to" the rails in. the

manner explained hereinbefore. The inductors l2 and 93- are connected together so that'theelectromotive forces induced therein due to current fiowlng in opposite directions in the rails are.

additive and. the inductors are connected to the input terminals of the first stage of the amplifier.

The three stage amplifier includes electron.

each electron tube is normally heated and an.

active condition.

A voltage regulator inthe. form. of at poten tiometer type resistor. RI is connected across ter-- mi nals B32 and N32 of. the current source as will be apparent from an inspectionof the drawing, to pr'o'vide suitable control: vo'ltagesffor the several circuits; of the amplifier as will: appear as the specification progresses.

A grid'or input. circuit is provided tor the first stage tube by connecting its control. grid fl' to one terminal. of the inductor- I:2-l:3 over wire l8, connecting the. other terminal of. inductor l 2'-t3 to the negative terminal. M- of resistor RI over wire l9 and by connecting the cathode 211 of tube VT'I to a selected terminal. 2+ of resistor B l The negative terminalv of; re-' sistor R! is connected directly'to the negative terminal N32 of the current source and grid I! of tube VT! is thus provided with a negative bias voltage equal to the voltage'drop in that portion of resistor RI between. terminal 2lz and' its negative terminal 41;. A plate circuit for tube VTl can be traced from positiveiterminal 1332 of. the current source over wires 22 and 2-3--.. a. resistor 24,. plate 25 of. tube-V'It, intervening tube space to cathode 2d, tenninal 2| of resistor Rlf, that portion of" resistor R1"

betweenthe terminals

21 and 41 and to the negative terminal N32 of the current source.

The control grid 26 of the second stage tube VTZ is coupled to the plate circuit of the firststage tube VT through the well-known resistor coupling type of circuit and which coupling circi-iit includes a condenser Cl and a grid leak resistor 21-. The cathode of tube is connected. to: a selected terminal- 29 of resistor R! to provide apredetermined negative grid. bias voltage for tube- VTZ. The: plate: circuit of tube VTZ involves positive terminal 332,; wire- 22,. a resistor 69, plate 30 ot tube VTZ, intervening tube space to cathode: 2.8,. terminal 29 of resistor El and that portion of resistor'Rl bettweeniterminal- 29 and terminal 41 to the: nega-= tire terminal N32 or the current source.

The control grid 31' of? the third; and final stage tube VT3 is" resistance"- coupled to the plate circuit of: tube W112, this coupling; including a condenser C2 and. a grid; lealc" resistor-.32;

The cathode 33 of tube VT3 isconnected to a presented terminal 34 of resistor RI. An equalizing circuit to be shortly explained is interposed in the grid circuit of tube VT3 to regulate the potential of grid 3| with respect to cathode 33. The plate circuit of tube VT3 extends from positive terminal B32 of the current source over wire 65, winding of neutral relay NR, plate 66 of tube VT3, intervening tube space to cathode 33, terminal 34 of resistor RI and that portion of resistor'RI between terminals 34 and M to the negative terminal N32of the current source. The relay NR is a neutral relay and is provided with a contact member 35 having overlapping front and back contacts 36 and 31 respectively, the arrangement being such that when relay NR is energized by current of a predetermined intermediate or normal value, contact member 35 is held at a mid position where it is in engagement with both front contact 36 and back contact 37 as shown in the drawing. When the energization of relay NR is increased a predetermined amount above the intermediate value, then contact member 35 is raised to a picked up position where it is out of engagement with back contact 3'! and is in engagement only with front contact 36. When the energization of relay NR is reduced a predetermined amount below the aforementioned intermediate value, contact member 35 is released and becomes disengaged from front contact 36 and remains only in engagement with back contact 31. Relay NR is also provided with a second contact member 38 which is adjusted to engage an associated front contact 39 only when the energization of the relay is increased the predetermined amount above said intermediate value and which contact member engages back contact 40 when the energiz'ation of the relay is reduced the predetermined amount below said intermediate value. At the intermediate energization of relay NR contact member 38 is out of engagement with both front contact 39 and back contact 40 as shown in the drawing.

The equalizing circuit interposed in the grid circuit of tube VT3 comprises two parallel circuit paths which are controlled over the overlapping contacts 36 and 31 of relay NR to regulate the grid voltage of tube VT3 according to the position of relay NR. A first one of these circuit pathsincludes a resistor'R3 and is connected between front contact 36 of relay NR and a terminal 6| of resistor RI, while the second one of the circuit paths includes a resistor R4 and is connected between back contact'31 of relay NR and a terminal 42 of resistor RI. Terminals GI and 42 of resistor RI are located at points preselected on opposite sides of terminal 34 of resistor RI to which latter terminal cathode 33 of tube VT3 is connected. Hence the voltagedrop in resistor RI between the

terminals

42 and 34 serves as a source of positive voltage for the second circuit path including resistor R4 and the voltage drop in resistor RI between terminals 34 and 6| serves as a source of negative voltage for the first circuit path including resistor R3. The contact member 35 of relay NR is connected to grid 3| of tube VT3 over a resistor R2 and grid leak resistor 32. Two condensers C3 and C4 are connected to the opposite ends of resistor R2 and a common terminal of condensers C3 and C4 is connected to cathode 33 of tube VT3, resistor R2 and condensers C3 and C4 forming a filter the function of which will be referred to when the operation of the apparatus is described.

When neutral relay NR is energized at its intermediate value and contact member 35 engages both front contact 36' and back contact 31, both circuit paths of the equalizing circuit are connected to the rid circuit of tube VT3. The parts are so proportioned that the resultant voltage derived from the positive voltage supplied through the second circuit path and the negative voltage supplied through the first circuit path establishes a predetermined grid bias voltage for tube VT3 which is effective to cause the predetermined normal plate circuit current to flow and which in turn creates the intermediate energization of relay .NR. If for any reason the plate circuit current of tube VT3 increases to a point where relay NR picks up contact member 35 and back contact 3! is opened, there is effected through the first circuit path of the equalizing circuit a negative grid voltage which tends to reduce the plate circuit current to its normal value. When the plate circuit current is reduced below that required to energize relay NR at its intermediate value and contact member 35 is released to open front contact 36, there is effected through the second circuit path of the equalizing circuit a positive grid voltage which tends to increase the plate circuit current back to its normal value.

The code following relay MR is a polar relay of the type whose polar armature remains in the position to which it was last moved when the relay is deenergized and this relay is provided with two

windings

43 and 44 and the energization of which windings is controlled over contact member 38 of relay 'NR. When relay NR is energized by current of intermediate valuev and contact member 38 is out of engagement with both front contact 33 and back contact 40, code following relay MR is deenergized. When relay NR is picked up and contact 38-39 is closed the top winding 43 of relay MR is connected across terminals B32 and N32 of the current source and relay MR is energized at apolarity as required to operate its contact member 45 to the righthandposition to engage a normal polar contact 41, and when the energization of relay NR i reduced to release the relay so that contact member 33 engages back contact 40, the winding 44 of relay MR is connected across terminals B32 and N32 and relay MR is energized as required to operate polar contact member 45 to the left hand position to engage reverse contact 46. Code following relay MR when operated to alternately close contacts 46 and 4! causes direct current to be alternately supplied to the two portions of primary winding 43 of a decoding transformer DT and an alternating electromotive force is induced in secondary winding 49 of transformer DT, secondary winding 49 being connected to the input terminals of the decoding unit DU.

The decoding unit DU may be any one of several well-known forms and may be the tuned circuit arrangement covered by Letters Patent of the United States No. 1,773,515, granted August 19, 1930 to C. C. Buchanan for Railway traffic controlling apparatus. It is suificient for the instant application to point out that control relays A, R and L connected to the output side of decoding unit DU are selectively energized according to the frequency of the electromotive force applied to the input terminals of the decoding unit, the arrangement being such that relays A and L are effectively energized and picked up in response to an electromotive force of a frequency caused by operation .of code following relay MR at a rate corresponding to the 180 coderate :of the track circuit .current impulses, relays R and L are effectively energized and picked up and relay A is released in response to an electromotive force of a frequency caused by operation of relay MR at a rate corresponding to the .120 code' rate of the track circuit current impulses, and relay L is effectively energized and picked up and relays A and R are released in response to an electromotive force of a frequency caused by operation of relay MR at a rate corresponding to the track circuit current impulses of the '75 code rate. Again, when relay MR is inactive, relays A, R and L are all released.

Relays A, R and L are used to govern the operating circuits of signal CS. These operating circuits are those commonly provided and it is to be noted that when relay A is picked up closing front contact 50, an operating circuit is closed for lamp 5| and that lamp is illuminated to cause signal CS to display a first or clear signal indication. When relay A is released, closing back contact 52, and relay R is picked up closing front contact 53, an operating circuit is formed for lamps 5t and 55 in multiple and these lamps are illuminated to cause signal CS to display a second or approach-medium signal indication. When relays A and R are releasedclosing back contacts .52 and 56, respectively, and

relay L is picked up closing front ccntact5'l, an operating circuit is formed for lamp 58 and that lamp is illuminated to cause signal CS to display a third or approach signal indication. Again, when relays A, R and L are released closing back

contacts

52,56 and 59, respectively, an

operating circuit is formed for lamp 611 and that lamp is illuminated to cause signal CS to display a slow speed signal indication.

In describing the operation of the apparatus, I shall assume that the train TC on which the train carried apparatus is mounted occupies track section DE as shown in the drawing. When the rails are shunted ahead of train TC and no current flows in the rails so that no electromotive force is received by the inductors l2 and Hi, the grid bias voltage applied to tube VT3 through the equalizing circuit causes the predetermined normal plate circuit current for tube VT3 and the intermediate energization of relay NR is effected and its two contact members 35and 38 are held .at the mid position. Under such normal conditions code following relay MR is deenergized and inactive with the result that relays A, R and L are released and lamp 60 is illuminated so that the slow speed indication is displayed by the cab signal CS.

I shall next assume that trafiic conditions in advance of section DE are such as to cause either relay WA to be picked up .or to cause WA to be released and relay WR to be picked up so that direct current impulses of the 180 code rate are supplied to the track rails of section DE. Each such code impulse of direct current induces an electromotive force in inductors I 2 .and [3 which electromotive force is amplified at tubes VT! and VT2 in the usual manner and a corresponding amplified electromotive force is applied to the grid circuit of the final stage tube VT3. The connections are such that this amplified electromotive force drives control grid 3! of tube VT3 positive in potential with respect to cathode 33 causing current to flow in the grid circuit and the plate circuitcurrent to be increased. This increase in the plate circuit current causes relay NR to be picked up to open back "contact 35-31 and to close front contact 38-39,

grid 3| of tube VT3 negative inpotential with respect to cathode 33, Such negative potential of grid 31 is supplemented by the negative voltage applied through resistor R3 of the first "circuit path of the equalizing circuit; The resultant negative grid voltage causes the plate circuit current to be decreased to a value where relay NR is released to open front contacts 35-36 and 38 39 and to close back contacts 35-31 and 384ll. The closing of back contact 38 completes the circuit of the lower winding 44 of relay MR and relay MR is energized to operate its contact member 45 to its left-hand position. The opening of frontcontact 35-35 and closing of back contact 3-5-31 changes the negative voltage applied through the first circuit path of the equalizing circuit to a positive voltage applied through the second path of the equalizing circuit, and this positive voltage opposes the negative voltage applied from condenser C2. The charge of condenser C2 is discharged through a circuit including resistor 29, that portion ofresistor RI between its positive terminal and terminal 42,

resistor R4, back contact 35-31 of relay MR, resistor R2 and grid leak resistor 32. The time constant of condenserCZ and the above traced discharge circuit is such that the charge on condenser C2 leaks away relatively slow and after a predetermined time interval the positive grid voltage applied through the second circuit path of the equalizing circuit effects a less negative voltage for grid SI and the plate circuit current of that tube is increasedtoward its normal value. The time constant of condenser C2 and its associated discharge circuit is such that the charge of condenser C2 is discharged during the-interval between successiveimpulses of the track circuit current and hence condenser C2 is discharged and the above operation of charging condenser C2 is repeated for the next code impulse of the track circuit current. a I

I have found that when the amplified impulse of electromotive force is su-fiicient to causerelay NR to be released and remain in such released position for a certain length of time there is an accumulated efiect built up so that after a few successive impulses the grid voltage changes produced by such impulses tend to cause neutral relay N-R to be retained a substantially equal length of time in its picked up and released positions. In other words the equalizing circuit associated with the final stage tube VT3 is constantly seeking to so regulate the grid 'vo'ltageof that tube as to cause neutral relay NR to be picked up and released for substantially equal periods of time. It follows that when neutral relay NR is thus operated with substantially equal on and off periods the code following relay MR is also operated for substantially equal on and off periods. That .is code following relay MR is operated at substantially equal on and oil periods notwithstanding the code impulses of direct current which cause the operation of relay MR are short as compared to the duration between successive impulses of current. The filter comprising resistor R2 and condensers C3 and'C4 function to smooth out the abrupt voltage changes which take place when contact member 35 is operated from one position to the other so that the voltage level for control grid 3| of tube VT3 is gradually changed to correspond to the motive force produced by the coded impulses of direct current, variations in the voltage of the current source B32N3'2, variations in the code rate and temperature. It is'apparent that when the traffic conditions in advance of section DE are such as to cause current impulses of the code rate'of either 120 or 75 to be'applied to the trackrails of section DE, the operation of the apparatus carried on the train is substantially the same as that described above in connection with track circuit current impulses of the 180 code rate, except for the code rate at which neutral relay NR and in turn code following relay MB is operated. v

It is clear that one stage of amplification of the apparatus carried on the train may be omitted when the code impulses of the track circuit current are of a relatively high energy level and also that additional stages of amplification may be included in the amplifier if desired.

It is also to be observed that since tubes V'Il,

VT2 and VT3 are of a high. vacuum type and always under the control of the corresponding grid voltage, the apparatus restores itself to an inactive condition whenever the code impulses received from the track circuit cease.

It is to be seen, therefore, that I have provided train carried train control apparatus incorporating a novel and improved multiple stage amplifier each of which stages includes a high vacuum type of electron tube and the final stage of which amplifier is providedwith an equalizing circuit effective'to cause substantially equal on and off operation periods of a code following relay associated with the'plate circuit of the final stage tube, notwithstanding the code impulses of direct current are of short duration as compared with the duration between successive impulses of the current and notwithstanding variations in magnitude of such code impulses of current and voltage variations of the train carried source of current.

Although I have herein shown and described only one form of railway traflic controlling apparatus embodying my invention, it is understood that various changes and modifications may be made therein within the scope of the appended claims without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

1. In railway trafiic controlling apparatus for use with a track circuit supplied with code impulses of direct current, the combination comprising; an electron tube having a plate, a cathode and a control grid; a condenser, a grid leak resistor, a grid circuit including saidcondenser and grid leakresistor for said tube, means to couple said grid circuit to the track circuit to charge said condenser during each such code impulse of direct current for rendering said control grid negative in potential with respect to the cathode subsequent to each such current impulse,

means including said grid leak resistor to discharge said condenser between successive code impulses of current, a neutral relay, a plate circuit including said relay and a current source for said tube to operate said relay in response to the variations of grid potential efiected through said condenser, an equalizing circuit including two parallel paths and connected to said grid circuit over respective front and back contacts of said relay, means in said parallel paths to create a positive voltage in a selected one of 'said paths and a negative voltage in the other of said paths to modify the potential of the grid with respect to the cathode as effected by said condenser according as said relay is picked up or released, and a signal controlling device governed over contacts of said relay when operated.

2. In railway trafiic controlling apparatus for use with a track circuit supplied with code impulses of direct current, the combination comprising; an electron tube having a plate, a cathode and a control grid; a condenser, a grid leak resistor, a grid circuit including said condenser and grid leak resistor for said tube, means to couple said grid circuit to the track circuit to charge said condenser during each such code impulse of direct current for rendering said control grid negative in potential with respect to the cathode subsequent to each such current impulse, means including said grid leak resistor to discharge said condenser between successive code impulses of current, a neutral relay, a current source, a plate circuit including said relay and current source for said tube to operate the relay in response to the variations of grid potential effected through said condenser, another resistor connected across said current source, an equalizing circuit including two parallel paths connected to said grid circuit over respective front and back contacts of said relay and to preselected mid terminals of said other resistor to apply to the control grid a positive bias voltage when said relay 'is released and a negative bias voltage when the relay is picked up, and a signal controlling device governed over contacts of said relay when operated.

3. In railway traffic controlling apparatus for use with a track circuit supplied with'code impulses of *direct current, the combination comprising; an electron tube having a plate, a cathode and a controlgrid; a condensen'a grid leak resistor, a grid circuit including said condenser and grid leak resistor for said tube',mea'ns to couple said grid circuit to the track circuit to charge said condenser during each such code impulse of direct current for rendering said control grid negative in potential with respect to the cathode subsequent to each such current impulse, means including said grid leak resistor to discharge said condenser between successive code impulses of current, a neutral relay having a contact member provided with overlapping front and back contacts, a current source, a plate circuit including said relay and current source for said tube to operate the relay in response to the variations of grid potential efiected through said condenser, another resistor connected across said current source, an equalizing circuit including a first and a second circuit path in parallel and which are connected to said grid circuit over said overlapping front and back contacts respectively, said first and second circuit paths connected to preselected mid terminals of said other resistor to apply to said control grid a bias voltage according as said relay is at a mid position closing both said overlapping contacts or is picked up closing only the front contact or is released closing only the back contact, another contact member for said relay having front and back contacts closed only when the relay is picked up and released respectively, and a code following relay operated over a circuit including said last mentioned front and back contacts.

4. In railway traific controlling apparatus for use with a track circuit supplied with code impulses of direct current, the combination comprising; an electron tube having a plate, a cathode and a control grid; a condenser, a grid leak resistor, a grid circuit including :said grid leak resistor for said tube, means including said condenser to couple said :grid circuit to said track circuit to charge said condenser during each such code impulse of direct current for rendering said control grid negative in potential with respect to said cathode subsequent to each such current impulse, means includingsaid grid leak resistor to discharge said condenser between successive code impulses of current, a neutral relay, a current source, a plate circuit including said neutral relay and current source for said 'tube to operate the relay in response to the variations of grid potential effected by said condenser, another resistor connected across said current source, a first and a second circuit path in parallel, said first circuit path connected'be-tween said control grid and a preselected mid terminal of said other resistor over a front contact of said neutral relay to apply to the grid a negative bias voltage, said second circuit path connected between said control grid and another preselected mid terminal of said other resistor over a back contact of said neutral relay to apply to the grid a positive bias voltage, and a code following relay controlled over a circuit including a contact of said neutral relay.

5. In railway traffic controlling apparatus for use with a track circuit supplied with code impulses of direct current, the combination comprising; an electron tube having a plate, a cathode and a control grid; a source of direct current, a first resistor connected across said current source, a grid leak resistor, a grid circuit for said tube and including said cathode connected to a mid terminal of said first resistor and said control grid connected through said grid leak resistor to two mid terminals of said first resistor on opposite sides of said first mentioned mid terminal over a first and a second circuit path in parallel, a condenser, means including said condenser to couple said grid circuit to said track circuit to charge said condenser in response to each such code impulse of direct current for rendering said grid negative in potential with respect to the cathode subsequent to each such current impulse, said grid circuit effective to discharge said condenser between successive code impulses of current, a neutral relay, a plate circuit including said relay and said current source for the tube to operate the relay in response to the variations of grid potential effected through said condenser, a front and a back contact of said neutral relay interposed in said first and second circuit paths respectively to modify the grid potential effected through said condenser by voltages derived from said first resistor to control the on and off operation periods of said relay, and a signaling device controlled over a contact of said relay.

6. In railway trafiic controlling apparatus for cde and a control grid; a source of direct current, a first resistor connected across said current source, a grid leak resistor, a grid circuit for said tube and including said cathode connected to a mid terminal of said first resistor and said control grid connected through said grid leak resistor to two mid terminals of said first resistor on opposite sides of said first mentioned mid terminal over a first and a second circuit path in parallel, a condenser, means including said condenser to couple said grid circuit to said track circuit to charge said condenser in response to each such code impulse of direct current for rendering said grid negative in potential with respect to the cathode subsequent to each such current impulse, said grid circuit effective to discharge said condenser between successive code impulses of current, a neutral relay having a con-tact member provided with overlapping front and back contacts, a plate circuit including said relay and said current source to operate the relay in response to the variations of grid potential effected through said condenser, said contact member interposed in said grid circuit with its front and back contacts included in said first and second circuit paths respectively to apply t0 the gridcirc-uit a first, a second or a third voltage derived from said first resistor according as said relay is at a mid position,*is picked up or is released for governing the on and off operation periods of said neutral relay; and a code following relay governed over other contacts of said neutral relay.

'7. In railway traffic controlling apparatus for use with a track circuit supplied with code impulses of direct current, the combination comprising, a multiple stage amplifier including a first and a second electron tube, means to couple the grid of said first tube to said track circuit to amplify in its plate circuit the electromotive force derived from such code impulse of direct current, means including a condenser to couple the grid of said second tube to the plate circuit of the first tube to charge the condenser in response to each such amplified electromotive force to effect a negative grid voltage for the second tube subsequent to each such electromotive force, means including a grid leak resistor to discharge the condenser between successive electromotive forces, a neutral relay having a contact member provided with overlapping front and back contacts, a plate circuit for said second tube and including said neutral relay to operate the relay by the grid voltage derived through said condenser,

an equalizing circuit including two parallel circuit paths which are connected to the grid of said second tube over said contact member with its front contact included in one path and its back contact included in the other path, means to apply a negative voltage to the grid of said second tube over said one path and a positive voltage over said other path to equalize the on and off operation periods of said relay, another contact member for said neutral relay and provided with a front and a back contact, and a code following relay controlled over the last mentioned front and back contacts.

8. In railway traflic controlling apparatus for use with a track circuit supplied with code impulses of direct current, the combination comprising, an amplifier including an electron tube,

use with a track circuit supplied withcode impulses of direct current, the combination comprising; electron tube having a plate, a cath- -means includinga condenser to couple the grid ofsaid-"tube to the track circuit to charge the condenser in response to each such current impulse to effect a negative grid Voltage for the tube subsequent to each such current impulse,

means including a grid leak resistor to discharge the condenser between successive impulses, a neutral relay having a contact member provided with overlapping front and back contacts, a plate circuit for said tube and including said neutral re-: 10

lay to operate the relay by the grid voltage derived through said condenser, an equalizing circuit including two parallel circuit paths which are connected to the grid of said tube over said in one path and its back contact included in the other path, means to apply a negative voltage to the grid of said tube over said one path and a positive voltage over said other path to equalize the on and off operation periods of said re- -20 lay, a filter comprising a resistor and at least on condenser and interposed in the connection between said contact member and said grid of the tube to smooth out the abrupt voltage changes when said front and back contacts 316 13.;

opened, another contact member for said neutral relay and provided with a front and a back contact, and a code following relay operated contact member with its front contact included '15 prising; an electron tube having a plate, a oath ode and control grid; a source of direct current, a first resistor connected across said current source, a grid circuit for said tube including the cathode connected to a preselected mid terminal of said resistor and said grid connected to said first resistor over another resistor, a condenser, means including said condenser to couple said grid circuit to said track circuit to apply to grid an electromotive force in response to each such code impulse of direct current, said electromotive force effective to cause grid circuit current to flow to change said condenser and render the grid negative in potential with respect to the cathode subsequent to each such electromotive force, circuit means to discharge said condenser between successive electromotive forces, a neutral relay, a plate circuit for said tube and including said relay and said current source to operate the relay in response to the variations of the grid potential efiected through said condenser, an equalizing circuit including two parallel resistors and respective front and back contacts of saidrelay and interposed in the grid circuit between said other resistor and said one resistor with said two parallel resistors connected to said one resistor on opposite sides of said mid terminal to apply a positive or a negative bias voltage to said tube according as said relay is released or picked up, and a railway traflic controlling device controlled over a contact of said neutral relay when operated.

WILLARD P. PLACE.