US2098041A - Continuous inductive coded cab signaling system - Google Patents

Description

W. H. HOPPE Nov. 2, 1937.

CONTINUOUS INDUCTIVE CODED CAB SIGNALING SYSTEM Filed March 19, 1936 2 Sheets-Sheet l INVE T R w M ATTORNEY 2 Sheets She et 2 INVENTO W M45;- 1 EY w. H.- HOPPE Filed March 19, 1936 CONTINUOUS INDUCTIVE CODED CAB SIGNALING SYSTEM Nov. 2, 1937.

m fla l I m H Evil I v M 235i I I A t Qmw xuE ouncd F mm m e LQ 0 m m Tv L I1 E NQM wmm L svwmm I I .u L: NW u ma Q 2N Q3 h glall Na Z T .NON SN Patented Nov. 2, 1937 CONTINUOUS mnuc'rrvnconnn can SIG- NALING SYSTEM Walter H. Hoppe, Rochester, N. Y., assignor to geieral RailwaySignal Company, Rochester,

Ap lication March 19', 1936, Serial No. 69,618 22 Claims. (01. 246-63) This invention relates to train control and cab signaling systems and it more particularly per.- tains to a coder and a decoder for use in train control and cab signaling systems of the continuous inductive coded type.

A train control or cab signaling system of th continuous inductive type is one in which car-carried electro-responsive relays and devices are maintained energized in response to current in the track rails, so that failure of the current supply will result in the deenergization of the devices. In other words, the system operates on the closed circuit principle which causes a more restrictive I indication to be given in the event of current failure i A continuous inductive coded type system is one in which currentin the track rails is coded, with the car-carried relays operating in combination in accordance with the character of the 2 code applied to the track circuit and received by the apparatuson the car. The present invention is illustrated in the drawings as applied to a railway cab signaling system but it will be obvious, since the present invention is more particularly as directed to a vacuum tube coder and 'zto the use of a vacuum tube decoder instead of the usual mechanical coder and relay type decoder, that the invention may be used in other systems, such as train control and the like.

In coding the track circuit current in cab signaling systems of the type under consideration, it is expedient to provide apparatus along the trackway for characterizing the code, that is, applying impulses in one code which are distinctive from impulses in another code.

- .The code forming or chopper arrangement in the present invention is an improvement on the similar apparatus disclosed inmyprionapplication Ser. No. 29,116 filed June 29, 1935.

The decoder arrangement-in the presentinvenziilati'ng the usual fixed frequency alternating curment; which is usually cycle current. By the of a f, chopper" of the type disclosed in the present invention, it has been found that a more constantand reliable. coding arrangement is pro- 55. vided than formerly obtained from motor-grivep' apparatus, and since there are no mechanically moving parts in such a coder, it. is more reliable and more economical to maintain.

By making use of the particular type of vacuum tube arrangement disclosedin the present invention instead of the usual decoder relay, it has been found that a more reliable decoder is provided for responding to the code characters received by the car-carried apparatus, and since there are no mechanically moving parts in such a decoder it is more reliable and more economical to maintain.

By making use of the particular type of vacuum tube disclosed in the present invention inplace of the usual decoder relay, it has been found that the decoder more faithfully responds to the code characters received by the car-carried apparatus, and since there are no mechanically moving parts in such a decoder it is more reliable and more economical to maintain. The decoder portion of the present invention is an improvement over the decoder disclosed in the prior application of Reichard Ser. No. 15,645 filed April 10, 1935, and no claim to the invention disclosed in said Reichard application is made herein.

In view of the foregoing and other important considerations it is proposed, in accordance with the present invention, to employ a vacuum tube coder arranged to chop or modulate a 100 cycle current supply at rates of '75, and impulses per minute. Although the particular embodiment chosen to illustrate the present invention makes use of an oscillator frequency of 100 cycles it is necessary to make use of frequencies which are multiples of the rate of rotation of the motor shaft. For example, with a motor shaft rotating at 20 R. P. M., the codes usuallyprovided by code wheels or cam contactors are 80, 120 and 180 a impulses per minute.

-By making use of the vacuum tube arrangement of the type proposed in-the presentinvention for the decoder or code following device in connection with the car-carried apparatus, the

u ual time lag following the start of each ,train per second and codes of 75, 120 and 180 per minof 100 cycle impulses, due to'the inductive reactance of the relay (when-a relay type decoder is used) is-eliminated, the usual time required for change-over from one contact to another is eliminated other disadvantages in connection with a may of the mechanical type are overcome.

Other objects, purposes and characteristic features of the present invention will be apparent from the accompanying .drawings when considered in connection with the following description.

Fig. 1 illustrates in diagrammatic form one embodiment of trackway .apparatus and one embodiment of car-carried apparatus in accord- .ance with the present invention.

Fig. 2 illustrates diagrammatically a modified form of apparatus which may be used in place of the car-carried apparatus illustrated in Fig. 1.

Coding apparatus The trackway apparatus has been illustrated as applied to a railway track having rails I divided by insulating joints 2 into sections A, B and 0. Each section is preferably provided with a track circuit comprising the track rails themselves, a circuit including a supply transformer T1 (with suitable exponent) at the exit end of the section for supplying alternating current to the rails and a circuit including one winding of a track relay T (with suitable exponent) at the entrance end of the section.

Each track relay, in the form shown, is of the poly-phase motor type, comprising two stator windings 3 and 4 of relay T ( windings 33 and 34 of relay '1") and a rotor 5 (35 of relay T) which actuates contact finger 6 of relay T (36 of relay T Winding 3 of relay 'I' and winding 33 of relay '1 are the track windings of the track relays and are connected directly with the track rails of the corresponding section, while the other windings (4 of T and 34 of T are the polarizing windings permanently supplied with alternating current from the same source as the track rails, that is supply buses I and 8.

A 110 volt cycle transformer is illustrated in the drawings with its secondary winding connected to buses I and 8 which, as above mentioned, are the 60 cycle buses. A separate 100 cycle transformer has one terminal of its secondary connected to bus 1 and the other terminal of its secondary connected to bus l8. Bus 1 is therefore common to both the 60 cycle and 100 cycle circuits.

When current is sent through the track winding 3 of track relay T for example, in one phase, the rotor 5 is actuated in one sense. When current is sent through the track winding 3 in an opposite phase the rotor 5 is actuated in the opposite sense, and when there is no current in the track winding, or no current in the polarizing winding, or no current in either winding, the

relay is deenergized and the rotor assumes a neuvarious other circuits as will be more clearly pointed out later in the description.

Since the apparatus of the various sections is the same, like parts of each section have been designated by like reference characters having a distinguishing exponent corresponding to the section. Furthermore, the vacuum tube coder CH and its control by the track relay, as well as the selection of its out-put codes, has been illussake of simplicity they have not all been illustrated in the accompanying drawings. These signals may be of any suitable type and controlled by the track relay in its normal, reverse and neutral positions." Since the track relay manifests clear, caution and stop conditions by actuating its contacts to normal, reverse and neutral positions respectively, it is obvious that these maniiestations may be provided by operating semaphore or light signals over ci'rcuits controlled by the track relay contacts. This portion of the railway signaling system however forms no part of the present invention. As an example of the control of wayside signals, signals 9, r and y are illustrated as controlled by contact I 5 of relay T At each signal location a neutral type distant relay D (with suitable exponent) is provided and controlled over a line circuit in such a way that it is normally deenergized, being energized when a train enters the section. Relay D switches the track circuit from the 60 cycle track current to the cycle coded current.

A track repeater relay TP (with suitable exponent), of the slow-acting neutral type, is associated with each track relay. Its function is to reverse the alternating current applied to the track at the exit end of the section for reversing the track relay at the entrance end when the next section in advance is occupied.

Although the TP and D relays and the wayside signals are illustrated as being energized from direct current, it is obvious that they can be energized from an alternating current source of supply, such as the volt 60 cycle buses. In this event the relays will be of the alternating current type.

The coder connected to the exit end of each section by the picking up of the associated D relay comprises vacuum tube VT Since it is proposed to code or modulate a 100 cycle source of alternating current, this source is illustrated as being applied to the buses 1 and i8 by means of the 100 cycle transformer. Although the vacuum tube coder-associated with the exit end of section B is the only one illustrated in detail, it will be understood that those at the exit ends of other sections are of similar arrangement.

Vacuum tubes VTIA and VT comprise a chopper or code impulser, the function of which is to provide the low, medium and high rate impulses for making up the codes which are applied to the track circuit under various conditions, as determined by the selection of inductor L L r L by contact 30 of relay T The g chopper modulates the 100 cycle current in accordance with the selected rate, this current being applied to the track circuit in accordance with the position of contact ")0 of relay '1',

by way of contacts and 6| of relay U and contacts 62 and 63 of relay TP in a manner which will be described in detail.

It will be of course obvious that, if necessary, the 100 cycle modulated current may be stepped up or amplified by means of a power amplifier before it is applied to the track circuit in order to obtain a current value suitable for operating the car-carried code responsive device.

Tubes VTI A and VT are of the gas filled type, known by the trade name Thyratron". Tube VT comprises filament 20, cathode 2|, plate 22 and grid 23. In theillustration the grid is normally biasedby battery B through resistance R. Tube VTIA comprises filament I90, cathode 8|, plate 92 and grid 93. v

As is well known, discharge devices of this type exhibit a trigger action tending to permit space current to flow when once started, regardless of the subsequent grid potential. In other words, when the plate is rendered positive, the tube is triggered or fired by swinging the grid sufiiciently positive with respect to its normal value. Space current then flows in the plate circuit under the control of the plate potential alone and can only be stopped by opening the space current circuit, or by lowering the plate potential to the cut-off value. This means that, when the tube is fired, the grid loses control and plate current is nly stopped by removing the positive plate potential or lowering it to the cut-ofi value as determined by the characteristics of the tube.

Decoding apparatus Referring to the car-carried signaling apparatus shown above the track in lfig. 1, this apparatus includes two inductors or receivers 40 and 4|, each comprising a laminated core structure having projected poles and containing a winding disposed over the track rails directly ahead of the first axle and wheels W of the train. These receivers are so connected in series that voltage induced in their. windings; due to alternating current flowing in one direction in one rail and in the other direction in the otherstage voltage amplifier tube VT, of the ordinary amplifier type, is connected. R" is the grid resistor and R is a resistance in the filament circuit for obtaining the grid bias for. operating the tube at the proper point on its characteristic curve. The out-put of the first stage voltage amplifier is connected to the in-put of a second stage voltage amplifier, comprising tube VT, by coupling transformer 46. The in-put of tube VZl! includes a rectifier RC with the grid connected to this rectifier and a point between resistances R and R Tube V'I is of the gaseous are discharge type and has low internal plate resistance, high amplification constant and requires only moderate voltages to drive it. One device having these desirable characteristics is the Raytheon Production Corporation, RK-IOO tube. This tube comprises the usual filament ll (not shown connected since it may be lighted in any well known manner) plate II, "Cathanode" I2, cathode" and control grid 14. The characteristics of this 1 tube and its features of operation have been clearly set forth in an article beginning on page 23 of the Q. S. T. Magazine for June, 1935, andneed not be repeated 'here, except to point out how these features function in the present invention. r a

The out-put of VT is coupled to the in-put of a "chopper device comprising two gaseous are discharge devices similar to the tube VT and known to the trade as Thyratron tubes VT and VT, and the out-put of these tubes supply chopped energy to the primary winding of master transformer 46 in accordance with the modulated or chopped current received from the track rails.

The secondary of transformer 46 connects to the decoding relay circuits, comprising a circuit including condenser C and primary winding of transformer 41, tuned to the high or 180 per minute code rate.

Another circuit connected to the secondary of transformer 46 includes con- The secondaries of these three transformers include full-wave rectifier units RC RC andRC for passing unidirectional current through associated relays HR, MR and LR respectively, when coded current of 180, 120 and impulses per minute respectively are received. Relays HR, MR and LR are comparatively quick in picking up so that they will pick up on a single impulse of the code rate to which they respond. Relays HR and MR may or may not release during the'intervals between impulses, since slow acting repeating relay HP picks up and remains up during the reception'of the 180 per minute code and slow acting repeating relay MP picks up and remains u during the reception of the per minute code. Relay LR, being slow to release, holds up during the reception of the 75 per minute code.

Resistances R and R are for the purpose of limiting the current in the out-put of tubes VT and VT to the values limited by the tube characteristics. Resistances R and R are for the purposeof limiting the grid current of these tubes and also cooperate with condenser C to provide proper time phasing for the in-put potentials of these tubes for switching from one to the other, so that the upper and lower windings of transformer 46 will be alternately energized. (It is a timing and phasing condenser to provide the proper firing time of tubes VT and VT". R is the plate resistor for tube VT and condenser C is for the purpose of smoothing out or maintaining the voltage across R more nearly uniform.

R is a grid leak for tubeVT used when required. R1 is a voltage divider for providing a connection to the mid-potential point of the filaments of. VT and VT. It will be understood that the filaments of the tubes may be energized inany approved manner, such as by means of a filament battery or rectified alternating current.

vention to any such values; Operation I Coding.--A description will first be given of the coding as controlled by the operation of the apparatus illustrated below the track in Fig. 1. In the following description, it will be assumed that the filaments of all tubes are lighted, either continuously, or the filaments of tubes V'TIA and VT may be connected to the source of supply by the operation of the D relay when a car enters the associated section. The heater elements or cathodes of the tubes are thus rendered active.

With the track sections in the conditions illustrated in Fig. 1, the chopper tube VT is not operating because the lower winding of transformer PT is open at front contact SI of .relay D As will be seen from the following description, the plate potential for VT is that which is induced across the terminals of the upper winding of transformer PT, therefore when the 100 cycle supply circuit, including the lower winding of this transformer, is open the tube is rendered inactive.

With a car in section A as illustrated, the carcarried apparatus is receiving t e 180 rate code (clear) because the next two ections are unoccupied and relay T is in its normal position. The car in block A will therefore receive the 180 code when blocks B--C are unoccupied.

If section C is occupied, relay T will be in its neutral position which deenergizes relay TP at open contact 36. With relay TP deenergized the 60 cycle current to block B is reversed, which in turn causes relay T to switch its contacts to their reverse positions. Contacts of relay T (corresponding to contacts 30 and 100 of relay '1) in their reverse positions cause the 120 rate code (second section in advance occupied) to be applied to sectionA. The car in block A will therefore receive the 120 code when block B is unoccupied and block C is occupied.

With section B occupied, relay T will be in its neutralposition which deenergizes relay TF at' open contact 6. Relay 'I'P reverses the 60 cycle current to section A, but due to the shunt provided by the car in block A, the track relay (not shown) connected to section A is in its neutral position. Contacts of relay T (corresponding to contacts 30 and I of relay T in their neutral positions cause the '75 rate code (next section in advance occupied) to be applied to section A. The car in block A will therefore receivethe 75' code when block B is occupied.

With section A occupied (by another car when the illustrated car enters block A) no code will be received by the illustrated car-carried apparatus because of the shunt ahead of the receiver coils 40 and 4|. The above code rates are selected and applied by the coder in a manner which will" be obvious from the following description relating to the operation when a car enters section B.

When a car shunt is applied to the rails of section B, winding 3 of relay T is shunted which 7 viii) (right hand) position (assuming block C unoccupied chopper-CH is conditioned for moduhigh- (180) code .rate.

lating the 100 cycle alternating current at the I The operation of the :.chopper' tube to'eifect the modulation or "chopfping of the -100 cycle current for application to the'track-rails of section B will be described later. J16

With relay T in reverse (left hand) posiup positions.

tion, manifesting the occupancy of the second section in advance of section B (section D for example) contact 30 causes chopper CH to modulate the 100 cycle current at the medium (120) code rate, and this code is applied to the rails of section B over the above-described circuit including contact ID!) of relay T, but this time in its reverse position.

With relay '1 in its neutral position, manifesting the occupancy of the next section in advance of section B (section C) contact 30 causes "chopper" CH to modulate the 100 cycle current at the low (75) code rate andthis code is applied to the rails of section B over the above-described circuit including contact I00 of relay '1', but this time in its neutral position. The circuit may be traced from the right-hand'terminal of the secondary of the 100 cycle transformer, bus I8, lower winding of transformer PT, contact I00 of relay '1 in its neutral position, front contact 60 of relay D back contact 63 of relay TP (deenergized because of open contact 36 of relay T lower winding of transformer TT back contact 62 of relay TP and bus I to the left-hand terminal of the-100 cycle transformer.

The circuit for relay D including conductor I2, is for the purpose of switching the 100 cycle coded current onto block A when a car enters this section. Similarly, the circuit including contact 90 of relay T and conductor I23 is for the purpose of switching the 100cycle coding current onto section C when a car enters this section;

With section B unoccupied and relay T actuated to the right, as an indication that the next two sections in advance are unoccupied as above described, a circuit is closed by contact l for lighting wayside lamp 9. With section C occupied, relays T and I? will be down for actuating the contacts of relay T to the leftas previously described, which closes a circuit at contact for lighting wayside lamp 'It will now be explained how the 100 cycle alternating current supply is "chopped" or modulated by the operation of-tubes VTiA and VT in accordance with the position of contact 30 of relay '1', which operation is typical of the operation at other locations.

The 100 cycle supply circuit extends from the secondary winding of the 100 cycle power transformer to the primary of track transformer TV and includes the lower winding of transformer PT. This circuit was previously traced in detail and includes contacts of relay D in their picked Therefore, because of transformer PT, a voltage of comparatively high frequency (100 cycles per second) is induced in the output circuit of tube VT including plate 22 and cathode 2l, when relay D is picked up. This 100 cycle alternating voltage is applied to the track. by way of transformer 'IT and is modulated at a comparatively low rate by tube VT in cooperation with auxiliary tube VTI A, which varies the reactance in the circuit including bus H3. The current in this circuit is at a maximum value when tube VT conducts and at a minimum value Because of transformer PT the track voltage is likewise at a maximum value when the tube VT conducts and at a minimum value when this tube is non-conducting. Therefore the 100 cycle voltage applied to the track circuit is modulated to produce envelopes or blocks at rates determined by the rate at which tube VT modulates when space current flow in this tube is stopped.

the reactance in the supply circuit, which is in turn determined. by the position of contact 90 as will now be explained.

with 100 cycle voltage applied to the plate circuits of tubes VTIA and VT{ by transformers PT and PT respectively, it will first be assumed that contact 39 is in its normal position as illustrated. When the voltage of the upper terminal of the secondary winding of transformer P'I' swings positive, the gas within the tube is ionized and plate current flows from this terminal, platecath'ode 92-9l, load resistor R to the lower (negative) terminal of the transformer winding. This is because grid 93 is not sufliciently negative to prevent "firing the tube.

When the voltage of the upper terminal of the secondary winding of transformer PT swings negative, the tube is de-ionized and the flow of plate current is stopped. This operation is repeated foreach positive and negative swing of the 100 cycle per second voltageapplied to the a plate circuit of tube VTIA. Since condenser C is connected in multiple with load resistor B, it will gradually accumulate a charge across its terminals each time current flows through R, with the terminal of C which is connected to grid 93 becoming more and more negative with respect to the terminal of (3 which is connected to cathode 9i.

The terminal of C which is connected to grid 93, and consequentlygrid 93 itself, will finally become sufiiciently negative to prevent firing which prevents firing of tube VTlA, this tube,

is again fired" by the positive swings of the plate as before and this cycle of operations is repeated at a rate which is determined by the LCR values of the above circuit.

The value of L is such that tube Will. is fired" as above described 130 times per minute. The value of L is such that tube VTIA is "fired l20times per minute. The value of I. is such.

, that tube VTIA is jfired" '75 times per minute.

Tube VT is a repeater or amplifier of tube VTIA, in that it repeats the firing" rate of VTiA. Since the input circuit of VT, including grid 23 and cathode 28, is connected. across resistor B,

it will be obvious that the voltage drop acrossthis resistor (due to the current through-R as above described) will "fire" VT at the same rate that VTlA is fired. of grid bias battery B and the characteristics of tube V'll being such that the positive swings of the terminal of R'which is connected to grid 23,

renders grid 23 sufficiently positive with respect to cathode H for tube VT to fire" on each positive swing of plate 22. Then, at the first positive swing oi. plate 25, when grid 29 is less positive than the "triggering value of the tube,

this tube fails to fire" and therefore the cycles of firing" and non-firing of VTIA are repeated by W.

From the above it will be seen that the 100 cycle current is supplied to transformer over a circuit whose reactance is varied at a rate'determined by the selection made by contact 39. with contact 30 in the position shown, this rate This is due to the values will be 180 per minute. With contact 30 in its reverse position, this rate will be 120 per minute due to inductance L -With contact in its neutral position, this rate will be-75 per minute due to inductance L A brief statement of the above operation is that cycle alternating voltage is applied to the track in blocks of maximum and minimum values, with these blocks occurring at a rate determined by the rate at which the reactance of the circuit including the primary of transformer TI is varied, which is in turn determined by the firing? and ncn-firing periods of tube VT which is in turn determined by the constants of the grid circuit of tube VTIA as selected by contact 30. It will now be explained how these blocks of maximum and minimum values of the 100 cycle potentials are applied to the track rails at the '75, and per minute rates, are detected by the car-carried apparatus and decoded for operating the cab signals.

Decoding.-When the receiver coil ill-8E pick up 100 cycle impulses in blocks or m dulations of 180 per minute, as applied to the track rails of section B under clear conditions (sections C and D unoccupied as above explained), the induced current in the secondary of transformer Mt flows through the circuit including resistance R and condenser C This current is efiective to so control tube V'I' (due to the potential difference set up between the grid and cathode connected across the condenser C that it produces 100 cycle current chopped at the 180 per minute rate in the primary winding of transformer $5.

'In other words tube V'I is an ordinary voltage amplifier tube for stepping up the voltage waves applied to its in-put for energizing transformer 45 connected in its out-put.

In the operation of the code receiving car-carried apparatus, it is desired to fire the "chopper, comprising tubes VT and VT at the earliest point in each block of the train of I00 cycle waves received, in order to provide as great a percentage of "on or impulse period as possible. This is accomplished by the rectifier-amp ifier arrangement including tube VT, having the advantages that low energy is required for driving it, high out-putvoltage is obtained for firing the chopper? and the length of the impulse or "on" period is a maximum.

The cathanode E2 of tube VT is normally maintained at a comparatively low positive potential with respect to cathode l3 by the IR drop acrossresistor R", which with the voltage developed in transformer 35 ionizes the tube so that a comparatively low developed voltage attransformer 65 is required to fire it. Furthermore, when the positive potential is removed from cathanode" E2, the tube is extinguished (plate current is cut oil) the same as if a "cathancde potential existed and a high negative bias were applied to grid it. If the voltage for firing and extinguishing tube V';[ were only that across the secondary of transformer 45' and due to the signal pickedup by the receiver, it will be obvious that the comparatively low signal volt- 6 normal voltage by way of rectifier RC and applied to the input of tube VT comprising grid 14 and cathode 13, which fires the tube. Since the normal'voltage between cathanode l2 and cathode I3 is just below the ionizing value, the

loss of the signal voltage in the input circuit extinguishes the tube. Thus practically a constant firing voltage over a relatively wide range is provided for V1 by relatively weak voltage of variable magnitude rece ved from the out-put of the voltage amplifier VT.

The blocks of 180 per minute coded impulses in the out-put of 'VT are available for firing or triggering the chopper, which in turn applies impulses of 180 per minute to master transformer 4 6 for operating relay HR. This out-put includes plate resistor R bridged by condenser C, which as above mentioned, smooths out the pulsating waves in the out-put circuit.

Current impulses in the output circuit of tube VT flow through resistor R and obviously these impulses of current produce a voltage across the terminals oil-t when and only when impulse rurrent flows in-the output circuit. Since the current flow of these impulses is always upward through resistor R the lower terminal of R is rendered positive with respect to its upper terminal, but only when impulse current flows in the output of W. v

The impulses in the output circuit of tube VT are applied to the input circuit of tube VT over a path which includes a connection from the upper terminal of R tothe filament of VT, by way of voltage divider R The lower terminal of R leads to the grid of VT by way of resistor R These impulses render the grid of VT positive with respect to the filament of this tube, therefore the tube willbe fifired by an impulse in the output of W.

Since tubes VT and VT have direct current applied to their platecircuits, there will be no negative half cycles to extinguish a fired tube, as in the case of tubes VTIA and VT. It will now be explained how tube V1 is fired and how VT and VT are alternately extinguished after firing.

After tube .VT has been fired, as above described, by an impulse through resistor R it will remain fired during the absence of voltage at the terminals of R It will be assumed that tube VT is extinguished at this time. Upon the application of voltage to the terminals of R tube VT will be fired and tube VT will be extinguished. Then tube VT will remain fired duringithe absence of voltage of terminals R This action is repeated by the presence and absence of voltage across the terminals of R to first fire VT then to fire VT then to extinguish VT, then to "fire VT ,"then to extinguish VT etc. This provides pulsating energy at the secondary terminals of transformer (46, since the primary windings of this transformer are connected in the output circuits of tubes VT and VT The above operation of firing and quenching tubes VT and VT. is not new with applicant, a similar arrangement being shown in Fig. 3 and described on page 5, lines 4 to 43 inclusive of Patent No. 1,971,755; The operation of the present arrangement will be understood by engineers, from the above discussion, it being understood that condenser G acts as a phasing condenser to provide proper firing of tube VT5. Also, that resistors R and R are for the purpose of limiting the grid current and tube VT for cooperating with condenser C to determine its charging time. Resistor R is the usual grid leak and may or may not be required as practical conditions dictate.

During the time that VT is conducting, condenser C is being charged, with its lower terminal taking on a positive charge and its upper terminal taking on a negative charge. This is because its lower terminal is connected to (+)220, through It and awinding oftransformer 46 in series, with its upper terminal connected to the plate of VT. During the time that V1 is non-conducting VT fires and quenches VT as will now be described.

Since the plates of the tubes are tied together by condenser '08 and-since this condenser is charged with its upper terminal negative and its lower terminal positive, as above explained, the plate of tube VT will swing negative with respect to its filament, because the condenser potential will be applied through the plate-filament circuit of VT across the plate-filament circuit of VT in opposition to the potential from the 220 volt direct current source. Since condenser C! cannot discharge immediately, the opposite potentials across the plate-filament circuit of VT cause this tube to become non-conducting, orinother words, it is quenched. By so choosing the circuit constants that the existing ions in tube VT can diffuse before the plate voltage again becomes positive (by the dissipation of the charge on C the grid of tube VT resumes control and the tube is extinguished. Similarly when the grid of tube VT next swings positive, this tube will conduct and condenser C will function to extinguish VT in a similar manner, since it is oppositely charged by the firing of VT.

It will be seen from the above that tubes VT and VT alternately conduct in response to a series of pulsating impulses in the out-put-of Since the conducting path for each tube of the pair is througha primary winding of transformer $6, an alternating voltage is applied to buses 8| and 82 connected to the secondary winding of this transformer, in blocks having a frequency dependent upon the code rate, in the assumed example 180 per minute.

It is believed obvious that the reception of the 120 or the code rate will likewise apply blocks of alternating voltage at these rates to'buses 8| and 82. Because of the tuned circuit including transformer 41, the 180 rate will cause unidirectional impulses to be applied'through rectifier.

relay HR will be up and relays MR. and LR will be; down. A circuit is now closed for picking up relay HP which extends from back contact as of relay MR, winding of relay HP and front contact 84 of.relay HR to Lamp G is lighted over a circuit completed at front contact 85 of relay HP. With a first caution code rate) being received, relaym will be up and relays HR and LR will be down. A circuit is now closed for picking up relay MP which extends from (4-). front contact 83 of relav extinguishes itself during the negative half-' *except that they are in the 200 series.

winding of relay MP and back contact 81 of relay HR to Lamp YG is lighted over a circuit completed at back contact 85 of relay HP and front contact 86 of relay MP. With a more restricted caution code rate) being received,

relay LR will be up and relays MR and HR. will be down. Lamp YR is lighted over a circuit extending from back contact of relay HP, back contact 86 of relay MP, front'contact 81 of relay LR and lamp YR to With a stop condition no code willbe received, which effects the release of all relays and a circuit is closed for lighting lamp R extending from 6+), back contact 85 of relay HP, back contact 86 of relay MP, back contact 81 of relay LR and lamp R to Likewise, in the event of a trouble condition which prevents the coding of the cycle current but permits the reception of continuous 100 cycle current, none of the "relays will be picked up and the above circuit will light lamp R.

Fig. 2 Modification The modification of Figc2 is similar to the carcarried apparatus of Fig. 1. All tubes in Fig. 2,

however, are operated from alternating current and a single chopper tube VT is used instead.

of the two tubes VT and VT of Fig. l. The apparatus in Fig. 2 has been given reference characters corresponding to similar parts in Fig. 1, Buses 28B and 282 correspond to buses 8i and 82 of Fig. 1 and it will be understood that the same tuned circuit arrangement for operating the relays and lights illustratedfin Fig. 1 may be used in Fig. 2. It is therefore believed unnecessary to duplicate this portion of the Fig. 1 apparatus in Fig. 2. e m

The primary of transformer 2M connects to the receivers by way of the filter, the ,same as in Fig. l. Tube V1 is shown connectedto a source of direct current plate voltage and it will be obvious that this may be rectified alternating current derived from the power transformer, or it may be from a battery'- or direct current generator. The voltages indicated at the terminals of the transformer windings are typical only and may be varied to suit various requirements,

The voltage in the secondary of transformer 244 is stepped up by voltage amplifier and the out-put of this tube develops voltage for driving VT by the voltage induced in the secondary winding of transformer 245. The firing oi-V'I' is maintained at the critical points by rendering its'-cathanode" 212 positive by the voltage drop in resistors R and R through which the plate current of VT flows, as in Fig. l. A voltage is developed in theput-put of VT for firing" VT but since an, alternating voltage is used for the plate circuit of'V'I it cycles, as above pointed out, and thus no extinguishing tube is required. 4

Having thus described one specific embodiment of a cab signaling system, it is desired to be understood that the particular arrangements illustrated a d suggested are only typical of applicants in ention and are not intended to indicate the exact circuit design and specific arrangement of parts to carry out the features oi the invention. These particular forms have been chosen to facilitate in thedisclosure, rather than to limit the number of forms which the invention may assume and it is further desired to bB-lll'ldfilStOOd that various modification may be made in order to meet the various problems encountered in practice. Furthermore, the arrangements illustrated may be used in a train control system as well as in a cab signaling system, the system may be varied in the number of track sections to which the invention is applied and the amount of apparatus at'each section and carried by the car may be varied to suit local conditions, all without in any manner departing from the spirit or scope of. the present invention, except as limited by the appended claims.

What I claim is:

1. In a track circuit; track rails; a first source of alternating current and a second source of alternating current; a polyphase track relay; means controlled by different traflic conditions for connecting said first source of current to said of alternating current and a second source of alternating current; a. polyphase track relay; means controlled by different trafilc conditions for connecting said first source of current to said track relay in different phase relations, whereby said track relay is selectively operated; means including a. reactive circuit for connecting said second source of current to said track rails; and means controlled by said second source of current for selectivelyvarying the reactance oi said reactive circuit at diflerent code rates in accordance with the position of said track relay, whereby said second source of current is applied to said track rails in code formations.

3. In a track circuit; trackrails; a first source .of alternating current and a second sourceof alternating current; a polyphase track relay; means controlled by different tramc conditions fonconnecting said first source of current to said track relay in different phase relations, whereby said track relay is selectively operated: means including a reactive circuit for connecting said second source of current to said track rails;

. means controlled by said second source oi current for selectively varying the reactance oi said reactive circuit at difierent code rates in accord ance with the position of said track relay, whereby said second source of current is applied to said track rails in code formations; and a decoder controlled by the current in said track rails for decoding said code formations.

d. Ina track circuit, 'track rails, a sgurce of alternating current, means including a reactive circuit for applying a potential derived from said source of ,current to said treckrails, a vacuum tube modulator, means controlled by said alternating current for operating said modulator,

means controlled by traific conditions for causing said modulator to modulate the reactance of s reactive circuit, and means controlled by the modulated reactance of said circuit for modulating the potential applied to said track rails.

, 5. In a track circuit, track rails, a. source of alternating current; means including a reactive, circuit for applying a'potentlal derived from said source of current to said trackrails, a vacuum tube modulator, meanscontrolledby-fsaid alternating current for operating said modulator,

means controlled by trai'flc conditions forcepsing said modulator to modulate the reactance of said reactive circuit at diflferentcoded rates, and means controlled by the modulated reactance of said circuit for modulating the potential applied to said track rails at said coded rates.

6. In atrack circuit, track rails, a source of alternating current, means including ,a reactive circuit for applying a potential derived from said source of current to said track rails, a vacuum tube modulator having input and output circuits, means controlled by said alternating current for energizing the output circuit of said modulator, means responsive to traflic conditions and including the input circuit of said modulator for causing its output circuit to modulate the reactance of said reactive circuit, and means controlled by the modulated reactance of said reactive circuit for modulating the potential applied to said track rails.

'7. In atrack circuit, track rails, a source of alternating current, means including a reactive circuit for applying a potential derived from said source of current to said track rails, a vacuum tube modulator having input and output circuits, means controlled by said alternating current for energizing the output circuit of said modulator, means responsive to traflic conditions and including the input circuit of said modulator for causing its output circuit to modulate the reactance of said reactive circuit at different coded rates, and means controlled. by the modulated reactance of said reactive circuit for modulating the -potential applied to said track rails at said coded rates.

8. In a decoder for detecting and decoding codes of electrical impulses in a railway track circuit, an electrostatically controlled are discharge tube having input and output circuits, a plurality of signals, means for detecting said impulses, means for applying the detected impulses to said input circuit, a source of current connected to saidoutput circuit, means responsive to the application of said impulses to said input circuit for starting current flow from said source through said output circuit, an arc quenching means associated with said tube, means controlled by said impulses for causing said are quenching means to stop the flow of current in said output circuit, and means controlled by the current flow in said output circuit for operating said signals in accordance with the codes of impulses in said track circuit.

9. Ina decoder for detecting and decoding codes of electrical impulses in a railway track circuit, a pair of electrostatically controlled arc' discharge tubes having input and output circuits, a plurality of signals, means for detecting said impulses, means for applying the detected impulses to said input circuits in opposite phase relation, a source of current connected to said out- 'put circuits, means responsive to the application of said impulses to said input circuits for alternately starting current flow from said source throughsaid output circuits,an arc quenching means associated with each of said tubes, means controlled by said impulses for causing said arc quenching means to alternately stop the flow of current in said output circuits, and means conplurality of signals, means for detecting said impulses, means for amplifying the detected impulses and applying the amplified impulses to said input circuit, a source of current connected to said output circuit, means responsive to the application of said amplified impulses to said input circuit for starting current flow from said source through said output circuit, an arc quenching means associated with said tube, means controlled by ,said amplified impulses for causing said are quenching means to stop the flow of current in said output circuit, and means controlled by the current flow in said output circuit for opof current connected to said output circuits; are

quenching means connected to the respective tubes; means controlled by the alternate response of said input circuits to said detected impulses for causing repeated current impulses to alternately flow from said source through the output circuits of said tubes; and means actuated by the flow of current through the output circuit of one tube for generating a potential in the arc quenching means of the other tube.

12. In a cab signaling system for railroads; a receiving circuit; a control circuit to be controlled by code impulses received by said receiving circuit; apparatus for repeating said -code 1mpulses from said receiving circuit to said control circuit, comprising a source of current, a gaseous ionizable arc discharge path interposed between said source of current and said control circuit;

arc quenching means associated with said path; 4 and'means actuated by a current impulse transmitted to said control circuit across said path for generating a potential which causes said are quenching means to quench the current across said path.

13. In a cab signaling system for railroads; a receiving circuit; a control circuit to be controlled by code impulses received by said receiving circuit; apparatus for repeating said code impulses-from said receiving circuit to said control circuit, comprising a source of current, a gaseous ionizable arc discharge path interposed between said source of current and said control circuit;

are quenching means associated with said path; I

and means controlled in part by one of said code impulses and in part actuated by a current impulse transmitted to said control circuit across said path for generating a potential which causes said are quenching means to quench the current across said path.

14. In a cab signaling system for railroads; a receiving circuit; a control circuit to be controlled by code impulses received bysaid receiving circuit; apparatus for repeating said code impulses from said receiving circuit to said control circuit, comprising a source of current, a pair of gaseous ionizable arc discharge paths interposed between said source of current andsaid control circuit; are quenching means associated with each of said paths; means controlled by the impulses received by said receiving circuit for alter- .decoder for detecting and decoding said coded impulses, said decoder including an electrostatically controlled arc discharge device rendered conductive by said impulses. a

16. In combination; a coder for applying coded impulses to a track circuit; a decoder carried by a railway vehicle; and means controlled by said decoder for detecting and decoding said coded impulses, said decoder including an electrostatically controlled arc discharge device rendered conductive by a low impedance high amplification amplifier driven by said impulses.

17. In combination; a coder for applying coded impulses to a track circuit; a decoder carried by a railway vehicle; and means controlled by said decoder for detecting and decoding said \coded impulses, said decoder including a pair of electrostatically controlled arc discharge tubes alternately rendered conductive by said impulses and each tube alternately rendered non-conductive by'current flowing through the other tube.

18. In a coded track circuit for railroads, track rails, a load circuit including said track rails, circuit means for connectingsaid load circuit to a source of high frequency alternating current, and an arc discharge device ,included in said circuit means for applying current from said current source to said load circuit at different low frequency rates.

19. In a coded track circuit for railroads, track rails, a load circuit including said track rails, circuit means for connecting said load circuit to a source of high frequency alternating current, a pair of arc discharge devices included in said circuit means for applying current from, said cu'rrent source to said load circuit at different low frequency rates, and control means so connected in said circuit means and including one of said arc discharge devices for rendering the other of said are discharge devices non-conducting.

20. In a coded track circuit for railroads, track rails, a load circuit including said track rails, circuit means for connecting said load circuit to a source of high frequency alternating current, a

. pair of arc discharge devices included in said circuit means for applying current from said current source to said load circuit at diiferent low frequency rates, control means so connected in said circuit means and including one of said are discharge devices for rendering the other of said are discharge devices non-conducting, and means connected to said load circuit for selectively and visually indicating said diiferent low frequency rates.

21. In a cab signaling system for railroads, track rails, means for .applying high frequency alternating current to said rails at different low frequency rates, a car carried receiving means for receiving said different low frequency rates, an

' indicator for visually indicating the different low frequency rates being received, a pair of inversely connected arc discharge devices included in saidreceiving means for controlling the transfer of said different low frequency rates from said rails to said indicator, control means. connected to sequentially cause said are discharge devices to become conducting in response to the receipt of said alternating current, and means responsive to one of said are discharge devices becoming conducting for rendering the. other of said arc discharge devices non-conducting.

22. In a cab signaling system for railroads, track rails, means for applying high frequency alternating current to said rails at diiferent low frequency rates, acar carried receiving means for receiving said diflerent low frequency rates, an indicator for visually indicating the different low frequency rates being received, a pair. of inversely connected arc discharge devices included in said receiving means for controlling the transfer of said diiferent low frequency rates from said WALTER. n. Koren.

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