US2679555A - System to prevent false operation due to amplifier failure in coded carrier signal systems - Google Patents

Description

LLISO 2,679,555

ERATION DUE TO AMPLIFIER IN VEN TOR.

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H15 HTTOHIVEY Patented May 25, 1954 UNITED STATES PATENT OFFICE,

SYSTEM TO PREVEN T FALSE OPERATION DUE TO AMPLIFIER FAILURE IN CODED CARRIER SIGNAL SYSTEMS Leslie R. Allison, Pittsburgh, Pa., assignor to Westinghouse Air Brak Pa., a corporation- Original application Febr 75,188, new Patent No. ber 15, 1953. Divided 22, 1953, Serial No. 356

1 Claim. 1

My invention relates to vacuum tube amplifier circuits, and more particularly to vacuum tube amplifier circuits for use with coded carrier current.

The present application is a division of my copending application Serial No. 75,188, filed February 8, 1949, Circuits for Coded Carrier Currents, issued December 15, 1953, as Patent No. 2,662,934.

There are many signaling systems which use coded, carrier current and for which systems exacting safety requirements are prescribed because the operation must be as nearly one hundred per cent safe as can be reasonably obtained. Also, a failure of the system if it does occur should be on the side of safety. For example, railway cab signal systems in many cases use alternating railway cab signal systems the track rails are arranged in track sections and each track track circuit that inresponse to the coded alternating current flowing in the rails. This electromotive force is used to operate a train carried code following relay which in turn governs the cab signals and other train control devices. The electromotive force picked up by the inductors is of a low energy level and an amplifier is interposed between the inductors and the code following relay.

Due to the safety requirements set up for these e Company, of Pennsylvania Wilmerding,

uary 8, 1949, Serial No. 2,662,934, d

ated Decemand this application May intermittent opening of the circuit due to the vibration of control means.

Other features, objects and advantages of my invention will appear as the specification progresses.

In practicing my invention I provide a vacuum tube amplifier circuit network that includes an input filter.

relay.

I provide a vacuum tube that is constructed in such a manner that each electrode or grid is brought out to an external base pin or terminal 50 that a circuit may be or.-

ranged to have the control grid element and its two terminals in series therewith. That is to say, the vacuum tube is provided with two external terminals which are connected to the pposite ends or at least to two spaced points of the control grid. The conrtol grid and its two terminals in series are included in a circuit which comprises resistive or electrical conductive elements and capacitive elements, the resistive elements being connected to one of the grid elements and the capacitive elements being connected to the other terminal of the control grid. Preferably the secondary winding of the filter transformer is made at least one of the conductive elements of this circuit and a capacitor of the filter is preferably made at least one of the capacitive elements of the circuit. This circuit including the control grid and its two terminals is connected to the cathode of the tube to form a control grid cathode circuit, a bias voltage source being interposed in the circuit adjacent the cathode. This bias voltage source is preferably poled to bias the control grid negative in potential with respect to the cathode by a voltage sufficient to give substantially zero anode current when no signaling energy is received. This con trol grid cathode circuit is connected to the two terminals of the control grid in such a manner that no portion of the circuit can become open without either the negative bias voltage of the control grid being maintained subsequent to the open circuit condition or the bias voltage being reduced at such a gradual rate subsequent to the open circuit that the anode current builds up so slowly that any impulse induced in the coupling transformer as a result of this building up of the anode current is insufficient to operate the code following relay. In this way an intermittent open circuit in any point of the circuit network would not result in energy impulses being passed to the code following relay for operation thereof.

I shall describe one form of vacuum tube ampliner circuits embodying my invention and shall then point out the novel features thereof in claims.

The accompanying drawing is a diagrammatic view showing a form of vacuum tube amplifier circuit embodying my invention.

In the drawing the amplifier circuit is illustrated as being used with a railway cab signal system, but it is to be understood that while the vacuum tube amplifier circuits provided by this invention are peculiarly adaptable for use in railway cab signal systems, the circuit is not limited to this one use and there are many other places where the circuit can be used to an advantage.

Wherever the term vacuum tube is used in the specification and claims, it is understood to mean a device consisting of an evacuated enclosure containing a number of electrodes between two or more of which conduction of elec tricity through the vacuum or contained gas may take place. That is, the term vacuum tube is here used to cover an electron tube or a gas tube.

Referring to the drawing, the reference characters la and lb designate the track rails of a railway and which rails are formed in the usual manner into track sections. The rails of each section are included in a track circuit, not shown, having a source of alternating current connected across the rails at the exit end of the section. The alternating current is of a designated frequency and is coded at any one of a plurality of different code rates according to different traffic conditions. The trackway apparatus for supplying the coded current to the rails la and lb is not shown since its specific structure forms no part of my invention and there are several welliznown arrangements that can be used. For example, the trackway apparatus may be similar to that disclosed in Letters Patent of the United states No. 1,986,679, granted January 1, 1935, to Lloyd 'v'. Lewis, for Railway Trafiic Controlling Apparatus.

As an aid in the understanding of my invention the alternating current supplied to the rails is and lb will be assumed to have a frequency of 109 cycles per second and as being coded at 180, and 75 interruptions per minute to refleet clear, approach medium, and approach traffic conditions, respectively. The absence of rail current or the presence of non-coded rail current reflects a stop or slow speed traffic condition. Thus each code is made up of alternate on periods during which current flows in the rails and off periods during which no current flows in the rails. It will be understood, however, that my invention is not limited to the above assumed frequency for the alternating current and the above mentioned code rates for the coding thereof.

The train carried apparatus shown in the drawing includes an inductor 1N and an amplifying unit AM.

The inductor unit IN includes two windings i i and it which are mounted on the train in inductive relationship with the rails la and lb, respectively. Thus an electromotive force is induced in the windings l l and I2 due to the coded alternating current supplied to the rails in the manner described above. The windings H and l). are connected to add their electromotive forces vhen current flows in opposite directions in the two track rails la and lb at any given instance. Consequently the inductors ll and 12 and the trackway apparatus associated therewith constitute a source of coded carrier current. The windings ii and i2 of the inductor IN are connected by Wires l3 and it to input terminals TC and FT of the amplifier unit AM.

The amplifying unit AM comprises a filter Fl. a vacuum tube VT, a coupling or master transformer MT, and a code following or master relay MB. The filter Fl comprises capacitors Cl and C2 and a transformer Tl having independent primary and secondary windings l5 and I6, respectively, but an autotransformer may be used. The primary winding 15 of transformer Tl and the capacitor Cl are connected in series across the terminals TC and FT, the parts being proportioned for this circuit to be tuned to series resonance at the frequency of the carrier of the signaling current, which in the case here used for illustration is a current of cycles per second.

The secondary winding H3 and the capacitor C2 are included in the filter Fl in a manner to be more fully discussed hereinafter.

The vacuum tube VT is preferably a high vacuum indirectly heated cathode tube but other types of tubes may be used. As disclosed, the tube VT is provided with a filament or heater ll, a cathode it, an anode or plate l9, a screen grid 2G, and a control grid ill, The tube VT is of conventional construction except the wire or element forming the control grid 2| has both ends thereof brought out to separate base or terminal pins which are indicated by the numerals l and This construction permits a circuit to be established through the tube with the control grid ill in series therewith. This construction of the control grid 2| plished in any suitable manner. may be accomplished by mounting the wire forming the control grid on an insulating member and connecting the two ends of the wire to terminal pins i and The remaining elements of the tube VT are brought out to base pins in the usual construction, the filament i! being connected to base pins 2 and 77, the cathode l8 to a base pin 8, the screen grid 29 to a base pin 4 and the anode iii to a base pin 3.

The tube VT is designed for operation on a single 32 volt source of direct current, it being contemplated that the usual train lighting generator or battery will serve as a source of energy for the amplifying unit AM. In the drawing, the source of energy for the amplifying unit is indicated by the terminal B32 and the negative terminal 0. It is to be understood, however, that the tube may be designed to use a power source of some other voltage and if desired the filament may be heated from a low voltage source and the anode and screen grid excited from a high voltage source. The filament or heater IT of tube VT is connected directly across the terminals B32 and C, as will be apparent by an inspection of Fig. 1, and the tube is in an active condition. Two resistors RI and R2 in series are also connected across the terminals B32 and C to form a voltage divider from which a bias Voltage is obtained, as will appear shortly.

An anode circuit is formed for the tube VT by the anode it being connected to terminal B32 through a winding 22 of the coupling or master transformer MT and the cathode it of the tube being connected to the junction terminal of the resistors R! and The screen grid 26 is also connected to the positive terminal B32 of the power source.

The control grid 2i and its two terminals I and 5 are included in a circuit that is connected to the secondary winding [6 of the filter transformer TI, and the capacitor C2, which are connected in multiple to form a circuit which is resonant at the carrier frequency, namely 100 cycles per second. This tuned circuit has its top terminal connected through asymmetric unit RX to grid terminal i of tube VT and the other grid terminal 5 is connected through resistor R3 to the lower terminal of the tuned secondary winding it. a capacitor Cd is connected across the tuned winding is and the asymmetric unit RX in series. The unit RX may be any one of several known forms of asymmetric units, such as for example, a copper-oxide rectifier unit. The control grid is biased negatively in potential with respect to the cathode by a voltage equal to the voltage drop across the resistor RI, this resistor forming a source of bias voltage. The parts are so proportioned that the negative bias voltage supplied to the control grid 2! from the resistor RI through resistor R3, is sufficient to bias the tube to a substantially zero anode current, this being the preferred arrangement although a bias of a different value may be provided.

The winding 22 of the coupling transformer MT is provided with a by-pass capacitor 23 and a secondary winding 24 of the transformer is connected to the operating winding of the code following relay MR. Relay MR is preferably a stick polar relay operable in response to a predetermined value of energization. The relay MB is provided with a contact member 25 which is operated in one direction to a first position when a current impulse of one polarity is supplied to may be accomthe relay winding and the member 25 is operated in the other direction to a second position when the energizing impulse is of the opposite polarity. The contact member 25 is used to govern decoding and signaling means of any of the well-known arrangements, and which equipment is not shown for the sake of simplicity since it forms no part of my present invention and its showing is not required for a full understanding thereof. The decoding and signaling apparatus may be similar to that disclosed in Letters Patent of the United States No. 2,462,454, granted to me on February 22, 1949, for Train Carried Cab Signal Apparatus. It is suiiicient for the present application to point out that code operation of the relay MR at the 188, 120, and 75 code rates effects a clear, approach medium, and approach cab signal indication, respectively. Also, when relay MR is deenergized and is not operated a stop or slow speed cab signal is effected.

In describing the operation of the apparatus, I shall first consider that the tube VT is heated and that no signaling current is being supplied to the rails I a and lb. Under this condition the bias voltage derived from resistor Ri for the control grid 2! effects a substantially zero anode cab signal. I shall next assume that alternating is induced in the windings i I and I 2 of the inductor. This induced electroinotive force is applied to the terminals TC and FT of positlve direction, so that the grid 2i is driven in the positive direction in opposition to the fixed value of the anode current during each on code period of the coded carrier current and the anode current decreases to substantially zero during each "01? code period. Ihe carrier variations of the anode current are icy-passed by capacitor 23, but the code variations in the value of the anode current create corresponding impulses in secondary winding 24, the impulse being of one polarity when the current increases during the on code period, and being of the opposite polarity when the current decreases during the code period. These impulses induced in The operation of the apparatus when current of either the or 75 code rate is supplied to the rails is the'same as above described for current Of code rate except that the relay MR is operated at rates corresponding to the 12s and '75 code rates of the rail current and corresponding cab signal conditions are established.

It is apparent that electromotive forces picked up by the inductor IN due to alternating current of a frequency other than 100 cycles per second will be substantially suppressed due to the input filter Fl. In other words, the amplifying unit is substantially immune to currents other than the 100 cycle signaling current.

I shall next consider open circuit conditions for the apparatus and the protection provided against false operation of the relay MR due to an open circuit condition when no signaling current is supplied to the rails. In the first place the screen grid 20 which is connected to the positive terminal B32, effects a higher degree of sensitivity for the tube than would prevail if a lower voltage were applied to the screen grid. Thus, an open circuit in the connection of the screen grid 20 results in a lower sensitivity for the amplifier tube and if there is a failure it will be that not enough energy is supplied to the relay MB for operation thereof in response to the rail current. With the relay MR not operated the stop or slow speed signal is created and which would be a more restrictive signal. That is, the failure, if any, due to an open circuit in the screen grid connection would be on the side of safety.

Again, it is clear that any open circuit in the anode circuit of the tube when no signaling energy is supplied to the rails will cause no electromotive force to be induced in winding M for energizing the relay MR because the anode current is normally of zero value.

Considering the effects resulting from an open circuit in the circuit associated with the control grid of the tube, if an open circuit occurs in the secondary winding l6 portion of the control grid circuit, the negative bias is maintained on, the control grid through the resistor R3. If an open circuit occurs in the resistor R3 portion of the circuit, the negative bias is maintained during the charging of the capacitor 64- due to the voltage loop of resistor R! applied through the tube space between the cathode and the control grid. This charge of the capacitor C4 builds up slowly due to the relatively high resistance of the tube space and the corresponding building up of the anode current due to the lack of the bias voltage on the control grid is so gradual that any electromotive force induced in the secondary winding 24 of transformer MT is insufiicient to operate the relay MR. Thus, there is no operation of the relay MR due to an open circuit in the secondary winding portion of the grid circuit. It should be noted that since the entire length of the control grid 2i forms a part of the circuit associated with the control grid, a break in the grid within the tube is checked just as much as a break in the circuit outside of the tube. It follows from the foregoing description of the operation of the apparatus that the amplifier circuits are immune to extraneous current, and a break or intermittent break in any circuit element does not result in an operation of the relay Although I have herein only one form of vacuum embodying my invention, it is to be understood that various changes and modifications may be made therein within the scope of the appended claim without departing from the spirit and scope of my invention.

Having thus described my invention, what I claim is:

In vacuum tube amplifier circuits, a vacuum tube having an anode, a cathode and a control grid; said tube provided with two external terminals one connected to each end of said control grid, an anode circuit including a power source connected to said anode and cathode to produce a current flow in the anode circuit as governed by applied to said control grid, a winding adapted to receive a coded carrier signaling current, a capacitor, an asymmetric unit, a resistor, a direct voltage bias source; a grid circuit including series said winding, said asymmetric unit, control grid and its two terminals and said resistor; said capacitor connected across said grid circuit at a point between said asymmetric unit and said grid and a point between said resistor and said winding, and said bias voltage source having its positive terminal connected to said cathode and its negative terminal connected to said point between said resistor and winding to bias said control grid negative in potential with respect to said cathode, and said asymmetric unit poled to pass the half cycles of said carrier signaling current tending to oppose said negative bias voltage of the control grid.

shown and described tube amplifier circuit No references cited.

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