Pulse Code System for Railroad Track Circuits

My invention pertains to a pulse code system for transmitting data through the rails of a railroad track section. More particularly, the invention pertains to a unique pulse code system for transmitting, through the rails included in a railroad track circuit, data including both information and commands in addition to the functions of train detection and movement control.

Pulse codes, for example of an on/off direct current energy type with rates below 7 Hz, have long been used in track circuits in railroad signaling systems. These DC coded track circuits detect the presence or absence of trains within the circuit and transmit indications of advance traffic conditions which control the signals governing the train movements. The length of such track circuits may be as much as 15,000 feet which is a distinct advantage in high speed signaling systems. Such track circuits have been highly successful even though they transmit a limited amount or scope of information. One problem which has been solved over the years is that of the energy storage effect in the rails which is equivalent to a resistor-capacitor series network across the rails tending to prolong the on-time, that is, the energy on periods, of the code. Such track circuits are normally provided with a resistor shunt to quickly drain this charge from the rails during each energy off period. On occasion, a modulated alternating current may be used as the rail current, that is, the code pulses are of alternating current of a selected frequency. Such pulses may be used to control cab signals carried on the trains in addition to control of the wayside signals. Such alternating current coded track circuits are of shorter weight because of the high rail attenuation to the alternating current. It is desirable, of course, to replace the coding and decoding relays with solid state devices. However, direct substitution into the DC coded track circuit of such devices creates interfacing problems because of the track storage characteristic. Isolation between the rails and the solid state devices is also required to provide transient protection and noise reduction. Solutions to overcome the energy storage problem are possible but are complicated by the necessity for using an added means to shunt the rails during the off periods of the code pulses. The possible alternative is a bi-polar code similar to a DC pulse code but including a plurality of pulses in each code transmission. In other words, each code group includes a selected number of pulses so that the track energy storage effect is substantially eliminated within each code transmission. The result is a low frequency alternating current so that transformer coupling to the rails from the wayside apparatus is possible. This solves the interface and isolation requirements and makes it possible to transmit an increased amount of data through the rails of the track circuit.

Accordingly, an object of my invention is an improved pulse code system for transmitting data through the rails of a railroad track section.

Another object of the invention is pulse code apparatus for transmitting data through the rails of a railroad track using a code format which eliminates the track storage energy factor.

Also an object of my invention is a pulse code system which transmits data through the rails of a track circuit by a bi-polar code having a selected number of pulses with the pulse length designating the character of each pulse.

A further object of the invention is a pulse code system for transmitting information through the rails of a railroad track with a low frequency alternating current which is effectively a bi-polar direct current code with a predetermined number of pulses in each group with selected length characteristics to determine the data transmitted.

It is also an object of my invention to provide a code system for a railroad track section in which a bi-polar pulse code is used to transmit information through the rails with individual pulses having selected length characteristics to create a pattern which eliminates track energy storage distortion.

Yet another object of the invention is apparatus to transmit data in either direction through the rails of a railroad track section in which the operation of the power supply at each location to supply operating energy to the apparatus is dependent on the reception from the central data processor unit of a check signal indicating the correct operation of all elements of the system.

A still further object of my invention is a pulse code system for a railroad track section in which a low frequency alternating current in the form of bi-polar code pulses is alternately transmitted from each end, successive pulses in each code group being of opposite polarity and having selected lengths, long or short, to form a pattern which designates the data transmitted, a central processing unit at each location decoding the received pulses to register the data and checking the correct operation of each system element, this processing unit also providing a check signal, which maintains the apparatus power supply active to provide operating energy, only when correct operation of the total system is assured.

Other objects, features, and advantages of the invention will become apparent from the following specification and appended claims when taken in connection with the accompanying drawings.

According to the invention, a solid state code transmitter and receiver device is located at each end of a railroad track section to alternately transmit data codes through the rails to be received by the other end receiver element. Each code is a low frequency alternating current but with a wave form of a bi-polar direct current code that consists of a selected number of code pulses. Because of the alternating current characteristics of the code, the transmitter/receiver may be transformer coupled to the rails which isolates the solid state devices from the rail transients and provides an interface element. The pulses of this code are alternately of opposite polarity and each pulse is of a selected length, that is, long or short, to establish a code pattern which designates specific information being transmitted. The code formats are also preselected, that is, the combination of pulse lengths and opposite polarities, so that the capacitor storage effect of the rails is effectively balanced out during each code transmission. In each transmitted code, the first and last steps are synchronizing pulses which are always of relative positive polarity and have a short character. In one specific pattern which is illustrated, nine pulses are included in each code pattern with the inner seven being used to transmit the actual desired data. However, to maintain a balance of the positive and negative energy during each code, not all of the possible combinations of the seven pulses are used.

At each wayside location where adjacent track sections are adjoining, a single central data processor unit (CPU) provides control and/or data processing for the pair of associated transmitter/receivers which are connected one to each track circuit, that is, to the rails of the corresponding track section. The CPU correlates the local conditions and establishes the pulse code transmitted in each direction through the rails. Each processor unit also decodes the received pulses to register the data received from the other end of the corresponding track section. Preferably, this processing unit is a microprocessor device of solid state design such as are well known in the art. It incorporates, or associates with, the necessary memory such as programmable read only memory (PROM) devices which are considered as included in the specific showing. The CPU also receives inputs from local devices which detect train presence and traffic conditions and record other data which is to be reported. Some of the data may be received through the adjacent track section for retransmission to a central control point. Received data is registered in solid state relays and is used to control traffic and perform other functions.

The processor unit also monitors the operation of the output register relays, the input signals from the wayside logic and detectors, and other functions through the use of monitor devices and feedback signals. When these operational checks and monitoring determine that the system operation is proper and/or agrees and compares with that which is expected, the CPU generates a signal having a predetermined special characteristic. When this signal is then applied to the local power supply, it generates energy for the operation of the system apparatus at that location. The operation of this power supply element is dependent on the continued reception of the special signal from the processor and its absence inhibits the operation. This shuts down system operation at that location when an indication of improper operation or failure of any of the system elements is indicated and assures vitality of the system operation.

Before defining my invention in the appended claims, I shall describe in more specific detail a preferred arrangement of the pulse code system for track circuits embodying the invention, as illustrated in the accompanying drawings in which:

FIG. 1 is a schematic illustration of a pulse code system applied at the opposite ends of one section of railroad track.

FIG. 2 is a chart illustrating a sample pattern of a code pulse group transmitted through the rails by the apparatus embodying the invention.

FIG. 3 is a schematic block diagram showing in conventional form and greater detail apparatus at one wayside location in the system of FIG. 1.

FIG. 4 is a schematic flow diagram illustrating the checking arrangement for vitally checking the operation of the apparatus associated with one end of a track section or track circuit.

In each of the drawings, the same or similar parts of the apparatus are designated by the same or similar reference characters.

Referring to FIG. 1, across the top is illustrated a stretch of railroad track with each rail represented by a conventional single line symbol. The track is divided into insulated track sections, for example, the section T shown in its entirity and bounded at left and right by the conventionally shown insulated joints J. At each end of section T, a code transmitter/receiver device is coupled to the rails by an isolation transformer shown by a conventional symbol. The transmitter/receiver is illustrated by a conventional block, designated XMTR-RCVR, since the particular transmitter and receiver circuitry is not critical to the understanding of the invention. At each location, a similar transmitter/receiver device is coupled to the rails of the adjacent track section on the opposite side of the insulated joints J. It is to be noted that the transformer winding connections to the rails are reversed on each side of the joints so that, assuming similar polarity in the transformer track windings, the failure of an insulated joint may be detected by the opposing polarities occuring in the same rail.

The pair of transmitter/receiver units at each location are associated with a central data processing unit conventionally shown by the block designated CPU. Preferably the CPU is a solid state microprocessor device, such as are well known in the art, with sufficient memory to function in the pulse code system designed. This memory may be in the form of read only memory (ROM) or programmable read only memory (PROM) units in accordance with the operation or function desired. The pulse code to be transmitted from a location is developed by the CPU and supplied to the XMTR block for transmission through the rails. The code received through the rails from the XMTR at the other end of the section is applied by the RCVR element to the CPU for decoding. The transmitted code is developed in accordance with local input signals coupled into the CPU over relay contacts. The decoded functions or data from the received code are registered in output relays which, in keeping with the system, are solid state devices. The manner of applying the collected data for transmission and the supply of the decoded information to the registry relays is described in more detail shortly.

FIG. 2 illustrates a typical wave form of a pulse code group including nine pulses or steps which are of alternately positive and negative polarity. The polarity signifies that which appears on a selected rail in the section, for example, the upper rail of section T in FIG. 1 and the lower rail in each adjoining section. The patterns of pulse code groups of the invention are not restricted entirely to those including nine steps but such length is used in one specific system. An odd number of steps is preferable in order to obtain an unequal number of pulses of the two polarities to enable each track section to have a polarity opposite to that of an adjacent track section. As shown in FIG. 2, a long pulse is considered to represent a binary digit 1 while the short pulse represents the other digit 0. The first and last pulses of each pattern always have a positive polarity and a short character to serve as guard or synchronizing pulses. This feature, together with the odd number of pulses, also provides for detection of insulated joint failure since normally the adjacent section has a positive polarity on the other rail during these guard steps. In addition, code patterns used are so selected that the positive and negative energy substantially balances and thus the problem of track energy storage is eliminated so that no distortion occurs. The use of the odd number of pulses and balanced energy levels substantially avoids residual direct current in the coupling transformers.

Although the code appears to be patterned after a conventional DC track code, with bi-polar characteristics, it is actually an alternating current with bi-polar pulses with a maximum length for each nine step code pattern of less than 500 milliseconds, as an example from one installation. The pulses are kept relatively short in the overall time periods and a very short period of time is provided after each pulse group is transmitted to allow the apparatus at the receiver location to decode before transmitting a response.

The message or data transmitted is in accordance with a combination of long and short pulses of either polarity of the seven inner pulses, i.e., excluding the first and last guard pulses. Because the positive and negative energy must be balanced to avoid track energy storage distortion, not all possible long/short combinations of the seven pulses can be used. As will appear in other figures, input data or information to be transmitted is translated from a normal five bit form by the CPU in accordance with a predetermined tabulation into selected balanced long/short combinations of seven pulses which are then transmitted. Decoding is accomplished in the reverse direction by the CPU from received seven pulse codes into corresponding five bit outputs.

FIG. 3 is a block diagram and flow chart of the basic elements in the operation at one wayside location. The principal element is the processor CPU which, as previously mentioned, is preferably a microprocessor with the necessary associated PROM units. At the bottom of the drawing conventional blocks designate the transmitter and receiver units, one set for each adjoining track section to correspond with the arrangements shown in FIG. 1. The general inputs and outputs for the CPU are channeled through buffer elements, for example, amplifiers, to isolate the local apparatus from the processor. There is an input network, of course, from each track section while the indicated outputs which include certain common check procedures, are supplied for either section. The CPU also controls solid state output relay devices to register the received codes. Although only one is shown for each section, in practice there are normally five output relays for each section. A power supply unit, shown by conventional block, provides operating energy especially for the output relays.

It is to be noted that the operation of each relay and its output are monitored and reported back to the CPU. This monitoring network represents a vital check system to assure the correct operation of the arrangement. The processor is responsive to these feedback or check signals, if all are received in proper condition and characteristic, to produce a special signal which is applied as indicated to the power supply unit. This latter unit remains operational to supply operating energy only when the special signal is actively received. In other words, the absence of this signal shuts down the power supply so that the apparatus at this wayside location lacks operating energy and operation ceases. This condition will continue until the fault or improper operation is corrected.

An expanded version of the vital check arrangement is shown in FIG. 4, although still using conventional blocks and flow chart layout. This arrangement includes only one half of the network associated with the processor unit at a location, that is, the checking network related only to one of the adjacent track sections. The solid state relays shown in the upper right are controlled by the CPU in accordance with the received code. Only two of the five relays are specifically illustrated, each being the same and having similar connections to the processor. The output and operation of each relay is monitored and a signal returned to the CPU through a monitor buffering device as long as proper operation of the relay is detected. Each monitoring network is dynamically tested on a periodic basis to assure proper operation and integrity of not only the output relay but also the monitor device and circuits.

To assure proper operation of the inputs to the CPU from the external local relay logic, additional monitor checks are provided to assure the integrity of the external wiring and relay contacts shown at the lower right. To provide a dynamic check of the input devices, two periodic signals are produced by the processor, each of the same frequency but exactly 180.degree. out of phase with each other, as conventionally represented by the two square waveform symbols adjacent the parallel output channels from the CPU. These signals are amplified by the two output buffer devices shown, the lower buffer providing the complementary waveform to the upper one. As shown, the upper buffer is connected in multiple to all the external input relay back contacts and the lower buffer is connected in multiple to all the external input relay front contacts. Then as long as each input relay remains in either its energized or deenergized position and the input wiring remains intact, each buffer input device, which is individually connected to the respective external input relay heel contact, will have an AC waveform to buffer into the processor. In this manner, the processor will receive either the signal produced by the upper output buffer or its complement as produced by the lower output buffer at all times through each of its input buffers. The processor can establish whether the external relay is energized or deenergized by the phase of the signal received from each input buffer. The five sets of input contacts 1 to 5 shown in the lower right represent the respective states of five external logic relays which have been energized or deenergized by the conditions of associated equipment in accordance with various field conditions. The processor will receive the signal as amplified by the lower output buffer over input contacts 1, 3, and 4 and the signal as amplified by the upper output buffer over input contacts 2 and 5 and thus correctly interpret that corresponding relays 1, 3, and 4 are energized and relays 2 and 5 are deenergized. The CPU then selects, in accordance with the preset tabulation, the corresponding combination of seven code pulses for transmission.

If the CPU receives all proper monitor signals, it generates a check signal output to the power supply as shown at the upper part of the figure. This signal is illustrated conventionally as a square wave signal but, for example, in one installation is a signal having a frequency of 500 Hz. The power supply or generator shown in the upper right may specifically be a DC to DC converter to generate operating energy of a regulated nature for the solid state relays. Operation of this supply is dependent on the continued reception of the check signal, that is, the 500 Hz signal from the CPU. If no check signal is received, the power supply operation ceases and all the output relays move to their deenergized condition since no operating energy is provided. This shuts down the pulse code system apparatus at this location, which is a vital check, until any fault may be determined and corrected.

The arrangement of the invention thus provides an effective and efficient pulse code system using solid state elements for transmitting data through the rails of a track section. Codes are alternately transmitted in each direction carrying such data as train detection, advanced traffic conditions, and other information pertinent to train operation or control. Each code is actually an alternating current but with a wave form equivalent to a bi-polar DC pattern. This eliminates distortion due to track storage effect, that is, the opposite polarities cancel the usual track storage, and allows a track circuit length equivalent to that obtainable with the single polarity DC code known in the art. Checks and feedbacks into the control processor provide a vital check of the proper operation of the apparatus. Operation of the power supply which provides energy at least for the operation of the output relays is dependent on the continued reception of a special check signal from the processor unit. This signal is produced only as long as the vital monitoring operation indicates correct operation by and absence of faults in the apparatus. Detection of apparatus faults or improper operation, e.g., absence of any signal on an input buffer, shuts down the system until correction is accomplished.

Although I have herein shown and described but one arrangement embodying the track circuit pulse code system of my invention, it is to be understood that various changes and modifications therein may be made, within the scope of the appended claims, without departing from the spirit and scope of my invention.