HK1173115B - Method and apparatus for determination of the track occupancy state of a track circuit on a railway line via sequential decoding - Google Patents

Description

Method and device for determining the track occupation status of a track circuit on a railway line by sequential decoding

Technical Field

The invention relates to a method and a device for determining the occupation status of a track circuit on a railway line by sequential decoding. In particular, the present invention relates to the detection of the presence of a train or other vehicle movable on a track circuit of a railway line.

Background

According to the railway jargon, the track circuit is a section of railway track of variable length (from tens to thousands of meters) electrically insulated from the adjacent sections of railway track and having a low voltage applied to a set of two rails. The application of voltage on the charged rail takes place at one end of the track section and a voltage detector is applied in parallel with the supply point. When there is no vehicle on said track section, the detector extracts a voltage that is not zero, since the charged rail is not short-circuited by the presence of the train axles, whereas in the case of any railway vehicle arriving in the track section it short-circuits the rails to each other through its own axle and triggers the passage of a current detected by the detector or sensor during the absence of voltage across the two rails.

The technique thus enables continuous generation of information about the presence of a vehicle (stationary or travelling) in a track section, as such, for automatic control of a railway line.

The information received by a track circuit is reliable if the track circuit is absolutely electrically isolated from ground or from adjacent track circuits. Furthermore, the measurement environment is extremely noisy (enough to take into account the traction noise of the electric locomotive), and the measurement method must be practically immune even to high intensity noise signals. In addition, in the absence of trains on the circuit, the current supplied by the generator is not zero as a result of the dispersive resistance between the insulated joints and as a result of the dispersive resistance between the tracks (which depends on, for example, the railway ballast).

One proposed solution envisages transmitting an alternating voltage signal on the circuit, associated with which is a unique code word constituted by arranging a preset number of positive and negative half-waves of the alternating voltage according to a predetermined sequence.

The signal is extracted by the receiving block and then compared with the unique predetermined code word to verify whether the information is correct or whether the received signal is otherwise noise in nature.

Even if efficient, the system does not assume that the noise is "in-band" noise, i.e., noise having spectral content in the frequencies at which the unique codewords present in the transmitted sequence have spectral content.

Disclosure of Invention

The object of the present invention is to overcome the aforementioned drawbacks and to find a reliable method for reliably detecting a signal identifying the occupation status of a track circuit.

The invention relates to a method and a device, in which a signal of low alternating voltage is phase-modulated by a predetermined digital sequence of at least three mutually orthogonal unique digital code words in a track circuit forming part of a railway line, so that a sequential coding is achieved.

The encoding consists in associating the information with a code sequence that uniquely identifies it with respect to all other information and enables the receiver to extract the information from the track circuit concerned, but not from the adjacent circuits. One aspect of the invention relates to a device for verifying the occupation of a track circuit on a railway line having the features of claim 1.

A further aspect of the invention relates to a method for verifying the occupation of a track circuit on a railway line exhibiting the features of claim 7.

Drawings

The features and advantages of the method and the device according to the invention will appear more clearly from the following description of an embodiment thereof, provided purely by way of non-limiting example, with reference to the accompanying drawings, which show a block diagram of the device according to the invention.

Detailed Description

With reference to the previous figures, the device according to the invention is applied to a track circuit essentially comprising a pair of rails R formed by parallel metal section elements (metal section elements), generally T-shaped, mounted transversely to a load-bearing structure formed by sleepers made of wood, steel or cement. Each track circuit is separated from adjacent sections by electrically insulating joints G. A plurality of adjacent track circuits insulated from each other exist on the railway line.

The device according to the invention for each track circuit comprises a transmission block 2, which transmission block 2 is able to transmit to the circuit a predetermined sequence of code words that are different from each other (for example mutually orthogonal), phase-modulating the alternating voltage signal.

For the purposes of the present invention, "orthogonal" means that the scalar product between two orthogonal codewords is zero.

Preferably, each codeword is obtained by arranging a preset number of positive and negative half-waves of said alternating voltage according to a predetermined series.

In particular, a so-called spreading word S is generated, which comprises, for example, 16 chips, wherein each chip is equivalent to a sinusoidal cycle at the considered frequency, wherein a chip with a value "1" envisages a sinusoidal cycle at the considered frequency with a phase of zero, and a chip with a value "0" envisages a sinusoidal cycle at a phase of 180 °.

Said voltage signal on which the code word is superimposed or with which the code word is associated is a 50Hz, 83.3Hz or conventional voltage signal of another frequency for detecting the passage of a train on the track circuit.

By exploiting said property, the device of the invention further comprises a block 3 and a block 4, the block 3 being intended to extract or detect a voltage signal that changes its value between a maximum value in the absence of a train and a minimum value when the presence of a train closes the electrical track circuit, the block 4 being intended to process said signal.

The detected signal is sent to a processing block comprising a microprocessor and at least one analog-to-digital converter for converting the extracted signal.

The processing block 4 is adapted to compare said predetermined sequence of at least three predetermined code words with the extracted signal.

Normally, the extracted or detected signal should contain the correct predetermined sequence of unique code words. In the presence of stable noise, it is possible that two or more of the predetermined code words are received within a time interval in which the sequence of code words is expected to be received, one of the code words being correct and the other being the result of said noise.

Through the processing block, the invention can identify noise, reconstruct correct predetermined time sequence, and really determine whether the track is actually occupied, and generate the emission of an occupation signal, wherein the occupation signal has two states, namely 'occupied' and 'idle', and reveals the occupation state of the track.

According to a preferred embodiment of the present invention, the transmitter repeatedly transmits a predetermined sequence (ABC-sbc.) of at least three different code words (e.g., a first word a, a second word B, and a third word C) for a predetermined time interval.

Advantageously, the sequence may comprise a first pair, a second pair and a third pair of words, which are identical, so as to be able to perform the detection twice in one and the same time interval for each word (for example, AABBCC-AABBCC.). In this way, the reliability of the measurement is improved.

The receive block is initially synchronized with the transmit block. During each predetermined time interval it detects the transmitted signal. The processing block knows what should be the correct sequence (ABC) and compares the signal detected in the first time interval with the three code words of the sequence. If a single code word (e.g. a) is present as a result of the comparison, this essentially means that there is no noise and the detection of the signal is carried out at the next second time interval. If instead it is detected that there are a first code word and a second code word (e.g. a + C) that are different from each other, the amplitude and phase of the frequency components of both are measured. In this case, one of the two words may in fact be stationary noise. In the second time interval, ideally, only word B should be received; the comparison between the detected signal and the three code words of the sequence is repeated. If the stationary noise is present in the second time interval, the presence of two code words (e.g., B + C) is verified, one of those detected in the preceding time interval: in the example, word C. Further, during the time interval, a measure is made of an amplitude or energy value associated with the frequency component of the word. If the amplitude value of the frequency component present in the first time interval coincides with the value of the second time interval, it can be regarded as a value of stationary noise. Turning to a third time interval, it is expected that only the third code word is received, in this example C, which may be greater than or equal to the value of the stationary noise identified in the previous two time intervals.

If the vector subtraction between the calculated vector value of stationary noise (due to the value detected in the preceding time interval) and the vector of the codeword detected in the third time interval is positive and corresponds to the predetermined nominal value of the third word, the result is reliable for being able to determine whether the track circuit under examination is occupied, regardless of the (in-band) noise introduced on the spectral line of the code.

The comparison and subtraction method is repeated for all codewords (a, B, C).

Power value K_A、K_BAnd K_CCompared with a threshold value K, the power value K_A、K_BAnd K_CAssociated with the cross-correlation with the three codewords (a, B, C) of said sequence and "cleaned" of the contribution of the stable in-band perturbation; if at least one of the values is below a threshold, the measurement method considers the track circuit "occupied"; otherwise, it judges that the track is "free".

The comparison between the words is performed by performing a scalar product between the signal and the code words of the sequence assigned to the particular track circuit.

Claims (9)

1. An apparatus for determining the state of occupation of a track circuit on a railway line provided with a plurality of track circuits adjacent to each other, said track circuit comprising a pair of rails (R) formed by parallel metallic sectional elements between which a voltage can be applied, each track circuit being separated from the adjacent section by electrically insulating joints (G),

characterized in that the device comprises:

-a transmission block (2) able to transmit an alternating voltage signal to the track circuit, associated with which is a predetermined sequence of at least three code words distinct from each other, each word being transmitted in said sequence at preset time intervals;

at least one detection block (3) for detecting a voltage signal from the track circuit; and

at least one processing block (4) adapted to compare the predetermined sequence of at least three predetermined unique code words with the extracted signal.

2. The apparatus of claim 1, wherein the processing block calculates a scalar product between the voltage signal and each code word of a predetermined sequence assigned to the track circuit to obtain an energy value for each word.

3. The apparatus of claim 1, wherein the processing block comprises a microprocessor and at least one analog-to-digital converter for converting the extracted signal.

4. The apparatus of claim 1, wherein each codeword of the sequence is orthogonal to other codewords of the same sequence.

5. The apparatus of claim 1, wherein the voltage is an alternating voltage, and each codeword is formed by arranging a preset number of positive and negative half-waves of the alternating voltage according to a predetermined series.

6. The apparatus of claim 5, wherein each word comprises 16 chips, wherein each chip is equivalent to a sinusoidal cycle at the considered frequency, in which case a chip with a value of "1" is equivalent to a sinusoidal cycle at the considered frequency with a phase of zero, and a chip with a value of "0" is equivalent to a sinusoidal cycle with a phase of 180 °.

7. A method for verifying the occupation of a track circuit on a railway line provided with a plurality of track circuits adjacent to each other, said track circuit comprising a pair of rails (R) formed by parallel metallic sectional elements (B) between which a voltage can be applied,

characterized in that the method comprises the following steps:

a) transmitting a voltage signal on the track circuit;

b) associating with said signal a predetermined sequence of at least three code words different from each other, each word being transmitted in said sequence at preset time intervals;

c) detecting a voltage signal through the circuit;

d) comparing the detected voltage signal with all code words of the sequence in each of the preset time intervals to obtain an energy value of each frequency component of the word;

e) verifying the presence of the same frequency components of the code words having the same energy value in two consecutive time intervals;

f) detecting a code word and its frequency component and subtracting said same energy value from it by vector subtraction in a time interval after said two time intervals in which the same frequency component of the code word having the same energy value has been verified to be present;

g) comparing the value of the code word obtained in step f) with a predetermined nominal value of the word;

h) issuing a signal regarding occupancy of the track circuit based on the processing.

8. The method according to claim 7, wherein the comparison and subtraction process of the preceding steps d), e), f) is repeated for all codewords of the sequence.

9. Method according to claim 8, wherein a power value as a result of the subtraction, which power value is associated with the cross-correlation of the three code words of the sequence, is compared with a threshold value, and a signal indicating track circuit occupation is put into an "occupied" state if at least one of the values is below the threshold value, and otherwise the signal is put into an "idle" state.