EP0470416A2 - Track circuit with cross-correlation - Google Patents

Abstract

A track circuit is disclosed, the receiver (E) of which carries out, for the purpose of track-release indication, a cross-correlation between a track voltage tapped off on the track (GL) and a reference voltage which is derived from the transmission signal of the track circuit transmitter (S) or generated separately. The maximum of the cross-correlation is sought by receiver (E) and compared with a predetermined threshold value. An embodiment with purely digital operation uses a track current source as transmitter which is controlled by a completely modulated transmission signal which is read out cyclically from a ROM. A microcomputer serves for calculating the cross-correlation function in the receiver (E) and for evaluating and tracking the maximum. The reference voltage is generated with the aid of a further ROM in the receiver (E) which is programmed in the same way as the transmission-side ROM. <IMAGE>

Description

The invention relates to a track circuit according to the preamble of claim 1.

Such a track circuit is known from an essay by D. Poole and D. Barker with the title "Digitally coded track circuit", the content of which at the international conference "Electric Railway Systems for a New Century", which took place from September 22nd to 25th 1987, was held in London, England, and was also printed as conference paper (IEE, London, England, 1987, pp xii + 400.). To check whether the track voltage recorded contains modulation impressed on the track current, a correlation of the modulation signal obtained on the receiver side with a target signal known to the track circuit receiver and modulated on the track current on the transmitter side is carried out here. So-called gold codes, which have particularly well-defined autocorrelation properties, are used as modulation signals.

Such a track circuit is also known from "Signal + Draht" 81 (1989) Issue 7/8, pages 158 ff. However, instead of a correlator, a code comparator is used to compare the modulation signal obtained on the receiver side with a target code used for modulation in the track current circuit transmitter.

The known track circuits are complex due to the components required for filtering and demodulation and are not drift-free due to the use of analog techniques.

The invention has for its object to provide a track circuit of the type mentioned that does not require special filters and demodulators and works without drift.

This object is achieved by the features specified in the characterizing part of patent claim 1.

The track circuit according to the invention no longer requires filter components, since the cross-correlation itself has an excellent filter effect. Only those signal components of the track voltage contribute to the value of the cross-correlation function which, over time, correspond to the reference voltage synchronous with the modulated output voltage of the track circuit transmitter.

What the track current modulation looks like is also irrelevant as long as the time course of the output voltage of the track current circuit transmitter is known to the track circuit receiver and the modulation contains sufficient frequency components that are not related to the carrier frequency.

That the track circuit receiver knows the output voltage of the track circuit transmitter can, for example, as stated in claim 2, be ensured by a direct supply of this output voltage to the track circuit receiver, which is particularly useful when the track circuit transmitter and track circuit receiver are housed in the same subrack.

A further development of the invention is specified in claim 3 and provides for the output of the finished modulated track circuit end signal from a pre-programmed read-only memory. This saves a special modulator for modulating a track current carrier signal. Since the track current circuit end signal is available here in digital form, it does not represent a major effort to transmit it in digital form as a reference signal to the receiver. The transmission is thus less susceptible to interference. A special A / D conversion in the track circuit receiver with digitally working correlator is not necessary.

An embodiment of the invention reproduced in claim 4 relates to the conversion of the track current circuit end signal stored in digital form into a control signal for a track current source.

The embodiments described in claims 3 and 4 do not require the presence of a transmission line as claimed in claim 2 if the reference voltage required for cross-correlation can be made available to the track circuit receiver in some other way.

Claims 5 and 6 therefore correspond to claims 3 and 4 except for the reference to claim 2.

As a further development of the invention, patent claim 7, which refers back to patent claims 5 and 6, provides for the generation of the reference voltage required by the correlator in the track circuit receiver with the aid of a read-only memory which is preprogrammed in the same way as the read-only memory of the track circuit transmitter and with a reading frequency of the track circuit transmitter which is the same frequency Clock is read out. This eliminates the need for a transmission line between the track circuit transmitter and the track circuit receiver. The latter is particularly advantageous when the track circuit transmitter and the track circuit receiver are to be accommodated in a spatially separate manner.

Claim 8 relates to a possibility of distinguishing a busy message due to real occupancy of the track circuit from a busy message due to a fault (e.g. overloading of the track circuit receiver input when the loop is interrupted).

A development of the invention specified in claim 9 relates to simplification in the direct transmission of a reference signal from the track circuit transmitter to the track circuit receiver.

Claim 10, finally, relates to the use of a computer for performing the correlator function and evaluating the correlator output voltage.

• Fig. 1 zeigt schematisch die Ausbildung eines isolierstoßfreien Gleisstromkreises an einem Gleis,
• Fig. 2 zeigt einen Gleisstromkreissender nach der Erfindung,
• Fig. 3 zeigt einen Gleisstromkreisempfänger nach der Erfindung.

An embodiment of the track circuit according to the invention will now be described in detail with reference to 3 figures:

• 1 shows schematically the formation of an insulation shock-free track circuit on a track,
• 2 shows a track circuit transmitter according to the invention,
• Fig. 3 shows a track circuit receiver according to the invention.

1 shows a track GL, the rails SCH of which are electrically connected to one another by two rail connectors (so-called S connectors) SV1 and SV2. The rail connectors are short-circuits, which firstly allow the drive reverse current to be equalized between the two rails and secondly form electrical isolating joints that each separate two adjacent track circuits. A track section GA lying between the two rail connectors SV1 and SV2 is secured by a track circuit. It is fed at a feed point ES by a track current circuit transmitter S via a first coupling loop KS1, which is inductively coupled to the rails and the rail connector SV1, with a modulated track current. The track current flows via the rail connector SV2 located at an exit point AS and induces a track voltage in a second coupling loop KS2 which is inductively coupled to the rail connector SV2 and the rails and is evaluated by a track circuit receiver E. Further coupling loops KS3, KS4 shown in FIG. 1 belong to neighboring track circuits. A signal line L connects the track current circuit transmitter S and the track circuit receiver E to one another and is used for the transmission of synchronization signals or code selection signals. Of course, instead of a feed-in and feed-out via coupling loops, a direct feed-in and feed-out or a direct feed-in with inductive coupling-out can also be provided. The latter is e.g. common in middle-fed double track circuits.

The track circuit receiver E then outputs a track clear signal via a track clear signal channel GF to an interlocking SW if the track voltage picked up via the coupling loop KS2 exceeds a predetermined threshold value and additionally has the modulation impressed on the track current by the track current circuit transmitter. If the track circuit is short-circuited by axles of a vehicle, the track voltage drops below the threshold value and a busy message is output to the signal box via a track occupancy signaling channel GB.

The additional criterion agreement of the modulation in the transmit and in the receive signal as a prerequisite for a track vacancy detection is necessary despite the highest possible selectivity of the track circuit receiver, since the phase-gated vehicles in service today can generate interference currents of any frequency and therefore it cannot be ruled out that in the occupied track section the threshold value of the track voltage is exceeded, which would cause a track vacancy detection without an additional criterion. If a modulation comparison is also carried out and the output of a track vacancy detection is made dependent on the correspondence of the modulation signals, the track vacancy detection is to be regarded as safe, because it cannot be ruled out that a vehicle emulates the exact modulation code.

The track circuit shown schematically in Fig. 1 and implemented in a known manner contains a large number of components, e.g. Tuning modules and input filters that ensure the selective reception of the track current frequency and other frequencies, e.g. filter out the different track current frequencies of the neighboring tracks. The tuning modules and input filters must be specially designed for each track current frequency and individually adapted to each track circuit.

In Fig. 2, a track circuit transmitter is shown schematically how it can be used in a track circuit according to the invention.

Various transmission signal sequences (carrier + modulation) are stored in advance in the form of a sequence of bytes in a programmable read-only memory PLC. Each byte contained in the memory specifies a very specific amplitude value of the transmission signal.

A clock generator TG controls two counters Z1 and Z2, the counter Z2 directly and the counter Z1 via a divider TL. The counter Z1 outputs a sequence of addresses of the bytes stored in the read-only memory and thus ensures that a corresponding sequence of bytes is output on the adjustable counter Z2.

This sequence of bytes, if it is dense enough, e.g. 10 bytes per carrier period already represents the finished (modulated) transmission signal, which, repeated cyclically, only needs to be converted into an analog signal and amplified by a low-pass filter in order to be fed into the track GL.

The counter Z2 takes care of the D / A conversion if it is preset in parallel by each byte read in and is clocked back by the fast clock of the clock generator and, for example, L- during the clocking back. Outputs signal at its output. It thus generates a pulse width modulated analog signal at its output, which can be used directly to control a track power source.

The read-only memory can easily be designed so large that several different transmission signal cycles are stored and e.g. can be selected using a selector switch TA, not shown, using the higher-order address bits of the memory. Different track current profiles can thus be assigned to neighboring track circuits.

For example, a memory can be used which has 16 address bits, 12 of which are used to select and output the total of 2 ¹² bytes of the respectively selected transmission signal cycle. The remaining 4 (more significant) address bits are then used to select 2 ⁴ = 16 different transmission signal cycles.

The output signal of the read-only memory is additionally transmitted in digital form to the track circuit receiver E via a data line L1 and is fed there to a correlator which carries out a cross-correlation between a track voltage tapped at the exit point of the track section and the voltage transmitted by the track circuit transmitter.

For this purpose, the track voltage is amplified and converted into digital form.

z.B. über jeden Signalzyklus berechnet und die Verschiebungszeit ₇ so einregelt, daß KKF maximal wird. Der Rechner bewertet auch die Höhe des Maximums gegenüber einem vorgegebenen, fest abgespeicherten Schwellwert und gibt ein Gleisfreimeldesignal ab, wenn das Maximum der Kreuzkorrelationsfunktion den Schwellwert übersteigt. Bleibt das Maximum der Kreuzkorrelationsfunktion unterhalb des Schwellwertes, wird der Gleisabschnitt besetzt gemeldet. Eine zusätzliche Störungsmeldung wird ausgegeben, wenn ein hoher Effektivwert der Gleisspannung festgestellt wird, jedoch die Korrelationsfunktion einen niedrigen Maximalwert aufweist. Die Bestimmung des Effektivwertes der Gleisspannung kann dabei durch Berechnung der Autokorrelationsfunktion des Gleisspannungssignals erfolgen, deren Wert dem Effektivwert entspricht.A microcomputer is expediently used as the correlator, which has the value of the cross-correlation function

For example, calculated over each signal cycle and the shift time ₇ adjusted so that KKF becomes maximum. The computer also evaluates the height of the maximum in relation to a predetermined, permanently stored threshold value and emits a track vacancy signal if the maximum of the cross-correlation function exceeds the threshold value. If the maximum of the cross-correlation function remains below the threshold value, the track section is reported occupied. An additional error message is issued if a high RMS value of the track voltage is determined, but the correlation function has a low maximum value. The RMS value of the track voltage can be determined by calculating the autocorrelation function of the track voltage signal, the value of which corresponds to the RMS value.

3 shows a track circuit receiver which, as described above, has a computer R as a correlator and an A / D converter W for converting the track voltage tapped at track GL into digital form. The computer gets its work cycle from a quartz-stabilized clock generator TG1. However, the computer does not receive its reference signal required for correlation with the track voltage signal from the track current circuit transmitter, but from a receiver-side read-only memory SPE, the size and content of which corresponds exactly to the read-only memory PLC of the track current circuit transmitter. The computer controls the output of the respectively selected signal cycle via a bus B and reads it in as a reference signal. If the clock of the clock generator TG1 matches the clock of the clock generator TG of the track circuit transmitter and the same signal cycle is set on the selection switch as on the selection switch of the track circuit transmitter, the signal read out by the computer R from the memory SPE corresponds exactly to the transmission signal of the track circuit transmitter and can be used as a reference signal . Small deviations in the quartz frequencies of the two clock generators are corrected by tracking the time shift ₇ when determining the maximum of the cross-correlation function.

The track circuit receiver according to FIG. 3 thus enables the output of a track vacancy signal to a track vacancy detection channel GF, a track occupancy report to a track occupancy reporting channel GB and a fault report to a fault reporting channel ST without requiring an additional direct connection between the track circuit transmitter and the track circuit receiver.

Claims (10)

1. Track circuit with a track circuit transmitter, which feeds a modulated track current into the rails of a track section at an infeed point and with a track circuit receiver containing a correlator, which detects and picks up and absorbs a track value that is present at an exit point on the rails of the track section and is induced there in a coupling loop issues a free message for the track section when the part of the track voltage recorded caused by the track current fed in has a predetermined minimum amplitude and additionally contains a modulation impressed on the track current, characterized in that the correlator (R) of the track circuit receiver (E) carries out a cross-correlation of the track voltage recorded with a reference voltage which corresponds in time with the output voltage of the track circuit transmitter (S), thereby determining the maximum of the cross-correlation function and outputting a track vacancy signal if this maximum has a predetermined threshold value exceeds. 2. Track circuit according to claim 1, characterized in that a transmission line (L) is provided between the track circuit transmitter and the track circuit receiver, via which the correlator of the track circuit receiver the output voltage of the track circuit transmitter or a signal derived therefrom is supplied as a reference voltage. 3. Track circuit according to claim 2, characterized in that a controllable current source is used as the track current transmitter, which is a previously generated, stored in a read-only memory (PLC) as a result of digital amplitude values and is cyclically read out from this with a stabilized clock transmitted signal as a control signal. 4. Track circuit according to claim 3, characterized in that the controllable current source contains a presettable counter (Z2) which works as a pulse width modulator and converts successive bytes read from the read-only memory (PLC) of the transmission signal into control pulses, the width of which is specified in the respective byte Amplitude value is proportional. 5. Track circuit according to claim 1, characterized in that a controllable current source is used as the track current transmitter, which is a previously generated, stored in a read-only memory (PLC) as a result of digital amplitude values and is cyclically read out from this with a stabilized clock transmitted signal as a control signal. 6. Track circuit according to claim 5, characterized in that the controllable current source contains a presettable counter (Z2) which operates as a pulse width modulator and converts successive bytes read from the read-only memory (PLC) of the transmission signal into control pulses, the width of which is specified in the respective byte Amplitude value is proportional. 7. track circuit according to claim 5 or 6, characterized in that the correlator (R) of the track circuit receiver (E) as a reference voltage, a previously generated, the stored in the read-only memory of the track circuit transmitter, corresponding in a reception-side read-only memory (SPE) and stored with this a stabilized signal, which is read out in the track current circuit transmitter (S) for reading out the transmission signal, has the same frequency. 8. Track circuit according to one of the preceding claims, characterized in that an effective value determination of the track voltage signal is additionally carried out in the track circuit receiver and that a fault message is output when an effective value of the track voltage signal exceeding a predetermined threshold value is measured at a low maximum value of the cross-correlation function. 9. Track circuit according to claim 2, characterized in that the correlator for searching the maximum of the cross-correlation function correlates the signum of the reference voltage with the track voltage recorded. 10. Track circuit according to one of the preceding claims, characterized in that a microcomputer is used as the correlator (R) and for evaluating the correlator output voltage.

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