Electrical system, arrangement and method applicable to railroad tracks Technical field

The present invention relates to railroad safety systems, and especially to track va cancy issues relating to the presence of the train in view of a signalling and control system (i.e. SCS), and also relating to issues concerning broken rail.

Background

Railroad systems require a lot of general safety related equipment and systems for ensuring a smooth and safe traffic environment for the various train traffic types (passenger trains, cargo trains), and also for lighter traffic which might cross the railroads via level crossings by cars, lorries, bikes or as pedestrian traffic. Therefore, there is a great need for having reliable sensing systems for incoming trains e.g. in a level crossing so that the barriers can reliably be lowered for car traffic control well before the passing train.

A general system concerning these issues for the railroad systems is called as Sig nalling and Control System (SCS). Traffic control may also be centralized to prem ises specialized in monitoring the traffic and various movement related information and track vacancy issues across the railroad network. Safety Integrity Level (SIL) in turn means relative levels of risk-reduction provided by a safety function, for in stance for railroad traffic. SIL may also specify a target level of risk reduction. SIL may also be defined as performance measurement required for a certain safety in strumented function. For instance, there can be a requirement for SIL where there is a safety-related malfunction only once per 10 years or more rarely.

Concerning incoming train sensing for e.g. level crossings, prior art has supplied AC electricity to the rails of the track, and further away from this spot, there has been placed a diode, which transfers the signal to a DC signal. In the starting spot, a DC relay has been placed to sense the transferred DC signal. This logic is not suitable for any electric rail roads because the supplied electric signal for the electric trains themselves will have its return current along the metal rails, and this will disturb the operational logic completely. Thus, such a prior art method is only suitable for non electric railroad tracks. That restricts significantly the operational possibilities of this prior art method, which is a major deficiency. This diode applying track circuit is currently not widely used anymore. 2

In prior art, the vacancy of the railroad track has been determined by creating a separate electric circuit so that the rails themselves form part of the monitoring cir cuit with a relay locating along this circuit. Such a circuit can be called as a track circuit. In absence of the train, the power supply signal will propagate via a relay in normal operational mode. The power supply signal may be an AC signal, DC signal, or a signal operating in audio frequencies. For a track circuit applying audio frequen cies, see “Audio frequency jointless track circuits for main line applications”, Equip ment Specification by RailCorp, vs. 1 .2, issued May 2010, reconfirmed 2 July 2019. This system is applicable to track lengths of 50-600 meters, and it uses frequencies 1700, 2000, 2300 and 2600 Hz. If there is a train on the rail section part of this electric circuit, the metal wheels and the axis of the carriage or locomotive will short- circuit this track circuit. Then the current is not anymore passing via the relay, and the relay will switch based on this change. This is an indicator of the train, i.e. of the non-vacancy within the dedicated track section. This can be used to output a red light indicator for the respective track section to the incoming traffic from another direction and well before the monitored location sensing the non-vacancy. The cir cuit structure requires insulating non-metal pieces along the rails themselves, so that the circuit can be defined to locate within a predefined longitudinal area from the relay (the power supply feeding the circuit from another end). The longitudinal length of a track circuit may be in a range of tens of meters to approximately 2 kilometers; thus, the length is restricted which is a drawback of this technique. Such non-metal pieces can have a short length (like a few centimeters), as they just insu late two consequent sections of the metallic rails electrically from one another.

These AC or DC feeding track circuits (fed from another end) are quite widely used in railroad systems, and certainly more than the diode applying track circuits.

In another prior art, a track vacancy detection section may sense and “calculate” in certain locations along the track, how many axes passes these dedicated locations. This can be implemented by dedicated sensors. The principle could be otherwise the same as in the previously discussed prior art. If there are two different sensors locating in known distance from one another, this system is able to calculate the speed of the passing train as well, from the “time stamps” of the passing of the axes.

US 4,728,063 (“Petit”) discloses sending an AC signal along the railroad tracks from the starting location. The signal is sent in a desired frequency, and along the tracks it applies repeaters, where the applied frequency is altered compared to previous repeaters. When the received signal in a certain track location among a longer track 3 length is considered missing, Petit determines that between the current repeater and the previous repeater location there is a broken rail. Repeaters are regular elec tric devices supplied themselves by regular DC supply. Also DC electricity is used in communication links between the end blocks, which is the common prior art prac tice in many 1950’s to 1970’s solutions; except Petit applies this for sensing broken rail and not for sensing the incoming train near the level crossing. Figure 4 shows a kind of AC/AC transfer between two different frequencies in an intermediate re peater, and Figure 3 shows the same in a respective end unit in the ends of the track block. The TX signal of the repeater is created by oscillator 62 and power amplifier 64. Bandpass filtering is present as well, as element 56 in Figure 3 and the element “BPF” in Figure 4.

US 3,987,989 ("Geiger”) discloses an incoming train tracking system from year 1975. Geiger traditionally inputs modulated AC carrier wave signal to the rails of the railroad track. All embodiments of Geiger comprise the same basic principle.

US 6,371 ,417 ("Southon”) discloses keeping track i.e. calculating the train wheels (or passing of them) in a certain location and a related controlling system. With an AC electric signal they tune a resonant tank circuit (in an input end), and thereafter there are coils in the circuit which monitor the eddy current losses caused by the train wheels. In practice the passing metallic wheel will change the magnetic field induced by the coil, and this change can be measured with a circuit. With this prin ciple, Southon is able to obtain the presence data of the train, movement direction and speed, measured in several locations, and these pieces of information may be applied as input data for the general train traffic monitoring system, or for the safety related apparatuses like for barrier control in a level crossing.

US 5,752,677 ("Richley”) discloses controlling of model railroads (miniatured sys tems) in a sense whether there is a locomotive or carriage in some given part of the track, or another type of physical hindrance affecting the model train’s movements. Richley feeds high frequency AC signal to the rails of the model track, where they sense impedance changes of the rails i.e. a possibly cross-circuiting or low-imped ance physical ’’intermediate” element made of electrically conductive material in a certain location between the rails, like the main axis of the carriage. In the measure ment end, there is some monitoring of the DC component, from where they are able to directly see a ’’barrier” locating on top of the rails in a given location, via the changed impedance value. The basic principle is according to the general 1950...70’s prior art but changed in a model railway world. Richley is from year 1996. 4

There are two main problems in the prior art. The first problem is that in previous arrangements for tracking the train along the longer range of the tracks, there has been a requirement to install very long sections of physical cable along the railroad tracks between the two (or more) measurement spots, e.g. right next to the tracks in a groove in the ground for instance. This has required a lot of physical labour with appropriate earth-moving machinery.

The second main problem is that several solutions above are feasibly only in non electric railroad tracks. Nowadays this requirement would restrict the use of these principles only to very rarely used track sections mainly used for cargo only. In Fin land, this requirement would mean that the respective principle would work only for very rural and rarely used railroad tracks mainly meant for cargo-based traffic only, such as for instance between Kontiomaki - Ammansaari, Hyvinkaa - Karjaa or Lau- rila (Keminmaa) - Kolari; all these track sections currently not served with any reg ular passenger traffic except the last one forming a part of Oulu - Kolari railway connection where the rare passenger traffic arriving and departing Kolari is operated by diesel locomotives. Thus, there is a need to find a monitoring system applicable to all kinds of railroad tracks; whether electric or non-electric; and whether currently used for mainly cargo-based traffic, for rare industrial (private) use, or by both reg ular passenger and cargo trains.

Summary

The present invention introduces an arrangement for monitoring railroad track va cancy or broken rail. It describes a circuitry-based arrangement connectable directly to the rails of the railroad track. The invention enables a simpler functional instal ment where there is no need for installing long sections of cables into the ground besides the track starting e.g. from a vehicular crossing, and which cables would be required to extend even 1 ...1 ,5 km along the track.

The present invention determines and uses two different locations along the railroad track. We call them later as first and second locations for simplicity; and their pur poses will be further clarified with the enclosed drawings. The present invention feeds direct current (DC) into the rails in the first location along the tracks. The sec ond location may locate e.g. 1-1.5 kilometers from the first location. In the second location, an oscillator arrangement is connected into the rails there. The oscillator circuit will “detect” the incoming DC signal, if there is an intact rail between the two locations, and if the rail between the two locations is free from trains. In such a case, 5 the oscillator will output an alternating current signal back to the rails, which will in turn propagate back towards the first location. In case there is a moving or stationary train between the two locations, the DC signal will pass via the wheels and the wheel axis of the train (i.e. locomotive or carriage), which means that the oscillator signal does not detect a DC input. The same situation occurs in case of a broken rail be tween the two locations, when the DC signal won’t reach the oscillator circuit in the second location.

Thus, the oscillator circuit will feed the AC signal back to the rails in the second location only, if a train-free and intact rail prevails for the whole length between the two locations. This is a good indication for safety-focused indications serving the CCS system of the railroad system. In the present invention, the AC signal, or the lack of it, is detected in a relay of a device unit close or on the first location. The main electrical supply from the top wirings above the train track will not have a harm ful effect in this AC signal detection, which is a major advantage as the present invention is as such applicable to electric railroad lines. The AC signal frequency may be selected to be between 50 Hz and 2000 Hz, for instance. As a singular value example, 200 Hz may be selected but this is also merely just an embodiment. The device unit may be provided with a high-pass filter with e.g. 100 Hz cut-off frequency, which ensures that the 50 Hz main electric supply will be filtered off and it will not harmfully effect the detection of the AC signal output by the oscillator circuit.

In other words, the present invention introduces an arrangement (10) for monitoring railroad track vacancy or a broken rail, according to a first aspect of the present invention. The arrangement is characterized in that the arrangement comprises:

- a DC voltage source (11), configured to feed direct current voltage into rails (19a-b) of the railroad track, the DC voltage source (11 ) locating in a first loca tion along the railroad track,

- a dedicated DC/AC converting part (12, 13), configured to trigger an AC signal on and into the rails (19a-b) based on a sensed DC voltage originating from the DC voltage source (11 ), the dedicated DC/AC converting part (12, 13) locating in a second location along the railroad track, and

- an AC measurement circuitry (14, 15, 16, 17, 18), comprising a high- or a band pass filter (14), and a detector (18), locating in the first location along the railroad track.

In an embodiment of the present invention, the arrangement further comprises a relay in or connected to the AC measurement circuitry (14, 15, 16, 17, 18), which 6 relay is configured to switch, when a pending AC signal disappears as sensed by the detector (18).

In an embodiment of the present invention, the arrangement is configured to work according to an operational principle, where in case of a train locating between the first and second locations, the axis of a carriage or a locomotive of the train will form a part of the current-flowing circuit induced by the DC voltage source (11 ), thus keeping the AC signal untriggered in the dedicated DC/AC converting part (12, 13).

In an embodiment of the present invention, the arrangement is configured to work according to an operational principle, where in case of a broken rail locating between the first and second locations, the circuit induced by the DC voltage source (11 ) will be cut, thus keeping the AC signal untriggered in the dedicated DC/AC converting part (12, 13).

In an embodiment of the present invention, the dedicated DC/AC converting part (12, 13) comprises an oscillator (12) and a FET (13), whose gate is connected to the oscillator (12), and whose source and drain are connected to the two rails (19a- b), respectively.

In an embodiment of the present invention, the AC measurement circuitry (14, 15, 16, 17, 18) further comprises a transformer (15), a rectifier circuit (16) and a balanc ing capacitor (17).

In an embodiment of the present invention, the cut-off frequency of the high-pass filter (14) is configured to be a value higher than 50 Hz and less than 100 Hz.

In an embodiment of the present invention, the oscillator (12) output signal fre quency is selected from a range of 100 ... 300 Hz.

In an embodiment of the present invention, the high-pass filter (14) is configured to prevent the electrical main power signal of 50 Hz to proceed from the rails (19a-b) into the detector (18).

In an embodiment of the present invention, the distance between the first and sec ond locations is selected between 1 ... 2 kilometers. 7

In an embodiment of the present invention, the arrangement (10) is set to work with a device unit, wherein the device unit comprises the relay, and where the elements of the arrangement (10) are controlled by a processor, controller, or by an external computer.

According to a second aspect of the present invention, it introduces a method for monitoring railroad track vacancy or a broken rail. The method is characterized in that the method comprises the steps of:

- feeding direct current voltage into rails (19a-b) of the railroad track by a DC voltage source (11 ), the DC voltage source (11 ) locating in a first location along the railroad track,

- triggering an AC signal on and into the rails (19a-b) by a dedicated DC/AC con verting part (12, 13) based on a sensed DC voltage originating from the DC voltage source (11 ), the dedicated DC/AC converting part (12, 13) locating in a second location along the railroad track,

- which AC signal is set to proceed back along the rails (19a-b) and further into an AC measurement circuitry (14, 15, 16, 17, 18), comprising a high- or a band pass filter (14), and a detector (18), locating in the first location along the railroad track.

Brief description of the drawings

FIG. 1 illustrates an embodiment of the circuit structure and electric principle ac cording to an example of the present invention.

Detailed description

The present invention introduces an arrangement for monitoring railroad track va cancy or broken rail, and a respective monitoring method as well. The railroad track vacancy can be monitored in a freely selectable section of the tracks; for both elec tric and non-electric railways. In an embodiment of the present invention, the se lectable section of the tracks is determined to be between a selected first location and a selected second location. For instance, the first location may locate close to a level crossing in a device unit, which controls also the barriers of the level crossing prohibiting the vehicular access across the train line. Respectively, the second lo cation may locate along the train tracks in a certain distance from the first location; enabling an incoming train to be noticed well before that train would pass the level crossing. In this way the device unit may lower the barriers and turn on the warning 8 signs well before the train has reached the actual location of the level crossing. The speed limit of the respective train track section may also affect the desired length between the first and second locations. In any way, the present invention does not require any instalment of physical cables along the railroad tracks between the first and second locations; therefore, the length between these two locations can be se lected based on the monitored track length requirements and usual speeds of the trains in the respective track section, and any other required conditions or parame ters affecting the situation. In an embodiment of the present invention, the railroad track length to be monitored may be around 1 ... 1 ,5 km long section along the railroad tracks. In practice, the maximum track section length which can be moni tored with the presented method and apparatus, is several kilometers and certainly much more than with presently applied track circuits according to the prior art.

FIG. 1 illustrates an embodiment of the electric circuit structure (i.e. arrangement 10) and electric principle according to an example of the present invention, for mon itoring presence of a train in a predetermined railroad track section, and/or for mon itoring a discontinuity along the train tracks (i.e. rails 19a, 19b) in the predetermined railroad track section. The latter functionality can be also called as tracking a broken rail along the train tracks.

The presented electric principle and electric circuit structure (i.e. arrangement 10) comprises a DC voltage source 11 in the first location along the tracks. Furthermore, the circuit structure comprises an AC measurement circuitry 14-18 in the first loca tion; in practice realized rather close or adjacent to the DC voltage feeding point, but not necessarily in the same exact feeding point of the DC voltage source 11 on the rails of the track; meaning that the exact longitudinal locations of the connecting wires for elements 11 and 14-18 on the tracks can be different. Both the DC voltage source 11 and the AC measurement circuitry 14-18 are connected directly to the metallic rails 19a-b of the train track, thus making the rails 19a-b themselves an active part of the created electric circuitry. The positive terminal of the DC input voltage is connected to the upper rail 19a (depicted from the above), and the nega tive terminal of the DC input voltage is connected to the lower rail 19b, but of course, the order could be the opposite. Similarly, the AC measurement circuitry 14-18 is connected to both rails 19a-b a little bit apart from the input voltage feeding point, for instance. 9

In an embodiment, the AC measurement circuitry 14-18 comprises a high-pass (“HPF”) or a band-pass filter (“BPF”) 14, a transformer 15, a rectifier circuit 16 (de picted as a bridge rectifier comprising four diodes), a balancing capacitor 17 and a detector 18. The whole arrangement 10 may be controlled by a controller, a proces sor or a computer (not shown in Fig. 1 ).

In the predetermined range from the first location, there is the second location of the train tracks, which comprise a second required part of the electric circuit structure (i.e. arrangement 10); and this part can be called as a dedicated DC/AC converting part 12-13. It comprises an oscillator 12 and a FET 13 (i.e. Field-effect transistor). These components are connected between the rails 19a-b in the second location so that the oscillator 12 basically takes an incoming DC voltage as an input and creates AC voltage as its output. The FET 13 works its part in this transformation. The in coming DS (drain-to-source) voltage for the oscillator 12 is supplied by the gate of FET 13, where the drain and the source terminals are connected to the rails 19a, 19b, respectively, in this embodiment.

As the fed DC voltage is directly affecting the drain to source voltage (VDS) of the FET 13, this will make the FET 13 conductive, meaning that we’ll have a positive ID (drain current) and Is (source current) as well. The operational conductivity of the FET 13 will also affect the gate of the FET 13, creating a gate voltage VG. This voltage VG will act as an input DC voltage trigger for the AC signal to be created by the oscillator 12.

In the dedicated DC/AC converting part 12, 13, the oscillator 12 frequency may be selected among various possible frequency values. In a preferred embodiment ac cording to the present invention, the selected frequency is selected to be a value higher than 50 Flz, because the main electric power supply signal operates in 50 Hz in electric railroads e.g. in Finland. In one embodiment, the oscillator 12 frequency is selected to be between 100 ... 300 Hz. In yet another embodiment, the oscillator 12 frequency is selected to be 200 Hz.

In other words for the above description about the FET 13 connection within the arrangement 10, the dedicated DC/AC converting part 12, 13 further comprises a FET 13, whose gate is connected to the oscillator 12, and whose source and drain are connected to the rails 19a-b, in an embodiment of the invention. Such a connec tion may be used to act like a DC/AC converter acting in a circuit formed partly by metallic rails 19a-b of the train track, where the incoming signal propagates from left 10 to right (see Fig. 1 ) and the converted signal propagates in the opposite direction, from right to left. Thus, the first and second locations along the train track define the practical ends of the defined electrical “circuitry”. It can be said that the arrangement 10 sends a DC signal along the tracks, and in the second location the signal “bounces and converts” into an AC signal, which can be sensed back in the 1 ^st lo cation. As the rails 19a-b form an intact metallic route, the created circuit may have a longitudinal length in a range spanning several kilometers. One restriction of the present invention within the range between the first and second locations is that the rails 19a-b should not include completely insulating sections or pieces which would cut the conductive route for the DC or AC electric signals. However, separate rail track pieces which are electrically otherwise separated because of a railway switch or branching (i.e. dividing) rail, can be connected electrically in series with appropri ate conductive means (i.e. connective wires). With this way, there can be railway switches or dividing rail branches between the first and second locations, and the observed rail section would cover all parts connected in series. In this sense, the length of the observed area can also be increased, without requiring any longitudinal cabling instalments along the railroad tracks. The high-pass or band-pass filtering 14 (discussed later in detail) makes it sure that the originally sent DC electric signal nor the main power supply signal (in 50 Hz frequency) will not affect i.e. disturb the sensed AC signal.

Furthermore, as the electrical circuitry is largely formed of the metallic conductive rails 19a-b, there is no need to install long sections of cables along the tracks be tween the first and second locations. This is a major advantage of the present in vention. This applies to intactly (no branches) extending railroad tracks, and also any railroad sections which are connected one after another in series (see the pre vious paragraph).

Thus, the present invention works also for branched or divided sections of the rails. Such railroad branches or “branched areas” are common near the stations and in the end parts of railway yards, and naturally also in regular division locations of two railroad tracks. The presented arrangement for monitoring railroad track vacancy or broken rail works also in this case for the whole branched area. The branched area covers all the rail branches which are in electrical connection with the first location (the DC feeding point). When the train emerges on the branched area on any divided section of the rails, it will short-circuit the DC circuit, and the second location with its dedicated DC/AC converting part 12-13 will not “see” the DC voltage from the DC source anymore. 11

As mentioned above, the AC-converted, “bounced” signal is directed to the AC measurement circuitry 14-18 which comprises a high-pass or a band-pass filter 14, a transformer 15, a rectifier circuit 16, a balancing capacitor 17 and a detector 18, in an embodiment of the invention. The rectifier circuit 16 may comprise one or sev eral diodes, or a bridge connection as depicted in Fig. 1 .

In an embodiment, the second element in the AC measurement circuitry 14-18, which is the transformer 15, may have a voltage change ratio of 1 :2.

In an embodiment, the high-pass filter 14 cut-off frequency can be selected e.g. between 60 ... 90 Hz, if the oscillator 12 frequency is 100 Hz or larger.

If the oscillator 12 frequency is selected e.g. to 200 Hz, then a band-pass filter 14 letting through signals between frequencies 100 Hz and 300 Hz can be used, for instance. Then, the 50 Hz main power supply signal won’t reach the AC measure ment circuitry 14-18 from the rails 19a, 19b. Of course, any other appropriate cut off frequency values can be selected for the used filtering, no matter whether a high- pass filter or a band-pass filter is selected to be used.

The detector 18 is connected to a relay of a device unit, which may be set to switch when there is a sensed difference between presence and non-presence of the AC signal. Furthermore, the device unit and all above defined elements part of the ar rangement 10 may be controlled by a processor, controller, or by a separate com puter. Such a computer may also locate externally, or as a server in a cloud. Thus, either local or remote controlling/monitoring of the DC voltage source 11 , the detec tor 18 and the relay is enabled. There may be a user interface, which enables the setting of the DC input voltage magnitudes, and/or the setting of the high-pass filter 14 cut-off frequency (if tunable in the first place).

The main operational principle of the invention is as follows. The arrangement 10 is configured to work according to an operational principle, where in case of a train locating between the first and second locations, the axis of a carriage or a locomo tive of the train will form a part of the current-flowing circuit induced by the DC volt age source 11 , thus keeping the AC signal untriggered in the dedicated DC/AC con verting part 12, 13. In other words, when a train or a locomotive is present between the first and second locations, the created DC voltage will short-circuit via the me tallic wheels and their connecting axis, meaning that the rest of the circuit from the train location towards the second location will be electrically cut, i.e. redundant. In 12 this way, the VDS of the FET 13 in the dedicated DC/AC converting part 12, 13 will be zero in the presence of the train in that section. Because of this, the oscillator 12 input voltage will remain zero as well, meaning that the oscillator 12 output is zero too. Thus, the part of the rails 19a-b between the train and the dedicated DC/AC converting part 12, 13 will be missing both the DC and the AC signals. This means further that the detector 18 will not sense any received signal (i.e. no AC nor DC signal). This change in the reception and detection of the AC signal will trigger the relay, and it will be sensed by the controlling logic operated by the respective com puter or controller. This piece of data (i.e. information) can be fed into the control room data or directly into a control signal for the barriers of the level crossing, for instance.

Respectively for the second operational area enabled by the present invention, the arrangement 10 is configured to work according to an operational principle, where in case of a broken rail locating between the first and second locations, the circuit induced by the DC voltage source 11 will be cut, thus keeping the AC signal untrig gered in the dedicated DC/AC converting part 12, 13. In this situation, the created electrical circuit is simply cut in the case of a broken rail locating between the first and second locations. This results in the same input voltages as in the previous paragraphs, i.e. VDS = 0, meaning that no AC signal is created by the oscillator 12. The detector 18 will sense that the received AC signal amplitude is zero, triggering the relay as described in the previous paragraph. In an embodiment, if the system knows otherwise (i.e. from other control room information, like e.g. GPS-based lo- cationing) that there is no train in the given railroad track section, the system may output a warning, and the maintenance personnel may be sent to inspect the rail road section for finding and repairing the broken rail location. Naturally, all the train traffic can be halted close to the broken rail location, when such a warning is first received, by the light-signal devices along the train tracks.

Just for clarification of the determined terminology; when we define and discuss the first location and the second location, they are not meant to be restricted only to a single exact place on the train tracks for the first location, and respectively, to an other single exact place on the train tracks for the second location. On the contrary, the first location is meant to mean a certain area along the train tracks, where the device unit locates. The input DC voltage 11 connection point may locate in a bit different location than the connections for the AC signal towards the AC measure ment circuitry 14-18. Also the second location means an area (i.e. a range along the tracks) where the elements 12 and 13 are connected, and not an exact singular 13 positional location along the train tracks. What is important in the present invention, is that the mutual distance between these two areas is long enough in order for the present invention to be practical in sensing the incoming train (or a stationary but closely locating train). Usually, this mutual distance is around 1 ... 2 kilometers, for instance, when considering level crossings and their warning systems. However, for usage situations in (or close to) railway switches e.g. near train stations, where the train speeds are smaller, the distances between the first and second locations may be clearly shorter, like e.g. tens of meters. Such a vacancy or occupancy information along a shorter section of the railroad tracks can be even used as added information for controlling switches (i.e. for ensuring or double-checking the vacancy of the switch concerning a train on the switching area of the tracks), or providing appropri ate information to a train traffic control room or to the train station premises or to information screens on the station platforms, for instance.

Additionally, the arrangement described in the present invention may be used as an input data for an interlocking system, or to a signal box of the railroad system. In this sense, the present invention may connect to the overall safety arrangements involved in the train traffic control itself and also in connection to the level crossings of the railroads. The present invention may also be used in providing positioning data of the trains in the rail network; either for passenger services e.g. via a smartphone app, or to other passenger information channels, such as in-train screens or information screens in the train stations or platforms. We note that by using solely the invented principle for locationing of the trains, the positioning accu racy is only approximate as the inspected train track section may be 1 ... 2 kilome ters long. However, the present invention may be used as an assisting tool for any other locationing systems applied for the trains in the railroad track network.

The present invention is not restricted merely to the embodiments discussed above but the present invention may vary within the scope determined by the claims.