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The present invention relates to a signal lamp arrangement for signalling information to the participants (in particular vehicle drivers) of track bound traffic. Track bound traffic includes railway traffic and other traffic of vehicles which are bound to a track during movement. The binding of the vehicle to the track is not necessarily realised by mechanical means, as it is the case with railway traffic by means of rails. Other means may be, for example, magnetic fields or automatic control which controls the vehicle not to leave the track. However, the most common application of track bound traffic is railway traffic. The present invention also relates to a system for operating the signal lamps. Key components of such a system are several lamps and at least one interlocking device which serves to control the operating state of the signal lamps.
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Conventional signal lamps comprise light sources having tungsten filaments. The filament is heated and emits light. This type of lamp is activated through its power port, i.e. the interlocking device controls an electric current to either flow through the filament or not to flow through the filament. Appropriate means to perform the control of the current are relays or electronic switches.
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It is of vital importance in all track bound traffic for the central interlocking device or interlocking system (which may comprise more than one interlocking device) to know with absolute certainty whether each individual signal lamp is switched on or switched off. If a lamp fails and the interlocking system does not have any information about the failure the interlocking system cannot initiate any other action and vehicles on the track may collide or may leave the track. Conventional lamps are therefore supervised by measuring the current that passes through them.
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Recently, LED (light emitting diode) lamps, or more broadly speaking, semiconductor lamps have started to replace conventional lamps for illuminating purposes, but also for signalling in traffic of non-track bound applications, such as crossings of streets for automobiles. However, the control devices for controlling these signal lamps cannot be compared with interlocking systems for track bound traffic. Drivers of non-track bound vehicles always (at least theoretically) have the choice to leave the present driving lane. Also, the length of the brake path of track bound vehicles is usually much longer than the length of the brake path of automobiles for example. As a result, the interlocking system of track bound traffic systems are much more complex and usually need to take into account the operating state of many signal lamps when a specific signal lamp is to be switched.
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Although semiconductor lamps are usually more reliable, i.e. they have a better mean operation time to failure relation, they have also disadvantages. Semiconductor lamps can fail in such a way that they still draw electric current when no light is emitted. In addition, it may happen that a semiconductor lamp emits light, although the power port, which is the lamp connected to, is switched off. The reason for this is that semiconductor lamps need very little power to emit light and, for example, an electric current may be induced into the lamp by magnetic induction. In particular, these two disadvantages are the reasons why semiconductor lamps have not been used for track bound traffic signalling, until recently.
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It is an object of the present invention to provide a signal lamp arrangement for signalling information for track bound traffic and to provide a method of operating such a signal lamp arrangement. The signal lamp arrangement shall be operated in a manner which requires low effort but is safe with respect to the signalling function to be performed by the lamp.
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It is a basic idea of the present invention to control the operating state of the signal lamp arrangement using control data instead of controlling the operating state by switching on or switching off the electric current to the lamp. This control, which is performed using control data, is understood to be the control of an interlocking system or interlocking arrangement. In particular, this means that the interlocking system does not directly control the switching of the lamp by switching the electric current, but rather controls the lamp arrangement by transmitting control data. The interlocking system or arrangement is understood to be a central system controlling a plurality of signal lamps. For example, the interlocking system may be installed in a central building of a railway operator. On the other hand, the signal lamps which are to be controlled may be distributed all over the railway network or part of the railway network.
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The signal lamp arrangement itself comprises a control device. This control device receives the control data and may operate the signal lamp by switching on or switching off an electric current which causes the lamp to emit light. Consequently, the signal lamp arrangement may comprise a power port for receiving electric power for the lamp and may further comprise a receiving data port for receiving the control data. One advantage of the invention is that the power source for the electric current to the lamp may be located near to the signal lamp arrangement compared to the distance between the signal lamp arrangement and the interlocking system or interlocking device. Consequently, only a data connection between the interlocking device and the signal lamp arrangement is necessary for the control of the signal lamp arrangement. In addition, the same data distribution network can be used to transfer control data from the interlocking device or interlocking system to many signal lamp arrangements. For example, a data communication structure, such as a data bus, can be used to transfer the control data. A data bus is understood to be a data communication structure wherein data to and/or from different devices connected to the bus can at feast partially use the same data transfer path for transferring data between them. Examples of a data communication system will be given below.
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Since there is no need for a power connection from the interlocking device to the signal lamp arrangement, energy losses are reduced and failure of the system due to power line failure can be avoided.
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However, a further advantage is that the data connection between the signal lamp arrangement and the interlocking device gives the opportunity to transfer additional data to and/or from the signal lamp arrangement. Additional data is meant to be data which goes beyond the basic control data that just contains the information to switch on or to switch off a specific signal lamp.
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The invention is particularly useful for signal lamp arrangements comprising at least one semiconductor lamp. However, the invention may also be applied to a signal lamp arrangement comprising a conventional lamp, such as a tungsten filament lamp.
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In particular, the following is proposed: A signal lamp arrangement for signalling information for track bound traffic, wherein the signal lamp arrangement comprises
- at least one lamp which is adapted to generate light and
- a control device for controlling an operating state of the at least one lamp, wherein the operating state corresponds to a predetermined signalling information.
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The control device is connected to a receiving data port of the arrangement and the control device is adapted to receive data via the data port and is adapted to control the operating state of the at least one lamp depending on the data received via the data port.
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Furthermore, the following is proposed: A method of operating a signal lamp arrangement for signalling information for track bound traffic, wherein
- control data is transferred to a control device of the signal lamp arrangement and
- the control device controls the operating state of at least one lamp of the signal lamp arrangement depending on the received control data.
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Preferably, the lamp arrangement also comprises a detection device for detecting the operating state of the at least one lamp. For example, the detection device may comprise at least one light sensor for detecting whether the at least one lamp is emitting light or not (or is emitting light having a predefined minimum intensity or a higher light intensity). Furthermore it is preferred that the detection result generated by detection device, or that the outcome of a data operation performed on the detection result is transferred from the lamp arrangement via a sending port to a remote device. The remote device may be the interlocking system or part of the interlocking system.
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The data which are transferred to the control device via the receiving port or which is transferred from the control device via the sending port generally comprises at least some information. Therefore, it is also possible to describe the transfer of the data as transferring at least one message. The receiving port receives messages which are considered by the control device and the sending port (if present) sends messages to at least one communication partner, in particular the interlocking arrangement.
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The data may be digital data and the data transfer may be performed using technology which is well-known for transferring data between computers. For example, TCP/IP (Transfer Control Protocol / Internet Protocol) may be used via an Ethernet data connection. Ethernet is a type of networking technology. Data is broken into packets and each packet is transmitted in particular using the Carrier Sense Multiple Access / Collision Detect (CSMA/CD) algorithm until it arrives at the destination without colliding with any other packet. Ethernet in the modem switched (point-to-point) form is standardised in IEEE 802.3 (Institute of Electrical and Electronics Engineers, Inc.). However, other communication specifications can also be used to transfer the data to and from the signal lamp arrangement, such as RS485 (now EIA-485) which is a OSI (Open Systems Interconnection) model physical layer electrical specification of a two-wire, half-duplex, multipoint serial connection.
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For example, the operating states which are controlled by the control device may be selected from the following group of operating states: "lamp on", "lamp off", "lamp flashing" (i.e. the lamp is repeatedly switched on and off). Not all of these operating states may be available for all lamps. For example, one lamp or all lamps of a specific lamp arrangement can be controlled to be either "on" (which means that the lamp emits light) or "off" (which means that the lamp does not emit light). Furthermore, there may be more operating states that mentioned in the group, such as "two lamps of the same signal lamp arrangement are switched on and off alternately".
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In particular, the arrangement may comprise a plurality of signal lamps wherein the operating state of each of the signal lamp is controlled by the control device depending on the data received via the data port.
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The signal lamp arrangement may be located at any location next to the track to which vehicles are bound during traffic and the communication receiver (such as a relay station within data transfer network or such as the interlocking arrangement) may be connected to the signal lamp arrangement via data communication lines of the data transfer network. The communication lines may be realised by electrical cables (including wires) and/or by wireless communication technology (such as W-LAN, wireless local area network).
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Preferably, the at least one lamp and the control device are integrated in a single lamp device. A single lamp device is understood to be a device which may be prefabricated and which comprises the at least one lamp and the control device. For example, the single lamp device may comprise a housing which contains the control device and the at least one lamp. The housing may further comprise a window made of transparent material wherein the at least one lamp is arranged to emit light through the window to the outside of the housing.
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Preferably, the at least one lamp is a semiconductor lamp, such as an LED (light emitting diode) lamp. A semiconductor lamp can either comprise just one semiconductor having comparatively high light power or can comprise plural semiconductor units which are operated in the same manner, i.e. are switched on and off at the same time. A plurality of semiconductor units within the same lamp has the advantage that the failure of one semiconductor unit does not necessarily result in the failure of the whole lamp.
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It is further preferred that the signal lamp arrangement comprises more than one lamp (e.g. one lamp which is adapted to emit green light, one lamp which is adapted to emit red light and one lamp which is adapted to emit white light).
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Preferably, digital data are transferred within a digital data communication system.
For example, the digital data may be data in hexadecimal format. Alternatively, or in addition, the data may be transferred to and/or from the signal lamp arrangement in data packets. Examples of such a data structure will be given in the description of the figures later. According to a particularly preferred embodiment of the invention, the control device is connected to a sending data port of the arrangement wherein the control device is adapted to send data concerning the operating state via the sending data port to a communication receiver outside of the arrangement.
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In particular, the communication receiver is the interlocking device or interlocking system. Preferably, the sending data port is connected to a different communication line than the receiving data port. For example, an Ethernet may comprise two data communication lines, one line for transferring data from an interlocking system to the signal lamp arrangements and one line for sending data from the signal lamp arrangements (and optionally from additional devices which are connected to the data transfer system) to the interlocking system. The interlocking system may be a distributed system having devices at different locations. Consequently, the different devices may be connected to the data transfer system at different connection points. For example, the data transfer system may comprise one or more network switches. A network switch is understood to be a device which is connected to the data transfer network and is adapted to realize the connection of different terminal devices to the network. A switch can be considered as an intelligent hub.
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The sending data port of the signal lamp arrangement allows transferring data concerning the actual operating state of the arrangement to the communication receiver outside of the arrangement. It is particularly preferred that the actual operating state is determined using at least one light sensor. The light sensor or another detecting device is arranged to detect the operating state of the lamp or of at least one of the lamps (in the following: the monitored lamp or the monitored lamps) of the lamp arrangement. If the detecting device comprises a light sensor or comprises a plurality of light sensors it/they detect light emitted from the at least one monitored lamp. Preferably, there is more than one light sensor arranged to detect the operating state of the same monitored lamp. If one of the light sensors fails, the operating state can still be detected.
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The control device of the signal lamp arrangement may be connected to the at least one light sensor and may be adapted to determine an actual operating state of the at least one monitored lamp by evaluating a detection signal received from the at least one light sensor. The actual operating state determined in this manner can be transferred to the communication receiver, in particular the interlocking system, by sending corresponding data via the sending data port of the arrangement. These data can also be called "status data".
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The embodiment of the invention described before is particularly reliable. The interlocking system will know with absolute certainty the operating state of each lamp which is monitored using at least one light sensor, Consequently, all disadvantages of semiconductor lamps which were mentioned in the introductory part of the description can be overcome.
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The present invention further includes: A system for generating signalling information for track bound traffic, wherein the system comprises the signal lamp arrangement (in one of the embodiments described here) and wherein the system further comprises an interlocking arrangement which is adapted to control the control device by transmitting control data to the receiving data port of the signal lamp arrangement.
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One specific embodiment of the method of operating the system includes the control data and the status data to be repeatedly transferred to or from the signal lamp arrangement in consecutive cycles, wherein each cycle comprises the control data, which is transferred to the control device, and the status data, which is transferred from the control device to the communication receiver. Consequently, the communication receiver (in particular the interlocking system) will receive status data in each cycle and it always knows the most recent operating state of the lamp.
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Examples of the invention will be described with reference to the attached drawings. The figures of the drawings show:
- Figure 1
- schematically a signal lamp arrangement having four lamps,
- Figure 2
- a system comprising a plurality of signal lamp arrangements, different power sources and an interlocking system,
- Figure 3
- the data structure of a first example of a data packet for setting the operating state of a lamp,
- Figure 4
- an example of a data packet which is transferred in order to request that a specific lamp or the corresponding control device reports the operating state of the lamp,
- Figure 5
- an example of a data packet containing information about the operating state of a specific lamp.
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Figure 1 shows a signal lamp arrangement 1, which may comprise a housing 11 and some devices 3, 12, 14, 15, 17 within the housing 11 which will be described in the following.
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The arrangement 1 comprises four signal lamps 3a, 3b, 3c, 3d. The first lamp 3a is adapted to emit red light if the lamp 3a is switched on. The second and the third lamp 3b, 3c are adapted to emit white light. The lamps 3b, 3c can be switched off and on independently of each other. The fourth lamp 3d is adapted to emit green light.
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For simplicity, the following devices are only shown in Figure 1 with respect to lamp 3d. However, corresponding additional devices may be provided for the first to third lamp 3a to 3c or some of the devices (e.g. device 14) can be adapted to operate together not only with lamp 3d but also with one or more than one of lamps 3a to 3c.
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The arrangement 1 comprises a control device 14 which is adapted to control the operating state of at least one of the lamps 3a to 3d. As shown, the control device 14 is connected to an actuation device 17 via a control signal line 16. The control device 14 can output corresponding signals via the line 16 to the actuation device 17 which signals cause the actuation device 17 to switch on or to switch off the lamp (here lamp 3d) which Is connected to the actuation device 17. Actuation device 17 is also connected to a power unit 12 of the arrangement 1 via a power line 19. The power unit 12 is connected to a power port 8 of the arrangement 1. Furthermore, the power unit 12 is also connected to the control device 14 in order to supply electric power for the operation of the control unit 14.
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Furthermore, the control device 14 is connected to a communication port 10 which is adapted to receive and to transmit data via a data communication arrangement not shown in Figure 1 (see Figure 2 for an example).
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Two light sensors 15a, 15b which are adapted to detect whether lamp 3d emits light are connected to the control device 14.
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The signal lamp arrangement 1 of Figure 1 may be operated as follows:
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A message may be received via communication port 10 by the control device 14. The message contains the information that signal lamp 3d is to be switched on (alternatively: switched off, or switched on and off repeatedly). As a result, control device 14 outputs a signal via line 16 to actuation device 17 which causes actuation device 17 to switch on (alternatively: switched off or repeatedly switch on and off) the power connection to lamp 3d so that the lamp 3d emits light (alternatively: stops emitting light or is flashing). The electric current which delivers the electric energy or power to lamp 3d is entering the arrangement 1 via power port 8, is processed (if applicable) by power unit 12, in order to adapt different voltages which may the arrangement 1 be connected to, and the resulting processed current is transferred to the actuation device 17.
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Further devices and/or connections may be provided in arrangement 1. Figure 1 is a simplified drawing. For example, the power connection between power unit 12 and actuation device 17 may comprise two wires at different electric potential.
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The two light sensors 15a, 15b detect whether lamp 3d emits light. If lamp 3d has been switched on, both light sensors 15a, 15b output a signal that lamp 3d is on. These two signals are received by control device 14 which compares the signals. If both signals contain the information that the lamp 3d is on, control device 14 decides that the lamp 3d is on. If the signals differ, control device 14 will save this information and will take this information into account in future situations. For example, if lamp 3d is switched off in the following and if sensor 15a still outputs the signal that lamp 3d is on, whereas light sensor 15b has noticed that lamp 3d has been switched off and consequently outputs a signal that lamp 3d is off, control device 14 decides that light sensor 15a is defect. Optionally, control device 14 may decide to output a message via communication port 10 to an interlocking system that sensor 15a is defect.
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It is assumed in the following that there is no defect and the description of the operation described above will be continued. Since the control device 14 has decided that lamp 3d is on it outputs a corresponding message via communication port 10 to a communication receiver, for example to the interlocking system. Consequently, the interlocking system, which sent the message to switch on lamp 3d, has received confirmation that the order has been fulfilled.
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Before the description of a specific embodiment will be continued, some optional features of the present invention will be described. These features not only refer to the example of Figure 1 and Figure 2 but also refer to other embodiments of the invention.
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Lamps of different types may be used, e.g. single light emitting diodes, multiple light emitting diodes, tungsten filament lamps, fluorescent lamps or others.
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In this document, a lamp is a single source of light (as seen by the train driver). A signal lamp is an arrangement of lamps with peripherals.
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Power may be supplied to the entire signal lamp arrangement through the power port. The power unit of the lamp arrangement may be made to handle a variety of voltage sources such as AC and DC supplies and any practical voltage level such as 12 V to 240 V. The power unit may generate the voltages that are needed by the control device and the lamps. The control device might need a stable 5 V DC to power one or more microprocessors which are part of the control device. The lamps might need a 12 V DC supply. Consequently, the power unit may be adapted to output different voltages.
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The control device handles the communication with the remote interlocking system (e.g. a computer) through the communication port and all decisions within the signal lamp arrangement are made by the control device. It receives orders from the interlocking system about the desired status of each lamp (e.g. on, off or flashing). Based on this, the control device orders each actuation device to activate or deactivate the respective lamp.
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The actuation device could be a simple relay that is (de)energised by the control device causing the supply voltage to the lamp to be (dis)engaged. It could also be a semiconductor switch. The control device preferably receives orders on a regular basis, several times per minute, so that any communication breakdown is quickly detected. The control device can be programmed to have a safe fall-back state to switch over to when a communication breakdown occurs. For example, this safe fall-back state will cause any approaching trains to stop, usually red lamp on and all other lamps off. In particular the safe fall-back state is a feature which can be realised not only in connection with the examples shown in the figures.
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The control device (which may comprise a logic unit) also reports the status of the lamps back to the interlocking system for confirmation. To know the true status of the lamps, light sensors can be mounted in such a way that they detect the emitted light (if any) coming from the respective lamp and from no other source (such as neighbouring lamps, the sun or the headlights of an approaching train). For example, the lamp may emit light to the outside of the housing through a window and there may be a rim of the window extending to the inside of the housing. In this case, the lights sensors may be placed on the opposite side of the rim when viewed from the transparent part of the window.
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Preferably, a plurality of light sensors is provided for each lamp so that a sensor failure can be detected and reported by the control device. The sensors may be constructed according to different technologies to avoid a situation where two sensors fail simultaneously in exactly the same way. Preferably, more than two sensors are provided for each lamp.
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Figure 2 shows a system having a plurality of signal lamp arrangements 1 a, 1b, 1 c, 1d. The number of four signal lamp arrangements is just an example. In practice, there will be many more signal lamp arrangements which are connected to and controlled by the same interlocking device. The interlocking device is denoted by reference numeral 21 and is connected to the signal lamp arrangements 1 via a common data bus 23. For example, the communication port 10 of the arrangement 1 shown in Figure 1 may be connected to the data bus 23.
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Furthermore, Figure 2 shows a plurality of power sources 24a, 24b, 24c. Power source 24a is connected to signal lamp arrangement 1 a, for example via power port 8. Power source 24a is adapted to provide electric power to just one signal lamp arrangement. The same applies to the second power source 24b which is connected to the second signal lamp arrangement 1 b.
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The third power source 24c is adapted to provide electric power to a plurality of signal lamp arrangements 1c, 1 d. The use of just one data bus 23 for transferring data from the interlocking device 21 to the different signal lamp arrangements 1 or vice versa reduces the amount and costs of cabling. However, the same interlocking device or interlocking system may be connected to more than one data bus.
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With reference to Figure 3 and Table 1 a data structure, namely a data packet is described. The data packet shown in Figure 3 comprises seven sub-packets 1 to 7. Sub-packet 1 comprises a data bit sequence that flags the beginning of a data package. In Figure 3, this bit sequence is denoted by STX. The same bit sequence is used for other data packets, such as the data packets shown in Figure 4 and 5.
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The last sub-packet in the data packet also contains a fixed bit sequence. However, this bit sequence flags the end of a data package and is in Figures 3 to 5 denoted by ETX. In the data packet of Figure 3, the last data packet is sub-packet 7, whereas the last sub-packet in the data packet of Figure 4 or Figure 5 is sub-packet 5 and 6.
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In order to protect data transfer against bit errors during transmission, the second last sub-packet always contains a check sum. The check sum technology is well-known in the art of data transfer and will not be described in detail. However, other technologies to secure the data transfer can be used alternatively.
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The three data packets shown in Figures 3 to 5 also have in common that the third sub-packet, sub-packet 3, contains the lamp identification which is a bit sequence uniquely assigned to a specific lamp which is referred to in the data packet. For example, the data packet shown in Figure 3 is intended to switch on lamp 3d of Figure 1. The corresponding data packet therefore contains in sub-packet 3 the unique bit sequence which identifies lamp 3d of Figure 1.
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The second sub-packet of the data packet shown in Figure 3 contains a fixed bit sequence that indicates that the data packet contains an order to bring the lamp identified in sub-packet 3 to the operating state defined in sub-packets 4 and 5 of the packet shown in Figure 3.
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The
sub-packet 4 defines the basic state of the lamp, for example on, off or flashing. Each of these basic operating states is assigned a specific bit sequence to, and the control devices of the lamp arrangements are adapted to recognise these bit sequences and to decide that the lamp should be at the corresponding operating state. Only if the basic state is "flashing", the flash frequency is defined by the bit sequence in
sub-packet 5 of the packet shown in
Figure 3.
Table 1: Explanation of the order sub-packets, see also Fig. 3 | Sub-packet number | Sub-packet content | Description | |
| 1 | Start of transmission | Fixed bit sequence that flags the beginning of a data package |
| 2 | Order | Fixed bit sequence that indicates that the data packet contains an order to a lamp on the bus |
| 3 | Lamp identification | Identifies which lamp the order is intended for (all lamps must have a unique identity) |
| 4 | Basic state | Bit sequence that indicates if the lamp should be on, off or flashing |
| 5 | Flash frequency | If the basic state is "flashing, the flash frequency is defined |
| 6 | Check sum | Protection against random bit errors during transmission. |
| 7 | End of transmission | Fixed bit sequence that flags the end of a data package |
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In the following, the data packet shown in
Figure 4 is described. Reference is also made to table 2.
Table 2: Explanation of the Status Request sub-packets, see also Fig. 4 | Sub-packet number | Sub-packet content | Description | |
| 1 | Start of transmission | Fixed bit sequence that flags the beginning of a data package |
| 2 | Status Request | Fixed bit sequence that indicates that the data packet contains a status request to a lamp on the bus |
| 3 | Lamp identification | Identifies which lamp the order is intended for (all lights must have a unique identity) |
| 4 | Checksum | Protection against random bit errors during transmission. |
| 5 | End of transmission | Fixed bit sequence that flags the end of a data package |
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The data packet shown in
Figure 4 contains five sub-packets only.
Sub-packets number 1, 3, 4 and 5 have been described.
Sub-packet number 2 contains a fixed bit sequence that indicates that the data packet contains a status request to the lamp which is identified in
sub-packet 3. Such a status request will be recognised by the control device which controls the operating state of the lamp and will cause the control device to report the present status of the lamp by sending a further data packet which is described in the following with reference to
Figure 5 and with reference to Table 3.
Table 3: Explanation of the Status Reply sub-packets, see also Fig. 5 | Sub-packet number | Sub-packet content | Description | |
| 1 | Start of transmission | Fixed bit sequence that flags the beginning of a data package |
| 2 | Status Reply | Fixed bit sequence that indicates that the data packet contains a status reply to the interlocking system. |
| 3 | Lamp identification | Identifies which lamp is replying (all lamps must have a unique identifier) |
| 4 | Basic State | Bit sequence that indicates if the lamp is on, off, flashing or in an unknown state. |
| 5 | Checksum | Protection against random bit errors during transmission. |
| 6 | End of transmission | Fixed bit sequence that flags the end of a data package |
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The packet shown in Figure 5 contains six sub-packets. The meaning and function of sub-packet 1, 3, 5 and 6 has been described. Sub-packet 2 contains a fixed bit sequence that indicates that the data packet contains a status reply to the interlocking system regarding the status of the lamp identified in sub-packet 3. Sub-packet 4 contains a bit sequence that indicates the operating state of the lamp indicated in sub-packet 3.
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The bit sequences which can be used to report the basic state are preferably same bit sequences which may be used in sub-packet 4 of the data packet shown in Figure 3. Optionally, the basic state may also be reported as "unknown", in case that there is a failure within the signal lamp arrangement, such as a defect of one or more than one of the light sensors which are assigned to the lamp and which measure light emitted by the lamp.
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Consequently, the interlocking system which has transferred a data packet of the type shown in Figure 4 will receive a data packet of the type shown in Figure 5 in response. If there is no such response, the interlocking system may decide that the status of the lamp is unknown.
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As an alternative to the use of data packets of the type shown in Figure 4, the data packets of the types shown in Figure 3 and Figure 5 may be sent automatically in cycles one after the other.
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In this case, the interlocking system may decide that the lamp is in an unknown state, if it does not receive a data packet of the type shown in Figure 5 in response to a data packet of a type shown in Figure 3.
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The communication protocol which is used to transfer the data packets shown in Figures 3 to 5 may be, for example RS485 or TCP/IP.
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A complete cycle of sending order-packets (the type of Figure 3) and of sending status reply packets (the type of Figure 5) may include one data packet of the type shown in Figure 3 for each lamp which is controlled by the same interlocking device and would include one status reply packet (the type of Figure 5) of each lamp. Consequently, the length of the cycle depends on the number of lamps which are controlled by the same interlocking device. The interlocking device knows all lamp identifiers of the lamps which are controlled by the device. For example, the list of the identifiers is saved in a data storage of the interlocking device. Furthermore, the control devices of the respective signal lamp arrangements know the identifiers of the lamp which are part of the signal lamp arrangement and which are controlled by the control device. Consequently, the respective control device recognises that a data packet of the type shown in Figure 3 or Figure 4 is intended for attention of the control device and it evaluates the information in the sub-packets of the data packets.
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For example, the signal lamp arrangement shown in Figure 1 would receive four data packets of the type of Figure 3 in each cycle of operation and would respond by sending four data packets concerning the status of each of the four lamps 3a to 3d according to the type shown in Figure 5 in each operating cycle.
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In the following, variants of the data communication between interlocking system and signal lamp arrangement or arrangements are described.
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For example, the data communication could be improved by sending additional information, for example in additional sub-packets of the data packets shown in Figure 3 to Figure 5. This additional Information may contain time stamps and/or sequence numbers. Time stamps would indicate the time when the data packet was sent by the sender, for example the interlocking system or the control device. The receiver of the packet can evaluate the time stamp and can compare the time of the time stamp with the time when the packet arrives or is evaluated. If there is an unusual time delay (for example if the time difference is greater than a predetermined threshold value) the receiver can report an error to the sender. Sequence numbers of the packets send via the data communication system may indicate in consecutive order the data packets which have been sent by a sender. Consequently, the receiver can monitor if it has received all data packets of the sequence. For example, the sequence number may be related to all packets which are to be sent to a specific lamp or to a specific control device.
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If a lamp is reported to be in an unknown state, the reason may be that different light sensors for sensing light emitted by the same lamp produce different sensor signals. For example, one sensor might output a signal meaning that the lamp is on and another sensor might output a signal meaning that the lamp is off. The interlocking system might differentiate between an unknown state of a lamp which is reported by the assigned control device and an unknown state caused by the fact that there is no status reply concerning the lamp or from the respective signal lamp arrangement. However, it is preferred that the interlocking system initiates the same action in both cases. For example, other signal lamp arrangements which are arranged at the same track as the signal lamp arrangement which is in the unknown state may be switched to "stop all vehicles on the track". This is usually done by emitting the order that these other signal lamp arrangements switch on their red lights. This action is an example of the fall-back state mentioned above.
