GB2501914A

GB2501914A - Security system monitoring a cable associated with a railway line or perimeter fence

Info

Publication number: GB2501914A
Application number: GB1208230.1A
Authority: GB
Inventors: Tom Robst
Original assignee: Thermocable Flexible Elements Ltd
Current assignee: Thermocable Flexible Elements Ltd
Priority date: 2012-05-10
Filing date: 2012-05-10
Publication date: 2013-11-13
Anticipated expiration: 2032-05-10
Also published as: GB201208230D0; GB2501914B

Abstract

A security system is provided comprising at least a linear sensor 106,108 and a controller 104 attached to the linear sensor. The controller is configured to detect a break in the linear sensor; determine the geographical position of the controller; and transmit a message including an indication of the geographical position of the controller if a break in the linear sensor is detected. The controller may further determine the length along the linear sensor at which the break has occurred. The controller may utilise time domain reflectometry to determine the length along the linear sensor. The transmitted message may further include an indication of the position of the break in the linear sensor. The linear sensor may comprise a twisted pair of wires (see figure 2), each wire having a polyethylene foam coating, and a resistance connected between ends of the pair of wires distal to the controller. A value of an electrical property of the linear sensor may be read in order to detect a break in the linear sensor. The electrical property may indicate an open circuit condition of the linear sensor.

Description

Security System The present invention relates to security systems and in particular security systems using linear sensors.

There are a large number of applications in which security systems can be used to help monitor the status of an entity. For example, a security system might be used to help monitor the integrity of an item or a perimeter, such as a wall or a fence. Some such applications are in remote locations in which there is little or no access to utility services.

Further, the entity being monitored can be very large in size and can require very many sensors in order to try and reliably monitor the state of the entity. The large number of sensors adds to the complexity and cost of the security system.

Even if sufficient sensors are provided to reliably monitor a large entity, if it is desired to determine the location of an anomalous event, then mechanisms need to be put in place to determine which of the many sensors detected the event of interest and also to try and determine positional information for that sensor. This also adds to the complexity and costs of a security system.

Linear sensors which detect vibrations can be used. However, these can be prone to false alarms, particularly when used in environments in which machinery is present which causes vibration during its normal operation.

It would therefore be beneficial to be able to provide a security system which can reliably monitor large items and provide information regarding the location of anomalous events in a simple way. Also, it would be beneficial to be able to reduce or eliminate false alarms so as to increase the confidence in alarm state detection.

According Lo a first aspect of the invention, there is provided a security system. The security system can include at least a first linear sensor and a controller attached to, or which can be attached to, the linear sensor. The controller can be configured to detect a break in the linear sensor. The controller can also be configured to determine the geographical position of the controller. The controller can further be configured to transmit a message including an indication of the geographical position of the controller if a break in the linear sensor is detected.

As a linear sensor is used, large, extensive entities can be reliably monitored, using a single sensor, rather than having to rely on multiple sensors. Further, the controller can detect a break in the linear sensor, which can correspond to an anomalous event happening to the entity whose security is being monitored. Such an event might be related to theft of or damage to the entity. Furthermore, the controller can determine its geographical location and transmit a message including its geographical location when a break in the linear sensor its detected and so the approximate location of the anomalous event can be determined automatically and quickly. Hence, when a very large entity is being monitored, it is easier to determine approximately whereabouts the anomalous event has occurred thereby reducing the time and effort required to take any action in response to the anomalous event, such as a repair.

The security system can further comprise a second linear sensor. The controller can be flmher configured to detect a break in either the first and/or second linear sensor and transmit a message including an indication of the geographical position of the controller if a break in the first and/or second linear sensor is detected. The system can include a plurality of linear sensors and be configured to operate for each linear sensor connected to it. Hence, a greater area can be monitored using multiple linear sensors and a single controller.

The controller can be further configured to determine a length along the first and/or the second linear sensor at which the break has occurred.

An electrical method can be used to determine a length along the linear sensor. The electrical method can be based on identifying the location of an open circuit in the linear sensor. Preferably, the controller is configured to usc time domain reflectometry to determine the length.

The controller can be further configured to increase the width of a subsequent signal pulse used in the time domain reflectometry if no reflected signal is received for a previous signal pulse. This helps to optimise the accuracy with which the position of the break can be measured.

The controller can include a counter. The counter can be used to determine a time used to calculate the length of the linear sensor at which the break exists. The counter can be a double data rate counter. The output of the counter can correspond to receipt of a return pulse and be used to calculate the length. The counter can be implemented by a complex programmable logic device.

The message can also include an indication of the position of the break in the first and/or second sensor. The indication can be a length or distance along the or each linear sensor from the controller at which a break in the or each linear sensor has been identified.

The controller can be further configured to periodically or continuously monitor the or each linear sensor for a break. Monitoring the or each linear sensor can include electrically monitoring. The controller can apply an electrical signal to the first andlor second linear sensor. The electrical signal can be a voltage. The value of the voltage can be known by the controller. The controller can further read a value of an electrical property of the linear sensor in order to detect a break in the linear sensor. The electrical property can be a voltage across the linear sensor.

The value of the electrical property can indicate an open circuit condition of the linear sensor. An open circuit can be indicated by the read value having approximately the same value as the voltage applied to the first and/or second linear sensor. The electrical signal is a first voltage and the read value can corresponds to the first voltage.

The or each linear sensor can comprise at least one pair of wires. The or each pair of wires can be a twisted pair. Each wire can have a coating. The coating can increase the characteristic impedance of the linear sensor. The coating can be extruded onto the wire.

The coating can be a foam. In particular the coating can be a polyethylene foam coating.

A resistor can be connected between ends of the pair of wires distal to the controller. The resistor can have an impedance substantially the same as the characteristic impedance of the linear sensor.

The strength of the wires of the linear sensor can be selected to break when a force of more than approximately 75N is applied to the linear sensor.

The diameter of each wire can be in the range of approximately 0.2mm to 1.0mm.

The characteristic impedance of the or each linear sensor can be greater than 50 ohms and preferably at least approximately 150 ohms. This helps to increase the length of the linear sensor over which the position of a break can be reliably detected.

The or each linear sensor can have a length of at least 1 OOm, at least SOOm, at least bOOm, at least 2000m or at least S000m.

The controller can be configured to wirelessly transmit the message. The message can be wirelessly transmitted using a mobile telephone standard and/or a wireless networking standard. Hence, the system can send notifications even from remote locations at which no wired communication connection is available.

The message can be an email message or an SMS message.

The security system as claimed in any preceding claim, and further comprising one or more batteries. The battery can be a rechargeable battery. The rechargeable battery can be part of the controller. The battery can be an external battery, and can be a lead acid battery.

The security system can further comprise a source of solar powered electrical power. The source can include one or more solar panels or similar.

A further aspect of the invention provides a security installation, comprising: the security system according to the preceding aspect of the invention and an extensive entity, wherein the or each linear sensor is intimately attached to the extensive entity.

The or each linear sensor can be arranged such that at least one wire of the linear sensor will break if the extensive entity is cut, broken or otherwise damaged.

The or each linear sensor can be attached to the extensive entity by a plurality of fixings, for example cable ties. The or each liner sensor can be attached to the extensive entity by bonding, for example, by an adhesive.

The extensive entity can be a cable.

The or each linear sensor can be provided within an outer housing of the cable.

The cable can be a ground cable associated with a railway line.

The extensive entity can be a perimeter structure. The perimeter structure can be a wall, a fence or a barrier or other similar structure.

The perimeter structure can be associated with a facility. The facility can be of various different types, such as, for example, a factory, an office, a prison, a hospital, an industrial plant, a military site, a defence site, a government site, a security site, a transportation site, an airport, a dock, a warehouse, a telecommunications site or a server farm.

A further aspect of the invention provides a method for monitoring the security of an entity. The method can comprise monitoring the integrity of a linear sensor attached to the entity to detect a break in the linear sensor. Responsive to detecting a break in the linear sensor, a message can be transmitted including an indication of the geographical position of the linear sensor.

The method can further comprise, responsive to detecting a break in the linear sensor, determining a length along the linear sensor at which the break has occurred. The message can further include an indication of the position of the break in the linear sensor.

The message can be transmitted wirelessly. Tile message can be an email or an SMS message.

The message can be transmitted to a remote recipient device. The recipient device can be a computing device.

The message can be transmitted to a wireless communication device. The wireless communication device can be a portable wireless communication device such as a laptop, PDA, notebook, tablet, telephone, and in particular a smart phone.

The message can be transmitted to a web server. The web server can be an email server or can host a website.

The method can further comprise aft aching the linear sensor intimately to the entity. The linear sensor can be attached using a plurality of fixings or by bonding, for example, using an adhesive.

The entity can be a cable, and in particular an electrical ground cable associated with a railway line.

The entity can be a perimeter structure associated with a facility.

Preferred features of the method can also include counterpart features to the preferred features of the previous aspects of the invention.

A further aspect of the invention provides a linear sensor. The linear sensor comprises a pair of wires. Each wire can have a coating of a material to increase a characteristic impedance of the linear sensor. Each wire can have a proximal end for connecting to a controller and a distal end. A resistor can be attached across the distal ends of the wires.

The impedance of the resistor can substantially match the characteristic impedance of the linear sensor.

The pair of wires can be twisted. The pair of wires can be covered with a metallic braid.

The linear sensor can include an outer housing or cover which encloses the pair of wires.

The linear sensor can be at least several hundred meters or a few kilometres long. For example, the linear sensor can be at least, or longer than, lOOm, 200m, 500m, l000m, 2000m or S000m.

The characteristic impedance can be greater than 50 ohms, and preferably at least 150 ohms.

The coating can have been extruded onto each wire.

The coating can be a foam. The foam can be of a dielectric material, such as polyethylene.

The foam can have been expanded during extrusion onto the wire.

An embodiment of the invention will now be described in detail, by way of example only, and with reference to the accompanying drawings, in which: Figure 1 shows a schematic block diagram of the security system according to the invention being used to monitor a cable; Figure 2 shows a schematic diagram illustrating a part of a linear sensor of the security system; Figure 3 shows a schematic block diagram illustrating a controller of the security system; Figure 4 shows a schematic circuit diagram illustrating an integrity checking circuit of the controller; and Figure 5 shows a process flow chart illustrating a method of operation of the controller of the security system according to the invention.

Similar items in the different Figures share common reference signs unless indicated otherwise.

With reference to Figure 1, there is shown a schematic block diagram of a security system according to the invention and providing part of a larger security installation generally designaied 102. The security system 100 includes a controller 104 and a first linear sensor 106 and a second linear sensor 108 each connected to the controller 104 at a proximal end. Each of the first and second linear sensors can be approximately 2km in length.

The security installation 102 includes a ground cable 110 associated with a railway line 112. The ground cable 110 is generally known in the art and is provided so as to provide a ground connection to discharge any electrical currents flowing in the rails of railway line 112. Railway ground cable 110 generally has a thick copper core with an outer sheath or housing. The first and second linear sensors are intimately connected to the ground cable 110, for example, by cable ties at intervals along the length of the linear sensors. It will be appreciated that the linear sensors can be attached in other ways. For example, the linear sensors can be adhered or bonded to the ground cable. Also, in other embodiments, the linear sensors can be provided as an integral part of the ground cable.

For example, the linear sensors and ground cable can have a common outer housing or sheath.

Controller 104 includes at least a first antenna 120. The controller can, in some embodiments, have an external source of power, such as an external battery or local connection to mains power 122 and / or a solar power source of electrical power 124, such as a solar panel or similar. However, in other embodiments, no external sources of electrical power may be provided and the controller 104 may have an onboard battery instead.

As ftirther illustrated in Figure 1, controller 104 can communicate via antenna 120 with a communication network 140. As illustrated in Figure 1, the controller 104 can wirelessly communicate with a local antenna 142 of a mobile or cellular telephone network in communication 144 with the network 140. Network 140 will be understood to include parts of the mobile or cellular telephone infrastructure and also one or more computers connected to or in communication with a wide area network, and in particular, the internet. A first server 146 is in communication with network 140, a first client computer 148, associated with user 150, is in communication with network 140. Further, a wireless communication device, such as a smart phone, 152, also associated with user 150, is in communication with network 140.

It will be appreciated, that in other embodiments, if a wired connection to network 140 is available close to the controller in a wired connection instead of a wireless connection may be provided. Alternatively, a wireless access point, rather than a mobile phone antenna, may provide the communication path to the network 140. lnespective of the specific physical layer connection, the controller 104 can send messages to devices connected to network 140 in order to notify the status of the entity under protection.

Owing to the significant amount of copper present in the ground cable 110, such ground cables are frequently stolen in order to sell the copper. Many railway lines are in remote locations and therefore it is particularly difficult to be able to determine when a ground cable has been stolen. Also, railway lines are typically very long, and so it is difficult also to determine the location at which any cable has been stolen, once the theft has been identified. The invention is therefore particularly applicable to providing increased security for the copper ground cable 110. However, it will be appreciated that the invention is not limited to this application. Rather, the invention can be used to provide enhanced security for any kind of extensive entity, particularly situated in remote locations. For example, the system can be used with perimeter structures, such as walls, fences or barriers and the linear sensors can be intimately connected to, or built into, the wall, structure or barrier such that if there is a break to the wall, structure or barrier, then the linear sensor will also become broken, and the controller can detect that break and issue an appropriate notification, as described in greater detail below.

Figure 2 shows a sectional view through a part of a one of the linear sensors 106, lOS, illustrating their physical construction and designated generally 160. Each linear sensor includes a pair of twisted wires, each including a copper core, 162, 164 having a coaling of polyethylene foam 166, 168 formed on the wire by extrusion. The wire 162, 164 is in the form of a copper core having a diameter in the range of approximately 0.2mm to 1mm, corresponding to breakage forces in the range of approximately 10 Newtons to 1,000 Newtons. The foam coating increases the characteristic impedance of the cable to approximately lSOOhms, compared to the typical impedance of a standard coaxial cable of approximately SOOhms. Having an enhanced characteristic impedance of the linear sensor cable improves the distance over which breakages can be detected using time domain refiectometry as described in greater detail below. Finally, the linear sensor cabic 160 has an outer coating 170 of polyethylene to provide environmental protection. In some embodiments, the linear sensor cable can also include a shield to reduce electromagnetic interference from external sources, such as RF transmitters or high voltage switch gear. For example, the shield can be provided in the form of a metallic braid arranged around the pair of twisted wires of the linear sensor cable.

The distal ends of the linear sensor are connected by a resistor of known value, e.g. lSOOhms, generally matching their characteristic impedance, and as illustrated in Figure 4, and described in greater detail below.

Figure 3 shows a schematic block diagram of the security system 100 and in particular the controller 104 in greater detail. Controller 104 includes a housing 200 enclosing various electrical circuits and components, as illustrated. Although not shown in Figure 3, controller 104 includes various connections, such as power and signal pulses, by which vertical power and control and data signals can be supplied to and transmitted between the various parts of the controller.

Controller 104 includes a power supply module 202. Power supply module 202 supplies various power signals to the other parts of the controller and includes battery charger circuitry to charge on board batter 203, which may be in the form of a lithium iron rechargeable battery. As described with reference to Figure 1, in some embodiments, a solar powered power source 124 may also be provided. In those embodiments, the power supply module also includes a maximum peak power tracking circuit to manage the solar panel 124. Also, if the security system is used in an environment in which mains power is available, then a supply of mains power 122 may be connected to the power supply module 202. Additionally, or alternatively, as a supply of power, or back up power, an external battery, 123, can also be provided, such as a lead acid battery.

Controller 104 also includes a combined communicator and locator module 204.

Communicator and locator module 204 provides functions to send messages to external devices and also to determine the geographical location of the controller 104. Although illustrated as a single module in Figure 3, two separate communicator and locator modules may be provided, however, the communicator and locator functions can be easily implemented in a combined or separate GSM/GPRS and GPS chipset, such as a Leon GSM/GPRS module and a Neo GPS module, each available from U-Blox AG of Switzerland The controller can include a first antenna 206 for communication purposes and a second antenna 208 for receiving location related signals, such as GPS signals. It will be appreciated that antennae 206 and 208 may in some circumstances be combined into a single antenna. Also, antennae 206 and 208 may actually be enclosed within housing 200 or may be external to housing 200.

Controller 104 also includes a pulse generator module 210 which can operate to generate pulses of variable widths for use in time domain reflectometry measurements of the linear sensor cables.

Controller 104 also includes a circuit 212 for checking the integrity of each of the linear sensors in order to detect a break in either or both of them. The integrity checking circuit 212 will be described in greater detail below with reference to Figure 4.

Finally, controller 104 includes a micro-processor and complex programmable logic device (CPLD) implementing a double data rate counter. As understood by a person of ordinary skill in the art, a double data rate counter can count at twice a nominal clock frequency by counting on both the rising and falling edge of a clock pulse. By implementing the double data rate counter using the complex programmable logic device, a lower specification micro processor can be used thereby reducing the cost and complexity of the controller.

Figure 4 shows a part of controller 104 including pulse generator 210 and a part of the integrity checking circuit 212 associated with the first linear sensor 106. It will be appreciated that a similar second integrity checking circuit is provided for the second linear detector 108 also. The first integrity checking circuit 230 includes a first resistor 232 of known value, e.g. 1 OkOhms, designated RI. A first end of resistor Ri is connected to a first voltage Vi and a second end is connected to a switch 234, the pole of which is connected to a line 236 from which voltage Vo can be read by microprocessor 214. The other contact of switch 234 is connected to an output of the pulse generator 210.

The pole 240 of switch 234 is also connected to first wire 162 of the linear sensor at its proximal end. The distal end of the first wire 162 is conncctcd to the distal end of the second wire 164 by resistor 242, designated R2, and having a value of approximately lSOOhms, matching the characteristic impedance of the linear sensor. The proximal end of the second wire 164 of linear sensor 106 is connected to a second ground terminal which is itself connected to ground via ground connection 216.

The integrity checking circuit 230 provides a low interference method for checking the integrity of the linear sensors as it produces substantially less EMI, for example to any external, nearby telecommunications cables, than if an approach were used in which high frequency signal pulses were continuously sent down the linear sensor to check its integrity. Hence, the two stage approach of using a low EMI DC voltage measurement signal initially to detect cable integrity and then using a pulsed approach to detect cable break length makes the system particularly suitable for use in environments in which EMI arising from the system needs to be low.

Operation of the security system 100 will now be described, with reference to the process flow chart illustrated in Figure 5.

Figure 5 shows a process flow chart illustrating a method 300 of operating the security system according to the invention. It will be appreciated that the overall process flow is controlled by microprocessor 214 with various operations carried out by the various components, modules and circuitry present in the controller 104.

After power on, at step 302, various initialisation routines are carried out by microprocessor 214. Once normal operation of the controller has been established, at step 304, the controller checks the integrity of each of the linear sensors attached to it. In particular, the microprocessor causes measuring voltage Vito be applied across resistor Rl and the first linear sensor 106 with switch 234 set in the first position illustrated in Figure 4. As will be appreciated, resistors Ri and R2 effectively act as a voltage divider in which the measured output voltage Vo is given by Vi x R2 Hence, if there is no (Rl÷R2) open or short circuit present in linear sensor 106, then Vo will have a low value above ground. Alternatively, if there is a short circuit present between wires 162 and 164 of linear sensor 106, then Vo will be close to ground, or approximately OV, depending on the inherent resistance of wires 162 and 164 and their length at which thc short circuit occurs. If on the other hand there is a break in cable 106 such that either wire 162 or 164 is broken, then an open circuit condition arises and the value of Vo will be approximately Vi.

Hence, at step 306, microprocessor 214 reads the voltage on line 236 and determines the value of Vo. It is determined at step 308 whether Vo is approximately equal to Vi or OV.

If Vo does equal Vi, then an open circuit condition has occurred in the first linear sensor indicating a break in the first or second wire and therefore a broken flag is set for the first linear sensor at step 310. If Vo is approximately equal to OV then a short circuit has occurred and again the broken flag is set for the 1" cable (but in the sense of indicating a fault in the cable). Otherwise, processing proceeds along line 312 and at step 314, the microprocessor reads Vo for the second linear sensor at step 314. The microprocessor determines at step 316 whether Vo equals Vi or OV and if so then a broken flag is set for the second cable. If Vo is not determined to be equal to Vi or OV at step 316 then processing proceeds as indicated by process flow line 320 to step 322.

At step 322, the microprocessor determines whether a broken flag has been set for either the first or second linear sensor. If a broken flag has not been set for either sensor, then processing proceeds to step 324. At step 324, the microprocessor instructs the UPS subsystem to determine the current location of the controller. It will be appreciated that the stage at which the location of the controller is determined is not essential. Further, once the location of the controller has been determined, it may be stored in memory and simply retrieved from memory. However, at some stage, the UPS system does determine the location of the controller. At step 326, the microprocessor instructs the USM / GPRS communication module to send a notification to a remote recipient device over the communication network. Depending on the nature of the recipient device, the notification may be sent using various formats. For example, the notification may be sent as an SMS message or an e-mail message. In this instance, as no break or fault in either linear sensor has been detected, the message may include an indication of the geographical position of the controller and also an indication of the status of the linear sensors as being unbroken or otherwise normal. Processing may then return, as illustrated by process flow line 328 to step 304. After a suitable delay, the integrity check signal may again be applied to the linear sensors to again determine whether there has been any break in the linear sensors since the last integrity check.

Returning to step 322, if the broken flag has been set for either cable, then processing proceeds to step 330. Switch 234 is activated by the microprocessor to connect the pulse generator 210 to the linear sensor for which a break or fault has been detected. At step 330, the microprocessor instmcts the pulse generator to generate and output an electrical signal in the form of a pulse and having a narrowest width available from the pulse generator. The microprocessor triggers pulse generation, and the CPLD counter starts counting on the rising edge of the generated pulse. If a return pulse is detected then the counter stops and at step 335, the polarity of the return pulse is determined. If an open circuit has occurred in the linear sensor, i.e. at least on of the wires has broken, then the return pulse will have the same polarity as the initially sent pulse. Alternatively, if there is a short circuit, then the return pulse will have the opposite polarity to the initially generated pulse. Hence, the microprocessor stores a data item or data items indicating whether the polarity of the returned pulse is the same or opposite to the initially sent pulse. At step 336, the microprocessor converts the counter value into a time value.

Using the speed of propagation of the pulse along the wire (typically approximately 3/4 of the speed of light), which is locally stored by the microprocessor, the distance that the pulse has travelled is calculated using speed multiplied by time. This corresponds to the return journey by the pulse and therefore the distance at which the break has occurred is half of the return journey distance of the pulse. Hence, at 336, the distance of the break or fault from the controller along the linear sensor is determined.

However, if at step 332, no return pulse is detected after a set time limit, then processing proceeds to step 334. At step 334, the pulse width is incremented and the microprocessor again triggers pulse generation of the pulse generator using the increased pulse width.

For example, the initial pulse width may be approximately lOnanoseconds. A short pulse width is preferred as it provides increased sensitivity to measurement of distance, owing to the increased sharpness of the rising edge of the pulse. As the pulse travels down the cable, the energy of the pulse is absorbed and the shape of the pulse changes such that a short pulse may not be detectable after it has travelled over a long distance. However, a broader pulse may be detectable over longer distances and therefore in the event that a short pulse cannot be used to measure a break at a long distance along the cablc, then the pulse width is increased until a return pulse can be detected.

As discussed above, the characteristic impedance of the linear sensor is increased compared to that of a conventional coaxial cable. This is because less pulse energy is absorbed for a cable with a high characteristic impedance. Hence, increasing the impedance of the linear sensor improves the ability to detect breaks over long distances.

When a return pulse is detected at step 332, then the microprocessor detennines the distance along the cable at which the break has occurred at step 336. The microprocessor then instructs the locator module at step 324 to determine the location of the controller and at step 326 a notification is sent using the USM! GPRS communication module. The microprocessor includes logic to determine whether to send a cable beak' message or a cable fault' message depending on the polarity of the return pulse as determined at step 335. When a break in the cable has been detected, then the notification includes the location of the controller, an indication of which of the linear sensors has been broken and also optionally, the distance along the linear sensor at which the break has occurred.

When a fault in the cable has been detected, then the notification includes the location of the controller, an indication of which of the linear sensors has a fault and also optionally, the distance along the linear sensor at which the fault has occurred.

It will be appreciated that in circumstances in which a break or fault in both linear sensors has been detected, then pulses are sent down each of the linear sensors to identify the position of the break or fault for each sensor and the notification can include details for both sensors.

As described above with reference to Figure 1, the notification sent by the controller 104 can be intended for various different remote receiver devices. For example, in one embodiment, a notification is only sent if a break in one of the sensors has been detected and the message can be sent as an SMS message to a wireless telecommunication device, such as a smart phone 152, associated with a user 150 responsible for the security of the item being monitored by the security system. For example, the end user 150, may be a maintenance or security manager of the railway and the message may be notification indicating the localion of the controller and an indication that a break has been detected in the sensor, and hence the railway ground cable 110. The user 150 therefore has an approximate indication of the location of the break in the sensor as the position of the controller 104 is communicated in the SMS message. Further, as the user receives the message in approximately real time, the user can instruct law enforcement and!or maintenance personnel to take any necessary action. Further, the SMS message may include an indication of the approximate length of the cable at which the break has occurred to help the law enforcement and/or maintenance personnel to determine more accurately the location of the break and/or theft.

Similarly, the message may be sent as an e-mail to an e-mail client on a client computer 148 associated with the end user 150. The e-mail may be sent to an e-mail server which pushes the e-mail notification to a client e-mail application resident on the end users computer 148. Additionally, or alternatively, the e-mail may be received by an application program running on the end users computer 148 which processes the information received in the e-mail in a variety of ways. Additionally, or alternatively, the controller may send raw data in the form of UDP packets to a server 146 which hosts a website providing access to information about the security and or fault status of the installation, in this instance, the railway ground cable 110. The web server may include an application with logic to process the received message to provide fhrther detailed information available to an end user via a web browser. Similarly, an application hosted on the end user's client machine 148 may also include logic to process the information received in raw data form from the controller so as to provide further information to the end user. For example, notifications may be sent even when no break or fault in the cable has been detected so that the current status of the cable can be displayed to an end user at all times. When a break or fault is detected, then the controller position information included in the notification can be processed so as to display a visual indication on a map as to the location of the controller to which the broken cable is attached. Additionally, or alternatively, based on other information available to the application, such as the position and direction of the entity being monitored, such as the path followed by the railway line and/or ground cable 110, the application may apply logic to try and more accurately determine the exact location of the break or fault, based on the distance along the linear sensor at which the break or fault has occurred. A visual indication may be provided on a map of the actual location of the break or fault in the cable. Additionally or alternatively, logic may be provided to ftrther process the position of the break or fault in order to determine some ancillary information which might be useftil in responding to the break or fault. For example, logic may determine a nearest road or access point by which law enforcement and/or maintenance personnel might access the site at which the break or fault has occurred. As will be appreciated, this can act as a deterrent in preventing theft of the cable. It can also improve the speed with which maintenance can be carried out to replace or repair the stolen length of cable thereby reducing down time of the railway line for safety reasons.

As linear sensors are used, covering a long distance, for example several kilometres, a reduced number of sensors can be used while still providing entire coverage of the entity being monitored. Further, even in remote locations in which no utilities are available, the controller, being self-contained or self-reliant in some embodiments, can still be used.

Further, owing to the inclusion of the UPS module providing positional information, it is possible to easily determine the location of the break or fault within a practicable distance, rather than having to search the entirety of a large structure in order to try and identify the location of a theft or damage or a fault. Furthermore, the provision of communication fianctionalities allows a notification, virtually in real time, of the occurrence of any break giving rise to an alarm status at a remote location thereby improving the speed with which remediative action can be taken.

As discussed above, the invention is not limited to the application of railway ground cables. Rather, the invention has a wide range of applications to extensive structures where security, based on damage to the structure is desired. Other applications include various perimeter structures, such as walls, fences or ban-icades in which it is desirable to identify a breach of the perimeter structure. These may have both civilian and non-civilian, military, commercial and other applications. As well as helping identify purposeful breakage, such as occurring during theft, the system can also be used to identify accidental breakage and thereby provide a safety system which is considered to fall within the general gambit of security systems per Se.

As discussed above, the diameter of the wires in the linear sensor are responsible for the load under which the linear sensor will break. The strength of the wires in the linear sensor can be tailored to break under a pre-determined load. For example, the load may be a compromise between forces likely to be experienced during handling of the sensor during installation, forces likely to occur during typical use of the entity being protected and excessive forces likely indicative of damage, theft or other mishandling of the entity to which the linear sensor is attached.

IS

As further discussed above, the linear sensor may be attached to the entity being protected in a number of ways. Some ancillary mechanical fastening means may be used. The linear sensor may be adhered or otherwise bonded continually, or in different locations, to the entity being monitored. The linear sensor may be formed as a part of the entity being protected. Generally, the linear sensor is intimately attached to the entity being protected such that damage to the entity being protected is likely also to result in breakage of one or more of the wires in the linear sensor.

Various modifications and changes to the specific embodiment described will be apparent to a person of ordinary skill in the art. Further, the description of the control in terms of functional modules is merely by way of clarify of explanation. The control is not necessarily limited to the structures used to describe its functional properties. The functions provided by the controller may be realised in other circuitry, modules and components as will be apparent to a person of ordinary skill in the art from the above teaching.

Claims

CLAiMS: 1. A security system, comprising: at least a first linear sensor; and S a controller attached to the linear sensor, wherein the controller is configured to: detect a break in the linear sensor; determine the geographical position of the controller; and transmit a message including an indication of the geographical position of the controller if a break in the linear sensor is detected. I0
2. The security system as claimed in claim 1, and further comprising: a second linear sensor, and wherein the controller is configured to: detect a break in either the first or second linear sensor; and transmit a message including an indication of the geographical position of the controller if a break in the first or second linear sensor is detected.
3. The security system as claimed in claim 1 or 2, wherein the controller is further configured to: determine a length along the first or second linear sensor at which the break has occurred.
4. The security system as claimed in claim 3, wherein the controller is configured to use time domain reflectometry to determine the length.
5. The security system as claimed in claim 4, wherein the controller is further configured to increase the width of a subsequent signal pulse used in the time domain reflectometry if no reflected signal is received for an previous signal pulse.
6, The security system as claimed in claim 4 or 5, wherein the controller includes a double data rate counter and wherein an output of the counter corresponding to receipt of a return pulse is used to calculate the length.
7. The security system as claimed in any of claims 3 to 6, wherein the message also includes an indication of the position of the break in the first or second sensor.
8. The security system as claimed in any preceding claim, wherein the controller is further configured to: apply an electrical signal to the first or second linear sensor; and read a value of an electrical property of the linear sensor in order to detect a break in the linear sensor.
9. The security system as claimed in claim 8, wherein the value of the electrical property indicates an open circuit condition of the linear sensor.
10. The security system as claimed in claim 8 or 9, wherein the electrical signal is a first voltage and the read value corresponds to the first voltage.
11. The security system as claimed in any preceding claim, wherein the or each linear sensor comprises: a twisted pair of wires, each wire having a polyethylene foam coating; and a resistance connected between ends of the pair of wires distal to the controller.
12. The security system as claimed in any preceding claim, wherein the characteristic impedance of the or each linear sensor is at least approximately 150 ohms.
13. The security system as claimed in any preceding claim, wherein the controller is configured to wirelessly transmit the message.
14. The security system as claimed in any preceding claim wherein the message is an email message or an SMS message.
15. The security system as claimed in any preceding claim, and further comprising a battery.
16. The security system as claimed in any preceding claim, and further comprising a source of solar powered electrical power.
17. A security installation, comprising: the security system as claimed in any preceding claim; and an extensive entity, wherein the or each linear sensor is intimately attached to the extensive entity.
18. The security installation as claimed in claim 1?, wherein the extensive entity is a cable.
19. The security installation as claimed in claim 18, wherein the or each linear sensor is provided within an outer housing of the cable.
20-The security installation as claimed in claim 18 or 19, where the cable is a ground cable associated with a railway line.
21. The security installation as claimed in claim 17, wherein the extensive entity is a perimeter structure.
22. The security installation as claimed in claim 21, wherein the perimeter structure is a wall, a fence or a barrier.
23. The security installation as claimed in claim 21, wherein the perimeter structure is associated with a facility and wherein the facility is selected from: a factory; an office; a prison; a hospital; an industrial plant; a military site; a defence site; a government site; a security site; a transportation site; an airport; a dock; a warehouse; a telecommunications site; a server farm.
24. A method for monitoring the security of an entity, the method comprising: monitoring the integrity of a linear sensor attached to the entity to detect a break in the linear sensor; and responsive to detecting a break in the linear sensor, transmitting a messagc including an indication of the geographical position of the linear sensor.
25. The method of claim 24, and further comprising: responsive to detecting a break in the linear sensor, determining a length along the linear sensor at which the break has occurred, and wherein the message includes an indication of the position of the break in the linear sensor.
26. The method as claimed in claim 24 or 25, wherein the message is transmitted wirelessly and wherein the message is an email or an SMS.
27. The method as claimed in claim 26, and wherein the message is transmitted to a wireless communication device.
28. The method as claimed in claim 26, and wherein the message is transmitted to a webserver.
29. The method as claimed in claim 28, and wherein the webserver is an email server or hosts a website.
30. The method as claimed in any of claims 24 to 29 and further comprising: attaching the linear sensor intimately to the entity.
31. The method as claimed in claim 30, wherein the entity is a ground cable associated with a railway line.
32. The method as claimed in claim 30, wherein the entity is a perimeter structure associated with a facility.
33. A linear sensor, comprising: a pair of wires, each wire having a coating of a material to increase a characteristic impedance of the linear sensor and each wire having a proximal end for connecting to a controller and a distal end; and a resistor attached across the distal ends of the wires, and wherein the impedance of the resistor substantially matches the characteristic impedance of the linear sensor.
34. The linear sensor as claimed in claim 33, wherein the linear sensor is at least l000m long.
35. The linear sensor as claimed in claim 33 or 34, wherein the characteristic impedance is greater than 50 ohms, and preferably at least 150 ohms.
36. The liiiear sensor as claimed in claimed in any of claims 33 to 35, wherein the coating has been extruded onto each wire.
37. The linear sensor as claimed in any of claims 33 to 36, wherein the coating is a foam.
38. The linear sensor as claimed in claim 37, wherein the foam was expanded during extrusion onto the wire.
39. The security system as claimed in claim 1, wherein the controller is configured to detect a break in the linear sensor using a low EMI detection method.
40. The security system as claimed in claim 39, wherein the controller is configured to apply a DC voltage to the linear sensor as part of the low EMI detection method.
41. The security system as claimed in claim 4, wherein the controller is configured to determine a polarity of a returned pulse and to use the polarity of the returned pulse to determine whether a break in the linear sensor or a fault in the linear sensor has occurred.
42. The linear sensor as claimed in any of claims 33 to 38, and further comprising a shield arranged to reduce the EMI generated by the linear sensor.
43. A security system or security installation substantially as hereinbefore described andlor as shown in the accompanying drawings.
44. A controller for a security system substantially as hereinbefore described andlor as shown in the accompanying drawings.
45. A linear sensor substantially as hereinbefore described andlor as shown in the accompanying drawings.
46. A method for monitoring the security of an entity substantially as hereinbefore described and/or as shown in the accompanying drawings.