EP0317101A2 - A security system and a signal-carrying member therefor - Google Patents
A security system and a signal-carrying member therefor Download PDFInfo
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- EP0317101A2 EP0317101A2 EP88310110A EP88310110A EP0317101A2 EP 0317101 A2 EP0317101 A2 EP 0317101A2 EP 88310110 A EP88310110 A EP 88310110A EP 88310110 A EP88310110 A EP 88310110A EP 0317101 A2 EP0317101 A2 EP 0317101A2
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- semi
- conductive
- signal
- layer
- tape
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01B—CABLES; CONDUCTORS; INSULATORS; SELECTION OF MATERIALS FOR THEIR CONDUCTIVE, INSULATING OR DIELECTRIC PROPERTIES
- H01B7/00—Insulated conductors or cables characterised by their form
- H01B7/32—Insulated conductors or cables characterised by their form with arrangements for indicating defects, e.g. breaks or leaks
- H01B7/328—Insulated conductors or cables characterised by their form with arrangements for indicating defects, e.g. breaks or leaks comprising violation sensing means
Definitions
- This invention relates to a security system for giving warning of attempted interference with an object to be protected.
- the system is particularly applicable to the protection of an elongate core, such as an electrical power or data-carrying core, optical fibres, or pipelines and tubes carrying air or other fluids.
- the invention is also applicable to detecting imminent failure of a core which is fundamental to the safety or operation of a control system such as an aircraft hydraulic system or a missile fire control system.
- a signal-carrying member for a security system comprising a core surrounded by means capable of transmitting an electrical signal, an electrically-insulating layer surrounding the core and said means capable of transmitting a signal, and a semi-conductive layer surrounding the insulating layer, the semi-conductive layer incorporating throughout semi-conductive fibres which protrude from the layer when the layer is pierced, the thickness of the insulating layer being substantially less than the length of such protruding fibres whereby piercing of the semi-conductive layer and the insulating layer by an object entering from outside and moving towards the core will cause semi-conductive fibres from the semi-conductive layer to be pushed through the insulating layer and form a conductive path between the semi-conductive layer and said means capable of transmitting a signal.
- FIG 1 there is shown a simple form of wrapped core forming a signal-carrying member which, together with a detector, forms a security system in accordance with the invention.
- the core 10 which can be a fluid-carrying tube but usually will be an electric cable, is wrapped with a first semi-conductive layer 11, then with an electrically insulating layer 12, and thereafter with a second semi-conductive layer 13, and around this an outer protective sheath 14 is formed.
- the semi-conductive layer and the insulation layer are both formed of tape which is wrapped helically around the core to 0.95 wraps, i.e. with a gap of 5% or thereabouts between turns to prevent overlap.
- wrapping is the preferred method.
- the protective sheath is conveniently a 0.5mm PVC coating applied by extrusion.
- the or each semi-conductive layer is made throughout of a fibrous material such that when a sharp object penetrates the wrapped layers surrounding the core the object will pull fragments of the outer semi-conductive layer 13 through the insulating layer 12 to touch, and so make electrical contact with, the inner semi-conductive layer 11.
- the insulating layer 12 should be thinner than the mean length of the conductive fibres produced by pushing an object through the semi-conductive layer. The insulating layer 12 should therefore be no thicker than, and preferably is thinner than, the semi-conductive layer 13.
- the preferred semi-conductive material is unsintered, carbon-loaded polytetrafluoroethylene (PTFE) tape having a volume resistivity of 1.0 ohm-cm or lower.
- the preferred insulating material is polyester film 0.001 inch (.0025 cm) maximum thickness coated with .0005 inch (.0013 cm) polyester adhesive. The insulating layer is wrapped to 1.1 wraps and subsequently sealed by passing the wrapped construction through an oven at 200°C.
- two resistive tracks are formed having a loop resistance of approximately 7k ohms per metre run.
- a resistor of value greater than 1 metre loop resistance say 10k ohms
- the total loop resistance may be monitored using a Wheatstone Bridge-type of device. Changes in the loop resistance will indicate a penetration of the layers, and measurement of this new loop resistance will indicate the distance along the core to the fault.
- FIG. 2 A simple circuit for the signal carrier of Figure 1 is shown in Figure 2 where the elongate resistors 11′ ,13′ formed by the inner and outer semi-conductive layers 11,13 are interconnected at one end by a resistor 16. At their opposite end the resistors are connected by a flying lead 17 to an electronic monitor 18.
- This monitor is capable of detecting a change in the total resistance of the resistors 11′ ,13′, 16 resulting from shorting across between the semi-conductive layers 11,13.
- the flying lead 17 is preferably a screened wire which filters high frequency signals.
- the monitor 18 is described in detail below.
- an interleaved wrap can be used.
- the construction firstly has a semi-conductive layer 11 applied over the core 10 as in Figure 1.
- a laminate of insulating tape 12 and semi-conductive tape 13, as shown in Figure 3, is then formed.
- the semi-conductive tape 13 extends over slightly less than the half width of the insulating tape to one side of the centre line of the insulating tape 12, and is secured to the insulating tape by hot melt adhesive.
- the laminate is then wrapped helically with overlap as shown diagrammatically in Figure 4.
- the width of the insulating tape is chosen to give a nominal 2-wrap construction using the known theory of tape wrapping.
- the semi-conductive tape width is (0.5W)-2mm x W where W is the width in millimeters of the insulating tape.
- Figure 5 illustrates a completely wrapped core using the laminated tape of Figure 3. It also demonstrates the preferable method of wrapping the outer semi-conductive layer 13 in the opposite direction to the inner semi-conductive layer 11.
- the preferred material would be 0.001 inch (.0025 cm) thick polyester film coated with 0.0005 inch (.0013 cm) hot melt adhesive (polyester) for the insulation, and 0.003 inch (.0076 cm) thick semi-conductive PTFE tape, of the same electrical and mechanical properties as used in Figure 1, for the semi-conductive layer.
- the outer sheath may be made of any convenient thermoplastic material and preferably PVC or polyurethane.
- the interleaved layer increases the difficulty of intentional interception compared to the Figure 1 construction, since the layers must be very carefully paired away to gain access to the core, without either cutting through the outer layer and causing an open circuit or shorting the two layers together.
- the construction of Figure 5 may be further complicated by adhering the layers together by coating the core in an adhesive before the first layer is applied, after the first layer, and after the second layer (interleaved) thus mechanically securing each layer to avoid the possibility of lifting the wraps and gaining access with a fine probe.
- both first and second semi-conductive layers can be wrapped using the laminated tape of Figure 3. This further complicates the act of interception, particularly if adhesive is applied between the layers.
- the semi-conductive layer in Figure 4 will be thicker than that of Figure 1 because of the extra insulation thickness and would preferably be 0.005 inch (.013 cm) thick.
- Figure 6 illustrates wrapping of the core with the laminated tape having the semi-conductive layer on the outside of the tape for both inner and outer wraps. This provides a double layer of insulating tape between the semi-conductive layers.
- the second wrap is wound with the semi-conductive layer on the inside of the tape. This provides a single layer of insulating tape between the semi-conductive layers.
- the monitor 18 is illustrated in Figure 9 which shows the conductor 20 of the flying lead connected to a terminal T1 at +V and the other conductor 21 of the flying lead connnected through a variable resistor 22 of value Rx to a terminal T2 at -V volts.
- Comparator integrated circuits IC1 and IC2 are connected with the terminals T1 and T2 and with the resistor 22 and the line resistor, formed by the series connected resistors ll′,l3′,l6 and having resistance R, in a bridge circuit coupled at node A between resistors l3′ and 22 and at B to an output device which may include relays.
- Rx is set to the same resistance value R as the total loop resistance of the detection layers, and + ⁇ V and - ⁇ V are of equal and opposite very small values, such as +/- 20 mv, then node 'A' is at zero volts, and the circuit works as a window comparator. Any small change to the loop resistance R will result in either IC1 or IC2 switching to give an output voltage at B. This in turn can be used to operate a relay or other latching device which can initiate an alarm.
- Temperature fluctuations will affect the loop resistance of the detection layer, this being a well-known feature of semi-conductive plastics, and for a detection layer that has to work for long periods in large fluctuating temperatures it is necessary to incorporate some form of compensating circuit.
- resistor 22(Rx) in Figure 9 is replaced with a resistive element of the same material as the detection layer and is exposed to the environment of the detection layer, then the loop resistance of the detection layer and Rx will compensate for each other and Node 'A' will remain at zero volts.
- a circuit such as that of Figure 10 can be used.
- two arms of the bridge are formed from the two semi-conductive layers, and a return 23 is taken from the far end at C to Node D at the input to IC1 and IC2. If the two layers are nominally of the same resistance and Rb is equal to the value of resistor 16 (Rc) then Node D is zero volts.
- this return is a very fine insulated copper wire, preferably 32AWG or smaller, and is laid under the first layer as shown in Figure 11. This basic principle can be used with any of the preceding examples.
- a further option to increase the detection layers resistance to attack is to apply a third semi-conductive layer as in Figure 12 where the copper return wire 23 is replaced by a semi-conductive layer 24. This considerably enhances the detection of intentional interception since a third semi-conductive layer introduces a number of variations utilising all the designs shown and thus offers a high level of design uncertainty to any interceptor.
- detection layer is provided by introducing a multiplicity of semi-conductive elements. This may, of course, be done by adding more layers and incorporating a further randomness such that any intentional interceptor does not know the exact design of the layers.
- Another way of incorporating a multiplicity of semi-conductive elements is to segment the semi-conductive tape into separate parallel spaced elements.
- the elements are laid as shown in Figure 13, and compressed between plain rollers to produce a tape as in Figure 14. If a maliable material is used such as unsintered PTFE for both the semi-conductive elements and the insulating tape, the new tape is homogeneous in appearance and is easily handled as a single tape.
- the preferred material for all the tapes is PTFE and the insulating tapes are preferably 0.0025 inch (.006 cm) thick and semi-conductive tapes 0.005 inch (.0013 cm) thick.
- a very effective 'trip wire' system can be incorporated.
- This element may be of narrow dimension (less than 1 mm) and attempts to remove a section of the outer jacket, would cause a high probability of cutting this element.
- adhesive is applied to the outer surface of this element such that it is bonded to the inner surface of the thermoplastic extruded jacket.
- two semi-conductive elements may be applied over the outer insulating layer as in Figure 17. These two elements are spaced apart and are preferably bonded to the extruded jacket. When the two elements have different potential, it becomes virtually impossible to remove a section of the jacket even if prior knowledge of the design is available.
- FIG. 17 In order to demonstrate the electrical operation of this design, reference is made to Figures 17 and 18.
- three resistive arms XX′, YY′ and ZZ′ are connected together at one end, XX′ and YY′ being interconnected via a resistor 40 of value Rc.
- YY′ and ZZ′ are directly interconnected at node C.
- the opposite end of XX′ is connected via lead 41 to terminal T1 at +V volts.
- the opposite end of YY′ is connected via lead 42 at node D to IC1 and IC2 and the opposite end of ZZ′ is connected via lead 43 and resistor 44 of value Rb to terminal T2 at -V volts.
- the null position is set close to zero volts and preferably not exactly zero but of the order of + or - 100 mV.
- balance arms XX′ and ZZ′ are approximately equal and Rc is equal to Rb.
- Rb is adjustable to finely tune the circuit. Therefore, node C is close to zero volts and node D is close to zero volts since the input impedance of the comparator circuits is very high.
- the semi-conductive elements of the inner conductive layer 31 is indicated by E1
- the elements of the hybrid third layer 33 by E2-E7 the elements of the fifth layer 35 by E8
- the two outermost elements by E9 and E10.
Abstract
Description
- This invention relates to a security system for giving warning of attempted interference with an object to be protected. The system is particularly applicable to the protection of an elongate core, such as an electrical power or data-carrying core, optical fibres, or pipelines and tubes carrying air or other fluids.
- In the case of a data-carrying core, such as telephone or computer lines, it is important to provide security from wire tapping or eavesdropping on confidential information carried by the core, and to protect data lines used for electronic transfer of money between financial institutions. Thus it is necessary not only to stop information being extracted but also to stop erroneous information being added or current information being changed.
- The invention is also applicable to detecting imminent failure of a core which is fundamental to the safety or operation of a control system such as an aircraft hydraulic system or a missile fire control system.
- It is known from US Patent 2691698 to provide a security telephone cable around which are wrapped two layers of metal foil spaced from each other by a layer of insulation. If the outer foil layer is interrupted or if the cable is cut through or pierced by an electrically conductive object, a warning signal can be produced. This system however is liable to be overcome by the use of a non-conductive cutting tool or probe. Moreover this cable is capable of being X-rayed by a potential intruder to enable its construction to be determined and thereby facilitate penetration.
- According to the present invention there is provided a signal-carrying member for a security system comprising a core surrounded by means capable of transmitting an electrical signal, an electrically-insulating layer surrounding the core and said means capable of transmitting a signal, and a semi-conductive layer surrounding the insulating layer, the semi-conductive layer incorporating throughout semi-conductive fibres which protrude from the layer when the layer is pierced, the thickness of the insulating layer being substantially less than the length of such protruding fibres whereby piercing of the semi-conductive layer and the insulating layer by an object entering from outside and moving towards the core will cause semi-conductive fibres from the semi-conductive layer to be pushed through the insulating layer and form a conductive path between the semi-conductive layer and said means capable of transmitting a signal.
- The invention will now be particularly described by way of example with reference to the accompanying drawings in which:-
- Figure 1 is a diagrammatic perspective view of a security system including a core surrounded by two semi-conductive layers separated by an insulating layer;
- Figure 2 is part of a circuit diagram of a simple security system according to the present invention;
- Figure 3 illustrates the production of a laminated tape comprising an insulating layer and a semi-conductive layer;
- Figure 4 is a diagrammatic representation of the wrapping of the laminated tape of Figure 3 around a core;
- Figure 5 is a diagrammatic representation of a complete cable incorporating the tape of Figure 3;
- Figure 6 is a longitudinal section through part of the wrapping of a cable incorporating a double wrap of tape according to Figure 3;
- Figure 7 is a longitudinal section through part of the wrapping of a cable incorporating a double wrap of a modified form;
- Figure 8 is a section through a cable in accordance with the present invention;
- Figure 9 is a circuit diagram of a simple security system according to the present invention;
- Figure 10 is a circuit diagram of a more complex security system according to the present invention;
- Figure 11 is a diagrammatic illustration of the wrapping of a cable for use with the circuit of Figure 10;
- Figure 12 is a diagrammatic illustration of an alternative method of wrapping a cable;
- Figure 13 is a longitudinal section through another embodiment of laminated tape for use in the system of the present invention;
- Figure 14 is a section through the tape of Figure 13 after rolling;
- Figure 15 is a section through a cable wrapped with three semi-conductive layers;
- Figures 16 and 17 are sections through modified forms of the wrapped cable of Figure 16; and
- Figure 18 is a circuit diagram of another form of the security system.
- In Figure 1, there is shown a simple form of wrapped core forming a signal-carrying member which, together with a detector, forms a security system in accordance with the invention.
- The
core 10, which can be a fluid-carrying tube but usually will be an electric cable, is wrapped with a firstsemi-conductive layer 11, then with an electrically insulatinglayer 12, and thereafter with a secondsemi-conductive layer 13, and around this an outerprotective sheath 14 is formed. This represents a basic form of signal-carryingmember 15. If however the core were provided with a conductive surface, for example a metal braid, itself forming a means capable of transmitting an electrical signal, the inner semi-conductive layer could be dispensed with. Nevertheless preferably the inner semi-conducive layer would still be retained. - In order to form a smooth wrapping, the semi-conductive layer and the insulation layer are both formed of tape which is wrapped helically around the core to 0.95 wraps, i.e. with a gap of 5% or thereabouts between turns to prevent overlap. Although each of the first three layers could be applied by extrusion, wrapping is the preferred method. The protective sheath is conveniently a 0.5mm PVC coating applied by extrusion.
- The or each semi-conductive layer is made throughout of a fibrous material such that when a sharp object penetrates the wrapped layers surrounding the core the object will pull fragments of the outer
semi-conductive layer 13 through theinsulating layer 12 to touch, and so make electrical contact with, the innersemi-conductive layer 11. In order to have a high probability of a conductive path being made, the insulatinglayer 12 should be thinner than the mean length of the conductive fibres produced by pushing an object through the semi-conductive layer. Theinsulating layer 12 should therefore be no thicker than, and preferably is thinner than, thesemi-conductive layer 13. - The preferred semi-conductive material is unsintered, carbon-loaded polytetrafluoroethylene (PTFE) tape having a volume resistivity of 1.0 ohm-cm or lower. The preferred insulating material is polyester film 0.001 inch (.0025 cm) maximum thickness coated with .0005 inch (.0013 cm) polyester adhesive. The insulating layer is wrapped to 1.1 wraps and subsequently sealed by passing the wrapped construction through an oven at 200°C.
- By making the layers as above, two resistive tracks are formed having a loop resistance of approximately 7k ohms per metre run. By terminating the layers at the far end with a resistor of value greater than 1 metre loop resistance, say 10k ohms, the total loop resistance may be monitored using a Wheatstone Bridge-type of device. Changes in the loop resistance will indicate a penetration of the layers, and measurement of this new loop resistance will indicate the distance along the core to the fault.
- A simple circuit for the signal carrier of Figure 1 is shown in Figure 2 where the
elongate resistors 11′ ,13′ formed by the inner and outersemi-conductive layers resistor 16. At their opposite end the resistors are connected by aflying lead 17 to anelectronic monitor 18. This monitor is capable of detecting a change in the total resistance of theresistors 11′ ,13′, 16 resulting from shorting across between thesemi-conductive layers flying lead 17 is preferably a screened wire which filters high frequency signals. Themonitor 18 is described in detail below. - Thus a simple detection system has been formed which will indicate penetration of the core wrapping by an object and hence potential failure of, or interference with, the core. Alternatively it can be used as a 'distance-to-fault' indicator, for example for underground cables.
- Although the embodiment of Figure 1 would protect against accidental penetration, it could be overcome by a criminal of modest skill who was aware of its construction.
- To provide a more secure system, an interleaved wrap can be used. The construction firstly has a
semi-conductive layer 11 applied over thecore 10 as in Figure 1. A laminate ofinsulating tape 12 andsemi-conductive tape 13, as shown in Figure 3, is then formed. In the laminate, thesemi-conductive tape 13 extends over slightly less than the half width of the insulating tape to one side of the centre line of theinsulating tape 12, and is secured to the insulating tape by hot melt adhesive. The laminate is then wrapped helically with overlap as shown diagrammatically in Figure 4. The width of the insulating tape is chosen to give a nominal 2-wrap construction using the known theory of tape wrapping. The semi-conductive tape width is (0.5W)-2mm x W where W is the width in millimeters of the insulating tape. Thus a semi-conductive track is wrapped around a core such that each turn of semi-conductive tape is insulated from the next turn and is insulated above and below in one operation. In practice, the gap shown between each turn in Figure 4, for ease of illustration, is closed by fine adjustment of the wrapping angle. - Figure 5 illustrates a completely wrapped core using the laminated tape of Figure 3. It also demonstrates the preferable method of wrapping the outer
semi-conductive layer 13 in the opposite direction to the innersemi-conductive layer 11. - The preferred material would be 0.001 inch (.0025 cm) thick polyester film coated with 0.0005 inch (.0013 cm) hot melt adhesive (polyester) for the insulation, and 0.003 inch (.0076 cm) thick semi-conductive PTFE tape, of the same electrical and mechanical properties as used in Figure 1, for the semi-conductive layer. The outer sheath may be made of any convenient thermoplastic material and preferably PVC or polyurethane.
- The interleaved layer increases the difficulty of intentional interception compared to the Figure 1 construction, since the layers must be very carefully paired away to gain access to the core, without either cutting through the outer layer and causing an open circuit or shorting the two layers together. The construction of Figure 5 may be further complicated by adhering the layers together by coating the core in an adhesive before the first layer is applied, after the first layer, and after the second layer (interleaved) thus mechanically securing each layer to avoid the possibility of lifting the wraps and gaining access with a fine probe.
- Alternatively, both first and second semi-conductive layers can be wrapped using the laminated tape of Figure 3. This further complicates the act of interception, particularly if adhesive is applied between the layers. The semi-conductive layer in Figure 4 will be thicker than that of Figure 1 because of the extra insulation thickness and would preferably be 0.005 inch (.013 cm) thick.
- Figure 6 illustrates wrapping of the core with the laminated tape having the semi-conductive layer on the outside of the tape for both inner and outer wraps. This provides a double layer of insulating tape between the semi-conductive layers. In Figures 7 and 8, the second wrap is wound with the semi-conductive layer on the inside of the tape. This provides a single layer of insulating tape between the semi-conductive layers.
- The
monitor 18 is illustrated in Figure 9 which shows theconductor 20 of the flying lead connected to a terminal T₁ at +V and theother conductor 21 of the flying lead connnected through avariable resistor 22 of value Rx to a terminal T₂ at -V volts. Comparator integrated circuits IC1 and IC2 are connected with the terminals T₁ and T₂ and with theresistor 22 and the line resistor, formed by the series connected resistors ll′,l3′,l6 and having resistance R, in a bridge circuit coupled at node A between resistors l3′ and 22 and at B to an output device which may include relays. If Rx is set to the same resistance value R as the total loop resistance of the detection layers, and +ΔV and -ΔV are of equal and opposite very small values, such as +/- 20 mv, then node 'A' is at zero volts, and the circuit works as a window comparator. Any small change to the loop resistance R will result in either IC1 or IC2 switching to give an output voltage at B. This in turn can be used to operate a relay or other latching device which can initiate an alarm. - Temperature fluctuations will affect the loop resistance of the detection layer, this being a well-known feature of semi-conductive plastics, and for a detection layer that has to work for long periods in large fluctuating temperatures it is necessary to incorporate some form of compensating circuit. For example, if resistor 22(Rx) in Figure 9 is replaced with a resistive element of the same material as the detection layer and is exposed to the environment of the detection layer, then the loop resistance of the detection layer and Rx will compensate for each other and Node 'A' will remain at zero volts.
- Alternatively, a circuit such as that of Figure 10 can be used. In this system, two arms of the bridge are formed from the two semi-conductive layers, and a
return 23 is taken from the far end at C to Node D at the input to IC1 and IC2. If the two layers are nominally of the same resistance and Rb is equal to the value of resistor 16 (Rc) then Node D is zero volts. In practice this return is a very fine insulated copper wire, preferably 32AWG or smaller, and is laid under the first layer as shown in Figure 11. This basic principle can be used with any of the preceding examples. - A further option to increase the detection layers resistance to attack is to apply a third semi-conductive layer as in Figure 12 where the
copper return wire 23 is replaced by asemi-conductive layer 24. This considerably enhances the detection of intentional interception since a third semi-conductive layer introduces a number of variations utilising all the designs shown and thus offers a high level of design uncertainty to any interceptor. - Further modifications of the detection layer are provided by introducing a multiplicity of semi-conductive elements. This may, of course, be done by adding more layers and incorporating a further randomness such that any intentional interceptor does not know the exact design of the layers.
- Another way of incorporating a multiplicity of semi-conductive elements is to segment the semi-conductive tape into separate parallel spaced elements. The elements are laid as shown in Figure 13, and compressed between plain rollers to produce a tape as in Figure 14. If a maliable material is used such as unsintered PTFE for both the semi-conductive elements and the insulating tape, the new tape is homogeneous in appearance and is easily handled as a single tape.
- When this tape is applied as an intermediary layer and laid up as in Figure 15, a highly complex detection layer is produced. The layers are applied as follows:
First layer 30 Semi-conductive tape 0.95 wraps, Second layer 32 Insulating tape 0.95 wraps, Third layer 33 Hybrid tape 0.95 wraps, Fourth layer 34 Insulating tape 0.95 wraps, Fifth layer 35 Semi-conductive tape 0.95 wraps, Sixth layer 36 Thermoplastic extrusion - The preferred material for all the tapes is PTFE and the insulating tapes are preferably 0.0025 inch (.006 cm) thick and semi-conductive tapes 0.005 inch (.0013 cm) thick.
- If a further insulating
layer 37 is added followed by one moresemi-conducting element 38 as in Figure 16, a very effective 'trip wire' system can be incorporated. This element may be of narrow dimension (less than 1 mm) and attempts to remove a section of the outer jacket, would cause a high probability of cutting this element. To increase this probability, adhesive is applied to the outer surface of this element such that it is bonded to the inner surface of the thermoplastic extruded jacket. - Alternatively, two semi-conductive elements may be applied over the outer insulating layer as in Figure 17. These two elements are spaced apart and are preferably bonded to the extruded jacket. When the two elements have different potential, it becomes virtually impossible to remove a section of the jacket even if prior knowledge of the design is available.
- In order to demonstrate the electrical operation of this design, reference is made to Figures 17 and 18. In the circuit of Figure 18, three resistive arms XX′, YY′ and ZZ′ are connected together at one end, XX′ and YY′ being interconnected via a
resistor 40 of value Rc. YY′ and ZZ′ are directly interconnected at node C. The opposite end of XX′ is connected via lead 41 to terminal T₁ at +V volts. The opposite end of YY′ is connected vialead 42 at node D to IC1 and IC2 and the opposite end of ZZ′ is connected vialead 43 andresistor 44 of value Rb to terminal T₂ at -V volts. - The null position is set close to zero volts and preferably not exactly zero but of the order of + or - 100 mV. In order to achieve this, balance arms XX′ and ZZ′ are approximately equal and Rc is equal to Rb. Rb is adjustable to finely tune the circuit. Therefore, node C is close to zero volts and node D is close to zero volts since the input impedance of the comparator circuits is very high.
- Referring to Figure 17, the semi-conductive elements of the inner
conductive layer 31 is indicated by E₁, the elements of the hybridthird layer 33 by E₂-E₇, the element of thefifth layer 35 by E₈ and the two outermost elements by E₉ and E₁₀. - If elements E₁ and E₈ are connected to form arm YY′ of Figure 18, elements E₂,E₃,E₆ and E₁₀ are connected in parallel to form arm XX′ and elements E₄,E₅,E₇ and E₉ are connected in parallel to form
arm 22′, the circuit will be in balance. If any one or more elements is open circuit or if any two elements from different arms are shorted together, then the circuit will imbalance and the alarm will sound. By incorporation of a switchingcircuit 45 to vary the connections, a pre-selected programme may be used which will confront any interceptor with a random pattern of terminations. - If the elements in the hybrid layer are made very narrow (less than 1mm wide) a great number of permutations can be pre-set into the detection layer. Another advantage of this system is that a situation may occur whereby an alarm is sounded due to a very small incision in the detection layer and the affected elements may be switched out, leaving the rest of the detection layer operational and thus continuing to provide cover until a repair can be effected.
Claims (11)
Priority Applications (1)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
AT88310110T ATE98045T1 (en) | 1987-11-19 | 1988-10-27 | SECURITY SYSTEM AND A SIGNAL CARRYING ELEMENT FOR IT. |
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
GB8727092A GB2212644B (en) | 1987-11-19 | 1987-11-19 | A signal-carrying member for a security system |
GB8727092 | 1987-11-19 |
Publications (3)
Publication Number | Publication Date |
---|---|
EP0317101A2 true EP0317101A2 (en) | 1989-05-24 |
EP0317101A3 EP0317101A3 (en) | 1989-09-27 |
EP0317101B1 EP0317101B1 (en) | 1993-12-01 |
Family
ID=10627211
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP88310110A Expired - Lifetime EP0317101B1 (en) | 1987-11-19 | 1988-10-27 | A security system and a signal-carrying member therefor |
Country Status (7)
Country | Link |
---|---|
EP (1) | EP0317101B1 (en) |
JP (1) | JPH01289017A (en) |
AT (1) | ATE98045T1 (en) |
AU (1) | AU2216688A (en) |
DE (1) | DE3886011T2 (en) |
GB (1) | GB2212644B (en) |
HK (1) | HK126693A (en) |
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EP0524003A1 (en) * | 1991-07-19 | 1993-01-20 | W.L. GORE & ASSOCIATES (UK) LTD | Protective sheath |
EP0715283A1 (en) * | 1988-06-17 | 1996-06-05 | W.L. Gore & Associates, Inc. | Security enclosure |
WO2000005797A1 (en) * | 1998-07-24 | 2000-02-03 | Regis Julien | System and method for safe transport of an actuating fluid and electrical power, and multipurpose cable used in said system |
EP1237163A2 (en) * | 2001-02-28 | 2002-09-04 | Optral, S.A. | Covering for any kind of cable to protect against animals and insects. |
US7479710B2 (en) | 2004-01-09 | 2009-01-20 | Afl Europe Gmbh | Electrical supply network |
FR2947665A1 (en) * | 2009-07-01 | 2011-01-07 | Nexans | CABLE COMPRISING DETECTION MEANS FOR DETECTING THE PRESENCE OF AN ELECTRICALLY CONDUCTIVE BODY OUTSIDE THE CABLE |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB2254720B (en) * | 1988-06-17 | 1993-02-17 | Gore & Ass | Security enclosures |
GB9016795D0 (en) * | 1990-07-31 | 1990-09-12 | Weyrad Electronics Ltd | Improvements relating to security systems |
CN103357137A (en) * | 2013-07-25 | 2013-10-23 | 成都陵川特种工业有限责任公司 | Apparatus for detecting fire extinguishing launcher |
CN111863334B (en) * | 2020-08-01 | 2021-08-27 | 江苏江扬特种电缆有限公司 | High-safety communication cable and using method thereof |
Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB378634A (en) * | 1930-08-08 | 1932-08-18 | Siemens Ag | Improvements in the protection of electrical conductors against glow discharge |
EP0049104A1 (en) * | 1980-09-25 | 1982-04-07 | BICC Limited | Electric cables comprising a semiconducting screening layer |
EP0120479A2 (en) * | 1983-03-23 | 1984-10-03 | Nippon Steel Corporation | Structure fastening cable |
Family Cites Families (1)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
JPS5146081B1 (en) * | 1970-12-28 | 1976-12-07 |
-
1987
- 1987-11-19 GB GB8727092A patent/GB2212644B/en not_active Expired - Fee Related
-
1988
- 1988-09-13 AU AU22166/88A patent/AU2216688A/en not_active Abandoned
- 1988-10-27 EP EP88310110A patent/EP0317101B1/en not_active Expired - Lifetime
- 1988-10-27 AT AT88310110T patent/ATE98045T1/en not_active IP Right Cessation
- 1988-10-27 DE DE3886011T patent/DE3886011T2/en not_active Expired - Fee Related
- 1988-11-18 JP JP63290369A patent/JPH01289017A/en active Pending
-
1993
- 1993-11-18 HK HK1266/93A patent/HK126693A/en not_active IP Right Cessation
Patent Citations (3)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
GB378634A (en) * | 1930-08-08 | 1932-08-18 | Siemens Ag | Improvements in the protection of electrical conductors against glow discharge |
EP0049104A1 (en) * | 1980-09-25 | 1982-04-07 | BICC Limited | Electric cables comprising a semiconducting screening layer |
EP0120479A2 (en) * | 1983-03-23 | 1984-10-03 | Nippon Steel Corporation | Structure fastening cable |
Cited By (11)
Publication number | Priority date | Publication date | Assignee | Title |
---|---|---|---|---|
EP0715283A1 (en) * | 1988-06-17 | 1996-06-05 | W.L. Gore & Associates, Inc. | Security enclosure |
EP0398594A2 (en) * | 1989-05-15 | 1990-11-22 | Westinghouse Electric Corporation | Means to detect and locate pinching and chafing of conduits |
EP0398594A3 (en) * | 1989-05-15 | 1991-08-14 | Westinghouse Electric Corporation | Means to detect and locate pinching and chafing of conduits |
EP0524003A1 (en) * | 1991-07-19 | 1993-01-20 | W.L. GORE & ASSOCIATES (UK) LTD | Protective sheath |
US5438474A (en) * | 1991-07-19 | 1995-08-01 | W. L. Gore & Associates (Uk) Ltd. | Protective sheath |
WO2000005797A1 (en) * | 1998-07-24 | 2000-02-03 | Regis Julien | System and method for safe transport of an actuating fluid and electrical power, and multipurpose cable used in said system |
EP1237163A2 (en) * | 2001-02-28 | 2002-09-04 | Optral, S.A. | Covering for any kind of cable to protect against animals and insects. |
EP1237163A3 (en) * | 2001-02-28 | 2003-09-17 | Optral, S.A. | Covering for any kind of cable to protect against animals and insects. |
US7479710B2 (en) | 2004-01-09 | 2009-01-20 | Afl Europe Gmbh | Electrical supply network |
FR2947665A1 (en) * | 2009-07-01 | 2011-01-07 | Nexans | CABLE COMPRISING DETECTION MEANS FOR DETECTING THE PRESENCE OF AN ELECTRICALLY CONDUCTIVE BODY OUTSIDE THE CABLE |
EP2299454A1 (en) | 2009-07-01 | 2011-03-23 | Nexans | Cable including means for detecting the presence of an electrically conducting body outside the cable |
Also Published As
Publication number | Publication date |
---|---|
EP0317101B1 (en) | 1993-12-01 |
GB8727092D0 (en) | 1987-12-23 |
GB2212644A (en) | 1989-07-26 |
AU2216688A (en) | 1989-05-25 |
ATE98045T1 (en) | 1993-12-15 |
DE3886011D1 (en) | 1994-01-13 |
DE3886011T2 (en) | 1994-06-16 |
HK126693A (en) | 1993-11-26 |
EP0317101A3 (en) | 1989-09-27 |
JPH01289017A (en) | 1989-11-21 |
GB2212644B (en) | 1991-10-09 |
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