GB2434018A

GB2434018A - Alarm system

Info

Publication number: GB2434018A
Application number: GB0600248A
Authority: GB
Inventors: Nigel Mills; James Garth Richens; John Henry Paul Millar
Original assignee: ELMDENE INTERNAT Ltd
Current assignee: ELMDENE INTERNAT Ltd
Priority date: 2006-01-06
Filing date: 2006-01-06
Publication date: 2007-07-11
Anticipated expiration: 2026-01-06
Also published as: GB0600248D0; GB2434018B

Abstract

An alarm system includes a six core (or wire) cable D extending from a magnetic contact such as a reed switch B. Each core has a plastics insulating sheath, all the sheaths being the same colour. A moveable sleeve C is provided over a small proportion of each core which is differently coloured or otherwise marked so that the separate cores can be identified during installation or servicing. The arrangement provides four operating connections and two anti-tampering connections which cannot be distinguished from one another if an outer sheath of the cable is breached. The common colour is preferably white. Typically, the reed switch B would be attached to a window or door frame to provide warning of an intruder.

Description

ALARM SYSTEM

Field of the Invention

The present invention relates to alarm systems, such as intruder and security alarms for buildings.

Background of the Invention

Security and intruder alarms for buildings and other premises are often provided with magnetic contacts that are used to detect the opening and closing of doors, windows, and so on. One example of a magnetic contact comprises a reed switch mounted in a housing on a door or window frame. The reed switch is operated by a magnet mounted in a housing on the closed door or window. When the door or window opens the magnet moves away from the reed switch and the electrical circuit opens.

Figure 1 illustrates an electrical circuit for a conventional alarm. There are four wire connections that link a control system to the magnetic contact. Two of these connections 11 A, 11 B are used as part of the operating circuit 10 to link to the magnetic contact reed switch itself 1 2A, while the other two connections 21 A, 21 B are used to form a tamper circuit 20. In some implementations, the tamper circuit may comprise a (mechanical) switch arrangement 22A within the housing of the reed switch that opens if the cover giving access to the electrical connections is removed.

In other implementations, the tamper circuit may comprise a continuous loop of wire sealed within the body of the magnetic contact (as indicated by the dotted line 22B in Figure 1 beneath the switch). It will be appreciated that certain alarm systems may omit the tamper circuit 20, in which case only two wire connections to the magnetic contact are required.

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Figure 2 illustrates a known alternative configuration for an alarm system, which is termed a Fully Supervised Loop (FSL) circuit 30. In this configuration, two resistors are added to the magnetic contact, the first resister RI 36A in parallel with the operating reed switch 35, and the second resister R2 38A in series with the mechanical tamper switch (where fitted) 37. The FSL configuration only requires two wire connections 31A, 31B. The resistance of the FSL circuit changes depending upon whether the door is open or closed, and upon whether or not the tamper detection system has been activated. The state of the system can therefore be determined by measuring a characteristic resistance change for the circuit between connectors 31 A and 3lB.

One advantage of an FSL system is that an adversary cannot simply short across two connection wires to bypass or override the operating circuit. On the other hand, the configuration of Figure 1 has the advantage that, unlike the configuration of Figure 2, it can be used to connect multiple magnetic contact switches in series with just two wires. In other words, connectors 1 1A and 1 lB can be used to drive multiple magnetic switches in series. In contrast, an FSL system would generally require a separate pair of connectors 31 A and 31 B for each magnetic contact, and so may be more difficult and time-consuming to wire up. Thus it can be seen that each of the conventional two wire and four wire configurations for an alarm has certain disadvantages.

Summary of the Invention

One embodiment of the present invention provides an alarm system having a six wire configuration including a multi-core cable for connection to a magnetic contact. The multi-core cable has six cores, each of the six cores having a plastic insulating sheath. The plastic sheaths of the six cores have substantially identical colouring.

The provision of substantially identical colouring for all of the six cores within the multi-core cable makes it far harder for an adversary to disable the alarm by splitting open the cable and shorting out the wires from certain cores. This is because it is not possible for the adversary to distinguish one core from another, given their identical colouring.

In one implementation the plastic sheaths of the six cores all have a single colour, for example white. In another implementation, the common colouring for all six cores may comprise a combination of colours, for example black and white.

In one implementation, at least one end of the multi-core cable includes markings on the six cores to distinguish one core from another. These markings are useful for an installer or service engineer to connect the alarm system up properly, since otherwise the common colouring of the various cores would prevent the engineer from knowing what connections to make. An alternative approach for the engineer might be to use electrical testing to identify the different cores, but for a six wire configuration this would be a rather complicated and time-consuming task. Note that since the markings are only at the ends (or one end) of the cable, they would not assist an adversary who tries to interfere with the cable somewhere along its length between the magnetic contact and the control system.

In some embodiments the markings comprise a distinctive sleeve on each core.

The distinctive sleeves may be provided with different colouring, an alphanumeric or shape identifier, etc, to indicate the particular core to which a given sleeve is attached.

Other forms of markings may also be used, for example, different wire lengths for the different cores (as extending from the end of the cable), or different forms of stripping for the ends of the different cores -e.g. no stripping, and stripping of different lengths.

In one embodiment, the sleeves (or other form of marking) can be moved along the cores of the cable. This is useful if the length of a core wire has to be trimmed for installation, in that the sleeve or other marking can then be moved (e.g. by sliding) up the core. This allows a sleeve to be retained on a core, even if the portion of the core to which the sleeve was originally attached is removed.

Another embodiment of the invention provides a method of installing an alarm system having a magnetic contact and a control unit. The method includes connecting the magnetic contact and the control unit using a multi-core cable into a six wire configuration. The multi-core cable has six cores, each of the six cores having a plastic insulating sheath. The plastic sheaths of the six cores all have substantially identical colouring.

Brief Description of the Drawings

Various embodiments of the invention will now be described in detail by way of example only with reference to the following drawings: Figure 1 is a schematic electrical circuit diagram of a known four-wire configuration for a security alarm; Figure 2 is a schematic electrical circuit diagram of a known two-wire configuration for a security alarm; Figure 3 is a schematic electrical circuit diagram of a six-wire configuration for an alarm system in accordance with one embodiment of the present invention; and Figure 4 is a diagram showing a six-core cable for use in an alarm system in accordance with one embodiment of the present invention.

Detailed Description

Figure 3 illustrates a six wire configuration 40 for an alarm system in accordance with one embodiment of the invention. The six wire configuration of Figure 3 includes an operating circuit 45 and a separate tamper circuit 47. The tamper circuit 47 is the same as the tamper circuit 12 shown in Figure 1, and has two wire connections 48A, 48B. The operating circuit 45 integrates a switch portion with two resistors Ri 44A and R2 44B that are located in parallel with the input and output to the switch. The switch portion is fed by a first pair of wire connectors 41 A, 41 B, while there is a separate connector 42A, 42B to each of the resistors 44A, 44B.

Overall, the configuration of circuit 40 has six wire connectors, four for the operating portion and two for the tamper detection circuit. By providing access through each of the six connections to different parts of the circuit, the six wire arrangement 40 of Figure 3 may be configured in accordance with the particular needs of a given installation. For example, it will be appreciated that the resistors in an FSL system are normally fixed by the manufacturer of the control unit and differ from one manufacturer to another. The six wire configuration of Figure 3 allows external resistors to be fitted if the internal resistors are inappropriate for a particular installation.

Note that the electrical configuration of Figure 3 is already known for certain alarm systems. In some implementations, a metal conduit is used to route the six connecting wires 41A, 41B, 42A, 42B, 48A, 48B between the control unit and the magnetic contact. However, although such a metal conduit is hard to break into, it is also relatively expensive. Furthermore, since a metal conduit is inflexible, it is unsuited to (portions of) some routes, and is more difficult to install. In some implementations of the six wire configuration of Figure 3 therefore, a multi-core plastic cable has been used to route the six connecting wires 41 A, 41 B, 42A, 42B, 48A, 48B. Such a plastic cable is physically flexible, and so can be routed where the cable is not easily visible, for example, within hollow walls or partitions.

Commercially available six-core cable has different coloured plastic insulating sheaths for each of the different cores. However, the use of such multi-core cable represents a potential security exposure, since having only a PVC sheath, it is vulnerable to attack using simple cutting tools. Accordingly, it is relatively easy for an adversary to get to the individual cores within the multi-core cable. In addition, in order to configure the alarm system of Figure 3 for FSL, specific individual cores are shorted together, usually in a junction box some distance from the operating contact.

The FSL condition is created only in the junction box itself, and so the connection from the junction box to the magnetic contact is not protected. If the individual core colours within the cable are known, then the appropriate cores corresponding to the switch circuit can be identified and shorted together, thereby overriding the detection switch.

Accordingly, the six wire alarm system of Figure 3 uses a multi-core cable having a common colour (or colouring) for all of the plastic insulating sheaths of the six cores that provide the six connecting wires 41A, 41B, 42A, 42B, 48A, 48B. As a result, if the outer sheath of the plastic cable is breached between a junction box and the magnetic contact, it is not possible to determine from the internal appearance of the cable alone which two cores carry the operating and/or tamper circuits. It is therefore much more difficult for an adversary to override or bypass these circuits.

One potential complication arising from the use of identically coloured cores within a multi-core cable is that it is now more difficult to install or service the alarm system, since it is not immediately apparent to an engineer how the different cores should be connected up. In theory this could be ascertained by appropriate electrical testing, but this is a rather complicated and time-consuming process (especially in comparison with a four wire configuration, such as illustrated in Figure 1).

Accordingly, in one embodiment, one or both of the ends of the multi-core cable are provided with some form of identification to allow the appropriate connections to be made. Such an embodiment is illustrated in Figure 4, in which a multicore cable D extends from a magnetic contact such as a reed switch B. The free connection end of the cable (i.e. the opposite end to the magnetic contact) has the six individual cores A exposed. Each of the cores A has its own plastic insulating sheath, which as mentioned above, all have a common colouring. Each of the sheaths is provided with a sleeve C that identifies its corresponding core. For example, the sleeves may have different colours or may be provided with any other suitable form of marking, e.g. a shape or some alphanumeric identifier, in order to label the corresponding core. In other implementations, rather than using a sleeve to identify the different cores, some other technique may be used, for example based on the exposed length of core from cable D, or the length of wire stripped for an individual coreA.

In one implementation, the sleeve or other form of label or identifier on the cores can be moved up and down the length of the core, for example by sliding. This ensures that if a core has to be trimmed in length, such as to make a desired contact, then if necessary the label can be moved from a portion of the core that is to be discarded to a portion of the core that is to be retained.

In conclusion, although a variety of embodiments have been described herein, these are provided by way of example only, and many variations and modifications on such embodiments will be apparent to the skilled person and fall within the scope of the present invention, which is defined by the appended claims and their equivalents.

Claims

Claims 1. An alarm system having a six wire configuration including a

multi-core cable for connection to a magnetic contact, wherein the multi-core cable has six cores, each of the six cores having a plastic insulating sheath, and wherein the plastic sheaths of the six cores have substantially identical colouring.

2. The alarm system of claim 1, wherein the plastic sheaths of the six cores all have a single colour.

3. The alarm system of claim I or 2, wherein at least one end of the multi-core cable includes markings on the six cores to distinguish one core from another.

4. The alarm system of claim 3, wherein said markings are only located at the opposite end of the cable to said magnetic contact.

5. The alarm system of claim 3 or 4, wherein said markings comprise a distinctive sleeve on each core.

6. The alarm system of claim 5, wherein each of said distinctive sleeves has a different colouring.

7. The alarm system of claim 5, wherein each of said distinctive sleeves has a different alphanumeric identifier.

8. The alarm system of any of claims 5 to 7, wherein said sleeves can be moved along the cores of the cable.

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9. An alarm system substantially as described herein with reference to the accompanying drawings.

10. A method of installing an alarm system having a magnetic contact and a control unit, the method including connecting the magnetic contact and the control unit using a multi-core cable into a six wire configuration, wherein the multi-core cable has six cores, each of the six cores having a plastic insulating sheath, and wherein the plastic sheaths of the six cores all have substantially identical colouring.

11. The method of claim 10, further comprising adding external resistors to the system to complement the internal resistors in the control unit.