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The philosophy of intrusion and perimeter detection

The functional definition of perimeter detection systems is subjective and is more frequently based on the features of products available on the market rather than an objective approach to the functions and features required for specific installation.

The evaluation of security systems can easily become very subjective if not properly structured. Previously, the evaluation of security systems lacked a structured approach. Therefore, you have to define, compare and evaluate systems on an objective basis.

This article describes perimeter detection features and functional components that can be used to define the needs of the client and generate a functional specification. The aim is a more scientific approach to the definition and evaluation of perimeter detection systems that can provide evaluation guidelines as well as provide an objective basis for agreement between parties.

Main characteristic of perimeter detection systems

In marketing, everyone always refers to the four Ps (product, place, promotion and price) as the backbone of the marketing philosophy. The keywords that comprehensively address the needs and requirements of the user for perimeter detection systems all start with a 'D' and we refer to the five Ds for perimeter detection systems.

* Design.

* Deterrence.

* Detection.

* Delay.

* Dependability.

Keep in mind that not one of these keywords contains cost as a factor as they only define the functional requirement of the barrier detection system. Cost will be a factor when choosing different hardware or product options available to satisfy the requirements. If the cost of such a system is too high, the client must re-think the functional specification. It is important to note that by scaling down a detection system in cost or function, the detection does not necessarily scale down in the same propositions. Detection is the backbone of a security system. Scaled down detection implies losing part of its backbone.

Design

Depending on the facility that has to be protected, the user will have certain aesthetic requirements regarding the design of the perimeter detection system so that it will blend with or even complement the surroundings. Typically, a barbed wires solution will not suit a residential complex and cannot contribute to a feeling of homeliness. The perimeter of a prison might be to keep prisoners in isolation, in which case a wall will prevent outsiders seeing in and vice versa. Prison authorities may elect corrective action in as normal as possible environment in which case a see-through perimeter is required.

Deterrence

The prime function of the system will be to detect intrusion, but it must still create the image of being difficult to penetrate. The perimeter detection system must also discourage intrusion. If not, the system will invite a lot of unnecessary intrusion attempts. Typically, infrared beams can detect a perimeter intruder. If such a system is to be erected around a prison without any physical barrier it will certainly generate numerous intrusion attempts that will obviously be unacceptable. Infrared will, on the other hand, be acceptable after hours at gate entrances to give warning of intrusion by, for example, a vehicle.

Detection

The function of detection is to generate an alarm when the perimeter is intruded. As most perimeter systems create a physical obstruction, detection can be defined as the event of barrier disturbance by an intruder. If the barrier is constructed in such a way that in order for an intruder to pass through it, it must disturb the barrier, the most obvious method would be to use the barrier to house or act as the detection facility as well. The use of a method like short circuit detection (SCD), various volumetric systems - for example infrared, microwave and acoustic systems - act as detection means but do not necessarily imply barrier intrusion.

Volumetric systems react on a sphere of influences and the barrier boundary can therefore not be defined exactly as is the case with a wire fence, and this will be unacceptable in most applications. Barrier or fence disturbance is a physical and mechanical action that causes mechanical reaction forces in a barrier or fence. If these forces can be measured and processed to distinguish an intruder from wind, temperature changes and other environmental influences, it will be the ultimate in detecting and reporting genuine intrusion attempts. Currently, this is achieved by means of optical fibre fences and/or tautwire sensors. Barrier disturbance can be measured as total fence disturbance (macro measurement) or the disturbance of certain elements for example one wire strand, of the fence (micro measurement). Micro measurement will be far more sensitive and accurate than macro measurement due to the global inertia and histeresis effects of the fence. In macro measurement a force on one wire strand is difficult to always detect, as this one wire must trigger the total macro system. Micro measurement will therefore be the ultimate solution if maximum detection capability is required for fence or barrier disturbance. With the micro measurement system each wire is connected to a sensor. A force on this wire is therefore immediately detected, as it cannot be blanketed by inertia of the total system.

Delay

Once an intruder has been detected the system must delay the intruder sufficiently to allow the security force to react. Delay structures are only of importance once a fence disturbance has occurred. Delays can be accomplished by altering the fence profile by fitting a back or top structure or barb tape rolls. The choice will depend on the required design factor of the barrier. Delay can also be accomplished through non-lethal electrical shock.

Dependability

This keyword focuses on both the reliability and maintainability of the system. A typical barbed wire short circuit detection fence is prone to collecting paper or debris that can cause false alarms and malfunctioning of the system. It is further quite labour-intensive to keep the fence clean.

Only after the user requirements have been listed in a functional specification can the market be investigated for available products. The possibility exists that some products may not be available from the market sector and have to be designed and developed for this specific requirement.

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