Modern perimeter security systems. Article updated 09.04 in 2023.

Vvedenskiy Boris Sergeevich,
candidate of physical and mathematical sciences

MODERN PERIMETER SECURITY SYSTEMS

Previous issues examined perimeter security systems of various types: optical, radio wave, radio beam, capacitive, etc. This final part of the article describes perimeter systems that are sensitive to vibrations and use sensor (microphone) cables or seismic sensors as signal sources.

The operating principle of such systems is based on the registration of mechanical vibrations or movements of the fence that occur when an intruder tries to destroy or overcome the perimeter. The sensitive element of such systems is usually a sensor cable that converts mechanical vibrations into an electrical signal. The cable is attached either directly to the fence or to a special light metal canopy above it. The cable signals are processed by an analyzer, which, in accordance with a specified algorithm, issues an alarm signal. Below we will briefly consider some domestic and foreign systems with sensory vibration-sensitive cables.

In the well-known Russian perimeter systems Aral and Dolphin, a multi-wire telephone cable is used as a sensitive element. When the cable is deformed, electric charges are induced in the insulating sheaths (triboelectric effect), which create pulse potentials between the conductors. The sensitive element is a kind of extended microphone, which is why such a cable is sometimes also called a microphone cable.

The Aral system is designed for installation on welded metal meshes of the SSTSP type. A 10-pair telephone cable of the TPPep 10x2x0.35 type is used as a sensitive element, which is recommended to be mounted in two passes on a fence about 2 meters high. On mesh canopies installed along the end of concrete or brick fences, the sensor cable is usually mounted in one pass (Fig. 1). The cable is connected to the electronic unit of the system (analyzer), which processes the sensor signals and generates an alarm signal if an intruder tries to cut the fence or climb over it. The length of the detection zone in favorable conditions can reach 500 m, but the recommended length of the actual zone usually does not exceed 250-300 m. The electronic unit of the Aral system has dimensions of 95x225x320 mm; It is powered by a DC source with a voltage of 10 — 30 V, the nominal power consumption is 0.5 W, the operating temperature range is from -50 ° C to + 50 ° C. The system is equipped with lightning protection elements.

The more advanced Dolphin-M system is similar to the Aral system in its technical characteristics and application tactics, but has more modern circuit solutions. Dolphin-M is also designed to protect fences made of welded metal mesh; the recommended length of one security zone is 250 m (up to 500 m for straight homogeneous perimeter sections). The Dolphin-M system provides the ability to calibrate sensitivity for a specific fence and allows automatic tuning out from industrial interference. The Dolphin-M electronic unit (photo 1) is made in a dust- and moisture-proof case with dimensions of 90x220x330 mm; power consumption is 0.1 W at a supply voltage of 20-30 V, the operating temperature range is from -50O to +50OC.

Photo 1. Electronic unit (sensor signal analyzer) of the Delfin-M perimeter security system.

The delivery set of the Aral and Dolphin-M systems, in addition to the sensitive cable and electronic unit, also includes connecting cables, a section cabinet for placing one or two electronic units and a set of accessories for installation. The complete delivery, which provides for the installation of a canopy, also includes the mesh itself, special posts and mesh fastening elements.

Most foreign vibration perimeter systems use a special coaxial cable that also operates on the triboelectric effect. Such a cable is used, for example, in the Intelli-Flex system, manufactured by the American company Senstar-Stellar. The triboelectric coaxial cable allows you to protect fences made of welded lattice or chain-link mesh. The system registers attempts to climb over the fence, cut through its cells or lift the mesh. The electronic unit of the Intelli-Flex system analyzes the number of pulses in a given time window (cutting the fence), as well as the integral energy of the signal during long-term impacts (climbing). On a standard US and European mesh fence up to 2.5 m high, the cable can be installed in one pass; a two-pass configuration is recommended to ensure greater reliability. In the latter case, the cable is attached along the upper and lower edges at distances equal to one third of the fence height. The maximum length of the protected zone can reach 300 m (2×300 m when using a two-zone analyzer).

To configure the Intelli-Flex system, a special programmer is used (photo 2), which is connected to the electronic unit and records signals accompanying attempts to actually overcome the perimeter. The signals recorded by the programmer are then used as criteria for detecting an intrusion. Each security zone requires individual configuration of the analyzer in several sections of the zone. It is possible to install a special weather sensor on each analyzer to monitor current weather conditions and adapt the signal processing algorithm.

Photo 2. Programmer for configuring the analyzer of the Intelli-Flex system by Senstar-Stellar (USA).

The two-zone electronic processing unit (analyzer) of the Intelli-Flex system has dimensions of 260x210x108 mm. Power is supplied from a source with a voltage of 11 — 24 V; the consumed current is 70 mA. The operating temperature range is from -40O to +70OC.

The English company Advanced Perimeter Systems (APS) produces the Flexiguard system, which also uses a special coaxial triboelectric cable as a sensing element. For typical perimeters, the system is available in two main modifications: FG2000 — for light metal fences (chain-link mesh and welded wire grating) and FG2500 — for so-called «palisade» European fences made of stamped thin-walled steel elements.

The FG5000 system from APS is designed to protect the perimeters of explosive facilities — petrochemical plants, gas stations, explosive warehouses, etc. The FG3000 modification is used to protect the walls and roofs of buildings.

The Flexiguard sensor cable is attached directly to the mesh fence using plastic ties installed every 100 mm. The cable is highly flexible and durable, which simplifies the installation process. The sensor is connected to the FS200 analyzer (photo 3), equipped with an automatic environmental control system. This system allows you to tune out signals caused by climatic influences (rain, wind, hail), and thereby significantly reduce the frequency of false alarms. The maximum length of the security zone is 300 m; to control the system, APS produces special control panels FG10 and FG20 for 10 and 20 zones, respectively. In addition to visual monitoring of alarm signals, these panels allow you to listen to the sensor's audio signals, which help identify the type of intrusion.

Photo 3. The FS200 analyzer of the APS Flexiguard system on a chain-link fence.

At the Moscow exhibition of security systems MIPS-98, the triboelectric cable security system was presented by the Turkish company Perpro. The PPS2 system is designed to protect fences made of mesh, wire grating and barbed wire. It is characterized by the fact that it reacts only to stretching of the fence cells and is insensitive to vibrations. The sensor cable is mounted on the mesh not along a straight line, but in the form of zigzags (photo 4), which increases the efficiency of registering an intruder climbing over the fence. The cable is triggered by an external stretching effect of 5 to 200 kg. To protect a 2.5 m high mesh or barbed wire fence, 3 to 5 sensor passes are required.

Photo 4. Sensor cable of the PPS2 system by Perpro (Turkey), mounted on a mesh fence.

The standard sensor cable of the PPS2 system is designed for a temperature range from -30 °C to +70 °C, and on request it is supplied in a special sheath and operates at temperatures down to -40 °C. The PPS2 system analyzer processes signals from two zones; the maximum length of each zone is 400 m.

Triboelectric coaxial cables are also used as sensors by the Italian company GPS Standard. The wired triboelectric perimeter detector type WPS implements the principle of deformation of stretched conductors. Several beams of a specially designed coaxial cable with a steel central core are stretched along the perimeter line at a distance of approximately 15 cm from each other, thus forming an additional physical barrier. When attempting to overcome such a barrier, the intruder deforms (stretches) the cable, in which an electric signal appears. After amplification, the signal is processed by a microprocessor, which issues an alarm signal. The system includes a concentrator that controls up to 8 sections of sensor cable, each of which can be up to 300 meters long. The software allows, by tracking cable signals, to automatically adapt the sensitivity of the system to the surrounding weather conditions. The cable signal amplifier unit has dimensions of 80x80x60 mm and consumes 1 mA at a voltage of 12 — 28 V. The concentrator with a microprocessor is made in the form of a unit measuring 125x125x50 mm; supply voltage is 12 — 28 V, current is 13 mA. A personal computer with special software is used for adjustment and maintenance of the system. The system is operational in the temperature range from -30O to +60OC.

GPS Standard also offers a CPS system with a coaxial microphone cable that is attached to an existing fence. The electronic unit continuously analyzes the signals from the sensor cable and, if a preset activity threshold is exceeded, generates an alarm. The system's microprocessor provides adaptation to weather conditions and interference rejection (wind, birds, etc.). Two sections of cable up to 300 m long are connected to the electronic unit; the unit has relay outputs for the «pre-alarm», «alarm» and «malfunction» signals. The dimensions of the electronic unit are 220x120x80 mm; it is powered by a source with a nominal voltage of 12 V at a current of up to 100 mA. A personal computer is used to program and monitor the system, in parallel with which a conventional alarm control panel can be connected. The CPS system operating temperature range is from -30O to +70OC.

The principle underlying the operation of the domestic perimeter system Drozd is interesting. The role of the sensor cable is performed by an ordinary field wire P-274, which, moving in the magnetic field of the earth, generates an electric signal. The sensor signals are processed by a special electronic unit. The system is available in several versions. On concrete, brick and wooden fences (a version of the system called Drozd-01), the sensitive element is mounted in several beams on brackets installed along the upper end of the fence. When mounted on mesh fences (option Drozd-02), the sensor is fixed directly to the fence; in this case, the system registers both cutting the fence and climbing over it. When used on barbed wire (option Drozd-03), the cable is fixed to the supports parallel to the main fence; to cover a zone 2.4 m high, 12-13 beams of the sensitive cable are required. Delivery options differ in the complete set of mounting devices. The maximum length of the perimeter section protected by the Drozd system is 500 m. The electronic unit of the system is powered by 10 — 30 V and consumes only 0.12 W. The dimensions of the electronic unit are 220x330x90 mm, the operating temperature range is from -50O to +50OC.

The detection capacity and the probability of false alarms of perimeter systems are determined mainly by the quality of the sensitive element (sensor cable or other sensor).

Therefore, the most advanced vibration-sensitive distributed sensors include specially designed electromagnetic microphone cables. When the cable moves or vibrates, voltage is induced in its conductors, similar to what happens in conventional electromagnetic microphones. Such sensors are characterized by high fidelity in reproducing fence vibrations and a high signal-to-noise ratio due to the low-resistance nature of the sensor itself.

An example of an electromagnetic microphone cable is the GW400k Guardwire series sensor, developed and manufactured by Geoquip (UK). The sensor cable (Fig. 2) contains two fixed and two moving conductors located in the gap between two semicircular strips made of flexible magnetic polymer. The cable core is covered with an insulating layer of Mylar and a screen made of aluminum foil, to which the ground wire is connected. On the outside, the sensor cable is protected by a durable polyethylene sheath.

The Guardwire sensor cable is mounted directly on the fence and senses vibrations created by the intruder. The movable conductors move in the gaps of the polymer magnets and an electric voltage is induced in them, which is recorded and processed by the analyzer.

Guardwire system analyzers (photo 5) provide dual-channel signal processing required to register two main types of intrusion: climbing over a fence (prolonged impact) or destruction of the fence (impact impact). The sensitivity of the system is set independently for each channel. Replaceable filters allow you to suppress interference (for example, from wind or rain) and optimize the system response for a given type of fence. In the channel for registering impact impacts (“fence cutting”), the duration of the “time window” and a certain number of “events” are set, after which the analyzer turns on the alarm signal. The dimensions of the analyzer are 160x260x90 mm, the supply voltage is 12 V, the consumed current is 100 mA, the operating temperature range of the sensor and analyzer is from -50O to +70OC. Maximum length of the security zone is 400 m.

Photo 5. GW475 analyzer of the Guardwire system

The Guardwire series equipment is designed to protect perimeter fences made of metal mesh, thin welded lattice, barbed wire or relatively light wooden fences. For more massive fences (heavy welded or forged lattices, etc.), Geoquip produces the Defensor system with an improved GDALPHA sensor cable (Fig. 3). This cable contains only two conductors, which are placed in polyethylene tubes with silicone grease, providing increased conductor mobility and, accordingly, signal level. To minimize external interference, the active conductors are formed as a twisted pair. The central multi-core wire acts as a strengthening element and limits thermal deformations of the sensor cable.

The Defensor system analyzer is close to the Guardwire system in its technical and operational characteristics. It has dimensions of 140x220x75 mm; supply voltage is 10 — 24 V, current consumption is 60 mA. The system is operational at temperatures from -50O to +70OC.

Both analyzers have standard relay outputs, configurable as normally closed or normally open. In addition to the alarm relay, the analyzer includes a fault relay, which signals cable damage, opening of system units, or power failure in the zone. Guardwire and Defensor analyzers also have audio outputs, which allows the operator to listen to the situation in each zone and identify an intrusion signal by ear.

Both systems — Guardwire and Defensor — are distinguished by the fact that they do not require adaptation to weather conditions or seasonal adjustment of parameters. Both systems also do not require a programmer or a computer with special software for setup and operation.

These systems, as well as systems with vibration-sensitive cables, respond to vibrations or deformations of the environment in contact with them. However, here, sensors are usually used that are installed directly in the ground or on massive walls and record low-frequency (seismic) vibrations (displacements) of the soil or wall.

The systems typically provide concealed installation and can protect both fenced and unfenced perimeters.

The Russian Duplet system is a seismic magnetometric detection device. The sensitive element of the device is a special KTPEDEP 10x2x0.5 cable with double shielding, laid directly in the ground at a depth of 30 — 40 cm along the protected perimeter. The cable records both seismic signals (ground vibrations) that occur when an intruder passes, and local changes in the magnetic field when ferromagnetic objects move. Three cable lines are located in parallel (Fig. 4) at a distance of 1 m from each other, providing a sensitivity zone 3 m wide; the maximum length of one zone is 500 m. The camouflage of the underground sensors makes the system invisible to the intruder. If necessary, electronic units can also be installed underground, placing them in special containers.

The single-zone kit of the Duplet system includes six beams of sensor cable with junction boxes, two amplifier units, a signal processing unit and a set of mounting accessories. The electronic units are powered from a source with a voltage of 20 — 30 V and consume 1.5 W; the operating temperature range of the system is from -50O to +50OC.

Unfortunately, the system perceives not only intruder signals, but also other seismic signals, so there should be no trees or large bushes in the detection zone, since the system can be triggered by the movement of their roots. For the same reasons, the minimum distance from the sensor to roads with car traffic should be 10 m, and to high-voltage power lines — 50 m. When servicing the system, seasonal routine maintenance is provided, during which the system is adjusted taking into account the actual state of the soil.

Simpler underground seismic-sensing systems are usually used to detect undermining under fences. The Russian Amulet system uses a single sensor cable to detect undermining, buried 5-20 cm in the ground along the fence line. When attempting to undermining, the intruder deforms the cable, which creates an electrical signal in the latter. The Amulet system can cover an area up to 1000 m long. It works in any soil except swampy and rocky soil. The electronic unit is designed to filter the signal, analyze its shape and count pulses. It has dimensions of 320x95x232 mm, is powered by a voltage of 20-30 V and consumes 0.2 W.

It should be noted that some other cable systems designed to protect fences are also well suited for organizing anti-undermining boundaries. Thus, when using Guardwire as an anti-undermining system, it is recommended to place the sensor cable in a steel pipe and lay it in a gravel-filled trench, which is arranged in order to increase the reliability of detection. The trench cross-section should not be less than 30×30 cm; the cable laying depth should be equal to half the trench depth.

To organize underground seismometric boundaries, the Italian company GPS Standard uses extended hydraulic pressure sensors. Such a system, called GPS, uses two or four special sensitive flexible hoses that are laid in the ground at a depth of 25 — 30 cm at a distance of 1 — 1.5 m from each other. A typical configuration for a two-zone underground GPS system is shown in Fig. 5. The hoses (1) are made of elastic polymer material; they are filled with antifreeze under pressure and connected to a special two-zone sensor (2) that measures the liquid pressure. Compensation valves (3) are used to automatically compensate for the pressure difference in the system hoses. The valve bodies, mounted underground, are made of plastic. The sensor contains highly sensitive membranes and a microprocessor for converting and analyzing signals, which are compared with typical images characteristic of real intrusions. After processing, the signals are fed to the central electronic unit, to which up to 16 sensors can be connected. It can be placed in installation cabinets or in a special 19-inch rack and contains a device for collecting, processing and transmitting information from sensors, as well as a relay unit. The unit also contains an RS-232 interface, through which external security equipment or a computer used to configure and monitor the system is connected. For these purposes, special software is included in the delivery set.

The GPS system is used to protect both fenced and unfenced perimeters. The detection zone width is 2.5 — 3.5 m; the system allows detecting an intruder who crosses the protected boundary by walking, running, jumping, rolling or by digging. Dynamic adjustment of parameters automatically changes the system response threshold when temperature and weather conditions change. Hydraulic sensors can be installed in various soils, under asphalt or paving slabs. High sensitivity of sensors requires that trees or large bushes be at least 3 — 4 meters from the hoses.

The GPS sensor mounted underground is placed in a metal case with a diameter of 135 and a height of 160 mm (two-pipe sensor). The sensor requires a source with a voltage of 12 — 18 V, the current consumption is 15 mA. The operating temperature range of the system is from -30O to +60OC.

One of the most advanced vibroseismic systems is the Psicon perimeter complex, manufactured by the English company Geoquip. Here, discrete seismic sensors, sometimes called geophones (photo 6), are used as sensors. Such a sensor is a conductive winding and a magnetic core placed inside it, which can freely oscillate along the winding axis. When the magnet oscillates, a voltage is induced in the coil, which is recorded by the analyzer. Geophone sensors are assembled into a beam of the required length and placed underground or attached to a fence. The high sensitivity of geophone sensors allows them to register very weak signals and detect an intruder overcoming, for example, a massive concrete or brick wall. When geophones are installed underground, the Psicon system reliably detects a cautiously walking or crawling person or an intruder who has jumped off a fence.

Photo 6. Geophone sensors and analyzer of the Psicon vibroseismic perimeter system from Geoquip (Great Britain).

In a typical configuration, the single-zone Psicon system contains 4 beams, each of which includes 16 discrete geophone sensors. The distance between the sensors is 3.2 m and the total length of one protected zone is about 100 meters. All 64 sensors are connected to a common analyzer, which processes the signals and issues an alarm signal when an intrusion is localized with an accuracy corresponding to the length of one beam (50 m). Geophone sensors are placed in hermetic rigid housings measuring 110x75x35 mm. All sensors are connected with an armored multi-core cable and are supplied in the form of beams ready for laying in the ground. The operating temperature range of the sensors is from -40O to +100OC.

The high sensitivity of the system's geophone sensors necessitates the use of a powerful «intelligent processor for signal processing and filtering out interference created by the environment (traffic noise, tree root movement, rain, etc.). The Psicon system uses a technology developed by Geoquip called TESPAR for this purpose. The system converts the analog signal from the sensors into a digital code sequence, which is then subjected to matrix transformation in the analyzer. The latter uses the principle of pattern recognition and comparison with the reference ones recorded in the analyzer's memory. The comparison occurs in real time and allows for reliable recognition of weak intruder signals against the background of even very intense interference or noise. The system can be «trained» directly at the site, storing both «alarm» and non-alarm» signals in the processor's memory. A portable computer connected to the port of the electronic unit is used to configure the system.

The Psicon analyzer has dimensions of 400x300x110 mm and consumes 500 mA at a nominal source voltage of 12 V. The analyzer's operating temperature range is from -25O to +70OC.

In some cases, the perimeter alarm system is combined with a means of actively repelling an intruder using a short electric impulse (electric shock), which is not life-threatening to a person. The English company APS in its Electro-Fence system suggests using a barrier or a canopy made of several parallel conductors for this purpose. An intruder trying to climb over such a barrier is exposed to a short (less than 1 millisecond) electric impulse, which does not threaten his life and does not harm his health, but is very unpleasant for a person and makes him give up trying to climb over the barrier or cut it. When an intruder comes into contact with the barrier, in addition to the repelling impulse, the system also generates an alarm signal.

Such barriers can be installed on existing fences or placed separately from them. Steel conductors with a diameter of 2.5 mm are placed at a distance of 95 mm from each other and stretched between metal posts along the entire height of the barrier (from 1 to 3 meters). These conductors simultaneously act as sensors and electric shock electrodes. The Electro-Fence system controller can manage one, two or six security zones. It registers intrusion attempts and generates an alarm signal, monitors the voltage on the conductors, and detects attempts to cut or short the conductors.

Perimeter protection is a complex task, for the effective solution of which the correct choice of a security system and the optimal combination of a physical barrier that impedes entry to the facility with security alarm systems are very important. Among the many modern perimeter security systems, it is impossible to single out one that would be the most universal and best from all points of view. Therefore, when designing perimeter security systems, it is necessary to take into account many factors: the possibility of allocating an alienation strip, terrain, fence design and material, vegetation, the presence of railways or highways nearby, etc.

The specifics of Russian conditions for the design and operation of perimeter systems are associated with a variety of climatic conditions. The system must withstand seasonal temperature fluctuations, strong winds, snowfalls and blizzards, frost, hail, rain, fog, etc. All these factors, as well as economic constraints, make the choice of the optimal perimeter system a difficult task, requiring high qualifications of the designer and the ability to navigate the variety of technical security equipment currently produced.