| Modern perimeter security systems.
Boris Sergeevich Vvedensky,
MODERN PERIMETER SECURITY SYSTEMS 1. Introduction 1.1. The perimeter is the first line of defense Modern electronic security systems are very diverse and generally quite effective. However, most of them have a common drawback: they cannot provide early detection of an intrusion into the territory of the facility. Such systems, as a rule, are focused on detecting an intruder who has already penetrated the protected area or building. This applies, in particular, to video surveillance systems; They can often only confirm the fact of an intrusion with the help of a video recording device after it has already occurred. A skilled intruder always counts on a certain time “window” that passes from the moment of entry to the moment the alarm is triggered. Minimizing this time interval is a fundamental factor determining the effectiveness of any security system, and in this sense, the attractiveness of a perimeter security alarm is undeniable. The perimeter boundary of the object is the best place for early detection of intrusion, since the intruder interacts primarily with the physical perimeter and creates disturbances that can be registered by special sensors. If the perimeter is a fence in the form of a metal grate, then it must be cut or overcome from above; if it is a wall or barrier, then it must be climbed over; if it is a wall or roof of a building, then they must be destroyed; if it is an open area, then it must be crossed. All these actions cause physical contact of the intruder with the perimeter, which provides an ideal opportunity for electronic detection, as it creates a certain level of vibrations containing a specific audible “image” of the intrusion. Under certain conditions, the intruder may avoid physical contact with the perimeter. In this case, “volumetric intrusion sensors” can be used, usually acting as a secondary line of defense. The sensor of any perimeter system reacts to the appearance of an intruder in the security zone or certain actions of the intruder. The sensor signals are analyzed by an electronic unit (analyzer or processor), which, in turn, generates an alarm signal when a specified threshold level of activity in the security zone is exceeded. 1.2. General requirements for perimeter systems Any perimeter security system must meet a certain set of criteria, some of which are listed below:
It is obvious that a perimeter security system should have the highest possible sensitivity to detect even an experienced intruder. At the same time, this system should ensure the lowest possible probability of false alarms. The reasons for false alarms may be different. The system may, for example, react when birds or small animals appear in the security zone. An alarm signal may appear during strong wind, hail or rain. In addition, a false alarm may occur due to “technological” reasons: improper installation of sensors on the fence, incorrect settings of electronic units or simply an unsatisfactory engineering condition of the fence itself, which may, for example, vibrate in a strong wind. Today, the market for perimeter systems, both domestic and imported, is quite wide. However, choosing the most effective system that meets the specific requirements of the facility can sometimes be difficult. When choosing and designing a system, many factors must be taken into account — the type of fence, topography and terrain, the possibility of allocating a right-of-way, the presence of vegetation, the proximity of railways, overpasses and highways, the presence of power lines. A very important factor is the qualifications and experience of the organization that designs and installs the perimeter security system. Experience shows that often the effectiveness of a system is determined not so much by its initial technical parameters as by the correctness of the choice and the competence of its installation. To evaluate the effectiveness of perimeter systems, special testing grounds are most often used. Security systems are mounted there on standard fences and evaluated using special methods, simulating various actions of an intruder — destruction of the fence, climbing over, digging, etc. 1.3. Specifics of the use of perimeter systems The peculiarity of perimeter systems is that they are usually structurally integrated with the fence and the signals generated by the security system depend to a large extent on both the physical and mechanical characteristics of the fence (material, height, rigidity, etc.) and on the correct installation of the sensors (choice of mounting location, mounting method, elimination of random vibrations of the fence, etc.). The correct choice of the type of security system that most adequately meets the given type of fence is of great importance. Perimeter systems usually use a system of distributed or discrete sensors, the total length of which can be several kilometers. Such a system must ensure high reliability with wide variations in ambient temperature, rain, snow, strong wind. Therefore, any system must provide appropriate automatic adaptation to weather conditions and the possibility of remote diagnostics. Any perimeter system must be easily integrated with other security systems, in particular, with a video surveillance system. 2. Radio beam systems Such systems contain a receiver and a transmitter of microwave signals, which form a detection zone in the form of an elongated ellipsoid of rotation (Fig. 1). The length of a separate security zone is determined by the distance between the receiver and the transmitter, and the diameter of the zone varies from fractions of a meter to several meters. Fig. 1. Operating principle of a radio beam system. The operating principle of such systems is based on the analysis of changes in the amplitude and phase of the received signal that occur when a foreign object appears in the zone. The systems are applicable where direct visibility between the receiver and the transmitter is ensured, i.e. the surface profile should be sufficiently smooth and there should be no bushes, large trees, etc. in the security zone. Radio beam systems are used both for installation along fences and for protecting unfenced areas of the perimeter. These systems are usually designed to detect an intruder who overcomes the security line at full height or bending over. A common disadvantage of radio beam systems is the presence of “dead” zones — the sensitivity of the system is reduced near the receiver and transmitter, so the receivers and transmitters of neighboring zones must be installed with an overlap of several meters. In addition, radio beam systems are not sensitive enough directly above the ground (30 — 40 cm), which can allow an intruder to overcome the security line by crawling. The relatively wide sensitivity zone of the system limits its use at sites where people, vehicles, etc. may accidentally enter the detection zone. In such situations, it is recommended to equip a pre-zone with an additional fence to prevent false alarms. The radio beam system units are installed either on the ground (using special racks) or on a fence or wall of a building. When installing the system on the ground, it is necessary to prepare the protected area, plan the territory, remove bushes, trees and foreign objects. During operation, it is necessary to periodically mow the grass and remove snow. If the snow cover is significant (more than 0.5 m), it is necessary to change the height of the units on the racks and perform additional adjustment. Let's consider several radio beam perimeter systems System “Gefest”, manufactured by Dedal, is designed to protect fenced and unfenced boundaries from 10 to 200 meters long. It can detect a person moving at full height or hunched over. The sensitivity zone is 2.5 m high and 5 m wide. The system's receiver analyzes changes in the signal amplitude and, if the specified threshold is exceeded, switches on the alarm relay. The system uses an original detection processing algorithm with separate sensitivity adjustment for the near and middle sections of the sensitivity zone. The system does not trigger when small animals or birds appear in the zone; it is resistant to snow, rain and wind. The delivery set includes a transmitter, receiver, power supply, installation kit and connecting cables. The receiver and transmitter are housed in impact-resistant polystyrene housings with dimensions of 260 x 210 x 60 mm. Operating temperature range is from -40 to +50 degrees Celsius, supply voltage is 12 V, power consumption is 1 W. Remote monitoring of the system's performance is provided. The “Grotto”system, similar in purpose, allows you to protect perimeter sections up to 300 m long with a detection zone width of 6 m. The improved design of the receiver and transmitter units has increased the homogeneity of the electromagnetic field and virtually eliminated areas of low sensitivity at the edges of the zone. The system remains operational and does not require additional adjustment at a snow depth of up to 70 cm. For zones up to 500 m long, you can use the “Barrier” radio beam security device,similar in design to the Gefest system.” Perimeter radio beam system RLD-94(Photo 1) is available in three modifications: for sections 30, 100 and 300 m long. The 100 and 300 m modifications are a basic set (for 30 m) equipped with additional reflectors. The device uses a pulse synchronous mode of operation, which reduces energy consumption and increases noise immunity to electromagnetic interference. The RLD-94 system is widely used in security systems of nuclear power plants, large enterprises, customs terminals, etc.
Photo 1. Perimeter radio beam system RDL-94. Among the foreign radio beam systems presented on the Russian market, we can note the “Model 16001” by Senstar-Stellar (USA). The system allows you to protect zones up to 240 m long and is designed for installation on the ground, on the end of a fence or on the wall of a building. A distinctive feature of the transmitter is the ability to adjust the angular width of the radiation pattern within the range from 11O to 24O and thus optimize the cross-section of the sensitive zone. A wide range of radio beam security devices is produced by the Italian company CIAS. Devices of the Ermusa seriesare compact and are intended for use both indoors and outdoors for barriers 40-80 m long. Photo 2 shows the units of the ERMO 482 radio beam systemby CIAS. The devices are available in several modifications — for lines of 50, 80, 120 and 200 m. The parabolic antennas used in the units provide low beam divergence, which allows using this system even in conditions of intensive urban traffic. The transmitter radiation frequency is 10.58 GHz, powered by a battery or network adapter. The diameter of the unit is 310 mm, the depth is 270 mm, the weight is 3 kg. The units are mounted on prefabricated metal rods, allowing the emitter and receiver to be installed at a height of up to 1 meter. The box for the power supply and battery is structurally combined with the rod. Operating temperature range -25О to +55О С.
Photo 2. ERMO 482 system. All of the listed systems provide only one security zone and are used on straight sections of the perimeter. On sections with a non-straight border or with complex terrain, a multi-zone system consisting of several sets of equipment should be used. Multi-zone radio beam systems with one common signal processing unit have been developed for small objects. Included in the “Protvа” systemincludes five transmit-receive pairs and a signal analyzer unit. Each transmit-receive pair allows you to protect an area up to 100 m long. The entire set is well suited for protecting, for example, a small warehouse — 4 perimeter zones and 1 gate protection zone. There are remote control and manual shutdown modes for any channel. The system is powered from an alternating current network (220 V or 36 V) or from a 24 V direct current source. Operating temperature from -50O to +50O C; humidity — up to 98% (at a temperature of +35O C). For special applications, a quickly deployable field system “Vitim” has been created(Photo 3). It is used to organize temporary security lines in unprepared areas. The set consists of 11 receiving and transmitting devices, allowing you to organize 10 separate security areas 100 m long. Each of the 11 racks contains a built-in battery to power the devices. The receivers are connected to a remote indicator unit, which shows the number of the area in which the alarm signal occurred. A special feature of the system is the use of a radio beam to send alarm signals. This allows you to quickly deploy the system — no more than 1 hour is required to install and configure 10 zones. The device is widely used at facilities of the Ministry of Defense.
Photo 3. The Vitim system. All the above radio wave detectors are “two-position devices — the kit includes a transmitter and a receiver. Simpler and cheaper are single-position” devices, which are essentially low-power radars. They can be used to protect areas up to 20 m long — gates and windows of warehouses, vehicle entry zones, etc. The peculiarity of single-position systems compared to two-position ones is a less clear boundary of the sensitive zone, “blurred” edges. Single-position systems “Agat-3P and “Agat-SP3” are intended for indoor use (operating temperature from -5O to +50O C). The electronic unit has dimensions of 260 x 210 x 60 mm; supply voltage 12 V, power consumption 0.5 W. Detection range is 16 and 20 m respectively, transverse dimensions of the sensitive zone are 5 x 5 m. Single-position device “Agat-SP3U”can be used outdoors (operating temperature from -40O to +50O C). The device is compact (unit size 110 x 80 x 45 mm) and has low power consumption (less than 0.1 W at a voltage of 12…30 V). The sensitive zone size is 20 x 5 x 5 m. All devices in the Agat series have sensitivity adjustment and an adaptive response threshold. 3. Radio wave systems The sensitive element of such a system is a pair of parallel conductors (cables), to which a transmitter and receiver of radio signals are connected, respectively. A sensitive zone is formed around the conducting pair (“open antenna”), the diameter of which depends on the mutual arrangement of the conductors. When a person appears in the sensitive zone, the signal at the receiver output changes and the system generates an alarm. When using radio wave systems on fences, cables are installed either on special stands on the upper end of the fence, or directly on the surface of the fence. Modifications of radio wave systems are also produced for the protection of unfenced areas. In this case, cables are installed in the ground to a depth of 15 — 30 cm. Such a security system is hidden, but is subject to strong influence of weather conditions, which reduce the stability of its parameters. The advantages of radio wave systems over beam systems are independence from the soil profile and precise adherence to the fence line. One of the most famous domestic radio wave security devices is the “Uran-M” systemdeveloped by NIKIRET (Zarechny, Penza Region). The two-wire line (Fig. 2) is secured to vertical or inclined brackets (console) made of dielectric (included in the delivery set). The conductors used are field telephone wire P-274M, which provides sufficient mechanical strength and resistance to atmospheric influences. The length of one security zone is between 10 and 250 m. The distance between adjacent brackets is usually 6…8 m, in areas with strong winds it is recommended to reduce it to 3…4 m.
Fig. 2. Schematic diagram of a two-wire radio wave device. For extended perimeters, several “Uran-M” kits are used. To eliminate the influence of neighboring zones, a mutual synchronization mode of up to 22 — 25 separate kits is provided. Radio wave systems can be installed on almost any rigid fences (brick, concrete, metal). The Uran-M system includes: a master block connected to one side of the wire line, and a signal processing block connected to the other side of the line. The master block generates a high-frequency pulse signal that creates an electromagnetic field between the conductors. The detection zone has an ellipse cross-section, with the conductors located at the foci. The distance between the conductors is usually 0.4 m; the detection zone is 0.5 x 0.8 m in size. The system is configured to detect objects weighing more than 30-40 kg and does not trigger when birds or small animals enter the zone. The system does not trigger when vehicles are moving at a distance of more than 3 m from sensitive conductors. Supply voltage is 20…30 V, supply current is no more than 100 mA. Remote performance monitoring mode is provided. The security device is resistant to heavy rain (up to 40 mm/hour), snow, hail and wind at a speed of up to 20 m/sec. The electronic units have dimensions of 255 x 165 x 110 mm, they remain operational in the temperature range from -40O to +40O. The design of the units provides protection against external electromagnetic interference and high humidity. The American company Senstar-Stellar offers a radio wave device “H-Field”with cables laid directly into the ground. Such a system is designed to protect open spaces, approaches to objects, etc. Two parallel cables (receiving and transmitting) are buried in any soil to a depth of 10-15 cm and at a distance of approximately 2 meters from each other (Fig. 3). An electromagnetic field (detection zone) 3 m wide and 1 m high is formed around the cables above the soil surface. The maximum length of one detection zone is 150 m. The cables are connected to the receiver and transmitter (or to a common receiving and transmitting unit — transceiver), respectively. The effectiveness of intruder detection is ensured by the fact that for the selected frequency, the human body is like an antenna 1/4 the length of the radio wave, and therefore the intruder greatly changes the parameters of the received signal.
Fig. 3. H-Field system cable layout diagram. The signal processing algorithm in the H-Field system assumes that three conditions are met: The “H-Field” system provides covert installation of sensors with an arbitrary security line profile. The cables are insensitive to seismic and acoustic effects, they can be mounted in the ground, under asphalt roads, etc. One of the modern radio wave detection technologies is called RAFID Radio Frequency Intruder Detection (Radio Frequency Intrusion Detection). This security system was created by the English company Geoquip, widely known for its perimeter systems on sensor microphone cables. In the simplest case, the RAFID system contains a pair of “Emitting Feeders” (EF), one of which is the emitting and the other is the receiving antenna of the radio frequency field. The output signal of the receiver is continuously monitored by the analyzer. The IF is a specially designed coaxial cable containing an inner wire insulated by a dielectric from the outer shield (Fig. 4). The outer shield can be a copper braid similar to the braid of a conventional coaxial cable. The IF is characterized by so-called ports, i.e. holes in the shield located at regular intervals. The cable design ensures the emission of an electromagnetic field when current passes through it. An invisible electromagnetic field is formed near both cables, the configuration of which depends on the mutual arrangement of the IF.
Fig. 4. Design of the radiating feeder of the RAFID system. An object that enters the radio frequency field changes the phase and amplitude of the received signal (Doppler effect), as a result of which the analyzer generates an alarm signal. The cables are arranged parallel to each other and mounted on a rigid wall or other fence, providing a detection zone, as shown in Fig. 5. (The distance between the cables and their arrangement are determined by the specific customer requirements and detection conditions).
Fig. 5 (a, b) detection zones of the RAFID system. RAFID system cables are installed on rigid fences (concrete, brick, wood) or directly in the ground. The number of cable lines (2 or 3) and their location on the fence are determined by the task facing the security system. So, if it is necessary to register an intruder trying to climb over the fence, then the cables are located near the middle line of the fence (approximately at half its height), see Fig. 5a. In this case, near the lower part of the fence, an insensitive zone can be left — an “alley for animals”, to which the system should not react. If it is necessary to detect an intruder just approaching the perimeter line, then in this case one of the cables is attached to the lower part of the fence or directly in the ground at some distance from the wall (Fig. 5b). The system uses a powerful processor to process signals, which allows the system to be “trained” directly at the site. The processor stores both typical intrusion signals and non-alarming signals from the surrounding environment (passing vehicles, etc.). When the actual registered signal matches one of the alarm images stored in the memory, the system generates an alarm signal. The system is virtually unaffected by atmospheric factors such as rain, fog, hail, snow, smoke, and is used in various climatic zones. Conclusion The operating principle of all the security systems described above is based on the use of electromagnetic waves in the radio frequency range. However, other systems have been developed and successfully used to protect perimeters, which work with various types of detectors: optical infrared sensors (beam and passive), seismic vibration sensors, microphone cables, capacitive systems, fiber-optic cables, etc. They will be discussed in the next issues of the magazine. |
