Vibration microphone detection devices.
Vibration microphone detection devices (SDD) are designed to detect an intruder by the vibrations they create in a strong engineering barrier (physical barrier) during penetration into a protected facility.
The operating principle of such detection devices is based on recording mechanical vibrations or movements of the fence that occur when an intruder attempts to destroy or overcome an engineering barrier. The sensitive element of the systems is a specially designed electromagnetic microphone cable that converts mechanical vibrations into an electrical signal. The cable is attached directly to the fence or to a special metal canopy above it. The cable signals are sent to the signal processing unit, which issues an alarm signal in accordance with a specified algorithm.
The functional diagram of the detector is shown in Fig. 1.13.
With regard to the vibration microphone detector, its elements are:
— external impact — is mechanical vibrations or movement of the fence, which occur when an intruder tries to destroy or overcome an engineering barrier.
— the sensitive element of the detector is the microphone cable,
— signal processing unit — is present.
Therefore, the functional diagram of the vibration microphone detector will look like (Fig. 2.15):
Fig. 2.16 shows the design of an electrodynamic alpha sensor cable, specially designed to detect vibrations during perimeter protection. Two polymer magnets are placed in the protective sheath of the cable. Fluoroplastic tubes are laid in their magnetic gaps, in which movable sensitive conductors move freely. To reduce friction, the tubes are coated with silicone grease from the inside. When the cable body is displaced under the influence of vibration, the magnets move, and the conductors remain in place. Under the influence of an alternating magnetic field, an electric current is generated in the conductors, which is received by the signal processing unit.
Fig. 2.16. The electrodynamic alpha sensor cable is passive. It does not require an external source of electrical energy, but generates electrical current itself. The sensitivity of the electrodynamic sensor is very high. It is comparable to the sensitivity of a microphone capsule. These sensors are characterized by the stability of their parameters and provide a high signal-to-noise ratio, referred to the analyzer input.
Another example of a microphone cable is a sensor. Shown in Fig. 2.17. The sensor cable 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. The sensor cable is protected from the outside by a durable polyethylene sheath.
To minimize external interference, the active conductors are formed as a twisted pair. The central multi-core conductors act as reinforcing elements and limit thermal deformations of the sensor cable.
For massive fences (heavy welded or forged bars, etc.), an improved sensor cable (Fig. 2.18) can be used, which contains only two conductors, which are placed in polyethylene tubes with silicone grease, providing increased mobility of the conductors and, accordingly, the signal level.
The physical principle of operation of the microphone cable is as follows. In accordance with the law of electromagnetic induction in a conducting circuit located in an alternating magnetic field, EMF-induction occurs ε, which is determined by Faraday's law as: ε = N
where: N is the number of conductors located in an alternating magnetic field,
— change in magnetic flux over time.
Induction in a conductor moving in a magnetic field is determined as:
U = — B l v
where: U is the induced voltage,
B – magnetic induction, determines the density of magnetic flux
[B] = [ ] = T (Tesla)
L – length of conductor,
v – speed of conductor in magnetic field.
The sign «–» means that with increasing magnetic flux, the direction of induced current is opposite to that determined by the gimlet rule.
B = μ μо H
where: H – magnetic field strength, determined by the properties of polymer magnets and the size of the magnetic gap.
μo – magnetic constant, μo = 1.257. 10 — 6 [ ]
μ – relative magnetic permeability of the medium.
Thus:
1. The conductors are located in the magnetic field of a flexible magnetic polymer.
2. Local deformations of the microphone cable (caused by vibration of the controlled fence) lead to the displacement of the flexible magnetic polymer relative to the conductors. This causes an alternating magnetic field to arise, which induces voltage in the conductors.
3. The magnitude of the induced voltage depends on:
— the speed of movement of the conductors in the magnetic field;
— the properties of the polymer magnets and the size of the magnetic gap;
— the number of conductors in the cable;
— the size of the local section of the cable that has undergone deformation.
Signal processing unit
The signal processing unit is designed to:
— process the signal from the sensitive element;
— alarm signal generation;
— remote monitoring of the triboelectric detector performance.
Processing of the signal from the sensitive element includes:
— signal frequency analysis;
— signal amplitude analysis;
— logical processing.
When analyzing the signal frequency, frequency filtering is performed using filters:
— high frequency, ensuring the identification of signs of the intruder «biting» the wire elements (mesh) of the fence;
— low frequency, ensuring the identification of signs of the intruder overcoming the engineering barrier by «climbing».
When analyzing the signal amplitude, amplitude filtering is performed in order to identify signs of the intruder overcoming the engineering barrier, rather than the impact on the barrier by various mechanical means, which can be considered as interference.
The functional diagram of the signal processing unit is shown in Figure 2.19.
In this case, the signal from the sensitive element goes not to the input signal amplifier, but to the input device. This is explained by the fact that a more powerful electrical signal is removed from the microphone cable.
Main technical characteristics
Receiving an electric signal during the movement of conductors relative to a flexible polymer magnet during deformations of a microphone cable sensing element fixed to a fence vibrating during penetration of an intruder into the protected area. The number of inputs (arms) for connecting sensing elements is up to two. The length of the section blocked by one arm in a single-pass scheme is usually not less than 250 meters. One detector in a single-pass scheme usually blocks not less than 500 meters.The detection zone of a vibration microphone detector is a certain area of the engineering barrier located around the sensitive element. The dimensions of the zone are determined by the strength characteristics of the barrier and the sensitivity of the detector.
In addition to the devices already mentioned, the review section of the material presents well-known detectors of Russian and foreign manufacture on the market. Not all of them are microphone detection devices, but there is no confusion here. The fact is that this material is the first in a series of reviews of perimeter detection devices, and our goal is to provide readers with the most complete information about the devices presented on the Russian market.
Vibration-sensitive perimeter security system Defensor (Geoquip, UK) It is designed to protect metal and wooden fences. The system uses an electromagnetic microphone cable with a pair of conductors located in the gaps between extended magnets. The sensor is attached to the fence being protected. When the sensor vibrates, its conductors move in the magnetic field, and a voltage is generated in them, displaying the activity on the fence. The sensor is characterized by high sensitivity and a wide frequency band. The analyzer registers two main types of intrusion: breaking through the fence and climbing over it. The analyzer is equipped with relay outputs for alarm and tampering signals, as well as a self-diagnostic system. The length of the security zone is up to 300 m. Analyzer power supply: 10-24 V/90 mA. Operating temperature range from -40 ° C to + 70 ° C, equipment sealing according to IP65 standards.
Two-channel vibration detector TREZOR-V 02 («Vostok-special systems», Russia)
It is designed to detect an intruder who overcomes the barrier, as well as to destroy or dismantle its canvas. It is designed to control «light» metal barriers: welded (SSCP) or twisted metal mesh (chain-link), barbed wire or tape (AKL), thin metal sheets (corrugated sheet).
It has universality and high efficiency of use due to adjustment by 8 parameters. There is a function of tuning out interference (strong wind, rain, etc.).
Length of cable sensing element up to 2×1000 m. Outdoor version (IP65, operating temperature range from -40°С to +60°С). Supply voltage 10-30 VDC.
Power consumption no more than 400 mW (with remote control connected -500 mW). Detection probability not less than 0.95.
SL-3 vibration detector (Rbtec, Israel)
It is designed to block various types of fences: metal panel fences, barbed wire fences and reinforced barbed tape (RBT).
The SL-3 sensor line consists of several (up to 33) multi-vector vibration sensors connected by a cable at intervals of 3 meters. The unique characteristics of the sensor provide high sensitivity and noise immunity, which is the key to successful protection of the facility.
The sensor line is mounted on the fence so that each section has at least one sensor. One sensor line allows blocking up to 100 meters of the boundary with a fence height of no more than 3 meters. The presence of 2-stage lightning protection ensures reliable operation of the product in thunderstorm conditions.
Godograph-Universal (NIKIRET, Russia)
It is intended for organizing security lines for extended areas of terrain. Depending on the type of sensitive elements, it can be used as a vibration SS (to detect an intruder overcoming a barrier by climbing over, destroying, or digging) or a seismic SS (to detect an intruder moving along the ground surface).
The vibration cable sensing element (SE) is installed on:
— barriers made of welded mesh with or without a box, volumetric or flat spiral AKL;
— canopies made of three-dimensional and flat spiral ACL, welded mesh;
— barriers made of reinforced concrete slabs;
— barriers made of corrugated sheets;
— into the ground under the barrier to a depth of 1 m.
The seismic sensitive element is installed in the ground in open areas or along the barriers. It is possible to create one or two independent sections of the security line up to 250 m long each. Operating temperature range from -50°C to +50°C.
Vibration security device «MURENA-2» (Firm «YUMIRS», Russia)
The new generation of vibration detectors of the MURENA-2 series has a completely modernized algorithm for analyzing signals from the vibration cable sensor, the sensitive element (SE). The new version of the MURENA-2 program analyzes the entire frequency spectrum of the signal from the suspected intruder attempting to overcome the barrier on which the vibration cable (SE) is installed.
When installing MURENA-2 on the barrier, attempts to climb over, dig under (when the SE is buried in the ground), destroy the barrier by sawing or «biting out» the mesh rods are recorded.
At the same time, provocative effects of the intruder are completely «cut off»: single blows or a series of blows on the barrier, as well as short-term shaking of the barrier.
The MURENA-2 unit has 4 independent inputs for connecting a CE. Each input can be used to connect a CE up to 500 meters long. The total length of the area protected by one MURENA-2 unit is up to 1000 meters. An additional 1000 meters of CE can be installed on top of the fence.
The MURENA-2 is configured using a laptop or a desktop computer in the security room.
Rubicon-1 detector («Rovalent», Belarus)
Designed to protect the territory from penetration, control the violation of the integrity of flexible fencing elements — welded and woven wire mesh, barbed wire, rigid palisade fences.
Autonomous mode: outputting signals to the control panel. Centralized mode: as part of integrated security systems and a radio security complex.
It has two independent security zones of 300 m each, sensitive cable — KTV-MF, TPPeP, E-Flex, etc. Programming is carried out from a computer or keyboard. Events are indicated separately for each security zone. The detector is protected from electromagnetic and radio interference, and can recognize attempts to penetrate in difficult weather conditions.
Independent registration of two types of intrusion into the protected area — climbing over and cutting the fence. Monitoring of sensitive elements for breaks and short circuits.
MICALERT-303 System (RBtec, Israel)
Designed for passive intrusion detection and is a sensor microphone cable and a signal processing unit. The system is installed on various types of mesh metal fences.
The signal processing unit analyzes the characteristic noise effects created by an intrusion attempt. The system is able to recognize signals generated by an attempt to penetrate the fence and ignores noise caused by weather conditions, thereby preventing false alarms.
It is supplied in three basic configurations: a set for protecting one or two zones, or as a complete integrated system that includes a control center and software. The standard length of the protected zone is 305 meters.
(Continued in the next issue)