Peripheral and Perimeter Protection
It is a set of electronic security systems designed to protect a certain area (perimeter) in outdoor enclosures and also indoors, preventing intrusions and burglary (home-jacking).
These are systems that warn of an ongoing intrusion attempt on the perimeter of the property.
Types of technologies
The infrared barrier based its technology in sending and receiving an infrared signal – a cell in the emitter column produces a beam of infrared light, totally invisible to the naked eye, which is captured by the receiver cell.
This system consists of two modules, a emitter and a receiver which are installed facing each other on the protection line to form an invisible detection zone that, if interrupted, generates an alarm.
The emitter sends a beam of directional invisible light (900 nm wavelength)
The receiver has an electronic “eye” that analyzes the signal amplitude.
To one set of light beams is given commonly the name of beam and there are several types of technology used in the infrared barriers:
Continuous beam technology
In this technology, light emission is continuous and directional (emitter cell – receiver cell), which is easily interrupted causing often false alarms and consequently a low level of security.
Pulse beam technology
In this technology, light emission takes place at intervals and the emitted light may be received by various cells, which minimizes false alarms , thus providing a higher level of security.
This technology provides the possibility to create multiplexed channels, grouping one or more beams, and select which channel each receiver will receive.
This type of transmission also allows the establishment of a synchronization mechanism in order to further enhance immunity to false alarms and the security provided.
D.I.S. 100 Hz Technology
With this new technology developed by SORHEA, there is no longer the term emitter cell and receptor cell, all cells are to have double function, emitter and receiver, by passing the cells to bidirectionally communicate and perform a double scanning of the detection zone, while still allowing multiplexing beams to optical synchronization at the frequency of 100 Hz.
D.I.S. – Dual Interlaced Scanning
This technology makes the various beams totally independent, allowing group adjacent beams and configure the detection zones, thus achieving doubling the detection zone.
Another advantage of this technology is that, due to the optical synchronization between cells, it is possible to provide them with double AGC – Automatic Gain Control, thereby offsetting the variations of the signal received by the receiver in order to ensure at all times the correct functioning of the barrier, further increasing the security and immunity to false alarms.
Also because of this feature is guaranteed easy alignment of the beams, i.e. provided that the cells are aligned “in line of sight” the AGC will compensate any misalignment of the beams.
So, with this type of cells, the optimum alignment of the beam is extremely easy to be performed by one person, because the manufacturer usually includes into the cell an alignment aid interface, consisting of an optical viewfinder, an indicator LED and a powerful buzzer.
The fact that all cells are bidirectional provides that alarm information are available on all columns and consequently the network cables to the alarm contacts are freely set according to local needs and constraints, simplifying it and by limiting work construction required for their development, thus lowering the investment in security.
Reach of an Infrared Barrier
The range of an infrared active cell varies with the visibility:
Theoretical Maximum Reach: 2550m
- When the visibility is 200 m, the range reaches 250m
- When visibility is 60m (dense fog), the reach is 100m
Microwave barriers consist of emitters that generate waves at a frequency of 9900MHz and receivers that analyze signals from these emitters.
The detection zone is represented by a lobe which unfolds from the emitter head to the receiver head.
If a moving obstacle through the secured field between the transmitter and receiver, it is detected by the receiver that immediately sends the information.
The greater the distance between the emitter and the receiver, the greater is the width of the lobe.
The higher the level of sensitivity, the bigger is the lobe.
DUAL SENSOR TECHNOLOGY
Are sensors that combine two technologies to perform the detection, the most commonly used in such equipments are the passive infrared and microwave technologies.
- Passive Infrared – Any object or person naturally emits radiation in the infrared range, which is the heat radiated by each of us.The main difference between this natural radiation and the active infrared is in the fact that this radiation is not stimulated, but naturally emitted.A passive infrared sensor detects motion by variation of temperatures in the detection field.
- Microwave – A microwave sensor combines the operations of both sender and receiver in one device.The microwave pulse signal emitted is reflected by the environment surrounding the sensor and captured by the receptor. The movement in the detection zone modifies the reflected signal and the change is analyzed and compared with the original signal.
The dual technology sensors operate as follows: when the PIR detects a movement it activates the microwave sensor. If the latter also detects motion, the alarm is triggered.
Both technologies are sensitive to different phenomena. The passive infrared sensor is sensitive to heat and microwave to weather conditions (rain, snow, fog…) random movements, such as the vegetation in the wind, are not regarded as an intrusion. The combination of the two technologies results in increased system reliability.
This type of detector if correctly adapted may be used in addition to or as part of a barrier system.
When equipped with two or more sets « sender – receiver » has lobes that are oriented in order to be able to protect even the “blind spots” that are formed near the attachment points of the sensor.
TRIPLE TECHNOLOGY BARRIERS
There are also barrier systems that use and combine three different technologies: Active Infrared, Microwave and Doppler.
Given its large detection power and efficiency, these equipments are typically used for perimeter protection of high security perimeters, such as: prisons, military and nuclear installations, and generally in all high-risk sites.
Intrusion is detected by interruption of the infrared beams and one of the two other technologies (Microwave / Doppler).
The addition of the hiperfrequency Doppler eliminates the “blind spots” which is created by a microwave barrier at the foot of the column, it is not necessary to carry out the crossing of the columns beams to be 100% effective, this type of barrier functions in two directions, which involves lower costs.
DETECTION BY IMPACT
The impact detection technology is based on the vibration analysis using a sensor cable.
Building wall penetration detection systems
These are systems designed to detect intrusion attempts on walls of buildings by cutting, drilling, impact of vehicles, etc.
In some of these systems is used fibre optic technology, insensitive to electromagnetic interference, which is effective on several supports such as: metal, brick or block prefabricated.
Its principle of operation is as follows: the fibre carries a light signal, when there is an intrusion attempt (shock against the wall) the signal is deformed, this deformation of the signal is analyzed by the Central Unit and the intrusion is detected.
This type of system is very reliable, but has the disadvantage of having to be installed during the construction of the building or when any remodelling.
Other of such systems, and for the same purpose, use another type of technology, although based on the same principle: vibration analysis using a sensor cable, do it otherwise.
Its principle of operation is as follows: in the cable, at defined spaces are inserted vibration detection sensors, which transmit, through the cable, the detection information to the Central Unit.
In this type of installation, the cable is fixed on the inner wall of the building, which makes the installation more practical, facilitating the implementation of these systems in existing buildings.
Detection systems for fences
In these systems, a cable is installed along the fence to be protected connected to a central unit. The system collects information from invasion by climbing, cutting or breakage of the holder.
The operating principle is simple – the Central Unit sends constant impulses over the cable core, when there is a sharp impact on the fence, the electric field inside the cable is changed and the detection is carried out.
The early detection systems used the linear detection, i.e., they considered that the amount of “noise” was constant throughout the fence, which led to numerous false alarms because, as is known, along a fence not always it has the same strain and sometimes is even composed of several types of mesh or material and even use fence holders with very diverse resistances and settlement processes.
The most recent detection systems use a special cable comprising a core and two symmetrically and equally spaced of the core parallel conductors.
The cable core carries, at the same time, the power to the system and the data and alarms communication.
The presence of these two parallel conductors is what makes all the difference – when there is a sharp impact in the fence, the core and the two conductors “shake up” and the electric field inside the cable is changed by generating an induction effect, when induced pulses reach the central unit, it calculates the time of return pulses, which allows for an accurate detection of the point of impact.
As we have seen, the level of “noise” in each section of the fence can vary greatly depending on the installation strain, on the various types of mesh or materials used and also on the fence holders, which may have very diverse resistances and settlement processes; therefore it is important to minimize the amount of false alarms.
This type of technology that uses this special cable, just depends on the software and processing quality of its Central Unit to set a better or worse detection system.
The best current systems allow to calibrate, by the meter, the whole cable length according to the type and state of the fence and freely set the size and sensitivity of detection areas, which means that do not react to repetitive events, such as wind, rain or car traffic (if the fence is near to a road/street) and let you know the precise point of impact.
And detection zones may have the length and be as many as necessary, is also possible to disable parts of the cable to be able to cross roads, buildings, etc.
Active fence systems
There is little to say of these systems, for their operation and detection power are obvious – the fence is made up of panels and posts sensitive to vibration.
Any cut or tear, climbing or attempt to climb, will trigger the alarm.
These are systems with detection efficiency of almost 100% and where false alarms tend to zero.
DETECTION BY MAGNETIC FIELD (buried cable)
The magnetic field detection technology is based on the analysis of changes in the magnetic field generated between two parallel and equispaced cables buried along the perimeter to be protected.
The operating principle is simple – the Central Unit generates a constant magnetic field along the cables, when the magnetic field changes the detection is made.
This type of system can detect the intrusion point with an accuracy of less than three meters; it is possible to calibrate the detection threshold depending on the type of soil in which the cable is buried.
Any movement within the sensing field creates a modification of the magnetic signal.
These changes are analyzed and compared with the calibration profile.
When the threshold of disturbance of the magnetic field is exceeded, detection is made.
A simple walk along the way of the cable is enough to calibrate the system, adjusting the power of detection to the type of soil.
The system allows a specific adjustment for triggering at any point within the protected perimeter.
This feature allows to calibrate the entire cable length according to the type of soil and freely sizing the detection zones, allowing to know the precise point of intrusion. And detection zones may have the length and be as many as necessary.
TELEMETRIC DETECTION BY INFRARED LASER
A telemetric infrared laser detector is a system emitter / receiver of infrared impulses that analyzes the “return time” of these very same impulses.
The detection principle is based on the variation of that “return time” caused by an intrusion in the scanning field or modification of the reference environment.
Only one of such devices is capable of, if so constructed, sweeping 360 degrees around the perimeter to protect.
Can be fitted horizontally to a 360 degrees detection, or vertically, thus configuring a “curtain” of detection to, for example, with a single device, protect the entire facade of a building.