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There are two types of -systems: active and passive. Active systems demand use of the transmitter and the receiver under the attitude to each other. Besides waves-beams can be rather simply found out. All this is the reason of wider use of passive systems. A number of firms are engaged in manufacture of -systems: Advanced Device Laboratory (Belgium), B.A. Security Systems (England), Silent Watchman (USA), MESL, etc. One of such simple PC-systems is the system of firm Barnes Engineering/160 / which we shall consider more in detail. Functioning of system is based on fixing of invisible radiation of the moving person by the -gauge. The person generates the thermal radiation equivalent to radiation of a 500-wadded lamp and having length of a wave of 10 microns. The radius of detection of one gauge lays within the limits of 5...15 m, the protected area in horizontal and vertical planes up to 70 degrees. For increase in these parameters enough simple escalating of elements of system. At hit of the going person in a field of detection of system on an output of the gauge there are two typically polarized pulses which are subject to strengthening. The logic device in the control device allocates these signals from background and.... Certain time the sound or visual alarm signal submits. The gauge used in system should be sensitive, inexpensive and simple in manufacture. It should react only to radiation with length of a wave 10 microns and not work from light sources. The opportunity to make complex geometrical surfaces of the gauge without significant changes in characteristics is necessary also. Such gauges represent on the firm basis thermo elements as it is made in mass production of semi-conductor elements. The system having an opportunity of use up to 10 gauges with one control device also reacts to change temperature from 0,1 degrees With and is higher. There is a protection against extraneous intervention. If the infringer moves with a speed of 0,06...3 km/s on distance up to 9 m from the gauge a given out signal will surpass own noise of system more than in 10 times. In view of measures on prevention of false alarms it is possible to count, that such cases arise not more often than time in two years. Installation of gauges is very simple and can be made in such places where use of gauges of other types is undesirable.
There can be a natural question: whether the refined infringer is capable, using the most complex methods "to deceive" system? The probability of it is smallest. The temperature background of a premise is rather non-uniform even in those premises where the constant temperature (machine halls, storehouses of magnetic data carriers, etc.) is supported is relative. Distinctions in heat conductivity, reflective ability and the geometrical sizes of subjects in a premise alongside with heterogeneity of walls and overlapping create heterogeneity of a thermal background. For example, in the right part of a premise the temperature can be 22, and in S.Poetomu left 20 degrees moving for the screen having temperature 21 degree With, the infringer will be all the same found out, as it is impossible to maintain temperature precisely of the screen in the right part of a room 22, and in all real left 20 degrees even a situation when application of the screen will cause occurrence of stronger signal, than a signal from the unprotected infringer. On a basis draw the following conclusions:
1) In passive systems there is no radiation..... “Are deceived “even by the skilled infringer.
2) Absence of issue of energy allows doing devices simple, reliable, not demanding maintenance service, cheap and long-living. Absence of moving parts conducts to absence of deterioration.
3) Installation of system is simple. The field of vision is great and does not demand exact configuration the transmitter and the receiver, as in active systems.
4) Gauges do not react to the majority of sources of false alarms. Before submission of an alarm signal logic circuits should find out two pulses of opposite polarity during is established a time interval. Convoy streams, systems of heating, air-conditioning do not cause occurrence of such signals.
5) Systems have the wide field of vision, enough two gauges for fields of protection of a premise from penetration from any direction.
6) Active systems (PC, OUSE, the microwave, etc.) can react to events outside of the given premise (noise, light sources, vibration, etc.), that can cause occurrence of false alarms. Passive systems of this lack have no.
The only thing, but not basic lack of passive security systems is necessity of installation of the big number of gauges for protection of long corridors. The active systems having the big radius of action (up to 100 m), demand only installation of reflectors. Laser and optical systems (working in a seen part of a spectrum) react to crossing by the infringer of a light beam. They are applied basically to protection of internal premises of buildings as at external application because of the big number of probable influences they are a source of constant false alarms. Other lack of optical systems is the opportunity of their detection by the infringer, though this lack and non-principal. In the literature examples of optical systems which though and it is easy founding results, but represent a formidable barrier. The structure of optical systems includes light sources, mirrors and receivers. In the rest these systems differ from others systems, using various active gauges a little. In 1977 on conference on problems of counteraction of criminality the message/61/about the new optical device has been made. Action of the device is based on.... Air, the surface of a body of the person caused by temperature distinction and air. The optical image of thermal turbulence is projected on a plane of the detector. The system works effectively even if the person is latent by the screen or costs (stands) motionlessly. If it is required to supervise premises of the big area additional mirrors are applied some. The receiver represents 8 silicon photo cells with alternating polarity. The electronic system will consist of the strip filter, the two-half-period rectifier, Schmidt's trigger and the device of submission of an alarm signal (alarm or a lamp). The maximal length of a beam does not exceed 30 m, speed of movement of the infringer inside a protected premise should be 0,2 km/s. In a premise where such system is established, in order to prevent false alarms there should not be sources of heat and drafts.
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