Exterior Intrusion Sensors
The Usage of Sensors for the Perimeter Protection
Considering the location of the house near Madinat Zayed and the local tropic-desert climate, performing the analysis of the possibly used sensors for the perimeter protection, one may ignore all their disadvantages associated with the abundant rainfall or the low temperatures. There is a plan of the perimeter security system after the change of the environment. Both magnetic field sensor and video motion detection operate in accordance with the OR configuration, that allows the insurance of the proper level of the security.
Unfortunately, the changes in the environment made the usage of the previously used sensors impossible to protect the territory from the fans and cameramen. Therefore, one should avoid the seismic pressure and ported coaxial cable sensors. The reasons for the rejection of these sensor types are their weaknesses and peculiarities of their functioning in the presence of the ground vibration and the large number of wild animals, surrounding the building, which are as follows. Since the coaxial cable sensor reacts to the movement of the materials with the high dielectric constant and high conductivity near the cables, it will capture the movement of both the metalized and living moving objects, including the wild animals, attracted with the freshwater (Garcia, 2007).
Thus, during the usage of this type of the sensors the sufficiently high nuisance alarm rate will occur. However the most sensitive disadvantage in this case are the blind zones, which occupy more than one third of the entire perimeter, caused by the inability of the coaxial cable sensor to operate under the water column and near the stationary metallic object, represented here with the rails (Garcia, 2007). Thus, the nearest metal objects or the service lines one should exclude from the detection area that can not be made at the household level.
A significant disadvantage of the seismic pressure sensors is their sensitivity to the several noise sources, which can lead to the increase of the false alarms rate (Garcia, 2007). In this case, the cultural noise, which affects the sensor, is the activity of the railway, which causes the considerable ground vibration. This type of noise is highly dependent on the amount of the human activity, and in case of the public railway, its activity is not limited to a certain daytime, the harmful noise will occur all the time.
Thus, instead of the two perimeter sensors concealed into the ground, one should use only the single underground sensor – the magnetic field one. This type of sensor definitely reacts to the people with a variety of the recording equipment, and with the extremely high probability, it will respond to the appearance of any human in its action field. The reason for this is the fact that the current sensor type is a covert and passive one, thus, the offenders will hardly identify its principle of the operation (Garcia, 2007). The magnetic field sensor will be effective only during the detection of human beings, as the modern person rarely leaves the home or the hiding place with no metal objects on the body, which may include the metal jewelry, the buckles and button on the clothes, the keys or some gadgets and so on. Thus, the magnetic field sensor will not record the presence of the animals (only in the extremely rare cases), but will react to the emergence of the intruders.
Despite the fact that the video motion sensors require the presence of the illumination at night (Garcia, 2007), as well as the existence of a sufficiently large number of the sensors immediately in order to provide the continuous monitoring of the entire perimeter of the exclusion of all possible blind spots, they will be the most suitable sensor type for the second circuit of the perimeter defense. These features increase the energy costs of the sensors’ operation during and, thus, make their usage quite expensive. However, these sensors can cover even the gate zone of the facility and the pond area as well, where it is extremely complicated to locate the magnetic field sensor. In addition, the sensors’ sensitivity setting will limit their response only with the creatures, which are commensurate with the human that will ensure a sufficiently low false alarm rate.
Unfortunately, the other covert sensors will never provide the insurance of the proper perimeter protection, since no covert sensors will function properly in the emerging environmental conditions. For instance, the fiber-optical cable, hidden under a layer of ground of about 3 centimeters can be extremely effective in alarming when the intruder steps over it (Garcia, 2007). However, although the sensor is not affected by the noise, which occurred due to the vibration of the land, it still does not allow distinguishing between the human and the animal, so its usage in the defense of the perimeter in this case is not advisable.
Among the visible exterior sensors, the most suitable in the case of the land vibration and the large number of the wild animals is the sensor fence. Mounted on the top of a brick fence, the taut-wire sensor is insensitive to the vibration, and does not react to the light objects, such as small animals and birds, but captures the climbing of the more weighted violator (Garcia, 2007). Its disadvantage, which suggests the occurrence of the false alarms during the glaciations is not common for the climate conditions of the area of the facility’s location (Garcia, 2007). However, it is necessary to take into account the brick wall’s height of 1.8 m, at which the sufficiently high cameraman or the fan can easily look over it without triggering the security sensor. This makes the usage of this type of the sensors inadmissible in the customer’s situation.
The other visible safety sensors are not suitable for the emerged environment conditions, because, first, it is extremely difficult to mask them and it is unacceptable for the customer. Secondly, most of them, fixing the infrared waves or microwaves cannot determine the difference between the human and the animals. In addition, the microwave sensors having the insensitive zone in the close proximity are not able to overlap the blind zone of the magnetic field sensor on a pond (Garcia, 2007).
Why sensors should always be installed with proper overlap at sector boundaries?
Projecting the security system, the designer has to ensure the continuous line of detection. It can be achieved by overlapping the action sector boundaries of the sectors of the single or various types. In the case, when the blind zones in the detection system occur, there is a high probability that the intruder may benefit because of this defect in accordance to his criminal purposes, or during the escape. The cross sensitivity test in the adjacent channels and the triggering of the sensors at their boundary operating allows the quick response considering the movement of the offender in any direction. The overlapping of the operating boundaries of the sensors of the various types may provide the continuous fixation of the movements when one of the used sensors is unacceptable in the current point due to some reasons. The similar technique was used in the first section of this project, when the video detectors overlapped the dead band of the magnetic field sensors in the pond and the gate area of the desert house.
Why should a high-security perimeter system require more than a single sensor type?
The foremost advantage of the combination of the various sensor types is a significant increase of the probability of the detection. If the false alarm of each sensor included in the high-security perimeter system, occurred due to the completely different physical phenomena (those events were independent), the probability of the detection of the overall system would be equal to the product of the detection probabilities of each of the sensors that would noticeably decrease the nuisance alarm rate. As some sensor types have the similar noise detection properties, the challenge for the designer during the development of the perimeter security systems while combining different types of the sensors is to provide the least impact of the common interfering influences to both sensors.
The various levels of the sensitivity of each sensor in the case of one or another noise of both natural and industrial origin allow collectively to avoid the useless actions of the security guards in the case of the false alarm, saving their time and energy and giving them an opportunity not to miss the actually meaningful call. It is noteworthy as well that the significant advantage of the dual sensors’ technology security system is the high immunity to the possible errors of the installer and the environmental changes after the installation and the configuration.
What are the advantages and disadvantages of combining sensor outputs in an AND or an OR configuration?
The AND configuration assumes the triggering of the general alarm of the security system only when both protection circles sensors signal about the penetration of the intruder. If the single sensor indicates about the disturbance, the system stays idle. This configuration is preferable, when the sensors have not been optimally selected due to certain reasons and permit the noise alarms occurring far more often than is needed. It will assume a notable reducing of the nuisance alarm rate of the overall perimeter protection system. However, it will reduce the probability of the detection of the entire system.
In the case of the OR configuration of the sensors the general alarm triggers when any of the used sensors reacts or they both indicate about the penetration of the intruder. Considering the OR configuration features, if one of the sensors has the high nuisance alarm rate, it will greatly increase the same parameter of the entire system. However, the probability of detection with this configuration is higher than with the previous one because the entire perimeter protecting system will react in the case when at least one of the sensors indicates the threat.
What problems do you expect with an explosive detector system at the entrance to a mall?
During the installation of the explosive detector system at the mall entrance one may face the following challenges. The first is the cost of the used sensors and their operational maintenance. Second, for the rapid detection of the explosives at the entrance to the mall there should be the specially allocated small chamber with a slight bandwidth and extremely intensive ventilation, which would enable the movement of the explosive particles from the dangerous object to the sensor place in a few seconds. The other requirement should be the presence of the cameras, which monitor the entrance and the indoors. They should have no blind spots and enable the timely determination of the location of the explosive in the mall. Certainly, more effective detection of the explosives occurs in the facility with the established checkpoint. However, this will significantly reduce the popularity of the mall and the speed of the customer service.
In what circumstances could metal detectors be useful at the exit of a facility?
The metal detectors allow the scanning of a person and respond with the beep signal on a specified amount of the metal, which could be weapons or carry any other threat to the company, including embezzlement. However, this equipment one can be used not only in the building’s entrances to provide the safety of the personnel and the people inside, but in the exits as well. It is accomplished in order to avoid the stealing at the industrial enterprises, which operate with the precious metals or produce the unique electronics. If the signal occurs, the guard uses the manual metal detector or asks to show the contents of the bag. It is noteworthy that the current metal detectors can not only react with the sound signal, but to determine the specific properties of the metal objects, for instance, on the basis of the exemplary weight of the object. Thus, the metal detector one uses in the exit of the facility in the cases, when the insurance of the personnel safety has the same priority as the need to avoid the continuing plunder by the workers and, therefore, the losses of the company.