Electronic Perimeter Security FAQs
To produce the best possible perimeter security systems requires a combination of a physical barrier, like the Metalith™ earth filled protective barriers, control point bollards, popup wedges and gates, plus electronic surveillance equipment. To assist companies or governmental purchasers understand a little about the various electronic security systems that are available, we have included the following Electronic Perimeter Security FAQs.
Passive sensors detect energy submitted by the target, or detect a change in the environment associated with the presence of the target.
Active sensors transmit some form of energy and detect a change in the received energy created by a disturbance caused by a target.
A line-of-sight system usually refers to a clear line-of-sight between the transmitter and receiver of an active sensor.
Fence disturbance sensors are installed on security fences and typically constructed with chain-link mesh. They use several kinds of transducers used to detect motion or shock caused by an intruder attempting to climb or cut through the fence.
Fence disturbance sensors respond to all mechanical disturbances so noises such and wind and debris blown by wind, rain, and nearby traffic activity can cause nuisance alarms.
Taut wire sensor fences consist of high tensile strength parallel, horizontal wires that connect to transducers near the midpoint of the wire span. Since these wires are under tension, they are able to detect climbing or cutting of the wires.
Taut wire fence sensors are much less susceptible to nuisance alarms than fence disturbance sensors.
Electric field or capacitance sensors can be set to detect intruders up to 1 meter beyond the actual wire of the fence.
Electric field or capacitance sensors are susceptible to lightning, rain, fence motion, and small animals. Also, ice storms may cause damage to the wires.
Video motion detection uses existing closed-circuit television (CCTV) cameras to sense a change in the video signal level viewed on the scene. A computer that is set to recognize movement in a particular area, point, or grid on an image usually accomplishes motion detection. When the computer detects a change in the set image under the set parameters, an alarm is generated that indicates there was movement in that set zone.
Video motion detection only works with fixed cameras, so pan/tilt/zoom cameras cannot be used since any motion of the camera and the change of the video image produces an alarm. The reliability of the detection can be lowered during conditions of reduced visibility that is caused by fog, snow, heavy rain, or loss of lighting at night.
Microwave sensor security systems use transmitters and receivers working in the 10 Gigahertz (GHz) or 24 GHz microwave range. If the microwave sensors do not receive a reflection back in a certain time period due to an intruder's movement, an alarm is activated
There are some inherent problems using microwave systems in large open areas. First, the ground must be flat so that objects do not shadow the beams. Second, the microwave antennas should not be placed greater than 120 yards between each other since a crawler may not be detected due to dead zones created in the first few meters in front of the antennas. Finally, there should not be any standing water in the area since this will create a moving reflective zone
Passive infrared (PIR) sensors detect electromagnetic radiated energy generated by sources that produce temperatures below that of visible light. The sensors focus on a narrow bandwidth measured in microns with the human body producing energy in the region of 7-14 microns. These sensors use the Rate of Change measurement to process and evaluate an unshielded/unprotected intruder walking through a designated zone. When the radiation change captured by the lens exceeds the set parameters, it triggers an alarm.
There are some defeat mechanisms that can be deployed against passive infrared systems. These include shadowing, cloaking, or masking an intruder's heat signature from the passive infrared field of view.
Active infrared sensors use two units, a transmitter and a receiver. Unlike the microwave units, the active infrared sensors use a transmitter that generates a multiple frequency straight-line beam to the receiving unit that creates a sort of ‘fence' between these two units. If an intruder passing through this field of detection interrupts the signal, it will cause an alarm.
First it is critical for the active infrared sensors to align the two infrared towers together to obtain a clear line of sight. Older models had problems sensing everything that moved including animals and vegetation blown by the wind. The newer active infrared sensors can be adjusted for animals and vegetation to pass through without being detected, but still creating an alarm when a human intruder or vehicle pass through the beam. Tunneling and bridging can cause problems for these systems.
Infrastructure Defense Technologies' earth filled protective barriers are designed to stop the intruders attempting to penetrate a facility's perimeter security by using a vehicle or explosives. Call us today at 1-800-379-1822, email us at firstname.lastname@example.org, or send a fax using 815-323-1317 to get an immediate quote for your perimeter security problems. Stop them before they cause serious security issues, critical infrastructure damage, or disaster.
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