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An evaluation of various on-fence sensor technologies can help you specify the right one for your customer.
Securing commercial and governmental facilities usually begins with the electronic protection of all exterior doors, windows and, in high-security applications, the walls. With this approach alone, however, by the time an alarm sounds, someone may be inside the structure.
One way to heighten security for assets, as well as people, is to establish a barrier around the protected facility. This not only identifies the protected area so unauthorized people know their legal limits, but it also makes it more difficult for criminals to launch an attack. Probably the most common barrier used for this task is a chain-link fence.
The most common chain-link fence used in this kind of application is typically 7 ft. high, made of #11 AWG metal fabric with 1 to 2-in. posts at 10-ft. intervals. The fence fabric usually is interwoven with 2-in. openings and is often topped with several strands of barbed wire, spaced 6 in. apart. Barbed wires often are angled at 30 to 45 deg. to discourage climbing.
These fence features are designed to discourage cutting of, climbing over, and crawling under a fence. Despite this, two experienced perpetrators can easily breach such a fence in 4 or 5 sec. To detect such a breach, the building's electronic security system should be extended to include the fence itself.
There are two basic types of fence protection systems: buried and on-fence. Buried fence-detection systems are suitable for many applications; however, the focus of this article is on-fence systems.
Point-Type Systems
There are two general sensing technologies in the on-fence category: point and line.
Point-type systems use individual sensors that a security dealer must mount directly to fence posts or fabric at some specific interval. Sensor spacing usually dictates how sensitive the system will be to cutting, climbing, and fabric lifting.
For example, most manufacturers call for sensors to be placed at 20-ft. intervals for nominal results (see illustration below). To increase the...