The perimeter alarm system employs technologies such as microwave, active infrared, and electronic fencing to create a protective barrier—visible or invisible—at the boundary of the protected area. When an intrusion occurs across this boundary, the corresponding zone detector triggers an alarm signal, which is sent to the central alarm control unit. Simultaneously, visual and auditory warnings are activated, indicating the exact location of the breach. Additionally, the system can be integrated with perimeter analog electronic screens, video surveillance systems, access control mechanisms, and high-intensity lighting for enhanced security.
In recent years, perimeter defense systems have become a fundamental and essential component of modern security infrastructure. These systems are not only prevalent in high-security environments like military facilities, barracks, airports, ports, and government buildings but are also increasingly adopted in residential communities. The demand for such systems has seen significant growth, particularly in areas where cable theft remains a common threat.
Common Cable Theft Prevention Technologies
1. Power Carrier Communication Monitoring System
Power carrier communication is a concept that combines power and communication technologies. This method (as shown in Figure 1) involves transmitting a detection carrier signal along the monitored cable. The monitoring center receives this signal through the same cable. If the cable is cut or damaged, the signal transmission is interrupted. If the alarm system fails to receive the signal, it automatically triggers an alert. One of the main advantages of this technique is that it uses existing cables for signal transmission without requiring additional wiring, making it easy to install and highly discreet. It also offers a wide coverage range—often several kilometers. However, this method does not deter potential thieves and lacks the ability to capture video evidence. Moreover, single-unit power carrier systems face challenges in terms of integration and system scalability.
2. Capacitance Detection and Monitoring System
The capacitance detection method works by using a pair of empty cables connected at one end to short the terminals, while the other end is linked to an oscillator in the alarm system. Normally, when the cable is intact, the oscillator remains inactive. However, if the cable is cut, it acts as a simple capacitor, causing the oscillator to generate a signal that triggers an alarm. The frequency of the output signal changes depending on how the cable is disconnected. Figure 2 illustrates the basic model of this detection method.
3. Current Detection Monitoring System
This system assesses the integrity of the cable by monitoring whether current is flowing through the loop. Under normal conditions, the system remains silent. However, if no current is detected, the alarm is triggered. While effective in many scenarios, this method has limitations. It cannot detect theft in voltage-based systems where there is no current, such as in subway tunnels or road tunnel ventilation cables. Additionally, the system only activates when all branch cables are cut, since the total current would then be zero. This means that partial cuts may go undetected, creating potential vulnerabilities in the system.
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