Analysis of cable anti-theft technology and application requirements in different fields

Release time: 2021-12-21 14:56

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Perimeter alarm system is in the protection of the boundary of the use of microwave, active infrared, electronic fence and other technologies to form a visible or invisible "protective wall", when the wall behavior occurs, the corresponding detector in the defense area will send alarm signals, and sent to the control center of the alarm control host, sound and light warning at the same time to display the alarm position, but also linkage perimeter analog electronic screen. Even linkage camera monitoring system, access control system, strong lighting system, etc.
In recent years, perimeter defense system has become a basic and indispensable security subsystem of the security system. It can be seen not only in high-end fields such as munitions factories, military camps, airports, ports and government agencies, but also widely used in residential areas, and maintains a fairly high application growth rate in these fields. Cable anti-theft is a common use of technology.
Several common cable anti-theft technologies
1. Anti-theft of power carrier communication monitoring system
Power carrier belongs to a concept derived from the interdisciplinary subject of power and communication. The power carrier communication method (as shown in Figure 1) makes use of signal transmission means in the wire and cable anti-theft system to load the detection carrier signal on the cable in the detection range, and the alarm in the monitoring center is connected with the carrier signal on the monitored cable. Once the signal transmission is interrupted due to the cable exit section, the alarm will automatically alarm and play a warning role. Power carrier communication is one of the most widely used anti-theft means at present, because it transmits the carrier signal on the monitored cable, no additional lines are needed, so the power carrier communication has the advantages of easy installation, covert detection, wide monitoring range (up to several kilometers) and so on. However, because the cable theft can only alarm to deter criminals, and video evidence cannot be obtained, the single power carrier communication is facing the challenge of integration and systemization.
2, capacitance detection and monitoring system anti-theft
The principle of capacitance detection method is to first use a pair of vacant cable short circuit cable terminal, the other end is connected to the alarm on the multi-resonant swing, when the cable is working normally, the alarm oscillator does not produce vibration phenomenon; When the cable out of the section, the empty cable into a simple capacitor, oscillator output signal, cause alarm, and the frequency of the oscillator output signal with the cable is cut off different location and change. Figure 2 shows the basic model of capacitance detection method.
3, current detection type monitoring system anti-theft
The integrity of the cable system is judged by detecting whether there is transmission current in the cable loop online. That is to say, when the cable is working normally, the detection system does not respond; When there is no current transmission in the cable, the detection system will start the alarm system. The current detection system cannot be used in the cable anti-theft system with voltage but no current, such as subway tunnel or highway tunnel blower power cable. In addition, the system can only alarm when all branches of the circuit system are cut (because the total current of the cable loop is zero when all branches of the cable are cut). Therefore, the current detection type monitoring system has the hidden danger of "no warning".
Analysis of application requirements of cable anti-theft technology in different fields
1, street lamp buried cable anti-theft alarm
With the rapid development of the integration of urban and rural areas, the rapid development of municipal construction has been accelerated. Street lamp is the main body of urban landscape lighting at night, bearing an important role, street lamp cable has now been basically converted from overhead laying to buried laying, street lamp cable buried laying mainly include: directly buried laying, pipeline laying, cable trench laying, etc. No matter what kind of installation is hidden danger of theft, which leads to serious consequences such as economic loss and public order disorder.
Ideal street lamp buried cable anti-theft system, the most important requirement is in the light off period, alarm anti-theft system requirements end without any form of power supply; The alarm anti-theft system is not directly related to the circuit state (cable length, street lamp type, etc.) when the light is on. As many lines as possible are used to communicate with the control room through a master control device.
2, highway power cable anti-theft alarm
Power cables are mainly used on expressways, and one of the core problems in the development of anti-theft alarm system for expressways is signal detection when cables are abnormal. According to the requirements of highway cable, the main requirements of anti-theft system are: availability, reliability (low false alarm rate), advanced nature (alarm differentiation), scalability (networking with high-speed traffic police system) and so on. At present, power carrier communication is mainly used, but there are still the following problems to be solved:
The transformer of power distribution system has a blocking effect on power carrier communication information.
The three-phase power system in the circuit has 10-20dB signal loss. When the communication distance is relatively close, the general carrier signal can only be transmitted on the single-phase line.
The power line has its own pulse interference. The frequency of alternating current in our country is 50Hz. There is a secondary wave peak in a single cycle of the sine curve, so it will produce a secondary pulse interference.
Different signal coupling modes correspond to different power carrier communication signal loss.
Power lines can cause deformation of data signals.
To sum up, the power carrier communication method in cable anti-theft system is worth studying and developing. It also indicates that the technology of power carrier cable anti-theft system is not fully mature. At present, the best cable anti-theft system in China is an enterprise producing anti-theft cable system in Hangzhou.