As an important part of the security system, perimeter defense has increased significantly with the rapid development of the industry in recent years, and it has been widely used in campuses, factories, residential areas and other perimeters. For example, Minhang District of Shanghai will begin to install electronic fences for all public and private schools in the region in the near future to improve the security level of schools. Hangzhou Xiaoshan Property Company, such as Taihe and Mongkok City, has also installed electronic fences to improve the safety of residents. The application in schools, factories and other places in other places is gradually increasing. This paper discusses the application and development of perimeter alarm system based on several projects of Hangzhou Ruidun Electronics.

Generally, the purpose of setting up a perimeter alarm system is to establish a safe and reliable place, strengthen the management of entrances and exits, prevent other people from entering the outside world, prevent illegal people from climbing over the fence, and send out an alarm and notify the security department in case of unexpected situations within the perimeter. The specific requirements generally include:

1. The equipment is absolutely safe, with zero damage.

2. If the perimeter is not equipped with video surveillance facilities, then the perimeter alarm equipment must have a high deterrent, so that criminals will be discouraged by psychological pressure, or try to block intruders and prolong the invasion time. However, if the perimeter is equipped with the corresponding video monitoring facilities, the intruder's invasion picture will be recorded, and the intruder can be found out in a short time after the alarm comes out from the perimeter, and invisible perimeter alarm products can be selected.

3. The perimeter alarm equipment has high anti-beating ability, and the process of repairing the equipment is simple and the cost is extremely low.

Hangzhou Ruidun Electronics Co., Ltd. is a high-tech enterprise specializing in R&D, manufacturing, sales and service of "intelligent perimeter alarm system". In the field of security technology, the company relies on keen market sense and strong technical force to develop security products that are most suitable for perimeter protection. Its main perimeter protection systems are:

Electronic fence system, electrostatic induction perimeter system, vibrating cable perimeter system, buried leakage cable alarm system.

Applications include substations, residential quarters, enterprises and institutions, airports, prisons, warehouses, museums, zoos, pastures, military restricted areas, etc. With high-quality products, perfect service and innovative business philosophy, the company has won the trust and support of customers.

Components of perimeter alarm system:

Perimeter burglar alarm is mainly used to prevent illegal persons from climbing over the fence into the perimeter to commit crimes, so a complete and detailed defense area will be divided in planning. General perimeter alarm system is divided into three parts: front-end alarm, signal transmission, monitoring center and lightning protection grounding.

1. front-end alarm part

In the absence of video surveillance facilities around the perimeter, after the intruders invade the perimeter, the traffic on campus is extremely large, and it is difficult to find out the intruders in a short time. Generally, the following two products can be selected to block the intruders:

(1) Pulse electronic fence

During normal operation, the defense area detector generates a pulse voltage with adjustable amplitude voltage, duration ≤0.1S, interval time ≤ 1.5S and energy ≤5.0J according to the national standard, and outputs this pulse voltage to the front-end electronic fence. When someone invades (breaks the wire, short circuit or touches the net) and damages the electronic fence, the defense area detector will immediately send an alarm signal to the alarm host, and at the same time output a switch signal to start the on-site sound and light alarm, etc.

While the electronic fence meets the needs of the campus, the products greatly improve the three functions of blocking, deterrence and alarm. With both tangible electronic fence and intelligent alarm multi-zone host, this product has become a brand-new perimeter security system product, which can stop intruders and can be easily repaired after being damaged.

This product is not limited by terrain height, twists and turns, corners, etc., so perimeter protection can be achieved without dead angle, breaking the limitation that infrared correlation, microwave wall, etc. can only be used in sight distance and flat and regular areas, and at the same time, it can automatically adapt to outdoor long-term temperature and humidity changes, and resist harsh environment, etc.

(2) Electrostatic induction fence

When the carrier signal given by the detector of the electrostatic cable alarm system passes through the cable, the carrier wave oscillates between 0 points, so that a stable alternating electric field is generated around the cable. When an organism approaches, its electrostatic field will change the alternating electric field, and the detector will judge whether to trigger the alarm based on this change amplitude.

The electrostatic fence has strong anti-destructiveness. Generally, when it is close to the detection cable of 10-15cm, it will give an alarm. Touching or cutting the detection cable will even give an alarm. The sensing sensitivity can be set by itself according to the user's specific usage. After the detector is connected with the alarm host, it has the functions of anti-shearing, anti-dismantling and anti-short-circuiting. If the signal line is cut off, the alarm host will give an alarm.

Electrostatic cables also have perfect anti-static and lightning protection measures, and are generally insensitive to quenching electromagnetic interference in nature; Such as lightning, space ionization, electromagnetic storm, quenching current, etc. At the same time, it can be powered by batteries, and it can work for a long time in case of power failure.

Compared with similar alarms, the electrostatic cable has higher sensitivity, more reliable operation, and better adaptability to complex environment. Besides the alarm function, it also has the function of blocking and deterring, so as to achieve better security.

With the assistance of video monitoring facilities around the perimeter, although the flow of people on the campus is huge after the intruders invade the campus, the intruders can be found in a short time according to the pictures recorded by the monitoring equipment. The following two alarm products can be selected for the alarm products:

(3) Vibration cable

The vibration cable is composed of a core wire, a pressure-sensitive film, a shielding layer and a jacket. After the pressure-sensitive film is deformed, an electric signal will be generated and transmitted to the detector by the core wire. The greater the deformation, the greater the amplitude of this electric signal, and the detector will judge whether to trigger an alarm based on the amplitude of this signal. Immediately after the alarm is triggered, the detector sends an on or off signal to the host for alarm.

This product is suitable for all kinds of complex terrain, leaving no dead angle. The vibration cable can be fixed on the barbed wire according to the perimeter shape or buried in the ground to be installed in a roundabout way. Or it can be directly coated on the top of the enclosure wall and then covered with an outdoor wooden floor, which can prevent damage and increase the stress area.

Because the vibrating cable reflects the unclear position of the site, the intruder does not know the existence of the perimeter, so it is not easy to be damaged when the position is uncertain. Among many outdoor detection equipments, vibration cable is one of the few false alarms. After damage, it is fastened with waterproof tape, which can be used continuously without affecting the effect.

(4) Leaked cable

Two buried cables are laid in parallel in each leakage protection zone, one for energy transmission and the other for energy reception. The area where the two cables are located is in a state of capacitive coupling. Objectively, one of the two cables can be regarded as an anode and the other as a cathode. Because the positive and negative electrons form a stable distribution around the two cables, when an object with a certain density and quality crosses the two cables, the stable distribution will be broken, and the capacitive reactance of the receiving cable will change. The detector will judge whether to trigger an alarm based on this change.

Because the leakage cable does not reflect the site location and the detection magnetic field is invisible, the intruder does not know that the perimeter exists, so it is not easy to be damaged when the location is uncertain. Among many outdoor detection equipments, the leakage cable is one of the few false alarms.

2. Transmission part

According to the area of each perimeter, combined with the price and the selected product factors, the following transmission modes can be selected for general perimeter projects:

(1) The transmission mode of RS-485 can be selected for the perimeter less than 1200m, and the shielded twisted pair is used for transmission.

(2) The transmission mode of RS-485 can be selected if the perimeter is less than 2KM, and the corresponding signal extender is equipped (the specific transmission distance depends on the equipped signal extender).

(3) The perimeter is below 10KM, and the used perimeter alarm products are pulse electronic fences and equipped with corresponding alarm hosts. A new transmission mode -CAN can be selected, and shielded twisted-pair transmission can be used (common twisted-pair transmission can be used below 2KM). Moreover, there is no need for address modules to be divided into defense zones, which greatly saves the cost.

(4) The perimeter is more than 2KM, and instead of pulse electronic fence products, the transmission mode of optical cable can be selected.

3. Monitoring center

The monitoring center can make different precautions against level modulation according to the actual economic bearing capacity of the campus. Generally, there are general grades and advanced grades. Generally, only the alarm host needs to be installed, and then the alarm number displayed on the host keyboard can be observed to understand the alarm situation in the alarm area. Advanced level, equipped with linkage module and video surveillance system linkage, at the same time of alarm, the system will automatically pop up the alarm area picture to know the alarm situation.

Lightning protection and grounding of the system

The lightning protection design of the system is carried out according to the three-level lightning protection standard. The alarm equipment installed outdoors adopts lightning protection and grounding measures, and special lightning protection devices for power arrester and signal line lightning protector are set. The independent grounding network is made of copper-clad steel grounding rod, and there is a good lightning protection grounding wire at its bottom. The grounding bus should be made of copper wire, which shall not be short-circuited or mixed with the zero line of high-voltage power grid, and the grounding resistance shall not exceed 4 ohms.

Power surge suppressor shall be installed in the power distribution cabinet of equipment monitoring room to protect the safety of load and equipment operation. At the same time, the machine room should be specially grounded, and the grounding of equipment and frame should be separated, and the grounding resistance of the system should not exceed 4 ohms. When common earthing net is used, its grounding resistance shall not exceed 1 ohm.

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Although our government has asked to deepen the awareness of security and speed up the construction of modern security technology system, the overall situation of China's security system construction is not optimistic at present. It is quite difficult to really establish a comprehensive and effective security system due to the constraints of the local economy, culture and their own situation. "Social security, our responsibility", Ruidun will continue to adhere to the enterprise spirit of "honesty, dedication, responsibility and innovation", always keep in mind the mission of "leading the industry and serving the country", and make unremitting efforts for the construction of quality life and the development of a harmonious society.