Analysis of infrared alarm system in enterprise security system

Abstract: Enterprise security system is mainly based on seven subsystems of three-layer structure. It mainly includes three levels: front-end information capture, intermediate information conversion and transmission, and background information processing, as well as seven subsystems: infrared alarm system, electronic fence alarm system, video surveillance system, fire alarm system, access control system, manual telephone alarm system and security information comprehensive management system.

The enterprise security system is mainly based on seven subsystems of a three-layer structure. It mainly includes three levels: front-end information capture, intermediate information conversion and transmission, and background information processing, as well as seven subsystems: infrared alarm system, electronic fence alarm system, video surveillance system, fire alarm system, access control system, manual telephone alarm system, and security information integrated management system. Let's first introduce the infrared alarm system among the seven systems:

1. Infrared alarm system

The infrared alarm system is an integrated anti-theft system composed of several infrared alarms. The infrared anti-theft alarm consists of an infrared detection circuit and an alarm circuit. It is a practical self-defense deterrent alarm tool. After installing an infrared anti-theft alarm in the defense area, once a thief enters the defense area, the alarm will immediately send out a harsh alarm periodically to deter the thief. The device has the advantages of stable performance, rapid response, easy installation, and simple use.

2. Classification and principle of infrared alarm

Infrared alarms are divided into active infrared alarms and passive infrared alarms. Active infrared intrusion alarms are composed of a transmitter and a receiver. The transmitter is composed of a power supply, a light source and an optical system, and the receiver is composed of an optical system, a photoelectric sensor, an amplifier, a signal processor and other parts. The active infrared alarm is an infrared beam blocking alarm. The infrared light emitting diode in the transmitter emits a modulated infrared beam (the wavelength of this beam is about 0.8 to 0.95 microns) under the stimulation of the power supply, and is transformed into parallel light and emitted by the optical system. This beam is received by the receiver, and the infrared photoelectric sensor in the receiver converts the optical signal into a signal, which is transmitted to the alarm controller after circuit processing. The infrared rays emitted by the transmitter pass through the prevention area to the receiver, forming a warning line. Under normal circumstances, the receiver receives a stable light signal. When someone invades the warning line, the infrared beam is blocked, and the infrared signal received by the receiver changes. This change is extracted, amplified and properly processed, and the controller sends an alarm signal. At present, this type of alarm includes two-beam, three-beam and multi-beam infrared fences. It is generally used in perimeter defense. Its biggest advantage is its long defense distance, which can reach more than ten times the detection distance of passive infrared.

Passive infrared alarms mainly judge whether someone is moving based on changes in external infrared energy. The infrared energy of the human body is different from that of the environment. When a person passes through the detection area, the position of the different infrared energy collected by the alarm changes, and then an alarm is issued through analysis. The human body has a constant body temperature, generally around 37 degrees, and emits infrared rays with a specific wavelength of about 10μm. The passive infrared alarm works by detecting infrared rays of about 10μm emitted by the human body. The infrared rays of about 10μm emitted by the human body are enhanced by the Fresnel filter and gathered on the infrared sensing source. The infrared sensing source usually uses a pyroelectric element. When this element receives a change in the temperature of the human body's infrared radiation, it will lose its charge balance and release the charge outward. The subsequent circuit can generate an alarm signal after detection and processing.

1. The passive infrared alarm is aimed at detecting human body radiation, so the pyroelectric element must be very sensitive to infrared radiation with a wavelength of about 10μm.

2. In order to be sensitive only to the infrared radiation of the human body, its radiation surface is usually covered with a special Fresnel filter, so that the interference from the environment is significantly controlled.

3. The sensor contains two pyroelectric elements connected in series or in parallel. The polarization directions of the two electrodes are opposite. The background radiation has almost the same effect on the two pyroelectric elements, which cancels out their pyroelectric effects, so the alarm has no signal output.

[page]

4. Once a person invades the detection area, the infrared radiation of the human body is focused by part of the mirror and received by the pyroelectric element. However, the heat received by the two pyroelectric elements is different, and the pyroelectricity is also different and cannot be offset. After signal processing, an alarm is triggered.

3. How do enterprises choose the type of alarm?

Passive infrared alarms mainly judge whether someone is moving based on changes in external infrared energy. The infrared energy of the human body is different from that of the environment. When a person passes through the detection area, the position of the different infrared energy collected by the alarm changes, and then an alarm is issued through analysis.

However, in the external environment, not only the human body can emit infrared energy, but many objects can also emit infrared energy under certain conditions, and this energy is particularly prominent in visible light, so the resistance to white light interference of any passive infrared alarm has become an important indicator. It is recommended that enterprises use passive alarms indoors, because the indoor light is stable and the infrared energy is relatively constant, and the detection effect is very good in this environment. When choosing an infrared alarm, enterprises should make a choice based on their own environmental characteristics, so that the infrared anti-theft system can play the greatest role.

Compared with passive infrared alarms, active infrared systems are generally used for perimeter protection. When choosing active infrared alarms, you also need to pay attention to the following issues:

1. Active infrared intrusion alarms are seriously affected by fog. When used outdoors, you should choose devices with automatic gain function (such devices will automatically adjust their sensitivity when the climate changes); in addition, the detection distance of the selected device should leave a margin of more than 20% of the actual warning distance to reduce false alarms caused by climate change. Active infrared intrusion detectors should not be used outdoors in foggy areas or dirty and windy areas.

2. When used outdoors, be sure to use a dual-beam or triple-beam active infrared intrusion alarm to reduce false alarms caused by animals, fallen leaves, etc.

3. When using active infrared intrusion alarms on walls, roofs or open areas, you should choose devices with lightning protection functions. When there are folding walls and the distance is relatively close, you can choose reflective devices to reduce the number of alarms used.