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| Overview Of Alarm Detectors And Solutions To False Alarms |
| 2021.02.24 |
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The alarm detector is an alarm instrument that uses modern science and technology to prevent crime and detect criminal activities in time. There are many types, from the working principle can be divided into switch alarm detector, sound alarm detector, sensor alarm detector, infrared alarm detector, laser alarm detector and so on. With the development of television technology and electronic computer technology, an advanced monitoring, control and alarm system using television and computer jointly appeared. There are two ways to transmit the alarm signal: wireless and wired. With the strengthening of crime technology prevention work. The alarm detector has played an obvious role.
The alarm detector is an electronic device that generates an alarm function through physical methods or electronic technology. It is mainly composed of an alarm host and alarm accessories. Usually during use, the anti-theft alarm accessories detect intrusions that occur in the armed monitoring area or are actively triggered by the accessories to generate an alarm signal. The alarm signal is transmitted to the alarm host, and the alarm host issues an alarm prompt.
The alarm prompts of alarm detector are generally divided into two types: one is the sounding of the on-site siren, and the other is to convey the alarm information to the designated person or system platform through the network or communication.
Basic Structure
The alarm system is an important facility to prevent accidents such as robbery and theft. In the event of an emergency, the location of the incident can be accurately displayed in the security control center through sound and light alarm signals, so that emergency measures can be taken quickly. The alarm system with the entrance and exit control system, the closed-circuit television monitoring system, the visitor intercom system and the electronic patrol system together constitute a security system.
The alarm detector is composed of sensors and signal processing. It is used to detect the intrusion behavior of intruders. The device composed of electronic and mechanical parts is the key to the anti-theft alarm system, and the sensor is the core element of the alarm detector. Sensors with different principles can constitute alarm detection devices of different types, different purposes, and different detection purposes.
False Alarm Problem
False alarm principle of alarm detector
False alarms and omissions in the alarm system are mainly due to the following reasons. The anti-interference ability of wireless detectors shows that the same frequency interference is easy to cause false alarms. Infrared detectors are not accurate enough to judge intrusions, causing false alarm. Infrared detectors are easily affected by environmental factors such as temperature and light, which may cause false alarms. The power supply system of the wireless detector is short of power, and the information is not effectively transmitted when the power is low, which makes the detection range of the detector shorter or does not work, resulting in false alarms. Because both the host and the detector use the wireless encoding method to set the repeated code, the host and the detector re-code and cause false alarms.
Reasons and solutions for false alarms of alarms detectors
1. False alarm caused by improper system design
Equipment selection is the key to system design. There are many types of alarm equipment, each with its own characteristics, scope of application and limitations. Improper selection will cause false alarms. For example, the use of vibration detectors close to the seismic source (airfields, railways) can easily cause false alarms of the system; the use of ultrasonic detectors in places where bats frequent the system will also cause the system to false alarms, because the bats emit ultrasonic waves; High-frequency sounds such as rings and metal impact sounds can cause false alarms of single-technology glass break detectors... Therefore, to reduce false alarms caused by improper equipment selection, system designers must be very familiar with the principles, characteristics, and characteristics of various alarm equipment. Applicable scope and limitations. At the same time, it is also necessary to grasp the on-site environmental conditions, climate conditions, electromagnetic field intensity and illuminance changes, etc., in order to select alarm equipment according to local conditions.
In addition to the selection of equipment, improper system design is also manifested in the installation location, installation angle, protective measures and system wiring of the equipment. For example, when the passive infrared intrusion detector is installed against the air conditioner and the ventilation fan, it will cause the system to falsely alarm; if the active infrared detector used outdoors is not equipped with proper shading protection (the sunshade is best for protection), it is bound to be causes a false alarm of the system; if the distance between the alarm line and the power line, lighting line and other strong current lines is too small, and the anti-electromagnetic interference measures are not added, the system will also generate a false alarm.
2 False alarm caused by improper construction
This part of the problem is mainly manifested in the following aspects:
⑴ The construction is not strictly according to the design requirements.
⑵Equipment installation is not firm or the inclination angle is inappropriate.
⑶ The solder joints have false soldering, burrs, or improper shielding measures.
⑷The sensitivity of the equipment is poorly adjusted.
⑸ The testing equipment used for construction does not meet the measurement requirements.
The solution to the above problems is to strengthen the supervision and management of the construction process and implement the supervision system of security projects as soon as possible, which is very conducive to improving the quality of the project and reducing false alarms caused by the construction process.
3. False alarm caused by improper use of users
Improper use by users often causes false alarms by the alarm system. For example: a window with a magnetic switch is not plugged in, and it is blown open at night; the staff accidentally enters the warning zone; accidentally triggers the emergency alarm device; the system check-in personnel misuses; not paying attention to the change of the working procedure, etc. The cause of the false alarm of the system. Analyzing the user's improper use, clarifying the error and improving the user's level, can greatly reduce the number of false alarms of the alarm system.
4. False alarm caused by environmental noise
False alarms caused by environmental noise are caused by the alarm system under normal working conditions. They are unavoidable in principle, but they are unnecessary in fact, and are false alarms. For example: hot air currents cause false alarms of passive infrared intrusion detectors; high-frequency sound causes false alarms of single-technology glass break detectors; ultrasonic sources cause false alarms of ultrasonic detectors, etc. A more effective measure to reduce such false alarms is to use double-tech detectors (detectors with two different principles at the same time detect the "target", the alarm will send out an alarm signal). Current products include: microwave-passive infrared dual tech detector,etc. However, some environmental noise double-tech detectors are powerless, such as: rats in the prevention zone; pets walking around in the room, etc. For this reason, scientific and technical personnel have introduced micro-processing technology into the alarm system, so that it has certain identification and thinking ability, and can judge to a certain extent whether it is an intruder or an alarm caused by environmental noise.
Therefore, to reduce false alarms, it is indispensable to start with civil air defense. The establishment of an alarm information confirmation mechanism can reduce the number of alarms. After the alarm center receives the alarm information, it should first issue a confirmation signal to the alarm host, indicating that the center has received it, and the alarm host should resend it if it does not receive the confirmation signal. In terms of technology, a variety of methods are used to confirm the alarm signal, such as installing multiple detectors (commonly used is dual infrared + infrared + microwave), and sending an alarm signal to the host when multiple detectors detect an intrusion signal at the same time , Thereby reducing the false alarm rate.
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