Analysis and solution of false alarm problem in home burglar alarm system
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There is no authoritative definition about false alarms. Generally speaking, in China, “there is no dangerous situation. The alarm system sends out an alarm signal, which is a false alarm.†According to this definition, the false alarm rate of the home burglar alarm system (for a certain period of time) The ratio of the number of system false alarms to the total number of alarms is generally above 95%. In some western countries, the definition of false alarm is: “false alarm refers to the alarm signal that the police do not need the police to actually dispatch the police, which does not include those caused by bad natural weather and other special circumstances that cannot be handled by the alarm company and users. According to this definition, the US UL standard states: "Each alarm system can only have up to four false alarms per year."
The above two definitions are from different angles and each makes sense. Limited to the length of the text, only the former definition of the analysis of the alarm system to generate false alarms, in order to specifically develop a feasible measure to reduce false alarms.
1 False alarm caused by malfunction of anti-theft alarm equipment
The product cannot be completed under the specified conditions and within the specified time, and is called a fault. The types of faults are damaging faults and drifting faults.
Damage failures include all failures and sudden failures of performance. Such faults are usually caused by damage to components or poor manufacturing processes (such as solder joints).
A drift fault is a fault caused by the drift of the parameters of the component and the voltage of the power supply. For example, if the temperature is too high, it will cause a change in the resistance value. At this time, the device behaves as good or bad. In fact, factors such as ambient temperature, component manufacturing process, equipment manufacturing process, usage time, storage time, and power load can cause component parameters to change and produce drift faults.
Whether it is a damaging fault or a drifting fault will cause the system to false alarm. To reduce the false alarms generated, efforts should be made from the following aspects.
(1) The production equipment of alarm equipment must improve the design level and technological level of the product. At the same time as the system design, it also needs to be designed, such as redundant design, electromagnetic compatibility design, three-proof design (moisture proof, anti-defense). Salt spray, anti-fungal), drift and design. On this basis, improve the reliability of the product manufacturing process, such as strict screening of component quality; strict quality supervision and management of the production process to ensure that product quality meets the requirements of relevant standards.
Units or individuals that sell alarm equipment shall conduct strict incoming inspection. The inspection contents are: product quality inspection certificate; industrial production license or safety certification certificate or production registration approval certificate of the production enterprise.
(2) The administrative department shall organize regular and irregular inspections and spot checks on the security market, and find that illegal activities in the production and sale of security products shall be handled in strict accordance with the provisions of the “Administrative Measures for Safety Technology Prevention Productsâ€.
(3) The alarm system construction unit (user) shall clearly require the construction unit to select the products that have passed the inspection by the authorized testing organization in the corresponding project documents; the foreign equipment shall use the products imported by the formal channels and qualified according to the international advanced standards.
(4) In order to ensure the good working condition of the alarm system, a regular inspection and maintenance system must be established. Incidentally, at present, the maintenance method of China's alarm system needs to be resolved. It is best to repair the maintenance of the project construction unit for the maintenance of the professional maintenance company. This will not only facilitate the use of maintenance resources (maintenance personnel, maintenance equipment, maintenance spare parts, etc.). The improvement of the maintenance level, more importantly, can improve the reliability of the security system.
2 false alarm caused by improper design and construction of the alarm system
2.1 False alarm caused by improper system design
Equipment selection is the key to system design, and there are many types of alarm equipment, each with its own characteristics, scope of application and limitations. If improperly selected, it will cause false alarms. For example, the use of a vibrating detector near the near-source (airport, railway) can easily cause false alarms in the system; the use of ultrasonic detectors in places where bats are often present also causes the system to falsely alarm, because the bat emits ultrasonic waves; High-frequency sounds such as electric ringtones and metal impact sounds can cause false alarms of single-tech glass break detectors. Therefore, system designers should be familiar with the principles and characteristics of various alarm devices to reduce false alarms caused by improper equipment selection. , scope of application and limitations. At the same time, it is necessary to master the on-site environmental conditions, climate conditions, electromagnetic field strength and illuminance changes, etc., in order to select alarm equipment according to local conditions.
In addition to equipment selection, improper system design is also reflected in equipment installation location, installation angle, protective measures and system wiring. For example, when a passive infrared intrusion detector is installed against an air conditioner or a ventilating fan, it will cause a false alarm of the system; if the outdoor active infrared detector is not properly shielded from the sun (the sun shield is also best protected), it is bound to be Cause the system's false alarm; when the distance between the alarm line and the power line, lighting line and other strong electric lines is less than 1.5m, without the anti-electromagnetic interference measures, the system will also generate false alarms......
2.2 False alarm caused by improper construction
This part of the problem is mainly reflected in the following aspects:
(1) Construction is not strictly in accordance with design requirements.
(2) The equipment is not installed securely or the angle of inclination is not suitable.
(3) The solder joint has a virtual weld or burr, or the shielding measures are not appropriate.
(4) The sensitivity of the device is not well adjusted.
(5) The testing equipment 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 security engineering supervision system as soon as possible, which is conducive to improving the quality of the project and reducing false alarms caused by the construction link.
3 false alarm caused by improper use of the user
Improper use by the user often causes false alarms of the alarm system. For example: the window with the magnetic switch is not inserted, and the wind is blown away at night; the staff mistakenly enters the warning zone; the emergency alarm device is accidentally triggered; the system check-in personnel misuse; the work program change is not noticed, etc. The cause of the system's false alarm. Analysis of the user's improper use, to find out where the error is, improve the level of the user, can greatly reduce the number of false alarms of the alarm system.
4 false alarm caused by environmental noise
The false alarm caused by environmental noise refers to the alarm system generated under normal working conditions, which is inevitable in principle, and the fact is unnecessary, which is a false alarm. For example: hot air caused by false alarm of passive infrared intrusion detector; high frequency sound caused false alarm of single technical glass broken detector; ultrasonic source caused false alarm of ultrasonic detector. A more effective measure to reduce such false alarms is to use a dual detector (two different detectors detect the "target" at the same time, and the alarm will send an alarm signal). The current products include: microwave-passive infrared double-decker, voice-vibration glass-breaking double-decker, ultrasonic-passive infrared double-dec. However, some environmental noise double detectors can't do anything, for example: mice in the guard zone; pets walking around the room. To this end, the scientific and technical personnel have introduced the micro-processing technology into the alarm system, so that it has certain identification and thinking ability, and can judge to some extent whether it is an intruder or an alarm caused by environmental noise.
With the development of sensing technology and computer technology, the promotion and application of large-scale integrated circuits, the intelligence level of the alarm system will continue to increase, and the false alarm phenomenon caused by environmental noise will surely decrease.