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| False alarm analysis and failure maintenance of anti-theft alarm system |
| 2021.06.02 |
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False alarms of anti-theft alarm systems are more common. What causes false alarms? How to repair it?
1. What is false positive
There is currently no authoritative definition of false alarms. In our country, it is generally believed that: "If there is no dangerous situation, the alarm system sends out an alarm signal is a false alarm." According to this definition, the false alarm rate of the alarm system (in a certain period of time, the system The ratio of the number of 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 is dispatched without the actual situation, which does not include those caused by severe natural weather and other special environments that cannot be manipulated by alarm companies and users. According to this definition, the American UL standard stipulates: “Each alarm system can only have a maximum of four false alarms per year.”
2. False alarm caused by failure of alarm equipment
The failure of the product to complete the specified function under the specified conditions and within the specified time is called a failure. The types of faults are destructive faults and drifting faults.
Destructive failures include total performance failure and sudden failure. This type of failure is usually caused by damage to components or poor production processes (such as virtual soldering, etc.).
Drifting fault refers to the fault caused by the drift of the parameters of the components and the power supply voltage. For example, if the temperature is too high, the resistance value of the resistance will change. At this time, the performance of the equipment will be good and bad. In fact, factors such as ambient temperature, component manufacturing process, equipment manufacturing process, use time, storage time, and power load may cause changes in component parameters and cause drift failures.
Both damaging faults and drifting faults will make the system false alarms. To reduce the resulting false alarms, efforts should be made from the following aspects.
(1) Manufacturers of alarm equipment must improve the design level and technological level of their products. While designing the system, they also need to design reliability, such as redundant design, electromagnetic compatibility design, and three-proof design (moisture-proof, salt-proof). Fog, anti-mold), drift reliability design, etc. 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, etc., to ensure that product quality meets the requirements of relevant standards.
Units or individuals selling alarm equipment should carry out strict purchase inspections. The inspection contents include: product quality inspection certificate; industrial production license or safety certification certificate or production registration approval letter of the manufacturer.
(2) The management department shall organize regular or irregular inspections and random inspections of the security market, and find that illegal activities in the production and sales of security products shall be dealt with in strict accordance with the provisions of the "Administrative Measures for Security Technology Prevention Products".
(3) The alarm system construction unit (user) should clearly require the construction unit to select products that are qualified by an authorized testing agency in the corresponding engineering documents; foreign equipment should select products that are imported through regular channels and that are qualified according to 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. By the way, the current maintenance methods of the alarm system in our country need to be resolved. It is best to change the maintenance of the project contractor to the maintenance of a professional maintenance company. This will not only facilitate the utilization 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 safety protection system.
3. False alarms caused by improper design and construction of the alarm system
1. False alarm caused by improper system design
Equipment selection is the key to system design. There are many types of alarm devices, 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 (airports, railways) can easily cause false alarms of the system; the use of ultrasonic detectors in places where bats frequently haunt will also cause the system to false alarms, because the bats emit ultrasonic waves; High-frequency sounds such as ringtones 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 application scope of various alarm equipment And limitations. At the same time, it is 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 and equipment, improper system design is also manifested in the installation location, installation angle, protective measures and system wiring of the equipment and equipment. For example: when the passive infrared intrusion detector is installed against the air conditioner and ventilation fan, it will cause the system to false 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; when the distance between the alarm line and the power line, lighting line and other strong current lines is less than 1.5m, without the anti-electromagnetic interference measures, 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:
(1) The construction is not strictly in accordance with the design requirements.
(2) The equipment is not installed firmly or the inclination angle is inappropriate.
(3) The solder joints have false soldering, burrs, or improper shielding measures.
(4) The sensitivity of the equipment is poorly adjusted.
(5) 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. This is very conducive to improving the quality of the project and reducing false alarms caused by the construction process.
3. False alarm caused by environmental noise
False alarms caused by environmental noise are caused by the alarm system under normal working conditions. It is unavoidable in principle, but it is unnecessary in fact. It is a false alarm. 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-check detectors (detectors with two different principles simultaneously detect the "target", and the alarm will send out an alarm signal). Current products include: microwave-passive infrared dual discriminator, voice control-vibration glass breaking dual discriminator, ultrasonic-passive infrared dual discriminator, etc. However, some environmental noise double-detection detectors are extremely powerful, such as: rats in the prevention area; pets walking 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.
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