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First, the principle of passive infrared detector
In nature, any object above the absolute temperature (-273 degrees) will generate an infrared spectrum. In the passive infrared warning zone, when no object moves, the pyroelectric infrared sensor only senses the background temperature. When moving objects Entering the warning area, through the Fresnel lens, the pyroelectric infrared sensor senses the difference between the temperature of the moving object and the background temperature, and changes the infrared signal into an electrical signal that is emitted after the alarm. Passive infrared detectors do not have an emission in the infrared spectrum.
Second, false alarms caused by equipment failure
1. Destructive failure. Including total performance failure and sudden failure. Such failures are usually caused by damage to components or poor production processes (such as false soldering, false soldering, etc.).
2. Drift failure. It refers to the failure caused by excessive drift of the parameters of the component and the power supply voltage. For example, the temperature is too high, which will cause the resistance value to change. At this time, the device behaves in good and bad conditions.
Third, false alarms caused by environmental changes
1. Insufficient equipment installation and frequent movements cause false alarms;
2. False alarms caused by temperature changes of air conditioners and ventilation fans;
3. The door or window in the prevention area is not closed, and a person or animal passes by causing a false alarm;
4. When the temperature difference between indoor and outdoor is large, the wind blows the curtain to cause false alarm;
5. Multiple detectors transmit signals at the same time, which can cause false alarms or interference (only for wireless type);
6. The alarm system's wrong code causes false alarm to other wireless infrared detectors. Every time the device behaves better and worse (only wireless type).
Fourth, the solution
1. Install the infrared detector according to the installation requirements of the instruction;
2. Avoid areas with strong temperature differences and air convection;
3. The doors and windows in the prevention area are closed, and the detector should be turned on normally;
4. Close doors or windows or bind curtains;
5. Reduce the cross-detection range of the prevention area and avoid transmitting alarm signals at the same time;
6, fast and accurate when the code is matched to prevent mis-recorded information.
V. Guarantee of low false positives
1, "0" misleading product misleading. It is believed that all products that use PIR as the detection sensor have no absolute "0" false alarm products at present, and can only rely on continuous technical optimization to reduce the frequency and number of false alarms. The reason is that the infrared detector only judges the specific environment and specific conditions according to the program set in the microprocessor of the detector in advance. The sensitivity of detection is changed by changes in the environment and conditions. Controlling changes in the environment is the key to reducing false positives.
2. CCC certification. CCC compulsory certification of qualified products is necessary, and high-quality electronic components, strict quality system maintenance, credible quality commitment and perfect after-sales service must be selected.
3. Multi-technology combination discrimination improves the reliability of the detector. The current products are: passive infrared detector, microwave + passive infrared dual detector, sound control + vibration glass broken dual detector, ultrasonic + passive infrared dual detector Wait.
4. Special circumstances. Some environmental noise detectors are powerless, for example: rats appear in the precautionary zone; pets move around the room. To this end, scientific and technological personnel have introduced micro-processing technology into the alarm system, so that they have a certain ability of identification and logical discrimination, and can to a certain extent determine whether the alarm is caused by an intruder or environmental noise.