In nature, any object higher than the absolute temperature (-273 degrees) will produce infrared spectrum. In the passive infrared warning zone, when no object moves, the pyroelectric infrared sensor only senses the background temperature. 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 converts the change of the infrared signal into an electrical signal to send an alarm signal. The passive infrared detector itself has no infrared spectrum emission.
First, the principle of passive infrared detector
In nature, any object higher than the absolute temperature (-273 degrees) will produce infrared spectrum. In the passive infrared warning zone, when no object moves, the pyroelectric infrared sensor only senses the background temperature. 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 converts the change of the infrared signal into an electrical signal to send an alarm signal. The passive infrared detector itself has no infrared spectrum emission.
Second, False alarm caused by equipment failure
1. Destructive failure. Including total failure of performance and sudden failure. Such failures are usually caused by damage to components or poor production processes (such as virtual soldering, false soldering, etc.).
2. Drift fault. It refers to the failure caused by the excessive 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 resistor will change, and the device will be good or bad at this time.
Third, False alarms caused by environmental changes
1. The equipment is not installed firmly and often moves to cause false alarms;
2. False alarms caused by temperature changes of air conditioners and ventilation fans;
3. The door or window of the prevention area is not closed, and people or animals pass by and cause false alarms;
4. When the temperature difference between indoor and outdoor is large, the wind blowing the curtain will cause false alarm;
5. Multiple detectors transmit signals at the same time, which can cause false negatives or interference (only for wireless types);
6. The code error of the alarm system will cause false alarms to other wireless infrared detectors. Sometimes the device behaves in good and bad times (wireless only).
Fourth, the solution
1. Install the infrared detector according to the installation requirements of the manual;
2. Avoid areas with strong temperature difference and air convection;
3. The doors and windows of the prevention area are closed, pay attention to the normal opening of the detector;
4. Close doors and windows or bind curtains;
5. Reduce the cross detection range of the prevention area and avoid sending alarm signals at the same time;
6. Fast and accurate code matching to prevent misrecording information.
Fifth, Guarantee of low false positives
1. "0" misleading products falsely reported. It should be believed that for products that use PIR as a detection sensor, there is currently no absolute "0" false positive product, and we can only rely on continuous technical optimization to reduce the frequency and number of false positives. The reason is that the infrared detector only discriminates the specific environment and specific conditions according to the pre-set program in the detector's microprocessor. The sensitivity of detection is changed by changes in the environment and conditions, and controlling changes in the environment is the key to reducing false alarms.
2. CCC certification. Compulsory CCC certification of qualified products is necessary, and high-quality electronic components must be selected, strict quality system maintenance, credible quality commitment and perfect after-sales service.
3. Multi-technological combination judgment improves the reliability of the detector. The current products are: passive infrared detector, microwave + passive infrared double detection detector, voice control + vibration glass breaking double detection detector, ultrasonic + passive infrared dual detection detector Wait.
4. Special circumstances. Some environmental noise detectors are powerless, for example: rats are in the prevention area; pets are walking in the living room, etc. To this end, the scientific and technical personnel have introduced the micro-processing technology into the alarm system, so that it has a certain ability of identification and logical judgment, and can judge to a certain extent whether it is an alarm caused by an intruder or an environmental noise.
