The working principle of the passive infrared detector is mainly based on the infrared spectrum generated by the human body. In the natural world, any object above the absolute temperature (-273 degrees) will produce infrared spectrum, in the passive infrared warning zone, when there is no When the object moves, the pyroelectric infrared sensor senses only the background temperature. When the moving object enters the warning zone, the pyroelectric infrared sensor senses the difference between the moving object temperature and the background temperature through the Fresnel lens, and the infrared signal is transmitted. The alarm signal sent after the change is converted into an electrical signal.
Generally, passive infrared detectors are wall-mounted and ceiling-mounted, and the main installation location is based on the area of â€‹â€‹protection. Passive infrared detectors come in a variety of models, from indoors to outdoors, from wired to wireless, from single-infrared to three-infrared, from wall-mounted to ceiling-mounted. The detectors to be installed must take into account the size of the space. , the surrounding environment, the characteristics of the entrance and exit and other actual conditions, so as to choose the right product.
So what do we need to pay attention to when installing infrared detectors on a daily basis?
1. Determine the installation height according to the instructions.
The installation height of the detector is not arbitrary, it will directly affect the sensitivity of the detector and the effect of preventing small animals. Generally, the installation height of the wall-mounted infrared detector is 2.0-2.2 meters.
2. Should not face glass doors and windows
There are two problems with the glass door and window: First, the white light interference, although the passive infrared detector (PIR) has a strong suppression function for white light, but after all, it is not 100% suppression, do not face the glass door and window, can avoid glare The second is to avoid complex environmental disturbances outside the door and window, such as direct sunlight, crowds, mobile vehicles, etc.
3. It is not appropriate to face hot and cold vents or cold and heat sources
Passive infrared detectors have a close relationship with temperature changes. Both hot and cold vents and cold and heat sources can cause false alarms. For some low-performance detectors, sometimes air convection through doors and windows will also Caused a false positive.
4. It is not appropriate to face large objects that are easy to swing
Large swings of large objects can instantaneously cause sudden airflow changes in the detection area, which may also cause false alarms; for example, outdoor detectors should avoid large trees and tall shrubs.
5. Reasonable location
Should not detect screens, furniture, large bonsai or other partitions within the scope of detection; do not install two wireless infrared detectors in the same space to avoid the phenomenon of interference caused by simultaneous triggering; infrared detectors should be indoors The walking line is at an angle, the detector is least sensitive to radial movement reactions, and most sensitive to tangential (ie, perpendicular to the radius). Choosing the right installation location on site is an extremely important part of avoiding false alarms from infrared detectors and achieving high detection sensitivity.
After the detector is installed, debugging the detector is the last thing to do. The debugging of the passive infrared detector is generally a step test, that is, the debugging personnel walks the S-shaped line in the warning area to sense the length and width of the warning range to test whether the entire alarm system meets the requirements. The specifications can be consulted to properly adjust the sensitivity of the detector. Too high or low sensitivity will affect the prevention effect.
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