Infrared detectors are a key component of anti-theft alarm systems, directly determining the sensitivity and stability of the system, and ensuring the quality of the entire system. In recent years, there have been significant improvements in both technological mastery and production capacity, thanks to Chinese manufacturers continuously absorbing foreign product design and production technology, and striving to reduce costs, which has led to the recognition of Chinese security products by engineering companies. In addition, low prices have an important attraction for the first party, making domestic products grow rapidly in the market. Although the quality of domestic products still lags behind that of imported products, Chinese security products still have a competitive advantage when users are not familiar with them.
Many foreign manufacturers also acknowledge that in the past, foreign companies relied heavily on technological advantages to cope with the cost advantage of Chinese domestic products. However, in recent years, the gap has narrowed and the advantages have gradually decreased. This shows that Chinese manufacturers have gradually caught up with foreign manufacturers in technology, and some manufacturers have more innovative capabilities, launching distinctive products, which greatly improves the level of Chinese security products. This phenomenon mainly comes from many manufacturers' emphasis on brand awareness and product quality, increasing investment and research and development efforts.
The principle and characteristics of infrared detectors
The human body has a constant body temperature, usually around 37 degrees Celsius, and emits infrared radiation with a specific wavelength of around 10 μ m. Passive infrared detectors work by detecting the infrared radiation emitted by the human body at around 10 μ m. The infrared radiation of about 10 μ m emitted by the human body is enhanced by a Fresnel filter and focused on the infrared sensing source. Infrared induction sources usually use pyroelectric elements, which lose their charge balance when they receive changes in the temperature of human infrared radiation and release charges outward. The subsequent circuit can generate an alarm signal after detection and processing.
Passive infrared detectors are designed to detect human radiation, so pyroelectric elements must be very sensitive to infrared radiation with a wavelength of around 10 μ m.
In order to be sensitive only to the infrared radiation of the human body, a special Fresnel filter is usually covered on its radiation surface, which significantly controls environmental interference.
3. Its sensor consists of two pyroelectric elements connected in series or parallel. Moreover, the two polarization directions produced are exactly opposite, and the environmental background radiation has almost the same effect on the two pyroelectric elements, causing their discharge effects to cancel each other out, resulting in no signal output from the detector.
Once a person invades the detection area, the infrared radiation from the human body is partially focused by the mirror and received by the pyroelectric element. However, the heat received by the two pyroelectric elements is different, and the pyroelectric cannot be cancelled out. After signal processing, an alarm is triggered.
Advantages and disadvantages of passive infrared depth sensors
Advantages: It does not emit any type of radiation, has low power consumption, good concealment, and is inexpensive.
Disadvantages: Easy to be interfered by various heat sources and sunlight sources; Passive infrared penetration is poor, and the infrared radiation of the human body is easily blocked, making it difficult for detectors to receive; Susceptible to interference from radio frequency radiation; When the ambient temperature is close to the human body temperature, the detection and sensitivity decrease significantly, sometimes causing short-term malfunction.