How Does An Infrared Sensor Work

Infrared is a kind of light invisible to the human eye, so it has all the characteristics of light, and all substances above absolute zero, that is, -273 °C, can generate infrared. According to the characteristics of infrared rays, infrared rays are used in various sensors, such as infrared temperature and humidity sensors, human infrared detectors and so on. Infrared sensors are also divided into different types according to the way they are emitted and the way they are converted into energy.

Let's take a closer look at the working principles and characteristics of different infrared sensors. According to different emission methods, infrared sensors can be divided into two types: active and passive.

Active infrared sensor

The transmitter of the active infrared sensor emits a modulated infrared beam, which is received by the infrared receiver, thereby forming a warning line composed of infrared beams. When it is blocked by leaves, rain, small animals, snow, sand, and fog, the alarm should not be reported, and the alarm will be issued when people or objects of considerable size are blocked. Active infrared detector technology mainly adopts one transmitter and one receiver, which belongs to linear prevention. Now it has developed from the original single beam to multi beam, and it can also double transmitter and receiver to minimize the false alarm rate, thereby enhancing the stability of the product. sex, reliability.

Since infrared is a detection medium with good incoherence of environmental factors (for sound, lightning, vibration, various artificial light sources and electromagnetic interference sources in the environment, it has good incoherence); it is also a product with good coherence of target factors ( Only the target that blocks the infrared beam will trigger the alarm), so the active infrared sensor will be further promoted and applied.

Passive infrared sensor

Passive infrared sensors work by detecting infrared rays emitted by the human body. The sensor collects the infrared radiation from the outside world and concentrates it on the infrared sensor. Infrared sensors usually use pyroelectric elements, which will release charges when receiving infrared radiation temperature changes, and generate an alarm after detection and processing. This sensor is aimed at detecting human radiation. Therefore, the radiation-sensitive element must be very sensitive to infrared radiation with a wavelength of about 10 μm. In order to be sensitive to the infrared radiation of the human body, its radiation surface is usually covered with a special filter, so that the interference of the environment is obviously controlled.

A passive infrared sensor consists of two pyroelectric elements connected in series or parallel to each other. Moreover, the polarization directions of the two electrodes are opposite, and the background radiation of the environment has almost the same effect on the two pyroelectric elements, so that the electric discharge effects cancel each other out, so the detector has no signal output. Once the intruder enters the detection area, the infrared radiation of the human body is focused by part of the mirror and received by the pyroelectric element, but the heat received by the two pyroelectric elements is different, and the pyroelectricity is also different, which cannot be offset. After signal processing And call the police. Passive infrared sensors are widely used in human infrared detectors. According to the different energy conversion methods, infrared sensors can be divided into two types: photonic type and pyroelectric type.

Conclusion

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