Do You Know the Types of Infrared Sensors?(1)

An infrared ray is a kind of light invisible to human eyes, so it has all the characteristics of light. But at the same time, there is another kind of infrared that also has a very significant thermal effect. All substances above absolute zero, i.e. -273 ℃, can produce infrared rays.

According to different ways of emitting, infrared sensors can be divided into active and passive.

Working principle and characteristics of active infrared sensor

The transmitter of the active infrared sensor sends out a modulated infrared beam, which is received by the infrared receiver, thus forming a warning line composed of infrared beams. In case of leaves, rain, small animals, snow, sand, and fog, the alarm shall not be given, and the alarm will be given if people or objects of a considerable volume are blocked.

Active infrared detector technology mainly adopts one engine and one receiver, which belongs to linear prevention. Now it has developed from the initial beam to multiple beams, and it can also double engine and double receiver to minimize the false alarm rate, to enhance the stability and reliability of the product.

Because infrared ray belongs to the detection medium with good incoherence of environmental factors (for sound, lighting, vibration, various artificial light sources, and electromagnetic interference sources in the environment, it has good incoherence); At the same time, 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.

Working principle and characteristics of passive infrared sensor

The passive infrared sensor works by detecting the infrared ray emitted by the human body. The sensor collects the infrared radiation from the outside and then gathers it on the infrared sensor. Infrared sensors usually use pyroelectric elements, which will release charges when the temperature changes after receiving infrared radiation and generate an alarm after detection and processing.

This kind of sensor is aimed at detecting human radiation. Therefore, the radiation-sensitive element has a wavelength of 10 μ The infrared radiation of about M must be very sensitive. To be sensitive to the infrared radiation of the human body, its radiation surface is usually covered with special filters, so that the interference of the environment is controlled.

The passive infrared sensor consists of two pyroelectric elements connected in series or parallel. Moreover, the two electric polarization directions are exactly opposite, and the environmental background radiation has almost the same effect on the two pyroelectric elements so that the pyroelectric effects produced by them offset each other, so the detector has no signal output.

Once the intruder enters the detection area, the infrared radiation of the human body is focused through part of the mirror and received by the pyroelectric element. However, the two pyroelectric elements receive different heat and pyroelectricity, which cannot be offset, and the alarm will be sent after signal processing.

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