PIR sensor is a kind of sensor that uses infrared ray to process data. It has the advantage of high sensitivity. The PIR sensor can control the operation of the drive device. PIR sensors are commonly used in non-contact temperature measurement, gas composition analysis and nondestructive testing, and are widely used in medicine, military, space technology and environmental engineering. For example, the PIR sensor is used to remotely measure the thermal image of the human body surface temperature, and the abnormal temperature can be found.

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 also a very significant thermal effect of infrared. All substances above absolute zero, i.e. - 273 ℃, can produce infrared rays. According to different sending modes, PIR sensors can be divided into active and passive ones.

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

The active infrared detector technology mainly adopts one sending and one receiving, which belongs to linear prevention. Now it has developed from the original beam to multiple beams, and it can also send and receive two beams to minimize the false alarm rate, thus enhancing the stability and reliability of the product.

As infrared ray belongs to the detection medium with good incoherence of environmental factors (sound, lightning, vibration, various artificial light sources and electromagnetic interference sources in the environment have good incoherence); At the same time, it is also a product with good coherence of target factors (only when the target of infrared beam is blocked, the alarm will be triggered), so the active PIR sensor will be further promoted and applied.

Passive PIR sensor works by detecting infrared ray emitted by human body. The sensor collects the external infrared radiation and then gathers it on the PIR sensor. PIR sensors usually use pyroelectric components, which will release charges when they receive changes in infrared radiation temperature, and will give an alarm after detection and processing.

This sensor is aimed at detecting human radiation. Therefore, the wavelength of radiation sensing element is 10 μ The infrared radiation around m must be very sensitive. In order to be sensitive to the infrared radiation of human body, its radiation surface is usually covered with special filters, so that the environmental interference is obviously controlled.

The passive PIR sensor consists of two pyroelectric elements connected in series or in parallel with each other. In addition, 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 their pyroelectric effects cancel 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 some mirrors, so that it is received by the pyroelectric element. However, the heat received by the two pyroelectric elements is different, and the pyroelectricity is also different, which cannot be offset, and the alarm is given after signal processing.

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