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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. The alarm shall not be given when it is blocked by leaves, rain, small animals, snow, sand, dust and fog, and the alarm will be given when it is blocked by people or objects of a considerable volume.
The active infrared detector technology mainly uses one transmission and one reception, which belongs to linear prevention. Now it has developed from the original but beam to multiple beams, and it can also send and receive two signals to minimize the false alarm rate, thus enhancing the stability and reliability of the product.
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 target factor coherence (only the target blocking the infrared beam can trigger the alarm), so the active infrared sensor will be further promoted and applied
Working principle and characteristics of 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 and then collects it on the infrared sensor. Infrared sensors usually use pyroelectric elements, which will release charge 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 body radiation. Therefore, the radiation sensitive element is sensitive to a wavelength of 10 μ M U.M must be very sensitive. In order to be sensitive to the infrared radiation of the human body, the radiation surface is usually covered with special filters, so that the interference of the environment is obviously controlled.
The passive infrared sensor consists of two pyroelectric elements connected in series or in 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 generated by them cancel each other, so the detector has no signal output.
Once the intruder enters the detection area, the infrared radiation of the human body will be focused through part of the mirrors and then received by the pyroelectric elements. However, the two pyroelectric elements receive different heat and the pyroelectricity is different, which cannot be offset. After signal processing, the alarm will be sent