Types of passive infrared detectors

The passive infrared detector optical system includes three types: Fresnel lens, parabolic mirror, and blocking sheet.

There are two effects of Fresnel lens: one is the focusing effect, which refracts (reflects) the infrared signal released by the pyrolysis on the PIR; the second function is to divide the warning area into several bright and dark areas. Fresnel lenses are convex lenses that project infrared images of objects on the surface of thermoelectric elements.

The optical system composed of parabolic reflectors has the advantages of less thermal energy absorption, small scattering loss, high efficiency, and high imaging accuracy, and is suitable for long-distance and large-range infrared detectors.

The shielding sheet does not have a focused imaging effect on the radiation source, and the viewing distance is very close, which is usually used to form the look-down function of the infrared detector.

The pyroelectric infrared sensor is equipped with a pyroelectric device and a pre-amplifier circuit in a round metal cap. The square opening on the top of the metal cap is inlaid with a cold white light-resistant silicon infrared filter, and the bottom has metal pins, respectively. Power pin, ground pin, thermoelectric signal output pin.