8202（56＊23）Fresnel lens (flaky)

Fresnel lens (flaky):

8202 (56*23)

Focal length: 20MM

Distance: 12M

Angle: 110 degrees

The Fresnel optical lens structure converges the incident light into parallel rays, increasing the brightness of the screen within a certain viewing angle range. On one screen, up to 10,000 Fresnel lenses with different profiles were cut. The dot pitch of the Fresnel lens refers to the distance between two adjacent Fresnel lenses, that is, the size of each section. The common unit is mm; the dot pitch of the Fresnel lens represents the resolution of the screen and is equivalent. Within the area of the screen, the larger the unit of the distance between the Fresnel lens points, the higher the highest resolution that can be displayed. The size of the Fresnel lens dot is generally proportional to the size of the screen.

Passive infrared alarm passive infrared alarm does not radiate energy to the space, but rely on receiving infrared radiation emitted by the human body to alarm. Any object with a temperature is constantly radiating infrared rays to the outside world. The surface temperature of the human body is 36-27. C, most of its radiation energy is concentrated in the wavelength range of 8-12um. Passive infrared alarms can be divided into infrared detectors (infrared probes) and alarm control parts. Infrared detectors are currently the most widely used pyroelectric detectors, as a sensor that converts infrared radiation into electricity. If people's infrared radiation directly shines on the detector, of course, it will cause temperature changes and output signals, but in doing so, the detection distance is not far. In order to lengthen the detection distance of the detector, an additional optical system is required to collect infrared radiation. A metal-plated optical reflection system or a Fresnel lens made of plastic is generally used as a focusing system for infrared radiation. In the detection area, the body's infrared radiation energy received by the clothing is received by the detector's lens and focused on the pyroelectric sensor. When the human body (intruder) moves in this surveillance area, it sequentially enters a field of view and then walks out of this field of view. The pyroelectric sensor is seen by the human body in motion for a while and cannot be seen for a while. The infrared radiation constantly changes the temperature of the pyroelectric body so that it outputs one after another corresponding signal which is an alarm signal. The main features of the passive infrared alarm are the following: Since it is passive and does not actively emit infrared light, its power consumption is very small and it is easy to install. Compared with microwave alarms, infrared wavelengths cannot pass through ordinary buildings such as brick cement. When used indoors, there is no need to worry about false alarms due to outdoor moving targets.