PIR Motion Sensors Switch
Passive PIR sensors are widely applied to the fields such as electronic anti-theft alarm, human detection. They win great popularity among customers and specialists for their low price and stable technical performance.
Working principle and features of passive PIR infrared probe:
All human body has stable temperature, generally 37 °C. Therefore, they can send out infrared ray with specific wavelength- about 10UM. Passive PIR infrared probes keep themselves working by detecting these 10UM infrared rays created by human body, which are strengthened by Fresnel lens and then focus on the inductive source. Inductive source usually adopt pyro electric components, which will break the charge balance when receiving the changing human infrared radiation temperature, releasing charge to the outside. The follow-up circuit can create alarm signal after being detected.
1.This kind of probe aims at detecting infrared ray created by human body. So pyro electric components should be very sensitive to the infrared with 10UM wavelength.
2.In order to make it only sensitive to infrared created by human body, there is usually a piece of Fresnel optical filter covering the probe’s surface where it detects infrared ray, which can be immune to the ambient environment.
3.Passive infrared detector, whose sensor includes two serial or parallel pyro electric components,. And the done two electrodes have the opposite direction. The ambient background radiation has the same impact on these two pyro electric components, enabling it to produce pyro electric effect. Then the sensor has no signal sent out.
4.Once someone enters the detection range, the human infrared radiation is focused by some part of the lens and received by pyro electric components. But the two pyro electric components receive different heat and pyro electricity. They cannot counteract and make alarm after signal processing.
5.Fresnel filters have different detection range according to their different performance requirements. Thus they can generate different monitoring fields. The more the viewing fields are, the strict the monitoring will be.
Microwave Motion Sensors Switch
Developing and application of microwave sensors
Microwave are still the most advanced method used to detect motion objects. All that that use radar wave to detect the speed of a motion object is based on the theory of Doppler effect. This is a theory about the physical phenomenon discovered by an Austria physicist in nineteenth century.
The theoretical basis of Doppler is time. Wave is composed of frequency and amplitude. Once radio wave in the travel process encounters an object, it will be reflected, and the frequency and amplitude of its reflected wave will change in accordance with the moving state of the object. If the object is immobile, the frequency of the reflected wave will not change. However, if the object moves toward the direction of radio wave, the reflected wave will be compressed, and therefore the frequency of the very wave will increase. Conversely, if the object moves to the opposite direction of a radio wave, the frequency of the reflected wave will decrease.
