A PIR motion sensor is used to sense movement of humans, animals, or other objects. They are commonly used in burglar alarms and automatically-activated lighting systems.
An individual PIR sensor detects changes in the amount of infrared radiation impinging upon it, which varies depending on the temperature and surface characteristics of the objects in front of the sensor.When an object, such as a human, passes in front of the background, such as a wall, the temperature at that point in the sensor's field of view will rise from room temperature to body temperature, and then back again. The sensor converts the resulting change in the incoming infrared radiation into a change in the output voltage, and this triggers the detection. Objects of similar temperature but different surface characteristics may also have a different infrared emission pattern, and thus moving them with respect to the background may trigger the detector as well.
PIR motion sensor can detect static human body. It is assembled with fresnel lens, photosensitive element，photosensitive circuit, mechanical part and mechanical control part. Mechanical part and mechanical control part drive the infrared induction part to do side-to-side movement or circular motion, changing position which cause relative motion between sensor and human body. So no matter the human body is moving or static, photosensitive element will always cause polarized differential pressure. Meanwhile, photosensitive circuit send out a identification signal of motion detection, which will achieve the purpose of detecting static human body.
LED motion sensor lamp detects the luminous environment by infrared radiation which senses human body. And by time delay switch, the lamp tuturns on and off. LED motion sensor lamp is also called LED human body sensor lamp.
LED motion sensor lamp have three function module which are infrared sensing module, luminous sensing module and time delay switch module. The luminous sensing module detects the light intensity and decide whether activate the other module or not. The below two cases are included:
1.In daytime or intense light, luminous sensing module locks infrared sensing module and time delay module, basing on the induction value.
2.At night or in dim light, luminous sensing module activates infrared sensing module and time delay module and sets them on standby.
When motion deteced within sensing range, infrared sensing module will be activated and detect the signal, which will trigger the time delay module. If man stays in the range, LED will stay on. After leaving the range, no infrared signal will be detected and the time delay switch will automatically turn off LED motion sensor lamp within preset time. Then all the modules return to standby state, waiting for next period.
Microwave sensor lamp consumes low power. It won't be influenced by temperature, humidity, light, airflow, dust and other environmental causes. Microwave sensor lamp has a long service life and it is safe and reliable. This lamp is currently widely used in both indoors and outdoors lighting such as underground parkings, corridors, passageways, public toilets, elevators.
Activation: After powering on the sensor, oscillating circuit inside will automatically generate a frequency of 5.8 GHz + / 75 MHZ, which is called local frequency amplification B. After amplified, the local frequency as a electromagnetic wave carrier, will be launched to the air by high-frequency tube, the antenna.
Reception: The launched electromagnetic wave will be selected by frequency selection network after rejecting by surrounding objects. Send the electromanetic wave together with the original 5.8G frequency and run the phase comparison. The differential signal we get is used as self-inspect basic signal.
First Detection: When a moving object around, the reflected electromanetic wave goes through the circuit analysis. The resulted signal is different from the self-inspect basic signal. It will
Fresnel lens
The Fresnel lens is by the French physicist augustine Augustin Fresnel. The Fresnel (j), he invented in 1822 first use this lens design are used to establish the Fresnel lens system - a glass lighthouse lens.
The Fresnel lens is a kind of micro-structure of optical element, look from the front its like a dart dish, by a ring a part of concentric garden composition.
The Fresnel lens in heat release the role of an infrared have two: one is focusing role, will soon heat release infrared signal reflection refraction (in), the second function is on PIR will detect area is divided into several Ming area and dark area, make into the moving object detection area to temperature changes in the form of heat release on PIR changes infrared signal.
The Fresnel lens, simply say to be in the lens side have equi-distant tooth tattoo. Through these tooth tattoo, can achieve to specified spectrum light band tong (reflecting or refraction) role. The traditional grinding optical equipment band-pass optical filters are expensive. The Fresnel lens can greatly reduce costs. A typical example is PIR (passive infrared detector). PIR used widely in alarm. If you take a look, you will find in each PIR on all have a plastic little hat. This is the Fresnel lens. Little hat internal are engraved the tooth tattoo. This kind of Fresnel lens can be incident light frequency peak limited to 10 micron around (human infrared ray radiation peak).
Pyroelectric infrared sensor
Pyroelectric infrared sensor is mainly composed of a kind of tall thermoelectric coefficients of materials, such as zirconium lead titanate department ceramics, litao3, acid three made gedaliah titanium size for 2 * 1mm detection devices. In each detector loaded within one or two detection devices, and two detection with the polar components in series and to suppress because of its own temperature rise of interference. By detecting components will explore and receive the infrared radiation into a glimmer of voltage signal, the outfit is in probe inside the mosfet enlargement outward output. In order to improve the detection sensitivity in order to increase the probe detecting distance, be in commonly the probe ahead furnish a Fresnel lens, using the Fresnel lens special optical principle, the probe ahead produce a variations of the "blind" and "high sensitive area", in order to improve its detection rx sensitivity. When someone from the lens body before walked out of the infrared ray continually alternate from "blind" enter "high sensitive area", this makes receives the infrared signal to suddenly suddenly weak pulse form strong input, thus strong its energy prices.
The Fresnel lens and amplifying circuit suitably, but will amplification 70 decibels, such pyroelectric infrared sensor can be detected 10 ~ 40 meters geographical area action.
Human radiation wavelengths of infrared center for 9 ~ 10 -- um, but detection components in the wavelength of sensitivity 0.2 ~ 20 - um range almost constant. The sensor has opened a top equipped with filter slice window, the filter can through light wavelength range for 7 ~ 10 -- um, and it fits in the human body infrared radiation detection, and for other wavelength of infrared by filter to absorb so that they formed a special used to detect human radiation infrared sensors.
