Main working principle and characteristics of 1 passive infrared detector
Passive infrared detectors work by detecting infrared rays emitted by the human body. The detector collects external infrared radiation and then collects it on the infrared sensor. Infrared sensors usually use pyroelectric elements, which will release charges when the temperature changes after receiving infrared radiation, and will give an alarm after detection and processing.
This detector is used to detect human radiation. Therefore, the radiation sensitive element must be very sensitive to infrared radiation with a wavelength of about 65438±00 μm m. ..
In order to be sensitive to human infrared radiation, its radiation surface is usually covered with special filters, so that environmental interference is obviously controlled.
Passive infrared detector, whose sensor includes two pyroelectric elements connected in series or in parallel. Moreover, the two polarization directions are just opposite, and the environmental background radiation has almost the same effect on the two pyroelectric elements, so that their discharge effects cancel each other out, so the detector has no signal output.
Once the intruder enters the detection area, the infrared radiation of human body is focused by some mirrors and received by pyroelectric elements. However, the heat received by the two pyroelectric elements is different, and the pyroelectric is also different, which cannot be offset. After signal processing, an alarm is given.
The acquisition of multiple fields of view is a reflective focusing composed of multiple normal small mirrors, which is called a reflective optical system. The other is a transmissive optical system, which is a polygonal lens-Fresnel lens, which focuses on the infrared sensor through Fresnel lens.
It should be pointed out that several beams of light other than passive red light indicate that there are several fields of view, instead of passive infrared light emitting infrared light. The more horizons, the stricter the control.
Advantages and disadvantages of passive infrared detectors;
Advantages:
It does not emit any kind of radiation, so the power consumption of the equipment is very small and the concealment is good.
low in price
Disadvantages:
It is easily interfered by various heat sources and solar light sources.
Passive infrared penetration is poor, and human infrared radiation is easily blocked and not easily received by detectors.
Vulnerable to radio frequency radiation interference.
When the ambient temperature is close to the human body temperature, the detection and sensitivity are obviously decreased, and sometimes short-term failure occurs.
Overview of new passive infrared detection technology
Aiming at the shortcomings of the passive infrared detector mentioned above, combined with the infrared detection technology of lane detector, a detailed analysis is carried out.
Through the analysis of the shortcomings of passive infrared detectors, it is found that the problems of false alarm and decreased detection ability should be solved in fact. False alarm problem: In order to reduce the false alarm rate, excluding false alarm and other factors can greatly reduce the false alarm rate.
1. False alarm factors can be divided into two categories:
External factors:
External light heat source (especially white light source): such as sunlight, lighting source, etc.
External RF signals, etc.
internal factor
Internally, due to the noise and interference of devices, such as the signal transient of photothermal blood release sensor.
In view of the above situation, the new generation infrared detector of lane detector adopts some independent technologies to solve this kind of problem.
Firstly, two photothermal sensors connected by different circuits are applied to the focus of infrared lens. The special lens divides the coverage area into a plurality of protection areas with trapezoidal sensitivity, and ensures the signal strength in the protection areas. The unique lens can also be used as an infrared filter. The black lens with special surface treatment allows visible light and short-wave infrared rays (which are found in most places with white light sources) to enter and then be absorbed by its black base. The black infrared lens only reflects the infrared ray with the wavelength in line with human movement, and then reflects it to the photothermal sensor. The detector can prevent white light interference by obtaining a patented white light filter. If someone enters or leaves one or several areas covered by the detector, the detector should be able to detect the change of infrared radiation energy. After the A/D converter digitizes the signal sent by the sensor, it is analyzed by Visatec (all-digital intelligent signal analysis technology based on fast thinking logic) signal processor, and then an alarm signal is sent out.
This process involves all the standards in detection, such as signal amplitude, time, format, energy and spectrum, plus the statistical information actually extracted from the site. These standards must be combined with judgment to test their rationality, and the detector will give an alarm only after the results meet the standards of forced entry. Digitizing the signal of photothermal sensor can eliminate the transient of signal and the interference of electromagnetic wave.
2. Deterioration of detection ability:
The decline of detection ability can be divided into several aspects:
The distribution of each detection field of view of the detector is unreasonable, such as the gap is too large.
The detector is blocked. Such as paper, clothes, etc. Foam and spray (a common means of intruders).
Because there is little difference between body temperature and environment, the detection ability decreases.
In view of the above situation, the lane detector adopts the following methods to solve the problem:
Two photothermal sensors connected by different circuits are located at the focusing point of the black infrared lens.
The lens divides the coverage area into several fields of view with the same sensitivity, and ensures the signal strength of the fields of view, and the fields of view are staggered to form a compact distribution form similar to a chessboard.
Anti-blocking monitoring:
The unique electronic adaptive shielding component can monitor the detector to prevent it from being damaged by shielding. If the detector window or any area near the detector is blocked by some objects, such as foam, metal sheet, spray, hat, cardboard, box, clothes, etc., it will enter the alarm state. In daytime mode, once the detector is blocked, the blocking alarm will be displayed on the anti-blocking monitoring output relay and the alarm output relay. The alarm relay will stop and the anti-jam output will start until the jam is released.
Lane detector passive infrared detector common passive infrared detector.
Basic technical performance indicators and installation methods There are many types of detection range, which can meet the requirements of various occasions, and the maximum detection distance of a single machine can reach 150m. The same model with different mirrors can realize the conversion between wide-angle and long-distance curtain detection. The general detection distance is 15m. After the product is equipped with reflector, it can reach 25m.
The working temperature is -20 ~+50℃, and the technical parameters have little influence in this range. Usually room temperature.
The shell type conforms to various standards of IP3 1-IP65 to prevent insects and airflow from entering. Among them, the outdoor type has a metal shell, which has strong protective ability and can adapt to harsh environment. Generally, it is IP3 1.
The test function is working. The wiring test function is generally not available.
Day/night state transition includes day/night state transition, generally only working state.
The unique design technology of detection loop (with plug) and sensor makes the installation of detector easier and easier, and it is easy to be damaged during installation.
Self-check complete voltage monitoring electronic circuit and automatic periodic self-check function of inductor.
Unique anti-small pet filtering function
When solving false alarm and preventing harm, filter circuit is provided to prevent noise and sudden change of internal circuit, and the signal of photothermal sensor is digitized to eliminate signal transient. Usually not.
Eliminate external white light source, unique black mirror technology and white light filter, and eliminate visible light and short-wave infrared. not have
Eliminate external radio frequency and other signals, digitize signals and eliminate interference. not have
Detector shielding has a unique electronic adaptive anti-shielding function. not have
Detect line damage, whether in withdrawal or deployment, and monitor the line around the clock. Some detectors have
Intelligent analysis Visates high-intelligence signal analysis technology, all-digital high-intelligence signal analysis technology based on fast thinking logic, and the signal processor sends an alarm signal after analysis. This process involves all the standards in detection, such as signal amplitude, time, format, energy and spectrum, plus the statistical information actually extracted from the site. These standards must be combined with judgment to test their rationality, and the detector will give an alarm only after the results meet the standards of forced entry. not have
In order to improve the detection ability, the sensitivity of the detection field of view is improved. At the focal point of the infrared lens, two photothermal sensors connected by different circuits are applied. The special lens divides the coverage area into several protection zones with the same sensitivity, and ensures the signal strength in the protection zones.
The field of view distribution of the detector is staggered, forming a compact distribution form similar to a chessboard.
Micro-temperature difference identification can quickly detect the micro-temperature change in the field of view through the difference method.
Intelligent temperature detection: tiny temperature changes in the field of view can be quickly detected by the difference method.
3. Other new technology applications:
Unique anti-small pet filtering function
Complete voltage monitoring
Automatic periodic self-inspection function of electronic circuits and sensors
Unique electronic circuit (with plug) and sensor separation design technology make the installation of the detector easier.
The completely sealed detector can prevent insects and airflow from entering.
3. Some views on dual geophones in Chinese mainland area.
At present, Chinese mainland's dual-identification anti-theft detector (infrared+microwave) occupies a certain share in the market, but it is quite similar to the common dual-identification anti-theft detector (infrared+microwave).
Dual-purpose anti-theft detector (infrared+microwave) was first produced under the condition of high false alarm rate of ordinary simple passive infrared detector, while intelligent passive infrared detector of lane detector greatly reduced the false alarm rate.
Although the common dual-identification burglar detector (infrared+microwave) adopts the relationship between infrared alarm and microwave alarm, it also reduces the detection ability.
Microwave itself has a certain penetration ability (such as walls, etc.). ), which increases the false alarm rate.
Microwave can be shielded by metal, which increases the detection limit in practical applications (such as refrigerators).