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Infrared Detectors Infrared is a section of the geomagnetic spectrum that lies between the microwave and visible wavelengths, with wavelengths between 780 and 100,000 nanometers. The detector made using the basic theory and characteristics of infrared rays becomes an infrared detector.
The active infrared detector is composed of active infrared light emitter and receiver. The infrared transmitter drives the infrared light emitting diode to emit and emit a modulated infrared light beam. The infrared receiver receives the infrared radiation energy emitted by the transmitting end through a phototransistor and converts it into an electric signal through photoelectric conversion. Infrared light is in the visible range of the human eye. After being focused by the beam, an infrared beam is formed between the transceivers. After passing through this invisible blockade line, it will obstruct all or part of the infrared beam. The receiving end will automatically recognize the beam due to changes in the infrared beam. Whether alarm.
When infrared detectors are installed and deployed, in order to increase the protection surface and reduce false alarms, dual-beam or multi-beam methods are generally adopted. Only when two or more of the multiple beams are blocked at the same time, the alarm is triggered. This method can ensure that if small animals, leaves, dust, rain, snow, and fog are obstructed, no alarm will be issued, and an alarm will occur if a person or a considerable volume of objects is blocked.
Passive infrared detector The passive infrared detector does not require an additional infrared radiation source and does not radiate any energy to itself. Instead, the detector directly detects the infrared radiation from the target. It is therefore called a passive type. The passive infrared detector is composed of an optical system, a thermal sensor and an alarm controller. The core component of the passive infrared sensor can detect the change of thermal radiation within a stereo guard area through the cooperation of the optical system. When a target is intruded and moves within a range, it will cause changes in infrared radiation in the area, and the infrared detector can detect this change in infrared radiation and send an alarm signal.
Passive infrared detectors, whose sensors contain two pyroelectric elements connected in series or in parallel. In addition, the two polarization directions are reversed. The ambient background radiation has almost the same effect on the two pyroelectric elements, causing them to cancel each other's charge generation effect. Therefore, the detector has no signal output and once the intruder enters the detection area. Inside, the infrared radiation of the human body is focused by the partial mirror and thus received by the pyroelectric element. However, the heat received by the two pyroelectric elements is different, and the pyroelectricity is also different and can not be cancelled.
PIR detectors prevent false alarms:
The use of temperature compensation circuit makes the detector better adaptable to different temperature environment. Adopts multiple infrared infrared sensor and adopts non-Niel lens to prevent pets from using white light interference. Passive infrared detector is installed and installed.
There should be no obstructions in the detection area. Do not point the detector at a target whose temperature changes rapidly. For example, the microwave intrusion detector at the vent is a high-frequency radio wave with a very short wavelength, usually between 0.001 m and 1 m. Since the microwave wavelength is comparable to the general object geometry, it is easily reflected by the object. According to the working principle microwave intrusion detectors can be classified into mobile microwave detectors and barrier microwave detectors.
Radar type microwave detector The radar type microwave detector sets the microwave receiver and transmitter together. The basic principle is to use the microwave Doppler effect. The so-called Doppler effect means that when there is relative movement between the source (source or electromagnetic wave) and the receiver, the frequency of the received signal will change.
The Doppler effect of electromagnetic waves: The oscillating source emits an electromagnetic wave of frequency f0 and propagates forward at a constant speed. If the receiver is stationary relative to the oscillating source, then the frequency of the signal emitted by it is the same as the frequency of the oscillating source. If the receiver has a relative radial movement close to the oscillating source, the frequency of the signal emitted by the receiver is higher than that of the oscillating source. Signal frequency; conversely, if the receiver has relative radial movement away from the oscillator, the frequency of the signal transmitted by the receiver is lower than the signal frequency of the oscillator.
Therefore, the receiver can find the moving target according to the Doppler shift between the reflected signal and the transmitted signal, and determine its radial velocity.
Wall type microwave detector Wall type microwave detector is a microwave detector that utilizes the principle of field interference or beam blocking principle to separate microwave receiving and transmitting equipment. The microwave transmitter has a microwave oscillation source, usually adopting the pulse debugging mode, and uses the antenna to transmit and modulate the microwave beam. The microwave signal received by the microwave receiver is sent to the alarm control circuit after signal processing such as amplification and detection. When there is no shield between the receiver and the transmitter, the detected signal has a certain intensity; when an obstruction occurs between the receiver and the transmitter, the microwave received by the receiving antenna is damaged due to the normal propagation of the microwave. The signal strength is weakened, so it is possible to use the strength of the signal received by the microwave receiver to determine whether it is an intruder again.
Shuangjian detector Shuangjian detector generally refers to passive infrared plus microwave simultaneous detection to reduce false alarms. The main principle is to use the Doppler effect of the microwave, that is, the probe actively emits microwaves and reflects back on the object. If the object is stationary, the reflection frequency is constant; if the object is moving, the frequency of the reflection will change, and the probe will compare the microwave received with the frequency of the emitted microwave to make a correct judgment. When both infrared and microwave signals are generated, an alarm is triggered. In areas where the environment is relatively harsh, such as aisles, factories, warehouses, etc., it is easy to wind up to trigger passive infrared, and the flowing air does not reflect microwaves, so no false alarms will occur, thereby greatly reducing false alarms caused by environmental factors. When installing, avoid interference of nearby metal objects with microwaves. Fluorescent lamps reflect microwaves and cause interference, so filters must be used to filter out interference from reflected waves.
Laser Invasion Detectors Laser detectors are similar to active infrared detectors in that they consist of transmitter and receiver. The transmitter emits a laser beam that impinges on the receiver. When an intruding target appears on the cordon, the laser beam is blocked and the receiver's receiving status changes to generate an alarm signal.
A laser transmitter is set up at the beginning of the protection zone, and the directional strong laser beam emitted by it is directed towards the receiver. The receiver converts the received optical signal into a digital signal through an optoelectronic device and is processed by the microcontroller. When the confirmation signal is normal, all the indicator lights are off, and the monitoring state is maintained. When the light beam is interrupted, the signal is abnormal and the indicator light is on at the same time, and the alarm signal is output at the same time, so as to realize the full-distance monitoring of the laser light path.
Compared with similar active detectors, laser intrusion detection systems have significantly increased their adaptability to harsh climate conditions. The laser beam has a large emission power density, a small divergence angle, a concentrated beam, and a good directivity. Under the condition of using the same power device, the power density of the receiver beam is several hundred to several thousand times that of the infrared receiver. Therefore, under the same climatic conditions, the transmission attenuation of laser is much smaller than that of other similar detectors, and the ability to penetrate rain and fog is strong. The detection distance can reach several hundred meters to several kilometers, which greatly reduces the false alarm caused by the climate.
Anti-theft alarm intrusion detection technology
Intrusion detectors are devices consisting of sensors and signal processors that are used to detect the intruder's intrusion of electronic and mechanical components. Classification of intrusion detectors can be classified into switch-type intrusion detectors, vibration-type intrusion detectors, sound detectors, ultrasonic intrusion detectors, infrasound detectors, active and passive infrared intrusion detectors, and microwaves depending on the characteristics of the sensors used. Intrusion detectors, laser intrusion detectors, video motion intrusion detectors, and multiple technology composite intrusion detectors. It can also be divided into point-type intrusion detectors, linear intrusion detectors, surface intrusion detectors, and space-based intrusion detectors.