The System Study And Design Of Active Infrared Intrusion Detection

The intrusion detection technology in security guarding falls into two types, i.e. active detection and passive detection. Common active detection technology is based on light curtains structure, which is simple and reliable, but in need that the emission and receiving units have to be detached. It is not convenient for quick arming since the wire settings are restricted by environment. While common passive detection technology such as pyroelectricity far infrared detectors offer the advantages like easy installation and good elusiveness but it is easily influenced by environment temperature. The detector often falls invalid when the object temperature approaches environment temperature. The detection distance has relationship with the thermal radiation intensity of detection targets, which makes it very uncertain while used in complex environments. Therefore, a novel detection mode has to be developed to overcome the inadequacies mentioned above.Active infrared protecting media takes remarkable advantages over other detection media in circumference intrusion detection applications with characteristics like invisibility, irrelevance between environment and object, harmlessness to human body. And the additional advantages like light weight and low power dissipation, make it common detection media in security technologies.The operating principle of infrared intrusion detection system is introduced. And a design scheme of active infrared detection system is proposed on questions that passive infrared intrusion detectors can be easily influenced by weather, background, distance and body emissivity. Simulations and basic application researches are conducted. This scheme integrates the common active and passive detection, and can be used for civil security as well as auxiliary defence of army vigilance. Seen from his own working experiences, many important places in troops such as weapon rooms, ammunition depots, oil tanks and external roads are mainly guarded by guardsmen, which makes it hard to avoid carelessness and bugs. If the utility of electronic guarding technologies such as active infrared intrusion detectors are introduced, lawbreakers will be prevented to snatch weapons and ammunition, and produce terrorist incidents. And active impulsion and facilitation can be achieved in increasing border control range, expanding control space, shortening the handling time after dangerous omens are detected and enhancing the quick reaction ability of troops. Main works in this thesis include:1. The scheme of active infrared detection system applicable to complex environments is proposed, whose working wavelength lies in near infrared band. And corresponding infrared optical system is designed.2. Pulsatory current driven light source technology is used in reflective infrared detector in concrete circuit. The pulsatory current driven mode have the advantages like far detection range, strong anti-interference, greatly dropped power dissipation of infrared emission tube over traditional mean current driven mode. NE555 chip is used to design multivibrator and the frequency of emission pulses required are met by adjusting parameters of exterior capacitance and resistance, which works better than writing programs with the clock function of MCU. Design method of the driver of infrared camera system is also proposed.3. The self-adaptive technology based on the duty ratio tuning is studied. The emission power from infrared emitting diode is in proportion to peak impulse current, which is in turn somehow tied into the duty ratio of emission pulse. The 74LS04 inverter is used as trigger switch and the duty ratio of emission pulse is changed by adjusting the resistance value of variable resistance of multivibrator, which is fulfilled by MCU.4. Since the infrared signal received by infrared detector is very weak and vulnerable to the external and systematic noise, high-precision, low-noise and small drifting analog amplifying circuit is used to transform the light current outputted by detector to voltage signal, which is roughly disposed by band-pass filtering in filter circuit, the interference and noise signal partly suppressed and removed. The alternating signal then goes through phase sensitive detection in lock-in amplifier circuit, noise greatly restrained and detectivity and SNR efficaciously increased. Finally, the signal is sent into the MCU controlled system by A/D circuit.5. The hardware and software in this system are subject to experimental testing and simulation and the error analysis of the signal waveform is committed. Corresponding solutions specific to some existing problems are presented.