Basic introduction of infrared detector
A proximity detector (sensor) is a detection device that can trigger an alarm when an intruder approaches it. In the proximity detector, there is usually a high-frequency LC oscillating circuit. The LC circuit of the oscillating circuit is connected to the external metal parts through wires. When the human body approaches, the electromagnetic resonance of the space will change the resonance frequency of the LC circuit, causing the oscillation frequency to change. The detection circuit of the detector can recognize this frequency change and issue a warning signal.
Proximity detectors are more suitable for indoor use, such as providing protection for writing desks, file cabinets, safes, and other special objects, as well as protecting doors and windows. Usually the object to be protected is metal, which can actually form part of the protection circuit, so as soon as someone tries to damage the system, an alarm will be triggered immediately.
The main advantages of the proximity detection system are its versatility and versatility. It can be used to protect almost any object and will not be excited by interference a few meters away. Once someone approaches or touches a jewelry box, file cabinet, door or window to prepare for theft, an alarm will be triggered, but normal business work in the vicinity can proceed as usual.
The circuit design of the proximity detector needs to pay attention to several key technical points: â‘ frequency selection, the frequency is too low, the detection sensitivity is low, and the high is easy to produce false alarms, and the frequency point of the radio should be avoided as much as possible; â‘¡ the power consumption should be small , Proximity detectors are sometimes made into a small portable alarm, need to use battery power, and the use of battery power is also helpful to improve the anti-interference ability of the circuit, reduce false alarms; â‘¢ LC resonant frequency of the oscillatory circuit, will also be affected by the external environment Factors (such as temperature and humidity), so it is meaningless to detect the slow change of the oscillation frequency. It should detect the sudden change of the oscillation frequency. Only the "abrupt" oscillation frequency is related to the possible robbery.
Motion / shock detector The sensor that the machine can detect the position of a fixed object being moved is called a motion detector. In fact, movement is ubiquitous, the earth is rotating, and everything on the earth is "moving". What we want to detect here is actually relative movement. For example, the objects placed on the desktop are removed from the desktop, and the parked vehicles are Started or moved, etc.
The mobile detector material is most suitable for the protection of valuable and confidential special objects such as file cabinets and safes, and is also suitable for use in combination with other systems to prevent thieves from breaking into the wall. The effectiveness of the motion detector is closely related to the correctness of the application. It is often used to provide protection for special objects with people in the protected area under normal circumstances.
To detect the movement of a vigilant object, we must find the physical quantity changes that can be generated by the movement. At least there are: mechanical methods, optical methods, electromagnetic methods, vibration detection methods. Active light intrusion detector light travels in a straight line, so it is called "ray" If the propagation path of light is blocked, the light is interrupted and the light cannot continue to propagate. Active optical intrusion detector is to use the linear propagation characteristics of light for intrusion detection. It consists of an optical transmitter and an optical receiver. The receiver and transmitter are installed separately. An optical warning line is formed between the transceiver and the intruder crosses the warning. When the line is blocked, the light is blocked, and the receiver loses light and emits an alarm signal.
In general, infrared radiation outside the visible light spectrum is selected as the light source of the transmitter, so that intruders cannot detect the presence of warning light. In order to avoid interference from natural sunlight, two technical measures are usually adopted:
â‘ Add a color filter on the light receiving window of the receiver to filter other light;
â‘¡Amplitude (intensity) modulation of the transmitter light, the specific method is: use infrared light-emitting diodes as the light-emitting device of the transmitter light source, and use a modulation signal with a frequency of several KHz to carry out the voltage or current of the power supply of the transmitter light source Modulation, so that the intensity of the light emitted by the transmitter also changes according to the law of the modulated signal. In the receiver, the infrared receiving diode is used to receive the optical signal, and the frequency-selective amplification is performed on the signal by an amplifier with a tuning loop, so that the interference of other signals with different frequencies from the modulated signal can be filtered out, and the sunlight is not subject to any modulation Of the stable light, the signal it produces on the receiving diode is naturally filtered out without a response.
Passive infrared detectors use the physical principle of "black body radiation": as long as the temperature of an object is higher than absolute zero, it will continuously radiate light around, and the wavelength of the radiated light is related to the temperature of the object. The human body can emit far-infrared rays at normal body temperature and cannot see it with the naked eye, but this kind of far-infrared rays can be detected by infrared sensors, so intruders can be detected. The core component of this type of detector is a pyroelectric infrared detection element. It is equipped with a "Phenel" lens made of transparent plastic, which can monitor a certain spatial range. It is easy to install, has high sensitivity, and does not require an auxiliary light source. It consumes less power and has a relatively low cost, so it is now a popular electronic security product component.
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