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The simple alarm system consists of a front-end detector, an intermediate transmission section, and a control panel. Larger systems can also regard the detector and the control panel as the front-end part, and the transmission part is from the alarm host to the alarm receiver. The central alarm part is regarded as the back-end part.
2, the alarm system according to the different information transmission methods, which can be divided into several?
According to different information transmission methods, there are two kinds of wired and wireless between the detector and the host. From the host to the central alarm can also be divided into two kinds of wired and wireless, which cable system can be divided into two types based on the phone line transmission and bus-based transmission.
3, which types of detectors are divided into? What are the common types on the market?
Infrared, microwave, vibration, smoke, gas, glass breakage, pressure, ultrasonic and so on. The infrared detector can also be divided into active infrared and passive infrared. Smoke can be divided into ion and photoelectric type. There are common infrared detectors (passive infrared), on the radio, fences (active infrared), double Kam detectors, vibration detectors, glass break detectors.
4. How does active infrared detector work?
The active infrared detector consists of an infrared transmitter and an infrared receiver. The infrared emitter emits a beam or a majority of the modulated infrared light toward the infrared receiver. When there is no obstruction between the transmitter and receiver, the detector will not alarm. When an object is obstructed, the receiver output signal changes and the detector alarms.
5. How does a passive infrared detector work?
There are two key components in the passive infrared detector. One is a Fresnel lens and the other is a pyroelectric sensor. Any object above the absolute temperature (-273o) in nature will produce infrared radiation, and the wavelength of infrared energy released by objects at different temperatures will also be different. The human body has a constant body temperature and differs from the ambient temperature. When the human body moves, this change in the difference is detected by the pyroelectric sensor through the Fresnel lens, thereby outputting an alarm signal.
6. How does a microwave detector work?
Microwave detectors use the principle of Doppler effect. In the microwave section, when transmitting at a frequency, when the emitted microwave encounters a fixed object, the frequency of the reflected microwave is not changed, ie, the signal is sent out and the detector does not send an alarm signal. When the microwave that is launched meets a moving object, the frequency of the reflected microwave will change, that is, the microwave detector will send an alarm signal.
7. What is a dual infrared detector? What is a quad infrared detector?
A detector that integrates two pyroelectric sensors with the same performance and opposite polarities is a dual detector. The four-element detector is a detector that integrates four pyroelectric sensors with the same performance and opposite polarities.
8, the role of Fresnel lens?
The Fresnel lens has 2 functions. One is to refract or reflect the infrared radiation of pyrolysis to the pyroelectric sensor. The other is to divide the detection area into several bright areas and dark areas. When the human body moves within the detection range, it will enter the Fresnel lens one by one. In the viewing zone, the pyroelectric sensor “sees†the moving human body for a while and then “sees†it, so that the human body movement can generate a continuously changing signal on the pyroelectric sensor in the form of a temperature change.
9. What is Shuangjian detector? What are the common Shuangjian detectors on the market?
In order to overcome the deficiencies of a single technology detector, two kinds of detectors with different technical principles are usually integrated together. Only when the sensors of the two detection technologies detect the movement of the human body are the detectors called alarm detectors. The common Shuangjian detector on the market is mostly microwave + passive infrared, and there are infrared + air pressure detectors and audio + air pressure detectors and other products.
10. What is Sanjian detector? What is a quadrant detector?
In order to further improve the performance of the detector, a detector that adds a microprocessor technology on the basis of Shuangjian detector is called Sanjian detector. The addition of a second technology detector to the Sanjian detector becomes a quadrant detector.
11. What is a shock detector?
Vibration detectors are used as an alarm basis to detect vibration signals generated by intruders performing various sabotage activities. For example, intruders can cause vibration of these objects when they perform wall-breaking, hole-drilling, and safe-breaking activities. A detector that triggers an alarm with these vibration signals is called a vibration detector.
12. What are the common vibration detectors? What is its working principle?
According to the different vibration sensors used, the vibration detectors can be classified into: mechanical vibration detectors, inertial rod electronic vibration detectors, electric vibration detectors, piezoelectric crystal vibration detectors, and electronic comprehensive vibration detectors. And other types. Recently, piezoelectric crystal vibration detectors are commonly used. The principle is to use the piezoelectric effect of a piezoelectric crystal. Piezoelectric crystal is a kind of special crystal, which can transform the mechanical force applied to it into a corresponding size electric signal. The frequency and amplitude of its electric signal are proportional to the frequency and amplitude of mechanical vibration, when the signal value reaches When the value is set, an alarm signal is issued.
13. How does a glass break detector work?
When the glass is struck and the glass is not yet broken, an ultra-low-frequency elastic vibration wave is generated. The mechanical vibration wave is lower than 20 Hz and belongs to the infrasonic wave. The loud and harsh sound produced by the broken glass is in the range of 10 to 15 KHZ, which is a high-frequency sound. When the detector detects both low frequency and high frequency sound frequencies, an alarm signal will be generated.
14. What is the detector standard output signal?
The detector standard output signal is a switch signal, normally open, normally closed, and normally open/normally closed.
15. What is temperature compensation?
In general, human body temperature is always much higher than the ambient temperature. When the intruder moves, the sensor receives a large amplitude of the infrared change signal and triggers an alarm. When the ambient temperature rises close to the human body temperature, the amplitude of the infrared change signal received by the sensor when the intruder is in motion is very small, so that it may be because the signal is less than the trigger threshold and no alarm is given.
Temperature compensation automatically increases the gain of the invader signal amplifier when the ambient temperature is close to the human body temperature, thereby keeping the alien intruder's signal from being captured, without affecting the sensitivity due to the ambient temperature.
15 knowledge of alarm system
1. What part of the alarm system consists of?