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technology principle of Security alarm system

1、 Summary of anti-theft alarm system


Simple alarm system consists of front-end detectors, intermediate transmission part and the alarm host. Detector and alarm host can be seen as a front-end part for large alarm system, the transmission part is from alarm host to alarm receiver, center alarm receiver and computer are seen as back-end part.

2、 Anti-theft security alarm system as per data transmission mode:    

 According to different data transmission mode, it can be divided into wired and wireless between detector and host. Also the connection between the host and CMS it can be divided into 2 kinds, wired and wireless, of which the wired system still can be divided into 2 types, transmission based on telephone line and transmission based on bus line. Wireless is transferred by GSM.

3、Types and working principle of detector

As per the installation of detector, it can be divided into: wall-mounted, ceiling and   surface mounted

As per the detecting range of detector, it can be divided into: wide angle, curtain and all-directional.

As per the detecting principle and working mode, it can be divided into: infrared,    microwave, infrared microwave combination, vibration, smoke, gas, glass break,  ultrasonic, etc. The infrared detector also can be divided into active and passive.  Smoke detector can be divided into ionic and photoelectric.

1)、Active infrared detectors: consist of infrared transmitter and infrared receiver. Infrared transmitter emits a beam or multiple beams infrared light which were modulated to infrared receiver. When there is no any obstruction between transmitter and receiver, the alarm will be not triggered. When something shades, the receiver output signal changes, then detector alarms.

2)、Passive infrared detector: there are 2 key elements, one is a Fresnel lens, the other is a Pyroelectric sensors. Any objects in nature that higher than absolute temperature(- 273 o) will generate infrared radiation, objects with different temperature release different wavelength of infrared energy. Human body has a constant body temperature, different from the surrounding environment. When human moves, this variety of the difference can be detected by the pyroelectric sensor through Fresnel lens, thus output the alarm signal.

3)、Microwave detector: adopt Doppler effect theory. In the microwave range, when sending in a frequency, the emitted microwave met a fixed object, the reflected microwave frequency will not change, that’s f(T) = f(R), and the detector will not send the alarm signal. When the emitted microwave met a moving object, the reflected microwave frequency will change, that’s f(T) f(R), microwave detector will send out the alarm signal at this time.

4)、Vibration detector: vibration detector detect an intruder who is doing various sabotage  and regard as its vibration signal according to alarm, for example, when an intruder is drilling the wall, drilling holes, destroying the ATM, prying safety box and doing such kinds sabotages, it can cause the vibration of these objects. To trigger the alarm detector with the vibration signal is called a vibration detector.

5)、Dual infrared detector and Quad infrared detector: Integrate into 2 pyroelectric     sensors which with same performance and contrary polarity, this detector with 2   detecting sources is dual infrared detector. Likewise, integrate into 4 pyroelectric sensors    which with same performance and contrary polarity, this detector with 4 detecting sources is quad  infrared detector.

6)、Dual tech detector: to overcome the defects of single tech detector, usually will    integrate into 2 different technology theory, only when the two detection technologies detecting the human moves can it alarm, this detector called dual tech detector. The common dual tech detector on the market is microwave + passive infrared.

7)、Triple tech detector and quad tech detector: the triple detector jus a publicity stunt for some domestic manufacturers and sellers, take the microprocessor technology as a detecting mode. In fact, this is only a detector with three technology. If it is triple tech, then infrared microprocessor pet immunity anti-masking anti-fake can be called six tech? The real triple tech detector have to possess 3 kinds of detecting technology, such as: passive infrared + microwave, ultrasonic detector.

4、technology theory of infrared detector


Take passive infrared alarm detector and active infrared alarm detector as an example

Passive infrared detector

1)Temperature and infrared: under the condition of room temperature, any objects have radiation. The higher temperature for object, the stronger radiation for infrared. Human are warm-blooded, infrared radiation is the most stable. We called the passive infrared, that is to say, the detector itself will not emit any energy detector, but only passively to receive and detect the infrared radiation from the environment, to detect infrared radiation from the environment. Detector adapts to the environment after installed for several seconds, when no human or animal access into the detection area, the infrared radiation on-site is stable, once human infrared radiation get in, the pyroelectric elements will generate the abrupt electrical signal via optical system focus. Thus send the alarm. The cordon which formed by passive infrared intrusion detector can reach tens of meters.

2)The composition of the passive infrared detectors mainly is composed of optical  system, thermal sensor (or called infrared sensor) and alarm control and so on. Its core is invisible infrared detecting element, it can detect the radiation changes in a 3D protecting space via synergism of the optical system. The detecting wavelength range of the infrared sensor is 8 ~ 14μm, infrared peak wavelength of radiation for human body is about 10μm, just within the range.

3)Type and application scope of passive infrared detector:


According to its different structures, the alert area and detecting distance is also different, which can be roughly divided into two kinds: single beam type and multi-beams type. Single beam PIR adopted the reflective confocal optical system, using the planar reflective mirror to piece the infrared radiation from the target into the infrared sensor. The viewing angle for this type detector is narrower, generally under 5 °, but active distance is longer, can up to hundreds of meters. Therefore, it is also known as straight line control passive infrared detector, suitable for protecting a long and narrow corridor, gallery and blockaded doors windows and walls.

The alert scope shows multiple single beam state in different directions, form a 3D fan-shaded hot areas, from top to bottom is divided into several rows, constitute a 3D alert. The above lens are more, bottom are less. As the infrared radiation from face, knees, arms is stronger, just face toward the above lens. Bottom lens are less, one reason is the infrared radiation from lower part of human is weaker, second is to prevent from interfering by the infrared radiation from the small animals.

Multi-beams PIR alert viewing angle is much bigger than the single beam, level   angle can larger than 90 °, and the biggest vertical angle can reach 90 °, but    active distance closer. All the lens focus to the internal pyroelectric parts, so the   sensitivity is higher, it will alarm as long as people walk inside the lens viewing   scope. Infrared penetration is poor, in protecting area should not have tall objects, otherwise it won’t be able to alarm when someone moving in shadows, don't over against the heat source and the highlight source, especially air condition and      heater. Otherwise constantly changing steam flow will cause false alarms. To solve the problem of objects masking, we invented the ceiling passive infrared intrusion  detector. Installed on the ceiling face down 360 ° to alert, as long as inside the   protecting scope, it will trigger the alarm no matter intrude from which direction, it  is widely used in the bank business hall, public activity area in supermarket and  such kinds of larger space.

-font-q~ l:�] 0�` o-fareast-theme-font: minor-fareast;mso-hansi-theme-font:minor-latin;mso-bidi-font-family:"Times New Roman"; mso-bidi-theme-font:minor-bidi;mso-ansi-language:EN-US;mso-fareast-language: ZH-CN;mso-bidi-language:AR-SA'>m, infrared peak wavelength of radiation for human body is about 10μm, just within the range.

4)Characteristics of the passive alarm detector: due to the good detecting performance, easy arm, cheap price, thus it is widely used. Its weakness is higher false alarm compared to the active detector.


active infrared detector:

Active infrared detector is composed of infrared transmitter, infrared receiver and alarm controller. Generally the optical system build-in transmitter and receiver adopts the optical lens. It plays on a role that an infrared beam can be focused into a thinner parallel beam, so that the infrared energy can be delivered intensely. Infrared in the spectrum scope that people cannot see, if someone walks through the invisible lines, the whole infrared light or segments must be covered. Therefore the signal strength of receiver output will change, thus start the alarm controller to send out alarm signal. Active infrared detector should not alarm when met small animals, leaves, dust, rain, snow, fog, it will alarm when met human or objects with equivalent volume. Due to the narrow beam, installation for transmitter and receiver have to be solid and reliable, and should not be affected by the ground vibration to cause the displacement and lead to a false alarm, optical system have to be kept cleaning and maintaining.