Procurement and installation Intrusion detector There are the following ten common questions:
Question 1: Generally speaking, when selecting and installing Intrusion detector There is a rule that is "indoor passive, outdoor active". Is this the general selection principle of intrusion detectors?
Answer: The so-called passive and active are distinguished by the detection means of the detector. Passive infrared detector refers to a detector with pyroelectric sensing element (PIR element) as the main detection means. The alarm is triggered by the temperature change within the detection range. Usually, it senses a three-dimensional area, while the indoor general ambient temperature is constant. When there are intruders, the detector will sense the difference between the human body temperature and the background temperature and give an alarm, However, due to the unstable ambient temperature outdoors, the use of ordinary passive detectors will cause a large false alarm rate. The detection range of the passive infrared detector is 120 degrees from left to right and 75 degrees from top to bottom. Its detection range is much wider than that of the active infrared detector. It is generally installed in the room or hall indoors.
Active infrared detectors generally refer to photoelectric opposite detectors. Such detectors are always composed of a photoelectric emitter and a light receiver. The emitter emits an infrared beam invisible to the human eye, and the light receiver receives the energy of the infrared beam. It is always used in pairs: one emits, one receives. When someone crosses the monitoring and protection area, the invisible infrared beam will be blocked and an alarm will be triggered. The ambient temperature has little impact on it. Just mentioned that the detection range of the passive infrared detector is a three-dimensional space. Relatively speaking, the detection range of the active infrared detector can be described as a plane, which is mainly installed in windows, walls and important entrances and exits. Its detection range is only between the projector and the light receiver. When people or objects pass through its middle, an alarm will be triggered. Active infrared detectors are seldom used indoors due to the problems of detection efficiency, range and cost.
Question 2: When the active infrared detector is used for perimeter protection, there will still be dead angles. How to solve this problem?
Answer: Due to the problems of the active infrared detector itself or the geographical environment of the detection area, there will be some small areas or small dead corners that cannot be completely sealed with the opposite radiation detector, which will bring certain hidden dangers to the security system and reduce the reliability of the entire system. Like the cask effect, the whole security level is determined by the weakest link in the system. Therefore, in order to solve these weak links, it is necessary to select some small curtain detectors for outdoor use to seal dead corners.
Question 3: Since the passive infrared detector is a weak signal detection equipment, some details during installation may directly affect the detection effect of the detector. So what are the requirements for angle and height during installation? What is not suitable for installation?
Answer: To a large extent, the sensitivity and detection range of the detector are directly related to the installation height. Generally, the optimal installation height of the passive infrared detector is 2.1 m to 2.5 m. If it is a pet proof detector, it will have higher requirements for the installation height. If it is installed too high, the downward blind area will be large, and if it is too low, it may not be detected for the remote position, so it is also necessary to step measurement in practical applications. For example, if the curtain detector, which belongs to the passive infrared principle, needs to be installed on the window, the installation height is 25cm from the window sill. If it is too high, people can drill under the detector, and if it is too low, people can cross from above.
The principle of passive infrared is to monitor the temperature difference. When the external temperature is about 37 degrees, it basically fails, so it should not be installed near the heat source. In addition, attention should be paid to avoiding the opening of air holes, air conditioners, radiators and other fluid areas that can change the ambient temperature, as well as the shielding of the middle (even transparent, such as glass). Also, avoid electric fans, clothes to hang in the sun, curtains and other objects that are easy to move. Places with frequent animal activities should also be avoided. If it is difficult to avoid them in actual needs, special attention should be paid to the use of anti pet detectors.
Question 4: What are the regulations for the installation of active infrared detectors?
Answer: There are some common sense installation specifications for the installation of active infrared detectors according to the specific situation of the human body. For example, if a person invades, the invasion distance will be greater than 20cm whether it is across or sideways, so the installation height should generally not exceed 20cm; When encountering an arc wall corner, the distance between the tangent line and the arc shall not be greater than 20cm; When installed on the fence, the distance between the fence edge and the center of the detector shall not be greater than 20cm, etc. In addition, the active infrared detector requires that the mounting bracket be stable and firm, and there should be no shaking. A slight deviation may lead to the failure of the detector. At the same time, there should be no blocked branches, weeds, etc. within the detection range, so as to avoid too many false positives. In addition, it is necessary to consider the linearization of its detection, which is difficult to shape some complex and changeable areas.
Question 5: The detection range of the active infrared detector determines its detection area, but the nominal distance of the general manufacturer does not match the actual working distance, so how to determine the best installation distance?
Answer: Due to the defect of infrared technology, there is a certain error between the measured distance and the nominal distance when the active infrared detector is used for perimeter protection, which is also reasonable. However, if the error is too large, it is the quality of the product itself. The manufacturer's indication is the working distance under the best weather conditions, but in fact it is difficult to reach such conditions, and even if it does, it will not last for a long time. Therefore, in a stable environment, the detection distance of the detector can also reach the nominal distance of the manufacturer, and even sometimes the detection distance is much higher than the nominal distance. But in reality, the outdoor environment is an unstable environment, especially in rainy and foggy days, which will cause great energy loss of infrared light, and the nominal distance is often not reached. Therefore, in practice, it is often installed according to 50% to 70% of the nominal distance of the manufacturer. Therefore, when selecting the anti missile products for anti-theft, actual measurement is the most critical.
Question 6: At present, the commonly used detectors are wired. If they are installed indoors, there are many circuits such as TV, audio, lighting and so on. How can these circuits not affect the normal work of the detector? In addition, there is a certain distance between the lines of the detector and the host. How can we protect these lines from being cut?
solution Answer: General detectors generally adopt four wire system, in which two wires are power supply (generally DC12V) and the other two wires are signals (generally NO/NC switching value signals). According to the engineering specifications, strong current and weak current should be routed separately, and the signal line of the detector is the switching value signal itself, which is not easily affected by environmental interference, so TV, audio, lighting and other lines will not be affected. Also, during installation, do not install it together with strong current and electrical appliances that can generate strong magnetic fields, and do not connect the lines with strong current lines.
Whether indoor or outdoor, there is a certain distance between the wire alarm detector and the host circuit, so the protection of the detector circuit is particularly important. At present, detectors generally have shear prevention function. For the protection of connecting lines, on the one hand, according to the grade of the project, they can be protected through steel pipes, PVC pipes, cable trays or buried; On the other hand, an easy way to prevent the line from being cut is to connect the line end resistance. Every regular manufacturer's host has this function. In addition, the defense detection circuit of qualified alarm host will respond to the cutting of the line. Once the line is cut, the host will think that the detector is in an abnormal working state.
However, according to the current development status of security, it is not enough to only have the shear prevention function. Because with the open operation of the security industry, internal theft or technical crimes are increasing year by year, only detectors with self-protection function can better protect others.
Question 7: Active infrared working devices are mainly lenses at the transmitting and receiving ends. What problems are likely to occur when they are adjusted?
Answer: If these two lenses are not adjusted correctly, the direct result is that they deviate from the central area, resulting in poor reception.
The adjustment of the active infrared detector should generally be based on the voltage output value of the optical receiver. Observe the output voltage of the optical receiver by fine tuning the deflection angle and vertical angle of the lens. The higher the voltage, the more accurate the detector is, and the lower the false alarm rate. Generally, the radiation detector will have a minimum output voltage index. The current radio is relatively simple in installation and debugging. As long as it is correctly installed according to the installation method provided by the manufacturer, it will not cause problems in general.
Question 8: Sensitivity is the most direct factor affecting the false alarm rate or false alarm rate of the detector. How to adjust the sensitivity so that the false alarm rate and false alarm rate can reach the ideal effect?
Answer: In conventional detection technology, sensitivity is a contradiction between false positives and false positives. Adjusting sensitivity to reduce false positives will inevitably lead to an increase in false positives; On the contrary, increasing sensitivity to reduce false positives will lead to an increase in false positives. It is difficult to accurately grasp this "degree" in practical application.
The specific setting of sensitivity shall be determined according to the actual environment. Generally speaking, if the application environment is relatively harsh, such as birds or leaf floaters that often block the beam, it should be set at the low sensitivity gear. The active infrared detector should choose the appropriate response time: too short is likely to cause unnecessary interference, such as birds flying over, small animals passing through, etc; If it is too long, it will fail to report. The minimum shading time is usually determined at a speed of 10 m/s. Sometimes due to seasonal changes, the sensitivity should be adjusted separately in winter and summer.
Question 9: At present, there are two beam infrared detectors and four beam infrared detectors. Is the more beams, the better the detection effect?
Answer: Four beam detector means more stability, lower false alarm rate and stronger ability to adapt to the environment. It also means the increase of cost, which is generally used in long-distance environment (nominal distance exceeds 100 meters). The more light beams, the better the detection effect. It depends on where they are used. If the place is small, we need to use less light beams to reduce its false alarm rate. If the place is large, we need to use more light beams to reduce its false alarm rate.
The main purpose of the multi beam detector is to prevent false alarm, because its principle is to cover all the beams before giving an alarm. From this point of view, as long as it is more than two beams and detects objects within the range of the human body, it has nothing to do with the number of beams, but only with the coverage area of the beam. Of course, at present, some products are regarded as infrared barriers for application, which is due to the consideration of combining multiple beam detectors.
Question 10: The dual detector utilizes the dual technology of infrared and microwave, which reduces the false alarm rate and improves the accuracy. But since the microwave technology itself can penetrate walls and other obstacles (as well as its shielding to metal), will the stability and reliability of the dual detector be greatly affected?
Answer: The microwave detection range of the dual detector is generally wider than that of the passive infrared detector. Generally, the dual detector of manufacturers is equipped with a microwave range adjustment knob. During the commissioning process, the indicator light of the detector is observed by walking test, Make the microwave range as indoor as possible and close to the detection range of passive infrared through the microwave range adjustment knob and the angle of the mounting bracket. The microwave sensitivity must not be too large, because the microwave only has penetrability, and attention should be paid to when debugging.
Will microwave technology affect the stability and reliability of the detector itself? It is understood that the answer is of course no. Some manufacturers have also done a lot of useful work in this regard: such as increasing the frequency (its K-band frequency is 2-5 times of other commonly used microwave frequencies) to reduce leakage; Improve the shaping degree of microwave, use special waveguide shaped antenna to make microwave and infrared highly composite, and further reduce the microwave energy leaked outside the protection area.
Wuxi Dehang Technology Co., Ltd. provides professional IT services, Wuxi broadcast system, Wuxi projector installation, monitoring engineering, network maintenance, Wuxi Security Monitoring , Wuxi remote monitoring , Wuxi Monitoring , Wuxi cabling project, Wuxi monitoring and installation company, Wuxi LAN cabling, Wuxi IT outsourcing, Wuxi network maintenance, Wuxi generic cabling system, Wuxi generic cabling company, Wuxi monitoring and installation company, Wuxi The server Wuxi generic cabling company, generic cabling system, surveillance camera, we have professional scheme design engineers and professional construction team, and we will make every effort to meet customer requirements and ensure project quality.
