Q: Generally speaking, there is a rule when choosing and installing an intruder, namely, 'passive indoor use, active outdoor use'. Is this a universal matching principle?
A: The so-called passive and active are distinguished by the detection means of the detector. A passive infrared detector is a detector that uses a pyroelectric sensing element (PIR element) as the main detection means. The alarm is triggered by a temperature change in the detection range. Usually, a three-dimensional area is sensed, and the general ambient temperature in the room is constant. When there is an intruder, the detector will sense the difference between the human body temperature and the background temperature and alarm, while the outdoors due to the unstable ambient temperature, if you use an ordinary passive detector will cause a great false positive rate. The range of detection of passive infrared detectors is 120 degrees left and right, and 75 degrees up and down. Its detection range is wider than that of active infrared detectors. It is usually installed in a room or hall.
Active infrared detectors generally refer to photoelectric detectors. These detectors always consist of a photo-emitting end and a photo-receiving end. The transmitting end emits an infrared beam that is invisible to the human eye, and the receiving end receives the infrared beam. Energy, it is always used in pairs: one launch, one receive. When someone traverses the surveillance zone, an invisible infrared beam is blocked and an alarm is triggered. The ambient temperature has little effect on it. As mentioned earlier, the detection range of a passive infrared detector is a three-dimensional space. Relatively speaking, the detection range of an active infrared detector can be described as a surface. It is mainly installed on windows, fences, and important entrances and exits. Its detection range is Only between the emitter and the receiver is an alarm triggered when someone or object passes through it. Due to the detection efficiency, range and cost in the room, active infrared detectors are rarely used.
Q: There are still dead angles when the active infrared detector is used for perimeter protection. How to solve this problem?
A: Due to the problem of the active infrared detector itself or the geographical environment of the detection area, there may be some small areas or small dead angles that cannot be completely sealed by the radiation detector. This brings certain hidden troubles to the security system and reduces the entire area. System reliability. Like the barrel effect, the entire security rating is determined by the weakest link in the system. Therefore, in order to solve these weak links, it is very necessary to use some outdoor curtain detectors to seal the corners.
Q: Since the PIR detector is a kind of weak signal detection device, some details of the installation may directly affect the detection effect of the detector. Then what are the requirements on the angle and height when installing it? What are the places that are not suitable for installation?
A: To a large extent, the sensitivity, detection range, and installation height of the detector are directly related to each other. The optimal installation height of a typical passive infrared detector is 2.1 to 2.5 meters. If it is a pet-proof detector, then it is Mounting height requirements will be higher. If the installation is too high, the blind spot will be large. If it is too low, it may not be able to detect the far position. Therefore, the actual application also needs to be measured. For example, a curtain detector that belongs to the principle of passive infrared, if it needs to be installed on a window, the installation height at this time is 25CM from the window sill. If it is too high, people can drill it from under the probe if the distance is too low. May be crossed from above.
The principle of passive infrared is to monitor the temperature difference. When the outside temperature is about 37 degrees, it basically fails, so do not install near the heat source. In addition, it is necessary to pay attention to avoid fluidity areas such as vents, air conditioners and radiators that can change the ambient temperature, and also to block the shielding of the middle shield (even transparent glass, for example). Also, avoid moving objects such as fans, drying clothes, and curtains. Places where animal activity is frequent should also be avoided. If it is difficult to avoid the actual needs, then special attention should be paid to using a pet-proof detector.
Q: What are the rules for the installation of active infrared detectors?
A: The installation of the active infrared detector has some common sense installation specifications according to the specific conditions of the human body. For example, if a human invades, the invasion distance will be greater than 20cm regardless of whether it is horizontal or lateral. Therefore, the installation height should not be lower than the minimum. 20cm; In the case of arc-type corners, the distance from the tangent to the arc shall not be greater than 20cm; when mounted on the fence, the distance between the edge of the fence and the center of the detector shall not be greater than 20cm. In addition, active infrared detectors require that the mounting bracket is stable and firm, and there should not be shaking. A slight deviation may cause the detector to fail. At the same time, there should not be sheltered branches and weeds in the detection range, so as to avoid causing too many false alarms. . There is also a need to consider the linearization of its detection, which is difficult to shape for some complicated and varied shapes.
Q: The detection distance of the active infrared detector determines its detection area. The nominal distance and the actual working distance of the general manufacturer do not match. How to determine the optimal installation distance?
A: 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. This is also reasonable, but if the error is too large, it is the quality of the product itself. Manufacturers mark the working distance in the best weather conditions, but it is actually difficult to achieve such conditions, even if it does not last for a long time. Therefore, in a stable environment, the detector's detection distance can also reach the manufacturer's nominal distance, and sometimes the detection distance will be much higher than the nominal distance. However, under actual circumstances, the outdoor environment is an unstable environment. In particular, the rain and fog will cause the loss of infrared light energy. At this time, the nominal distance is often not reached. Therefore, in practice, it is often installed in accordance with 50% to 70% of the nominal distance of the manufacturer. Therefore, the actual measurement is the most critical when selecting the anti-theft product.
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