Recently, the Ministry of housing and urban rural development, together with 16 departments including the central office of information technology, the Ministry of education, the Ministry of science and technology, and the Ministry of industry and information technology, jointly issued the “guidance on accelerating the development of digital home and improving the quality of living”, which clearly pointed out that it is necessary to strengthen the construction of digital home engineering facilities, strengthen the setting of intelligent products in residential buildings, and improve the quality of new fully decorated residential buildings, It is clearly required to set up basic fire-fighting products including automatic fire alarm equipment indoors. As a part of fire protection, smoke sensing equipment is a compulsory supporting facility for new residential buildings. It is likely to be the first step for intelligent fire protection to move towards the rigid configuration of residential communities. It is expected to become the standard configuration of residential communities in the future.

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Fire fighting is not only to deal with the fire that has happened, but also to prevent and eliminate hidden dangers in advance. The smoke detector is such a key equipment, once there is a sign of suspected fire, it will send out a warning, to win time for fire fighting and escape“ However, according to the statistics of the American Fire Protection Association, 23% of the deaths come from places where smoke detectors are installed. This is because traditional smoke detectors are often unable to distinguish the types of smoke, which can easily lead to false positives and be stopped artificially, which eventually leads to tragedy. ” Zhu Zhen, marketing manager of ADI, pointed out at the 2021 Munich Shanghai Electronics Exhibition that “in addition, the traditional smoke sensing equipment still has some problems, such as too large volume, different specifications, difficult debugging and so on, and the smoke sensing equipment is facing the requirements of technological change.”

Behind the awkwardness of false alarm, the hidden danger of fire protection is highlighted, and the technology of smoke detection is changing at the right time

In the late night of a winter, the fire center of a smart town prompts the fire, and the smoke detection sound and light alarm system constantly prompts XX residents that there is smoke at home. Several phone calls failed to contact the owner. The property security guard has urgently found the owner’s home. When he comes home from the night shift, the owner who has just taken a bath looks at the fire alarm. After careful investigation with the owner, it turned out that the smoke detector in the corridor was misinformed because of the fog in the bath, and a fire ended with an embarrassing apology from the property. This is a real scene that Zhu Zhen shared with the industry at the exhibition“ Embarrassment is small and safety is big. This kind of false alarm led some owners to stop using smoke detectors. ” “More and more property owners are aware of the hidden dangers of traditional smoke detection equipment,” Zhu said

“The main defect of the traditional smoke detector comes from the use of monochrome LED as the measurement light source.” Zhu Zhen shares. The classic photoelectric smoke alarm is designed in a discrete way and works through forward scattering. The LED light of a specific wavelength (usually in the infrared range) is scattered by particles to the photodiode. If the dark light or extinction caused by particles between the light source (LED) and the detector (photodiode) is measured, it indicates that smoke enters the alarm.

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Forward scattering system with infrared LED

“The smoke detection device with this design can only distinguish the concentration of smoke, but cannot identify the type of smoke. Whether it is burning smoke, steam or cooking oil smoke, as long as the concentration reaches a certain threshold, the alarm will produce an alarm. Frequent false alarm interference is the primary reason for people to disable the smoke alarm.” Zhu Zhen pointed out. In order to solve this problem, some changes have taken place in the formulation of smoke detection related standards, hoping to promote the improvement of smoke alarm detection accuracy from top to bottom: the latest UL standard to be released in June 2021 will update polyurethane combustion, smoldering and cooking nuisance, namely hamburger smoke interference alarm test. In this test, it must be able to distinguish between the smog produced by hamburger patty and the smog produced by flammable polyurethane.

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In the on-site sensitivity detection of simulated water vapor interference, the traditional scheme gives an alarm quickly, while the ADI double light detection scheme has no false alarm

For this reason, ADI launched a fully integrated smoke detector module adpd188bi, striving to thoroughly solve these problems existing in the classic smoke alarm“ Adpd188bi integrates two LED emitters, a blue light emitter and an infrared emitter. So it can not only monitor the concentration of smoke, but also monitor the particle diameter of smoke, so as to distinguish normal smoke and fire smoke Zhu Zhen introduced. The wavelength of blue LED is 470 nm, and the wavelength of infrared LED is 850 nm. These LEDs emit light pulses in two independent time slots, and the emitted light is scattered back to the device by particles in the air. This method not only supports the measurement of single wavelength, but also supports the analysis of ratio composition, so as to further reduce the false alarm rate.

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Apdpd188bi test results of hamburger smoke and flammable polyurethane smoke in smoke-free room

As shown in the figure above, the two signal curves emitted by adpd188bi are very different in the two scenarios, indicating that the sensor can clearly distinguish the two types of smoke. It can be seen that the signal changes with time, the polyurethane reaches the alarm threshold after 220 seconds, and the time length is 1 / 4 of the hamburger smoke reaching the alarm threshold (after more than 1000 seconds). After burning for 4 minutes, the critical level can be detected. The high signal-to-noise ratio of the sensor can also be used to clearly distinguish and record the change of particle concentration. For example, the part circled in the right figure, in the flammable polyurethane test, the slope suddenly increases.

With high consistency, small size and low power consumption under full integration, all-round application implementation is promoted

The market is changing with each passing day. For manufacturers of smoke sensing equipment, they naturally hope that they can put into mass production as soon as they get the solution“ However, due to the fact that the traditional discrete solutions from sensing to signal conditioning and back-end data reading and analysis are completed by independent devices, it is difficult to achieve high product consistency, and product verification has become the main process. ” Zhu Zhen said, “adpd188bi is a complete light measurement system using optical dual wavelength technology for smoke detection. Each chip is calibrated separately before leaving the factory, and only a small number of external components are needed to realize commercial product design. The most significant benefit of this is that the consistency of product performance is very good. “

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Integrated optical design can greatly simplify the optical design and provide significant system enhancements

Under the fixed current, the luminous intensity of different LEDs is usually very different, so in the past, the calibration of smoke alarm was carried out by smoke alarm manufacturers. The slope and offset between LED luminous intensity and current can be calibrated to ensure that all LEDs maintain the same performance. In adpd188bi, because the LED and the whole signal path are integrated together, ADI will calibrate the sensor module in advance, which can reduce the difference between devices. In addition, the adpd188bi calibration coefficient is stored in the chip’s nonvolatile memory (eFuse register). By reading these coefficients, the difference between chips can be reduced as much as possible. This means that the alarm threshold can be set more accurately in the algorithm, so as to reduce the false alarm rate. Because smoke alarm manufacturers can use pre calibrated modules, the system design is simplified in this step.

Another significant advantage of high integration is that the overall circuit size is smaller, making the smoke detector smaller and more suitable for residential and commercial buildings. In addition, the smaller size and short pulse of LED make the power consumption of this module lower than that of traditional detector, and the power consumption of infrared LED is only ~ 5 μ W / Hz, the service life of the smoke sensor battery under this scheme can even reach more than 5 years, which significantly reduces the maintenance cost of the property in the later stage.

“In addition, adpd188bi can provide a complete optical subsystem solution for smoke detectors. As the whole solution is manufactured, tested and verified by Adi, the supply chain is simpler and the risk of customers can be greatly reduced.” Zhu Zhen added, “ADI also provides a smoke chamber with evaluation permission to solve the impact of ambient light, dust, insects, etc., and is fully suitable for adpd188bi’s integrated optoelectronic devices using the backscatter system.” It is worth mentioning that ADI has also developed smoke detector reference design and complete reference algorithm, including UL 217 test data setting and algorithm after design and testing to meet UL requirements, so as to speed up customer development cycle and reduce cost and project risk.

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This article summarizes

According to the consulting data of intelligent research, the market scale of China’s fire industry will exceed 350 billion yuan in 2019, and it is estimated that the market scale will reach 446.5 billion yuan in 2022. At the same time, according to the relevant notice of the State Council, we encourage the application of new technologies such as the Internet of things to improve the ability of fire prevention prediction and information acquisition. According to the preliminary estimation, the installation scale of smoke detectors in China is expected to reach 700 million in the next five years“ I believe that with the improvement of living standards, this new type of smoke sensor can improve the alarm accuracy, reduce the false alarm rate, fundamentally solve the pain points of the existing smoke sensor, and effectively protect the safety of people’s lives and property. It is facing a very broad market at present and in the future. ” Zhu Zhen emphasized.

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