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

Fire fighting is not only to deal with the fire that has occurred, but also to prevent and eliminate hidden dangers in advance. The smoke detector is such a key equipment. Once there are signs of suspected fire, it will send out warning reminders 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 equipped with smoke detectors. This is because the traditional smoke detectors often can not distinguish the type of smoke, which is easy to cause false alarm, which is artificially disabled, and finally leads to tragedy. ” At the 2021 Shanghai Electronics Exhibition in Munich, Zhu Zhen, marketing manager of ADI, pointed out that “in addition, the traditional smoke sensing equipment still has too large volume, different specifications and difficult commissioning, and the smoke sensing equipment is facing the requirements of technological change.”

Behind the embarrassment of false positives, fire hazards are highlighted, and the change of smoke detection technology is at the right time

Late one winter night, the fire center of a smart town prompted a fire, and the information of smoke detection audible and visual alarm system constantly prompted XX residents to have smoke at home. Several phone calls failed to contact the owner. The property security guard had urgently found the owner’s home. The owner who had just taken a bath after coming home from the next night shift looked blankly and faced the security guard’s inquiry about the fire. After careful investigation with the owner, it turned out that the smoke detector in the corridor was misinformed because of the fog of bathing, and a fire alarm ended with an embarrassing apology from the property. This is a real scene shared by Zhu Zhen with people in the industry at the Mu exhibition site“ Embarrassment is small and safety is big. This false alarm led some owners to stop using smoke detectors. ” Zhu Zhen said, “more and more properties recognize the potential safety hazards brought by traditional smoke detection equipment itself.”

“The main defect of traditional smoke detector comes from the use of monochrome LED as measurement light source.” Zhu Zhen shared. The classic photoelectric smoke alarm is designed in a discrete way and functions through forward scattering, in which the LED light of a specific wavelength (usually in the infrared range) is scattered on the photodiode by particles. 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.

Design of infrared LED forward scattering system based on smoke detector

Forward scattering system with infrared LED

“The smoke detection device made with this design can only distinguish the concentration of smoke, but can not identify the type of smoke. Whether it is combustion smoke, water vapor or oil smoke generated during cooking, as long as the concentration reaches a certain threshold, the alarm will generate an alarm. Frequent false alarm and disturbance are the primary reason why people disable the smoke alarm.” Zhu Zhen pointed out. In order to solve this problem, some changes have taken place in the formulation of relevant standards for smoke detection. It is hoped to improve the detection accuracy of smoke alarm from top to bottom: Polyurethane combustion, smoldering and cooking nuisance, namely hamburger smoke interference alarm test, will be updated in the latest UL standard to be released in June 2021. In this test, it must be possible to distinguish between smoke from hamburger patties and smoke from flammable polyurethane.

In the field analog water vapor interference sensitivity detection, the traditional scheme gives an alarm quickly, while the ADI dual light detection scheme has no false alarm

Therefore, ADI has launched a fully integrated smoke detector module adpd188bi to completely solve these problems existing in the classic smoke alarm“ Adpd188bi integrates two LED transmitters, a blue light transmitter and an infrared transmitter. Therefore, it can not only monitor the concentration of smoke, but also monitor the particle diameter of smoke to distinguish between normal smoke and fire smoke. ” Zhu Zhen introduced. The blue LED has a wavelength of 470nm and the infrared LED has a wavelength of 850nm. 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 dual color light wavelength monitoring not only supports the measurement of a single wavelength, but also supports the analysis of ratio composition, so as to further reduce the false alarm rate.

Design of infrared LED forward scattering system based on smoke detector

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

As shown in the above figure, the two signal curves sent 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. Polyurethane reaches the alarm threshold after 220 seconds, and the time length is 1 / 4 of Hamburg smoke reaching the alarm threshold (after more than 1000 seconds). A critical level can be detected after 4 minutes of polyurethane combustion. 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, in the part circled in the right figure, the slope suddenly increases in the flammable polyurethane test.

With high consistency, small size and low power consumption, the application is promoted in an all-round way

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

Design of infrared LED forward scattering system based on smoke detector

Integrated optical design greatly simplifies optical design and provides significant system enhancements

Under fixed current, the luminous intensity of different LEDs usually varies greatly. Therefore, in the past, the smoke alarm manufacturer carried out smoke alarm calibration to calibrate the slope and offset between LED luminous intensity and current, which can ensure that all LEDs maintain the same performance. In adpd188bi, because the LED and the whole signal path are integrated together, ADI will pre calibrate the sensor module, which can reduce the difference between devices. In addition, the adpd188bi calibration coefficient is stored in the nonvolatile memory (i.e. eFuse register) of the chip. 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. Since smoke alarm manufacturers can use pre calibrated modules, the system design is also 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 the short pulse of LED make the power consumption of this module lower than that of traditional detector, and the working power consumption of infrared LED is only ~ 5 μ W / Hz, the service life of the smoke sensing battery under this scheme can even reach more than 5 years, significantly reducing the later maintenance cost of the property.

“In addition, adpd188bi can provide a complete optical subsystem solution for smoke detectors. Since 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 an evaluation license to solve the effects of ambient light, dust and insects, and is fully applicable to the integrated optoelectronic devices of adpd188bi and the use of backscatter system.” It is worth mentioning that ADI has also developed smoke detector reference design and complete reference algorithms, including UL 217 test data settings and algorithms designed and tested to meet UL requirements, so as to speed up customer development cycle and reduce costs and project risks.

Summary of this paper

According to Zhiyan consulting data, the market scale of China’s fire industry will exceed 350 billion yuan in 2019 and is expected to reach 446.5 billion yuan in 2022. At the same time, according to the relevant notice of the State Council, encourage the application of new technologies such as the Internet of things to improve the ability of fire prevention prediction and information acquisition. It is preliminarily estimated that 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 can improve the alarm accuracy, reduce the false alarm rate, fundamentally solve the pain points of the existing smoke, and effectively ensure the safety of people’s lives and property. It is facing a very broad market at present and in the future. ” Zhu Zhen stressed.

        Editor in charge: PJ

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