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A solution to reduce the false alarm rate of smoke products

As society progresses and urbanization develops faster and faster, mankind pays more and more attention to fire safety. As an important part of the fire safety system, smoke alarm equipment is accepted and used by more and more people. Existing smoke sensing solutions, such as ionization sensors and photoelectric sensors, can measure smoke well. The general ionization sensor solution will alarm the traditional smoke relatively quickly, which depends on the design of the smoke cavity maze. The photoelectric sensor can alarm the smoke produced by smoldering objects earlier, so as to prevent the occurrence of fire in advance.But these two methods can dry the burnt burger or steam

As society progresses and urbanization develops faster and faster, mankind pays more and more attention to fire safety. As an important part of the fire safety system, smoke alarm equipment is accepted and used by more and more people. Existing smoke sensing solutions, such as ionization sensors and photoelectric sensors, can measure smoke well. The general ionization sensor solution will alarm the traditional smoke relatively quickly, which depends on the design of the smoke cavity maze. The photoelectric sensor can alarm the smoke produced by smoldering objects earlier, so as to prevent the occurrence of fire in advance. However, these two methods have poor recognition of burnt hamburgers or water vapor interference conditions, and false alarms are prone to occur. It requires experienced software personnel to distinguish them from real smoke.

Technology-based authorized distributor Excelpoint Shijian recommended us a new product from ADI that can solve this problem-ADPD188BI. This product is mainly designed to meet the requirements of the UL217 Rev8 standard in the North American market. After system testing, the ADPD188BI solution can fully meet the requirements of UL217 standard. The product adopts the design of dual phototubes. The chip integrates infrared light and blue LED. Through the emitted light of different wavelengths, the size of the measured substance can be indirectly judged by the ratio, so as to distinguish the real smoke and the interference source. Purpose.

A solution to reduce the false alarm rate of smoke products

In this regard, ADI agent-Excelpoint Shijian company engineer Abel Bian conducted a series of tests in the laboratory. The following figure shows some test results. Engineers use European standard test smoke boxes to detect aerosol smoke.

Figure 1, Figure 3, and Figure 5 are the sampling values ​​displayed on the ADPD188BI evaluation board and the PTR (ratio of received light to emitted light power) ratio of blue light and infrared light. In the figure, SlotA represents the PTR value of blue light, and SlotB represents the PTR value of infrared light. The purpose of this is to minimize the impact of noise interference on the results.

A solution to reduce the false alarm rate of smoke productsA solution to reduce the false alarm rate of smoke products

【Picture 1】 【Picture 2】

Figure 1 and Figure 2 show the initial value of ADPD188BI when the masking rate is 0. It can be seen that the average PTR value of blue and infrared light is about 11.53. The ratio is about 0.970.

A solution to reduce the false alarm rate of smoke productsA solution to reduce the false alarm rate of smoke products

【Picture Three】 【Picture Four】

Figure 3 and Figure 4 show the initial value of ADPD188BI when the masking rate is 0.2. It can be seen that the average PTR value of blue and infrared light is about 11.73. The ratio is about 0.983.

A solution to reduce the false alarm rate of smoke productsA solution to reduce the false alarm rate of smoke products

【Picture Five】 【Picture Six】

Figure 5 and Figure 6 show the initial value of ADPD188BI when the occlusion rate is 0.4. It can be seen that the average PTR value of blue and infrared light is about 12.13. The ratio is about 1.005.

“We can process the observed PTR value through smoothing filtering to make smoke alarm judgments, which is the same as the previous method.” Abel said, “Second, we can also use the slope of the PTR ratio to increase, and Corresponding to the two parameters of the shading ratio (such as 12%/foot) in the standard, it is judged whether the measured substance belongs to the smoke caused by real combustion.”

After that, Abel did another experiment, but due to the limited experimental conditions, he just used a simple humidifier to simulate the water mist situation. Through this experiment, it can be seen that the ratio of PTR is a very important parameter at this time, which can help judge the occurrence of real smoke.

A solution to reduce the false alarm rate of smoke products

[PTRA/PTRB shows the change trend of the PTR ratio of all sampled outputs, which shows that under different shading ratios, the PTR ratio will also change slightly (PRTA means blue light, PTRB means infrared light)]

A solution to reduce the false alarm rate of smoke products

[ThePTRoutputvalues​​ofinfraredlightandbluelightindicatethedegreeofchangeinsmokeconcentrationItcanbeseenthatPRTAismoresensitivetochangesinsmokeconcentrationthanPRTB】

The above are the experimental results of Abel for aerosol testing. It can be seen that in terms of accuracy, very fine collection can be achieved, and the additional PTR ratio information can allow software personnel to obtain more judgment basis. At a lower shading ratio, the actual flame occurrence can be judged in advance.

Finally, in order to show the output changes of the product for different smoke sources, he tested the smoke input of high-temperature water vapor and human smoking. The specific results are as follows:

A solution to reduce the false alarm rate of smoke products

The protrusion in the first half of the picture above is the output of high-temperature steam produced by the electric kettle after it is boiled. Excluding the result of dew condensation, it can be seen that when encountering high temperature water vapor, the PTR value of the two lights will rise instantly, exceeding 35nW/mW.

After a period of air cooling and water vapor cleaning, the output change caused by smoking can be seen in the second half. Of course, this is closer to the sensor. The output value is the result of the higher smoke shielding rate, and the maximum can reach about 25nW/mW.

A solution to reduce the false alarm rate of smoke products

[Results of PTRA/PTRB, high temperature water vapor and smoke exhaled by the human body]

The above figure can well show the importance of PTR ratio for judging substances. It can be seen in the first half that the PTR ratio of high-temperature water vapor rises instantly, and the ratio is also close to about 1.8. In the second half, the PTR ratio rose relatively slowly, and the ratio was around 1.55.

Experimental results

Ratio information cannot be used alone to distinguish between real smoke and interference smoke. Software personnel can make relatively stable experimental statistics through the rising speed of the PTR value and the final ratio, and use this as the basis for judging the type of smoke, thereby minimizing the reduction False alarm rate.

Application significance of this product design

In view of the above test results, you can easily place the product in a more complex environment to prevent and monitor the occurrence of fires, such as:

-The bathroom can reduce the false alarm interference of the water mist on the product.

-The kitchen can reduce the false alarm interference of the kitchen fume to the product.

-The warehouse can reduce the false alarm interference of dust on the product.

Through the sensor dual-tube topology, it is possible to increase the basis for judging the environmental state, reduce the difficulty of the algorithm, and achieve more reliable alarms.

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