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How to choose a smoke detector?

34 Published by xia, Crystal Nov 29,2019

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Selection of smoke detectors

Wireless photoelectric smoke sensor

1.Select the detector according to the characteristics of the fire

① There is a smoldering stage at the beginning of the fire, which generates a large amount of smoke and a small amount of heat, and there is little or no flame radiation, so a smoke detector should be selected.

② The rapid development of fires generates a large amount of heat, smoke and flame radiation. Smoke detectors, temperature detectors, flame detectors, or combinations there of can be selected.

③ The fire develops rapidly, there is strong flame radiation and a small amount of smoke and heat, and a flame detector should be selected.

④ The characteristics of fire formation are unpredictable, and pattern recognition tests can be performed, and detectors can be selected based on the test results.

2.Select the detector according to the environmental characteristics of the installation site

① Relative humidity is greater than 95% for a long time, airflow velocity is greater than 5m / s, there is a large amount of dust and water mist trapped, and corrosive gases may be generated. Under normal circumstances, there is smoke trapped, which produces alcohol, ether, ketone and other organic substances Place, it is not suitable to use ion smoke detectors.

② In places where smoldering may occur or a fire is not early enough to cause serious damage, a temperature detector should not be used; in a place with a temperature below 0 ° C, a fixed temperature detector should not be used; in a place where the temperature changes normally, it should not Use a differential temperature detector.

③ Flame detectors are not suitable for the following situations:

A. Flameless fire may occur;

B. Smoke spreads before the flames:

C, the lens of the detector is easily contaminated;

D. The “line of sight” of the detector is easily blocked;

E. The detector is easy to be directly or indirectly illuminated by sunlight or other light sources:

F. Under normal circumstances, there are open flame operations and x-ray and arc light effects.

3. Select the detector based on the height of the room

The selection of the sensitivity of the detector should be based on the performance of the detector and the place of use. Under normal circumstances (when there is no fire alarm), the system should not make a false alarm. At present, most domestic high-rise buildings use photo-inductor temperature detectors. Temperature-sensing detectors are only used in individual places, kitchens, generator rooms, garages, and places with gas fire extinguishing devices. When only “type detectors” are used, misoperations are prone to occur in the linked system, which will inevitably cause unnecessary losses, especially in systems that are subject to false alarms. Therefore, two or more types of detectors should be selected. They It is a logical relationship of “AND”. When two or two kinds of detectors alarm at the same time, the linkage device will act, so as to ensure particularly unnecessary losses.

In short, the choice of detector should be based on the actual environmental conditions to select a suitable detector to achieve the purpose of timely and accurate alarm.

What is the difference between ionic and photoelectric?

Wireless photoelectric smoke sensor

First of all, let’s understand what a photoelectric smoke detector is and how it works. The photoelectric smoke detector-we also call it a point detector. The photoelectric smoke detector uses the Smoke is an alarm device developed to change the basic property of light transmission characteristics. There is an optical maze inside the photoelectric smoke detector and an infrared radiation tube is installed. When there is no smoke, the infrared receiving tube cannot receive the infrared light emitted by the infrared transmitting tube. However, when smoke and dust enter the optical maze, the smoke and dust pass through the refracting, In the reflection, the receiving tube receives infrared light, and the intelligent alarm circuit judges whether the threshold is exceeded, and if it exceeds the threshold, an alarm will be issued.

Ionic smoke detectors have an ionization chamber. The radioactive element used in the ionization chamber is thorium 241 (Am241), which has an intensity of about 0.8 microcuries. It is generally in a balanced state under normal conditions, but if smoke and dust enter it, The ionization chamber will then destroy this equilibrium relationship, and an alarm will be issued when the smoke concentration reaches a certain threshold.

Ionic smoke detectors are more sensitive to those tiny smoke particles, while photoelectric smoke detectors are just the opposite. Photoelectric smoke detectors are more sensitive to those larger smoke particles. If the fire smoke and dust are all larger particles, then it is better to use photoelectric smoke detectors, and if the smoke and dust generated by the fire are relatively small particles, then it is better to use ionic smoke detectors, so whether the ionic smoke detector is better or photoelectric,the smoke detector is good. This needs to be determined according to your needs. It is not possible to generalize which is good and which is not. We need to analyze specific problems and analyze them based on actual conditions.

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