Distinguish types of fire detectors
Fire detectors are usually divided into 3 types: smoke detectors, heat detectors and spark detectors. Depending on the area, different types of fire detectors are selected for installation in that area
f fire detectors are devices that are sensitive to fire incidents such as smoke generation, temperature increase, and sparks. They are responsible for detecting fires and transmitting that information to the central control cabinet.
Today, Dong Nam Fire Protection will introduce to customers different types of fire detectors to help customers understand in the simplest way about fire detectors and their operations.
Based on sensors:
- Heat detector: Uses a sensor for temperature increase to detect fire, usually made in 3 groups A, B, C. Group A has a fixed temperature from 60o C to 75oC. Group B has a fixed temperature from 80oC to 95oC. Group C has a temperature from 120oC to 135oC.
- Smoke detector: Uses an analytical sensor to identify smoke in the air to give a fire warning. - Spark detector: Uses an infrared flame sensor to detect a fire. 1. Smoke sensor fire detector. - Based on the physical properties of smoke caused by a fire, two basic types of smoke detectors are manufactured: Ion smoke detector (Ionization Smoke Detector) and optical smoke detector (Photoelectric Smoke Detector). a. Ion smoke detector
- Ion smoke detectors are made based on the conductive effect of air when ionized, using an Ion chamber to detect smoke. This can chamber is divided into 2 compartments, 1 compartment is closed to make it difficult for smoke to penetrate and is called the sample compartment, the other 1 compartment is kept in constant contact with the outside called the analysis compartment.
Sơ đồ nguyên lý hoạt động đầu báo cháy khói dạng Ion
- Effects of humidity, air dust and atmospheric pressure: Changes in humidity or atmospheric pressure will affect the ion chamber similar to the effect when combustion products enter. And so the possibility of a fake fire detector is quite high. To overcome this drawback, people have designed a detector with a ''dual ion'' chamber structure.
- The analysis chamber, also known as the sensor chamber, is directly affected by environmental conditions such as humidity, air pressure, smoke, dust,... everything in the air.
- Ion chamber, also known as reference ion chamber, this chamber is not affected by external factors, because with that special structure, only small particles can penetrate. Particles such as dirt, smoke, and combustion products are large in size and difficult to penetrate. An electronic circuit is designed to monitor the two ion chambers, comparing the output current between them.
b. Optical smoke detector.
- Optical smoke detectors are fire detectors made on the principle of diffusion and absorption of light by smoke molecules when light propagates in the air. The smoke created by a fire will affect the flow of light particles moving through the normal air. Smoke can block or obscure the lights. They are also the cause of light rays being refracted and deflected. Optical smoke detectors have been designed based on the principles of light and the effects of smoke on them.
Sơ đồ nguyên lý cấu tạo của đầu báo quang truyền thẳng
2. Đầu báo cháy nhiệt.
- Đầu báo nhiệt là những đầu báo cháy được thiết kế dựa trên nguyên lý sự gia tăng nhiệt độ môi trường nơi có đám cháy xảy ra. Khi có đám cháy nhiệt lượng sẽ tỏa ra và chúng được phân tán tới các vùng không gian xung quanh qua truyền nhiệt hoặc đối lưu không khí.
- Thông thường sẽ có 2 kiểu đầu báo cháy nhiệt đó là đầu báo nhiệt cố định và đầu báo nhiệt gia tăng.
Biểu đồ sự gia tăng nhiệt độ đám cháy
a. Fixed heat detector.
- Is the simplest type, composed of a temperature sensor that measures the ambient air temperature. The temperature threshold depends on the requirements and the manufacturer offers thresholds: 57, 70, 100 degrees Celsius.
- Fixed heat detectors only work when the ambient temperature reaches a limit regardless of the rate of heat increase.
b. Increased heat detector
-The increased heat detector is a type of fire detector that will operate and keep the signal to the center. Temperature sensors measure changes in ambient air temperature. If the temperature increases by 5 - 7 degrees Celsius per minute, the detector will emit an alarm signal.
-The heat increase detector only works when the heat increase rate reaches the limit, regardless of the ambient temperature level.
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