Classification of fire parametersAccording to the difference of fire parameters detected by fire detectors, they can be divided into several categories, such as temperature sensing, smoke sensing, gas sensing and compound.A temperature fire detector: This is a fire detector that responds to abnormal temperatures, temperature rise rates, and temperature differences. It can be divided into fixed temperature detector, temperature reaches or exceeds a predetermined value when the response of fire detectors; fire detector response temperature sensor factory heating rate exceeds a predetermined value when the temperature sensing fire detector constant temperature fire detector -- both on temperature and the two functions of constant temperature. Because of the use of different sensitive elements, such as thermal resistance, thermocouple, bimetal, Yi Rong metal, film box and semiconductor, a fire detector can be derived.Smoke fire detector: This is a fire detector that responds to combustion or pyrolysis of solid or liquid particles. Because it detects the concentration of aerosols or smoke particles produced in the early stages of combustion, some countries call the pyrotechnic detector a "early detection" detector.Aerosol or smoke particles can change the light intensity, reduce the ion current in the ionization chamber, and change the ionization constant of the air capacitor, and some properties of the semiconductor. As a result, smoke fire detectors can be divided into several types, such as ion type, photoelectric type, capacitance type and semiconductor type. Among them, the photoelectric smoke fire detector: according to its principle of action, but also can be divided into light reduction type (using smoke particles on the light path shielding principle) and astigmatism (using smoke particles on light scattering principle) two kinds.
Structural modeling classificationAccording to the structure of fire detectors, classification can be divided into linear and point type of two categories.Linear fire detector: This is a fire detector that responds to the fire parameters around a continuous line. The continuous lines can be either hard or soft. An air line type differential temperature detector consists of an elongated copper tube or a stainless steel tube that forms a "hard" continuous line. Another example is the infrared beam linear smoke smoke detector, which consists of two infrared beams in the middle of the emitter and receiver.Point detector: This is a fire detector that responds to the fire parameters around a point. Most fire detectors belong to point type fire detectors.
For flammable and explosive occasions, fire detectors mainly detect the concentration of gas in their surrounding space and alarm before the concentration reaches the lower limit of explosion. In individual cases, fire detectors can also detect pressure and sound waves.The classification of fire detectors is complicated. The practical classification methods include structural modeling method, fire detection parameter classification method and environment classification method.
Automatic fire alarm system consists of fire detector and fire alarm controller. A fire detector is a "sensory organ" of the system that monitors the presence of fire in the environment. Once a fire occurs, the characteristic physical quantities of the fire, such as temperature, smoke, gas and radiation intensity, are converted into electrical signals, and action is immediately taken to send an alarm signal to the fire alarm controller.
