Types of fire detectors?

Automatic fire alarm system consists of fire detectors and fire alarm controller. Fire detector is the system's "sense organs", its role is to monitor the environment there is no fire. Once there is a fire, the fire characteristics of physical quantities, such as temperature, smoke, gas and radiation light intensity converted into electrical signals, and immediately act to send an alarm signal to the fire alarm controller. For flammable and explosive occasions, the fire detector mainly detects the gas concentration in the space around it and alarms before the concentration reaches the lower explosive limit. In some cases, the fire detector can also detect pressure and sound waves.

The classification of fire detectors is complex. Practical classification methods are structural modeling classification, detection of fire parameters classification and use of environmental classification.

(A) structural modeling classification

According to the structural modeling classification of fire detectors can be divided into two categories of line and point type.

Line fire detector: this is a response to a continuous line around the fire parameters of the fire detector, the continuous line can be "hard", can also be "soft". Such as air line type differential temperature fire detector, is a thin copper or stainless steel tube from a long continuous line of "hard". Another example is the infrared beam line-type smoke detector, is by the transmitter and receiver of the two in the middle of the infrared beam constitutes a "soft" continuous line.

Point detector: This is a fire detector that responds to fire parameters around a point. Most fire detectors, belong to the point-type fire detectors.

(ii) detection of fire parameters classification

Based on the fire detector detection of fire parameters, can be divided into temperature-sensitive, smoke-sensitive, light-sensitive, gas and composite and other categories.

Temperature-sensitive fire detectors: this is a response to abnormal temperatures, the rate of temperature rise and temperature difference of the fire detector. Can be divided into fixed temperature fire detector - the temperature reaches or exceeds the predetermined value of the response of the fire detector; differential temperature fire detector plant temperature rise rate exceeds the predetermined value of the response of the temperature-sensitive fire detector: differential fixed temperature fire detector - both differential temperature, fixed temperature two kinds of Temperature-sensitive fire detectors with both differential temperature and constant temperature functions. Temperature-sensitive fire detectors, due to the use of different sensitive components, such as thermistors, thermocouples, bimetals, fusible metals, membrane boxes and semiconductors, etc., and can be derived from a variety of temperature-sensitive fire detectors.

Smoke detectors: this is a response to combustion or pyrolysis of solid or liquid particles produced by the fire detector. Because it can detect the aerosol or smoke particles produced in the early stages of combustion of substances concentration, therefore, some countries call the smoke detector fire detector for the "early detection" detector.

Aerosol or smoke particles can change the light intensity, reduce the ionization chamber ion current and change the air capacitor of the electrolytic constant semiconductor certain properties. As a result, the smoke detectors can be divided into ionic, photoelectric, capacitive and semiconductor type and so on. One of the photoelectric smoke detectors: according to the different principles of action, can also be divided into light-reducing type (the application of smoke particles on the principle of light path blocking) and diffuse type (the application of smoke particles on the principle of light scattering) two kinds.

Light-sensitive fire detectors: light-sensitive fire detectors are also known as flame detectors. This is a response to the flame radiation of infrared, ultraviolet, visible light fire detector, mainly infrared flame type and ultraviolet flame type two.

Gas fire detector: this is a response to combustion or pyrolysis of the gas produced by the fire detector. In flammable and explosive occasions in the main detection of gas (dust) concentration, generally adjusted in the lower explosive limit concentration of 1/5-1/6 when the action alarm. Used as a gas fire detector to detect gas (dust) concentration of the sensing element mainly platinum wire, drill palladium {black and white elements) and metal oxide semiconductors (such as metal oxides, chalcogenide crystals and spinel) and so on.

Composite fire detector: this is a response to more than two fire parameters of the fire detector. Mainly temperature-sensitive smoke fire detector, light-sensitive smoke fire detector, light-sensitive temperature-sensitive fire detector.

Other fire detectors

Leakage current sensing fire detectors to detect the size of the leakage current: there is a detection of electrostatic potential of electrostatic induction type fire detectors; there are also some special occasions, the requirements of the detection of extremely sensitive, extremely rapid action, and even the requirements of the detection of explosions produced by the sound of some parameters of the change (such as changes in pressure) signals to inhibit the elimination of explosion Accidents occurring micro-differential pressure type fire detector; and the use of ultrasonic principle of detecting fire ultrasonic fire detector and so on.