Today, automatic fire alarm systems are a mandatory engineering system of any building. Not only the safety of property, but, most importantly, the health and life of people depends on their error-free operation. Timely and reliable fire detection gives people the opportunity to evacuate to a safe area, and fire brigades - to quickly begin to extinguish a fire, preventing its spread.
Detector Types
Fire detectors as part of an automatic fire alarm are designed to detect a fire. Depending on the principle of action, they are divided into types. It:
- smoke detector - reacts to the appearance of smoke in the room;
- thermal sensor - triggers when the set temperature is exceeded;
- flame detector - captures the visible or infrared radiation of the flame;
- gas analyzer - registers combustion products, such as carbon monoxide.
The correct choice of the detector allows you to timely detect the source of the fire.
Fire load and detector type
Premises for various purposes have their own specifics in the development of fire and the manifestation of its factors. Crucial is the fire load - all objects and materials in the room. For example, the ignition of paints or fuels is accompanied by a bright flame, which can be detected by a flame detector. But the same flame sensor will not be effective in rooms with storage of materials prone to smoldering, a smoke detector will react to smoke from smoldering materials.
Smoke detectors
The most common and effective fire detection tool is an automatic smoke detector. After all, smoke emission is characteristic of the combustion process of many substances, such as paper, wood, textiles, cable products, electronic equipment, etc. These sensors are designed to detect fires that are accompanied by smoke in the early stages of a fire. Detectors of this type are effective for installation in residential buildings, public buildings, industrial and storage facilities with a circulation of materials prone to smoke during combustion.
The principle of operation of smoke detectors
The action of smoke sensors is based on the scattering of light on microparticles of smoke. Sensor emitter, usually an LED operating in the light or infrared range. It irradiates the air in the smoke chamber, with smoke, part of the light flux is reflected from the smoke particles and scattered. This scattered radiation is fixed on the photodetector. Based on the analysis of the photodetector signal, the microprocessor puts the detector into alarm state. Depending on the concentration of the emitter and receiver, the detectors can be point and linear. The names of devices of this type begin with "IP 212", followed by a digital designation of the model. In the designation, the letters are decoded as “fire detector”, the first number 2 is “smoke”, the number 12 is “optical”. Thus, the entire marking "IP 212" means: "Optical smoke detector."
Point smoke detectors
In devices of this type, the emitter and receiver are installed in one housing on different sides of the smoke chamber. Perforation of the sensor housing allows unhindered penetration of smoke into the smoke chamber. Thus, the optical-electronic smoke detector controls the degree of smoke in the room at only one point. Sensors of this type are compact, easy to install and efficient. Their main disadvantage is the limited controlled area not exceeding 80 sq.m. In most cases, point detectors are mounted on the ceiling, in increments depending on the height of the room. But it is possible to install them on walls, under the ceiling.
Linear Smoke Detectors
In these sensors, the emitter and receiver are made in the form of separate devices installed on different sides of the room. Thus, the emitter beam passes through the entire room and controls its smoke. As a rule, the range of detectors of this type does not exceed 150 m. There are options for devices in which the emitter and receiver are installed in one housing, and their optical axes are directed in the same direction. For the operation of such a detector, an additional reflector (reflector) is used, mounted on the opposite wall and returning the transmitter beam to the receiver. The linear smoke detector is mainly used to protect long and tall rooms, such as halls, indoor arenas, galleries. They are installed on the walls under the ceiling, the emitter on one wall, the receiver on the opposite. In high rooms, such as atriums, sensors are installed in several tiers.
Sensor sensitivity
The most important parameter of smoke detectors is their sensitivity. It characterizes the ability of the sensor to capture the minimum concentration of smoke particles in the analyzed air. This value is measured in dB and is in the range of 0.05-0.2 dB. The difference between high-quality sensors is the ability to maintain their sensitivity when changing orientation, supply voltage, light, temperature and other external factors. To check the photodetector, special laser pointers or aerosols are used to remotely monitor the detector's performance.
Analog and Address Systems
In fire alarm systems, the detectors are connected by a loop to the control panel, which analyzes their condition and, in case of operation, issues an alarm. Depending on the method of transmitting their status, the detectors are either analog or addressable.
The smoke analog detector is connected in parallel to the loop and, when triggered, sharply reduces its resistance, in other words, it shorts the loop. This change in loop resistance is recorded by the control panel. As a rule, the connection of analog detectors is performed by a two-wire loop, which also supplies power. But there are four-wire connection options. The disadvantage of such a system is the inability to continuously monitor the detector’s performance, in addition, sometimes a loop trip is detected without indicating a triggered sensor.
The optical-electronic smoke detector is equipped with a microprocessor that monitors the state of the sensor and, if necessary, adjusts its settings. Such sensors are connected to a digital loop, in which each detector is assigned its own number. In such a system, not only data on the operation of the detector and its number, but also service information on operability, dust, etc., are received by the control panel.
In the cases of most modern detectors, LEDs are built-in, which determine their condition with their blinking.
Autonomous fire detectors
Often there is no need to install an automatic fire alarm installation, it is enough to simply inform about the occurrence of a fire of people in the same room. An autonomous smoke detector is intended for these purposes. These devices combine a smoke sensor and a sound siren (siren). When the premises smoke, the detector detects the presence of smoke and with its sound signal notifies people about the presence of a dangerous concentration of smoke. Such sensors are self-powered - built-in batteries, the capacities of which are enough to operate for three years.
These detectors are ideal for installation in an apartment or a small house. Some models allow you to combine sensors in a small network, for example within the apartment. On the case of such a sensor there is an LED indicator, the color and flashing frequency of which indicate its condition.