Today, automatic fire alarm installations are a mandatory engineering system of any building. Not only the safety of property depends on their faultless work, but also, most importantly, the he alth and life of people. Timely and reliable fire detection gives people the opportunity to evacuate to a safe area, and fire brigades to quickly start extinguishing the fire, preventing it from spreading.
Types of detectors
Fire detectors as part of an automatic fire alarm system are designed to detect fire. Depending on the principle of action, they are divided into types. This is:
- smoke detector - reacts to the appearance of smoke in the room;
- thermal sensor - triggered 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 detect the source of the fire in a timely manner.
Fire load and detector type
Premises of variousappointments have their own specifics in the development of a fire and the manifestation of its factors. Of decisive importance is the fire load - all objects and materials in the room. For example, the fire of paints or fuel is accompanied by a bright flame, which can be detected by a flame detector. But the same flame detector will not be effective in rooms with the storage of materials prone to smoldering, a smoke detector will react to smoke from smoldering materials.
Smoke detectors
The most common and effective means of detecting a fire is an automatic smoke detector. After all, the release of smoke 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 accompanied by the release of smoke in the early stages of a fire. Detectors of this type are effective when installed in residential buildings, public buildings, production and storage facilities with the circulation of materials that are prone to emit smoke during combustion.
The principle of operation of smoke detectors
Smoke sensors are based on light scattering on smoke microparticles. The emitter of a sensor, usually an LED, operating in the light or infrared range. It irradiates the air in the smoke chamber, when smoked, part of the light flux is reflected from the smoke particles and scattered. This scattered radiation is recorded on a photodetector. Microprocessor-based signal analysis of the photodetector translatesthe detector is in alarm. 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 the digital designation of the model. In the designation, the letters stand for “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 the same housing on opposite sides of the smoke chamber. The perforation of the sensor body ensures 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. This type of sensor is compact, easy to install and efficient. Their main drawback is the limited controlled area, not exceeding 80 sq.m. In most cases, point detectors are installed on the ceiling, in increments depending on the height of the room. But it is possible to install them on the walls, under the floor.
Linear smoke detectors
In these sensors, the emitter and receiver are made as 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 this type of detectors does not exceed 150 m. There are device options in which the emitter and receiverare installed in one housing, and their optical axes are directed in one direction. For the operation of such a detector, an additional reflector (reflector) is used, which is installed on the opposite wall and returns the transmitter beam to the receiver. The linear smoke detector is mainly used to protect long and high spaces, 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, illumination, temperature and other external factors. To check the photodetector, special laser pointers or aerosols are used, which allow remote control of the detector's performance.
Analog and address systems
In fire alarm systems, detectors are connected by a loop to the control panel, which analyzes their condition and, if triggered, issues an alarm signal. Depending on the method of transmissionstate detectors are either analog or addressable.
An analog fire smoke detector is connected in parallel to the loop and, when triggered, sharply reduces its resistance, in other words, short-circuits the loop. This change in the resistance of the loop is fixed by the control panel. As a rule, the connection of analog detectors is carried out by a two-wire loop, through which power is also supplied. But there are options for connecting in a four-wire scheme. The disadvantage of such a system is the inability to continuously monitor the performance of the detector, in addition, sometimes the loop is triggered without indicating the triggered sensor.
The optical-electronic addressable smoke detector is equipped with a microprocessor that monitors the state of the sensor and, if necessary, corrects its settings. Such sensors are connected to a digital loop, in which each detector is assigned its own number. In such a system, the control panel receives not only data on the detector triggering and its number, but also service information on performance, dust content, etc.
The cases of most modern detectors have built-in LEDs that determine their status by blinking.
Autonomous fire detectors
Often there is no need to install an automatic fire alarm installation, it is enough just to notify people in the same room about the occurrence of a fire. For these purposes, an autonomous smoke detector is intended. These devices combine a smoke sensor and a sound annunciator.(siren). When the room is filled with 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 capacity of which is enough to work for three years.
These detectors are ideal for installation in an apartment or small house. Some models allow you to combine sensors into a small network, for example, within an apartment. On the body of such a sensor there is an LED indicator, the color and frequency of flashing of which indicate its condition.
