Smoke detector: types, characteristics, installation

Today, automatic fire alarm systems are the mandatory engineering system of any building. From their unerring work depends not only on the safety of property, but, most importantly, the health and lives of people. Timely and reliable detection of ignition gives people the opportunity to evacuate to a safe zone, and fire brigades - quickly start extinguishing the fire, preventing its spread.

Types of detectors

Fire detectors in the automatic fire alarm are designed to detect fire. Depending on the principle of action, they are subdivided into species. It:

• Smoke detector - reacts to the appearance of smoke in the room;
• Thermal sensor - triggers when the set temperature is exceeded;
• The flame detector - fixes the visible or infrared radiation of the flame;
• Gas analyzer - registers combustion products, such as carbon monoxide.

The correct selection of the detector allows you to detect the source of the fire in a timely manner.

Fire load and type of detector

Premises for different purposes have their own specifics in the development of a fire and the manifestation of its factors. Crucial is the fire load - all items and materials that are in the room. For example, the ignition of paints or fuel is accompanied by a bright flame, which can be fixed by a flame detector. But the same flame sensor will not be effective in premises with storage of materials prone to decay, smoke smoke from smoldering materials will be reacted by a smoke detector.

Smoke Detectors

The most common and effective means of detecting a fire is an automatic smoke detector. After all, the emission of smoke is inherent in the burning 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 for installation in residential buildings, public buildings, industrial and storage facilities with a turnover of materials prone to smoke emission during combustion.

The principle of operation of smoke detectors

At the heart of the action of smoke sensors is the scattering of light by the smoke microparticles. 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 dissipated. This scattered radiation is fixed to the photodetector. The microprocessor, based on the analysis of the photodetector signal, switches the detector into an alarm condition. Depending on the concentration of the emitter and the receiver, the detectors can be point and linear. The names of devices of this type begin with "IP 212", then there is a digital designation of the model. In the designation letters are deciphered as "fire detector", the first digit 2 - "smoke", the number 12 - "optical". Thus, all the marking "ИП 212" means: "Fire Smoke Detector Optical".

Point smoke detectors

In devices of this type, the transmitter and receiver are installed in the same housing on opposite sides of the smoke chamber. Perforation of the sensor housing ensures unimpeded penetration of smoke into the smoke chamber. Thus, the smoke detector optic-electronic detector controls the smoke level of the room only at one point. Sensors of this type are compact, easy to install and effective. Their main disadvantage is a 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 they can be installed 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 beam of the radiator passes through the entire room and controls its smoke. Typically, the range of detectors of this type does not exceed 150 m. There are variants of devices in which the emitter and receiver are installed in one housing and their optical axes are directed in one direction. For operation of such a detector an additional light reflector (cataphot) is installed, installed on the opposite wall and returning the beam of the transmitter to the receiver. A linear smoke detector is mainly used to protect long and tall rooms, such as halls, covered arenas, galleries. They are installed on the walls under the ceiling, the radiator on one wall, the receiver on the opposite. In high spaces, for example atriums, the sensors are installed in several tiers.

Sensitivity of the sensor

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 quality sensors is the ability to maintain their sensitivity when changing orientation, supply voltage, illumination, temperature and other external factors. To test the photodetector, use special laser pointers or aerosols that allow remote monitoring of the detector's operability.

Analog and address systems

In fire alarm systems, the detectors are connected with a loop to the receiving and monitoring device, which analyzes their condition and, in the event of an alarm, generates an alarm. Depending on the method of transmission of its state, the detectors are analog or addressable.

Smoke detector analog smoke detector is connected to the loop in parallel and when triggered it sharply reduces its resistance, in other words, shorts the loop. This change in the resistance of the loop and fixed by the receiving-control device. Typically, the connection of analog detectors is carried out by a two-wire loop, which also supplies power. But there are options for connecting a four-wire circuit. The disadvantage of such a system is the inability to continuously monitor the detector's performance, in addition, it sometimes fixes the operation of the loop without indicating the triggered sensor.

The addressable smoke detector optic-electronic detector is equipped with a microprocessor that monitors the status 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, the receiving and monitoring device receives not only data on the operation of the detector and its number, but also service information on operability, dustiness, etc.

In the case of most modern detectors, LEDs are built in, their blinking determining their state.

Autonomous fire detectors

Often, there is no need to install an automatic fire alarm system, it is enough to simply notify people who are in the same room of a fire. For these purposes, the smoke detector is self-contained. These devices combine a smoke detector and a siren. When the room is smoked, 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 have self-contained power - built-in batteries, whose capacity is sufficient for operation for three years.

These detectors are ideal for installation in an apartment or a small house. Some models allow you to combine sensors into a small network, for example, within an apartment. On the case of such a sensor there is an LED indicator, the color and the periodicity of the flashing indicate its state.