A fire hazard can threaten both production and domestic premises. To prevent damage and other consequences from fires in residential buildings and industrial facilities, fire alarm systems are installed. The most important unit of control in the system is a fire alarm sensor (fire detector), the features and purpose of which we will consider in this article.
Device and principle of operation
In practice, the response of the sensor can be carried out due to the appearance of smoke, an increase in temperature, the release of certain gases. There are devices that respond to only one value or several at once. The latter option is more practical as it covers several factors. For example, consider the device of such a sensor.
Structurally, the fire alarm sensor consists of the following components:
- Housing - designed to protect electronic devices from dust settling, which can affect the accuracy of measurements and response.
- Optical sensor - is a photodetector that responds to changes in the degree of illumination.
- Thermal sensor - captures temperature changes in the corresponding area or segment.
- CO, CO2 content sensor - controls the percentage of carbon monoxide and carbon dioxide, as integral components of the products of smoldering and combustion.
- Infrared sensor - designed to fix light radiation in a specific area.
Let us consider the principle of operation using the example of the initial stage of ignition before the appearance of smoke and fire, directly in the area of operation of a fire detector. Let's say the temperature starts to rise in the hearth, warm air masses rise up to the place installation of the fire alarm sensor, and the cold air will go down, as shown in the figure below:
In this case, a sharp rise in temperature is detected by a thermal sensor, which will provide information about the beginning of the ignition. In the event of an open flame, the infrared sensor would be the first to react to infrared radiation. We will consider in more detail the types of fire alarm sensors below.
Varieties
The first fire detection devices were developed over a hundred years ago. During this time, they have undergone a significant evolution, both in terms of design features and in relation to the principle of operation. In accordance with clause 4.1 of GOST R 53325-2012, all fire detectors are divided into several categories. They can be automatic or manual depending on the method of activation.
If we consider a fire detector depending on the factor controlled by it, then they can be divided into:
- thermal;
- smoke;
- flame;
- gas;
- combined.
In addition to the above criteria, in accordance with cl. 4.1.1.4 GOST R 53325-2012 it is allowed to use other signs for classification.
According to the method of data transmission, the sensors can be threshold and analog. Depending on the type of reaction to the factor estimated by the sensor, the threshold models can be maximum, differential, or mixed.
Depending on the state of the environment in which the sensor controls the fire factor, they are divided into:
- for the control of gaseous media - the classic version used indoors;
- to detect signs of fire in a liquid medium;
- to monitor the state of the bulk medium - submersible sensors are installed;
- to control the state of solids - the sensor itself is located directly on the surface.
Depending on the coverage of the monitored area, fire detectors can be point, linear or multipoint. According to the power supply method, power supply can be carried out through a loop, a separate wire or through an autonomous source. Also, the fire alarm sensor can be triggered from one action (class A) or several actions (class B).
Depending on the method of communication between the sensor and the control panel, fire detectors are divided into:
- wired;
- fiber optic;
- radio channel;
- combined.
In the light of the above classification, the most interesting is the division according to the controlled factor. In practice, models are used both with one parameter for analysis, and with several at once.